Removal of methomyl in water by leaves-generated biochar: effect of metallic coating, kinetics, and important role of hydroxyl radical

Methomyl (MET) can exist as fatal water pollutant due to its high leachability, and solubility, which is urgently to be efficiently removed. This work investigated its removal in water by cost-effective biochar; in which, the efficiencies of leaves-generated biochar (BC) as non-modified bio-adsorbent, and copper oxide/BC (COBC) and hematite (Fe2O3)/BC (MBC) as modified bio-adsorbents were compared. At initial concentration of 20.0 mg/L in purified water, the respective removals by BC, COBC, and MBC were 21.3%, 16.4%, and 18.9% within 360 min at 0.5 g/L dosage, which were increased to 33.8%, 18.9%, and 26.1% at an increased dosage of 1.0 g/L. However, the removal efficiencies of combined method with non-modified, and the modified bio-adsorbents were increased less. The removal was increased from 33.8% to 47.0% by increasing BC dosage to 1.5 g/L, and removal was further increased to 54.0% when MET concentration was decreased to 10.0 mg/L. The removal of MET by BC was pH-dependent, and removal could be increased up to 80.0% at pH 11.0; while, the influence of temperature was slight. With analyses of the effect of dissolved oxygen, and free-radical quenching experiment, both the adsorption, and hydroxyl radical (•OH) induced degradation were found responsible for removal. Finally, removal in tap water (TW) was investigated, which indicated that the leaves-generated BC was suitable for MET removal in real water.