Co-catalysis of trace dissolved Fe(iii) with biochar in hydrogen peroxide activation for enhanced oxidation of pollutants

Activation of hydrogen peroxide (H(2)O(2)) with biochar is a sustainable and low-cost approach for advanced oxidation of organic pollutants, but faces the challenge of a low yield of hydroxyl radical (˙OH). Herein, we hypothesize that the activation efficiency of H(2)O(2) can be enhanced through co-catalysis of trace dissolved iron (Fe) with biochar. Two biochar samples derived from different feedstock, namely LB from liquor-making residue and WB from wood sawdust, were tested in the co-catalytic systems using trace Fe(iii) (0.3 mg L(−1)). The cumulative ˙OH production in [Fe(iii) + LB]/H(2)O(2) was measured to be 3.28 times that in LB/H(2)O(2), while the cumulative ˙OH production in [Fe(iii) + WB]/H(2)O(2) was 11.9 times that in WB/H(2)O(2). No extra consumption of H(2)O(2) was observed in LB/H(2)O(2) or WB/H(2)O(2) after addition of trace Fe(iii). Consequently, the reaction rate constants (k(obs)) for oxidation of pollutants (2,4-dichlorophenoxyacetic acid and sulfamethazine) were enhanced by 3.13–9.16 times. Other iron species including dissolved Fe(ii) and iron minerals showed a similar effect on catalyzing 2,4-D oxidation by biochar/H(2)O(2). The interactions involved in adsorption and reduction of Fe(iii) by biochar in which the defects acted as electron donors and oxygen-containing functional groups bridged the electron transfer. The fast regeneration of Fe(ii) in the co-catalytic system resulted in the sustainable ˙OH production, thus the efficient oxidation of pollutants comparable to other advanced oxidation processes was achieved by using dissolved iron at a concentration as low as the concentration that can be found in natural water.