Lignin-impregnated biochar assisted with microwave irradiation for CO2 capture: adsorption performance and mechanism

Bamboo biochar was modified by lignin impregnation and microwave irradiation to enhance its performance for CO2 capture. The pore structure of lignin-impregnated biochar was significantly affected by the impregnation ratio. The maximum specific surface area of 377.32 m(2) g(-1) and micropore volume of 0.163 cm(3) g(-1) were observed on the biochar with an impregnation ratio of 1:20 (mass ratio of lignin to biochar). Lignin impregnation increased the CO2 adsorption capacity of biochar up to 134.46 mg g(-1). Correlation analysis confirmed the crucial role of biochar's pore structure in adsorption. The Avrami model fitted the CO2 capture curves well. The calculation of adsorption activation energy suggested that the adsorption process was dominated by physical mechanism assisted with partial chemical mechanism. Meanwhile, Langmuir isotherm analysis indicated that lignin impregnation transformed the larger pores of biochar into more uniform micropores, thereby making the adsorption process closer to monolayer adsorption. Both the high reusability (89.79-99.06%) after 10 successive cycles and the excellent CO2 selectivity in competitive adsorption confirmed that lignin-impregnated biochar is an outstanding adsorbent for CO2 capture. Highlights center dot Microwave energy absorbed by biochar carbonized the impregnated lignin to increase micropore structure. center dot CO2 uptake on lignin-impregnated biochar reached 134.46 mg g(-1) and was associated with micropore, alkalinity, and temperature. center dot CO2 adsorption on lignin-impregnated biochar was governed by physisorption with slight chemisorption. center dot Lignin-impregnated biochar demonstrated excellent reusability and selectivity in CO2 capture