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

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 (V_micropore) 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 V_micropore 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.