Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden.
Langmuir. 2011 Sep 6;27(17):11118-28. doi: 10.1021/la202033p. Epub 2011 Aug 9.
We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO(2) than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO(2) and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO(2) was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO(2) under dry conditions. Significant amounts of physisorbed, linear CO(2) were detected at relatively high partial pressures of CO(2), such that they could adsorb only after the reactive amine groups were consumed.
我们研究了平衡吸附和吸收动力学，并确定了在二氧化碳吸附到胺改性硅胶上时形成的分子种类。双连续硅石（AMS-6 和 MCM-48）通过（3-氨丙基）三乙氧基硅烷或（3-氨丙基）甲基二乙氧基硅烷进行后合成修饰，并且胺改性 AMS-6 比胺改性 MCM-48 吸附更多的 CO(2)。通过原位傅里叶变换红外光谱，我们表明胺基团与 CO(2)反应，并在干燥和潮湿条件下形成氨基甲酸铵离子对和氨基甲酸。氨基甲酸由氢键稳定，并且氨基甲酸铵离子对在具有高密度胺基团的吸附剂上优先形成。在干燥条件下，通过缩合氨基甲酸和硅醇基团，缓慢形成硅丙基氨基甲酸酯。具有高胺含量的样品中形成的氨基甲酸铵离子对与硅丙基氨基甲酸酯的比例高于具有低胺含量的样品。在干燥或潮湿条件下均未形成碳酸氢盐或碳酸盐。在水存在下，CO(2)的吸收得到增强，这可以通过在这些条件下观察到的额外胺基团的释放以及相关的氨基甲酸铵离子对的形成来合理化。在干燥条件下吸附 CO(2)时，观察到第四个不可逆形成的部分存在明显证据。在 CO(2)的相对高分压下，检测到大量物理吸附的线性 CO(2)，使得它们只能在反应性胺基团被消耗后才能吸附。
