Intrinsic properties of biochar for electron transfer

The past decades witness a rapid development on biochar as adsorbent, catalyst, or modifier for wastewater treatment and soil amendment. During these processes, the electron transfer (ET) of biochar is common and essential. However, there is a scarcity of comprehensive information about the specific roles of biochar properties in ET behavior. Therefore, this review scrutinized the relationship of ET and biochar intrinsic properties, including biochar-derived dissolved organic matter, persistent free radicals, oxygen functional groups, non-metal heteroatoms, metal dopants, graphitization degree, and defects. Furthermore, we showcased the recent progresses on the oxidation–reduction of heavy metal oxyanions and degradation of organic pollutants via ET of biochar. Afterwards, both experimental and theoretical techniques about how to analyze ET were summarized. Eventually, the future direction and challenge for ET of biochar were suggested, such as systematic study on structure–function relationship, computation-assisted molecular-level analysis, complicated influence of actual environment, unified and standard electrochemical test method as well as targeted control strategy. This review dedicates to sharpening the deep understanding of ET via biochar.