Monte Carlo simulation on the adsorption properties of carbon tetrachloride, neopentane, and cyclohexane in MCM-41

The adsorption properties of carbon tetrachloride, neopentane, and cyclohexane in MCM-41 with heterogeneous and cylindrical pores have been studied by using grand canonical ensemble Monte Carlo simulation. The adsorption isotherm, average potential of adsorbate, isosteric heat of adsorption, and number density of molecules in MCM-41 were calculated. The simulated isotherms were compared with experimental ones. Also, different adsorption behaviors in MCM-41 with pore diameter of 2.2 and 3.2 nm were discussed. The capillary-condensation pressure increased for a given adsorbate with an increase in pore diameter. The average densities of carbon tetrachloride, neopentane, and cyclohexane in the two different pores above the capillary-condensation pressure were smaller than the corresponding liquid densities by about 12%. The adsorbate molecules did not form the multilayer in pore below the capillary-condensation pressure. The number of adsorption layers of molecules was constant in a given pore for the three adsorbates above the capillary-condensation pressure. Carbon tetrachloride molecules in pore were also ordered along the pore axis.     

Effect of particle morphology and pore size on the release kinetics of ephedrine from mesoporous MCM-41 materials

Ephedrine was loaded onto siliceous mesoporous materials of different pore sizes, and the corresponding drug release into simulated body fluid at pH 7.4 and 37?°C was measured against time over a period of 72?h. The mesoporous materials designated MCM-41(C_N) were prepared at different pore sizes using a self-assembly mechanism. The pore size was controlled by the use of alkyltrimethylammonium bromide (C_NTAB) surfactants having different alkyl chain lengths (C₁₀, C₁₂, and C₁₄). The three mesoporous materials showed good ephedrine-loading capacities from dry ethanolic solutions, which slightly increased with the pore size of MCM-41(C_N). From the drug release profiles, the overall release of ephedrine followed the order: MCM-41(C₁₂)?>?MCM-41(C₁₄)?>?MCM-41(C₁₀), with the release of ephedrine attaining 92% of the drug load from MCM-41(C₁₂). Ephedrine release approached 60% of the drug load in 6?h and 92% in 20?h. The results of in vitro release kinetics indicate that pore size is not the only factor affecting ephedrine release, but also pore channel length and overall particle morphology.     

MCM-41的孔径和添加量对环氧树脂力学性能的影响

以1,3,5三甲苯(TMB)为扩孔剂,水热合成了5种不同孔径(2.7～5.9 nm)的介孔二氧化硅MCM-41粉体,采用溶液共混法制备了MCM-41环氧树脂复合材料,研究了MCM-41孔径和添加质量对复合材料力学性能的影响。结果表明,添加1%最大孔径的MCM-41时,复合材料的力学性能达到最佳,拉伸强度、弯曲强度、弯曲模量分别比纯环氧树脂提高了54.6%、30.1%、68.3%。     

Isomerization of Norbornadiene to Quadricyclane Using Ti-Containing MCM-41 as Photocatalysts

Heterogeneous Ti-containing MCM-41 materials were prepared for the photocatalytic isomerization of norbornadiene to quadricyclane with the aim of replacing homogeneous sensitizers. Chemical grafting produces quantum-size TiO₂ crystallites highly dispersed in the pore of MCM-41. Isomorphous substitution generates Ti species in the framework of MCM-41, but some non-framework species are formed with increasing Ti content. It is found that Ti-containing MCM-41 materials show significantly higher photocatalytic activity than bulk TiO₂, and the framework Ti species are more active than the surface-dispersed species.     

Chemical Stability of Ti-Modified MCM-41 Catalysts in the Hydroxylation of Benzene in the Liquid Phase

Ti-substituted MCM-41 and Ti-grafted MCM-41 materials possessing both well-ordered long-range and pore structures have been used as catalysts for the hydroxylation of benzene in the liquid phase. The stability of the catalytic performance and the changes in the structural characteristics of Ti-modified MCM-41 resulting from the hydroxylation reaction have been investigated. It has been found that Ti-grafted MCM-41 exhibits better stability of catalytic performance than Ti-substituted MCM-41. For the Ti-substituted MCM-41, the migration of framework Ti into non-framework sites results in a decrease in the catalytic performance and the partial collapse of the pore structure. For the Ti-grafted MCM-41, the hydroxylation of benzene induces a smaller decrease in the pore volume and specific surface area than that observed for Ti-substituted MCM-41.     

Effect of pore size on the performance of mesoporous material supported chiral Mn(III) salen complex for the epoxidation of unfunctionalized olefins

A series of mesoporous MCM-41 and MCM-48 materials with different pore sizes were synthesized and used as supports to immobilize chiral Mn(III) salen complex. The heterogeneous catalysts were characterized by XRD, FT-IR, DR UV–vis, and N₂ sorption, and the results indicated the successful immobilization of chiral Mn(III) salen complex. The confinement effect of pore size on the catalytic performance of the heterogeneous catalysts was studied for the asymmetric epoxidation of unfunctionalized olefins with m-chloroperoxybenzoic acid as an oxidant. It was found that the conversions and enantiomeric excess (ee) values were closely correlated with the pore sizes of parent supports. The catalysts immobilized on the large-pore mesoporous supports exhibited higher conversions, and for the catalysts immobilized on MCM-41 materials, the ee values improved with increasing pore size. However, for the MCM-48 material-supported catalysts, the compatible pore size of the support with the substrate was beneficial for obtaining higher enantioselectivity in olefin epoxidation.     

Direct impregnation method for preparing sulfated zirconia supported on mesoporous silica

A new method has been developed to prepare sulfated zirconia (S–ZrO₂) supported on mesoporous silica. With direct exchange of metal containing precursors for the surfactants in the as-synthesized MCM-41 materials, the problem of fill-up of the mesoporous structure was avoided and high sulfur content was achieved. By using this method, the composite of S–ZrO₂/MCM-41 with ZrO₂ content higher than 60 wt.% can be easily obtained without serious blockage of the pore structure of MCM-41. Nevertheless, the pore size and pore volume of the resultant S–ZrO₂/MCM-41 composites were found to vary markedly with the loading of ZrO₂. The strong acidic character of the obtained composites was examined by using them as catalysts in n-butane isomerization. Introduction of other metals such as aluminum as promoter into S–ZrO₂/MCM-41 can be easily conducted by the direct impregnation method.     

Effects of organo-functionalization and sulfonation of MCM-41on the proton selectivities of MCM-41/Nafion composite membranes for DMFC

Siliceous MCM-41 and various organo-functionalized MCM-41s have been successfully synthesized by co-condensation method with/without the addition of NaF. The results of XRD, FT-IR and TG/DTG analyses show that the organo-functional groups incorporated into silicate framework of MCM-41 have been stably anchored to the silicate framework even after surfactant extraction and subsequent sulfonation. It also shows that the addition of NaF to synthesis mixture could lead to well-resolved MCM-41 but the incorporation of organo-functional groups could be disturbed by F⁻ anions, especially for vinyl group, enhancing the polycondensation than co-condensation. The proton conductivities of composite membranes fabricated by as-synthesized siliceous MCM-41s synthesized with/without the addition of NaF (M41F and M41) are lower than those of composite membranes fabricated by their calcined MCM-41s synthesized with/without the addition of NaF (CM41F and CM41) regardless of the addition of NaF while their methanol permeability are opposite, mainly due to pore blocking by surfactant. The results also clearly show that the higher and increasing methanol permeability of composite membrane fabricated with CM41 than fabricated with CM41F with powder content is ascribed to the combined effect of larger pore and broader pore size distribution and poorer adhesion between powder and Nafion dispersion.FT-IR and TGA results clearly show that the methanol permeability of composite membranes fabricated with various organo-functinalized- and sulfonated-MCM-41 strongly depends on the residual void space within the pore channel of MCM-41 resulting from the amount of incorporated organo-functional groups and hydrophilicity of sulfonic groups attached to organo-functional groups. It is also seen that the synthesis condition of MCM-41 such as the addition of NaF significantly affects the degree of organo-functionalization, especially for vinyl groups and thus sulfonation.     

The porosity and morphology of mesoporous silica agglomerates

The synthesis of mesoporous MCM-41 silica materials was investigated at various conditions. A series of ordered mesopores MCM-41 silica materials was synthesized in concentrated reaction mixtures. The influence of water concentration at the constant ratio of the remaining reagents on the morphology and structural parameters of MCM-41 was studied. Hexadecyltrimethylammonium bromide CTAB was used as a structure-directing agent. The pore size, the wall thickness and cylindrical pores array were characterized by powder X-ray diffraction and nitrogen adsorption. The presented results show that in concentrated reaction mixtures, the pore size and the thickness of the pore walls remain practically constant. However, the dimensions of silica particles depend strongly on the water concentration. A high regularity of pore structure for large MCM-41 particles synthesized in concentrated solution was supported by independent AFM technique.     

Effect of cationic template on the adsorption of aromatic compounds in MCM-41

The effect of cationic template on the adsorption of aromatic compounds in MCM-41 was investigated in the present work. Various MCM-41 samples were prepared through controlling template removal during the synthesis of MCM-41 materials in which cationic surfactant was used as a template. The properties of synthesized samples were characterized with X-ray diffraction (XRD), nitrogen adsorption, FTIR and thermogravimetric analysis etc. The adsorption equilibriums of toluene, cumene and water on MCM-41 samples were measured using a digital microbalance. Compared with parent MCM-41 with template removed completely (denoted as MCM-41), the samples with template partially removed (denoted as C-MCM-41) exhibited moderate adsorption capacity for aromatic compounds. However, the adsorption equilibrium of water showed that the hydrophobicity on the surface of C-MCM-41 was significantly enhanced. The combination of moderate adsorption capacity for aromatics and hydrophobicity for water is desirable for the applications including removal of VOCs. It was found that the adsorption behaviors of aromatic compounds and water in various MCM-41 samples were governed by both porosity and cationic spots generated by cationic templates; and the former played a more important role than the latter when aromatics were adsorbed. The porosity and cation density of the MCM-41 material can be tailored by controlling the removal of the cationic template from the pore structure. The influence of template extraction methods on the structure and adsorption properties of MCM-41 materials has also been addressed.     

Physisorption of nitrogen by porous materials

Nitrogen adsorption at 77 K is widely used for the determination of the surface area and pore size distribution of various porous materials. The first stage in the interpretation of a nitrogen isotherm is the identification of the physisorption mechanism(s): that is monolayer-multilayer adsorption, capillary condensation or micropore filling. The Brunauer-Emmett-Teller (BET) method cannot be used to provide a reliable evaluation of the surface area if the solid contains pores of molecular dimensions (i.e. narrow micropores). Furthermore, with such materials, it is necessary to use different probe molecules to determine the pore size distribution. Capillary condensation is involved as a secondary process in the filling of mesopores (pore width in the range 2–50 nm). Recent work on MCM-41, a model mesoporous adsorbent, has confirmed that capillary condensation-evaporation can occur reversibly in open-ended pores of about 4 nm width.     

合成条件对介孔氧化硅材料孔径尺寸的影响

分别在室温酸性、室温碱性、水热碱性条件下合成了介孔氧化硅材料MCM－41,通过XRD,HRTEM,氮气吸附等手段对介孔氧化硅材料进行了表征,并探讨了3种条件下材料介孔尺寸的变化。结果表明：室温酸性条件下合成的MCM－41材料具有最小的介孔尺寸,碱性条件则有利于合成较大孔径的样品。另外还发现无机盐离子的添加、反应温度的变化及煅烧过程均可以影响介孔尺寸,并提出了无机盐离子通过影响表面活性剂胶团的荷电性质和尺寸而改变材料孔径尺寸的模型。     

Separation and Recovery of Tetramethyl Ammonium Hydroxide with Mesoporous Silica Having a Hexagonal Structure (MCM-41)

Separation and recovery of tetramethyl ammonium hydroxide (TMAH) was investigated using several types of MCM-41 (mesoporous silica having hexagonal structure) adsorbents. The MCM-41s were prepared by hydrothermal synthesis with structure-directing agents with different alkyl chains. The prepared MCM-41s were characterized with X-ray diffraction, transmission electron microscope, nitrogen gas adsorption, and zeta potential, and then used for adsorption of TMAH. The adsorption of TMAH with MCM-41s increased with pH up to pH ≈ 10 and then decreased as the MCM-41 dissolved. The adsorption of TMAH progressed via the Langmuir mechanism. The maximum adsorption corresponded to the pore diameter and the pore volume of the MCM-41s. MCM-41 also possesses selectivity for TMAH against phenol. The chromatographic operation was conducted using granulated MCM-41 to avoid excessive pressure-drop through the packed column and quantitative adsorption-elution processing of TMAH could be achieved.     

Adsorption and Activity of Proteins onto Mesoporous Silica

The adsorption and activity of cytochrome c onto two different MCM-41 materials, MCM-41/28 and MCM-41/45 with average pore diameters of 28 and 45 Å respectively, is presented. Nitrogen gas adsorption/desorption isotherms before and after protein adsorption, and peroxidative activity profiles of the adsorbed protein demonstrate that the protein is adsorbed into the mesoporosity and remains active. The adsorption of a range of different proteins onto both MCM-41/28 and 45 shows how protein properties affect adsorption.     

MCM-41介孔材料的合成条件和特性对吸附镉离子的影响

以气相氧化硅为硅源,十六烷基三甲基溴化铵(cetyl trimethyl ammonium bromide,CTAB)为模板剂,分别在碱性[氢氧化钠(NaOH),四乙基氢氧化铵,tetraethyl ammonium hydroxide,(C2Hs)4NOH(TEAOH)]和酸性介质条件[盐酸(HCl)]T水热合成了MCM-41有序介孔材料MCM-41-N,MCM-41-T和MCM-41-H.用X射线衍射、氮气吸附-脱附等手段对比分析了合成的3种MCM-41介孔材料的物相、比表面积、孔径、孔体积等,发现酸性介质中合成的介孔材料的孔径最大.在此基础上,利用MCM-41介孔材料对比研究了处理含镉离子(Cd2 )废水的效果和机理,确定了不同介孔材料用量、不同初始pH值条件下MCM-41介孔材料对水中Cd2 的吸附率和吸附量.结果表明:介孔材料用量相同时,溶液pH值的增大有利于提高3种MCM-41介孔材料对水中Cd2 的处理效果.在pH值从7.0到8.0的过程中,其吸附率有1个突变,MCM-41-T的Cd2 吸附率从35.65%提高到62.15%;MCM-41-N的从38.80%提高到69.40%;MCM-41-H的从50.22%提高到73.47%.孔径最大的MCM-41-H对Cd2 的吸附效果最佳,最大吸附率为89.56%,最大吸附容量为8.57 mg/g.吸附溶液pH值的大小和介孔材料的孔径尺寸是决定吸附量大小的关键因素,因此,重点应通过优化合成工艺提高介孔材料的孔径.     

Comparative Study of the Acidic and Catalytic Properties of the Mesoporous Material H-MCM-41 and Zeolite H-Y

The objective of this work is to give a comparative characterization of aluminosilicate MCM-41 and zeolite Y, in particular with respect to acidity and catalytic properties in hydrocarbon cracking. These studies are compared to a well investigated amorphous aluminosilicate, based on the fact that the new mesoporous MCM-41 materials are a mixture of ordered material with amorphous pore walls. Characterization of differently treated MCM-41 materials and zeolite Y for comparison by N₂ sorption, XRD, TPAD (Temperature Programmed Ammonia Desorption) with in situ FT-IR in combination with catalytic testing by MAT (Micro Activity Test) is discussed. Combination of the characterization data and the catalytic testing gives an interesting explanation of the surface properties especially in comparison with zeolite Y.     

Evaluation of various types of Al-MCM-41 materials as catalysts in biomass pyrolysis for the production of bio-fuels and chemicals

MCM-41, is one of the latest members of the mesoporous family of materials. They possess a hexagonal array of uniform mesopores (1.4–10 nm), high surface areas (>1000 m²/g) and moderate acidity. Due to these properties the MCM-41 materials are currently under study in a variety of processes as catalysts or catalyst supports. The objective of this study was to evaluate different types of MCM-41 materials as potential catalysts in the catalytic biomass pyrolysis process. We expected that the very high pore size and the mild acidity of these materials could be beneficial to reformulate the high molecular weight primary molecules from biomass pyrolysis producing useful chemical (and especially phenolic compounds) and lighter bio-oil with less heavy molecules. Three different samples of Al-MCM-41 materials (with different Si/Al ratio) and three metal containing mesoporous samples (Cu–Al-MCM-41, Fe–Al-MCM-41 and Zn–Al-MCM-41) have been synthesised, characterized and tested as catalysts in the biomass catalytic pyrolysis process using a fixed bed pyrolysis combined with a fixed catalytic reactor and two different types of biomass feeds. Compared to conventional (non-catalytic) pyrolysis, it was found that the presence of the MCM-41 material alters significantly the quality of the pyrolysis products. All catalysts were found to increase the amount of phenolic compounds, which are very important in the chemical (adhesives) industry. A low Si/Al ratio was found to have a positive effect on product yields and composition. Fe–Al-MCM-41 and Cu–Al-MCM-41 are the best metal-containing catalysts in terms of phenols production. The presence of the Al-MCM-41 material was also found to decrease the fraction of undesirable oxygenated compounds in the bio-oil produced, which is an indication that the bio-oil produced is more stable.     

Design and synthesis of near-IR luminescent mesoporous materials covalently linked with tris(8-hydroxyquinolinate)lanthanide(III) complexes

By using the bifunctional ligand, 8-hydroxyquinoline-functionalized organosilane (Q-Si), the new mesoporous material Q–MCM-41 covalently bonded with 8-hydroxyquinoline was synthesized. Through the ligand exchange reaction, the new near-infrared (NIR) luminescent mesoporous LnQ₃–MCM-41 (Ln = Er, Nd, Yb) materials were prepared by linking the lanthanide quinolinate complexes to the ordered mesoporous Q–MCM-41 material. The LnQ₃–MCM-41 materials were characterized by powder X-ray diffraction and N₂ adsorption/desorption, and they all show the characteristic mesoporous structure of MCM-41 with highly uniform pore size distributions. Fluorescence spectra of these LnQ₃–MCM-41 materials were recorded and the corresponding luminescence decay analyses were measured. After ligand-mediated excitation, all the emission spectra of the LnQ₃–MCM-41 materials show the characteristic NIR-luminescence of the corresponding lanthanide ions via the intramolecular energy transfer from the ligands to the lanthanide ions. The good luminescent performances enable these NIR-luminescent mesoporous materials to have potential applications in optical amplification (operating at 1.3 or 1.5 μm) and laser systems, etc.     

介孔材料对乳液聚合稳定性的影响

研究了十二烷基硫酸钠(SDS)在不同介孔材料(MCM-41、MCM-48、SBA-15)存在下的临界胶束浓度(CMC),讨论了介孔材料对间歇乳液聚合的影响。研究表明:孔径最大的介孔材料SBA-15存在下SDS的CMC增加最多;在聚合体系中加入介孔材料对单体转化率没有影响,但增加了乳液聚合时的凝聚率,其中使用小孔径的MCM-41凝聚物较少,而颗粒较大的MCM-48凝聚物较多,同时所得乳液聚合物的分子量下降,分子量分布变宽。     

镧系金属掺杂MCM-41的合成、表征及其脱硝性能研究

以正硅酸乙酯、硝酸镧、硝酸铈为原料,十六烷基三甲基溴化铵作模板剂,水热条件下合成镧、铈掺杂介孔分子筛。采用 XRD、FT-IR和氮气吸附脱附等对镧系金属掺杂MCM-41 进行表征,并以氨为还原剂研究其选择性催化还原一氧化氮活性以及反应条件（包括镧系掺量、反应温度、空速、氨氮比等）对催化性能的影响。本文旨在掺杂镧系金属提高分子筛的脱硝性能。镧系掺杂的分子筛改变了骨架增强了反应活性,稀土金属的高电荷密度使分子筛催化活性提高。结果表明,镧系金属镧、铈成功进入MCM-41 介孔材料的骨架内并保持有序的六方介孔结构,随着镧系掺杂量的增加,介孔有序性降低。当n（镧系金属）/n（硅）=0.04 、空速为4 000 h-1、n（氨气）/n（一氧化氮）为1 时 Ln-MCM-41催化剂在350 ℃反应时能保持较高活性。镧系掺杂的介孔分子筛能更有效地提高催化性能。