Surface Of Mesoporous Materials Research Articles

Amine and Sulfonic Acid Anchored Porous Silica as Recyclable Heterogeneous Catalysts for Ring‐Opening of Oxiranes

AbstractMCM type mesoporous silica materials can be used as potential catalysts with appropriate functionalization, for increasing selectivity and yield of the desired products. Co‐condensation or post‐synthesis treatment is the most common process of surface functionalization of mesoporous materials for the introduction of catalytic groups to their internal pore surfaces. In this work two different functional moieties were introduced on the surface of mesoporous material; one, a base functional group (3‐aminopropyl)triethoxysilane (APTES) and another, an acid functional group (3‐mercaptopropyl)triethoxysilane (MPTES). The materials were characterized thoroughly by powder XRD, BET, FT‐IR, TGA, NMR, SEM, TEM, etc. The results confirmed successful grafting of both the functional groups. The functionalized materials were tested in ring opening of different oxiranes; and the base functionalized MCM‐48 was found to be catalytically more active than acid functionalized material and was correlated mechanistically. Conversion of morpholine and piperidine with base functionalized material was found to be 93 and 91 %, respectively; and with acid functionalized material, 52 % of conversion of morpholine and 57 % conversion of piperidine was observed. Amine modified mesoporous MCM‐48 and MCM‐41 were found to be totally heterogeneous in nature and the catalysts were reusable up to 4 times without leaching.

Preparation and characterization of antibacterial mesoporous sieves with N-halamine

In this work, a novel antibacterial mesoporous material containing N-halamine was prepared. The N-halamine precursor monomer, 3-(3′-hydroxypropyl)-5,5-dimethylhydantoin (APDMH), was synthesized. After modification with siloxane agents, the precursor monomer was polymerized onto the surface of mesoporous materials (SBA-15). The initial and modified samples were characterized by SEM, TEM, FT-IR, TG, XRD, small-angle X-ray scattering diffraction, and BET analyses. The results showed that the N-halamine precursor was successfully grafted onto the surface of the mesoporous materials and that the morphology was affected slightly. The surface area of SBA-15 did not change significantly after modification. After being treated with commercial sodium hypochlorite solution, the modified material became antibacterial. The polymeric N-halamine mesoporous material exhibited excellent antibacterial activity and could inactivate 6.70 and 7.00 logs of Staphylococcus aureus (ATCC 6538) and E. coli O157:H7 (ATCC 43895), respectively, within 5 min of contact. The N-halamine-modified mesoporous material with potent antibacterial efficacy has potential in the application of water treatment and biomaterial areas.

Surface structuring of mesoporous materials by controlled synthesis of nanocavities

A process for the creation of uniform nanocavities on the surface of mesoporous materials using atomic layer deposition (ALD) and nanotemplate surface patterning is presented. Prior to grafting the organic nanotemplate, the surface of silica SBA-15 was pre-treated with an ALD coating of one monolayer of TiO2. The templates were then surrounded by Al2O3 as wall material using further ALD treatment. Template removal is achieved at moderate temperatures by reaction with ozone preventing damages to the structure which might occur at higher temperatures. By this approach a homogeneous distribution of uniform nanocavities of conical shape with 1–2 nm diameter, reflecting the size and geometry of the calixarene template molecules, was obtained. To monitor the various steps of the synthesis detailed characterization using N2 adsorption/desorption isotherms, FTIR, UV–Vis, and XP spectroscopy as well as thermal analysis and TEM was applied. Results from FTIR and UV–Vis spectroscopy reveal the successful formation of a covalent template-to-substrate binding, which remains unchanged during wall formation but breaks up during ozone treatment. Supporting XPS and TGA measurements give insight into the changing composition of the modified SBA-15 surface during synthesis and template removal in particular.

CO₂ adsorption on amine-functionalized periodic mesoporous benzenesilicas.

CO2 adsorption was investigated on amine-functionalized mesoporous silica (SBA-15) and periodic mesoporous organosilica (PMO) samples. Hexagonally (p6mm) ordered mesoporous SBA-15 and benzene-PMO (BPMO) samples were prepared in the presence of Pluronic P123 block copolymer template under acidic conditions. Three kinds of amine-containing organosilanes and polyethylenimine were used to functionalize SBA-15 and BPMO. Small-angle X-ray scattering and nitrogen adsorption isotherms showed that these samples featured ordered mesostructure, high surface area, and narrow pore size distributions. Solid-state (13)C- and (29)Si cross-polarization magic-angle spinning NMR spectra showed chemical linkage between amine-containing modifiers and the surface of mesoporous materials. The chemically linked amine-containing modifiers were found to be on both the inner and outer surfaces. N-[3-(trimethoxysilyl)propyl]ethylenediamine-modified BPMO (A2-BPMO) sample exhibited the highest CO2 uptake (i.e., ∼3.03 mmol/g measured on a volumetric adsorption analyzer) and the fastest adsorption rate (i.e., ∼13 min to attain 90% of the maximum amount) among all the samples studied. Selectivity and reproducibility measurements for the A2-BPMO sample showed quite good performance in flowing N2 gas at 40 mL/min and CO2 gas of 60 mL/min at 25 °C.

Comparative Studies on Drug Delivery Behavior of Mesoporous Silicas

In this work, we compared drug delivery behaviors of two different mesoporous materials, SBA-15 and MCM-41. For this work, mesoporous materials were modified with alkylsilane-containing secondary dialkylammonium ions (SAPH) and macrocyclic materials (DB24C8). The mesostructure and modified surface of mesoporous materials were characterized by muti-techniques. We used ibuprofen, lysozyme, and cytochrome c as the drug molecules. The photoluminescent spectra of releasing drug molecules from mesoporous materials showed controlled releasing behavior on adding base solutions. We found that the drug release behavior was strongly dependent on the pore size of the materials and the size of the drug molecules.

Efficient and reversible CO2 capture by amine functionalized-silica gel confined task-specific ionic liquid system

Simple, efficient and practical CO2 capture method is reported using task-specific ionic liquid (IL) supported onto the amine-functionalized silica gel. The results have been shown that both the capacity and rate of the CO2 absorption notably increase in the supported IL/molecular sieve 4Å system in comparison of homogeneous IL. Additionally, it has shown that the prepared material is capable for reversible carbon dioxide absorption for at least 10 cycles without significant loss of efficiency. The presence of the amine-based IL and the surface bonded amine groups increase the capacity of CO2 absorption even in a CO2/CH4 gas mixture through the formation of ammonium carbamate onto the surface of mesoporous material.

Tuning the Surface of Mesoporous Materials Towards Hydrophobicity-Effects in Olefin Epoxidation

Tuning the Surface of Mesoporous Materials Towards Hydrophobicity-Effects in Olefin Epoxidation

Synthesis and characterization of ionic liquid-functionalized alumino-silicate MCM-41 hybrid mesoporous materials

Ionic liquid-functionalized alumino-silicate MCM-41 hybrid mesoporous materials have been synthesized with two-step approach, by means of in situ skeleton doping with aluminium and post surface grafting with N-methylimidazole ionic liquid groups. The samples were characterized by X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), N2 adsorption–desorption, Fourier transform infrared (FTIR) spectra, 27Al and 13C MAS NMR spectra and temperature-programmed desorption (TPD) of NH3. The results indicated that the bifunctionalized MCM-41 possessed ordered mesostructure. Aluminium was efficiently introduced into the framework of the mesostructure, generating Lewis and Brönsted acid sites. N-methylimidazole ionic liquid groups were covalently grafted onto the surface of mesoporous materials. The as-synthesized bifunctional MCM-41 showed good catalytic performance in the coupling reaction of CO2 and propylene oxide.

Immobilization of hemoglobin within channel of mesoporous TiO2-SiO2 composite

In this investigation, mesoporous TiO2-SiO2 composites with different Ti/Si molecular ratios were synthesized by one pot method. Apart from the characterization by small angle X-ray diffraction (SAXRD), transmission electron microscope (TEM) and N2 absorption-desorption isotherms, these mesoporous materials were used in the adsorption and enrich of biological molecules. The results demonstrate that TiO2-SiO2 composites possess the ordered mesoporous structure with uniform pore. Bovine hemoglobin (BHb) can be immobilized within the mesopore of the composite and the immobilization amount increases with the Ti/Si molecular ratio. It is speculated that the strong electrostatic interaction between biomolecule and the inner surface of mesoporous materials enhances the adsorption of BHb. Moreover, our investigation confirms that the absorbed BHb still effectively retains its bioactivity, which is very significant for the potential application of this hybrid material in biocatalysis.

Microwave-Assisted Grafting to MCM-41 Silica and its Application as Catalyst in Flow Chemistry

Finding environmentally gentle methods to graft Lewis acid on the surface of mesoporous materials is a topic of current interest. Herein we describe the optimization of a preparation procedure of a mesoporous silica-supported ErIII catalyst using the microwave-assisted post-calcination functionalization of Mobil Composition of Matter-41 silica as the key step. The required time for functionalization was reduced from several hours to 10 min using sealed-vessel microwave technology. Control experiments using conventional heating at the same temperature demonstrated that the rate increase is owing to a simple thermal/kinetic effect as a result of the higher reaction temperature. The resulting ErIII catalyst was tested for the first time as a catalyst in the continuous flow deprotection of benzaldehyde dimethylacetal and a complete leaching study was performed.

A Dynamic Magic Angle Spinning NMR Study of the Local Mobility of Alanine in an Aqueous Environment at the Inner Surface of Mesoporous Materials

Dynamic deuterium magic angle spinning NMR has been applied to study the slow motion of small molecules close to a silica surface. In particular, alanine-d(3) molecules dissolved in an aqueous solution were loaded into the pores of the mesoporous materials SBA-15 and MCM-41. Deuterium spectra were measured as a function of the water content of these materials and the temperature. From the analysis of these spectra and the corresponding proton spectra, using a simple molecular exchange model, relatively slow desorption rates of the binding of alanine to the inner pore surface were obtained and were correlated with the low proton concentrations at the pore surfaces.

Carbon-13 CP MAS NMR Study on Structures of Octadecyl Chains Influenced by Co-Presence of 3-Aminopropyl Chains on SBA-15

Functionalized SAB-15 samples by octadecyltrimethoxysilane (OTC) were studied by 13C magic angle spinning (MAS) cross polarization (CP) nuclear magnetic resonance (NMR) spectroscopy. In the SBA-15 sample fully functionalized by 3-aminopropyltrimethoxysilane (APS) and OTC in 1:1 molar ratio, octadecyl chains were observed to have, on average, more trans conformation than those in the SBA-15 samples fully modified by OTC only. Our results confirm that long chain molecules tend to organize themselves better in the co-presence of short chain molecules on the surface of mesoporous materials by packing of the different length chains in an interdigitized fashion even when the short chains are long enough to have three carbons and a functional group at the ends. In addition, our results indicate that solid-state 13C CP MAS NMR spectroscopy is a simple and non-destructive method to probe the molecular structures of the domains composed of long alkyl chains.

Chemical Immobilization of Heteropolyacid Catalyst on Inorganic Mesoporous Material for use as an Oxidation Catalyst

Recent progress on the chemical immobilization of heteropolyacid (HPA) catalyst on inorganic mesoporous material is reported in this review. Mesostructured cellular foam silica, mesoporous carbon, and nitrogen-containing mesoporous carbon were used as supporting materials. The mesoporous materials were modified to have a positive charge, and thus, to provide sites for the immobilization of HPA catalyst. By taking advantage of the overall negative charge of heteropolyanion, the HPA catalyst was chemically immobilized on the surface-modified mesoporous material as a charge-compensating component. Characterization results showed that the HPA catalyst was finely and molecularly dispersed on the surface of mesoporous material via strong chemical immobilization, and that the pore structure of mesoporous material was still maintained even after the immobilization of HPA catalyst. The supported HPA catalysts were applied to the model vapor-phase ethanol conversion, 2-propanol conversion, and methacrolein oxidation reactions. The supported HPA catalyst showed a better oxidation catalytic activity than the unsupported HPA catalyst in the model reactions. The enhanced oxidation catalytic performance of the supported HPA catalyst was attributed to the finely dispersed HPA catalyst, which was chemically immobilized on the positive site of mesoporous material by sacrificing its proton (Bronsted acid site). The HPA catalyst chemically immobilized on mesoporous material served as an excellent oxidation catalyst.