Surface-initiated catalytic ethylene polymerization within nano-channels of ordered mesoporous silicas for synthesis of hybrid silica composites containing covalently tethered polyethylene

A surface-initiated catalytic ethylene polymerization technique is successfully demonstrated herein for the covalent surface-grafting of polyethylene chains within nanochannels of mesoporous silicas to give hybrid mesoporous silica/polyethylene composite materials. In this technique, a Pd−diimine catalyst, [(ArNC(Me)-(Me)CNAr)Pd(Me)(NCMe)]⁺(Ar = 2,6-(iPr)₂C₆H₃) (1), was first covalently immobilized onto two ordered mesoporous silicas (SBA-15 and MSU-F) containing surface-bound acryloyl functionalities to render the mesoporous silica-supported chelate Pd−diimine catalysts (Pd-SBA15 and Pd-MSUF, respectively). Surface-initiated ethylene polymerizations within mesopores were subsequently carried out with Pd-SBA15 and Pd-MSUF at an ethylene pressure of 400 psi and 5 °C. A mechanistic study on the polymerization behavior and the confining effects of silica meso-structures on polymer growth has been undertaken. The covalent surface-grafting of polyethylene within silica nanochannels was confirmed by the results from Fourier-transformed infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), nitrogen adsorption-desorption, electron microscopy, and proton nuclear magnetic resonance (¹H NMR). The content of grafted polyethylene in the composites can be adjusted in a wide range by varying polymerization time. This represents the first report on the covalent surface functionalization of mesoporous silicas with polyethylene via surface-initiated ethylene polymerization.     

A biomimetic mesoporous silica–polymer composite scaffold for bone tissue engineering

A biomimetic organic–inorganic composite system comprising of microspheres fabricated from combination of a biodegradable polymer poly(lactide-co-glycolide) (PLGA) and bioactive mesoporous silica (SBA-15) has been developed through sintering technique for bone regeneration applications. The morphological and structural properties of the SBA-15/PLGA composite scaffold were evaluated using electron microscopy and fourier transform infrared spectroscopy and the results showed spherical morphology and composite nature. The presence of mesopores in the silica was confirmed through nitrogen adsorption–desorption isotherms. The surface area and pore size of mesoporous silica were found to be 792 m² g^?1 and 3.7 nm, respectively. The thermal characteristics of the SBA-15/PLGA composites studied using thermogravimetry analysis shows a weight loss of around 80% with the degradation occurring at 324?°C. The prepared scaffold is also found to support the adhesion and proliferation of osteoblast cells. The expression of specific bone markers is significantly enhanced in the SBA-15/PLGA composite scaffold when compared with the pristine polymeric scaffold indicating the positive effect of mesoporous silica. Hence, these SBA-15/PLGA composite scaffolds can be explored further for bone regeneration applications.     

Novel Two-Step Synthesis of Controlled Size and Shape Platinum Nanoparticles Encapsulated in Mesoporous Silica

Uniform shape and size platinum nanoparticles encapsulated in mesoporous silica (SBA-15) were prepared in the same solution by a novel two-step method. Platinum nanoparticles were prepared in aqueous solution of K₂PtCl₄, the reduction was carried out by bubbling hydrogen, the capping material was tri-block poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer. The mesoporous silica was synthesized using the same copolymer as template from tetraethyl orthosilicate by hydrolysis in acidic conditions. The Pt-nanoparticles-in-mesoporous-silica system was characterized by a combination of low-angle powder X-ray diffraction, transmission electron microscopy and N₂ porosimetry. The platinum nanoparticles are encapsulated in the mesopores and retained their size and morphology. It appears that this hybrid material should be a superior three-dimensional high-surface-area catalyst for selective platinum-catalyzed reactions.     

聚噻吩/SBA-15的合成与表征

以FeC l3为氧化剂,采用原位化学聚合的方法制备了聚噻吩/SBA-15新型复合材料,并对其结构和性能进行了表征。结果表明,小角X射线衍射和氮气吸附与脱附说明复合材料具有规则的介孔结构并且孔径明显小于分子筛SBA-15的孔径,红外光谱分析进一步证明PT进入了SBA-15的介孔孔道内,热重分析表明,聚噻吩进入孔道之后热稳定性得到了提高。     

Hierarchical mesoporous silica microspheres as unique hard-template for preparation of hierarchical mesoporous TiO2 microspheres with trimodal mesoporosities via nanocasting

This work for the first time reported that hierarchical meso-mesoporous SBA-15 silica microspheres (HMM-SiO₂-MSs) can serve as a unique and suitable hard-template for the nanocasting preparation of mesoporous TiO₂ with both hierarchical mesostructures and well-preserved microsphere particle morphology. A two-step impregnation (TSI) method was developed and customized and its effectiveness was studied in comparison with the single-step impregnation method. Trimodal mesoporosities and their origin are newly recognized and analyzed. The materials were examined by various techniques, including the FE-SEM, N₂ sorption, TEM and XRD. Under optimized conditions, the hierarchical mesostructures and spherical particle morphology of HMM-SiO₂-MSs can be replicated for HMM-TiO₂-MSs. The high surface area and pore volume of HMM-TiO₂-MSs reach 194 m² g^-1 and 0.68 cm³ g^-1, respectively, with the latter more than twice those templated by conventional SBA-15s. Besides HMM-TiO₂-MSs, such HMM-SiO₂-MSs as hard-template might be extended to the preparation of other materials with hierarchical mesostructures.     

Mesoporous silicas containing carboxylic acid: Preparation,thermal degradation,and catalytic performance

The calcination and thermal degradation behaviors of surfactants in mesoporous silicas SBA-15 and MCM-41 were investigated by FT-IR, ¹³C CP/MAS NMR, TG/DTA, and GPC. It was found that carboxylic acid-containing products were generated as active components in the mesopores of SBA-15 and MCM-41 from the triblock copolymer (PEO)₂₀(PPO)₇₀(PEO)₂₀ and cetyltrimethylammonium bromide (CTAB), respectively; the latter materials were used as templates. The carboxylic acid-containing mesoporous silica obtained showed a catalytic activity for hydrolysis of sucrose. The acidity was evaluated by means of NaOH titration. The acidity sensitively depended on both the calcination temperature and the atmosphere; the maximum appeared at 150 °C in air for SBA-15 where the highest activity was observed. However, the product in MCM-41 showed a lower catalytic activity than that in SBA-15. The SBA-15 product was easily leached from the mesopores of SBA-15 into the solution, but the degree of leaching for MCM-41 was considerably smaller than that for SBA-15.     

Effects of mesoporous SBA-15 contents on the properties of polystyrene composites via in-situ emulsion polymerization

Different loading of mesoporous molecular sieve SBA-15 was used to prepare polystyrene (PS)/SBA-15 composite materials via in-situ emulsion polymerization. The influence of SBA-15 silica on the styrene emulsion polymerization was studied regarding to the monomer conversion, particle size and particle size distribution, stability and viscosity of the resulting emulsion. The structure and properties of the composites were investigated by infrared spectroscopy (IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and gel permeation chromatography (GPC). In addition, the glass transition temperature (T_g), thermal mechanical property and thermal stability of the composite film were measured by differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), respectively. The results indicated that the composite emulsion showed high monomer conversion, thick viscosity, low coagulum, uniform particle size and broad size distribution. Molecular weight of the polymer decreased with the increase of mesoporous silica. SBA-15 silica was dispersed evenly in PS matrix at a loading of 5 %. The PS/SBA-15 composite material containing 10 % silica maintained a certain ordered structure. DMA results demonstrated that PS/SBA-15 composite exhibited greater storage modulus and high T_g compared to pure PS. The improved thermal stability and T_g of the composite were also confirmed by the TGA and DSC.     

High loading of short WS2 slabs inside SBA-15: promotion with nickel and performance in hydrodesulfurization and hydrogenation

Layered nanoslabs of a WS₂ phase with a well-defined hexagonal crystalline structure, average slab length of 3.6 nm, and stacking number of 3.2 were inserted into the nanotubular channels of SBA-15, an ordered pure silica material (surface area of 800 m²/g, uniform mesopore diameter of 6.5 nm) at loadings up to 60 wt.%. Sonication of a slurry containing SBA-15 in a W(CO)₆–sulfur–diphenylmethane solution yielded an amorphous WS₂ phase inside the mesopores. By sulfidation with 1.5% dimethyldisulfide in toluene under a hydrogen flow at 593 K and 5.4 MPa, the amorphous phase was transformed into hexagonal crystalline WS₂ nanoslabs (as shown by XRD, HRTEM, and selected area electron diffraction (SAED)). The WS₂ nanoslabs were distributed exclusively inside the mesopores in a uniform manner (HRTEM, quantitative microanalysis), without blocking the pores (N₂-sorption), and were oriented with their edge planes toward the support surface. This study constitutes the first report of such a combination of high loading of a well-defined crystalline catalytic phase into the nanotubular channels of mesoporous silica without blocking them. The first well-resolved HRTEM images of the well-defined crystalline catalytic phase (WS₂) inside the SBA-15 nanotubes are presented. A Ni component was introduced into the WS₂/SBA-15 composite by impregnation from an aqueous solution of nickel acetate. It increased the catalytic activity up to a Ni/W ratio of 0.4. In the hydrodesulfurization (HDS) of dibenzothiophene and the hydrogenation (HYD) of toluene, the activity of the optimized NiWS/SBA-15 catalyst was 1.4 and 7.3 times higher, respectively, than that of a sulfided commercial CoMo/Al₂O₃. This finding illustrates the excellent potential of high loading NiWS/SBA-15 catalysts for deep hydrotreatment of petroleum feedstocks.     

Direct synthesis of SILVER nanoparticles and polyaniline into the MESOPORES of SBA-15

The uniform structural pores architecture in nanoscopic domain of ordered mesoporous silicas, such as MCM-41 and SBA-15, can be used as a confined space to produce nanomaterials with controlled dimensions and cylindrical shape. In this study, we report the synthesis of a ternary nanocomposite constituted of silver nanoparticles and polyaniline concomitantly produced in the presence of SBA-15. The synthetic process involved firstly the adsorption of aniline vapor into the silica pores followed by its polymerization by reacting with the silver salt (AgN(SO₂CF₃)₂) solubilized in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (BMImTf₂N). With this synthetic approach the reaction proceeded quickly and efficiently, generating the silver-polyaniline nanocomposite mainly into pores and without collapsing the silica mesostructure. Surface area and pore volume of SBA-15 decreased after the reaction proceeded, indicating the formation of polyaniline and silver nanoparticles composite inside the pores and complementary analysis evidenced the presence of some silver nanoparticles outside pores. The measured electrical conductivity of the ternary composite in the order of 10^?6 S cm^?1 was coherent to the presence of the polymer and silver nanoparticles inside the pores of the insulator SBA-15 mesostructure rather than on the surface of the particles. The prepared SBA-15 ternary nanocomposite presented higher silver nanoparticles loadings of and superior surface area than the ones observed to small pore silicas, such MCM-41. The improvement in textural properties of the nanocomposite are favorable aspects for the further development of sensors and catalysts.

Open image in new window

Graphical abstract SBA-15 as a nanoreactor to produce AgNP-PANI nanocomposite, using an ionic liquid (BMImTf₂N) as solvent

     

Luminescent Organic–Inorganic Hybrids of Functionalized Mesoporous Silica SBA-15 by Thio-Salicylidene Schiff Base

Novel organic–inorganic mesoporous luminescent hybrid material N,N′-bis(salicylidene)-thiocarbohydrazide (BSTC-SBA-15) has been obtained by co-condensation of tetraethyl orthosilicate and the organosilane in the presence of Pluronic P123 surfactant as a template. N,N′-bis(salicylidene)-thiocarbohydrazide (BSTC) grafted to the coupling agent 3-(triethoxysilyl)-propyl isocyanate (TESPIC) was used as the precursor for the preparation of mesoporous materials. In addition, for comparison, SBA-15 doped with organic ligand BSTC was also synthesized, denoted as BSTC/SBA-15. This organic–inorganic hybrid material was well-characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy (HRTEM), and photoluminescence spectra, which reveals that they all have high surface area, uniformity in the mesostructure. The resulting materials (BSTC-SBA-15 and BSTC/SBA-15) exhibit regular uniform microstructures, and no phase separation happened for the organic and the inorganic compounds was covalently linked through Si–O bonds via a self-assemble process. Furthermore, the two materials have different luminescence range: BSTC/SBA-15 presents the strong dominant green luminescence, while BSTC-functionalized material BSTC-SBA-15 shows the dominant blue emission.     

Synthesis and characterization of Co-containing SBA-15 catalysts

Two Co-SBA-15 catalysts were synthesized and characterized by thermogravimetry, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, porosity, UV–visible diffuse reflectance and temperature programmed reduction with H₂. The first catalyst was prepared synthesizing SBA-15 and then adding Co ions by impregnation (Co_imprSBA-15). The second catalyst was prepared using a more complex procedure of immobilization of cobalt ions in the presence of pyridine and H₂O₂ on –COOH groups anchored to the SBA-15 structure [Co-SBA-15(COOH)]. These COOH groups were created starting from cyano groups introduced during the synthesis of the periodic mesoporous materials as 4-triethoxysilylbutyronitrile. Characterization of the samples indicates that in both cases the typical 2D periodical hexagonal structure of SBA-15 was obtained, but with less ordered packing in the second case. The cobalt is highly dispersed in the SBA-15 (up to 9% w/w) and is present mainly as Co²⁺ ions in highly distorted tetrahedral or square pyramidal coordination. Some coordinatively unsaturated Co(II) Lewis acid centers are present in Co_imprSBA-15, while in Co-SBA-15(COOH) coordination of pyridine to cobalt tentatively may induce the formation of Co³⁺ ions, although in both catalysts the dominant species are Co²⁺ ions in a very close environment.     

A comparative study of the preparation and physical properties of polystyrene–silica mesocomposite and nanocomposite materials

In this paper, a comparative study with regard to the preparation and physical properties of as‐prepared polystyrene–silica mesocomposite (PSM) and polystyrene‐silica nanocomposite (PSN) materials is presented. Vinyl‐modified mesoporous silica particles with a wormhole structure were first prepared by doping a sol‐gel metal oxide with an optically active non‐surfactant (dibenzoyl‐L ‐tartaric acid) as a template, followed by template removal through Soxhlet extraction. The as‐prepared silica particles with/without mesopores were subsequently characterized using the Brunauer–Emmett–Teller method and transmission electron microscopy (TEM) and Fourier transform infrared, ¹³C NMR and ²⁹Si NMR solid‐state spectroscopy. A specific feed amount of silica particles was subsequently reacted with styrene monomer by free radical polymerization to yield a series of PSM and corresponding PSN materials. Both as‐prepared composite systems were further characterized using TEM and scanning electron microscopy/energy‐dispersive X‐ray mapping studies. A systematic comparative study of the physical properties of both as‐prepared composite materials clearly illustrated that PSM had effectively enhanced thermal stability, optical clarity and dielectric properties compared to the corresponding PSN counterpart. Evaluation was carried out using thermogravimetric analysis, differential scanning calorimetry, UV‐visible transmission spectroscopy and dielectric constant measurements. Copyright © 2011 Society of Chemical Industry     

Novel composite polymer electrolyte comprising poly(ethylene oxide) and triblock copolymer/mesostructured silica hybrid used for lithium polymer battery

Ordered mesoporous materials, due to its potential applications in catalysis, separation technologies, and nano-science have attracted much attention in the past few years. In this work, a novel PEO-based composite polymer electrolyte by using organic-inorganic hybrid EO₂₀PO₇₀EO₂₀ @ mesoporous silica (P123 @ SBA-15) as the filler has been developed. The interactions between P123 @ SBA-15 hybrid and PEO chains are studied by X-ray diffraction (XRD), differential scanning calorimeter (DSC), and FT-IR techniques. The effects of P123 @ SBA-15 on the electrochemical properties of the PEO-based electrolyte, such as ionic conductivity, lithium ion transference number are studied by electrochemical ac impedance spectroscopy and steady-state current method. The experiment results show that P123 @ SBA-15 can enhance the ionic conductivity and increase the lithium ion transference number of PEO-based electrolyte, which are induced by the special topology structure of P123 in P123 @ SBA-15 hybrid, at the same time. The excellent lithium transport properties and broad electrochemical stability window suggesting that PEO-LiClO₄/P123 @ SBA-15 composite polymer electrolyte can be used as candidate electrolyte materials for lithium polymer batteries.     

Physicochemical properties of poly(ethylene oxide)-based composite polymer electrolytes with a silane-modified mesoporous silica SBA-15

Mesoporous silica SBA-15 was surface-modified by γ-glycidoxypropyltrimethoxy silane (GPTMS), and novel poly(ethylene oxide) (PEO)-based composite polymer electrolytes (CPE) using the silane-modified SBA-15 (SBA-15-GPTMS) as filler were prepared and characterized. The results of the low-angle X-ray diffraction (XRD) patterns and Fourier-transform infrared (FT-IR) spectroscopy indicated that GPTMS has been successfully attached to the surface of SBA-15 with a high degree of mesoscopic hexagonal pore structure. The incorporation of SBA-15-GPTMS in the PEO-LiClO₄ matrix effectively reduced the PEO crystallinity and obviously improved the conductivity and electrochemical stability of the CPEs. The CPE with 10 wt.% SBA-15-GPTMS provided the highest conductivity among all the tested CPEs, about 2-3 orders of magnitude higher than that of the PEO-LiClO₄ matrix below the melting temperature of PEO. The reasons that the CPEs using SBA-15-GPTMS as filler showed higher conductivity than that with SBA-15 were discussed.     

Catalytic Behavior of Alumina-Promoted Sulfated Zirconia Supported on Mesoporous Silica in Butane Isomerization

Alumina-promoted sulfated zirconia was supported on mesoporous molecular sieves of pure-silica MCM-41 and SBA-15. The catalysts were prepared by direct impregnation of metal sulfate onto the as-synthesized MCM-41 and SBA-15 materials, followed by solid state dispersion and thermal decomposition. Measurements of XRD and nitrogen adsorption isotherms showed that the structures of resultant materials retain well-ordered pores, even with ZrO₂ loading as high as 50 wt%. The characterization results indicated that most of the promoted sulfated zirconia were well dispersed on the internal surface of the ordered mesopores. The catalytic behavior of the alumina-promoted sulfated zirconia supported on mesoporous silica was studied in n-butane isomerization. The supports of mesoporous structures led to high dispersion of sulfated zirconia in the meta-stable tetragonal phase, which was the catalytic active phase. The high performance of alumina-promoted catalysts was ascribed to the sulfur retention by alumina.     

Synthesis and characterization of the SBA-15/carbon cryogel nanocomposites

The ordered mesoporous silica SBA-15 materials were synthesized using Pluronic P123 (non-ionic triblock copolymer, EO₂₀PO₇₀O₂₀), under acidic conditions. SBA-15/carbon cryogel composites were obtained by sol–gel polycondensation of resorcinol and formaldehyde followed by freeze drying, and subsequent pyrolysis, in the presence of different amounts of SBA-15. For comparison purpose, SBA-15/carbon composite was also prepared using sucrose as carbon source. These materials were characterized by room temperature nitrogen adsorption–desorption measurement, X-ray diffraction, scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. It was revealed that the samples have amorphous structure, high specific surface area (350–520 m² g^?1) and developed meso- as well as microporosity. The porosity of structure depends on the carbon source and Si/C ratio which can be easily controlled by varying concentration of starting solution.     

Acidichromic Spiropyran-Functionalized Mesoporous Silica: Towards Stimuli-Responsive Metal Ion Separations Media

Abstract

An acidichromic silyl spiropyran was synthesized and covalently immobilized on the surface of mesoporous silica (SBA-15) through either post-modification or a co-condensation route. The integration of the spiropyran into the porous silica was probed by thermogravimetric analysis, nitrogen adsorption/desorption studies and UV-Vis optical spectroscopy. While the co-condensation route provides the higher spiropyran loading levels, it also leads to two different states of attachment. Both synthetic procedures favor the formation of the open, merocyanine form of the spiropyran within the framework, but this form can be readily switched from a protonated to a deprotonated state by treatment with buffered aqueous solutions. Preliminary evaluation of the metal ion sorption capabilities of the spiro-functionalized SBA-15 for selected monovalent, divalent, and trivalent metal ions indicates that the spiropyran-modified materials show modestly improved cation exchange characteristics versus the unfunctionalized mesoporous framework.     

Ultrasonic assisted organo-modification of mesoporous SBA-15 with N-trimellitylimido-l-methionine and preparation of the poly(amide–imide)/SBA nanocomposites

Mesoporous SBA-15 materials were functionalized with N-trimellitylimido-l-methionine through ultrasonic irradiation, and the resulting functionalized materials were investigated as reinforcing agent for the preparation of the polymer based nanocomposites (NCs). An optically active and organo-soluble l-methionine containing poly(amide–imide) (PAI) was synthesized by the direct step-growth polymerization reaction of the above chiral diacid and 3,5-diamino-N-(pyridin-3-yl) benzamide in molten tetrabutylammonium bromide as a green solvent. A simple solution blending process was used to efficiently disperse modified-SBA into the chiral PAI to obtain PAI/modified-SBA NCs. The obtained NCs were characterized by Fourier transform-infrared spectroscopy, thermogravimetry analysis (TGA), X-ray diffraction, field emission-scanning electron microscopy, and transmission electron microscopy (TEM) techniques. TGA data indicated an increasing in thermal stability of the NCs when compared to the pure polymer. TEM images show well-ordered hexagonal arrays of mesopores SBA and the average distances between neighboring pores is around 3–5 nm.     

Catalytic aerobic oxidation of ethylbenzene over Co/SBA-15

Co(II)O was highly dispersed in the mesopores of SBA-15 by alcoholic impregnation method and characterized by XRD, TEM, UV–VIS DRS, TPR, and XRF techniques. It was found that tetrahedral coordinated Co(II)O was stabilized by SBA-15 at low Co-loading. Co/SBA-15 showed much higher activity than Co(OAc)₂ or Co₃O₄ in the liquid-phase aerobic oxidation of ethylbenzene under solvent-free condition.     

Nanocrystalline CeO2 in SBA-15: Performance of Pt/CeO2/SBA-15 Catalyst for Water-gas-shift Reaction

CeO₂ particles confined within the pores of an SBA-15 mesoporous silica host were prepared by incipient wetness impregnation (IMP) and deposition precipitation (DP) methods. The materials were characterized by XRD, N₂-adsorption and temperature programmed reduction (TPR) to evaluate the structure, texture, and redox properties. The preparation procedure had significant impact on the assembling mode of CeO₂ inside the SBA-15 mesopores. A high dispersion of CeO₂ particles was achieved via DP, whereas the dispersion of CeO₂ prepared by IMP was found to be inhomogeneous and CeO₂ partially blocked the pores. The CO conversion in the water-gas-shift reaction was enhanced over 1 wt% Pt supported on CeO₂-modified SBA-15 obtained by DP.