Preparation and evaluation of fine-tuned micropore biochar by lignin impregnation for CO2 and VOCs adsorption

[Display omitted] •Lignin impregnation optimized the microporous structure of biochar.•Lignin impregnated biochar enhanced CO2 capture by 1.98–22.48%.•Biochar maintained high reusability of 93.98%-98.21% after 10 cycles.•Lignin impregnated biochar is a promising adsorbent for CO2 and VOCs. The pore structure of adsorbent plays a critical role during the CO2 and volatile organic compounds (VOCs) adsorption. To improve the adsorption performance, fine-tuned micropore biochar was prepared by impregnation using sodium lignosulfonate as precursor. And the impregnated biochar was characterized and used as adsorbent to adsorb CO2 and VOCs (benzene and acetone). The results showed that the specific surface area (SSA) and micropore volume (Vmicropore) of impregnated biochar increased 3.27 and 5.02 times, which enhanced the CO2 adsorption amount obviously (77.02–102.88 mg/g). The pore structure of biochar was critical to CO2 capture, and high SSA, large Vmicropore and narrow aperture were benefits for the adsorption. Both Avrami fractional model and Freundlich model fitted the adsorption better, indicating the CO2 adsorption on impregnated biochar was multilayer adsorption and determined by both physical and chemical mechanisms. The adsorption was overwhelming exothermic process, thus increasing the temperature from 0 ℃ to 65 ℃ would decrease the adsorption amount by 74.22%-79.40%. High reusability (93.98%-98.21%) after 10 times adsorption-desorption cycles acknowledged the biochar was promising CO2 adsorbents. In addition, the impregnated biochar exhibited excellent VOCs adsorption performance, with the adsorption amount being 31.35–61.14 mg/g and 44.67–80.99 mg/g for benzene and acetone, respectively. All the results showed lignin impregnated biochar is a promising adsorbent for CO2 capture and pollution adsorption.