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Journal of Materials Chemistry A

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This article can be cited before page numbers have been issued to do this please use Y ZHANG S

Yuan Y Zhao H Wang and C He J Mater Chem A 2014 DOI 101039C4TA01057D

Graphical abstract

A novel yttrium-doped graphene oxide (GOY) composite was firstly prepared and its

photocatalytic performance was investigated by degradation of MB

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Synthesis of novel Yttrium-doped graphene oxide nanocomposite 1

for dye removal 2

Ya Zhang1

Saisai Yuan2 Yanhua Zhao

1 Honggui Wang

1 Chenda He

1 3

1 Jiangsu Key Laboratory of Environmental Material and Engineering School of Environmental Science 4

and Engineering Yangzhou University Yangzhou 225127 PR China 5

2 School of Chemistry and Chemical Engineering Yangzhou University Yangzhou 225009 PR China 6

7

ABSTRACT 8

A novel yttrium-doped graphene oxide (GOY) composite was prepared by hydrothermal 9

method The morphology results showed that the graphene oxide (GO) can successfully 10

composite with yttrium and the as-prepared GOY had a nanoflake structure From the 11

photoelectrochemical analysis and photoluminescence (PL) spectra the primary role of GO 12

in Y2O3 was confirmed as an electron conductor enhancing the photocurrent density As 13

expected the as-obtained GOY composites had better photocatalytic performance on 14

decomposition of methylene blue molecules than bare GO and Y2O3 The 5 GOY (10 mg) 15

could degrade MB (25 ppm) thoroughly (~100 ) within 10 min which was quite 16

comparable with the commercial TiO2 P25 under UV irradiation A possible 17

mechanism of photocatalysis was also been presented 18

19

Keywords Yttrium-doped graphene oxide Methylene blue Ultraviolet light Photocatalyst 20

21

1 Introduction 22

Nowadays the growing population has led to the increasing contamination of surface 23

and ground water Organic dyes used in textile and food industries are one of the important 24

sources of the environmental contaminations due to their non-biodegradability and high 25

toxicity to aquatic creatures and carcinogenic effects on humans12

Semiconductor 26

photocatalysis has been extensively studied as a viable water treatment method34

27

Photocatalyst which accelerates light-driven chemical reactions has been paid a great 28

Corresponding author Tel +86-514-87979528 E-mail address zhangyayzueducn (Y Zhang) hcdyzueducn (CD

He)

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attention due to fascinating properties such as quantum confinement and enhanced reactivity5 1

Up to date diverse photocatalytic materials have been introduced including TiO2 ZnO 2

Fe3O4 SnO2 and BiVO43 6-10

Graphene oxide (GO) a two-dimensional sheet of sp2

3

hybridized carbon composing of only carbon oxygen and hydrogen has a high specific 4

surface area and tunable electronic structure11ndash13

Due to its extraordinary physical properties 5

high chemical and thermal stability graphene has been receiving recent attention as a support 6

for catalysts13-15

Recently a TiO2 nanorod-decorated graphene sheets has been prepared by 7

Jang and coworkers14

This nanocomposite had highly efficient photocatalytic activities under 8

visible-light irradiation Wang et al has reported a high-performance and recyclable 9

visible-light photocatalysis cobalt ferrite and graphene composite15

The spontaneous 10

exfoliated GO as an auxiliary co-catalyst has been reported that it can remarkably enhanced 11

the photocatalytic hydrogen production of TiO216

Although graphene has shown potential 12

applications in water treatment as a photocatalyst further optimization or modification of the 13

GO structure is still necessary for enhancing its photocatalytic activity 14

Impurity doping with proper oxidation state is useful for red shifting the absorption edge 15

as well as reducing the rate of electron-hole pairrsquos recombination which improves the 16

photocatalytic activity of a photocatalyst41718

It is reported that yttrium doping in TiO2 gives 17

improved photocatalytic response attributed to the visible light absorption electron-hole 18

pairrsquos separation higher interfacial charge transfer lower crystallite size and high specific 19

surface area419-21

This property enhances the performance of Y-based catalysts used in 20

wastewater treatment 21

In this work a novel yttrium-doped GO (GOY) was firstly synthesized via hydrothermal 22

method with different GO doping concentration The as-synthesized samples were 23

characterized by XRD FT-IR FESEM HRTEM and XPS The corresponding photocatalytic 24

activity was evaluated by measuring the photocatalytic degradation of methylene blue (MB) 25

and methlene orange (MO) degradation under UV irradiation A possible 26

mechanism of photocatalysis was also been presented based on the results of 27

photoelectrochemical analysis and PL spectra 28

29

30

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2 Experimental 1

Yttrium (III) nitrate hexahydrate (Y(NO3)3middot6H2O) polyvinylpyrrolidone ((C6H9NO)n) 2

ethanol graphite NaCl H2SO4 H2O2 P2O5 and K2S2O7 were purchased from Sinopharm 3

Chemical Reagent Company TiO2 P25 was obtained from Evonik Industries All the reagents 4

were of analytical grade and used as received without further treatment All solutions were 5

prepared with DI water 6

21 Preparation of Y2O3 and GO Y2O3 composite catalysts 7

GO was prepared via a modified Hummer method as reported previously22

In a typical 8

synthesis procedure 0776 g Yttrium (III) nitrate hexahydrate (Y(NO3)3middot6H2O) 0223g 9

polyvinylpyrrolidone ((C6H9NO)n) and certain amounts of GO were dissolved in a 7 mL DI 10

water and 33 mL ethanol Then the solution dissolved under magnetic stirring The obtained 11

transparent solution was transferred into a 50 mL polytetrafluoroethylene (PTFE) 12

(Teflon)-lined steel autoclaves and heated at 180 oC for 16 h After cooling to ambient 13

temperature the precipitate was centrifuged washed several times with ethanol and dried at 14

60 oC in an oven As a control experiment Y2O3 nanoparticles were prepared under the same 15

conditions without adding GO The Y-doped GO composite containing 5 10 20 and 50 mg 16

GO are denoted as 5 GOY 10 GOY 20 GOY and 50 GOY respectively 17

22 Characterization 18

The X-ray diffraction (XRD) patterns were obtained by a Bruker D8 advance X-ray 19

diffractometer using monochromatic Cu Kα radiation (λ = 15406 Aring) with an accelerating 20

voltage of 40 kV and current of 40 mA The 2θ range used in the measurement was from 10 21

to 70 The FT-IR spectra of the samples were measured on a Cary 610670 microscope 22

(Varian US) with scanning from 4000 to 400 cm-1

by using KBr pellets under ambient 23

temperature Thermogravimetric analysis (TGA) was performed with a PE Pyris-1 instrument 24

at a heating rate of 10 oC min

-1 under N2 atmosphere Field emission scanning electron 25

microscopy (FESEM) was examined on a field-emission scanning electron microanalyzer 26

(Hitachi S-4800 Japan) Energy dispersive X-ray spectroscopy (EDX) was performed on a 27

XL-30ESEM scanning electron microscopy High-resolution transmission electron 28

microscopy (HRTEM) was recorded on a Tecnai G2 F30 S-TWIN transmission electron 29

microscopes X-ray photoelectron spectroscopy (XPS) measurements were carried out with 30

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an ESCALAB 250 photoelectron spectrometer using Al Kα radiation (Thermo-VG Scientific 1

US) The photoluminescence (PL) spectra were measured with a JY HRD double grating 2

monochromator at room temperature 3

23 Degradation of methylene blue (MB) and methylene orange (MO) 4

Photocatalysis experiments were carried out in a BL-GHX-V photochemical reactor 5

(Shanghai Bilon Instrument Co Ltd) The UV source (λ lt 420 nm) was provided by a 500 W 6

high-pressure mercury lamp Reactor and UV source were surrounded by a circulating water 7

jacket to maintain constant temperature UV irradiation photocatalytic activities of GO Y2O3 8

and GOY composite were evaluated through the degradation of MB and MO 9

A stock solution of MB (or MO) at 1000 ppm was prepared using DI water In a typical 10

run 005 g of photocatalyst was dispersed in a 20 mL MB (or MO) (25 ppm) Then the 11

suspension was stirred for 30 min in the dark to ensure adsorptiondesorption equilibrium 12

before light illumination At each specific sampling time aqueous sample was withdrawn by 13

a 5 mL syringe and filtered immediately by a 022 μm filter film to remove the catalyst 14

particles before analysis All experiments were repeated at least two times and averages were 15

reported The concentration of MB (or MO) was then determined by measuring the 16

absorbance at λmax 600 nm via UV-vis spectrophotometer To determine the catalytic 17

recycling properties the catalyst was separated after reaction for 30 min and washed 18

thoroughly with ultrapure water and ethanol followed by drying at 60 oC for 12 h in vacuum 19

oven Finally the catalyst was separated by magnet and redispersed in a new reaction system 20

for subsequent catalytic experiments under the same reaction conditions The reduction ratio 21

of MB (or MO) was calculated using the following expression 22

Degradation ratio of MB = times100 23

where A0 and At were the absorbance intensities when illuminated for 0 (that is just after the 24

dark adsorption) and t min respectively 25

24 Photoelectrochemical Measurements 26

All photoelectrochemical characteristics were performed in the electrolytic cell 27

consisted of a GO Y2O3 or GOY composites (2 mg mL-1 100 μL) coated FTO glass working 28

electrode (2cm2cm) a platinum wire counter electrode and a saturated calomel reference 29

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electrode (SCE) on a Model CHI 660E electrochemical workstation under a 500 W 1

high-pressure mercury lamp irradiation 2

3

3 Results and discussion 4

31 FT-IR spectra XRD and TGA Analysis 5

FT-IR measurement is employed to investigate the bonding interactions in GO before 6

and after the oxidation process FT-IR spectra of GO Y2O3 and 5 GOY are shown in Fig 1 7

In the spectrum of GO the peak at about 1721 cm-1

is attributed to the stretching vibrations of 8

C=O The peaks appear at about 1223 and 1564 cm-1

correspond to the stretching vibrations 9

of C-O and C=C respectively23

The FT-IR spectra of Y2O3 and 5 GOY composite have 10

similar curve shape while a new peak appears at 1550 cm-1

of 5 GOY This result indicates 11

the GO has successfully composited with Y2O3 12

Fig 2 shows the crystal structure of GO Y2O3 and 5 GOY composite GO shows a 13

sharp peak at 2θ = 105o corresponding to the (001) reflection of graphite oxide

152425 The 14

diffraction peaks observed at 2θ = 421deg originate from disorderedly stacked GO sheets26

The 15

peaks located at 198deg 286deg 351deg 501deg 494deg and 512deg (2θ) result from the presence of 16

Y2O3 which are in agreement with the theoretical data of hematite (JCPDS No 41-0015)2728

17

In the pattern of 5 GOY the presence of diffraction peak at 2θ of 421deg indicating that GO 18

exists in the composite material It should be noted that there is a diffraction peak observed at 19

2θ = 101deg on both patterns of Y2O3 and 5 GOY which originates from intermediate YO(OH) 20

structure27

21

Fig 3 presents results of TGA analysis of the as-synthesized GO Y2O3 and 5 GOY 22

composite powder The samples were heated from room temperature to 600 degC at 5 degC min-1

23

under N2 flow As can be seen in Fig3 GO starts to lose mass upon heating even below 24

100 degC The major mass loss occurs at about 200 degC is caused by pyrolysis of the 25

oxygen-containing functional groups generating CO CO2 and stream29-31

Y2O3 and 5 GOY 26

have the same shape and show mass losses at three temperature ~100 320 and 400 degC The 27

first mass loss at about 100 degC is related to dehydration of free and physically absorbed 28

molecular water The next mass loss at about 320 degC is supposed to be related with the first 29

dehydration of chemisorbed and combined water from Y(OH)33233

The third mass loss at 30

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about 400 degC confirms dehydration of structural water from YOOH phase34

1

32 Morphology Characterization 2

The morphology of the as-obtained samples are examined by FESEM It can be 3

observed in Fig 4A that the as-prepared Y2O3 illustrates a uniform flake-like shape with 4

irregular edges Its lateral size ranges from 70 to 150 nm and thickness is around 10 to 20 nm 5

It can be observed that the prepared graphene oxide illustrates the flake-like shape and 6

layer-layer structure of graphene oxide edges (Fig 4B) Fig 4C and D displays the 7

morphologies of 5 GOY and 20 GOY composites respectively As can be seen with GO 8

content increasing the flake-like structure becomes irregular At the same time GO and Y2O3 9

aggregate The EDX profile (Fig 4D insert) exhibits strong carbon oxygen and yttrium peaks 10

Fig 4E and F exhibit HRTEM images of the GOY composite As shown in Fig 4E and F the 11

lattice fringes of Y2O3 nanocrystals and GO are simultaneously observed indicating strong 12

interactions between Y and the GO support The resolved lattice fringes of (111) planes (d = 13

031 nm) are attributed to GO and the lattice fringes of (111) planes (d = 027 nm) are 14

assigned to Y2O3 nanocrystals 15

33 XPS analysis 16

Fig 5A shows the XPS full survey spectra in the binding energy range of 0-1100 eV for 17

GO Y2O3 5 GOY and 20 GOY composite As shown in Fig 5A all the samples contain C 18

and O however the Y-contained samples show two peaks at about 1582 eV and 1600 eV 19

which are attributed to Y6 Fig 5B-D shows the high-resolution XPS regional spectra of Y 3d 20

O 1s and C 1s for 5 GOY respectively The relatively strong peaks at 1581 eV and 1599 eV 21

can be attributed to Y 3d52 and Y 3d32 respectively (Fig 5B) These results are in agreement 22

with values of Y2O3 reported in the literature35

It is well reported that yttrium retards the 23

combination of photogenerated electron-hole pairs41718

this may be due to the presence of 24

extra hydroxyl species to delay recombination through hole trapping6 Three kinds of surface 25

oxygen species could be distinguished in the O 1s spectra as shown in Fig 5C The binding 26

energy of 5309 eV 5318 and 5330 eV are ascribed to the lattice oxygen the hydroxyl 27

groups and the C-OH respectively36

As shown in Fig 5D the XPS spectrum of C 1s from 5 28

GOY is collected which can be deconvoluted into four peaks sp2 bonded carbon at 2848 eV 29

(CndashC) epoxyhydroxyls at 2860 eV (CndashO) carbonyls at 2879 eV (C=O) and carboxyls at 30

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2891 eV (OndashC=O) indicating the high percentage of oxygen-contained functional groups37

1

Chemisorbed surface hydroxyl groups can enhance photocatalysis by trapping photoinduced 2

holes resulting in an increase in the formation of highly oxidizing OH radicals38

3

34 Photocatalytic Activity for dye degradation 4

For comparative purposes the photodegradation efficiencies of MB and MO mediated 5

by the different photocatalysts under UV irradiation are shown in Fig 6 Before comparison 6

the adsorption and photodegradation performances of GO Y2O3 and 5 GOY on MB were 7

investigated (Fig S1) As displayed in Fig S1 both Y2O3 and 5 GOY have good adsorption 8

affinity to MB After stirring for 30 min under dark about 80 MB could be absorbed by 9

Y2O3 and 5 GOY which is much better than GO (lower than 20) After photocatalysis for 10

35min MB can be degraded thoroughly by 5 GOY Then the photocatalytic activities of the 11

GO Y2O3 5 GOY 10 GOY 20 GOY and 50 GOY composite photocatalysts were compared 12

via the reduction of MB and MO under ambient temperature Photodegradation time is 35 13

min It has been reported that a large surface area helps to increase the photocatalytic reaction 14

sites39

From the O1s spectrum of Y2O3 (Fig S2 supplementary material) the oxygen 15

composition of Y2O3 and 5 GOY samples at different states (Table S1 supplementary 16

material) more OH radicals are available in 5 GOY As expected under UV irradiation the 17

degradation of MB is slower than 10 with a GO photocatalyst However the conversion of 18

MB reaches 95 after 35 min when using Y2O3 as a photocatalyst The four kinds of GOY 19

samples exhibite better photocatalytic properties in the degradation of MB than bare GO and 20

Y2O3 under UV irradiation Moreover with increasing the amount of GO the degradation of 21

MB increases slowly Considering the simplicity and economy of the MB degradation 5 22

GOY is selected as the photocatalyst in the following experiments The photocatalytic 23

activities of 5 GOY was compared with commercial TiO2 P25 (Fig S3 supplementary 24

material) indicating the photocatalytic property of 5 GOY was quite comparable with P25 25

The GOY composites also have photocatalytic activities to MO As can be seen in Fig 6 GO 26

has good affinity to MO and the 50 GOY has best degradation efficiency to MO among the 27

GOY composites 28

The photocatalyst dosage may affect the MB degradation efficiency Fig 7A illustrates 29

MB degradation at varying photocatalyst dosages (5 to 10 mg) MB degradation efficiency 30

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increases with increasing the contact time In addition with increasing the dosage the MB 1

degradation efficiency slowly increases As displayed in Fig 7A the best dosage is 10 mg 2

As the MB concentration may also influence degradation MB degradation under various 3

concentration of MB is investigated It can be seen clearly in Fig 7B that MB conversion 4

efficiency is as much as 100 after degradation for 35 min when the MB concentration is 5

lower than 25 mg L-1

The conversion efficiency will decrease when the MB concentration is 6

higher than 275 mg L-1

The final conversion efficiency will no more than 90 if 300 mg 7

L-1

MB solution is used 8

Because the solution pH can remarkably influence MB degradation the effect of initial 9

pH on the degradation of MB with 5 GOY catalyst is determined as presented in Fig 7C As 10

shown in Fig 7C the conversion of MB will finally reach 100 when the solution pH is 11

lower than 519 If the solution pH controlled at 63 the conversion efficiency will decrease 12

sharply and only 80 MB will convert after 35 min Therefore the solution pH is set at 41 13

35 Photocatalytic mechanism 14

The magnitude of the photocurrent represents the charge collection efficiency of the 15

electrode surface and indirectly indicates the separated efficiency of electron-hole pairs40

16

From the insert of Fig 8 5 GOY modified photoelectrode is prompted in generating 17

photocurrent under visible and UV-visible light GOY photoelectrodes yield the greater 18

photocurrent than Y2O3 photoelectrode under UV irradiation in Fig 8 19

Fig 9 shows the PL spectra of the Y2O3 and GOY photocatalysts With Y2O3 as 20

photocatalyst the PL signal centered around 450 nm is detected revealing that ∙OH radicals 21

are generated on the irradiated Y2O3 When GOY nanocomposites are used as the 22

photocatalysts the PL signal intensity is increased which suggests that the yield of ∙OH 23

radicals is enhanced on the irradiated GOY nanocomposite The enhancement in 24

photoactivity can be attributed to the remarkable synergistic effect of the combination of 25

Y2O3 and the GO sheets leading to the efficient separation of photogenerated carriers in the 26

Y2O3 and GO coupling system 27

It is well known that the photodegradation process of the photocatalysts is strongly 28

relative to electron-hole pairs generated by light irradiation on catalysts The photogenerated 29

electrons and holes can migrate to the surface of the catalysts and then can be trapped 30

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generally by the oxygen and surface hydroxyls to ultimately produce hydroxyl radicals (middotOH) 1

that react with the adsorbed reactants41

As we know Y2O3 is n-type semiconductor with a 2

wide band gap about 56 eV42

To understand the charge separation process of Y2O3 and 3

GOYs the band edge positions of conduction band (CB) and valence band (VB) of 4

semiconductor Y2O3 has been calculated by the following equation43

5

EVB = X - Ee + 05Eg (1) 6

ECB = EVB - Eg (2) 7

where is the absolute electronegativity of the semiconductor e is the energy of free 8

electrons on the hydrogen scale (sim45 eV) and g is the bandgap energy of the 9

semiconductor The value of for Y2O3 is obtained by the arithmetic mean of the electron 10

affinity and the first ionization of the constituent atoms reported in the literatures44

to be 535 11

eV Thus the CB and VB potentials of Y2O3 are calculated to be -195 and 365 eV versus 12

normal hydrogen electrode (NHE) respectively It can be seen that the VB potential of 13

sample is more positive than the redox potential of OHminus∙OH (189 VNHE) indicating that 14

the photogenerated holes have strong oxidative ability and they can oxidize OHminus into ∙OH In 15

addition the CB potential of sample is negative enough to reduce O2 to O2∙ minus

(minus013 VNHE) 16

via eminus 17

Based on these results a possible mechanism for the photocatalytic is proposed as 18

follows and shown in Fig 10 19

Y2O3 + hν rarr Y2O3 (h+e) (3) 20

Y2O3 (e) + GO rarr Y2O3 + GO (e) (4) 21

GO (e) + O2 rarr GO + O2bullminus (5) 22

Y2O3 (h) + OHminus rarrY2O3 + OH

bull (6) 23

Y2O3 (h) + O2bullminus

+ OHbull + MB rarr CO2 +H2O+SO4

2minus + NO3

minus + Cl

minus (7) 24

25

4 Conclusions 26

In conclusion a novel GOY nanocomposite with different GO content has been obtained 27

via a one-step hydrothermal method The FT-IR XRD EDX and XPS results showed the 28

yttrium was successfully composited with GO The morphology characterization showed the 29

as-obtained GOY had nanoflake structure After stirring for 30 min under dark about 80 30

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MB could be absorbed by Y2O3 and 5 GOY The as-prepared GOY had good degradation 1

performance on both MB and MO under UV irradiation Compared with other GOY 2

composites 5 GOY had better photocatalytic activity to MB Factors such as dosages of 3

photocatalyst contaminant concentration and solution pH on MB conversion were also 4

investigated and discussed The catalyst also showed good stability and recyclability It is 5

expected that the GOY nanocomposite would be a potential candidate for treatment of dye 6

containing wastewater 7

8

Acknowledgments 9

This work was supported by the National Natural Science Foundation of China (No 10

21307104) Natural Science Foundation of Jiangsu Province China (NoBK20130438) the 11

Scientific Research Project of Environmental Fund of Yangzhou City (YHK1303) and 12

Jiangsu Key Laboratory of Environmental Material and Engineering (K12031) We thank the 13

Testing Center of Yangzhou University for sample characterization 14

15

Notes and References 16

1 B K Korbahti K Artut C Gecgel A Ozer Chem Eng J 2011 173 677-688 17

2 V K Gupta D Pathania S Agarwal P Singh J Hazard Mater 2012 243 179-186 18

3 N Wetchakun S Chaiwichain B Inceesungvorn K Pingmuang S Phanichphant A I 19

Minett J Chen ACS Appl Mater Interfaces 2012 4 3718-3723 20

4 Y F Li D Xu J I Oh W Shen X Li Y Yu ACS Catal 2012 2 391-398 21

5 M Khan W B Cao J Mol Catal A Chem 2013 376 71-77 22

6 Y F Wu Q J Zhang X F Yin H Q Cheng RSC Advances 2013 3 9670-9676 23

7 F H Chu C W Huang C L Hsin C W Wang S Y Yu P H Yeh W W Wu 24

Nanoscale 2012 4 1471-1475 25

8 L J Xu J L Wang Environ Sci Technol 2012 46 10145-10153 26

9 Y C Zhang J Li H Y Xu Appl Catal B 2012 123-124 18-26 27

10 S Usai S Obreg n A I Becerro G ol n J Phys Chem C 2013 117 24479-24484 28

11 A K Geim K S Novoselov Nat Mater 2007 6 183-191 29

12 K-Y Shin J-Y Hong J Jang Adv Mater 2011 23 2113-2118 30

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Figure captions 1

2

Figure 1 FT-IR spectra of GO Y2O3 and 5 GOY composites 3

Figure 2 XRD patterns of GO Y2O3 and 5 GOY composites 4

Figure 3 TGA curves of GO Y2O3 and 5 GOY composites 5

Figure 4 FESEM images of (A) Y2O3 (Insert low magnification) (B) GO (C) 5 GOY and 6

(D) 20 GOY composites (Insert EDS spectrum of 20 GOY sample) (E) and (F) 7

HRTEM images of 5 GOY taken after intense ultrasonic dispersion in ethanol for 30 8

min 9

Figure 5 XPS spectra (A) full survey spectra of GO Y2O3 and GOY nanocomposite (B) Y 10

3d of 5 GOY (C) O 1s of 5 GOY (D) C 1s of 5 GOY 11

Figure 6 Comparison of photodegradation efficiency using as-synthesized GO Y2O3 and 12

GOY composites 13

Figure 7 (A) Effect of dosage on MB conversion MB concentration 25 ppm pH = 41 (B) 14

Effect of MB concentration on the degradation Dosage 10 mg pH = 41 (C) Effect of 15

solution pH on MB conversion MB concentration 25 ppm Dosage 10 mg 16

Figure 8 Photocurrent responses of GO Y2O3 and 5 GOY photoelectrodes under UV 17

illumination Insert Photocurrent responses of 5 GOY under different illumination 18

conditions Scan rate 50 mVs The electrolyte solution was 05 M NaCl 19

Figure 9 PL spectra of Y2O3 5 GOY and 20 GOY samples (λex = 258 nm) 20

Figure 10 Proposed mechanism for the photodegradation of MB on GOY composite21

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Figure 1 1

2

3

4

500 1000 1500 2000 2500 3000 3500 4000

1657

Tra

ns

mit

tan

ce

Wavenumber cm-1

1657

1550

1564 17211223

1436

1436

GO

Y2O

3

5GOY

5

6

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Figure 2 1

2

3

10 20 30 40 50 60 70

5GOY2O

3

Inte

ns

ity

a

u

2degree

GO

Y2O

3

4

5

6

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Figure 3 1

2

0 100 200 300 400 500 60040

50

60

70

80

90

100

5GOY

Y2O

3

GO

We

igh

t

Temperature oC

3

4

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Figure 4 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

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Figure 5 1

2

3

1200 1000 800 600 400 200 0

Y 3d

C 1s

20 GOY

5 GOY

Y2O

3

Inte

ns

ity

a

u

Binding Energy eV

GO

O 1s

A

150 155 160 165 170 175

Inte

ns

ity

a

u

Binding Energy eV

Y 3d32

BY 3d

52

4

5

6

526 528 530 532 534 536

Inte

ns

ity

a

u

Binding Energy eV

O 1sC

282 284 286 288 290 292

Inte

ns

ity

a

u

Binding Energy eV

C-C

C-OC=O O-C=O

DC 1s

7

8

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1

Figure 6 2

3

00

02

04

06

08

10

12

Y2O

3

20GOY

50GOY

10GOY

5GOYCo

nv

ers

ion

Photocatalysts

MO

MB

GO

4

5

6

7

8

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Figure 7 1

2

-5 0 5 10 15 20 25 30 35 40060

070

080

090

Co

nv

ers

ion

Time min

5 mg

6 mg

7 mg

8 mg

9 mg

10 mg

A100

-5 0 5 10 15 20 25 30 35 40

060

070

080

090

Co

nv

ers

ion

Time min

200 mg L-1

225 mg L-1

250 mg L-1

275 mg L-1

300 mg L-1

B100

3

4

-5 0 5 10 15 20 25 30 35 40

110

050

060

070

080

090

Co

nv

ers

ion

Time min

pH 303

pH 418

pH 519

pH 630

100

C

5

6

7

8

9

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1

2

Figure 8 3

4

5

6

7

02 00 -02 -04

0

5

10

15

20j

A

cm

-2

E V (vs SCE)

Y2O

3

GO

5GOY

02 01 00 -01 -02 -0300

05

10

15

20

25

30

35

j A

cm

-2

E V (vs SCE)

Uv

Vis

Dark

5GOY

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1

2

Figure 9 3

4

400 450 500 550 600 650 700 750 800

Inte

ns

ity

a

u

Wavelength nm

20 GOY

5 GOY

Y2O

3

5

6

7

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1

Figure 10 2

3

4

5

6

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