Hydrothermal synthesis of TiO2 anatase nanocrystals using hexaprismatic-shaped oxo-carboxylate complexes

Abstract

The molecular structural chemistry of titanium oxo-carboxylate complexes is critically reviewed with particular emphasis on the understanding of the various characterised molecular shapes. Among the four crucial parameters thought to have a structural influence on these shapes (nature of the OR alkoxy group, molar ratio C = O/Ti, stoichiometric ratio S = XCOOH/Ti and chemical nature of the carboxylic X moiety), it was concluded that the nature of R group, the C ratio and the steric hindrance of X were of minor importance. From the available data, it was also concluded that a high S ratio seems to favour corner-sharing versus edge-sharing of TiO 6 octahedra and that it was not possible to establish a clear correlation between the pK a value of the carboxylic acid and the observed molecular shape. During this study, a new titanium oxo-carboxylate complex was obtained by reacting titanium isopropoxide with phenylacetic acid (PAAH, X = PhCH 2 at S = 3/2). This hexaprismatic Ti 6 O 6 (OPr i ) 6 (PAA) 6 complex was characterised by single-crystal X-ray diffraction and used as a molecular precursor of TiO 2 anatase nanocrystals after hydrolysis by NMe 4 OH and autoclaving at T = 200 °C. The size and size distribution of these nanocrystals were found to decrease as the R = Ti/NMe 4 ratio was increased. Nucleation and growth of anatase nanocrystals was found to be deeply modified by the presence of phenylacetate ions in the solution, but there was no evidence of an influence of the molecular anisotropy of the molecular precursor on the final shape of the nanocrystals. To cite this article: A. Rammal et al., C. R. Chimie 5 (2002) 59-66 © 2002 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS hydrothermal synthesis / titanium oxo-carboxylates / nanocrystals / titania / anataseRésumé -Les structures moléculaires des oxo-carboxylates de titane connus à ce jour ont été passées en revue de manière critique. Parmi les quatre paramètres cruciaux pouvant avoir une influence sur la forme moléculaire (nature du groupement alkyle R, rapport molaire C = O/Ti, rapport stoechiométrique S = XCOOH/Ti et nature du radical X), on constate que la nature de R, le rapport C et l'encombrement stérique procuré par le radical X n'ont qu'une importance mineure. À partir des données collectées, on peut aussi conclure qu'un rapport S élevé favorise, pour les octaèdres TiO 6 , le partage des sommets au détriment du partage d'arêtes. Par ailleurs, il n'a pas été possible d'établir une relation claire entre le pK a de l'acide carboxylique utilisé et la structure moléculaire finale des complexes. Au cours de cette étude, un nouvel oxo-carboxylate de titane a été obtenu en faisant réagir l'isopropoxyde de titane avec l'acide phénylacétique (PAAH, X = PhCH 2 ) dans un rapport S = 3/2. Par diffraction des rayons X sur monocristal, il a été montré que ce nouveau complexe, de formule Ti 6 O 6 (OPr i ) 6 (PAA) 6 , adoptait une forme prismatique hexagonale déjà connue. Ces complexes ont été ensuite hydrolysés par l'hydroxyde de tétraméth...

In situ polymerization of titanium isopropoxide in polycaprolactone: Properties and characterization of the hybrid nanocomposites

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Preparation, characterization, and growth mechanism of a novel aligned nanosquare anatase in large quantities in the presence of TMAOH

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