Synthesis of NaMoO3F and Na5W3O9F5 with Morphological Controllability in Non-Aqueous Solvents

Synthesis of Fluoride-Substituted Layered Perovskites ZnMoO4 with an Enhanced Photocatalytic Activity

Oxyfluorides possess considerable attention for their multiple excellent properties, but the conventional high-temperature solid-state syntheses have seen bottlenecks in the synthesis of new compounds. Herein, we report a novel layered oxyfluoride ZnMoO4:F, which is prepared by a facile hydrothermal method using ZnF2 as the fluoride source. The fluoride anions are successfully introduced into the oxygen sublattice, which is confirmed by a combined analysis using XRD, STEM, and TGA techniques. The as-synthesized ZnMoO4:F has an absorption edge at around 550 nm, indicating a red shift of Eg to the visible region compared to the oxide counterpart. The layered oxyfluoride exhibits an enhanced photocatalytic active for hydrogen evolution under simulated sunlight (λ > 350 nm), and the activity of ZnMoO4:F (651.9 μmol g-1) was 2 times higher than that of ZnMoO4 (309.7 μmol g-1). Further electrochemical analysis has shown that the conduction band position plays a critical role in the high performances of ZnMoO4:F. This work sheds new light on the future design and synthesis of novel fluoride-doped materials for photocatalysis applications.

Utility of NaMoO3F as a Precursor for Homogeneous Distribution of Cobalt Dopants in Molybdenum Oxynitrides

Molybdenum nitrides and their related compounds have been focused as a catalyst for several reactions. Although the doping into molybdenum nitrides lead to the higher catalytic activity, the simultaneous control of the morphology, the crystallinity, and the dopant state in doped MoN cannot be easily achieved due to the limitation of the synthesis method. In this study, one of the mixed anion compounds, NaMoO 3 F was used as a precursor for molybdenum oxynitrides with hexagonal MoN phase. This route led to the homogeneous distribution of cobalt in the molybdenum oxynitride compared with that obtained by the other method. The cobalt-doped molybdenum oxynitride from NaMoO 3 F exhibited high oxygen reduction reaction catalytic activity due to the high distribution of cobalt in the crystal. This paper proposes that the mixed anion compounds can be a unique precursor for the other materials to expand the controllability of materials toward improvement of their activity.

Electrochemical Crystal Growth of Titanium Oxyfluorides-A Strategy for Development of Electron-Doped Materials

We report on the growth of single crystals of an electron-doped titanium oxyfluoride, Li₂Ti(O,F)₃, employing high-temperature electrolysis of TiO₂ with a eutectic Li₂MoO₄-LiF melt. Greenish octahedral-shaped crystals (∼30 μm in size) with a cubic rocksalt-type structure were successfully obtained by precisely tuning the applied voltage. The temperature-dependent magnetic susceptibility data revealed a paramagnetic behavior at low temperatures, ensuring the presence of Ti³⁺ ions (mean valence number of +3.78; F/Ti ∼ 0.15). The crystals exhibited clear visible-light absorption and produced H₂ from water in the presence of a sacrificial reagent under UV-light irradiation. Li₂Ti(O,F)₃ more efficiently produced H₂ compared with a nondoped oxyfluoride Li₅Ti₂O₆F, likely due to the doped electrons for the former. This work highlights a promising electrochemical approach toward growing electron-doped oxyfluoride crystals.

Cation Substitution of Hexagonal Triple Perovskites: A Case in Trimetallic Tellurates A2A'BTe2O9

Three new tellurates, namely, K₂BaPb_0.62Ba_0.38Te₂O₉ (1), Rb₂BaPb_0.7Ba_0.3Te₂O₉ (2), and Ba₂KLiTe₂O₉ (3), with hexagonal triple-perovskite structures have been designed via a cation substitution strategy. All three centrosymmetric compounds crystallize in the same hexagonal space group P6₃/mmc. In their structures, the [BTe₂O₉] (B = Pb/Ba for 1 and 2 and Li for 3) groups construct the final three-dimensional framework using face-sharing [Te₂O₉] dimmers and vertex-linked [BO₆] linkages. Meanwhile, the theoretical calculations demonstrate the numerical differences of their birefringence. Thermal stability analysis and differential scanning calorimetry were performed, and UV-vis-NIR diffuse reflectance spectra and infrared spectra of the three title compounds were also characterized and analyzed.