Hydroxyapatite (hap) microparticles were synthesized by reacting separate aqueous solutions of calcium chloride CaCl




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НазваниеHydroxyapatite (hap) microparticles were synthesized by reacting separate aqueous solutions of calcium chloride CaCl
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Дата конвертации11.02.2013
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Abstract


Hydroxyapatite (HAP) microparticles were synthesized by reacting separate aqueous solutions of calcium chloride CaCl2 and potassium phosphate KH2PO4- together. The final precipitation was then characterized by SEM for particle morphology and size distribution. The particles were found to be porous, polydispersed spherulites with radial plate-like protrusions. Since HAP is formed by the uptake of hydroxide group (OH-) into its structure, the transformation from ACP to HAP was captured in situ by the change of pH value versus time. The transformation can be roughly divided into four stages. The transformation begins with the formation of ionic clusters, which then aggregate into amorphous calcium phosphate (ACP) clusters. These ACP clusters then transformed to HAP through structural and compositional modification. HAP synthesis is very sensitive to experimental conditions and the influence of different supersaturation ratios of Ca2+ to PO4- ions in the initial reacting solution on the induction time was recorded. It was found that supersaturation and induction time has an inverse relationship, increasing supersaturation speeds up the formation of HAP.

ZnO quantum dots were synthesized by drop-wise addition of sodium hydroxide (NaOH) solution in ethanol into zinc acetate solution in ethanol. To stabilize the nanoparticles in water for bioapplications, the nanoparticles were also coated with silica through the addition and hydrolization of tetraethyl orthosilicate (TEOS). The coated particles were re-dispersed in ethanol, and also in water. Original uncoated ZnO nanoparticles, coated ZnO particles in ethanol, and coated ZnO particles in water were characterized by SEM and TEM for particle size and morphology. ZnO nanoparticles were spherical with diameters of 10nm or below. The silica-coated ZnO particles were larger, between 50nm to 100nm and in ethanol; the population was monodispersed showing that the coating enhanced colloidal stability. In water, however, SEM images revealed that the particles aggregated, indicating that the colloidal stability rendered by the silica coating in ethanol was not sufficient under solutions of higher surface tension. In water, high intensity emission (~530nm) maxima of silica-coated ZnO nanoparticles was recorded over a minimum of 30 days of storage. The results indicate that the coating provided sufficient protection for the surface luminescent centers.

The zeta potential of the silica-coated ZnO nanoparticles were measured and the surface charge was found to be negative, which is potentially favorable for HAP growth. The pH trend for HAP synthesis with the presence of the coated nanoparticles, however, showed an absence of the usual sigmoidal trend. With no significant drop in pH it is clear that the presence of the silica-coated ZnO particles has a significant impact on the formation of HAP.








Table of Contents




Abstract 1

1Introduction 2

1.1Motivation 2

1.2Objectives of the Project 3

2Background 4

2.1Hydroxyapatite (HAP) 4

Properties, Stages of Formation & Morphology. 4

2.2Quantum Dots (QDs) 10

ZnO nanocrystals 11

3Experimental Section 14

3.1Synthesis of HAP particles 14

3.2Synthesis of ZnO Quantum Dots 14

3.3Instrumentation 14

4Results and Discussion 14

4.1HAP: phase transformation, supersaturation and induction time, and morphology. 15

4.2 ZnO QDs: Dynamic formation, stability, particle size, and dispersion 18

4.3Encapsulating Silica-Coated ZnO QDs in HAP 23

5Conclusion & Future Work 24

6References 25



List of Figures


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