In situ production of hydrogen peroxide from Fe, Mo co-doped N@TiO2 for organic pollutant degradation

Abstract

Degradation of organic pollutants by in-situ electrochemically synthetic hydrogen peroxide (H₂O₂) in electro-Fenton (EF) system is important for the treatment of wastewater. In this work, a Fe, Mo co-doped N@TiO₂ electrocatalyst was constructed for H₂O₂ generation and applied to the degradation of organic dyes. The FeMoN@TiO₂ catalyst in 0.1 M KOH exhibits excellent 2e^- Oxygen reduction reaction (ORR) activity and stability, with a yield of up to 1409 mmol gcat^-1h⁻¹ and Faraday efficiency (FE) of 83.4 % at −0.7 V (relative to SCE) for more than 10 h. The in situ generated H₂O₂ delivers benign organic dyes degradation ability with high methylene blue (MB) removal rate of 98.2 % after 2 h in 0.1 M KOH without adding Fe²⁺. After adding Fe²⁺, the EF process occurs to degrade dyes more efficiently, with Congo red and phenol removal rates of more than 99.0 % and Ciprofloxacin (CIP) removal rate of more than 96.0 % in 0.1 M Na₂SO₄ solution. It is found that Mo doping increases the active sites of the catalyst, while the dopant of Fe can enhance can improve the electron transfer rate between the catalyst and reactants. Additionally, the synergistic Fe and Mo modulate the electronic structure of Ti, increasing the concentrations of Ti³⁺ and chemiadsorbed O. This enhances the electronic conductivity and the reactivity of the catalyst, leading to improved ability for H₂O₂ generation and organic pollutants degradation. Radical quenching experiments show that the in-situ generated H₂O₂ reacts with added Fe²⁺ to produce a large amount of ·OH, which is the main active substance for organic pollutants degradation. This study provides new insights for non-precious metal oxides to replace precious metals towards in-situ production of H₂O₂ and degradation of pollutants.