Defect Engineering Boosted Peroxydisulfate Activation of Dual-Vacancy Cu–Fe Spinel Oxides for Soil Organics Decontamination

Oxygen-limited environments in a compact soil medium significantly restrict the charge transfer of catalysts to degrade organics, considerably reducing the catalytic performance. Defect engineering has been proposed to modulate electronic structures and enrich active sites of catalysts, but single vacancy defects are still insufficient to overcome the slow redox cycling between different valence states of metals. Herein, sulfur-doped CuFe2O4/biochar (S–CuFe2O4/BC) with oxygen and sulfur dual vacancies was synthesized for peroxydisulfate (PDS) activation. Experimental and theoretical analysis reveals that the S-doping treatment significantly raises the electron delocalization to enlarge FeOh–O covalency, thereby lowering the charge transfer energy to favor FeOh–PDS interaction with higher oxidants' utilization efficiency. Consequently, more than 2-fold increase in the pseudo-first-order rate constant and longevity for organics degradation was demonstrated. The stronger capability of the selective adsorption-oxidation toward hydrophobic organic contaminants was also achieved. This work offers an insightful understanding for collaboratively stimulating the intrinsic activity of the catalyst for soil organics decontamination.