Lignin-based hierarchical porous biochar prepared from negative pressure pyrolysis enhanced CO 2 and VOCs adsorption

Lignin -based biochar was obtained under different pressures (-0.1 MPa, 0 MPa and 0.1 MPa), then characterized and researched for CO 2 capture and volatile organic compounds (VOCs) adsorption. Negative pressure pyrolysis (-0.1 MPa) resulted in a hierarchical porous biochar with maximum specific surface area (1577.48 m 2 /g), micropore volume (0.695 cm 3 g -1 ) and the lowest average pore size (1.81 nm) after acid washing for removing ash. The CO 2 uptake of biochar reached as high as 159.42 mg g -1 due to its excellent micropore structure. The Avrami model and Freundlich model fitted the adsorption process better, indicating the CO 2 capture on biochar was mainly multilayer physical adsorption mechanisms. In addition, biochar was applied to adsorb benzene and showed maximum adsorption capacity of 470.03 mg g -1 . The linear correlation analysis confirmed that the porosity of biochar (specific surface area and micropore volume) was critical to CO 2 and VOCs adsorption performance. Finally, high reusability of 83.9 %-98.7 % for CO 2 capture and 97.5 %-98.7 % for benzene adsorption after 10 adsorption/desorption cycles were obtained. Therefore, negative pressure pyrolysis could be a promising method for hierarchical porous biochar production for treating various atmosphere pollutants.