Enhanced activation of peroxymonosulfate for 2,4-dichlorophenoxyacetic acid elimination by Mo/VO43−: in situ vanadium cyclic utilization

The solid vanadium (V) oxides are known for their excellent catalytic ability in varied gas/liquid phase reactions. However, there is a paucity of studies that utilize liquid-phase VO₄³⁻ activation of peroxymonosulfate(PMS) for the degradation of organic pollutants. In this study, VO₄³⁻/PMS system was explored for oxidative degradation of 2,4-dichlorophenoxyacetic acid (2,4-D), and molybdenum (Mo) was introduced to promote the regeneration of low-valent vanadium species and enhance the removal of 2,4-D. Compared with the VO₄³⁻/PMS process, the Mo/VO₄³⁻/PMS system showed significant improvement in PMS decomposition and 2,4-D degradation by 31.2 % and 72.3 %, respectively within 20 min. The quantitative detection of vanadium concentration by high performance liquid chromatography (HPLC) and the valence changes of Mo and V on the surface of Mo powder by X-ray photoelectron spectroscopy (XPS) revealed that V(Ⅴ) was reduced to V(Ⅳ) and V(Ⅲ) by Mo⁰ and Mo⁴⁺, and Mo⁰ and Mo⁴⁺ were oxidized to Mo⁶⁺, constituting a rapid redox process to enhance the activation of PMS. In addition, Cl⁻, NO₃⁻ and humic acid (HA) showed ignorant inhibition on the degradation process, while HCO₃⁻ significantly depressed the degradation of 2,4-D, probably due to its buffer effect on solution pH. This study highlighted that the dissolved oxygenated V ions can be solidly utilized in the advanced oxidation technology for the elimination of organics.