Porous carbonaceous materials such as activated carbons and carbon molecular sieves are widely used as solid adsorbents because of their wide availability, high surface area, excellent thermal and chemical stability, and tunable porosity and surface functionality. They have thus been studied extensively as alternatives to organic amine-based liquid sorbents used industrially for post-combustion CO2 capture. Relatively weak interaction of CO2 with the carbon surface, resulting from physical adsorption, allows a good regenerability for the carbon adsorbents. However, it also causes a low CO2 capacity and CO2/N2 selectivity at low CO2 pressure (e.g., 0.1 bar) and high adsorption temperature (e.g., 75 °C) that are typical conditions for CO2 capture from flue gas. To enhance CO2 affinity and consequently its adsorption capacity and selectivity, nitrogen- containing functional groups are often incorporated into the framework of porous carbons by various strategies, e.g., using nitrogen-containing compounds as carbon precursors, post-synthesis nitrogen-doping with gaseous NH3, covalently grafting nitrogen functional groups on the carbon surface, and physical impregnation with specific compounds containing desired nitrogen groups. The former two methods can not have a fine control on the formed nitrogen groups, majorly producing pyridinic and pyrrolic nitrogen species that have a limited increase in the CO2 affinity because of their relatively weak basicity. The latter two methods allow a precise control on the incorporated nitrogen groups in molecular level, making it possible to investigate fundamental relationship between the structure and function of the adsorption sites. Besides, pore structure (e.g., pore diameter and volume) and surface composition of porous carbons are also expected to have a significant effect on the structure and stability of the incorporated functional groups, thus influencing their CO2 adsorption performance.
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机译：由于其可用性，高表面积，优异的热和化学稳定性，以及可调谐孔隙率和表面功能，多孔碳质材料如活性炭和碳分子筛，诸如活性炭和碳分子筛网的固体吸附剂。因此，它们已经广泛地研究了工业上用于燃烧二氧化碳捕获的有机胺基液体吸附剂的替代品。 CO 2与物理吸附引起的碳表面相对较弱的CO2相互作用，允许碳吸附剂的良好再生性。然而，它还在低CO 2压力（例如，0.1巴）和高吸附温度（例如，75℃）下导致低CO 2容量和CO 2 / N 2选择性，这是来自烟道气的CO2捕获的典型条件。提高CO 2亲和力并因此通过各种策略掺入含氮含量和选择性，含氮官能团通过各种策略掺入多孔碳的骨架中，例如，使用含氮化合物作为碳前体，合成后氮气掺杂与气态NH3的氮气掺杂，共价接种碳表面上的氮官能团，与含有所需氮基团的特异性化合物的物理浸渍。前两种方法不能对所形成的氮基团具有细微控制，主要产生吡啶和吡咯的氮物质，其由于其相对较弱的碱性而具有有限的CO 2亲和力。后两种方法允许在分子水平上对掺入的氮基团进行精确控制，使得可以研究吸附位点的结构和功能之间的基本关系。此外，还预期孔结构（例如，孔径和体积）和多孔碳的表面组成对掺入的官能团的结构和稳定性产生显着影响，从而影响其CO 2吸附性能。
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