Transition metal doped apatites as inert non-toxic pigments
Seah, Jasmine Si Han
Date of Issue2016-03-29
School of Materials Science and Engineering
Transition metal doped apatite, specifically copper-doped hydroxyapatite, Ca10(PO4)6Cux(OH)y, were synthesized via solid state reaction for this study. The aim was to investigate the properties of these compounds and so as to broaden and identify potential applications. Therefore, this report presents a study of synthesis, characterisation and structure analysis of Ca10(PO4)6Cux(OH)y, with x = 0, 0.2, 0.4 and 0.8. The crystal structures of apatite compounds are hexagonal with space group P63/m. The CaO6 columns and PO4 groups linked together forms in a honeycomb hexagonal network with one-dimensional channels extending through the structure. This form of crystal structure is retained when apatite was doped with copper. The synthesized samples underwent phase characterisation using X-ray diffraction followed by Rietveld refinements of the data collected with the aid of the TOPAS4-1 software. Furthermore, attempts for qualitative and quantitative analysis of the compounds were performed with various techniques such as X-ray Absorption Spectroscopy (XAS), UV-Visible Spectroscopy (UV-Vis), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Pulsed Laser Deposition (PLD). Characterisation techniques have provided evidence that the copper atoms reside in the hexagonal apatite channels as they substitute part of the hydroxyl molecules that was previously occupying those sites. The evidences include the increasing lattice parameters of the crystal structure, decreasing intensity bands attributed to the libration modes of the OH molecules, which was identified using FTIR, together with the decreasing weight percentage of O in the materials with an increasing amount of copper present in the compound. Furthermore, the use of XAS and UV-Vis have suggested the presence of copper in the oxidation states of +1, +2 and +3 all existing in the compound. While it can be determined that the copper has an average oxidation state of +2, it is difficult to quantify the remaining copper ions and identify the reason for the range of oxidation states and will require further work. In addition, SEM has affirmed that the synthesized compounds have a particle size ranging between 1-10µm and this synthetic technique has the capability of producing powder samples with uniform particle size distribution. Lastly, PLD has opened a new avenue of potential applications for the compound as the experiment provided evidence that it was possible to deposit the copper-doped hydroxyapatite compound onto a quartz substrate and the resulting thin-film was crystalline and calcium-deficient.
Final Year Project (FYP)
Nanyang Technological University