Degradation of Bisphenol-Type Pollutants in CNTs-Fe₃O₄-nZVI Heterogeneous Fenton-Like System: Response Surface Optimization and Mechanism Elucidation

Phenolic compounds are widespread industrial pollutants that threaten aquatic ecosystems and human health. Herein, carbon nanotube-supported Fe₃O₄-loaded nano-zero-valent iron (CNTs-Fe₃O₄-nZVI) composites were synthesized via liquid-phase reduction and employed as heterogeneous Fenton-like catalysts with H₂O₂ to degrade bisphenol F (BPF) and bisphenol S (BPS) in aqueous solution. The effects of H₂O₂ concentration, catalyst dosage, and initial pH on degradation efficiency were systematically investigated, and reaction conditions were optimized using the Box-Behnken response surface methodology (RSM). Results showed that at 25 °C, pH 3.0, a catalyst dosage of 0.8 g L⁻ 1 , and H₂O₂ concentrations of 10 mmol L⁻ 1 (for BPF) and 15 mmol L⁻ 1 (for BPS), the degradation efficiencies of BPF and BPS reached 98.03% and 94.30%, respectively, in good agreement with the model-predicted values (96.94% and 93.92%). After four reuse cycles, the degradation efficiencies remained above 70%, confirming good stability and reusability. Isotherm data fitted the Freundlich model better than the Langmuir model for both BPF ( R 2 = 0.9484) and BPS ( R 2 = 0.9091), with negative intercepts indicating multilayer adsorption on heterogeneous surfaces. The adsorption affinity for BPF ( K F = 8.25) was nearly double that for BPS ( K F = 4.37), revealing structure-dependent interfacial interactions. Radical quenching and mass spectrometry indicated HO· oxidation and benzene ring cleavage as the primary BPS degradation pathways. The optimized conditions were determined as H₂O₂ 10.74 mmol L⁻ 1 , catalyst 0.733 g L⁻ 1 , and pH 2.836 by RSM. TOC removal reached 64.22% for BPF and 67.97% for BPS, and ecotoxicity assessment confirmed that the degradation intermediates exhibited substantially reduced toxicity, demonstrating effective detoxification.