Molecular Understanding of the Bulk Composition of Crystalline Nonstoichiometric Hydroxyapatites: Application to the Rationalization of Structure-Reactivity Relationships
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 comp...
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Published in | European journal of inorganic chemistry Vol. 2016; no. 17; pp. 2709 - 2720 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
Weinheim
Blackwell Publishing Ltd
01.06.2016
Wiley Subscription Services, Inc Wiley-VCH Verlag |
Subjects | |
Online Access | Get full text |
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Summary: | 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.
Real hydroxyapatites contain many bulk structural defects, the relative content of which cannot simply be deduced from the Ca/P ratio alone. In particular, the defects impact the OH content, which controls the acid–base properties of this system for many catalytic reactions. |
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Bibliography: | ark:/67375/WNG-JVXMBKLD-J istex:953A8B6BFA45A7E5DAB03C1D722CF4B1EB988BA4 ArticleID:EJIC201600244 Supporting Information ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 1434-1948 1099-0682 |
DOI: | 10.1002/ejic.201600244 |