介孔材料的合成、性能以及应用

自从1992年美孚公司成功地研究开发出介孔材料M41S后，由于其具有不同寻常的结构特点-比较均一的孔径（2-50nm）而且连续可调、较高的比表面积、较大的孔体积、孔的长程有序性以及较好的热稳定性等，具有巨大的潜在应用价值，立即引起了全世界的关注。目前，世界各国的研究主要集中在研究介孔材料的特性、形成机理、介孔材料形貌、结构和孔径的控制、新一代介孔材料的研究开发、介孔材料的改性以及介孔材料的应用等方面。本论文主要在介孔材料的合成、性能以及应用方面开展了研究。选用头尾都是憎水的三嵌段共聚物为模板制备出具有三维无序虫状孔道的介孔材料和以有孔氧化铝膜为模板制备了形态可控的介孔材料，即具有介孔结构高有序纳米管。采用一步法合成了介孔Ag／silica和Y2O3：Eu／silica材料，采用基底受限法制备了银和Y2O3：Eu纳米粒子，同时研究了Ag／silic。作为催化剂时催化性能。（1）在酸性条件下，利用头尾都是憎水的三嵌段共聚物SBS为模板、TEOS为硅源，分别选用丁酮和甲苯作选择性溶剂，通过微乳技术制备出具有三维无序虫状孔道的介孔硅材料。我们通过在SBS胶束溶液中加入TEOS／水的油水混合乳液使SBS胶束与TEOS／水混合乳液之间形成一个界面，从而使TEOS这个界面上完全水解而且生成的小分子硅齐聚物包附在SBS胶束的外表面。经过加热则使TEOS凝聚同时形成具有介孔结构的SBS／硅材料。最后，通过锻烧以移除SBS，从而得到介孔硅材料。在选用甲苯作溶剂，研究发现随着SBS用量的增加或形成胶束温度的升高比表面积、孔体积和孔径等都相应减小。因此，这两个参数可以方便地调节介孔材料的孔径、表面积和孔体积等，进而更好地控制介孔材料的性能。所制备介孔材料的壁厚与SBS用量和形成胶束温度无关，且均超过IOnm，因而材料具有较好的热稳定性，这有利于其进一步在催化剂、吸附和分离等领域应用。（2）以有孔的氧化铝膜为模板制备了具有介孔结构高有序纳米管，即在加热条件下将P123一TEOS薄膜通过毛细力引入有孔的氧化铝膜孔内，同时根据优先润湿机理使P123一TEOS组分润湿氧化铝孔的内壁并同时伴随嵌段共聚物胶束的重排、TEOS组分的凝聚收缩，随后通过烧结手段除去嵌段共聚物、通过溶解手段除去氧化铝模板，这样便在硅基底上得到了形态可控的介孔材料即有序排列的具有介孔结构的纳米管。在一定时间范围内，退火时间对纳米管的形成和生长高度有一定的影响。纳米管垂直于硅基底且纳米管套内的介孔以六方形式排列在整个纳米管套同时介孔孔道相互平行，所制备的纳米管能保持受限在氧化铝模板时的尺寸而且稳定地粘附在硅基底上。（3）在酸性条件下，采用一步法即在模板剂（P123）形成胶束之后，加入硝酸银或氧化铺和氧化忆混合物同P123胶束形成新的复合体，随后加入硅源（TEOS）以包附在复合体的外表面，从而形成具有介孔相的复合物，通过热处理我们分别制备了高有序的具有二维六方结构的介孔Ag／silica和Y203：Eu／silica材料，其中金属银或YZO3：Eu纳米粒子分散在有序的介孔孔道内。二者的比表面积、孔体积和孔径分别为786m2／g、1．22cm3／g、6．Znm和791m2／g、0．95cm3／g、3．snm。另外，我们采用基底受限法，利用旋涂法分别使介孔Ag／silica和YZO3：E记silica材料分散在硅基底上，通过溶解法除去硅墙后便得到了没有聚集的且具有狭窄粒径分布的金属银（2．5-5．snm）和姚03：Eu（1．5-3．onm）纳米粒子。原子力显微镜（AFM）证实所得到的纳米粒子呈现良好的分散状态，具有狭窄的粒径分布而且粒子尺寸都小于其介孔材料孔径。（4）分别用一步法制备的介孔Ag／SBA－－15材料和金属银作为甲醇氧化制备甲醛反应的催化剂，利用甲醇转化率表示催化剂活性、甲醛和二氧化碳产率表示催化剂选择性来研究二者催化性能。由于具有高的比表面积（786扩／g）、较大的孔体积（1．22cm3／g）、较大的孔径（6．2nm）、狭窄的孔径分布和有序的介孔孔洞等特性，在反应温度473K-723K范围内，同本体银作催化剂相比尽管银仅占体系总重量的0．94wt％，介孔Ag／silic。材料却显示出极高的催化活性和催化选择性。

Microwave-assisted hydrothermal synthesis of hydroxy-sodalite zeolite membrane

A high quality pure hydroxy-sodalite zeolite membrane was successfully synthesized on an alpha-Al2O3 support by a novel microwave-assisted hydrothermal synthesis (MARS) method. Influence of synthesis conditions, such as synthesis time, synthesis procedure, etc., on the formation of hydroxy-sodalite zeolite membrane by MAHS method was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and gas permeation measurements. The synthesis of hydroxy-sodalite zeolite membrane by MAHS method only needed 45 min and synthesis was more than 8 times faster than by the conventional hydrothermal synthesis (CHS) method. A pure hydroxy-sodalite zeolite membrane was easily synthesized by MAHS method, while a zeolite membrane, which consisted of NaX zeolite, NaA zeolite and hydroxy-sodalite zeolite, was usually synthesized by CHS method. The effect of preparation procedures had a dramatic impact on the formation of hydroxy-sodalite zeolite membrane and a single-stage synthesis procedure produced a pure hydroxy-sodalite zeolite membrane. The pure hydroxy-sodalite zeolite membrane synthesized by MARS method was found to be well inter-grown and the thickness of the membrane was 6-7 mum. Gas permeation results showed that the hydrogen/n-butane permselectivity of the hydroxy-sodalite zeolite membrane was larger than 1000. (C) 2004 Elsevier Inc. All rights reserved.

Crystallization and Si incorporation mechanisms of SAPO-34

In this study of the synthesis of SAPO-34 molecular sieves, XRD, SEM, XRF, IR and NMR techniques were applied to monitor the crystalloid, structure and composition changes of the samples in the whole crystallization process in order to get evidence for the crystallization as well as Si incorporation mechanism of SATO-34. XRD results revealed that the crystallization contained two stages. In the first 2.5 h (the earlier stage), high up to similar to80% of relative crystallinity could be achieved and the crystal size of SAPO-34 was almost the same as that of any longer time, indicating a fast crystallization feature of the synthesis. In this stage, IR revealed that the formation of SAPO-34 framework structure was accompanied by the diminution of hydroxyls, suggesting that crystal nuclei of SAPO-34 may arise from the structure rearrangement of the initial gel and the condensation of the hydroxyls. NMR results reveal that the template and the ageing period are crucial for the later crystallization of SAPO-34. Preliminary structure units similar to the framework of SAPO-34 have already formed before the crystallization began (0 h and low temperature). Evidence from IR, NMR, and XRF shows that the formation of the SAPO-34 may be a type of gel conversion mechanism, the solution support and the appropriate solution circumstance are two important parameters of the crystallization of SAPO-34. Meanwhile, NMR measurements demonstrated that about 80% of total Si atoms directly take part in the formation of the crystal nuclei as well as in the growth of the crystal grains in the earlier stage (<2.5 h). Evidence tends to support that Si incorporation is by direct participation mechanism rather than by the Si substitution mechanism for P in this stage (<2.5 h). In the later stage (>2.5 h), the relative content of Si increased slightly with a little decrease of Al and P. The increase of Si(4Al) and the appearance of the Si(3Al), Si(2Al), Si(1Al) and Si(OAl) in this stage suggest that substitution of the Si atoms for the phosphorus and for the phosphorus and aluminum pair takes place in the crystallization. The relationship among structure, acidity and crystallization process is established, which suggests a possibility to improve the acidity and catalytic properties by choosing a optimum crystallization time, thus controlling the number and distribution of Si in the framework of SAPO-34. (C) 2002 Elsevier Science Inc. All rights reserved.

Fabrication, characterization of spherical CaWO4:Ln@MCM-41(Ln=Eu3+, Dy3+, Sm3+, Er3+) composites and their applications as drug release systems

Spherical MCM-41 particles with a diameter of about 150 nm have been successfully coated with CaWO4:Ln (Ln = Eu3+, Dy3+, Sm3+, Er3+) phosphor layers through a simple Pechini sol-gel process. The obtained CaWO4:Ln@MCM-41 composites, which kept the mesoporous structure of MCM-41 and the luminescent properties of phosphors, were investigated as a drug delivery system using aspirin (ASPL) as a model drug.