PDA/SiO2大孔复合材料固定化荧光假单胞菌脂肪酶

以具有三维骨架结构的大孔聚合物为模板制备SiO_2大孔材料,通过多巴胺在SiO_2大孔材料孔道表面的原位聚合制得聚多巴胺表面功能化修饰的二氧化硅大孔材料(PDA/SiO_2)。应用SEM、EDX、MIP、BET、TG-DTA和FTIR等技术对修饰前后的材料进行表征。以PDA/SiO_2为载体固定荧光假单胞菌脂肪酶(PFL),优化固定化条件并对比游离脂肪酶和固定化脂肪酶的性质。结果表明SiO_2大孔材料具有三维连续贯通的孔道结构,孔径分布在300~500 nm,聚多巴胺修饰后形成聚多巴胺/二氧化硅复合纳米薄膜构筑的大孔材料。在固定化时间为14 h、p H值为8、初始脂肪酶浓度为0.4 mg·m L-1时,固定化效果最佳,酶活回收率达246%。与游离脂肪酶相比,固定化脂肪酶有更宽的温度和p H适用范围、热稳定性显著提高,并展现出良好的储存稳定性和操作稳定性,固定化脂肪酶的Km低于游离脂肪酶的,酶与底物的亲和性较好。     

大尺寸SiO2大孔材料固定化漆酶

以表面固定Cu2+的改性大尺寸SiO2大孔材料作为载体,考察了时间、pH和给酶量对漆酶固定化效果的影响,并对固定化漆酶的活性和稳定性进行了研究。结果表明:5 h时吸附达到平衡,pH为4.5、漆酶与载体比例为5 mg·g-1时固定化效果最好,酶活回收率可达到100.4%;固定化漆酶的最适pH和最适温度较游离漆酶的均有升高且范围变宽,固定化后,漆酶的pH稳定性和热稳定性都得到显著提高;固定化漆酶的K m值略高于游离漆酶的;固定化漆酶具有良好的操作稳定性,与底物反应反复操作10批次后剩余酶活为72.7%。     

Effect of PEG with different <Emphasis Type="Italic">M</Emphasis><Subscript>W</Subscript> as template direction reagent on preparation of porous TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> with assistance of supercritical CO<Subscript>2</Subscript>

Titania–silica composite have been prepared using polyethylene glycol (PEG) with different molecular weights (M _w), PEG20000, PEG10000, and PEG2000, as template in supercritical carbon dioxide (SC CO₂). The composite precursors were dissolved in SC CO₂ and impregnated into PEG templates using SC CO₂ as swelling agent and carrier. After removing the template by calcination at suitable temperature, the titania–silica composite were obtained. The composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and nitrogen sorption–desorption experiment. Photocatalytic activity of the samples has been investigated by photodegradation of methyl orange. Results indicate that there are many Si–O–Ti linkages in the TiO₂/SiO₂ composite; the PEG template has a significant influence on the structure of TiO₂/SiO₂. In addition, the TiO₂/SiO₂ prepared with PEG10000 exhibited high photocatalytic efficiency. So this work supplies a clue to control and obtain the TiO₂/SiO₂ composite with different photocatalytic reactivity with the aid of suitable PEG template in supercritical CO₂.     

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.     

静电自组装制备纳米TiO2/SiO2光催化材料

采用静电自组装方法制备了纳米TiO2/SiO2光催化材料。采用巯丙基三甲氧基硅烷偶联剂对SiO2进行干法改性,采用双氧水/冰醋酸将偶联剂巯基基团氧化为磺酸基基团。在正负电荷的吸引下,带负电荷的SiO2与带正电荷的钛聚合阳离子自发地组装在一起,经一定温度热处理得到纳米TiO2/SiO2光催化材料。采用XRD、FTIR、PL、UV-Vis DRS、SEM和ICP等对材料进行了分析和表征。采用甲基橙溶液评价材料的光催化性能。结果表明:SiO2促使锐钛矿的形成,抑制锐钛矿向金红石的转变,减小TiO2的晶粒尺寸,使得TiO2光吸收波长发生蓝移。TiO2与SiO2通过Si-O-Ti键发生结合。采用静电自组装方法制备的材料中TiO2的含量高于传统方法,导致材料的光催化性能有所提高。     

Synthesis of nanosized TiO2/SiO2 catalysts by the ultrasonic microemulsion method and their photocatalytic activity

Nanosized TiO₂/SiO₂ catalysts prepared by hydrolysis of titanium n-butoxide in microemulsion showed enhanced photocatalytic activity. In the presence of catalyst ME-2 and after 90 min irradiation by UV light, methylene blue was completely converted evidenced by the absence of its absorption band in the UV-Vis spectra. This catalyst demonstrated much better degradation ability than P-25 and naked TiO₂.     

Characterization of immobilized catalases and their application in pasteurization of milk with H2O2

The catalase (fromAspergillus niger) has been immobilized by a chemical method on the pous SiO₂ modified with γ-aminopropyltrietoxysilane, followed with glutaraldehyde and by a physical method in alginate and γ-carrageenan gel. Optimum support:enzyme ratios and pH values were determined for modified SiO₂ in a series of immobilization reactions of catalase in the presence of the crosslinking agent glutaraldehyde, and for alginate and γ-carrageenan in the presence of hemoglobin and bovine serum albimine. pH and temperaturedependent activity variations and the stability properties of immobilized catalase preparations were investigated. Rate constants for H₂O₂ decomposition and catalase deactivation were determined. The decomposition rate of H₂O₂ used in the cold pasteurizatioan of milk were investigated in a discontinuous batch type reactor system. Activity half-lives of immobilized catalase were determined.     

Hydrogenation of Benzonitrile on Sn-Pt/SiO2 Catalysts Prepared by Introducing SnEt4 to Pt/SiO2: Role of Tin

Liquid phase hydrogenation of benzonitrile was studied over Sn-Pt/SiO₂ catalysts prepared by introducing tetraethyl tin onto the 3 wt.% Pt/SiO₂ catalyst. Tin content of the catalysts ranged from 0.05 to 0.63 wt.%, whereas Sn/Pt surface atomic ratios determined by chemisorption measurements were between 0.1 to 3.5. Dibenzylamine selectivity influenced to a small extent by the level of conversion and the Sn/Pt ratio wasca. 75 %. The addition of tin to Pt in the range of (Sn/Pt)_surface = 0.50–1.25 led to an increase in the turnover frequency (TOF) by a factor of 2. TOF showed a maximum at a surface atomic ratio of Sn/Pt = 1. The enhancement of catalyst activity upon the addition of tin is explained by the formation of Sn⁺-Pt ensemble sites on the surface of bimetallic nanoclusters. It is suggested that highly dispersed positively charged tin species, by polarizing the triple bond, enhance the reactivity of the -CN group. Calcination at 300°C followed by re-reduction of the catalysts resulted in a monotonic decrease of specific activity with increasing Sn/Pt ratio.     

Preparation of Cu/SiO2 Catalyst by Solution Exchange of Wet Silica Gel

Structural formation process of Ni/SiO₂ and Cu/SiO₂ catalysts prepared by solution exchange of wet silica gel was investigated. Microstructures of Cu/SiO₂ and Ni/SiO₂ were quite different from each other. In the case of Cu/SiO₂, Cu particles with diameter of ca. 3–5 nm dispersed homogeneously at less Cu content, and the particle size of Cu as well as pore size of silica gel support increased with increasing Cu content. In the Ni/SiO₂, the Ni particles with diameter of ca. 6–10 nm gathered densely to form aggregates in silica matrix resulting in sea-island structure, whereas the size of Ni particle slightly increased with increasing Ni content. The difference in the structure of the metal-silica composites is probably caused by the difference in interaction between silica gel network and metal ions during drying and heating processes.     

The Effect of SiO2 Addition on the Grain Size and Photocatalytic Activity of TiO2 Thin Films

The uniform transparent TiO₂/SiO₂ nanometer composite thin films were prepared via sol-gel method on the soda lime glass substrates, and were characterized by X-ray photoelectron spectroscopy (XPS), FTIR spectroscopy, UV-VIS spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and BET surface areas. It was found that the addition of SiO₂ to TiO₂ thin films could suppress the grain growth of TiO₂ crystal and increase the hydroxyl content of the surface of TiO₂ films. The photocatalytic activity of the as-prepared TiO₂/SiO₂ composite thin films increases for SiO₂ content of less than 5 mol%.     

Sol-gel coatings for chemical protection of stainless steel

Sol-gel thin coatings of ZrO₂, SiO₂, 70SiO₂-30TiO₂ and 88SiO₂-12Al₂O₃ compositions (mole %) have been prepared from sonocatalyzed sols and deposited by dip-coating technique on 316L stainless steel foils. The influence of the coatings on the chemical corrosion of the substrate has been measured through potentiodynamic polarization curves in aqueous 15% H₂SO₄ solution between 25 and 50°C. The values of the corrosion potential, polarization resistance and corrosion rate have been determined. Analysis of the data combined with scanning electron microscopy studies indicate that the films act as a geometric blocking against exposure to the corrosive media and increase the lifetime of the substrate up to a factor 8.5.     

Application of manganese (II) phthalocyanine synthesized in situ in the SiO2/SnO2 mixed oxide matrix for determination of dissolved oxygen by electrochemical techniques

This work describes the in situ immobilization of Mn(II) phthalocyanine (MnPc) in a porous SiO₂/SnO₂ mixed oxide matrix obtained by the sol gel processing method. The chemically modified matrix SiO₂/SnO₂/MnPc, possessing an estimated amount of 8 × 10⁻¹⁰ mol cm⁻² of MnPc on the surface, was used to prepare an electrode to analyze dissolved oxygen in water by an electrochemical technique. The electrode was prepared by mixing the material with ultrapure graphite and evaluated using differential pulse voltammetry. Dissolved O₂ was reduced at −0.31 V with a limit of detection (LOD) equal to 7.0 × 10⁻⁴ mmol L⁻¹. A mechanism involving four electrons in O₂ reduction was determined by the rotating disk electrode technique.     

Densification of Sol-Gel Thin Films by Ultraviolet and Vacuum Ultraviolet Irradiations

Structural changes in SiO₂ and TiO₂ gel films were investigated using ultraviolet (UV) and vacuum ultraviolet (VUV) irradiations. A significant compaction with dehydration of SiO₂ gel films was induced by irradiation of photons in the range of 9–18 eV. The refractive index and the shrinkage of the irradiated SiO₂ gel films were comparable to those obtained by sintering at 1000°C. Densification of TiO₂ gel films was also observed with irradiation of 5–14 eV photons. However, effects of the irradiation on TiO₂ gel were smaller that those on SiO₂ gel. The structural changes in the gel films are attributed to electronic excitations which are induced by irradiation with photons having higher energies than the bandgap of the oxides. The photo-induced effects are presumed to depend on the optical properties and structure of the gels.     

Supported oxorhenate catalysts prepared by thermal spreading of metal Re for methanol conversion to methylal

TiO₂-anatase and SiO₂ supported oxorhenate catalysts were prepared by an original and simple technique based on the oxidative dispersion of metallic rhenium under dry conditions. The dispersion process of the supported oxorhenate phase as a function of the rhenium coverage and the support properties are discussed on the base of in situ characterization. The structures of the as prepared catalysts were found to be comparable to those of materials prepared using the incipient wetness impregnation technique. The absence of water in the preparation technique has made it possible to highlight the role of the hydration level on the rhenium oxide volatilization. The as-prepared Re/TiO₂ catalysts were found to be effective for the direct conversion of methanol to methylal.     

Preparation and characterization of CuO/SiO2 and NiO/SiO2 with bimodal pore structure by sol-gel method

CuO/SiO₂ and NiO/SiO₂ with bimodal pore structure were prepared by sol-gel reactions of Tetra-methoxysilane (TMOS) and the respective metal nitrate in the presence of poly (ethylene oxide) (PEO) with an average molecular weight of 10 000 and the catalyst of acetic acid. In this process, the interconnected macroporous morphology was formed when transitional structures of spinodal decomposition were frozen by the sol-gel transition of silica. The addition of copper and nickel into the silica-PEO system had a negligible effect on the morphology formation. In gel formation, it was found that NiO crystalline sizes in the samples increased with decreasing Si/Ni molar ratio. It was considered that PEO interacted with both silica and nickel cations. In the CuO/SiO₂ with the presence of PEO_, CuO crystalline sizes were larger than those of NiO/SiO_2. It was considered that there was no obvious interaction between the Cu cation and PEO, most of the copper ions in wet silica gel were present in the outer solution. They easily aggregated as copper salts in the drying process of wet gel and decomposed into CuO particles in heating. While in the CuO/SiO₂ with the absence of PEO, the Cu was selectively entrapped as small particles in the gel skeleton due to the interaction between Cu aqua complex and silica gel network.     

Sol-Gel Derived TiO2-SiO2 Fibres

TiO₂−SiO₂ fibres with 0, 5, 10 and 20 volume % SiO₂ have been prepared by drawing from a gel followed by sintering at different temperatures. Nearly one meter long fibres can be drawn easily in conditions of about 50% relative humidity. Addition of SiO₂ inhibits the crystallisation of TiO₂ and also the anatase → rutile transformation and improves the strength of the fibres. While the pure TiO₂ fibres are brittle, those with 5, 10 and 20 volume % SiO₂ are flexible and strong. Tensile strength values as high as 3 GPa have been achieved in the 10 volume % SiO₂−TiO₂ fibres. Fibres heated above 900°C are brittle. The shape of the cross section of the fibres is found to depend on their diameters.     

Synthesis of nanosized TiO2/SiO2 particles using microwave processes and their photocatalytic activity on the decomposition of orange II

The nanosized titania and TiO₂/SiO₂ particles were prepared by the microwave-hydrothermal method. The effect of physical properties TTIP/TEOS ratio and calcination temperature has been investigated. The major phase of the pure TiO₂ particle is of the anatase structure, and a rutile peak was observed above 800°C. In TiO₂/SiO₂ particles, however, no significant rutile phase was observed, although the calcination temperature was 900°C. No peaks for the silica crystal phase were observed at either silica/titania ratio. The crystallite size of TiO₂/SiO₂ particles decreases as compared to pure TiO₂ at high calcination temperatures. The TiO₂/SiO₂ particles show higher activity on the photocatalytic decomposition of orange II as compared to pure TiO₂ particles.     

吸附法制备CuO-Ag/SiO2纳米复合物

利用吸附法原位制备CuO/SiO2、CuO-Ag/SiO2纳米复合物,研究了不同吸附质体系中预负载的纳米Ag粒子对CuO的影响。结果表明:Ag粒子对CuO的影响因吸附质的不同而不同。以Cu(Ac)2为吸附质,纳米Ag几乎没有影响;以NaOH为吸附质,纳米Ag使得CuO的晶粒粒径增大。这一结果与铜物种对Ag晶粒粒径的影响规律完全不同。通过比较不同吸附质的吸附行为,Cu(OH)2与硅胶表面的相互作用被认为是导致这一现象的原因。     

Gas-phase phenyl acetate conversion on AlPO4, γ-Al2O3 and SiO2 catalysts

The conversion of phenyl acetate over AlPO₄ (Al/P=1), γ-Al₂O₃ and SiO₂ catalysts generated phenol, by deacetylation, ando-hydroxycetophenone, by Fries rearrangement, as the main reaction products. The activity for Fries rerrangement was in accordance with the acidity data measuredversus cyclohexene skeletal isomerization. Thus, AlPO₄ showed the highest activity. Moreover,o-hydroxy-acetophenone formation increased with the reaction temperature. Besides, in AlPO₄ catalysts 4-methylcoumarin and 2-methylchromone were also found, although in low amounts.     

Synthesis and Polymerization Kinetics of Polystyrene Grafting using Azo-groups Bounded SiO2 as an Initiator

This work presents a new method for synthesis of inorganic/organic hybrid nanoparticles via the in-situ polymerization by the use of the azo-groups bounded silica nanoparticles as a radical initiator and styrene as a model vinyl-monomer. The synthesis and the structure of silica/polystyrene (SiO₂/PS), and the polymerization kinetics of the styrene initiated by the azo-groups bounded SiO₂ nanoparticles are studied with techniques such as FTIR, XPS, DSC, GPC, and TEM. Results show that the SiO₂-g-PS nanoparticles are synthesized successfully, and the resulting hybrid nanoparticles have a core-shell structure with SiO₂ in the core and the polystyrene on the outside layer. The percentage of the grafted PS on the SiO₂ surface increases with the progress of the polymerization before 6 h, and the largest amount of the grafted PS reaches 33% of the silica nanoparticles.

Consequently, the size of the nanoparticles increases ca. 20 nm upon the polystyrene grafting. The molecular weight of the grafted PS increases with the polymerization, and it has reached a much large value in the first several polymerization hours while it keeps a constant value approximately in the following polymerization process. Meanwhile, the polydispersity index of the grafted PS gradually increases with the progress of the polymerization. These phenomena agree with the theory of the traditional free radical polymerization very well.