Morphology control of anatase TiO₂ for well-defined surface chemistry

Abstract

A specific allotrope of titanium dioxide (anatase) was synthesized both with a standard thermodynamic morphology ({101}-anatase) and with a highly anisotropic morphology ({001}-anatase) dominated by the {001} facet (81%). The surface chemistry of both samples after dehydroxylation was studied by 1H NMR and FT-IR. The influence of surface fluorides on the surface chemistry was also studied by 1H NMR, FT-IR and DFT. Full attribution of the IR spectra of anatase with dominant {001} facets could be provided based on experimental data and further confirmed by DFT. Our results showed that chemisorbed H2O molecules are still present on anatase after dehydroxylation at 350 °C, and that the type of surface hydroxyls present on the {001} facet is dependent on the presence of fluorides. They also provided general insight into the nature of the surface species on both fluorinated and fluorine-free anatase. The use of vanadium oxychloride (VOCl3) allowed the determination of the accessibility of the various OH groups spectroscopically observed.

Structure, Morphology, and Faceting of TiO2 Photocatalysts by the Debye Scattering Equation Method. The P25 and P90 Cases of Study

“…Among those NCs which are well known to adopt a clear morphology with non-orthogonal faceting, titania, in the form of anatase, is a paradigmatic case. As anticipated, slightly truncated square bipyramids, exposing {101} and {001} facets, are predicted to be the equilibrium shape in bulk anatase and are frequently imaged also at the nanoscale [7,49].…”

Visible Light-Driven Photocatalytic Activity and Kinetics of Fe-Doped TiO2 Prepared by a Three-Block Copolymer Templating Approach

“…As expected, the OH spectra are dominated by the IR features of the H-bond, due to the presence of adsorbed water: in particular, the bands at 3630 cm −1 and ~3460 cm −1 (asterisks) are, respectively, ascribed to the asymmetric and symmetric OH stretching modes of H 2 O molecules strongly adsorbed on Ti 4+ sites, the corresponding bending mode being observed at 1620 cm −1 (not shown). The bands at 3674 and 3644 cm −1 are ascribed to different types of Ti-OH species, usually observed at the surface of anatase crystalline planes [ 58 ]. Interestingly, with the Fe(2.5)-TiO 2 sample an additional band is seen at 3360 cm −1 : the band is tentatively ascribed to the presence of another kind of OH species [ 59 ], induced by the presence of Fe at the NPs surface, as the same band was hardly discernible with the Fe(1.0)-TiO 2 sample, but still visible with the Fe(3.5)-TiO 2 sample, in agreement with the, respectively, low and high Fe contents.…”

Direct Synthesis of Dimethyl Ether from Syngas on Bifunctional Hybrid Catalysts Based on Supported H3PW12O40 and Cu-ZnO(Al): Effect of Heteropolyacid Loading on Hybrid Structure and Catalytic Activity

“…There is no significant displacement or widening of the HPW signals in the xHPW/Ti acid catalysts which indicates that the Keggin structure of HPW has not been significantly distorted after supporting on TiO2. In the region 3800-2500 cm −1 , the titania support (Figure 2a) presents a broad band around 3332 cm −1 corresponding to physisorbed water molecules and contributions at 3528 and 3638 cm −1 ascribed to isolated hydroxyl groups on TiO2 and dissociatively adsorbed water on TiO2 respectively [31]. The physisorbed water on TiO2 was corroborated by the band of the OH bending at 1636 cm −1 [32].…”