摘要
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°C焙烧2h后,其形貌和结构不发生变化.
In this study, plate like Silicalite-1 samples with controlled thickness were synthesized using a SiO2-TPAOH-H20-NH,F （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 NH,F/SiO2 molar ratio reached 0.4. Further increase of the molar ratio of NH,F/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 ℃.
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
2013年第8期1809-1813,共5页
Acta Physico-Chimica Sinica
基金
supported by the National High Technology Research and Development Program of China(863)(2009AA064201)
National Sci-Tech Support Plan,China(2012BAE05B00)~~
