Solubility Of Zinc Oxide Research Articles

A multi-technique analytical approach to support (eco)toxicological investigation of zinc oxide nanoparticles

Understanding the mechanism of toxicity of nanoparticles and their behavior in biological environments is crucial for designing materials with reduced side effects and improved performance. Among the factors influencing nanoparticle behavior in biological environments, the release and bioavailability of potentially toxic metal ions can alter equilibria and cause adverse effects. In this study, we applied two on-line Field-Flow Fractionation (FFF) strategies and compared the results with off-line benchmarking centrifugal ultrafiltration to assess a key descriptor, namely the solubility of zinc oxide (ZnO) nanoparticles. We found that, at the highest nanoparticle concentrations, the nanoparticle-ion ratio quickly reaches equilibrium, and the stability is not significantly affected by the separation technique. However, at lower concentrations, dynamic, non-equilibrium behavior occurs, and the results depend on the method used to separate the solid from the ionic fraction, where FFF yielded a more representative dissolution pattern. To support the (eco)toxicological profiling of the investigated nanoparticles, we generated experimental data on colloidal stability over typical (eco)toxicological assay durations. The Zeta Potential vs pH curves revealed two distinct scenarios typical of surfaces that have undergone significant modification, most likely due to pH-dependent dissolution and re-precipitation of surface groups. Finally, to enhance hazard assessment screening, we investigated ion-dependent toxicity and the effects of exposure to fresh water. Using an in vitro human skin model, we evaluated the cytotoxicity of fresh and aged ZnO nanoparticles (exposed for 72 h in M7), revealing time-dependent, dose-dependent, and nanoparticle-dependent cytotoxicity, with lower toxicity observed in the case of aged samples.

Application of zincon analysis to investigate the zinc speciation in aqueous media for further understanding of ZnO solubility

The environmental accumulation and toxicity potential of metal oxide nanoparticles because of their increasing use in various commercial products have increased the interest in understanding the behavior of these materials in the aquatic environment. For example, zinc oxide (ZnO) is used in various industrial applications but exhibits partial solubility in aqueous media, therefore it has potential aquatoxic action. ZnO dissolves in water by releasing Zn2+ ions; thus, understanding the complexation behavior of these ions with water is crucial to be able to give a complete description of the fate of ZnO in aquatic environment. In this study, we propose application of a reliable and facile route based on the zincon analysis to further understand the Zn2+ complexation when ZnO is placed in aqueous media. To evaluate this, eight Zn2+ standards at a certain concentration were first prepared in the pH range between 7.0 and 10.0. Samples were analyzed via Inductive Coupled Plasma-Mass spectrometry (ICP-MS/MS) and the zincon analysis by monitoring their UV absorbance maximum at 620 nm. Analysis before and after centrifugation aided the investigation of the pH dependent complexation of Zn2+. In the centrifuged samples, the measured zinc ion fraction decreased, suggesting precipitation of zinc as zinc hydroxide (Zn(OH)2(s)) in the solid form from the solution when the pH was increased from 7.0 to 10.0. However, there was no significant decrease in the non-centrifuged samples in the same pH range. These results show that the zincon analysis can be used to quantify both Zn2+(aq) ions and Zn(OH)2. Moreover, the zincon results were consistent with the results of ICP-MS/MS analyses. The centrifugation helps to sediment solid hydroxide particles enabling one to predict fraction of the ions and the hydroxides. Solid hydroxide precipitate was characterized by FTIR, XRD, SEM and EDX; and formation of orthorhombic Zn(OH)2 phase was confirmed.

Исследование растворимости оксида цинка в растворах гидроксида натрия

The study of solutions obtained during the leaching of zinc-containing raw materials makes it possible to solve environmental problems associated with the need for more complete processing of raw materials and the elimination of both new and previously accumulated waste, as well as additionally obtain valuable components. The purpose of this work was to study the solubility of zinc oxide in sodium hydroxide solutions at different ranges of temperature and concentrations.

The effect of liquid phase chemistry on the densification and strength of cold sintered ZnO

Cold sintering is a chemo-mechanical densification process which allows densification of ceramics at low temperatures below 300 °C. This substantial reduction in the sintering temperature is enabled by an externally applied pressure and a compatible transient liquid phase. In this paper, ZnO is cold sintered using various commercial organic acids: formic, acetic and citric acid. The effect of these different transient phases on densification, microstructural evolution and mechanical response is investigated. Fourier transform infrared spectroscopy, thermogravimetric analyses and transmission electron microscopy were conducted to explain the chemical interactions in the cold sintering process. High relative densities (∼ 96 %) were achieved by formic and acetic acid, whereas poor densification was obtained for citric acid (< 80 %), despite the higher expected solubility of zinc oxide. The higher biaxial strength found in samples sintered with formic acid compared to acetic acid (i.e. ∼90 MPa vs. ∼40 MPa) is discussed supported by fractographic analyses.

The pH dependence of dissolution kinetics of zinc oxide

Zinc oxide (ZnO) powders are used as feed additives for supplementation in diet of animals. Because zinc dissolution rate strongly influences the digestibility of zinc by animals and their stomach has variable pH, the dissolution kinetics of ZnO are studied at the several pH of relevance between 2 and 4. The dissolution of ZnO has been investigated with the help of modeling the dissolution kinetics measured in vitro at various pH. Dissolution is faster in acidic medium. But the acceleration of dissolution at low pH is moderate compared to what would be expected on the basis of the strong pH dependence of ZnO solubility. The concentration of Zn2+ in the quiescent medium at the surface of ZnO particles is much lower than its solubility. It is proposed as a rationale, that hydroxide anions released during dissolution accumulate at the surface of the positively charged ZnO surface, and that the dissolution kinetics is mainly controlled by the diffusion of H+ ions from the bulk solution to the surface.

A comparative study on the shape-dependent biological activity of nanostructured zinc oxide

Monitoring and stimulating in biological systems are strongly dependent on the nature of the interfaces between biological systems and devices; in addition, one-dimensional nanostructures show high-charge accumulation at their surfaces which result in forming a conductive pathway between devices and cells. ZnO nanostructures because of their dual semiconducting properties and their piezoelectricity show a great potential to deploy in optoelectronic devices, biosensors and transducers in biological systems. For this purpose, we introduced a novel one-step hydrothermal nanowire array fabrication and compared it with ZnO nanorods array and ZnO compact film. Grazing incidence X-ray Diffraction (GIXRD), field-emission scanning electron microscope (FE-SEM), disperse X-ray spectroscopy (EDS) detector and inductively couples plasma optical emission spectrometry (ICP-OES) were used for physical and chemical characterizations of the arrays. In addition, we investigated the ability of zinc oxide nanostructures to control cell adhesion and viability of neuron-like PC12 cells. Furthermore, we examined the zinc oxide solubility and our results indicated that cytotoxicity were occurred in 2.23 ± 0.41 µg/ml concentration of zinc ions which was much less than the safe amount of zinc ions (10.23 ± 0.41 µg/ml) reported in previous studies. It is believed that ZnO dissociation behavior crucially affects cell fates even in rare amounts.

ZnO Interactions with Biomatrices: Effect of Particle Size on ZnO-Protein Corona.

Zinc oxide (ZnO) nanoparticles (NPs) have been widely used for food fortification, because zinc is essential for many enzyme and hormone activities and cellular functions, but public concern about their potential toxicity is increasing. Interactions between ZnO and biomatrices might affect the oral absorption, distribution, and toxicity of ZnO, which may be influenced by particle size. In this study, ZnO interactions with biomatrices were investigated by examining the physicochemical properties, solubility, protein fluorescence quenching, particle–protein corona, and intestinal transport with respect to the particle size (bulk vs. nano) in simulated gastrointestinal (GI) and plasma fluids and in rat-extracted fluids. The results demonstrate that the hydrodynamic radii and zeta potentials of bulk ZnO and nano ZnO in biofluids changed in different ways, and that nano ZnO induced higher protein fluorescence quenching than bulk ZnO. However, ZnO solubility and its intestinal transport mechanism were unaffected by particle size. Proteomic analysis revealed that albumin, fibrinogen, and fibronectin play roles in particle–plasma protein corona, regardless of particle size. Furthermore, nano ZnO was found to interact more strongly with plasma proteins. These observations show that bulk ZnO and nano ZnO interact with biomatrices in different ways and highlight the need for further study of their long-term toxicity.

Molecular dynamics simulations of zinc oxide solubility: From bulk down to nanoparticles

The solubility of metal oxides is one of the key descriptors for the evaluation of their potential toxic effects, both in the bulk form and in nanoparticulated aggregates. Current work presents a new methodology for the in silico assessment of the solubility of metal oxides, which is demonstrated using a well-studied system, ZnO. The calculation of the solubility is based on statistical thermodynamics tools combined with Density Functional Tight Binding theory for the evaluation of the free energy exchange during the dissolution process. Models of small ZnO clusters are used for describing the final dissolved material, since the complete ionic dissolution of ZnO is hindered by the formation of O2− anions in solution, which are highly unstable. Results show very good agreement between the computed solubility values and experimental data for ZnO bulk, up to 0.5 mg L−1 and equivalents of 50 μg L−1 for the free Zn2+ cation in solution. However, the reference model for solid nanoparticles formed by free space nanoparticles can only give a limited quantitative solubility evaluation for ZnO nanoparticles.

Pulse Deposition of Zinc in Electrolytes with Reduced Zinc Oxide Solubility

Electrochemical deposition of Zn under DC and various frequencies of pulse deposition modes were studied in electrolytes with reduced zinc solubility - 6 M KOH + 1.8 M KF + 1.8 M K2CO3 saturated by zinc oxide. Current density was set up to the level of the mossy deposit creation under DC condition in common 6 M KOH. Morphology of deposit was visualized by scanning electron microscopy and distribution of particle size was calculated. Moreover XRD measurements were performed for monitoring of structure changes and investigation of preferable particle orientation. The results show that the pulse deposition significantly influences the morphology of the deposit along wide range of pulse frequencies 0.5 - 500 Hz. On one hand the pulse deposition significantly inhibits dendrite formation and thus increases the maximum allowed deposition current, but on the other hand it also influences the size and position of the deposited zinc particles.

Assessment of zinc solubilizing potentiality of Acinetobacter sp. isolated from rice rhizosphere

In the present investigation, there were 143 Zinc solubilizing bacterial isolates obtained from rice rhizosphere soil samples using Tris-mineral salt growth medium supplemented with insoluble source of zinc such as Zinc Oxide (ZnO) and Zinc Carbonate (ZnCO3) individually. Among the ZSB isolates, there was maximum zinc solubilizing halo zone observed with the isolate AGM3 followed by AGM9 both on ZnO and ZnCO3 amended solid tris-mineral salt growth medium with the diameter of 13.21 mm, 10.71 mm and 11.74 mm, 7.90 mm respectively. Similarly, in broth assay, the AGM3 showed high value of zinc solubilization than AGM9 in both ZnO and ZnCO3 supplemented medium with a value of 36.54 μg Zn ml−1, 35.40 μg Zn ml−1 and 33.14 μg Zn ml−1, 32.69 μg Zn ml−1 respectively. The SEM images of AGM3 exhibited better solubility of ZnO than ZnCO3. Both AGM3 and AGM9 bacterial isolates were confirmed as Acinetobacter sp. through biochemical and 16S rRNA gene analysis. IAA productivity of isolate AGM3 showed highest at a level of 45.61 μg mL−1 than AGM9 at 37.27 μg mL−1. In pot experiment, among the all treatments, the combined use of AGM3 and AGM9 with ZnO and ZnCO3 resulted maximum in plant growth. The assay of fractionation of soil zinc after harvest showed an increase in exchangeable zinc, manganese oxide found bound zinc, crystalline and amorphours bound zinc and a decrease organically complexed and carbonate bound zinc compared to untreated control.

Deposition of ZnO rods by electrochemically induced hydrolysis

Galvanostatic electrodeposition of zinc oxide on gold electrodes was studied. Depositions were made from KCl solutions using oxygen reduction for driving the pH induced precipitation. The main focus was the influence of current density on the morphology and density of the deposit. The size, shape and density of the zinc oxide layer were shown to strongly depend on the current density. With an average rod diameter of 82nm and a rod density of 36μm−2 optimal conditions were found at −1.41mAcm−2. The experimental results are discussed within the context of zinc oxide solubility and the near surface pH. For this purpose a simple model for surface pH is considered, based on concentration profiles of reaction products near an RDE and the speciation of zinc in aqueous solution.

Alternative etching methods to expand nanocasting, and use in the synthesis of hierarchically porous nickel oxide, zinc oxide, and copper monoliths

Abstract

Effect of sodium silicate on the solubility of zinc oxide of the Na2O–ZnO–H2O equilibrium system

Abstract There is a competitive reaction of zinc and silica in the alkali leaching process of zinc oxide ore, leading to low zinc leaching rate. To increase leaching rate of zinc, the effect of sodium silicate on the solubility of zinc oxide of the Na 2 O–ZnO–SiO 2 –H 2 O equilibrium system is studied by adding Na 2 SiO 3 and ZnO to NaOH solution. Results show that zinc oxide equilibrium concentration increases with temperature from 25 to 75 °C at the same molar ratio of Na 2 O to SiO 2 . The equilibrium concentration of zinc oxide initially increases and then declines with the increasing concentration of Na 2 O. This leads to the maximum ZnO concentration, which increases with temperature but decreases with the increasing dosage of sodium silicate. The precipitate of disodium zinc silicate (Na 2 (ZnSiO 4 )) generates due to the reaction of silicate SiO 3 2 − and Zn(OH) 4 2 − in the solution of Na 2 O–ZnO–H 2 O equilibrium system. High zinc leaching rate can be obtained when the Na 2 O concentration is lower than the values indicated by the “peak” points at higher molar ratios of Na 2 O to SiO 2 and temperatures.

Measurements of zinc oxide solubility in sodium hydroxide solution from 25 to 100 °C

The solubility of zinc oxide in sodium hydroxide solution was measured in a closed polytetrafluoroethylene vessel from 25 to 100 °C. The ZnO solubility was determined by employing the method of isothermal solution saturation. The results show that only ZnO solid exists in the equilibrium state in the low concentration alkali regions, and the solubility of zinc oxide is almost invariable with temperature. With the increase of alkali concentration, equilibrium solid turns from ZnO to NaZn(OH)3 suddenly, this mutation is called invariant point, 3: 55ents on the X-ray intensities from Ti3-2aL ce dynamics of the compounds AlCo and AlNi []tweight. The alkali concentration of the invariant points increases with increasing temperature, but the solubility of NaZn(OH)3 decreases with increasing alkali concentration at the same temperature. At the same Na2O concentration, the higher the temperature is, the higher the solubility of NaZn(OH)3 is.

Solubility of nano‐zinc oxide in environmentally and biologically important matrices

Increasing manufacture and use of engineered nanoparticles is leading to a greater probability for release of engineered nanoparticles into the environment and exposure to organisms. In particular, zinc oxide (ZnO) is toxic, although it is unclear whether this toxicity is due to the zinc oxide nanoparticles, dissolution to Zn(2+) , or some combination thereof. The goal of this study was to determine the relative solubilities of both commercially available and in-house synthesized ZnO in matrices used for environmental fate and transport or biological toxicity studies. Dissolution of ZnO was observed in nanopure water (7.18-7.40 mg/L dissolved Zn, as measured by filtration) and Roswell Park Memorial Institute medium (RPMI-1640) (∼5 mg/L), but much more dissolution was observed in Dulbecco's modified Eagle's medium, in which the dissolved Zn concentration exceeded 34 mg/L. Moderately hard water exhibited low Zn solubility, likely because of precipitation of a Zn carbonate solid phase. Precipitation of a Zn-containing solid phase in RPMI also appeared to limit Zn solubility. Equilibrium conditions with respect to ZnO solubility were not apparent in these matrices, even after more than 1,000 h of dissolution. These results suggest that solution chemistry exerts a strong influence on ZnO dissolution and can result in limits on Zn solubility from precipitation of less soluble solid phases.

Commercial Zinc Oxide (Zn2+) as an Efficient and Environmentally Benign Catalyst for Homogeneous Benzoylation of Hydroxyl Functional Groups

AbstractThe solvent‐free O‐acylation of some alcohols with benzoyl chloride was carried out to the corresponding benzoylated products in good to excellent yields by the mediation of a catalytic amount (5 mol%) of the commercially available and inexpensive zinc oxide in short reaction times. This methodology represents an eco‐friendly and simple catalytic alternative for benzoylation of primary, secondary, tertiary, and benzylic alcohols with ZnO. This catalytic system was homogeneous because of high solubility of zinc oxide in the reaction medium. Findings showed that ZnO was dissolved in hydrochloric acid, created in situ, after a few minutes. Although, others argued on the catalytic role of solid phase zinc oxide under a heterogeneous condition, it is not surprising to emphasize on the catalytic function of Zn2+ in the benzoylation of alcohols under homogeneous reaction conditions. Zinc oxide served as pre‐catalyst to form Zn2+, as the catalytically active species.

Zinc Bioavailability Is Improved by the Micronised Dispersion of Zinc Oxide with the Addition of L-Histidine in Zinc-Deficient Rats

Zinc fortification of milk or soft drinks is usually used to combat zinc deficiencies in developing countries. Water-soluble zinc compounds, such as zinc sulfate or zinc citrate, are better absorbed but have an unacceptable taste. A micronised, dispersible zinc oxide (MDZnO), which does not have such a problem concerning taste, had higher solubility compared to ZnO (zinc oxide) in an artificial gastric solution. MDZnO was tested for its bioavailability using zinc-deficient Wistar rats. Prior to the experiment, rats were fed zinc-deficient diet for 3 wk and were orally administered control (distilled water) or zinc solutions (ZnO, ZnO+L-histidine (His), MDZnO, MDZnO+His, 1 mg zinc/kg or 3.2 mg His/kg body weight). Compared to ZnO, MDZnO showed a lag in peak time and a lengthy period of continued high plasma zinc concentration after the single oral administration of zinc compounds. Addition of His to MDZnO elevated serum zinc concentration. Serum zinc concentration (area under the curve) in rats administered MDZnO with His was significantly higher than in rats administered distilled water (p<0.05). Liver zinc level was significantly higher in rats administered MDZnO with His compared with control rats (p<0.05), although the level was not affected by the administration with ZnO alone, ZnO+His, or MDZnO alone. In conclusion, the solubility of ZnO was elevated by the micronised dispersion tecnique and an in vivo study using zinc-deficient rats confirmed that its bioavailability was significantly improved compared to ZnO and the coadministration of His additively enhanced the bioavailability of MDZnO.

Preparation of a copoly (dl-lactic/glycolic acid)-zinc oxide complex and its utilization to microcapsules containing recombinant human growth hormone

A procedure to prepare a complex of copoly (dl-lactic/glycolic acid) and zinc oxide (PLGA-zinc oxide complex) was developed. Out of sparingly water-soluble zinc compounds, zinc oxide was most remarkably soluble in a PLGA/dichloromethane solution and the dissolution rates became faster as the water contents in the PLGA/dichloromethane solutions increased. Since the solubility of zinc oxide was saturated at approximately 0.5-fold molar ratio to PLGA and water was generated with dissolution of zinc oxide in the PLGA/dichloromethane solutions, it is suggested that zinc oxide interacts with the terminal carboxyl group of PLGA. In addition, the glass-transition temperature of a solid material obtained by vacuum-drying the PLGA/dichloromethane solution dissolving zinc oxide became higher as the zinc content increased, suggesting that the formation of a PLGA-zinc oxide complex. Microcapsules were prepared with the PLGA-zinc oxide complex using recombinant human growth hormone (rhGH) in order to evaluate an effect of the complex on protein release and stability of protein in the microcapsules. Released rhGH amount from the microcapsules prepared with the PLGA-zinc oxide complex after subcutaneous administration in rats was significantly larger than that from microcapsules prepared with PLGA alone, indicating that rhGH molecules in the microcapsules was stabilized by the PLGA-zinc oxide complex.

New Measurements of the Solubility of Zinc Oxide from 150 to 350°C

The solubility of zincite (ZnO) has been re-evaluated in noncomplexing solutions over a wide range of pH and from 150 to 350°C at pressures ranging from slightly above saturation vapor pressure to significantly higher pressures in NaOH, NH3, F3CSO3H/F3CSO3 Na (HTr/NaTr), CH3COOH/NaOH, and HTr/NH3 solutions using a hydrogen-electrode concentration cell (HECC) and a flow-through cell with downstream acid injection. The new results, coupled with our earlier results at 75–100°C, indicate that the solubility of zinc oxide is higher than we recently reported,(1) but substantially lower than previous estimates available in the scientific literature. It is believed that deposition of ZnO or a zinc hydroxide phase must have occurred near the solubility minimum in the HECC sample lines in our earlier study; a problem that is overcome in the flow cell by injecting acid into the sample line before the solution is depressurized and cooled to room temperature.

The solubility of zinc oxide in 0.03 m NaTr as a function of temperature, with in situ pH measurement

The solubility of zincite (ZnO) has been measured in noncomplexing solutions over a wide range of pH m (4–11), and temperature (75–200°C) at 0.03 mol · kg −1 ionic strength in NaTr media (sodium trifluoromethanesulfonate, a noncomplexing 1:1 electrolyte), in a hydrogen electrode concentration cell (HECC), which provided continuous in situ measurement of hydrogen ion molality. Total zinc content was analyzed by atomic absorption using graphite furnace, flame, and inductively coupled plasma (ICP) spectrometers. The direction of approach to the equilibrium saturation state was varied to demonstrate that the system was reversible thermodynamically. Separate experiments were performed in alkaline solutions (0.03 mol · kg −1 NaOH) at 25 and 50°C in polypropylene syringes, and between 50 and 290°C in a Teflon-lined pressure vessel. The aim of these experiments was to reach higher pH m (>8 depending on the temperature) to determine the thermodynamic properties of the negatively charged species, Zn(OH) 3 −. A least-squares regression of the results obtained at this ionic strength was used to determine the molal solubility products (Q sn) of zincite. The solubility products (Q sn) were extrapolated to infinite dilution (K sn), permitting calculation of the thermodynamic properties of aqueous species of zinc for comparison with previous work.