In this study, BiVO4 photocatalysts were synthesized by hydrothermal method using Bi(NO3)3 5H2O and NH4VO3 as raw materials followed by calcination at different temperatures in the range from 350 °C to 600 °C. The as-synthesized BiVO4 samples were characterized by a number of physicochemical techniques including X-ray diffraction (XRD), Raman analysis, Scanning Electron Microscopy (SEM), and UV-Visible (UV-Vis) light diffuse reflectance spectrophotometry. The effect of temperatures calcination on structure, surface morphology, visible-light photocatalytic activity and light absorption performance of BiVO4 was discussed in details

Do, Sy Trung

Hoang, Ho Huy

Lam, Tri Duc

Linh, Nong Xuan

Nguyen, Duy Trinh

Nguyen, Hai Thanh

Nguyen, Huu Vinh

Vo, Dai-Viet N.

Vu, Hien Thi

UMP Institutional Repository

IOP Conference Series: Materials Science and EngineeringPAPER • OPEN ACCESSA Facile Synthesis and Properties of Bismuth Vanadate (BiVO4)Photocatalyst by Hydrothermal MethodTo cite this article: Nguyen Duy Trinh et al 2019 IOP Conf. Ser.: Mater. Sci. Eng. 542 012059 View the article online for updates and enhancements.This content was downloaded from IP address 103.53.34.15 on 15/10/2019 at 03:11Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributionof this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Published under licence by IOP Publishing LtdICMEMSCE 2018IOP Conf. Series: Materials Science and Engineering 542 (2019) 012059IOP Publishingdoi:10.1088/1757-899X/542/1/0120591A Facile Synthesis and Properties of Bismuth Vanadate (BiVO4) Photocatalyst by Hydrothermal Method  Nguyen Duy Trinh1,2*, Ho Huy Hoang1,3, Nong Xuan Linh1,3, Nguyen Huu Vinh1, Hien Thi Vu4, Hai Thanh Nguyen5, Dai-Viet N. Vo6, Sy Trung Do7, Lam Tri Duc1  1NTT  Hi-Tech Institute, Nguyen Tat Thanh University, Ho Chi Minh City, Vietnam 2Department of Chemical Engineering, Pukyong National University, Busan, South Korea  3Faculty of Chemical Engineering and Food Technology, Nguyen Tat Thanh University, Ho Chi Minh City, Vietnam 4Faculty of Hydro-Meteology, HCMC University of Natural Resources and Environment, Ho Chi Minh City, Viet Nam 5Son La Hydro Power Company, Son La Province, Vietnam 6Faculty of Chemical and Natural Resources Engineering, Universiti Malaysia Pahang, Malaysia 7Institute of Chemistry, Vietnam Academy of Science and Technology, Ha Noi, Vietnam *Corresponding author: ndtrinh@ntt.edu.vn; labams2013@gmail.com  Abstract. In this study, BiVO4 photocatalysts were synthesized by hydrothermal method using Bi(NO3)3∙5H2O and NH4VO3 as raw materials followed by calcination at different temperatures in the range from 350 oC to 600 oC. The as-synthesized BiVO4 samples were characterized by a number of physicochemical techniques including X-ray diffraction (XRD), Raman analysis, Scanning Electron Microscopy (SEM), and UV-Visible (UV-Vis) light diffuse reflectance spectrophotometry. The effect of temperatures calcination on structure, surface morphology, visible-light photocatalytic activity and light absorption performance of BiVO4 was discussed in details.  1.  Introduction  In chemistry, the traditional photocatalysts comprise mainly metal oxides such as TiO2, ZnO, SnO2 and CeO2. These photocatalysts are semiconductors with relatively low band-gap and are therefore suitable for absorbing natural or artificial light and exhibiting photochemical activity [1-10]. Optical catalysts play an important role in many areas such as environmental improvement, photovoltaic applications, bio-applications, clean energy production, sensors, nanoscale electronic components and solar battery. One of such photocatalysts is the BiVO4, which has been attracting a lot of attention due to its remarkable features, including low band gap energy, good dispersion, non-toxicity and high photochemical activity under visible light irradiation. Several synthesis methods have been utilized in order to prepare BiVO4 powder of high quality with predominantly solid-state including aqueous-based and hydrothermal methods [11-15].  In this study, a simple solution-based preparation method under acidic conditions has been selected and adopted, involving the calcination of obtained BiVO4 precipitates at different temperatures. Subsequently, an in-depth analysis of important physical parameters of as-obtained products allows for a coherent correlation with the different photocatalytic O2 evolution. The insights gained from this analysis contribute to the better understanding of the visible-light water oxidation mechanisms and more efficient optimization of photocatalytic materials. The objective of this study was to synthesize ICMEMSCE 2018IOP Conf. Series: Materials Science and Engineering 542 (2019) 012059IOP Publishingdoi:10.1088/1757-899X/542/1/0120592 BiVO4 materials by hydrothermal method. Following that, the as-synthesized samples were calcined at different temperatures ranging from 350 oC to 600 oC. Structural properties of material samples calcined at different calcination temperatures from 350 oC to 600 oC were characterized using analytical methods including XRD, SEM and UV-Vis-DRS. 2. Materials and Method  2.1. Materials Chemicals used in this study include Ammonium metavanadate (NH4VO3, ≥ 98%, Sigma-Aldrich), Bismuth (III) nitrate pentahydrate (Bi(NO3)3.5H2O, ≥ 98.0%, Sigma-Aldrich), Nitric acid (HNO3, 65-68%), and ammonia solution (NH4OH 25-28%, Xilong). Chemicals for analysis: Rhodamine B (RhB, Jihuada), Distilled water (from Lasany's two-storey water machine). 2.2. Synthesis of BiVO4 photocatalyst by hydrothermal method The typical preparation process comprises six-step as follows: (1) 4 mmol of Bi(NO3)3.5H2O was dissolved in 20 mL of 4M HNO3 solution; (2) another solution was prepared by dissolving a stoichiometric of NH4VO3 in 40 mL of hot water; (3) The two solution was mixed together and stirred for about 1 hour to achieve a stable and homogeneous state; (4) The pH of the mixture is adjusted with NH4OH or HNO3 solution; (5) The mixture was sealed in an autoclave, and subjected to heat at 160 oC for 24 hour under pressure. At the end of the process, the precipitate was filtered, washed with distilled water and dried overnight at 110 °C; (6) The obtained solid was calcined in air at different temperature (350 oC, 400 oC, 450 oC, 500 oC and 600 oC) for 2 hour. To investigate the effects of calcination temperature on the formation of crystalline and phase structure of BiVO4, BiVO4 samples synthesized by hydrothermal method were calcined at different temperature (350 – 600 oC) to analyze the structural crystals of BiVO4.  Scheme 1. Process of synthesis of materials by hydrothermal method.  In this study, BiVO4 was synthesized by hydrothermal followed by calcination process at different temperatures (from 350 °C to 600 °C) as shown in Table 1.  Table 1: Statistical samples and aggregate conditions Calcinated Sample Heat  (oC) Time (h) Sample characteristics Efficiency  (g) BVO-350 oC 350 oC 2 Yellow powder 83% BVO-400 oC 400 oC 2 Yellow powder 90% BVO-450 oC 450 oC 2 Yellow powder 81% BVO-500 oC 500 oC 2 Yellow powder 83% BVO-600 oC 600 oC 2 Yellow powder 78% 2.3. Characterization Samples were analyzed on Jeol JSM 7401F Scanning Electron Microscope instrument, at the Institute of Chemistry, Vietnamese Academy of Science and Technology. X-ray diffraction (XRD) powder analysis was carried out with a Rigaku D/max-RB12KW X-ray diffractometer using Cu Kα radiation (λ = 1.5418 Å) in the 2θ range of 4–80o at room temperature. The XRD was developed by William L.Bragg in 1913, in which the Bragg equation (1) is considered as a condition for diffraction:   ICMEMSCE 2018IOP Conf. Series: Materials Science and Engineering 542 (2019) 012059IOP Publishingdoi:10.1088/1757-899X/542/1/0120593        , where λ is the X-ray wavelength (1.5418Å). The diffraction angle θ corresponds to the diffraction peaks on the diffraction pattern defined θ = arcsin (nλ / 2dhkl), n, or diffraction patterns, takes the values of 1, 2 or 3 . 3. Results and Discussion  The crystalline structure of BiVO4 was confirmed by XRD patterns as shown in the Figure 1. The results showed that all samples had strong diffraction peaks at 28o and 30.6o, and split diffraction peaks at 18.5o, 34o, and 46o. This result corresponds to the standard of the BiVO4 crystalline monoclinic scheelite crystal (m-BiVO4, JCPDS card no. 14-00688) and is consistent with previous studies [15]. In addition, all samples show the characteristic peak splitting diffractions at 2θ = 18.5, 34 and 46 o [16]. Even though monoclinic phase was observed at every calcination temperature, splitting of the these characteristic peaks becomes more pronounced as the calcination temperature increases, which likely signifies the increasing crystallinity degree of the (s-m) phase in BiVO4 samples [16,17].  Figure 1. a) XRD diagram of BiVO4 samples, b) XRD is at 2º from 16o to 20o, c) The XRD detail diagram at 2θ from 33o to 34.5o, d) The XRD detail diagram 2θ from 44o to 47o. Crystal shape, particle size and particle distribution of the material were observed through SEM images which are given in the Figure 2. Visually, materials and structures have flattened shape which is 1 μm in size and is 1 μm in flange size. At calcination temperatures of 450 oC, , the form of the materials is spherical and rod-shaped.   Figure 2. SEM images of the samples BiVO4  in: BVO-450oC. The vibrational properties of the BiVO4 crystals were studied through Raman scattering spectrum at room temperature as shown in the Figure 3. The results show that the samples exhibited specific vibration levels for the m-s crystalline BiVO4 and the thermal increases through the hydrothermal method, the intensity of these oscillations decreases, affecting the crystalline structure of the material.  In the Figure 3, Raman spectra of BiVO4 powders were excited by a red (648 nm) laser and corresponding spectra. Raman spectroscopy can provide structural information and is also a sensitive method for the investigation of the crystallization, local structure, and electronic properties of materials. Raman bands at around 210, 324, 366, 640, 710, and 826 cm–1 were observed for all samples. These are the typical vibrational bands of BiVO4 [15,18]. The structural information of ICMEMSCE 2018IOP Conf. Series: Materials Science and Engineering 542 (2019) 012059IOP Publishingdoi:10.1088/1757-899X/542/1/0120594 BiVO4 is given by the band centered at 210 cm-1 . The asymmetric and symmetric formations of VO4 tetrahedron are given by the bands centered at 324 and 366 cm–1, respectively. The Raman band at 640 cm–1 can be assigned to the asymmetric stretching vibration of the shorter V-O bond. The stretching modes of two vibrational modes of V–O bonds are determined by the bands centered at 710 and 826 cm–1. These two bands provide valuable information about the structural variations among the powder samples calcined at different temperatures. It has been observed a positive shift in the vibrational mode of V-O, which varies from 825.30 to 827.52 cm-1. The Raman stretching frequencies and the respective metal-oxygen bond lengths share an inverse relationship which describes that a higher stretching frequency will correspond to a lower metal-oxygen bond length. By utilizing the expression for bond length [18,19]: V( cm–1 )= 21349 exp(-1.9176 R(oA)) (2), where V is the stretching Raman frequency for V–O, it can be seen that the bond length varies from 1.6964 oA to 1.6950 oA for 350 oC and 600 oC sample, respectively [20].  Figure 3. Location of the sample Raman scattering spectrum The photocatalytic performance of samples was strongly associated with the optical absorption property. Therefore, UV-vis diffuse reflectance spectra (DRS) was utilized to further investigate the absorption band the band gap energy values of the crystals. It can be seen from Figure 4 that all of the five samples showed absorption bands in the visible light region, and the absorption edges of the samples exhibit a slight red shift when the Bi is present. The optical band gap energies of the five samples were estimated from the absorption spectra by using the following relationship: αhν = A(hν − Eg)n/2 where α, hν, A and Eg are the absorption coefficient, the photon energy, constant, and the optical band gap energy, respectively. The value of n depends on whether the transition is direct (n = 1) or indirect (n = 4), and it was determined to be unity on the absorption spectra. The band gap energy was determined by extrapolating the linear part of (αhν)2 vs. hν plot of the energy axis as showed in Figure 4. The 2.42 eV value for pure m-BiVO4 is in agreement with the literature [21].  Figure 4. UV-vis diffuse reflectance spectra (DRS) of BiVO4 and Plot of the transformed Kubelka–Munk functions vs. the energy of light. 4.  Conclusion  In this study, BiVO4 photocatalyst was synthesized by a simple hydrothermal followed by calcination process at different temperatures (350 °C, 400 oC, 450 oC, 500 oC, 600 oC). The structure of materials were evaluated by chemical and physical methods such as XRD and SEM modern. The results indicate that the calcining at different temperature affects the formation of the crystal form of BiVO4. UV-vis diffuse reflectance spectra (DRS) was utilized to further investigate the absorption band the band gap energy values of the BiVO4 crystals ICMEMSCE 2018IOP Conf. Series: Materials Science and Engineering 542 (2019) 012059IOP Publishingdoi:10.1088/1757-899X/542/1/0120595 Acknowledgments: This research is funded by Nguyen Tat Thanh University, Ho Chi Minh City, Vietnam References [1]  Zhang M, Zhen Y, Sun F and Xu C 2016 Materials Science and Engineering: B 209 37–44 [2]  Yang S G, Pakhomov A B, Hung S T and Wong C Y 2002 IEEE Transactions on Magnetics 38 2877–9 [3]  Bach L G, Cao X T, Ho V T T, Islam M R and Lim K T 2015 Molecular Crystals and Liquid Crystals 618 120–8 [4]  Cao X T, Bach L G, Islam M R and Lim K T 2015 Molecular Crystals and Liquid Crystals 618 111–9 [5]  Bach L G, Nguyen N G and Ho V T T 2016 International Journal of Photoenergy 2016 1–7 [6]  Bach L G, Quynh B T P and Lim K T 2016 Molecular Crystals and Liquid Crystals 635 12–7 [7]  Bach L G, Nguyen T D, Thuong N T, Van H T T and Lim K T 2019 Journal of Nanoscience and Nanotechnology 19 1192–5 [8]  Bach L G, Cao X T, Quynh B T P, Ho V T T and Lim K T 2017 Molecular Crystals and Liquid Crystals 644 183–9 [9]  Chu M, Nguyen L, Mai X, Thuan D, Bach L, Nguyen D and Nguyen D 2018 Metals 8 851 [10]  Nguyen V, Nguyen T, Bach L, Hoang T, Bui Q, Tran L, Nguyen C, Vo D-V and Do S 2018 Catalysts 8 487 [11]  Nguyen H V, Thuan T V, Do S T, Nguyen D T, Vo D V N and Bach L G 2018 Applied Mechanics and Materials 876 52–6 [12]  Nguyen D T and Hong S-S 2017 Journal of Nanoscience and Nanotechnology 17 2690–4 [13]  Huynh T T, Van Nguyen A, Pham H Q, Vinh N H, Bach L G and Thanh Ho V T 2018 Journal of Nanoscience and Nanotechnology 18 6928–33 [14]  Luo J, Fu P, Qu Y, Lin Z and Zeng W 2018 Physica E: Low-dimensional Systems and Nanostructures 103 71–5 [15]  Zhang X, Huang Y, Ma F, Zhang Z and Wei X 2018 Journal of Physics and Chemistry of Solids 121 85–92 [16]  Yu J and Kudo A 2006 Advanced Functional Materials 16 2163–9 [17]  Walsh A, Yan Y, Huda M N, Al-Jassim M M and Wei S-H 2009 Chemistry of Materials 21 547–51 [18]  Thalluri S M, Martinez Suarez C, Hernández S, Bensaid S, Saracco G and Russo N 2014 Chemical Engineering Journal 245 124–32 [19]  Saison T, Chemin N, Chanéac C, Durupthy O, Ruaux V, Mariey L, Maugé F, Beaunier P and Jolivet J-P 2011 The Journal of Physical Chemistry C 115 5657–66 [20]  Dong L, Zhang X, Dong X, Zhang X, Ma C, Ma H, Xue M and Shi F 2013 Journal of Colloid and Interface Science 393 126–9 [21]  Thalluri S R M, Martinez-Suarez C, Virga A, Russo N and Saracco G 2013 International Journal of Chemical Engineering and Applications 305–9 [22]  Kiwi J and Nadtochenko V 2005 Langmuir 21 4631–41  

A facile synthesis and properties of bismuth vanadate (BiVO4) photocatalyst by hydrothermal method

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A facile synthesis and properties of bismuth vanadate (BiVO4) photocatalyst by hydrothermal method

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