MFI沸石具有規則的孔道結構及良好的化學與機械穩定性,由於方向性沸石膜在科 學上具有潛在的應用價值,尤其b軸直孔道朝上可以控制通過分子大小的b方向性,廣泛 應用於石油化工的膜分離、觸媒催化及吸附。超薄連續沸石膜的發展對於新興領域的應 用極為重要,如半導體工業製程低介電絕緣材料、光學抗反射層塗覆及航太鋁合金材料 的抗腐蝕層,若能開發超薄b方向性MFI沸石膜有助於新興領域的應用擴展。
本研究提出一種基於局限空間溶解與再結晶(confined space dissolution and recrystallization)程序的蒸汽輔助平面成長法,將預塗覆b軸向的沸石微晶單層 (microcrystal monolayer),精確控制結構引導劑TPAOH的表面劑量,在飽和蒸汽條件下, 矽晶片表面溶出的矽源供微晶結晶相互成長而融合,得到超薄(100~500 nm) b方向的MFI 沸石連續膜。相較於其他合成方法,本方法能有效抑制沸石微晶非方向或雙晶成長,解 決膜厚增加喪失方向性的缺點,合成的沸石膜具有可靠度高與高再現性等優點。
本文首先比較三種微晶層組裝方法,將微米與次微米的MFI微晶組裝於不同材質與 類型的基板,以製備b軸向的晶種層,結果顯示直接塗覆法對於組裝晶種層覆蓋率最高, 為最有效率的組裝方法。基板的表面性質對於組裝晶種層空隙率有著重要的影響,濺鍍 Pt膜的微晶層組裝,可得到有次序排列與整齊堆積,覆蓋率高達90 %的晶種層。
MFI微晶層組裝於矽晶片基板的蒸汽輔助成長特性研究,針對微晶層特性、蒸氣反 應溫度、蒸汽含水分及TPAOH表面劑量及有機鹼種類等影響MFI沸石膜成長的重要參數 進行探討。在蒸汽輔助平面成長條件下,以0.75×0.35×1.15μm3組裝於矽晶片的b方向 MFI微晶層,滴覆2 ug/cm2的TPAOH作為結構引導劑,在185°C飽和蒸汽反應8小時,得 到膜厚500 nm的b方向MFI連續膜。以TPAOH有機鹼合成MFI沸石膜的晶體為六角形外, 其他有機模板均為矩形形貌。文中提出蒸汽輔助平面成長的成長模式,說明預塗覆於矽 晶片b方性微晶層在飽和蒸汽條件下,高溫鹼性環境提供微晶間隙侷限空間進行溶解-再 結晶程序,微晶沿矽晶片平面成長,形成b方向MFI沸石膜,此一方法提供合成沸石膜膜 厚、方向性及沸石形貌等微結構可調控的成長模式。
MFI微晶層直接塗覆於不同材質(矽晶片、石英及玻璃)與類型基材蒸汽輔助成長特 性的研究,探討基材表面蒸汽輔助成長過程,溶出物質對於合成MFI沸石膜微結構的影 響,利用MFI沸石膜與石英基材結合強度的特性,提供MFI沸石膜轉移至其他基板的可 行性。在矽晶片基材濺鍍Pt膜與塗覆有機犧牲層,探討飽和蒸汽鹼性環境,矽晶片表面 溶出的矽源擴散至微晶層,完全為Pt膜阻隔與有機犧牲層減緩,對於沸石膜成長特性的 影響,最後,利用有機高分子犧牲層可溶於水的特性,應用於發展無支撐MFI沸石膜合 成方法。;Zeolite films could find applications in wide range of fields such as selective membranes, catalysis and adsorption due to their well-defined unique pore structures as well as high thermal and chemical stability. In addition, MFI zeolite thin films exhibit excellent corrosion resistance, low framework density, and high mechanical strength. Recently, strong attention has been transferred to the synthesis of high quality coatings that may find application in many different industrial fields such ascorrosion-resistant coatings for aerospace alloys, low-k layers for computer chips  and anti-reflective coating in optical devices . A number of novel applications of zeolites depend on the ability to create thin, adhesive films on various substrates. For such uses, the preparation of continuous MFI films with defined crystal morphology, film thickness, and preferential crystal orientation is highly desired.
A simple method based on confined space dissolution and recrystallization has been developed to synthesize continuous b-oriented MFI zeolite films on flat substrates, through the steaming of pre-coated microcrystal monolayer. The b-oriented MFI monolayer dosed with alkyl ammonium hydroxide and was then subjected to steam under high temperature to initiate the dissolution of seed crystals and crystallization at the gaps between the
microcrystals, which grow laterally and eventually form a continuous film.Comparison of two different synthesis methods, the advantages of CSDR method lie in the ease control of the thickness and crystal orientation while prohibit the incorporation of newly formed crystals.
Several silicalite-1 microcrystals were used as seeds to fabricate a close-packed b-oriented MFI monolayer by three assembly techniques, including interfacial-aided, dynamic interfacial and manual assembly. Seed crystals could be successfully assembled into a compact and highly b-oriented MFI monolayer on various substrates by manual assembly method. Surface characteristics of substrates have important influence on the fabrication of close-packed b-oriented MFI monolayer. It was found that the monolayer coverage about 90% could be obtained on the Pt deposition on Si-wafer by manual assembly.
The effects of synthesis parameters (i.e. the steaming temperature, the size of the seed crystals, the water content in the steam and the surface dosage of TPAOH) on the microstructure of MFI zeolite film were investigated in detail.The type of TAAOH significantly influenced the crystal morphology; TPAOH produced elongated hexagonal prisms, whereas all other TAAOHs led to rectangular crystals. On the MFI microcrystal monolayer, continuous and b-oriented MFI films can be obtained after steam assisted in-plane growth for 8 h at 185°C, leading to the formation of 350 nm-thick MFI zeolite film. Based on the film formation of MFI microcrystal monolayer, a confined space dissolution and recrystallization procedure was proposed to explain oriented MFI zeolite films onsubstrates
directlycould be favorable to the intergrowth of MFI zeolite crystals along thein-plane direction.
For comparison purposes, the steaming growth of pre-coated microcrystal monolayers also carried out using glass and quartz plate as film support. The dissolution of the quartz substrate is very limited under the steam reaction. Thus, MFI zeolite film could be readily detached from the quartz substrate, transferred and bonded onto target substrates. For the deposited Pt film substrate, the diffusion of Si from the Si-wafer into seed monolayer was completely prohibited. Since, the seed crystal itself was used as the SiO2 source for seed crystals growth, result in the formation rate for the silicalite-1 films slower than that the bare substrate. Finally, we report an approach to the fabrication of free-standing MFI zeolite films involves the use of a sacrificial layer, which was composed of soluble polymer and leaved the freestanding thin film behind by dissolving the sacrificial layer in water