Anionic Surfactant Templated Mesoporous Silica Research Articles

Acid-redox bifunctional Fe/Al-AMS catalyst: Simultaneously oriented introducing Fe2O3 in the channels and Al in the framework of AMS and its enhanced catalytic performance

For the silica-supported catalysts, the acid-free property and weak interaction between metal active centers and silica cause great limitations in their catalytic applications. In this work, a modified metal-assisted templating method was designed for simultaneously introducing different metal sites into two different locations to obtain a novel bifunctional catalyst, in which the acid sites are produced by incorporating Al species in the framework and the redox sites are brought by encapsulating Fe2O3 in the channels of anionic surfactant-templated mesoporous silica (AMS), respectively. The functionalized Fe-APTES micelles establish a critical effect between the surfactant head groups and silica species by counterion-mediated interaction, and the adjustable pH value makes the co-hydrolysis of Al species and silica resource. The results show that Fe2O3 are highly dispersed in the channels with a strong interaction, and the framework Al species produce large amount of weak Lewis acid sites. The reaction of phenol hydroxylation was proceeded under the condition of phenol/H2O2 = 1:2 (molar ratio), reaction temperature 30 °C, reaction time 4 h. For this reaction, the redox active sites and acid sites in Fe/Al-AMS catalysts are both effective. In specific, the well-dispersed Fe2O3 in the confined channels will provide more exposed active sites, and more importantly, by replacement of toxic mineral acids, a large amount of surface acid groups stimulates and adsorbs more hydroxyl radicals, leading to the improvement of catalytic activity, also for the selectivity of hydroquinone. Compared with the reference catalysts, by the synergic effect of the metal active centers and surface acid groups, 3Fe/Al-AMS catalyst displays the best catalytic performance (Conv. 46.6%, CAT Select. 49.9%, HQ Select. 33.3%) and stability in the phenol hydroxylation reaction. This oriented introduction pathway of multiple metals in different locations of silica reveals new vision in the development of multi-functional catalysts for other catalytic applications.

In situ incorporation of well-dispersed Cu–Fe oxides in the mesochannels of AMS and their utilization as catalysts towards the Fenton-like degradation of methylene blue

Multi-components active metal oxide-supported catalysts are highly promising in heterogeneous catalysis due to some special promoting effects. In this study, by the controllable amount of Cu, Cu–Fe decorated anionic surfactant-templated mesoporous silica (Cu x Fe/AMS) was directly prepared. The obtained catalysts were characterized by X-ray diffraction, N2 adsorption–desorption, inductively coupling plasma emission spectroscopy, scanning electron microscopy, transmission electron microscopy, UV–visible, hydrogen temperature-programmed reduction, and X-ray photoelectron spectroscopy techniques. The results revealed that bimetallic Cu–Fe oxides were directly formed and highly dispersed in the mesochannels during the calcinations and the introduction of Cu2+ and Fe2+ on the micelles has influence on the structure properties. As compared to the monometallic Fe-modified AMS, the presence of Cu promotes the effects between Fe species and silica wall, leading to the better dispersion of Fe in the mesochannels of AMS. Finally, a series of Cu–Fe-modified AMS were used as Fenton-like catalysts and exhibited good catalytic activity in the degradation of methylene blue (MB), which resulted from high dispersion of Fe species and synergetic effect between Cu and Fe active sites. 1.0 was the optimum molar ratio of Cu2+ to Fe2+ ions to achieve the best catalytic activity and stability.

A Facile Method for the Direct Introduction of FeOxin Mesoporous AMS Through A Templating Route (S−[MN]+I−) and Its Catalytic Application

A facile method has been developed to incorporate FeOx into the channels of anionic surfactant-templated mesoporous silica (AMS). This synthesized method was based on a novel templating route (S−[MN]+I−), in which Sar-Na (N-Lauroylsarcosine sodium) was employed as structure-directing agent (S−), Fe ion functionalized APATES (N-[3-(Trimethoxysilyl)propyl]ethylenediamine) as co-structure directing agent ([MN]+). The Fe ion functionalized APATES (Fe[APATES]+) could establish a critical interaction between the surfactant head group and silica species by counterion-mediated interaction during the synthesis process. The synthesized samples were characterized with XRD, N2 adsorption, XPS, FT-IR, UV-vis, H2-TPR, TEM. The results revealed that FeOx species could be highly dispersed onto the pore channel surface and have a strong interaction with the silica wall. Furthermore, this catalyst of FeOx-AMS exhibited high catalytic performances for the hydroxylation of phenol.

Facile synthesis of functionalized ionic surfactant templated mesoporous silica for incorporation of poorly water-soluble drug

The present paper reported amino group functionalized anionic surfactant templated mesoporous silica (Amino-AMS) for loading and release of poorly water-soluble drug indomethacin (IMC) and carboxyl group functionalized cationic surfactant templated mesoporous silica (Carboxyl-CMS) for loading and release of poorly water-soluble drug famotidine (FMT). Herein, Amino-AMS and Carboxyl-CMS were facilely synthesized using co-condensation method through two types of silane coupling agent. Amino-AMS was spherical nanoparticles, and Carboxyl-CMS was well-formed spherical nanosphere with a thin layer presented at the edge. Drug loading capacity was obviously enhanced when using Amino-AMS and Carboxyl-CMS as drug carriers due to the stronger hydrogen bonding force formed between surface modified carrier and drug. Amino-AMS and Carboxyl-CMS had the ability to transform crystalline state of loaded drug from crystalline phase to amorphous phase. Therefore, IMC loaded Amino-AMS presented obviously faster release than IMC because amorphous phase of IMC favored its dissolution. The application of asymmetric membrane capsule delayed FMT release significantly, and Carboxyl-CMS favored sustained release of FMT due to its long mesoporous channels and strong interaction formed between its carboxyl group and amino group of FMT.

Precursor Mediated Synthesis of Nanostructured Silicas: From Precursor-Surfactant Ion Pairs to Structured Materials.

The synthesis of nanostructured anionic-surfactant-templated mesoporous silica (AMS) recently appeared as a new strategy for the formation of nanostructured silica based materials. This method is based on the use of anionic surfactants together with a co-structure-directing agent (CSDA), mostly a silylated ammonium precursor. The presence of this CSDA is necessary in order to create ionic interactions between template and silica forming phases and to ensure sufficient affinity between the two phases. This synthetic strategy was for the first time applied in view of the synthesis of surface functionalized silica bearing ammonium groups and was then extended on the formation of materials functionalized with anionic carboxylate and bifunctional amine-carboxylate groups. In the field of silica hybrid materials, the “anionic templating” strategy has recently been applied for the synthesis of silica hybrid materials from cationic precursors. Starting from di- or oligosilylated imidazolium and ammonium precursors, only template directed hydrolysis-polycondensation reactions involving complementary anionic surfactants allowed accessing structured ionosilica hybrid materials. The mechanistic particularity of this approach resides in the formation of precursor-surfactant ion pairs in the hydrolysis-polycondensation mixture. This review gives a systematic overview over the various types of materials accessed from this cooperative ionic templating approach and highlights the high potential of this original strategy for the formation of nanostructured silica based materials which appears as a complementary strategy to conventional soft templating approaches.

ChemInform Abstract: Anionic Surfactant Templated Mesoporous Silicas (AMSs)

AbstractReview: tutorial review; 63 refs.

Anionic surfactant templated mesoporous silicas (AMSs)

This tutorial review highlights the research on anionic surfactant templated mesoporous silica (AMS), which employs a co-structure directing agent (CSDA) to establish the critical interaction between the surfactant head group and silica species. As the geometry of anionic surfactants can be readily tuned via the ionisation of the surfactant head group, AMS materials possess a variety of mesostructures and morphologies. Chiral mesoporous silica (CMS) and helical ribbons can be formed via the chiral packing of the surfactant. Due to the pairing effect between the CSDA and the surfactant, a regular array of the organic groups is formed based on the stoichiometry and geometric arrangement of the surfactant, which produces functionalised materials with a uniform distribution of their organic groups. Furthermore, a brief introduction to the applications and future requirements of AMS is also included. This review is addressed to researchers and students interested in diverse areas of chemistry, particularly inorganic, physical, supramolecular and materials chemistry (63 references).

Silver Ion Modified Anionic Surfactant Templated Mesoporous Silica Adsorption Materials for the Removal of Dimethyl Sulfide at Ambient Temperature

Silver ion modified mesoporous silica (Ag-AMS-2) was prepared by using N-lauroyl-L-glutamic acid as structure directing agents and applied to dimethly sulfide (DMS) removal at ambient temperatures. The silver ion interacted with the amino group through coordination bonds and then the silver ion were as the adsorptive sites of the DMS. These Ag-AMS-2 materials were characterized by X-ray diffraction (XRD), nitrogen adsorption desorption, high-resolution transmission electron microscopy (HRTEM), thermal analysis and inductively coupled plasma optical emission spectrometry (ICP-OES). The performance of these Ag-AMS-2 materials as DMS adsorbents was tested using a dynamic breakthrough test. And these samples showed high removal efficiency and high saturation adsorption capacity of DMS.

Surfactant-assisted controlled release of hydrophobic drugs using anionic surfactant templated mesoporous silica nanoparticles

A series of mesoporous silica nanoparticles (MSNs) were synthesized using the co-structure directing method. A non-cytotoxic anionic surfactant, undec-1-en-11-yltetra(ethylene glycol) phosphate monoester surfactant (PMES), was used as a structure directing agent (SDA) together with aminopropyltrimethoxysilane that functioned as a co-structure directing agent (CSDA). The morphology and mesoporous structure of these materials were tuned by changing the molar ratio of CSDA and SDA. These mesoporous nanomaterials containing PMES inside the pores showed excellent biocompatibility in vitro. The cellular internalization and endosome escape of PMES–MSNs in cervical cancer cells (HeLa) was demonstrated by flow cytometry and confocal microscopy, respectively. The PMES–MSNs were used as drug delivery carriers for resveratrol, a low water solubility drug, by taking advantage of the hydrophobic environment created by the PMES micelle inside the pores. This surfactant-assisted delivery strategy was tested under physiological conditions showing an increase of the drug loading compared to the material without surfactant and steady release of resveratrol. Finally, the therapeutic properties of resveratrol-loaded PMES–MSNs were evaluated in vitro using HeLa and Chinese hamster ovarian cells. We envision that this surfactant-assisted drug delivery method using MSNs as nanovehicles would lead to a new generation of carrier materials for intracellular delivery of a variety of hydrophobic therapeutic agents.

Synthesis of amino group functionalized monodispersed mesoporous silica nanospheres using anionic surfactant

A series of anionic surfactant templated mesoporous silica (AMS) monodispersed nanospheres were synthesized by anionic surfactant, co-structure-directing agent (CSDA) bearing amino group, and silica source in the presence of nonionic surfactant. The amino group functionalized well-ordered cubic Fd-3 m, bi-continuous cubic Ia-3 d and disordered structures with tunable pore size from 2.2 to 9.2 nm and the particle size from 30 to 320 nm, have been synthesized by changing the type of the surfactant, the concentration of the nonionic and anionic surfactant and the reaction temperature. Loadings of the amino groups were determined in the range of 2.7–3.4 mmol/g. It has been found that, the higher concentration of the nonionic and the anionic surfactant, the shorter chain length of the anionic surfactant and the higher reaction temperature favor the formation of mesoporous silica nanospheres with larger particle size. These functional AMS nanospheres may find potential use in catalysis, sensor devices and bio-applications, etc.

Effect of alcohol on morphology and mesostructure control of anionic-surfactant-templated mesoporous silica (AMS)

In the synthesis of anionic-surfactant-templated mesoporous silica (AMS), the effects of alcohols have been investigated for the first time. Without the addition of extra alcohols, spherical mesoporous silica with radially oriented mesopores could be obtained through the anionic surfactant templating route. By using alcohols with different carbon chain length such as ethanol, n-butanol, hexanol and 1-octanol as the additives, different morphologies and mesostructures of mesoporous silica were obtained. It was found that both the types and concentrations of alcohols in the synthesis solution could tune the morphologies and mesostructures of the AMS, giving rise to the formation of hexagonal mesoporous discs and particles with novel multi-layered inner structure. In general alcohol with appropriate carbon chain length such as n-butanol and hexanol could act as the co-surfactant in the synthesis of mesoporous silica templated by anionic surfactant.

Hydrothermal Phase Transformation of Bicontinuous Cubic Mesoporous Material AMS-6

The controlled synthesis of ordered anionic surfactant templated mesoporous silica with cubic Ia3 structure (AMS-6) is reported via prolonged periods of hydrothermal treatment (HT). The cubic Ia3 m ...

Anionic surfactant-templated mesoporous silica (AMS) nano-spheres with radially oriented mesopores

Mesoporous silica nano-spheres with pore size larger than 3 nm were synthesized using an anionic surfactant as the template. These nano-spheres possess centrosymmetric radial mesopores (emanating from the spherical center to the exterior surface) and form stable suspension. The spherical size and mesostructure can be finely tuned by changing the pH value of the synthetic system in the range of 8.8 to 6.4. In addition, when the pH value was decreased to 5.8, instead of spheres, anisotropic morphologies such as elliptical, peanutlike and trifurcate particles were obtained, exhibiting core/shell structure due to the different orientations of the mesopores in the core and the shell of the particles. It is proposed that the evolution of the morphologies and mesostructures of the products templated by anionic surfactants strongly depend on the pH value of the synthetic system.

Amino and quaternary ammonium group functionalized mesoporous silica: An efficient ion-exchange method to remove anionic surfactant from AMS

Amino and quaternary ammonium group functionalized mesoporous silicas have been obtained by extracting the surfactant from anionic surfactant templated mesoporous silica (AMS) synthesized on the basis of the electrostatic interactions between the anionic surfactant and co-structure-directing agents (CSDA) such as 3-aminopropyltrimethoxysilane (APS) and N-trimethoxylsilylpropyl- N,N,N-trimethyl ammonium chloride (TMAPS). Mineral acid (HCl) and base (ethanol amine (EA)) or salt (ammounium acetate (AAC)) extractants, proved efficient to remove anionic surfactant from AMS materials synthesized with TMAPS and APS, respectively. The extraction method of AMS materials reported here is facile and efficient based on an ion-exchange process between the extractant and the quarternized or protonated amino groups on the walls of the mesopores. After extraction, the materials possess ordered mesoporous structures with properties similar to those of calcined materials. The existence and loading amount of amino or quaternary ammonium groups on the surface of the mesopores has been characterized by solid state 13C NMR and CHN elemental analysis.

Microporous Silica Hollow Nanospheres Templated by Anionic Polypeptide

Anionic polypeptide, the poly(sodium L-glutamate), was applied to fabricate microporous silica hollow nanospheres templated by the secondary structures of the polypeptide as porogens. In the synthesis, 3-aminopropyltrimethoxysilane (APMS) and tetraethyl orthosilicate (TEOS) were used as the silica sources, and the coassembly followed the mechanism of the anionic surfactant-templated mesoporous silica (AMS) through a S –N +-I – pathway, where S indicates the anionic polypeptide, I indicates inorganic precursors (TEOS), and N indicates costructure-directing agent (APMS), which interacted with the negatively charged anionic polypeptide secondary structures electrostatically and cocondensed with silica source to form the silica framework. The product was subjected to characterizations of X-ray diffraction (XRD), infrared (IR) spectroscopy, thermogravimetric (TG) analysis, scanning electron microscopy (SEM), transmitted electron microscopy (TEM), and nitrogen adsorption-desorption measurement. It was found that the pH value of the synthesis solution was an important factor to the morphological control of the silica products. Besides the microporous hollow nanospheres, microporous submicron silica solid and hollow spheres were also obtained facilely by changing the synthesis parameters. Our study further implied that anionic polypeptides, which were able to control mineralization of calcium carbonate and calcium phosphate, could also induce silica condensation in the presence of proper silica precursors. It was also expected that functional calcium carbonate (phosphate)/silica-nanocomposite materials would be fabricated under the control of the anionic polypeptide.

Molecular design of the surfactant and the co-structure-directing agent (CSDA) toward rational synthesis of targeted anionic surfactant templated mesoporous silica

The formation of anionic surfactant templated mesoporous silica (AMS) is investigated from the perspective of the geometrical molecular design of the surfactant and the co-structure-directing agent (CSDA) toward the rational synthesis of the targeted mesostructure. Increasing the geometrical size of two types of head group of the anionic surfactant in the order (i) sulfonate, sulfate and phosphate, and (ii) carboxylate, N-acylalanate/N-acylglycinate and N-acylglutamate, resulted in the mesophase changing from a disordered or lamellar phase to two-dimensional (2D) hexagonal (p6mm) and three-dimensional (3D) cage-type (hexagonal and a modulated cubic phase) with increasing order of the organic/inorganic interface curvature. A change in the chain length of the surfactant also led to different surfactant packing and mesophase interfacial curvatures, and resulted in a change in mesophase from a modulated cage-type mesophase to cubic Fdm, cubic Pmn and a disordered cage-type mesophase. The geometrical change in the CSDA resulted in an increasing micellar curvature in the order: aminopropyl < N-methylaminopropyl < N,N-dimethylaminopropyl trimethoxysilane, which led to a change of mesophase from bicontinuous cubic Pnm to 2D-hexagonal p6mm. An increase in the CSDA/surfactant ratio in the synthesis gave rise to the mesophase change from a disordered cage-type mesophase to cubic Fmm or from lamellar to 2D-hexagonal p6mm, and elemental analysis results showed that the mesoporous silicas have an increased loading of organic moieties using the CSDA method.

Formation Mechanism of Anionic Surfactant-Templated Mesoporous Silica

The synthesis mechanism of anionic surfactant-templated mesoporous silica (AMS) is described. A family of highly ordered mesoporous silica structures have been synthesized via an approach based on ...

Amino-functionalized mesoporous silica synthesized by an anionic surfactant templating route

A “S−N+∼I− pathway” (S−: anionic surfactant, N+: cationic amino group and I: inorganic species) for the synthesis of mesoporous silica has been developed by using 3-aminopropyltriethoxysilane (APS) as a co-structure directing agent (CSDA), which can interact with the anionic head group in the surfactant (SDA). Thus synthesized mesoporous silica has been designated as AMS (Anionic-surfactant-templated Mesoporous Silica). Removal of the anionic surfactant by extraction led to the functionalized AMS containing amino groups on the silica surface. Amino-functionalized AMS using 3-aminopropyltriethoxysilane (APS) and lauric acid sodium salt (LAS) as CSDA and SDA, respectively, was synthesized with varying proportions of APS in the silica sources (x-APS-AMS, where x is the proportion of APS in the silica sources, x = 0.1–0.6). In 0.4-APS-AMS, the content of amino groups derived from APS estimated by CHN elemental analysis and the argentometric titration was 2.36 and 2.24 mmol g−1, respectively, suggesting that almost all the aminopropyl moieties were on the surfaces in contrast to the MCM-41 type materials synthesized with a cationic surfactant. Thus obtained amino-functionalized AMS via the anionic surfactant templating route shows a higher adsorption capacity for Co2+ cations than amino-functionalized MCM-41 prepared by the direct co-condensation method via a conventional cationic templating route. There was also a marked difference in the activity for the Knoevenagel reaction between amino-functionalized AMS and MCM-41, indicating a significant difference in the state of aminopropyl moieties exposed to the surfaces.