Mesostructured Silica Research Articles

Vertically Aligned and Ordered One-Dimensional Mesoscale Polyaniline.

The growth of vertically aligned and ordered polyaniline nanofilaments is controlled by potentiostatic polymerization through hexagonally packed and oriented mesoporous silica films. In such small pore template (2 nm in diameter), quasi-single PANI chains are likely to be produced. From chronoamperometric experiments and using films of various thicknesses (100-200 nm) it is possible to evidence the electropolymerization transients, wherein each stage of polymerization (induction period, growth, and overgrowth of polyaniline on mesoporous silica films) is clearly identified. The advantageous effect of mesostructured silica thin films as hard templates for the generation of isolated polyaniline nanofilaments is demonstrated from enhancement of the reversibility between the conductive and the nonconductive states of polyaniline and the higher electroactive surface areas displayed for all mesoporous silica/PANI composites. The possibility to control and tailor the growth of conducting polymer nanofilaments offers numerous opportunities for applications in various fields including energy, sensors and biosensors, photovoltaics, nanophotonics, or nanoelectronics.

Synthesis of Zirconium Modified Spherical Mesostructured Cellular Silica Foams and Its Hydrodesulfurization Performance for FCC Diesel

Zr modified spherical mesostructured cellular silica foams (MCFs) with different Zr contents were successfully synthesized via an incipient wetness impregnation method. The characterization results of FTIR, SEM, and SAXS indicated that zirconium was fabricated into the silicon framework; meanwhile, the parent sphere-like morphology and topological structure were retained. Additionally, BET results showed that the as-synthesized materials possessed ultralarge pore volume (1.56 cm3/g), large pore size (15.9 nm), and high surface area (467 m2/g) when the weight percentage of Zr in the support was 12.6%, demonstrating that MCFs would be an alternative support for hydrotreating catalyst. Furthermore, the corresponding supported NiMo/Zr-MCFs catalysts were well-characterized. It was found that zirconium as an electronic promoter not only facilitated the formation of NiMoO4 precursor but also enhanced the redox ability of the catalysts as well as brought Brønsted and Lewis acid sites into MCFs, which were conducive to the hydrodesulfurization (HDS) performance. Then the catalyst activities were evaluated by using FCC diesel as feedstock, in which NiMo/Zr-MCFs-6.9 catalyst (Si/Zr = 20) had the highest hydrodesulfurization (97.3%) and hydrodenitrogenation efficiencies (98.1%); correspondingly, the main reasons could be ascribed to its desirable textural property, suitable redox ability, appropriate dispersion degree of active metals, and moderate acid property.

Cyclodextrin-functionalized mesostructured silica nanoparticles for removal of polycyclic aromatic hydrocarbons.

Polycyclic aromatic hydrocarbons (PAHs) are the byproducts of the incomplete combustion of carbon-based fuels, and have high affinity towards DNA strands, ultimately exerting their carcinogenic effects. They are ubiquitousenvironmental contaminants,and can accumulate on tissues due to their lipophilic nature. In this article, we describe a novel concept for PAH removal from aqueous solutions using cyclodextrin-functionalized mesostructured silica nanoparticles (CDMSNs) and pristine mesostructured silica nanoparticles (MSNs). The adsorption applications of MSNs are greatly restricted due to the absence of surface functional groups on such particles. In this regard, cyclodextrins can serve as ideal functional molecules with their toroidal, cone-type structure, capable of inclusion-complex formation with many hydrophobic molecules, including genotoxic PAHs. The CDMSNs were synthesized by the surfactant-templated, NaOH-catalyzed condensation reactions of tetraethyl orthosilicate (TEOS) in the presence of two different types of cyclodextrin (i.e. hydroxypropyl-β-cyclodextrin (HP-β-CD) and native β-cyclodextrin (β-CD)). The physical incorporation of CD moieties was supported by XPS, FT-IR, NMR, TGA and solid-state 13C NMR. The CDMSNs were treated with aqueous solutions of five different PAHs (e.g. pyrene, anthracene, phenanthrene, fluorene and fluoranthene). The functionalization of MSNs with cyclodextrin moieties significantly boosted the sorption capacity (q) of the MSNs up to ∼2-fold, and the q ranged between 0.3 and 1.65mg per gram CDMSNs, of which the performance was comparable to that of the activated carbon.

Scalable Synthesis of Acidic Mesostructured Silica–Carbon Nanocomposite Catalysts by Rotary Evaporation

AbstractThe front cover artwork for Issue 1/2017 is a collaboration between the Centre for Surface Chemistry and Catalysis (KU Leuven, Belgium) and Guangzhou Institute of Energy Conversion (China). The image shows a novel practical and scalable synthesis method for ordered mesoporous silica‐carbon nanocomposites. See the Communication itself at https://doi.org/10.1002/cctc.201600939.

Cover Picture: Scalable Synthesis of Acidic Mesostructured Silica–Carbon Nanocomposite Catalysts by Rotary Evaporation (ChemCatChem 1/2017)

The Front Cover shows a practical and scalable soft templating synthesis procedure to prepare ordered mesoporous silica-carbon nanocomposites, in which the use of a rotavapor is essential to achieve a fast and reproducible synthesis.In their Communication, R. Zhong et al. demonstrate this convenient method, in which the synthesis sol comprises of green and cheap sucrose as carbon source, besides TEOS as silica source and F127 as the soft template. The porous composites are easily decorated with sulphonic acid groups, and these acid forms show promising applications as acid catalyst for the transformation of biomass-derived substrates to value-added chemicals. More information can be found in the Communication by R. Zhong et al. on page 65 in Issue 1, 2017 (DOI: 10.1002/cctc.201600939).

Pt nanoparticles immobilized in mesostructured silica: a non-leaching catalyst for 1-octene hydrosilylation.

A catalyst containing small (ca. 2.5 nm) and crystalline Pt nanoparticles embedded into the walls of a mesostructured silica framework was found to be highly active in alkene hydrosilylation reaching TONs of ca. 105. More importantly, no Pt leaching was detected. This result is remarkable because Pt leaching is a recurrent problem in alkene hydrosilylation, which often prevents heterogeneous catalysts from being used industrially. This result is in contrast to the significant Pt leaching observed for other Pt/SiO2 catalysts.

Confined crystallization of a HKUST-1 metal–organic framework within mesostructured silica with enhanced structural resistance towards water

A HKUST-1 metal–organic framework was crystallized in the NH2-modified mesostructured silica FDU-12 in order to improve its structural stability upon water exposure.

Preparation and characterization of mesostructured cellular foam silica supported Cu–Ce mixed oxide catalysts for CO oxidation

A series of mesostructured cellular foam (MCF) silica supported CuO–CeO2 catalysts with various total metal loadings (10–40 wt%) and various Cu/Ce ratios (Cu/Ce = 1/9, 2/8, and 3/7 wt/wt) were prepared and tested for CO oxidation.

Fouling and biofouling resistance of metal-doped mesostructured silica/polyethersulfone ultrafiltration membranes

Hybrid polyethersulfone-based ultrafiltration membranes were prepared by incorporating metal (Ag and Cu) and/or amine-functionalized mesostructured SBA-15 silica particles. The doping particles were included into the casting solution to obtain a total solids load of 3.6wt% in the final membranes. The physicochemical characterization of particles and membranes showed a good dispersion of metals inside the mesoporous structure of silica as well as a reduced skin layer, higher pore interconnectivity, and a larger amount of pores in membranes doped with the hydrophilic fillers. Membrane surface was also slightly less hydrophobic in hybrid membranes. Membrane performance was significantly improved as result of considerable increase of water permeation without affect negatively the membrane selectivity. The organic antifouling properties were enhanced with significant permeability improvement without compromising membrane rejection performance. In addition to it, metal-loaded silica allowed preparing membranes with high antibacterial activity. The removal of colonies of Escherichia coli and Staphylococcus aureus was complete either on membrane surface or in the liquid in contact with membranes when exposed to a 1/500 nutrient broth medium for 20h at 36°C. The rate of metal release depended on metal speciation and represented a 0.1–0.6% of the total metal content of membranes.

Fast, Efficient and Environmentally Friendly Extraction of Cu(II) and Zn(II) by Hybrid Silicas Impregnated with Acidic Organic Extractants

The extraction of copper and zinc by mesostructured silicas impregnated with organic acidic chelators, an acylisoxazolone 3-phenyl-4-benzoyl-5-isoxazolone (HPBI), an acylpyrazolone 1-phenyl-3-methyl-4-stearoyl-5-pyrazolone (HPMSP) and an organophosphoric acid di-(2-ethylhexyl)-phosphoric acid (DEHPA) was performed in a sulfate medium. Various factors such as the pH of the aqueous phase, the chelators’ concentration in the silica matrix, the extraction equilibrium time and the extraction capacity of the two cations on silica were studied. The cations were extracted at very acidic pH with very high extraction rates. The stripping of cations was achieved at pH’s that were more acidic than those utilized for the extraction by maintaining the structure intact. Finally, their separation was successfully conducted in the cases of the three chelators.

Sequential Vapor Infiltration Treatment Enhances the Ionic Current Rectification Performance of Composite Membranes Based on Mesoporous Silica Confined in Anodic Alumina.

Ionic current rectification of nanofluidic diode membranes has been studied widely in recent years because it is analogous to the functionality of biological ion channels in principle. We report a new method to fabricate ionic current rectification membranes based on mesoporous silica confined in anodic aluminum oxide (AAO) membranes. Two types of mesostructured silica nanocomposites, hexagonal structure and nanoparticle stacked structure, were used to asymmetrically fill nanochannels of AAO membranes by a vapor-phase synthesis (VPS) method with aspiration approach and were further modified via sequence vapor infiltration (SVI) treatment. The ionic current measurements indicated that SVI treatment can modulate the asymmetric ionic transport in prepared membranes, which exhibited clear ionic current rectification phenomenon under optimal conditions. The ionic current rectifying behavior is derived from the asymmetry of surface conformations, silica species components, and hydrophobic wettability, which are created by the asymmetrical filling type, silica depositions on the heterogeneous membranes, and the condensation of silanol groups. This article provides a considerable strategy to fabricate composite membranes with obvious ionic current rectification performance via the cooperation of the VPS method and SVI treatment and opens up the potential of mesoporous silica confined in AAO membranes to mimic fluid transport in biological processes.

Strategies for introducing titania onto mesostructured silica nanoparticles targeting enhanced photocatalytic activity of visible-light-responsive Ti-MSN catalysts

Titanium-mesostructured silica nanoparticles (Ti-MSN) catalysts which are excellent photocatalytic materials for the environment were prepared by supporting mesostructured silica nanoparticles (MSNs) with titanium species synthesized by three different approaches: microwave and in situ and ex situ electrochemical methods, denoted as Ti-MSN-M, Ti-MSN-I, and Ti-MSN-E, respectively. The physicochemical properties of the catalysts were investigated via XRD, 29Si NMR, N2 adsorption-desorption, FTIR, ESR, and UV-DRS analyses. Characterization results revealed that the introduction of mesoporous titania nanoparticles (MTNs) prepared by the microwave method onto MSNs (Ti-MSN-M) did not significantly affect the silica framework. However, the silica network in the Ti-MSN-I and Ti-MSN-E was rather disrupted, particularly for the former catalyst, due to the desilication accompanied by isomorphous substitution of Ti in the MSN framework to form SiOTi bonds. Ti was also found to be exchanged with the terminal hydroxyl groups of all catalysts to form the SiOTi bonds. The addition of Ti species onto MSNs also increased the number of oxygen vacancies (Vo) and metal defect sites. Photocatalytic testing on the decolorization of Congo red (CR) resulted in the following order: Ti-MSN-I (94%) > Ti-MSN-M (90%) > Ti-MSN-E (34%). The Vo and metal defect sites were responsible in lowering the band gap of catalysts and decreasing the electron–hole recombination, while the great numbers of SiOTi bonds as well as large surface area and pore volume increased the active sites and offered a good surface contact with light to enhance the activity of catalysts. A kinetic study demonstrated that the photodegradation followed the pseudo-first-order Langmuir-Hinshelwood model. Ti-MSN-I and Ti-MSN-M maintained their activities for up to five runs without serious catalyst deactivation, indicating their potential for the degradation of dye in wastewater. Mineralization measurements of CR by TOC and BOD5 analyses after 3 h of contact time were 85.7% and 87.6% using Ti-MSN-M, while 83.7% and 80.3% using Ti-MSN-I, respectively. Optimization by response surface methodology showed that the catalyst dosage, pH, and TiO2 loading were the significant factors in the decolorization of CR. This study demonstrated that these two green technologies; electrochemical and MW have a great potential to be used in synthesis of various advanced materials for greener and more sustainable processes.

Effect of Hg on CO2 capture by solid sorbents in the presence of acid gases

Carbon dioxide Capture and Storage (CCS) is the main technology to mitigate CO2 emissions in the energy sector, being reversibly adsorption of CO2 on solid sorbents one of the most promising processes to be operated in post-combustion technology. Given the current state of development a number of problems still need to be addressed before solid sorbents can be employed for CO2 capture. One of these problems is the effect that some impurities in the flue gas have on the behavior of the sorbents. The aim of this work is to identify and evaluate the role of mercury species in flue gas containing acid gases on the performance of sorbents employed for CO2 capture. The influence of mercury on CO2 retention capacity was assessed using three commercial activated carbons (NORIT GCN, AIRPEL 1DS-1 and AIRPEL ULTRA DS5) and two mesostructured silica sorbents containing amino groups (SBA-PEI and SBA-TEPA). When Hg0 was incorporated into the gas stream, the behavior of the sorbents was modified. In general, the CO2 adsorption capacity decreased in the presence of Hg0 suggesting competition by both compounds for the same active sites. The strongest effect of Hg0 on CO2 adsorption was observed in the activated carbon with the highest micropore volume.

Effect of Amine Structure on CO2 Adsorption of Modified Poly(ethyleneimine)-Impregnated Mesostructured Silica Sorbents

Abstract Poly(ethyleneimine) (PEI) was modified to study the effect of amine type and introduced hydroxy groups on its ability to capture carbon dioxide. Amines were impregnated in as-synthesized mesostructured silica (MSU-F) to fabricate solid amines, and the resulting samples were characterized via 13C nuclear magnetic resonance spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy. Nitrogen contents, structural properties, adsorption capacity, and sorbent durability during CO2 adsorption/desorption processes were measured to study the CO2 sorption performances of the sorbents. Reaction between PEI and propylene oxide (PO) altered the ratio of primary, secondary, and tertiary amines and also produced hydroxy groups on amine molecules. With a specific reactant ratio, a modified amine-impregnated sorbent (M-EP10) showed a CO2 adsorption capacity and amine efficiency of 13.90 wt % and 0.37, respectively, which were higher than that of the pristine PEI-impregnated sorbent. The new adsorbents also showed excellent stability in cyclic adsorption–desorption operations, even under pure CO2 desorption conditions in which commercial PEI adsorbents are known to lose CO2 adsorption capacity owing to urea formation.

Scalable Synthesis of Acidic Mesostructured Silica–Carbon Nanocomposite Catalysts by Rotary Evaporation

AbstractA practical and scalable synthesis for the mass production of well‐ordered mesoporous silica–carbon composites by using a fast rotary‐evaporation‐induced self‐assembly method in the absence of any additional support is presented.

Dehydration of sorbitol to isosorbide in melted phase with propyl-sulfonic functionalized SBA-15: Influence of catalyst hydrophobization

Propyl sulfonic acid functionalized mesostructured SBA-15 silicas have been used to promote the dehydration of sorbitol to isosorbide, in melted phase, under atmospheric pressure. These materials were prepared with different acid capacities and modified with different types of methylsilane functionalities, looking for an enhancement of the catalytic activity of these solid acids in the studied reaction. These two strategies seemed not only to condition the way in which reactants interact with the surface and the catalytic acid sites, i.e. through variations in the hydrophilic/hydrophobic balance, but a change in the acid strength of the catalytic sites is also influenced. Results indicate that increasing the acid loading slowed down the first reaction stage (sorbitol to sorbitan) but boosted the second one (sorbitan to isosorbide), because the interaction of the same sorbitol molecule with more than one acid site difficult its conversion, but increase acid strength, favoring the second dehydration step. Similarly, the organic modification of the solid acid SBA-15-based materials with hydrophobic methylsilane functionalities moieties reduced the affinity of the sorbitol substrate for the catalyst surface, but it also enhanced acid strength as well as the accesibility of sulfonic acids, slowing down the first step, but enhancing the second one. Despite of the influence of both assayed strategies on the catalytic performance of the tested materials is opposite in both dehydration steps, the positive influence of the same on the second reaction stage was proved to be dominant, because of being the limiting step on the conversion of sorbitol to isosorbide. In this way, using highly acid loaded sulfonic acid functionalized SBA-15 modified with surface grafted methylsilanes can be considered the right combination to maximize isosorbide production using these catalysts.

Investigation of a novel fluorinated surfactant-based system for the design of spherical wormhole-like mesoporous silica

In contrast to hydrogenated based systems that led to many studies, fluorinated surfactants have been little reported. Thanks to their high chemical and thermal stability, these compounds are considered as suitable candidates for the synthesis of porous materials with an enhanced hydrothermal stability. This study reports the synthesis of a new fluorinated surfactant, 2-trifluoromethyl-7,7,8,8,9,9,10,10,11,11,12,12,12-tridecafluoro-4-thia-1-dodecanoic acid (FSC) obtained from the thiol-ene radical addition of 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octanethiol onto 2-trifluoromethyl acrylic acid in 85% yield. In the aim of achieving micelles in water to design mesoporous materials according to the cooperative templating mechanism, FSC was modified with water-soluble telechelic diamine (Jeffamine) ED-600. The modified surfactant was deeply characterized by spectroscopic methods and the FSC-Jeffamine ED-600 micellar system was used as porogen to prepare mesoporous materials via the cooperative templating mechanism. Spherical wormhole-like mesostructured silica materials of high specific surface area (850m2/g) and homogeneous pore size distribution (ca. 3.4nm) were obtained by conveniently adjusting the porogen/silica molar ratio and the hydrothermal conditions.

Mesoporous silica templated by polyion complex micelles: A versatile approach for controlling the mesostructure

The possibility to structure silica materials using polyion complex (PIC) micelles of poly-L-lysine (PLL) and poly(ethylene oxide)-b-poly(acrylic acid) (PEO-b-PAA) as novel structure directing agents was evidenced. More importantly the potential of such polyion complexes to act as versatile systems allowing an easy control of the silica mesostructure was revealed, thus providing materials with adjustable physico-chemical properties. Different mesostructures (lamellar, wormlike) and morphologies (bulk, nanoparticles) were obtained by simply varying the initial composition of the reaction medium, namely the ratio between the two polymers, the amount of silica relative to the polymers and the overall mass concentration, which in turn governed the chemical composition of the obtained hybrid organic/inorganic materials. All the processing parameters-induced mesostructural variations were rationalized with respect to the chemical compositions of the resulting hybrid materials, which were discussed based on competing chemical equilibria between species responsible for the mesostructuring; the results were interpreted in terms of interfacial curvature changes.

Interlayer-free hybrid carbon-silica membranes for processing brackish to brine salt solutions by pervaporation

Mesoporous, interlayer-free, hybrid carbon-silica matrices and membranes based on tetraethoxysilane (TEOS), organosilica of triethoxyvinylsilane (TEVS) and pluronic triblock copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (P123) were successfully prepared using an acid-base catalysed sol-gel method for desalination applications. These membranes were carbonized to form the hybrid carbon-silica structures under inert conditions in vacuum and nitrogen. The effects of calcination conditions on the structure-property relationship of the carbon-silica xerogels were elucidated, and the membrane performances were systematically studied using brackish (1wt%) to brine (15wt%) feed concentrations of sodium chloride solution and feed temperatures (25–60°C) under pervaporation process. Vacuum calcined (CS-Vc) membrane produced a slightly more mesoporous matrix and higher carbon yield than the nitrogen calcined (CS-N2) membrane, and hence, led to comparatively superior desalination performance. CS-Vc membranes produced high water fluxes of 26.5 (1wt%, 60°C) and 9.2 (15wt%, 60°C) Lm−2h−1 with salt rejections of 99.5% and 98.6%, respectively. This study demonstrates that the combined strategy of hybrid organosilica with polymeric template and vacuum calcination offered the carbonized silica mesostructure membranes with excellent separation of water from the hydrated salt ions, and importantly, high water fluxes particularly for processing brine salt solutions.

Preparation of meso-structured silica–calcium mixed oxide (MSCMO) catalyst for converting Vietnamese rubber seed oil to biodiesel

This report covered some new contributions in catalyst preparation and characterization. Meso-structured silica–calcium mixed oxide catalyst possessed both acidic and basic sites was synthesized through co-condensation method in alkaline environment using tetraethylorthosilicate, CaO, and cetyltrimethylammoniumbromide. The co-condensation process was established at 90 °C for 24 h obtaining white-gel precipitate which was dried at 120 °C followed by calcination at 550 °C for 5 h. The as-synthesized catalyst was used in conversion of rich free fatty acid rubber seed oil (22 %wt) in Vietnam to fatty acid methyl esters (FAMEs) in mild conditions such as temperature of 120 °C, time of 4 h, catalyst dosage of 3 %wt, methanol/oil mass ratio of 2.5/1 and agitating speed of 550 rpm achieving the reaction yield of 95.4 %. The catalyst were characterized by various techniques such as X-ray diffraction, transmission electron spectroscopy, Nitrogen Adsorption–Desorption Analysis (BET), temperature programmed desorption (NH3 and CO2-TPD). Especially, X-ray absorption spectroscopies was applied to explain the occurrence of acid and base sites on catalysts surface. The analysis showed the sixfold coordinated calcium sites characterizing for the mixed oxide structure of CaO–SiO2. The results helped to simulate the bonding structure around the Ca sites indicating the electrostatic charge differences along the Ca–O–Si connections and the ability for occurring the defect sites containing the O2− moieties corresponding to the acidity and basicity of the catalysts respectively. Gas chromatography–mass spectroscopy was also used to determine the composition of the FAMEs showing high purity of these products.