Lignin-based hierarchical porous biochar prepared from negative pressure pyrolysis enhanced CO2 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 CO2 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 m2 g−1), micropore volume (0.695 cm3 g-1) and lowest average pore size (1.81 nm) after acid washing for removing ash. The CO2 uptake of biochar reached as high as 159.42 mg g-1 due to excellent micropore structure of biochar. The Avrami model and Freundlich model fitted the adsorption process better, indicating the CO2 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 the CO2 and VOCs adsorption performance. Finally, high reusability of 83.9%-98.7% for CO2 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.