Study on the effect and mechanism of NaOH on the modification of fluorapatite: A new method of preparing fluor-hydroxyapatite

Abstract

Fluorapatite (FA) and fluor-hydroxyapatite (FHA) have good biocompatibility to substitute for human hard tissue, whereas FA has more cytotoxic and genotoxic effects than FHA. In this study, a new method named nitric acid dissolution-recrystallization was proposed to achieve the modification of FA, and NaOH was used to introduce OH- into FA to prepare FHA in the recrystallization process. The effect and mechanism of NaOH/pH value on the modification of FA were investigated using XRD analysis, SEM detection, EDTA complexometric titration, and FT-IR measurements. XRD and SEM analyses indicated that the synthesized FHA at the pH value of 8.00 had the highest crystallinity and the largest crystal size, reaching 38.10 nm, and the crystal was in the form of short rods with a length of about 1 μm. It was found that the content of the F element in the synthesized FHA decreased as the pH value of the reaction system increased. When the pH value reached 8.00, the content of F was 0.60%, and the values of x and (2-x) in FHA [Ca10(PO4)6Fx(OH)2-x] were 0.16 and 1.84, respectively. FT-IR analysis further confirmed that the content of OH- in FHA obtained at the pH value of 8.00 was noticeably higher than that obtained at the pH value of 4.46. This work could provide a new prospect for utilizing FA to prepare FHA and be of great significance.