活性炭表面氮氧官能团对CO2吸附的微孔效应及吸附行为耦合影响研究

This study focuses on the design and preparation of activated carbon doped with nitrogen- and oxygen-containing functional groups for CO2 separation via functional adsorption. Through controlling the activation and carbonization conditions, the regulation of the pore size distribution of activated carbon will be achieved. Besides, the static and dynamic adsorption properties of CO2 as well as the adsorption heat will be analyzed, and the influence of single and coexisting nitrogen/oxygen functional groups correlated with the pore structure of activated carbon on its adsorption behaviors will be investigated both qualitatively and quantitatively. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), inelastic neutron scattering (INS), Raman spectroscopy (RS), and X-ray absorption fine structure spectroscopy (XAFS)will be employed to characterize the interaction between the active sites of surface functional groups on activated carbon and guest molecules as well as their state changes before and after adsorption to further investigate the micropore effect of nitrogen- and oxygen-containing functional groups on CO2 adsorption and the mechanism involved. Moreover, the microcosmic mechanism of CO2 adsorption on doped activated carbon model will be studied using density functional theory (DFT) and grand canonical Monte Carlo simulations (GCMC). Parameters like the adsorption capacity, the adsorption potential energy, the bond length between functional groups and CO2 molecules, charge transfer and electronic structure will be calculated for activated carbon with or without functional groups, and their variation will be discussed. Therefore, further theoretical verification and explanations regarding the micropore effect of nitrogen- and oxygen-containing functional groups and their synergistic effect mechanism will be provided from the perspective of quantum chemistry. The research results will provide theoretical and technical basis for the design, controllable preparation and application of functionalized adsorbent materials for CO2 adsorption.

基于吸附分离CO2目的，通过对活性炭孔径分布与表面基团的调控，设计制备氮氧基团掺杂的功能化活性炭。比较分析其CO2静态与动态吸附性能，及吸附热的变化规律，定性定量地从单独和共存氮氧官能团，关联孔结构的角度上探讨它们对吸附行为的影响。应用XPS、FTIR、NMR、INS、RS、XAFS等技术表征活性炭吸附前后表面官能团活性位与客体分子之间的相互作用及其状态变化，进一步探讨氮氧基团在CO2吸附时的微孔效应及其作用机制；运用量子化学中的密度泛函理论和蒙特卡洛理论，研究CO2在活性炭掺杂模型上的微观吸附机理。探究基团负载前后CO2在活性炭上的吸附量，吸附势能，基团和客体分子作用键长，电荷转移，电子结构等参数变化规律。对活性炭中N/O基团的微孔效应，及其协同影响机理从量子化学角度上进行进一步理论验证和诠释。研究成果将对有CO2功能化吸附材料设计，可控制备，及其应用提供理论和技术支撑。

大量的温室气体被排放到大气中，由此所带来的气候与环境问题持续恶化，绿色低碳的可持续发展理念已成为国际共识。为了确保“双碳”战略目标的顺利实现，如何减少和控制CO2的排放成为了一个重要的研究课题。本研究项目旨在针对CO2吸附分离技术，系统的揭示CO2在多孔炭上的吸附基本作用原理，理清多孔炭表面官能团、孔径分布对CO2吸附行为的耦合影响，为我国CO2捕集技术的发展提供扎实的理论基础。本研究通过制备一系列独特孔隙结构和表面氮氧官能团掺杂的高性能CO2吸附剂，利用分子模拟技术计算分析CO2吸附行为，实现吸附过程的可视化，详细探讨了吸附过程中的基本原理，我们发现CO2在多孔炭表面上的吸附可看作是气相CO2分子转移吸附剂内部空间的过程，故吸附剂的孔隙结构对吸附过程有重要影响。本研究系统证明了在常规吸附条件下(25℃，1bar) CO2在多孔炭上的吸附容量主要取决于孔径小于0.7 nm的窄微孔含量，与比表面积、总孔体积等孔结构参数无直接关联。我们还发现虽然2~50 nm 范围内的中孔不能够提供吸附点位，但是可作为CO2分子的传输通道，减少从界面到窄微孔的传输阻力。相关的研究成果发表在Carbon和ACS Sustainable Chemistry & Engineering 等权威期刊；同时吸附的过程是依靠CO2分子与吸附界面间的范德华作用力进行的，即可以理解为CO2与界面之间的作用力大于CO2分子间作用力。本研究发现引入的氮氧等官能团可以通过静电作用、氢键作用或酸碱作用提升多孔炭对CO2分子的亲和力，并提高CO2的吸附分离性能，相关的研究成果发表在Carbon、CEJ、Applied Surface Science 、Fuel、Energy & Fuels、Microporous and Mesoporous Materials等权威期刊；我们通过量化评估二者的吸附性能，以氮-氧共掺杂为例，粗略估计出孔结构和官能团的贡献率分别为62%和38%。我们也进一步阐述了官能团的引入对CO2吸附适宜孔径的影响，结果表明当孔径大于0.35 nm时，掺杂才具有明显的效果。本研究还发现了表面官能团和孔径之间对于CO2的选择性吸附也存在一定的协同作用。相关的研究成果发表在CEJ 、Fuel、Applied Surface Science等权威期刊。