N-n+ homojunction of S-doped SnFe2O4 to inhibit surface-state-mediated electrons adverse trapping for enhanced photocatalysis performance

Abstract

How to make full use of solar energy and improve the efficiency of charges separation of photocatalysis has been a concern for scientists all along. To achieve this, this work designed an n-n+ homojunction of S-doped SnFe2O4 and applied it to near infrared driven photocatalytic degradation and sterilization. The experimental results demonstrated that S doping significantly enhanced the photocatalytic performance of SnFe2O4. The degradation rate of ciprofloxacin and the removal rate of Staphylococcus aureus (S. aureus) reached up to approximately 65 % and 100 % after 6 h irradiation, respectively. The S-doping could increase the content of shallow trap states in SnFe2O4, effectively inhibiting the recombination of photogenerated electrons and holes. Moreover, S-doping also enhances the n-type character and forms n-n+ homojunction. This n-n+ homojunction generates a built-in electric field within the sample, which causes band bending and promotes photogenerated charges transfer and separation. Consequently, more carries are available for the generation of reactive oxygen species. Free radical quenching experiments and ESR tests show that •O2− is the main free radical in the photocatalysis. In addition, DFT calculations confirmed the enhanced activation of O2 after S doping. This work provides a feasible way to effectively promote charges separation and transfer in metalloid-based photocatalysts.