## 2 Materials and Methods  
Bismuth nitrate pentahydrate (Bi(NO\({}_{3}\))\({}_{3}\):5H\({}_{2}\)O) crystal and nitric acid (HNO\({}_{3}\)) were purchased from Wako Pure Chemical Industries (Osaka, Japan). Sodium hydroxide (NaOH) granule was purchased from Kanto Chemical Co., Inc., (Tokyo, Japan) vanadium (III) acetylacetonate (C\({}_{10}\)H\({}_{14}\)O\({}_{5}\)V) crystal from Strem Chemicals Inc., (Newburyport, MA, USA) and methylene blue dye powder from Waldeck GmbH & Co. KG (Munster, Germany). Ultrapure water was used in all experiments. All chemicals were analytical grade and used as received, without further purification.  
Flowerlike BiVO\({}_{4}\) microspheres were synthesized by a simple template-free precipitation method at 60 \({}^{\circ}\)C for 24 h. Then, 4.2 g of Bi(NO\({}_{3}\))\({}_{3}\):5H\({}_{2}\)O and 0.27 g of C\({}_{10}\)H\({}_{14}\)O\({}_{5}\)V were dissolved in 100 mL of HNO\({}_{3}\) at a concentration of 4 mol L\({}^{-1}\). Ultrapure water was added until it reached a final volume of 500 mL. The solution was stirred until a clear light blue solution was formed. Then, the pH of the solution was adjusted to 12 by adding NaOH. The solution changes color from clear light blue to bluish precipitate and brownish precipitate, which indicates the change from acidic to neutral to alkaline state. The suspension was inserted into an oil bath at 60 \({}^{\circ}\)C for 24 h without stirring. The resulting yellow precipitate was retrieved by centrifugation, and washed several times with distilled water and absolute ethanol. The yellow precipitate was then dried at 60 \({}^{\circ}\)C for 24 h and was calcined at different temperatures (300 \({}^{\circ}\)C, 400 \({}^{\circ}\)C, 500 \({}^{\circ}\)C and 600 \({}^{\circ}\)C) for further study.  
The samples were analyzed with an X-ray diffractometer (XRD; RINT 2000, Rigaku Corp., Tokyo, Japan) operated at 30 kV and 40 mA with Cu K\(\alpha\) radiation (\(\lambda\) = 1.54178 A). Data were collected in the angular range of 20 = 15-80\({}^{\circ}\). Field emission scanning electron microscopy images were obtained from a Hitachi FE-SEM SU8000 (Tokyo, Japan). UV-visible diffusion reflectance spectra were measured at room temperature with a JASCO V-7200 UV-Vis-NIR Spectrophotometer  
Figure 1: Structure of methylene blue dye.  
(Jasco Products Company, Oklahoma City, OK, USA). The reflectance was then converted to absorbance by using the Kubelka-Munk method. The size of the particles was recorded by zeta potential and an Otsuka Electronics ELSZ-2000 particle analyzer (Otsuka Electronics Co., Ltd., Osaka. Japan) at room temperature, using ultrapure water as a solution. Further analysis was conducted with a Thermo Scientific Nicolet 4700 Fourier-transform infrared spectroscopy analyzer (Thermo Fisher Scientific, Waltham, MA, USA), a Horiba-Jovin Yvon T64000 micro Raman spectrometer (HORIBA Jobin Yvon IBH Ltd., Paris, France), and a JASCO FP8500 fluorescence spectrometer.  
Photocatalysis evaluation test was conducted as follows: 4 mL of methylene blue solution at a concentration of 0.3 mg/100 mL was placed in a 100 mL Pyrex vessel. Then, 96 mL of ultrapure water was added to the aqueous solution. After that, 0.3 g of BiVO\({}_{4}\) powder was added for each experiment. The experiments were conducted under the presence of visible light (\(\lambda>\) 400 nm). The solution was magnetically stirred to ensure uniformity. The samples were then filtered by using a syringe membrane filter (Millex; Millipore Corp., Burlington, MA, USA) to remove the photocatalyst particles. Samples were taken from the solution every 30 min and placed inside a UV-Vis spectrophotometer cell in order to measure the maximum absorption of wavelength for the dye and the rate of degradation. The percentage of degradation was calculated by the formula [1 \(-\) (C/C0)] \(\times\) 100%, where C\({}_{0}\) is the initial concentration of the dye solution and C is the concentration of the dye at each 30-min interval.