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Molecular Understanding of the Bulk Composition of Crystalline Nonstoichiometric Hydroxyapatites: Application to the Rationalization of Structure–Reactivity Relationships
Author(s) -
Ben Osman Manel,
Krafft Jean Marc,
Millot Yannick,
Averseng Frederic,
Yoshioka Tetsuya,
Kubo Jun,
Costentin Guylène
Publication year - 2016
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201600244
Subject(s) - chemistry , stoichiometry , hydroxyapatites , reactivity (psychology) , carbonate , raman spectroscopy , catalysis , inorganic chemistry , analytical chemistry (journal) , chromatography , organic chemistry , calcium , medicine , physics , alternative medicine , pathology , optics
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, 31 P NMR and Raman characterizations, hydroxyapatites were obtained with a range of structural defects compared with the ideal stoichiometric compound. If the amount of HPO 4 2– 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.