钴基催化剂在费-托反应过程中的失活行为

 考察了 Co/SiO₂, Co/Ru/SiO₂ 和疏水改性 Co/Ru/SiO₂ 催化剂在费-托合成过程中的稳定性.结果发现, 随着反应的进行, 三种催化剂都呈现一定程度的失活,它们稳定性高低顺序为: 疏水改性 Co/Ru/SiO₂ > Co/SiO₂ > Co/Ru/SiO₂. Co/SiO₂ 催化剂的失活是由于催化剂上 Co 晶粒的长大和硅酸钴物种的生成, 而 Co/Ru/SiO₂和疏水改性 Co/Ru/SiO₂的失活则是由于催化剂上 Co 晶粒的长大所致. 由于 Co/Ru/SiO₂ 催化剂的 Co 晶粒比 Co/SiO₂催化剂的小得多, 在反应过程中更容易长大, 所以 Co/Ru/SiO₂催化剂稳定性更差; 而疏水改性 Co/Ru/SiO₂催化剂表面的疏水性既抑制了硅酸钴物种的形成, 又使 Co 晶粒长大较慢, 因此其稳定性最高.     

A study of the formation of solid solutions of tristrontium silicate with some oxyorthosilicates of the rare earths (La,Nd, Y)

Summary Chemical and x-ray diffraction analyses showed that there are homogeneous regions lying between 100 and 90%Sr₃SiO₅ in the system Sr₃SiO₅-La₂SiO₅ and in the system Sr₃SiO₅-Nd₂SiO₅. In the system Sr₃SiO₅-Y₂SiO₅ the solubility limit of Y₂SiO₅ in Sr₃SiO₅ is 3%.     

Effects of the ratio of Fe to Co over Fe-CO/SiO2 bimetallic catalysts on their catalytic performance for Fischer-Tropsch synthesis

The Fe-Co/SiO2 bimetallic catalysts with different ratios of Fe to Co were prepared by aqueous incipient wetness impregnation. The catalysts of 10%Fe:0%Co/SiO2, 10%Fe:6%Co/SiO2, 10%Fe:2%Co/SiO2, 10%Fe:10%Co/SiO2, 6%Fe:10%Co/SiO2, 2%Fe:10%Co/SiO2 and 0%Fe: 10%Co/SiO2 by mass were tested in a fixed reactor by the Fischer-Tropsch synthesis. Activity and hydrocarbon distribution were found to be determined by the ratio of iron to cobalt of the catalysts. Higher iron content inhibited the activity, whereas higher cobalt content enhanced the activity of the Fe:Co/SiO2 catalysts. On the other hand, for the catalysts of 10%Fe:6%Co/SiO2, 10%Fe:10%Co/SiO2, 6%Fe:10%Co/SiO2, and 2%Fe:10%Co/SiO2, the total C2–C4 fraction increased (from 10.65% to 26.78%) and C5+ fraction decreased (from 75.75% to 57.63%) at 523 K. Temperature programmed reduction revealed that the addition of cobalt enhanced the reducibility of the Fe:Co/SiO2 catalyst. Metal oxides were present in those catalysts as shown by XRD. The Fe-Co alloy phase was found in the 2%Fe:10%Co/SiO2, 6%Fe:10%Co/SiO2, 10%Fe:10%Co/SiO2, 10%Fe:6%Co/SiO2 catalysts and their crystals were perfect.     

SiO2@CdTe@Au复合纳米粒子的制备与非线性吸收特性

应用SiO₂纳米粒子、CdTe量子点和Au纳米粒子,采用逐层吸附法制备SiO₂@CdTe@Au纳米复合材料。同时对样品进行了测试和表征,从多个方面证明纳米复合材料成功制备。利用Z扫描技术测量了SiO₂@CdTe和SiO₂@CdTe@Au纳米复合材料在纳秒激光脉冲作用下的非线性吸收光学特性。实验结果表明：SiO₂@CdTe和SiO₂@CdTe@Au纳米复合材料均表现出饱和吸收特性。SiO₂@CdTe@Au较SiO₂@CdTe纳米复合材料具有更强的非线性光学特性,并对其机理进行了分析。     

Determination of the standard Gibbs free energies of formation of the silicates of cobalt,magnesium, and strontium by e.m.f. measurements

Standard Gibbs free energies of formation of the silicates in the quasi-binaries: CoO and SiO₂, MgO and SiO₂, and SrO and SiO₂ were determined with the help of solid-state galvanic cells in the temperature ranges 1273 to 1673 K, 1373 to 1573 K, and 1323 to 1473 K, respectively. Stabilized ZrO₂ was used as an electrolyte for the CoO and SiO₂ system. For the MgO and SiO₂ system MgF₂, and for the SrO and SiO₂ system SrF₂, was used as an electrolyte embedded in a silicate-matrix phase.     

Effect of hydrophilic SiO2 additive in cathode catalyst layers on proton exchange membrane fuel cells

Hydrophilic nanosized SiO₂ and sulfonated SiO₂ particles were added to the cathode catalyst layer (CL) to improve the water wettability and the performance of a proton exchange membrane fuel cell (PEMFC) at low humidity. It was found that both nanosized SiO₂ and sulfonated SiO₂ additive improved the hydrophilicity of the cathode CL by the contact angle measurement. Contrary to nanosized SiO₂, sulfonated SiO₂ improved the conductivity of the cathode CL. Increased wettability of the cathode CL from SiO₂ maintained fuel cell at hydration conditions. This phenomenon had a profound influence on electrode performance at low humidity. Since the sulfonic groups in sulfonated SiO₂ improved the proton conductivity of the cathode CL, the cell with sulfonated SiO₂ showed better performance.     

Size effect of silica nanoparticles on thermal decomposition of PMMA

The size effect of silica nanoparticles (SiO₂) on thermal decomposition of poly(methylmethacrylate) (PMMA) was investigated by the controlled rate thermogravimetry. Thermal degradation temperature of PMMA–SiO₂ composites depended on both fraction and size of SiO₂, the thermal degradation temperature of 23 nm (diameter) SiO₂–PMMA (6.1 wt%) was 13.5 °C higher than that of PMMA. The thermal stabilities of 17 nm SiO₂–PMMA (3.2 wt%) and 13 nm SiO₂–PMMA (4.8 wt%) were 21 and 23 °C, respectively, higher than that of PMMA without SiO₂. The degree of degradation improvement was increased linearly with the surface area of SiO₂. The number of surface hydroxyl group in unit volume of SiO₂ particle increased with increasing the specific surface area of SiO₂, and the interaction between hydroxide group of SiO₂ and carbonyl group of PMMA had an important role to improve the thermal stability of PMMA.     

Construction of SiO2-TiO2/g-C3N4 composite photocatalyst for hydrogen production and pollutant degradation: Insight into the effect of SiO2

Using low-cost precipitated silica (SiO₂) as the carrier, a ternary SiO₂-TiO₂/g-C₃N₄ composite photocatalyst was prepared via the sol-gel method associated with a wet-grinding process. The as-prepared composite exhibits photocatalytic hydrogen production and pollutant degradation performance under solar-like irradiation. The effect of SiO₂ carrier on the properties of the heterostructure between TiO₂ and g-C₃N₄ (CN) was systematically studied. It is found that SiO₂ has important effects on promoting the interaction between TiO₂ and CN. The particle size of TiO₂ and CN was obviously reduced during the calcination process due to the effects of SiO₂. Especially, the TiO₂ particles exhibit monodispersed state with particle size below 10 nm (quantum dots), resulting in the improvement of the contact area and the interaction between TiO₂ and CN, and leading to the formation of efficient TiO₂/CN Z-scheme heterostructure in SiO₂-TiO₂/CN. Besides, the introduction of SiO₂ can increase the specific surface area and light absorption of SiO₂-TiO₂/CN, further promoting the photocatalytic reaction. As expected, the optimum SiO₂-TiO₂/CN composite exhibits 12.3, 3.1 and 2.9 times higher photocatalytic hydrogen production rate than that of SiO₂-TiO₂, CN and TiO₂/CN under solar-like irradiation, while the photocatalytic active component in SiO₂-TiO₂/CN is only about 60 wt%. Moreover, the rhodamine B degradation rate of SiO₂-TiO₂/CN is also higher than that of SiO₂-TiO₂, CN and TiO₂/CN.     

Immobilization of glucose oxidase on rod-like and vesicle-like mesoporous silica for enhancing current responses of glucose biosensors

The use of rod-like and vesicle-like mesoporous SiO₂ particles for fabricating high performance glucose biosensors is reported. The distinctively high surface areas of mesoporous structures of SiO₂ rendered the adsorption of glucose oxidase (GOx) feasible. Both morphologies of SiO₂ enhanced the sensitivities of glucose biosensors, but by a factor of 36 for vesicle-like SiO₂ and 18 for rod-like SiO₂, respectively. The greater enhancement of vesicle-like SiO₂ can be accounted for by its higher specific surface area (509 m² g⁻¹) and larger total pore volume (1.49 cm³ g⁻¹). Interestingly, the current responses of GOx immobilized in interior channels of the mesoporous SiO₂ were enhanced much more than those of simple mixtures of GOx and the mesoporous SiO₂. This suggests that the enhancement of current responses arise not only from the high surface area of SiO₂ for high enzyme loading, but also from the improved enzyme activity upon its adsorption on mesoporous SiO₂. Also compared were the performances of glucose biosensors with GOx immobilized on mesoporous SiO₂ by physical adsorption and by covalent binding to 3-aminopropyltrimethoxysilane (APTMS) modified SiO₂ using glutaraldehyde as the cross-linker. The covalent binding approach resulted in higher enzyme loading but lower current sensitivity than with the physical adsorption.     

A New Practical Route to ZSM‐5 Nanoparticles and Optimization of Synthetic Parameters through D‐optimal Design of Experiments

A D‐optimal experimental design with three levels of SiO₂/Al₂O₃, template/SiO₂, H₂O/SiO₂, Na₂O/SiO₂ and TPABr/TPAOH ratio parameters has been used to optimize the experimental parameters by an analysis of variances (ANOVA). The effects of these ratios in the initial synthetic mixture on the size of the ZSM‐5 zeolite nanoparticles have been studied. XRD and FE‐SEM analyses were used to characterize synthetic samples. Fischer test results showed that H₂O/SiO₂ and TPABr/TPAOH ratios are the most and least effective parameters, respectively, in the range studied. The most important two‐way interaction variables were the interaction of template/SiO₂ and TPABr/TPAOH molar ratios. The average particle size was in the 34–79 nm range. Furthermore, a mathematical model for the synthesis of ZSM‐5 zeolite nanoparticles was derived using experimental results. The optimized gel composition is as follows: SiO₂/Al₂O₃₌91.20, template/SiO₂₌0.16, H₂O/SiO₂₌40.42, Na₂O/SiO₂₌0.0147 and TPABr/TPAOH=0.     

Photocatalytic characteristics of TiO2 supported on SiO2

The photocatalytic decomposition of acetaldehyde was carried out on TiO₂/SiO₂. The presence of a support (SiO₂) in TiO₂/SiO₂ helped to promote the efficiency of the photocatalyst. The silica support enhanced the effective surface area of TiO₂ and adsorption of acetaldehyde on TiO₂/SiO₂. TiO₂/SiO₂ synthesized from Ti(SO₄)₂ showed promoting effect on acetaldehyde decomposition. The XPS results revealed that TiO₂/SiO₂ prepared with Ti(SO₄)₂ generated SO ₄ ^2? sites on the TiO₂ surface. The increased acidity could promote the adsorption of acetaldehyde and photocatalytic degradation of acetaldehyde. The sulfate ion seemed to generate the bifunctional sites (acid sites and photoactive sites) and promoted the acetaldehyde decomposition on TiO₂/SiO₂.     

Synthesis and properties of silica/polystyrene/polyaniline conductive composite particles

In this study, silica/polystyrene/polyaniline (SiO₂/PS/PANI) conductive composite particles were synthesized by four sequential reactions. The nanosized SiO₂ particles were synthesized from tetraethoxysilane (TEOS) by a sol–gel process with water as the solvent medium, followed by a surface modification with triethoxyvinylsilane; then the surface modified SiO₂ particles were used as seeds to synthesize SiO₂/PS composite particles with soapless seeded emulsion polymerization. Finally, the SiO₂/PS particles were used as seeds to synthesize the SiO₂/PS/PANI conductive composite particles. The sol–gel process of SiO₂, the effect of surface modification, and several other factors that influenced polymerization of styrene in the soapless seeded emulsion polymerization will be discussed. Either potassium persulfate (KPS) or 2,2′‐azobis(isobutyramidine) dihydrochloride (AIBA) was used as the initiator to synthesize the uniform SiO₂/PS particles successfully, and the cross‐section morphology of the SiO₂/PS particles was found to be of a core–shell structure, with SiO₂ as the core, and PS as the shell. The SiO₂/PS particles were well dispersed in many organic solvents. In the following step to synthesize SiO₂/PS/PANI conductive composite particles, sodium dodecyl sulfate (SDS) played an important role, specifically, to absorb aniline onto the surfaces of the SiO₂/PS particles to carry out the polymerization of aniline over the entire surface of the particles. The conductivity of the SiO₂/PS/PANI composite particles approached that of semiconductive materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 342–354, 2005     

Dispersion stability and rheological behavior of suspensions of polystyrene coated fumed silica particles in polystyrene solutions

Polystyrene coated silica（SiO₂@PS） core-shell composite particles with averaged diameter of about 290 nm were prepared by in situ emulsion polymerization of styrene on the surface ofγ-methacryloxypropyltrimethoxysilane grafted SiO₂ nanoparticles of 20-50 nm in diameter.Rheological behavior and dispersion stability of SiO₂@PS suspension in 10 wt%PS solution were compared with suspensions of untreated SiO₂ and silane modified SiO₂ nanoparticles.Suspensions of the untreated and the silane modified SiO₂ exhibited obvious shear thinning.The SiO-2@PS suspension exhibits shear viscosity considerably smaller than suspensions of untreated and silane modified SiO₂ at low shear rates.Transmission electron microscopy showed that the composite particles can uniformly and stably disperse in PS solution compared to other suspensions,implying that the PS shell can effectively enhance the particle compatibility with PS macromolecules in solution.     

Evaluation of Chitosan Derivatives Modified Mesoporous Silica Nanoparticles as Delivery Carrier

Chitosan is a non-toxic biological material, but chitosan is insoluble in water, which hinders the development and utilization of chitosan. Chitosan derivatives N-2-Hydroxypropyl trimethyl ammonium chloride (N-2-HACC) and carboxymethyl chitosan (CMCS) with good water solubility were synthesized by our laboratory. In this study, we synthesized mesoporous SiO₂ nanoparticles by the emulsion, and then the mesoporous SiO₂ nanoparticles were modified with γ-aminopropyltriethoxysilane to synthesize aminated mesoporous SiO₂ nanoparticles; CMCS and N-2-HACC was used to cross-link the aminated mesoporous SiO₂ nanoparticles to construct SiO₂@CMCS-N-2-HACC nanoparticles. Because the aminated mesoporous SiO₂ nanoparticles with positively charged can react with the mucous membranes, the virus enters the body mainly through mucous membranes, so Newcastle disease virus (NDV) was selected as the model drug to evaluate the performance of the SiO₂@CMCS-N-2-HACC nanoparticles. We prepared the SiO₂@CMCS-N-2-HACC nanoparticles loaded with inactivated NDV (NDV/SiO₂@CMCS-N-2-HACC). The SiO₂@CMCS-N-2-HACC nanoparticles as delivery carrier had high loading capacity, low cytotoxicity, good acid resistance and bile resistance and enteric solubility, and the structure of NDV protein encapsulated in the nano vaccine was not destroyed. In addition, the SiO₂@CMCS-N-2-HACC nanoparticles could sustain slowly released NDV. Therefore, the SiO₂@CMCS-N-2-HACC nanoparticles have the potential to be served as delivery vehicle for vaccine and/or drug.     

制备过程对 Pd-SiW12/SiO2 催化剂在乙烯选择氧化制乙酸反应中催化性能的影响

 采用不同负载顺序或制备过程制备了 Pd-SiW12/SiO2 催化剂, 考察了它们在乙烯直接氧化制乙酸反应中的催化性能. 结果表明, Pd 和 SiW12 的负载顺序与 Pd 负载后的处理条件对 Pd-SiW12/SiO2 催化剂上 Pd 的分散度影响较大, 但对催化剂表面 B 酸量影响不大, 而 Pd 分散度较高时, 相应催化剂活性较高. 将 Pd 和 SiW12 同时负载于 SiO2 上时, 催化剂表现出较高的催化乙烯直接氧化制乙酸反应活性.     

具有双亲特性的水相哑铃型SiO2纳米粒子的制备

以纳米SiO2水溶胶为原料,3?氨丙基三乙氧基硅烷(APTES)和3?氯丙基三乙氧基硅烷(CPTES)为改性剂,在水基环境下分别对SiO2纳米粒子进行改性,得到了具有亲水特性的APTES改性SiO2粒子和具有亲油特性的CPTES改性SiO2粒子水溶胶。2种粒子按不同比例混合,利用接枝在SiO2粒子表面氨基和氯丙基的取代反应,使得2种具有亲水/亲油特性的改性SiO2纳米粒子偶联,制备了粒径为40~50 nm的哑铃型SiO2纳米粒子。并通过透射电镜(TEM)、傅里叶变换红外光谱(FT?IR)、X射线光电子能谱(XPS)以及动态光散射(DLS)等方法对其进行了系统表征。结果表明,2种粒子成功偶联形成了具有哑铃型结构的水相SiO2纳米粒子,该粒子两面具有不同的亲水性,粒径近似等于APTES改性SiO2粒子和CPTES改性SiO2粒子的粒径之和。     

Influence of SiO2 nanoparticles on electro-optical and thermophysical properties of polyacrylate/liquid crystal composites

ABSTRACT

In this paper, SiO₂ nanoparticle-doped polymer dispersed liquid crystal (PDLC) lenses are made from a mixture of prepolymer, 5CB liquid crystal and SiO₂ nanoparticles by the polymerisation induced phase separation (PIPS) process. The effect of SiO₂ nanoparticles on the electro-optical properties of PDLC ?lms are studied. It is established that SiO₂ nanoparticles affect the microstructure of PDLC ?lms signi?cantly because of the formed agglomerates of SiO₂ nanoparticles. Results show an improvement in the electro-optical properties and a decrease in the response time for doped systems with small amount of SiO₂ nanoparticles. We also observe a shift of nematic–isotropic transition temperature as a function of SiO₂ nanoparticle contents. A good agreement between the electro-optical study and thermophysical properties is reached.     

Synthesis and characterization of polyaniline/silicon dioxide composites and preparation of conductive films

The focus of this study was to synthesize the inherently conductive polymer polyaniline using an optimized process to prepare polyaniline/silicon dioxide (PANI/SiO₂) composites by in situ polymerization and ex situ solution mixing. PANI and PANI/SiO₂ composite films were prepared by drop‐by‐drop and spin coating methods. The electrical conductivities of HCl doped PANI film and PANI/SiO₂ composite films were measured according to the standard four‐point‐probe technique. The composite films exhibited an increase in electrical conductivity over neat PANI. PANI and PANI/SiO₂ composites were also investigated by spectroscopic methods including UV‐Vis, FT‐IR, and Photoluminescence. UV‐Vis and FT‐IR studies showed that SiO₂ particles affect the quinoid units along the polymer backbone and indicate strong interactions between the SiO₂ particles and the quinoidal sites of PANI (doping effect). The photoluminescence properties of PANI and PANI/SiO₂ composites were studied and the PANI/SiO₂ composites showed increased intensity as compared to neat PANI. The increase of conductivity of PANI/SiO₂ composite may be partially due to the doping or impurity effect of SiO₂ where the silicon dioxides compete with chloride ions. The morphology of particles and films were examined by a scanning electron microscope (SEM). SEM measurements indicated that the SiO₂ were well dispersed and isolated in composite films. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of propylene glycol methyl ether over amine modified porous silica

Amine functionalized silica catalysts (3-aminopropyltrimethoxysilane (APTMS)) NH₂/SiO₂, (Diazabicycloundecene/SiO₂) DBU/SiO₂ and (1,5,7-triazabicyclo[4,4,0]dec-5-ene/SiO₂) TBD/SiO₂, which were characterized by ²⁹Si NMR, element analysis and indicator dye adsorption, were prepared by ultrasonic technique under mild conditions. Such hybrid solid bases showed high catalytic activity and good reusability towards for the synthesis of propylene glycol methyl ether.     

Solid mechanochemical preparation of core‐shell SiO2 particles and their improvement on the mechanical properties of PVC composites

In this article, a solid mechanochemical route to prepare core‐shell structured particles was introduced. X‐ray photoelectron spectrum, transmission electron microscope and dissolving experimental results indicated the formation of [(inorganic particle)/(elastomer)] core‐shell structured particles. The thermal stable experiments showed that untreated SiO₂ can cause dehydrochlorination of poly(vinyl chloride) (PVC) and discoloration of PVC/SiO₂ composites and the formation of core‐shell structured SiO₂ particles will improve the thermal stability of PVC/SiO₂ composites. The mechanical properties and rheological results showed that the formation of core‐shell structured SiO₂ particles can both improve the mechanical and processing properties of PVC/SiO₂ composite. ACR in PVC/(SiO₂‐PMMA‐ACR) composites acted not only as toughener for PVC matrix but also as cushion breaker if the content of ACR is enough. Meanwhile compared with other SiO₂ particles the formation of core‐shell structured SiO₂ particles can decrease the apparent viscosity, increase the critical shear rate and improve the appearance of extrudes of PVC/SiO₂ composites. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 938–948, 2008