ZnO Powders Research Articles

Influence of the filling ratio of vial in chemical surface and physicochemical properties of ZnO nanoparticles obtained by planetary ball milling process

The production of nanoparticles (Np) is an important sector in current technological development. Processes such as high‐energy grinding are among the most promising because of their high efficiency and low energy cost. In this sense, the filling ratio of vial (FRV) is one of the most interesting and poorly studied process variables that can optimize the production of Np on a large scale. In the present work, dry ZnO Np are produced, with different FRV values (40%, 38%, 23%, and 10%), as well as wet samples. The results show that the variation of the FRV allows to generate an energetic increase of the grinding, modifying the morphology, the particle size, and the surface area of the ZnO powders, without generating structural or chemical changes. The X‐ray diffraction (XRD) results show the presence of the zincite phase (hexagonal) with a variation in crystallinity depending on the FRV, which is due to the deformation of the Np during the process. The XPS results showed a slight chemical shift (variation in binding energy) as a function of grinding because of the activation shown by deformation. UV–VIS analyses showed a marked increase in the magnitude of absorbed intensity for all analyzed samples compared with the commercial powder. These results confirm that FRV is a sensitive parameter in the process of obtaining ZnO Np by the planetary mill technique, which allows efficient control of its characteristics for a given application.

Evaluation of the Role of the Activating Application Method in the Cold Sintering Process of ZnO Ceramics Using Ammonium Chloride.

The influence of the method of applying the activating additive ammonium chloride and its concentration on the density and microstructure of zinc oxide ceramic obtained by cold sintering at 244 °C was investigated. The activating agent was applied by two methods: impregnation and subsequent autoclave treatment. When the powder was activated by the impregnation method, the crystal sizes remained at the initial level of 0.17-0.19 μm. After the autoclave treatment, the crystal sizes increased to 0.31-0.53 μm. Samples of cold sintering ZnO with relative density up to 0.96 and average grain sizes 0.29-0.86 μm were obtained. ZnO powders and ceramic samples were analyzed using SEM, TGA/DSC, and XRD to reveal the effect of the powder activation method and cold sintering conditions on the material microstructure. The effect of ammonium chloride concentration on grain growth and microstructure of ceramic samples is shown. It was found that the average grain size of ceramic samples with an increase in additive concentration passes through a minimum. In cold sintering of the autoclave activated powder, the effect of reducing the average grain size was observed. The results of this work are discussed on the basis of the idea of the solid-phase mobility of the crystal structure arising when interacting with an aqueous medium.

Получение высокодисперсного порошка оксида цинка путем сжигания смеси нитрата цинка с глицином и его применение для фотокаталитического разложения фенола

The paper presents the results of a detailed study of the process and products of combustion during self-propagating high-temperature synthesis (SHS) of ZnO zinc oxide powder from mixtures of such common reagents as oxidizer zinc nitrate and reducing agent (fuel) glycine, as well as the application of synthesized highly dispersed submicron and nanosized ZnO powder for the phenol photocatalytic decomposition under the action of ultraviolet irradiation. An aqueous solution of a mixture of reagents (the SHS-S process or Solution Combustion Synthesis – SCS) and the gel from a mixture of initial dry reagents formed when they were moistened due to hygroscopicity (the SHS-G process or Gel Combustion Synthesis – GCS) were combusted. The authors studied the phase and chemical compositions, the structure of the combustion product, and the effect of calcination in an oxidizing air medium and grinding in drum ball and planetary-centrifugal mills, as well as in mortar, on them and their photocatalythic activity. The study showed that calcination considerably increases the photocatalytic activity of combustion products due to a significant decrease in carbon impurity in the unburned fuel remains, and grinding in mills reduces the photocatalytic activity due to iron contamination and coarsening of ZnO particle agglomerates. The difference between the photocatalytic activity of the SHS-G and SHS-S products in the phenol decomposition is evident only at the initial stage of ultraviolet irradiation, after which this difference disappears. The authors discuss the direction of further research to increase significantly the photocatalytic activity of zinc oxide synthesized during combustion to use it effectively for the phenol decomposition under the action of visible light.

Enhanced Catalytic Palladium Embedded Inside Porous Silicon for Improved Hydrogen Gas Sensing

In this work, we reported on room temperature porous silicon (PS) and embedding PS using simple and economical techniques of electrochemical etching and thermal evaporation. The PS substrate was prepared using the technique of electrochemically etching the n-type Si (100) wafer at a constant current density of 10 mA/cm2 for 10 min under the illumination of incandescent white light. After PS formation, Ge pieces were thermally evaporated onto the two PS substrates in a vacuum condition. This was then followed by the deposition of the ZnO layer onto the Ge/PS substrate by the same method using commercial 99.9% pure ZnO powders. The three samples were identified as PS, Ge/PS and ZnO/Ge/PS samples, respectively. Pd finger contacts were deposited on the PS and embedding PS (Ge/PS and ZnO/Ge/PS) to form Pd on PS hydrogen sensors using RF magnetron sputtering. SEM and EDX suggested the presence of substantial Ge and ZnO inside the uniform circular pores for Ge/PS and ZnO/Ge/PS samples, respectively. Raman spectra showed that good crystalline Ge and ZnO nanostructures embedded inside the pores were obtained. For hydrogen sensing, Pd on ZnO/Ge/PS Schottky diode exhibited a dramatic change of current after exposure to H2 as compared to PS and Ge/PS devices. It is observed that the sensitivity increased exponentially with the hydrogen flow rate for all the sensors. The ZnO/Ge/PS showed more sensitivity towards H2 than that of PS and Ge/PS especially at high flow rate of H2 with higher current gain (69.11) and shorter response (180 s) and recovery times (30 s).

Enhanced Tribocatalytic Degradation of Organic Pollutants by ZnO Nanoparticles of High Crystallinity

More and more metal oxide nanomaterials are being synthesized and investigated for degradation of organic pollutants through harvesting friction energy, yet the strategy to optimize their performance for this application has not been carefully explored up to date. In this work, three commercially available ZnO powders are selected and compared for tribocatalytic degradation of organic dyes, among which ZnO-1 and ZnO-2 are agglomerates of spherical nanoparticles around 20 nm, and ZnO-3 are particles of high crystallinity with a regular prismatic shape and smooth surfaces, ranging from 50 to 150 nm. Compared with ZnO-1 and ZnO-2, ZnO-3 exhibits a much higher tribocatalytic degradation performance, and a high degradation rate constant of 6.566 × 10-2 min-1 is achieved for RhB, which is superior compared with previous tribocatalytic reports. The stability and universality of ZnO-3 were demonstrated through cycling tests and degradation of different types of dyes. Furthermore, the mechanism of tribocatalysis revealed that h+ was the main active species in the degradation process by ZnO. This work highlights the great significance of high crystallinity rather than a large specific surface area for the development of high-performance tribocatalysts and demonstrates the great potential of tribocatalysis for water remediation.

Influence of the Sintering Temperature of Zinc Oxide Powder on the Varistor Properties of Structures Based on It

The manufacture of varistors by chemical synthesis is a promising scientific direction. Among the methods of chemical synthesis, the sol-gel method stands out especially, it has an advantage over the classical method due to a more homogenous distribution of ZnO grains and does not require high sintering temperature, moreover, unlike most chemical synthesis methods, it is much cheaper and environmentally friendly. The main purpose of this work is the synthesis of ZnO powder by the sol-gel method, followed by the manufacture of varistor structures and the study of the dependence of their parameters on the sintering temperature and operating temperature. During the work, ZnO powder was synthesized by the sol-gel method, with further fabrication of varistor structures, at sintering temperatures of 1000 °C and 1100 °C. The structure of instrumental samples was studied by scanning electron microscopy, and the current-voltage characteristics were also measured in the temperature range of 20—200 °C. The non-linearity coefficients of the current-voltage characteristic at 20 °C and the temperature coefficient of resistance were calculated. Thus, for the sample sintered at 1000 °C, the coefficient of non-linearity was 1.973 and the temperature coefficient of resistance was 0.649, and for the sample which was sintered at 1100 °C, the coefficient of non-linearity was 1.142 and the temperature coefficient of resistance was 1.0428. These results which were obtained during the work allow us to speak about an increasing in the degree of development of interfaces with the increase in the sintering temperature in turn.

Facile synthesis of uniformly coated ZnO@Bi2O3 composites anode for long-cycle-life zinc–nickel battery

Zinc–nickel battery attracts much attention because of their excellent rate performance and high operating voltage. However, their applications are strongly restricted by the poor cycling performance, which is caused by the degradation of the zinc anode during battery cycling. To overcome such limitation, a facile strategy to prepare homogeneously Bi2O3 coated ZnO composites is proposed. The reaction is conducted in the liquid phase based on redox reaction of Bi3+ and I− to directly grow BiOI on commercial ZnO powders, which are then converted to ZnO@Bi2O3 by further heat treatment. Benefiting from the uniform Bi2O3 coating, the solubility of ZnO is effectively reduced. The well-connected metallic Bi network is formed, which serves as the conductive substrate for uniform zinc deposition and hence inhibits the dendrites growth. The assembled zinc–nickel battery based on ZnO@Bi2O3 composites exhibits significantly prolonged cycling life. Even under a high discharge current of 10 A (~ 138 mA cm−2), the battery can keep cycling during 400 cycles with discharge voltage higher than 1.1 V, which is extended by 3 and 1.7 times compared with that of electrodes based on pure ZnO and physical mixture of Bi2O3 and ZnO. This work provides a facile strategy for synthesizing uniformly Bi2O3 coated ZnO composites, which is helpful for large-scale synthesis of high-performance zinc anodes in practical application.

Embedded thin film fabrication via glass welding by an ultrafast laser

ABSTRACT In this paper, we proposed a technique, ultrafast laser machining–picosecond laser welding, to fabricate an embedded thin film by placing a coating material (ZnO powders) between the interface of two glass substrates. We researched the thickness (embedding depth of ZnO powders) and the formation mechanism of the embedded thin film and the zinc content and distribution. Under our experimental conditions, an embedded thin film of 600 μm thickness was formed. At a distance of 340 μm within the embedded thin film, the zinc content peaked at 400 cps. Finally, we fabricate an embedded thin film with the bonding strength of 12.22 MPa. This technique breaks through the bottlenecks of thin films fabricated by conventional lasers, such as long duration, low precision and serious chemical pollution, which has great significance for achieving high-end manufacturing of thin-film devices.

Highly Cyclic Stability and Absorbent Activity of Carbide Slag Doped with MgO and ZnO for Thermochemical Energy Storage.

Carbide slag is a solid waste with a high content of reactive CaO, which can be used as an active material for the chemical absorption of CO2 and calcium looping. Calcium looping of CaO-based absorbents is one of the most promising methods of thermochemical energy storage. However, the sintering of pores and a reduction in the CO2 diffusion rates as the carbonization/calcination cyclic reaction progresses have posed challenges to the practical application of CaO-based absorbents. This study proposes a method for alleviating the sintering of the pore structure by improving the activity and cycling stability of such absorbents by doping carbide slag with MgO and ZnO powders. Results showed that the raw material ratio, reaction temperature, and reaction time have a considerable influence on the CO2 absorption rate. Furthermore, the specific surface area and pore volume of the absorbents increased with increasing ZnO and MgO doping levels in the carbide slag. Thus, the problems of sintering and clogging of pores in CaO-based absorbents were effectively alleviated, and the MgO and ZnO-doped absorbents CMZ85 and CMZ90 maintained 41-42% CO2 absorption after 10 cycles. These results confirmed that the cyclic stability and absorbent activity improved significantly with the MgO and ZnO doping of carbide slag for the calcium looping process.

TITANIUM DIOXIDE SOL-GEL/ZINC OXIDE POWDER-COATED CLAY BEADS IN PHOTOCATALYTIC REACTOR

Catalyst Immobilization methods are important for providing better recovery of catalyst in photocatalytic treatment. The aim is to characterize and evaluate the photocatalytic performance of TiO2/ZnO-coated clay beads. The titanium dioxide/zinc oxide (TiO2/ZnO)-coated clay beads were prepared via the sol-gel process. Various ZnO powder ratios gave different TiO2/ZnO composites sol. Four layers of TiO2/ZnO sol were coated on clay beads and dried in the oven at 100°C for 30 min. The coated clay beads were calcined at 500°C for one hour for every two layers. Characterization of coated clay beads was done using a scanning electron microscope and energy dispersive spectroscopy. The increased surface area on small agglomeration and optimum loading of ZnO (5 g) resulted in the highest degradation efficiency recorded at 86.57%. An effective catalyst immobilization achieved a good recycling performance on clay beads. Degradation rate data were presented by pseudo-first-order kinetics. It was observed that the average degradation rate for TiO2/5 g ZnO is 0.00836 min–1. The actual results in this work can be applied as a guideline for the preparation of TiO2/ZnO-coated clay beads with high photocatalytic performance.

Optical Properties of ZnO Powders Modified with ZnO Nanoparticles

Optical Properties of ZnO Powders Modified with ZnO Nanoparticles

Highly selective ppm level LPG sensors based on SnO2-ZnO nanocomposites operable at low temperature

The nanoscaled SnO2, ZnO and SnO2-ZnO nanocomposite powders were prepared by microwave aided ultrasonication technique by employing centrifuge for the collection of dried powder of the materials. The fabrication of thick films of the pure ZnO and SnO2-ZnO nanocomposite powders were made by simple screen printing technique. The crystallographic phases of the pure ZnO and SnO2 doped ZnO are hexagonal in nature. The average crystallite size of 0 (pure), 1, 3, 5, 7 and 9 wt% of SnO2 doped ZnO films was found to be 30.2, 30.3, 109.7, 37.9, 36.8 and 45.6 nm, respectively. The SEM micrographs depict the porous nature of the thick films. The EDS analysis reveals that the pure ZnO and SnO2 doped ZnO films are oxygen deficient and show a semiconducting nature. The symmetric I-V characteristics depict the ohmic and non-ohmic natures of the thick films. The electrical resistivity measurements indicate a negative temperature coefficient of resistance. The gravimetric analysis shows that the average thickness of the pure ZnO thick film is 28 µm. The LPG response versus doping concentration plot suggests that the (1 wt%) SnO2 doped ZnO thick film exhibits crucial response to 100 ppm LPG at 50 °C and 100 °C. Therefore, the SnO2 doped ZnO thick film can be applicable in the field of LPG sensing with rapid response and recovery.

Enhanced sulfadiazine degradation in a multi-electrode paralleling DBD plasma system coupled with ZnO/cellulose acetate films

Catalysis of the ZnO/cellulose acetate (CA) films in a multi-electrode paralleling dielectric barrier discharge (DBD) system for sulfadiazine (SDZ) degradation was investigated in this study. The catalysis was induced by the multiple physical and chemical effects produced during the DBD process. The obtained results on the reactive species formation revealed that the more O3, •OH as well as 1O2 could be formed by the addition of the ZnO/CA films into the DBD plasma system. The optimal additive conditions of the catalyst were 4 pieces of 3% the ZnO/CA films addition. There was a better catalytic effect of the ZnO/CA films than the equal amount of the nano ZnO powder addition. The ZnO/CA films still took on the catalytic activity after four cycles usage in the DBD plasma system. The possible degradation pathways were also speculated by analyzing the inorganic and organic intermediates formed during the SDZ degradation.

ZnO and cobalt decorated ZnO NPs: Synthesis, photocatalysis and antimicrobial applications

The rapid growth of pollutants, both biological and non-biological, puts environmental systems in jeopardy. In view of this, the current study demonstrates the synthesis of undoped and Cobalt-doped zinc oxide nanoparticles (Co doped ZnO NPs) via co-precipitation method. The confirmation of incorporation of the Co dopant into ZnO NPs was verified through various spectroscopic and microscopic techniques. UV-absorption spectra of cobalt-doped ZnO NPs revealed a red shift with change of absorption spectra from 356 nm to 377 nm as compared to undoped ZnO NPs. XRD studies inferred that the average crystallite size of 0.5% and 1% Co-doped ZnO powder was obtained to be ∼16 nm and 14 nm respectively. A drop in band gap value from 3.48 eV to 3.30 eV provided as substantive evidence of the successful integration of Co2+ ions inside the ZnO matrix. FESEM and HRTEM studies revealed that the obtained ZnO NPs are in narrow size distribution (15–20 nm) with a wurtzite crystal structure. The synthesized ZnO and Co–ZnO NPs showed excellent photocatalytic and antimicrobial potency towards reactive brown dye (RB-1) and two bacterial strains, respectively. 1% Co-doped ZnO demonstrated the maximum photocatalytic activity (∼95%), in contrast to 0.5% Co-doped ZnO and undoped ZnO. Thus, the findings of this work support the developed system has a dual role as the photocatalyst, and antibacterial agent for efficient environmental remediation.

Preparation, Characterization and Antiradical Activity of Zinc Oxide Nanoparticles

Zinc oxide nanoparticles (ZnO NPs) have recently been studied as a multi-functional and multi-target nanomedicine for cancer treatment. They can be used not only as a nanocarrier for delivery of the chemotherapy drug but also as an antiradical agent due to their photo-catalytic and photo-oxidizing abilities. Our previous work showed a potential use of commercial-available ZnO NPs without and with carboplatin for the treatment of retinoblastoma. The aim of this work was to synthesize ZnO NPs having smaller particle size than the commercial ones, i.e., 100 nm average diameter, in order to improve the reaction time. ZnO NPs were prepared by a sol-gel technique and calcined with different calcination conditions. The structure and particle size of ZnO powders were characterized using an x-ray diffractometer and a particle size analyzer. Average nanoparticle sizes of 16.32 ± 1.64 nm were achieved at a calcination temperature of 300 degree Celsius and 1 hour holding time. The antiradical activity of prepared ZnO NPs in cooperation with ultraviolet irradiation was assessed using a putative model of cancer cells, i.e., 2,2(diphenyl-1-picryhydrazyl) radicals (DPPH*). An optical spectroscopy was used to detect the decrease in peak absorbance of the antiradical solution at a wavelength of 515 nm, which in turn can be used to calculate the percent remaining of DPPH*. The disappearance of DPPH* with respect to the reaction time revealed that prepared ZnO NPs (16.32 ± 1.64 nm) improved response time as compared with ZnO NPs (100 nm). Moreover, the effective ZnO concentrations to reduce the initial DPPH* concentration by 50%, also known as the EC50 value in the present study, is lower indicating the improvement of anti-proliferative activity when compared to the commercial ZnO NPs.

Exciton-Assisted UV Stimulated Emission with Incoherent Feedback in Polydisperse Crystalline ZnO Powder

A comparative analysis of the features of UV-stimulated emission (SE) of various disordered active materials based on ZnO crystallites for a random laser (RL) was carried out. The superlinear increase in the intensity of the UV photoluminescence (PL) band of polydisperse nano-micro-crystalline (PNMC) ZnO powder at a wavelength of λ = 387 nm and some narrowing of its halfwidth in the range of 20 ÷ 15 nm with increasing pump intensity indicates random lasing with incoherent feedback (FB). The properties of similar UV PL bands under the same conditions of a thin film containing hexagonal ZnO microdisks, as well as samples of monodisperse ZnO nanopowder with nanoparticle sizes of 100 nm, indicate stimulated radiation with coherent feedback. It is shown that, among the studied materials, PNMC ZnO powder with widely dispersed crystallites ranges in size from 50 nm to several microns, which in turn, consists of nanograins with dimensions of ~25 nm, is the most suitable for creating a random laser with incoherent feedback at room temperature. The dominant factor of UV SE in PNMC ZnO powder is radiation transitions under exciton–exciton scattering conditions. The possible mechanisms of this random emission with the continuous spectrum are discussed. The average optical gain coefficient αg at λ = 387 nm in this RL system is estimated as αg~150 cm−1.

Novel ZnO photocatalysts for pollutants’ abatement under solar radiation at pilot plant scale

This study reports on the photocatalytic properties and efficiency of sol-gel ZnO powders, investigated at laboratory scale (1.32 L vessel reactor), under simulated solar radiation, in static regime and at pilot plant scale using Compound Parabolic Collector (CPC) photo-reactors (10 L), under solar radiation. The removal of phenol and imidacloprid in a concentration range of 1–50 mg/L was investigated. Optimal operating conditions were identified at laboratory scale and validated in the solar CPC photoreactors, as follows: the type of photocatalyst (ZnO annealed at 550 °C, Z550), the catalyst load (200 mg/L), the water matrix (natural water). Good photocatalytic efficiencies were recorded after 4 h of solar irradiation (QUV∼25 kJ/L) in optimized conditions: 89 % for phenol and 92 % for imidacloprid at 5 mg/L initial pollutant concentration. Thus, the ZnO powder represents a promising photocatalyst able to remove traces of organic pollutants from wastewaters.

Study of the Composition, Structure, Optical Properties, and Radiation Stability of ZnO Powder Modified with SiO2 Nanoparticles

Study of the Composition, Structure, Optical Properties, and Radiation Stability of ZnO Powder Modified with SiO2 Nanoparticles

Sol-Gel Synthesis of Zinc oxide Semiconductor Powder for Varistor Structures

Synthesis of ZnO powders created by the sol-gel method for the use in the production of varistors is currently one of the promising areas. This method allows mixing of additives at the atomic level, which promotes a homogeneous distribution of impurities, it also makes it possible to control the particle size, which contributes to the miniaturization of the varistor and does not require secondary heating, and is also an environmentally friendly method. In this work, we carry out the synthesis of ZnO varistor powder with further fabrication of the varistor structure within the framework of the sol-gel method, as well as the study of the obtained samples at all stages of work. During the synthesis process, the ZnO powder was obtained by the sol-gel method, from which samples of varistor structures were made, at a sintering temperature of 900 °C. During the synthesis, the sol was studied at all stages of maturation by IR-Fourier spectroscopy; during the study, the formation of nano-aggregates in the gel and the presence of ZnO in the resulting powder were obtained. The structure of the instrumental samples was studied by scanning electron microscopy, during which the average grain size of ZnO was calculated as 0.25μm. The constructed volt-ampere characteristics in the voltage range of —220...220 Vhad a distinct non-linearity with a coefficient of 2.36.

Microstructure and thermoelectric properties of Al-doped ZnO ceramic prepared by spark plasma sintering

The high thermal and low electrical conductivities of ZnO ceramics have hindered their thermoelectric applications. The doping of ZnO with group 3 elements can enhance the thermoelectric properties. In this work, Al (2 at%) doped ZnO powder was sintered using spark plasma sintering at varying parameters (such as temperature (550–700 ℃), pressure (250–500 MPa) and the temperature of pressure application (Room Temperature (RT) and Holding Time (HT))). Maximum relative density of 98.9% was achieved at a temperature and pressure of 650 °C and 250 MPa, respectively. The Al-doped ZnO ceramics improved in electrical conductivity which caused a decrease in the Seebeck coefficient because of increased carrier concentration. The reduction in the grain size due to inhibiting growth effects of aluminum lead to a decrease in the thermal conductivity through phonon scattering at the grain boundaries. Hence, ZT of 0016 at 500 °C was obtained. This study indicated that Al-doped ZnO ceramics can be sintered at very low temperature of 650 °C. These conditions allow to retain the nanostructure, which is beneficial in improving the thermoelectric properties.