Recent advances in biochar-based catalysts: Properties, applications and mechanisms for pollution remediation

Biochar (BC) is one of the most remarkable materials for environmental remediation. An increasing number of researchers have attempted to utilize BC as a catalyst to generate reactive oxygen species (ROS) and sulfate radicals. This work focuses on the development and progress of BC-based catalysts in different systems, including redox systems, Fenton-like systems, sonocatalytic systems and photocatalytic systems. Most importantly, the catalytic performance and mechanism of different types of BC-based catalysts are thoroughly investigated. Furthermore, the applications of BC-based catalysts in wastewater, sediments, soil and gas are presented. Special attention is paid to the factors involved in the generation of ROS and sulfate radicals, such as oxygen-containing functional groups (OFGs), persistent free radicals (PFRs) and redox properties. The generation processes of ROS and sulfate radicals are presented in detail. And the removal pathways of three mechanisms are elaborated. Furthermore, research in this field is still at an early stage, and many improvements are required before the technology can be efficiently scaled up and put into practice. This review enriches the knowledge about the generation processes of ROS and sulfate radicals by BC-based catalysts and improves the understanding of the catalytic performance and catalytic mechanism of BC-based catalysts for pollutants.