Characterization and adsorption performance of biochars derived from three key biomass constituents

Abstract The effects of biomass constituents on biochar adsorption performance are still unclear. In this work, three main biomass constituents, lignin, cellulose and xylan (hemicellulose), were converted into biochar. These biochars showed obvious differences, which were observed by physicochemical characteristics analysis. Based on the acid-base titration, the contents of functional groups on different biochars decreased as lignin > hemicellulose > cellulose. The findings from elemental analyses showed that the degree of lignin pyrolysis was lower than cellulose and hemicellulose; however, lignin biochar had the highest yield and ash content. The scanning electron micrographs demonstrated that both lignin and xylan biochars were similarly spherical, while cellulose biochar was fibrous. Furthermore, the sulfadimidine (SMT) adsorption experiments revealed that physicochemical characteristics of biochars obviously affected the adsorption behavior. Cellulose and xylan biochars indicated similar pH-dependent sorption patterns, but the latter exhibited higher adsorption capacity. In contrast, lignin biochar had no adsorption capacity due to the high ash content. The adsorption was dominated by the electrostatic repulsion, EDA interactions, hydrogen bonds and negative charge-assisted hydrogen-bond. Overall, these observations are of significant importance for guiding in the selection of feedstock used for biochar preparation and predicting the sorption behavior of SMT on biochars.