Singlet oxygen triggered by robust bimetallic MoFe/TiO2 nanospheres of highly efficacy in solar-light-driven peroxymonosulfate activation for organic pollutants removal

Sulfate-radical (SO4 center dot-) based Advanced Oxidation Process (SR-AOP), which is mainly generated from peroxymonosulfate (PMS) activation, is an excellent route for water treatment. Bimetallic nanoparticles have been widely applied in electronic, chemical, biological, and mechanical fields, etc.; however, few researchers have attempted to adopt bimetallic nanoparticles in environmental remediation. Further, in recent years, element molybdenum (Mo) has addressed much more environmental field attention than ever. Although singlet oxygen (O-1(2)) generated commonly in SR-AOPs, its generation mechanism remains controversial. Hence, in this work, bimetallic MoFe/TiO2 nanospheres were rationally constructed via a facile two-step methodology. Undoubtedly, it exhibited superior performance for the degradation of organic pollutants (e.g., rhodamine, phenol, 4-chlorophenol and sulfadiazine) irradiated by simulated solar light. Both photo-generated electrons and transition metallic redox couples (i.e., Mo6+/Mo4+, Fe3+/Fe2+ and Mo4+/Fe3+) play vital roles in the PMS activation. Distinct from conventional SR-AOPs, sulfate radicals (SO4 center dot-), hydroxyl radicals ((OH)-O-center dot) and peroxymonosulfate radicals (SO5 center dot-) indeed participate in the transformation and generation of singlet oxygen (O-1(2)). With the combination of DFT calculation, the Mo sites on the bimetallic MoFe (110) facet are more favorable to adsorb PMS molecules, then followed by the dissociation of PMS progressing on the Mo sites. Electrons transferring from the Mo atoms to the Fe atoms facilitated the adsorption of the negatively charged HSO5- anions, resulting in enhanced PMS activation efficiency. Considering its novelty and generation mechanism, this work highlights the mechanism of O-1(2) generation from PMS reduction and oxidation simultaneously and furnishes theoretical support for further relevant studies.

Automated summary

This study constructed bimetallic MoFe/TiO2 nanospheres, which showed superior performance in degrading organic pollutants under simulated solar light. Photo-generated electrons and transition metallic redox couples played vital roles in the PMS activation process. Different from traditional SR-AOPs, sulfate radicals, hydroxyl radicals, and peroxymonosulfate radicals indeed participated in the generation of singlet oxygen.