Solution-based fabrication of a graphene–ZnO nanocomposite

Graphene-based composites represent a new class of materials with potential for many applications. Graphene can be attached to a metal, a semiconductor, or any polymer. In this work, our approach was to attach graphene to a well-known semiconductor, ZnO. We synthesized graphene–ZnO composites by a simple, low-cost, environmentally friendly solvothermal method, carrying out the reaction in different conditions in order to discover the optimum condition, and also to obtain a high-quality product. Our research demonstrated that the optimum temperature to obtain a high-quality product is 180 °C for 20 h. All obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy, electron dispersion spectrometry, X-ray photoelectron spectrometry, Raman spectroscopy, Fourier transform infrared spectrometry, UV–visible spectrophotometry, and thermogravimetric analysis. The XRD confirmed that the crystal structure of the ZnO in the nanocomposite was wurtzite type. The prepared composite was stable to 800 °C with its 80 % weight.     

PVA-Based Sol–Gel Synthesis and Characterization of CdO–ZnO Nanocomposite

CdO–ZnO nanocomposite was fabricated by a sol–gel pyrrolysis method based on the poly vinyl alcohol (PVA) polymeric network. The prepared nanocomposite was carefully characterized using scanning electron microscopy, X-Ray dispersive energy analysis, ICP-atomic emission spectroscopy, X-Ray diffraction, transmission electron microscopy and UV–visible spectroscopy. The structure, composition, and morphology of this composite depend on a number of aspects: the amounts of cadmium salt, zinc salt, and PVA in the initial solution, the solvent composition, and the pyrrolysis temperature. The obtained results showed that the nanocomposite had excellent linear nanoclusters created from nanograins. Each nanograin was made of a CdO core, completely covered by ZnO layers. Total diameter of each nanograin was 70–90 nm.     

Preparation and optical–electrical properties of Al-doped ZnO films

Among the various semiconducting metal oxide materials, ZnO thin films are highly attractive in the development of materials area. In this paper, Al-doped ZnO thin films were prepared by sol–gel dipping and drawing technology and their composition, structure and optical–electrical properties were investigated. XRD results shows that the Al-doped ZnO thin film is of polycrystalline hexagonal wurtzite structure, and the (002) face of the thin film has the strongest orientation at the annealing temperature of 550 °C. The surface resistance of Al-doped ZnO thin film firstly drops and then increases with the increase in annealing temperature. Al doping concentration is also an important factor for improving the conductivity of modified ZnO thin films, and the surface resistance has the tendency to drop at first and then to increase when the Al concentration is increasing. The surface resistance of modified ZnO thin films drops to the lowest point of 139 KΩ sq^?1 when the Al concentration is 1.6 at% and the annealing temperature is 500 °C. The light transmission measurements show that the doping concentration has little influence on light transmittance. The transmittance at the visible region of films is all over 80 %, and the highest value is up to 91 %.     

Effect of ZnO nanoparticles on kinetics of thermal degradation and final properties of ethylene–propylene–diene rubber systems

The morphology, thermal degradation behavior in addition to static and dynamic mechanical properties of various ethylene?Cpropylene?Cdiene (EPDM) rubber compounds containing nano-zinc oxide (NZnO) were investigated compared to those of EPDM with ordinary-sized ZnO (OSZnO). The field-emission scanning electron microscopy studies showed that unlike the conventional system, the formation of large size ZnO agglomerates was discouraged for NZnO filled systems. Thermogravimetric analysis (TG) revealed that the thermal degradation of EPDM system was delayed upon the inclusion of NZnO instead of OSZnO in the compound. The kinetic analysis of TG data based on Friedman and Kissinger methods showed that the nanocomposite samples exhibited higher activation energy (E _a ) and lower order of reaction (n) over the conventional system, suggesting the enhancement of thermal stability upon decreasing ZnO particle size. The results obtained from dynamic mechanical analysis and static mechanical characterizations in terms of hardness, resilience, and abrasion tests interestingly indicated that NZnO not merely could act as a thermal insulator, but also could perform as a nano-filler to improve the final performance of EPDM elastomers.     

Effect of annealing on photoluminescence of blue-emitting ZnO nanoparticles by sol–gel method

In this work, we investigated the influence of annealing on the crystallinity, microstructures, and photoluminescence (PL) properties of ZnO nanoparticles prepared by sol–gel method. The annealing was carried out both in air and vacuum. X-ray powder diffraction, scanning electron microscopy, and ultraviolet–visible spectroscopy were used to characterize the crystal structures, diameter, surface morphology, and PL properties of ZnO nanoparticles. It has been found that both the as-grown and annealed ZnO nanoparticles had a hexagonal wurtzite crystal structure, and their average diameter and crystallinity increased with the anneal time and temperature. Pure blue-emitting behavior was observed in all samples. The emission intensity of ZnO nanoparticles was found to be enhanced after annealing, but it was highly dependent on the annealing conditions. Optimal annealing conditions both in air and vacuum were obtained for achieving maximum emission intensity in the ZnO nanoparticles. The dependence of PL properties of the ZnO nanoparticles on the annealing conditions was discussed.     

Application of heating microscopy to the study of thermal behaviour of ZnO–P2O5–WO3 glasses

The effect of WO₃ on thermal behaviour and thermal stability of ZnO–P₂O₅–WO₃ glasses prepared in compositional series (100 ? x)[0.5ZnO–0.5P₂O₅] ? xWO₃ (x = 0–60) was investigated by heating microscopy and the results were correlated with the results determined by conventional thermodilatometry and differential thermal analysis. Thermoanalytical studies showed that the glass transformation temperature and dilatation softening temperature increase with increasing WO₃ content while thermal expansion coefficient decreases. The highest stability towards crystallization possess glasses containing 20–30 mol% WO₃. Major compounds formed by the crystallization of the glasses were Zn(PO₃)₂, WO₃ and W₁₈P₂O₅₉. The values of sphere temperature, hemisphere temperature and flow temperature obtained using heating microscopy were strongly influenced by the degree of crystallization process at the sintering.     

The Thermal Synthesis of the ZnO–Bi2O3 Pigments

A zinc oxide pigment with an admixture of bismut oxide has been prepared as new yellow pigment for colouring of plastics and paints. The effect of the Bi₂ O₃ in the starting mixture on the colour hue of the pigment has been evaluated. The calcination conditions of the pigment synthesis have been established. The synthesis of these pigments was followed by thermal analysis using a derivatograph apparatus in our laboratory. The optimum conditions for the synthesis of pigments and the properties of the products have been estimated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of calcination temperature on the photocatalytic property of Fe–Cu–ZnO/graphene under visible light irradiation

Fe–Cu–ZnO/graphene composites are prepared by sol-gel method. The influence of the calcination temperature on the catalytic performance of Fe–Cu–ZnO/graphene composites has been studied and their physicochemical properties are characterized via X-ray diffraction (XRD), fourier transform infrared spectrometer (FTIR), scanning electron microscopy (SEM), thermogravimetry-differential scanning calorimetry (TG-DSC) and UV-Vis diffuse reflectance spectra (UV–Vis–DRS). The results show that Fe–Cu–ZnO/graphene composite calcined at 400°C exhibits the highest photocatalytic activity and the degradation rate of dark green dye in aqueous medium achieves 99.28% under exposure of visible light irradiation. The zinc species in the catalyst calcined at 400°C are all converted to the hexagonal wurtzite structures, and Cu²⁺ and Fe³⁺ are substituted ions in Zn²⁺ sites or incorporated into interstitial sites in the ZnO lattice which broaden the spectral response range to visible light. Meanwhile, the electrical properties of graphene are excellent which contribute to the enhanced charge carrier separation, extended light absorption, and increased surface hydroxyl groups. In addition, the catalyst is found to be relatively high reusable.     

Preparation of thiazolidin-4-one derivatives using ZnO–NiO–NiFe2O4 nano-composite system

The hydrothermal synthesis of ZnO–NiO–NiFe₂O₄ nano-composite is reported. The sample was utilized to characterize via XRD, FE-SEM, EDS, FT-IR, UV–Vis, and BET techniques. The sample consisted of three different phases as ZnO (hexagonal), NiO (cubic), and NiFe₂O₄ (cubic) with the average particle size as 34 nm and specific surface area, average pore diameter, and pore volume as 64.35 m² g^?1, 13.02 nm, and 0.201 cm³ g^?1, respectively. Catalytic behavior of the nano-composite was investigated on the synthesis of thiazolidin-4-one derivatives under thermal and ultrasonic irradiation condition. Our results show that the catalytic activity of ZnO–NiO–NiFe₂O₄ nano-composite is much higher than ZnO, NiO, and NiFe₂O₄ metal oxides. All products were prepared in high yields with short reaction times. In addition, the catalyst was recovered for at least five times.

     

Reinvestigation of Phase Equilibria in the V2O5–ZnO System

A diagram of phase equilibria established in a two-component oxide system V_{2 5}–ZnO has been worked out applying differential thermal analysis and X-ray phase analysis as well as depending on investigations carried out with the aid of high-temperature X-ray attachment and scanning electron microscope linked to an X-ray microanalyser. This revised version was published online in July 2006 with corrections to the Cover Date.     

Orientation degree dependence of magnetic properties of Co doped ZnO thin films by sol–gel process

Co-doped ZnO films were successfully fabricated on Si substrates by sol–gel process. The effects of Co concentration and preheating temperature on the structure and magnetic properties of the Zn_1−x Co _x O films were systematically studied. The results revealed that the films were highly c-axis oriented and contained no impurity phase. With preheating temperature increasing, the orientation degree of the films decreased. When the Co concentration and oxygen vacancy of the films are almost changeless, the enhancement of ferromagnetism in films originates from the orientation degree of the films increasing.     

I-V Characteristics of ZnO?ZnO contact during oxygen adsorption

The adsorption of oxygen on ZnO has been studied by observing the nonohmic characteristics of contacted ZnO crystals. When the sample assembly was evacuated at 773 K, there was a negative peak at the bias of 10 mV in the(I-kV) vs. V plot. When the assembly was exposed to oxygen at 298–573 K, the mean conductivity decreased and a negative peak at the bias of 50–230 mV was found in the(I-kV) vs. V plot. To analyze the experimental results, a simple model was developed assuming the contact to be of two semiconductor surfaces separated by a finite distance. From the experimental results and theoretical suggestions, we estimated the height of surface barrier during oxygen adsorption.     

Enhancement of cyanide photocatalytic degradation using sol–gel ZnO sensitized with cobalt phthalocyanine

In this work, the photodegradation of cyanide in aqueous suspension was used to determine the photocatalytic activity of sol–gel prepared ZnO which was impregnated with the Co (II) phthalocyanine (CoPc), as sensitizer. The prepared catalyst was characterized by Scanning Electron Microscopy (SEM) with Energy Dispersed Spectroscopy (EDS) detector, X-Ray Diffraction (XRD), Fourier Transform Infrared spectroscopy (FT-IR) and Diffuse UV–Vis Reflectance spectroscopy. Specific surface area was calculated from nitrogen adsorption isotherm using BET method. Compared with commercial ZnO and TiO₂ Degussa P25 photocatalysts, the sol–gel prepared ZnO catalyst sensitized with cobalt phthalocyanine showed the highest activities for degradation of cyanide in aqueous solution under visible light irradiation.     

Synthesis of ZnO nanobundles via Sol–Gel route and application to glucose biosensor

ZnO nanobundles were fabricated by Sol–Gel route. The as-prepared ZnO nanobundles were characterized by XRD, FE-SEM, TEM and PL. ZnO nanobundles structure are composed of many nanorods of about 80 nm in diameter and 0.6 μm in length. It showed weaker UV emission and stronger green emission. A glucose biosensor was constructed using these ZnO nanobundles as supporting materials for glucose oxidase (GO_X) loading by chitosan-assisted cross-linking technique. The biosensor exhibits a high affinity, high sensitivity, and fast response for glucose detection. These results demonstrate that zinc oxide nanostructures have potential applications in biosensors.     

Calcination temperature-dependent morphology of photocatalytic ZnO nanoparticles prepared by an electrochemical–thermal method

ZnO nanoparticles (NPs) with tunable morphologies were synthesized by a hybrid electrochemical–thermal method at different calcination temperatures without the use of any surfactant or template. The NPs were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction, dynamic light scattering, thermogravimetry–differential thermal analysis, scanning electron microscope and N₂ gas adsorption–desorption studies. The FT-IR spectra of ZnO NPs showed a band at 450 cm^?1, a characteristic of ZnO, which remained fairly unchanged at calcination temperatures even above 300 °C, indicating complete conversion of the precursor to ZnO. The products were thermally stable above 300 °C. The ZnO NPs were present in a hexagonal wurtzite phase and the crystallinity of ZnO increased with an increasing calcination temperature. The ZnO NPs calcined at lower temperature were mesoporous in nature. The surface areas of ZnO NPs calcined at 300 and 400 °C were 51.10 and 40.60 m² g^?1, respectively, which are significantly larger than commercial ZnO nanopowder. Surface diffusion has been found to be the key mechanism of sintering during heating from 300 to 700 °C with the activation energy of sintering as 8.33 kJ mol^?1. The photocatalytic activity of ZnO NPs calcined at different temperatures evaluated by photocatalytic degradation of methylene blue under sunlight showed strong dependence on the surface area of ZnO NPs. The ZnO NPs with high surface area showed enhanced photocatalytic activity.     

Improved photocatalytic degradation of reactive blue 81 using NiO-doped ZnO–ZrO2 nanoparticles

In this study, the photocatalytic degradation of Reactive Blue 81 (RB81) using synthesized NiO-doped ZnO–ZrO₂ nanoparticles under UV irradiation was investigated. Then, the products were characterized by Scanning electron microscope (SEM), X-ray diffraction (XRD), and diffuse reflectance spectroscopy (DRS). The removal rate of RB81 using ZnO–ZrO₂ after 180?min of irradiation was 96.7%. Nickel oxide (NiO) was used as an additive to ZnO–ZrO₂ for improvement of RB81 degradation via photocatalysis process. Photodegradation of RB81 was achieved to 100% using ZnO–ZrO₂–NiO nanoparticles with ratio of 1:2:0.3 after 180?min of irradiation. There was a red shift in absorption bands (from 410?nm to 435?nm) observed in increasing of NiO to ZnO–ZrO₂ nanoparticle, that it might lead to a higher photocatalytic activity under visible light. Response surface methodology (RSM) was used for optimization of experimental and these results were obtained: solution pH = 3, ZnO–ZrO₂–NiO dosage = 15?mg/L, and the initial RB81 concentration = 5?mg/L. The photodegredation of RB81 followed pseudo-first order kinetic according to the Langmuir–Hinshelwood model.     

Optical and structural characteristics of yttrium doped ZnO films using sol–gel technology

Yttrium-doped ZnO gel was spin-coated on the SiO₂/Si substrate. The as-prepared ZnO:Y (YZO) thin films then underwent a rapid thermal annealing (RTA) process conducted at various temperatures. The structural and photoluminescence characteristics of the YZO films were discussed thereafter. Our results indicated that the grain size of YZO thin films being treated with various annealing temperatures became smaller as compared to the ones without being doped with yttrium. Furthermore, unlike other ZnO films, the grains of YZO thin films appeared to separate from one another rather than aggregating together as both types of the films were annealed under the same environment. The photoluminescence characteristic measured showed that the UV emission was the only radiation obtained. However, the UV emission intensity of YZO thin film was much stronger than that of the ZnO thin film after annealing them with the same condition. It was also found that the intensity increased with an increase in the annealing temperature, which was caused by the exciton generated and the texture surface of the YZO thin film.     

Fabrication of surface-patterned ZnO thin films using sol–gel methods and nanoimprint lithography

Surface-patterned ZnO thin films were fabricated by direct imprinting on ZnO sol and subsequent annealing process. The polymer-based ZnO sols were deposited on various substrates for the nanoimprint lithography and converted to surface-patterned ZnO gel films during the thermal curing nanoimprint process. Finally, crystalline ZnO films were obtained by subsequent annealing of the patterned ZnO gel films. The optical characterization indicates that the surface patterning of ZnO thin films can lead to an enhanced transmittance. Large-scale ZnO thin films with different patterns can be fabricated by various easy-made ordered templates using this combination of sol–gel and nanoimprint lithography techniques.     

Enhanced superhydrophobicity of electrospun carbon nanofiber membranes by hydrothermal growth of ZnO nanorods for oil–water separation

Development of electrospun nanofiber membranes with the selective wettability characteristics for effectively separating oil–water mixtures is an extremely advisable strategy. In this study, a superhydrophobic electrospinning carbon nanofiber (F/ZnO/CNF) membrane was successfully prepared by electrospinning and in-situ growth of ZnO, and subsequent fluorination reaction with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (POTS). Benefiting from the influence of needle-like nanostructure and low surface energy, the as-prepared F/ZnO/CNF membrane shows excellent superhydrophobicity. When the growth duration of ZnO is 3 h, the obtained F/ZnO/CNF-3 membrane possesses outstanding water contact angle (WCA, 159.7°) and splendid oil–water separation efficiency (>99 %). Meanwhile, due to its the superior environmental stability the obtained F/ZnO/CNF-3 membrane exhibits excellent low and high temperature resistance, and enhanced resistance to various organic solvents in the face of a series of harsh environments.     

Effect of annealing temperature on the quality of Al-doped ZnO thin films prepared by sol–gel method

The different thermal expansion coefficients and lattice mismatch between ZnO and Al may produce residual stress in Al-ZnO (AZO) thin films. Annealing processes can be applied to modulate this residual stress. In this study, three different rapid thermal annealing (RTA) temperatures (350, 450, and 600 °C) were applied to an AZO thin film, prepared using sol–gel method. The mechanical properties, optical properties, and structure of the AZO thin film were investigated experimentally. The results show that increasing the RTA temperature increased the Young’s modulus and hardness of the films. The grain size of the films also increased with increasing RTA temperature. However, the film thickness and shear stress component decreased with increasing RTA temperature. Both compressive and tensile stress decreased gradually with increasing film thickness after RTA treatment. It was demonstrated that the use of a relatively high RTA temperature can effectively relax the residual stress in AZO thin films.