High ZnO Content Research Articles

Effect of the Medium Composition on the Zn2+ Lixiviation and the Antifouling Properties of a Glass with a High ZnO Content.

The dissolution of an antimicrobial ZnO-glass in the form of powder and in the form of sintered pellets were studied in water, artificial seawater, biological complex media such as common bacterial/yeast growth media (Luria Bertani (LB), yeast extract, tryptone), and human serum. It has been established that the media containing amino acids and proteins produce a high lixiviation of Zn2+ from the glass due to the ability of zinc and zinc oxide to react with amino acids and proteins to form complex organic compounds. The process of Zn2+ lixiviation from the glass network has been studied by X-ray photoelectron spectroscopy (XPS). From these results we can state that the process of lixiviation of Zn2+ from the glass network is similar to the one observed in sodalime glasses, where Na+ is lixiviated to the media first and the fraction of Zn that acts as modifiers (~2/3) is lixiviated in second place. After the subsequent collapse of the outer surface glass layer (about 200–300 nm thick layer) the dissolution process starts again. Antifouling properties against different bacteria (S. epidermidis, S. aureus, P. aeruginosa, E. coli, and M. lutea) have also been established for the glass pellets.

Synthesis, thermal and structural properties of pure TeO2 glass and zinc-tellurite glasses

We have synthesized pure TeO2 glass and glasses in the systems xZnO−(1−x)TeO2 (0≤x≤0.50) and yAl2O3−(1−y)TeO2 (0≤y≤0.03) by melting in Pt crucibles, and measured their glass transition temperature (Tg), density (ρ) and Raman spectra to correlate glass properties with structure. For pure TeO2 glass, synthesized using our newly developed intermittent quenching technique, we find onset- and midpoint-Tg at 301.1 and 306.7°C and ρ=5.62g/cm3, in clear disagreement with TeO2 glass melted in alumina crucible for which we find Tg≈380°C and ρ=4.86g/cm3. This latter method, used frequently in the literature, was shown by Raman spectroscopy to introduce Al2O3 in the tellurite matrix which becomes cross-linked by Te-O-Al bridges, resulting in the increase of Tg and decrease of ρ. Raman spectroscopy showed also that doping TeO2 with ZnO or Al2O3 causes the progressive conversion of TeO4 trigonal bipyramids to TeO3+1 polyhedra with two terminal oxygens, and then to TeO3 trigonal pyramids with three terminal oxygens. This structural transformation is reflected in the composition dependence of the volume per mole TeO2 evaluated from density data. The ZnO-dependence of this parameter is described by two linear parts with an inflection point at x=0.25, which indicates an increasing rate of forming terminal TeO bonds at higher ZnO contents. The Tg was found to increase with ZnO and Al2O3 contents and this was attributed to the glass-forming ability of both oxides, while density was found to decrease due mainly to replacement of the heavier TeO2 by the lighter ZnO and Al2O3. The results of this study are discussed with reference to previous works on TeO2 and zinc-tellurite glasses.

Photocatalytic degradation of methylene blue by C3N4/ZnO: the effect of the melamine/ZnO ratios

The C3N4/ZnO composite photocatalysts were synthesized by mechanical milling combined with a calcination process. Various ratios of melamine and ZnO powders were milled by a planetary ball mill for 10 h. After heating at 540∘C for 3 h in air, melamine was converted to C3N4 but the formation of C3N4 depended on the ratios of the melamine and ZnO (M/Z) powders. From the experimental results, the conversion of melamine to C3N4 could be inhibited by ZnO particles; as there was no detectable C3N4 in the sample at low M/Z values or high ZnO contents. The photocatalytic activities of prepared samples were investigated under the illumination of blacklight and fluorescent lamps as the low wattage light source. The C3N4 /ZnO showed a better photocatalytic activity than ZnO to degrade a methylene blue (MB) dye solution using blacklight lamps, but there is no significant difference in photocatalytic activities between ZnO and prepared C3N4/ZnO under visible light by the fluorescent lamps. However, the prepared C3N4/ZnO can well function under illumination by Xe lamp as the high power light source. Ecotoxicities of MB solutions before and after photocatalytic process were also studied through growth inhibition of the alga Chlorella vulgaris.

Crystal growth in zinc borosilicate glasses

Glass samples with a molar composition (64+x)ZnO–(16−x)B2O3–20SiO2, where x=0 or 1, were successfully synthesized using a melt-quenching technique. Based on differential thermal analysis data, the produced glass samples were submitted to controlled heat-treatments at selected temperatures (610, 615 and 620°C) during various times ranging from 8 to 30h. The crystallization of willemite (Zn2SiO4) within the glass matrix was confirmed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Under specific heat-treatment conditions, transparent nanocomposite glass-ceramics were obtained, as confirmed by UV–vis spectroscopy. The influence of temperature, holding time and glass composition on crystal growth was investigated. The mean crystallite size was determined by image analysis on SEM micrographs. The results indicated an increase on the crystallite size and density with time and temperature. The change of crystallite size with time for the heat-treatments at 615 and 620°C depended on the glass composition. Under fixed heat-treatment conditions, the crystallite density was comparatively higher for the glass composition with higher ZnO content.

Transparent Nanocrystalline Glass-Ceramic System for Organic Pollutants Degradation

Because of the superior photocatalytic activities of nanocrystalline TiO2 and ZnO under UV irradiation, they were embedded into the glass system (SiO2, TiO2, ZnO, B2O3, Na2O, K2O, P2O5, Li2O and BaO) to provide easy separation from the aqueous system. Different contents of TiO2 and ZnO have been investigated. Conversion to glass-ceramic materials was carried out by heat treatment at 450 °C, which is the onset of the nucleation peak according to the differential thermal analysis (DTA) result, for different times. This heat treatment regime preserves the transparency of the prepared materials in the visible region and good absorption in the UV region. The high content of TiO2 or ZnO caused an improvement of microhardness of the prepared materials, though the presence of the two oxides with the same ratio decreased the microhardness values. Photocatalytic activity of the prepared glass-ceramic materials was investigated according to their efficiency for the degradation of humic acid (HA), the major precursor of disinfection by-products (DBPs), from water. All samples were proved to be photoactive with different extents. Four hours heat treatment at 450 °C appears to be the best conditions for the development of TiO2 and ZnO crystals leading to better photocatalytic activity.

Observation of > 5 wt % zinc at the Kimberley outcrop, Gale crater, Mars

AbstractZinc‐enriched targets have been detected at the Kimberley formation, Gale crater, Mars, using the Chemistry Camera (ChemCam) instrument. The Zn content is analyzed with a univariate calibration based on the 481.2 nm emission line. The limit of quantification for ZnO is 3 wt % (at 95% confidence level) and 1 wt % (at 68% confidence level). The limit of detection is shown to be around 0.5 wt %. As of sol 950, 12 targets on Mars present high ZnO content ranging from 1.0 wt % to 8.4 wt % (Yarrada, sol 628). Those Zn‐enriched targets are almost entirely located at the Dillinger member of the Kimberley formation, where high Mn and alkali contents were also detected, probably in different phases. Zn enrichment does not depend on the textures of the rocks (coarse‐grained sandstones, pebbly conglomerates, and resistant fins). The lack of sulfur enhancement suggests that Zn is not present in the sphalerite phase. Zn appears somewhat correlated with Na2O and the ChemCam hydration index, suggesting that it could be in an amorphous clay phase (such as sauconite). On Earth, such an enrichment would be consistent with a supergene alteration of a sphalerite gossan cap in a primary siliciclastic bedrock or a possible hypogene nonsulfide zinc deposition where Zn, Fe, Mn would have been transported in a reduced sulfur‐poor fluid and precipitated rapidly in the form of oxides.

Antibacterial and Antifungal Activity of ZnO Containing Glasses.

A new family of non-toxic biocides based on low melting point (1250°C) transparent glasses with high content of ZnO (15–40wt%) belonging to the miscibility region of the B2O3-SiO2-Na2O-ZnO system has been developed. These glasses have shown an excellent biocide activity (logarithmic reduction >3) against Gram- (E. coli), Gram+ (S. aureus) and yeast (C. krusei); they are chemically stable in different media (distilled water, sea-like water, LB and DMEN media) as well as biocompatible. The cytotoxicity was evaluated by the Neutral Red Uptake using NIH-3T3 (mouse embryonic fibroblast cells) and the cell viability was >80%. These new glasses can be considered in several and important applications in the field of inorganic non-toxic biocide agents such as medical implants, surgical equipment, protective apparels in hospitals, water purifications systems, food packaging, food storages or textiles.

Synthesis and characterization of resorcinol–formaldehyde resin chars doped by zinc oxide

Polycondensation polymerization of resorcinol–formaldehyde (RF) mixtures in water with addition of different amounts of zinc acetate and then carbonization of dried gels are studied to prepare ZnO doped chars. Zinc acetate as a catalyst of resorcinol–formaldehyde polycondensation affects structural features of the RF resin (RFR) and, therefore, the texture of chars prepared from Zn-doped RFR. The ZnO doped chars are characterized using thermogravimetry, low temperature nitrogen adsorption/desorption, Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM). At a relatively high content of zinc acetate (1mol per 10–40mol of resorcinol) in the reaction mixture, the formation of crystallites of ZnO (zincite) occurs in a shape of straight nanorods of 20–130nm in diameter and 1–3μm in length. At a small content of zinc acetate (1mol per 100–500mol of resorcinol), ZnO in composites is XRD amorphous and does not form individual particles. The ZnO doped chars are pure nanoporous at a minimal ZnO content and nano-mesoporous or nano-meso-macroporous at a higher ZnO content.

Origins of microspherules from the Permian–Triassic boundary event layers in South China

Volcanism and impact scenarios are two of the most plausible ways of interpreting the causes of the largest biological mass extinction at the end-Permian. Microspherules have previously been widely reported from tens of different Permian–Triassic boundary (PTB) sections in South China and some other regions. These microspherules have been interpreted as either the product of volcanic eruptions or an impact event. In order to test these scenarios, we collected 60 samples from 12 intensively-studied PTB sections in South China. In addition, four soil samples close to these PTB layers were also collected for comparison. Our investigation indicates that abundant microspherules with mosaic or dot shape crystals on rounded surface are present in the surface samples in the PTB layers at Meishan, Meili, and Shatian sections and most soil background samples in South China. Those microspherules consist of four different types based on their main chemical composition, surface features, and internal structure including iron, magnetite–silicate, glassy, pyrite microspherules and framboids. In contrast, microspherules have not been found in a few sections in remote areas such as the Selong Xishan section in Tibet and the Dalongkou section in Xinjiang, Northwest China, in the deeply-excavated samples at the Shangsi section and the hard tuff layers around the PTB at the Xiaochehe Section in Guiyang. Microspherules decrease in abundance with depth in PTB clay beds. All these microspherules except the pyrite microspherules and framboids are found in both the PTB layers and the nearby soil background samples. The iron microspherules are pure iron oxides such as magnetite, hematite or maghemite and contain low concentrations of nickel and chromium, and lack an Ni–Fe core and general extraterrestrial mineral wüstite. All these external and chemical characteristics suggest that most of iron microspherules previously reported from PTB sections in South China are modern industrial fly ashes. A low ratio of Fe3 +/FeTotal in crystals of magnetite–silicate microspherules and high ZnO contents can identify them as industrial contaminants. The pyrite microspherules and framboidal pyrite found from bed 24e and bed 26 at the Meishan sections are of depositional or/and diagenetic origins, and only the rounded quartz and the fragments containing extremely high SiO2 and TiO2 are possibly of volcanic origin.

Changes induced in a ZnS:Cr-based electroluminescent waveguide structure by intrinsic near-infrared laser radiation

The causes of changes that occur in a thin-film electroluminescent metal-insulator-semiconductor-insulator-metal waveguide structure based on ZnS:Cr (Cr concentration of ∼4 × 1020 cm−3) upon lasing (λ ≈ 2.6 μm) and that induce lasing cessation are studied. It is established that lasing ceases because of light-scattering inhomogeneities formed in the structure and, hence, optical losses enhance. The origin of the inhomogeneities and the causes of their formation are clarified by studying the surface topology and the crystal structure of constituent layers of the samples before and after lasing. The studies are performed by means of atomic force microscopy and X-ray radiography. It is shown that a substantial increase in the sizes of grains on the surface of the structure is the manifestation of changes induced in the ZnS:Cr film by recrystallization. Recrystallization is initiated by local heating by absorbed laser radiation in existing Cr clusters and quickened by a strong electric field (>1 MV cm−1). The changes observed in the ZnS:Cr film are as follows: the textured growth of ZnS crystallites, an increase in the content of Cr clusters, and the appearance of some CrS and a rather high ZnO content. Some ways for improving the stability of lasing in the ZnS:Cr-based waveguide structures are proposed.

Enhanced dielectric, ferroelectric, and electrostrictive properties of Pb(Mg1/3Nb2/3)0.9Ti0.1O3 ceramics by ZnO modification

The effects of ZnO modification on the dielectric, ferroelectric, and electrostrictive properties of 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 (PMNT) ceramics are systematically studied in this work. The PMNT/xZnO (with x = 0, 0.4, 2.0, 4.0, and 11.0 mol. %) ceramics of complex perovskite structure were prepared by solid state reaction and sintering process. It is found that the maximum value of the dielectric constant decreases with increasing ZnO amount up to x = 4.0 mol. %, and then significantly increases with x = 11.0 mol. %. The temperature of maximum dielectric constant tends to increase, while the diffuseness of the dielectric peak is reduced, with increasing ZnO content. The remanent polarization and the coercive field increase with increasing ZnO concentration. The induced strain and the electrostrictive coefficient reach the maximum values of 0.10% (at E = 10 kV/cm) and 12.94 × 10−16 m2/V2, respectively, with x = 2.0 mol. % ZnO. The ceramic doped with a high ZnO content (11.0 mol. %) exhibits a macroscopically polar phase with a well-developed ferroelectric hysteresis loop and butterfly-shaped bipolar piezoelectric response. This enhanced long-range polarization and the resulting properties are attributed to the effects of the partial substitution of Zn2+ for Mg2+, which favors a higher degree of polar order and a lower degree of relaxor behavior.

Study on the Possibility of Using ZnO to Increase the Desulfurization Potential of Blast Furnace Slag and Sulfide Capacities

AbstractZinc oxide has recently been suggested to be a potential material for hot metal desulfurization. The present work was carried out to examine whether ZnO could help the remaining blast furnace (BF) slag to capture sulfur. For this purpose, slags prepared with relatively high ZnO content was equilibrated with either liquid silver or liquid copper under controlled oxygen potential at 1773 K. It was found that most of the ZnO escaped during the experiment, indicating thereby that ZnO could not increase the desulfurization potential of the BF slag in the case of hot metal. The experimental data were used to evaluate the sulfide capacities of the studied slags. In some of the slags equilibrated with silver, the MgO activities were evaluated.

Investigation of Structure and Mechanical Behavior of Polyamide 6/ZnO and Polyamide 6/Al<sub>2</sub>O<sub>3</sub> Nanocomposites

In this work we investigate mechanical properties and structure of PA6/ZnO and PA6/Al2O3 nanocomposites to understand the effect of different nanoparticles on the polymer matrix. Mechanical experiment results show that the mechanical reinforcement effect after loading ZnO nanoparticles is better than that of loading Al2O3 nanoparticles. At 10% ZnO loading, the elastic modulus increases to about two times of that of pure PA6, and the yield stress increases about 30%. And the elongation at break has no obvious decrease even at high ZnO loading. In order to understand the reason of better mechanical reinforcement after incorporating ZnO nanoparticles, microstructure and crystallization behavior of the samples were investigated. The results indicate that the better reinforcement of mechanical properties after loading ZnO was attributed to enhanced interfacial adhesion between ZnO nanoparticles and PA6 matrix at high ZnO content.

Thermophysical and pool boiling characteristics of ZnO-ethylene glycol nanofluids

Thermal conductivity and viscosity of surfactant free and stable ethylene glycol (EG) based ZnO-nanofluids, prepared using long duration sonication, have been investigated both as a function of ZnO nanoparticle volume fraction and temperature (10–70 °C). Thermal conductivity enhancement of > 40% have been observed (ZnO volume fraction: 0.0375), which is substantially higher than that reported earlier on EG based oxide nanofluids. The observed enhancement of the studied ZnO-EG nanofluids is comparable to that of graphene oxide (0.04 volume fraction)–EG nanofluids. Viscosity of ZnO-EG nanofluids displays transition from Newtonian behavior at lower ZnO concentration to non-Newtonian characteristics at higher ZnO content and lower temperatures. Most importantly, viscosity of ZnO-EG nanofluid is found to be nearly independent of ZnO nanoparticle loading. The large thermal conductivity enhancement and marginal viscosity penalty of ZnO-EG nanofluids is believed to be the consequence of prolonged ultrasonication (∼60 h), which results in superior fragmentation and uniform distribution of ZnO nanoparticle clusters in the base fluid (EG). Results on the pool boiling characteristics of ZnO-EG nanofluids are reported first time and an enhancement of ∼22% in the boiling heat transfer coefficient is achieved with 0.016 volume fraction of ZnO nanoparticle loading. Finally, surfactant free ZnO-EG based nanofluids, prepared using long duration sonication, possesses all the features (viz, high thermal conductivity enhancement, nearly no viscosity penalty and enhanced heat transfer coefficient) required for an energy efficient coolant.

Photocatalytic and optical properties of nanocomposite TiO2-ZnO thin films

Nanocomposite TiO 2 -ZnO thin films, with different ZnO content, were deposited by electron-beam evaporation on glass and Si(1 0 0) substrates. The resulting films were annealed in air for 1 h at 450 °C. X-ray diffraction revealed the presence of monoclinic β -TiO 2 and hexagonal ZnO for the films prepared with ZnO content of 0 at.% and 100 at.%, respectively. Mixed monoclinic β -TiO 2 and hexagonal ZnO phases were observed at higher ZnO content between 50 at.% and 85 at.%. Spectroscopic ellipsometry (SE) was employed to determine the film thickness and optical constants. A two-layer model was used to describe the experimental ellipsometric data. At any wavelength longer than 390 nm, the refractive index decreases gradually with increasing ZnO content in the composite films. The optical band gap increased with increasing ZnO content. The photocatalytic behavior of TiO 2 -ZnO thin films was mainly evaluated by measuring the decomposition of methylene blue. The nanocomposite film with ZnO content of 8 at.% has the best photocatalytic activities.

Preparation and properties of poly(propylene carbonate) and nanosized ZnO composite films for packaging applications

AbstractA series of polypropylene carbonate (PPC)/ZnO nanocomposite films with different ZnO contents were prepared via a solution blending method. The morphological structures, thermal properties, oxygen permeability, water sorption, and antibacterial properties of the films were investigated as a function of ZnO concentration. While all of the composite films with less than 5 wt % ZnO exhibited good dispersion of ZnO in the PPC matrix, FTIR and SEM results revealed that solution blending did not lead to a strong interaction between PPC and unmodified ZnO. As such, poor dispersion was induced in the composite films with a high ZnO content. By incorporating inorganic ZnO filler nanoparticles, the diffusion coefficient, water uptake in equilibrium, and oxygen permeability decreased as the content of ZnO increased. The PPC/ZnO nanocomposite films also displayed a good inhibitory effect on the growth of bacteria in the antimicrobial analysis. The enhancement in the physical properties achieved by incorporating ZnO is advantageous in packaging applications, where antimicrobial and environmental‐friendly properties, as well as good water and oxygen barrier characteristics are required. Furthermore, UV light below ∼ 350 nm can be efficiently absorbed by incorporating ZnO nanoparticles into a PPC matrix. ZnO nanoparticles can also improve the weatherability of a PPC film. In future research, the compatibility and dispersion of the PPC matrix polymer and the inorganic ZnO filler nanoparticles should be increased. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

Effects of interface affinity on the rheological properties of zinc oxide nanoparticle-suspended polymer solutions

The effects of the interface affinity between the nanoparticle and polymer matrix on the rheological properties of nanoparticle suspended-polymer solutions were investigated. Two polymers, polar polyacrylonitrile (PAN) and nonpolar polystyrene (PS), were selected, and the cosolvent was N,N-dimethylacetamide and 0.1∼5 wt% of polar ZnO nanoparticles in the polymer were used. The inclusion of ZnO notably increased the viscosity (γ′) of the PAN solutions, even at such a low loading level of 0.1 wt%. A maximum value of γ′ was observed at a 1 wt% of ZnO content. On the other hand, the γ′ of the PS solutions decreased with increasing ZnO content. Both the PAN and PS suspension systems exhibited a notable decrease in γ′ above a critical ZnO content. Although the PAN solutions showed a lower loss tangent (tanδ) at higher ZnO contents, the PS solutions containing > 2 wt% ZnO showed higher tanδ above a frequency of 2 rad/s. On the Cole-Cole plot, the PAN solutions did not give a single master curve depending on the ZnO content. However, the PS solutions showed little scattering from the master curve of a slope of ca. 1. ZnO increased the relaxation time of the PAN solutions but decreased the relaxation time of the PS solutions. Open image in new window

Laser Patterning of ZnO Crystals on the Surface of Borosilicate Glass

The laser‐induced crystallization technique has been applied to a borosilicate glass with a high ZnO content in order to pattern ZnO crystals on the glass surface. A glass with the composition of 65.5ZnO–19B2O3–9.5SiO2–6Sm2O3 is developed, in which Sm2O3 is added to transfer laser energy to thermal energy, and it is found that usual heat treatments in an electric furnace results in the formation of ZnO crystals with a hexagonal wurztite structure not only at the surface but also inside the glass. It is confirmed from X‐ray diffraction analyses and micro‐Raman scattering spectra that ZnO crystals are formed at the glass surface by irradiations of Yb:YVO4 fiber laser (wavelength: 1080 nm, power: 1.3 W, scanning speed: S=7 μm/s). The present study is a first step for spatially selected patterning and design of functional ZnO crystals by laser‐induced crystallization in glasses.

H 2 production by steam-quenching of Zn vapor in a hot-wall aerosol flow reactor

Hydrogen production by steam-hydrolysis of zinc is investigated as part of a two-step water-splitting thermochemical cycle based on ZnO/Zn redox reactions. The hydrolysis reactor consists of a hot-wall tube containing a flow of Zn(g) that is steam-quenched to co-produce H 2 and Zn/ZnO nanoparticles. The effects of the quenching gas flow rate and reactor wall temperature on the Zn-to-ZnO chemical conversion and particle yield are examined. Solid products are characterized by X-ray diffraction, N 2 adsorption, and SEM microscopy. Quench rates of 2–6×10 4 K/s yielded conversions of up to 95% at the expense of low particle yield due to significant wall deposition with subsequent hydrolysis. Aerosol particles with hexagonal structure were formed by Zn evaporation–condensation containing low ZnO mass fraction. In contrast, operation at quench rates up to 10 6 K/s led to increased particle yield but lower conversion. Filamentary and rod-like particles were formed with high ZnO content by surface reaction and coagulation.

Pseudobrookite ceramic pigments: Crystal structural, optical and technological properties

Pseudobrookite pigments were synthesised by the conventional ceramic route, calcining at 1300 °C four mixtures, with a Fe 2O 3:TiO 2 ratio ranging from 47:53 to 40:60, and were characterised by XRPD, DRS and colouring performance in several ceramic matrices. Titania in moderate excess of the Fe 2TiO 5 stoichiometry, necessary to minimise the occurrence of unreacted precursors, induced lattice parameters smaller than ideal pseudobrookite, in agreement with the different radii of Ti 4+ and Fe 3+ ions. These pigments exhibit a peculiar, intensely brown coloration originated by several light absorptions in the visible spectrum due to both d 5 electronic transitions and a magnetically-coupled paired transition between iron ions in adjacent lattice sites. A doubling of the 6A 1 → 4T 1 and 4T 2 bands is related to the occurrence of Fe 3+ in both octahedral sites of pseudobrookite. Besides, distinct metal–oxygen distances imply different energy absorptions in good accordance with the crystal field theory, despite the strongly covalent character of the Fe–O bonding. Although an entropy-stabilised phase, pseudobrookite persists dispersed in glazes and glassy coatings even after fast firing at 1200 °C, so being suitable as ceramic pigment. However, its colouring performance depends on the chemico-physical properties of ceramic matrices: saturated brown shades achieved in low temperature glasses shift to a lighter brown in opacified glazes and fade to a light gray in wall tile glazes, where the high CaO and ZnO content contributes to rapidly dissolve pseudobrookite.