In situ synthesis of CoFe-LDH on biochar for peroxymonosulfate activation toward sulfamethoxazole degradation: cooperation of radical and non-radical pathways

Abstract

Developing an efficient, low-cost and stable catalyst to activate peroxymonosulfate (PMS) for pollutant degradation is crucial in environmental remediation. Herein, Co₁Fe₁ layered double hydroxide (Co₁Fe₁-LDH) was in situ loaded on biochar (BC) derived from rape straw for sulfamethoxazole (SMX) degradation via activating PMS. It could be found that the optimal catalyst (BC/Co₁Fe₁-LDH-4) exhibited the highest SMX degradation efficiency of 94.8% within 5 min reaction, far more than pristine Co₁Fe₁-LDH (58.5%), which might be ascribed to the synergistic effects between Co₁Fe₁-LDH and BC during the reaction. For one thing, BC itself participated in the catalytic degradation reaction as an activator and made the catalyst have excellent adsorption and degradation performance. For another, BC as a carrier not only effectively inhibited the agglomeration of Co₁Fe₁-LDH to increase the active sites, but also accelerated the Co²⁺/Co³⁺ and Fe²⁺/Fe³⁺ cycles to reduce the leaching of metal ions. Meanwhile the leaching of trace metal ions also promoted the degradation of SMX to a certain extent, indicating that the catalytic mechanism was a combination of homogeneous and heterogeneous catalysis, and the latter was dominant. The quenching trials, electron paramagnetic resonance (EPR) and electrochemical measurements implied that the radical and non-radical processes were involved in the reaction, where SO₄˙⁻, ˙OH and O₂˙⁻ were the main radical species to drive the radical process, and ¹O₂ and direct electron transfer were responsible for the non-radical process. In addition, the possible SMX degradation pathways were reasonably proposed by high-performance liquid chromatography-mass spectrometry (HPLC-MS) tests and the SMX mineralization degree was provided through total organic carbon (TOC) measurements. This present work provides new insight into the construction of highly efficient PMS activation catalysts for environmental wastewater treatment.