The pH Effect on the Growth of Hexagonal and Monoclinic Hydroxyapatite Synthesized by the Hydrothermal Method

Abstract

Summary. In the present work, a study of H+ effects on the microstructure and morphology of hydroxyapatite synthesized by the hydrothermal method is reported. The synthesis was realized with pH values of 10, 9.6, 9, 8, and 7. To know the particle size distribution, growth habit, chemical composition, and crystalline phases present, SEM-EDS, XRD, AFM, and FTIR spectroscopy techniques were used and completed with Rietveld analysis. The obtained results showed an important effect of H+ on the morphological and crystallographic characteristics of the hydroxyapatite, demonstrating that the shape and nanoparticle size, as well as the number of crystalline phases, can change depending on the pH during the synthesis. It was observed that there is an increase in the formation of the monoclinic phase and a decrease of the hexagonal phase when the pH value diminishes from 9.6 to 7. The crystallite size also decreases from 46.69 to 19.56 nm. An explanation of the role of pH on the final characteristics of the hydroxyapatite was related to the amount of H+ and OH- ions, and it was included in this work.

Impact of physicochemical changes in milk ultrafiltration permeate concentrated by reverse osmosis on calcium phosphate precipitation

“…39 pH has a significant impact on the morphological structure of HAP, and alkalinization is known to increase the size of HAP particles, which is in line with our results. 40 A pH increased to more than 9.6 can cause particles to change shape and shift from rods to semispherical particles. This is partly due to an alteration in the electrical charge, which affects the distribution of the OH − ions.…”

“…This is partly due to an alteration in the electrical charge, which affects the distribution of the OH − ions. 40 …”

Development, In-Vitro Characterization and In-Vivo Osteoinductive Efficacy of a Novel Biomimetically-Precipitated Nanocrystalline Calcium Phosphate With Internally-Incorporated Bone Morphogenetic Protein-2

“…Many in-vivo studies have proved that even after 9 months of implantation sintered HA remained at the implantation sites with hardly any sign of resorption (Klein et al, 1983;Okuda et al, 2008;Diez-Escudero et al, 2017). Synthetic HA for fabricating bone-defect-filling materials is usually achieved via wet chemical precipitation, where calcium and phosphate precursors are mixed with ammonium hydroxide (NH 4 OH) as a precipitation agent (Massit et al, 2018;López-Ortiz et al, 2020;Nimishakavi et al, 2021). The thereby-achieved HA is in fine powder and still needs to be sintered at 600-1,300 °C for 1-48 h, where the grain size is significantly increased to facilitate the formation of granules with sufficient stiffness (Champion, 2013;Rodríguez-Lugo et al, 2018).…”

El pH como parámetro en la síntesis de hidroxiapatita y cloroapatita a partir del método hidrotermal asistido por microondas

“…Otro punto fundamental para la obtención de HAp y ClAp, son las condiciones de síntesis, como: la concentración, la temperatura de reacción, tiempo de reacción y pH, mismos que contribuyen a tener un mayor control del tamaño y forma de la partícula, lo que permite ampliar los campos de aplicaciones para estas apatitas (Ciobanu et al, 2013;López-Ortiz et al, 2020;Mehdi Sadat-Shojai et al, 2013;V. Rodríguez-Lugo et al, 2018;Sánchez-Campos et al, 2021;Zuo et al, 2017).…”