Novel post-treatment of ultrasound assisting with acid washing enhance lignin-based biochar for CO2 capture: Adsorption performance and mechanism

Lignin biochar was acid washed and then treated with ultrasound at different time durations to improve its sorption of CO2. Raman, XRD, FTIR spectrum and thermostability test confirmed that this post-treatment method cleaned the surface of the pristine biochar and enlarged its porosity by opening pores blocked by ash and organic components. As a result, specific surface areas and micropore volumes of post-treated biochars increased 7.3–8.6 and 8.2–8.8 times, respectively, while their ash contents decreased from 76.31% to 6.12%-13.63%. More importantly, CO2 uptake of the post-treated biochar reached 178.75 mg/g, which could be ascribed to developed micropore structure. Adsorption kinetic and isotherm analyses showed that CO2 was adsorbed onto the post-treated biochar mainly through multilayer physical adsorption. The high adsorption capacity, terrific reusability (99.46% after 10 cycles) and excellent selectivity of the post-treated biochar suggest that acid washing assisted with ultrasonic treatment is a promising modification technique for biochar, promoting its engineering application in CO2 capture.