Swelling properties and bioactivity of silica gel/pHEMA nanocomposites

A novel hydrogel based on 2-hydroxyethyl- methacrilate and SiO₂ nanoparticles was prepared. The filler was added at a concentration of 30% w/w of silica nanoparticles to the mass of polymer. The composite material was characterised as far as concerns swelling behaviour in comparison to pHEMA. Swelling ratio of modified pHEMA was higher. Bioactivity of both SiO₂ nanoparticles and the modified hydrogel was evaluated by soaking samples into a simulated body fluid (SBF). FT-IR spectroscopy, scanning electron microscopy (SEM) and energy dispersive system (EDS) results suggest silica nanoparticles keep bioactive in the polymer. SiO₂ filler in a p(HEMA) matrix makes the composite bioactive. Therefore, these composites can be used to make bioactive scaffold for bone engineering.     

Characterization of di-phasic nanoscale composites derived from xerogels

Di-phasic xerogel-derived composites, such as SiO₂AgCl, SiO₂-AIPO₄, SiO₂-CePO₄, SiO₂ -Nd₂O₃, SiO₂-CdS, SiO₂CrPO₄, SiO₂-BaSO₄ and SiO₂-PbCrO₄ have been characterized in detail by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED) techniques. The SiO₂-AgCl photochromic composites with small amounts of AgCl did not show any crystallinity either by XRD or by SAED. Thin edges of these SiO₂-AgCl composites did not reveal discrete AgCl particles because these are too small to be resolved even by TEM and are expected to be in the range 1.5 to 2.5 nm in size based on the pore size of silica gel. A few large AgCI-Ag particles precipitated on the outside of silica gel were, however, detected by TEM-SAED in silica gels with higher concentrations of AgCl. The SiO₂-AIPO₄ and SiO₂-Nd₂O₃ composites are noncrystalline and did not show any periodic structure by TEM and SAED. Heat treatments to 400 or 600° C did not crystallize the AIPO₄ or Nd₂O₃ phases. On the other hand, SiO₂-CePO₄ and SiO₂-CdS composites showed lath-like particles of CePO₄ and irregular particles of presumably CdS on the surfaces of silica gels. The SiO₂-BaSO₄ and SiO₂-PbCrO₄ composites showed crystals of BaSO₄ and PbCrO₄ which are too large to be incorporated in the silica gel pores. These results show that the size and crystallinity of a second phase within silica gels can be controlled by the appropriate manipulation of the different parameters, and to do so is an important advantage for this new class of diphasic nanoscale composite xerogel materials.     

Influence of graphene oxide sheets on the pore structure and filtration performance of a novel graphene oxide/silica/polyacrylonitrile mixed matrix membrane

The novel graphene oxide (GO)/silica (SiO₂)/polyacrylonitrile (PAN) mixed matrix membranes (MMMs) with high filtration flux and excellent antifouling performance were designed and fabricated in situ by the method of non-solvent induced phase separation (NIPS) from the precursor of PAN hybridized with GO, tetraethoxysilane and 3-aminopropyltriethoxysilane. The influences of GO sheets on the pore and chemical structure, hydrophilic nature and filtration performance of derived GO/SiO₂/PAN MMMs were investigated by the scanning electron microscopy, field emission scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray, Fourier transform infrared spectrometer, pure water contact angles and filtration performance. Results indicated that in situ incorporation of GO sheets and SiO₂ molecules into PAN matrix via NIPS reconstructs the porous structure of derived GO/SiO₂/PAN MMMs with the upright finger-like holes, porous bottom, thinner top layer and high porosity. The spontaneous surface migration or segregation of hydrophilic GO sheets and SiO₂ molecules as well as their synergistic interaction occurred during NIPS greatly ameliorate the top surface structure and property of derived membranes with smoother surface, uniform pore structure and good hydrophilicity. The derived GO/SiO₂/PAN MMMs exhibit a high water filtration flux of 387 L m^?2 h^?1 with the bull serum albumin rejection rate up to 99% and significant enhancement of antifouling performance.     

Effect of surface modification of nanosilica on crystallization,thermal and mechanical properties of poly(vinylidene fluoride)

Composites were prepared by solution blending ploy(vinylidene fluoride) (PVDF) and nanosilica which modified by different organic modifiers. Infrared analysis showed that the crystalline structure of PVDF was changed by the addition of RNS-A (silica with amino terminated group), while similar crystalline structure as pure PVDF was observed for composites with DNS-0 and DNS-2, unmodified silica and alkyl terminated group silica, respectively. With differential scanning calorimeter (DSC) and dynamic mechanic thermal analysis (DMTA) techniques, crystalline structure, thermal, and mechanical properties of the composite films were examined. As the DSC results showed, addition of SiO₂ would lead to the increased cooling crystallization temperature (T _c), implying that SiO₂ nanoparticles could act as nucleating agents, however the degree of crystallinity of PVDF was not elevated significantly. In the complementary modulated DSC curves, multi-melting peaks associated with non-reversing portion were observed and were explained from the viewpoint of melting-recrystallization in the DSC heating scan. In addition, dynamic mechanical properties as well as the thermal stability of the composites are also influenced by SiO₂. As manifested by the corresponding DMTA and thermogravimetric analysis (TGA) results, a strong interaction should exist between PVDF and SiO₂ nanoparticles.     

Synthesis and characterization of TiO<Subscript>2</Subscript>-incorporated silica foams

Titania-incorporated silica (TiO₂–SiO₂) porous materials have great applications in diverse areas. In this work, TiO₂–SiO₂ porous materials with tunable Si/Ti molar ratio (R) have been successfully prepared through a one-pot method under a near-neutral condition. With decreasing Si/Ti R, a phase transition from a macroporous foam-like structure to mesostructure is observed. The resultant TiO₂–SiO₂ porous materials possess large surface areas and high pore volumes. In addition, the titania species are homogenously dispersed in silica matrix when Si/Ti R ≥ 10. Our contribution provides a convenient method to synthesize TiO₂/SiO₂ porous materials with very large pore size, high pore volume, and relatively high titania content well dispersed in the silica wall framework.     

Preparation,properties and thermal control applications of silica aerogel infiltrated with solid–liquid phase change materials

In this study, silica aerogel saturated with erythritol as phase change materials (PCMs) was prepared by melt infiltration. The properties of the composite were determined by scanning electronic microscope (SEM), Fourier transformation-infrared spectroscope (FT-IR) and differential scanning calorimeter (DSC). In the novel composite, erythritol with high latent heat of fusion was used as PCM for thermal control, whereas nanoporous silica aerogel was prepared as the phase change matrix to provide structural strength and prevent leakage of the melted erythritol. Nitrogen gas adsorption curves and SEM analysis indicate that the pore structure of silica aerogel was porous and connected with each other. FT-IR analysis showed that the composite formation of silica aerogel and erythritol were physical, whereas DSC analysis showed that the melting point and heat storage capacity of the composite were 123.8°C and 289.92?kJ/kg, respectively. The thermal protection properties of phase change composites were designed under laboratory conditions using a thermal measurement setup of a simulated thermal environment of an aircraft. The phase change composite produced by the study can be used for thermal protection applications. Compared with the paraffin–silica aerogel composite, the erythritol–silica aerogel composite could rapidly control the rising temperature by absorbing heat under high thermal environments.     

Fabrication and characterization of three dimensional woven carbon fiber/silica ceramic matrix composites

Carbon fiber reinforced fused silica composites exhibit the advantages of excellent mechanical properties, high heat resistance, low thermal expansion and low density, but low impact resistance or toughness. A novel modified slurry impregnation and hot pressing (SIHP) method was adopted to fabricate a new type of three dimensional orthogonal woven structure carbon fiber reinforced silica ceramic matrix composites (3D Cf/SiO₂ CMCs) with higher density and lower porosity. Physical characterization, flexural behavior, impact performance and toughening mechanism of the composites were investigated by three-point bending tests, impact tests, and scanning electron microscopy analysis. The 3D Cf/SiO₂ CMC showed a higher flexural strength in both warp (201.6%) and weft (263.6%) directions than those of pure SiO₂ and failed at a non-brittle mode due to the fiber debonding and pullout, and a delaminated failure of the 3D preform. The maximum impact energy absorption of the 3D Cf/SiO₂ CMC was 96.9 kJ/m², almost 4 times as much as those for typical other carbon fiber reinforced CMCs.     

Mechanical behaviour and microstructural characterization of 3D four‐directional braided SiO2f/SiO2 composites

In this paper, SiO_2f/SiO₂ composites reinforced by 3D four‐directional braided quartz preform were prepared by the silica sol‐infiltration‐sintering method in a relatively low sintering temperature (450 °C). To characterize the mechanical properties of the composites, mechanical testing was carried out under various loading conditions, including tensile, flexural and shear loading. The microstructure and the fracture behaviour of the 3D four‐directional braided SiO_2f/SiO₂ composites were studied. The tensile strength, flexural strength and the in‐plane shear strength were 30.8 MPa, 64.0 MPa and 22.0 MPa, respectively. The as‐fabricated composite exhibited highly nonlinear stress–strain behaviour under all the three types of loading. The tensile and flexural fracture mechanisms were fully discussed. The fracture mode of the 3D four‐directional braided SiO_2f/SiO₂ composite in the Iosipescu shear testing was based on a mixed mechanism because of the multi‐directivity of the composite. Owing to low sintered temperature, the fibre/matrix interfacial strength was weak. The SiO_2f/SiO₂ composites showed non‐catastrophic behaviour resulting from extensive fibre pull‐out during the failure process.     

Preparation of granular X-type zeolite/activated carbon composite from elutrilithe by adding pitch and solid SiO2

The preparation of granular X-type zeolite/activated carbon composites from a locally available elutrilithe by adding pitch powder and solid SiO₂ was studied, and the variations in the synthesis process of zeolite X were investigated. The preparation steps of the composite involved (1) calcination of pre-shaped mixture (2) activation of the carbonaceous material from elutrilithe and pitch to prepare activated carbon and (3) hydrothermal conversion (zeolitisation) of aluminosilicate in elutrilithe and additional SiO₂ to zeolite X in alkaline medium. The adding of additional SiO₂ in the reaction system to adjust SiO₂/Al₂O₃ ratio of the reaction mixture was necessary for the formation of zeolite X. The characterization of XRD, SEM and N₂ adsorption of the resulting composites had a hierarchical pore structure, which shows that pure X-type zeolite phase with high crystallinity could be obtained regardless of the content of carbon in the composites.     

Preparation of silica/polyacrylamide/polyethylene nanocomposite via in situ polymerization

SiO₂/polyacrylamide (PAM) composite was prepared via the polymerization of acrylamide in the presence of silica sol in water/hexane emulsion, and pure SiO₂ was also prepared without the use of acrylamide in the same way. Field emission scanning electron micrographs (FESEM) showed that PAM covered the silica nanoparticles to form SiO₂/PAM nanospheres, which loosely agglomerated to form SiO₂/PAM secondary particles, while SiO₂ secondary particles were made up of tightly agglomerated silica nanoparticles. Metallocene catalyst was then immobilized over SiO₂ and SiO₂/PAM respectively to prepare supported metallocene catalyst for ethylene polymerization. Transmission electron micrographs (TEM) showed that support particles broke up to smaller particles and even nanoparticles in polyethylene (PE) matrix when the support particles were the fragile SiO₂/PAM secondary particles, which shows a novel way to prepare silica/polyacrylamide/polyethylene nanocomposite.     

高体积分数SiCp/A356复合材料的显微组织和电导率

铝基复合材料在电子封装领域存在着潜在的应用前景。为获得高体积分数的铝基复合材料,利用压力浸渗法制备了高体积分数SiC颗粒增强A356复合材料(SiC_p/A356),通过金相显微镜、XRD、SEM和EDS等分析手段对其物相、显微结构和电导率进行了表征。结果表明:用该方法制备的SiC_p/A356复合材料组织致密,颗粒分布均匀,界面结合性能较好;SiC增强颗粒与A356基体界面反应控制良好,仅有少量Al4C3脆性相生成。SiC粉体经颗粒表面氧化处理在其表面生成一层SiO_2薄膜,虽抑制了界面反应的发生,但也使复合材料的收缩减小,电阻率增大,导电性能变差。     

Fabrication of porous TiO2 nanofiber and its photocatalytic activity

Porous TiO₂-based nanofiber was fabricated via a combined electrospinning and alkali-dissolution method. TiO₂/SiO₂ composite nanofiber was firstly prepared by electrospinning and sintering, and then silica was leached out with alkaline solution from the bulk of TiO₂/SiO₂ composite nanofiber to produce porous microstructure. The thermal decomposition and phase structure of the composite nanofiber precursor was investigated with TG/DSC and XRD, and optimal sintering temperature was obtained. SEM-EDX and FT-IR characterization show that most silica can be dissolved out from the composite nanofiber and thus porous nanofiber with excellent microstructure can be spontaneously formed. The effect of composite nanofiber composition on porous microstructure was studied, and it is found that the composite nanofiber with 20wt% silica can produce better porous microstructure compared to those with 10wt% and 30wt% silica. Meanwhile, porous TiO₂ nanofiber with 20wt% silica shows higher degradation efficiency to Congo Red.     

Preparation of ultra-low dielectric constant silica/polyimide nanofiber membranes by electrospinning

Ultra-low dielectric constant silica/polyimide (SiO₂/PI) composite nanofiber membranes are prepared by the combined sol–gel and electrospinning techniques. The emulsion composed of partially hydrolyzed tetraethoxysilane (TEOS) and polyamic acid (PAA) is spun to yield the precursor of the SiO₂/PI fibers with a core–shell structure due to phase separation. The dielectric constant (k) of the composite membranes varies from 1.78 to 1.32 with increasing content of SiO₂. The fibers accumulate and form the film with a large amount of pores leading the lower k. In addition, the interfacial reaction between SiO₂ and the PI matrix reduces the value of k as the SiO₂ concentration is increased. The thermal stability of PI increase after mixing with SiO₂ and the SiO₂/PI composite fibers have large commercial potential in the electronics industry.     

Diatom Frustules Decorated with Co Nanoparticles for the Advanced Anode of Li-Ion Batteries

Silica is regarded as a promising anode material for lithium-ion batteries (LIBs) because of its high theoretical capacity. However, large volume variation and poor electrical conductivity are limiting factors for the development of SiO₂ anode materials. To solve this problem, combining SiO₂ with a conductive phase and designing hollow porous structures are effective ways. In this work, The Co(II)-EDTA chelate on the surface of diatom biosilica (DBS) frustules and obtained DBS@C-Co composites decorated with Co nanoparticles by calcination without a reducing atmosphere is first precipitated. The unique three-dimensional structure of diatom frustules provides enough space for the volume change of silica during lithiation/delithiation. Co nanoparticles effectively improve the electrical conductivity and electrochemical activity of silica. Through the synergistic effect of the hollow porous structure, carbon layer and Co nanoparticles, the DBS@C-Co-60 composite delivers a high reversible capacity of >620 mAh g⁻¹ at 100 mA g⁻¹ after 270 cycles. This study provides a new method for the synthesis of metal/silica composites and an opportunity for the development of natural resources as advanced active materials for LIBs.     

Modification of the structural,textural, and mechanical properties of an Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al composite on the addition of an Al-SBA-15-type mesoporous phase

The formation of the pore structure of metal–ceramic materials based on Al₂O₃/Al composites has been studied in detail by modifying them via the incorporation of SBA-15-type mesoporous materials. The composition, pore structure, pore size, and morphology of the composite particles have been studied using nitrogen adsorption/desorption isotherms, scanning electron microscopy, and X-ray diffraction. We have produced Al-SBA-15/Al₂O₃/Al monoliths that combine properties of both adsorbents and permeable materials, but the incorporation of Al-SBA-15 into an Al₂O₃/Al matrix reduces the permeability and mechanical strength of the composites.     

Preparation and properties of SiO2 matrix composites doped with AlN particles

SiO₂ matrix composites doped with AlN particles were prepared by hot-pressing process. Mechanical properties of SiO₂ matrix composites can be greatly improved by doping with AlN particles. Flexural strength and fracture toughness of 30 vol%AlN-SiO₂ composite sintered at 1400°C reached 200 MPa and 2.96 MPa·m^1/2. XRD analysis indicated that, up to 1400°C, no chemical reaction occurred between SiO₂ matrix and AlN particles suggesting an excellent chemical compatibility of SiO₂ matrix with AlN particles. The influences of hot-pressing temperature and the content of AlN particles on dielectric properties of SiO₂-AlN composites were studied. The temperature and frequency dependency of dielectric properties of SiO₂-AlN composites were also studied. Residual flexural strength of SiO₂-AlN composites decreased with increasing temperature difference. The critical temperature difference was estimated about 600°C.     

Carbon-loaded porous composites produced by matrix carbonization of poly(vinylidene fluoride)

Using poly(vinylidene fluoride) (PVDF) carbonization at 750° C in fine-particle silica and its mixtures with graphite, we have prepared carbon-loaded porous composites which offer benzene absorption from 0.90 to 1.52 ml/g, compressive strength of 6 MPa, and Brinell hardness of up to 18 MPa. We observed the formation of various nanostructures (spheres, spherical segments, and layered platelets) and sizes (several to hundred nanometers). X-ray photoelectron and energy dispersive x-ray spectroscopy data indicate the presence of C-C, C =C, CO, COO, and CHF groups on the carbon surface. X-ray emission spectroscopy data show that the silica matrix composite prepared via PVDF carbonization contains small carbon clusters weakly bonded to the matrix. The silica/graphite matrix composite contains multilayer carbon films strongly bonded to the matrix. The OK _α spectra of both composites are similar to the spectrum of pure SiO₂.     

Synthesis and characterization of Ti-SBA-16 ordered mesoporous silica composite

Ti-SBA-16 mesoporous silica with a cubic Im3m structure has been successfully synthesized through prehydrolysis of a silica precursor in the presence of a tri-block copolymer F127 under acidic condition. X-ray diffraction (XRD) shows that the highly ordered mesostructure was maintained even at the high loading of titanium up to 5.5 (bulk molar ratio SiO₂/TiO₂). UV–vis and Raman spectroscopy reveal that the titanium species was highly dispersed in the silica framework with tetrahedral coordinate and octahedral coordinate, respectively. N₂-adsorption data exhibit that the BET surface, pore size and pore volume were maintained with an increase of titanium species loading for this cubic Im3m mesoporous composite. SEM image shows its amorphous morphology. The synthesis of mesoporous TiO₂-containing SBA-16 composite with a cubic Im3m structure will open new applications for catalysts.     

Synthesis and characterization of a nanocomposite NiO/SiO2 from a sustainable source of SiO2

ABSTRACT

The search for raw materials obtained from renewable sources is necessary for the sustainable development in the production of engineering materials. In this study, we present the hydrothermal synthesis of biogenic silica extracted from rice husk for the production of NiO/SiO₂ nanocomposite by Pechini method and employed an alternative strategy for the use of tetraethylorthosilicate as precursor agent. The synthesized nanocomposite presents amorphous SiO₂ nanoparticles dispersed in a NiO matrix as observed in the x-ray diffraction patterns and by scanning electron microscopy characterization. The average size of the crystallite measured by XRD was 11?nm. The formation of the aimed composite containing 83% of NiO crystalline phase and 17% of SiO₂ in amorphous phase was confirmed by Infrared and Raman spectroscopic analyses. These results demonstrate that it is possible to develop synthetic routes to produce new materials using several raw materials from sustainable sources and thus reducing environmental impact.     

Microstructural development in Al/MgAl2O4 in situ metal matrix composite using value-added silica sources

Abstract

Al/MgAl₂O₄ in situ metal matrix composites have been synthesized using value-added silica sources (microsilica and rice husk ash) containing ～97% SiO₂ in Al-5 wt.% Mg alloy. The thermodynamics and kinetics of MgAl₂O₄ formation are discussed in detail. The MgO and MgAl₂O₄ phases were found to dominate in microsilica (MS) and rice husk ash (RHA) value-added composites, respectively, during the initial stage of holding the composites at 750 °C. A transition phase between MgO and MgAl₂O₄ was detected by the scanning electron microscopy and energy-dispersive spectroscopy (SEM–EDS) analysis of the particles extracted from the composite using 25% NaOH solution. This confirms that MgO is gradually transformed to MgAl₂O₄ by the reaction 3SiO_2(s)+2MgO_(s)+4Al_(l)→2MgAl₂O_4(s)+3Si_(l). The stoichiometry of MgAl₂O₄, n, computed by a new methodology is between 0.79 and 1.18. The reaction between the silica sources and the molten metal stopped after 55% of the silica source was consumed. A gradual increase in mean MgAl₂O₄ crystallite size, D, from 24 to 36 nm was observed in the samples held for 10 h.