Heterogeneous biochar-based catalytic advanced oxidation of emerging contaminants: Detailed synergy and radical generation mechanism

Abstract

Conventional heterogeneous catalysts utilized for the advanced oxidation of emerging contaminants often suffer from limitations such as agglomeration, surface passivation, wide bandgap, and low surface area, which hinder their practical applicability. Engineered biochar presents a cost-effective alternative, offering tunable physicochemical properties like sp²-hybridized graphitic structure, structural defects, high specific surface area, and surface-bound persistent free radicals that can address the challenges faced by commonly used heterogeneous catalysts. Rational design of biochar-based catalysts requires understanding the physicochemical properties of biochar contributing to synergy between the biochar and conventional metal-based catalysts. Despite the advancements in biochar research, the synergistic role of engineered biochar-based catalysts in catalytic advanced oxidation processes (CAOPs) remains unclear. This review meticulously examines the interfacial synergy of engineered biochar with conventional catalysts used in non-energy-assisted CAOPs and energy-assisted CAOPs. A wide range of oxidant activation systems involving peroxymonosulfate, persulfate, ozone, hydrogen peroxide, peracetic acid, percarbonate, and periodate are discussed along with sonocatalysis and photocatalysis. Additionally, radical formation mechanisms are discussed in detail, highlighting how molecular and interfacial properties of biochar aid in enhanced radical generation, providing insights into the rational design of biochar-based catalysts for efficient emerging contaminant degradation.