Showing papers on "Zinc published in 2005"

Enhanced Sintering of Yttrium‐Doped Barium Zirconate by Addition of ZnO

Abstract: The influence of transition metal oxides additives, especially zinc oxide, on the densification and electrical properties of doped barium zirconate have been examined. With the use of zinc oxide as a sintering aid, BaZr_(0.85)V_(0.15)O_(3-δ) was readily sintered to above 93% of theoretical density at 1300 degrees C. Scanning electron microscopic investigations showed Zn accumulation in the intergranular regions. Thermogravimetric analysis of the material under flowing CO_2 showed ZnO-modified barium zirconate to exhibit excellent chemical stability. The conductivity, as measured by A.C. impedance spectroscopy under H_2O saturated nitrogen, was slightly lower than that of unmodified barium zirconate. Electromotive force measurements under fuel cell conditions revealed the total ionic transport number to be ~0.9 at 600 degrees C. The combination of electrical and chemical properties and good sinterabifity render ZnO-modified barium zirconate an excellent candidate for reduced temperature solid oxide fuel cell applications.

Zinc Oxide Nanoparticles with Defects

Abstract: Zinc oxide in the form of nanoscale materials can be regarded as one of the most important semiconductor oxides at present. However, the question of how chemical defects influence the properties of nanoscale zinc oxide materials has seldom been addressed. In this paper, we report on the introduction of defects into nanoscale ZnO, their comprehensive analysis using a combination of techniques (powder X-ray diffraction (PXRD), X-ray absorption spectroscopy/extended X-ray absorption fine structure (XAS/EXAFS), electron paramagnetic resonance (EPR), magic-angle spinning nuclear magnetic resonance (MAS-NMR), Fourier-transform infrared (FTIR), UV-vis, and photoluminescence (PL) spectroscopies coupled with ab-initio calculations), and the investigation of correlations between the different types of defects. It is seen that defect-rich zinc oxide can be obtained under kinetically controlled conditions of ZnO formation. This is realized by the thermolysis of molecular, organometallic precursors in which ZnO is pre-organized on a molecular scale. It is seen that these precursors form ZnO at low temperatures far from thermodynamic equilibrium. The resulting nanocrystalline ZnO is rich in defects. Depending on conditions, ZnO of high microstructural strain, high content of oxygen vacancies, and particular content of heteroatom impurities can be obtained. It is shown how the mentioned defects influence the electronic properties of the semiconductor nanoparticles.

Solution-processed zinc oxide field-effect transistors based on self-assembly of colloidal nanorods.

Abstract: Colloidal zinc oxide (ZnO) nanocrystals are attractive candidates for a low-temperature and solution-processible semiconductor for high-performance thin-film field-effect transistors (TFTs). Here we show that by controlling the shape of the nanocrystals from spheres to rods the semiconducting properties of spin-coated ZnO films can be much improved as a result of increasing particle size and self-alignment of the nanorods along the substrate. Postdeposition hydrothermal growth in an aqueous zinc ion solution has been found to further enhance grain size and connectivity and improve device performance. TFT devices made from 65-nm-long and 10-nm-wide nanorods deposited by spin coating have been fabricated at moderate temperatures of 230 °C with mobilities of 0.61 cm2V-1s-1 and on/off ratios of 3 × 105 after postdeposition growth, which is comparable to the characteristics of TFTs fabricated by traditional sputtering methods.

Controlled growth of well-aligned ZnO nanorod array using a novel solution method.

Abstract: A simple method of synthesizing nanomaterials and the ability to control the size and position of them are crucial for fabricating nanodevices. In this work, we developed a novel ammonia aqueous solution method for growing well-aligned ZnO nanorod arrays on a silicon substrate. For ZnO nanorod growth, a thin zinc metal seed layer was deposited on a silicon substrate by thermal evaporation. Uniform ZnO nanorods were grown on the zinc-coated silicon substrate in aqueous solution containing zinc nitrate and ammonia water. The growth temperature was as low as 60−90 °C and a 4-in. wafer size scale up was possible. The morphology of a zinc metal seed layer, pH, growth temperature, and concentration of zinc salt in aqueous solution were important parameters to determine growth characteristics such as average diameters and lengths of ZnO nanorods. We could demonstrate the discrete controlled growth of ZnO nanorods using sequential, tailored growth steps. By combining our novel solution method and general photolit...

Efficient light harvesting by using green Zn-porphyrin-sensitized nanocrystalline TiO2 films.

Abstract: A series of novel zinc metalloporphyrins, cyano-3-(2‘-(5‘,10‘,15‘,20‘-tetraphenylporphyrinato zinc(II))yl)-acrylic acid (Zn-3), 3-(trans-2‘-(5‘,10‘,15‘,20‘-tetraphenylporphyrinato zinc(II))yl)-acrylic acid (Zn-5), 2-cyano-5-(2‘-(5‘,10‘,15‘,20‘-tetraphenylporphyrinato zinc(II))yl)-penta-2,4-dienoic acid (Zn-8), 4-(trans-2‘-(2‘ ‘-(5‘ ‘,10‘ ‘,15‘ ‘,20‘ ‘-tetraphenylporphyrinato zinc(II))yl)ethen-1‘-yl))-1,2-benzenedicarboxylic acid (Zn-11), and 2-cyano-3-[4‘-(trans-2‘ ‘-(2‘ ‘‘-(5‘ ‘‘,10‘ ‘‘,15‘ ‘‘,20‘ ‘‘-tetraphenylporphyrinato zinc(II))yl) ethen-1‘ ‘-yl)-phenyl]-acrylic acid (Zn-13) were synthesized and characterized by using various spectroscopic techniques. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations show that key molecular orbitals (MOs) of porphyrins Zn-5 and Zn-3 are stabilized and extended out onto the substituent by π-conjugation, causing enhancement and red shifts of visible transitions and increasing the possibility of electron transfer from the substituent. The porp...

Overall Water Splitting on (Ga1-xZnx)(N1-xOx) Solid Solution Photocatalyst: Relationship between Physical Properties and Photocatalytic Activity

Abstract: The physical and photocatalytic properties of a novel solid solution between GaN and ZnO, (Ga1-xZnx)(N1-xOx), are investigated. Nitridation of a mixture of Ga2O3 and ZnO at 1123 K for 5−30 h under NH3 flow results in the formation of a (Ga1-xZnx)(N1-xOx) solid solution with x = 0.05−0.22. With increasing nitridation time, the zinc and oxygen concentrations decrease due to reduction of ZnO and volatilization of zinc, and the crystallinity and band gap energy of the product increase. The highest activity for overall water splitting is obtained for (Ga1-xZnx)(N1-xOx) with x = 0.12 after nitridation for 15 h. The crystallinity of the catalyst is also found to increase with increasing the ratio of ZnO to Ga2O3 in the starting material, resulting in an increase in activity.

Composition/structural evolution and optical properties of ZnO/Zn nanoparticles by laser ablation in liquid media.

Abstract: We present composition-controlled synthesis of ZnO-Zn composite nanoparticles by laser ablation of a zinc metal target in pure water or in aqueous solution of sodium dodecyl sulfate (SDS). By SDS concentration, composition and size of the nanoparticles can be controlled in a wide range. Relative amounts of the components Zn and ZnO, the particle size, and the microstructure can evolve with SDS concentration in solution. High SDS concentration corresponds to high relative amount of Zn nanoparticles existing as the core in the core/ shell nanostructures, whereas low SDS concentration leads to high ZnO amount. This was explained by a dynamic mechanism on the basis of the competition between aqueous oxidation and SDS capping protection. Correspondingly, optical absorption spectra evolve from the excitonic peak of ZnO (about 350 nm) to the Zn surface plasmon resonance (about 242 nm) with rise of SDS concentration. A blue (about 450 nm) photoluminescence was observed in the obtained ZnO nanoparticles, which was attributed to existence of interstitial zinc in ZnO lattices. This study has revealed that laser ablation of active metal in liquid media is an appropriate method to synthesize a series of metal oxide semiconductor-metal composite nanoparticles with controlled composition and size.

Removal of Heavy Metals by Waste Tea Leaves from Aqueous Solution

Abstract: In this paper, tea leaves were shown to be an effective, low-cost biosorbent. Removal of lead, iron, zinc and nickel from 20 mg/L metal solution by dried biomass of waste tea leaves amounted to 96, 91, 72 and 58 %, respectively, at equilibrium, which followed Langmuir and Freundlich adsorption isotherms. Adsorption of metal was in the order of Pb > Fe > Zn > Ni from 5-100 mg/L of metal solution. From a multi-metallic mixture, 92.5, 84 and 73.2 % of lead, iron and zinc, respectively, were removed. Fourier transform infrared (FTIR) studies indicated that the carboxyl group was involved in the binding of lead and iron, whereas the amine group was involved in the binding of nickel and zinc. A flow through sorption column packed with dried biomass demonstrated a sorption capacity of 73 mg Pb/g of biomass, indicating its potential in cleaning metal containing wastewater. The metal laden biomass obtained could be disposed off by incineration.

Sol-Gel Preparation of Transparent and Conductive Aluminum-Doped Zinc Oxide Films with Highly Preferential Crystal Orientation

Abstract: Transparent aluminum-doped zinc oxide (ZnO) films were prepared via the sol-gel method on silica-glass substrates from 2-methoxyethanol solutions of zinc acetate and aluminum chloride that contained monoethanolamine. Dip coating was conducted at room temperature, with substrate withdrawal rates of 1.2-7.0 cm/min. After each deposition, the films were heat-treated in air at 200°-450°C for 10 min (pre-heat-treatment). After six to fourteen layers had been deposited, the films were then subjected to annealing in air at 500°-800°C for 1 h (the first post-heat-treatment), followed by annealing in nitrogen at 500°-700°C for 15 min to 4 h (the second post-heat-treatment). All the films obtained were transparent and showed only an extremely sharp ZnO (002) peak in the X-ray diffractometry (XRD) patterns. The effects of the aluminum content, the substrate withdrawal speed, and the heat-treatment conditions on the electrical resistivity of the films were studied. All these factors strongly affected the resistivity. The lowest resistivity value (6.5 10-3 Omegacm) was achieved in a film that contained 0.5 at.% aluminum, prepared with a low substrate withdrawal speed (1.2 cm/min), and a pre-heat-treatment of individual layer at 400°C in air and a post-heat-treatment of the entire film at 600°C in air, followed by a post-heat-treatment at 600°C in nitrogen. These preparation parameters also affected the degree of crystal orientation, which was revealed by the intensity of the ZnO (002) XRD peak. Higher crystal orientation was effective in reducing the film resistivity, whereas the higher grain-packing density and possible aluminum segregation were thought to have positive and negative effects, respectively, in reducing the resistivity.

Optical Properties of Zinc Aluminate, Zinc Gallate, and Zinc Aluminogallate Spinels

Abstract: The optical spectra of zinc aluminate (ZnAl2O4), zinc gallate (ZnGa2O4), and zinc aluminogallate (ZnAlGaO4) spinel powders were studied at wavelengths in the range of 250-900 nm using reflectance spectroscopy. The ZnAl2O4 and ZnGa2O4 powders were synthesized by using conventional ceramic processing techniques and had systematic variations in the molar ratio of ZnO to M2O3 (M = Al or Ga). The cubic spinel crystal structure of each composition was confirmed via powder X-ray diffractometry. The ZnAl2O4 powders showed optical properties in the ultraviolet wavelength region and had combined characteristics that were similar to that of ZnO (wurtzite structure) and Al2O3 (corundum structure), which result from the similar local environments of the zinc and aluminum cations within the cubic spinel crystal structure. A mechanically induced optical absorption (optomechanical effect) in the ultraviolet wavelength region was also observed in ZnAl2O4. The ZnGa2O4 powder followed a similar behavior, with the exception that the optomechanical effect did not occur in the gallate. The ZnAlGaO4 showed optical spectra that were intermediate to that of the endpoint compositions.

Syntheses, crystal structures, and luminescent properties of three novel zinc coordination polymers with tetrazolyl ligands

Abstract: The syntheses and luminescent properties of three novel zinc coordination polymers containing tetrazolyl ligands are described. In situ [2+3] cycloaddition reactions of acetonitrile or p-tolylnitrile with sodium azide in the presence of Zn(ClO4)2 as a Lewis acid (Demko−Sharpless tetrazole synthesis method) under hydrothermal (solvothermal) reaction conditions gave [Zn(CH3CN4)2]3(H2O) (1) and [Zn(4-MPTZ)2] (3) [4-MPTZ = 5-(4-methylphenyl)tetrazole], respectively. On the other hand, [Zn(HCN4)2] (2) was obtained by directly reacting tetrazole with Zn(OAc)2 under hydrothermal reaction conditions. The structure of 1 shows a super-diamond-like topological network with a diamond subunit as a connecting node. For 2, a diamond-like topological network is also found, but it is 2-fold interpenetrated. The structure of 3 reveals a 2D layered network with a hexagonal net, with the adjacent layers in the network stacked in an ABAB sequence. Photoluminescence studies revealed coordination polymers 1, 2, and 3 exhibit st...

Changes in Zinc Speciation in Field Soil after Contamination with Zinc Oxide

Abstract: Recent studies on the speciation of Zn in contaminated soils confirmed the formation of Zn-layered double hydroxide (LDH) and Zn−phyllosilicate phases. However, no information on the kinetics of th...

Solvent hydrolysis and templating effects in the synthesis of metal-organic frameworks

Abstract: Hydrolysis of the DMF or DEF solvent influences the nature of the product observed in the reaction between zinc(II) nitrate and 1,4-benzenedicarboxylic acid, with dialkylammonium cations able to template the formation of anionic networks.

On the formation and stability of p-type conductivity in nitrogen-doped zinc oxide

Abstract: The behavior of nitrogen in ZnO thin films grown by high-vacuum plasma-assisted chemical vapor deposition is examined. Highly oriented (002) films doped with 0–2at.% N were characterized by x-ray photoelectron spectroscopy, x-ray diffraction (XRD), Seebeck, and Hall measurements. XRD measurements revealed that the zinc oxide lattice constant decreased systematically with nitrogen doping. The as-deposited films were p-type at high doping levels, as confirmed by both Seebeck and Hall measurements. However, it was observed that hole conduction decreased and films reverted to n-type conductivity in a period of several days. This change was accompanied by a simultaneous increase in the lattice constant. The transient electrical behavior may be explained by compensation caused either by hydrogen donors or through defect formation processes common to analogous II-VI semiconductors.

The Micromolar Zinc-Binding Domain on the NMDA Receptor Subunit NR2B

Abstract: Eukaryotic ionotropic glutamate receptor subunits possess a large N-terminal domain (NTD) distinct from the neighboring agonist-binding domain. In NMDA receptors, the NTDs of NR2A and NR2B form modulatory domains binding allosteric inhibitors. Despite a high sequence homology, these two domains have been shown to bind two ligands of strikingly different chemical nature. Whereas the NTD of NR2A binds zinc with high (nanomolar) affinity, the NTD of NR2B binds the synthetic neuroprotectant ifenprodil and its derivatives. Using both NTD-mutated/deleted receptors and isolated NTDs, we now show that the NTD of NR2B, in contrast to NR2C and NR2D, also binds zinc, but with a lower affinity. Furthermore, we present evidence that zinc and ifenprodil compete for an overlapping binding site. This modulatory binding site accounts for the submicromolar zinc inhibition of NR1/NR2B receptors. Given that zinc is accumulated and released at many glutamatergic synapses in the CNS, these findings suggest that zinc is the endogenous ligand of the NTD of both NR2A and NR2B, the two major NR2 subunits. Thus, NMDA receptors contain zinc sensors capable of detecting extracellular zinc over a wide concentration range depending on their NR2 subunit composition. The coexistence of subunit-specific zinc-binding sites of high (nanomolar) and low (micromolar) affinity on NMDA receptors raises the possibility that zinc exerts both a tonic and a phasic control of membrane excitability.

Prediction of Zinc, Cadmium, Lead, and Copper Availability to Wheat in Contaminated Soils Using Chemical Speciation, Diffusive Gradients in Thin Films, Extraction, and Isotopic Dilution Techniques

Abstract: To predict the availability of metals to plants, it is important to understand both solution- and solid-phase processes in the soil, including the kinetics of metal release from its binding agent (ligand and/or particle). The present study examined the speciation and availability of Zn, Cd, Pb, and Cu in a range of well-equilibrated metal-contaminated soils from diverse sources using several techniques as a basis for predicting metal uptake by plants. Wheat (Triticum aestivum L.) was grown in 13 metal-contaminated soils and metal tissue concentrations (Zn, Cd, Pb, and Cu) in plant shoots were compared with total soil metal concentrations, total soluble metal, and free metal activities (pM2+) in soil pore waters, 0.01 M CaCl2–extractable metal concentrations, E values measured by isotope dilution, and effective metal concentrations, CE, measured by diffusive gradients in thin films (DGT). In the DGT technique, ions are dynamically removed by their diffusion through a gel to a binding resin, while E values represent the isotopically exchangeable (labile) metal pools. Free metal activities (Zn2+, Cd2+, and Pb2+) in soil pore waters were determined using a Donnan dialysis technique. Plant Zn and Cd concentrations were highly related to CE, while relationships for Zn and Cd with respect to the other measures of metals in the soils were generally lower, except for CaCl2–extractable Cd. These results suggest that the kinetically labile solid-phase pool of metal, which is included in the DGT measurement, played an important role in Zn and Cd uptake by wheat along with the labile metal in soil solution. Plant Pb concentrations were highly related to both soil pore water concentrations and CE, indicating that supply from the solid phase may not be so important for Pb. Predictions of Cu uptake by wheat from these soils by the various measures of Cu were generally poor, except surprisingly for total Cu.

On the nature of T(Al2Mg3Zn3) and S(Al2CuMg) phases present in as-cast and annealed 7055 aluminum alloy

Abstract: Aluminum alloys, encompassed by AA 7055 alloy composition, having the nominal zinc content (i.e. 8 wt.%) but varying copper and magnesium contents across the alloy composition range were examined in the as-cast form by a combination of light microscopy, scanning electron microscopy (SEM), electron probe micro analysis (EPMA) and X-ray diffraction (XRD). It is observed that for all compositions, the second phases based on η(MgZn2), T(Al2Mg3Zn3) and S(Al2CuMg) are present. The T phase dissolves copper up to 28 wt.%, whilst the S phase shows metastable solubility of zinc that may range up to 30 wt.%. In alloys with magnesium at the lower limit and the copper contents approaching the upper limit of the alloy composition, the θ phase (Al2Cu) of the constituent binary Al–Cu system is further observed. The θ phase (Al2Cu) does not dissolve either zinc or magnesium. Below the nominal composition, the alloys could be homogenized substantially using a commercially viable homogenization treatment leaving small amounts of undissolved S phase that does not contain any zinc.

Improving zinc efficiency of cereals under zinc deficiency

Abstract: One of the widest ranging abiotic stresses in world agriculture arises from low zinc (Zn) availability in calcareous soils, particularly in cereals. Cereal species greatly differ in their zinc effici ency (ZE), defined in this article as the ability of a plant to grow and yield well under Zn deficiency. ZE has been attributed mainly to the effi - ciency of acquisition of Zn under conditions of low soil Zn availability rather than to its utilization or (re)-translocation within a plant. A higher Zn acquisition efficiency, further, may be due to either or all of the following: an efficient ionic Zn uptake system, better root architecture, i.e. long and fine roots with architecture favouring exploitation of Zn from larger soil volume, higher synthesis and release of Zn-mobilizing phytosiderophore by the roots and uptake of Zn-phytosiderophore complex. Seed Zn content has also been suggested to affect ZE. This article attempts to examine critically the scanty and scattered reports available on the status of Zn defi ciency globally; morphological, biochemical and physiological basis of regulation of ZE in cereals and approaches to improve ZE in terms of grain productivity and grain Zn vis-a-vis its bioavailability under conditions of poor Zn availability. A causal relationship between important Zn-containing enzymes, viz. carbonic anhydrase (CA), Cu/Zn-superoxide dismutase (SOD) activities and ZE is reported in wheat and other cereal species. Enhanced production and release of Fe-mobilizing phytometallophores known as phytosiderophores (PS), is another mech anism relevant for cereal species in adaptation to zinc deficiency.