L. El Mir

ZnO:Ca nanopowders with enhanced CO2 sensing properties

Calcium doped ZnO (CZO) nanopowders with [Ca]/[Zn] atomic ratios of 0, 0.01, 0.03 and 0.05 were prepared via a sol-gel route and characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy (FT-IR). Characterization data showed that undoped and Ca-doped ZnO samples have a hexagonal wurtzite structure with a slight distortion of the ZnO lattice and no extra secondary phases, suggesting the substitution of Ca ions in the ZnO structure.Chemo-resistive devices based on a thick layer of the synthesized CZO nanoparticles were fabricated and their electrical and sensing properties towards CO2 were investigated. Sensing tests have demonstrated that Ca loading is the key factor in modulating the electrical properties and strongly improving the response of ZnO matrix towards CO2. An increased CO2 adsorption with Ca loading has been also evidenced by FT-IR, providing the basis for the formulation of a plausible mechanism for CO2 sensing operating on these sensors.

Sol–gel synthesis, structural, optical and magnetic properties of Co-doped ZnO nanoparticles

Abstract We report the synthesis of Zn1−xCoxO nanoparticles prepared by a sol–gel processing technique for x ranging from 0 to 0.05. The structural, morphological, optical and magnetic properties of the as-prepared nanoparticles were investigated by XRD, XPS, transmission electron microscopy, UV measurements, photoluminescence and superconducting quantum interference device. The structural properties showed that the obtained nanoparticles are single phase wurtzite structure and no secondary phases were detected which indicated that Co ions substituted for Zn ions. The energy gap decreased gradually with increasing doping concentration of Co. The photoluminescence spectra show a shift of the position of the ultraviolet emission to long wavelength and the intensity decreases with increasing Co. The Magnetic measurements at room temperature reveal diamagnetic behavior for sample with lower concentration and the presence of both paramagnetic and ferromagnetic behavior for increasing concentration.

Synthesis of Co-doped ZnO nanoparticles by sol–gel method and its characterization

AbstractCobalt doped ZnO nanoparticles with different Co contents have been synthesized by a sol–gel processing technique. In our approach, the water for hydrolysis was slowly released by esterification reaction followed by a supercritical drying in ethyl alcohol. The structural, morphological, optical and magnetic properties of the as-prepared nanoparticles were investigated by XRD, transmission electron microscopy, UV measurements, photoluminescence and superconducting quantum interference device. The structural properties showed that the obtained nanoparticles are in wurtzite single crystalline phase and no secondary phases were detected which indicated that Co substituted Zn ions. The energy band gap of the ZnO host matrix decreases gradually by increasing the doping concentration. The photoluminescence spectra exhibit intensive emission in the UV range. This emission presents a small shift to longer wavelengths and remarkable decreases in the intensity with increasing Co content. The Magnetic measurements at room temperature reveal diamagnetic behavior for the samples with lower doping concentrations; however, at higher Co content, we noted the presence of both paramagnetic and ferromagnetic behaviors.

Gas sensing properties of Al-doped ZnO for UV-activated CO detection

Al-doped ZnO (AZO) samples were prepared using a modified sol–gel route and charaterized by means of trasmission electron microscopy, x-ray diffraction and photoluminescence analysis. Resistive planar devices based on thick films of AZO deposited on interdigitated alumina substrates were fabricated and investigated as UV light activated CO sensors. CO sensing tests were performed in both dark and illumination condition by exposing the samples to UV radiation (λ = 400 nm).Under UV light, Al-doped ZnO gas sensors operated at lower temperature than in dark. Furthermore, by photoactivation we also promoted CO sensitivity and made signal recovery of AZO sensors faster. Results demonstrate that Al-doped ZnO might be a promising sensing material for the detection of CO under UV illumination.

Effects of zinc oxide nanoparticles and/or zinc chloride on biochemical parameters and mineral levels in rat liver and kidney

The aim of this study was to assess the potential subacute toxicity of zinc oxide (ZnO) nanoparticles (NPs) in Wistar rats in comparison with reference toxicant, zinc chloride (ZnCl2), of a non-nanoparticulate form. We therefore studied the relationships between zinc (Zn) accumulation, liver and kidney trace element levels, and plasmatic biochemical parameters. Rats in all groups were treated by intraperitoneal injection of ZnO NPs and/or ZnCl2 solution (25 mg/kg) every other day for 10 days. The contents of trace element in the liver and kidney were slightly modulated after ZnO NPs and/or ZnCl2 solution exposure. The same treatment increased the aspartate aminotransferase activity and uric acid concentration. However, ZnO NPs or ZnCl2 solution decreased the creatinine levels, whereas the combined intake of ZnO NPs and ZnCl2 decreased the glucose concentration. Interestingly, the analysis of the lyophilized powder of liver using the x-ray diffractometer showed the degradation of ZnO NPs in ZnO-treated group, instead there is a lack of NPs ZnO biosynthesis from the ZnCl2 solution injected in rats. These investigations suggest that combined injection of ZnO NPs and ZnCl2 solution has a possible toxic effect in rats. This effect could be related to Zn2+ ion release and accumulation of this element in organs. Our findings provide crucial information that ZnO appeared to be absorbed in the organs in an ionic form rather than in a particulate form.

Excellent CO gas sensor based on Ga-doped ZnO nanoparticles

AbstractSol–gel technique was utilized to prepare pure and Ga-doped ZnO nanopowders. To investigate the morphological and microstructural properties, transmission electron microscopy analysis and X-ray powder diffraction have been used. From microstructure analysis we showed that pure and Ga-doped ZnO nanoparticles were polycrystalline, and exhibited hexagonal wurtzite structure. Chemoresistive devices consisting of a thick layer of synthesized nanoparticles on interdigitated alumina substrates have been fabricated and their electrical and sensing characteristics were investigated. The sensor performances of the samples for carbon monoxide (CO) were reported. The results indicated that doped sensor exhibited higher response and quick response/recovery dynamics compared to a ZnO-based sensor. These interesting sensing properties were discussed on the basis of the characterization data were reported.

Synthesis and characterisation of electrical conducting nanoporous carbon structures based on pyrogallol-formaldehyde

Electrical conducting carbon (ECC) nanoporous structures were explored by changing the pyrolysis temperature of organic xerogel compounds prepared by sol-gel method from pyrogallol-formaldehyde (PF) mixture in water using picric acid as catalyst. The effect of these preparation parameters on the structural and electrical properties of the obtained ECCs was studied. The obtained results revealed that, the polymeric insulating xerogel phase was transformed progressively with pyrolysis temperature into carbon conducting phase. The temperature-dependent conductivity of the ECC structures show a semiconducting behaviour and the I(V) characteristics present a negative differential resistance.

Effect of Ca-doping on microstructure and photocatalytic activity of ZnO nanoparticles synthesized by sol gel method

Abstract We report the synthesis of Zn1−xCaxO nanoparticles prepared by a sol–gel processing technique for x ranging from 0 to 0.05. The structural, morphological and optical properties of the nanoparticles were investigated by X-ray diffraction, transition electron microscopy, UV measurements, and photoluminescence spectroscopy. The photoactivity of the Ca-doping ZnO photocatalysts was evaluated by the photocatalytic degradation of methylene blue dye. The structural properties showed that the obtained nanoparticles are in wurtzite single crystalline phase and no secondary phases were detected which indicated that Ca substituted Zn ions. The absorption edge of the prepared photocatalysts is clearly shifted to the visible region as compared to undoped ZnO. The study of the effect of Ca loading on the photocatalytic activity shows that the Zn0.96Ca0.04O is the most photoactive. The effect of some parameters such as catalyst loading, initial dye concentration and light intensity were investigated.

Nanoporous activated carbon for fast uptake of heavy metals from aqueous solution

AbstractA novel nanoporous activated carbon (NAC), based on organic xerogel compounds, was prepared at 650°C pyrolysis temperature by sol–gel method from pyrogallol and formaldehyde (PF-650) mixtures in water using perchloric acid as catalyst. The performance of NAC was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen porosimetry. The metal uptake characteristics were explored using well-established and effective parameters including pH, contact time, initial metal ion concentration, and temperature. Optimum adsorptions of Co2+ and Cd2+ were observed at pH 6.0 and 7.0, respectively. Langmuir model gave a better fit than the other models, and kinetic studies revealed that the adsorption is fast and its data are well fitted by the pseudo-second-order kinetic model and thermodynamic properties, i.e. ΔG°, ΔH°, and ΔS°, showed that adsorption of Co2+ and Cd2+ onto NAC was endothermic, spontaneous, and feasible in the temperature range of 300–328 K.

Graphene Oxide/Poly(3-hexylthiophene) Nanocomposite Thin-Film Phototransistor for Logic Circuit Applications

Graphene is a sheet-structured material that lacks a forbidden band, being a good candidate for use in radiofrequency applications. We have elaborated graphene-oxide-doped poly(3-hexylthiophene) nanocomposite to increase the interlayer distance and thereby open a large bandgap for use in the field of logic circuits. Graphene oxide/poly(3-hexylthiophene) (GO/P3HT) nanocomposite thin-film transistors (TFTs) were fabricated on silicon oxide substrate by spin coating method. The current–voltage (I–V) characteristics of TFTs with various P3HT compositions were studied in the dark and under light illumination. The photocurrent, charge carrier mobility, subthreshold voltage, density of interface states, density of occupied states, and ION/IOFF ratio of the devices strongly depended on the P3HT weight ratio in the composite. The effects of white-light illumination on the electrical parameters of the transistors were investigated. The results indicated that GO/P3HT nanocomposite thin-film transistors have high potential for use in radiofrequency applications, and their feasibility for use in digital applications has been demonstrated.