Molecular Understanding of the Bulk Composition of Crystalline Nonstoichiometric Hydroxyapatites: Application to the Rationalization of Structure-Reactivity Relationships

Abstract : Crystalline hydroxyapatite samples (HAps) have been prepared by using the co-precipitation method under various pH conditions, leading to nonstoichiometric solids (1.65 < Ca/P < 1.77). The aim of this study was to rationalize the sensitivity of the catalytic activity of HAps to their bulk compositions going from the macroscopic level expressed by the Ca/P ratio to the molecular level properties of the bulk. From DRIFT, 31P NMR and Raman characterizations, hydroxyapatites were obtained with a range of structural defects compared with the ideal stoichiometric compound. If the amount of HPO42– and B-type carbonates directly impacts the Ca/P ratio, it is not the case for A-type carbonates. All these defects, and especially the A-type carbonates, participate in the modulation of OH content inside the channels. Irrespective of the Ca/P values, the OH concentration appears to be perfectly related to the surface basic reactivity measured through 2-methyl-3-butyn-2-ol (MBOH) conversion. Thus, except for the similar carbonate content (in cases of low Ca/P values), the Ca/P ratio is not sufficient to predict the catalytic behavior of all HAps synthesized under various conditions: in the case of variable carbonate content monitored under different pH conditions, a larger range of Ca/P ratio can be obtained including over-stoichiometric HAps samples (Ca/P > 1.67), and the bulk OH concentration becomes a much better descriptor than the Ca/P ratio to account for the basic reactivity.
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https://hal.sorbonne-universite.fr/hal-01378491
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Submitted on : Monday, October 10, 2016 - 11:41:06 AM
Last modification on : Thursday, April 4, 2019 - 1:37:20 AM

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Manel Ben Osman, Jean Marc Krafft, Yannick Millot, Frederic Averseng, Tetsuya Yoshioka, et al.. Molecular Understanding of the Bulk Composition of Crystalline Nonstoichiometric Hydroxyapatites: Application to the Rationalization of Structure-Reactivity Relationships. European Journal of Inorganic Chemistry, Wiley-VCH Verlag, 2016, 2016 (17), pp.2709 - 2720. ⟨10.1002/ejic.201600244⟩. ⟨hal-01378491⟩

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