TY - JOUR
T1 - Surface structure, hydration, and cationic sites of nanohydroxyapatite
T2 - UHR-TEM, IR, and microgravimetric studies
AU - Bertinetti, Luca
AU - Tampieri, Anna
AU - Landi, Elena
AU - Ducati, Caterina
AU - Midgley, Paul A.
AU - Coluccia, Salvatore
AU - Martra, Gianmario
PY - 2007/3/15
Y1 - 2007/3/15
N2 - A multi-technique study devoted to investigate the surface features of nanosized hydroxyapatite (HA) was carried out. UHR-TEM observation provided evidence that HA nanoparticles are constituted by a crystalline core, elongated in the direction of the crystallographic c-axis, coated by an amorphous layer 1-2 nm thick. By means of IR spectroscopy and microgravimetry, the amount of water and hydroxy groups on the surface was evaluated. For the as-prepared material, it was found that the first hydration layer is mainly constituted by H2O molecules interacting through a coordinative bond with Ca 2+ in a 1:1 ratio, while hydroxy groups account only for ca. 20% of surface hydration species. Outgassing at increasing temperatures up to 300°C resulted in a complete surface dehydration, accompanied by a decrease of the capability to readsorb water. Possible changes of the local structure of surface Ca2+ ions were probed by IR spectra of adsorbed CO. The combination of these data with rehydration tests suggested that a significant part of surface Ca2+ ions, once dehydrated, can undergo a relaxation inward the surface, progressively more irreversible as the outgassing temperature increases.
AB - A multi-technique study devoted to investigate the surface features of nanosized hydroxyapatite (HA) was carried out. UHR-TEM observation provided evidence that HA nanoparticles are constituted by a crystalline core, elongated in the direction of the crystallographic c-axis, coated by an amorphous layer 1-2 nm thick. By means of IR spectroscopy and microgravimetry, the amount of water and hydroxy groups on the surface was evaluated. For the as-prepared material, it was found that the first hydration layer is mainly constituted by H2O molecules interacting through a coordinative bond with Ca 2+ in a 1:1 ratio, while hydroxy groups account only for ca. 20% of surface hydration species. Outgassing at increasing temperatures up to 300°C resulted in a complete surface dehydration, accompanied by a decrease of the capability to readsorb water. Possible changes of the local structure of surface Ca2+ ions were probed by IR spectra of adsorbed CO. The combination of these data with rehydration tests suggested that a significant part of surface Ca2+ ions, once dehydrated, can undergo a relaxation inward the surface, progressively more irreversible as the outgassing temperature increases.
UR - http://www.scopus.com/inward/record.url?scp=34047262561&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=34047262561&partnerID=8YFLogxK
U2 - 10.1021/jp066040s
DO - 10.1021/jp066040s
M3 - Article
AN - SCOPUS:34047262561
SN - 1932-7447
VL - 111
SP - 4027
EP - 4035
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 10
ER -