Chung-Hsin Wu
National Kaohsiung University of Science and Technology, Taiwan
Title: Hydrothermal synthesis of novel BiVO4/Ag3VO4 composite with high visible-light-induced photocatalytic activity
Biography
Biography: Chung-Hsin Wu
Abstract
A hydrothermal process is utilized to synthesize silver orthovanadate (Ag3VO4, AVO), bismuth orthovanadate (BiVO4, BVO) and BiVO4/Ag3VO4 composite (BVO/AVO). The precursors of AVO were silver nitrate (AgNO3) and sodium orthovanadate (Na3VO4), and those of BVO were bismuth nitrate (Bi(NO3)3) and ammonium metavanadate (NH4VO3). The Bi/Ag molar ratio in the BVO/AVO preparation was 1/3. The effects of heating time (6, 12 and 24h) and temperature (393, 433 and 473K) on the synthesis of AVO were elucidated. C.I. Reactive Red 2 (RR2) was used as the parent compound in evaluating the photocatalytic activity of all prepared photocatalysts. The optimal experimental conditions for synthesizing AVO by the hydrothermal method included initial heating at 393 K for 6 h. A 400 W Xe lamp was used as the light source. A quartz appliance that was filled with 2 M NaNO2 solution was placed on the top of the photo-reactor to filter out the ultraviolent (UV) and to provide visible-light (Vis). The rates of RR2 photodegradation by all photocatalysts under UV and Vis irradiation followed a pseudo-first-order kinetic model. The RR2 photodegradation rate constants in the UV/AVO, Vis/AVO, UV/BVO, Vis/BVO, UV/BVO/AVO, Vis/BVO/AVO and solar/BVO/AVO systems were 1.43, 0.03, 0.55, 0.16, 5.06, 2.39 and 2.48 hr-1, respectively. BVO/AVO exhibited the highest photocatalytic activity of all the prepared photocatalysts. This investigation suggested that the coupling of BVO greatly inhibited the recombination of photo-generated electron-hole pairs in AVO, revealing that the separation of photo-generated electron-hole pairs in BVO/AVO was more efficient than that in AVO. Adding isopropanol to the RR2 solution slightly reduced the rate of RR2 photodegradation but adding Cr(VI) and EDTA-2Na markedly slowed RR2 photodegradation. The experimental results suggested that the photogenerated holes and superoxide radicals were the main oxidative species for RR2 photodegradation in AVO and BVO/AVO systems.