A glucose sensor made of an enzymatic clay-modified electrode and methyl viologen mediator

A novel glucose sensor has been contrived by immobilizing glucose oxidase between two nontronite clay coatings on glassy carbon electrode with methyl viologen as mediator. The sandwich configuration proved to be very effective in the determination of glucose. The response of the glucose sensor was determined by measuring cyclic voltammetric peak current values under aerobic solution conditions. The effects of the amount of enzyme immobilized, the operating pH, and the common interferences on the response of the glucose sensor were studied. The detection limit was 5 μM, with a linear range extending to about 6 mM, giving a dynamic range of over 3 orders of magnitude for 0.1 mM methyl viologen. When stored in pH 7 phosphate buffer at 4 °C, the sensor shows almost no change in performance after operating for at least 2 months. A mechanism for the operation of the glucose sensor is also proposed.     

Gelation kinetics of an organically modified silicate

The gelation of solutions containing mixtures of tetraethoxysilane (TEOS) and polydimethyl siloxane (PDMS) with isopropanol, H₂O, and HCl as the catalyst was studied at various temperatures in closed systems. Large variations in the gelation rates were observed with varying temperatures, and different acid and water contents. The gelation rates were found to increase with increasing temperature as well as with HCl, content. However, decreasing the water concentration (the molar ratio H₂OTEOS<3) had a more significant effect in decreasing the gelation rate. Apparent activation energies were obtained from Arrhenius plots of gelation time against temperature and they were shown to change with acid content. The microstructural evolution in the final, dried gels appeared to be related to the degree of network linkage in the present system.     

TiO2掺杂PbO2电极及其在电解法制臭氧中的应用研究

为了提高电极对臭氧生成反应的电催化活性,采用纳米复合电镀技术制备了TiO2改性PbO2电极.分别采用X射线衍射和X射线荧光光谱分析了其晶体结构和组分含量。将该电极用于电解法制备臭氧,并考察了电流密度、电镀极间距、电镀液pH值以及TiO2颗粒粒径对电极性能的影响.实验结果表明,改性后的PbO2电极使臭氧生成反应的电流效率由11.9%提高到了12.9%.电镀电流密度和电镀极间距的提高有利于提高电极催化活性.TiO2的掺杂会降低PbO2电极的晶胞粒径,有利于提高电极的电催化活性.     

Au@BSA prepared under alkaline conditions as an electrochemical non-enzymatic glucose sensor interface

Au@BSA was prepared at pH 8, pH 9, pH 10, pH 11, pH 11.4, and pH 12 as the working electrode of the non-enzymatic glucose sensor by biological template method. The six kinds of gold-cluster film working electrodes sintered by Au@BSA show golden color, especially the golden films corresponding to pH 8 and pH 12 are obvious. The gold-cluster films at pH 8, pH 9, pH 10, and pH 11 showed mono-layer gold nanoparticles, while the gold-cluster film at pH 11.4 showed porous structure. The gold-cluster film prepared at pH 12 presents a multi-layer 3D structure composed of a large number of gold nanoparticles. The linear detection range of the non-enzymatic glucose sensor prepared at pH 8 is the widest among the six sensors, and its sensitivity is also better than the other four sensors except the sensor prepared at pH 12. The sensor with the gold-cluster film-modified working electrode prepared at pH 12 show the highest sensitivity (330.002 μA mM^?1 cm^?2), because multi-layer 3D structure can bring more electric catalytic active site for this sensor. The electrochemical impedance spectroscopy showed that the specific surface area of the sensor prepared at pH 12 was much larger than that of the other five sensors. We provide a pH cycling method for once shaping preparation that can be extended to other metal films or metal-oxide films electrochemical interfaces. The Au@BSA non-enzymatic glucose sensor prepared in this paper is stable and can resist the toxicity of excessive chloride ions without losing activity.

     

Development of a modified electrode with amine-functionalized TiO2/multi-walled carbon nanotubes nanocomposite for electrochemical sensing of the atypical neuroleptic drug olanzapine

In this work, using of amine-functionalized TiO₂/multi-walled carbon nanotubes (NH₂-TiO₂-MWCNTs) nanocomposite for modification of glassy carbon electrode (GCE) was investigated. The nanocomposite was characterized by Fourier transformed infrared spectroscopy, transmission electron microscopy and scanning electron microscopy. The efficiency of modified electrode for electrocatalytic the oxidation of olanzapine was studied by cyclic voltammetry, square wave voltammetry and chronoamperometry. The electrochemical measurements were carried out in phosphate-buffered solution (PBS, pH 5.0). The NH₂-TiO₂-MWCNTs/GCE provided high surface area and more sensitive performance. The charge transfer coefficient (α) and the apparent charge transfer rate constant (k_s) were calculated to be equal to 0.42 and 0.173 s^? 1, respectively. The square wave voltammetry exhibited two linear dynamic ranges and a detection limit of 0.09 μM of olanzapine. In addition, the modified electrode was employed for the determination of olanzapine in pharmaceutical and human blood serum samples in order to illustrate the applicability of proposed method.     

An electrochemical sensor based on Pt/g-C3N4/polyaniline nanocomposite for detection of Hg2+

The synthesis of Pt/g-C₃N₄/polyaniline nanocomposites (Pt/g-C₃N₄/PAn NCs) via the direct reduction of Pt (II) in the presence of L-cysteine as the reducing agent is presented in this study. X-ray diffraction analysis showed that the Pt cations were reduced to metallic Pt in the presence of L-cysteine. Field emission scanning electron microscope images confirmed a low agglomeration of metallic Pt when synthesized in the presence of g-C₃N₄. Electrochemical impedance spectroscopy results showed that the low conductivity of g-C₃N₄ is compensated with the presence of polyaniline (PAn). A glassy carbon electrode modified with the Pt/g-C₃N₄/PAn NCs showed high selectivity and sensitivity for the detection of Hg²⁺. The presence of active sites in the g-C₃N₄ and PAn enhanced the adsorption of Hg²⁺. The voltammetric response was linear in the concentration range of 1–500 nM Hg²⁺, with the detection limit of 0.014 nM (at S/N = 3).     

Reinforcement of polyurethane composites with an organically modified montmorillonite

A clay with reactive activity prepared by treatment of natural montmorillonite with Methylene-bis-ortho-chloroaniline (MOCA) was incorporated into polyurethane matrix and a series of PU/clay nanocomposites were obtained by in situ polymerization. The microstructure of the nanocomposites with different content of the clay was examined by atomic force microscopy (AFM). The thermal and mechanical properties of the nanocomposites with different organic clay content were characterized by dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). It was found that the moduli and thermal stability of the nanocomposites were improved with augment of clay, especially, for the PU/9 wt% MO-MMT nanocomposite, compared to pure PU, the storage modulus and the loss modulus were increased by about 300% and 667% at −45 °C, respectively.     

Ionic liquid-assisted hydrothermal synthesis of TiO2 nanoparticles and its applications towards the photocatalytic activity and electrochemical sensor

This work reports the synthesis of TiO₂ nanoparticles via ionic liquid-assisted hydrothermal method at 130?°C for two days. The obtained product was characterised by various techniques. The X-ray diffraction data reveal the anatase phase TiO₂ nanoparticles with crystallite size 37 nm. The Fourier transform infrared spectrum shows a band at 400 cm^?1 due to Ti–O–Ti stretching vibration, in addition to the presence of ionic liquid. The UV–Vis spectrum of TiO₂ nanoparticles shows an absorption band at 314 nm which indicates a blueshift compared with that of bulk TiO_2. The transmission electron microscopy images show almost spherical-shaped nanoparticles with an average diameter of 40–80 nm. TiO₂ nanoparticles exhibit excellent photocatalytic activity for the degradation of trypan blue, and also help in the reduction of Cr⁺⁶ to Cr⁺³. TiO₂ nanoparticles modified glassy carbon electrode exhibits better electrocatalytic oxidation towards dopamine compared with bare glassy carbon electrode.     

Preparation of silicon oxycarbide glass fibers from organically modified silicates

Silicon oxycarbide glass fibers have been successfully drawn from organically modified silicates (ORMOSILs) by the sol-gel method. The gel fibers were drawn from a precursor composed of tetraethyl orthosilicate (TEOS) and polydimethyl siloxane (PDMS) with different weight fraction. The organics in the fiber underwent decomposition to at temperatures higher than 300°C. The existence of oxycarbide phases were detected using infrared spectroscopy and solid state ²⁹Si NMR and was found in the fibers with heating temperatures higher than 700°C in nitrogen atmosphere. X-ray powder diffraction patterns showed that the fibers were still amorphous even after heat treatment at 1000°C for one hour.     

Synthesis of TiO2/GO composite film via an electrochemical route

A nano-structured film composed of TiO2 and reduced graphite oxide (GO) was synthesized on ITO glass via a typical electrochemical route. A mixed solvent of Ti(SO4)2 and GO was prepared, with the addition of H2O2, HNO3 and DMF at different ratio. A setup of two electrodes of ITO glass in a plastic cell and an electrochemical analyzer is used for the film forming. The film is characterized with a microstructure of GO plates being perpendicular to the glass substrate, since GO in the electrolyte solvent is separated as small plates at about several nanometers in diameter. TiO2 is found being deposited between these GO plates. This microstructure is quite different from the film formed by normal deposition, where the GO plates are generally parallel to the substrate. The oxygen containing groups of C=O, C-O-C and C-OH on the GO surface are reduced because of neighboring to TiO2, it means two phases being bonded to each other at the interface. The photoelectric current of the composite film is compared with the pure TiO2 film, the former one is almost one time higher than the latter one. The degradation of methyl orange of two kinds of film is also analyzed under the irradiation of ultraviolet light. The photocatalytic activity of two kinds of film presents the same trend of variation as that of photoelectric current. These results suggest that the photoexcited electrons of TiO2 may quickly transfer to the glass substrate through the reduced GO neighbor, that owns a better conductivity, and so far decrease the recovery of excited electron-hole. The unordinary microstructure of the composite film may favor both to the electron transmission between the GO and ITO glass substrate, and to the light excitation of TiO2. The microstructure of different films was studies by AFM, XPS, FESEM. The photo-electrochemical property was measured by an electrochemical instrument Model CHI660C with Blupoint4 as a UV light source.     

Photo-induced superhydrophilicity of nanocomposite TiO2-SiO2 thin film

In this work, TiO₂ and TiO₂-SiO₂ thin films on glass substrates were prepared by the sol-gel dip coating process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to evaluate the structural and chemical properties of the films. The super-hydrophilicity was assessed by water contact angle measurement. XRD measurements confirmed the presence of polycrystalline anatase and rutile phases in the films. The water contact angle measurements showed that addition of SiO₂ has a significant effect on the super-hydrophilicity of TiO₂ thin films, especially if they are stored in a dark place.     

Ce/ TiO2纳米复合粉体的制备及其性能评价

以锐钛矿型纳米TiO2和硫酸铈为主要原料，采用浸渍法制备了Ce／TiO2纳米复合材料。采用滴定法研究TiO2对Ce^4＋的吸附，结果表明，在pH值为2-7的范围内TiO2对铈离子的吸附量接近100％。采用X射线衍射（XRD）进行物相结构分析，发现在700℃下焙烧仍保持锐钛型结构，而在800℃下焙烧出现了金红石型TiO2和CeO2，说明铈离子的存在减缓了TiO2的晶型转变。最后以甲基橙为目标降解物评价了Ce^4＋／TiO2复合粉体的光催化反应活性。     

A methyl parathion electrochemical sensor based on Nano-TiO2, graphene composite film modified electrode

A methyl parathion electrochemical sensor based on nano-TiO₂ and graphene composite film modified glassy carbon electrode has been developed. The electrochemical behavior of MP at the sensor was investigated by cyclic voltammetry and linear sweep voltammetry. Scanning electron microscopy was used to characterize the surface morphology of nano-TiO₂ and graphene composite film. Compared with a bare glassy carbon electrode or a mono-film modified electrode, the redox peak currents of methyl parathion on the composite film modified electrode improved greatly, indicating that the sensor showed good catalytic effects. The optimal experimental condition was obtained. The results indicated that the linear sweep voltammetry responses of methyl parathion, in pH 5.2 acetate buffer solution with open-circuit accumulation for 2 min, were linear with concentrations of methyl parathion in two ranges of 0.002～5 μM and 5～100 μM. The linear equations were i_Pc(μA) = 0.0136 + 4.965c_MP(μM) (R₁² = 0.9911) and i_Pc(μA) = 21.87 + 0.8206c_MP(μM) (R₂² = 0.9914), respectively. The detection limit was 1.0 nM (S/N = 3). The sensor exhibited high sensitivity and good reproducibility as well as certain anti-interference ability. It was applied to the determination of residual MP in fresh apple sample with the recovery of 92%～102%. The result was satisfactory.     

Mn2O3 porous microsheets prepared by a chemical precipitation method as an effective electrochemical sensor for non-enzymatic glucose detection

Journal of Materials Science - To conveniently construct an electrochemical non-enzymatic glucose sensor, Mn2O3 porous microsheets are utilized as electrode materials in glucose detection. Mn2O3...     

Selective adsorption of tannin from flavonoids by organically modified attapulgite clay

In this study, selective adsorption of tannin on organically modified attapulgite clay was investigated. Tannin was selectively removed from model tannin/flavonoids mixtures in the solution. In adsorption isotherm experiments of tannin, obtained data fitted well to the Freundlich model. The surface sites of the octodecyl trimethyl ammonium chloride (OTMAC)-attapulgite were heterogeneous. The effect of pH on tannin adsorption was also investigated and the results showed that the adsorbed amount of tannin was highest at pH 6.0. The enthalpy values of adsorption of tannin on OTMAC-attapulgite at pH 4.0, 6.0 and 8.0 were −49.80, −74.31 and −38.62 kJ/mol, respectively. At 2–5.3 and 7.4–10, the driving forces for the adsorption may be the hydrophobic force and hydrogen bonding. And at pH 5.3–7.4 the electrostatic force may be the most important one. These facts implied that the selective adsorption of tannin on OTMAC-attapulgite was driven by the collaboration of hydrogen bonding, electrostatic force and hydrophobic interactions of tannin molecular with adsorbent. The low adsorption of isoflavones of soybean and the puerarin was ascribed to less phenolic hydroxyls of them than those of tannin, which made the low electrostatic interactions and hydrogen bonding interactions between the tannin and OTMAC-attapulgite adsorbent.     

S／TiO2纳米氧敏材料的结构与吸脱附特性

以TiCl3为钛源,采用溶胶一凝胶法,在500℃(1h)烧结获得非金属离子(硫)掺杂TiO2的纳米粉体,利用XRD,FT-IR,UV-vis,ESEM,Zeta电位,XRF,TPD等表征S/TiO2结构特性.结果表明,硫掺杂有利于其向金红石相转变,低掺杂浓度(2at%)时,硫主要以S4 形式存在,当掺杂量为25at%时,部分掺杂硫以S2-形式替代O2-,由于两者间的电负性差异,导致表面上Ti3 、Ti4 周围的电子云密度增加,从而提高样品对氧气的吸附活性,使其表面的富余电子向吸附氧转移,提高了氧敏特性.S/TiO2敏感体表面的吸附氧以氧分子形式脱附(≤550℃),而在高温(≥600℃)下主要以SO2形式脱附.     

TiO2基氧化物半导体氧敏传感器的研究开发进展

综合介绍TiO2基氧化物半导体氧敏传感器的研究发展历史和TiO2材料的特性,比较了各种氧敏机理、制备方法、传感器的氧敏特性,就制备方法－材料微观结构－氧敏性能关系中的几个重要问题,进行了深入的探讨,并对今后的研究开发与产业化,结合本课题组的研究工作,提出了几点建议。     

MWCNT/TiO2复合材料光催化活性研究

以多壁碳纳米管(MWCNT)为基核,以钛酸丁酯为前驱体,分别用溶胶-凝胶法和水热法制备碳纳米管/二氧化钛纳米复合光催化材料.用X射线衍射仪(XRD)、透射电子显微镜(TEM)对样品进行了表征,研究了溶胶-凝胶法和水热法工艺的控制对碳纳米管/二氧化钛复合光催化剂显微组织及性能的影响.以甲基橙为目标降解物,考察了样品的自然光催化活性.结果表明,所得复合粉体中仅有碳纳米管和锐钛型二氧化钛两种物相,其中采用水热法所得样品,其纳米级的球形二氧化钛颗粒可均匀吸附在碳纳米管表面.