Anionic ligands driven efficient ofloxacin degradation over LaMnO3 suspended particles in water due to the enhanced peroxymonosulfate activation

Peroxymonosulfate (PMS) activation as an in-situ chemical oxidation (ISCO) process, has been widely explored in water decontamination. In this study, we proposed to study the effects of typical organic ligands on the PMS activation performance of inorganic metal-based particles since their coexistence in natural water. Interestingly, the ofloxacin (OFX) degradation was promoted from 32.9% (without ligand) to 96.3% and 95.8% by ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) and the rate constants increased by 5.2 and 21.8 times. While the removal efficiency was depressed to 22.61%, 8.47% and 4.73% in the presence of glycine (GLY), citric acid (CA) and oxalic acid (OA). Characterization results proved that the different functions were dependent on different molecular structures of organic ligands due to different solvation and steric hindrance. Among the tested ligands, more metal ion leached into solution and caused homogeneous PMS activation by NTA. Only EDTA can induce the generation of surface Mn(II) and oxygen vacancy in LaMnO3. Mn(II) was the active site for PMS conversion into SO4•− via an electron transfer process while oxygen vacancy was responsible for 1O2 generation by PMS self-decomposition. Moreover, ligands concentration and initial solution pH were found to greatly affect the OFX degradation efficiency and involved reactive oxygen species (SO4•− at pH 5.0 and 1O2 at pH 9.0). Its impact on the OFX degradation intermediates and reaction mechanism was finally discussed. Hence, ligand induced in-situ heterogeneous PMS activation in water decontamination should be considered.