Activation of sulfite with cationic vacancy-enriched Co3O4 for highly efficient tetracycline abatement

Tetracycline contamination in the aqueous environments has attracted increasing attention owing to the antibiotic resistance. Heterogeneous advanced oxidation processes (AOPs) based on sulfite activation with metal oxides have been proposed for tetracycline abatement, yet the overall efficiency is hampered by the sluggish redox cycling of metal species. Herein, we report a novel process combining sulfite with cationic vacancy-enriched Co 3 O 4 (simplified as Co 3 O 4 -Vc), which enables the acceleration of sulfite autoxidation to generate radicals. Structural and morphological characterizations of Co 3 O 4 -Vc are performed and the effect of pH and radical scavengers on tetracycline abatement are studied. At the lower dosge of 0.01 g/L Co 3 O 4 -Vc and sulfite, tetracycline can be removed by 90–100 % within 10 min for pH 8.0–10.0, in which HO • and SO 4 •− are identified as the main reactive radicals and quantified as 1.0 and 4.2 μM, respectively. Radical quenching with methanol and tert-butanol, together with EPR using DMPO, evidence the formation of SO 3 •− and confirm SO 4 •− as the dominant oxidizing species for TC abatement. Mechanistically, cationic vacancies accelerate the >Co(III)/>Co(II) redox cycle, thereby sustaining rapid radical chain propagation. DFT calculations reveal that the cationic vacancies lead to a significant reduction in the adsorption energy of sulfite on the Co 3 O 4 -Vc surface to −1.674 eV, thereby facilitating sulfite adsorption and activation. Bader charge analysis indicates that the amount of electrons transferred from sulfite to Co active sites increases to 0.39 |e|, further accelerating interfacial electron transfer and radical generation. This study suggests that the Co 3 O 4 -Vc/sulfite process can achieve efficient abatement of organic pollutants and exhibit application potential in the practical water treatment.