Construction of Z-Scheme PCN-222/CoFe2O4 heterojunction for efficient photo-Fenton tetracycline hydrochloride degradation: Mechanistic and Pathways

Abstract

This study successfully constructed Z-scheme heterojunction photocatalysts (P/CF-x) by compositing the metal-organic framework (MOF) PCN-222 with spinel ferrite CoFe₂O₄ via a ball-milling method for efficient visible-light-driven photo-Fenton degradation of tetracycline hydrochloride (TCH). The optimized P/CF-20 composite achieved 99.46% degradation of 0.02 g·L^-1 TCH within 30 minutes, with an apparent rate constant of 0.1452 min^-1 under optimized conditions (0.1 g·L^-1 catalyst, pH 6, 250 μL 30 wt% H₂O₂). The enhanced performance originates from the Z-scheme heterojunction, which promotes efficient separation of photogenerated charge carriers: electrons from the conduction band of PCN-222 recombine with holes from the valence band of CoFe₂O₄, preserving highly oxidative h⁺ and reductive e⁻. The interfacial charge transfer mechanism was validated through XPS, PL, TRPL, SPV and EIS analyses. EPR and radical trapping experiments confirmed that h⁺, ·OH, and ·O₂⁻are the dominant reactive species, with h⁺ playing a primary role. LC-MS analysis revealed two degradation pathways, involves hydroxylation, demethylation, ring-opening reactions, dehydration, radical-mediated cleavage, and finally mineralization into CO₂, H₂O, and NH₄⁺. Furthermore, P/CF-20 exhibited excellent stability (>96% efficiency after 6 cycles) and magnetic recoverability (saturation magnetization: 13.35 emu·g⁻¹). This work provides a novel strategy for designing efficient and recyclable heterogeneous photo-Fenton catalysts, offering potential applications in antibiotic-containing wastewater treatment.