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 °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.