The catalytic reduction mechanisms of metal-doped TiO2 for nitrate produced from non-thermal discharge plasma: The interfacial photogenerated electron transfer and reduction process

Nitrogen from the air under discharge plasma may yield abundant nitrate causing secondary pollution. In this study, metal-doped TiO2 not only prolonged the lifetime of the generated electrons but also provided efficient active sites for both nitrate reduction and organic matters degradation. Fe/TiO2 was more efficient for phenol removal but did not support NO3− reduction, because the Fe3+/Fe2+ impurity band was beneficial for more rapid •OH generation. Ag/TiO2 was most active for NO3− reduction but least active for phenol removal, because photo-electrons were utilized to generate abundant H2 rather than •OH. The bimetal comprising Ag and Cu facilitated the decomposition of phenol into HCOOH, which could be oxidized to CO2−• on the holes of Ag-Cu/TiO2, while NO3− could be reduced by CO2−•. The combination of plasma with Ag-Cu/TiO2 efficiently oxidized phenol and accelerated NO3− reduction, which can be demonstrated scientific significance for non-thermal discharge plasma technology in wastewater remediation.