Activation of H₂O₂-HCO₃^- by Ca₂Co₂O₅ for pollutant degradation

The bicarbonate-activated hydrogen peroxide (BAP) system is widely studied for organic pollutant degradation in wastewater treatment. Ca₂Co₂O₅, a heterogeneous catalyst containing multivalent cobalt including Co(II) and Co(III), was herein investigated as a BAP activator, and Acid Orange 7 (AO7) was used as a model pollutant. Ca₂Co₂O₅ exhibited good activation performance. The degradation rate and the initial rate constant of the Ca₂Co₂O₅-activated BAP system were 5.4 and 11.2 times as high as the BAP system, respectively. The removal rate of AO7 reached 90.9% in 30 min under optimal conditions (AO7 20 mg/L, Ca₂Co₂O₅ 0.2 g/L, H₂O₂ 1 mM, NaHCO₃ 5 mM, pH 8.5, 25℃). The Ca₂Co₂O₅ catalyst exhibited good stability and recyclability, retaining 85% of AO7 removal rate in the fifth run. Compared to the BAP system, a lower dosage of H₂O₂ was required and a higher initial concentration of pollutants allowed for effective degradation in the Ca₂Co₂O₅-BAP system. X-ray photoelectron spectroscopy was used to analyze the catalytic mechanism. The analysis showed that the good catalytic performance of Ca₂Co₂O₅ attributes to its high proportion of oxygen vacancies and Co(III) species, and the presence of Ca. The active species O₂^•-, •OH, and ¹O₂ are responsible for the degradation, as indicated by the quenching experiments. The degradation mechanism of AO7 was speculated based on UV-Vis spectral analysis and the identification of degradation intermediates. The azo form, naphthalene and benzoic rings in the AO7 structure are destroyed in the decomposition. This research provides a feasible approach to designing effective and reusable BAP activators for pollutant degradation in wastewater treatment.