Renewable biochar derived from mixed sewage sludge and pine sawdust for carbon dioxide capture

Carbon dioxide (CO 2 ) is the main anthropogenic greenhouse gas contributing to global warming. In this study, a series of KOH-modified biochars derived from feedstock mixtures (i.e., S3W7 biomass consisting of 70% pine sawdust and 30% sewage sludge; S5W5 biomass consisting of 50% pine sawdust and 50% sewage sludge) at different temperature (i.e., 600–800 °C) were prepared for evaluating CO 2 adsorption performance. The KOH-activated biochars prepared with S3W7 biomass displayed larger surface areas and micropore volumes compared to those of S5W5 biochars. In particular, the highest CO 2 adsorption capacity (177.1 mg/g) was observed on S3W7 biomass at 700 °C (S3W7–700K), due to the largest surface area (2623 m 2 /g) and the highest micropore volume (0.68 cm 3 /g). Furthermore, surface functional groups, hydrophobicity, and aromaticity of biochar and presence of hetero atoms (N) also were actively involved in CO 2 adsorption of biochar. In addition, in situ DRIFTS analysis advanced current understanding for the chemical sorption mechanisms by identifying the transformation composites of CO 2 on biochars, and characterizing the weakly adsorbed and newly formed mineral species (e.g., carbonates) during the CO 2 sorption process. This study may provide an insight into the research of CO 2 capture by identifying physical and chemical adsorption, and expand the effective utilization of natural biomass-based biochar for mitigation greenhouse gas emission. • Highly porous carbons derived form a mixed biomass of sewage sludge and pine sawdust. • S3W7–700K displayed high surface area up to 2623 m 2 /g. • S3W7–700K exhibited superior CO 2 adsorption capacity (177.1 mg/g). • In situ DRIFT spectroscopy revealed the importance of chemical adsorption. • It behaves perfect cyclic regeneration performance as high as 92% retention.