ZnO Crystallites Research Articles

Preparation and evaluation of active Cu-Zn-Al mixed oxides to CS2 removal for CO2 ultra-purification

A simple synthesis route for the formation of Cu-Zn-Al-oxide with high surface area and porosity has been presented, tuned, and evaluated for CS2 removal from CO2 stream. Saturation of aqueous suspension of raw Cu, Zn, Al oxides with a stream of CO2 at mild conditions and subsequent thermal treatment was used for preparation of a series of materials with the same (Cu + Zn/Al) molar ratio but differentiated carbonate content. They were characterized by techniques: X-ray diffraction (XRD), differential thermal gravimetry with evolved gas analysis (DTG/EGA), N2 sorption, scanning electron microscopy and energy dispersive spectroscopy SEM-EDS and were subjected to tests for CS2 sorption from the CO2 stream at 90 °C. It was shown that Cu-Zn-Al sorbents can effectively remove CS2 if the specific surface area exceeds 40 m2/g and the mean CuO and ZnO crystallites size is not greater than 15 nm. Obtaining active sorbents of sulphur compounds by CO2 saturation of raw Cu, Zn, Al oxides can be an effective route for preparation of active traps for CS2 removal from CO2 at low temperature.

X-ray Nanospectroscopy Reveals Binary Defect Populations in Sub-micrometric ZnO Crystallites

Besides its many applications in electronics, photonics, and catalysis, ZnO has also been extensively used as the pigment zinc white ever since its introduction in the first half of the 19th century. It is shown here that zinc whites (ZnO formed through zinc vapor oxidation) form a chemically binary system, with each of the sub-micrometric crystallites belonging to either of two distinct classes. The observation of the two classes is done based on X-ray absorption nanospectroscopy and was determined to be caused by differences in the populations of anisotropic crystal defects. A theoretical assessment of the vapor oxidation synthesis method is formulated that predicts that the binary distinction in crystal defect populations is caused by local variations in synthesis parameters. As the crystal defect population in ZnO has been shown to be related to its catalytic properties, these results provide fundamental insights on the link between the intrinsic properties of zinc white and its degradation issues in oil paint.

The effect of pH on Synthesis of ZnO-Natural Zeolite Nanocomposite by Co-Precipitation Method

Currently, the method being developed to overcome environmental pollution generated by synthetic dyes produced from the textile industry wastewater is by photocatalysis using photocatalyst materials. Photocatalysis is a relatively inexpensive and easy method to implement. Photocatalysts that have received major attention and widely studied are metal oxide semiconductors such as ZnO. Photocatalyst activity can be increased through the development of supporting materials such as zeolites. This study aims to synthesize ZnO-natural zeolite photocatalysts nanocomposite by co-precipitation method in order to take advantage of the adsorbent and catalyst properties in the natural zeolites and the photocatalyst properties in the ZnO. To study the effect of pH, ZnO-natural zeolite nanocomposites are synthesized with different pH under alkaline conditions (pH of 8-11). Nanocomposite materials obtained then tested its photocatalyst activity in degrading of 50 ppm procion red synthetic dyes. The ZnO-natural zeolite nanocomposites produced were characterized by using XRD, SEM, and BET. The synthesized ZnO-natural zeolite nanocomposite showed the best results at pH of 10, with the ZnO crystallite size of 20.99 nm, the surface area of 134.35 m2/g, and the Zn contained of 10.05%. Procion red degradation of 75.54% was attained by using ZnO-natural zeolite nanocomposite photocatalyst after 120 minutes of UV irradiation.

Enhanced isopropanol sensing of coral-like ZnO–ZrO2 composites

Both p-type ZrO2 and n-type ZnO are widely adopted oxides towards trace gas detections; however, their combinations to achieve an enhanced gas sensing performance are rarely reported. Herein, we adopted a simple solution combustion technique to synthesize ZnO–ZrO2 composites for isopropanol sensing. The one-step combustion achieved coral-like macro/mesoporous hierarchical architectures. It is found that, when the Zr/Zn molar ratio is less than 0.02, all Zr atoms were doped into ZnO crystallites; whilst ZrO2 appeared when the ratio is beyond 0.03. When utilized to detect trace isopropanol in air, the response increases linearly with the increasing concentration of the target gas in the range of 10–1000 ppm. At the optimal operation temperature of 350 °C, the largest slope (0.18 ppm−1) is recorded for the ZnO–ZrO2 composite with a Zr/Zn molar ratio of 0.04 and the slope is 23 times that of pure ZnO (0.0078 ppm−1). It exhibits also a fast response time and recovery time of 19 s and 8 s, respectively, under 100 ppm isopropanol. The impressive gas sensing property can be contributed to both the macro-/mesoporous structure, which facilitates an intimate contact between the target gas and the sensing site, and the p–n junction induced built-in electric field, which favors the charge separation.

Raman study of laser-induced formation of II–VI nanocrystals in zinc-doped As–S(Se) films

Zn-doped As2Se3 and As2S3 films were prepared by thermal evaporation. Their amorphous structure was confirmed by Raman spectroscopy. Zinc chalcogenide nanocrystals can be formed in the films under laser irradiation due to the photoenhanced diffusion of atoms in the arsenic chalcogenide films, which enables aggregation of Zn and S(Se) atoms in nanocrystals. For As2S3:Zn films, not only ZnS, but also ZnO crystallites can be formed under irradiation with UV laser light due to oxidation of the film surface with abundant zinc atoms.

ZnO–C3N4 solar light -driven nanophotocatalysts on floating recycled PET bottle as support for degradation of oil spill

Oil spill from explosion of oil wells and tankers threatens the life of sea creatures. Photocatalytic oxidation of oil spill is a promising way due to its low cost, complete conversion and the capability of using free and abundant sunlight. For better interaction between oil, photocatalyst and the light, it is recommended to use floating photocatalysts. In this research, recycled drinking bottles made of polyethylene terephthalate (PET) were used as a floating support for C3N4 and ZnO photocatalysts. ZnO–C3N4/r-PET composite with various amounts of ZnO (0, 5, 10 and 15 wt.%) were synthesized and characterized by means of X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM-EDX), N2-sorption isotherm (BET-BJH), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR) and UV–vis diffuse reflectance spectroscopy (UV–Vis DRS). The as-prepared ZnO–C3N4/r-PET nanocomposites were tested for the photocatalytic degradation of benzene. The results show that by increasing the amount of ZnO, the particle size decreased, size distribution narrowed and a more homogenous morphology was observed. Moreover, pore volume, pore diameter and BET surface area increased. In details, ZnO crystallite size reduced from 32 nm in ZnO–C3N4/r-PET nanocomposite with 5 wt.% of ZnO to 18 nm in similar nanocomposite with 15 wt.% of ZnO. Increasing the ZnO amount, broadened the band gap but enhanced the light absorption in visible and UV regions. Good interaction between C3N4 and ZnO was confirmed in TEM image. The highest degradation performance was obtained in the presence of 15 wt.% of ZnO. In fact by decreasing the amount of ZnO in the ZnO–C3N4/r-PET composite, the photodegradation rate decreased significantly. Influence of operating parameters like pH, catalyst loading, benzene volume percent and simulated sea conditions on photodegradation of floating benzene were also studied in details.

Growing continuous zinc oxide layers with reproducible nanostructures on the seeded alumina substrates using spray pyrolysis

The growth of zinc oxide thin films with controlled nanostructures on the heat resistant dielectric substrates is important for the fabrication of gas sensors, transparent electric heating elements, pyroelectric electron emitters, and many other potential electronic and optoelectronic applications. The preferred substrate for many of these applications is alumina, but the production of uniform ZnO layers on alumina is hindered by the large lattice mismatch between ZnO and Al2O3 hexagonal crystal structures. Here, we systematically investigate the growth process of ZnO thin films on alumina substrates using the ultrasonic spray pyrolysis (USP) of zinc chloride solutions in ethanol and, for the first time, demonstrate the deposition of uniform layers on the alumina substrates appropriately seeded using magnetron sputtering prior to USP. On the pristine substrates, random nucleation of the isolated nanocrystallites results in uneven layers, and extending the growth process leads to the hierarchical growth of facetted ZnO nanorods and pyramids with weak physical attachments to the substrate surface. In similar conditions, USP deposition on the seeded substrates reproducibly results in continuous networks of densely packed ZnO crystallites intimately attached to the substrate surface with adjustable thickness and electrical conductance. These results are compared with those obtained for SnO2 in similar conditions. Regardless of its tetragonal crystal structure, SnO2 reproducibly forms even layers on the pristine alumina substrates.

Enhanced low-level acetone detection by zinc/tin bi-metallic oxides nanocomposite with long-term stability

Zinc/tin bi-metallic oxides nanocomposites (ZTNs) were fabricated by a simple hydrothermal process. The characterization of the ZTNs by X-ray diffraction (XRD), field effect scanning electron microscopy (FESEM), and Brunauer–Emmett–Teller (BET) confirmed the formation of a mixture of the ZnO and SnO2 crystallites in porous nanocomposite with nanosheet morphology. Acetone gas-sensing features of the ZTN sensor (ZTS) were studied at different operating temperatures as a function of low gas concentration from 0.5 to 10 ppm. The ZTS responses were 54.4, 42.3, and 30% toward 10, 2, and 0.5 ppm acetone concentration, respectively, at an optimum operating temperature of 110 °C. Our low-cost device showed the appropriate ability for the acetone gas detection at low level with attractive stability and selectivity, which suggests it as a reliable biomarker sensor in health monitoring. The acetone gas-sensing mechanism of the sensor was analyzed and discussed as well, through the standard thermionic emission model and the gas molecules adsorption/desorption process.

UV-activated ZnO/CdO n-n isotype heterostructure as breath sensor

The demand for developing a non-invasive sensor towards disease diagnosis such as diabetes, renal dysfunction, and cancer has been increasing tremendously. The presence of biomarkers such as ammonia, acetone, and ethanol in human exhaled breath indicates the onset of various diseases. In this context, the present investigation is focused on developing a cost-effective acetone sensor using isotype ZnO/CdO heterostructure thin film by spray pyrolysis technique. The sensing signatures of the heterostructure was examined in the presence of light activation using UV LED light. Structural analysis of the heterostructure divulged the growth of cubic phased CdO and hexagonal phased ZnO crystallites towards (1 1 1) and (1 0 1) planes respectively. Spin-orbit splitting of Cd 3d subshells was confirmed through the surface analysis. The heterostructure showed selective photo-response of 540 towards acetone at room temperature. Response and recovery times were observed as 61 and 47 s respectively towards 1 ppm of acetone vapor. The linear detection range of the sensor was observed to be 1–100 ppm with long-term stability. Since the sensor showed the lowest detection limit of 1 ppm, the sensor can be used for the identification of acetone from exhaled breath for disease diagnosis.

Structural Features of Pseudomorphic Spinel-Structure Films on R-Sapphire Substrates

А suspension of submicron ZnO crystallites in acetone is applied to epi-ready R(10$$\bar {1}$$2) sapphire plates with dimensions of ~10 × 10 × 0.5 mm. The composite is dried and annealed in air in a tube furnace at 1200°C for 60 min. According to the data of electron and scanning probe microscopy, X-ray and electron diffraction, thin oriented ZnAl2O4 zinc spinel films are formed on the sapphire substrate with the mutual orientation of lattices following the epitaxial relationships: (311)ZnAl2O4||(10$$\bar {1}$$2)Al2O3; 〈332〉ZnAl2O4||〈11$$\bar {2}$$0〉 Al2O3; 〈110〉ZnAl2O4||〈1$$\bar {1}$$01〉Al2O3. Due to the relatively high synthesis temperature of the films (1200°C) and the most intense cathodoluminescence of the film in the near-infrared (IR) spectrum, the formation of normal zinc spinel can be assumed. The obtained ZnAl2O4 films with the (311)-plane orientation parallel to the R plane of the sapphire substrate are supposed to be used to grow magnetic NiFe2O4 and CoFe2O4 films having the (311) plane with an easy-axis magnetization anisotropy oriented along the 〈311〉 direction.

Multifractal analysis of ZnO nanoparticles.

ZnO nanoparticles (NPs) have variety of applications in different fields due to its size, structure, as well as physical and chemical properties. One of its prominent characteristics is its antibacterial behavior. Nonlinear Dynamical Theory (NLD) has a vast scope in the field of material science, especially when subtle correlations are searched for to extract hidden information. Since nano-ZnO materials may be used in inhibiting pathogens, its nonlinear features can be quantified and calibrated with the help of NLD tools. Multi-fractal Analysis (MFA) is an important diagnostic tool of NLD for not only analyzing nonlinear signal or images, but also predicting any spurious events likely to occur in the system under study. Thus, the analysis of the surface texture of the ZnO nano particles formed, using the TEM images and relate it with the variations of the XRD signal using NLD tools, is our first attempt reported here. Further, tools of MFA are used, for the first time, to see if there exists any correlation between the texture of the nano particles formed and the Zone of Inhibition (ZoI) we obtain as an output after allowing certain pathogens inhibit in the presence of the same nano particles. Analysis of TEM images guide us to predict the texture and structure of crystallites of ZnO:Cu samples which are responsible for overall behavior of inhibiting pathogens. In this paper, MFA of ZoI images, TEM images, and signal of four different Cu-doped ZnO nanoparticles are carried out and their outcomes are calibrated for estimating the size and pattern of unknown NPs synthesized under similar physical and chemical condition. Moreover, that MFA can be used reliably to predict spurious or abnormal surface structure or bacterial inhibition is also established.

Synthesis, characterization and influence of pH on indium doped zinc oxide nanostructures

Indium doped zinc oxide (In:ZnO) nanostructures were synthesized using the refluxed sol-gel method at pH levels of 7, 8, 9, 10, 11 and 12 for the precursor solution, adjusted by the addition of aqueous sodium hydroxide to the solution mixture of zinc and indium salts. X-ray diffraction (XRD) patterns revealed intense diffraction peaks of wurtizite In:ZnO nanocrystals with increased broadenings due to the incorporation of larger size In3+ ions to the lattice sites of Zn2+ ions. The substitution process of the dopant ions into the lattice sites and the size of the crystallites were influenced and facilitated by the pH of the solution. The crystallite size decreased from 23 nm to 19 nm with an increase of pH level of the precursor solution. The micrograph from field emission scanning electron microscopy (FE-SEM) showed an aggregated mixture of spindle- and cone-like morphology which decreased in size as the solution pH increased. Transmission electron microscopy (TEM) also confirmed the morphology and the decrease in size of the structures obtained by FE-SEM measurements. The UV–Vis reflectance analysis also demonstrated that the optical properties of In:ZnO crystallites improved with the increase in pH of the solution, as shown by the blue shift of the absorption edge of the reflectance spectra. The energy band gap increased nearly linearly from 3.22 eV to 3.26 eV with the increased pH values from 7 to 12 which was attributed to the Burstein-Moss effect. Photoluminescence (PL) measurements show a significant change in the emission characteristics. Both excitonic and defect level emission bands were shifted to shorter wavelength as the pH level increased, verifying the widening of the energy band gap. The relative intensity ratios of excitonic to defect level emission bands (INBE/IDLE) decreased generally as the pH level increased, indicating the increased concentration of the defects of oxygen interstitials and vacancies in the produced nanostructures. All measurements exhibited in this study confirmed that increasing the alkalinity of the synthesis solution enhanced the production of highly crystalline In-doped ZnO nanostructures for a better and suitable material in the area of biomedical, solar cell and other optoelectronics applications.

Novel carbonaceous ZnO composite prepared through inert-ambient pyrolysis of the zinc anthranilate complex

In this work we present the analysis of products of the pyrolysis, at 600 °C, of zinc anthranilate complex in open air and in the nitrogen ambient of a sealed tube. The resulting powder samples were characterized by x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (FESEM), and transmittance electron microscopy (HR-TEM). Open-air pyrolysis (OAP) yields well-crystallized ZnO, whereas sealed-tube pyrolysis (STP) produces a black powder that is found to be a composite (ZnO/C) of graphitic carbon and nanocrystalline, nearly monodisperse ZnO. The composite is carbon-rich. The relatively large size of ZnO crystallites from OAP and their much smaller size in the STP product suggest that carbon formation in the sealed tube restricts the growth of ZnO nanocrystals. When ZnO/C was annealed in air at 650 °C for 1 h, the oxide crystallites retained their average size, with all carbon removed. To investigate the possibility of using ZnO/C as electrode material in capacitors, electrochemical investigations electrode were carried out using cyclic voltammetry and galvanostatic charge-discharge, with 0.5 M KOH as electrolyte. The specific capacitance of the ZnO/C composite was found to be 124.7 F g−1 at 5 mV s−1 scan rate, indicating the suitability of ZnO/C as electrode material because of the measured voltammograms and charge-discharge characteristics.

Synthesis of octahedral-like ZnO/ZnFe2O4 heterojunction photocatalysts with superior photocatalytic activity

Octahedral-like ZnO/ZnFe2O4 heterojunction photocatalysts were synthesized via a solvothermal method followed by thermal treatment. Appropriate amount of CH3COONa was introduced into the synthesis process to supply a moderate alkaline condition and slowly accelerate hydrolysis of ZnSO4 and FeCl3. The structure, morphology and photoelectric properties of samples were analyzed, and the results indicated that the as-synthesized samples with octahedral-like morphology and superior light absorption characteristics were assembled of ZnO and ZnFe2O4 crystallites as well as dispersed in various orientations. Compared with ZnO and ZnFe2O4, the ZnO/ZnFe2O4 photocatalysts exhibited enhanced photocatalytic activity in degradation of methylene blue. Especially, the optimal photocatalyst (ZF3) showed the highest catalytic activity, achieving 91.2% and 82.7% degradation efficiency after 120 min of UV–vis (350 ≤ λ ≤ 780 nm) and 140 min of visible-light (λ ≥ 420 nm) irradiation, respectively. The degradation process agreed well with pseudo-first-order kinetics. The improved photocatalytic activity was attributed to the synergetic effect of low bandgap energy, mesoporous structure and efficient charge separation, which enhanced the visible-light utilization and adsorption of pollutants.

Self-assembled zinc oxide hierarchical structures with enhanced antibacterial properties from stacked chain-like zinc oxalate compounds

Single ZnO crystallites assembled into porous hierarchical structures have been prepared by topotactic thermal decomposition of in situ obtained zinc oxalate precursors, whose synthesis involves a redox reaction between 1,2-ethanediol and nitrate ion. For the first time it was demonstrated that post-synthesis protocols of the precursors (e.g. ultrasound irradiation, hydrolytic decomposition) master the hydrogen bonds formed between oxalate chains, allowing that way the adjustment of materials properties (morphology, porosity and optical) and a rational introduction of different dopants (Eu3+/Er3+). The ZnO surface reactivity is confirmed by the significant biocidal activity of the obtained materials against Gram-positive and Gram-negative planktonic and biofilm-embedded cells, superior to those reported in the literature for other ZnO-based materials or antibiotics, associated also with a good biocompatibility.

Formation of a ZnO–C Composite with a Nanocrystalline Structure

The formation of a nanocrystalline composite of a ZnO–C system with simultaneous mechanical activation of a mixture of zinc oxide and graphite powders in a ball mill in an inert atmosphere is studied. It is shown that the presence of graphite reduces the efficiency of dispersing ZnO crystallites. The following principal dispersion mechanisms of graphite are determined: the fragmentation of particles due to the impact of grinding bodies and the exfoliation of flakes by submicron zinc oxide particles. It has been established that a composite system is formed as a result of the prolonged mechanical activation effect on the ZnO–graphite mixture, which is a nanocrystalline zinc oxide powder with uniformly distributed inclusions of micro- and nanocrystalline graphite, turbostratic carbon, exfoliated graphene structures, and amorphous carbon.

Photoactive and Non-Hazardous Kaolinite/ZnO Nanocomposite: Characterization and Reproducibility of the Preparation Process.

Photoactive and non-hazardous kaolinite/ZnO nanocomposite with 50 wt.% of ZnO nanoparticles was prepared using simple and cheap hydrothermal method. The resulting solid phase was separated by decantation, and dried at 105 °C. Calcination of the nanocomposites at 600 °C led to the kaolinite-metakaolinite phase transformation, to further growth of ZnO crystallites, and to significant increase in photodegradation activity. Whereas, for the several applications, e.g., in brake industry, the larger amount of composites is needed, thus, the evaluation of the reproducibility of preparation process is one of the crucial parameter. Prepared nanocomposites were deeply characterized by using X-ray fluorescence spectroscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and Rietveld quantitative phase analysis. Photodegradation activity was evaluated by the discoloration of Acid Orange 7 aqueous solution under UV irradiation. All used analytical techniques and methods confirm the reproducibility of the preparation process and as well that ZnO nanoparticles are anchored tightly on the clay surface which prevents the release to the environment.

Transparent ZnO crystallized glass ceramics for photocatalytic and antibacterial applications

The synthesis of the transparent ZnO crystallized 9.35K2O-9.35CaO-42.05ZnO-23.36B2O3-9.35SiO2-6.54Al2O3 glass was done using a melt-quenching and heat-treatment route. Three different heat treatments were provided to get different amounts of ZnO crystals in the glass matrix. The X-ray diffraction technique confirmed the ZnO crystallization in the glass matrix. Further characterization was performed using Raman and photoluminescence techniques. The bandgap decreased (3.75–3.14 eV) with an increase in ZnO crystallization. The flower-type morphology of ZnO crystallites was observed using a scanning electron microscope. Contact angle measurements showed an increase in hydrophilicity with the increase in ZnO crystallization. During the photocatalytic ink test using smart Resazurin (Rz) ink, ZnO crystallized glass samples cleaned all ink within 5 h. 78% degradation was observed in Rhodamine B dye (pollutant) using one of the ZnO crystallized samples during the photocatalytic dye degradation test, showing its promising photocatalytic properties. ZnO crystallized glasses portrayed good antibacterial property against Escherichia coli (Gram-negative bacteria). Complete depletion of bacteria within 60 min exposure under ultraviolet irradiation was recorded with one of the ZnO crystallized glasses without any external intervention.

On the transformation of "zincone"-like into porous ZnO thin films from sub-saturated plasma enhanced atomic layer deposition.

The synthesis of nanoporous ZnO thin films is achieved through annealing of zinc-alkoxide (“zincone”-like) layers obtained by plasma-enhanced atomic layer deposition (PE-ALD). The zincone-like layers are deposited through sub-saturated PE-ALD adopting diethylzinc and O2 plasma with doses below self-limiting values. Nanoporous ZnO thin films were subsequently obtained by calcination of the zincone-like layers between 100–600 °C. Spectroscopic ellipsometry (SE) and X-ray diffraction (XRD) were adopted in situ during calcination to investigate the removal of carbon impurities, development of controlled porosity, and formation and growth of ZnO crystallites. The layers developed controlled nanoporosity in the range of 1–5%, with pore sizes between 0.27 and 2.00 nm as measured with ellipsometric porosimetry (EP), as a function of the plasma dose and post-annealing temperature. Moreover, the crystallinity and crystallite orientation could be tuned, ranging from a powder-like to a (100) preferential growth in the out-of-plane direction, as measured by synchrotron-radiation grazing incidence XRD. Calcination temperature ranges were identified in which pore formation and subsequent crystal growth occurred, giving insights in the manufacturing of nanoporous ZnO from Zn-based hybrid materials.

Effect of Li+ addition on growth behavior of ZnO during anodic dissolution of Zn negative electrode

Discharge behavior of the Zn negative electrode was investigated to elucidate the effects of Li+ as an additive in Zn batteries. Li+ influenced the dissolution of Zn as well as the formation of ZnO (passivation). The dissolution reaction was enhanced by Li+; step-flow dissolution at the Zn surface changed to dissolution from the entire surface. SEM observations of the ZnO formed due to the supersaturation of zincate ions showed morphological changes from acicular crystals to particulate clusters upon introduction of Li+; also, ZnO peaks in XRD patterns decreased. These changes indicated that Li+ suppressed the growth of ZnO, which was caused by the adsorption or incorporation of Li+ into the ZnO crystallites. In situ Raman analysis was carried out to monitor such a difference in the nucleation and growth processes. An E2 mode corresponding to crystalline wurtzite ZnO was dominant in the solution without Li+, while this mode diminished and an E1 (LO) mode corresponding to excess Zn in the interstitial sites of ZnO became strong in the presence of Li+. It was suggested that the Zn excess was introduced due to dominance of nucleation (reactions between zincate species) over the growth process (zincate decomposition at the surface).