WB-assisted activation of periodate by Fe(III) for decontamination: Periodate concentration-dependent mechanistic shift

The iron-activated periodate (PI) process may be limited by the sluggish kinetics of Fe(II) regeneration and Fe(III) accumulation. Herein, tungsten boride (WB), serving as a co-catalyst, can effectively overcome the inherent drawback of oxidation reactions. The WB/Fe(III)/PI system exhibited different removal efficiencies toward sulfisoxazole (SIZ) under varying PI concentrations. Based on the qualitative and semiquantitative tests, the generation of reactive species changes with various PI concentrations. Specifically, at low PI concentration, Fe(IV), generated via Fe(II)-mediated PI activation following WB-driven Fe(III) reduction, was the primary reactive species responsible for rapid SIZ removal. However, at high PI concentrations, the limited generation of Fe(IV) contributes only marginally to SIZ removal. In situ Raman characterization and electrochemical tests revealed that at high PI concentration, WB could react with PI and Fe(III) to form high-potential metastable intermediates (WB-Fe(III)-PI*), facilitating direct electron transfer pathway (ETP) from the SIZ to PI. Density functional theory (DFT) calculations further confirmed the interactions among WB, Fe(III), and PI. Besides, at low PI concentrations, the WB/Fe(III)/PI system selectively and rapidly oxidized oxygen-transfer-prone pollutants, while at high PI concentrations, it favored sustained oxidation of electron-rich pollutants. Additionally, WB exhibits excellent reusability during cyclic use. This comprehensive investigation deepens insight into PI-based co-catalytic process and offers an efficient strategy for selecting appropriate oxidant concentrations for wastewater treatment.