Synergistic activation of peroxymonosulfate by the laminate metals of MgMnFe-layered double hydroxides for imidacloprid degradation

Abstract

Mg, Mn and Fe as environmental-friendly elements were introduced into the laminates of layered double hydroxides (LDHs) to synthesize MgMnFe-LDHs for peroxymonosulfate (PMS) activation to degrade imidacloprid (IMI). The catalytic activity of MgMnFe-LDHs was influenced by the Mn content in the LDH laminates, and Mg2Mn1Fe with Mn/Mg = 0.5 exhibited superior performance that 250 mg/L of dosage achieving 93.1 % degradation of IMI (10 mg/L) by activating PMS (0.65 mM) within 30 min. The mesoporous structure facilitated the contact between PMS and active sites, the abundant surface hydroxyl groups (–OH) provided sites for PMS complexation, and the synergism of Mn and Fe promoted PMS adsorption and electron transfer ability of Mg2Mn1Fe, thereby accelerating the production of SO4•− and •OH. The primary active sites were identified by density functional theory calculations that H-OI-OII-SO3- is absorbed through the binding of OI site with –OH of Mg2Mn1Fe, and the adsorption is more likely to occur on –OH connected with Mg-Mn-Fe rather than Mg-Mg-Fe and Mg-Mg-Mn. Based on the identification of degradation products, the degradation reaction types of IMI were proposed, including the opening of imidazole ring, carbonylation, denitrification, hydroxylation, dechlorination, and N-dealkylation. This study provides new insights into the design of efficient and environmentally-friendly LDH-based catalysts for PMS activation and the interaction mechanism between PMS and hydroxyl groups in LDH laminates.