Hydroxyapatite (HAP) nanoparticles production by sol-gel procedures & direct precipitation from aqueous solution with optimum processing condition

Hydroxyapatite (HAp) is a composite from calcium phosphate family with chemical structure of Ca 10(P04)6(0H)z. There are very huge demands for synthetic HAp due to its structural and chemical similarities as in bone particles. Scientists have carried out many studies to produce synthetic HAp and they manage to fmd several methods in producing synthetic HAp. The study presents the effect of two wet chemistry methods which are solgel procedures and direct precipitation method to produce hydroxyapatite (HAp) nanoparticles. In sol-gel procedures, two precursors are being used, which are calcium nitrate tetrahydrate, Ca(N03)2AH20 and phosphorous pentoxide, P205• In this method, both precursors are being dissolved in ethanol where their Ca/P molar ratio is maintained at 10:3. Next, in direct precipitation method, two precursors are being used, which are calcium nitrate tetrahydrate, Ca(N03)2AH20 and ammonium phosphate trihydrate, [(N~)3P04 .3H20]. By this method, both precursors are being dissolved in distilled water where their Ca/P molar ratio is maintained at 10:6. After the samples have been prepared, they are being analyzed by using three analytical tools which are X-Ray Diffraction (XRD), Fourier-Transform Infrared (FTIR) and Scatming Electron Microscopy (SEM). In sol-gel procedures, XRD show that the method has successfully prepared HAp nanoparticles that have the size range of 16-34 nm. Besides, FTIR spectra also manage to show all crucial functional groups that show the presence of HAp which are phosphate group and hydroxyl group. Finally, the results from SEM show scattering of fine particles with few agglomerations. However, in direct precipitation method, XRD show that the method failed to produce pure HAp due to the absence of crucial peaks which are peaks at 26° and 31.8°. Besides, the results from XRD showed that the samples that have been prepared are amorphous calcium phosphate (ACP) and this is proven by FTIR spectra, where the spectra are wide and the peaks divert from where it supposed to be located. However, SEM images show similar results, where there are scattering of fine particles with few agglomerations. On the other hand, Design of Expert (DoE) by using Response Surface Methodology (RSM) is used to identify the optinmm processing conditions for both methods. In sol-gel procedures, the optimum processing conditions that are obtained are at stirring rate of 500 rpm, aging time of 5 hours and sintering temperature of 600 °C. However, in direct precipitation method, the optimmn processing conditions cannot be identified, due to the failure of preparing the pure HAp nanoparticles. Antimicrobial test is also being carried out, which is to identify the ability of HAp nanoparticles as antimicrobial agent. In order to assess the ability of HAp nanoparticles as antimicrobial agent, HAp nanoparticles are being dissolved in two different solutions, which are distilled water and citric acid solution. Positively, both sets of study show inhibition zone which prove that HAp nanoparticles can act as antimicrobial agent.