Insights into mechanochemical assisted preparation of lignin-based N-doped porous carbon with tunable porosity and ultrahigh surface oxygen content for efficient CO2 capture

Biomass based porous carbon is a green and low-cost promising adsorbents for CO2 capture. However, most of these porous carbon were prepared under high-temperature and even multistep pyrolysis, and possessed poor textural properties and controllability. Here, enzymatic hydrolysis lignin (EHL) was used as carbon source to prepare O-rich N-doped porous carbon (LNPC) through a synthesis strategy that coupled hydrothermal treatment, mechanochemical assistance, and low-temperature activation for the first time. These porous carbon had the large specific surface areas (602.2 ∼ 2030.7 m2/g), high microporosity, and abundant ultramicroporous (Vultra) (0.19 cm3/g), as well as significant N doping and high O content (30.93 ∼ 55.32%). And the effects of the coupling method, activation temperature, and mechanical pressure and residence time on structural properties of lignin based porous carbon were investigated in detail. We found that the residence time had a good linear correlation for surface areas and micropore volume, respectively, meanwhile, the mechanical pressing exhibited better linear correlation for O content of LNPC, implied the preparation method had good controllability. LSY-P20-T20 prepared at activation temperature of 600 ℃ with the mechanical pressure and time (20 MPa and 20 min) had the highest Vultra, and high O content, and possessed the highest CO2 uptake (5.00 mmol/g). Subsequently, we found that the narrow micropore volume (with d < 1.0 nm) was the main factor for CO2 adsorption capacity, while O content showed more significant impact on determining CO2/N2 selectivity and isosteric heat of adsorption (Qst) of LNPCs. This work provided a new feasible approach for cost-effective carbon-based adsorbents for CO2 capture.