Mesoporous Molecular Sieve MCM-41 Research Articles

Formation of CdS nanoparticles within functionalized siliceous MCM-41

Cadmium sulfide nanoparticles were prepared within the siliceous MCM-41 mesoporous molecular sieve, whose surface was functionalized with 3-mercaptopropyltrimethoxysilane at different temperatures. Their size, estimated from diffuse reflectance UV/VIS spectra, decreases with increasing number of introduced thiol groups acting as anchors.

Preparation of high thermal stability MCM-41 in the low surfactant/silicon molar ratio synthesis systems

The preparation of a mesoporous molecular sieve MCM-41 both with bimodal framework and textural mesopores and with high thermal stability that results from a thicker wall has been achieved by decreasing surfactant/silicon ratio of synthesis gel. The resultant material retains porosity and large BET surface area even after thermal treatment at 1273 K for 1 h in air.

Encapsulation of fluorescein into MCM-41 mesoporous molecular sieve by a sol–gel method

MCM-41-hosted fluorescein mesophase was prepared by addition of the dye into the sol–gel mixture for the synthesis of MCM-41 mesoporous molecular sieve under microwave radiation. The as-synthesized organo-silica-surfactant material possessed hexagonal mesostructure with short-range symmetry and a uniform nanosize of about 30 nm. Furthermore, fluorescence spectrum, increase in lifetime and lack of aggregation at high concentration were discussed in terms of the effect of the host–guest interaction on these properties.

Synthesis of TMBQ using Cu(II)-substituted MCM-41 as the catalyst

Mesoporous MCM-41 molecular sieves substituted with various amounts of Cu(II) and Al(III) were synthesized by the hydrothermal method. The resultant materials were characterized by XRD, XANES, surface area and pore size measurement, EPR and 27Al solid state NMR. The Cu(II)-substituted MCM-41 was found to be an efficient catalyst in the oxidation of trimethylphenol (TMP) to trimethylbenzoquinone (TMBQ) at mild reaction conditions. The latter is an intermediate in the manufacture of Vitamin E. The optimal activity was obtained when MCM-41 was concomitantly substituted with small amounts of Cu(II) and Al(III). The liquid phase reactions were extremely sensitive to the oxidant and solvent used. With acetonitrile as solvent, hydrogen peroxide and tert-butyl hydrogen peroxide were effective oxidants but with benzaldehyde as solvent, oxygen gas was also an effective oxidant.

A novel morphology of mesoporous molecular sieve MCM-41

Mesoporous molecular sieve MCM-41 and its Ti-modified derivative have been synthesised in a mild alkali condition using cetylpyridinium bromide as template. The (0 0 1) surface of the MCM-41 particles shows a paintbrush-like morphology formed by bundles of silica nanotubes. The smallest silica form in the mesoporous phases, single silica nanotubes, was also observed on the surface.

Synthesis of Nano-sized MCM-41 Mesoporous Molecular Sieve by

Synthesis of Nano-sized MCM-41 Mesoporous Molecular Sieve by

Preparation of high thermal stability MCM-41 in the low surfactant/silicon molar ratio synthesis systems

Low surfactant/silicon molar ratio synthesis systems were investigated for the preparation of a high thermal stability mesoporous molecular sieve MCM-41. Tetraethyl orthosilicate containing cetyltrimethylammonium bromide (CTAB) and NaOH were used to prepare synthesis gel which was analyzed by XRD diffractograms and N adsorption isotherms. The XRD patterns exhibited high-intensity peaks.

Investigating the state of Fe and La in MCM-41 mesoporous molecular sieve materials

Fe-containing, La-containing, siliceous and aluminum silicate MCM-41 mesoporous materials were synthesized using water glass as silica source. The states of Fe(III) and La(III) species were investigated by thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), framework infrared (FTIR), electron spin resonance (ESR) and Mössbauer spectroscopic techniques. It was shown that Fe(III) or La(III) species was incorporated into framework. Because the Fe–O or La–O bond is longer than Si–O bond, Fe(III) or La(III) species was limited to insert into framework and transformed from tetrahedrally coordinated state to octahedrally coordinated state upon calcination to remove template.

Preparation, characterization and photocatalytic properties of singly and doubly titania-modified mesoporous silicate MCM-41 by varying titanium precursors

A series of titania-modified MCM-41 have been synthesized from varying three kinds of titanium precursors [Ti(OBun)4, Ti(OBun)3(acac), Ti(OBun)2(acac)2] respectively and mesoporous molecular sieve MCM-41, in which titania existed as single or double layers. The samples were characterized by powder X-ray diffraction (XRD), nitrogen adsorption–desorption at 77 K, 29Si MAS NMR, FTIR and Raman spectroscopy, as well as by solid state diffuse reflectance UV–VIS spectroscopy. The titanium precursor was cocondensed with the active silanol groups of MCM-41 via Si–O–Ti bonds and the resulting titania modified the mesopore walls of MCM-41 after hydrolysis and calcination. In the titania-modified MCM-41 samples, although the titania species were in an amorphous state and in tetrahedral coordination rather than octahedral coordination, which exists extensively in crystalline titania, they exhibited high photocatalytic activity for the photodecomposition of phenol and the photoreduction of Cr(VI) to Cr(III).

Hydrothermal stability of MCM-48 improved by post-synthesis restructuring in salt solution

The hydrothermal stability of the mesoporous silica molecular sieves MCM-48 has been found to increase if the as-synthesized materials containing surfactant are heated in an aqueous solution of salts. Although the optimum treatment conditions depended on details of the synthesis procedures, this post-synthesis technique led to a significant improvement in the hydrothermal stability of various MCM-48 materials that were synthesized using cationic surfactants alone or cationic-neutral surfactant mixtures. These results were concluded as due to the restructuring effects of the pore walls by magic angle spinning 29Si NMR spectroscopy, nitrogen adsorption and scanning electron microscopy.

Electron Spin Resonance Investigations on the Location and Reducibility of Zirconium in Mesoporous Zr−MCM-41 Molecular Sieves

Zirconium containing mesoporous MCM-41 molecular sieves with Si/Zr ratios of 96 (A), 55 (B), 39 (C), and 23 (D) were synthesized and characterized by X-ray diffraction (XRD), surface area and pore size distribution measurements, and FTIR, diffuse reflectance UV−visible (DRUV−vis), 29Si MAS NMR, and electron spin resonance (ESR) spectroscopic techniques. The XRD patterns indicated an increase in the d100 spacing (from 36.77 to 40.88 A) with increasing Zr content. The samples showed a characteristic oxygen to zirconium charge-transfer band at 210 nm in the DRUV−vis spectra, consistent with monatomic dispersion of zirconium in Zr−MCM-41. Reduction of zirconium from the +4 to the +3 state was achieved by reaction with LiAlH4 at 298 K or with dry hydrogen at high temperatures. In samples A and B, Zr is located mostly in the pore walls, in substitutional locations (type I‘) and in C and D, it is present at the surface of the pores (type I‘ ‘) in addition to the substitutional locations. Zr(III) ions, in type I‘...

Carbonization of 1,4-diiodo-1,3-butadiyne and 1-iodo-1,3,5-hexatriyne inside the MCM-41 molecular sieve

1,4-Diiodo-1,3-butadiyne and a new derivative 1-iodo-1,3,5-hexatriyne were polymerised to prepare a carbonaceous material with oligoyne segments. The polymerisation was initiated by UV radiation (C 4I 2) or simply by a concentration rise after evaporation of the solvent (C 6HI). The formation of oligoyne was followed by FTIR in KBr pellets, in which the polymerisation occurred. Both precursors were also polymerised in the channels of the siliceous MCM-41 mesoporous molecular sieve. Polymeric carbon, confined in the channels, showed a broad IR band at 2090–2180 cm −1 corresponding to conjugated sp-bonded carbons. The intraporous polymerization was followed by chemical analysis, X-ray diffraction and nitrogen adsorption. Both the precursors and the polymerization products showed improved chemical and thermal stability if they were confined inside the MCM-41 matrix.

Effects of cation composition in MCM-41 mesoporous molecular sieves on the structures of encapsulated 4-pentyl-4′-cyanobiphenyl liquid crystals

The proportions of the various states are determined by the cation composition of the matrix for liquid-crystal material encapsulated in the pore spaces of mesoporous molecular sieves of MCM-41 type having high aluminum contents. The liquid-crystal properties are retained in the encapsulated state.

Oriented films of mesoporous MCM-41 macroporous tubules via pulsed laser deposition

All-silica mesoporous MCM-41 molecular sieve films consisting of oriented macroporous tubules have been prepared utilizing pulsed laser deposition and a series of post-hydrothermal treatments. The molecular sieve films were deposited on polished silicon wafer substrates with the pores oriented perpendicular to the surface of the substrate.

Characterization of Ordered Mesoporous Gallium MCM-41 Synthesized at Room Temperature

A series of highly ordered mesoporous gallium-containing MCM-41 molecular sieves with variable Si/Ga (100−10) ratios have been synthesized at room temperature. The synthesized Ga−MCM-41 was investigated by powder X-ray diffraction, transmission electron microscopy, thermal analysis, N2 adsorption measurement, and 29Si and 71Ga nuclear magnetic resonance (NMR); optimal synthesis conditions have thus been established. We were successful in synthesizing highly ordered material at room temperature using gallium nitrate as the source of gallium, and the surfactant was the cetyltrimethylammonium cation [(C16H33N(CH3)3]+. 71Ga NMR of calcined and uncalcined Ga−MCM-41 demonstrated that gallium was substituted for Si with tetrahedral coordination in the Ga−MCM-41 structure. N2 adsorption measurements indicate that high mesoporosity exists over the entire range of Ga−MCM-41 with an average pore diameter of 38.3 Å.

Physicochemical Characterization of Chromium Oxides Immobilized in Mesoporous MeMCM-41 (Me = Al, Ti, and Zr) Molecular Sieves

A series of mesoporous siliceous MCM-41 (SiMCM-41) molecular sieves with silicon partially substituted by Al, Ti, and Zr were synthesized hydrothermally. A combination of electron spin resonance (ESR), diffuse reflectance UV−vis spectroscopy (UV−vis), Raman spectroscopy, and temperature-programmed reduction (TPR) was used successfully to characterize the chemical environment of chromium in Cr/MeMCM-41 (Me = Al, Ti, and Zr). UV−vis, ESR, and Raman spectroscopy show that Cr2O3 is present in SiMCM-41, ZrMCM-41, and AlMCM-41. With increasing Al content in AlMCM-41, the amount of Cr2O3 increases, which contrasts with Cr/SiO2·Al2O3. Cr2O3 is reduced in Cr/TiMCM-41 with a Si/Ti ratio of less than 25 compared to higher ratios. The results reveal a strong interaction between chromium and surface titanium centers, which immobilizes the chromium species and reduces the formation of Cr2O3. UV−vis and Raman spectra show that Cr/MeMCM-41 materials are dominated by dichromate. The overall intensity of Cr(V) increases in...

New sorbents for olefin/paraffin separations by adsorption via π-complexation: synthesis and effects of substrates

New adsorbents for olefin/paraffin separations are synthesized by effective dispersion of Ag + cations on high-surface-area substrates. Two techniques for synthesis are compared: thermal monolayer dispersion and incipient wetness impregnation. The incipient wetness impregnation technique yields the best sorbents that show the highest selectivities, olefin capacities, reversibility and fast rates. AgNO 3 is dispersed on three substrates ( γ-Al 2O 3, SiO 2 and MCM-41 mesoporous molecular sieve) via incipient wetness impregnation for ethane/ethylene and propane/propylene separations. The surface chemistry of the substrate plays an important role in olefin adsorption. The silica surface (on both silica gel and MCM-41) provides a better substrate due to its lack of Lewis acid sites (unlike γ-Al 2O 3), and consequently the Ag atoms in these sorbents are more capable of forming π-complexation bonds with olefins. ESCA results indicate a transfer of electron density from Ag + to the Lewis acid sites of alumina, hence weakens the π-complexation bonds with olefins.

Nb-containing mesoporous molecular sieves — a possible application in the catalytic processes

Nb-containing MCM-41 mesoporous molecular sieves were modified with ammonium and copper cations and characterised by ESR, FTIR and H 2-TPR techniques. The prepared materials were tested in the following catalytic reactions: NO decomposition, reduction of NO with NH 3, hydrosulphurisation of methanol, and oxidation of thioethers with hydrogen peroxide. The oxidising character of the NbMCM-41 mesoporous molecular sieves was revealed, which induces their application as very active and selective catalysts in the oxidation of thioethers with H 2O 2 to sulphoxides. HNbMCM-41 samples, which exhibit Lewis acidity after dehydroxylation, are selective catalysts in the methanethiol synthesis in the reaction between methanol and hydrogen sulphide. Copper modified NbMCM-41 sieves indicate the higher reducibility of cupric cations than that observed when AlMCM-41 matrix for copper is used. The higher reducibility of cupric ions does not cause a higher activity in the catalytic NO decomposition.

Characterization of galloaluminosilicate MCM-41 molecular sieve

A series of mesoporous galloaluminosilicate MCM-41 molecular sieves with various compositions have been synthesized. Hexadecyltrimethylammonium bromide was used as an organic surfactant in the synthesis. These materials were characterized with nitrogen sorption, powder X-ray diffraction (XRD), differential thermal analysis (DTA), thermogramitric analysis (TGA) , scanning electron microscope (SEM), transmission electron microscope (TEM) and solid state NMR. The solid products had the MCM-41 structure and contained only atomically dispersed gallium consistent with the framework gallium in MCM-41. Incorporation of either Ga or Al into the framework of MCM-41 affects the long-range order of the mesopores without damaging the essentially mesoporous nature of the materials. Gallium was easier to incorporate into the framework than aluminum. All of the materials had a uniform pore size distribution with pore size around 30 A. The morphologies of [Ga, AL]-MCM-41 were spherical particle packages. A small amount of aluminum had been expelled from the framework of MCM-41 upon calcination at 550°C.

Photoionization of N-Alkylphenothiazines in Mesoporous SiMCM-41, AlMCM-41, and TiMCM-41 Molecular Sieves

Electron spin resonance and diffuse reflectance spectroscopy have been used to monitor the photoionization yields of N-alkylphenothiazine cation radicals (PCn+) generated by UV irradiation within mesoporous SiMCM-41, AlMCM-41, and TiMCM-41 molecular sieves. Mesoporous SiMCM-41 and AlMCM-41 molecular sieves are efficient for accomplishing stable photoproduced electron transfer of N-alkylphenothiazine molecules (PCn) at room temperature and at 77 K. A series of mesoporous TiMCM-41 molecular sieves with variable amounts of framework titanium have been hydrothermally synthesized and used for PCn photoionization in comparison with SiMCM-41 and AlMCM-41 molecular sieves. The addition of Ti into the framework of SiMCM-41 increases the net PCn+ cation radical photoyield at room temperature and 77 K. Thus, Ti in the TiMCM-41 framework is suggested to act as a better electron acceptor in competition with SiMCM-41 and AlMCM-41 molecular sieves. The photoionization efficiency to form PCn+ cation radicals increases in the order SiMCM-41 < AlMCM-41 < TiMCM-41. The photooxidation yields decrease as the alkyl chain lengths of the PCn molecules increase from methylphenothiazine (PC1) to hexadecylphenothiazine (PC16). Diffuse reflectance (DR) UV−visible spectra support the formation of some radical cation dimer as the alkyl chain length increases from PC1 to PC16 in all MCM-41 materials and thus the photoionization yields decrease from PC1 to PC16. The photoyield is higher by about 2.5 times at 77 K compared to room temperature. The PCn+ cation radicals are stable in SiMCM-41, AlMCM-41, and TiMCM-41 at room temperature for several hours and do not decay at 77 K. The observed photoyields of PCn molecules in mesoporous MCM-41 molecular sieves suggest that these materials can be utilized effectively for solar energy conversion and storage.