Oxygen vacancies-enriched Fe-Cu bimetallic minerals-based magnetic biochar activated peroxydisulfate for durable sulfonamides degradation: pH-dependence adsorption and singlet oxygen evolution mechanism

Abstract

The construction of oxygen vacancies (Vo) is a promising strategy for designing an efficient catalyst toward peroxydisulfate (PDS) activation. However, the unstable interface electron transfer and deactivation of Vo have been the bottleneck, and Vo-mediated PDS activation mechanisms remain vaguely interpreted. Herein, we innovatively synthesized a low-cost and durable Fe-Cu bimetallic mineral-based magnetic biochar with abundant Vo (Fe-CuFe2O4@BC). Fe-CuFe2O4@BC exhibited 6.64, 22.91, and 79.22-fold PDS activation rates for sulfamethazine (SMT) degradation (100%) and mineralization (91.58%) compared with Fe@BC, Cu@BC, and pristine BC, respectively. The outstanding performance of the Fe-CuFe2O4@BC/PDS system was ascribed to the Vo-induced sustainable electron transfer and singlet oxygen (1O2) generation, determined by chemical probes and kinetics study. pH-dependence adsorption of SMT dominated by the strengthened H-bonding and π–π EDA interaction was the key rate-limited step to PDS activation. Based on the surface investigation, electronic measurement, and Density functional theory (DFT) calculations, we proposed new insights into the electron-rich Vo and electron-deficient Cu co-induced PDS activation mechanism. Different from conventional perspectives, Vo preferentially activated PDS to generate 1O2, subsequently delocalizing and accumulating residual electrons from the Cu site. Simultaneously, metastable copper intermediates activated PDS through thermodynamically feasible reactions, promoting nano-confinement Vo-triggered 1O2 pathway. This study provides a new perspective for synthesizing Vo-rich catalysts and essentially deepens insights into nonradical mechanisms of refractory organics.