MCM-41 Host Research Articles

Synthesis of Sm (III) complex immobilized in MCM-41: A new heterogeneous catalyst for the facile synthesis of 5-substituted 1H-tetrazoles via [3 + 2] cycloaddition of nitriles and sodium azide

Samarium (III) complex immobilized in MCM-41 were synthesized via post-functionalization modification of MCM-41. The catalysts were characterized by Fourier transforms infrared (FT-IR) spectra, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analyses (TGA). The results show that the 3,4,5-tri hydroxyphenyl acetic acid ligand and Sm ions are attached to the MCM-41 host. The catalysts were tested in the synthesis of 5-substituted 1H-tetrazoles. This catalyst is an efficient catalyst for [3 + 2] cycloaddition with NaN3 to prepare 5-substituted 1H-tetrazoles. The catalyst was recycled for up to six cycles without significant loss of activity.

Pepper fragrant essential oil (PFEO) and functionalized MCM-41 nanoparticles: formation, characterization, and bactericidal activity.

It is well known that plant essential oils have good antimicrobial activity. However, their strong volatility and intense odor limit their application. Mesoporous silica (MCM-41), a non-toxic mesoporous material with excellent loading capability, is a promising delivery system for different types of food ingredients in the food industry. In this study, we first performed component analysis of pepper fragrant essential oil (PFEO) by gas chromatography-mass spectrometry (GC-MS), then the MCM-41 host was prepared, and the essential oil functionalized nanoparticles (EONs) were formed by embedding PFEO into mesoporous silica particles. Further analysis indicated that the particle size and zeta potential of EONs were 717 ± 13.38 nm and - 43.90 ± 0.67 mV, respectively. Transmission electron microscopy (TEM) images showed that EONs had an inerratic morphology and stable structure. The bactericidal activities of PFEO and EONs against Escherichia coli (E. coli), Salmonella enterica (S. enterica), Staphylococcus aureus (S. aureus) and Listeria monocytogenes (L. monocytogenes) were subsequently tested using the twofold dilution method. Results indicated that, after 48 h incubation, minimum bactericidal concentrations (MBC) of EONs used against gram-negative bacteria were decreased to a greater degree than those of PFEO, suggesting that nanoencapsulation by MCM-41 can improve antimicrobial activity. Atomic force microscopy (AFM) observation also confirmed that EONs showed a notable inhibitory effect against E. coli by disrupting cell membrane structure. Pepper fragrant essential oil nanoencapsulation could be a very promising organic delivery system in food industry for antimicrobial activity enhancement. © 2019 Society of Chemical Industry.

Nanocrystallization of Rare Tolbutamide Form V in Mesoporous MCM-41 Silica.

Encapsulation of pharmaceuticals inside nanoporous materials is of increasing interest due to their possible applications as new generation therapeutics, theranostic platforms, or smart devices. Mesoporous silicas are leading materials to be used as nanohosts for pharmaceuticals. Further development of new generation of nanoscale therapeutics requires complete understanding of the complex host-guest interactions of organic molecules confined in nanosized chambers at different length scales. In this context, we present results showing control over formation and phase transition of nanosize crystals of model flexible pharmaceutical molecule tolbutamide confined inside 3.2 nm pores of the MCM-41 host. Using low loading levels (up to 30 wt %), we were able to stabilize the drug in highly dynamic amorphous/disordered state or direct the crystallization of the drug into highly metastable nanocrystalline form V of tolbutamide (at loading levels of 40 and 50 wt %), providing first experimental evidence for crystallization of pharmaceuticals inside the pores as narrow as 3.2 nm.

Light emitting diodes based on blends of quasi-2D lead halide perovskites stabilized within mesoporous silica matrix

The effective synthesis and embedding of semiconducting perovskite blends inside the pores of different mesoporous silica matrices is reported, as well as the implementation of these composites for the first time, as the single and active layer in light emitting diodes. The reported perovskites are blends of quasi-two dimensional hybrid organic-inorganic semiconductors based on lead halides. These blends have been synthesized within the pores of calcined or non-calcined MCM-41 hosts, of two different types, and were optically characterized with UV and PL spectroscopies, as well as structurally with XRD, BET, TEM and SEM techniques. Perovskites reside within the pores of the final dried samples, where degradation protection is provided from chemicals, including water. Moreover, the final white powder like composites exhibit naked-eye visible luminescence as well as electroluminescence under daylight.

Synthesis and Luminescence of Eu‐N2,N6‐Bis(2‐hydroxyethyl)pyridine‐2,6‐dicarboxamide Complexes Containing Mesoporous Material

AbstractLigand N2,N6‐bis(2‐hydroxyethyl)pyridine‐2,6‐dicarboxamide (L=BHPC) was synthesized and used to construct lanthanide‐based mesoporous material Eu‐L‐MCM‐41. In the structure of resulting Eu‐L‐MCM‐41, Eu3+ was chelated by BHPC, and the Eu‐L complexes were anchored into the forming MCM‐41 host by the reaction between the hydroxyl group and active Si‐OH. The mesoporous material Eu‐L‐MCM‐41 was characterized by UV, IR, small‐angle X‐ray diffraction (SAXRD) patterns, nitrogen adsorption/desorption isotherms, TGA and fluorescence spectra. The results indicate that ligand and Eu3+ have been introduced into the MCM‐41 host, and Eu‐L‐MCM‐41 exhibits characteristic luminescence of Eu3+.

Multi-component hybrids of surfactant functionalized europium tetrakis (β-diketonate) in MCM-41(m) and polymer modified ZnO for luminescence integration

Surfactant dodecyl(11-(methacryloyloxy)undecyl)dimethylammonium bromide (DMDA) is utilized as the chemical linkage to assemble multi-component photofunctional hybrids. Europium (III) tetrakis (β-diketonate) complexes (β-diketonate (L)=2-thenoyltrifluoroacetonate (TTA), 4,4,4-trifluoro-1-phenyl-1,3-butanedionate (BTA), trifluoroacetylacetonate (TAA)) are connected with DMDA via anion exchange reaction to form Eu(L)4DMDA. Then Eu(TTA)4DMDA system is encapsulated into (3-aminopropyl)triethoxysilane functionalized MCM-41 host, resulting in MCM-41(m)-Eu(L)4DMDA assembly. At the same time, methacrylic-group-modified ZnO nanoparticles (designated ZnO-MAA) are prepared through sol–gel reaction between zinc methacrylate and LiOH. Finally ZnO-MAA and MCM-41(m)-Eu(L)4DMDA are covalently bonded together with copolymerization reaction between MAA and DMDA units at the presence of benzoyl peroxide (BPO). The detailed physical characterization and especially the photoluminescence of these hybrid materials are studied in detail. Besides the uniformity is kept in the mesostructure, the characteristic emission of both Eu3+ complex system and modified ZnO unit are obtained. It is interesting that the white luminescence is obtained for MCM-41(m)-Eu(TAA)4DMDA-ZnO by the emission integration of ZnO unit and Eu3+. The results provide a strategy to assemble multi-component hybrids in mesoporous host.

Study of hydrogen adsorption properties on MCM-41 mesoporous materials modified with nickel

MCM-41 samples were modified with different Ni loadings by wet impregnation method and characterized by XRD, ICP, EPMA-EDS, N2 adsorption–desorption and hydrogen adsorption at 77 K at high and low pressure conditions. The hydrogen adsorption studies for the MCM-41 host and the impregnated samples showed that small amounts of Ni ions in MCM-41 improved the hydrogen storage capacity by spillover effect.

Luminescent hybrid materials based on covalent attachment of Eu(III)-tris(bipyridinedicarboxylate) in the mesoporous silica host MCM-41.

A luminescent inorganic-organic hybrid material was synthesized by covalent immobilization of a europium bipyridine carboxylate complex on the inner pore walls of the mesoporous silica host MCM-41 using the grafting method. Guest-host binding was achieved through double functionalization of the host surface with organosilane reagents (trimethylsilyl, TMS, and aminopropyltriethoxysilane, APTES) followed by reaction of the active amino sites of the APTES residue with the ligand 2,2'-bipyridyl-6,6'-dicarboxylic acid. Addition of EuCl3 solution dissolved in ethanol results in the formation of an immobilized complex having the probable formula Eu(L)x(3 ≥ x ≥ 1)(H2O)y, whose detailed photophysical properties were investigated. In the final step, an additional 2,2'-bipyridine-6 monocarboxylic acid ligand was added in an attempt to complete the coordination sphere of the rare earth ion. Each of the synthesis steps was monitored by (1)H, (13)C, and (29)Si solid state NMR spectroscopies, allowing for a quantitative assessment of the progress of the reaction and the influence of the paramagnetic species on the spectra. Based on these data and additional characterizations by chemical analysis, thermogravimetric analysis (TGA), N2 sorption, X-ray diffraction and FT-IR spectroscopy, a comprehensive quantitative picture of the covalent binding and complexation process was developed.

Nanoscale zero-valent iron supported on mesoporous silica: Characterization and reactivity for Cr(VI) removal from aqueous solution

MCM-41-supported nanoscale zero-valent iron (nZVI) was sytnhesized by impregnating the mesoporous silica martix with ferric chloride, followed by chemical reduction with NaHB4. The samples were studied with a combination of characterization techniques such as powder X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) and Mössbauer spectroscopy, N2 adsorption measurements, transmission electron microscopy (TEM), magnetization measurements, and thermal analysis methods. The experimental data revealed development of nanoscale zero-valent iron particles with an elliptical shape and a maximum size of ∼80nm, which were randomly distributed and immobilized on the mesoporous silica surface. Surface area measurements showed that the porous MCM-41 host matrix maintains its hexagonal mesoporous order structure and exhibits a considerable high surface area (609m2/g). Mössbauer and magnetization measurements confirmed the presence of core–shell iron nanoparticles composed of a ferromagnetic metallic core and an oxide/hydroxide shell. The kinetic studies demonstrated a rapid removal of Cr(VI) ions from the aqueous solutions in the presence of these stabilized nZVI particles on MCM-41, and a considerably increased reduction capacity per unit mass of material in comparison to that of unsupported nZVI. The results also indicate a highly pH-dependent reduction efficiency of the material, whereas their kinetics was described by a pseudo-first order kinetic model.

Light-Triggered Eradication of Acinetobacter baumannii by Means of NO Delivery from a Porous Material with an Entrapped Metal Nitrosyl

A photoactive manganese nitrosyl, namely [Mn(PaPy(3))(NO)](ClO(4)) ({Mn-NO}), has been loaded into the columnar pores of an MCM-41 host. Strong interaction between the polar nitrosyl and the -OH groups on the host wall leads to excellent entrapment of the NO donor within the porous host. With the aluminosilicate-based host (Al-MCM-41), the loading is further enhanced due to electrostatic interaction of the cationic species with the aluminum sites. The extent of loading has been determined via analytical techniques including N(2) adsorption/desorption isometry. Powder X-ray diffraction studies on the loaded materials afford patterns typical of an ordered mesoporous silicate consisting of a hexagonal array of unidimensional channels (with slight loss of crystallinity). Elemental mapping of the loaded particles confirms the incorporation of {Mn-NO} into the porous MCM-41 structure and attests to the homogeneity of the guest molecule distribution throughout individual particles. When suspensions of the loaded materials in saline solution are exposed to low-power (10-100 mW) visible light, rapid release of NO is observed. With continuous exposure, a steady release of 50-80 μM of NO is attained with 5 mg of material/mL buffer within 5 min, and the NO flux is maintained for a period of ~60 min. Rapid bursts of 5-10 μM NO are noted with short light pulses. Loss of either the nitrosyl or its photoproduct(s) from these materials in biological media is minimal over long periods of time. The NO release profiles suggest potential use of these powdery biocompatible materials as NO donors where the delivery of NO (a strong antibiotic) could be controlled via the exposure of light. Such prediction has been confirmed with the successful eradication of both drug-susceptible and drug-resistant Acinetobacter baumannii in a soft-tissue infection model through light-triggered NO delivery.

ZnFe2O4-TiO2Nanoparticles within Mesoporous MCM-41

A novel nanocomposite ZnFe2O4-TiO2/MCM-41 (ZTM) was synthesized by a sol-gel method and characterized through X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N2 adsorption-desorption, Raman spectroscopy, and ultraviolet visible (UV-vis) spectrophotometry. The results confirmed the incorporation of ZnFe2O4-TiO2 nanoparticles inside the pores of the mesoporous MCM-41 host without destroying its integrity. ZnFe2O4 nanoparticles can inhibit the transformation of anatase into rutile phase of TiO2. Incorporation of ZnFe2O4-TiO2 within MCM-41 avoided the agglomeration of nanoparticles and reduced the band gap energy of TiO2 to enhance its visible light photocatalytic activity. UV-vis absorption edges of ZTM nanocomposites redshifted with the increase of Zn/Ti molar ratio. The nanocomposite approach could be a potential choice for enhancing the photoactivity of TiO2, indicating an interesting application in the photodegradation and photoelectric fields.

Heterogenization of [Ti(η 5-C 5HMe 4)Cl 3] on to MCM-41 and organomodified MCM-41 to form epoxidation catalyst

This paper describes the heterogenization of a tetramethylmonocyclopentadienyl titanium (IV) trichloride complex, [Ti(η 5-C 5HMe 4)Cl 3] onto mesoporous MCM-41. Its immobilization has been performed via a straightforward grafting process of the organometallic precursor in the pores of an MCM-41 host material and by reaction with previously organomodified MCM-41 material with a hydroxyl triazine based compound. Applying all-silica MCM-41 hosts, stable and heterogeneous liquid-phase epoxidation catalysts are obtained. Powder X-ray diffraction and nitrogen adsorption–desorption analysis indicated that the structural integrity of the support has been preserved during the titanium complex immobilization. These materials have been also extensively characterized using diffuse reflectance UV–vis, 13C and 28Si MAS NMR and FT-IR spectroscopy. With these techniques the strong adsorption of the intact catalytic complex within an all-silica MCM-41 host is demonstrated. These materials have been tested as catalyst for the epoxidation of aliphatic and aromatic alkenes with TBHP as oxidant exhibiting a significant selectivity toward the epoxide with negligible leaching of titanium species. The conversion values are moderated, being the olefin trend reactivity 1-octene > cyclohexene > styrene.

Fe(III)-salim anchored MCM-41: synthesis, characterization and catalytic activity towards liquid phase cyclohexane oxidation

A novel organic–inorganic hybrid catalyst [MCM-41-FeIII(salim)] was synthesized by covalently anchoring FeIII(salim) complex into the pore channels of MCM-41. The material was synthesized by the co-condensation of tetraethyl orthosilicate (TEOS) and the precursor of salicylaldehyde modified with 3-aminopropyl triethoxysilane in the presence of cetyltrimethyl ammonium bromide (CTAB). The Fe(III)-salicylideneimine MCM-41 mesoporous silica was generated (in situ) by taking MCM-41-salimH (I) and FeCl3 in ethanol solution. The immobilization of the complex on the functionalized silica was confirmed by small angle X-ray diffraction (XRD), N2 adsorption–desorption, electron paramagnetic resonance (EPR), Fourier transform infrared spectroscopy (FT-IR) and diffuse reflectance UV–vis spectroscopy. Solid state CP-MAS NMR spectroscopy of 29Si (29Si CP-MAS NMR) showed a highly condensed siloxane network. Catalytic activity of the supported catalyst was examined by the oxidation of cyclohexane. Cyclohexane was successfully oxidized in good conversion (68%) to cyclohexanone, as a major product with 72% selectivity using tert. butylhydroperoxide as oxidant and acetonitrile as solvent. The catalysts can be reused up to three cycles without losing much of its activity. Fe(III)-salicylideneimine immobilized MCM-41 hybrid mesoporous silica was prepared by covalent anchoring of schiffbase complex to MCM-41 host and used for liquid phase oxidation of cyclohexane.

Interrogating Confined Proton-Transfer Reaction Dynamics within Mesoporous Nanotubes

We report on steady-state and time (ns to fs regime) resolved studies of H-bonding interactions and proton-transfer reaction dynamics of silica-based mesoporous material MCM-41 with an H-bond donor and acceptor guest aromatic molecule (7-hydroxyquinoline, 7HQ). We observed the ground state reaction which leads to the formation of intermediates and products of the confined molecular probe. We compare this behavior with the observed one for the dye adsorbed on the surface of silica particles, lacking the nanotubes. The result clearly shows that the formation of keto (or zwitterionic) tautomers at the ground state is enhanced by the confinement provided by the channels of MCM-41. Introduction of hydrophobic groups (by silylation of the OH groups in regular MCM-41 host) changes the ground state tautomeric equilibria and the emission behavior. A new lifetime (3.19 ns, suggested being due to a more stabilized anion of the guest) was observed in addition to the ones due to confined bound enol (0.26 ns), anion (1...

Synthesis and Characterization of Biopolymer Composites from the Inside Out

The metal catalyzed ring-opening polymerization of d,l-lactide monomer inside the nanometer-sized channels of MCM-41 and SBA-15 hosts, creating an organic−inorganic hybrid polymeric material, is described. Detailed characterization of the polylactide/mesoporous silica organic−inorganic composite by multiple spectroscopic, microscopy, and calorimetric methods, as well as solvent extraction, reveals that the resulting in situ synthesized composite is unique relative to physical or solution-cast mixtures of polylactide and the mesoporous host. In this contribution, we focus on the incorporation of the stannous octanoate (Sn2+) catalyst inside the mesoporous host channels prior to monomer introduction and subsequent polymerization and specifically target the differentiation of polymerization chemistry that occurs inside the host channels versus less desirable reactions on the exterior surface of the mesoporous host crystallites.

Femtosecond Dynamics Within Nanotubes and Nanocavities of Mesoporous and Zeolite Materials

The steady-state, picosecond and femtosecond time-resolved emission of Sudan I within MX (M = Na + , Li + Mg 2+ ), NaY zeolites, and MCM-41 mesoporous silica have been studied in the presence of solvents. The results show that the rate constant of the initial excited-state intramolecular proton-transfer (ESIPT) reactior in the trans-azoenol (trans-AZO) structure to give the trans-ketohydrazone (trans-HYZ) form of Sudan remains ultrafast (τ < 50 fs) as in pure solution. However, within these nanohosts, the time necessary for a trans—cis isomerization in the formed trans-HYZ tautomer to yield the cis-HYZ structure increases. The largest effect was obtained when the MX hosts contained polar and H-bonding solvents (water, methanol) The result is explained in terms of a stronger solvation of the metal cation enhancing its shielding and therefore lowering its interaction with the included dye. The use of different metal cations of MX zeolite shows thai nanosolvation of cations (M + ) increases the measured times for isomerization and relaxation of the excitec structures of Sudan I. Furthermore, the observation of similar times for NaX, NaY, and MCM-41 (hosts different in polarity and diameter of the pore/cavity) suggests that that the trans—cis isomerization occurs by an inversion mechanism. The slowing of the dynamics within the nanopores is reminiscent of that occurring in biological media, such as within proteins, and it should be relevant to photonic devices using this kind of nanomaterials.

&lt;b&gt;PREPARATION, CHARACTERIZATION AND OPTICAL PROPERTIES OF MCM-41/RHODAMINE B&lt;/b&gt;

Nanometer MCM-41 molecular sieve and rhodamine B (RhB) have been used for the host and guest, respectively, to prepare host-guest (nanometer MCM-41)-RhB composite materials by liquid-phase grafting method. Powder X-ray diffraction, chemical analysis, infrared spectroscopy, low temperature nitrogen adsorption-desorption technique and diffuse reflectance absorption spectroscopy were used to characterize the prepared (nanometer MCM-41)-RhB host-guest composite material. The results showed that the framework of the molecular sieve in the host-guest composite material is well retained and highly ordered. The RhB was confined and dispersed inside the channels of the host material. A blue-shift of 56 nm in the UV-vis diffuse reflection absorption spectrum of the host-guest composite material prepared further indicated that RhB trapped in the channels of the molecular sieve. The guest was stereoscopically confined by the channels of the nanometer MCM-41 host. The prepared host-guest composite material shows luminescence. The material has the potentiality as luminescence material. KEY WORDS : Host-guest nanocomposite material, Nanometer MCM-41 molecular sieve host, Rhodamine B guest, Characterization, Luminescence Bull. Chem. Soc. Ethiop. 2009 , 23(1), 145-150.

Synthesis and optical properties of mesoporous MCM-41 containing doped TiO 2 nanoparticles

Nanosized TiO 2 is a kind of high-performance and functional inorganic material, the widespread use of TiO 2 is impaired by some defects of its structure, wide band gap (3.2 eV), and agglomeration easily occurred during the synthesis process. Uniform ordered channels of mesoporous materials, such as MCM-41, can control the particle size of TiO 2 and efficiently prevent particles from agglomeration. Tetraethylorthosilicate (TEOS) and tetrabutyl titanate were used as the silica source and Ti source respectively to synthesize the TiO 2/MCM-41 (TM) doped with different ions. MCM-41 was synthesized using a hydrothermal route; metal ions were incorporated into the pore channels of MCM-41 via a sol–gel method. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), ultraviolet–visible (UV–vis) spectrophotometry, N 2 adsorption–desorption measurements and X-ray photoelectron spectroscopy (XPS) confirmed the incorporation of TiO 2 nanoparticles inside the pores of the mesoporous MCM-41 host without destroying its integrity. Specific surface area of TM composites increased, but the pore size and the pore volume decreased compared with that of pure MCM-41. The UV–vis spectra demonstrate that all the absorbance peaks of TM composites have a blue shift. The absorbance peaks of TM composites doped with different metal ions shift again. Ce-doped TM shows red shift markedly, which provides the possibility for preparing visible-light reactive photocatalyst.

Covalently bonding assembly and photophysical properties of luminescent molecular hybrids Eu–TTA–Si and Eu–TTASi–MCM-41 by modified thenoyltrifluoroacetone

In the context, the two novel kinds of hybrid materials, TTA–Si directly chemically bonded molecular hybrids and the corresponding MCM-41 host assembling hybrids were prepared. The organic–inorganic mesoporous luminescent materials were synthesized by linking Eu 3+ complexes to the functionalized ordered mesoporous MCM-41 with modified thenoyltrifluoroacetone (TTA–Si) by co-condensation of tetraethoxysilane (TEOS) in the presence of the cetyltrimethylammonium bromide (CTAB) surfactant as template. Thenoyltrifluoroacetone (TTA) was grafted with coupling agent 3-(triethoxysilyl)-propyl isocyanate and the as-derived functional bridge molecule (denoted as TTA–Si) was introduced into inorganic polymeric host MCM-41 through covalent bonds, resulting in the molecular hybrid material. The luminescence properties of these resulting materials were characterized in detail, and the results reveal that they all have high surface area, uniformity in the mesostructure and crystallinity. The efficient intramolecular energy transfer in mesoporous material Eu–TTASi–MCM-41 mainly occurs between the modified ligand TTA–Si and the central Eu 3+ ion. In addition, the constructed covalently bonded hybrids present the longer luminescent lifetimes than common Eu(III) β-diketones complexes for improvement of stability. Especially the mesoporous luminescent material Eu–TTASi–MCM-41possesses high luminescence quantum efficiency .

Photophysical properties of a naphthalimide derivative encapsulated within Si-MCM-41, Ce-MCM-41 and Al-MCM-41

4-Piperazinyl- N-methyl-1,8-naphthalimide (PMN) was synthesized and encapsulated into mesoporous molecular sieves. The fluorescent emission spectra and fluorescence decay of PMN/M-MCM-41 (where M = Si, Ce, Al) were used to investigate the photophysical properties of the hybrid composites. The emission intensity of 4-piperazinyl- N-methyl-1,8-naphthalimide can be increased by decreasing the pH environment of the hybrid composites; the emission intensity varied with different MCM-41 hosts in the order: PMN/Al-MCM-41 > PMN/Si-MCM-41 > PMN/Ce-MCM-41; the fluorescence lifetime of PMN molecules followed the same order. The reasons for the improved fluorescence intensity and the prolonged lifetime of PMN in a low pH environment and Al-MCM-41 are discussed.