CO2 adsorption mechanisms on activated nano-sized biocarbons: Investigation through in situ DRIFTS, quasi in-situ XPS and XRD

As the most economical and feasible technology, CO2 capture has attracted enormous attention in recent years. This study investigated the CO2 capture potential using nanoporous biocarbons derived from mixture of sewage sludge and pine sawdust through modification of ZnCl2 + CO2. ZnCl2 + CO2 activated nanoporous biocarbons exhibited higher surface areas, pore volumes, tunable microporosity, compared to the char obtained by ZnCl2 activation. The highest CO2 adsorption capacity of 179.7 mg/g was observed for ZnCl2 + CO2 modified biocarbons pyrolyzed at 700 °C (BC700C), with surface area of 1952 m2/g and micropore volume of 0.65 cm3/g, respectively. In order to advance current acknowledge on the transformation process during CO2 capture, in situ DRIFTS, quasi in-situ XPS and XRD, were employed for identifying the transformation composites of CO2 on nanoporous activated biocarbons. The presence of nitrogen especially pyrrolic-/pyridonic-N was found to be conductive to CO2 adsorption and carbonates were induced by mineralogical reactions during CO2 capture process. Furthermore, the physiochemical characteristics of nano-sized biocarbons, i.e., hydrophobicity and aromaticity, also positively correlated to CO2 adsorption. In general, it was found that BC700C exhibited superior selectivity of CO2 over N2, excellent recyclability (97.8%) after 6 consecutive adsorption–desorption cycles, suggesting the long-term practical potential. This strategy developed in the present work can provide a reference for future rational design of highly robust nanoporous biocarbons for CO2 capture applications.