Quantifying the contributions of surface area and redox-active moieties to electron exchange capacities of biochar.

Redox properties play a critical part in enabling biochar to participate in geochemical redox cycles. To manufacture biochar with targeted redox properties, it is essential to define the correlation of redox properties with the structure and moieties of biochar. However, previous studies focused on moieties, while structural parameters were overlooked. Furthermore, most publications used a single-factor analysis for certain types of moieties with other moieties possibly ignored. Herein, four kinds of representative biomass components, cellulose, lignin, casein, and starch, were pyrolyzed at low, intermediate, and high temperatures to obtain biochar with distinct structures and moieties. Then, the partial least-squares modeling was implemented to evaluate the quantitative contributions of structure and moieties to redox properties with the results obtained by characterizing the biochar. In addition to redox-active moieties, specific surface area was also found to be critical to the redox properties. The cellulose-derived chars exhibited better electron-donating capacities, while the lignin-derived chars exhibited better electron-accepting capacities. The starch-derived chars pyrolyzed at 700℃ possessed both high electron-donating and electron-accepting capacities. The casein-derived biochar exhibited weak redox capacities. These findings show the importance of structural influences on the redox properties and provide feedstock choices when applying and producing biochar with targeted redox properties.