Enhanced conversion from H₂O₂ to ¹O₂ on Cu–N centers: Investigation of mechanisms and application in alkaline wastewater treatment

Heterogeneous Fenton-like systems using H₂O₂ as an oxidant have been extensively investigated in acidic and neutral conditions, but usually, they become ineffective under alkaline conditions. In this study, a cuprous graphitic carbon nitride material (Cu–CN) was prepared that can generate singlet oxygen (¹O₂) from H₂O₂. The results demonstrate that at pH 11, 95 % of 50 mg/L p-chlorophenol (4-CP) can be effectively eliminated within 120 min. Through semi-quantitative analysis and density functional theory calculations, it has been confirmed that ¹O₂ is the dominant reactive oxygen species in this system under alkaline conditions. The main pathway for ¹O₂ generation involves the formation of a complex between ^·O₂^– and Cu(II)-N sites, and the subsequent intramolecular electron transfer. To enhance the stability and separation performance of this catalyst, polyethylene glycol (PEG) was employed as a binder to combine Cu–CN with Fe₃O₄. The terminal hydroxyl groups in PEG were cross-liked by metals, thus forming a solid and magnetic composite (CuFe@PEG). Compared to Cu–CN, CuFe@PEG exhibited remarkable performance with 93 % retention of its original capacity for 4-CP removal at pH 11. Furthermore, after seven cycles, the degradation efficiency only decreased by 6.36 %. This study introduces a novel approach for utilizing Fenton-like reactions in treating alkaline wastewater.