Preparation of Tantalum-Based Oxynitride Nanosheets by Exfoliation of a Layered Oxynitride, CsCa₂Ta₃O_{10–<i>x</i>}N_<i>y</i>, and Their Photocatalytic Activity

Calcium tantalum oxynitride [Ca₂Ta₃O_9.7N_0.2]⁻ nanosheets were prepared by exfoliating a layered perovskite oxynitride (CsCa₂Ta₃O_9.7N_0.2) via proton exchange and two-step intercalation of ethylamine and tetrabutylammonium ions. Monolayer nanosheet was prepared by the above processes, although some bilayer or trilayer nanosheets were also produced. The [Ca₂Ta₃O_9.7N_0.2]⁻ nanosheets exhibited photocatalytic activity for H₂ evolution from water under visible light irradiation. In contrast, CsCa₂Ta₃O_9.7N_0.2 exhibited very low photocatalytic activity for H₂ evolution under the visible light irradiation, even when methanol was added to water as a sacrificial agent. The improved photocatalytic activity originates from the characteristics of nanosheets such as their molecular thickness and large surface area. Further, the Rh-loaded [Ca₂Ta₃O_9.7N_0.2]⁻ nanosheets restacked with protons exhibited photocatalytic activity for H₂ and O₂ evolution from pure water under UV-light irradiation. The ratio of H₂/O₂ evolved was around 3. The ratio of N/O in the catalyst remained the same after the photocatalytic reaction, signifying that there was no decomposition of the catalyst during the reaction. This indicates that the present N-doped nanosheet is stable in the photocatalytic reaction

One-Pot Soft-Templating Method to Synthesize Crystalline Mesoporous Tantalum Oxide and Its Photocatalytic Activity for Overall Water Splitting

Crystalline mesoporous Ta₂O₅ has been successfully synthesized by a one-pot route using P-123 as the structure directing agent (SDA). A series of crystalline mesoporous Ta₂O₅ samples has been prepared by changing the calcination temperature. The surface area decreased and the pore size increased with the increasing calcination temperature, which were the results of crystallite growth. At the same time, the pore volume was well maintained, which means limited shrinkage during the calcination of elevated temperature. The porous structure and crystal structure of as-synthesized mesoporous Ta₂O₅ were characterized by XRD, TG-DTA, SEM, TEM, and N₂ sorption techniques. The photocatalytic activity of the as-synthesized mesoporous Ta₂O₅ with the cocatalyst NiO_<i>x</i> for overall water splitting under ultraviolet (UV) light irradiation was systematically evaluated. The photocatalytic activity of crystalline mesoporous Ta₂O₅ showed about 3 times that of commercial Ta₂O₅ powder and 22 times that of amorphous mesoporous Ta₂O₅

Synthesis and Investigation of the Effect of Substitution on the Structure, Physical Properties, and Electrochemical Properties of Anthracenodifuran Derivatives

A series of <i>syn</i>/<i>anti</i> mixtures of anthradifuran (ADF) and substituent compounds were systematically synthesized, and the effect of substitution at the 5,11-positions on the neutral and radical states of ADF was investigated. All compounds were measured and analyzed by absorption and fluorescence spectroscopy, cyclic voltammetry, electrochemical absorption spectroscopy, and DFT calculations. The absorption spectra of 5,11-substituent compounds in their neutral state were red-shifted. In addition, the substituted compounds exhibited increased thermal stability with respect to the parent <b>1a</b> because of elongation of the π-conjugation and an increased steric hindrance effect due to the bulky ethynyl substituent groups. The cyclic voltammograms of all of the compounds exhibited irreversible reduction potentials and irreversible oxidation potentials, except in the case of (trimethylsilyl)­silylethynyl-substituted ADF. When the materials were subjected to oxidation/reduction potentials, the radical cation and anion species were generated. The absorption spectra of the radical-cation species of the compounds exhibited similar characteristics and similar absorption ranges (550–1400 nm), whereas the spectra of the radical anion species were blue-shifted (550–850 nm) compared than that of the parent <b>1a</b>^{<b>•–</b>} (550–1100 nm). The DFT computation results suggested that the radical states of lowest energy transitions occurred primarily from π to π_SOMO or from π_SOMO to π*

Visible-Light-Driven Photocatalytic Hydrogen Generation on Nanosized TiO₂‑II Stabilized by High-Pressure Torsion

Photocatalytic activity of pure TiO₂ is limited to ultraviolet (UV) light due to the wide bandgap of anatase and rutile phases. The bandgap of high-pressure phases of TiO₂ can theoretically coincide with visible light, but these phases are unstable at ambient pressure. In this work, the high-pressure TiO₂-II (columbite) phase with large fractions of oxygen vacancies was stabilized by inducing plastic strain to anatase under 6 GPa. The material could absorb visible light as a consequence of bandgap narrowing by ∼0.7 eV. Formation of nanosized TiO₂-II enhanced the hydrogen generation efficiency under visible light, and the efficiency improved after removing the oxygen vacancies by annealing