Transformations of dimeric and tetrameric glycolato peroxotitanates and their thermal decompositions for the preparations of anatase and rutile oxides

Photoactivation of titanium-oxo cluster [Ti6O6(OR)6(O2C t Bu)6]: mechanism, photoactivated structures, and onward reactivity with O2 to a peroxide complex

The molecular titanium-oxo cluster [Ti₆O₆(OⁱPr)₆(O₂C ^t Bu)₆] (1) can be photoactivated by UV light, resulting in a deeply coloured mixed valent (photoreduced) Ti (iii/iv) cluster, alongside alcohol and ketone (photooxidised) organic products. Mechanistic studies indicate that a two-electron (not free-radical) mechanism occurs in this process, which utilises the cluster structure to facilitate multielectron reactions. The photoreduced products [Ti₆O₆(OⁱPr)₄(O₂C ^t Bu)₆(sol)₂], sol = ⁱPrOH (2) or pyridine (3), can be isolated in good yield and are structurally characterized, each with two, uniquely arranged, antiferromagnetically coupled d-electrons. 2 and 3 undergo onward oxidation under air, with 3 cleanly transforming into peroxide complex, [Ti₆O₆(OⁱPr)₄(O₂C ^t Bu)₆(py)(O₂)] (5). 5 reacts with isopropanol to regenerate the initial cluster (1) completing a closed cycle, and suggesting opportunities for the deployment of these easily made and tuneable clusters for sustainable photocatalytic processes using air and light. The redox reactivity described here is only possible in a cluster with multiple Ti sites, which can perform multi-electron processes and can adjust its shape to accommodate changes in electron density.

The Influence of Annealing on the Optical Properties and Microstructure Recrystallization of the TiO2 Layers Produced by Means of the E-BEAM Technique

Titanium dioxide films, about 200 nm in thickness, were deposited using the e-BEAM technique at room temperature and at 227 °C (500K) and then annealed in UHV conditions (as well as in the presence of oxygen (at 850 °C). The fabricated dielectric films were examined using X-ray powder diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and spectroscopic ellipsometry. The applied experimental techniques allowed us to characterize the phase composition and the phase transformation of the fabricated TiO₂ coatings. The films produced at room temperature are amorphous but after annealing consist of anatase crystallites. The layers fabricated at 227 °C contain both anatase and rutile phases. In this case the anatase crystallites are accumulated near the substrate interface whilst the rutile crystallites were formed closer to the surface of the TiO₂ film. It should be emphasized that these two phases of TiO₂ are distinctly separated from each other.

Synthesis, Structural and Physicochemical Characterization of a Titanium(IV) Compound with the Hydroxamate Ligand N,2-Dihydroxybenzamide

The siderophore organic ligand N,2-dihydroxybenzamide (H2dihybe) incorporates the hydroxamate group, in addition to the phenoxy group in the ortho-position and reveals a very rich coordination chemistry with potential applications in medicine, materials, and physical sciences. The reaction of H2dihybe with TiCl4 in methyl alcohol and KOH yielded the tetranuclear titanium oxo-cluster (TOC) [TiIV4(μ-O)2(HOCH3)4(μ-Hdihybe)4(Hdihybe)4]Cl4∙10H2O∙12CH3OH (1). The titanium compound was characterized by single-crystal X-ray structure analysis, ESI-MS, 13C, and 1H NMR spectroscopy, solid-state and solution UV-Vis, IR vibrational, and luminescence spectroscopies and molecular orbital calculations. The inorganic core Ti4(μ-O)2 of 1 constitutes a rare structural motif for discrete TiIV4 oxo-clusters. High-resolution ESI-MS studies of 1 in methyl alcohol revealed the presence of isotopic distribution patterns which can be attributed to the tetranuclear clusters containing the inorganic core {Ti4(μ-O)2}. Solid-state IR spectroscopy of 1 showed the presence of an intense band at ~800 cm-1 which is absent in the spectrum of the H2dihybe and was attributed to the high-energy ν(Ti2-μ-O) stretching mode. The ν(C=O) in 1 is red-shifted by ~10 cm-1, while the ν(N-O) is blue-shifted by ~20 cm-1 in comparison to H2dihybe. Density Functional Theory (DFT) calculations reveal that in the experimental and theoretically predicted IR absorbance spectra of the ligand and Ti-complex, the main bands observed in the experimental spectra are also present in the calculated spectra supporting the proposed structural model. 1H and 13C NMR solution (CD3OD) studies of 1 reveal that it retains its integrity in CD3OD. The observed NMR changes upon addition of base to a CD3OD solution of 1, are due to an acid-base equilibrium and not a change in the TiIV coordination environment while the decrease in the complex's lability is due to the improved electron-donating properties which arise from the ligand deprotonation. Luminescence spectroscopic studies of 1 in solution reveal a dual narrow luminescence at different excitation wavelengths. The TOC 1 exhibits a band-gap of 1.98 eV which renders it a promising candidate for photocatalytic investigations.

Facile synthesis of brookite TiO2 nanoparticles

Brookite is the most difficult TiO2 polymorph to obtain in phase pure form. Here we report on a facile synthesis method for phase-pure brookite nanoparticles using a broad range of titanium precursors. General availability of phase pure brookite opens up multiple research activities to explore both fundamental properties as well as applications. The synthesis method is scalable and thus it potentially allows for large-scale industrial production.