Synthesis of Hydroxyapatite Coatings for Biomedical and Catalytic Application

Hydroxyapatite (Ca10(PO4)6(OH) 2, HA) has drawn considerable interest in biomedical and catalytic applications due to its excellent biocompatibility, adsorption capacity, and ion exchange capacity. The first part of this thesis focused on imparting antibacterial property to HA coatings for biomedical applications. Ag nanoparticles were electrochemically deposited on HA coatings. The Ag/HA composite coatings displayed inconsistent antibacterial properties. Heat treatment was found to improve the antimicrobial activity of the composite coatings because the oxidation of Ag nanoparticles was enhanced by the heat treatment and thus more Ag + ions can be released to inhibit the bacterial growth. Antibacterial coatings were also obtained by electrochemically depositing HA coatings on TiO2 nanotubes prepared by anodization of Ti plates. A model drug compound was loaded in the HA/nanotubular TiO2 composite coatings. The drug release profile of the coating exhibited an initial burst release followed by a sustained release. Tests of bacterial growth and deposition of calcium phosphate from simulated body fluid suggest that the antibiotics-loaded HA/nanotubular TiO2 composite coatings can inhibit the growth of bacteria without compromising bioactivity.;The second part explored the enhancement of catalytic activity by using hydroxyapatite coatings as catalyst supports. A multi-stage electrochemical method was developed to synthesize palladium (Pd) nanoparticles supported on HA coatings. The size and number density of the Pd nanoparticles can be controlled by adjusting the duration of the first and second stages of electrochemical reduction. The resulting HA-supported Pd nanoparticles demonstrated remarkably higher catalytic activity than commercial Pd nanoparticles in the degradation of methyl orange by NaBH4. The high surface area and the complex oxidation states of the HA-supported Pd nanoparticles are believed to account for the enhanced catalytic activity. In addition, TiO2 nanoparticles were hydrothermally deposited on yttrium/fluorine co-doped hydroxyapatite (YF-HA) films. Photoreduction of Ag+ ions was carried out to investigate the effect of the internal polarization of the YF-HA films on the photocatalytic activity of TiO2 nanoparticles. Significantly more Ag nanoparticles were produced on YF-HA supports than on depolarized YF-HA supports. It is believed that the internal electric polarization of the YF-HA support drives the photogenerated electrons and holes toward different directions, which mitigates the recombination of charge carriers and thus enhances the photocatalytic efficiency.