Visible-light Ag/AgBr/ferrihydrite catalyst with enhanced heterogeneous photo-Fenton reactivity via electron transfer from Ag/AgBr to ferrihydrite

Herein, we have reported an effective strategy to solve the rate-limiting step in a heterogeneous Fenton reaction, i.e., the generation of Fe(II) from Fe(III), which also inevitably consumes a large amount of H2O2. For the first time, a novel heterogeneous photo-Fenton catalyst - Ag/AgBr/ferrihydrite (Ag/AgBr/Fh) was successfully developed by combing AgBr with ferrihydrite (Fh) and then in-situ generating Ag nanoparticles on the surface of AgBr/Fh. This strategy can introduce photo-generated electrons from semiconductor-based plasmonic photocatalysts to heterogeneous Fenton catalysts and significantly increase the efficiency to degrade contaminants. The presence of both AgBr and Ag nanoparticles was proved by a combination of structural characterization studies (i.e., XRD, SEM, TEM, and XPS). Under visible light irradiation, the generated Fe(II) on the samples and the degradation rate constants of bisphenol A (BPA) followed the same order: Ag/AgBr/Fh > AgBr/Fh > Fh, which could be attributed to the accelerated reduction of Fe(III) to Fe(II) by the photo-generated electrons from AgBr and Ag nanoparticles, and also profit from the strong electron trapping ability of Ag nanoparticles in separating the electron-hole pairs of AgBr. The Ag/AgBr/Fh system could produce more hydroxyl radicals (•OH), and its catalytic performance was less affected by decreasing H2O2 concentration, which suggested a more efficient utilization of H2O2. The Ag/AgBr/Fh system exhibits relatively high photo-Fenton reactivity even at neutral pH. In addition, a much lower Fe3+ dissolution indicates that a large portion of the contribution is from the direct heterogeneous Fenton reaction in this system.