Heterogeneous fenton oxidation of methylene blue with Fe-impregnated biochar catalyst

Abstract

Fe-impregnated biochar (Fe-BC) as high-efficiency heterogeneous Fenton catalyst was synthesized and evaluated in detail for its catalytic activity, stability and reusability under various conditions. The optimal conditions for the Fenton oxidation of methylene blue (MB) as model dye were determined as 0.075 g/L H₂O₂, 0.5 g/L Fe-BC for 0.1 g/L MB, which resulted in optimum Dye:Fe_cat:H₂O₂ ratio of 1:5:0.75 (on g/L basis) or [Dye]:[Fe_total]:[H₂O₂] molar ratio of 1:6.2:7.0 respectively.

The effective degradation of MB was identified over a wider pH range, and even after four consecutive runs Fe-BC maintained above 95% MB removal rate within 3 min of treatment with low Fe release, indicating strong stability and reusability. Under the optimum Dye:Fe_cat:H₂O₂ (g/L) condition at initial pH 4, the Fe-BC achieved 99.9% removal efficiency of MB within 3 min in heterogeneous Fenton reaction (HEFR) with much less H₂O₂ concentration and low catalyst dosage, demonstrating its efficiency and cost-effectiveness compared to other Fenton reaction catalysts.

The removal velocity of MB showed two rate steps: a fast first stage followed by a slow stage with the rate in the order of H₂O₂/Fe-BC ⋙ H₂O₂/biochar > biochar > H₂O₂. Overall, the developed Fe-BC is more economical with strong stability and recyclability for use in HEFR for treating recalcitrant pollutants.