Synthesis and Characterisation of Zinc Oxide and Sodium Zirconate particles

Presented in this thesis are findings from investigations into the hydrothermal synthesis and growth sequence of (a) zinc oxide (ZnO) particles and (b) synthesis via normal evaporation drying and spray drying of sodium zirconate powders (Na2ZrO3) for CO2 capture applications. Particle characterisation involved the usage mainly of X-ray diffraction analysis, and scanning and transmission electron microscopy to acquire information on changes in particle properties as synthesis conditions were varied. Zinc oxide particles were grown hydrothermally from suspensions produced by drop-wise mixing of a zinc acetate solution and aqueous sodium hydroxide. The precursor suspensions were heated in an acid digestion vessel at a steady rate (5 oC per min), to a dwell temperature of 120°C and then held for different dwell times. Analysis of characterisation results revealed that particle growth occurred through a hierarchical process, starting with zinc oxide nanocrystallites which self-assembled into ≤20 nm wide particles. Progression of hierarchical growth led to the emergence of hexagonal ZnO microrods through the stacking along the direction of hexagonal layers, (each ~50 nm thick), made up of the assembled ≤20 nm particles. The process ended with the formation of hexagonal double rods (≤1.8 µm and width ≤0.6 µm) through multiple mechanisms, including secondary growth of rods off the basal layers of fully developed pre-existing rods, end-to-end attachment of rods, and possibly growth via crystal twinning. In another series of experiments, the sequential multistage growth process of high aspect ratio zinc oxide rods are presented for hydrothermal treatment of a precursor suspension obtained by titration of a solution of zinc acetate dissolved in distilled water against an ammonium hydroxide solution. In this case, particle growth commenced with the emergence of metastable octahedral wulfingite [Ɛ-Zn(OH)2] particles which transformed to high aspect ratio hexagonal ZnO microrods with increased reaction times. Finally, sodium zirconate powders composed of nanoscale primary particles were synthesized via evaporation drying and spray drying of a mixture of sodium acetate and zirconium acetate in nitric acid for applications in CO2 capture. Loose agglomerates (~10 µm) of irregular shaped particles were obtained from evaporation drying, while < 5 µm porous and hollow granules with nanoparticle sub-structure were obtained from spray drying. Phase composition of calcined powders from both synthesis methods was mainly Na2ZrO3 with minor proportions of monoclinic ZrO2. Analysis of results from subjecting both powders to multiple carbonation (700 oC, 22 % CO2 atmosphere) and decarbonation (900 oC, 100 % N2 atmosphere) in thermogravimetric analysis (TGA) cycles showed that the spray dried powder had a superior CO¬2 uptake performance, providing ~ 80 % CO2 uptake efficiency (molar uptake/theoretical molar uptake) compared to ~ 45 % and ~ 15 % for the evaporation dried and commercial powders respectively. The improved performance of the spray dried sample was attributed to the morphology of the particles, as the relatively high porosity of the hollow granules enabled a faster rate of gas-solid reactions relative to the evaporation dried powder

Data to support study of Structural transformations and spin-crossover in [FeL2]2+ salts (L = 4-{tertbutylsulfanyl}-2,6-di{pyrazol-1-yl}pyridine) − the influence of bulky ligand substituents

Desolvation of [FeL2][BF4]2·xMeNO2 occurs via an intermediate phase, exhibiting hysteretic spin-crossover (SCO) with a reverse step in its warming branch. Incomplete SCO in the final product phase reflects disorder of an L ligand. [FeL2][BF4]2·yMe2CO contains five complex cations per asymmetric unit, four of which undergo gradual SCO in at least two discrete steps

Temperature-Stable Dielectric Ceramics based on Na₀.₅Bi₀.₅TiO₃

Multiple ion substitutions to Na0.5Bi0.5TiO3 give rise to favourable dielectric properties over the technologically important temperature range −55 °C to 300 °C. A relative permittivity, εr, = 1300 ± 15% was recorded, with low loss tangent, tanδ ≤ 0.025, for temperatures from 310 °C to 0 °C, tanδ increasing to 0.05 at −55 °C (1 kHz) in the targeted solid solution (1–x)[0.85Na0.5Bi0.5TiO3–0.15Ba0.8Ca0.2Ti1-yZryO3]–xNaNbO3: x = 0.3, y = 0.2. The εr-T plots for NaNbO3 contents x < 0.2 exhibited a frequency-dependent inflection below the temperature of a broad dielectric peak. Higher levels of niobate substitution resulted in a single peak with frequency dispersion, typical of a normal relaxor ferroelectric. Experimental trends in properties suggest that the dielectric inflection is the true relaxor dielectric peak and appears as an inflection due to overlap with an independent broad dielectric peak. Process-related cation and oxygen vacancies and their possible contributions to dielectric properties are discussed

Systematic Investigation of the Physicochemical Factors That Contribute to the Toxicity of ZnO Nanoparticles

ZnO nanoparticles (NPs) are prone to dissolution, and uncertainty remains whether biological/cellular responses to ZnO NPs are solely due to the release of Zn²⁺ or whether the NPs themselves have additional toxic effects. We address this by establishing ZnO NP solubility in dispersion media (Dulbecco’s modified Eagle’s medium, DMEM) held under conditions identical to those employed for cell culture (37 °C, 5% CO₂, and pH 7.68) and by systematic comparison of cell–NP interaction for three different ZnO NP preparations. For NPs at concentrations up to 5.5 μg ZnO/mL, dissolution is complete (with the majority of the soluble zinc complexed to dissolved ligands in the medium), taking ca. 1 h for uncoated and ca. 6 h for polymer coated ones. Above 5.5 μg/mL, the results are consistent with the formation of zinc carbonate, keeping the solubilized zinc fixed to 67 μM of which only 0.45 μM is as free Zn²⁺, i.e., not complexed to dissolved ligands. At these relatively high concentrations, NPs with an aliphatic polyether-coating show slower dissolution (i.e., slower free Zn²⁺ release) and reprecipitation kinetics compared to those of uncoated NPs, requiring more than 48 h to reach thermodynamic equilibrium. Cytotoxicity (MTT) and DNA damage (Comet) assay dose–response curves for three epithelial cell lines suggest that dissolution and reprecipitation dominate for uncoated ZnO NPs. Transmission electron microscopy combined with the monitoring of intracellular Zn²⁺ concentrations and ZnO–NP interactions with model lipid membranes indicate that an aliphatic polyether coat on ZnO NPs increases cellular uptake, enhancing toxicity by enabling intracellular dissolution and release of Zn²⁺. Similarly, we demonstrate that needle-like NP morphologies enhance toxicity by apparently frustrating cellular uptake. To limit toxicity, ZnO NPs with nonacicular morphologies and coatings that only weakly interact with cellular membranes are recommended

Systematic investigation of the physicochemical factors that contribute to the toxicity of ZnO nanoparticles.

ZnO nanoparticles (NPs) are prone to dissolution, and uncertainty remains whether biological/cellular responses to ZnO NPs are solely due to the release of Zn(2+) or whether the NPs themselves have additional toxic effects. We address this by establishing ZnO NP solubility in dispersion media (Dulbecco's modified Eagle's medium, DMEM) held under conditions identical to those employed for cell culture (37 °C, 5% CO2, and pH 7.68) and by systematic comparison of cell-NP interaction for three different ZnO NP preparations. For NPs at concentrations up to 5.5 μg ZnO/mL, dissolution is complete (with the majority of the soluble zinc complexed to dissolved ligands in the medium), taking ca. 1 h for uncoated and ca. 6 h for polymer coated ones. Above 5.5 μg/mL, the results are consistent with the formation of zinc carbonate, keeping the solubilized zinc fixed to 67 μM of which only 0.45 μM is as free Zn(2+), i.e., not complexed to dissolved ligands. At these relatively high concentrations, NPs with an aliphatic polyether-coating show slower dissolution (i.e., slower free Zn(2+) release) and reprecipitation kinetics compared to those of uncoated NPs, requiring more than 48 h to reach thermodynamic equilibrium. Cytotoxicity (MTT) and DNA damage (Comet) assay dose-response curves for three epithelial cell lines suggest that dissolution and reprecipitation dominate for uncoated ZnO NPs. Transmission electron microscopy combined with the monitoring of intracellular Zn(2+) concentrations and ZnO-NP interactions with model lipid membranes indicate that an aliphatic polyether coat on ZnO NPs increases cellular uptake, enhancing toxicity by enabling intracellular dissolution and release of Zn(2+). Similarly, we demonstrate that needle-like NP morphologies enhance toxicity by apparently frustrating cellular uptake. To limit toxicity, ZnO NPs with nonacicular morphologies and coatings that only weakly interact with cellular membranes are recommended