Abstract:
A novel composite of nickel oxide-gold supported on magnetic hydroxyapatite nanocomposite (Au-NiO-HAp@γ-Fe₂O₃) was successfully synthesized via a combination of co-precipitation and impregnation methods. The application as a photocatalyst for organic dye degradation under visible light was investigated. Gold nanoparticles (AuNPs) were incorporated into the composite in order to improve the photocatalytic activity via localized surface plasmon resonance. Magnetic nanoparticles (γ-Fe₂O₃) were also incorporated in order to allow easy and rapid magnetic separation of the photocatalyst through the application of an external magnetic field. Crystalline phases of γ-Fe₂O₃, HAp, and NiO were confirmed by XRD. The presence of AuNPs with the size of 3.3 nm was confirmed by TEM. The amount of Au and NiO in the composites was determined by ICP-OES. The photocatalytic performance of the synthesized magnetic composite was investigated using methylene blue (MB) as a model dye. Approximately 56% of MB was removed during the photocatalytic process. Nevertheless, in an analogous experiment performed without Au-NiO-HAp@ γ-Fe₂O₃, similar removal percentage of MB was obtained. This finding indicated that the intended catalytic process, either under UV light or visible light, did not significantly affect the degradation of MB. Further experiments revealed that the removal of MB was also not induced by heat derived from the system. Instead, the degradation of MB likely resulted from its self-photolysis that occurred during a sufficiently long reaction time (> 2 h). The failure of Au-NiO-HAp@ γ-Fe₂O₃ to catalyze the degradation of MB may in part be attributable to the effect of non-overlapping frontier electronic bands of NiO and HAp.
