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.