MCM-41 Mesoporous Materials Research Articles

Optimization of MCM-48 synthesis using factorial design

Abstract MCM-48 mesoporous materials were hydrothermally synthesized according to the 22 factorial design by varying the crystallization time and temperature of the synthesis gel, and characterized by means of X-ray diffraction analysis and adsorption of N2. In the crystallization temperature and time conditions used, specific areas between 924 to 1102 m2.g-1, pore volumes between 0.015 to 0.087 cm3.g-1 and pore diameters between 3.2 to 4.0 nm were obtained. It was observed that for the syntheses performed at high temperature, the crystallization time should be reduced so that the material structure is formed.

Tagra extends Azelis distribution territory to include India, Australia & New Zealand

MCM-41 mesoporous materials and silicoaluminophosphates (SAPO-5) were prepared by gel hydrothermal crystallization. Both series of materials were modified by transition metals (chromium or iron close to 1 wt%). The synthesized solids were characterized by chemical analysis, XRD, nitrogen adsorption–desorption isotherms, SEM, EPR, XPS, IR of ammonia or pyridine adsorption studies, and 29Si, 27Al and 31P NMR. The catalysts were evaluated in the n-butane isomerization in order to assess their properties with regard to alkane transformations. The properties of the solids were modified by adding metals that altered the morphology, structural features and acidic character of the solids and result in an efficient performance in the transformation of n-butane in comparison with the pure counterparts. The introduction of Cr or Fe enhanced the catalytic ability of silicoaluminophosphates to produce isobutane. Fe and Cr modified silicoaluminophosphates were shown to be more efficient in the transformation of n-butane in comparison with the MCM-41 analogues. However, the activity of these iron-containing molecular sieves was considered too low in comparison with performances of iron-modified modernite. This was ascribed to an initial redox C4 activation step occurring in synergy with Brønsted sites with sufficient acid strength which is indeed higher than that provided by MCM-41 and SAPO molecular sieves.

High performance methyl orange capture on magnetic nanoporous MCM-41 prepared by incipient wetness impregnation method

The Magnetic nanoporous material Fe/MCM-41 was prepared, and its physical characterization studied, to determine the effect of its properties on separation efficiency of methyl orange (MO) from wastewater by adsorption process. The experimental results were analyzed for both adsorbent mesoporous material samples, MCM-41 and magnetic Fe/MCM-41, in order to select the best operating conditions for the different studied parameters, which are: constant temperature (20 °C), pH: (2) adsorbent dosage (0.03 gm), contact time (10minute) and concentrations (30mg/L). The results demonstrate that the adsorption processes can be well fitted by the Langmuir isotherm model for pure MCM-41, with a correlation coefficient of (0.999), and fitted by the Freundlich isotherm model for magnetic Fe/ MCM-41, with a correlation coefficient of (0.994). The adsorption kinetics of MO on to MCM-41 and Fe/MCM-41 are well described by a pseudo-second-order kinetic model.

Synthesis and characterization of M-5NSA-MCM-41, (M = Cr, Fe) as reusable catalysts for the selective oxidation of sulfides to sulfoxides and oxidative coupling of thiols into disulfides in the presence of H2O2

Schiff base functionalized MCM-41 mesoporous materials were synthesized by post-grafting of 5-nitri-salicylaldehyde onto amino-modified MCM-41 and followed by anchoring of Fe+3 and Cr+3 ions via complex formation into MCM-41. These supported complexes were characterized by Fourier transforms infrared spectroscopy, thermogravimetric analysis, powder X-ray diffraction and N2 adsorption–desorption isotherms. A variety of aromatic and aliphatic sulfides and thiols including different functional groups were successfully converted into corresponding products in good to excellent yields at room temperature. The designed catalytic systems prevent effectively the over-oxidation of sulfides and thiols to sulfones and thiosulfonate. Other beneficial features include short reaction times, simple work-up, and recyclability and reusability of the catalysts for up to five consecutive runs without significant loss of their catalytic activity and selectivity.

Synthesis and characterization of thiol-functionalized MCM-41 nanofibers and its application as photocatalyst

In this paper, the simple fabrication of MCM-41 mesoporous material nanofibers (NFs) by an electrospinning technique was suggested. The morphology of the MCM-41nanofibers (MCM-41NFs) depended on spinning voltages. Tetraethylorthosilicate (TEOS) and polyvinyl alcohol (PVA) were used as a silica source and fiber forming polymer for MCM-41NFs synthesis, respectively. MCM-41NFs were modified with organic silicanes (3-mercaptopropyltrimethoxysilane). Thiol–functionalized MCM-41 nanofibers (MCM-41-SHNFs) prepared has been used for dispersing of AgBr nanoparticles (NPs) by precipitation method. The MCM-41 and AgBr/MCM-41-SHNFs photocatalyst were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray powder diffraction (XRD), diffuse reflectance spectroscopy (DRS), Brunauer-Emmett-Teller (BET) and nitrogen adsorption–desorption measurements. The smooth and long MCM-41NFs were observed in voltages less than 16 kV. TEM and SEM images showed synthesis of MCM-41NFs with a diameter of 200 nm. The BET results indicated that the pore diameter and surface area of calcined MCM-41NFs were reduced in thiol - functionalized MCM-41 and AgBr/MCM-41-SHNF nanocomposite. Silver bromide, with different weight percentage (30%, 40% and 50%) was coupled into MCM-41-SH nanofibers. The images displayed presence of AgBr NPs with particle size ∼35 nm over nanofibers support. The AgBr/MCM-41-SH nanofibers were used for the photocatalytic degradation of methyl blue (MB) under visible light. The results showed that for the various AgBr loadings in the composites, MB photocatalytic degradation efficiency arrived at the maximum of 60% at 40% loading, or with 40AgBr/MCM-41-SHNFs photocatalyst. The MB removal reached 87% at 0.25 g/L of the 40AgBr/MCM-41-SHNFs dosage, 3.2 ppm of initial MB concentration, and 6.5 of unadjusted initial pH. The cycle experiments on the AgBr/MCM-41-SHNFs photocatalyst indicated that NFs enhance photoinduced stability of photosensitive silver compounds in all cycles. The MCM-41-SHNFs reduced photocorrosion of AgBr NPs. On the basis of the experimental results, a possible mechanism for the enhanced photocatalytic activity and photoinduced stability of AgBr/MCM-41-SHNFs photocatalyst was proposed. The enhancement of photocatalytic activity was attributed to the increase of separation efficiency of electrons and holes in AgBr. The MCM-41-SHNF played an important role in decreasing recombination of photogenerated electrons-holes and increasing MB absorption.

Fabrication of MCM-41 fibers with well-ordered hexagonal mesostructure controlled in acidic and alkaline media

In this paper, synthesis and characterization of two type morphologies of the MCM-41mesoporous material, nano and microfibers, were investigated by electrospinning technique. The synthesis was performed in acidic and alkaline media, separately. The MCM-41 morphologies were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray powder diffraction (XRD), and nitrogen adsorption–desorption measurement. Tetraethylorthosilicate (TEOS) and cetyltrimethylammonium bromide (CTAB) were used as silica and template sources for the synthesis of MCM-41 morphologies, respectively. The SEM results showed that MCM-41 nanofibers were spun in acidic media and microfibers of MCM-41 were produced in alkaline media. The XRD study revealed a long range structural ordering of mesoporous materials. The TEM results indicated rough surfaces with uniform average diameter 200nm for nanofibers and 2µm for microfibers. The pore diameter and surface area of calcined MCM-41 nanofibers were 2.2nm and 970m2/g, respectively. For the MCM-41 microfibers, pore sizes of 2.7nm and surface areas 420m2/g was measured.

Understanding the role of nickel on the hydrogen storage capacity of Ni/MCM-41 materials

In this study, we prepared MCM-41 mesoporous materials modified with different Ni contents, as promising materials for hydrogen storage. We focused on the role of dispersed nickel as a way of promoting the interaction with hydrogen as an alternative to improve hydrogen storage materials. In addition, the reducibility of Ni/MCM-41 materials was studied, and the hydrogen adsorption in the reduced materials was evaluated, in order to compare the behaviour of reduced and unreduced Ni/MCM-41 materials in hydrogen storage at 77 and 293 K. Hydrogen adsorption isotherms were measured at 77 K and 293 K, and at low and high-pressure conditions respectively. The results obtained show that the amount of hydrogen stored was highly enhanced by the dispersion of small amounts of Ni nanoparticles both at 77 and 293 K.Experimental techniques such as TPR, XPS, N2 adsorption-desorption and computational methods (DFT) were used in order to interpret the results and contribute to the understanding of hydrogen adsorption on Ni/MCM-41 materials.

Mesoporous MCM-41 material for hydrogen storage: A short review

Decreasing supply of fossil fuels and concerns about environmental issues makes hydrogen a good alternative to fossil fuel sources as it is an environmentally friendly energy carrier. However, the storage of hydrogen is the main challenge to its effective use. For the utilization of hydrogen, the development of safe, effective and high capacity storage media is needed. MCM-41 that is most commonly used in catalytic applications has been also considered for hydrogen storage due to its high surface area, uniform pore size and good adsorption properties. There are a number of researches in which MCM-41 is now also considered as hydrogen storage media with a maximum reported hydrogen uptake of 2.01 wt%. However, there is not any review specifically on the hydrogen storage of MCM-41. Therefore, the present review highlights the recent studies on the use of MCM-41 as hydrogen storage media as well as its synthesis conditions and the effect of loading metal on the storage capacity.

Experimental and theoretical study of quercetin complexes formed on pure silica and Zn-modified mesoporous MCM-41 and SBA-16 materials

SBA-16 and MCM-41 silica materials were synthesized and modified by post-synthesis method with different amounts of Zn (2 and 4 wt.%). Quercetin, a flavonol compound, was loaded by incipient wetness impregnation method on the pure silica and Zn-modified mesoporous MCM-41 and SBA-16 supports. The parent and drug loaded formulations were characterized by powder XRD, N2 physisorption, thermal analysis, TEM, UV Vis and FT-IR spectroscopies. The formation of Zn:quercetin complex was studied by FT-IR spectroscopy and quantum-chemical calculations. Loading of quercetin on mesoporous carriers made the sustained delivery of the bioactive compound possible in a buffer with pH = 5.5, typical of dermal formulations. The results from the release experiments are in good accordance with the interaction energy between the bioactive molecule and non-modified and Zn-modified mesoporous materials, predicted by the quantum-chemical calculations. For the first time the formation of the most stable Zn quercetin complexes loaded on the mesoporous silica materials were determined. The obtained mesoporous delivery systems with Zn-quercetin complex are promising as dermal formulations.

One-step synthesis of periodic ion imprinted mesoporous silica particles for highly specific removal of Cd2+ from mine wastewater

Combining the advantages of MCM-41 mesoporous materials and molecularly imprinted polymers, we designed and synthesized periodic Cd2+ imprinted mesoporous silica (Cd-IMS) through a one-step hydrothermal process. Bifunctional ligand monomers [3-(γ-aminoethylamino)-propyltrimethoxysilane] and template ions (Cd2+) were immobilized in the hexagonal channel walls of MCM-41, prior to polymerization. The resultant Cd-IMS revealed a highly ordered hexagonal structure, nano-sized pore diameters and wall thicknesses, and a large surface area. In addition, this material revealed good binding properties, including a large adsorption capacity (saturation adsorption capacity of 40 mg/g), highly specific recognition ability (maximum imprinting factor of 3.0), and rapid adsorption kinetics (equilibration within 5 min). Selectivity coefficients [KCd-IMS (Cd2+)/KCd-IMS (Cu2+ or Pb2+)] of the Cd-IMS material demonstrated values of up to 2.29 and 3.08, respectively. Following six cycles of Cd2+ adsorption, the recovery of Cd-IMS remained stable at around 89.3 %, proving its recycling potential. Furthermore, Cd-IMS was successfully applied to selectively separate and remove Cd2+ from mineral wastewater samples, with high Cd2+ recovery rates. This suggests that the routine recovery of Cd2+ from wastewater may be realized in an economically viable manner.

Synthesis of N-methylaniline over molecular sieve catalysts

The preparation of N-methylaniline in two various processes: alkylation of aniline with methanol and hydroalkylation of nitrobenzene with methanol has been studied. Bifunctional molecular sieves containing metal copper as the hydrogenating component and zeolites BEA, MOR, MFI, FAU (Y) and mesoporous material MCM-41 as an alkylating component were used as catalysts. It has been shown that the modification of samples with copper nitrate increases the number of Lewis acid sites and decreases the number of Bronsted acid sites as copper embeds into cation exchange positions. It has been determined that the catalyst modification with copper increases the activity and enhances the selectivity towards N-alkylated products.

Mesoporous silica based MCM-41 as solid-phase extraction sorbent combined with micro-liquid chromatography–quadrupole-mass spectrometry for the analysis of pharmaceuticals in waters

This paper reports the first application of the silica based mesoporous material MCM-41 as a sorbent in solid phase extraction, to pre-concentrate pharmaceuticals of very different polarity (atenolol, nadolol, pindolol, timolol, bisoprolol, metoprolol, betaxolol, ketoprofen, naproxen, ibuprofen, diclofenac, tolfenamic acid, flufenamic acid and meclofenamic acid) in surface waters. The analytes were extracted from 100mL water samples at pH 2.0 (containing 10−3mol/L of sodium chloride) by passing the solution through a cartridge filled with 100mg of MCM-41. Following elution, the pharmaceuticals were determined by micro-liquid chromatography and triple quadrupole-mass spectrometry. Two selected reaction monitoring transitions were monitored per compound, the most intense one being used for quantification and the second one for confirmation. Matrix effect was found in real waters for most analytes and was overcome using the standard addition method, which compared favorably with the matrix matched calibration method. The detection limits in solvent (acetonitrile:water 10:90, v/v) ranged from 0.01 to 1.48μg/L and in real water extracts from 0.10 to 3.85μg/L (0.001–0.0385μg/L in the water samples). The quantitation limits in solvent were in the range 0.02–4.93μg/L, whereas in real water extracts were between 0.45 and 10.00μg/L (0.0045 and 0.1000μg/L in the water samples). When ultrapure water samples were spiked at two concentration levels of each pharmaceutical (0.1 and 0.2μg/L) and quantified using solvent based calibration graphs, recoveries were near 100%. However, recoveries for most pharmaceuticals were comparable or better than de described above, when river water samples (spiked at the same concentration levels) were quantified by the standard addition method and slightly worse using the matrix matched calibration method. Five real samples (two rivers, one dam and two fountain water samples) were analyzed by the developed method, atenolol, timolol, betaxolol, nadolol and diclofenac being found in some of them, at levels higher than their quantitation limits.

Effect of aluminum sulfate addition on the thermal storage performance of mesoporous SBA-15 and MCM-41 materials

Aluminum sulfate salt hydrate was dispersed on two different porous supports (MCM-41 and SBA-15) presenting a hydrophobic behavior at low relative humidity (P/P0≤0.3) with the objective to increase the energy density of the formed composites compared to pure host materials. Two different series of composite materials (MCM-41(Al2)x and SBA-15(Al2)x) with 3, 5 and 7wt% of aluminum sulfate were prepared by wetness impregnation method and tested for thermochemical heat storage at low-temperature. The dehydration heats, the water sorption capacities and the physicochemical characteristics have been determined for both series of composites.MCM-41(Al2)x and SBA-15(Al2)x composites exhibit much higher sorption capacities (up to 0.17 and 0.09kgH2Okg−1 respectively) than those observed for pure host materials, 0.04 and 0.02kgH2Okg−1 respectively for MCM-41 and SBA-15 at P/P0=0.3. These improved results were clearly linked to the interaction of water vapor with the confined salt. Water was found to be sorbed by the impregnated salt rather than by the host matrix. The textural properties such as specific surface area, pore size distributions and pore volumes are the most relevant properties of these materials in relation with their potential use. The best performance was observed for MCM-41(Al2)7 composite with ≈612kJkg−1sample. This encouraging result indicates that it is possible to use MCM-41(Al2)x and SBA-15(Al2)x composites at low water vapor pressure for thermochemical heat storage purposes.

Quantum effects in the sorption kinetics of4He by mesoporous materials

Sorption and desorption of 4He by a mesoporous silicate material MCM-41 was studied in the temperature range of 1.5–290 K. It was shown that for T = 25–290 K the thermal activation mechanism is dominant in the sorption kinetics of 4He atoms by an MCM-41 sample. Its activation energy was estimated as Ea ≈ 164.8 K. For T = 12–23 K, the diffusion of 4He atoms in the MCM-41 was practically independent of temperature, which typically occurs when the tunnelling mechanism of diffusion dominates over the thermally activated one. A change in the mobility of 4He atoms in MCM-41 channels was observed at T = 6–12 K, which may be indicative of the formation upon cooling (or decay upon heating) of a 4He monolayer and subsequent multilayers on the inner surfaces of the channels. Below 6 K, the diffusion coefficients of 4He are only weakly temperature dependent, which may be attributed to the behavior of quantum 4He liquid in the MCM-41 channels covered with several layers of 4He atoms.

Application of mesoporous carbon and modified mesoporous carbon for treatment of DMF sewage

Mesoporous carbon (MC) was prepared in soft template, and potassium ferricyanide was added into MC to prepare the modified mesoporous carbon (MMC). TEM, SEM, FT-IR, and N2 adsorption–desorption were used to characterize the textural properties of mesoporous materials. The BET specific surface area, pore volume, and the pore size of MC and MMC were 607.6321 and 304.7475 m2/g, 0.313552 and 0.603573 cm3/g, and 5.4356 and 7.9227 nm, respectively. The adsorption capabilities of MC and MMC were compared with the silica mesoporous material MCM-41. The influences of different adsorption conditions were optimized. For MC, the optimums of adsorbent dose, DMF initial concentration, rotating speed, and pH were 0.002 mg/50 mL, 200 mg/L, 200 r/min, and 4, respectively. MMC showed the highest DMF adsorption capacity at adsorbent dose 0.002 g/50 mL, DMF initial concentration 1000 mg/L, rotating speed 1000 r/min, pH more than 9, and contact time of less than 20 min. Meanwhile for MC, MMC, Pseudo-second-order equation was used to fit adsorption kinetics data. And adsorption process could be well fitted by Langmuir and Freundlich adsorption isotherms of MC, MMC. The results showed that MMC was a perfect adsorbent for DMF, and it was easy to separation and recycle. The recycling property of MMC was still relatively better than other two adsorbents.

Palladium complex-based catalysts stabilized on mesostructured silica: reactivity in methane combustion

Novel catalysts were successfully obtained using hybrid composite silica-based mesoporous materials MCM-41 type LUS and Pd(II) complexes. The metal site localization was controlled using two different synthetic routes, namely in situ functionalization and post-grafting synthesis (ex situ synthesis). These materials were characterized by XRD, FT-IR, EPR, N2 physisorption, TEM, SEM and H2 chemisorption. The catalytic performance was investigated on methane combustion reaction under CH4/O2/He (1/4/95 vol%) continuous flow at temperature below 450 °C. It has been proved that the palladium complex is embedded inside the mesostructured walls for the materials synthesized by the in situ method; while it is grafted at the wall surface for the one resulted from ex situ path. The latter material performed the best catalytic activity at temperatures below 450 °C thanks to a better dispersion of smallest PdO nanoparticles that optimizes the accessibility of the reactants to the actives sites in the mesoporous channels.

Catalytic Capture of CO2with Template-Containing Zn/MCM-41 and Its Transformation to Solid Carbonate

Mesoporous MCM-41 materials modified by zinc have been prepared by non hydrothermal procedure. Zinc has been introduced by the direct synthesis (DS), template ion-exchange (TIE) and wet impregnation (WI) methods. The catalysts were characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy-scanning electron microscopy (EDX-SEM), thermogravimetric and differential thermal analyses (TGA-DTA), Fourier transform infrared spectroscopy (FTIR) and N2 adsorption/desorption measurements. The obtained catalysts were investigated for hydration of CO2 and its precipitation as CaCO3 at room temperature. We investigated the effect of synthesis method and cationic template on catalytic activity of Zn/MCM-41 catalysts. The results showed that template containing Zn/MCM-41 prepared by template ion exchange technique has high CO2 hydration activity. This high activity is due to the presence of strong basic sites. It was also found that this catalyst can be easily recovered from the reaction mixture and reused without activation.

Study on the effect of atmospheric gases adsorbed in MnFe2O4/MCM-41 nanocomposite on ortho-positronium annihilation

Abstract In this paper, results of positron annihilation lifetime spectroscopy (PALS) studies of MnFe2O4/MCM-41 nanocomposites in N2 and O2 atmosphere have been presented. In particular, the influence of manganese ferrite loading and gas filling on pick-off ortho-positronium (o-Ps) annihilation processes in the investigated samples was a point of interest. Disappearance of the longest-lived o-Ps component with τ5 present in the PAL spectrum of initial MCM-41 mesoporous material in the PAL spectra of MnFe2O4-impregnated MCM-41 measured in vacuum is a result of either a strong chemical o-Ps quenching or the Ps inhibition effects. The intensity I 4 of the medium-lived component initially increases, reaching a maximum value for the sample with minimum manganese ferrite content, and then decreases monotonically. Analogous dependence for the intensity I 3 of the shortest-lived component shows a maximum at higher MnFe2O4 content. Filling of open pores present in the studied nanocomposites by N2 or O2 at ambient pressure causes partial reappearance of the τ4 and τ5 components, except a sample with maximum ferrite content. The lifetimes of these components measured in O2 are shortened in comparison to that observed in N2 because of paramagnetic quenching. Anti-inhibition and anti-quenching effects of atmospheric gases observed in the MnFe2O4/MCM-41 samples are a result of neutralization of some surface active centers acting as inhibitors and weakening of pick-off annihilation mechanism, respectively.

MCM-41-SO3H: an efficient, reusable, heterogeneous catalyst for the one-pot, three-component synthesis of pyrano[3,2-b]pyrans

MCM-41-SO3H, ordered mesoporous silica material MCM-41 with covalently anchored sulfonic acid groups, was used as a solid acid catalyst for the convenient, efficient, and ‘green’ synthesis of 2-amino-6-(hydroxymethyl)-8-oxo-4-aryl-4,8-dihydropyrano[3,2-b]pyrans via a one-pot, three-component reaction of 5-hydroxy-2-(hydroxymethyl)-4H-pyran-4-one, aldehydes and malononitrile in aqueous media.

Pore size effect on the stabilization of amorphous drug in a mesoporous material: Insights from molecular simulation

In this work, molecular dynamics simulation techniques are employed to study the effect of mesoporous MCM41 material in stabilizing ibuprofen amorphous drug. Our simulation results show that the intermolecular interaction occurring between ibuprofen amorphous drugs and mesoporous material decreases the possibility of self-organization of ibuprofen molecules and therefore prevents recrystallization. The maximum pore diameter of mesoporous MCM41 found to be effective in stabilizing the amorphous ibuprofen was about 20 nm. The methodology used in this study provides valuable insight towards molecular level understanding of confined amorphous active pharmaceutical ingredients (APIs).