Modifying MCM-41 as an efficient nitrosamine trap in aqueous solution

The attempt of preparing efficient adsorbent to capture nitrosamines in aqueous solution is reported in this paper, in order to develop new mesoporous functional materials for environment protection. Adsorption of nitrosamines in an aqueous solution containing the tobacco-extract, by zeolite and mesoporous silica was investigated in detail. The influence of structural parameters such as pore size, Si/Al ratio and cation on the adsorption of zeolite was examined. Emphatically, two modification methods, one-pot synthesis and solid state grinding were employed to incorporate aluminum in mesoporous silica MCM-41 since MCM-41 possesses the suitable pore size for the trap of tobacco specific nitrosamines (TSNAs) in solution. The resulting composites were characterized by XRD, N₂ adsorption at 77 K, FTIR and NH₃-TPD to inspect their property and function. The impact of modifier amount and preparative method on the actual adsorption of the Al-containing composite was investigated.     

Vanadium silicalite-1 nanoparticles deposition onto the mesoporous walls of SBA-15. Mechanistic insights from a combined EPR and Raman study

Continuous Wave (CW) and pulsed Electron Paramagnetic Resonance (EPR) spectroscopy in conjunction with Raman spectroscopy are used to investigate the properties of Vanadium Silicalite-1 (VS-1) nanoparticles dispersed onto the mesoporous walls of SBA-15 silica. The properties of the deposited zeolite nanoparticles are found to be remarkably different from those of the full grown VS-1 zeolite. Monitoring of the local VO(2+) environment in the noncalcined nanoparticles in SBA-15 reveals that, in contrast to the full grown zeolite case, these sites are highly hydrophilic. Also, the stability of the TPAOH template is found to be affected by acidification of the nanoparticles. These results promise to be of great importance in elucidating the formation mechanism of TPAOH-templated zeolitic nanoparticles and their incorporation in mesoporous silica materials.     

高度有序介孔氧化硅材料SBA-15：高浓度氨基官能化及氨基及氨基团的可利用性

采用简单的方法合成高浓度氨基修饰的高度有序氧化硅材料并深入研究氨基官能化材料的孔结构以及氨基的存在状态和可利用性。结果表明,氨基基团共价连接到SBA-15的孔表面,即使初始合成体系中的APTES（氨丙基三乙氧基硅烷）浓度高达30mol%时材料依然保持高度的有序性。合成体系中APTES浓度为20％的样品还保持良好的介孔结构,比表面积为680 m²·g^-1,孔容为0.89 cm³·g^-1,此介孔结构中的氨基官能团对镍离子表现出很强的亲和力,Ni²⁺的吸附量高达1.88 mmol·g^-1,相比之下未官能化的SBA-15对Ni²⁺没有吸附作用。当初始合成体系中APTES的浓度进一步增大到30％时,修饰到介孔氧化硅材料的氨基含量也随之增大,但由于材料的孔隙度急剧降低,这些氨基的可利用性也降低。     

Nanofusion: mesoporous zeolites made easy

A new path to zeolites: Nanofusion is a template-free, one-step process that gives mesoporous zeolite beta with tunable mesopore diameters in very short reaction times. The hierarchical materials are built from zeolite beta nanocrystals in concentrated gels. The nanocrystals can either be retrieved as individual particles in a colloidal suspension or are directly fused into mesoporous zeolitic materials (see scheme).     

Direct synthesis and catalytic applications of ordered large pore aminopropyl-functionalized SBA-15 mesoporous materials

SBA-15 mesoporous silica has been functionalized with aminopropyl groups through a simple co-condensation approach of tetraethyl orthosilicate (TEOS) and (3-aminopropyl)triethoxysilane (APTES) using amphiphilic block copolymers under acidic conditions. The organic-modified SBA-15 materials have hexagonal crystallographic order, pore diameter up to 60 A, and the content of aminopropyl groups up to 2.3 mmol g(-1). The influences of TEOS prehydrolysis period and APTES concentration on the crystallographic order, pore size, surface area, and pore volume were examined. TEOS prehydrolysis prior to the addition of APTES was found essential to obtain well-ordered mesoporous materials with amino functionality. The amount of APTES incorporated in the silica framework increased with the APTES concentration in the synthesis gel, while the ordering of the mesoporous structure gradually decreased. Analysis with TG, IR, and solid state NMR spectra demonstrated that the aminopropyl groups incorporated in SBA-15 were not decomposed during the preparation procedure and the surfactant P123 was fully removed through ethanol extraction. The modified SBA-15 was an excellent base catalyst in Knoevenagel and Michael addition reactions.     

Post-synthesis deposition of V-zeolitic nanoparticles in SBA-15

A post-synthesis deposition of vanadium silicalite-1 zeolite nanoparticles in the pores of SBA-15 results in a highly ordered hexagonal templated silica material with V-silicalite zeolitic plugs, giving rise to an increased crystallinity of the amorphous mesoporous walls.     

沸石对亚硝胺吸附及降解的研究进展

亚硝胺是吸烟导致癌症的重要因素, 如何在成分复杂的环境烟气中吸附和催化降解亚硝胺成为沸石吸附和催化的难题. 本文剖析了沸石对亚硝胺的特殊选择性吸附, 讨论了沸石降解亚硝胺的机制以及金属氧化物对沸石去除亚硝胺效率的促进作用, 并回顾了相关研究领域的动态和展望环境净化沸石新材料的发展方向.     

Effect of amine functionalization of spherical MCM-41 and SBA-15 on controlled drug release

MCM-41 and SBA-15 silica materials with spherical morphology and different particle sizes were synthesized and modified by post-synthesis method with 3-aminopropyltriethoxysilane (APTES). A comparative study of the adsorption and release of a model drug, ibuprofen, were carried out. The modified and drug loaded mesoporous materials were characterized by XRD, TEM, N₂ physisorption, thermal analysis, elemental analysis and FT-IR spectroscopy. Surface modification with amino groups resulted in high degree of ibuprofen loading and slow rate of release for MCM-41, whereas it was the opposite for SBA-15. The adsorbed drug content and the delivery rate can be predetermined by the choice of mesoporous material with the appropriate structural characteristics and surface functionality.     

Separation of alcohols and alcohols/O2 mixtures using zeolite MFI membranes

Two different types of supported silicalite membranes were employed for the separation of alcohols and alcohols/O₂ mixtures: in one of them the zeolite material was deposited on the top of the γ-alumina supports, while in the other the zeolitic material was mainly present in the porous structure of the α-alumina supports. While both kinds of membranes were able to separate the above mixtures, the second type of membranes having the zeolite material inside the support performed more efficiently. The maximum selectivity reported in this work is 7415 for the ethanol/O₂ separation in an ethanol/methanol/O₂ mixture. For a better understanding of the separation mechanism, the performance of both zeolite membranes was compared to that of a mesoporous silica membrane. Also, the adsorption of methanol and propanol on silicalite crystals was measured using a microbalance.     

A novel template-free sol–gel synthesis of silica materials with mesoporous structures and zeolitic walls

Hierarchical porous materials with zeolite structures show great promise in catalysis due to combining the advantages of zeolites and mesoporous materials. Here a novel template-free sol–gel method is developed to synthesize hierarchical porous silica materials. This method involves solvothermal recrystallization of the xerogel converted from uniform silicalite-1 precursor sol via vacuum drying process. The zeolite sol and the solid samples were characterized by laser light scattering, XRD, N₂ adsorption/desorption isotherm, FTIR, SEM, TEM and thermal analysis technologies. The results show that we obtain two novel materials with different mesoporous structures and silicalite-1 walls by using different recrystallization media, one of which has irregular arrays of mesopores, the other possesses 3D wormhole mesoporous structure. We speculate that formation of different mesoporous structures results from different nucleation and growth process of materials     

Effects of amino groups and microstructure of organic mesoporous silica supported metallocene catalysts on ethylene polymerization

<正>Mesoporous silica(MS),3-aminopropyltriethoxysilane(APTES) modified mesoporous silica(AMS),bis(3- trimethoxysilylpropyl)amine modified mesoporous silica(BAMS) and APTES modified solid spherical silica(AS) were prepared and used to immobilize metallocene catalysts for ethylene polymerization.Gel permeation chromatography results showed that polyethylenes(PEs) catalyzed by AMS(or BAMS) supported metallocene catalysts at the molar ratios of Al/Zr =100,300 and 500 were of bimodal molecular weight distribution(BMWD);while PEs catalyzed by the above catalysts at the molar ratios of Al/Zr≥800 were of monomodal molecular weight distribution(MMWD).However,MS(or AS) supported metallocene catalysts could only produce PEs with MMWD in spite of the molar ratio of Al/Zr.It was because that AMS(or BAMS) supported catalysts possessed two active sites for ethylene polymerization at low molar ratios of Al/Zr due to the combination effects of mesopore geometrical constraint and amino groups of the supports,which was confirmed by X-ray photoelectron spectroscopy.This brings forward a novel and easy method for the synthesis of polyolefin with BMWD.     

Adsorption and protection of plasmid DNA on mesoporous silica nanoparticles modified with various amounts of organosilane

Ordered MCM-41-type mesoporous silica nanoparticles (MSNs) with pore size of 2.6 nm were synthesized and were further modified with various amounts of 3-aminopropyltriethoxysilane (APTES), respectively, by a direct co-condensation method. These amine functionalized mesoporous silica nanoparticles (Am-MSNs) were employed to complex with plasmid DNA (pDNA) to study their adsorption and protection capacities. The results demonstrate the MSNs functionalized with aminopropyl groups present advanced adsorption capacities for pDNA immobilization. And Am-MSNs with high APTES amount lead to high amount of pDNA adsorption. Further investigation of pDNA protection shows that Am-MSNs with moderate APTES amount could completely protect pDNA from enzymatic degradation, while those with smaller and/or higher amount of APTES could partially provide protection of pDNA.     

由纳米晶前驱体组装有序介孔silicalite-1分子筛

采用两步法将不同尺寸的silicalite-1分子筛纳米晶种通过自组装合成了一系列有序介孔silicalite-1分子筛。首先将强碱性的silicalite-1前驱体分别加热不同时间得到纳米晶种,然后在类似合成SBA-15的强酸性条件下组装成有序的介孔材料。合成条件的剧烈变化阻止了分子筛晶种的继续长大,并在三嵌段共聚物模板的诱导下组装成有序介孔材料。这种“自下而上”的方法制备有序介孔分子筛同时包含微孔和介孔。氮气吸脱附结果表明所制备的介孔分子筛材料均表现了很大的比表面积(730 m2/g以上)。     

酸诱导介观相转变硅基介孔材料的合成机理及其改性

采用两步法以三嵌段共聚物P104(PEO27-PPO61-PEO27)为模板剂合成介孔材料, 研究了介孔材料结构随体系pH 值的变化, 探讨了体系中介观相转变的机理. 研究表明,随着pH 的升高, 发现体系中无机物种和模板剂所组成的介观相发生了转变,由P6mm 的SBA-15(pH=1.51-2.67)2D六角孔道结构转变为3D 蠕虫状孔道的MSU-X(pH=3.93-4.56)结构. 对所得的两种不同种类的硅基材料以γ-胺丙基三乙氧基硅烷(APTES: NH2(CH2)3Si(C2H5O)3)进行表面烷基化改性结果表明, 在同样的条件下, 经过改性后MSU-X类介孔材料孔壁上接枝的烷基数目要远超过SBA-15 类介孔材料.     

Study of the effect of organo-substituted trialkoxysilanes on the textural and structural properties of mesoporous silica

The effect of additives of organo-substituted trialkoxysilanes: (3-aminopropyl)triethoxysilane (APTES), (2-cyanoethyl)triethoxysilane (CNETES), and tris(trimethylsiloxy)silane (TTMSS) as cosources of silica on its textural and structural properties was studied. The influence of organo-substituted trialkoxysilane additives on the variation of porous structure parameters of mesoporous silica during the hydrothermal treatment was demonstrated. The synthesized mesoporous silica samples were characterized by low-temperature nitrogen adsorption, X-ray powder diffraction, scanning electron microscopy, thermal and elemental analysis, and Raman spectroscopy.     

模板法制备的有序介孔Co3O4的电化学电容行为

以介孔硅作为模板合成有序的介孔Co3O4, 在6 mol/L KOH电解液里进行电化学性能的测试. 结果表明具有有序介孔结构的Co3O4, 其比容量可以达到250 F/g, 大约为在550 ℃下直接煅烧Co(NO3)&#8226;6H2O所得的Co3O4容量的4倍. 其外该材料还表现出良好的倍率特性, 这一现象可归因于有序的介孔结构增大了有效的反应表面积, 同时有利于离子在其中传递.     

介孔钛硅新催化材料

本文综述了介孔钛硅新催化材料的制备方法,归纳评述了各类介孔钛硅材料的制备技术和相应的产物的结构特点,介绍了现有的表征介孔钛硅材料孔结构和钛活性位的重要技术手段和特征,概括了含钛介孔材料在有机物液相催化选择氧化方面的应用,讨论了提高钛位的催化活性、结构稳定性、疏水性、钛硅比等的技术方法;提出了介孔钛硅材料研究存在的问题并展望了将来的研究方向。     

沸石表面有机金属化学ZSM-5外表面上——Ge(n-C4H9)x基团的接枝及其性质研究

用气体分析及IR,NMR和元素分析等方法研究了真空系统中230℃和280℃下四丁基锗在ZSM-5沸石表面上的接枝反应,并对所得沸石的热稳定性和吸附性质进行了表征,与作者曾报道的硅胶及丝光沸石上的反应类似,四丁基锗也能与ZSM-5沸石表面上的硅羟基发生缩合反应,在其外表面或孔口生成组成为(=Si-O)xGe(n-C4H9)4-x(x=2~3)的表面有机锗化合物,在２３０℃接枝丁基锗基团不影响沸石的结构和表面积,仅改变它的孔口大小,在改性后的沸石上,Ｎ２的吸附性质没有改变,而不同分子尺寸的烃,加正已烷,２-甲基戊烷,２,３-二甲基丁烷却呈现出完全不同于起始ＺＳＭ-５沸石的择形吸附效应.     

Crystals in crystals-nanocrystals within mesoporous zeolite single crystals

A major factor governing the performance of catalytically active particles supported on a zeolite carrier is the degree of dispersion. It is shown that the introduction of noncrystallographic mesopores into zeolite single crystals (silicalite-1, ZSM-5) may increase the degree of particle dispersion. As representative examples, a metal (Pt), an alloy (PtSn), and a metal carbide (beta-Mo(2)C) were supported on conventional and mesoporous zeolite carriers, respectively, and the degree of particle dispersion was compared by TEM imaging. On conventional zeolites, the supported material aggregated on the outer surface of the zeolite particles, particularly after thermal treatment. When using mesoporous zeolites, the particles were evenly distributed throughout the mesopore system of the zeolitic support, even after calcination, leading to nanocrystals within mesoporous zeolite single crystals.     

New insights into zeolite formation from molecular modeling

We review recent molecular modeling efforts to shed light on the mechanisms of zeolite formation. We focus on studies that model the early stages of silica polymerization and zeolite nucleation. Electronic structure calculations, classical molecular dynamics, atomistic Monte Carlo simulations and Monte Carlo simulations of lattice models have been used to probe the formation of zeolites and mesoporous materials. Results from these modeling studies predict that in early stages of formation, the silicate material is amorphous. Cluster growth is predicted to occur primarily through Ostwald ripening, and by aggregation of small fragments.