Mechanisms for the enhanced photo-Fenton activity of ferrihydrite modified with BiVO4 at neutral pH
Heterogeneous photo-Fenton catalysts generally show very weak photo-Fenton activity at near-neutral pH because of the relatively low rate of Fe 2+ regeneration. The aim of this work is to develop novel heterogeneous photo-Fenton catalysts, which can accelerate the regeneration of Fe 2+ and thus have superior photo-Fenton activity at near-neutral pH. In this study, ferrihydrite (Fh) was modified with BiVO 4 to synthesize BiVO 4 /Fh composites, and we expected that the photogenerated electrons from BiVO 4 would accelerate the regeneration of Fe 2+ on Fh. Mechanistic investigation of H 2 O 2 consumption showed that the introduction of BiVO 4 promoted the decomposition of H 2 O 2 into reactive oxygen species (ROS). In addition, the presence of BiVO 4 deterred O 2 − production and accelerated the formation of OH, according to the results of ROS formation, as shown with EPR spectroscopy and fluorescent probes tools. Furthermore, the Fe 2+ concentration on the surface of BiVO 4 /Fh was higher than that on Fh based on the results of XPS characterization and quantitative measurement with a 1,10-phenanthroline spectrophotometric method. These results demonstrated that the introduction of BiVO 4 can accelerate the reduction of Fe 3+ to Fe 2+ by transferring photogenerated electrons from BiVO 4 to Fe 3+ on the surface of Fh. Meanwhile, a higher decolorization efficiency of acid red 18 by BiVO 4 /Fh than by Fh and pure BiVO 4 verified that the introduction of BiVO 4 can significantly enhance the photo-Fenton catalytic activity of Fh even at near-neutral pH. Overall, our work has important implications for understanding the photo-Fenton mechanisms on semiconductor modified heterogeneous photo-Fenton catalysts and confirms that the introduction of a semiconductor can enhance the photo-Fenton catalytic activity of heterogeneous photo-Fenton catalysts in acidic and neutral pH.
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