Surface-bound radicals generated from cobalt single-atom catalyst: Mechanism of boosting Fenton-like reactions

Abstract

Surface-bound radicals have been reported to be emerging crucial reactive species in Fenton-like reactions for environmental treatment. However, their identification on catalyst surface and contribution to pollutant degradation have never been well addressed. In this study, single Co atom anchored on Al-doped SiO2 (Co@Al-SiO2) catalyst was well designed for peroxymonosulfate (PMS) activation to produce a high concentration of surface-bound sulfate radicals (SO4[rad]−) and reached 100 % removal percentage of antibiotics, dyes and volatile organic compounds (VOCs) pollutants within several minutes. In-situ cyclic voltammetry-electrochemical quartz crystal microbalance (CV-EQCM) and the derived calculation method were firstly employed to quantitatively identify the surface-bound SO4[rad]−. Results show that abundant surface-bound SO4[rad]− was generated on Co-Si bond and its concentration reached 1.17 × 10−6 mol/m2, which was very close to the theoretical maximum (1.34 × 10−6 mol/m2). Further experiments demonstrated that Co atoms can provide rich binding sites for SO4[rad]−, resulting in the enrichment of surface-bound SO4[rad]− in nanoscale surface. This behavior can remarkably boost the degradation kinetics towards various organic contaminants. Coupled with a membrane in water treatment, this system showed an outstanding performance for degradation of pollutants such as dyes (>99 %) with the flow rate of 20 ml/min after 0.5 s, which was considerably faster than traditional treatments. This study provides a fundamental insight into surface-bound radical, guiding the rational design of catalyst for Fenton-like reactions in environmental application.