Doping tungsten in iron-cobalt layered double hydroxides with interwoven ultra-thin nanosheet structures enhances the degradation of metronidazole by activating calcium sulfite

Abstract

Tungsten-doped iron-cobalt layered bimetallic hydroxides (CoFeW-LDHs) were used for activating sulfite to degrade metronidazole (MTZ) in this study. The characterization results confirmed the presence of vertically aligned hierarchical ultrathin nanosheets forming a porous network, which enhances the material's ability to activate CaSO3. The study investigated the optimal Co/Fe/W atomic ratio in the catalysts and examined the impact of various parameters, such as catalyst dosage, CaSO3 concentration, initial pH, and MTZ concentration. Under the best experimental conditions identified, the degradation rate of MTZ reached 95% within 60 min. Mechanism analysis revealed that W doping promoted oxidation–reduction reactions between Co(Ⅱ)/Co(Ⅲ) and Fe(Ⅲ)/Fe(Ⅱ) on the catalyst surface, facilitating CaSO3 activation and the continuous generation of reactive oxygen species (ROS) like 1O2 and SO4•−. Based on experimental, density functional theory (DFT), and quantitative structure–activity relationship analyses, the study proposed a degradation pathway and evaluated the ecotoxicity of MTZ and its intermediates. MTZ was found to be converted via three pathways into low or non-toxic intermediates, ultimately mineralizing into small inorganic molecules. Even after five cycles, Co3FeW-LDHs maintained a removal efficiency of over 90% for MTZ. The material's ease of synthesis, high activity, and stability suggest significant potential for practical application in environmental cleanup efforts.