Non-radical peroxymonosulfate activation by CoAl-LDO for sulfamethoxazole degradation: Role of Co-Al synergy

Layered double hydroxide (LDH)-derived materials are promising catalysts for peroxymonosulfate (PMS) activation, yet achieving both high catalytic activity and structural stability remains challenging. Here, a nano-layered cobalt-aluminum layered double oxide (CoAl-LDO) was synthesized from LDH precursors and employed for PMS activation toward sulfamethoxazole (SMX) degradation. The results revealed that Co₂Al₁-LDO exhibited optimal catalytic activity. It achieved 90.34% SMX removal within 9 min with an apparent rate constant of 0.193 min^-1. The catalyst also showed excellent stability, retaining over 75% of its initial activity after five cycles with negligible metal leaching. The superior performance was attributed to the synergistic interaction between Co and Al species. Al³⁺ stabilized the layered framework, suppressed cobalt leaching, and facilitated the Co²⁺/Co³⁺ redox cycle. In addition, the mesoporous structure with a high specific surface area (168.376 m²/g) enhanced PMS activation by providing abundant accessible active sites and accelerating mass transfer. Mechanistic investigations revealed a non-radical-dominated PMS activation mechanism, in which ¹O₂ and O₂^•- contributed more than 90% of the oxidation capacity, while direct electron transfer further enhanced SMX degradation. A TOC removal of 42.02% was achieved, indicating effective mineralization of SMX. DFT calculations and LC-MS analysis revealed that SMX degradation mainly proceeded through isoxazole ring opening, sulfonamide bond cleavage, and benzene ring hydroxylation. Toxicity assessment further confirmed that most degradation intermediates exhibited lower toxicity than the parent compound. This work provided new insights into the design of stable LDH-derived bimetallic catalysts for non-radical PMS activation and antibiotic wastewater treatment.