Bismuth Vanadate -Based Visible-Light Driven Photocatalysts with Hierarchical Nanostructures Synthesized through Deep Eutectic Solvents for Organic Pollutant Removal

• Main Author: Dhayanantha Prabu Jaihindh
• Other Authors: Yen-Pei Fu
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/e7c6dh

博士 === 國立東華大學 === 材料科學與工程學系 === 107 === Photocatalysis is a series of advanced light-induced redox reaction processes resulting in the degradation and mineralization of organic pollutants in the presence of oxygen and water. Due to their capability to destroy contaminants under mild conditions, photocatalytic processes have attracted considerable attention in the field of waste-water treatment. However, photocatalytic reactions using the traditional pure TiO2 photocatalyst suffer from low energy efficiencies under solar irradiation. This low efficiency in the utilization of solar energy lies in its incapability in absorbing visible lights and also the high recombination rate of photo-excited species in photocatalysts. In addition, difficulties in the separation of fluids from micro- or nano-scale catalysts in large scale systems substantially impact cost efficiency in practice. In this thesis, strategies are explored which address these issues in order to improve the feasibility of solar photocatalysis. The preparation photocatalytic transition metal-oxide semiconductor materials are investigated, namely bismuth-based heterogeneous photocatalysts using Deep eutectic solvents (DESs) as green solvents. This research is focused on the design of visible-light-active metal-oxide photocatalysts to increase the absorption of visible light and to decrease the rates of electron-hole recombination, resulting in a high photocatalytic efficiency in regards to the degradation of organic pollutants. In First study deals synthesis of BiOCl/BiVO4 n- p heterojunction photocatalysts was synthesized using DESs reline (Choline chloride: Urea, 1:2) via simple one-pot sol-gel method at room temperature. BiOCl/BiVO4 sheet like structure was characterized and experimentally investigated for the degradation of Methylene blue, rhodamine B under visible light irradiation and also the mechanism was investigated using scavenger experiment. To improve the photocatalytic activity and electron-hole pair recombination time, the silver nanowires combined with BiOCl/BiVO4. Here, we report a one dimensional (1D) AgNWs combined with BiOCl/BiVO4 photocatalysts. The BiOCl/BiVO4@5% Ag NWs photocatalysts exhibited the highest photoactivity, and the degradation efficiency of MB and RhB was 97% and 96% as compared to bare BiVO4 and BiOCl/BiVO4, respectively. The appearance of elemental AgNWs during the photocatalytic reaction would be in favor to enhanced visible light absorption, the facilitated photoinduced electrons transfer, and the enhanced separation of photoinduced electron−hole pairs contributed to the improvement of photocatalytic activities. Also, BiOCl/BiVO4@AgNWs photocatalysts are attributed to the formation of p-n heterojunctions between BiOCl and BiVO4, leading to an effective separation of photo-generated electron hole pair. The significantly enhanced photocatalytic activity should be ascribed to the fabrication of a BiOCl/BiVO4 heterojunction, which can result in an efficient interfacial charge transfer, and it can be proved by Photoluminescence, Linear Sweep Voltammetry and Electrochemical Impedance Spectroscopy. The second study proposed, the preparation of hierarchically nanostructured shuriken like bismuth vanadate (BiVO4) as a bifunctional catalyst for photocatalytic degradation and electrochemical detection of highly toxic hexavalent chromium (Cr(VI)) using the green Deep Eutectic Solvent reline by Solvothermal method, which allows morphology control in one of the less energy-intensive routes. The reline solvents leads the role of a latent supramolecular catalysts where the enhance in reaction rate from solvent driven pre-organization of the reactant is most remarkable. The SEM results showed a good dispersion of BiVO4 catalyst and the HR-TEM revealed an average particle size of ca. 5–10 nm. As a result, the BiVO4 exhibited good photocatalytic activity under UV-light about 95% reduction of Cr(VI) to Cr(III) was observed in 160 min. The recyclability of BiVO4 catalyst exhibited an appreciable reusability and stability of the catalyst towards the photocatalytic reduction of Cr(VI). Also, the BiVO4-modified screen printed carbon electrode (BiVO4/SPCE) displayed an excellent electrochemical performance towards the electrochemical detection of Cr(VI). Besides, the BiVO4/SPCE demonstrated tremendous electrocatalytic activity, lower linear range (0.01–264.5 µM), detection limit (0.0035 µM) and good storage stability towards the detection of Cr(VI). Importantly, the BiVO4 modified electrode was also found to be a good recovery in water samples for practical applications. The shape dependent nanostructured BiVO4 catalyst could also be used an effective electrode material for energy storage and hybrid capacitor in future. Keywords: Deep eutectic solvents, Bismuth based photocatalysts, p-n heterojunction, organic pollutant removal, Cr(VI) removal, electrochemical sensing