大孔磷酸铝分子筛VPI—5与MCM—9的合成与表征

1988年,Davis等首次合成了一种具有十八元环、孔道直径大于10~(-7) cm的新型VPI-5分子筛。次年7月,他们又详细报道了以四丁基氢氧化铵为结构导向剂合成的VPI-5分子筛。以二正丙胺(DPA)为结构导向剂也可合成VPI-5,但文献对这一合成产物没有给予必要的结构表征。MCM-9是Derouane等首先合成的,他们在反应混合物中加有正己醇,并采用液-固相反应方法制备了这种与VPI-5结构相似的磷酸硅铝分子筛。我们以二正丙胺为结构导向剂,用水热晶化法合成了VPI-5和MCM-9 2种大孔分子筛,并对其进行了结构表征。     

影响水热合成VPI-5及Si-VPI-5的因素

使用二正丙胺(DPA)和二正丁胺(DBA)作结构导向剂合成出VPI-5和Si-VPI-5,并以二异丙胺(DIPA)为结构导向剂成功地合成出高结晶度的超大孔磷酸铝分子筛VPI-5,其XRD谱图中未检测出其他杂质峰.VPI-5分子筛不同于一般中微孔磷酸铝分子筛,合成条件极其苛刻,为此对原料组成、成胶条件、陈化时间和温度、晶化时间和温度、结构导向剂种类、pH等合成条件对VPI-5分子筛结晶度的影响作了较为详尽的研究,结果表明有机胺在晶化过程中具有结构导向作用,但不起空间填充作用,加有机胺前的陈化过程是必要的.     

有机硅骨架修饰的磷酸铝分子筛VPI-5的合成

分别以1,2-双(三乙氧基硅基)乙烷(BTESE)、1,2-双(三乙氧基硅基)乙烯(BTESEE)和苯基三乙氧基硅烷(PTES)为硅源, 通过一步法直接合成有机硅骨架修饰的磷酸铝分子筛VPI-5. 系统考察了各反应参数对产物结构与性质的影响, 并对产物的结构进行了表征. 表征结果表明, 有机基团通过硅原子被引入到分子筛骨架中. 有机基团的引入增加了分子筛的亲油性, 并且不同的有机基团对分子筛的亲油性的提高程度不同.     

VPI—5分子筛热相变转化成ALPO4—8的研究

VPI-5是具有十八元环超大孔道的磷酸铝分子筛,在加热过程中,随着孔道中的水分子的脱除,其骨架结构转化成具有十四元环孔道的AlPO_4-8分子筛。采用XRD及骨架结构模型计算等方法研究了这一相变过程,并对相变机理进行了探讨。     

锌硅分子筛VPI-7的合成及表征

本文在Na₂O-ZnO-SiO₂-H₂O水热体系中研究了温度、Na₂O/SiO₂、SiO₂/ZnO对合成锌硅分子筛VPI-7的影响,并以XRD、SEM、FT-IR等手段对晶化产物进行表征。实验表明:(1)SiO₂/ZnO比在3.5～10的范围内,可以合成VPI-7的纯相,且随着SiO₂/ZnO比的增加,产物的相对结晶度增大;(2)合     

一种新颖的十八元环超大孔分子筛骨架拓扑结构CJU—18的设计

提出了一种新颖的十八元环超大孔分子筛的拓扑结构模型——CJU-18,它属钙霞石笼作用于六方晶系的P_(63)/mmc空间群.与VPI-5类似,具有平行于c方向的十八元环直孔道结构,但侧面有十元环孔道,通过计算该结构模型各原子间的键长、键角,认为该结构有可能存在,采用POWD-MODELING程序,计算了它的理论XRD谱图并绘制出其立体拓扑结构。     

Synthesis and Characterization of the Large Pore Molecular Sieves VPI-5 and Si-VPI-5

The large pore molecular sieves VPI-5 and Si VPI-5 were synthesized by using three organic amines (dipropylamine, diisopropylamine and dipentylamine) as the structure-directing agents. Compared with general alumlnophosphate molecular sieves, the synthesis of the molecular sieves of VPI-5 type ls of many unique features. Both VPI-5 and Si-VPI-5 were characterized by XRD, IR, TG-DTA, and MAS-NMR.     

超大孔磷酸铝分子筛的合成及性能

1988年Davis等首次报道了以二正丙胺和四丁基氢氧化铵为结构导向剂合成出一种命名为VPI-5的新型磷酸铝超大孔分子筛。它是一族具有相同三维拓朴学骨架的磷酸铝系分子筛,该结构的对称性属六方晶系,P6_3cm空间群,单位晶胞由36个TO_2组成,晶胞参数α=1.8989nm,c=0.8112nm,其主孔道由18员环构成,孔直径约为1.2-1.3nm。     

Synthesis of Large Pore Molecular Sieve VPI-5 by Using Various Organic Amines

The molecular sieve VPI-5 was synthesized by using various organic amines (DEA, Di-PA, DBA, DPenA, TBA, DEOA and TEOA) as the structure-directing agent. The use of DPA enlarged the range of the crystallization temperature from 110℃ to 190℃ in the synthesis of VPI-5, while the use of TEOA changed the composition of the reactants in a broad variety. Diamines are the typical amines in the synthesis of VPI-5. Among them DBA and DPA are the most favorite structure-directing agents for the synthesis of VPI-5 molecular sieve.     

The Mechanism of Phase Transition of Molecular Sieve VPI-5 into AlPO4-8

The aluminophosphate molecular sieve VPI-5 has received much attention as a new structure containing one-dimensional circular pores circumscribed by 18 tetrahedral atoms. The AlPO_4-8 is another new type of structure which was found to contain 1 4-ring open pores. Recently, we have successfully synthesized the molecular sieves of VPI-5 and AlPO_4-8, and found that the mixture of VPI-5 and AlPO_4-8 was easily formed under similar conditions, and VPI-5 can be converted to AlPO_4-8 by dehydration via heating. It is suggested that there exists relationship between the structures of VPI-5 and A1PO_4-8. Therefore, the study on the transition and relationship between VPI-5 and A1PO_4-8 is very important for designing and preparing new molecular sieves with new structures.     

Emission spectroscopic investigation of triplet diarylcarbene generated in molecular sieve VPI-5

We report an attempt to generate and characterize a triplet carbene, bis(2,4,6-trichlorophenyl)carbene ((3)1), in zeolites Y and L and in a molecular sieve VPI-5 in which a possible dimerization and reaction with the precursor of carbene are significantly retarded, thus making the triplet carbene longer lived than in solution at room temperature. The adsorption of a corresponding diazomethane (1-N(2)), the precursor of 1, was carefully examined by comparing the absorption spectrum after adsorption with that of 1-N(2) in n-pentane, which revealed that 1-N(2) was adsorbed with the diazo group intact only in VPI-5, while in other zeolites 1-N(2) was found to be decomposed upon adsorption. This difference in reactivity of the hosts was ascribed to the absence of Br?nsted-acid sites in VPI-5. The photoirradiation of 1-N(2) in VPI-5 at 77 K was monitored by emission spectroscopy, which revealed that bis(2,4,6-trichlorophenyl)methyl radical (1-H) was produced as the only detectable species under these conditions. This is interpreted as indicating that nascent (3)1 may undergo efficient hydrogen abstraction as a result of multiple excitation by repeated refraction and reflection of the light in a light-scattering medium. In accord with this interpretation, the emission due to (3)1 was observed when irradiation was carried out on a translucent glassy sample prepared by submerging VPI-5 incorporating 1-N(2) in a refractive-index-matching fluid such as propylene glycol or glycerol. ESR signals ascribable to (3)1 were also observed under these conditions. Laser photolysis of 1-N(2) in VPI-5 at room temperature with fast detection of both emission and absorption showed that the bands due to 1-H were detected in the nanosecond time regime probably because of the extremely fast H abstraction by (3)1. However, a variable-temperature ESR study showed that the signals due to (3)1 survive up to 220 K in VPI-5 while the signals disappear at 120 K in 2-methyltetrahydrofuran, suggesting that triplet carbene is stabilized in VPI-5. Thus, a triplet carbene was generated and characterized in a zeolite for the first time and shown to be stabilized extrinsically. The present study also proposes a solution to the issues of acidic sites and multiple excitation often observed in zeolites.     

Mechanism of CIT-6 and VPI-8 crystallization from zincosilicate gels

The crystallisation of CIT-6, a large-pore zincosilicate with the framework topology of zeolite Beta and synthesised from clear hydrogels that contain, tetraethylammonium (TEA+), Li+ and Zn2+ cations, proceeds initially through the formation of an amorphous solid that incorporates all the initial Zn species. Nucleation of the *BEA phase is effected by reorganisation of the amorphous phase, whereas crystal growth involves the incorporation of soluble species also. A highly crystalline CIT-6 material is obtained after 164 h of synthesis at 140 degrees C. Scanning electron microscopy (SEM) shows that this sample exhibits two different types of crystals: well-defined pseudo-cubic crystals and rounded crystals. The latter has a broad crystal-size distribution. If crystallisation is continued with longer synthesis times, the VPI-8 crystalline phase appears, and a new population of needle-shaped crystals is detected in the SEM images. This new crystalline phase is nucleated on the surface of the rounded CIT-6 crystals, which disappear as the crystallisation progresses, while no changes are observed in the population of pseudo-cubic CIT-6 crystals. At higher crystallisation temperatures these phase transformations are accelerated, and the formation of VPI-8 is favoured over that of CIT-6.     

Raman and 29Si MAS NMR spectroscopy of framework materials containing three-membered rings

Raman and ²⁹Si MAS NMR spectroscopies are evaluated for the identification of three-membered rings (3MR) in framework oxide materials. Raman and ²⁹Si MAS NMR spectra from the 3MR-containing materials euclase, phenakite, clinohedrite, willemite, lovdarite, VPI-7, ZSM-18 and dipotassium zinc tetrasilicate are presented. The Raman spectra from these materials do not exhibit common bands representing vibrational modes assignable to individual 3MR. The dense beryllosilicate and zincosilicate minerals exhibit ²⁹Si MAS NMR resonances indicative of silicon positioned in 3MR while the molecular sieves lovdarite and VPI-7 give ²⁹Si MAS NMR resonances that can be assigned to silicons located at the center of “spiro-5” units that are constructed from two 3MR. Silicon atoms located in isolated 3MR in the molecular sieves ZSM-18 and dipotassium zinc tetrasilicate do not exhibit ²⁹Si MAS NMR resonances that can be distinguished from those assigned to silicons residing in 4MR and larger.The ²⁹Si MAS NMR spectra from the new materials VPI-8, VPI-9 and VPI-10 do not exhibit ²⁹Si MAS NMR resonances indicative of “spiro-5” units. The presence of isolated 3MR in these materials cannot be ruled out from the ²⁹Si MAS NMR spectroscopic results.     

Unexpectedly low translational mobility of methane and tetrafluoromethane in the large-pore molecular sieve VPI-5

Molecular diffusion of methane and tetrafluoromethane in the microporous material VPI-5 was studied by pulsed field gradient nuclear magnetic resonance (PFG NMR) and NMR exchange experiments. The translational mobility of both molecules in VPI-5 was found to be at least two orders of magnitude smaller than in ZSM-5. This is surprising since the channels in VPI-5 are about two times as wide as those in ZSM-5. The surprisingly small translational mobility in VPI-5 could be caused by a more complete stabilization effect or by single-file diffusion. The intracrystalline mean life time of methane in VPI-5 directly measured in the NMR tracer exchange experiments was found to be in satisfactory agreement with the value estimated on the basis of the PFG NMR data on translational mobility for ordinary intracrystalline diffusion. It must be ruled out, therefore, that molecular transportation over length scales of the order of the crystallite dimensions is controlled by single-file diffusion.     

TG and DSC investigation of the dehydration of the extra large pore aluminophosphate molecular sieve VPI-5 and related materials

The dehydration of a series of VPI-5 and H3 samples, synthesized under various conditions, as well as the solid state transformation of VPI-5 to AlPO₄-8 have been investigated using combined TG-DTG-DSC and high-resolution solid state³¹P-NMR. The TG curves show a quasi-continuous release of water, the total loss being characteristic for each sample. Complete dehydration is achieved when the samples are heated from 20°C to about 150°C at various beating rates. Besides the main dehydration effect, several weak endothermic peaks are observed. These generally non-reproducible modulated peaks, recorded at high heating rates, are presumably due to the interactions of the water molecules leaving the channels of VPI-5 with the randomly positioned fragments stemming from the destruction of the water triple helix assemblage. The non-isothermal kinetic parameters of the dehydration have been evaluated from the TG and DTG curves recorded at low heating rates. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Hydroxyapatite grown on a native extracellular matrix: initial interactions with human fibroblasts

Proteins are known to modulate the physical properties of minerals, and thus we anticipate that they will strongly influence the structure and the biological properties of biomimetically prepared carbonate-containing hydroxyapatite. This study was designed to learn more about the main morphological characteristics of hydroxyapatite layer grown on different substrates coated with an extracellular matrix, a biological matrix that was produced by cultured osteoblast-like cells. The hydroxyapatite growth was carried out in a simulated body fluid, a solution that resembles the human blood plasma. It was found that the extracellular matrix may serve as a template for the mineralization of biomimetic hydroxyapatite on the surface of materials like stainless steel, silicon, and silica glass, leading to the formation of a homogeneous layer. The latter was consisting of nanometer-sized hydroxyapatite crystals grouped in particles with regular sphere shape and with a significantly higher average diameter in comparison to samples without extracellular matrix coating. Subsequent in vitro studies with living fibroblasts showed that the cellular behavior depended on the type of underlying substrate used for the hydroxyapatite growth, as well as on the immersion time of the samples in the simulated body fluid. Increasing the thickness of the hydroxyapatite layer altered visibly the cellular response, and the fibroblasts developed stellate morphology on the samples with a hydroxyapatite-extracellular matrix coating. Preadsorption with fibronectin significantly improved the initial cell adhesion and spreading to all surfaces. Thus, such an approach may contribute to the development of surfaces with better tissue compatibility.