Accelerating of Fe2+ regeneration in Fenton reaction by biochar: Pivotal roles of carbon defects as electron donor and shuttle

Abstract

Accelerating Fe2+ regeneration emerges as a promising approach to boost Fenton reaction. However, most co-catalysts to accelerate Fe2+ regeneration embrace drawbacks including cumbersome synthesis, expensive precursors and metal leaching. Herein, we report an approach to remarkably accelerate Fe2+ regeneration by metal-free biochar. Quantitatively, the overall reaction rate constant for Fe2+ regeneration by biochar was 9.68 × 10−4, and correspondingly the concentration of OH• generated in biochar/Fe2+/H2O2 system was 2.08 times higher than that in Fe2+/H2O2. Favored by this, satisfying performance on both mineralization and detoxification on sulfamethoxazole was achieved. Moreover, 99.6 % of Chemical Oxygen Demand (COD) was removed from medical wastewater in a biochar-packed fixed-bed column, while comparably the traditional Fenton process achieved only 14.6 %. Distinguished with traditional knowledge, surface carboxyl groups on the surface of biochar were identified as reactive sites to capture Fe3+, while, carbon defects played multifunctional roles as electron donors and shuttle to reduce Fe3+. Besides, advantages including negligible metal leaching, low interferences from water matrixes and suppression of toxic BrO3− generation suggested the strategy promising. The achievements shed light on the acceleration of Fe2+ regeneration in Fenton processes in an economic and environmentally-friendly way, and also the modulation of the reactivity of biochar.