Singlet oxygen-oriented degradation of sulfamethoxazole by Li-Al LDH activated peroxymonosulfate

Lithium-aluminum layered double hydroxides (Li-Al LDHs) are a unique group of LDHs and their applications have attracted wide attention. Herein, Li-Al LDH was prepared using the hydrothermal method and was then used to activate peroxymonosulfates (PMS) for degrading sulfamethoxazole (SMX). It was found that 0.4 g/L catalysts, 1.57 mM PMS, and pH = 11.00 were the optimal conditions for the degradation process of the Li-Al LDH/PMS system at 30 degrees C. Under these conditions, the degradation rate of 80 mg/L SMX could reach 98.2% within 130 min. Meanwhile, the catalyst also showed superior stability and recoverability. After five cycles, the degradation rate of SMX was still higher than 95.3%. Based on free radical scavenging experiments and electron spin resonance results, both the radical and nonradical pathways synergistically completed the degradation in the Li-Al LDH/PMS system, with the nonfree radical (singlet oxygen) playing the predominant role. A reasonable degradation pathway was also proposed based on the detection of intermediates in the degradation process. The Li-Al LDH/PMS system, as expected, has great potential for efficient wastewater catalytic treatment.