Hou Kun, Shen Li, Li Fuyou, Bian Zuqiang, Huang Chunhui
State Key Laboratory of Rare Earth Material Chemistry and Applications, Peking University, Beijing 100871, P. R. China.
J Phys Chem B. 2006 May 18;110(19):9452-60. doi: 10.1021/jp054873x.
In this paper, we developed a facile way to synthesize highly ordered optically active MCM-48 at room temperature, by using mixtures of hemicyanine dye N-alkyl-2-[p-(N,N-diethylamino)-o-(alkyloxy)]pyridinium bromide (denoted as o-CnPOCm, Scheme 1) and cetyltrimethylammonium bromide (CTAB) as the structure-directing agents. The mesoporous materials were systematically characterized by powder X-ray diffraction, transmission electron microscopy, nitrogen sorption, and thermogravimetry. The resultant MCM-48 exhibits unusually high thermal stability. For example, in the case of o-C(2)POC(14), it can retain its cubic structure even under calcinations at 900 degrees C for 5 h, although the pore size is shifted to the micropore region because of shrinkage of the framework. The typical surface area and pore volume are 980 m(2)/g and 0.44 cm(3)/g, respectively, for the powder calcined under such a high temperature. This is the first report of room-temperature synthesis of MCM-48 with such good thermal stability using cationic-cationic mixed surfactant as the structure-directing agent. The fluorescence lifetimes of the as-synthesized mesostructured MCM-48 were also measured, and the result showed that the incorporated dye molecules have a 1 order of magnitude longer lifetime than that of free species in solution, showing that the hemicyanine dye molecules are well dispersed within the CTAB surfactant matrix. Furthermore, we compared eight other dye congeners (Scheme 1) to fully investigate the mesophase resulting from the dye-CTAB system. The results show that, upon addition of the dye surfactant to the starting mixtures, the mesostructured silica undergoes an intrinsic phase-transition process; however, specific dye geometry is required to obtain MCM-48 at room temperature. Those functionalities as well as the designed synthesis of this novel mesostructured MCM-48 material promise a bright future in multifunctional optical and electric nano- and microdevices (e.g., waveguides, laser, light-emitting diodes, etc.) and also shed light on the self-assembly behavior in complex colloidal system.
在本文中,我们开发了一种简便的方法,通过使用半菁染料N-烷基-2-[对-(N,N-二乙氨基)-邻-(烷氧基)]吡啶溴化物(表示为o-CnPOCm,方案1)和十六烷基三甲基溴化铵(CTAB)的混合物作为结构导向剂,在室温下合成高度有序的光学活性MCM-48。通过粉末X射线衍射、透射电子显微镜、氮气吸附和热重分析对介孔材料进行了系统表征。所得的MCM-48表现出异常高的热稳定性。例如,在o-C(2)POC(14)的情况下,即使在900℃煅烧5小时,它仍能保持其立方结构,尽管由于骨架收缩,孔径转移到了微孔区域。对于在如此高温下煅烧的粉末,典型的比表面积和孔体积分别为980 m²/g和0.44 cm³/g。这是首次报道使用阳离子-阳离子混合表面活性剂作为结构导向剂在室温下合成具有如此良好热稳定性的MCM-48。还测量了合成的介孔结构MCM-48的荧光寿命,结果表明,掺入的染料分子的寿命比溶液中游离物种的寿命长1个数量级,这表明半菁染料分子在CTAB表面活性剂基质中分散良好。此外,我们比较了其他八种染料同系物(方案1),以全面研究染料-CTAB系统产生的中间相。结果表明,在起始混合物中加入染料表面活性剂后,介孔结构的二氧化硅会经历一个内在的相变过程;然而,需要特定的染料几何结构才能在室温下获得MCM-48。这些功能以及这种新型介孔结构MCM-48材料的设计合成在多功能光学和电学纳米及微器件(如波导、激光器、发光二极管等)方面有着光明的前景,也为复杂胶体系统中的自组装行为提供了启示。