厚度可控薄板形Silicalite-1的制备

通过精细调整控制合成条件, 在SiO₂-TPAOH-H₂O-NH₄F (TPAOH: 四丙基氢氧化铵)体系中制备出了厚度可控的薄板型Silicalite-1 分子筛材料, 并利用扫描电镜(SEM)、高分辨透射电镜(HRTEM)、粉末X射线衍射(XRD)及差热-热重分析(TG-DTA)对样品的结构信息、样品形貌及物理化学性质进行了表征. 研究表明, NH₄F浓度和反应体系pH 值对Silicalite-1 分子筛的形貌起着重要的导向作用. 随着NH₄F/SiO₂的摩尔比(n(NH₄F)/n(SiO₂))由0 增加到0.18, 分子筛形貌由交互生长的椭圆形变为板形, 其厚度也逐渐变薄; 当n(NH₄F)/n(SiO₂)=0.4 时, 厚度达到最薄. 继续增加NH₄F/SiO₂的摩尔比, 其厚度增加, 这是由于F^-提高了样品结晶度. HRTEM研究表明b轴垂直于平面, 由于在MFI 结构的材料中, b轴方向是其直孔道方向, 这种材料有利于客体分子的进出. 还研究了样品的热稳性, 所有样品在1100℃焙烧2 h后, 其形貌和结构不发生变化.

Synthesis of Plate Like Silicalite-1 with Controlled Thickness

In this study, plate like Silicalite-1 samples with controlled thickness were synthesized using a SiO₂-TPAOH-H₂O-NH₄F (TPAOH: tetrapropylammonium hydroxide) system by careful tuning of the synthetic parameters. Samples were fully characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and thermogravimetry-differential thermal analysis (TG-DTA). We confirmed that the concentration of NH₄F and pH of the initial gel played important roles in controlling sample morphology. The morphologies of the samples changed from ellipse to plate like shapes as the molar ratio of NH₄F to SiO₂ was increased from 0 to 0.18. In addition, the thickness of the plates was controlled by regulating the amount of NH₄F in the gel. The thickness of the sample decreased as the amount of NH₄F increased, and reached its minimum when the NH₄F/SiO₂ molar ratio reached 0.4. Further increase of the molar ratio of NH₄F/SiO₂ increased the thickness of the plates because of their improved crystallinity. In these plate like particles, the b axis was perpendicular to the plate, as confirmed by HRTEM, which implies that these materials could show good accessibility for guest molecules because the b axis is the straight channel in MFI structures. All of the plate like Silicalite-1 samples were highly stable and their morphologies were retained even after treatment at 1100℃.