Enhancing CO₂ adsorption performance of porous nitrogen-doped carbon materials derived from ZIFs: Insights into pore structure and surface chemistry

In this work, a novel approach for the synthesis of porous nitrogen-doped carbon materials (PNCs) with a highly microporous structure through low-temperature carbonization of ZIF-8 and ZIF-61 assisted by KCl and NaCl is reported. The introduction of KCl and NaCl during the carbonization process can adjust the surface chemical properties and pore structures of the PNCs derived from ZIF-8 and ZIF-61. The effects of pore structures and surface groups of PNCs on CO2 adsorption capacity are explored. Results show that the cumulative pore volume in the pore size range of 5-7 & Aring; (V5-7 & Aring;), pyrrolic-N content, and COOH content exert favorable influences on CO2 adsorption capacity at 1 bar and 25 degrees C. Notably, V5-7 & Aring; is the key factor in enhancing the CO2 adsorption capacity of PNCs. Moreover, the degree of contribution of V5-7 & Aring;, V7-9 & Aring;, pyrrolic-N content, pyridinic-N content, and COOH content to the CO2 adsorption capacity is evaluated by establishing a multiple linear regression equation, and the results show that on the basis of PNCs possessing optimum pore structures (V5-7 & Aring; > 0.10 cm(3)/g), pyrrolic-N content in PNCs becoming the dominant contributor to CO2 adsorption capacity. The as-prepared 2CN8-KCl-600 sample demonstrates high CO2 adsorption capacity, which reaches 4.61 mmol/g at 25 degrees C and 6.70 mmol/g at 0 degrees C (1 bar), respectively. Besides, 2CN8-KCl-600 exhibits high CO2/N-2 selectivity (39.5) under the typical flue gas scenario and high cycling stability. This work offers a novel perspective on preparing highly efficient carbon-based adsorbents for CO2 and provides the fundamental understanding for enhanced CO2 adsorption performance on PNCs.