温度响应性超分子介孔材料的构筑及其吸附性能研究

Temperature-responsive supramolecular mesporous materials and their application in the adsorption

摘要:

设计合成了具有C₂-对称结构的芳香性螺旋桨两亲分子，通过核磁共振（NMR）、基质辅助飞行时间质谱（MALDI-TOF-MS）对分子结构进行表征，利用透射电子显微镜（TEM）、原子力显微镜（AFM）等表征组装形貌，并通过荧光显微镜证明其多孔结构．结果表明：这种螺旋桨分子在水溶液中自组装成大小在7~14 nm左右的超分子介孔球体，折叠的芳香性螺旋桨的组装给予超疏水性空腔（比表面积为250 m²/g），利用介孔的超疏水环境成功实现了对染料分子尼罗红（NR）和有机污染物双酚A（BPA）的吸附；升高温度时由于亲水嵌段的最低临界相转变温度（LCST）影响，折叠的螺旋桨分子转化为共平面，从而使介孔组装体转变为实心的纤维．利用这种结构转变，成功实现被吸附的污染物的释放，恢复吸附容量．这种可控的超分子介孔的构筑，为实现吸附剂的再生提供可靠的路线．

Abstract:

The propeller-shaped aromatic amphiphile consist of C2-symmetric aromatic core with two peripheral moieties containing tetra-phenyl carbazole and oligo （ethylene oxide） dendrons was synthesized. The structure of this molecule was characterized by 1H and 13C NMR spectroscopies and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy （MALDI-TOF MS） and were shown to be in full agreement with the structure presented. The self-assembly behavior of folded aromatic propeller in aqueous solution was further investigated through transmission electron microscopy （TEM） and atomic force microscopy （AFM）. Both TEM and AFM results indicated that this molecule self-assembled into hollow spheres and the diameter ranged from 7 nm to 14 nm. The mesoporosity of spheres was further confirmed by staining with Nile Red using fluorescence microscopy. The langmuir adsorption isotherm gave the surface area （S0） is close to 250 m²/g. The high surface area with aromatic environment of hollow spheres is also suitable for efficient to remove of organic pollutant bisphenol A （BPA）. The removal efficiency was found to be 90% for pollutant BPA. Notably， the folded architecture of propeller is observed to be flattened as heating， which was reflected in the red-shifted adsorption maximum and fluorescence quenching. This thermo-responsive switching can be explained by the fact that the oligo （ethylene oxide） dendrons exhibit a lower critical solution temperature（LCST）behavior in aqueous media. Above the LCST， the ethylene oxide dendrons are dehydrated， which requires a reduced interfacial area. To avoid the hydrophobic aromatic segments confront in aqueous environment， aromatic segments would be flattened to reduce hydrophobic area， driving the porous materials closed to forms solid fibers. Using the self-reorganization， the absorbed molecules were released from the porous materials. Thus， the supramolecular absorbents can be recovered through cooling after filtration.