Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden.
Langmuir. 2011 Apr 5;27(7):3822-34. doi: 10.1021/la104629m. Epub 2011 Mar 1.
Mesoporous silica particles (Davisil) were functionalized with aminopropyltriethoxysilane (APTES) in a fractional factorial design with 19 different synthesis and uptake experiments. The number of amino groups and the uptake of CO(2) were optimized in a 2(V)(5-1) design. Most important to functionalization was the amount of water present during synthesis, the reaction time, and pretreating the silica with a mineral acid; certain two-way interactions were shown to be statistically significant as well. Modifications performed at 110 or 80 °C showed no significant differences concerning amine content or uptake of CO(2). Properly choosing center points for the discrete variables is problematic and is somewhat related to the lack of fit with respect to CO(2) uptake; the regression was good. Solid-state (29)Si NMR showed that the APTES was mainly fully condensed. Specific surface areas did not correlate with the number of n-propylamine groups on the silica, which is indicative of differential levels of heterogeneity in the coverage of propylamines. The uptake of CO(2) and N(2) was measured from -20 to 70 °C and from 0 to 1 bar and parametrized by the Freundlich isotherm. Amine-modified silica adsorbed significant amounts of CO(2), especially at the low partial pressure, which is important for CO(2) capture from flue gas. At such pressures, samples with a high density of amine (4 amines/nm(2)) showed a much higher uptake of CO(2) than did those with densities of ∼2-3 amines/nm(2), reflecting differential tendencies to form propylammonium-propylcarbamate ion pairs; these require close proximity among amine groups to form. Water affected the uptake of carbon dioxide in different ways. Certain samples took up more moist CO(2) gas than dry CO(2), and others took up less moist CO(2) than dry CO(2), which is indicative of differential tendencies toward water adsorption. We conclude that experimental design is a time-efficient approach to the functionalization of silica with propylamine groups.
介孔硅粒子（Davisil）经氨丙基三乙氧基硅烷（APTES）功能化，采用 19 次不同的合成和吸收实验进行部分因子设计。在 2(V)(5-1)设计中优化了氨基数量和 CO(2)的吸收。对功能化最重要的是合成过程中存在的水量、反应时间以及用矿物酸预处理二氧化硅；某些双向相互作用也表现出具有统计学意义。在 110 或 80°C 下进行的修饰在胺含量或 CO(2)吸收方面没有显示出显著差异。对于离散变量选择合适的中心点是有问题的，并且与 CO(2)吸收的拟合不良有些相关；回归是良好的。固态（29）Si NMR 表明 APTES 主要完全缩合。比表面积与二氧化硅上的正丙胺基团数量没有相关性，这表明丙胺覆盖率存在不同程度的异质性。在-20 至 70°C 和 0 至 1 巴的范围内测量了 CO(2)和 N(2)的吸收，并通过 Freundlich 等温线进行了参数化。改性硅胶吸附了大量的 CO(2)，尤其是在低分压下，这对于从烟道气中捕获 CO(2)很重要。在这样的压力下，密度高的胺（4 个胺/nm(2)）的样品显示出比密度约为 2-3 个胺/nm(2)的样品更高的 CO(2)吸收，这反映了形成丙基铵-丙基氨基甲酸酯离子对的不同趋势；这些需要胺基团之间的近距离才能形成。水以不同的方式影响二氧化碳的吸收。某些样品吸收的湿 CO(2)气体比干 CO(2)多，而其他样品吸收的湿 CO(2)气体比干 CO(2)少，这表明对水吸附的不同趋势。我们得出的结论是，实验设计是一种高效的方法，可以用丙胺基团对硅胶进行功能化。
