Yang Wenshen, Liu Xiufeng, Zhang Liu, Zhang Baoquan
School of Chemical Engineering and Technology, State Key Laboratory of Chemical Engineering, Tianjin University, Tianjin 300072, China.
Langmuir. 2009 Feb 17;25(4):2271-7. doi: 10.1021/la803514g.
The synthesis and microstructure manipulation of SAPO-5 films on porous alpha-Al2O3 substrates (samples F-1 through F-6) have been studied with the main focus on the effect of Si content, substrate setting, and the structure-directing function of a precoated chitosan thin layer. Without the chitosan layer, the supported SAPO-5 film synthesized under traditional heating is not continuous with either pin holes or crystal boundaries. The preferentially c-oriented SAPO-5 top-layer over a closely packed layer of SAPO-5 crystals was synthesized on the porous alpha-Al2O3 substrate using the chitosan thin layer as the structure-directing matrix. According to the characterization using scanning electron microscopy (SEM) and X-ray diffraction (XRD), the thickness of the c-oriented SAPO-5 top-layer is changed from 1.5 to 10 microm while keeping the thickness of the packed layer of SAPO-5 crystals almost unchanged. Electron probe microanalysis (EPMA) demonstrates that P, Al, Si, and C contents within the two-layer film are uniformly distributed. The percentage of c-oriented crystal grains in the resulting SAPO-5 films evaluated by using the pole-figure analysis is over 70% (71.2% for F-4, 74.2% for F-5, and 75.9% for F-6). On the basis of our experimental observations, it has been indicated that the gradual dissolution of chitosan in the acid precursor solution is accompanied with the formation of the SAPO-5 top-layer and the packed layer of SAPO-5 crystals in the hydrothermal reaction, and both the surface and the entire body of the chitosan layer serve as a three-dimensional structure-directing matrix.
对多孔α-Al₂O₃衬底（样品F-1至F-6）上SAPO-5薄膜的合成及微观结构调控进行了研究，主要聚焦于硅含量、衬底设置以及预涂壳聚糖薄层的结构导向功能的影响。在没有壳聚糖层的情况下，传统加热合成的负载型SAPO-5薄膜不连续，存在针孔或晶界。以壳聚糖薄层为结构导向基质，在多孔α-Al₂O₃衬底上合成了在紧密堆积的SAPO-5晶体层之上优先c取向的SAPO-5顶层。根据扫描电子显微镜（SEM）和X射线衍射（XRD）表征，c取向的SAPO-5顶层厚度从1.5微米变化到10微米，而SAPO-5晶体紧密堆积层的厚度几乎不变。电子探针微分析（EPMA）表明两层薄膜内的P、Al、Si和C含量均匀分布。通过极图分析评估，所得SAPO-5薄膜中c取向晶粒的百分比超过70%（F-4为71.2%，F-5为74.2%，F-6为75.9%）。基于我们的实验观察，已表明壳聚糖在酸性前驱体溶液中的逐渐溶解伴随着水热反应中SAPO-5顶层和SAPO-5晶体紧密堆积层的形成，并且壳聚糖层的表面和整体都作为三维结构导向基质。
