Acetalization of glycerol using mesoporous MoO3/SiO2 solid acid catalyst

Acetalization of glycerol with various aldehydes has been carried out using mesoporous MoO₃/SiO₂ as a solid acid catalyst. A series of MoO₃/SiO₂ catalysts with varying MoO₃ loadings (1–20 mol%) were prepared by sol–gel technique using ethyl silicate-40 and ammonium heptamolybdate as silica and molybdenum source respectively. The sol–gel derived samples were calcined at 500 °C and characterized using various physicochemical characterization techniques. The XRD of the calcined samples showed the formation of amorphous phase up to 10 mol% MoO₃ loading and at higher loading of crystalline α-MoO₃ on amorphous silica support. TEM analyses of the materials showed the uniform distribution of MoO₃ nanoparticles on amorphous silica support. Raman spectroscopy showed the formation of silicomolybdic acid at low Mo loading and a mixture of α-MoO₃ and polymolybdate species at high Mo loadings. Moreover the Raman spectra of intermediate loading samples also suggest the presence of β-MoO₃. Acetalization of glycerol with benzaldehyde was carried out using series of MoO₃/SiO₂ catalysts with varying MoO₃ loadings (1–20 mol%). Among the series, MoO₃/SiO₂ with 20 mol% MoO₃ loadings was found to be the most active catalyst in acetalization under mild conditions. Maximum conversion of benzaldehyde (72%) was obtained in 8 h at 100 °C with 60% selectivity for the six-membered acetal using 20% MoO₃/SiO₂. Interestingly with substituted benzaldehydes under same reaction conditions the conversion of aldehydes decreased with increase in selectivity for six-membered acetals. These results indicate the potential of this catalyst for the acetalization of glycerol for an environmentally benign process.     

MnO2/SiO2–SO3H nanocomposite as hydrogen peroxide scavenger for durability improvement in proton exchange membranes

Membrane durability was a key problem to the development of proton exchange membrane fuel cells (PEMFCs). A novel nanocomposite MnO₂/SiO₂–SO₃H was prepared to mitigate the hydrogen peroxide attack to the membranes at fuel cell condition. The nanocomposites were synthesized by the wet chemical method and three-step functionalization. The crystal structure was characterized by X-ray powder diffraction (XRD), the crystallite size and the distribution of the nanocomposites were investigated by TEM. SEM-EDX was used to analyze the elemental distribution on the surface of the nanocomposite. And the surface functional groups (–SO₃H) were evaluated by FT-IR. The amount of sulfonic acid groups introduced onto the silica surface was determined by titration method. The radical scavenging ability was estimated by UV–VIS spectroscopy using dimethyl sulfoxide (DMSO) as the trapping agent. The membrane durability was investigated via ex situ Fenton test and in situ open circuit voltage (OCV) accelerated test. In these tests, the fluoride emission rate (FER) reduced by nearly one order of magnitude with the dispersion of MnO₂/SiO₂–SO₃H nanocomposites into Nafion membrane, suggesting that MnO₂/SiO₂–SO₃H nanocomposites had a promising application to mitigate the degradation of the proton exchange membrane.     

Fabrication of mesoporous SiO2–C–Fe3O4/γ–Fe2O3 and SiO2–C–Fe magnetic composites

A synthetic method for the fabrication of silica-based mesoporous magnetic (Fe or iron oxide spinel) nanocomposites with enhanced adsorption and magnetic capabilities is presented. The successful in situ synthesis of magnetic nanoparticles is a consequence of the incorporation of a small amount of carbon into the pores of the silica, this step being essential for the generation of relatively large iron oxide magnetic nanocrystals (10 ± 3 nm) and for the formation of iron nanoparticles. These composites combine good magnetic properties (superparamagnetic behaviour in the case of SiO₂–C–Fe₃O₄/γ–Fe₂O₃ samples) with a large and accessible porosity made up of wide mesopores (>9 nm). In the present work, we have demonstrated the usefulness of this kind of composite for the adsorption of a globular protein (hemoglobin). The results obtained show that a significant amount of hemoglobin can be immobilized within the pores of these materials (up to 180 mg g⁻¹ for some of the samples). Moreover, we have proved that the composite loaded with hemoglobin can be easily manipulated by means of an external magnetic field.     

不同基底对TiO2和SiO2薄膜的光学性能的影响

采用溶胶-凝胶法分别在K9玻璃、单晶硅和石英玻璃基底上制备了纳米TiO₂和SiO₂薄膜。利用SEM、UV-Vis及反射式椭圆偏振光谱仪对薄膜的微观结构及光学特性进行了表征和分析。结果表明:3种基底中, 单晶硅基底上TiO₂和SiO₂薄膜折射率最大;在非晶态K9玻璃和石英玻璃基底上TiO₂薄膜折射率和透光率差异较大;SiO₂薄膜在非晶态基底上折射率、透光率相近;3种基底上薄膜的折射率和消光系数都有随波长增大而减小的趋势, 同时Cauchy模型能较好的描述单晶硅基底上两种薄膜在400~800 nm波段的光学性能。     

不同基底对TiO2和SiO2薄膜的光学性能的影响

采用溶胶-凝胶法分别在K9玻璃、单晶硅和石英玻璃基底上制备了纳米TiO₂和SiO₂薄膜。利用SEM、UV-Vis及反射式椭圆偏振光谱仪对薄膜的微观结构及光学特性进行了表征和分析。结果表明：3种基底中, 单晶硅基底上TiO₂和SiO₂薄膜折射率最大;在非晶态K9玻璃和石英玻璃基底上TiO₂薄膜折射率和透光率差异较大;SiO₂薄膜在非晶态基底上折射率、透光率相近;3种基底上薄膜的折射率和消光系数都有随波长增大而减小的趋势, 同时Cauchy模型能较好的描述单晶硅基底上两种薄膜在400~800 nm波段的光学性能。     

Synthesis and characterization of Fe2O3/SiO2 nanocomposites

Fe₂O₃/SiO₂ nanocomposites based on fumed silica A-300 (S_BET = 337 m²/g) with iron oxide deposits at different content were synthesized using Fe(III) acetylacetonate (Fe(acac)₃) dissolved in isopropyl alcohol or carbon tetrachloride for impregnation of the nanosilica powder at different amounts of Fe(acac)₃ then oxidized in air at 400–900 °C. Samples with Fe(acac)₃ adsorbed onto nanosilica and samples with Fe₂O₃/SiO₂ including 6–17 wt% of Fe₂O₃ were investigated using XRD, XPS, TG/DTA, TPD MS, FTIR, AFM, nitrogen adsorption, Mössbauer spectroscopy, and quantum chemistry methods. The structural characteristics and phase composition of Fe₂O₃ deposits depend on reaction conditions, solvent type, content of grafted iron oxide, and post-reaction treatments. The iron oxide deposits on A-300 (impregnated by the Fe(acac)₃ solution in isopropanol) treated at 500–600 °C include several phases characterized by different nanoparticle size distributions; however, in the case of impregnation of A-300 by the Fe(acac)₃ solution in carbon tetrachloride only α-Fe₂O₃ phase is formed in addition to amorphous Fe₂O₃. The Fe₂O₃/SiO₂ materials remain loose (similar to the A-300 matrix) at the bulk density of 0.12–0.15 g/cm³ and S_BET = 265–310 m²/g.     

Influence of copper species on silver grain size in Ag–CuO–SiO2 ternary nanocomposites

The influence of Cu species on Ag grain size in Ag–CuO–SiO₂ ternary nanocomposites prepared by adsorbed-layer nanoreactor technique (ALRT)was investigated. Ag and CuO nanoparticles were synthesized on the silica surface one after the other, then the grain size of Ag was determined by X-ray diffraction. Ag grains became smaller with increase in amount of Cu, whether Cu species was fed before or after Ag species, implying that the grain growth of Ag was inhibited by the appearance of Cu(OH)₂ in both feeding sequences. Furthermore, after taken away the effect of alkaline concentration on Ag grain size, the inhibition effects of two feeding sequences become more similar.     

ZrO2?SiO2 mixed oxides as supports for platinum catalysts

Mixed ZrO₂–SiO₂ oxides were prepared by the sol-gel method and used as supports for platinum catalysts. Activity tests show that Pt/ZrO₂–SiO₂ catalysts can be used in the aromatization of n-heptane.     

The synthesis and characteristic study of 6FDA-6FHP-NLO polyimide/SiO2 nanohybrid materials

Hybrid nanocomposite films of silica (SiO₂) in polyimide (PI) from 4,4^′-(hexafluoroisopropylidene) diphthalic arhydride (6FDA), 2,2-Bis (3-amino-4-hydroxyphenyl) hexafluoropropane (6FHP) and nonlinear optical (NLO) molecule have been successfully fabricated by an in situ sol-gel process. The silica content in the hybrid films was varied from 0 to 22.5 wt%. These nanocomposite films exhibit fair good optical transparency. Fourier transform infrared (FTIR) spectroscopy results confirm the formation of SiO₂ particles in PI matrix. Scanning electron microscope (SEM) images show that the SiO₂ phase is well dispersed in the polymer matrix. Their glass transition behavior and thermal stability were investigated by differential scanning calorimeter (DSC) and thermal gravimetric analysis (TG).     

New PVDF organic–inorganic membranes: The effect of SiO2 nanoparticles content on the transport performance of anion-exchange membranes

Organic–inorganic anion-exchange membranes based on poly(vinylidene fluoride)/SiO₂ were prepared and quaternary ammonium groups were introduced by the reaction of the epoxy groups of glycidyl methacrylate with trimethylamine. Various membranes were prepared with different weight fraction of nano-sized SiO₂ particles. The effect of silica content on the performance of these anion-exchange membranes was extensively characterized in terms of transport properties (TSP). The hydrophilic nature, swelling and TSP of these anion-exchange membranes were dependent on nanoparticles content in the membrane matrix. Higher TSP values of these membranes were obtained, which increased with increasing silica content. The hydrophilic property of the membranes was improved in presence of silica. Results of the effect of silica content on the membrane conductivity were confirmed by the analysis of phenomenological coefficients using non-equilibrium thermodynamic principles. It can be concluded that these anion-exchange membranes prepared with 2% loading with nanoparticles exhibited better transport properties, which may be used for their application in electro-driven separation or for other electrochemical processes.     

费托合成CeO2助Co/SiO2催化剂的失活

在固定床反应器上考察了原粒度(1～3mm)CeO2助Co/SiO2催化剂的费托反应性能,提出了催化剂失活的机理,并采用程序升温还原、X射线衍射和X射线光电子能谱对催化剂进行了表征.结果表明,在1.5MPa,488K和400h-1条件下进行的300h稳定性实验中,原粒度CeO2助Co/SiO2催化剂上的CO平均转化率达到41%,液态烃选择性达到85%,液态烃中C10 烃的质量含量占88%以上.反应器出口的催化剂中有少量的CoO和Co2SiO4生成.催化剂的失活过程受动力学控制而非热力学控制,催化剂的失活机理为:高分散的纳米Co离子在反应器出口高水蒸气压力的作用下,以CoO为中间物种,与水合SiO2作用生成Co2SiO4,即Co H2O→CoO H2,SiO2 H2O→OSi(OH)2,2CoO OSi(OH)2→Co2SiO4 H2O.     

Preparation and characterization of SiO2/TiO2 composite microspheres with microporous SiO2 core/mesoporous TiO2 shell

SiO₂/TiO₂ composite microspheres with microporous SiO₂ core/mesoporous TiO₂ shell structures were prepared by hydrolysis of titanium tetrabutylorthotitanate (TTBT) in the presence of microporous silica microspheres using hydroxypropyl cellulose (HPC) as a surface esterification agent and porous template, and then dried and calcined at different temperatures. The as-prepared products were characterized with differential thermal analysis and thermogravimetric (DTA/TG), scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption. The results showed that composite particles were about 1.8 μm in diameter, and had a spherical morphology and a narrow size distribution. Uniform mesoporous titania coatings on the surfaces of microporous silica microspheres could be obtained by adjusting the HPC concentration to an optimal concentration of about 3.2 mmol L⁻¹. The anatase and rutile phase in the SiO₂/TiO₂ composite microspheres began to form at 700 and 900 °C, respectively. At 700 °C, the specific surface area and pore volume of the SiO₂/TiO₂ composite microspheres were 552 and 0.652 mL g⁻¹, respectively. However, at 900 °C, the specific surface area and pore volume significantly decreased due to the phase transformation from anatase to rutile.     

Cyclohexanol dehydrogenation over Cu/SiO2 and CuO/SiO2: A comparison

Various CuO/SiO₂ catalysts were prepared and characterized by XRD, surface area and metal area measurements. While dehydrogenation activity for cyclohexanol was observed at 473–573 K on reduced catalysts, it was observed only at 573 K on the unreduced catalyst.IICT Communication No: 3261     

SiO2/ZnO复合纳米粒子的制备及表征

采用双注控制沉积法(Controlled Double-Jet Precipitation,CDJP)将反应物添加到含有SiO₂的溶液中,通过直接的表面反应来制备单分散的SiO₂/ZnO复合纳米粒子,并对其进行了表征。透射电镜(TEM)观察表明,SiO₂表面有一层ZnO纳米颗粒或薄层。对复合纳米粒子SiO₂/ZnO进行X射线衍射(XRD)分析,复合颗粒的衍射峰与单独的氧化锌的衍射峰完全一致。能量弥散X射线法(EDX)分析表明,复合颗粒中含有Zn、Si、O元素。荧光光谱表明有ZnO的吸收峰。     

Rheology and phase structure of PP/EPDM/SiO2 ternary composites

In this article, the rheological properties of polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM)/silicon dioxide (SiO₂) ternary composites were systematically investigated. Two kinds of nano-SiO₂ particles (with hydrophobic (denoted as A-SiO₂) or hydrophilic (denoted as B-SiO₂)) as well as two processing methods (one-step or two-step) were first employed to prepare PP/EPDM/SiO₂ ternary composites. Then the deep mixing and morphology evolution of polymer composite with mixing time were assessed by rheological method, on the focus of formation of filler-network, and compared with scanning electron microscopy (SEM) observations. Linear viscoelastic behavior was observed for PP/EPDM and PP/SiO₂ binary system, showing no evidence of the formation of filler-network structure. However, a solid-like rheological behavior, which was attributed to the formation of the filler-network structure as confirmed by SEM observation, could be observed in some PP/EPDM/SiO₂ ternary systems, depending on the SiO₂ surface property, processing method and EPDM content. It seemed that SiO₂ with hydrophilic surface was necessary for the formation of filler-network in PP/EPDM/SiO₂ ternary system. Besides, two-step processing method made the solid-like behavior occurred at an earlier stage compared with that of a one-step processing method, also, the higher elastomer content facilitated the formation of the filler-network structure. The results were in good agreement with those reported in our previous publications [Yang H, Zhang Q, Guo M, Wang C, Du R, Fu Q. Polymer 2006;47:2106] [Yang H, Zhang X, Qu C, Li B, Zhang L, Zhang Q, et al. Polymer 2007;48:860].     

Antireflective and Self-cleaning Properties of SiO2/TiO2 Double-Layer Films Prepared by Cost-E ective Sol-Gel Process

SiO₂/TiO₂ double-layer films with antireflective and self-cleaning properties were prepared by dip-coating glass substrate into cost-effective SiO₂ and TiO₂ sol successively and subse-quently being calcined at 500 oC. The optical and structural properties of films have been in-vestigated by UV-visible spectrophotometer and field emission scanning electron microscope, respectively. At the same time, self-cleaning property generated from superhydrophilicity and photocatalysis was obtained. The results indicated that the as-prepared SiO₂/TiO₂ double-layer films show maximum transmittance of 95% and self-cleaning property.     

Preparation, characterization, and infrared emissivity property of optically active polyurethane/TiO2/SiO2 multilayered microspheres

Optically active polyurethane/titania/silica (LPU/TiO₂/SiO₂) multilayered core–shell composite microspheres were prepared by the combination of titania deposition on the surface of silica spheres and subsequent polymer grafting. LPU/TiO₂/SiO₂ was characterized by FT-IR, UV–vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), SEM and TEM, and the infrared emissivity value (8–14 μm) was investigated in addition. The results indicated that titania and polyurethane had been successfully coated onto the surfaces of silica microspheres. LPU/TiO₂/SiO₂ exhibited clearly multilayered core–shell construction. The infrared emissivity values reduced along with the increase of covering layers thus proved that the interfacial interactions had direct influence on the infrared emissivity. Besides, LPU/TiO₂/SiO₂ multilayered microspheres based on the optically active polyurethane took advantages of the orderly secondary structure and strengthened interfacial synergistic actions. Consequently, it possessed the lowest infrared emissivity value.     

CO2在纳米SiO2/TiO2悬浮体系中的光催化还原

用水热法合成了氧化硅改性的具有高比表面积、高催化活性的锐钛型二氧化钛, 并在其悬浮体系中将CO₂光催化还原合成甲醇. 采用XRD, TEM, 物理吸附, UV-Vis吸收光谱和FTIR等表征手段对催化剂结构特征进行了研究. 结果表明: 添加氧化硅后, 氧化硅和二氧化钛之间形成Si—O—Ti键, 抑制了TiO₂晶粒生长, 提高了锐钛型TiO₂的比表面积, 且随着含硅量的增加, SiO₂/TiO₂的UV吸收逐步蓝移, 禁带宽度增加. 还原反应结果表明: SiO₂/TiO₂具有光催化还原活性, 且随着含硅量的增加先增加后减小, 当SiO₂质量分数为3.5%时, SiO₂/TiO₂复合催化剂反应活性最强, 5 h内甲醇产量可达到21.0 mg/L, 并有少量甲醛生成.     

Role of CO2 in dehydrogenation of propane over CrOX/SiO2 catalyst with low Cr content

When ethene alone was contacted with silica supported cobalt catalyst (Co/SiO₂), ethene homologation took place with considerable activity. Moreover, the propene metathesis reaction was suppressed ca. 1/6 fold as much as in the case using MoO_X/SiO₂ catalyst. The possibility of selective homologation with a lower activity for metathesis was suggested for the cobalt-based catalyst system.     

Anti-fungal activity of SiO2/Ag2S nanocomposites against Aspergillus niger

Submicron particles of amorphous SiO₂ have been used to grow Ag₂S nanophases at their surfaces. SEM and TEM analysis showed morphological well-defined nanocomposite particles consisting of Ag₂S nanocrystals dispersed over the silica surfaces. These SiO₂/Ag₂S nanocomposites were investigated as anti-fungal agents against Aspergillus niger in different experimental conditions, including as nanofillers in cellulosic fibres. The anti-fungal activity in these composite systems is suggested to result from a synergistic effect due to Ag₂S anti-fungal centres and the SiO₂ surfaces in promoting the adsorption of the fungus.