978-1-5386-7482-6/18/$31.00©2018 IEEE. Effect of pH Variation on Structural, Optical and Shape Morphology of BiVO 4 Photocatalysts Manifa Noor, 1,* M. A. Al Mamun, 1 M A Matin, 1 Md. Fakhrul Islam, 1 Saima Haque, 1 Farabi Rahman, 1 M. N. Hossain 1 , M A Hakim 1 1 Department of Glass and Ceramic Engineering, Bangladesh University of Engineering and Technology Dhaka 1000, Bangladesh * rakin.manifa@gmail.com Abstract—Visible light driven photocatalysts have gathered enormous interest in recent years because of their capability to harvest energy directly from sunlight by water splitting and also to purify water. Bismuth Vanadate (BVO) is one of the most potential photocatalysts for water pollutant degradation and hydrogen production by oxidation of water. In our study, highly crystalline Bismuth Vanadate nanoparticles have been synthesized by a straightforward hydrothermal route where pH is varied to observe the change in morphology of the particles. Thermal analysis confirmed the tetragonal to monoclinic phase transformation temperature at 350 ºC. A hierarchical development of monoclinic – tetragonal heterostructure of Bismuth Vanadate is further confirmed by Rietveld refinement of XRD patterns and the obtained particle size is 27nm. Band gap energy has been tailored through control of pH to explore the optical band gap for suitable photocatalytic properties. It is found that a heterostructure composed of rod and spherical shaped nanoparticles for a pH value 6.5, closer to neutral, demonstrating better optical properties for efficient photocatalytic activity with a band gap energy of 1.8 eV. Index Terms—Bismuth Vanadate, hydrothermal, photocatalyst, Rietveld refinement I. INTRODUCTION Energy requirement and reduction of environment pollution are the most concerning issues of the current world. The rapid growth of population all over the world demands more energy as well as pure water. Fossil fuels, the main source of energy, are destructive to the environment because of the Green House effect. Water pollution is also one of the most alarming subjects as the water level is rising due to Green House effect but the quantity of pure water is decreasing. So it is necessary to develop green technologies for energy production as well as the degradation of water pollutants. Capturing solar energy for energy production by H2 generation from water splitting and degrading water pollutants by photochemical reaction can play a vital role to mitigate the energy and pure water crisis. When a photocatalyst absorbs sunlight, the photo excited electron goes from valence band to conduction band which in turns generates a pair of electron-hole and this electron-hole pair can oxidize or reduce other chemical compounds adhered to the photocatalysts’ surface. This redox reaction can be utilized to produce H2 energy by oxidation of water and to disintegrate water pollutants [1-6]. For this reason, the innovation of a photocatalyst with practical application has become a crying need to the researchers all over the world. Fujishima and Honda [17] discovered the water splitting phenomenon for the first time and since then the quest for developing such photocatalyst has remained still unsatisfied to the researchers. Several binary and ternary metal oxides have been developed such as TiO2, Ag3VO4, InNbO4, InVO4, and BiVO4. Among these oxides, BiVO4 is considered as the most propitious candidate due to its non-toxicity and variable synthesis routes like sol-gel, co-precipitation, solid-state, hydrothermal, chemical bath deposition etc [8-12]. Park et al. reported that monoclinic scheelite phase ofBismuth Vanadate (m-BiVO4) is a very promising photocatalyst with the ability to absorb a high amount of visible light[13]. But in most synthetic process, the synthesized nanoparticles have large crystal sizes and low surface areas [14-15]. Therefore, a search for developing m-BiVO4 with large surface area and high photocatalytic activity is still going on. Fig 1: (a) Crystal structure of monoclinic BiVO4 showing its 2 fold symmetry (b) Phase transformation with temperature The natural source of BiVO4 is pucherite which has orthorhombic crystal structure [16]. It is possible to synthesize scheelite and zircon type crystal structure of BiVO4 in laboratory. Scheelite type structure can be both monoclinic and tetragonal while Zircon type structure contains tetragonal 10th International Conference on Electrical and Computer Engineering 20-22 December, 2018, Dhaka, Bangladesh 81