Critical Review on Biochar-Supported Catalysts for Pollutant Degradation and Sustainable Biorefinery

Biochar (BC) is a material synthesized from biomass by thermochemical conversion. Physicochemical and functional properties of BCs can be enhanced by several methods of activation or functionalization. The activated and functionalized BCs with a large surface area and abundant surface functional groups can serve as effective catalysts or catalyst supports for various chemical transformations as well as for adsorption/sorption/enrichment of low-concentration pollutant streams. Among them, remediation of environmental contaminants and production of a range of bioproducts in biorefineries have attracted much attention in the context of achieving green and sustainable development. Although the applications of BC as adsorbents in removal of pollutants have been discussed extensively, there is a lot of untapped potential with new applications of BCs as catalysts or catalyst supports for advanced oxidation processes (AOPs) and sustainable biorefineries. In this review, the production and activation/functionalization of BCs are scrutinized. The mechanisms of activated and functionalized BC and BC-supported catalysts in degradation of organic contaminants via AOPs assisted with hydrogen peroxide (H₂O₂), peroxydisulfate (PDS), and peroxymonosulfate (PMS) are reviewed. Emerging applications of BC as catalyst for production of biodiesel and high-value chemicals, tar removal, bio-syngas reforming, and energy storage and conversion devices are discussed in detail.