Tianyuan Xu,Runliang Zhu,Gangqiang Zhu,Jianxi Zhu,Xiaoliang Liang,Yanping Zhu,Hongping He
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.
The Fe-based materials were considered very attractive for the treatment of wastewater using peroxymonosulfate (PMS) activation. However, the difficulties to restore the active Fe 2+ oxidation state restrict them to attained sustainable efficiency. In this work, a new strategy was introduced to accelerate the regeneration of Fe 2+ state through constructing an electron-rich MoS 4 2− centre in the inter-layers of FeMgAl layered double hydroxide (MoS 4 -LDH) catalyst. The dual centre MoS 4 -LDH catalyst was found more efficient as clear from the observed atrazine (ATZ) degradation rate of 0.117 min −1 , 100 times higher than the Fe 3+ /PMS or 25–50 times higher than the Fe based single centre NO 3 -LDH/PMS, CO 3 -LDH/PMS or S 2 O 4 -LDH/PMS systems, respectively. This boosted efficiency was related to the electron-rich MoS 4 2− centre which allows the constant electron transfer to reduce the electron-deficient Fe 3+ center at MoS 4 -LDH surface and thereby accelerating the Fe 2+ /Fe 3+ redox cycle during reaction. Furthermore, the MoS 4 -LDH/PMS system exhibited a broader effective pH (3.0–9.0), good stability and minimum influence of background electrolyte or organic matter. The degradation pathway of ATZ based on free radical (SO 4 – and OH), involving the redox cycles of Fe 3+ /Fe 2+ and Mo 6+ /Mo 4+ was proposed for the activation of PMS . This work highlighted the essential role of MoS 4 2− moiety, to accelerate the Fe 3+ reduction at the surface of the LDH catalyst through the continuous feeding of electrons.
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