Structural regulation of ultra-microporous biomass-derived carbon materials induced by molten salt synergistic activation and its application in CO2 capture

The development of high-performance biomass-based carbon materials for CO2 adsorption is considered to be a promising strategy due to the advantages of renewable raw materials, energy efficiency, and easy operation. Herein, two molten salt systems, KHCO3-KCl and K2CO3-KCl, are used to prepare corn stalk-based porous carbon. The KHAC-KCl with ultra-high specific surface area of 2512 m2/g and rich ultra-microporous structure is successfully prepared when the KHCO3-KCl system is used. Series characterization methods are used to explore the influence of molten salt systems on the physicochemical properties of materials. It is found that both molten salt systems can significantly increase the oxygen-containing functional groups in carbon materials. The difference is that the KHCO3-KCl system can significantly increase the ultra-micropore proportion (48.6 % to 66.2 %) and the specific surface area (1551 m2/g to 2512 m2/g), while the K2CO3-KCl system cannot. Mechanism study shows that the KHCO3-KCl system can significantly affect the interaction between the pyrolysis reactions of the three components of lignocellulose, thereby regulating the physical and chemical properties of the material to achieve synergistic activation. CO2 adsorption studies show that KHAC-KCl exhibits excellent CO2 adsorption properties, reaching a high adsorption capacity of 7.3 mmol/g and 3.6 mmol/g at 273 K and 298 K, respectively. Furthermore, the material exhibits suitable Qst value (20–40 KJ/mol), high CO2/N2 selectivity (35 at 273 K and 22 at 298 K) and excellent cycling stability. This work can provide guidance for the preparation of low-cost and efficient CO2 adsorbents from renewable biomass.