Mesoporous MCM-41 Research Articles

Insights on a Hierarchical MFI Zeolite: A Combined Spectroscopic and Catalytic Approach for Exploring the Multilevel Porous System Down to the Active Sites.

The hierarchization of zeolites to overcome the major drawbacks related to molecular diffusion limitation in micropores is a popular concept in heterogeneous catalysis. Despite the constant increase of new synthesis strategies to produce such hierarchical systems, the deep knowledge of their structural arrangement and how the zeolitic lattice is organized in a multilevel porous system is often missing. This information is essential to design a structure, tuning the porosity and the distribution of easily accessible active sites, and successively controlling the catalytic properties. In the present work, the synthesis of one of the most sophisticated forms of the hierarchical ZSM-5 zeolite has been reproduced, obtaining two multilevel porous materials with different crystallinity degrees, with the final aim of investigating and clarifying the finest features of their active sites. For this purpose, an extended characterization step by means of a unique multitechnique approach has been performed, thus revealing the active site nature, abundance, and distribution. IR spectroscopy with different molecular probes and a targeted catalytic test based on the hydroconversion reaction of n-decane were the toolbox for disclosing how the MFI lattice takes part in the hierarchical structure and how it, working in synergy with the mesoporous system, confers to this material a totally new shape–size selectivity. Merging the information obtained for the synthesized hierarchical zeolite with the characterization results of two reference materials (a mesoporous aluminum-containing MCM-41 and a microporous commercial ZSM-5), it was possible to define an internal and external map of the pore network of this complex and unique molecular sieve, where strong Brønsted acidic sites are located at the mouth of the MFI micropores and, at the same time, exposed at the surface of the mesoporous channels. Hence, the possibility of easily releasing bulky products is ensured and the application possibilities of the MFI lattice are expanded beyond cracking reactions.

Synthesis of rice husk-based ion-imprinted polymer for selective capturing Cu(II) from aqueous solution and re-use of its waste material in Glaser coupling reaction

With the deepening of the concept of recycling economy and green chemistry, selective capture of Cu(II) from wastewater by biosorbent and reuse of the spent Cu(II)-loaded adsorbent are of great significance. Herein, we synthesized composite of rice husk (RH) with mesoporous silica MCM-41 (RH@MCM-41) modified by organosilane containing amino and schiff groups as functional monomer and cross-linking agent. The silica modified RH@MCM-41 was employed as supporter to fabricate copper ion-imprinted polymers as absorbents (named as RM-CIIPs) via surface ion imprinting technique. Adsorption isotherms, kinetics, selectivity and mechanism of RM-CIIPs to remove Cu(II) were investigated with respect to different adsorption condition. Furthermore, we explored the catalytic activity of spent Cu(II)-loaded adsorbent in Glaser coupling reaction. Batch adsorption studies revealed that RM-CIIP-3 prepared with functional monomer shows the best adsorption capacity (91.4 mg/g) for Cu(II), and adsorption equilibrium could be reached within 30 min. RM-CIIP-3 exhibited an excellent selectivity for capturing Cu(II) and reusability in six adsorption/desorption cycles. More importantly, the spent Cu(II)-loaded adsorbent could be used as bio-heterogeneous catalyst and afford the desired product (1,4-diphenylbutadiyne) in 99.1% yield. Our research indicates an eco-friendly systematic strategy to utilize the waste material as an adsorbent for removing heavy metals and catalyst for industry.

Influence of Vanadium incorporated mesoporous silica on the decolorization of orange G under visible light irradiation

Mesoporous MCM-41 material was synthesized and it was successfully incorporated with Vanadium at room temperature by simple co-precipitation method. Higher portion of V+5 was noticed in the framework of V-MCM-41 material without disturbing the mesoporosity. The materials were characterized by X-ray diffraction (XRD), Nitrogen adsorption-desorption studies (BET method, SBET), scanning electron microscope coupled with electron dispersive x-ray spectroscopy (SEM-EDAX), and UV-Vis diffused reflectance (UV-Vis DRS) techniques. The catalytic activity of the synthesized materials were investigated toward the removal of orange G dye (OG) and was observed that the VMCM-41 has superior catalytic activity in the presence of hydrogen peroxide.

Hydrodesulfurization of 4,6-Dimethyldibenzothiophene and the Diesel Oil Fraction on NiMo Catalysts Supported over Proton-Exchanged AlMCM-41 and TiMCM-41 Extrudates

NiMo catalysts supported on mesoporous MCM-41 type materials shaped with binder were tested for activity in the hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and the diesel fuel fraction (0.92 wt% of sulfur). The aim of the investigation was to evaluate the effect of ion exchange with protons of Al- or Ti-substituted MCM-41 mesoporous supports. The subjected catalytic systems were NiMo/HAlMCM-41 and NiMo/HTiMCM-41, and for comparison purposes NiMo/AlMCM-41 and NiMo/TiMCM-41. The samples were characterized by N2 sorption (at 77 K), XRD, TEM, XPS, SEM and Py–IR. It was found that the functionalization of AlMCM-41 and TiMCM-41 with protons increased the conversion of 4,6-DMDBT and the pseudo-first-order rate constant. Correspondingly, 4,6-DMDBT HDS reactions over the NiMo/HTiMCM-41 catalyst proceeded to a similar extent via hydrogenation and direct desulfurization, whereas over the NiMo/HAlMCM-41 they proceeded mainly via direct desulfurization. Furthermore, the ion-exchanged catalysts displayed two-fold higher efficiency in direct desulfurization than their non-modified counterparts. The NiMo/HTiMCM-41 catalyst exhibited the highest catalytic efficiency in the HDS of 4,6-DMDBT and the diesel oil fraction. The high activity of the NiMo/HTiMCM-41 catalyst is mainly attributed to its appropriate acidity, as well as the metal–support interaction providing both the high dispersion of the active phase and the desirable multilayered stacking morphology of the active phase slabs.

Shape-selective alkylation of benzene with ethylene over a core–shell ZSM-5@MCM-41 composite material

A series of ZSM-5@MCM-41 core–shell composite materials prepared via a multi-cycle-sol–gel coating strategy is investigated as the catalyst for benzene alkylation with ethylene, in which both ethylbenzene and para-diethylbenzene ( p- DEB) are aimed as the target products. With multi-cycle-sol–gel coating, the external acid sites on the samples are gradually passivated by the inert MCM-41 shell. As a result, the shape selectivity to p- DEB is greatly enhanced. Nevertheless, the coating of mesoporous MCM-41 shell on ZSM-5 accelerates deactivation of the catalyst only due to the dilution effect of ZSM-5 content in the catalyst at the same space velocity, which is a reason that core–shell ZSM-5@MCM-41 will potentially be a practical catalyst in shape selective alkylation of benzene. In order to enhance the yield of p- DEB on ZSM-5@MCM-41, the reaction conditions at the fixed bed reactor including temperature, the molar rate of benzene to ethylene and GHSV, are also optimized.

Preparation of novel CaMoO4:Eu3+-MCM-41 nanocomposites and their applications and monitoring as drug release systems

Bortezomib loaded CaMoO4:Eu3+-MCM-41 nanocomposites were prepared and used in drug release studies. The surface of the synthesized mesoporous MCM-41 was functionalized with CaMoO4:Eu3+ with the gel obtained by Pechini sol-gel method. After calcination at 700 °C, CaMoO4:Eu3+-MCM-41 nanocomposites were obtained onto which Bortezomib was loaded via supercritical carbon dioxide technique at 200 bars and 40 °C. Structural characterization of MCM-41and the nanocomposites were made via XRD, FT-IR and Raman spectroscopies. Their particle sizes and morphologies were investigated by FE-SEM. The amount of drug loaded onto the nanocomposites was investigated by TG. Pore volumes were determined by N2 adsorption/desorption analysis. In vitro drug release studies were performed at 37 °C in SBF. The amount of drug released was determined via UV–vis spectrometric analysis. Luminescent properties and the release process were investigated by monitoring the changes in the luminescence intensity over time via photoluminescence spectrometer. MTT method was used for cell viability/toxicity studies.

Integrating Halloysite Nanostraws in Porous Catalyst Supports to Enhance Molecular Transport.

In many porous catalyst supports, the accessibility of interior catalytic sites to reactant species could be restricted due to limitations of reactant transport through pores comparable to reactant dimensions. The interplay between reaction and diffusion in porous catalysts is defined through the Thiele modulus and the effectiveness factor, with diffusional restrictions leading to high Thiele moduli, reduced effectivess factors, and a reduction in the observed reaction rate. We demonstrate a method to integrate ceramic nanostraws into the interior of ordered mesoporous silica MCM-41 to mitigate diffusional restrictions. The nanostraws are the natural aluminosilicate tubular clay minerals known as halloysite. Such halloysite nanotubes (HNTs) have a lumen diameter of 15–30 nm, which is significantly larger than the 2–4 nm pores of MCM-41, thus facilitating entry and egress of larger molecules to the interior of the pellet. The method of integrating HNT nanostraws into MCM-41 is through a ship-in-a-bottle approach of synthesizing MCM-41 in the confined volume of an aerosol droplet that contains HNT nanotubes. The concept is applied to a system in which microcrystallites of Ni@ZSM-5 are incorporated into MCM-41. Using the liquid phase reduction of nitrophenol as a model reaction catalyzed by Ni@ZSM-5, we show that the insertion of HNT nanostraws into this composite leads to a 50% increase in the effectiveness factor. The process of integrating nanostraws into MCM-41 through the aerosol-assisted approach is a one-step facile method that complements traditional catalyst preparation techniques. The facile and scalable synthesis technique toward the mitigation of diffusional restrictions has implications to catalysis and separation technologies.

Hybrid catalyst with combined Lewis and Brønsted acidity based on ZrIV substituted polyoxometalate grafted on mesoporous MCM-41 silica for esterification of renewable levulinic acid

Materials which synergistically combine Lewis and Brønsted acid properties hold potential for applications as efficient heterogeneous catalysts for preparation of biofuels and biolubricants. Herein we report new heterogeneous catalysts based on grafting the intact Lewis metal (ZrIV) substituted Keggin polyoxometalate (POM) on mesoporous silica support. A new approach for immobilization of the POM in MCM-41 silica was developed by co-condensation of Si source (tetraethyl orthosilicate, TEOS) with POM salt in the presence of a template molecule as an alternative to the commonly used acidic POM form and impregnation procedure for catalyst preparation. The proposed synthesis method in combination with extraction of the template proceeded with preservation of the intact POM structure and resulted in hybrid catalysts with in situ generated Brønsted acid sites in addition to the Lewis acidity provided by the metal centers. Textural properties of the catalysts were characterized by X-ray diffraction, N2 physisorption and transmission electron microscopy (TEM). Insight into POM stability and structural transformations during synthesis, template removal and impregnation was provided by solid state 31P and 29Si NMR spectroscopy. Catalytic activity was studied in esterification reactions of levulinic acid with ethanol or octanol to value-added esters. The directly synthesized POM-functionalized hybrid catalysts exceeded the post synthesis impregnated ones, demonstrating significantly higher catalytic activity, recyclability and resistance against leaching. The proposed approach for immobilization of Lewis metal POMs in MCM-41 silica framework with in situ generation of the active Brønsted acid sites opens prospects for the development of efficient hybrid catalysts for esterification reaction, which overcomes the main limitations of common POM based catalysts such as low stability of the acid sites during the synthesis and the catalytic reaction, low surface area, agglomeration of the catalytically active phase and low stability of the Lewis metal center in presence of water.

Synthesis and electro-catalytic evaluation of Ti(IV)-anchored heterogeneous mesoporous material for uric acid analysis

A simple and modified synthetic strategy has been developed for the preparation of Ti(IV) anchored mesoporous MCM-41 material from the commercially available starting material of titanocene dichloride and MCM-41. The vacuum diffusion process has been utilized for anchoring Ti(IV) on MCM-41 (Ti-MCM-41) via surface activation instead of the chemical activation process. The modified Ti-MCM-41/glassy carbon electrode (GCE) was developed from Ti-MCM-41 and evaluated for the selective sensing of mammalian metabolic bio-marker of uric acid (UA) by the electrochemical method. The modified electrode (Ti-MCM-41/GCE) shows an excellent selective electrochemical response with UA, good linear competence in wide range concentrations (10–110 nM) and scan rates (50–900 mV s−1) and a low limit of detection up to 2.98 nM in the category of silica based mesoporous material. The selectivity and sensitivity of the electrode were tested with various potential organic interferents that exhibit good anti-interferents activity. The proposed modified electrode is potentially useful for commercial sensing application of UA since the analysis of human urine samples under various age people are good agreements with recovered UA by the standard addition method. The stability and reproducibility of the Ti-MCM-41/GCE were tested and the results are reproducible in a number of electro-catalytic cycles.

Cu attached functionalized mesoporous MCM-41: a novel heterogeneous nanocatalyst for eco-friendly one-step thioether formation reaction and synthesis of 5-substituted 1H-tetrazoles

Cu attached functionalized mesoporous MCM-41: a novel heterogeneous nanocatalyst for eco-friendly one-step thioether formation reaction and synthesis of 5-substituted 1H-tetrazoles

Facile Preparation of Mesoporous MCM-48 Containing Silver Nanoparticles with Fly Ash as Raw Materials for CO Catalytic Oxidation.

An environmentally friendly method was proposed to prepare mesoporous Mobil Composition of Matter No.48 (MCM-48) using fly ash as the silica source. Silver nanoparticles were infiltrated on MCM-48 facilely by an in situ post-reduction method and evaluated as an effective catalyst for CO oxidation. The as-prepared MCM-48 and Ag/MCM-48 nanoparticles were characterized by XRD, N2 adsorption/desorption, and TEM. Investigations by means of XPS for Ag/MCM-48 were performed in order to illuminate the surface composition of the samples. Studies revealed the strong influence of the loading of Ag nanoparticles on catalysts in the oxidation of CO. CO conversion values for Ag/MCM-48 of 10% and 100% were achieved at temperatures of 220 °C and 270 °C, respectively, indicating that the Ag-decorated MCM-48 catalyst is extremely active for CO oxidation.

Facile preparation of ordered mesoporous Nb,Ta-MCM-41 by hydrothermal direct synthesis using columbite ore as metal source

– The current study aims to prepare an Nb,Ta-containing ordered mesoporous catalyst MCM-41, using hydrated mixed oxide of niobium and tantalum, extracted from the columbite ore processing, as an alternative source of these metals. Direct hydrothermal synthesis was employed to incorporate the metals into the molecular sieve structure using the TEOS + sodium silicate mixture as silica source and varying Nb and Ta content in terms of Si/Me (Me = Nb and Ta) molar ratios of 60, 30 and 15 to evaluate the influence of the charge of these metals on both structural formation and properties of the material. The material was characterized by XRD, SEM, TEM, N2 adsorption, UV–Vis-DRS, and FTIR investigations to the incorporation of the metal into the MCM-41 framework. The techniques employed proved the successful replacement of Si atoms by metallic cations of Nb and Ta. The catalyst showed good structural order preservation and surface area (>600 m2 g-1) with mesoporous behavior with capillary condensation even at a higher metal load. This research signifies a successful procedure of a novel bimetallic mesoporous material with promising properties for several applications using an abundant ore as a metal source.

Synthesis and application of Cu(II) immobilized MCM-41 based solid Lewis acid catalyst for aminolysis reaction under solvent-free condition

In this paper, a Cu(II) immobilized periodic mesoporous organosilica (PMOs) was synthesized and used as a reusable solid Lewis acid catalyst for the aminolysis of epoxides under solvent-free conditions. An amide-based ligand, l-propylsilyl (1) having a specific binding pocket was prepared and fabricated on mesoporous MCM-41 to produce mesoporous organosilica l-propylsilyl@MCM-41 (2). Further, it has been utilized for anchoring Cu(II) ions under controlled reaction conditions to yield solid Lewis acid catalyst Cu(II)-l-propylsilyl@MCM-41 (3). The synthesized catalyst 3 exhibits significantly higher catalytic activity for aminolysis compared to hitherto known solid Lewis acid catalysts. An extensive range of β-amino alcohols with high regio and stereoselectivity were prepared by using catalyst 3. The catalyst was recovered easily and reused eight times without any loss in its catalytic activity. Furthermore, the synthesis of clinically significant propranolol (β-blocker) from α- naphthyl glycidyl ether was attained successfully using catalyst 3 in a very decent yield.

Incorporation of one or dual Brønsted acidic sites within the mesopores of MCM-41: Synthesis and catalytic activity in acetalization reaction

In recent years, various kinds of heterogeneous acid catalysts have been prepared and utilized for different catalytic applications. Among them, designing the easily recoverable catalysts containing two distinct Brønsted acidic sites with enhanced catalytic properties is promising. In this work, modification of the mesopores of MCM-41 as a siliceous solid support with two suitable nitrogen-containing amino- and piperazine-propylsilyl groups followed by covalent interaction with 1,4-butane sultone introduced sulfonic acid groups to this mesoporous material. The additional electrostatic interaction with phosphotungstic acid groups generated the second acidic sites on ammonium and piperazinium moieties. The successful synthesis of these solid acid catalysts was confirmed by FT-IR, energy dispersive X-ray (EDX), and inductively coupled plasma optical emission (ICP-OES) spectroscopies; CHN elemental analysis; nitrogen sorption; and XRD techniques. The catalytic experiments in benzaldehyde acetalization with ethylene glycol resulted in moderate to high activity from 76% to 97% within 2 h. Moreover, the higher catalytic activity was related to the one possessing two kinds of acidic sites due to the synergistic effect between these acidic sites.

One-pot synthesis of spiro[indoline-3,2′-pyrrolidin]-ones catalyzed by mesoporous molecular sieve MCM-41

A heterogeneous catalytic system (unfunctional mesoporous material MCM-41), which efficiently promoted one-pot synthesis of spiro[indoline-3,2′-pyrrolidin]-ones, has been developed. Under mild reaction conditions, a series of spiro[indoline-3,2′-pyrrolidin]-ones derivatives were synthesized in good yields (up to 95%) in water/ethanol = 2/1 as solvent. Notably, the unfunctional MCM-41 catalyst could be easily recovered by centrifugation and reused at least 10 times without loss in activity. And the scale up experiments also demonstrated the practicability of the catalystic system. Reusability, operational simplicity and eco-friendly are highlight of this study.

Phosphotungestic acid supported mesoporous MCM-41 coated NiFe2O4 magnetic nanoparticles as highly effective green nanocatalysts for coumarin and xanthene synthesis

Phosphotungestic acid supported mesoporous MCM-41 coated NiFe2O4 magnetic nanoparticles as highly effective green nanocatalysts for coumarin and xanthene synthesis

Highly efficient nano-Fe/Cu bimetal-loaded mesoporous silica Fe/Cu-MCM-41 for the removal of Cr(VI): Kinetics, mechanism and performance

Zero valent iron (Fe0) can reduce Cr(VI) in water, where Fe0 and Fe(Ⅱ) are possible electron donors, but passivation and aggregation easily occur to Fe0. To improve the performance of Fe0, a new hybridization strategy of Fe/Cu bimetal and silica-based mesoporous molecular sieve MCM-41 for the removal of Cr(VI) from water has been proposed. The results show that the two-dimensional mesoporous structure of MCM-41 can provide skeleton support for Fe0, improve the mass transfer rate, and overcome the aggregation bottleneck of Fe0. The Cr(VI) removal rate reached 98.98% (pH = 2) after 40 min. The analytical results revealed Cr(VI) removal process: Cr(VI) adsorbed onto Fe/Cu-MCM-41 by electrostatic attraction and other molecular inter-atomic forces. The second metal, Cu, can inhibit the passivation of Fe0 and promote Fe(Ⅱ)through the formation of Fe/Cu battery, thereby promoting the electron transfer. The resulting Cr(Ⅲ) is precipitated as FeCr2O4 and CrxFe1−x(OH)3.

Optimization of protein extraction and ELISA immunodetection from protein-based paint models with mesoporous silica nanoparticles and MCM41

Protein-based biological materials such as albumin, casein and collagen are found in various cultural heritage (CH) artefacts. This study focuses on the study of protein binders from easel paintings media. Proteins have complex structures which are difficult to identify with non-invasive spectroscopic methods (FT-IR, Raman, UV). Immunoassays such as ELISA determine the protein’s source of origin which is necessary for art objects. To increase the detection and identification of proteins by immunoassays, the efficiency of micro-extraction of proteins from heritage materials is a crucial step. Extractions mediated by cycles of orbital agitation and ultrasonic radiation give the possibility to extract proteins from easel painting sample. In this work, protein-based paint models coupled with silica nanoparticles were used for micro-extraction. Nanoparticles possess high surface-to-volume ratios that can attach bioactive molecules such as proteins and increase the total protein recovered from microsamples. Protein extracts were quantified with Bradford Assay in the presence of Coomassie blue. The protein recovery results were statistically computed, and the SPSS analysis shows significant (p < 0.05) increase in protein recovery, above 1.3 times for NPSiO2 and above 1.6 times for MCM-41. The statistical data shows evidence that silica nanoparticles intensify the total protein recovered from paint microsamples. Finally, ELISA was realized on the protein extracts to verify and compare the immunodetection of protein from the paint models with and without the use of silica nanoparticles.

Designing novel anticancer drug release vehicles based on mesoporous functionalized MCM-41 nanoparticles

Nanoparticles of mesoporous MCM-41 silica were synthesized, functionalized by 8-20% of hexamethylenetetramine (HMT) and employed as effective drug carriers. The carriers’ mesopores were filled with the cyclophosphamide (CP) anticancer medicine. The pore size, pore volume and surface area of pure MCM-41 were obtained equal to 32.54 Å, 0.89 cm3/g and 996.84 m2/g but they were noticeably decreased for the HMT-functionalized MCM-41 materials approving the HMT molecules were bound onto the surfaces and pores of such samples. The release of drug was performed in three neutral PBS, alkaline and acidic solutions. A sharply enhanced CP release was observed in approximately 24 h (burst release) while subsequently release of the drug was gradually boosted within 7 days indicating a sustained release behavior. The maximum drug release amount was measured in alkaline medium, moderate quantity in neutral solution and minimum value in acidic environment. The kinetic of the drug release was examined using the Korsmeyer-Peppas, Hixson-Crowel, Higuchi, first-order, and zero-order models and it was revealed that the CP release from the nanocarriers obeyed the Korsmeyer-Peppas model. Finally, it was decided that the MCM-41 sample containing 14% HMT was the most appropriate system as it had high/favorable quantities of drug loading plus drug release.

Sonochemical assisted preparation of ZnS–ZnO/MCM-41 based on blast furnace slag and electric arc furnace dust for Cr (VI) photoreduction

Iron/steel making industry is a weed that produces large quantities of slag and dust. The objective of the present study was to develop a procedure for obtaining and characterizing photocatalysts derived from this waste for chromium remediation. The MCM-41 was synthesized via sodium silicate (Na2SiO3) derived from Blast Furnace Slag (BFS), and ZnO and ZnS were synthesized based on zinc extracted from Electric Arc Furnace Dust (EAFD). Subsequently, ZnO/ZnS were sono-chemically loaded on the MCM-41 and were tested for the Cr (IV) photoreduction. The resultant ZnO, ZnS, MCM-41, and composites were characterized by X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX), N2adsorption–desorption isotherms, Fourier-transform infrared (FT-IR) spectrometry, Dynamic Light scattering, and Transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). A regular hexagonal structure of typical mesoporous MCM-41 had been proven by small-angle XRD, HRTEM, and N2 adsorption–desorption. The photoreduction activity of ZnS–ZnO/MCM-41 nanocomposite has obvious efficiency compared to ZnO and ZnO/MCM-41, achieving a 94% photoreduction of Cr (VI) in 180 min under UV irradiation. The slight activity loss after 4 cycles (84.7%) reveals the good photoreduction properties of catalysts. Based on these results, ZnS–ZnO/MCM-41 composite material seems to be high efficiency, green, stable, environment, and economical alternative to be used as a photocatalyst for the reduction of Cr (VI).