Kinetics of the carbothermic reduction of zinc sulfide in the presence of calcium oxide

The kinetics of the carbothermic reduction of zinc sulfide in the presence of calcium oxide has been investigated by atomic absorption spectroscopy (AAS) and thermogravimetric analysis system (TGA). Experimental results indicated that the rate of zinc yield could be increased by increasing the argon flow rate, the reaction temperature, the initial molar ratio of C/ZnS, or the initial molar ratio of CaO/ZnS. Furthermore, the rate was also found to increase with decrease in the sample height, the size of carbon aggregate or the initial bulk density. Based on these experimental data, an empirical rate equation of zinc yield has been formulated.     

Nonlinear growth of zinc tin oxide thin films prepared by atomic layer deposition

Zinc tin oxide (ZTO) thin films can be deposited by atomic layer deposition (ALD) with adjustable electrical, optical and structural properties. However, the ternary ALD processes usually suffer from low growth rate and difficulty in controlling film thickness and elemental composition, due to the interaction of ZnO and SnO₂ processes. In this work, ZTO thin films with different Sn levels are prepared by ALD super cycles using diethylzinc, tetrakis(dimethylamido)tin, and water. It is observed that both the film growth rate and atom composition show nonlinear variation versus [Sn]/([Sn]+[Zn]) cycle ratio. The experimental thickness measured by spectroscopic ellipsometry and X-ray reflectivity are much lower than the expected thickness linearly interpolated from pure ZnO and SnO_x films. The [Sn]/([Sn]+[Zn]) atom ratios estimated by X-ray photoelectron spectroscopy have higher values than that expected from the cycle ratios. Hence, to characterize the film growth behavior versus cycle ratio, a numerical method is proposed by simulating the effect of reduced density and reactivity of surface hydroxyls and surface etching reactions. The structure, electrical and optical properties of ZTO with different Sn levels are also examined by X-ray diffraction, atomic force microscope, Hall measurements and ultraviolet–visible–infrared transmittance spectroscopy. The ZTO turns out to be transparent nanocrystalline or amorphous films with smooth surface. With more Sn contents, the film resistivity gets higher (>1 Ω cm) and the optical bandgap rises from 3.47 to 3.83 eV.     

Removal of malachite green from aqueous solution by zinc oxide nanoparticle loaded on activated carbon: Kinetics and isotherm study

In this research, a novel adsorbent, zinc oxide nanoparticle loaded on activated carbon (ZnO-NP-AC) was synthesized by a simple, low cost and efficient procedure. Subsequently, this novel material was characterizated and identified by different techniques such as Brunauer, Emmett and Teller (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) analysis. Unique properties such as high surface area (>603 m²/g) and low pore size (<61 Å) and average particle size lower than 100 Å in addition to high reactive atom and presence of various functional groups make it possible for efficient removal of malachite green (MG). In batch experimental set-up, optimum conditions for quantitative removal of MG by ZnO-NP-AC was attained following searching effect of variables such as adsorbent dosage, initial dye concentration and pH. Optimum values were set as pH of 7.0, 0.015 g of ZnO-NP-AC at removal time of 15 min. Kinetic studies at various adsorbent dosage and initial MG concentration show that maximum MG removal was achieved within 15 min of the start of every experiment at most conditions. The adsorption of MG follows the pseudo-second-order rate equation in addition to interparticle diffusion model (with removal more than 95%) at all conditions. Equilibrium data fitted well with the Langmuir model at all amount of adsorbent, while maximum adsorption capacity was 322.58 mg g⁻¹ for 0.005 g of ZnO-NP-AC.     

Kinetics of sunflower oil methanolysis catalyzed by calcium oxide

The methanolysis of sunflower oil was studied in the presence of CaO previously calcined at various temperatures and the optimal temperature for CaO calcination was determined. The sigmoidal process kinetics was explained by the initial triglyceride (TG) mass transfer controlled region, followed by the chemical reaction controlled region in the latter reaction period. The TG mass transfer limitation was due to the small available active specific catalyst surface, which was mainly covered by adsorbed molecules of methanol. In the later phase, the adsorbed methanol concentration decreased, causing the increase of both the available active specific catalyst surface and the TG mass transfer rate, and the chemical reaction rate become smaller than the TG mass transfer rate.     

Relative yield and zinc uptake by rice from zinc sulphate and zinc oxide coatings onto urea

Zinc (Zn) deficiency is prevalent worldwide and is a barrier to achieving yield goals in crops. It is also now recognized as a leading risk factor for disease in humans in developing countries. In general, soil application of 5–17 kg of Zn ha⁻¹ year⁻¹ as zinc sulphate (ZnSO₄) or more is recommended. However, in developing rice growing countries of Asia, ZnSO₄ of desired quality is not readily available and is also quite expensive, so the farmers generally fail to apply Zn, resulting in rice crop yield loss. Availability of Zn-coated urea guarantees not only the availability of quality Zn but also ensures its application. Field experiments were therefore conducted during the rice seasons of 2005 and 2006 at the Indian Agricultural Research Institute, New Delhi, to evaluate the relative efficiency of 0.5, 1.0, 1.5 and 2.0% Zn as ZnSO₄- or zinc oxide (ZnO)-coated ureas for rice. Soil application of ZnSO₄ was also compared in 2006. Rice grain and straw yields, Zn concentrations in grain and straw, and Zn uptake by rice increased with the level of Zn coating onto urea. Crop response was the highest with 2.0% ZnSO₄-coated urea, and higher than with the same rate of ZnO-coated urea, possibly related to the higher water solubility of Zn in ZnSO₄. Crop response with ZnSO₄-coated urea was also higher than with the same rate of ZnSO₄ and urea applied separately to the soil. However, apparent recovery data suggest that 1.0% coating with ZnSO₄ may be a better choice from the point of view of the utilization of applied Zn. Increased Zn concentrations in rice grain due to application of Zn-coated urea is important from the point of view of Zn nutrition of humans, since rice is the staple food in developing countries of Asia. Also, increased Zn concentrations in rice straw is of importance as regards cattle nutrition since in developing countries of Asia rice straw is the major feed for farm cattle.     

Modulating self-biased near-UV photodetection of Gd-doped bismuth ferrite ceramics by introducing zinc oxide as electron transport layer

ZnO semiconductor offers many advantages as an electron transport layer (ETL) in photovoltaic-based devices, including high charge carrier mobility and hole-blocking ability. In this work, ZnO thin film is introduced as an ETL between (Bi_0.93Gd_0.07)FeO₃ (BFO7Gd) ferroelectric and ITO thin film to form ITO/ZnO/BFO7Gd/Au heterostructure. The device with the ETL exhibited a superior photoresponsivity than the one without ETL, reaching ～32% enhancement. Furthermore, a subsequent E-field poling on the ITO/ZnO/BFO7Gd/Au heterostructure resulted in an additional ～25% increase in photoresponsivity. The enhancement is mainly attributed to two factors: (1) high electron mobility and lower recombination rate resulting from the introduction of ZnO ETL, and (2) efficient charge separation facilitated by the polarization-driven internal E field that superimposes with the interfacial built-in E fields. The introduction of ZnO ETL and the utilization of the ferroelectric polarization prove to be an alternative route to further modulate the photosensing performance of BiFeO₃-based near-UV photodetectors.     

Seedless growth of zinc oxide flower-shaped structures on multilayer graphene by electrochemical deposition

A seedless growth of zinc oxide (ZnO) structures on multilayer (ML) graphene by electrochemical deposition without any pre-deposited ZnO seed layer or metal catalyst was studied. A high density of a mixture of vertically aligned/non-aligned ZnO rods and flower-shaped structures was obtained. ML graphene seems to generate the formation of flower-shaped structures due to the stacking boundaries. The nucleation of ZnO seems to be promoted at the stacking edges of ML graphene with the increase of applied current density, resulting in the formation of flower-shaped structures. The diameters of the rods/flower-shaped structures also increase with the applied current density. ZnO rods/flower-shaped structures with high aspect ratio over 5.0 and good crystallinity were obtained at the applied current densities of −0.5 and −1.0 mA/cm². The growth mechanism was proposed. The growth involves the formation of ZnO nucleation below 80°C and the enhancement of the growth of vertically non-aligned rods and flower-shaped structures at 80°C. Such ZnO/graphene hybrid structure provides several potential applications in sensing devices.     

Seed/catalyst-free growth of zinc oxide nanostructures on multilayer graphene by thermal evaporation

We report the seed/catalyst-free growth of ZnO on multilayer graphene by thermal evaporation of Zn in the presence of O₂ gas. The effects of substrate temperatures were studied. The changes of morphologies were very significant where the grown ZnO structures show three different structures, i.e., nanoclusters, nanorods, and thin films at 600°C, 800°C, and 1,000°C, respectively. High-density vertically aligned ZnO nanorods comparable to other methods were obtained. A growth mechanism was proposed based on the obtained results. The ZnO/graphene hybrid structure provides several potential applications in electronics and optoelectronics.     

Relative efficiency of zinc oxide and zinc sulphate-enriched urea for spring wheat

Field experiments conducted at the Indian Agricultural Research Institute, New Delhi during 2005–2007 showed that the application of small amounts of zinc (Zn) in the form 0.5–2.0% of Zn-enriched urea significantly increased yield attributes, grain and straw yield, Zn concentrations in the grain and straw and Zn uptake by spring wheat. The agronomic and crop recovery efficiency of applied Zn decreased as the level of Zn-enrichment was increased from 0.5 to 2%. Zinc sulphate (ZnSO₄) and zinc oxide (ZnO) were equally effective in increasing the grain yield of wheat. Based on these results, we recommend the application of a 0.5–1.0% Zn enrichment of urea with ZnSO₄ or a 1.0% Zn-enrichment with ZnO.     

Tailoring zinc oxide nanowire architectures collectively by catalytic vapor-liquid-solid growth,catalyst-free vapor-solid growth,and low-temperature hydrothermal growth

We present a comprehensive study of the fabrication of zinc oxide (ZnO) nanowires (NWs) with tailored structural morphologies and functional features by utilizing three major growth methods based on vapor-liquid-solid (VLS), vapor-solid (VS), and hydrothermal growth mechanisms. The vertically aligned ZnO NW (ZNW) array can be constructed with tailored length, diameter, and density by controlled catalytic epitaxial VLS growth; the catalyst-free VS growth can create a hierarchical ZNW assembly onto complementary topological frameworks, such as transparent conducting oxides and carbon nanotubes; and the hydrothermal growth practically enables low-temperature growth of conformal ZNWs on large-area and flexible substrates. The growth mechanism and tailoring of the ZNW architectures for each growth strategy were investigated in detail, combined with rational analyses and parametric experiments. This study provides a critical route to the purposeful tailoring of ZNW architectures toward targeted ZnO-driven applications that require specific ZNW morphologies, assembly configurations, and substrate materials for many diverse fields including energy conversion and harvesting, electronics, photonics, and smart and wearable sensors.     

Diameter control of ultrathin zinc oxide nanofibers synthesized by electrospinning

Electrospinning is a versatile technique, which can be used to generate nanofibers from a rich variety of materials. We investigate the variation of a zinc oxide (ZnO)-polyvinylpyrrolidone (PVP) composite structure in morphology by electrospinning from a series of mixture solutions of ZnO sol–gel and PVP. Calcination conditions for the crystallization of ZnO nanofibers and removal of the PVP component from the ZnO-PVP composite nanofibers were also studied. The progression of the ZnO-PVP composite structure from grains to nanofibers was observed, and ZnO-PVP nanofibers as thin as 29.9 ± 0.8 nm on average were successfully fabricated. The size of the resultant ZnO-PVP composite nanofibers was considerably affected by two parameters: the concentrations of zinc acetate and PVP in the precursor solution. The concentration of zinc acetate particularly influenced the diameter distribution of the ZnO-PVP nanofibers. The ZnO-PVP nanofibers could be subsequently converted into ZnO nanofibers of a pure wurtzite phase via calcination in air at 500°C for 2 h.     

Fabrication and characterization of zinc oxide nanoparticle coated magnetic iron oxide: Effect of S-layers adsorption on surface of oxide

Mixed zinc oxide nanoparticle coated magnetic iron oxide has been prepared by a sol–gel and co-precipitation routes. Magnetic iron oxide nanoparticles were synthesized by co-precipitation of ferric and ferrous ions with ammonia, and then zinc oxide was coated onto the surface of magnetic iron oxide by hydrolysis of zinc precursors. As a result, zinc oxide coated magnetic iron oxide nanoparticles with an average size of 68 nm were obtained. The crystalline bacterial cell surface layer)S-layer (used in this study was isolated from Lactobacillus helveticus ATCC 12046. The S-layer was adsorbed onto the surface of zinc oxide nanoparticle coated magnetic iron oxide. The nanoparticles were analyzed by X-ray powder diffractometry (XRD), infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM) were used to characterize the structural and the chemical features of the nanocomposites. The infrared spectra indicate that the S-layer-nanoparticle interaction occurs. This novel nanoparticle showed admirable potential in adsorption of S-layers on the surface of oxides for drug delivery.     

A study of kinetic effects due to using microfibrous entrapped zinc oxide sorbents for hydrogen sulfide removal

A modified Amundson model was proposed to characterize breakthrough curves during gas phase desulfurization using fixed bed reactors. It contains two characteristic variables: saturation time (τ) and shape factor (lumped K). The model has been verified experimentally at . Combined with mass transfer correlations, the model was utilized to investigate kinetic influences due to using microfibrous entrapped sorbent (MFES) with high void volume fraction. Because of the utilization of nanosize ZnO grains supported on highly porous SiO₂ particles (100-), the intra-particle diffusion resistance of MFES was minimized resulting in a saturation capacity near the theoretical value. The microfibrous entrapment and the use of small sorbent particles enhanced the external mass transfer rate; the high void volume fraction reduced the capacity density resulting in increased overall lumped K. As a result, MFES demonstrated a longer breakthrough time, a sharper breakthrough curve, and higher ZnO utilization than ZnO extrudates tested at equivalent conditions. Moreover, MFES can be optimally used as a polishing layer at the downstream end of a packed bed to maximize the overall desulfurization performance.     

Effect of rapid thermal annealing on the properties of zinc tin oxide films prepared by plasma-enhanced atomic layer deposition

The effect of rapid thermal annealing treatments on the microstructure, surface morphology, and optical characteristics of zinc tin oxide (ZTO) films produced by plasma-enhanced atomic layer deposition was investigated. The ZTO films were annealed in oxygen atmosphere for 2 min at four selected temperatures from 500 to 800 °C. The X-ray diffraction showed that the annealing temperature has a great influence on the crystalline characteristics of ZTO films. The film shows complete amorphous structure for as-deposited ZTO film. Meanwhile, the spinel zinc stannate Zn₂SnO₄ was obtained for the samples annealed from 500 to 800 °C, which shows polycrystalline nature. The X-ray photoelectron spectroscopy proved that the annealing process in oxygen gas can effectively can reduce the oxygen vacancy defects in the films. In addition, the photoluminescence spectroscopy manifests an ultraviolet emission with a broad peak range from 345 to 385 nm. Moreover, the ultraviolet luminescence intensity increases continuously with the increase of annealing temperature. Spectroscopic ellipsometry analyses demonstrate that the refractive index of annealed films increases as the increase of annealing temperature, while the extinction coefficient decreases gradually with the increase of annealing temperature in the visible light range.     

Effects of power and temperature on the structural,anti-icing,wettability, and optical properties of zinc oxide thin films

Zinc oxide semiconductors have received significant research attention over the past decade owing to their diverse applications. In this paper, we report the development and characterisation of ZnO thin films prepared by radio-frequency (RF) magnetron sputtering. The optical, anti-icing, wettability, and structural properties of the films were investigated at various sputtering power levels and temperatures. With an increase in the power from 175 to 250 W, the ZnO thin films showed fine (002) structures. X-ray diffraction analysis of the coated thin films revealed a considerable increase in the (002) peak intensity along the c-axis with increasing power and temperature. Increasing the sputtering power from 175 to 250 W and the deposition temperature from 150 to 300 °C led to an increase in the average size of the grains from 10.548 to 13.151 nm and from 9.97 to 13.151 nm, respectively. The water contact angle possibly depends on the RF power and temperature employed for material deposition. Within the 350–800 nm range, the prepared films achieved optical transmissions of 92%–88%, refractive indices of 1.52–1.50, and band gaps of 3.28–3.24 eV. The anti-icing properties were also improved by adjusting the sputtering power and temperature during material deposition.     

Seed/catalyst-free vertical growth of high-density electrodeposited zinc oxide nanostructures on a single-layer graphene

We report the seed/catalyst-free vertical growth of high-density electrodeposited ZnO nanostructures on a single-layer graphene. The absence of hexamethylenetetramine (HMTA) and heat has resulted in the formation of nanoflake-like ZnO structure. The results show that HMTA and heat are needed to promote the formation of hexagonal ZnO nanostructures. The applied current density plays important role in inducing the growth of ZnO on graphene as well as in controlling the shape, size, and density of ZnO nanostructures. High density of vertically aligned ZnO nanorods comparable to other methods was obtained. The quality of the ZnO nanostructures also depended strongly on the applied current density. The growth mechanism was proposed. According to the growth timing chart, the growth seems to involve two stages which are the formation of ZnO nucleation and the enhancement of the vertical growth of nanorods. ZnO/graphene hybrid structure provides several potential applications in electronics and optoelectronics such as photovoltaic devices, sensing devices, optical devices, and photodetectors.     

Kinetics of nitrous oxide decomposition over Cu-ZSM-5

The kinetics of nitrous oxide decomposition on an overexchanged Cu-ZSM-5 catalyst were measured using a gradientless reactor. Isothermal oscillations of nitrous oxide and oxygen concentrations can be observed in a broad range of experimental conditions. A transition of the catalytic activity during oscillations is accompanied by a change in the oxygen content of the catalyst and by the formation of traces of nitric oxide. The presence of excess oxygen does not significantly alter the behaviour of the catalyst whereas NO concentrations as low as 10 ppm quench the oscillations in the whole temperature range studied (375 to 450°C), maintaining steady-state operation at maximum catalytic activity. Reaction rates in this ‘ignited’ state are first order with respect to nitrous oxide concentration and not affected by either oxygen or nitric oxide. At temperatures above 400°C, the observed reaction rates are influenced by pore diffusion effects. In the region of intrinsic kinetics, the temperature dependence of the first order rate constant can be described by an activation energy of ca. 100 kJ/mol.     

氧化锌主含量测定方法的改进

通过大量的实践,对氧化锌主含量的测定方法进行了改进:首先使锌星锌氨络离子状态与干扰元素分离,pH值由原方法的10变为6,并加入相应的缓冲溶液.指示剂由铬黑T改为二甲酚橙,使滴定终点更易掌握,测定结果更加准确。     

Photoluminescence of zinc oxide nanopowder synthesized by a combustion method

Zinc oxide (ZnO) nanopowder was synthesized by a simple and quick combustion method using zinc nitrate as a precursor and glycine as a fuel material. The starting materials were mixed at room temperature and spontaneous ignition of which resulted into the ZnO nanopowder. The synthesized nanopowder was characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM), Infrared (IR) spectrophotometer and spectroflurometer in order to study the structural, morphological, compositional and photoluminescence (PL) properties. The ZnO powder shows polycrystalline nature with preferential peak (101) having crystallite size 25 nm. A significant band at 532 cm⁻¹ in the IR spectrum corroborates the presence of characteristic band of ZnO. Room temperature photoluminescence spectrum of the synthesized nanopowder exhibits a dominant, sharp and strong ultraviolet (UV) emission with a suppressed deep-level emission indicating good crystal quality and optical properties.