Thermogravimetric Investigations During the Synthesis of Silica-based MCM-41

MCM-41 material was synthesized starting from hydrogel containing colloidal fumed silica, sodium silicate, cetyltetramethylammonium bromide(CTMABr) as surfactant, and distilled water as solvent. These reactants were mixed to obtain a gel with the following composition: 4SiO₂:1Na₂O:1CTMABr:200H₂O. The hydrogel with pH=14 was hydrothermally treated at100°C, for 4 days. Each day, the pH was measured, and then adjusted to 9.5–10 by using 30%acetic acid solution. Thermogravimetry was the main technique, which was used to monitor the participation of the surfactant on the MCM-41 nanophase, being possible to determine the temperature ranges relative to water desorption as well as the surfactant decomposition and silanol condensation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Study of the Adsorption Properties of MCM-41 Molecular Sieves Prepared at Different Synthesis Times

The variation of surface properties of SiMCM-41 and AlMCM-41 nanoporous materials as function of synthesis time was examined. The main properties studied were: surface area, pore diameter, pore volume, mesoporous parameter, and wall thickness. Siliceous MCM-41 molecular sieves were synthesized starting from hydrogels with the following molar compositions: 4.58SiO₂:0.435Na₂O:1 CTMABr:200 H₂O for SiMCM-41, and 4.58SiO₂:0.485 Na₂O:1 CTMABr:0.038 Al₂O₃:200 H₂O, for AlMCM-41. Cetyltrimethylammonium bromide (CTMABr) was used as the structural template. The crystallographic parameters were obtained from XRD data and by nitrogen adsorption using the BET and BJH methods. The results obtained showed a significant variation of the surface properties of the MCM-41 materials as a function of the synthesis time reaching silica wall thickness of ca. 2 nm on the fourth day.     

Kinetic study of template removal of MCM-41 nanostructured material

The siliceous MCM-41 molecular sieve was synthesized starting from a hydrogel with the following molar composition: 4.58SiO₂:0.437Na₂O:1CTMABr:200H₂O. The cetyltetramethylammonium bromide (CTMABr) was used as structure template. A kinetic study of template removal after the syntheses was performed by Vyazovkin model-free kinetic method obtaining apparent activation energy of 166±8.2 kJ mol^-1. This revised version was published online in August 2006 with corrections to the Cover Date.     

Model-free kinetics applied for the removal of CTMA<Superscript>+</Superscript> and TPA<Superscript>+</Superscript> of the nanostructured hybrid AlMCM-41/ZSM-5 material

The nanostructured hybrid AlMCM-41/ZSM-5 composite was synthesized starting from a hydrogel with molar composition SiO₂:0.32Na₂O:0.03Al₂O₃:0.20TPABr:0.16CTMABr:55H₂O. The cetyltrimethylammonium bromide (CTMABr) and tetrapropylammonium bromide (TPABr) were used as templates. The above mentioned material presents morphological properties with specific characteristics, such as the surface area of the composite which is approximately half of the surface area of the conventional MCM-41. Another interesting feature is the formation of walls with the double of the density of the MCM-41 structure, which characterizes the hybrid material, resulting in a high stability material for catalytic application. The aim of this study is obtain optimized structures of the hybrid material and for this purpose variations in the synthesis time were carried out. A comparative analysis was performed including X-ray diffraction, Fourier transform infrared spectroscopy, and Thermogravimetry measurements. The model-free kinetic algorithms were applied in order to determinate conversion and apparent activation energy of the decomposition of the CTMA⁺ and TPA⁺ species from the hybrid AlMCM-41/ZSM-5.     

杂原子介孔Ce-MCM-41分子筛的制备及其吸附脱除甲硫醚性能

以十六烷基三甲基溴化铵为模板剂,正硅酸乙酯(TEOS)为硅源,硝酸铈为铈源,采用水热法合成了杂原子介孔分子筛Ce-MCM-41。XRD和FT-IR表征结果表明,当加入的Ce/Si物质的量比小于0.04时合成了规整有序的介孔结构,并将Ce原子引入到MCM-41骨架中。N₂吸附-脱附测试获得MCM-41和Ce-MCM-41(Ce/Si物质的量比为0.04)的平均孔径分别为2.82和2.46 nm,孔容分别为0.762 1和 0.689 4 m³/g,BET比表面积分别为986.42和756.8 m²/g。NH₃-TPD表征结果表明,Ce-MCM-41的酸性要明显强于MCM-41,但两种分子筛的酸性均较弱。利用合成的MCM-41和Ce-MCM-41吸附脱除甲硫醚浓度为58 μg(甲硫醚)/g的甲硫醚/氮气混合气中的甲硫醚。甲硫醚分子尺寸的模拟结果为0.464 8 nm,可以很容易地进入分子筛的介孔孔道中。由于Ce-MCM-41分子筛具有较多的酸量,其硫吸附容量7.52 mg(S)/g明显高于MCM-41的4.57 mg(S)/g。MCM-41和Ce-MCM-41都具有较好的再生性能,再生3次后硫吸附容量仍可恢复到初始容量的80%,分别为3.52和 5.86 mg(S)/g。     

Kinetic parameters of surfactant remotion occluded in the pores of the AlMCM-41 nanostructured materials

A series of AlMCM-41 molecular sieves was synthesized starting from a hydrogel with the following molar composition: 1CTMABr:4.58SiO₂:(0.437 + X)Na₂O:XAl₂O₃:200H₂O. Tetramethylammonium silicate (TMAS) was used as silicon source and cethyltrimethylammonium bromide (CTMABr) was used as structure template. The obtained materials were characterized by nitrogen adsorption, XRD, FT-IR and TG/DTG. Model-free kinetic algorithms were applied in order to determinate conversion, isoconversion and apparent activation energy to decomposition of CTMA+ species from the AlMCM-41 materials with different silicon/aluminium (Si/Al) ratios of 20, 40, 60 and 80.     

Preparation,characterization, and hydrogenation activity of new Rh0–MCM-41 catalysts prepared from as-synthesized MCM-41 and RhCl3

Impregnation of as-synthesized MCM-41 silica by ethanolic solutions of rhodium(III) chloride was tested as an alternative to its introduction into the synthesis gel to get, after calcination and reduction by H₂, highly dispersed metal(0) nanoparticles throughout the mesopores network. Rh(III) and Rh(0)–based solids thus obtained were analyzed by infrared spectroscopy, elemental analysis, transmission electron microscopy, N₂ sorption, and X-ray diffraction. Materials with 1.6 wt % of rhodium could be obtained as a result of CTA⁺/Rh³⁺ exchange. The determining role of CTA⁺ was emphasized through blank experiments. In a second series of materials, ethanol was also exploited for its ability to reduce Rh(III). All Rh(0)-based solids were tested as catalysts in the hydrogenation of styrene under mild temperature and pressure conditions. Catalysis performances of the most efficient sample (reduced by H₂) were further compared with those of a very similar material prepared by the introduction of Rh(III) directly into the synthesis gel of MCM-41 silica. Better cis selectivities in the hydrogenation of disubstituted arene derivatives were achieved with materials issued from the new preparation method.     

Application of RuO<Subscript>2</Subscript> Nanoparticles as Catalyst in Preparation of Indolo[3,2-a]Carbazoles

RuO₂ nanoparticles were readily prepared from RuCl₃·3H₂O via the formation of Ru-hydroxide precursor, followed by calcination at 550 °C. Under similar conditions, uniform dispersion of spherical RuO₂ nanoparticles over the surface of MCM-41 was also obtained. The synthesized materials were characterized by transmission electron microscopy (TEM), infrared spectroscopy (FT-IR), X-ray diffraction (XRD), BET surface area measurements, and magnetic measurements (VSM). The obtained RuO₂ nanoparticles found application as catalyst in preparation of indolo[3,2-a]carbazoles from the reaction of indoles and benzils. Under mild reaction conditions, satisfactory yields of the desired products were obtained. Stabilization of RuO₂ nanoparticles over the surface of MCM-41 (RuO₂–MCM41), however, had the advantage of easy recycling, although a slight decrease in efficiency after five successive runs was observed.     

Effect of the catalyst MCM-41 on the kinetic of the thermal decomposition of poly(ethylene terephthalate)

The aim of this work is to determine the activation energy for the thermal decomposition of poly(ethylene terephthalate)—PET, in the presence of a MCM-41 mesoporous catalyst. This material was synthesized by the hydrothermal method, using cetyltrimethylammonium as template. The PET sample has been submitted to thermal degradation alone and in presence of MCM-41 catalyst at a concentration of 25% in mass (MCM-41/PET). The degradation process was evaluated by thermogravimetry, at temperature range from 350 to 500 °C, under nitrogen atmosphere, with heating rates of 5, 10 and 25 °C min^?1. From TG, the activation energy, determined using the Flynn–Wall kinetic method, decreased from 231 kJ mol^?1, for the pure polymer (PET), to 195 kJ mol^?1, in the presence of the material (MCM-41/PET), showing the catalyst efficiency for the polymer decomposition process.     

NSAID naproxen in mesoporous matrix MCM-41: drug uptake and release properties

Hexagonally ordered mesoporous silica material MCM-41 (S_BET?=?1090?m²/g, pore size?=?31.2 ?) was synthesized and modified by 3-aminopropyl ligands. The differences in an uptake and subsequent release of anti-inflammatory drug naproxen from unmodified and amino modified MCM-41 samples were studied. The prepared materials were characterized by high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM), nitrogen adsorption/desorption, Fourier-Transform Infrared Spectroscopy (FT-IR), Small-angle X-ray scattering (SAXS), thermoanalytical methods (TG/DTA) and elemental analysis. The amount of the drug released was monitored with thin layer chromatography (TLC) with densitometric detection in defined time intervals. The amounts of the released naproxen from mesoporous silica MCM-41/napro and amine-modified silica sample A-MCM-41/napro were 95 and 90% of naproxen after 72?h. In this study we compare the differences of release profiles from mesoporous silica MCM-41 and mesoporous silica SBA-15.     

Metal-Chelate Immobilization of Lipase onto Polyethylenimine Coated MCM-41 for Apple Flavor Synthesis

An enzyme immobilized on a mesoporous silica nanoparticle can serve as a multiple catalyst for the synthesis of industrially useful chemicals. In this work, MCM-41 nanoparticles were coated with polyethylenimine (MCM-41@PEI) and further modified by chelation of divalent metal ions (M = Co²⁺, Cu²⁺, or Pd²⁺) to produce metal-chelated silica nanoparticles (MCM-41@PEI-M). Thermomyces lanuginosa lipase (TLL) was immobilized onto MCM-41, MCM-41@PEI, and MCM-41@PEI-M by physical adsorption. Maximum immobilization yield and efficiency of 75 ± 3.5 and 65 ± 2.7% were obtained for MCM@PEI-Co, respectively. The highest biocatalytic activity at extremely acidic and basic pH (pH = 3 and 10) values were achieved for MCM-PEI-Co and MCM-PEI-Cu, respectively. Optimum enzymatic activity was observed for MCM-41@PEI-Co at 75 °C, while immobilized lipase on the Co-chelated support retained 70% of its initial activity after 14 days of storage at room temperature. Due to its efficient catalytic performance, MCM-41@PEI-Co was selected for the synthesis of ethyl valerate in the presence of valeric acid and ethanol. The enzymatic esterification yield for immobilized lipase onto MCM-41@PEI-Co was 60 and 53%, respectively, after 24 h of incubation in n-hexane and dimethyl sulfoxide media.

Open image in new window

Graphical Abstract Divalent metal chelated polyethylenimine coated MCM-41 (MCM-41@PEI-M) was used for immobilization of Thermomyces lanuginosa lipase catalyzing green apple flavor preparation

     

The synthesis of MCM-41 nanomaterial from Algerian Bentonite: The effect of the mineral phase contents of clay on the structure properties of MCM-41

This study focuses on the MCM-41 material (Mobil Composition of Matter). The MCM-41 nanomaterial presents higher physical properties such as pore sizes, surface areas and pore volumes. This material is usually synthesized by using laboratory reagents as silicate sources and aluminium source. These laboratory reagents are still expensive and toxic for large scale production. The main aim of this work is to resolve this problem and to replace these expensive laboratory reagents by more cost effective ones. The volclay and Algerian bentonite low-cost mass clay materials are used as silicate and acuminate sources separately by adopting an alkaline fusion process to extract both silicon and aluminium (1 kg of silicium and aluminium from volclay and Algerian bentonite cost around 0.03 and 0.01 € whereas the same amount of silicon from ludox and aluminium from sodium aluminates cost around 350 €). The synthesis of MCM-41 from bentonite was carried out by the hydrothermal method using the supernatants of bentonite (in the form of sodium silicate and sodium aluminate). On the basis of the data obtained from powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and N₂ adsorption and desorption, the results revealed that the properties of MCM-41 synthesized from Algerian bentonite and volclay separately depend on both elemental composition and mineral phase contents of the used bentonite. Pure and highly ordered hexagonal mesoporous MCM-41 with uniform pore sizes and a high specific surface area have been successfully synthesized without any phases which exist in natural bentonite. The Algerian bentonite was chosen because of its low cost compared to volclay, another commercial clay source.     

Preparation of MnCo/MCM-41 catalysts with high performance for chlorobenzene combustion

MCM-41 was synthesized by a soft template technique. The specific surface area and pore volume of the MCM-41 were 805.9 m²/g and 0.795 cm³/g, respectively. MCM-41-supported manganese and cobalt oxide catalysts were prepared by an impregnation method. The energy dispersive X-ray spectroscopy clearly confirmed the existence of Mn, Co, and O, which indicated the successful loading of the active components on the surface of MCM-41. The structure and function of the catalysts were changed by modulating the molar ratio of manganese to cobalt. The 10%MnCo(6:1)/MCM-41 (Mn/Co molar ratio is 6:1) catalyst displayed the best catalytic activity according to the activity evaluation experiments, and chlorobenzene (1000 ppm) was totally decomposed at 270 °C. The high activity correlated with a high dispersion of the oxides and was attributed to the exposure of more active sites, which was demonstrated by X-ray diffraction and high-resolution transmission electron microscopy. The strong interactions between MnO₂, Co₃O₄, MnCoO_x, and MCM-41 indicated that cobalt promoted the redox cycles of the manganese system. The bimetal-oxide-based catalyst showed better catalytic activity than that of the single metal oxide catalysts, which was further confirmed by H₂ temperature-programmed reduction. Chlorobenzene temperature-programmed desorption results showed that 10%MnCo(6:1)/MCM-41 had higher adsorption strength for chlorobenzene than that of single metal catalysts. And stronger adsorption was beneficial for combustion of chlorobenzene. Furthermore, 10%MnCo(6:1)/MCM-41 was not deactivated during a continuous reaction for 1000 h at 260 °C and displayed good resistance to water and benzene, which indicated that the catalyst could be used in a wide range of applications.     

Increasing the efficiency of silicon and aluminum extraction from Volclay by a water iteration treatment for the synthesis of MCM-41 nanomaterials

This work aims to reduce the prices of a wide range of nanomaterials which are unreachable in the industry by using natural sources as silicon and aluminum precursors. In a previous work, silicon and aluminum have been extracted from Volclay after applying the alkaline fusion process at 550 °C, and a water treatment of this fused clay by adopting a weight ratio (1:4, fusion mass:H₂O) to synthesize Al-MCM-41 nanomaterials. In this study, the weight ratio of fusion mass:H₂O was increased to 1:8 to synthesize a highly structurally ordered MCM-41 under the same reaction conditions. The Al-MCM-41 nanomaterials are investigated by inductively coupled plasma optical emission spectrometry (ICP–OES), powder X-ray diffraction (XRD), N₂ adsorption–desorption measurements and scanning electron microscopy (ESEM). As a result, the increase in the weight ratio fusion mass:H₂O generates more silica and aluminum, which allows the formation of well-ordered MCM-41 nanomaterials with high pore volume (0.70 cm³/g), high surface area (1044 m²/g), and uniform mesoporous diameter (3.67 nm); as a consequence, the increase in the weight ratio fusion mass:H₂O leads to an increase in the mass of Al-MCM-41 (9.3 g for 1:8 compared to 5 g for 1:4), whereas the yield of production of mesoporous materials increases to 86%.     

Removal of Cr(VI) from aqueous solutions using EDCC-MCM-41: Isotherm,kinetics and thermodynamic evaluation

Abstract

EDCC-MCM-41, a novel ethylenediamine derivative of MCM-41 was synthesized from a sugar industry waste, bagasse fly ash. Studies were carried out on its ability to remove Cr(VI) from aqueous solution. Its performance was also compared with that of unmodified MCM-41 and an already known derivative NH₂-MCM-41 (both also synthesized from bagasse fly ash) at the same experimental conditions. Results show that the novel adsorbent produced a better sorption performance (adsorption capacity of 49.04?mg g^?1) than MCM-41 and NH₂-MCM-41 which produced adsorption capacities of 13.78?mg g^?1 and 25.29?mg g^?1 respectively. Thermodynamics, kinetics and isotherm studies confirm that the sorption process involving the novel adsorbent is favorable for Cr(VI) and can best be represented by pseudo-second-order kinetics model. The sorption process was also found to be multistep, involving both film diffusion and intraparticle diffusion into the pores on the adsorbent’s surface.

Abbreviations: BFA: Bagasse Fly Ash; MCM-41: Mobil Composition of matter no. 41; NH2-MCM-41: mine functionalized MCM-41; EDCC-MCM-41: Ethylenediamine grafted MCM-41; qe: Mass of material adsorbed at equilibrium per mass of adsorbent; qt: Mass of material adsorbed at any time t per mass of adsorbent; C0: The initial concentration; Ce: The residual concentration at equilibrium; Ct: Residual concentration at any time t; W: The weight of adsorbents; rRMSD: Root mean square deviation; R: Gas constant     

Thermal stability of amine-functionalized MCM-41 in different atmospheres

In the present work, we report on the thermal stability of NH₂-MCM-41 hybrid material under different atmospheres (nitrogen and air). The thermal stability of this hybrid material is very important because of its common use in catalysis, adsorption, biomedical and biotechnological applications, based on mesoporous and aminopropyl functionalities. Samples were prepared by one pot co-condensation method with different loadings of 3-aminopropyltriethoxysilane (APTES). The thermal stability of hybrid samples (NH₂-MCM-41) heat treated in nitrogen and air at 30–800 °C has been investigated. Samples were synthesized under basic media in the presence of cetyltrimethylammonium bromide (CTABr) as structure-directing agent, tetraethyl orthosilicate as silica source, and APTES as functionalizing agent with molar composition of 0.055 CTABr:045 SiO₂:0.054 APTES:5.32 NH₄OH:14.99 H₂O at 50 °C for 24 h at pH 12.4. The obtained hybrid materials have been characterized by thermogravimetric analysis (TG), derivative thermogravimetric analysis, differential scanning calorimetry, X-ray powder diffraction, Fourier-transform infrared spectroscopy, transmission electron microscopy, and surface area determination by the BET method. Based on TG measurements of the treated samples, it was found out that the thermal stability varied greatly in different atmospheres.     

Tetra-β-(2-(diethylamino)ethoxy) nickel phthalocyanine: synthesis and inclusion in MCM-41

In order to include phthalocyanine macromolecule in MCM-41 molecular sieve, a inclusion-suitable phthalocyanine derivative tetra-β-(2-(diethylamino)ethoxy) nickel phthalocyanine was synthesized, in two steps, from 4-nitrophthalonitrile and 2-(diethylamino)ethanol, and characterized by mass spectra, ¹H nuclear magnetic resonance spectroscopy, ultraviolet visible spectroscopy, infrared spectroscopy and elemental analysis, which confirmed the proposed molecular structure. The inclusion of synthesized phthalocyanine compound in MCM-41 was carried out by the in situ synthesis method using cetyltrimethyl ammonium bromide as structure template and tetraethyl orthosilicate as silica source in presence of this phthalocyanine compound. The inclusion material was studied by means of X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, nitrogen adsorption isotherm measurements, etc. Results showed that the macromolecular compound was successfully included into MCM-41, the obtained inclusion material displayed mainly prisms and globes, and the material was a kind of mesoporous materials with regularly hexagonal honeycomb array of uniform cylindrical pores and high surface area.     

SiO2载体表面原位合成MCM-41的结构特征

以溶液硅源和表面硅源两种合成路线在SiO₂颗粒表面进行了MCM-41的原位合成,结果发现以两种方式均可得到MCM-41的有序结构。溶液硅源原位合成MCM-41的长程结构较好,两种硅源原位合成的MCM-41均能够在脱除模板剂过程中保持其长程有序结构。表面硅源原位合成MCM-41的孔径分布较窄,最可几孔径为3.81nm。本文还考察了OH/CTABr及SiO₂/OH比对表面硅源原位合成MCM-41长程结构特征的影响。     

The Synthesis and Application of the Mesoporous Molecular Sieves MCM-41 — A Review

We report a “delayed neutralization” process for the preparation of highly-ordered aluminosilicate MCM-41 molecular sieves with high thermal and hydrothermal stability, and sharp pore size distribution. However, the structural order and pore size are dependent on the carbon chain length. In the mixture surfactant systems, the pore size of the MCM-41 materials could be fine-tuned. The pore size can be extended from 2.5 to 4.5 nm by adding a suitable amount of hydrocarbons. The tubular morphology of the MCM-41 material of 0.3 to 10 micrometers diameter, where the wall consists of coaxial cylindrical pores of nanometers MCM-41, can be obtained by careful control of the surfactant-water content and the rate of condensation of silica. An optimum condition for automatic synthesis of the hierarchical TWT structure has been accomplished. The addition of 1-alkanols as cosurfactant would not only improve the order of the MCM-41 hexagonal structure but also promote the formation of micrometer-sized hierarchical materials, for example: tubules-within-tubule and uniform-sized hollow spheres of diameter 5.0 ± 1.0 μm. However, the inside of the micron spheres has intricate structures possessing various topological genus ranks. The MCM-41 is a good supporter for Molybdenum oxide catalysts. The rate of deactivation in the catalytic reaction of ethyl-benzene dehydrogenation to styrene increases in the order: M_T < M_P < SiO₂. The physically mixed samples have higher catalytic activity than impregnated ones.