A novel ZIF-8@cellulose composite monolithic carbon via a facile template-free strategy for selective and efficient CO2 adsorption

In this work, hierarchically ZIF-8@Cellulose acetate composite monolithic carbon (ZCMC) was fabricated for the first time by combining a template-free thermally induced phase separation (TIPS) method with in-situ ZIF-8 crystals doping followed by KOH activation. By altering ZIF-8 content and activation temperature, a series of ZCMC samples were prepared in order to analyze the effect of pore structure and surface chemical characteristics on CO2 adsorption. The optimal sample of 20-ZCMC-800 exhibited the largest CO2 uptake of 7.30 (0 °C) and 4.26 mmol/g (25 °C) at 1 bar, which was competitive with the majority of the reported porous carbons. Additionally, the CO2 adsorption capacity after 10 cycles still remained at 96 % of its initial value and the ideal adsorption solution theory (IAST) CO2/N2 selectivity was 21.31 at 25 °C, indicating excellent recyclability and good selectivity. Furthermore, it was found that the CO2 adsorption capacity was considered to be linear relationship with micropore but independent on BET specific surface area. The contributions of N-containing functional groups and ZnO crystals created from ZIF-8 pyrolysis at high temperature for CO2 adsorption were thoroughly discussed under density functional theory (DFT) and grand canonical Monte Carlo (GCMC). It was found that pyrrole-N group contributed significantly to CO2 adsorption by hydrogen bonding and Lewis acid-base interactions, while the ZnO crystals displayed the strong interaction with CO2 by the chemisorption process. The CO2 adsorption performance of ZCMC was mostly determined by the joint effect of micropore structure and surface chemical compositions. The thermodynamic parameters of Qst ranged from 23.03 to 33.23 kJ/mol, revealing the CO2 adsorption still belonged to the scope of physisorption process. More importantly, the novel and feasible strategy presented herein is expected to provide an innovative approach for the design and discovery of ZIFs-based composite carbon materials for efficiently CO2 adsorption.