Synthesis of BiVO4 and Au/BiVO4 nanocomposites to achieve the visible-light-driven photocatalytic reduction of Cr+6 in pure and tap water Optimization of the reaction conditions
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AbstractHeterogeneous photocatalysis is used to mineralize organic pollutants and inactivate pathogens in water, whereas the removal of heavy metals is less explored. In this work, BiVO4 was synthesized through the hydrothermal route to achieve the photocatalytic reduction of Cr+6 in water. Monoclinic BiVO4 displayed high crystallinity and a fern-leaf-like form; specific surface area and bandgap energy were determined as 5.68 m2 g-1 and 2.49 eV, respectively. Surface plasmon resonance was identified in the Au/BiVO4 nanocomposites, while the specific surface was reduced to 3.16 m2 g-1 after the deposition of gold nanoparticles. Different sacrificial agents were tested to boost the photocatalytic performance of BiVO4, including methanol, ethanol, formic acid, dimethyl sulfoxide, and KI, finding the best results with 0.01 M formic acid. The optimal photocatalyst dosage was 1.5 g L-1, achieving the complete photoreduction of Cr+6 after 90 min of visible light irradiation. No improvement in the photocatalytic activity was observed when metallic gold nanoparticles were deposited on BiVO4 nanocomposites, more likely due to the reduced specific surface area. Chromium was precipitated on the BiVO4 surface as Cr+3, Cr+4 and Cr+5 oxidized species. The catalyst displayed high stability across three consecutive reaction cycles, and good performance was observed in tap water, with the complete photoreduction of Cr+6 upon 2 h of visible light irradiation. Purging dissolved O2 from the water was an essential factor to achieve the highest photocatalytic performance.
