Insight the CO2 adsorption onto biomass-pyrolysis derived char via experimental analysis coupled with DFT calculation

•Mechanism of CO2 adsorption on biomass derived carbon was explained using DFT methods.•Building the relationship between nucleophilicity and adsorption capacity of biochar.•Carboxyl and diketone groups are the most active O-containing sites.•TG-MS experiments proved the effect of nucleophilicity group of biochar on CO2 adsorption.