Isothermal template removal from MCM-41 in hydrogen flow

Thermal evacuation of template surfactant from MCM-41 in hydrogen atmosphere was investigated. Micelle templated silica was prepared using hexadecyltrimethylammonium bromide. The mechanism of template removal appears to be completely different in hydrogen as compared to calcination in air. It seems that moderate heating of as-synthesized MCM-41 (up to about 250 °C) in hydrogen stream for about 15 h is effective and simple method of template removal leaving no pure carbon residues on silica surface. Adsorption properties of partially evacuated MCM-41 samples were tested using gas chromatography. Products of template degradation were analyzed using GC–MS technique. The main products of template degradation at 250 °C in hydrogen flow are hexadecene and hexadecane-N,N-dimethylamine. Concentration of surface silanols for MCM-41 calcined and thermally treated in hydrogen flow was investigated by NMR technique.     

Effect of nanosized mesoporous MCM-41 (with template) material on properties of natural rubber nanocomposites

Abstract

Mesoporous mobil composition of matter 41 (MCM-41) (with template) was used directly as a new filler for naural rubber (NR). Inside the pore chanels, and on the outer surface of the MCM-41 particle, were cationic surfactant CTAB and Pluronic F₁₂₇ (molecular weight = 11 500) mixture. Results showed that the tensile properties and the thermal stability of NR/mesoporous MCM-41 (with template) nanocomposite were improved at low filler loading as compared with those of NR compound. Scanning electron microscopy observations revealed that enhancement of the interface was obtained by adding MCM-41 (with template).     

以离子液体为模板剂合成MCM-41介孔分子筛

以离子液体1-十六烷基-3-甲基溴代咪唑为模板剂,合成介孔分子筛MCM-41。考察了不同硅源[、C16mim]Br/SiO2配比、pH值、晶化时间等条件对合成MCM-41的影响。采用XRD和低温氮吸附对产物进行表征,结果表明该方法合成的样品具有较大比表面积和规整介孔孔道结构。     

以聚乙二醇/十六烷基三甲基溴化铵为模板剂制备MCM-41分子筛

通过将聚乙二醇(PEG)直接引入MCM-41分子筛合成模板剂十六烷基三甲基溴化铵溶液中,经脱洗和焙烧处理得到厚孔壁有序介孔材料.选用X射线衍射(xRD)、透射电子显微镜(TEM)和等温吸附(BET)对样品进行了表征,结果显示,添加PEG的合成产物孔壁厚度增加,孔壁厚度可达1.45 nm,孔径尺寸和比表面积减小,有序性降低,低相对分子质量PEG的添加有助于厚孔壁产物生成.     

介孔MCM-41对聚丙烯力学性能的影响

将纳米介孔MCM-41配制成悬浮液,采用熔融共混方法将其与聚丙烯共混,制备出综合力学性能较好的PP/MCM-41复合材料.透射电子显微镜(TEM)观测结果显示,MCM-41在悬浮液中呈纳米尺寸分散,无团聚现象;力学测试结果显示,当MCM-41的添加量为0.5%(质量分数)时,复合材料的拉伸、冲击、弯曲综合力学均较纯PP有所提高.     

Effect of Cobalt Precursors on the Dispersion of Cobalt on MCM-41

The photocatalytic activity of titanium dioxide supported on zeolites HZSM-5, HY and H was evaluated for a novel intermolecular cyclization of ethylenediamine with propylene glycol leading to dihydropyrazine. Titanium dioxide supported on zeolites has been prepared with 2 and 5 wt% of TiO₂ by solid-state reaction, impregnation and sol impregnation methods. From the characterization by XRD, BET, EDAX and TPD of NH₃, it is deduced that in all cases titanium dioxide is in small particles of anatase on zeolites. The highest photocatalytic activity was obtained with 2 wt% TiO₂/H prepared by solid-state reaction. The acidity determined by TPD of NH₃ was found to be lower for TiO₂/H than for TiO₂/HZSM-5 and TiO₂/HY. From the above observations, it can be concluded that adsorption, acidity and structure of zeolites have an influence on the activity of supported TiO₂.     

MgO/MCM-41对二氧化碳的吸/脱附性能的研究

采用等体积浸渍法制备MgO/MCM-41作为吸附剂,通过静态吸附法对其吸附性能进行了测定。结果表明,制得的吸附剂只存在一个碱性位,二氧化碳吸附后主要以碳酸氢盐的形式存在。当MgO的负载量为20%的时候,对二氧化碳的吸附量最大,在30℃条件下,其对二氧化碳的吸附量为46.6 mg/g。     

Effects of different structure-directing agents (SDA) in MCM-41 on the adsorption of CO2

CO₂ capturing technologies have attracted significant attention in order to limit emissions and reduce their negative effect on the environment. Mesoporous silica materials (MCM-41) are easily recyclable, affordable, and thermally and mechanically stable, providing added benefits in CO₂ capture. However, further studies are necessary to characterize the effects of MCM-41 pore size, adsorption temperature and surface silylation on CO₂ adsorption efficiency. In this work, mesoporous silica is synthesized using alkyltrimethylammonium bromide with different chain lengths (C_nH_2n + 1 N(CH₃)₃Br, n = 14, 16 and 18) as structure-directing agents, and the adsorption capacity of CO₂ on TTMCM-41 (C₁₇H₃₈NBr), CTMCM-41 (C₁₉H₄₂NBr), DTMCM-41(C₂₁H₄₆NBr) samples was measured gravimetrically at room temperature and pressure up to 40 bar. The silica structures were characterized by X-ray diffraction (XRD), nitrogen adsorption/desorption, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy (TEM). The XRD, N₂ adsorption–desorption and TEM measurements indicated the presence of a well-ordered hexagonal array with uniform mesostructures. The mesoporous silica obtained, denoted as TTMCM-41, CTMCM-41 and DTMCM-41, had distinct physical properties, such as BET surface area, hexagonal unit cell, pore volume, pore diameter and pore wall thickness. CTMCM-41 exhibited an adsorption capacity (0.58 g CO₂/g adsorbent) of more than DTMCM-41 (0.48 g CO₂/g adsorbent) and TTMCM-41 (0.42 g CO₂/g adsorbent). The results suggest that CTMCM-41 can be a better mesoporous adsorbent for CO₂ adsorption .     

Investigation of equilibrium and kinetic parameters of methylene blue adsorption onto MCM-41

Mesoporous MCM-41 was synthesized at room temperature using tetraethoxysilane (TEOS) with cetyltrimethylammonium bromide (CTAB) and employed as an effective adsorbent for the adsorption of methylene blue dye from aqueous solution. The as-synthesized MCM-41 was calcined at 250 and 550°C to study the relation between the surface area and pore volume with surfactant removal. The synthesized MCM-41 was characterized using thermo gravimetric analysis (TGA), X-ray diffraction (XRD) patterns, nitrogen adsorption/desorption isotherms and Fourier transform infrared (FT-IR) spectroscopy. The MCM-41 calcined at 550°C showed higher surface area (1,059 m² g^?1) with pore volume of 0.89 ml g^?1 and was used for the investigation of adsorption isotherms and kinetics. The experimental results indicated that the Freundlich and Redlich-Peterson models expressed the adsorption isotherm better than the Langmuir model. In addition, the influence of temperature and pH on adsorption was also investigated. The decrease in temperature or the increase in pH enhanced the adsorption of dye onto MCM-41. A maximum adsorption capacity of 1.5×10^?4 mol g^?1 was obtained at 30°C. The kinetic studies showed that the adsorption of dye on MCM-41 follows the pseudo-second-order kinetics.     

吸附法脱除芳香含硫化合物的研究进展

吸附法可以脱除加氢汽油、柴油中的芳香含硫化合物,是超低硫油品的一种具有工业前景的脱硫方法.详细介绍了分子筛吸附剂、氧化物吸附剂、络合吸附剂、分子印迹吸附剂和化学吸附吸附剂等的设计、再生的最新研究进展.吸附脱硫目前的主要问题在于对硫化物的吸附选择性低和再生与重复使用效果不好.     

模板剂碳链长度对MCM-41晶体结构的影响

The mesoporous molecular sieve （MCM）-41 using ionic liquid as template has been prepared. The typical template of ionic liquid was [C16mim]X. In this article, the use of 1-alkyl-3-methylimidazolium （[Cnmim]Br, where n= 12,14,16,18,20） salts as templates in the synthesis of MCM-41 is reported. The results showed that the synthesized MCM-41 had uniform pore diameter, high surface area and stable framework. The largest surface area of MCM-41 was the one prepared with [C14mim]Br as template. When using [C18min]Br as template, the narrowest pore distribution sample was obtained and the effect of surface tension of template solution to MCM-41 was first discussed.     

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.     

Characterisation and catalytic properties of MCM-41 and Pd/MCM-41 materials

Pure silica MCM-41 mesoporous molecular sieve material was synthesised and characterised by in situ synchrotron XRD, TEM, TGA/DTA and DRIFTS techniques. In situ energy dispersive XRD (EDXRD) confirmed the exact nature of the pore diameter of MCM-41 and the change in crystal structure on calcination. The IR band at 1057 cm^-1 of as-synthesised MCM-41 was shifted by 14 cm^-1 on heating to 673 K due to increased condensation of silanol groups to form Si-O-Si bridges. Calcined MCM-41 materials were used to support Pd, and the catalytic activities for 1-hexene and benzene selective hydrogenation were investigated. The Pd/MCM-41 catalyst showed high activity in hydrogenation of 1-hexene at an inlet reaction temperature of 298 K, but did not show any activity in hydrogenation for benzene. TEM results for the reduced Pd/MCM-41 catalysts revealed that the average Pd particle size was around 2-2.5 nm and these particles were located in the pores of MCM-41 and showed good distribution. TPR measurements showed that about 70% of palladium oxide (PdO) loading in the calcined catalysts was reduced at sub-ambient temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

改性MCM-41分子筛的合成与亚甲基蓝吸附性能

选用TEOS（正硅酸乙酯）做为硅源,CTAB（十六烷基三甲基溴化铵）做为表面活性剂,在碱性条件下水热合成MCM-41。实验采用3-氨丙基三甲基硅烷对MCM-41进行改性,成功得到氨基改性介孔材料NH₂-MCM-41吸附剂,并使用X射线衍射（XRD）对其做了表征。考察了各种实验条件下,比如温度、吸附剂的量、pH、亚甲基蓝初始浓度等条件下MCM-41和NH₂-MCM-41对水溶液中亚甲基蓝（MB）的吸附能力。MCM-41和氨基改性介孔材料NH₂-MCM-41均为平面六方介孔结构。结果表明,温度和pH是影响MCM-41和NH₂-MCM-41对亚甲基蓝吸附的最主要的因素。随着温度的升高,材料吸附能力增强,而过高或者过低的pH都会降低MCM-41和NH₂-MCM-41对亚甲基蓝的吸附能力。     

Silylated rice husk MCM-41 and its binary adsorption of water–toluene mixture

Mesoporous material, MCM-41, synthesized from rice husk (RH-MCM-41) was modified by loading silylating agent (either trimethylchlorosilane (TMCS), dimethyl-dichlorosilane (DMCS) or phenyl-trichlorosilane (PTCS)) with different concentrations (1–9 wt.%), and aging times, varied between 1, 6, 9, and 24 h. Properties of the silylated MCM-41 samples were characterized by XRD, FTIR, N₂ adsorption, and the binary adsorption of a water–toluene mixture for the breakthrough curves; afterwards, the hydrophobicity indices were determined. Silylating agent caused RH-MCM-41 to possess smaller average pore size and surface area, compared to parent RH-MCM-41. Using a silylating condition of 1 wt.% TMCS for 1 h, modified RH-MCM-41 showed satisfactory enhancement its of hydrophobicity without any significant surface modification. Due to the substitution of silane group onto RH-MCM-41, the hydrophobicity index was increased.     

MCM-41介孔分子筛吸附性能的热力学和动力学分析

实验以亚甲基蓝作为模型吸附质,探讨了MCM-41介孔分子筛对模型吸附质亚甲基蓝的吸附性能,并对其吸附过程进行了热力学和动力学分析。结果表明,MCM-41介孔分子筛的吸附率高达94%,对亚甲基兰的吸附符合二级吸附动力学,MCM-41对亚甲基兰的吸附行为属于Freundlich等温吸附,整个吸附过程属于放热反应。     

铝对固体超强酸/介孔分子筛催化性能的促进作用

采用浆态直接浸渍-焙烧方法制备了铝促进的固体超强酸／介孔分子筛材料，并采用XRD、N2吸附、吡啶吸附IR、反应表征等方法对其结构及性能进行了表征。铝的引入有利于形成和稳定样品表面的B酸，有助于稳定表面硫物种，而样品的比表面和孔容随着铝的加入变化不大。添加适量的铝能够大大提高正丁烷异构化的催化活性。     

Effect of Mg doping on photoluminescence of ZnO/MCM-41 nanocomposite

In this paper, photoluminescence (PL) behavior of Mg_xZn_1?xO/MCM-41 nanocomposite (where x = 0.05, 0.15, 0.25 and 0.30) is reported. Samples were characterized with small angle X-ray diffraction (SAXRD), wide angle XRD, BET (Brunauer–Emmet–Teller) surface area and pore size analyzer, field emission scanning electron microscope (FE-SEM), high resolution transmission electron microscope (HR-TEM) and PL spectrometer. The structure of MCM-41 was confirmed from both SAXRD and BET results. A broad PL band positioned at around 393 nm has been exhibited by ZnO/MCM-41 nanocomposite. With Mg doping, intensity of this PL band decreased for x = 0.05 and 0.15 and above this there was gradual enhancement in intensity. It was found that the intensity of the PL band, strongly depends on the particle size of ZnO. The increase in particle size along with MgO phase separation for x = 0.30 was proved by HR-TEM analysis. Interestingly, the differences in particle sizes at different concentrations of Mg did not account for shift in the PL band. A twofold enhancement in the intensity of PL band when x = 0.30 compared to bare ZnO/MCM-41 nanocomposite was observed. It is attributed for the increase in particle size which preserves the energy saved by passivation of ZnO nanoparticles and the other one is formation of heterojunction structures between ZnO and MgO. It was also evident from these results that there is increase in oxygen vacancies of ZnO crystallites with increase in particle size.     

新型纳米MCM-41合成研究

本实验合成未脱除模板剂的MCM-41分子筛,然后进行焙烧使模板剂炭化,生成碳纳米丝,留在孔道中。对MCM-41进行XRD检测,考察了晶化温度、晶化时间、硅铝比、水量等各因数的影响。结果表明,强酸性介孔晶体分子筛的生成,受铝含量的影响很大,模板剂的用量增加也有利于产物的生成,受水含量的影响不大。在实验的基础上,对一些不理想的步骤也提出了一些改进方法。     

苯乙烯在MCM-41介孔材料中聚合的研究

The polymerization of styrene in the media of MCM-41 is carried out by means of host-guest polymerization of styrene in MCM-41 mesoporous material with the aim to investigate the effects of interface and confinement of MCM-41 on host-guest interactions. Detailed physical properties of the mesoporous MCM-41 material containing polystyrene is characterized by XRD(X-ray diffraction), FT-IR(Fourier transform infrared), TGA(thermal gravimetric analysis), and nitrogen adsorption-desorption isotherms. We also find a great increase in the glass transition temperature of guest polystyrene influenced by the confined geometry of the host by differential scanning calorimetry(DSC).