Pore Development and Adsorption Mechanisms for CO2 Capture through Elaborate Precursor Regulation

Carbon capture, as a key component of carbon capture, utilization, and storage (CCUS), plays a vital role in climate change and environmental protection. Carbon-based adsorbents are the most promising adsorption materials for low cost and easily regenerated, which rely on well-developed pores to capture CO2. However, there are inconsistent conclusions about the micropore size suitable for CO2 capture. The conditions for micropore formation under comprehensive factors have not been explored in detail. Here, the microporous structure of coal-based porous carbon was studied by low-temperature gas adsorption and synchrotron radiation-induced small-angle X-ray (SAXS) technology. Combined with the parameters of the isothermal adsorption model, the pore characteristics and adsorption characteristics were explored. The results show that the order of precursor influence on the microporous structure is activator type > activation proportion > pretreatment scheme > precursor types. The uneven arrangement of aromatic structures is more difficult to be activated than large and multilayer aromatic structures. The ability of cesium (Cs) to produce ultramicropores (<0.5 nm) is 37% higher than that of K, through discretely distributed ion interlayer activation and high reactivity. In terms of CO2 adsorption, the highest physical adsorption of porous carbon can reach 3.89 mmol/g (25 °C, 1 bar). The adsorption of the slit pore within 0.4–0.5 nm has the highest adsorption potential energy, which determines the physical adsorption capacity. In addition, with the increase of the pore size, the slit pore transforms into complex structures such as cylindrical and composite holes arranged among aromatic layers. Interestingly, the vacancy defects in the cylindrical hole or dislocation defects in composite pores (branch pores) increase the adsorption sites, which offset the weakening of the adsorption potential energy. Therefore, the cumulative pore volume in the range of 0.6–0.7 nm has the best statistical significance for overall CO2 adsorption prediction. This study clarifies the influence of pore topology caused by the crystallite arrangement and adsorption sites generated by defects on CO2 adsorption. More importantly, the pore design in the study is the core strategy to improve the CO2 selectivity and adsorption capacity of porous carbon. Moreover, multilevel pores provide ideas for the development of porous carbon composites, which lays the foundation for low-cost carbon capture and high-value-added utilization of carbon materials.