Oxide Sol Research Articles

Simultaneous Sheet Cross-Linking and Deoxygenation in the Graphene Oxide Sol–Gel Transition

The precursor material to graphene aerogels is a hydrogel formed from an aqueous solution of graphene oxide. We investigate the time evolution of the physical and chemical properties of a graphene oxide suspension as it transitions to a hydrogel. Fully formed hydrogels undergo densification during reaction, forming mechanically stable monoliths. We demonstrate that the gelation process removes oxygen functional groups, partially re-forms the sp2 network, and creates bonds between graphene oxide sheets. Furthermore, these changes to the physical and chemical properties occur on exactly the same time scale, suggesting that they have a common origin. This discovery lends greater understanding to the formation of graphene oxide-based hydrogels, which could allow more flexibility and tunability in synthetic methods for graphene-like materials.

Single phase bead free PLZT(7/60/40) fibers processed by electrospinning method

The reported study presents the formation of PVA/PLZT composite fibers by the electrospinning process followed by conversion into single-phase PLZT fibers. High viscous polymer (PVA) solution and stabilized ceramic oxide (PLZT) sol were used as the starting constituents. Both of them were mixed in three different ratios (PVA:PLZT::4:1; 2:1 and 1:1) to make their composite solutions. Viscosity of the PVA solution and other three composite solutions was measured at room temperature. Subsequently, efforts were made to convert these composite solutions into fibrous form by using different combinations of electrospinning process parameters. The as-spun PVA/PLZT composite fibers were characterized by SEM measurements. The detailed SEM study revealed that the morphology of PVA/PLZT composite fibers significantly changed with the variation in viscosity of their corresponding composite solutions. The composite fibers prepared from the PVA and PLZT ratios of 4:1 (4 parts of PVA solution and 1 part of PLZT sol) and 2:1 (2 parts of PVA solution and 1 part of PLZT sol) showed bead free nature along with narrow fiber diameter distribution for certain electrospinning parameters. For the third ratio of the composite solution that is, PVA:PLZT::1:1, several combinations of the electrospinning process parameters were tried but the resulted fibrous network showed beaded fiber morphology throughout the deposition area. Calcination of the as-spun composite fibers at 650°C showed PVA free single phase PLZT fibers. The results revealed ~40% reduction of the diameter of calcined PLZT fibers with good fiber morphology.

Optical constants and near infrared emission of Er doped ZnO sol–gel thin films

Erbium (Er) doped zinc oxide (ZnO) sol–gel thin films were deposited on glass substrate using the spin coating method. The effect of erbium concentration and annealing temperature on structural and optical properties was studied. The annealed film was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectrum (EDX), micro-Raman, photoluminescence (PL) and UV–vis spectroscopy. All the films showed a wurtzite structure of polycrystalline nature with an average crystal size of 27.44nm at 500°C and 29.28nm at 600°C. The Raman spectra confirmed the absence of secondary phases in the Er doped ZnO films and the longitudinal optical phonon mode was upto the fifth order. Densely packed surfaces of the films were observed from SEM images. The presence and distribution of Zn, O and Er elements in the deposited films were confirmed by EDX analysis. The calculated value of exciton binding energy of ZnO film was 60meV with a maximum value of 72meV being observed for Er doped films. The near infra-red emission peak was observed at 1.63eV through PL spectra studies. The average transmission was 80% with the calculated value of optical band gap being 3.26–3.32eV. An increase in the refractive index value predicts the substitutional incorporation of Er ions in ZnO with the maximum optical conductivity being observed in the UV region.

Magnetic and magnetization properties of iron oxide thin films by microwave assisted sol–gel route

Iron oxide thin films have attracted worldwide attraction due to their technological importance in magnetic tunnel junctions, recording media, as a catalyst etc. However, the use of microwave energy for obtaining crystallinity and phase transition in the form of thin films has long being neglected. We here report preparation of iron oxide thin films using microwave energy instead of conventional heating methods during sol–gel synthesis. The solution was subjected to microwave radiations, for sol synthesis, with variation in microwave power. The maximum power used in this study is 800 W with variation in power as 136, 264, 440, 616 and 800 W. These are among the lowest powers applied for synthesis of iron oxide sol. XRD, FTIR and VSM results indicate that use of microwaves can lead to enhanced crystallinity and phase stability, thus enhancing the magnetic properties with variation in power of the incident microwaves. At low power of microwaves mixed phases of iron oxide exist whereas with increased power up to 616 W pure maghemite phase was obtained. Further increasing the microwave power to 800 W, results in formation of pure magnetite phase. FTIR bands at 477 and 550 cm−1 indicate formation of pure magnetite phase. The films exhibit ferromagnetic behaviour with saturation magnetization of 453 emu/cm3. Verwey transition, determined using low temperature electrical properties, reveals sharp reduction in resistivity at a temperature of 125 K.

Electrostatic and steric mechanisms of iron oxide nanoparticle sol stabilization by chitosan

With the use of the methods of dynamic and electrophoretic light scattering, the process of stabilization of iron oxide nanoparticle sols by chitosan (M = 12 × 104 and 44 × 104, degrees of deacetylation of 65 and 70%) in the pH range 1.8–6.5 at NaCl concentrations up to 1 mol/L has been studied. The disperse phase of the sols was a nanopowder of spherical deaggregated iron oxide nanoparticles 14 nm in weighted-average diameter prepared via laser evaporation. It has been shown that, in an acidic medium, chitosan is capable of efficient stabilization of the iron oxide sol via an electrostatic mechanism providing for an electrokinetic potential of +30 mV. As a result of further deionization of chitosan, the stabilization efficiency increases significantly owing to steric stabilization up to an electrolyte concentration of 1 mol/L. The nanoparticles are encapsulated inside the chitosan macromolecular coils in the course of successive bouts of electrostatic and steric stabilization. A new effect—the spontaneous deaggregation of nanoparticles during sol storage with a characteristic time around 5 days—has been observed.

Zinc oxide sol-containing diallylmethyl alkyl quaternary ammonium salt synthesized by sol–gel process: characterization and properties

Zinc oxide sols-containing quaternary ammonium bromide compounds, including diallylmethyl dodecyl/tetradecyl/hexadecyl/octadecyl ammonium bromide, were synthesized from zinc acetate and quaternary ammonium bromide compounds via sol–gel process. Effects of alkyl chain length and double allyl of quaternary ammonium salts on the stability of the sols were investigated. The sols were characterized by X-ray diffraction. Morphologies of the sols were observed with transmission electron microscopy. The various zinc oxide sols were applied to cotton fabrics. Antibacterial activity, UV resistance, and mechanical properties of the treated fabrics were tested. It was verified that alkyl chain length and double allyl of quaternary ammonium salts had effects on the stability of the sols. Application results showed that UV resistance and antibacterial rate of the fabric finished by zinc oxide sols-containing quaternary ammonium salts first increased and then decreased with an increase in the alkyl chain length of quaternary ammonium salts. However, the sols had negative effects on breaking strength and elongation at break of the fabric.

Preparation of zinc oxide/silica nanocomposite particles via consecutive sol–gel and flame-assisted spray-drying methods

Abstract ZnO/SiO 2 nanocomposites were prepared using consecutive sol–gel and flame-assisted spray-drying methods. Zinc oxide and silica sols were prepared individually from zinc acetate and water glass, respectively, via a sol–gel method. Subsequently, zinc oxide sol, silica sol, and a mixture of both were spray dried in a flame reactor to generate powder of pure zinc oxide, pure silica, and a ZnO/SiO 2 nanocomposite, respectively, in order to compare the characteristics. The generated particles were characterized via luminescence spectrophotometer, Fourier Transform Infrared (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) to obtain the photoluminescence spectra, chemical bonding, crystallinity, and morphology of the particles, respectively. The photoluminescence emission recorded at 250 nm excitation showed a peak at approximately 400 nm that was characterized by a violet band. The highest intensity was shown by a 75 mol% ZnO sample followed, in order, by 50 mol% ZnO, 25 mol% ZnO, and pure ZnO.

Aluminum-doped zinc oxide sol–gel thin films: Influence of the sol's water content on the resistivity

Thin films of indium tin oxide (ITO) have gained substantial interest due to their optical and electrical properties. Since ITO is an expensive material and indium is a rare element, considerable attempts have been made to replace it by, e.g., aluminum-doped zinc oxide (ZnO:Al). The production of ZnO:Al is less cost-intensive, especially if the sol–gel technique is applied, while its properties are comparable to those of ITO. In this study, we demonstrate that the electrical properties of ZnO:Al thin films can be improved considerably by the addition of small amounts of ultrapure water to the dip coating solution during the preparation. The lowest resistivity obtained with a film prepared from a sol containing 0.2M water is 2.8·10−3Ωcm. Optical modeling thus indicates an improvement of the free carrier mobility of films prepared from sols in the presence of additional water. The films prepared have an average thickness of 340nm and a solar transmittance above 85% after annealing in a forming gas atmosphere. Clearly, the addition of water to the sol has a positive impact on the resistivity of the final ZnO:Al thin film. We suggest the observed increase of the free carrier mobility to be due to an improved electron transfer at the grain boundaries between the spherical nanoparticles.

Synthesis of mesoporous bimetallic Pt-Sn catalytic coatings from polynuclear precursors for fine organic synthesis processes

A new method is developed to obtain nanosized catalytic Pt-Sn/TiO2 coatings on the inner surface of a capillary microreactor during adsorption of polynuclear carbonyl Pt-Sn complexes on mesoporous TiO2. Titanium oxide sol prepared in the presence of template (Pluronic F127 surfactant) is supported in dynamic mode. Pt-Sn bimetallic catalysts with an average particle size of 1.5–2 nm are synthesized by adsorption of the bimetallic [Pt3(CO)3(SnCl3)2(SnCl2·H2O)] 2− complex followed by thermal treatment. Physicochemical properties of samples (thickness, structure and morphology, chemical composition of the material, electronic state, specific surface area, pore volume and size distribution) are characterized by a set of methods (HR TEM, SEM, powder XRD, XRF, XPS, low-temperature nitrogen adsorption). Conditions to prepare the uniform non-peelable Pt-Sn/TiO2 coating on the inner surface of a silica capillary with good adhesion are determined. To increase the TiO2 thickness, multilayered TiO2 films are synthesized by layerby layer deposition. The coating thickness is found to increase with an increase in the capillary diameter. The coating of a capillary with a diameter of 0.55 mm after 14-fold deposition is characterized by a thickness of 2 μm and an average pore size of 5.4 nm. The solvent effect on the adsorption of Pt-Sn carbonyl complexes into the TiO2 support is studied. The amount of the adsorbed complex increases in the following order: ethanol < acetone ∼ tetrahydrofuran. The physicochemical properties of the active component (surface concentration, dispersion, and composition) can be fine-tuned by varying the deposition method, precursor concentration in the initial solution, and temperature conditions of activation treatment. The catalyst activity in citral hydrogenation was 0.06–0.54 min−1, with the selectivity with respect to unsaturated alcohols reaching 90% at citral conversion above 95%.

Carbon fiber sheets coated with thin-films of SiO2 and γ-Al2O3 as electrodes in capacitive deionization: Relationship between properties of the oxide films and electrode performance

Nanoporous thin-film coatings of SiO2 and γ-Al2O3 on low surface area carbon fiber sheets may provide an alternative electrode material for capacitive deionization (CDI). In this paper, composite electrodes were fabricated by dipping a low surface area carbon fiber support (less than 2m2/g) into metal oxide sols of either acidic SiO2 (pH 2.9), basic SiO2 (pH 8.3) or γ-AlOOH. Furthermore, the number of times the supports were dipped into the respective sols was varied in an effort to deposit different quantities of the metal oxide. This resulted in composite electrodes with metal oxide contents ranging from 1.5 to 6.7% by weight and specific surface areas from 6 to 35m2/g. When these electrodes were submitted to CDI testing, the rate, as well as the quantity of Ca2+ removed, exceeded that of the uncoated carbon support, independent of the metal oxide coating utilized. Moreover, after 30min of removal, all of the composite electrodes removed >90% of the Ca2+ from a 1.0mM CaCl2 solution – an increase of over 30% as compared to that of the uncoated carbon. In addition, the rate of Ca2+ removal appeared to be dependent upon the nature of the metal oxide coating (SiO2>γ-Al2O3) on the carbon support. The ion removal observed in this work may be driven by electrical double layer formation, specific adsorption, and/or faradaic reactions, such as the oxidation of Cl− to ClO3−. During the regeneration of the electrode, it was shown that the application of an optimal electric potential increased the quantity of Ca2+ desorbed after 30min by approximately 60% for an uncoated pair of electrodes and 90% for a coated pair as compared with electrode regeneration performed under no applied potential. Furthermore, the coated electrode pair was able to withstand a higher voltage for regeneration than an uncoated pair before adsorption of counter-ions exceeded that of co-ions desorption.

A Concise Route to Fabricate TiO&lt;sub&gt;2&lt;/sub&gt; Nanoporous and Nanopillar Films Based on Block Copolymer Self-Assembly

This study developed a concise route to fabricate TiO2 nanoporous and nanopillar films based on the self-assembly of block-copolymer thin films in periodic nanostructures. We obtained the perpendicularly oriented cylindrical domains in polystyrene-b-poly (methyl methacrylate) (PS-b-PMMA) diblock copolymer (BCP) films by thermal annealing on ITO substrate modified by a cross-linkable random copolymer, and then these films were immersed into the titanium oxide sol in acetic acid for a few hours. The acetic acid in the sol can selectively swell the PMMA component, which results in titanium oxide sol being loaded to the PMMA component selectively. Then the films were calcined at high temperature to remove the PS-b-PMMA block copolymer, and simultaneously the titanium oxide was transferred in situ to the substrate. As a result, a highly ordered array of nanoporous and nanopillar TiO2 thin film is observed on the ITO substrates depending upon the block copolymer used with PS and PMMA cylinder-forming components. In principle, it can be a general and versatile approach for fabricating functional nanoparticle arrays.

Preparation of Cuprous Oxide Sol and Coated with Oleic Acid

nanocopper oxides (Cu2O) materials, which received much attention in recent years, have many promising applications in various areas. The nanocopper oxides were prepared by the reduction of aqueous cupric acetate, with hydrazine as a reductant. The nanocopper oxides Collosol would be very stability when coated by Oleic acid, the oleic acid coats Cu2O nanoparticle through chemical reaction between carboxyl at one end of oleic acid molecule. All the samples were characterized by XRD, SEM and FTIR analysis.

A sol–gel dip/spin coating method to prepare titanium oxide films

A dip/spin coating method for the preparation of titanium oxide films was proposed. Instead of placing an oxide sol on top of a substrate surface, the dip/spin coating was accomplished on the lower surface of the substrate where gravitational force exerted on the colloidal particles during spreading under a centrifugal force. The resulting TiO2 films were compared to those prepared using the conventional spin-coating and dip-coating methods. All the films were found to be composed primarily of anatase with a small amount of brookite. Compared to the films prepared using the conventional spin-coating and dip-coating methods, the TiO2 films fabricated using the dip/spin method had small and uniform grains with a unique structure, resulting in an increased photocatalytic activity when tested for degradation of methyl orange under UV irradiation.

Spontaneous Formation of Vertically Aligned Lamellae in Thin Films of Block Copolymer–Silica Hybrid Material

Abstract Vertical alignment of mesoscaled and phase-separated structures in organic–inorganic hybrid materials has significant potential for various applications. However, particular procedures and treatments are required to generate such pattern geometries. We demonstrate herein a simple and spontaneous process for vertical alignment of mesoscopic phase-separated structures in a hybrid material consisting of an amphiphilic block copolymer that possesses a thermotropic liquid crystal framework and silicate sol. By combining the thermotropic and lyotropic liquid crystal properties, the sol–gel condensation in this system spontaneously leads to the vertical alignment of mesoscopic lamellae. Most likely, the vertical molecular orientation formed in the thermotropic smectic liquid crystal domains promotes the vertical alignment of the mesoscaled lyotropic liquid crystalline structure of the hybrid film. The organic block components in the film could be selectively etched by ultraviolet light/ozone treatment and, consequently, provide a topologically undulated silica film that retains the vertical lamella structure of the precursor hybrid film. This approach via the hybridization with a metal oxide sol solution is advantageous in tuning the lateral pitch of the structure simply by adjusting the volume fraction of precursor sol content.

Nanometric Colloidal Sols of CeO2–ZrO2 Solid Solution as Catalyst Modifiers. I. Preparation and Structure

Abstract Stable nanometric colloidal sols consisting of fluorite-type metal oxides were prepared for use as chloride-free precursors for automotive catalysts. The aqueous solution containing metal carbonates and tetramethylammonium (TMA) ions was degassed and hydrothermally treated at 140–160 °C. Colloidal suspensions thus formed were purified by ultrafiltration to yield very stable and condensed sol solutions of CeO2 (CE), ZrO2 (ZR) and their solid solutions, CeO2–ZrO2 (CZ), which were stabilized by TMA. Each oxide sol contained 6–8 nm primary particles, but they formed aggregates larger than 40 nm. Local structural analysis by means of XAFS suggested that CZ sol exhibited two types of solid solution domains containing more or less Ce. The dried CZ sol exhibited higher thermal stability and oxygen storage capacity than CE and ZR sols.

Novel all solution processed heterojunction using p-type cupric oxide and n-type zinc oxide nanowires for solar cell applications

Nanostructured three-dimensional heterojunctional photovoltaic devices were synthesized through combination of hydrothermal synthesis of zinc oxide nanowires (ZnO NWs) and sol–gel derived cupric oxide. The ZnO NWs were prepared by the hydrothermal method at 90 °C, whereas the CuO thin films were synthesized by the sol–gel method. The derived CuO thin films were thoroughly characterized through scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy, UV–vis spectroscopy and electrical measurement. It was found that power conversion efficiency ~0.3% can be obtained through the proposed combination.

Characterization and Electrochemical Performances of Vanadium Oxide Films Doped with Metal Ions

Vanadium oxide films were prepared via the sol–gel process and dip coating method, using V2O5as raw materials and H2O2(volume fraction 30) as the solvent. Mn and Ni ions were added to vanadium oxide sol to prepare doping vanadium oxide films. The films were characterized by atomic force microscopy, FT-IR, X-ray diffraction and electrochemical techniques. The add-on of Metal ions will not affect the morphology of the vanadium oxide films, but change the valence of vanadium ion and vanadium oxide crystal phase. Furthermore, cyclic voltammetry curves show that metal ions doping vanadium oxide films exhibit reversible electrochemical reaction. But electrochemical impedance spectroscopy indicates pure vanadium oxide film has a better diffusion rate.

Electrochemical Performance of V&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt; Nano-Porous Aerogel Film

Nano-porous V2O5 aerogel films were prepared by dip-coating vanadium oxide sol onto ITO substrate, using V2O5 powder, Benz alcohol, Isopropanol as precursor materials. The nano pores were characterized by scaning electron microscope (SEM). The electrochemical properties were investigated by chronopotenyiometry(CP) and cyclic voltammograms(CV). Results showed that this porous V2O5 aerogel film exhibited good cycling stability with initial discharge capacity of 143mAh/g and 128 mAh/g after 18 cycles, staying 89.5 % of the initial discharge capacity, at a charge/discharge current density of 200 mA/g.

Structural Study of WO&lt;sub&gt;3&lt;/sub&gt; and MoO&lt;sub&gt;3&lt;/sub&gt; Compound Films in H&lt;sub&gt;2&lt;/sub&gt; Gasochromism

Sol-gel tequnique was used to prepare disordered tungsten oxide and molybdenum oxide sols. A series ratio of W:Mo compound sols were obtained via mettalic powder co-peroxided by H2O2 as precursors in ethonal. Compound films were achieved by dip-coating method. Fourier Transform Infrared Spectroscopy, Raman Spectroscopy were taken to characterize the structure of these compound films. Uv-visible Spectroscopy was used to test the gasochromic property. The results showed that the gasochromics property was much different from that of pure tungsten oxide and molybdenum oxide sol-gel thin films. The effect was origined from the structrue alteration, which was not due to the spectrum superposition but the co-reaction of W and Mo.

Preparation, characterization and application of ZnO sol containing quaternary ammonium salts

The zinc oxide sol containing quaternary ammonium salts (DMDAAC-ZnO) was synthesized by zinc acetate and dimethyldiallyl ammonium chloride via the sol–gel process. Effects of zinc acetate concentration, diethanolamine dosage and dimethyldiallyl ammonium chloride dosage on the absorbance-ratio and viscosity of the sol were investigated. Zinc oxide sols were characterized by XRD, TEM and FT-IR. DMDAAC-ZnO was applied to cotton samples and cotton samples treated were tested by antibacterial activity, UV resistance and breaking strength. The antibacterial activity and UV resistance of samples treated by zinc oxide sol containing quaternary ammonium salt were both better than sample treated by zinc oxide sol.