master thesis_yang_final revised

ENHANCEMENT OF PHOTOCATALYTIC ACTIVITY BY SITE POISONING

PLATINUM DOPED TITANIUM DIOXIDE

A Thesis

Presented to

The Graduate Faculty of The University of Akron

In Partial Fulfillment

of the Requirements for the Degree

Master of Science

Yang Chu

December, 2014

ii

ENHANCEMENT OF PHOTOCATALYTIC ACTIVITY BY SITE POISONING

PLATINUM DOPED TITANIUM DIOXIDE

Yang Chu

Thesis

Approved:

_________________________________

Advisor

Dr. Steven S.C. Chuang

_________________________________

Faculty Reader

Dr. Xiong Gong

_________________________________

Department Chair

Dr. Coleen Pugh

Accepted:

_________________________________

Dean of the College

Dr. Eric J. Amis

_________________________________

Interim Dean of the Graduate School

Dr. Rex Ramsier

_________________________________

Date

iii

ABSTRACT

Photoelectrochemical cell (PEC) is a device that could interconvert chemicals and

electricity with the energy of light by the photovoltaic effect1. PEC is widely studied

recently for hydrogen production and waste organics degradation2. The main structure is

composed of photocatalyst, electrolyte, counter electrode and power supply. Water and

organics are converted to hydrogen and carbon dioxide gases by irradiating the

photocatalyst with ultraviolet radiation. The challenge for commercialization is mainly

because of the low efficiency. Extensive research has been directed toward developing

highly active photocatalysts by the doping of platinum. Platinum doped titanium dioxide

(Pt-TiO2) has shown the ability to faster degrade organics than TiO23, 4

. The mechanism is

that the low potential of platinum that functions as a trap for the electrons and thus

reduces the electron-hole recombination. However, there has not been a significant

breakthrough that can lead PEC to commercialization. Recently, we hypothesize that

selectively poisoning the electron generating site could significantly reduce the electron-

hole recombination. Pt-TiO2 was treated with hydrogen sulfur (Pt-TiO2/H2S) at high

temperature and H2S were converted to sulfur and completely covered the platinum.

Characterization of TiO2, Pt-TiO2 and Pt-TiO2/H2S both in powder and thin film format

was done by infrared spectroscopy (IR), ultraviolet-visible spectroscopy (UV-vis), x-ray

diffraction (XRD), scanning electron microscopy (SEM), transmission electron

microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Ethanol and some

other organics are added in electrolyte to increase the current density of the PEC and

iv

produce more hydrogen due to the lower oxidation potential than water5. Comparing the

working electrode of TiO2, Pt-TiO2 and Pt-TiO2/H2S in PEC, we analyzed the different

amount of gaseous products, the current density and the degradation of methylene blue.

The results showed that Pt-TiO2/H2S has the best oxidative activity per unit thickness of

catalyst. This research will lead us to find the applications of PEC in utilization of the

shale gas that can provide the energy with high efficiency and environmental friendly in

the future.

v

ACKNOWLEDGEMENTS

Firstly, I will thank my advisor, Dr. Steven Chuang for giving me this opportunity to do

research in his group. He provided me this project and taught me how to think for the

science and technology. I really appreciate Dr. Xiong Gong to be the reader for my

master thesis. He is so busy but he still squeezes his time to help me improve my writing

skill. I would like to thank the group members of the photocatalyst, who are Mehdi

Lohrasbi, Piyapong Pattanapanishsawat, Dan Huang, Jie Yu. They taught me how to set

up the experiment and the way to analyze the data. They are friends more than the

colleagues.

Secondly, I am very grateful for my parents. They give me all their love and understand

to support me to finish my Master degree. They are always the strongest backup whatever

I meet all the problems. I also need to thank all my friends. They helped me overcome the

hardest time in USA and always encourage me to do my favorite things.

Last, I am thankful to my wise, Yu Zhang. She did everything she could to help me finish

my Master degree. She is the most important people to me and she will always be.

vi

TABLE OF CONTENTS

Page

LIST OF FIGURES ......................................................................................................... viii

LIST OF TALBES ........................................................................................................... xiii

CHAPTER

I. INTRODUCTION ........................................................................................................... 1

II. LITERATURE REVIEW ............................................................................................... 4

2.1. Photocatalysts .......................................................................................................... 4

2.2. Titanium dioxide ...................................................................................................... 4

2.3. Photoelectrochemical cell ........................................................................................ 7

III. EXPERIMENTAL ...................................................................................................... 12

3.1. Preparation and characterization of platinum doped titanium dioxide and platinum

....................................................................................................................................... 12

3.1.1. Preparation of platinum doped titanium dioxide ............................................ 12

3.1.2. Preparation of platinum doped titanium dioxide treated by hydrogen sulfide 13

3.1.3. Preparation of TiO2 thin film, Pt-TiO2 thin film and Pt-TiO2/H2S thin film ... 14

3.1.4 Characterization of catalysts in forms of powder and thin film ....................... 16

3.2. Setup of photoelectrochemical cell ........................................................................ 17

3.3. Characterization of gas products and solution in photoelectrochemical cell ......... 19

3.4. Experimental procedure of photoelectrochemical cell .......................................... 19

IV. RESULTS AND DISCUSSION .................................................................................. 22

4.1. Characterization of TiO2-based catalysts ............................................................... 22

4.1.1 TiO2-based catalysts in powder and thin film form ......................................... 22

vii

4.1.2 TEM analysis of TiO2-based catalyst in powder form ..................................... 23

4.1.3 SEM analysis of TiO2-based catalysts in thin film form.................................. 25

4.1.4 FTIR spectroscopy characterization of TiO2-based catalysts .......................... 25

4.1.5 UV-Vis spectroscopy characterization of TiO2-based catalysts ....................... 30

4.1.6 Two-dimensional wide angle X-ray diffraction spectroscopy of TiO2-based

catalysts. .................................................................................................................... 32

4.1.7 Energy-dispersive X-ray spectroscopy of TiO2-based catalysts ...................... 33

4.2. Results of photoelectrochemical cell ..................................................................... 33

4.2.1 Photoelectrochemical reactions ....................................................................... 33

4.2.2 Electrical experimental results of photoelectrochemical cell .......................... 34

4.2.3 Gas production results of photoelectrochemical cell experiment. ................... 37

4.2.4 Photo oxidation of methylene blue in the photoelectrochemical cell experiment

................................................................................................................................... 39

4.2.5 pH change ........................................................................................................ 42

4.3. Conclusions ............................................................................................................ 45

REFERENCES ................................................................................................................. 46

APPENDICES .................................................................................................................. 51

APPENDIX A DYE-SENSITIZED SOLAR CELLS (DSSC) ..................................... 52

APPENDIX B INTENSITY OF UV LIGHT................................................................ 72

APPENDIX C PHOTO DEGRDATION OF PVC THIN FILMS ................................ 80

APPENDIX D NFPA AND HMIS RATING OF CHEMICALS ................................ 104

viii

LIST OF FIGURES

Figure Page

1. Organization of master project and thesis ....................................................................... 3

2. Band positions of several semiconductors in contact with aqueous electrolyte at pH 1. 5

3. Ball and stick model for three different forms of titanium dioxide. ............................... 6

4. (a) Chemical structure of methylene blue and the IR band assignment. (b) Variations of

the IR intensity of MB bands at 1488 cm-1 during 240 min of the MB photocatalytic

degradation. ................................................................................................................... 7

5. Current-voltage profile of the photoelectrochemical cell.. ............................................. 8

6. Experimental procedure of Pt-TiO2 preparation ........................................................... 13

7. Experimental procedure of Pt-TiO2/H2S preparation .................................................... 14

8. Experimental procedure of TiO2 paste preparation ....................................................... 14

9. Experimental procedure of TiO2 thin film preparation ................................................. 15

10. Schematic (Left) and picture (Right) of DRIFT cell................................................... 17

11. (a) Schematic setup and (b) pictures of photoelectrochemical cell............................. 18

12. First experimental procedure of photoelectrochemical cell. ....................................... 20

13. Second experimental procedure of photoelectrochemical cell. .................................. 21

14. Photograph of TiO2, 0.5 wt.% Pt-TiO2, 1.0 wt.% Pt-TiO2, 3.0 wt.% Pt-TiO2 and 0.5

wt.% Pt-TiO2/H2S powder........................................................................................... 22

15. Photograph of TiO2, 0.5 wt.% Pt-TiO2, 1.0 wt.% Pt-TiO2, 3.0 wt.% Pt-TiO2 and 0.5

wt.% Pt-TiO2/H2S thin film. ....................................................................................... 23

16. TEM pictures of TiO2, 0.5 wt.% Pt-TiO2 ,1.0 wt.% Pt-TiO2, 3.0 wt.% Pt-TiO2 and 0.5

wt.% Pt-TiO2/H2S. ...................................................................................................... 24

17. SEM pictures of TiO2, 0.5 wt.% Pt-TiO2 and 0.5 wt.% Pt-TiO2/H2S in thin film from

top and cross sectional views. ..................................................................................... 25

ix

18. (a) Single beam and (b) absorbance FTIR spectra of TiO2, 0.5 wt.% Pt-TiO2 and 0.5

wt.% Pt-TiO2/H2S in powder form. Absorbance was obtained by absorbance

=log(1/I), where I was the intensity of single beam. .................................................. 28

19. (a) Single beam and (b) absorbance FTIR spectra of TiO2, 0.5 wt.% Pt-TiO2 and 0.5

wt.% Pt-TiO2/H2S in thin film form. Absorbance was obtained by absorbance

=log(1/I), where I was the intensity of single beam. .................................................. 29

20. UV-vis spectroscopy of TiO2, 0.5 wt.% Pt-TiO2 and 0.5 wt.% Pt-TiO2/H2S in (a)

powder and (b) thin film form. ................................................................................... 31

21. XRD spectroscopy of TiO2-based catalysts in powder form. ..................................... 32

22. Schematic representation of the operating principle and reactions of

photoelectrochemical cell. .......................................................................................... 34

23. Time profiles of current density at different forward bias voltage for TiO2, 0.5 wt.%

Pt-TiO2 and 0.5 wt.% TiO2/H2S as working electrode. ............................................... 36

24. Time profiles of MS intensity at different forward bias voltage for TiO2, 0.5 wt.% Pt-

TiO2 and 0.5 wt.% TiO2/H2S as working electrode. H2 and CO2 were detected from

the gas products........................................................................................................... 37

25. Pictures of the CO2 blub formation during the experiment. ....................................... 37

26. Photograph of electrolyte containing methylene blue (a) before and after degradation

by (b) TiO2, (c) 0.5 wt.% Pt-TiO2 and (d) 0.5 wt.% TiO2/H2S. .................................. 40

27. UV-visible spectroscopy of electrolyte containing methylene blue before and after

degradation by TiO2, 0.5 wt.% Pt-TiO2 and 0.5 wt.% TiO2/H2S. ............................... 41

28. The change of pH values and current density during the experiments. ...................... 43

29. Effect of different UV light intensity on the pH change. ............................................ 44

30. Representation of a dye-sensitized TiO2 solar cell and the processes involved in

energy conversion (S represents the dye-sensitizer and I-/I3

- is the charge mediator). 52

31. Experimental procedure for screen printing. .............................................................. 56

32. The instrument and schematic procedure for spin coating. ........................................ 56

33. Photographs of TiO2 thin film corresponding to the 8. ............................................... 57

34. Measurement of the efficiency of DSSC. ................................................................... 59

35. The calculation of the efficiency of DSSC based on the voltage-current profile. ...... 60

36. The chemical structure of N719. ................................................................................. 61

x

37. The chemical structures of (a) Dye1 and (b) Dye2. .................................................... 63

38. The synthetic route of Dye1. ....................................................................................... 64

39. The synthetic route of Dye2. ....................................................................................... 65

40. Pictures of N719, Dye1 and Dye2 in solution. ........................................................... 65

41. The pictures of TiO2 thin films after immersing in Dye1 and Dye2 for 24 h. ............ 66

42. Current-Voltage profile of two DSSCs with and without electrolyte. ........................ 69

43. (a) Single beam IR spectroscopy and (b) Absorbance of the chemicals and the

solution of PEG polymer electrolyte........................................................................... 71

44. Schematic setup of UV light measurement. ................................................................ 72

45. The distribution of UV light intensity at different positions. ...................................... 73

46. The intensity of UV light at different positions with optical fiber. ............................. 74

47. 2D distribution of UV light intensity with optical fiber. Distance between detector and

light source is 17cm. ................................................................................................... 75

48. 2D distribution of UV light intensity with an angle between optical fiber and photo

detector. Distance between detector and light source is 17cm. ................................... 77

49. The UV light intensity at different positions without optical fiber. ............................ 78

50. 2D distribution of UV light intensity without optical fiber. Distance between detector

and light source is 17cm. ............................................................................................ 79

51. Differential absorbance IR spectra of the PVC samples before and after 30 minutes of

UV irradiation (200 mw/cm2, Hg lamp). .................................................................... 81

52. Absorbance vs. time spectra of the PVC 8 mil film samples before and after 30

minutes of UV irradiation (200 mw/cm2, Hg lamp) at 3255cm

-1. .............................. 82



-1, 2923cm

-1 and

2850cm-1

. .................................................................................................................... 84



-1. .............................. 85



-1. .............................. 86

xi


minutes of UV irradiation (200 mw/cm2, Hg lamp) at 3255 cm

-1. ............................. 87



-1. ............................. 88

58. (a) Single beam spectra of PVC control sample collected during the UV degradation.

(b) IR difference spectra obtained by IR difference= -log(I/I0), where I is the single

beam at specified times and I0 is the single beam at 0 min. (c) Top view picture of the

PVC control sample at the end of the UV degradation experiment. (d) Variation in the

intensity of C-O stretch band at 1043 cm-1

. ................................................................ 90

59 (a) IR difference spectra of RX14426 + PVC sample obtained by IR difference= -

log(I/I0), where I is the single beam at specified times and I0 is the single beam at 0

min. (b) Top view picture of RX14426 + PVC sample at the end of UV degradation

experiment. (c) Variation in the intensity of C-O stretch band at 1043 cm-1

. ............. 91

60. (a) IR difference spectra of RX14427 + PVC sample obtained by IR difference= -


min. (b) Top view picture of RX14427 + PVC sample at the end of UV degradation


. ............. 92

61. (a) IR difference spectra of Tinuvin 328 + PVC sample obtained by IR difference= -


min. (b) Top view picture of Tinvuin 328 + PVC sample at the end of UV degradation


. ............. 93

62. DRIFT IR spectra of (a) PVC control sample, (b) RX14426 + PVC sample, (c)

RX14427 + PVC sample and (d) Tinuvin 328 + PVC sample. .................................. 94

63. Variation in the intensity of C-O stretch band at 1043 cm-1

of PVC control sample,

RX 14426 + PVC sample, RX14427 + PVC sample and Tinuvin 328 + PVC sample.

..................................................................................................................................... 95

64. Variation in the intensity of IR peaks at (a) 3306 cm-1

, (b) 2851 cm-1

, (c) 1784cm-1

,

(d) 1395 cm-1

of PVC control sample, RX 14426 + PVC sample, RX14427 + PVC

sample and Tinuvin 328 + PVC sample. ..................................................................... 96

65. The locations of Control sample, RX14426, RX14427 and Tinuvin 328 and the scan

area of the focal plane array. ....................................................................................... 97

66. Experimental setup for UV degradation of Control sample, RX14426, RX14427 and

Tinuivn 328 by focal plane array. ............................................................................... 98

67. Photographs of Control sample, RX14426, RX14427 and Tinuvin 328 before and

after UV degradation tested by focal plane array. Single beam spectra were collected.

Red color stands for the high intensity and blue color stands for the low intensity. .. 99

xii

68. IR absorbance spectra of Control sample, RX14426, RX14427 and Tinuvin 328

before and after UV degradation. .............................................................................. 100

69. IR difference spectra of Control sample, RX14426, RX14427 and Tinuvin 328 before

and after UV degradation. Spectra were obtained by IR difference= -log(I/I0), where I

is the single beam at 180 min and I0 is the single beam at 0 min. ............................ 101

70. Statistics results of all the old experiments for variation in the intensity of –OH band

at 3306 cm-1

, -CH and –CH2 band at 2924 cm-1

, C=O band at 1724 cm-1

and C-O

stretch band at 1043 cm-1

. ......................................................................................... 102

xiii

LIST OF TALBES

Table Page

1. Cell current-voltage characteristics for various electrolyte compositions under UVA

(Black light) illumination. ............................................................................................. 9

2. Cell current-voltage characteristics under UVA (Black Light) illumination for various

ethanol contents. ........................................................................................................... 9

3. Cell current–voltage characteristics under UVA (Black Light) illumination for various

reactants in the anode compartment. ............................................................................11

4. Literature results of the performance of photoelectrochemical cell. .............................11

5. Cutting off wavelength and band gap of TiO2-based catalysts. .................................... 31

6. Atomic percentage of Ti, O, Pt and S in thin film TiO2, 0.5 wt.% Pt-TiO2 and 0.5 wt.%

Pt-TiO2/H2S. ................................................................................................................ 33

7. Hydrogen and carbon dioxide production at different forward bias for TiO2, 0.5 wt.%

Pt-TiO2 and 0.5 wt.% TiO2/H2S as catalysts. .............................................................. 38

8. Comparison with the results in literature of the cell performance. ............................... 39

9. Results of the UV-visible spectroscopy of electrolyte containing methylene blue before

and after degradation by TiO2, 0.5 wt.% Pt-TiO2 and 0.5 wt.% TiO2/H2S. ................ 41

10. Quality of TiO2 thin film fabricated by different paste and casting methods. ............ 57

11. Experimental results of the performance of DSSCs. .................................................. 60

12. Experimental results of DSSC with copper-complex dye. ......................................... 67

13. Performance of two dye-sensitized solar cells with and without electrolyte. ............. 68

14. The UV light intensity at different positions............................................................... 73

15. NFPA and HMIS rating of chemicals ....................................................................... 104

1

CHAPTER I

INTRODUCTION

In nowadays, air pollution and water pollution has become a big issue in many countries,

especially in some developing countries. Most of the pollutions are caused by the coal-

fired power plant and oil refinery. Scientists have done many works to look for some

clean energy that will not cause the pollutions. Clean energy usually includes water

energy, wind energy, nuclear energy, geothermal energy and solar energy. Solar energy

has been more and more attractive recently because it is limitless and easy to obtain.

In 1991, Michael Grätzel discovered a new kind of solar cells which is called dye-

sensitized solar cells (DSSCs) 1. DSSC is a kind of inorganic solar cell which contains

titanium dioxide (TiO2) as working electrode, organic dye as initiator, platinum as

counter electrode and I3-/KI as electrolyte. The most important part in DSSC is TiO2

working electrode. TiO2 is a widely used semiconductor in science and also our daily life.

It can be coated on standard steel surgery blade due to its self-sterilization property. 2,3

The clothes and glasses with TiO2 thin film has been commercialized because of its self-

cleaning property.4-8

TiO2 also has the ability to degrade the toxicity and organic

pollution in gas and water. 9-12

All of the applications of TiO2 mentioned above is due to

its unique photocatalytic activity. Firstly, TiO2 has a wide band gap which is 3.2eV. It

helps TiO2 to both absorb the energy from visible light and ultraviolet light. Secondly,

TiO2 can form some reactive oxygen species on the surface when it is irradiated by the

2

light. The reactive oxygen species can oxidize some of the organic wastes and remove

them from water and gases. 13-16

Photoelectrochemical cell is a similar kind of solar cell with dye-sensitized solar cells and

it is firstly invented by Michael Grätzel in 2001.17

Both of them are designed based on

TiO2 as the working electrode. Photoelectrochemical cell can interconvert chemicals and

electricity with the energy of light by the photovoltaic effect.

The advantages of photoelectrochemical cell comparing to dye-sensitized solar cell is that

it can oxidize and degrade the organic wastes and water pollutions while it is producing

energy under sunlight.17

It can tremendously reduce the pollutions and generate limitless

solar energy if it can be successfully commercialized.

The limitation of photoelectrochemical cell is the low conversion efficiency. It is mainly

due to the electrolyte and photocatalyst. Especially for photocatalyst such as TiO2, the

efficiency is limited by the slow electron transfer and fast electron-hole recombination. 18

In this thesis, the modification of TiO2 was done by exposing to hydrogen sulfide after

doping with platinum. The cover of electron generating site on TiO2 by sulfur can

facilitate the interfacial electron to electron acceptors and decrease the fast electron-hole

recombination by serving as electron sink.

3

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4

CHAPTER II

LITERATURE REVIEW

2.1. Photocatalysts

The photoelectric effect has attracted lots of scientists and industries since the French

scientist Edmond Becquerel discovered it in 1839.19

This breakthrough makes people

believe that the energy convention from sunlight to electricity is possible. Photovoltaics

have the advantages to generate the electricity by separating the electron-hole pair in

semiconductor under sunlight. Semiconductor plays the significant role in this circulation

to generate electricity. More and more work have be done to discover more efficient

semiconductor which can be used as photocatalyst and generate electricity more and

faster. The energy levels of some common semiconductors were shown in figure 2.17

A

good photocatalyst is not only a semiconductor, it also requires an appropriate band gap

and energy level. Titanium dioxide is a good semiconductor which has been widely used

for photocatalyst.20

2.2. Titanium dioxide

TiO2 has a wide distribution on earth. It has three different forms which are called rutile,

anatase and brookite, respectively. The different crystal structures of each form are shown

in figure 3. The different crystal structures result in the different band gap. Since the

5

photocatalytic activity is strongly depended on the band gap of semiconductor, each form

of TiO2 has quite different behavior. Anatase has the highest photocatalytic activity and

brookite has the lowest. A commercialized TiO2 is named P25, which is a mixture of 20%

rutile and 80% anatase. In some literatures, it has a better performance than pure anatase.

21, 22 It is explained that adding of rutile will break the ordered crystal structure of anatase

and slow down electron hole recombination.

Figure 2. Band positions of several semiconductors in contact with aqueous electrolyte at

pH 1.

6

Figure 3. Ball and stick model for three different forms of titanium dioxide.

Although TiO2 is a good photocatalyst in many fields, it is still far away from the

practical use in solar cells. The disadvantages of TiO2 are the slow electron transfer and

fast electron hole recombination. To develop a practical TiO2-based photocatalytic

process, majority of studies on TiO2 focused on either enhancing its photocatalytic

activity or extending its absorption spectrum from UV to the visible range by adding a

second element to the TiO2 bulk structure.23-25

Platinum doped titanium dioxide had been

studied that platinum was useful to increase the performance of TiO2.26

The mechanism

was (i) to increase the •OH and oxidized species generated on Pt and (ii) slow down the

electron-hole recombination by serving as an electron sink.27-30

Zhiqiang Yu from our group studied the effect of Pt on the photocatalytic degradation

pathway of methylene blue over TiO2 under ambient conditions. From figure 4, we can

Rutile

Band gap: 3.0 eV

Anatase

Band gap: 3.2 eV

Brookite

Band gap: 3.4 eV

Ti atoms are gray

O atoms are red

7

clearly see that the degradation rate of methylene blue was faster over 0.5 wt.% Pt-TiO2

than that over TiO2. 3 wt.% Pt-TiO2 decreased the degradation rate because too much

platinum had covered the surface of TiO2 and decreased the amount of high active •OH

group.

Figure 4. (a) Chemical structure of methylene blue and the IR band assignment. (b)

Variations of the IR intensity of MB bands at 1488 cm-1 during 240 min of the MB

photocatalytic degradation.

2.3. Photoelectrochemical cell

Ever since the concept of photoelectrochemical cell was proposed by Michael Grätzel in

2001, it had been a hot topic for many years. People were attracted by the idea of

generating hydrogen as fuel and decomposing organic wastes at the same time. A lot of

work has been done to make it commercialized. Dr. Panagiotis Lianos’s group studied the

effect of electrolyte to the cell performance and proposed the possible reactions during

the photoelectrochemical procedure. 31-33

Methylene blue

(MB)

(a) (b)

8

The efficiency of the photoelectrochemical cell can be obtained by the current-voltage

profile which is measured by ampere meter.

Figure 5. Current-voltage profile of the photoelectrochemical cell.

The calculation of the efficiency is based on the equation below:

where Jsc is short circuit current density, Voc is open circuit voltage, Pmax is maximum

power, Pin is power of UV light and η is efficiency of photoelectrochemical cell.

Table 1 showed that the higher concentration of NaOH and H2SO4 could increase the

open circuit voltage (Voc) and short circuit current density (Jsc)31

. These two values were

directly related to the performance of the photoelectrochemical cell. Higher the Voc and

Jsc, the efficiency of the cell was higher. It was explained that the difference of pH value

between two electrolytes applied a chemical bias to the system and increased the

performance. The relationship between pH value and chemical bias could be expressed

by the equation:

∆V=0.059 ∆pH

9

where ∆V is the chemical bias and ∆pH is the difference of pH value.

Table 1. Cell current-voltage characteristics for various electrolyte compositions under

UVA (Black light) illumination.

Table 1 also showed that adding of ethanol to the base electrolyte had significantly

enhanced the performance of the photoelectrochemical cell. The author studied the

different contents of ethanol affected the efficiency of the cell. From table 2, we could see

1% of ethanol had already enhanced the performance 7 times. When the ethanol content

reached 20%, the maximum performance was obtained.

Table 2. Cell current-voltage characteristics under UVA (Black Light) illumination for

various ethanol contents.

The enhancement of performance by adding ethanol was explained by the reactions taken

place during the photoelectrochemical procedure. Reaction 1 showed that the TiO2 could

generate electron -hole pair under the UV light. The hole could oxidize water in reaction

10

2 or it could oxidize ethanol to carbon dioxide in reactions 3-5. However, the oxidized

potential for ethanol was much lower than that of water, so ethanol was preferred to be

oxidized first. The low oxidized potential resulted in the higher efficiency.32

The author also studied several kinds of organic waste which could be decomposed

during the photoelectrochemical reactions. The results were shown in table 3. We can see

that most of the organic wastes had enhanced the performance of the

photoelectrochemical cell compared to pure water. 34

Short circuit current density is the most important parameter to determine the

performance of the photoelectrochemical cell. Some results from the literature were listed

in table 4. Comparison between the literature results and my results will be discussed in

Chapter IV.

After achieving the goal to decompose the organic wastes and generate the hydrogen for

fuel, the main question was raised. How to further modify the photoelectrochemical cell

to get good enough performance for our daily life? This is what I try to solve in this

thesis.

(1)

(2)

(3)

(4)

(5)

(6)

11

Table 3. Cell current–voltage characteristics under UVA (Black Light) illumination for

various reactants in the anode compartment.

Table 4. Literature results of the performance of photoelectrochemical cell.

No. Working electrode Working electrolyte Jsc

(mA/cm2)

Literature

1 Nanocrystalline TiO2

film 0.2 M NaOH/ 20% EtOH 0.79 31


film 1.0 M NaOH/ 20% EtOH 0.89 32


film

1.0 M NaOH/

20% Glycerol 1.12 33

4 Titania nanotube 1 M KOH 0.112 34


film Not memtioned 0.55 35

12

CHAPTER III

EXPERIMENTAL

3.1. Preparation and characterization of platinum doped titanium dioxide and platinum

doped titanium dioxide treated by hydrogen sulfide

Platinum doped titanium dioxide (Pt-TiO2) and platinum doped titanium dioxide treated

by hydrogen sulfide (Pt-TiO2/H2S) were prepared by photo deposition. Titanium dioxide

(TiO2) was used as a control sample. Catalysts were characterized by Fourier transform

infrared spectroscopy (FTIR), 2D wide angle X-ray diffraction (WAXD), UV-Vis

spectroscopy, transmission electron microscopy (TEM), scanning electron microscope

(SEM) and energy-dispersive X-ray spectroscopy (EDS).

3.1.1. Preparation of platinum doped titanium dioxide

Platinum doped titanium dioxide (Pt-TiO2) was prepared by photo deposition method in

figure 6.18

0.5g titanium dioxide (P25, Degussa) and 66.6mg/133.3mg/399.9mg

chloroplatinic acid hexahydrate(IV) (99.9%, Alfa-Aesar) were added to the mixture of

28g deionized water and 2g ethanol (100%, Decon Labs, Inc.) in a quartz tube. The air in

the solution was removed by flowing the argon gas (Industrial Grade, Praxair) for ten

minutes. The tube was sealed well and stirred vigorously when it was exposed to UV-

visible light (Newsport, 350W Mercury lamp) for three hours. The solid was separated

from the solution by centrifuge and washed by DI water for three times. The solid was

dried in the oven at 300 0C for one hour and grounded to small powder. More platinum

13

was doped, the color was darker for the three samples. Products made by 66.6mg/

133.3mg/ 399.9mg chloroplatinic acid hexahydrate(IV) were marked as 0.5 wt.% Pt-

TiO2/ 1.0 wt.% Pt-TiO2/ 3.0 wt.% Pt-TiO2, respectively.

Figure 6. Experimental procedure of Pt-TiO2 preparation

3.1.2. Preparation of platinum doped titanium dioxide treated by hydrogen sulfide

0.5 wt.% Pt-TiO2 was used to prepare platinum doped titanium dioxide treated by

hydrogen sulfide (Pt-TiO2/H2S). 0.5 wt.% Pt-TiO2 was put in a quartz tube and heated at

450 0C for three hours in the hydrogen sulfide flow. The flow rate for hydrogen sulfide

was 10mL/min. After that, the solid was taken out and grounded to small powder (0.5

wt.% Pt-TiO2/H2S, figure 7).

14

Figure 7. Experimental procedure of Pt-TiO2/H2S preparation

3.1.3. Preparation of TiO2 thin film, Pt-TiO2 thin film and Pt-TiO2/H2S thin film

0.27g Polyethylene glycol (MW=20,000) and 1.8 mL deionized water were added into

the vial and mixed with hand. After all the PEG was dissolved, 0.9g TiO2/ Pt-TiO2/ Pt-

TiO2/H2S was added. Sonicator was applied to make them mix well. After adding 0.03

mL Triton X-100 (Laboratory grade, Sigma-Aldrich) and 0.06 mL acetylacetone (>99%,

Sigma-Aldrich), solution was sonicated for 30 min and stirred by magnetic bar for 2 days.

(Figure 8)

Figure 8. Experimental procedure of TiO2 paste preparation

15

Fluorine doped tin oxide coated glass slide (~7 Ω/sq, Sigma-Aldrich) was cut into

5cm*3.3cm and sonicated in water and ethanol three times alternatively. The pastes were

coated on the FTO glass by tape casting with a certain size (1cm*1cm). The thin films

were kept at room temperature for 30 min and sintered at both 150 0C and 450

0C for 30

min. (Increasing rate: 50/min). (Figure 9)

Figure 9. Experimental procedure of TiO2 thin film preparation

16

3.1.4 Characterization of catalysts in forms of powder and thin film

The morphology of the TiO2/ Pt-TiO2/ Pt-TiO2/H2S powders were characterized by TEM

(T12T/STEM, Tecnai) and the thin films were characterized by SEM (TM3030, Hitachi).

The samples of TEM were prepared by dipping a drop of catalysts mixed in DI water to a

carbon coated copper grids (SPI, 200 meshes). The thin films were characterized by SEM

without any further treatments. The absorption light and energy band gap of catalysts

were measured by UV-visible spectroscopy (U-3900, Hitachi). Fourier transform infrared

spectroscopy (Nicolet iS50R, Thermo scientific) was applied to detect the change of the

functional groups in catalysts. The catalysts were put in a diffuse reflectance infrared

Fourier transform spectroscopy (DRIFTS) cell (Figure 10). Two-dimensional wide angle

X-ray diffraction (2D WAXD) experiments were conducted on a Rigakua 18 kW rotating

anode X-ray generator using Cu Ka radiation (0.1542 nm) in transmission mode. The

attached detector was an R-AXIS-IV image plate system. The exposure time to obtain

high-quality patterns was 15 min. The peak positions were calibrated using silicon

crystals. Background scattering was subtracted from the sample pattern. 2D pattern was

integrated into one dimensional powder pattern. EDS was used to characterize the

distribution of elements in the TiO2-based catalysts.

17

Figure 10. Schematic (Left) and picture (Right) of DRIFT cell.

3.2. Setup of photoelectrochemical cell

The photoelectrochemical cell is a two component cell separated by a Nafion membrane

(0.180mm thick, ≥0.90 meq/g exchange capacity, Alfa Aesar) as shown in figure 11. The

top part has two gas ports which can allow the carrier gas to take out all the gas products

generated during the experiments. Platinum foil was used as a cathode which is also

known as counter electrode. The solution in top part is 0.1 mol/L sulfuric acid. Two pH

meters in both sides can monitor the pH change during the experiments. In the bottom

part, there are also two gas ports which allow us to take the gas products by syringe and

tested them in mass spectroscopy. FTO glass with catalysts coated on it was used as

anode which is also called working electrode. The solution in bottom part is 0.1 mol/L

sodium hydroxide water solution with 20 wt.% ethanol and 0.1 wt.% methylene blue

(≥82%, Sigma-Aldrich). The anode and cathode were connected by a galvanometer and a

power supply which can adjust the output voltage. The galvanometer was connected to a

computer which can record the change of current and voltage during the experiments.

The intensity of UV light was measured by photodiode sensor (818-UV/DB, Newport).

Sample

18

Figure 11. (a) Schematic setup and (b) pictures of photoelectrochemical cell

(b)

(a)

19

3.3. Characterization of gas products and solution in photoelectrochemical cell

The gas products generated during the experiments in photoelectrochemical cell were

characterized by mass spectroscopy (MS, Balzers QMG 112). The mass/charge responses

(i.e., m/z = 2, 28, 32 and 44 from H2, CO or N2, O2 and CO2) were analyzed to determine

the amount of the produced gases. Scotty gas (analytical standard, Supelco) was used to

calibrate the MS for H2 and CO2.

The oxidation rate of solution was monitored by UV-visible spectroscopy (Hitachi U-

3900). Methylene blue shows two peaks at 278.5 nm and 597.1 nm and the height was

proportional to the amount of methylene blue in the solution.

3.4. Experimental procedure of photoelectrochemical cell

Two experimental procedures were applied in this thesis. The first one focused on the

electrical measurement and gas products analysis. (Figure 12). The experiment was

started by applying a zero voltage power supply. The UV light was turned on at the

second minute. After waiting for 5 min, UV light was turned off. Increase the power

supply to 0.5 V and start to push the internal gas to MS by argon. After pushing for 3 min,

put the system into batch and turn on the UV light. Wait for another 5 min, turn off the

UV light and increase the voltage to 1.0V. Open the flow gas and push the gas products to

MS for analysis. After all the experiment, decrease the voltage to 0V again and stop the

measuring. The current and voltage were kept monitoring during the whole experiment.

Two pH values were also recorded.

The second experimental procedure focused on the pH change during the experiments. It

was designed with short time period and higher power supply voltage. It was shown in

figure 13.

20

Adjust the voltage to 0 V and

remove the air by argon

Wait for 2 min and put the system

into batch

Turn on UV light and wait for 15

min

Turn off UV light, open the gas flow

and carry the gas products to MS.

Increase the voltage to 0.5 V


min



Increase the voltage to 1.0 V


min



Decrease the voltage to 0 V

Wait for 2 min and stop the program

Figure 12. First experimental procedure of photoelectrochemical cell.

21

Adjust the voltage to 0V and remove the air by argon

Wait for 2 min and put the system into batch

Turn on UV light and wait for 3 min

Turn off UV light, open the gas flow and carry the gas products

to MS. Increase the voltage to 0.5 V.












to MS. Decrease the voltage to 0 V.

Wait for 2 min and stop the program.

Figure 13. Second experimental procedure of photoelectrochemical cell.

22

CHAPTER IV

RESULTS AND DISCUSSION

4.1. Characterization of TiO2-based catalysts

The characterizations of TiO2-based catalysts were both done in powder and thin film

format by IR, UV-vis, TEM and so on.

4.1.1 TiO2-based catalysts in powder and thin film form

The darkness of the color for TiO2, 0.5 wt.% Pt-TiO2, 1.0 wt.% Pt-TiO2, 3.0 wt.% Pt-TiO2

and , 0.5 wt.% Pt-TiO2/H2S increased step by step in figure 14. It shows that the doping

platinum was uniformly attached to TiO2 and the doping rate increased with the increase

amount of H4PtCl6. The color of 0.5 wt.% Pt-TiO2/H2S was darker than 0.5 wt.% Pt-TiO2

even 3.0 wt.% Pt-TiO2. It means that hydrogen sulfide treatment had some certain effect

to change the morphology of Pt-TiO2.

Figure 14. Photograph of TiO2, 0.5 wt.% Pt-TiO2, 1.0 wt.% Pt-TiO2, 3.0 wt.% Pt-TiO2

and 0.5 wt.% Pt-TiO2/H2S powder.

23

The thin film of TiO2, 0.5 wt.% Pt-TiO2 and 0.5 wt.% Pt-TiO2/H2S was shown in figure

15. The color also changed from white to dark grey. The high temperature calcine could

not change the color to white, which meant that the doping platinum and sulfur were not

removed in high temperature.

Figure 15. Photograph of TiO2, 0.5 wt.% Pt-TiO2, 1.0 wt.% Pt-TiO2, 3.0 wt.% Pt-TiO2

and 0.5 wt.% Pt-TiO2/H2S thin film.

4.1.2 TEM analysis of TiO2-based catalyst in powder form

The TEM picture of TiO2 in figure 16 showed the size of TiO2 was around 15~30 nm,

which matched the reported size in literature. 19

Platinum particles could be found in 0.5

wt.% Pt-TiO2 ,1.0 wt.% Pt-TiO2, 3.0 wt.% Pt-TiO2 and 0.5 wt.% Pt-TiO2/H2S. The size of

platinum is around 3~5nm. It further confirmed that platinum was successfully doped

into TiO2. Sulfur was not seen from the TEM pictures because sulfur was too small to

see.

TiO2

0.5 wt.%

Pt-TiO2

0.5 wt.% Pt-

TiO2/H

2S

24

Figure 16. TEM pictures of TiO2, 0.5 wt.% Pt-TiO2 ,1.0 wt.% Pt-TiO2, 3.0 wt.% Pt-TiO2

and 0.5 wt.% Pt-TiO2/H2S.

25

4.1.3 SEM analysis of TiO2-based catalysts in thin film form

The top view SEM pictures in figure 17 showed that TiO2 was much less porous than Pt-

TiO2 and Pt-TiO2/H2S. Hydrogen sulfide treatment increased the size of aggregates and

generated lager holes. The cross sectional view SEM pictures could show the thickness of

each thin film. From figure 17, the thickness of TiO2 was 22µm, which was much larger

than Pt-TiO2 and Pt-TiO2/H2S. The optimal thickness for photocatalyst was between 10 to

20 µm20

. The efficiency of Pt-TiO2/H2S was assumed to be significantly reduced by the

small thickness.

Figure 17. SEM pictures of TiO2, 0.5 wt.% Pt-TiO2 and 0.5 wt.% Pt-TiO2/H2S in thin

film from top and cross sectional views.

4.1.4 FTIR spectroscopy characterization of TiO2-based catalysts

The FTIR spectra of TiO2, Pt-TiO2 and Pt-TiO2/H2S in powder form were compared in

figure 18. The difference was the peaks at 3677 cm-1

, 3650 cm-1

and 3629 cm-1

increased

in Pt-TiO2 and Pt-TiO2/H2S compared to those in TiO2. These three peaks were assigned

26

to hydroxyl group attached to catalysts in three different ways. The hydroxyl groups can

interact with water or organics in the electrolyte and increase the rate of reaction. The

more the hydroxyl group, the photocatalytic activity was higher.

27

4000 3500 1500 10000.0

0.5

1.0

1.5

Pt-TiO2/H

2S

Pt-TiO2

Sin

gle

bea

m i

nte

nsi

ty (

a.u

.)

Wavenumber (cm-1)

TiO2

3650

3629

3677

3414

H2 O

(a)

28

Figure 18. (a) Single beam and (b) absorbance FTIR spectra of TiO2, 0.5 wt.% Pt-TiO2

and 0.5 wt.% Pt-TiO2/H2S in powder form. Absorbance was obtained by absorbance

=log(1/I), where I was the intensity of single beam.

The FTIR spectra of TiO2, Pt-TiO2 and Pt-TiO2/H2S in thin film form were also compared

in figure 19. Same with the powder, three peaks at 3677 cm-1

, 3650 cm-1

and 3629 cm-1

also increased in Pt-TiO2 and Pt-TiO2/H2S compared to those in TiO2. The assignment

was still the same. The only difference was the peak at 3711 cm-1

, which significantly

decreased in Pt-TiO2 and Pt-TiO2/H2S. The band at 3711 cm-1

was assigned to the free

hydroxyl group. More free hydroxyl group in TiO2 showed that the assembly of hydroxyl

group in TiO2 was better.

4000 3500 1500 10000

2

4

Pt-TiO2/H

2S

Pt-TiO2

Abso

rban

ce (

a.u

.)

Wavenumber (cm-1)

TiO2

3650

3629

3677

3414

H2 O

(b)

29

Figure 19. (a) Single beam and (b) absorbance FTIR spectra of TiO2, 0.5 wt.% Pt-TiO2

and 0.5 wt.% Pt-TiO2/H2S in thin film form. Absorbance was obtained by absorbance

=log(1/I), where I was the intensity of single beam.

4000 3500 1500 10000.0

0.5

1.0

1.5 3711

Pt-TiO2/H

2S

Pt-TiO2

Sin

gle

beam

inte

nsit

y (a

.u.)

Wavenumber (cm-1)

TiO2

3650

3629

3677

3414

H2 O

O

4000 3500 1500 10000.0

0.5

1.0

1.5

2.0 3711

Pt-TiO2/H

2S

Pt-TiO2

TiO2

Sin

gle

bea

m i

nte

nsi

ty (

a.u

.)

Wavenumber (cm-1)

3650

3629

3677

3414

H2 O

(a)

(b)

30

4.1.5 UV-Vis spectroscopy characterization of TiO2-based catalysts

The UV-vis spectra of TiO2-based catalysts were shown in figure 20. The baseline of Pt-

TiO2 and Pt-TiO2/H2S were higher than TiO2 because dark color could absorb visible

light. The cutting off wavelength was shifted from 388nm for TiO2 to 434nm for Pt-TiO2

and 442nm for Pt-TiO2/H2S. It was exactly the same both in powder and thin film form.

Cutting off wavelength was a very useful valve which could calculate the band gap based

on it. The equation was shown below:

band gap= /h C 21 (7)

where h is Planks constant, 6.626× 10−34 Joules sec. C is the speed of light, 3.0 x 108

meter/sec, λ is the cut off wavelength.

Based on the equation 7, the band gap of three catalysts could be calculated and listed in

table 5.

200 300 400 500 600 700 8000.0

0.5

1.0

1.5

2.0

Pt-TiO2/H

2S

Ab

sorb

ance

(a.

u.)

Wavelength (nm)

Pt-TiO2

TiO2

388 (TiO2)

434 (Pt-TiO2)

442 (Pt-TiO2/H

2S)

(a)

31

200 300 400 500 600 700 8000.0

0.5

1.0

Ab

sorb

ance

(a.

u.)

Wavelength (nm)

Pt-TiO2/H

2S

Pt-TiO2

TiO2

Figure 20. UV-vis spectroscopy of TiO2, 0.5 wt.% Pt-TiO2 and 0.5 wt.% Pt-TiO2/H2S in

(a) powder and (b) thin film form.

Table 5. Cutting off wavelength and band gap of TiO2-based catalysts.

TiO2 Pt-TiO2 Pt-TiO2/H2S

Cutting off wavelength 388 nm 434 nm 442 nm

Band gap 3.2 eV 2.9 eV 2.8 eV

The band gap decreased from 3.2 eV to 2.9 eV for Pt-TiO2 and 2.8 eV for Pt-TiO2/H2S.

The small band gap indicated that it would be easier to generate electron-hole pair and

slow down the recombination. The efficiency of Pt-TiO2/H2S was assumed to be the best

based on the small band gap.

(b)

32

4.1.6 Two-dimensional wide angle X-ray diffraction spectroscopy of TiO2-based

catalysts.

The XRD patterns of the three TiO2-based catalysts in powder form were shown in figure

21. All of them have the peaks of anatase and rutile, which matched the peaks in P25.

There were not many differences between these three samples. It indicated that the

neither of platinum doping and hydrogen sulfide treatment affected the crystal structure

of TiO2. The peak of platinum around 400 was hardly to see which meant the amount of

platinum was very little.

15 20 25 30 35 40 45

R

AR

A

R

2

Co

un

ts (

a.u

.)

Pt-TiO2/H

2S

Pt-TiO2

TiO2

Pt (111)

Figure 21. XRD spectroscopy of TiO2-based catalysts in powder form.

33

4.1.7 Energy-dispersive X-ray spectroscopy of TiO2-based catalysts

EDS was used to characterize the distribution of element in the TiO2-based catalysts in

thin film form. The results were listed in table 6.

The atomic percentage of Ti to O was around 1:2 in all the catalysts, which matched the

composition of TiO2. 0.1% platinum in Pt-TiO2 shows the platinum doping had

successfully introduced platinum into TiO2. Pt-TiO2/H2S has 0.26% sulfur which was

almost the same with platinum. It indicated that sulfur atoms were enough to cover all the

platinum atoms.

Table 6. Atomic percentage of Ti, O, Pt and S in thin film TiO2, 0.5 wt.% Pt-TiO2 and 0.5

wt.% Pt-TiO2/H2S.

Atom %

Ti O Pt S

TiO2 30.89 69.11 0 0

Pt-TiO2 35.02 64.87 0.1 0

Pt-TiO2/H2S 34.55 64.99 0.2 0.26

4.2. Results of photoelectrochemical cell

The results of photoelectrochemical cell were obtained by the voltammetry, pH meter and

MS results.

4.2.1 Photoelectrochemical reactions

The setup of photoelectrochemical cell had been talked about in the experimental part.

The reactions might happen during the experiment were shown in figure 22. When TiO2

were exposed to UV light, electron-hole pairs were generated inside TiO2. Electrons

34

would go through the out circuit and reduced the proton to hydrogen gas. Holes would

diffuse to the surface of TiO2 and oxide the organics such as the ethanol and methylene

blue to carbon dioxide. During the whole experimental process, hydrogen was generated

and organic wastes were decomposed.

h+

e-

Conduction band

Ec= -0.2V

Valance band

Ev= 3.0V

UV lightH2O

EtOH

e-

CO2

H2

Working

electrodeElectrolyte

Counter

electrode

3.2 V

Figure 22. Schematic representation of the operating principle and reactions of

photoelectrochemical cell.

4.2.2 Electrical experimental results of photoelectrochemical cell

All the catalysts of Pt-TiO2 and Pt-TiO2/H2S were referred to 0.5 wt.% Pt-TiO2 and 0.5

wt.% Pt-TiO2/H2S. First experimental procedure was used to collect the data below.

Figure 23 showed the results of current density collected during the experiment. Once the

V light was turned on, the current density suddenly increased from 0 mW/cm2 to around

0.5 mW/cm2. This result indicated that the UV light had a significant effect on the current

density of photoelectrochemical cell. This phenomenon was repeaand reproducible.

When the power supply provided 0V to the system, Pt-TiO2 has the highest current

35

density. Pt-TiO2/H2S was almost the same with TiO2. When the voltage increased to 0.5V,

Pt-TiO2 was still the highest. TiO2 was higher than Pt-TiO2/H2S at 0.5V. After the voltage

was increased to 1.0V, TiO2 has the highest current density. The results showed that Pt-

TiO2 has a better efficiency at low voltage than TiO2. It matched the literature results.18

At high voltage, hydrolysis played an important role in the reactions and the better

arrangement of TiO2 leaded to a higher performance. Pt-TiO2/H2S was not as good as the

other two catalysts due to the much thinner thickness. The effect of thickness was more

important than the performance of catalyst itself.

H2 and CO2 were all detected by MS during the experiment in figure 24. The areas of the

peaks were intergraded and the value was proportional to the amount of gases. The

amount of H2 increased with the increase of power supply voltage. However, the amount

of CO2 decreased with the increase of power supply voltage. It could be explained by that

hydrolysis dominated the reactions in the high voltage. If the hydrolysis was more than

photocatalytic reaction, ethanol was less reacted and less CO2 was produced. In the

opposite, H2 could always be produced either by hydrolysis and photocatalytic reaction. It

could also be proved by the pictures in figure 25. More CO2 bulb was formed at the lower

power supply voltage with the same TiO2-based catalyst. When the voltage was 0V, Pt-

TiO2/H2S produced most CO2. CO2 bulb could not be seen with TiO2. This result strongly

indicated that platinum doped TiO2 had much better performance than TiO2 in

decomposing organics. Hydrogen sulfide treatment could further increase the

performance.

36

0 10 20 30 40 50 60

0.0

0.5

1.0

1.5

UV

on

UV

off

UV

off

UV

on

UV

off

UV

on

TiO2

Pt-TiO2

Pt-TiO2/H

2S

Cu

rren

t d

en

sit

y (

mW

/cm

2)

Time (min)

1.0 V

0.5 V

0.0 V

Figure 23. Time profiles of current density at different forward bias voltage for TiO2, 0.5

wt.% Pt-TiO2 and 0.5 wt.% TiO2/H2S as working electrode.

37

4.2.3 Gas production results of photoelectrochemical cell experiment.

0 10 20 30 40 50 60

1.0 V0.5 V

H2

CO2

CO2

H2

0 V

H2

CO2

TiO2

Pt-TiO2

Pt-TiO2/H

2S

Ion

in

ten

sity

(a.

u.)

Time (min)

8.88E-13 1.14E-12 1.57E-12

7.71E-13 8.33E-13 1.24E-12

1.53E-12 1.85E-12

7.54E-13 6.65E-13 5.12E-13

8.47E-13 6.56E-13 4.90E-13

3.43E-13 3.15E-13

Figure 24. Time profiles of MS intensity at different forward bias voltage for TiO2, 0.5

wt.% Pt-TiO2 and 0.5 wt.% TiO2/H2S as working electrode. H2 and CO2 were detected

from the gas products.

Figure 25. Pictures of the CO2 blub formation during the experiment.

38

All the data of the photoelectrochemical cell experiment were organized in table 7. The

reaction produced similar hydrogen with TiO2 and Pt-TiO2/H2S. As we mentioned above,

the thickness of Pt-TiO2/H2S was much less than that of TiO2. If the thickness of Pt-

TiO2/H2S could be similar to TiO2, the hydrogen production of Pt-TiO2/H2S must be

much more than the other catalysts. More experiment would be done to verify this

conclusion. On the other hand, Pt-TiO2 and Pt-TiO2/H2S produced significant more CO2

than TiO2 which further confirmed the platinum doped TiO2 has better performance in

degradation of organic wastes. Considering the effect of thickness, Pt-TiO2/H2S was

supposed to be the best catalyst in hydrogen production and organic decomposing.

Table 7. Hydrogen and carbon dioxide production at different forward bias for TiO2, 0.5

wt.% Pt-TiO2 and 0.5 wt.% TiO2/H2S as catalysts.

39

Table 8. Comparison with the results in literature of the cell performance.

No

.

Working

electrode

Working

electrolyte

Jsc

(mA/cm2)

Current density

under 0.5V

forward bias

(mA/cm2)

Literat

ure

1 Nanocrystalline

TiO2 film

0.2 M NaOH/

20%EtOH 0.79 0.8 31

2 Nanocrystalline

TiO2 film

1.0 M NaOH/

20% EtOH 0.89 0.91 32

3 Nanocrystalline

TiO2 film

1.0 M NaOH/

20% Glycerol 1.12 - 33

4 Titania nanotube 1 M KOH 0.112 - 34

5 Nanocrystalline

TiO2 film Not mentioned 0.55 - 35

6 Nanocrystalline

TiO2 film

1.0 M NaOH/

20% EtOH 0.41 0.89

This

work

7 Nanocrystalline

Pt-TiO2 film

1.0 M NaOH/

20% EtOH 0.51 1.16

This

work

8 Nanocrystalline

Pt-TiO2/H2S film

1.0 M NaOH/

20% EtOH 0.38 0.64

This

work

From the comparison between the results of literature and my work in table 8, we can see

that the Jsc of my photoelectrochemical cell were lower than Dr. Lianos’s work.

However, the current density under 0.5V forward bias of my cell was higher than the

literature results. It indicated that my cell could work better under 0.5V forward bias.

4.2.4 Photo oxidation of methylene blue in the photoelectrochemical cell experiment

Methylene blue is a very excellent pigment in industry and academic. It is widely used as

an indicator in biology and chemistry to represent the organic wastes. In this

photoelectrochemical cell experiment, methylene blue was used to monitor the organic

degradation during the process. Figure 26 showed that all of the three solutions with

TiO2, Pt-TiO2 and Pt-TiO2/H2S have decomposed more or less methylene blue after the

reactions. For further observation, Pt-TiO2 decomposed the most methylene blue and the

color of the solution was lightest.

40

Figure 26. Photograph of electrolyte containing methylene blue (a) before and after

degradation by (b) TiO2, (c) 0.5 wt.% Pt-TiO2 and (d) 0.5 wt.% TiO2/H2S.

In order to get a more reliable and quantified results, UV-vis spectroscopy was used to

characterize the amount of residual methylene blue in the solutions. Figure 27 showed

that all of the methylene blue solutions had two peaks, which were located at 278.5nm

and 597.1nm. It was confirmed by the literature results.22, 23

200 300 400 500 600 700 8000.0

0.5

1.0

597.1278.5

Abso

rban

ce (

a.u

.)

Wavelength (nm)

Before degradation

After degradation by TiO2

After degradation by Pt-TiO2

After degradation by Pt-TiO2/H

2S

(b) (a) (c) (d)

41

Figure 27. UV-visible spectroscopy of electrolyte containing methylene blue before and

after degradation by TiO2, 0.5 wt.% Pt-TiO2 and 0.5 wt.% TiO2/H2S.

By comparing the peak height at 278.5 nm and 597.1 nm of all samples, the results were

obtained in table 9. The percentage of degradation of methylene blue showed that Pt-TiO2

had the best performance to decompose the methylene blue. This result matched the color

change in figure 26. Pt-TiO2/H2S had a much better performance than TiO2 even it has a

significantly less thickness. The conclusion could be drawn that the performance of

decomposing organic wastes was significantly increased by doping platinum to TiO2 in

photoelectrochemical cell.

Table 9. Results of the UV-visible spectroscopy of electrolyte containing methylene blue

before and after degradation by TiO2, 0.5 wt.% Pt-TiO2 and 0.5 wt.% TiO2/H2S.

278.5 nm 597.1 nm Average

Methylene blue

Peak

height

Degradation

percentage

Peak

height

Degradation

percentage

Degradation

percentage

Before degradation 0.265 0.00% 0.514 0.00% 0.00%

After degradation

by TiO2

0.194 26.79% 0.376 26.85% 26.82%

After degradation

by Pt-TiO2

0.098 63.02% 0.206 59.92% 61.47%

After degradation

by Pt-TiO2/H2S

0.142 46.42% 0.289 43.77% 45.09%

42

4.2.5 pH change

The second experimental procedure was used to collect the pH change during the

photoelectrochemical reactions. The two pH meters had kept monitoring the pH change

during the experiments. Figure 28 showed that the pH change of the acid electrolyte

strongly depended on the UV on and off. The pH increased once the UV light was turned

on and it decreased as soon as the UV light was turned off. The change of pH value was

similar to the change of current density. For the pH of base electrolyte, it didn’t change

much in the whole experiment.

The intensity of UV light also had a significant effect on the pH change. Figure 29

showed that pH didn’t change when the intensity of UV light was 10 mW/cm2. When the

intensity increased to 100 mW/cm2 and 1000 mW/cm

2, the pH increased once the UV

light was turned on. If the UV light was turned off, the pH decreased immediately. Both

the pH values in acid electrolyte and base electrolyte has the same trend. In addition, the

pH value had a larger increase or decrease with the larger intensity of UV light. The pH

value vibrated with the largest amplitude when the intensity of UV light was 1000

mW/cm2.

The mechanism of the pH change was still unknown. The future work will be done by

other students in this group.

43

0

2

4

0.8

0.9

0 5 10 15 20 25

12.3

12.4

UV

on

UV

on

UV

on

UV

on

UV

off

UV

off

UV

off

UV

off

UV

off

UV

on

2.0V1.5V

1.0V0.5V

Cu

rren

t d

ensi

ty

(m

A/c

m2)

0V

Base

Acid

Time (min)

pH

pH

Figure 28. The change of pH values and current density during the experiments.

44

0 5 10 15 20 251.30

1.35

1.40

1.45

1.50

1.55

1.60

2.0 V

1.5 V

1.0 V

0.5 V0.0 V

pH

Time (min)

1000 mW/cm2

100 mW/cm2

10 mW/cm2

0 5 10 15 20 2512.60

12.64

12.68

12.72

12.76

12.80

pH

Time (min)

2.0 V1.5 V1.0 V0.5 V0.0 V

Figure 29. Effect of different UV light intensity on the pH change.

45

4.3. Conclusions

Pt-TiO2 and Pt-TiO2/H2S has been successfully synthesized by photo deposition and

thermal deposition methods. A series of characterization have been done to confirm the

crystal structures and the distribution of elements. Two experiments of

photoelectrochemical cell were done to compare the photocatalytic activity of TiO2, Pt-

TiO2 and Pt-TiO2/H2S. Pt-TiO2 has a good performance both in hydrogen production and

organic wastes decomposition. Pt-TiO2/H2S is good at decomposing organic wastes but

worse than TiO2 in hydrogen production. It is likely due to the small thickness of thin

film. More experiments will be done to prove the effect of thickness to the cell

performance.

46

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51

APPENDICES

52

APPENDIX A

DYE-SENSITIZED SOLAR CELLS (DSSC)

As mentioned in the introduction, DSSC is a kind of inorganic solar cell which is

composed by semiconductor, organic dye, electrolyte and metal electrode. As shown in

figure 30, the organic dye S absorbs the light and activated to the higher energy level. The

electron from the dye injects to the semiconductor which is usually TiO2 and transfer

through the out circuit to the metal electrode. Then the electron reduces I- to I3

- and

completes the circulation. 41

Figure 30. Representation of a dye-sensitized TiO2 solar cell and the processes involved

in energy conversion (S represents the dye-sensitizer and I-/I3

- is the charge mediator).

TiO2 is the most significant part in DSSC. A lot work has been done to modify the TiO2

thin film to make the efficiency higher. In this thesis, different TiO2 structures and

coating methods were tested. The organic dye is usually Di-tetrabutylammonium cis-bis

(isothiocyanato) bis (2, 2’-bipyridyl-4, 4’-dicarboxylato) ruthenium (II) (N719), which is

53

extremely expensive. In the second part of this appendix, the cheap copper-complex dye

is discussed to compare with the commercialized N719.

I. Modification of TiO2 thin film and casting method

1. Preparation of TiO2 paste

1.1. Sol-gel recipe

1.1.1. 1% Sol-gel recipe

HCl solution (400 mL 0.1M, pH=1) was prepared by diluting 3.33mL of concentrated

HCl to achieve 400 ml solution. 5.0 g TiCl4 was added to the solution in a dropwise

manner under magnetic stirring (900 RPM, 0 oC).TiCl4 should also be kept at 0

oC before

adding. The solution was left stirred for 2h (0 oC). NH4OH was added to the solution

until pH reaches 8 (pH was determined by pH meter). The color of the gel became ivory

immediately and the viscosity increased a lot (like white cake) indicating the formation of

hydrated titanium oxide gel Ti(OH)4. After aging for 2h under magnetic stirring, the

white precipitate was separated by Buchner funnel and washed with distilled water for

several times until no Cl- ion was detected (use Ag

+ to detect).

The precipitate was put into a conical flask and dispersed in 100 mL DI under magnetic

stirring. 17.9g Hydrogen peroxide solution and 90mL DI water were added into the slurry

at 5 oC. The solution was kept stirring for 2h. After that, the solution was heated at 90

oC

for 8 h with a reflux condenser pipe.

Yellow transparent solution was gained at last.

1.1.2. 5% sol-gel recipe

After we gained the 1% TiO2 sol-gel, I left it on hot plate and turned it to 70 oC. The

weight of beaker and solution were measured. The solvent evaporated and solution was

54

concentrated. The weight of the solution remained was measured again. When the weight

was only one fifth of the original weight, the concentration was 5%. The solution became

highly viscous from solution to gel. The color was still yellow.

1.2. Normal TiO2 paste

1.8g TiO2(Anatase or P25), 3.6mL DI water, 0.54g PEG, 0.0642g Triton X-100 and

0.117g acetylacetone. PEG and DI water were added into the bottles first and mixed with

hand. TiO2 was added and sonicator was applied to make them mix well. After adding

Triton X-100 and acetylacetone, solution was sonicated for 30 min and stirred by

magnetic bar for 2 days.

1.3. Porous TiO2 paste

1.3.1. Method I42

In a typical preparation, a 0.4-g/L Pluronic P123 aqueous solution was mixed with

titanium ethoxide in pH=1 with stirring for 2h. The resulting solution was then treated

with ammonia solution until the pH was 7 and maintained at the same temperature for a

day. The white precipitate formed was extracted with dichloromethane twice then filtered

and washed with distilled water until no sulfate ion was found by BaCl2 solution test (0.1

M BaCl2). The washed samples were dried at 105 0C for a day and ground to fine powder

to give final products designated as P123–TiO2. P123-TiO2 was mixed with PEG, water,

Trion X-100 and acetylacetone to give a fine paste.

1.3.2. Method II43

1.6g Pluronic P123 was dissolved in 20 g ethanol. 3.4 g of titanium ethoxide and 0.3 mL

of concentrated HCl were added into the solution. The synthesized solution was dried at

55

room temperature to form a gel. Degussa P25 nanoparticles (Aerosil, ∼30 nm, BET 56

m2 /g) were added into the mesoporous TiO2 gel at 5% concentration by weight to obtain

mesoporous/P25 mixture films.

1.3.3. Method III

Directly mix commercial anatase with P123, water, Trion X-100 and acetylacetone and

stir for two days.

2. Preparation of TiO2 thin film

2.1. Tape casting

Magic tape was cut by a self-made model and stick to glasses. Use credit card to force the

air between glass and tape come out and make it flat. Some paste was put at one side of

the tape and a metal column was used to cast paste on glass as flat as possible. (Figure 9)

2.2. Screen printing

The screen characteristics are as follows: material, polyester; mesh count, 90T mesh/cm;

mesh opening, 60 μm; thread diameter, 50 μm; open surface, 29.8%; fabric thickness, 83

μm. The procedure was shown in figure 31.

2.3. Spin coating

The TiO2 paste was dropped on the FTO glass and spin coated. After it was dried, coat

another layer of TiO2 thin film. It was repeated five times for each sample. The RPM is

2000.

56

Figure 31. Experimental procedure for screen printing.

Figure 32. The instrument and schematic procedure for spin coating.

57

3. Results of TiO2 thin film

Table 10. Quality of TiO2 thin film fabricated by different paste and casting methods.

No

. TiO2 paste

Casting

method

Thickne

ss

Flexibilit

y*

Adhesio

n

Hardne

ss

1 1% Sol-gel TiO2 Spin coating 200 ~

400 nm Very good

Very

good

Very

good

2 1% Sol-gel TiO2 Screen

printing ~500 nm Very good

Very

good

Very

good

3 5% Sol-gel TiO2 Spin coating 200nm

~2 µm Normal Bad Normal

4 5% Sol-gel TiO2 Screen

printing 1~3 µm Good Good Normal

5 Normal TiO2 Screen

printing

10~20

µm Good Good Good

6 Normal TiO2 Tape casting 10~20

µm Good Good Good

7 Porous TiO2:

Method I Tape casting 5~10 µm Normal Bad

Very

bad

8 Porous TiO2:

Method II Tape casting 1~5 µm Bad Bad

Very

bad

9 Porous TiO2:

Method III Tape casting 1~5 µm Bad Bad

Very

bad

10 Dyesol** Screen

printing 15 µm Good Good Good

*The method for determining the thin film quality was based on the literature.43

** Dyesol is a commercialized DSSC product from Dyesol Company.

Figure 33. Photographs of TiO2 thin film corresponding to the 8.

58

From the results in table 10, 1% sol-gel TiO2 has the best quality. However, the thickness

for 1% sol-gel TiO2 is less than 1 µm which is much less than the optimal thickness for

DSSC. For all the porous TiO2, the thin films are all bad. They didn’t stick to the glass

hard and was easy to be scratched by fingers. Considered the thickness and other

properties of the TiO2 thin films, the normal TiO2 thin film may be the best for DSSC.

4. DSSC assembling

After the preparation of TiO2 thin films, the adsorption of dye was carried out by soaking

the film in 0.5 mM dye solutions at 80 0C. The dye, Di-tetrabutylammonium cis-bis

(isothiocyanato) bis (2, 2’-bipyridyl-4, 4’-dicarboxylato) ruthenium (II) (N719), was

obtained from Aldrich. The dye was allowed to soak at room temperature for 24 hours in

a mixture solution of tert-butyl alcohol and acetonitrile (1:1). Thereafter, the dye-

adsorbed TiO2 electrodes were taken out and rinsed with dry ethanol. The rinsing process

was repeated several times to completely remove unbound dyes. Finally, the dye-

adsorbed TiO2 films were dried in air. A counter electrode was prepared by sputtering

(Hitachi E-1045 ion sputter) a thin platinum layer on an FTO substrate 20 nm. The dye-

adsorbed TiO2 electrode and Pt counter electrode were assembled into a sandwich-sealed

type cell by heating with hot-melt Surlyn film (25 μm thickness, 1702, DuPont) as a

spacer. A drop of electrolyte solution (0.05 M I2, 0.5 M LiI, 0.5 M 4-tert-butylpyridine (t-

BPy) in acetonitrile) was injected through a hole in the counter electrode, which was then

sealed with the glass cement. The working area of the electrode is 0.25 cm2.

59

5. Efficiency test of DSSC

The efficiency of DSSC is measured by an advanced current-voltage meter. The light is

generated by a solar simulator (Newport, 94023A) with a 150 mW Xe lamp. The light

intensity is 100mW/cm2 which is AM 1.5 standard sunlight. The schematic setup is

shown in figure 34. The calculation of the efficiency is based on the equation below:

where Jsc is short circuit current density, Voc is open circuit voltage, Pmax is maximum

power of DSSC, Pin is power of UV light and η is efficiency of DSSC. Jsc and Voc can be

obtained from the voltage-current profile in figure 35.

Figure 34. Measurement of the efficiency of DSSC.

Power supply

150

150 mW Xe lamp

Cell

Measurement of Cell Perfromance

AM 1.5 simulated

sunlight

100 mW/cm2

Filter

Volt/Amp Meter

60

Figure 35. The calculation of the efficiency of DSSC based on the voltage-current profile.

Table 11. Experimental results of the performance of DSSCs.

No. TiO2 paste Casting

method

Voc

(V)

Jsc

(mA/cm2)

FF Efficiency

(%)

1 1% Sol-gel TiO2 Spin coating 0.163 0.0152 0.25 0.00063

2 1% Sol-gel TiO2 Screen printing 0.256 0.0072 0.26 0.00047

3 5% Sol-gel TiO2 Spin coating / / / /

4 5% Sol-gel TiO2 Screen printing 0.056 0.128 0.31 0.0022

5 Normal TiO2 Screen printing 0.724 5.216 0.64 2.4

6 Normal TiO2 Tape casting 0.733 8.068 0.69 4.1

7 Porous TiO2: Method I Tape casting / / / /

8 Porous TiO2: Method II Tape casting / / / /

9 Porous TiO2: Method III Tape casting / / / /

10 Dyesol Screen printing 0.730 10.88 0.65 5.2

From the results in table 11, the efficiency of 5% sol-gel TiO2 is higher than that of 1%

sol-gel TiO2. It indicates that the thickness is more important than the other properties for

the cell performance. For comparison the results of sample 5 and 6 in 10, we can see that

tape casting is better than screen printing. This is due to the arrangement of TiO2 and also

the thickness.

61

6. Conclusions

1% sol-gel TiO2 has the best adhesion and hardness properties among all the TiO2 thin

films. The efficiency of DSSC is strongly dependent on the thickness of TiO2 thin film.

II. Copper-complex dye

Di-tetrabutylammonium cis-bis (isothiocyanato) bis (2, 2’-bipyridyl-4, 4’-dicarboxylato)

ruthenium (II) (N719) is the most widely used organic dye in DSSC. It has a good

performance and already be commercialized. The only problem is that this N719 organic

dye is too expensive. It costs $316 per gram. It is an urgent problem needed to be solved

that another cheaper dye can replace N719.

Figure 36. The chemical structure of N719.

62

Based on the chemical structure of N719 in figure 36, we can see that there are two SCN

groups and two 2, 2’-bipyridyl-4, 4’-dicarboxylato groups. As my group member

accidently found that when the copper salt was mixed with tetraethylenepentamine

(TEPA) and aniline, the solution became dark blue. This inspired me to design the

copper-complex dye with TEPA and aniline and tested in DSSC.

Figure 37 shows the chemical structures of Cu(TEPA)(Aniline)2Cl2 (Dye1) and

Cu(TEPA)2(NO3)2 (Dye2). The synthetic route is shown in figure 38 and 39. All the

precursors used in the synthesis are very cheap. The approximate price for Dye1 and

Dye2 is just $1 per gram which is much cheaper than that of N719.

63

Figure 37. The chemical structures of (a) Dye1 and (b) Dye2.

(a)

(b)

64

10 mL H2O

0.002 mol CuCl2 0.002 mol TEPA+

Copper aqueous solution

Dye1

Dissolved

Stirring for 1 h

Auto clave at 403K for 2 h

0.004 mol anilineDissolved

Figure 38. The synthetic route of Dye1.

The synthesis for Dye1 and Dye2 were very easy. Copper precursors were just simply

mixed with TEPA and aniline and stirred for 1h. The colors of the both solution were

suddenly changed to dark blue when TEPA were added. It indicated that the TEPA had a

quite strong interaction with copper. The solutions were treated in auto clave at 403K for

2h in order to enhance the stability of Dye1 and Dye2. The blue color didn’t change after

the treatment, which indicated that the copper complexes were very stable.

The pictures of Dye1 and Dye2 were shown in figure 40. N719 was also included for the

comparison.

65

10 mL H2O

0.002 mol Cu(NO3)2 0.004 mol TEPA+

Copper aqueous solution

Dye2

Dissolved

Stirring for 1 h

Auto clave at 403K for 2 h

Figure 39. The synthetic route of Dye2.

Figure 40. Pictures of N719, Dye1 and Dye2 in solution.

N719 Dye1 Dye2

66

From the pictures in figure 40, the color of N719 was dark purple. Dye1and Dye2 both

had the dark blue color. From more specific observation, the color of Dye2 was darker

than Dye1. The reason might be the TEPA was replaced by aniline in Dye1.

Figure 41. The pictures of TiO2 thin films after immersing in Dye1 and Dye2 for 24 h.

After immersing in Dye1 and Dye2 for 24 h, the TiO2 thin films became blue. However,

the adsorption dye was not as strong as N719. It could be washed by ethanol. The reason

might be the solvent of Dye1 and Dye2 was water, which had a worse adhesion to TiO2

thin film.

The TiO2 thin films with Dye1 and Dye2 were assembled to DSSC and tested the

efficiency.

Dye1

Dye2

67

Table 12. Experimental results of DSSC with copper-complex dye.

Dye TiO2 Name Voc (V) Jsc (mA) FF Efficiency

(%)

Dye1

Sol-gel

TiO2

1 0.00016 0.014 0.41 2.60E-07

2 0.00017 0.0112 0.48 2.99E-07

3 0.00012 0.0108 0.48 1.54E-07

3 0.00012 0.0108 0.48 1.54E-07

Dyesol

1 0.559 0.048 0.24 6.40E-03

2 0.528 0.084 0.28 1.20E-02

Washed

dye 0.0099 0.0124 0 0

Normal

TiO2

1 0.465 0.028 0.46 5.70E-03

2 0.528 0.052 0.31 8.30E-03

Dye2 1 0.434 0.0196 0.39 3.30E-03

2 0.372 0.028 0.41 4.10E-03

N719 1 0.733 8.068 0.69 4.1

From the results in table 12, the Voc and Jsc for sol-gel TiO2 were both very low. It

indicated that the sol-gel TiO2 didn’t perform well in DSSC. It matched the results in the

first part of appendix. Compared the DSSC with washed dye and with dye, the results

were very obvious. The efficiency of the DSSC without dye was just 0 which indicated

that the dye were completely washed away. The DSSC with Dye1 had a good Voc which

was close to that with N719. The performance of DSSCs with Dye1 and Dye2 were

close, both of them had a good Voc. However, the Jsc of the DSSCs with Dye1 and Dye2

were significantly lower than that of N719, which resulted in the low efficiency of cells.

Conclusions

Copper-complex dyes were much cheaper than N719. The synthetic route was easy and

the dyes were quite stable. TiO2 thin films didn’t have a good adsorption of them, which

68

resulted in the low current and efficiency. However, the DSSCs with copper-complex dye

had a close voltage to that of N719 which might have some specific applications related

to high voltage.

III. Polymer electrolyte

1. P123 polymer electrolyte

Electrolyte is also an important part in dye-sensitized solar cells. The I-/I3

- redox pair can

be oxidized by the electron from counter electrode and completed the whole circulation.

However, the liquid electrolyte used in most of the DSSCs had a short lifetime. The

solvent in the liquid electrolyte was acetonitrile and it was easy to evaporate. As soon as

the solvent was gone, the DSSC was dead. So polymer electrolyte became a hot topic in

nowadays. 44-55

In this thesis, P123 was used as the polymer in polymer electrolyte.

Table 13. Performance of two dye-sensitized solar cells with and without electrolyte.

Cell No. Electrolyte Voc (V) Isc (mA) FF (%) Efficiency

(%)

1

No

electrolyte 0.59 0.00095 0.58 0.0013

Only P123 0.652 0.0058 0.49 0.0074

Polymer

electrolyte 0.59 0.194 0.53 0.24

2

No

electrolyte 0.776 0.00026 0.28 0.00022

Only P123 0.745 0.0016 0.30 0.0015

Polymer

electrolyte 0.559 0.12 0.47 0.13

The results in table 13 showed that DSSC without electrolyte still could work. It had the

high open circuit voltage around 0.6 V but very low short circuit current. It indicated that

69

electrolyte only affected the current and had nothing to do with the voltage. The results of

DSSC only with P123 had a better current compared to that without P123. It suggested

that the P123 could separate the working electrode and counter electrode and prevented

the short circuit. If the I-/I3

- redox couple were added in P123, it further increased the

current of DSSC. The results in 11 showed that DSSC with polymer electrolyte had the

efficiency more than 0.1%, which was not far away from that of DSSC with liquid

electrolyte.

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

0.00

0.05

0.10

0.15

0.20

0.25

Cu

rre

nt (m

A)

Voltage (V)

Cell 1_No electrolyte

Cell 1_P123

Cell 1_polymer electrolyte

Cell 2_No electrolyte

Cell 2_P123

Cell 2_polymer electrolyte

Figure 42. Current-Voltage profile of two DSSCs with and without electrolyte.

2. Crosslinking PEG polymer electrolyte.

70

PEG is most widely used polymer electrolyte for DSSC. The performance of crosslinking

PEG has been studied by a Korean scientist.48

The preparation method for the polymer

electrolyte was followed by the literature. HCl is used to initiate the cross-linking

reaction. GA is short for glutaraldehyde, which is a cross linking reagent.

From the IR results in figure 43a, the peak of –OH group shifted from 3467 cm-1

to 3495

cm-1

after crosslinking reaction. This indicated that the –OH group from PEG had been

changed due to the crosslinking reaction. This also matched the reported result in the

literature48

. From the absorbance spectra in figure 43b, some small peaks appeared

between 1400 cm-1

and 900 cm-1

after adding HCl. These small peaks could be assigned

to the new ether bonds which were generated after crosslinking. Both the evidences

proved that the PEG had been cross-linked in the polymer electrolyte.

The performance of the DSSCs with cross-linked PEG polymer electrolyte was tested.

The Voc was 0.68V and the Jsc was 0.006mV/cm2. The voltage was quite close to the

DSSC with liquid electrolyte in table 12. But the current was too low to get a good

efficiency.

71

4000 3500 3000 2500 2000 1500 1000 5000.0

0.5

1.0

1.5

2.0

Sin

gle

Be

am

In

ten

sity (

a.u

.)

Wavenumber (cm-1)

PEG

GA

PEG+GA

PEG+GA+HCl

3467cm-1

3495cm-1

4000 3500 3000 2500 2000 1500 1000

0.0

0.5

1.0

Ab

so

rba

nce

Wavenumber (cm-1)

PEG

GA

PEG+GA

PEG+GA+HCl

Figure 43. (a) Single beam IR spectroscopy and (b) Absorbance of the chemicals and the

solution of PEG polymer electrolyte.

(a)

(b)

72

APPENDIX B

INTENSITY OF UV LIGHT

All the TiO2 samples are very sensitive to the UV light, so the distribution of UV light is

significant to the results of the cell performance. In this chapter of appendix, the one-

dimension and two-dimension of the distribution of UV light were discussed.

150 mm

140 mm

12 mm

Detector

Move every 5 mm

Optical fiber

Figure 44. Schematic setup of UV light measurement.

73

The diameters of the photo detector and the optical fiber were 12mm and 10mm. Because

all the area of the detector had to be covered by UV light, it had to be a long distance

between the optical fiber and the detector. The setup was showed in figure 44. I write

down the intensity of the UV light at the certain position and move the detector in one-

dimension every 5 mm. The results were shown in table .

Table 14. The UV light intensity at different positions.

Distance (mm) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70

Power (mW) 12 12 12 11 10 8 7 4 4 3 2 1 1 1 0

Table 14 showed that the intensity of UV light was the strongest in the center of the light,

which was easy to understand. The intensity decreased rapidly when the detector moved

away from the center. The results were plotted in figure 45 and the distribution was also

stimulated by Gauss equation.

-60 -40 -20 0 20 40 60

0

2

4

6

8

10

12

14

Po

we

r (m

W)

Distance (mm)

Equation y=y0+A*exp(-0.5*((x-xc)/w)^2)

Adj. R-Square 0.98969

Value Standard Error

Power y0 -0.13113 0.22414

Power xc 1.60281E-14 0.4398

Power w 26.34781 0.75705

Power A 12.76479 0.24891

Figure 45. The distribution of UV light intensity at different positions.

74

The simulated curve in figure 45 was quite sharp which indicated that the distribution of

the UV light was not uniform.

In order to get the better understanding of the distribution of the UV light, two-dimension

distribution was also obtained. In this experiment, the detector moved in the whole area

of the light spot and every point was 5mm away.

-9.0 -7.5 -6.0 -4.5 -3.0 -1.5 0.0 1.5 3.0 4.5 6.0 7.5 9.0

-9.0

-7.5

-6.0

-4.5

-3.0

-1.5

0.0

1.5

3.0

4.5

6.0

7.5

9.0 0.2

0.4 0.5 0.6 0.5 0.3

0.6 1.9 3 3.2 2.6 1.3 0.3

0.3 1.9 5.9 12 14 12 6.2 1.4 0.3

0.7 4.4 19 27 31 25 14 5 0.8

1.3 7.5 25 33 37 31 21 9.7 1.7

1.5 88 24 29 35 30 21 11 2.4

1.3 7.6 20 24 26 23 17 9.5 1.8

0.9 5.3 11 17 17 15 12 5.8 0.7

0.3 2.6 7.1 10 11 10 6.5 2 0.3

0.6 2.5 4.3 4.5 3.5 1.4 0.3

0.4 0.6 0.7 0.5 0.3

0.2

UV light intensity (mW/cm2)

Y-a

xis

(cm

)

X-axis (cm)

Figure 46. The intensity of UV light at different positions with optical fiber.

Figure 46 showed that the intensity of every point was recorded. The maximum intensity

was 37 mW/cm2 of the center point.

75

Figure 47. 2D distribution of UV light intensity with optical fiber. Distance between

detector and light source is 17cm.

76

Figure 47 clearly showed that the intensity of UV light decreased rapidly away from the

center.

I also did the experiment when there was an angle between the detector and the light

source. In most of my photo degradation experiment, the angle was 450.

The intensity distribution of UV light in figure 48 showed a sharper circular cone. It

indicated that the light was much less uniform when there was an angle between the light

source and photo detector.

77

Figure 48. 2D distribution of UV light intensity with an angle between optical fiber and

photo detector. Distance between detector and light source is 17cm.

78

-7.5 -6.0 -4.5 -3.0 -1.5 0.0 1.5 3.0 4.5 6.0 7.5-7.5

-6.0

-4.5

-3.0

-1.5

0.0

1.5

3.0

4.5

6.0

7.5

9.0

0.7 0.31

26 20 4202

60 50 37 45334

99 77 65 24994611

120 99 84 42 11206825

110 85 79 36 0.71097224

66 62 56 14 0.3674811

41 39 20 0.74227

14 8 0.3151.5

0.50.3

UV light intensity (mW/cm2)

Y-a

xis

(cm

)

X-axis (cm)

Figure 49. The UV light intensity at different positions without optical fiber.

The optical fiber also had some effect on the distribution of UV light intensity. So I

directly shined the UV light of light source to the photo detector and did the same

experiment above.

In figure 49, the intensity of each point was shown. Compared to the intensity in figure

46, it increased three times. It indicated that the optical fiber had cut off some part of the

UV light and decreased the light intensity.

The 2D distribution was also shown in figure 50. Compared to the distribution of UV

light in figure 48, there was no significant difference between them. It indicated that the

optical fiber could only introduce the light direction but not change the distribution of

light intensity.

79

Figure 50. 2D distribution of UV light intensity without optical fiber. Distance between

detector and light source is 17cm.

80

APPENDIX C

PHOTO DEGRDATION OF PVC THIN FILMS

Photo degradation of organics or polymers was also an interesting project that our group

was working on. Due to the cooperation with Hallstar Company, they sent us several

samples of PVC thin films with different additives and asked as test the UV resistance of

each PVC thin film.

The sample named Control Sample didn’t have any additives in the PVC film. The

sample named RX14426 and RX14427 both had the UV resistance additives from

Hallstar Company. Another sample named Tinuvin 328 had the commercialized additives.

Most of the experiments were tested by in-situ DRIFT IR spectroscopy. UV light was

applied to accelerate the degradation rate of the samples in air. Samples with 4 mil and 8

mil thickness were both tested for comparing the effect of thickness.

I. In-situ DRIFT IR spectroscopy of each sample at 100 mW/cm2 UV light intensity

within 30 min.

Figure 51 showed that the several IR peaks were increased or decreased within 30 min

UV degradation. The peak at 3255 cm-1 was assigned to –OH group. The peaks at 2956

cm-1

, 2922 cm-1

and 2850 cm-1

were all assigned to –CH3 group. The peaks at 1784 cm-1

and 1705 cm-1

were assigned to –C=O group. The increase of –OH and –C=O groups

meant the generation of PVC degradation product. The decrease of –CH3 indicated the

81

disappearance of PVC. The slower increase or decrease of the reacting rate, the better UV

resistance of the PVC samples.

4000 3500 3000 2500 2000 1500 1000

2956 cm-1

2922 cm-1

2850 cm-1

1705 cm-1

1784 cm-1

PVC + Tinuvin 328

PVC + RX14427

30 min UV15 min UV0 min UV

PVC Control Sample

Wavenumber (cm-1)

0 min UV

15 min UV

30 min UV

Ab

so

rba

nce

(a

.u.)

0 min UV

15 min UV

30 min UV

0.1

3255 cm-1

Figure 51. Differential absorbance IR spectra of the PVC samples before and after 30

minutes of UV irradiation (200 mw/cm2, Hg lamp).

The increase of the intensity of the band at 3255 cm-1

and 1784 cm-1

indicted that the

PVC sample was oxidized.

82

0 5 10 15 20 25 30

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

UV on

PVC 8 mil film samples

3255 cm-1 wavenumber

Ab

so

rba

nce

(a

.u.)

Time (minutes)

Tinuvin 328_2

RX14427_7RX14427_6

RX14427_5

RX14427_4

RX14427_3RX14427_1

Control sample_3

Control sample_2

Tinuvin 328_1

Control sample_1

Figure 52. Absorbance vs. time spectra of the PVC 8 mil film samples before and after 30


-1.

In figure 52, the increasing rate of –OH group were shown. RX14427 increased the

slowest among the three samples. It indicated that RX14427 samples had the best

resistance to UV light from the –OH group.

83

0 5 10 15 20 25 30

-0.08

-0.06

-0.04

-0.02

0.00

0.02

Tinuvin 328

RX14427



Ab

so

rba

nce

(a

.u.)

Wavenumber (cm-1)

Control sample

0 5 10 15 20 25 30

-0.10

-0.08

-0.06

-0.04

-0.02

0.00



Wavenumber (cm-1)

Ab

so

rba

nce

(a

.u.)

Tinuvin 328

RX14427

Control sample

84

0 5 10 15 20 25 30

-0.08

-0.06

-0.04

-0.02

0.00



Wavenumber (cm-1)

Ab

so

rba

nce

(a

.u.)

Tinuvin 328

RX14427

Control sample



-1, 2923cm

-1 and 2850cm

-1.

All of these three bands were assigned to –CH3 group. From the results in figure 53, there

was no big difference among the three samples. The PVC was all reacted with a similar

degradation rate.

85

0 5 10 15 20 25 30

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

UV on



Ab

so

rba

nce

(a

.u.)

Time (minutes)

Tinuvin 328_2

RX14427_7RX14427_6

RX14427_5

RX14427_4

RX14427_3

Control sample_2

Control sample_3

RX14427_1

Control sample_1

Tinuvin 328_1



-1.

The reacting rate of the band at 1784 cm-1

showed that RX14427 had a much slower

degradation rate than Tinuvin 328. It indicated that RX14427 was better than Tinuvin 328

for UV resistance in the –C=O group.

86

0 5 10 15 20 25 30

0.00

0.05

0.10

0.15

0.20

0.25PVC 8 mil film samples


Wavenumber (cm-1)

Ab

so

rba

nce

(a

.u.)

Tinuvin 328

RX14427

Control sample



-1.

The results in figure 55 showed that both RX14427 and Tinuvin 328 had a slower

degradation rate than the control sample.

87

0 5 10 15 20 25 30

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

0.055PVC 4 mil film samples


RX14427_4

RX14427_3

RX14427_2

RX14427_1

Control sample_4

Control sample_3

Control sample_2

Control sample_1

Tinuvin 328_2

Ab

so

rba

nce

(a

.u.)

Time (minutes)

UV on

Tinuvin 328_1



-1.

For the samples with 4 mil thickness, the reproducibility of RX14427 was not good. It

was not reliable to raise a conclusion based on this result.

88

0 5 10 15 20 25 30

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

UV on

Ab

so

rba

nce

(a

.u.)

Tinuvin 328_2

Tinuvin 328_1

RX14427_4RX14427_3

RX14427_2

RX14427_1

Control sample_4

Control sample_3Control sample_2

Control sample_1

Time (minutes)





-1.

The reproducibility of RX14427 was better in figure 57. The degradation rate of control

sample was the slowest, which didn't match the results in the previous experiment.

Conclusions

1. The reproducibility for the Tinuvin 328 film samples was the best. We didn’t test it

many times because it always gave the stable signals and repeatable results.

2. The reproducibility for the RX14427 film samples was the worst. Even we tested it

more than four times, the results were still not convinced. The reason may be the

uniformity in the edge was not good. We cut a small piece (0.5cm*0.5cm) from the

edge of the aluminum foil every time and maybe the samples were not all the same at

that scale.

3. The reason why Tinuvin 328 had the worst UV resistance was due to several reasons:

a. The thickness of Tinuvin 328 had a big difference compared to the others.

b. Tinuvin 328 was not uniform in the PVC samples. The pieces we ran the

experiment didn’t have much Tinuvin 328 inside.

c. 30 minutes was not enough to determine the final oxidized rate under UV light.

89

II. In-situ DRIFT IR spectroscopy of each sample at 1000 mW/cm2 UV light intensity

within 180 min.

In order to study the IR difference when the samples were mostly degraded by UV light,

higher UV light intensity and longer time were applied in this experiment.

All of the four Hallstar samples were coated on aluminum foil, which the thickness is 20

mil. They were heated to 50 0C by a heating element during the in situ IR test for 3 hours.

350 W Mercury lamp was applied to provide the UV irradiation (1000mW/cm2).

90

PVC control sample

4000 3500 3000 2500 2000 1500 1000

1.0

Wavenumber (cm-1)

Sin

gle

bea

m i

nte

nsi

ty (

a.u

.)

180 min60 min

30 min10 min0 min

4000 3500 3000 2500 2000 1500 1000

89

8

10

43

12

83

13

95

17

84

17

05

18

04

33

06

29

71

29

10

28

51

IR d

iffe

ren

ce (

a.u

.)

Wavenumber (cm-1)

0.1

35

00

180 min - 0 min

60 min - 0 min

30 min - 0 min

10 min - 0 min

0 min - 0 min

(a) (b)

0 30 60 90 120 150 180

Time (min)

IR i

nte

nsi

ty a

t 1

04

3 c

m-1

(a.

u.)

0.05

0.5cm

(c)(d)

Figure 58. (a) Single beam spectra of PVC control sample collected during the UV

degradation. (b) IR difference spectra obtained by IR difference= -log(I/I0), where I is the

single beam at specified times and I0 is the single beam at 0 min. (c) Top view picture of

the PVC control sample at the end of the UV degradation experiment. (d) Variation in the

intensity of C-O stretch band at 1043 cm-1

.

The single beam IR spectra of PVC control sample in figure 58a didn't change much at

variation of time. So the difference IR spectra were used to distinguish the change during

the reaction. Figure 58b showed that PVC bands at 3500 cm-1

, 1804 cm-1

, 1359 cm-1

,

1283 cm-1

, 1043 cm-1

and 898 cm-1

were increased and bands at 2971 cm-1

, 2910 cm-1

and

2851 cm-1

were decreased during the UV degradation. (All the peaks from PVC were

marked red in all the figures). It indicated that the new –OH band and C=O band were

formed and CH2 and CH bands were disappeared. The other peaks like 3306 cm-1

, 1784

91

cm-1

and 1705 cm-1

were from the degradation of plasticizer (Paraplex G59). Figure 58c

showed that the color of PVC control sample was turned to dark brown at 50 0C after UV

degradation. In figure 58d, the intensity of peak at 1043 cm-1

was plotted versus the time

during the UV degradation. Due to the strong effect from the peak of plasticizer, the

peaks of PVC at 3500 cm-1

, 1804 cm-1

, 1359 cm-1

, 1283 cm-1

, 2971 cm-1

, 2910 cm-1

and

2851 cm-1

were not accurate to represent the degradation rate of PVC. So the C-O stretch

band at 1043 cm-1

was selected to show the degradation rate of PVC.

RX14426 + PVC sample

0 30 60 90 120 150 180

Time (min)

IR i

nte

nsi

ty a

t 10

43

cm

-1 (

a.u.)

0.05

4000 3500 3000 2500 2000 1500 1000

1804

Wavenumber (cm-1)

IR d

iffe

ren

ce (

a.u

.)

0.1 898

1043

1395

3306

2971

2910

2851

3500

1784

1705

180 min - 0 min

60 min - 0 min

30 min - 0 min

10 min - 0 min

0 min - 0 min

0.5cm

(c)

(a) (b)

Figure 59 (a) IR difference spectra of RX14426 + PVC sample obtained by IR

difference= -log(I/I0), where I is the single beam at specified times and I0 is the single

beam at 0 min. (b) Top view picture of RX14426 + PVC sample at the end of UV

degradation experiment. (c) Variation in the intensity of C-O stretch band at 1043 cm-1

.

92

Figure 59a showed that all the peaks at 3500 cm-1

, 1804 cm-1

, 1359 cm-1

, 1283 cm-1

, 2971

cm-1

, 2910 cm-1

, 2851 cm-1

, 1043 cm-1

and 898 cm-1

were increased or decreased because

of the degradation of PVC. Figure 59b and figure 59c are similar to figure 58c and figure

58d except that RX14426 + PVC sample degraded much slower than PVC control

sample.

RX14427 + PVC sample

4000 3500 3000 2500 2000 1500 1000

Wavenumber (cm-1)

IR d

iffe

ren

ce (

a.u

.)

0.1 18

04

89

8

10

43

13

95

33

06

29

71

29

10

28

51

35

00

17

84

17

05

180 min - 0 min

60 min - 0 min

30 min - 0 min

10 min - 0 min

0 min - 0 min

0 30 60 90 120 150 180

IR i

nte

nsi

ty a

t 10

43

cm

-1 (

a.u.)

Time (min)

0.05

(a) (b)

0.5cm

(c)

Figure 60. (a) IR difference spectra of RX14427 + PVC sample obtained by IR


beam at 0 min. (b) Top view picture of RX14427 + PVC sample at the end of UV


.

Figure 60a and figure 60b are similar to figure 59a and figure 59b which indicated that

RX14427+PVC sample were degraded after 3 hours under 1000 mW/cm2 UV irradiation.

93

In figure 60c, the signal was not stable and it made a lot of noise. However, it still

showed the increase at 1043 cm-1

of PVC degradation.

Tinuvin 328 + PVC sample

0 30 60 90 120 150 180

Time (min)

IR i

nte

nsi

ty a

t 10

43

cm

-1 (

a.u.)

0.05

4000 3500 3000 2500 2000 1500 1000

180 min - 0 min

60 min - 0 min

30 min - 0 min

10 min - 0 min

0.1

IR d

iffe

ren

ce (

a.u

.)

Wavenumber (cm-1)

1804

898

1043

1395

3306

2971

2910

2851

3500

1784

1705

0 min - 0 min

(a) (b)

(c)

0.5cm

Figure 61. (a) IR difference spectra of Tinuvin 328 + PVC sample obtained by IR


beam at 0 min. (b) Top view picture of Tinvuin 328 + PVC sample at the end of UV


.

In figure 61b, the color of Tinuvin 328+PVC sample slightly turned into brown which

were much lighter than the other three samples. It indicated that Tinuvin 328+PVC had

better UV resistance than others. Figure 61c also showed that the degradation rate of

Tinuvin 328+PVC increased much slowly.

94

4000 3500 3000 2500 2000 1500 1000

(a) PVC control sample

898

1043

1283

13951784

1705

1804

3306

2971

2910

2851

0.1 3500

180 min - 0 min

30 min - 0 min

0 min - 0 min

(c) RX14427 + PVC

(b) RX14426 + PVC

180 min - 0 min30 min - 0 min

0 min - 0 min

180 min - 0 min

30 min - 0 min

0 min - 0 min

(d) Tinuvin 328 + PVC

180 min - 0 min

30 min - 0 min

IR d

iffe

ren

ce (

a.u

.)

Wavenumber (cm-1)

0 min - 0 min

Figure 62. DRIFT IR spectra of (a) PVC control sample, (b) RX14426 + PVC sample, (c)

RX14427 + PVC sample and (d) Tinuvin 328 + PVC sample.

In figure 62, all the peaks of PVC at 3500 cm-1

, 1804 cm-1

, 1359 cm-1

, 1283 cm-1

, 2971

cm-1

, 2910 cm-1

, 2851 cm-1

, 1043 cm-1

and 898 cm-1

were increased or decreased during

the UV degradation. It indicated that all the PVC were degraded under strong UV

irradiation within enough time at 50 0C.

95

0 30 60 90 120 150 180

Tinuvin 328 + PVC

RX14426 + PVC

RX14427 + PVC

IR

inte

nsi

ty a

t 1043 c

m-1

(a.

u.)

Time (min)

0.05

PVC control sample

Figure 63. Variation in the intensity of C-O stretch band at 1043 cm-1

of PVC control

sample, RX 14426 + PVC sample, RX14427 + PVC sample and Tinuvin 328 + PVC

sample.

Figure 63 showed that four samples were all degraded but the degraded rates were quite

different. PVC control sample was degraded fastest after the first 30 min. The

degradation rates of RX14426+PVC sample and RX14427+PVC sample were almost the

same, which were slower than PVC control sample and faster than Tinuvin 328+PVC

sample. Tinuvin 328+PVC had the slowest rate which indicated it had the best UV

degradation.

96

0 30 60 90 120 150 180

Tinuvin 328+PVC

RX14426 + PVC

RX14427 + PVC

IR

in

ten

sity

at

33

06

cm

-1 (

a.u

.)

Time (min)

0.05

PVC control sample

0 30 60 90 120 150 180

Tinuvin 328+PVC

RX14426 + PVC

RX14427 + PVC

IR

in

ten

sity

at

28

51

cm

-1 (

a.u

.)

Time (min)

0.05

PVC control sample

0 30 60 90 120 150 180

Tinuvin 328+PVC

RX14426 + PVC

RX14427 + PVC

IR i

nte

nsi

ty a

t 1

78

4 c

m-1

(a.

u.)

Time (min)

0.05

PVC control sample

0 30 60 90 120 150 180

Tinuvin 328+PVC

RX14427 + PVC

IR

in

ten

sity

at

13

95

cm

-1 (

a.u

.)Time (min)

0.05

PVC control sample

(a) (b)

(c) (d)

Figure 64. Variation in the intensity of IR peaks at (a) 3306 cm-1

, (b) 2851 cm-1

, (c)

1784cm-1

, (d) 1395 cm-1

of PVC control sample, RX 14426 + PVC sample, RX14427 +

PVC sample and Tinuvin 328 + PVC sample.

The peaks at 3306 cm-1

and 1784 cm-1

were mainly from the degradation of plasticizer in

figure 64b and figure 64c. They were not very useful for judging the UV resistance of the

additives.

Figure 64d indicated that there was no big difference among RX14426, RX14427 and

Tinuvin 328 for the UV resistance. However, they were much better than the PVC control

sample.

Conclusion

97

The UV resistance of these four samples: Tinuvin 328>RX14427=RX14426>PVC

control sample.

III. Focal plane array IR spectroscopy.

An aluminum plate with four small holes in the middle was used as a cover to study the

focal plane array for Hallstar samples. The diameter of the aluminum plate was around 30

mm and the diameter of four holes are all 0.5 mm. Control sample, RX14426, RX14427

and Tinuvin 328 were put behind the aluminum plate and only a part of the sample can be

scanned by infrared. The locations of the four samples were shown in figure 65.

Figure 65. The locations of Control sample, RX14426, RX14427 and Tinuvin 328 and

the scan area of the focal plane array.

98

Figure 66. Experimental setup for UV degradation of Control sample, RX14426,

RX14427 and Tinuivn 328 by focal plane array.

99

Figure 67. Photographs of Control sample, RX14426, RX14427 and Tinuvin 328 before

and after UV degradation tested by focal plane array. Single beam spectra were collected.

Red color stands for the high intensity and blue color stands for the low intensity.

From figure 67, we can see that RX14426 can be seen clearly at 1724 cm-1

after degraded

by UV for 10 min. It also happens to Control sample at 180 min. This is due to the

sample lost during the experiments. The RX14426 and Control sample moved out of the

hole and we could not see them from the focal plane array. It can be proved by the IR

spectra below.

100

4000 3500 3000 2500 2000 1500 1000

Ab

sorb

ance

(a.

u.)

Control sample

RX14426

RX14427

180 min30 min10 min

Wavenumber (cm-1)

0 min

Tinuvin 328

180 min30 min10 min0 min



1043172429243306

Figure 68. IR absorbance spectra of Control sample, RX14426, RX14427 and Tinuvin

328 before and after UV degradation.

101

4000 3500 3000 2500 2000 1500 1000

1043172429243306

Control sample


180 min30 min10 min

0 min



RX14426

RX14427

IR d

iffe

rence

(a.

u.)

Wavenumber (cm-1)

Tinuvin 328

Figure 69. IR difference spectra of Control sample, RX14426, RX14427 and Tinuvin 328

before and after UV degradation. Spectra were obtained by IR difference= -log(I/I0),

where I is the single beam at 180 min and I0 is the single beam at 0 min.

Figure 69 shows that control sample was not detected at 180min. RX14426 was not

detected after 10 min. It indicates that our setup has some problem with the sample fix.

Samples would be moved by the gravity or the heating of UV light. From the present

results, RX14427 was degraded the slowest at all the four wavenumbers.

102

Figure 70. Statistics results of all the old experiments for variation in the intensity of –OH

band at 3306 cm-1

, -CH and –CH2 band at 2924 cm-1

, C=O band at 1724 cm-1

and C-O

stretch band at 1043 cm-1

.

From all the old results, we can say that RX14426 and RX14427 always had better UV

resistance at hydroxyl group, and C-O band. They are similar to Control sample and

Tinuvin at –CH, –CH2 band and C=O band. The reproducibility of RX14426 and

RX14427 are worse than control sample and Tinuvin 328.

Conclusions

1. RX14427 was degraded slowest at all of the four wavenumbers which are 3306 cm-1

(hydroxyl group), 2924 cm-1

(alkyl group), 1724 cm-1

(carbonyl group) and 1043 cm-1

(C-

O stretch) from the present results.

103

2. Control sample and Tinuvin 328 has better reproducibility than RX14426 and

RX14427 from the statistical results. But RX14426 and RX14427 had better UV

resistance to –OH band and C-O band.

104

APPENDIX D

NFPA AND HMIS RATING OF CHEMICALS

Tab

le 1

5. N

FPA

and H

MIS

rat

ing o

f ch

emic

als

1.

Nat

ion

al F

ire

Pro

tect

ion

Ass

oci

atio

n (

NF

PA

) ra

tin

g i

s ob

tain

ed f

rom

htt

p:/

/ww

w.n

fpa.

org

/

2.

Haz

ard

ou

s M

ater

ials

Id

enti

fica

tion

Syst

em (

HM

IS)

rati

ng i

s obta

ined

fro

m h

ttp

://w

ww

.sci

ence

lab

.com

/

master thesis_yang_final revised

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