Insight into the enhanced removal of dimethoate by ferrate(Ⅵ)/biochar system: Contributions of adsorption and active oxidants.

Dimethoate is a toxic organophosphorus insecticide and its contamination of water poses a threat to the surrounding ecosystem. In order to enhance the removal effect of ferrate (Fe(VI)) on dimethoate, modified graphene-like biochar (SIZBC) with reduction and adsorption properties was prepared in this study. Compared with Fe(VI) alone, the removal of dimethoate by Fe(VI)/SIZBC increased from 26 % to more than 97 %, and the reaction rate was accelerated by 34 times. The oxidizing property of Fe(VI) was enhanced by the reducing groups loaded on SIZBC, and more active species were produced with the contributions ranked as SO¯ > ∙OH > Fe(V). And the contributions of adsorption and active oxidants in the reaction process accounted for 25 % and 75 %, respectively. Enlarging the sulfite solution concentration of modified biochar, the transformation from ∙OH/Fe(V) to SO¯ was promoted in the system. As the concentration of Fe(Ⅵ) increased, the contributions of ∙OH and SO¯ gradually decreased and Fe(V) became the main active oxidant. Fe(VI)-induced core/shell nanoparticles exhibited in situ adsorption of phosphate which was a mineralization product of dimethoate, thus total phosphorus (TP) removal was increased by 27 %. Through the three degradation pathways, dimethoate and its toxic intermediates were further mineralized to inorganic substances. Finally, the Fe(VI)/SIZBC system was proven to be feasible for actual water treatment and was able to reduce water toxicity.