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RGO composite for visible light: Photocatalytic applications
Materials Science for Energy Technologies 2 (2019) 112–116
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Materials Science for Energy Technologies
CHINESE ROOTS GLOBAL IMPACT
journal homepage: www.keaipublishing.com/en/journals/materials-science-for-energy-technologies
Synthesis of yttrium doped BiOF/RGO composite for visible light: Photocatalytic applications S. Vadivel a,⇑, Bappi Paul b, D. Maruthamani a, M. Kumaravel a, T. Vijayaraghavan c, S. Hariganesh a, Ramyakrishna Pothu d a
Department of Chemistry, PSG College of Technology, Coimbatore 641004, India Department of Chemistry, National Institute of Technology Silchar, Silchar 788010, Assam, India Functional Materials Laboratory, PSG Institute of Advanced Studies, Coimbatore 641004, Tamilnadu, India d College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, PR China b c
a r t i c l e
i n f o
Article history: Received 21 August 2018 Revised 15 November 2018 Accepted 16 November 2018 Available online 28 November 2018 Keywords: BiOF Graphene Yttrium Semiconductors Visible light Photocatalysts
a b s t r a c t In this present work, yttrium doped bismuth oxy fluoride/reduced graphene oxide (Y-BiOF/RGO) composite was synthesized using a simple solvothermal method. As synthesized composite was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), UV–Vis diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) techniques. The photocatalytic property was evaluated towards the degradation of methylene blue (MB) dye under the visible-light irradiation. The characterization results highlighted that the efficient incorporation of both yttrium ions and RGO greatly reduced the recombination rate of BiOF and extended the visible-light absorption ability. As synergistic effects, the prepared Y-BiOF/RGO composite exhibited maximum degradation rate of 98% in 360 min, which is 6.5 times higher than pure BiOF. The clear mechanism for the enhanced photo-activity by YBiOF/RGO was discussed. Ó 2018 The Authors. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-ncnd/4.0/).
1. Introduction Rapid industrialization and modernization have brought up the human race to the highest level of comfort but considering the adverse impacts caused by these advancements were huge. The environment have been heavily deteriorated, especially air and water bodies are polluted by the untreated effluents disposed from various industries to the open environment. In the recent decades heterogeneous semiconductor photocatalysis have emerged as the best technique to protect the environment from hazardous pollutants. The ultimate need to develop a sustainable, low cost photocatalytic material is one of the greatest challenges in front of our research community. In recent years, Bi-based semiconductors gained huge attention in photocatalyst owing to their layered structures and direct band gap compared with traditional semiconductor photocatalysts like TiO2 and ZnO [1]. Among them, bismuth oxyhalides BiOX (where X = Cl, Br, I, F) with [Bi2O2] slabs interleaved by halogen atoms used as advanced photocatalytic material in this past decades. Thus, the BiOX semiconductors like BiOBr, BiOF are considered to be a direct band gap nature and BiOI, BiOCl ⇑ Corresponding author. E-mail address: [email protected] (S. Vadivel).
is indirect band gap material with remarkable photocatalytic properties. Among them BiOF has been considered as one of the UVactive photocatalytic material for dye degradation. However, the visible light-photocatalytic activity of BiOF is still poor and requires being further enhanced [2–4]. Recently, doping of metal ion into BiOF matrix is considered to be a simple method to speed up the separation rate and reduce the recombination efficiency in semiconductors matrix [5]. In our previous studies we developed an Ag-BiOF/g-C3N4 composite which exhibited remarkable degradation efficiency than pure BiOF towards methylene blue dye [6,7]. T. Jiang et al. developed BiOBr/BiOF hetereojunction by hydrothermal method for Rhodamine-B and nitrobenzene degradation under visible-light. Among the dopant ions which can couple with BiOF, yttrium has the ability to absorb a large part of the visible light [8]. Y-ions were widely employed to couple with some semiconductors to enhance the photocatalytic performance notably the Y-ZrO2 and Y-TiO2 systems have been developed. Recent studies revealed that the addition of RGO in semiconductor to enhance electron transport and thus prevent recombination rate due to its superior electrical conductivity and high surface area of RGO. Hu et Al. achieved the superior photocatalytic activity of BiOF towards the rhodamine-B dye by synergistic effect of graphene and bismuth oxide [9]. It therefore
https://doi.org/10.1016/j.mset.2018.11.006 2589-2991/Ó 2018 The Authors. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
S. Vadivel et al. / Materials Science for Energy Technologies 2 (2019) 112–116
appears that recent literatures clearly demonstrated that improved photocatalytic performance of BiOF can be enhanced through either doping for light absorption or adding RGO for reducing recombination rate. In this work, we have studied a novel ternary Y-BiOF/ RGO nanocomposite synthesized using a one-step facile solvothermal method toward MB dye degradation. 2. Experimental section 2.1. Synthesis The Y-BiOF/RGO composite was synthesized by in-situ solvothermal approach. Graphene oxide (GO) was synthesized by modified Hummers method, according to our previous reports [11]. Thus, 0.1 g of GO was dispersed in 20 mL of ethylene glycol (EG) under ultrasonic for 30 min and then stochiometric amount of Bi(NO3)35H2O, Y(NO3)36H2O and polyvinylpyrrolidone (PVP) [M.W.: 40,000 g/mol] were added into the above solution. Furthermore, stochiometric ammonium NH4F dissolved in 10 mL of double distilled water was mixed through EG solution. Then, the reaction mixture was transferred into a Teflon lined stainless steel autoclave and maintained at 180 °C for 16 h. Finally, the resultant precipitate was washed and dried at 70 °C in the vacuum oven over 5 h. 2.2. Characterization studies The crystal structure was confirmed using X-ray diffraction (XRD) analysis was measured on a Shimadzu XRD-6000 diffractometer (CuKa radiation, k = 1.54056 Å). The Fourier transform infrared spectroscopy analysis was carried out using Shimadzu FTIR-8400S with KBr as a standard. The morphological characterization was carried out in ZEISS SIGMA field-emission scanning electron microscopy (FE-SEM) and then JEOL – JEM 2100 high resolution transmission electron microscopy (HRTEM) images operated at 200 kV. UV–vis diffuse reflectance spectroscopy was performed using UV–Vis JASCO V750 spectrophotometer. The fluorescence emission spectrum was analyzed by spectrofluorophotometer (RF – 5301 PC model, Shimadzu). 2.3. Photocatalytic studies The photocatalytic studies of Y-BiOF/RGO samples were evaluated by degradation of MB under visible light irradiation. All controlled experiments were carried out using Heber scientific
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photocatalytic reactor with equipped a 300 W Xe lamp as the visible light source. In this experiment, 50 mg of photocatalysts was dispersed into 100 mL of MB (10 ppm) solution. The solution was stirred for 30 min in the dark to reach the adsorption-desorption equilibrium between the photocatalysts and the dye. For analyzing the degradation studies, roughly 3 mL of MB aliquot solution was taken out at given time intervals followed by centrifugation and the supernatant solution was analyzed by JASCO V750 UV–Vis spectrophotometer. The maximum absorption peak of the MB solution was fixed at 661 nm.
3. Results and discussion 3.1. Structural characterization Fig. 1(a) shows the XRD patterns of the as-prepared samples. The XRD peaks located at 2h values of 27.96°, 29.3°, 33.94°, 37.72°, 41.94°, 45.08°, 49.24° and 58.16° corresponds to the (1 0 1), (0 0 2), (1 1 0), (1 0 2), (0 0 3), (1 1 2), (2 0 0) and (2 1 1) planes of Zavaritskite phases of BiOF respectively. [JCPDS no. 73– 1595; space group P4/nmm]. The XRD spectra of BiOF were matched with the previous reports [5]. In the pattern of Y-BiOF and Y-BiOF/RGO composite, intensity of the planes at (1 0 1), (1 1 0), (1 1 2) and (2 1 1) facets were reduced and also no dominant characteristic peaks of Y2O3 was observed. This result suggested that Y3+ was substituted on Bi matrix due to the smaller ionic radii of Y3+ (1.04 Å) Bi3+ (1.14 Å). Moreover, the absence of RGO peaks might be a due to the low amount of addition or the weak diffraction intensities in the composite. The impurity peak shown at 51.85° stands for (3 1 1) plane of BiF3. Fig. 1(b) depicts the FT-IR spectra of GO, BiOF, Y-BiOF and YBiOF/RGO composite. For GO the peaks observed at 3450, 1735, 1375 and 1227 cm 1 corresponds to the OAH, C@O, CAOH and CAOAC stretching vibrations respectively which matches well with the previous reports [10]. For pure BiOF, the vibration absorption bands observed at 1641, 1387, 817 cm 1 and were assigned to surface adsorbed water molecules, NO3 , Bi-O bands for BiOF [10,11]. Moreover, the bands featuring the oxygen functionalities were almost vanished in the spectra of the Y-Doped BiOF, confirming the effective reduction of GO sheets. Additionally the peak at 1578 cm 1 arises due to skeletal vibrations of graphitic domains which further confirm the incorporation of graphene in system and no prominent additional peaks were observed due to Y doping in the photocatalyst.
Fig. 1. (a) XRD diffraction pattern of as-prepared samples and (b) FT-IR spectra.
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The morphology of as-prepared samples was analyzed by FESEM and TEM. Herein, Fig. 2(a) and (b) illustrated the FESEM micrographs of BiOF and Y-BiOF catalysts. BiOF comprises of asymmetrical rod like structures and whereas in Fig. 3(b) it evidences the well-defined dispersion of Y3+ ions over the BiOF rods similar to the Y-CeO3 [19]. Furthermore, Fig. 2(c) and (d) exhibit rod structure of BiOF and Y-BiOF/RGO composites respectively which coincides well with FESEM image. Fig. 2(c) and (d) shows that Y-BiOF was well dispersed over the RGO sheets and inserted image illustrates the SAED pattern that confirms the polycrystalline nature of the photocatalyst. The secondary spherical morphology was observed due to secondary phases of BiF3 structure.
BiOBr exhibited the highest photocatalytic activity compared with 10 wt% of Y3+ ions in BiOBr and Sara usai et al., shown 3 wt% of Y3+ in BiVO4 had enhanced photocatalytic activity than 5 wt% of Y3+ doped BiVO4 [17,18] but the graphene incorporated system shows improved photocativity due to higher charge carrier capacity. The photoluminescence (PL) spectra can be considered as a direct methodology to realize the separation efficiency of the photogenerated charge carriers. PL results shown in Fig. 3(b) were recorded with the excitation wavelength at 270 nm in room temperature. All samples exhibit a wide emission band between 350 nm and 390 nm. The peak intensity has been reduced with the influence of Y3+ ions and RGO compared to bare BiOF and YBiOF which indicated the prevention of electron-hole pair recombination rate and no secondary peaks were observed in the catalysts.
3.3. Optical properties
3.4. Photocatalytic degradation studies
The optical performances of semiconductor materials were characterized through UV–Vis diffuse reflectance spectra (DRS) and Photoluminescence emission spectra (PL) as displayed in Fig. 3(a) and (b) respectively. The absorption edge of pure BiOF and Y-doped BiOF and Y-BiOF/RGO occurs at 334 nm, 321 nm, and 348 nm respectively. Tauc’s plot relations was used to determine the band gap energy, BiOF showed band gap energy of 3.93 eV which was consistent with the previous reports [5]. Certainly, the band gap energy of Y3+ doped BiOF and Y/BiOF/RGO composite corresponds to 4.10 eV and 3.88 eV respectively. In accordance with the literature, the higher Y3+ doping has been exposed to cause the blue shift in band gap and it affects the behaviour of recombination rate in photocatalytic studies [12–16] For instance, Minqiang et al., reported that the 5 wt% of Y3+ ions in
The photocatalytic activities of as-obtained samples were evaluated by the degradation of MB under visible light irradiation. In Fig. 4(a) explains the UV–Vis absorption spectra of MB using BiOF, Y-BiOF and Y-BiOF/RGO for 6 h of irradiation. Fig. 4(b) was shown the degradation efficiency of MB i.e. (C/C0) with respect to degradation time. The blank studies indicated that MB does not have selfdegradation ability under visible irradiation. The pure BiOF and YBiOF exhibited 15.25%, 12.54% efficiency at 6 h visible irradiation time. Hence, it confirmed that the Y-BiOF sample exhibited lower photocatalytic activity than pure BiOF degradation of MB. Whereas, after the introduction of RGO with Y3+ ions doped BiOF exhibits 98% efficiency of MB degradation for 6 h irradiation. The pure BiOF has higher band gap energy and only active under the UV region, hence the light harvesting ability has been limited for
3.2. Morphological studies
Fig. 2. FESEM morphology studies of (a) pure BiOF (b) Y3+ doped BiOF; HRTEM image of (c) Y BiOF and (d) Y BiOF/RGO catalyst inset as their SAED pattern.
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Fig. 3. (a) UV-DRS Spectra and inset as band gap energy plot and (b) PL studies at excitation of 270 nm for pure BiOF, Y3+ doped BiOF and Y-BiOF/RGO composites respectively.
Fig. 4. (a) UV–vis absorption of photo degradation MB solution at 360 min and (b) Absorption rate of initial concentration (C0) and degradation concentration (C) versus time for Blank (MB solution), pure BiOF, Y3+ doped BiOF and Y-BiOF/RGO composites respectively.
Fig. 5. Photo degradation mechanism of Y-BiOF/RGO composites.
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photodegradation properties. Accordingly, the design of Y-BiOF/ RGO can be resolved as follows. We have proposed a possible mechanistic pathway for the photocatalytic degradation of MB by the Y-BiOF/RGO shown in the Fig. 5. Initially, under the irradiation, BiOF generated charge carriers (e /h+), the electrons from the valence band (VB) of BiOF excites to the conduction band (CB) from there it transfers to Y3+ ions which located on BiOF lattice. The occurrence of Y3+ amplified the transfer of electrons to RGO sheet. Thus RGO sheets provide an extended lifetime of photo-excited electron-hole pairs simultaneously the electrons in the RGO sheet reduces molecular oxygen O2 to O–2 which in turn reacts with the MB dye molecule at the same time the holes h+ at the VB also contributes by producing OH radicals from water that would also lead to the possibility of successful degradation of MB to harmless by products [20–22]. Based on the above analyses, the photocatalytic mechanism was concluded with the synergistic effect of Y-BiOF/ RGO composites. Thus, the Y-BiOF/RGO composite has evidence of photocatalytic activity under the visible light irradiation successfully. 4. Conclusion In summary, Y-BiOF/RGO composites were effectively synthesized through solvothermal techniques and confirmed via physicchemical characterizations. The experimental results reveal that Y3+ ions have capable to trapped the charge electron-hole pairs generated between [Bi2O2]2+ and [F2]2 layers, which supports to the photodegradation. Furthermore, addition of RGO to the composite enhanced the overall photocatalytic performance of Y-BiOF under visible irradiation. To knowledge, the synergistic properties of Y-BiOF/RGO composites were exposed to be an effective photocatalyst under the visible region. Conflict of interest None declared. Acknowledgement This work was financially supported by DST-Science and Engineering Research Board India, under ‘‘Early Career Research Award Scheme” (ECR/2016/001535/CS) to Dr. S. Vadivel. References [1] Jie Li, Yu. Ying, Lizhi Zhang, Bismuth oxyhalide nanomaterials: layered structures meet photocatalysis, Nanoscale 6 (2014) 8473–8488. [2] Hefeng Cheng, Baibiao Huang, Ying Dai, Engineering BiOX (X = Cl, Br, I) nanostructures for highly efficient photocatalytic applications, Nanoscale 6 (2014) 2009–2026. [3] Liqun Ye, Su. Yurong, Xiaoli Jin, Can Zhang HaiquanXie, Recent advances in BiOX (X = Cl, Br and I) photocatalysts: synthesis, modification, facet effects and mechanisms, Environ Sci. Nano 1 (2014) 90–112.
[4] Miao Wang, Qing-Li Huang, Xue-Tai Chen, Xiao-Zeng You, Room temperature synthesis of bismuthoxyfluoridenanosheets and nanorods, Mater. Lett. 61 (2007) 4666–4669. [5] FeiTeng SijiaZou, Chao Chang, Zailun Liu, Shurong Wang, Controllable synthesis of uniform BiOF nanosheets and the improved photocatalytic activity by high-energy (002) facet exposed and internal electric field, RSC Adv. 5 (2015) 88936–88942. [6] Su. Wenyue, Jian Wang, Yingxing Huang, Wanjun Wang, Wu. Ling, Xu.Xu. Wang, Ping Liu, Synthesis and catalytic performances of a novel photocatalyst BiOF, Scripta Mater. 62 (2010) 345–348. [7] S. Vadivel, V.P. Kamalakannan, N.P. Kavitha, T. SanthoshiniPriya, N. Balasubramanian, Development of novel Ag modified BiOF squares/g-C3N4 composite for photocatalytic applications, Mater. Sci. Semicond. Process. 41 (2016) 59–66. [8] Zong-Yan Zhao, Wen-Wu Dai, Structural, electronic, and optical properties of eu-doped BiOX (X = F, Cl, Br, I): a DFT+U study, Inorg. Chem. 53 (2014) 13001– 13011. [9] L. Hu, S. Dong, Q. Li, J. Feng, Y. Pi, M. Liu, J. Sun, J. Sun, Facile synthesis of BiOF/ Bi2O3/reduced graphene oxide photocatalyst with highly efficient and stable natural sunlight photocatalytic performance, J. Alloys Compd. 633 (2015) 256– 264. [10] Ya. Zhang, Saisai Yuan, Yanhua Zhao, Chenda He HongguiWanga, Synthesis of novel yttrium-doped graphene oxide nanocomposite for dye removal, J. Mater. Chem. A 2 (2014) 7897–7903. [11] S. Vadivel, M. Vanitha, A. Muthukrishnaraj, N. Balasubramanian, Graphene oxide–BiOBr composite material as highly efficient photocatalyst for degradation of methylene blue and rhodamine-B dyes, J. Water Process Eng. 1 (2014) 17–26. [12] T.E. Alves, H.V. Pessoni, A. Franco Junior, The effect of Y3+ substitution on the structural, optical band-gap, and magnetic properties of cobalt ferrite nanoparticles, Phys. Chem. Chem. Phys. 19 (2017) 16395–16405. [13] Alberto Escudero, Elisa Moretti, Manuel Ocaña, Synthesis and luminescence of uniform europium doped bismuth fluoride and bismuth oxyfluoride particles with different morphologies, Cryst Eng Comm 16 (2014) 3274–3283. [14] Anjalee D. Liyanage, Sanjaya D. Perera, Kui Tan, Yves Chabal, Kenneth J. Balkus Jr., Synthesis, characterization, and photocatalytic activity of Y doped CeO2 nanorods, ACS Catal. 4 (2014) 577–584. [15] A. Mukherjee, M. Sk, M. Hossain, S. Basu Pal, Effect of Y-doping on optical properties of multiferroics BiFeO3 nanoparticles, Appl. Nanosci. 2 (2012) 305– 310. [16] Sheng Yin, Wenmin Fan, Jun Di, Wu. Ting, Jiaxin Yan, Minqiang He, Jiexiang Xia, Huaming Li, La3+ doped BiOBr microsphere with enhanced visible light photocatalytic activities, Colloids Surf., A 513 (2017) 160–167. [17] Minqiang He, Weibing Li, Jiexiang Xia, Xu. Li, Jun Di, Xu Hui, Sheng Yin, Huaming Li, Mengna Li, The enhanced visible light photocatalytic activity of yttrium-doped BiOBr synthesized via a reactable ionic liquid, Appl. Surf. Sci. 331 (2015) 170–178. [18] Sara Usai, Sergio Obregon, Ana Isabel Becerro, Gerardo Colon, MonoclinicTetragonal heterostructured BiVO4 by yttrium doping with improved photocatalytic activity, J. Phys. Chem. C 117 (2013) 24479–24484. [19] Xu. Bin, Qitao Zhang, Saisai Yuan, Sixiao Liu, Ming Zhang, Teruhisa Ohno, Synthesis and photocatalytic performance of yttrium-doped CeO2 with a hollow sphere structure, Catal. Today 281 (2017) 135–143. [20] Xiaoling Yang, Wei Chen, Jianfei Huang, Ying Zhou, Yihua Zhu, Chunzhong Li, Rapid degradation of methylene blue in a novel heterogeneous Fe3O4@rGO@TiO2-catalyzed photo-Fenton system, Sci. Rep. 5 (2015) 10632. [21] Imran Aslam, M. Chuanbao Cao, M. Hassan Tanveer, Waheed S. Farooq, Muhammad Tahir Khan, Faryal Idrees, Syed Khalid, A novel Z-scheme WO3/ CdWO4 photocatalyst with enhanced visible-light photocatalytic activity for the degradation of organic pollutants, RSC Adv. 5 (2015) 6019–6026. [22] Imran Aslam, Chuanbao Cao, Muhammad Tanveer, Waheed Samraiz Khan, Muhammad Tahir, Muhammad Abid, Faryal Idrees, Faheem K. Butt, Zulfiqar Ali, Nasir Mahmood, Synergistic effect between WO3 and g-C3N4 towards efficient visible light-driven photocatalytic performance, New J. Chem. 38 (2014) 5462–5469.
Contents lists available at ScienceDirect
Materials Science for Energy Technologies
CHINESE ROOTS GLOBAL IMPACT
journal homepage: www.keaipublishing.com/en/journals/materials-science-for-energy-technologies
Synthesis of yttrium doped BiOF/RGO composite for visible light: Photocatalytic applications S. Vadivel a,⇑, Bappi Paul b, D. Maruthamani a, M. Kumaravel a, T. Vijayaraghavan c, S. Hariganesh a, Ramyakrishna Pothu d a
Department of Chemistry, PSG College of Technology, Coimbatore 641004, India Department of Chemistry, National Institute of Technology Silchar, Silchar 788010, Assam, India Functional Materials Laboratory, PSG Institute of Advanced Studies, Coimbatore 641004, Tamilnadu, India d College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, PR China b c
a r t i c l e
i n f o
Article history: Received 21 August 2018 Revised 15 November 2018 Accepted 16 November 2018 Available online 28 November 2018 Keywords: BiOF Graphene Yttrium Semiconductors Visible light Photocatalysts
a b s t r a c t In this present work, yttrium doped bismuth oxy fluoride/reduced graphene oxide (Y-BiOF/RGO) composite was synthesized using a simple solvothermal method. As synthesized composite was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), UV–Vis diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) techniques. The photocatalytic property was evaluated towards the degradation of methylene blue (MB) dye under the visible-light irradiation. The characterization results highlighted that the efficient incorporation of both yttrium ions and RGO greatly reduced the recombination rate of BiOF and extended the visible-light absorption ability. As synergistic effects, the prepared Y-BiOF/RGO composite exhibited maximum degradation rate of 98% in 360 min, which is 6.5 times higher than pure BiOF. The clear mechanism for the enhanced photo-activity by YBiOF/RGO was discussed. Ó 2018 The Authors. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-ncnd/4.0/).
1. Introduction Rapid industrialization and modernization have brought up the human race to the highest level of comfort but considering the adverse impacts caused by these advancements were huge. The environment have been heavily deteriorated, especially air and water bodies are polluted by the untreated effluents disposed from various industries to the open environment. In the recent decades heterogeneous semiconductor photocatalysis have emerged as the best technique to protect the environment from hazardous pollutants. The ultimate need to develop a sustainable, low cost photocatalytic material is one of the greatest challenges in front of our research community. In recent years, Bi-based semiconductors gained huge attention in photocatalyst owing to their layered structures and direct band gap compared with traditional semiconductor photocatalysts like TiO2 and ZnO [1]. Among them, bismuth oxyhalides BiOX (where X = Cl, Br, I, F) with [Bi2O2] slabs interleaved by halogen atoms used as advanced photocatalytic material in this past decades. Thus, the BiOX semiconductors like BiOBr, BiOF are considered to be a direct band gap nature and BiOI, BiOCl ⇑ Corresponding author. E-mail address: [email protected] (S. Vadivel).
is indirect band gap material with remarkable photocatalytic properties. Among them BiOF has been considered as one of the UVactive photocatalytic material for dye degradation. However, the visible light-photocatalytic activity of BiOF is still poor and requires being further enhanced [2–4]. Recently, doping of metal ion into BiOF matrix is considered to be a simple method to speed up the separation rate and reduce the recombination efficiency in semiconductors matrix [5]. In our previous studies we developed an Ag-BiOF/g-C3N4 composite which exhibited remarkable degradation efficiency than pure BiOF towards methylene blue dye [6,7]. T. Jiang et al. developed BiOBr/BiOF hetereojunction by hydrothermal method for Rhodamine-B and nitrobenzene degradation under visible-light. Among the dopant ions which can couple with BiOF, yttrium has the ability to absorb a large part of the visible light [8]. Y-ions were widely employed to couple with some semiconductors to enhance the photocatalytic performance notably the Y-ZrO2 and Y-TiO2 systems have been developed. Recent studies revealed that the addition of RGO in semiconductor to enhance electron transport and thus prevent recombination rate due to its superior electrical conductivity and high surface area of RGO. Hu et Al. achieved the superior photocatalytic activity of BiOF towards the rhodamine-B dye by synergistic effect of graphene and bismuth oxide [9]. It therefore
https://doi.org/10.1016/j.mset.2018.11.006 2589-2991/Ó 2018 The Authors. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
S. Vadivel et al. / Materials Science for Energy Technologies 2 (2019) 112–116
appears that recent literatures clearly demonstrated that improved photocatalytic performance of BiOF can be enhanced through either doping for light absorption or adding RGO for reducing recombination rate. In this work, we have studied a novel ternary Y-BiOF/ RGO nanocomposite synthesized using a one-step facile solvothermal method toward MB dye degradation. 2. Experimental section 2.1. Synthesis The Y-BiOF/RGO composite was synthesized by in-situ solvothermal approach. Graphene oxide (GO) was synthesized by modified Hummers method, according to our previous reports [11]. Thus, 0.1 g of GO was dispersed in 20 mL of ethylene glycol (EG) under ultrasonic for 30 min and then stochiometric amount of Bi(NO3)35H2O, Y(NO3)36H2O and polyvinylpyrrolidone (PVP) [M.W.: 40,000 g/mol] were added into the above solution. Furthermore, stochiometric ammonium NH4F dissolved in 10 mL of double distilled water was mixed through EG solution. Then, the reaction mixture was transferred into a Teflon lined stainless steel autoclave and maintained at 180 °C for 16 h. Finally, the resultant precipitate was washed and dried at 70 °C in the vacuum oven over 5 h. 2.2. Characterization studies The crystal structure was confirmed using X-ray diffraction (XRD) analysis was measured on a Shimadzu XRD-6000 diffractometer (CuKa radiation, k = 1.54056 Å). The Fourier transform infrared spectroscopy analysis was carried out using Shimadzu FTIR-8400S with KBr as a standard. The morphological characterization was carried out in ZEISS SIGMA field-emission scanning electron microscopy (FE-SEM) and then JEOL – JEM 2100 high resolution transmission electron microscopy (HRTEM) images operated at 200 kV. UV–vis diffuse reflectance spectroscopy was performed using UV–Vis JASCO V750 spectrophotometer. The fluorescence emission spectrum was analyzed by spectrofluorophotometer (RF – 5301 PC model, Shimadzu). 2.3. Photocatalytic studies The photocatalytic studies of Y-BiOF/RGO samples were evaluated by degradation of MB under visible light irradiation. All controlled experiments were carried out using Heber scientific
113
photocatalytic reactor with equipped a 300 W Xe lamp as the visible light source. In this experiment, 50 mg of photocatalysts was dispersed into 100 mL of MB (10 ppm) solution. The solution was stirred for 30 min in the dark to reach the adsorption-desorption equilibrium between the photocatalysts and the dye. For analyzing the degradation studies, roughly 3 mL of MB aliquot solution was taken out at given time intervals followed by centrifugation and the supernatant solution was analyzed by JASCO V750 UV–Vis spectrophotometer. The maximum absorption peak of the MB solution was fixed at 661 nm.
3. Results and discussion 3.1. Structural characterization Fig. 1(a) shows the XRD patterns of the as-prepared samples. The XRD peaks located at 2h values of 27.96°, 29.3°, 33.94°, 37.72°, 41.94°, 45.08°, 49.24° and 58.16° corresponds to the (1 0 1), (0 0 2), (1 1 0), (1 0 2), (0 0 3), (1 1 2), (2 0 0) and (2 1 1) planes of Zavaritskite phases of BiOF respectively. [JCPDS no. 73– 1595; space group P4/nmm]. The XRD spectra of BiOF were matched with the previous reports [5]. In the pattern of Y-BiOF and Y-BiOF/RGO composite, intensity of the planes at (1 0 1), (1 1 0), (1 1 2) and (2 1 1) facets were reduced and also no dominant characteristic peaks of Y2O3 was observed. This result suggested that Y3+ was substituted on Bi matrix due to the smaller ionic radii of Y3+ (1.04 Å) Bi3+ (1.14 Å). Moreover, the absence of RGO peaks might be a due to the low amount of addition or the weak diffraction intensities in the composite. The impurity peak shown at 51.85° stands for (3 1 1) plane of BiF3. Fig. 1(b) depicts the FT-IR spectra of GO, BiOF, Y-BiOF and YBiOF/RGO composite. For GO the peaks observed at 3450, 1735, 1375 and 1227 cm 1 corresponds to the OAH, C@O, CAOH and CAOAC stretching vibrations respectively which matches well with the previous reports [10]. For pure BiOF, the vibration absorption bands observed at 1641, 1387, 817 cm 1 and were assigned to surface adsorbed water molecules, NO3 , Bi-O bands for BiOF [10,11]. Moreover, the bands featuring the oxygen functionalities were almost vanished in the spectra of the Y-Doped BiOF, confirming the effective reduction of GO sheets. Additionally the peak at 1578 cm 1 arises due to skeletal vibrations of graphitic domains which further confirm the incorporation of graphene in system and no prominent additional peaks were observed due to Y doping in the photocatalyst.
Fig. 1. (a) XRD diffraction pattern of as-prepared samples and (b) FT-IR spectra.
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The morphology of as-prepared samples was analyzed by FESEM and TEM. Herein, Fig. 2(a) and (b) illustrated the FESEM micrographs of BiOF and Y-BiOF catalysts. BiOF comprises of asymmetrical rod like structures and whereas in Fig. 3(b) it evidences the well-defined dispersion of Y3+ ions over the BiOF rods similar to the Y-CeO3 [19]. Furthermore, Fig. 2(c) and (d) exhibit rod structure of BiOF and Y-BiOF/RGO composites respectively which coincides well with FESEM image. Fig. 2(c) and (d) shows that Y-BiOF was well dispersed over the RGO sheets and inserted image illustrates the SAED pattern that confirms the polycrystalline nature of the photocatalyst. The secondary spherical morphology was observed due to secondary phases of BiF3 structure.
BiOBr exhibited the highest photocatalytic activity compared with 10 wt% of Y3+ ions in BiOBr and Sara usai et al., shown 3 wt% of Y3+ in BiVO4 had enhanced photocatalytic activity than 5 wt% of Y3+ doped BiVO4 [17,18] but the graphene incorporated system shows improved photocativity due to higher charge carrier capacity. The photoluminescence (PL) spectra can be considered as a direct methodology to realize the separation efficiency of the photogenerated charge carriers. PL results shown in Fig. 3(b) were recorded with the excitation wavelength at 270 nm in room temperature. All samples exhibit a wide emission band between 350 nm and 390 nm. The peak intensity has been reduced with the influence of Y3+ ions and RGO compared to bare BiOF and YBiOF which indicated the prevention of electron-hole pair recombination rate and no secondary peaks were observed in the catalysts.
3.3. Optical properties
3.4. Photocatalytic degradation studies
The optical performances of semiconductor materials were characterized through UV–Vis diffuse reflectance spectra (DRS) and Photoluminescence emission spectra (PL) as displayed in Fig. 3(a) and (b) respectively. The absorption edge of pure BiOF and Y-doped BiOF and Y-BiOF/RGO occurs at 334 nm, 321 nm, and 348 nm respectively. Tauc’s plot relations was used to determine the band gap energy, BiOF showed band gap energy of 3.93 eV which was consistent with the previous reports [5]. Certainly, the band gap energy of Y3+ doped BiOF and Y/BiOF/RGO composite corresponds to 4.10 eV and 3.88 eV respectively. In accordance with the literature, the higher Y3+ doping has been exposed to cause the blue shift in band gap and it affects the behaviour of recombination rate in photocatalytic studies [12–16] For instance, Minqiang et al., reported that the 5 wt% of Y3+ ions in
The photocatalytic activities of as-obtained samples were evaluated by the degradation of MB under visible light irradiation. In Fig. 4(a) explains the UV–Vis absorption spectra of MB using BiOF, Y-BiOF and Y-BiOF/RGO for 6 h of irradiation. Fig. 4(b) was shown the degradation efficiency of MB i.e. (C/C0) with respect to degradation time. The blank studies indicated that MB does not have selfdegradation ability under visible irradiation. The pure BiOF and YBiOF exhibited 15.25%, 12.54% efficiency at 6 h visible irradiation time. Hence, it confirmed that the Y-BiOF sample exhibited lower photocatalytic activity than pure BiOF degradation of MB. Whereas, after the introduction of RGO with Y3+ ions doped BiOF exhibits 98% efficiency of MB degradation for 6 h irradiation. The pure BiOF has higher band gap energy and only active under the UV region, hence the light harvesting ability has been limited for
3.2. Morphological studies
Fig. 2. FESEM morphology studies of (a) pure BiOF (b) Y3+ doped BiOF; HRTEM image of (c) Y BiOF and (d) Y BiOF/RGO catalyst inset as their SAED pattern.
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Fig. 3. (a) UV-DRS Spectra and inset as band gap energy plot and (b) PL studies at excitation of 270 nm for pure BiOF, Y3+ doped BiOF and Y-BiOF/RGO composites respectively.
Fig. 4. (a) UV–vis absorption of photo degradation MB solution at 360 min and (b) Absorption rate of initial concentration (C0) and degradation concentration (C) versus time for Blank (MB solution), pure BiOF, Y3+ doped BiOF and Y-BiOF/RGO composites respectively.
Fig. 5. Photo degradation mechanism of Y-BiOF/RGO composites.
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photodegradation properties. Accordingly, the design of Y-BiOF/ RGO can be resolved as follows. We have proposed a possible mechanistic pathway for the photocatalytic degradation of MB by the Y-BiOF/RGO shown in the Fig. 5. Initially, under the irradiation, BiOF generated charge carriers (e /h+), the electrons from the valence band (VB) of BiOF excites to the conduction band (CB) from there it transfers to Y3+ ions which located on BiOF lattice. The occurrence of Y3+ amplified the transfer of electrons to RGO sheet. Thus RGO sheets provide an extended lifetime of photo-excited electron-hole pairs simultaneously the electrons in the RGO sheet reduces molecular oxygen O2 to O–2 which in turn reacts with the MB dye molecule at the same time the holes h+ at the VB also contributes by producing OH radicals from water that would also lead to the possibility of successful degradation of MB to harmless by products [20–22]. Based on the above analyses, the photocatalytic mechanism was concluded with the synergistic effect of Y-BiOF/ RGO composites. Thus, the Y-BiOF/RGO composite has evidence of photocatalytic activity under the visible light irradiation successfully. 4. Conclusion In summary, Y-BiOF/RGO composites were effectively synthesized through solvothermal techniques and confirmed via physicchemical characterizations. The experimental results reveal that Y3+ ions have capable to trapped the charge electron-hole pairs generated between [Bi2O2]2+ and [F2]2 layers, which supports to the photodegradation. Furthermore, addition of RGO to the composite enhanced the overall photocatalytic performance of Y-BiOF under visible irradiation. To knowledge, the synergistic properties of Y-BiOF/RGO composites were exposed to be an effective photocatalyst under the visible region. Conflict of interest None declared. Acknowledgement This work was financially supported by DST-Science and Engineering Research Board India, under ‘‘Early Career Research Award Scheme” (ECR/2016/001535/CS) to Dr. S. Vadivel. References [1] Jie Li, Yu. Ying, Lizhi Zhang, Bismuth oxyhalide nanomaterials: layered structures meet photocatalysis, Nanoscale 6 (2014) 8473–8488. [2] Hefeng Cheng, Baibiao Huang, Ying Dai, Engineering BiOX (X = Cl, Br, I) nanostructures for highly efficient photocatalytic applications, Nanoscale 6 (2014) 2009–2026. [3] Liqun Ye, Su. Yurong, Xiaoli Jin, Can Zhang HaiquanXie, Recent advances in BiOX (X = Cl, Br and I) photocatalysts: synthesis, modification, facet effects and mechanisms, Environ Sci. Nano 1 (2014) 90–112.
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