Physicochemical and functional properties of modified tin dioxide

Specimens of tin dioxide with modifying Sb and Pt additives are synthesized. Their physicochemical properties (specific surface area, porosity, and conductivity), chemisorption and catalytic activity in the model reaction of CO oxidation are studied. A considerable chemisorption of CO on SnO₂ and SnO₂-SbO _x is observed at 150–180°C. The oxidation of CO in the flow of gases starts in the same temperature range. An addition of platinum leads to a significant increase in the rate of CO oxidation, the reaction starts at 80°C. It is proposed that the process proceeds at the SnO₂/Pt interface.     

Electrical conducting behaviors in polymeric composites with carbonaceous fillers

Several kinds of polymer composites with carbonaceous fillers such as carbon black (CB), vapor‐grown carbon fiber (CF), and carbon nanotube (CNT) are prepared by a gelation/crystallization process or a melt mixing method. The electrical phenomena, changes of electrical conductivities with different filler's type, filler's concentration and temperatures, and the mechanism of electron transport in these carbon‐filled polymer composites are directly influenced by the geometric grain shape and aggregating morphology of the fillers dispersed in the polymer matrix. For the composites of CB and CF, long‐range macroscopic conduction are governed by the percolation phenomenon, the conduction is behaved through the conductive path formed by the conductors' contacting, and the thermal expansion changes the physical dimensions of the entire electrical network and leads to the changes in the electrical phenomenon. Microscopic conduction between conductive elements is influenced by the tunneling barrier or tunneling voltage, which varies with the temperature change, explaining the apparent observation of the temperature dependence of the composites. In comparison with fillers of CB and CF, the CNT performs unique electric properties for their nonspherical geometry and morphology as a three‐dimensional network (high structures), which has been visually proved by SEM photos in our former research, leading to the percolation threshold lower than 1% in the volume fraction and much less temperature dependence in its composites. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1037–1044, 2007     

Thermomechanical properties of polymeric composites based on 2-hydroxyethylmethacrylate and fumed silicas

Summary Thermomechanical properties have been investigated for the composites synthesized by the thermal polymerization of 2-hydroxyethylmethacrylate or its polymerization initiated with acrylamide complex of cobalt nitrate in the presence of the fumed silica or silicon hydride-containing silicas. The effect of the filler surface nature on temperature dependencies of deformability of the polymeric composites has been studied.     

The one-step preparation and electrochemical characteristics of tin dioxide nanocrystalline materials

Tin dioxide nanocrystallines were prepared by one-step synthesis method – using amphiphilic P123 as a template. The crystalline nanomaterials present the uniform nano-size 15 nm and somewhat ordered porous meso-frameworks with average pores sizes of 3.5 and 9.5 nm. Meanwhile, the nanomaterials as the anode materials in lithium ion battery deliver high reversible capacity 792 mAh g⁻¹ in the first cycle, which is equal to the theoretical capacity. No aggregation of nano-tin particles was observed and the cracking of structure by the large volume change is efficiently limited owing to the porous mesostructured nanomaterials in the charge/discharge processes. The improved electrochemical properties are attributed to the particle size and structure of materials.     

Low temperature H_2S sensor based on copper oxide/tin dioxide thick film

Nanostructured tin dioxide (SnO2) powders were prepared by a sol-gel dialytic process and and the doping of CuO on it was completed by a deposition-precipitation method.The thick film sensors were fabricated from the CuO/SnO2 polycrystalline powders.Sensing behavior of the sensor was investigated with various gases including CO,H2,NH3,hexane,acetone,ethanol,methanol and H2S in air.The as-synthesized gas sensor had much better response to H2S than to other gases.At the same time,the CuO/SnO2 sensor had enough sensitivity,together with fast response and recovery,to distinguish H2S from those gases at 160 and 210 ?C.Therefore,it might have promising applications in the future.     

Low temperature H2S sensor based on copper oxide/tin dioxide thick film

Nanostructured tin dioxide (SnO2) powders were prepared by a sol-gel dialytic process and and the doping of CuO on it was completed by a deposition-precipitation method. The thick film sensors were fabricated from the CuO/SnO2 polycrystalline powders. Sensing behavior of the sensor was investigated with various gases including CO, H2, NH3, hexane, acetone, ethanol, methanol and H2S in air. The as-synthesized gas sensor had much better response to H2S than to other gases. At the same time, the CuO/SnO2 sensor had enough sensitivity, together with fast response and recovery, to distinguish H2S from those gases at 160 and 210 ℃. Therefore, it might have promising applications in the future.     

Cyclic voltammetry and voltabsorptometry studies of redox proteins immobilised on nanocrystalline tin dioxide electrodes

Protein film cyclic voltammetry is a well-established technique for the study of redox proteins immobilised on electrode surfaces. In this paper, we use nanostructured SnO(2) electrodes to demonstrate that cyclic voltabsorptometry is an effective, complimentary approach to such studies of protein redox function. We exemplify this approach using two different redox systems: microperoxidase-11 (MP-11) and flavodoxin Desulfovibrio vulgaris Hildenborough (Fld). Both systems were immobilised on nanocrystalline SnO(2) electrodes and the resulting films investigated by simultaneous cyclic voltammetry and voltabsorptometry. We demonstrate that cyclic voltabsorptometry allows the unambiguous and background free observation of redox reactions for both systems studied.     

Conducting polymeric composites based on butadiene-acrylonitrile latex

The possibility of controlling the physicochemical and electric properties of conducting latex composites based on butadiene-acrylonitrile latex and carbon fillers, using data on the content of active centers on the filler surface and their distribution with respect to donor-acceptor properties, was examined. To make the fillers compatible with the latexes and prevent their coagulation, the fillers were modified with Leukanol.     

Properties of electrorheological fluids based on nanocrystalline cerium dioxide

Effect of conditions of nanocrystalline cerium dioxide preparation from aqueous solutions on its composition and physicochemical properties and on dielectric characteristics of CeO₂ suspensions in polydimethylsiloxane PMS-20 and the magnitude of electrorheological effect for these suspensions has been analyzed. Relationship between physicochemical properties of CeO₂ nanopowders and polarization and functional characteristics of electrorheological fluids derived therefrom has been established.     

A credible role of copper oxide on structure of nanocrystalline mesoporous titanium dioxide

Copper oxide-titania catalysts with nanocrystalline mesoporous structure were prepared by sol-gel technique using tetra isopropyl ortho titanate (TiPT) as the inorganic precursor and amino-2 ethanol as the swelling agent. Characterization was performed using X-ray diffraction (XRD), fourier transformed infrared spectra (FTIR), scanning electron microscopy (SEM), diffuse reflectance UV-Vis spectroscopy (DRS), and N₂ adsorption-desorption measurements. It was found that CuO (0.025–0.1 mol ratio) has some effect on the particle size, surface area, pore-volume, pore-diameter, crystallinity of the particles, and crystalline phase of TiO₂ nanocrystalline. The results indicated that 0.1 CuO-TiO₂ had higher surface area and total pore volume among all CuO-TiO₂ samples. The SBET value of 0.1 mol ratio CuO-load TiO₂ sample is approximately similar to that of Degussa P25 while its pore volume (0.1198 cm³ g^?1) is larger than Degussa P25 due to production of large number of pores. Therefore, the physical property of 0.1 CuO-TiO₂ catalyst is comparable with Degussa P25.At 823K, the 0.1 mol ratio CuO-load TiO2 sample shows the phase transformation from anatase to rutile in the ratio of 1:1.1. The synthesized CuO-TiO₂ nanocrystalline will be able to show photocatalytic reaction under visible light.     

Effect of synthesis conditions on the structure and sorption properties of films based on mesoporous tin dioxide

We have conducted a comparative study of the synthesis conditions for mesoporous materials and films based on tin dioxide in the presence of different types of templates, and we have studied their thermal stability and sorption properties. We demonstrate the advantage of using alcoholic reaction media and nonionic templates (triblock copolymers Pluronic-123 and Pluronic-127) to obtain thin films of mesoporous SnO₂ with relatively high parameters for the porous structure (V_meso = 0.15 cm³/g, S_BET = 147 m²/g) and cassiterite crystallite sizes down to 2.7 nm, significantly smaller than the thickness of the walls.     

Selective determination of drug resistant cancer cells on indium tin oxide electrode modified with nano titanium dioxide

A new electrochemical cell sensor, with low cost, simple fabrication, high selectivity and sensitivity was developed in this study. Titanium dioxide nanoparticles (nano-TiO₂) were assembled on the disposable indium tin oxide (ITO) electrodes for the immobilization of the drug sensitive leukemia K562/B.W. cells and drug resistant leukemia K562/ADM cells to fabricate the relative cell sensors. The different electrochemical behaviors of the probe allowed us to differentiate one type of leukemia cells from another. Furthermore, the results of electrochemical impedance spectroscopy indicated that the detection limit of the new cell sensor is 1.3 × 10³ cells ml^?1 with a linear range of 1.6 × 10⁴ to 1.0 × 10⁷ cells ml^?1. These results suggested the promising application of this nano-TiO₂ interface to construct the non-labeling potential-discriminative cell biosensors for clinical uses.     

Renewable resources as reinforcement of polymeric matrices: composites based on phenolic thermosets and chemically modified sisal fibers

Lignocellulosic materials can significantly contribute to the development of composites, since it is possible to chemically and/or physically modify their main components, cellulose, hemicelluloses and lignin. This may result in materials more stable and with more uniform properties. It has previously been shown that chemically modified sisal fibers by ClO(2) oxidation and reaction with FA and PFA presented a thin coating layer of PFA on their surface. FA and PFA were chosen as reagents because these alcohols can be obtained from renewable sources. In the present work, the effects of the polymeric coating layer as coupling agent in phenolic/sisal fibers composites were studied. For a more detailed characterization of the fibers, IGC was used to evaluate the changes that occurred at the sisal fibers surface after the chemical modifications. The dispersive and acid-base properties of untreated and treated sisal fibers surfaces were determined. Biodegradation experiments were also carried out. In a complementary study, another PFA modification was made on sisal fibers, using K2Cr2O(7) as oxidizing agent. In this case the oxidation effects involve mainly the cellulose polymer instead of lignin, as observed when the oxidation was carried out with ClO(2). The SEM images showed that the oxidation of sisal fibers followed by reaction with FA or PFA favored the fiber/phenolic matrix interaction at the interface. However, because the fibers were partially degraded by the chemical treatment, the impact strength of the sisal-reinforced composites decreased. By contrast, the chemical modification of fibers led to an increase of the water diffusion coefficient and to a decrease of the water absorption of the composites reinforced with modified fibers. The latter property is very important for certain applications, such as in the automotive industry.     

Electrocatalytic properties of platinum nanoparticles supported on fluorine tin dioxide/multi-walled carbon nanotube composites for methanol electrooxidation in acidic medium

Fluorine tin oxide (FTO) and multi-walled carbon nanotube (MWCNT) composites synthesized by a sol-gel process followed by a hydrothermal treatment process have been explored as a support for Pt nanoparticles (Pt-FTO/MWCNTs). X-ray diffraction analysis and high resolution transmission electron microscopy show that the Pt and FTO nanoparticles with crystallite size of around 4-8 nm are highly dispersed on the surface of MWCNTs. Pt-FTO/MWCNT catalyst is evaluated in terms of the electrochemical catalytic activity for methanol electrooxidation using cyclic voltammetry, steady state polarization experiments, and electrochemical impedance spectroscopy technique in acidic medium. The Pt-FTO/MWCNT catalyst exhibits a higher intrinsic catalytic activity for methanol electrooxidation with high stability during potential cycling than Pt nanoparticles supported on tin dioxide/multi-walled carbon nanotube composites. The results suggest that FTO/MWCNT composites could be considered as an alternative support for Pt-based electrocatalysts in direct alcohol fuel cells.     

Optical properties of the photorefractive polymeric composite with modified PVK polymer

Poly[N‐(2‐ethylhexyl)‐3‐vinylcarbazole has been synthesized by radical polymerization from N‐(2‐ethylhexyl)3‐vinyl‐carbazole. The 50‐μm thick photorefractive device containing 30 wt % piperidin‐4‐ylbenzylidene‐malononitrile showed a diffraction efficiency of 40% of 50 V/μm, which corresponded to a Δn of 0.8 × 10^?3. The photorefractive response time was τ₁ = 0.6 s. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1695–1702, 2009     

Synthesis and characterization of soft polymeric nanoparticles and composites with tunable properties

Polymeric particles comprising acrylonitrile (AN)‐based core and acrylamide derivative–based shell in the submicron range with positive and negative charges were synthesized via microemulsion polymerization. 2‐Acrylamido‐2‐methylpropane sulfonic acid (AMPS) and 3‐(acrylamidopropyl)‐trimethyl ammonium chloride (APTMACl) were used as shell‐forming charged monomers onto AN core for the synthesis of p(AN‐co‐AMPS) and p(AN‐co‐APTMACl), respectively, using an oil‐in‐water emulsion system. To tune the characteristics of the core–shell particles, AN moieties in the core were amidoximated to change the nature of the core from hydrophobic (nitrile) to hydrophilic (amidoxime) nature. Additionally, colloidal magnetite particles (Fe₃O₄) produced by chemical coprecipitation technique under alkaline and inert conditions were also included inside p(AN‐co‐AMPS) and p(AN‐co‐APTMACl) particles as dual‐responsive nanocomposites against pH and magnetic field. With the magnetic properties, AN‐based core with modifiable characteristics and acrylamide‐based polyelectrolyte shells with variable charges and sizes were further used as drug carriers. For potential targeted drug delivery application of the synthesized soft particles and their composites Naproxen and Trimethoprim were used as model drugs, and he release studies were carried in phosphate buffer saline (pH = 7.4) at ambient temperature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Semiconducting polymers based on charge-transfer complexes. IV. Electrical properties and structure of polymeric charge-transfer complexes

Model electron donor molecules, 10-methylphenothiazine and 4-(methylthio)anisole, and polymeric electron donors which contained these molecules on the side chains of N-acyl-substituted polyethylenimines, were complexed with the electron acceptors, dichlorodicyanoquinone (DDQ), tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), and tetranitrofluorenone (TNF). The model donors formed 1:1 complexes with all the acceptors except TCNE. The polymeric donors formed amorphous complexes with DDQ, TCNQ, and TCNE. Crystalline complexes were formed with TNF which had low melting points (lower than the model complexes and the pure polymer). This is apparently due to poor lateral packing of the polymer chains. Electrical resistivities were lower for all the polymer complexes than for the corresponding model complexes. Electrical resistivity also decreased with increase in complex crystallinity. In the best case the polymer complex was two hundred times as conducting as the model. The concentration of unpaired electrons measured by EPR was nearly independent of temperature. Most of the electrons seen are trapped and do not participate in conduction. Thermal activation energies for conduction were in the range of 0.5–1.8 eV and were nearly equal for the model and corresponding polymeric complexes. Elongation of polymer complex with TCNQ by rolling produces a decrease in resistivity in the roll direction, although the complex is amorphous. This reinforces the hypothesis that conduction is parallel to the polymer backbone. A polymer–tetranitrofluorenone complex was photoconducting, though the photoconductivity was smaller than the dark conductivity at the level of illumination used. Dember and Seebeck effects indicated that the major carrier in the complex was holes.     

电聚合卟啉衍生物修饰的碘离子选择性电极

用电化学方法将α,β,γ,δ-四(4-氨基苯基)卟啉单体聚合在铂丝电极上, 可制备化学修饰型I^-选择性电极.质子化卟啉衍生物的立体交联高聚大环与I^- 的作用具有强的主客体效应,使电极对I^-具有高的选择性,并呈现与经典Hofmeister 系列及一般金属卟啉中性载体膜电极不同的阴离子选择性次序:I^-》SCN^-》ClO~4^->NO~2^->Br^->NO~3^->Cl^->SO~4^2^-.电极对1×10^-^1～2.6×10^-^6mol ·dm^-^3呈线性响应,检测下限8.2×10^-^7mol·dm^-^3,斜率61±0.2mV/pI^-(27℃).测试了电极膜的交流阻抗行为.电极具有内阻小,响应快,抗毒化能力强,制备简单等优点     

Physicochemical and electrorheological properties of titanium dioxide modified with metal oxides

The properties of electrorheological fluids containing dispersed phase of titanium dioxide nanoparticles prepared via the sol-gel method and modified with metal oxides have been studied. Titanium dioxide has the anatase structure with crystallite sizes of 8–10 nm and a specific surface area of 90–140 m²/g. It has been found that the magnitude of the electrorheological response of the filler is determined by the specific surface area and the content of a modifying component. The strongest electrorheological response has been revealed for titanium dioxide modified with aluminum oxide at an Al content of 6.5–7.0 mol % relative to TiO₂.