One‐Step Grafting of Al2O3 onto Acid‐Made Mesoporous Silica

We report a one‐step convenient chemical coating method of high alumina content onto mesoporous silicas. Aluminia‐coated mesoporous silica with high surface area (?900 m²/g), tuneable pore size (2.0–3.0 nm) and high hydrothermal stability (> 60 h) is obtained. The method may also be generalized for grafting other metal oxides onto mesoporous silica in future work.     

Preparation and application of nanocatalysts via surface functionalization of mesoporous materials

Surface immobilization of active species onto mesoporous materials is gaining importance, especially in the design of functionalized mesoporous materials as a nanocatalyst through heterogenization of homogeneous catalytic systems. This article summarizes recent work on the synthesis, characterization and catalytic performance of the functionalized mesoporous catalysts performed by the present authors. A cationic rhenium(I) complex was encapsulated into mesoporous Al-MCM-41 molecular sieve using a ion-exchange method, yielding a new photocatalyst to be active for photocatalytic reduction of CO₂. Surface functionalization of mesoporous silica SBA-15 with sulfonic acid groups was investigated to give a solid acid catalyst. The chemically modified Fe-containing mesoporous materials, which are active for hydroxylation of phenol, were prepared by a surface-grafting method that iron salts are immobilized onto mesoporous Si-MCM-41 with the help of 3-aminopropyltrimethoxysilane as a linker. A cobalt(III) complex was heterogenized onto mesoporous silica SBA-15 containing carboxylic groups in order to utilize as a solid catalyst for the liquid-phase oxidation of aromatic hydrocarbons.     

Surface modification of polymeric microspheres using glycopolymers for biorecognition

We report the synthesis and characterization of sugar-containing microspheres consisting of poly(divinylbenzene) (PDVB) cores onto which chains of galactose- or mannose-bearing polymers have been grafted. PDVB particles prepared by distillation polymerization with a diameter of 2.4 μm containing residual surface vinyl groups were used as starting material. “Grafting from”, “grafting through” and “grafting to” techniques were performed and special interest was laid towards the resulting grafting densities. The surface modification via “grafting from” was conducted by reversible addition fragmentation chain transfer (RAFT) polymerization directly from the surface, whereas thiol-ene chemistry was used to affix glycopolymer chains onto the particle surface. The resulting sugar-covered microspheres were analyzed towards their protein recognition activity with a series of lectins.     

Grafting of vanadyl acetylacetonate onto organo-hexagonal mesoporous silica and catalytic activity in the allylic epoxidation of geraniol

Vanadyl(IV) acetylacetonate ([VO(acac)₂]) was grafted onto a hexagonal mesoporous silica (HMS) using three different methodologies: method A – direct complex immobilisation; method B – functionalisation of the HMS with 3-aminopropyltriethoxysilane (APTES) followed by the complex immobilisation; and method C – treatment of the APTES functionalised support prepared by method B with trimethylethoxysilane (TMS) to deactivate eventually unreacted surface silanol groups, followed by complex grafting.     

Comparative study of analytical methods for the determination of chromium in groundwater samples containing iron

Determination of chromium in groundwater samples containing iron may pose analytical problems due to sorption and fixation of chromium species onto Fe(III) hydroxides. Parks et al. (Water Res. 2004, 38, 2827) hypothesized that chromium species trapped inside Fe(III) hydroxides i.e. “fixed chromium” may not be soluble by HNO₃ digestion (APHA method 3030 B). In such cases, hydroxylamine digestion is required to release “fixed chromium”. To verify the hypothesis, we carried out this study on groundwater samples containing chromium and iron, using different methods of APHA and EPA. The results showed the presence of “fixed chromium”, ranged between 0.1 and 19.2 μg L^{− 1}, contributing 0.2 to 14.1% towards true total chromium. Digestion of samples with HNO₃ released Cr(III) bound to organic complexes, but not the “fixed chromium”. The hydroxylamine digestion released “fixed chromium”, but not the Cr(III) bound to organic complexes. Microwave digestion of samples with HNO₃ + HCl was effective for the release of both “fixed” and “Cr(III)-organic complexes”. Cr(III) was only adsorbed onto suspended matter, whereas Cr(VI), and Cr(III)-organic complexes were not adsorbed onto suspended matter due to their solubility. Sample pH, buffering capacity, and matrix have a significant influence on the adsorption and fixation of chromium species onto Fe(III) hydroxides.     

A novel approach to graft acrylates onto commercial silicones for release film fabrications by two-step emulsion synthesis

In this study, a two-step emulsion polymerization method was specially designed so as to effectively graft acrylate monomers onto commercial silicones and improve the properties of release films. FT-IR, DSC and grafting ratio tests showed that the grafting reaction happened and a high grafting ratio can be achieved when the silicone content was more than 20%. According to SEM-EDX result, the “sea-island” structure on the surface of release films made by acrylate-modified silicone latexes was proven. The silicones formed the continuous “sea” structure and the grafted acrylate polymers formed the segregated “island” structure. The carbon and silicon distributions were not uniform through the cross-section of release films made by acrylate-modified silicone latexes. After acrylate modification, the surface tension of silicone release films increased from 19-21 mN/m (before acrylate modification) to 30 mN/m and the release force increased from 8.1 g/in. to 47 g/in. As a result, the properties of release films have been effectively improved by our novel method for advanced applications.     

Imidazolium‐functionalized SBA‐15 type silica: efficient organocatalysts for Henry and cycloaddition reactions

We report the synthesis of mesoporous SBA‐15 type silica bearing ionic imidazolium substructures. Surface functionalization was achieved via post‐synthesis grafting reactions using bis‐silylated imidazolium precursors onto a mesoporous SBA‐15 type silica support. The grafting reactions were monitored via solid‐state NMR spectroscopy, nitrogen sorption, transmission electron microscopy and thermogravimetry. Post‐synthesis grafting is the most convenient way to achieve highly stable functionalized solids displaying excellent accessibility of the immobilized functional groups combined with high chemical stability. The solids obtained via post‐synthesis grafting reactions appeared as highly efficient and reusable heterogeneous organocatalysts for Henry reactions and the cycloadditions of CO₂ to epichlorohydrin. Copyright © 2013 John Wiley & Sons, Ltd.     

Hierarchically macro/mesoporous silica monoliths constructed with interconnecting micrometer-sized unit rods

Under typical dilute reactant compositions (3 ~ 5 wt% of surfactant template concentration) and conventional hydrothermal conditions for mesoporous materials synthesis, successful preparation of hierarchically macro/mesoporous silica monoliths was reported in this paper. The resultant materials were characterized by a series of techniques including powder X-ray diffraction, N₂ adsorption–desorption, SEM, TEM/EDS, and Hg porosimetry. A new kind of stable and hierarchically porous pure silica monoliths was confirmed, which are featured with highly ordered mesoporous structures, rod-shaped unit particles, large specific surface area of 492 m²/g, continuous macropores of about 4.0 μm in size and high macropore volume of about 13.1 cm³/g. Moreover, using the resultant silica monoliths as hard templates, carbon monoliths have been successfully replicated, which inherit the structural characters of parent silica materials. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Organo-modified mesoporous silica for sorption of carbon dioxide

Abstract  

Organo-modified mesoporous silica SBA-15 has been studied for sorption of carbon dioxide (CO₂). The SBA-15 sample was functionalized with a branched chain polymer, polyethylenimine (PEI), of different molecular weights (1,300 and 2,000 g mol⁻¹). Surface modification was carried out by impregnation of silica by PEI or by grafting with (3-chloropropyl)triethoxysilane, followed by substitution of chlorine atoms by PEI ligands. The prepared modified mesoporous materials were characterized by nitrogen adsorption/desorption at 77 K, high-resolution transmission electron microscopy, small-angle X-ray scattering, and thermal methods. Sorption of CO₂ was studied by gravimetric method at 303 K. The total amount of sorbed CO₂ varied between 0.19–0.67 mmol/g for respective samples. Regeneration of the materials after adsorption was achieved by thermal treatment at 343 K.     

Poly(hexamethylene terephthalate)-layered silicate nanocomposites

Nanocomposites of poly(hexamethylene terephthalate) (PHT) and montmorillonite organo-modified with alkylammonium cations bearing two primary hydroxyl functions, i.e., Cloisite^® 30B (CL30B) were synthesized. Organoclay incorporation was performed either by dispersion in the PHT matrix via melt blending or by in situ ring-opening polymerization of hexamethylene terephthalate cyclic oligomers c(HT). An additional procedure combining the two methods, preparation of a highly enriched inorganic “PHT-CL30B” nanohybrid masterbatch by in situ ring-opening polymerization and blending of the masterbatch with additional PHT was explored. The obtained nanocomposites contain 3% (w/w) of inorganics and displayed a mixture of intercalated morphology and exfoliated nanolayers as evidenced by X-ray diffraction and transmission electron microscopy. The nanocomposite obtained by the masterbatch technique exhibited a higher degree of exfoliation and displayed slightly higher glass transition temperatures, better mechanical properties and higher flame resistance. The improved results achieved with the “masterbatch route” are a consequence of the reactions occurring between the nanocomposite constituents allowing for the grafting of PHT chains onto the organoclay surface.     

Highly selective in situ metal ion determination by hybrid electrochemical "adsorption-desorption" and colorimetric methods

A novel and facile hybrid analytical method coupling electrochemical “adsorption–desorption” and colorimetric analyses was developed to detect heavy metal ions in turbid water samples. The target metal ions were deposited onto an electrode inserted into the original sample, which was referred to as the “adsorption” process. After changing the medium, the concentrated target metal ions were dissolved in a new, clean buffer (blank buffer), which was referred to as the “desorption” process. The concentrations of the target metal ions were measured by colorimetric analyses after the addition of specific indicator amounts. We demonstrated the applicability of this method by detecting Cd²⁺, Pb²⁺ and Cu²⁺ with co-depositing Bi³⁺ on portable screen-printed electrodes (SPEs). A good correlation (correlation coefficient of R = 0.997) was observed between concentrations ranging from 1 to 200 μM and absorbance values. After the multiple “desorption” process, the even better detection limits as low as 10, 10 and 100 nM were achieved for Cd²⁺, Pb²⁺ and Cu²⁺, respectively. The practicality of this hybrid method was confirmed by the detection of Cd²⁺, Pb²⁺ and Cu²⁺ in wastewater samples, and these results were in agreement with inductively coupled plasma atomic emission spectroscopy (ICP-AES). Overall, this hybrid method provides a simple, selective and effective technique for environmental pollutant analyses.     

Conducting polyaniline‐coated nano silica by in situ chemical oxidative grafting polymerization

Polyaniline (PAni) grafted nano silica were synthesized successfully by in situ polymerization of aniline (An) using ammonium persulphate (APS) as oxidant by three procedures: Firstly, γ‐(2,3‐epoxypropoxy)propyltrimethoxysilane (EPTMS) reacted with nano silica. Secondly, the EPTMS modified nano silica reacted with An as an initiator site introduced onto the silica surface, and finally PAni grafted silica was obtained by in situ chemical oxidative An. The chemical grafting of PAni was confirmed by FTIR and UV–Vis. The percentages of grafting EPTMS and An onto nano silica were 24.5 wt% and 10.3 wt%, respectively, calculated from elemental analysis (EA), while the percentage of grafting PAni was 157.7 wt% as a mass ratio of the grafting PAni and charged nano silica, investigated by TGA. In addition, characteristic agglomerate morphology of PAni was observed in the composite by SEM. The electrical conductivity of the product was 2.6 × 10^?6 S cm^?1 and it manifested that the resulted product was a typical semiconductor. Copyright © 2007 John Wiley & Sons, Ltd.     

Facile synthesis of mesoporous silica sublayer with hierarchical pore structure on ceramic membrane using anionic polyelectrolyte

A facile method for introducing mesoporous silica sublayer onto the surface of a ceramic membrane for use in liquid-phase separation is described. To reduce the electrostatic repulsion between the mesoporous silica sol and the ceramic membrane in highly acidic conditions (pH < 2), thus facilitating the approach of hydrolyzed silica sol to the surface of the membrane, poly(sodium 4-styrenesulfonate) (Na+PSS-, denoted as PSS-) was used as an ionic linker. The use of PSS- led to a significant reduction in positive charge on the ceramic membrane, as confirmed by experimental titration data. Consistent with the titration results, the amount of mesoporous silica particles on the surface of the ceramic membrane was low, in the absence of PSS- treatment, whereas mesoporous silica sublayer with hierarchical pore structure was produced, when 1 wt % PSS- was used. The results show that mesoporous silica grows in the confined surface, eventually forming a multistacked surface architecture. The mesoporous silica sublayer contained uniform, ordered (P6 mm) mesopores of ca. 7.5 nm from mesoporous silica as well as macropores ( approximately mum) from interparticle voids, as evidenced by transmission electron microscopy and scanning electron microscopy analyses. The morphologies of the supported mesoporous silica could be manipulated, thus permitting the generation of uniform needlelike forms or uniform spheroid particles by varying the concentration of PSS-.     

Organic functionalization of the surface of silica with arylsilanes. A new method for synthesizing organic-inorganic hybrid materials

Organic functionalization of a silica surface has been realized by employing arylsilanes. Grafting reactions of aryl(3-chloropropyl)dimethylsilanes (aryl = p-anisyl, p-tolyl, phenyl) with silica were carried out in heptane at 80 °C for 24 h. The ²⁹Si and ¹³C CP/MAS spectra of the obtained silica materials clearly showed that the 3-chloropropyldimethylsilyl moieties were cleanly grafted onto silica via a siloxane (Si-O-Si) bond accompanied by the release of the aryl groups. The loading amounts on FSM-type mesoporous silica (TMPS-4) with aryl(3-chloropropyl)dimethylsilanes were comparable to those with 2-propenylsilane and the most commonly used methoxysilane.     

Mesoporous mixed metal oxides derived from P123-templated Mg-Al layered double hydroxides

We report the preparation of mesoporous mixed metal oxides (MMOs) through a soft template method. Different amounts of P123 were used as structure directing agent to synthesize P123-templated Mg-Al layered double hydroxides (LDHs). After calcination of as-synthesized LDHs at 500 °C, the ordered mesopores were obtained by removal of P123. The mesoporous Mg-Al MMOs fabricated by using 2 wt% P123 exhibited a high specific surface area of 108.1 m²/g, and wide distribution of pore size (2-18 nm). An investigation of the “memory effect” of the mesoporous MMOs revealed that they were successfully reconstructed to ibuprofen intercalated LDHs having different gallery heights, which indicated different intercalation capacities. Due to their mesoporosity these unique MMOs have particular potential as drug or catalyst carriers.     

Thermal stability of high surface area silicon carbide materials

The synthesis of mesoporous silicon carbide by chemical vapor infiltration of dimethyl dichlorosilane into mesoporous silica SBA-15 and subsequent dissolution of the silica matrix with HF was investigated. The influence of the synthesis parameters of the composite material (SiC/SBA-15) on the final product (mesoporous SiC) was determined. Depending on the preparation conditions, materials with specific surface areas from 410 to 830 m² g⁻¹ and pore sizes between 2 and 10 nm with high mesopore volume (0.31-0.96 cm³ g⁻¹) were prepared. Additionally, the thermal stability of mesoporous silicon carbide at 1573 K in an inert atmosphere (argon) was investigated, and compared to that of SBA-15 and ordered mesoporous carbon (CMK-1). Mesoporous SiC has a much higher thermal textural stability as compared to SBA-15, but a lower stability than ordered mesoporous carbon CMK-1.     

Mechanochemical synthesis and physical–chemical properties of carbon–fluorocarbon nanocomposition materials. A review

There are the described novel class of porous carbon–fluorocarbon nanocomposition materials “C–CF_1+x”, prepared via the mechanochemical activation (MA) in the heterogeneous mixed systems “nano-C–nano-CF_1+x”, having an atomic ratio C:F as 1.14–4.0. As nano-C it was used thermally expanded graphite TEG and mesoporous carbon material NUMS (free porosity 45–95% and specific area 25–400 m²/g). As nano-CF_1+x these were used a superstoichiometric fluorocarbons FS and FT (CF_1.18–1.25) having the coherent diffraction area (CDA) ∼20–25 Å, free porosity 60–70%, sum O + H₂O in mixtures ∼0.1–0.5 wt.%, and metals sum <0.01 wt.%.Prepared nanocomposites “C–CF_1+x” were studied by FTIR, Raman, XPS C1s, O1s, F1s, X-ray diffraction and by chemical C, H, F-analyses. It was shown, that decrease of weight in systems “C–CF_1+x” does not exceed 0.5 wt.% and stated two main features of the temporary dynamics in changes for all MA-products. These are monotonous changes in bulk properties, such as decrease of C-nanophase relative amounts, confirmed with XRD. Simultaneously, a decrease of sp³-C–F and sp³-CF₂-groups at 1200 and 1320 cm⁻¹ and an origination of sp³-C–F-groups at 1080–1120 cm⁻¹, typical for C₂F-like structures are observed. Decrease of specific surface is corresponding to decrease in CDA sizes and dencity for all MA-products.O-containing admixtures in starting materials have a key influence to interactions in nano-“C–CF_1+x” systems during MA-processing, despite to their low content. The main O-contained participant is H₂O and it is interaction with sp³-C–F–bonds is leading to primary hydrolytic substitution of F onto OH with the origin of surface sp³-C–OH-bonds and their subsequent transformations into edged sp²>CO or/and into ester bridges C–O–C among basal and edged nano-C and nano-fluorocarbon blocks. The presence of basal sp³-C–OH and edged sp²>CO (sp²>COOH)-groups is confirmed by FTIR and XPS C1s and O1s spectra for all MA-nanocomposites in “C–CF_1+x” systems. Changes in the surface properties of prepared MA-“C–CF_1+x” nanocomposites are corresponded to the origin of extrema in properties for MA-time 6–10 min, such as content of surface C-nanophases and surface F with the simultaneous appearance of extrema in the specific electro conductivities and capacitances. The nature of observed phenomena is explained by the origin of chemical carbon nanosized contacts on particle surface and it is possible to use for practical applications. The main difference among MA-“C–CF_1+x” nanocomposites is that the “FS–TEG” systems are dominated by sp²-C–sp³-C–F electroconductive bridges, whereas in “NUMS–FT” systems the character of conductivity is determined by contribution of ester bridges C–O–C.     

Stepwise phosphine sulfide formation and metal-bridging reaction of tetradentate and tridentate phosphine ligands on palladium(II)

Kinetic studies on the stepwise phosphine sulfide formation reaction of the five-coordinate trigonal-bipyramidal Pd(II) complexes with the tripodal tetradentate phosphine ligand, [PdCl(pp₃)]Cl and [Pd(4-Cltp)(pp₃)](BF₄) (pp₃ = tris[2-(diphenylphosphino)ethyl]phosphine; 4-Cltp = 4-chlorothiophenolate), were carried out, and it was revealed that the reactions proceeded via the intermediate with a pendant dissociated phosphino group. Formation of the intermediate was utilized for the bridging reaction onto Pt(II) to form the phosphine-bridged linear trinuclear and cyclic tetranuclear mixed-metal complexes. Difference in the steric conversion mechanism in the phosphine-bridging reaction between the linear tridentate phosphine (bis[2-(diphenylphosphino)ethyl]phenylphosphine) and pp₃ is also reported.     

Hierarchical dendritic gold microstructure-based aptasensor for ultrasensitive electrochemical detection of thrombin using functionalized mesoporous silica nanospheres as signal tags

A sensitive electrochemical approach for the detection of thrombin was designed by using densely packed hierarchical dendritic gold microstructures (HDGMs) with secondary and tertiary branches as matrices, and thionine-functionalized mesoporous silica nanospheres as signal tags. To prepare the signal tags, the positively charged thionine (as an indicator) was initially adsorbed onto the mesoporous silica nanoparticles (MSNs). Then [AuCl₄]⁻ ions were in situ reduced on the thionine-modified MSNs by ascorbic acid to construct nanogold-decorated MSNs (GMSNs). The formed GMSNs were employed as label of the aminated aptamers. The assay was carried out in PBS, pH 7.4 with a sandwich-type assay mode by using the assembled thionine in the GMSNs as indicators. Compared with the pure silica nanoparticles, mesoporous silica could provide a larger surface for the immobilization of biomolecules and improve the sensitivity of the aptasensor. Under optimal conditions, the electrochemical aptasensors exhibited a wide linear range from 0.001 to 600 ng mL⁻¹ (i.e. 0.03 pM to 0.018 μM thrombin) with a low detection limit (LOD) of 0.5 pg mL⁻¹ (≈15 fM) thrombin at 3σ. No obvious non-specific adsorption was observed during a series of analyses to detect target analyte. The precision, selectivity and stability of the aptasensors were acceptable. Importantly, the methodology was evaluated with thrombin spiked samples in blank fetal calf serum, and the recoveries were 94.2–112%, indicating an exciting potential for thrombin detection.     

Highly permeable mesoporous silica membranes synthesized by vapor infiltration of tetraethoxysilane into non-ionic alkyl poly(oxyethylene) surfactant films

Mesoporous silica membranes were prepared on porous alumina substrates by a vapor infiltration of tetraethoxysilane (TEOS) into a non-ionic poly(oxyethylene) (Brij56) surfactant film. Periodic mesostructured silica membranes were formed on both α- and γ-alumina substrates pre-treated with polystyrene. The polystyrene polymer plugged the pores of the alumina substrates and inhibited the deposition of silica in the alumina pores, resulting in the formation of a very thin silica membrane without a silica/alumina composite layer at the interface between mesoporous silica and the alumina substrates. The calcined mesoporous silica membrane showed very high nitrogen permeance (>10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹). The single gas permeation was governed by the Knudsen diffusion mechanism. The durability of the mesoporous silica membrane against moisture in air was improved by a silylation with trimethylethoxysiliane.