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

Abstract

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 degrees C (sample label appended with "KC"). The pristine and activated biochars were evaluated in terms of physicochemical properties, CO2 adsorption capacity at 25 degrees C, adsorption kinetics, and regeneration ability. The WCMK biochar exhibited the highest CO2 adsorption capacity (2.92 mol/kg) with highest surface area (1408 m(2)/g), micropore area (690.18 m(2)/g), and micropore volume (0.36 cm(3)/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 N-2, fast adsorption and excellent regeneration abilities over 10 consecutive adsorption-desorption cycles. Activation of biochar, either with KOH or KOH thorn 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 thorn CO2 activation will be promising options for enhancing CO2 adsorption capacity of pristine biochar irrespective of the feedstock type.