Department of Chemical and Biological Engineering, Northwestern University , Technological Institute E136, 2145 Sheridan Road, Evanston, Illinois 60208-3120, United States.
ACS Appl Mater Interfaces. 2014 Jan 8;6(1):289-97. doi: 10.1021/am404182m. Epub 2013 Dec 20.
Macrocyclic calixarene molecules were modified with functional groups of different polarities at the upper rim and subsequently grafted to mesoporous silica supports through a single Si atom linker. The resulting materials were characterized by thermogravimetric analysis, UV-visible spectroscopy, nitrogen physisorption, and solid-state NMR spectroscopy. Materials were then used to separate acetone, n-butanol, and ethanol from dilute aqueous solution, as may be useful in the recovery of fermentation-based biofuels. For the purpose of modeling batch adsorption isotherms, the materials were considered to have one strong adsorption site per calixarene molecule and a larger number of weak adsorption sites on the silica surface and external to the calixarene cavity. The magnitude of the net free energy change of adsorption varied from approximately 15 to 20 kJ/mol and was found to decrease as upper-rim calixarene functional groups became more electron-withdrawing. Adsorption appears to be driven by weak van der Waals interactions with the calixarene cavity and, particularly for butanol, minimizing contacts with solvent water. In addition to demonstrating potentially useful new sorbents, these materials provide some of the first experimental estimates of the energy of interaction between aqueous solutes and hydrophobic calixarenes, which have previously been inaccessible because of the insolubility of most nonionic calixarene species in water.
大环杯芳烃分子在上缘用不同极性的官能团进行修饰，然后通过单个 Si 原子键合连接到介孔硅载体上。所得材料通过热重分析、紫外-可见光谱、氮气物理吸附和固态 NMR 光谱进行了表征。然后，将这些材料用于从稀水溶液中分离丙酮、正丁醇和乙醇，这可能有助于发酵生物燃料的回收。为了对批量吸附等温线进行建模，认为每个杯芳烃分子具有一个强吸附位，并且在硅表面和杯芳烃腔外部具有更多的弱吸附位。吸附的净自由能变化幅度约为 15 至 20 kJ/mol，并且发现随着上缘杯芳烃官能团变得更具吸电子性而减小。吸附似乎是由与杯芳烃腔的弱范德华相互作用驱动的，特别是对于正丁醇，尽量减少与溶剂水的接触。除了展示潜在有用的新型吸附剂外，这些材料还提供了以前由于大多数非离子杯芳烃在水中的不溶性而无法获得的水相溶质与疏水性杯芳烃之间相互作用能的首批实验估计值之一。
