Solvothermal Temperature Drives Morphological and Compositional Changes through Dehydroxyfluorination in Anatase Nanoparticles

Abstract

The reaction system employing titanium alkoxide and hydrofluoric acid under solvothermal conditions has been widely used to prepare anisotropic anatase crystals featuring a large percentage of reactive {001} facets. Nevertheless, such a reaction system leads to the stabilization of both the fluoride and hydroxide‐substituting oxide in the anatase network. The presence of both anions is compensated by the stabilization of titanium vacancies. In this work, we demonstrate that the synthesis temperature not only impacts the morphology of the as prepared nanoparticles but also their chemical composition/structural features. Depending on the reaction temperature, two main crystal growth mechanisms that are anisotropic and/or driven by oriented attachment were observed. The morphological changes are associated with a variation of the composition. Particularly, high temperature allows to eliminate most of the OH groups through oxolation reactions, but fluorine is thermally more stable as demonstrated by 1H and 19F solid‐state NMR spectroscopy. This work confirms that the abovementioned reaction system does not lead to pure titanium dioxide, which is an important aspect in linking composition/morphological features to the physico‐chemical properties.

There's no place like real-space: elucidating size-dependent atomic structure of nanomaterials using pair distribution function analysis

“…photocatalysis, 177,178 and it has also been the subject of several PDF studies. [179][180][181][182][183][184][185] One study focused on a combination of scattering techniques for the analysis of TiO 2 (B) nanocrystal morphology and faceting. 186 These particles are prone to aggregation which made unambiguous morphology determinations by TEM difficult.…”

Layered Lepidocrocite Type Structure Isolated by Revisiting the Sol–Gel Chemistry of Anatase TiO2: A New Anode Material for Batteries

“…28 The NMR resonances in the ranges 1-2 ppm and 4-5 ppm and at ~7.4 and ~9.0 ppm are therefore tentatively assigned to Ti -OH and Ti 3 -OH species, Ti 2 -OH and Ti 2 2 -OH species, Ti 3 -OH and Ti 4 -OH species, respectively ( Table 1), in agreement with recent studies on titanium oxy-hydroxy-fluoride containing titanium vacancies. 29,30 The broad resonance located at ~6.5 ppm is assigned to the H 2 O molecules. Its relative intensity (~33%) supports this assignment since based on the chemical composition, OH groups and H 2 O molecules account for 65% and 35% of the proton intensity, respectively.…”

Red-Shifted Absorptions of Cation-Defective and Surface-Functionalized Anatase with Enhanced Photoelectrochemical Properties

“…56 19 F solid-state NMR was also used to quantify the fluorine content on the studied samples by using reference samples. 20−22,55…”

“…20 This synthesis method allows to stabilize anisotropic particles with a large percentage of reactive (001) facets along with a high concentration of titanium vacancies arising from a large substitution rate of O 2– by F – /OH – . 21,22…”