Inorganic Hybrid Mesoporous Materials Research Articles

Tungstate supported mesoporous silica SBA‐15 with imidazolium framework as a hybrid nanocatalyst for selective oxidation of sulfides in the presence of hydrogen peroxide

In this work, a new heterogeneous catalyst (SBA‐15/Im/WO42−) was prepared, and then its performance in the oxidation of organic sulfides was studied (using 30% H2O2 as green oxidant under neutral reaction conditions). This organic–inorganic hybrid mesoporous material was characterized by various techniques, such as FT‐IR, inductively coupled plasma, X‐ray powder diffraction, high‐resolution‐transmission electron microscopy, N2 adsorption–desorption and thermogravimetric analysis. The catalyst was also applied to the selective oxidation of various sulfides. The hybrid catalyst was easily recovered, and was very stable and retained good activity for at least five successive runs without any additional activation. Moreover, there was no remarkable decrease in the activity and selectivity of the catalyst. The products could be easily isolated by just removing the solvent after filtering the catalyst. The yields of the catalytic productions through this catalyst were in the range from 75% to 97%.

Solid Phase Extraction of Pb(II) and Cd(II) in Food, Soil, and Water Samples Based on 1-(2-Pyridylazo)-2-Naphthol-Functionalized Organic–Inorganic Mesoporous Material with the aid of Experimental Design Methodology

An effective sorbent of 1-(2-Pyridylazo)-2-naphthol-functionalized mesoporous silica has been prepared to simultaneous separation and preconcentration of lead and cadmium ions in aqueous solution. Structural characterization of 1-(2-Pyridylazo)-2-naphthol-functionalized organic–inorganic hybrid mesoporous materials was conducted by Fourier transform infrared spectroscopy, transmission electron microscopy, N2 adsorption–desorption measurement, X-ray diffraction, and elemental and thermal analysis, which confirmed the successful grafting of organic moiety on mesoporous silica. The affecting parameters on adsorption and desorption steps were optimized by Box-Behnken design through response surface methodology. Three variables (pH value, sorption time, and amount of the sorbent) were selected as the main factors affecting sorption step, while four variables (type of eluent, eluent volume, eluent concentration, and elution time) were selected for desorption step in the optimization study. The optimized values by this optimization method were 10 mg, 8 min, 6.3, HCl, 1.6 mL, 1.2 mol L−l HCl, and 10 min, for amount of sorbent, sorption time, pH of solution, type, volume, and concentration of the eluent, and elution time, respectively. Under the optimized conditions, the detection limits of the proposed method for lead and cadmium ions were found to be 0.9 and 0.04 μg L−1, respectively, while the relative standard deviation (RSD) for five replicate measurements was calculated to be <3 % for both ions. For proving that the proposed method is reliable, a wide range of food, soil, and water samples with different and complex matrixes was used.

Organic-Inorganic Hybrid Mesoporous Materials as Regenerable Sensing Systems for the Recognition of Nitroaromatic Explosives.

Fluorescent organic-inorganic mesoporous hybrid materials have been prepared and characterised, and their behaviour against nitroaromatic explosives have been tested. MCM-41 silica was used as an inorganic scaffold and pyrene (P derivative containing trialkoxysilane moieties), dansyl and fluorescein (D and F derivatives also containing trialkoxysilane groups, respectively) fluorophores have been anchored on hybrid materials by a co-condensation method to obtain a homogenous distribution of dyes into the pores of the support. Six sensing materials have been prepared, of which SP, SD, SF were hydrophilic and SPh, SDh, SFh were hydrophobic. Template-free hydrophilic materials (SP, SD, SF) were obtained after repeated NH4 NO3 /ethanol extractions under temperature from as-synthesised (MP, MD and MF supports, respectively) solids. Hydrophobic materials (SPh, SDh, SFh) were prepared by using excess 1,1,1,3,3,3-hexamethyldisilazane with template-free hydrophilic (SP, SD and SF) materials. The six final materials displayed the typical emission bands of the grafted fluorophores. In particular, SP and SPh show the typical pyrene monomer (370-420 nm) and excimer (430-600 nm) emissions. SD and SDh exhibit the broad dansyl fluorescence band in the 450-600 nm range, whereas solids SF and SFh present sharp fluorescein emission centred at 525 nm. The fluorescent behaviour of the six final materials was tested in the presence of explosives (pentaerythritol tetranitrate (PETN), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), nitrobenzene (NB), 1,3,5-trinitrobenzene (TNB), 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), 2,4,6-trinitrophenylmethylnitramine (Tetryl) and picric acid (PA)). Only nitroaromatic compounds were able to induce emission quenching. As a general trend, the quenching degree depended on the nature of the final material. The best response was obtained with explosives PA and Tetryl, which were able to significantly quench the emission of the sensing supports. The observed quenching was ascribed to the π-π stacking interactions between the electron-donor fluorophores and the electron-withdrawing nitroaromatic explosives. When using SPh for Tetryl and PA, the limits of detection were 8.5 and 1.4 ppm, respectively, whereas they were 14.4 and 1.2 ppm for SDh. Principal component analysis algorithms were applied to the fluorescence measurements taken with the six hybrid materials and the seven explosives. The obtained score plot showed well-defined clusters for the seven explosives tested. Finally, solid SDh was applied to detect trace amounts of Tetryl in soil samples with good results.

ChemInform Abstract: Dendrimer—Silica Hybrid Mesoporous Materials

AbstractReview: about 100 refs.

Dendrimer–silica hybrid mesoporous materials

Dendrimers and silica inorganic materials are two effective building blocks that have attracted growing interest in both fundamental and applied material chemistry. The fruitful association of these soft and hard skeletons resulted in an unlimited library of materials and nanodevices with different tailored properties. The aim of this review is to shed light on different strategies of combination of dendrimer–silica materials. Special attention has been accorded to the porosity control and the accessibility of the functional groups of these organic–inorganic hybrid mesoporous materials.

Preparation of POSS-based organic–inorganic hybrid mesoporous materials networks through Schiff base chemistry

The synthesis of novel POSS-based organic–inorganic hybrid mesoporous materials networks functionalized with amine groups through Schiff base chemistry is reported. The material shows uniform mesoporous size. Nitrogen sorption analyses give high specific surface areas of 641–1103m2g−1 with pore volumes of 0.47–0.53mLg−1. The combined results of FTIR, solid 13C NMR and 29Si NMR show that the POSS building blocks are successfully weaved in the porous structure without obvious alteration of the POSS structural characteristics. The hybrid materials show excellent thermal stability.

Synthesis and Catalytic Performance of Organic–Inorganic Hybrid Mesoporous Material Having Basic Nanospace

Basic nanospace was synthesized by the homogeneous modification of FSM-16 with 3-(triethoxysilyl)pyridine, which is a rigid substrate without an alkyl chain as linker. Aldol condensation of butanal gave the corresponding dimer in high yields over 3-(triethoxysilyl)pyridine-modified FSM-16. A copper-pyridine complex was immobilized within the interior of FSM-16 using the modified pyridyl group as a ligand and the oxidative coupling polymerization of 2,5-dimethylphenol proceeded with high regio-selectivity. Basic nanospace was synthesized by the homogeneous modification of FSM-16 with 3-(triethoxysilyl)pyridine, which is a rigid substrate without an alkyl chain as linker. Aldol condensation of n-butyraldehyde gave the corresponding dimer in high yields over 3-(triethoxysilyl)pyridine-modified FSM-16. A copper-pyridine complex was immobilized within the interior of FSM-16 using a modified pyridyl group as the ligand and the oxidative polymerization of 2,5-dimethylphenol proceeded with high regio-selectivity.

Selective adsorption of bisphenol A by organic–inorganic hybrid mesoporous silicas

Organic–inorganic hybrid mesoporous material (Ph-MS) was synthesized by co-condensation of phenyltriethoxysilane and tetraethoxysilane. Ph-MS, which had pore size of 0.96 nm and surface area of 750 m 2/g, exhibited mesoscopic orderness and suitable textural properties to act as a potential adsorbent for bisphenol A (BPA), which is one of the endocrine disrupting chemicals. Ph-MS adsorbed most amount of BPA faster than powder activated carbon (PAC), and the kinetic adsorption data for Ph-MS was fitted well with the pseudo-second-order kinetic model. Maximum adsorption capacities of adsorbents were estimated from isotherm data using Langmuir model. Ph-MS exhibited high adsorption affinity to BPA showing large adsorption capacity of 351 mg/g, while showing little adsorption affinity to phenol (40 mg/g). PAC, which is one of the general adsorbents for organic compounds, showed large adsorption capacity for both BPA (337 mg/g) and phenol (253 mg/g). Adsorption selectivity of Ph-MS, defined as a relative equilibrium distribution coefficient, K RD, for BPA against phenol, was at least 5 times larger than that of PAC, showing high adsorption selectivity for BPA. The selective adsorption behavior of Ph-MS was discussed using the results of material characterizations including X-ray diffraction, N 2 adsorption/desorption measurements, and Fourier transform infrared spectroscopy, and the results of adsorption experiments.

Synthesis and characterization of hybrid MCM-41 materials for heavy metal adsorption

A small dithiocarbamate molecule, N-(2-Aminoethyl)dithiocarbamate, was synthesized, characterized and afterwards used to modify and activate the surfaces of MCM-41 materials. The structure and the surface charge properties of the starting and the novel organic–inorganic hybrid mesoporous materials were studied by means of powder X-ray diffraction, Fourier transform infrared spectroscopy, DTA/TG thermal analyses, surface area measurements and potentiometric acid–base titrations. The hybrid materials retained the regular hexagonal arrangement of cylindrical pores which is the characteristic of the MCM-41 solids, while a high content (2.57 mmol/g) of the organic molecules in the final products was achieved. Despite the high concentration of the dithiocarbamate molecules in the pores of the hybrid MCM-41 materials, final solids retained high specific surface areas (632 m 2/g) indicating a homogenous incorporation of the small organic molecules in the pores. A surface complexation model was developed to explain the results of the potentiometric titrations and to describe the surface charge and H-binding properties of the starting and final hybrid materials. These materials are promising heavy metal adsorbents due to the presence of the effective dithiocarbamate groups and the low pH value (3.2) of the point of zero charge.

Periodic Mesoporous Silicas and Organosilicas: An Overview Towards Catalysis

Micelle-templated mesoporous and organic–inorganic hybrid mesoporous materials are important in many fields of material research, especially for hosting catalysts in confined space. Among this class, the recent discovery of periodic mesoporous organosilicas (PMOs) represent an exciting new group of organic–inorganic nanocomposites targeted for a broad range of applications ranging from catalysis to microelectronics. Compared to the earlier generation of organic–inorganic hybrid mesoporous samples, obtained by the cocondensation reaction or by the grafting reaction, PMOs represent the right combination of organic and inorganic groups in the frame wall positions. This article reviews the current state of art in organic–inorganic hybrid mesoporous material research with special emphasis over periodic mesoporous organosilica materials having various redox centers (Ti, V, Cr) suitable for oxidation reactions as well as acidic sites (Al, –SO3H) for the organic transformation of bulky molecules.

Microwave-assisted synthesis of nioboorganosilicates and microwave-accelerated catalytic activity of thereof

A novel type of organic–inorganic hybrid mesoporous material, i.e., mesoporous silica with organic groups and niobium species as lattice fundamentals was prepared. This new material was synthesized by self-assembly of bridged silsesquioxane precursor containing ethane-bridging group that connects two silicon atoms to surpass an oxygen atom in the mesoporous framework. They had been synthesized by using nonionic template Pluronic P123 as a structure-directing agent under microwave irradiation. The properties of obtained materials were confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), adsorption measurements, DTG/TG, DR-UV–vis, Raman and FTIR spectroscopies. The Nb-PMOs were tested in the oxidation reaction of cyclohexene to epoxide in the liquid phase using hydrogen peroxide as an oxidant. The reaction took place under conventional thermal heating and for comparison in the presence of microwaves. The microwave-assisted cyclohexene oxidation over nioboorganosilicates was completed within 1 h in comparison to 36–40 h for conventional method with comparable conversion and slightly higher selectivity to cyclohexene epoxide.

One-Pot Synthesis of Organic–Inorganic Hybrid Mesoporous Materials for the Adsorption of Formaldehyde Vapor

One-pot synthesis method was applied to prepare the organic–inorganic hybrid mesoporous materials via the cocondensation reaction of tetraethoxysilane (TEOS) and three types of organoalkoxysilanes: 3-aminopropyltrimethoxysilane, n-(2-aminoethyl)-3-aminopropyltrimethoxysilane and 3-[2-(2-aminoethylamino)ethylamino] propyltrimethoxysilane. Pores of hybrid materials were generated by adding pore-forming agent, cetyltrimethylammonium bromide (CTAB), to the mixture during the synthesis step. Texture characteristics of the hybrid mesoporous materials were accessed by surface area and a pore-size analyzer. Fourier transform infrared (FTIR) was operated for identifying the pore surface functional groups. In addition, the hybrid mesoporous materials were applied to adsorb formaldehyde vapor. The experimental adsorption data of formaldehyde fitted well to both the Langmuir and Freundlich isotherm. Sample derived from n-(2-aminoethyl)-3-aminopropyltrimethoxysilane shows the highest adsorptive capacity.

Synthesis, characterization, and cadmium(II) uptake of iminodiacetic acid-modified mesoporous SBA-15

An organic–inorganic hybrid mesoporous material, iminodiacetic acid (IDA)-modified mesoporous SBA-15, was prepared by a two-step post-grafting method. By means of solid-state 13C CP-MAS NMR, thermogravimetic analysis (TGA), Fourier transform infrared (FT-IR), as well as X-ray photoelectron spectroscopy (XPS), the structural and physicochemical properties of the materials were characterized. The cadmium(II) uptake experiments show that the iminodiacetic acid-modified mesoporous SBA-15 (IDA-SBA-15) exhibits excellent ability to remove cadmium(II) from aqueous solutions. The cadmium(II) adsorption isotherm of iminodiacetic acid-modified mesoporous SBA-15 (IDA-SBA-15) is in good accordance with the Langmuir equation.

Acid strength variation due to spatial location of organosulfonic acid groups on mesoporous silica

Evaluation of acid strength was used to investigate the location of organosulfonic acid groups within mesoporous silica materials. Mesoporous silica functionalized with either propylsulfonic or arenesulfonic acid groups at different surface concentrations were synthesized via the co-condensation technique, and their resulting acid strength was determined in a methanol solution using potentiometric titration with the Gran Plot technique. A decrease in spatial distance between the sulfonic acid groups on the pore surface of the mesostructured materials was found to increase the acid strength of the resulting solid acid catalyst as result of acid site cooperativity. Comparison of these results with the catalytic performance of the organosulfonic acid-functionalized mesoporous silica materials in the methanol esterification of palmitic acid suggested that the reaction performance of these materials is not simply related to the effects induced by spatial location of the acidic sites on the acid solid catalyst. The results demonstrate the potential of intentionally designing the catalytic environments of the organic–inorganic hybrid mesoporous materials at the molecular level.

Organic–inorganic hybrid mesoporous silicas: functionalization, pore size, and morphology control

Topological design of mesoporous silica materials, pore architecture, pore size, and morphology are currently major issues in areas such as catalytic conversion of bulky molecules, adsorption, host-guest chemistry, etc. In this sense, we discuss the pore size-controlled mesostructure, framework functionalization, and morphology control of organic-inorganic hybrid mesoporous silicas by which we can improve the applicability of mesoporous materials. First, we explain that the sizes of hexagonal- and cubic-type pores in organic-inorganic hybrid mesoporous silicas are well controlled from 24.3 to 98.0 A by the direct micelle-control method using an organosilica precursor and surfactants with different alkyl chain lengths or triblock copolymers as templates and swelling agents incorporated in the formed micelles. Second, we describe that organic-inorganic hybrid mesoporous materials with various functional groups form various external morphologies such as rod, cauliflower, film, rope, spheroid, monolith, and fiber shapes. Third, we discuss that transition metals (Ti and Ru) and rare-earth ions (Eu(3+) and Tb(3+)) are used to modify organic-inorganic hybrid mesoporous silica materials. Such hybrid mesoporous silica materials are expected to be applied as excellent catalysts for organic reactions, photocatalysis, optical devices, etc.

Novel organic–inorganic hybrid mesoporous materials for boron adsorption

Amine groups and polyol groups were sequentially grafted on mesoporous SBA-15 and MCM-41 to synthesize novel organic–inorganic hybrid mesoporous materials as boron adsorbents by a two-step post-grafting method. By means of small-angle XRD, N 2 adsorption–desorption, solid-state NMR, Fourier transform infrared (FT-IR) and elemental analysis, the structure and physicochemical properties of the materials were characterized. The behaviors of the resulting adsorbents in adsorption of boron from solutions were investigated. The results show that the organic functional groups are successfully grafted on the SBA-15 and MCM-41, while the quantity and the distribution of the functional groups are varied due to the different pore properties of the materials. The boron adsorption isotherms of the adsorbents are in good accordance with the Langmuir equation. The polyol-functionalized SBA-15 was proved to be a promising adsorbent with the high adsorption capacity of boron up to 0.63 mmol/g as well as the high selectivity towards boron.

Synthesis, Characterization, and Boron Uptake of Organic–Inorganic Hybrid Mesoporous Materials

Abstract An organic–inorganic hybrid mesoporous material with polyol functional groups has been prepared by a two-step post-grafting method using mesoporous SBA-15 as the support, proven to be a promising adsorbent with the considerable uptake capacity, as well as the high selectivity towards boron.

Hybrid ethane–siloxane mesoporous materials with cubic symmetry

The structure of and synthesis conditions for an organic–inorganic hybrid mesoporous material, HMM-3, containing ethane fragments (–CH2CH2–) within the pore walls were studied. High resolution transmission electron microscope images and electron diffraction patterns obtained for different crystal axes of HMM-3 indicated that it was of the cubic Pm-3n space group, similar to mesoporous silica SBA-1. Scanning electron micrographs of HMM-3 in different directions confirmed that all of the produced HMM-3 particles had the crystal-like external morphology of a decaoctahedron (18-hedron) with six square {100} and 12 hexagon {110} planes with a cubic symmetry. The synthesis conditions for HMM-3 were optimized in a synthesis system comprising 1,2-bis(trimethoxysilyl)ethane (BTME), hexadecyltrimethylammonium chloride (C16TMA), sodium hydroxide (NaOH), and water (H2O). The highly ordered HMM-3 material was obtained at 95°C with the mixture ratio of BTME:C16TMA:NaOH:H2O=5.27:4.79:12:1773. The C16TMA/BTME ratio and C16TMA concentration affected the structural order of the produced mesophase. Only the cubic Pm-3n phase was formed even though the C16TMA/BTME ratio and the C16TMA concentration were varied with in wide ranges at 95°C.

Novel Mesoporous Materials with a Uniform Distribution of Organic Groups and Inorganic Oxide in Their Frameworks

Novel organic−inorganic hybrid mesoporous materials have been synthesized, in which organic and inorganic oxide moieties are distributed homogeneously at the molecular level in the framework, forming a covalently bonded network. They are highly ordered at the mesoscale, with two- and three-dimensional hexagonal symmetries and well-defined external morphologies. Nitrogen adsorption measurements show a uniform pore-size distribution with pore diameters of 31 and 27 A, and high surface areas of 750 and 1170 m2/g. The synthetic procedure to polymerize the organosilane monomer containing two trialkoxysilyl groups in the presence of surfactant can be applied to the synthesis of a variety of highly ordered organic−inorganic hybrid mesoporous materials.