Photoluminescence study of mesoporous MCM-41 and Ti-grafted MCM-41

Photoluminescence combined with diffuse reflectance UV—Vis spectroscopy was used to characterise both the pure siliceous MCM-41 and Ti-MCM-41 containing tetrahedral Ti(IV) species anchored onto the inner walls of the siliceous MCM-41. Both Ti-MCM-41 and MCM-41 showed complex photoemission signals and this study allows, for the first time, the distinction of the emission signals of tetrahedral Ti9IV) ions from those due to silica surface centres.     

Characteristics of molecular sorption on template containing mesoporous molecular sieves of type MCM-41

Template containing materials of type MCM-41 have properties of microporous substances. On absorption into the micropores of such materials the dependence of the characteristic absorption energies on the molecular mass of the sorptive is extreme, and the specific absorption volume decreases with increased molar volume of the sorptive. A model is proposed to explain the peculiarities of the absorption properties of the template containing materials. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 6, 367–372, November–December, 1999.     

Hydrogenation of naphthalene on noble-metal-containing mesoporous MCM-41 aluminosilicates

Aromatic saturation of oil fractions is a key process in the refining industry due to increasing demand for cleanest distillates with superior performances. In this study, the behavior of different catalysts containing 1 wt.% of noble-metal inside a mesoporous MCM-41 (Si:Al=20) framework was investigated in the hydrogenation of naphthalene, as preliminary step to investigate bimetallic catalysts. While at atmospheric pressure only Rh and Pd showed a low hydrogenation activity, in the tests performed at 6.0 MPa the catalytic activity grew, exhibiting the following order: Pt>RhPd>>>Ru≈Ir. However, all the catalysts required a large H₂ excess, to avoid a decrease in hydrogenation and ring-opening activity, and gave rise to the best performance for a contact time of 6.8 s, favouring at lower values the partial hydrogenation to tetralin and at higher values cracking reactions. Finally, all the catalysts showed low thio-tolerance, with significant deactivation already feeding 100 ppm wt. of dibenzothiophene (DBT), with a partial reversibility only for the Pt-containing catalyst (CAT 3).     

Epoxidation of cyclohexene on modified Ti-containing mesoporous MCM-41

Ti-MCM-41, B-Ti-MCM-41 and Ti-grafted MCM-41 were synthesized, characterized and studied in the epoxidation of cyclohexene. The synthetic methods and the effect of water in the oxidant are discussed.     

Double-layered co-microencapsulated ammonium polyphosphate and mesoporous MCM-41 in intumescent flame-retardant natural rubber composites

Double-layered co-microencapsulated ammonium polyphosphate (APP) and mesoporous MCM-41 (M(A&M)) were prepared using melamine–formaldehyde resin and zinc borate by in situ polymerization. The structure of the microcapsules was characterized by particle size analysis, Fourier-transform infrared spectroscopy, and scanning electron microscopy. Double-layered microencapsulation gave APP narrow particle size distribution. The flame-retardant and mechanical effects of M(A&M) in natural rubber (NR) were evaluated using the limiting oxygen index, UL 94 test, thermogravimetric analysis, and tensile test. Results indicated that the NR/M(A&M) composites had much better flame-retardant and mechanical properties than the NR/APP/MCM-41 composites. The limited oxygen index value of the NR/M(A&M) composite reached the maximum, and the UL-94 ratings were increased to V-0 when the ratio of APP to MCM-41 was 39:1 in microcapsule. The occurrence of a synergistic effect between MCM-41 and intumescent flame-retardant in the NR composites was proved. This investigation provided a promising formulation for flame-retardant NR composites.     

Beta zeolite colloidal nanocrystals supported on mesoporous MCM-41

Zeolite-based composite materials prepared by the embedding of the beta zeolite nanophase from aqueous colloidal solution into matrices of preformed Si(Al)MCM-41 mesoporous molecular sieves have been characterized by different methods (XRD, SEM, FTIR, N2 adsorption, and TPD of NH3). Their potential as catalysts for toluene disproportionation has been compared to mechanical mixtures of freeze-dried nanobeta crystallites with Si(Al)MCM-41 mesoporous materials. It is found that the zeolite catalyst efficiency is not substantially changed by the presence of mesopores belonging to the matrix. It is suggested that formation of intergrown aggregates from the colloidal nanobeta particles provides own highly developed textural mesoporosity that makes the contribution of the diffusional alleviation of the support negligible.     

Effect of rehydration on the porosity of MCM-41 mesoporous molecular sieves

In distinction from aluminosilicates, the porosity of the detemplated silicous MCM-41 is significantly reduced after several cycles of dehydration-rehydration. The stability of Si-MCM-41 is not changed by absorption-desorption of nonpolar hexane. An explanation is proposed for the effect of rehydration on the porosity of MCM-41. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 35, No. 1, pp. 50–55, January–February, 1999.     

Effective controlled release of captopril by silylation of mesoporous MCM-41.

The release of the water-soluble drug Captopril is controlled by tailoring the surface properties of mesoporous silica via stepwise silylation. The degree of silylation is manipulated by adjusting the initial concentration of silylanizing reagent (trimethylchlorosilane, TMCS). The silylanized and drug-loaded samples are characterized by powder X-ray diffraction, Fourier transform IR spectroscopy, N2 adsorption and desorption, 29Si cross-polarization magic angle spinning NMR spectroscopy, and transmission electron microscopy. The drug-loading amount is correlated to the Brunauer-Emmett-Teller surface area and surface hydrophilicity/hydrophobicity of the mesoporous silica material, while drug release profiles can be controlled by tailoring the surface properties and pore size.     

Titania nanoparticles synthesis in mesoporous molecular sieve MCM-41

Nanocrystalline titanium oxide (TiO(2)) is one of the most useful oxide material, because of its widespread applications in photocatalysis, solar energy conversion, sensors and optoelectronics. The control of particle size and monodispersity of TiO(2) nanoparticles is a challenging task. The use of MCM-41, an inorganic template of uniform pore size (2-10 nm), can overcome this difficulty and produce stable nanoparticles of uniform size and shape. Here, we demonstrate the synthesis of titania nanoparticles inside the pores of silica based MCM-41 forming a TiO(2)/Si-MCM composite. Composites are formed in the alcoholic medium by incipient wetness impregnation method. Titania particles of average 3 nm size are obtained. Effect of silica and titania precursors on the quality of nanoparticles has been investigated. The characterization of titania-MCM-41 composites has been carried out using a variety of techniques like UV-vis absorption spectroscopy, X-ray diffraction, FT-IR spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and photoluminescence spectroscopy. It has been found that the titania particles are co-ordinated with Si-MCM by SiOTi covalent bond.     

Solid-state NMR study of MCM-41-type mesoporous silica nanoparticles

A systematic study of the surface of MCM-41-type mesoporous silica nanoparticles prepared under low surfactant concentration was carried out using high-resolution solid-state nuclear magnetic resonance spectroscopy. The structures and concentrations of various species present during dehydration and rehydration of mesoporous silicas between -25 and 500 degrees C were detailed by employing one-dimensional and two-dimensional (1)H, (13)C, and (29)Si NMR, including (1)H signal intensity measurements, (1)H-(1)H homonuclear correlation experiments (double quantum, exchange, and RFDR), and (1)H-(29)Si heteronuclear correlation NMR. These experiments employed high MAS rates of up to 45 kHz. The study shows that the surfactant (CTAB) was almost completely removed by acid extraction. The residual molecules assumed prone positions along the pores, with the tailgroup being most mobile. The weakly adsorbed water was hydrogen bonded to the silanol groups, all of which were involved in such bonds under ambient humidity. Specific structures involving water and silanol groups were proposed for various stages of thermal treatment, which included dehydration, dehydroxylation, and subsequent rehydration.     

自制Ti/W-MCM-41介孔分子筛催化制备乳酸戊酯

采用自制的介孔分子筛Ti/W-MCM-41催化乳酸与正戊醇的酯化反应,合成了乳酸正戊酯;利用红外光谱仪分析了催化剂的化学特征,考察了分子筛的WO3质量分数、催化剂用量、醇酸物质的量比、反应时间、催化剂重复使用性能等因素对目标产物酯化率的影响.结果表明,在nSi∶nTi=30∶1,WO3质量分数10%,550℃下焙烧6h条件下制得的催化剂具有良好的催化性能;其催化合成乳酸正戊酯适宜的反应条件为:0.2mol乳酸,催化剂用量0.5g,n(正戊醇)∶n(乳酸)=1.6∶1,反应时间100min,酯化率可达94.4%.该催化剂使用7次酯化率仍可达86.6%.     

Modification of MCM-41 and SBA-15 mesoporous silicas by imidazolium ionic liquids

MCM-41 and SBA-15 mesoporous molecular sieves are modified with imidazolium ionic liquid (IL) via both physical adsorption and covalent grafting. The considerable effect of IL grafting on the porous structure and the particle morphology of mesoporous supports is shown. The pore size of these supports is found to be a key parameter determining the possibility of loading IL into such support materials.     

Synthesis of hollow spherical silica with MCM-41 mesoporous structure

Hollow spherical mesoporous silica was synthesized by using sodium silicate as a precursor and a low concentration of cetyltrimethylammonium bromide (CTAB) (0.154 mol dm^–3). The resulting hollow spherical particles were characterized with scanning electron microcopy (SEM), small-angle X-ray diffraction (SXRD), transmission electron microscopy (TEM), and N₂ gas adsorption and desorption techniques. The results showed that regular spherical mesoporous silica could be obtained only if the molar ratio of propanol to CTAB was in the range of approximately 8:1–9:1. The spherical particles were hollow (inside), and the shell consisted of smaller particles with a pore structure of hexagonal symmetry. With an increase of the molar ratio of propanol to CTAB, the distance (a value) between centers of two adjacent pores increased, and the pore structure of mesoporous silica became less ordered. N₂ adsorption–desorption curves revealed type IV isotherms and H1 hysteresis loops; with an increase of the molar ratio of propanol to CTAB, the pore size with Barrett–Joyner–Halenda (BJH) diameter of the most probable distribution decreased, but the half peak width of the pore size distribution peak increased     

Adsorption of diazinon and fenitothion on MCM-41 and MCM-48 mesoporous silicas from non-polar solvent

The adsorption of two common organophosphorus pesticides, diethoxy-[(2-isopropyl-6-methyl-4-pyrimidinyl)oxy]-thioxophosphorane (diazinon) and dimethoxy-(3-methyl-4-nitrophenoxy)-thioxophosphorane (fenitrothion), by MCM-41 and MCM-48 mesoporous silicas at room temperature was investigated. UVvis and IR spectroscopy, small-angle X-ray diffraction, and the specific surface area analysis (S _BET) were used to study the adsorption behavior of diazinon and fenitrothion. The results show that the MCM-41 and MCM-48 mesoporous silicas adsorb diazinon more efficiently than fenitrothion. The extraction of adsorbed materials from the adsorbents with polar solvents and subsequent analysis by ³¹P NMR showed that the adsorption of diazinon and fenitrothion on mesoporous silicas is destructive and non-destructive, respectively. Nitrogen adsorption measurements showed that the specific surface area of both silicas decreases after the adsorption of pesticides, and the larger effect is observed for diazinon. The article is published in the original.     

青霉素酰化酶在介孔分子筛MCM-41上的固定化研究

通过改变酶固定化时的pH值、温度、时间以及酶用量,研究了固定化条件对MCM-41载体上固定化青霉素酰化酶的酶活及其稳定性的影响,明确了酶活及其稳定性随固定化条件的变化规律,初步分析了青霉素酰化酶在介孔分子筛MCM-41上的固定化过程。     

Iron oxide/MCM-41 mesoporous nanocomposites and their magnetorheology

Mesoporous nanocomposite materials of magnetic iron oxide-containing MCM-41 (IO/MCM-41) were prepared by simple thermal oxidation of Fe-containing MCM-41 initially prepared by a direct synthesis route using Fe³⁺ salt. The magnetic saturation of the fabricated nanocomposite materials was measured using a vibrating sample magnetometer, while surface morphology and inner framework of the composite materials were studied using a field emission scanning electron microscope and a transmission electron microscope to confirm their mesoporous nanocomposite formation. The fabricated magnetic materials were then adopted as a magnetorheological (MR) fluid, where the IO/MCM-41 magnetic nanocomposites were dispersed in a nonmagnetic medium oil in addition to as an additive for carbonyl iron-based MR fluid. Their MR properties of flow curve along with yield stress and viscoelastic properties under applied magnetic fields were investigated using a rotational rheometer.     

Effect of titanium on the structure and properties of mesoporous MCM-41 molecular sieves

Mesoporous MSM-41 titanium silicate molecular sieves with high titanium content were synthesized. The hexagonal structure along with high specific surface and pore volume are retained up to Si/Ti≥5. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 3, pp. 177–182, May–June, 1999.     

Influence of the incorporated metal on template removal from MCM-41 type mesoporous materials

Al-modified MCM-41, La-modified MCM-41, and Ce-modified MCM-41 mesoporous materials were prepared with different molar ratios (Si/M = 10; 25; 50; 100 and 200) at room temperature. The materials were characterized using XRD, BET–BJH, and TG–DTA. The XRD showed four peaks, due to the ordered hexagonal array of parallel silica tubes, which could be indexed as (100), (110), (200), and (210), assuming a hexagonal unit cell. The surface area decreased as the concentration of the metal incorporated in the material increased. The thermal stability of the materials was around 650 °C. The CeO₂ phase made the mass transfer process more difficult, hindering Hofmann degradation and favoring oxidation.     

Thermogravimetry applied to characterization of fly ash-based MCM-41 mesoporous materials

The thermogravimetry (TG) was used for characterization of the fly ash (FA)-based MCM-41 mesoporous materials. MCM-41 mesoporous materials were synthesized using silica extracts from different FA. The synthesis of MCM-41 from FA was carried out by the hydrothermal method using the supernatants of coal FA (in the form of sodium silicate) and cationic cetyltrimethylammonium bromide (CTAB) surfactants as the structure-directing agents. On the basis of the data obtained from the TG analysis, thermal behaviour of FA-based MCM-41 mesoporous materials was assessed. This study has established the range of temperatures corresponding to the desorption of water, decomposition of the surfactant and condensation of silanol, thereby making the overall quality assessment of FA-based MCM-41 mesoporous materials.     

Formation at low surfactant concentrations and characterization of mesoporous MCM-41

At low concentrations of cetyltrimethylammonium bromide,all silica-based mesoporous materials with hexagonal phase have been synthesized via interactions between self-assembled surfactant molecule aggregates and aniomc silicate polymers.The resulting materials are characterized by XRD,FT-IR,solid state 29Si MAS NMR,thermal analysis and N2 adsorption-desorption measurements.After soluble ions are removed,the interactors between surfactant micelles and silicate polymers are reorganized and then form mesostructures 1 he hexagonal framework is sonsistent with amorphous silica gel.The structures of materials depend on the synthesis conditions Hydrothermal process improves the interactions between molecules and increases the degree of framework silicon atom polymerization The.surface area and the mesopore volume of the material prepared at 100℃ increase by 87% and 71 %,respectively,compared with those obtained at room temperature.