Sustainable gasification biochar as a high efficiency adsorbent for CO₂ capture: A facile method to designer biochar fabrication

Biochars can be a potential means of CO₂ capture if designed with hierarchical structures and suitable surface properties. Objective of this research was to assess the effectiveness of KOH activation and a combination of KOH and CO₂ activation for enhancing the CO₂ adsorption capacity of gasification biochar. Biochars were produced with either 100% wood chips (W) or a mixture of 70% wood chips and 30% chicken manure (WCM) through gasification, and then activated using either 1 M KOH (sample label appended with “K”) or 1 M KOH and 500 mL CO₂ min⁻¹ at 850 °C (sample label appended with “KC”). The pristine and activated biochars were evaluated in terms of physicochemical properties, CO₂ adsorption capacity at 25 °C, adsorption kinetics, and regeneration ability. The WCMK biochar exhibited the highest CO₂ adsorption capacity (2.92 mol/kg) with highest surface area (1408 m²/g), micropore area (690.18 m²/g), and micropore volume (0.36 cm³/g). WKC and WK showed comparable CO₂ adsorptions, both of which were lower than that of WCMK. Both WCMK and WKC showed considerable selectivity for CO₂ over N₂, fast adsorption and excellent regeneration abilities over 10 consecutive adsorption-desorption cycles. Activation of biochar, either with KOH or KOH + CO₂, enhanced its CO₂ adsorption capacity due to an increase in surface area and microporosity, irrespective of the feedstock type. However, hydrophobicity, and aromaticity of biochar and presence of hetero atoms (N and S) also positively influenced CO₂ adsorption capacity of biochar. Both KOH and KOH + CO₂ activation will be promising options for enhancing CO₂ adsorption capacity of pristine biochar irrespective of the feedstock type.