Coordination chemistry of Ca sites at the surface of nanosized hydroxyapatite: interaction with H₂O and CO.

The affinity towards water of a selection of well-defined, nanostructured hydroxyapatite (HA) samples was investigated by H(2)O vapour adsorption microcalorimetry and infrared (IR) spectroscopy. A large hydrophilicity of all investigated materials was confirmed. The surface features of hydrated HA were investigated on the as-synthesized samples pre-treated in mild conditions at T=303 K, whereas dehydrated HA features were characterized on samples activated at T=573 K.

Water adsorption on the stoichiometric (001) and (010) surfaces of hydroxyapatite: a periodic B3LYP study.

H2O adsorption on hexagonal hydroxyapatite (001) and (010) stoichiometric surfaces has been studied at B3LYP level with a localized Gaussian basis set of polarized double-zeta quality using the periodic CRYSTAL06 code. Because four Ca2+ cations are available at both surfaces, the considered H2O coverages span the 1/4 View Article and Find Full Text PDF

Functionalization of zeolitic cavities: grafting NH2 groups in framework T sites of B-SSZ-13--a way to obtain basic solids catalysts?

Insertion of B atoms into an Al-free zeolitic framework with CHA topology results in the formation of B-SSZ-13 zeotype with Si/B = 11. B K-edge NEXAFS testifies that B forms [B(OSi)4] units in a Td-like geometry (sp3-hybridized B atoms). According to B K-edge NEXAFS and IR, template burning results in the formation of [B(OSi)3] units in a D3h-like geometry (sp2-hybridized B atoms) with a break of a B-O-Si bond and the formation of a Si-OH group.

Molecular water on exposed Al3+ cations is a source of acidity in silicoaluminas.

Evidence about the remarkable acidic nature of molecular water adsorbed at the surface of mesoporous MCM-41 silicoaluminas (MSA) with a ratio of Si/Al = 25 is reported, coming from both infrared spectroscopy and ab initio calculations. By using CO as a probe, OH stretching and HOH bending modes of water adsorbed on coordinatively unsaturated Al ions (Lewis sites) at the surface of MSA have been detected for the first time. CO adsorption causes OH stretching frequencies to suffer a bathochromic shift of about -200/-250 cm(-1), whereas the HOH bending frequency undergoes a hypsochromic shift by about +10/+20 cm(-1).

Thermodynamic study of water adsorption in high-silica zeolites.

The joint use of microcalorimetric and computational approaches has been adopted to describe H2O interaction with cus Al(III) Lewis and Si(OH)+ Al- Brønsted acidic sites within H-BEA and H-MFI zeolites (both with approximately 6 Al/unit cell). Adsorption data obtained at 303 K were compared to experimental model systems, such as all-silica zeolites, amorphous silica, and silico-alumina, transition alumina. In parallel, ab initio molecular modeling was carried out to mimic, in a cluster approach, Lewis and Brønsted acidic sites, as well as a variety of Si-OH species either with H-bonding interacting (nests and pairs) or isolated.

The surface of ordered mesoporous benzene-silica hybrid material: an infrared and ab initio molecular modeling study.

Joint IR and computational results allow a detailed characterization of the surface properties of a mesoporous benzene-silica hybrid material with crystal-like wall structure. After outgassing at 450 degrees C, hydroxyl species mainly consist of noninteracting silanols, with both O-H and Si-O stretching modes at lower frequencies than those of SiOH in silica. Interaction with several probe molecules, followed both by experiment and calculus, shows that the aryl group in the coordination sphere of Si imparts a lesser acidity with respect to the isolated silanol in silica.

Periodic ab initio study of structural and vibrational features of hexagonal hydroxyapatite Ca10(PO4)6(OH)2.

Structural and vibrational features of hexagonal hydroxyapatite HA [Ca(10)(PO(4))(6)(OH)(2), space group P6(3)] are computed ab initio within a periodic approach using the CRYSTAL03 program and the B3LYP hybrid functional with a Gaussian-type basis set of polarized double zeta quality. Experimental lattice parameters and internal coordinates have been fully optimized and the final structure characterized by means of its band structure, density of states and Mulliken analysis. The full B3LYP harmonic vibrational spectrum of HA at Gamma point has also been computed and compares well with the available experimental IR and Raman data.