12 July 201712 July 2017

Nwabisa Takata

Synthesis and Characterization of C-TiO2 nanotubes using a template-assisted sol-gel technique

Supervisor: Prof. Edson L. MeyerCo-supervisor: Dr. Raymond T. Taziwa

12 July 2017

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Outline

Background Aim & Objectives Methodology Results

SEM Characterization of TNTs FTIR Characterization of TNTs XRD Characterization of TNTs Confocal Raman large area scan and depth profile of TNTs

Concluding Remarks Acknowledgements References

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Background

The solar energy that the earth receives in one hour, is said to be sufficient to meetthe total energy demand of the world for more than one year.

Harvesting solar energy into electricity using photovoltaic cells has become one ofthe most promising solution to modern energy issues, mainly because solar energyis produced without carbon-emission .

The development of alternative energy sources has been motivated by healthproblems, environmental concerns.

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Introduction

In 1991, Switzerland Professor Michael Grätzel and Dr Brian O’ Regan devisedDye Sensitized Solar Cells (DSSC), also referred to as Dye Sensitized Cells (DSC)or Grätzel Cell.

These cells are a third generation photovoltaic (solar) cell that convert any visiblelight into electrical energy, they which seek to mimic a part of the photosyntheticprocess [6].

DSSC currently have an efficiency of 13 %.

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Background

5

(a) (b)

DSSC, with TiO2 NPs. High electro-hole recombination. Hoping mechanism for transport of electrons. Poor collection of photon generated electrons. Long diffusion pathway of electrons. Low efficiencies.

DSSC, with TiO2 TNTs. Improved electron transport. Vectorial charge transfer of electrons. Enhanced collection of photon generated

electrons & short diffusion pathway of electrons

Improved efficiencies..

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Aim and Objectives

Aim

Synthesis and Characterization of un-doped and carbon doped TiO2 nanotubes

using template-assisted sol-gel technique.

Objectives

Synthesis of undoped and carbon doped TiO2 sol-gel precursor solutions.

Synthesis of undoped and carbon doped TiO2 nanotubes using AAM templates.

Structural/ morphological and elemental characterization of undoped and carbon doped

TiO2 nanotubes using SEM, SEM-EDX, FTIR, XRD and confocal Raman spectroscopy.

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Methodology

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ACACWaterEthanol

EthanolTiO(Bu)4 Mixing

2hrsImmersion Drying

at 25°C475°C for 1 hr.

1 M NaOH.

Drying at 25°C

3 daysA

B

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Results : SEM

• Surface SEManalysis hasrevealed a poresize range of 80-180 nm

Cross sectionalSEM analysis hasrevealed AAM oflength range of57.15 -59.9 µm

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(a) (b)

(c)

(a) Surface morphology of AAM’s , (b) Histogram for pore diameter size and (c) Cross sectional SEM of AAM’s

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Results : SEM

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(a) (b) (c)

(d) (e) (f)

(f)

Cross sectional SEM (a) Undoped TNTs, (b) 9 mM C-TNTs, (c) 27 mM C-TNTs , (d) 45 mM C-TNTs , (e) 75 mM C-TNTs and (f) EDX of TNTs.

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Results : SEM

Pore diameter of TNTs synthesized by a template-assisted sol-gel technique

Pore diameter is consistent to the pore diameter of TNTs.

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Results : FTIR

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• Ti-O-O460 1/cm• O-H3100-36001/cm

FTIR results for (a) un-doped TNTs, (b) 9mM C-TNTs (c) 27mM C-TNTs (d) 45 mM C-TNTs and (e) 75 Mm C-TNTs.

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Results : XRD

• Peaks arise from Anatase(JCPDS No. 21- 1272).

Diffraction peak at 40.60ºfor arises from [202]crystal plane of Brookitephase of TiO2 (JCPDSNo. 29-1360 TiO2).

Powder X-ray diffraction analysis of un-doped and C-TNTs fabricated by a template-assisted sol-gel technique

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Results : XRD

24.0 24.5 25.0 25.5 26.0 26.5 27.0

Inten

sity (

a.u)

2Theta Degrees

un-doped TNTs 9 mM C-TNTs 27 mM C-TNTs 45 mM C-TNTs 75 mM C-TNTs

10 20 30 40 50 60 70

25.40

25.45

25.50

25.55

25.60

XRD

Shift

C [Conc] dopant (mM)

(101)

d spacing (Å)

Lattice parameters (Å)

a c

Bulk Anatase 3.520 3.784 9.514

un-doped TNTs 3.490 3.761 9.143

9mM C-TNTs 3.489 3.769 9.197

27mM C-TNTs 3.476 3.742 9.461

45 mM C-TNTs 3.488 3.752 9.809

75 mM C-TNTs 3.501 3.742 9.830

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Results: CRM-LAS

100 200 300 400 500 600 700 800

B 1g(A

)

Eg(A)

Eg(A)

Eg(A)

B1g(R)Eg(R)

A1g(R)

A1g(A)B1g(A)B1g(B)

A 1g(A

)

E g(A

)

Eg(A)

CCD

cts

rel. 1/cm

(a) (c) (d) (e)

(f)

100 200 300 400 500 600 700 800

B 1g(B

)

B1g(A)B 1g(A

)

E g(A)

A 1g(A

)

E g(A)

Eg(A)

+

+

CCDs

cts

rel.1/cm

(b)

(g)

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Results: CRM-LAS

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100 200 300 400 500 600 700 800

CCD

cts

rel.1/cm

B 1g(A

)

B 1g(A

)

A 1g(A

)

Eg(A) E g(A)

Eg(A)

(a) (d)(c)

(e)

100 200 300 400 500 600 700 800

B 1g(A

)

A 1g(A

)

E g(A)

Eg(A)

Eg(A)

rel.1/cm

CCD

cts

(b) (f)

CRM-LAS(a) video image (b) Raman single spectra (c) & (d) draw images showing phase distribution of TiO2 (e) Is a combined image and (f) shows the corresponding colour coded spectr of (e).

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100 200 300 400 500 600 700 800

B1g

(B)

B1g(A)B1g

(A)

Eg(

A)

A1g

(A)

Eg(

A)

Eg(A)

+

+

CC

Ds

cts

rel.1/cm

(a)

100 200 300 400 500 600 700 800

CC

D c

ts

rel.1/cm

A1g

(A)

B1g

(A)

Eg(

A)

Eg(A)

Eg(A)

(d)

(e)

(c) (d)

(b)(f)

Results: CRM-Depth Profiling

CRM-Depth profiling(a) video image (b) Raman single spectra (c) & (d) draw images showing phase distribution of TiO2 (e) Is a combined image and (f) shows the corresponding colour coded spectra of (e).

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Results: CRM-Depth Profiling

100 200 300 400 500 600 700 800

CCD c

ts

rel.1/cm

B 1g(A)

B 1g(A) A 1g(A)

Eg(A) E g(A)Eg(A)

(a)(c) (d)

(e)

100 200 300 400 500 600 700 800B 1g(A) A 1g(A)B 1g(A)

B 1g(A) E g(A)Eg(A)

Eg(A)

rel. 1/cm

CCD c

ts

(b)

(f)

CRM-Depth profiling(a) video image (b) Raman single spectra (c) & (d) draw images showing phase distribution of TiO2 (e) Is a combined image and (f) shows the corresponding colour coded spectra of (e).

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Conclusion

SEM revealed presence of TNTs and changes in surface morphology as thedopant concentration increase.

SEM-EDX revealed presence of strong Ti and O signals. FTIR confirmed the presence of Ti-O bond at 480 1/cm. XRD revealed the presence of Anatase and Brookite. XRD has shown increase in lattice constant “c” with increase in dopant

concentration. CRM-LAS and CRM-depth profile confirmed presence of Brookite and Anatase

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Acknowledgements

God almighty for the gift of life.

My supervisors Prof E.L Meyer and Dr R Taziwa for their guidance and support in

this research..

I would like to extend my sincere gratitude to Sasol and NRF for their financial

support.

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References

1. N. S. Lewis, “Towards cost effective solar energy use,” Science, vol. 315, no. 5813, pp. 798-801, 2007.

2. R. P. Jayarama, Science and technology of photovoltaics, Leiden: CRC Press, 2010.

3. R. S. Ohl, “Light-sensitive electric device,” US Patent 2402662, 1941.

4. M. A. Green, “The path to 25% silicon solar cell efficiency. History of silicon cell evolution,” Progress in

Photovoltaics, vol. 17, no. 3, pp. 183-198, 2009.

5. S. Zhang, X. Yang, Y. Numata and L. Han, “Highly efficient dye-sensitized solar cells: Progress and future

challenges,” Energy & Environmental Science, vol. 6, no. 1443-1464, p. 5, 2013.

6. B. A. Zulkifilli, T. Kento, M. Daiki and A. Fujiki, “The basic research on the dye sensitized solar cells (DSSC),”

Journal of Clean Energy Technologies, vol. 3, no. 5, pp. 382-387, 2015.

7. F. Bella, C. Gerbaldi, C. Barolo and M. Gratzel, “Aqueous dye-sensitized solar cells,” Chemical Society Reviews,

vol. 44, pp. 3431-3473, 2015.

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THANK YOU FOR YOUR TIME AND ATTENTION!!!!

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