Removal of pesticides by layered double hydroxide modified different clay minerals and site energy analysis

Abstract

Layered double hydroxides (LDHs) modified montmorillonite, mica, illite, and chlorite to from composites adsorbents of LDH@Mt, LDH@Mi, LDH@Ill, and LDH@Chl were prepared for removal of atrazine (ATZ) and 4-chloro-2-methylphenoxyacetic acid (MCP), and characterized through XRD, FT-IR, BET, and SEM analyses. In kinetics study, four composite adsorbents well fitted pseudo-second-order kinetics and intraparticle diffusion. Generalized Langmuir model described adsorption process better than Langmuir model in isothermal study, indicating there were heterogeneous adsorption sites for ATZ/MCP on adsorbents. LDH@Mt possessed better adsorption performance for ATZ/MCP, and the adsorption capacities are 8.19 mg/g and 90.9 mg/g, respectively. Theory of site energy distribution analyzed the number of adsorption sites qualitatively, and showed that the accessible adsorption sites on LDH@Mt were more than that of other adsorbents. Thermodynamic analysis revealed that the removal processes were endothermic and spontaneous. The removal of ATZ/MCP by LDHs modified clays offers an effective approach for pesticides removal.