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

Carbon dioxide (CO) 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 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 adsorption capacity (177.1 mg/g) was observed on S3W7 biomass at 700 °C (S3W7-700K), due to the largest surface area (2623 m/g) and the highest micropore volume (0.68 cm/g). Furthermore, surface functional groups, hydrophobicity, and aromaticity of biochar and presence of hetero atoms (N) also were actively involved in CO adsorption of biochar. In addition, in situ DRIFTS analysis advanced current understanding for the chemical sorption mechanisms by identifying the transformation composites of CO on biochars, and characterizing the weakly adsorbed and newly formed mineral species (e.g., carbonates) during the CO sorption process. This study may provide an insight into the research of CO capture by identifying physical and chemical adsorption, and expand the effective utilization of natural biomass-based biochar for mitigation greenhouse gas emission.