4 research outputs found
Preparation of Tantalum-Based Oxynitride Nanosheets by Exfoliation of a Layered Oxynitride, CsCa<sub>2</sub>Ta<sub>3</sub>O<sub>10–<i>x</i></sub>N<sub><i>y</i></sub>, and Their Photocatalytic Activity
Calcium tantalum oxynitride [Ca<sub>2</sub>Ta<sub>3</sub>O<sub>9.7</sub>N<sub>0.2</sub>]<sup>−</sup> nanosheets were
prepared
by exfoliating a layered perovskite oxynitride (CsCa<sub>2</sub>Ta<sub>3</sub>O<sub>9.7</sub>N<sub>0.2</sub>) 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 [Ca<sub>2</sub>Ta<sub>3</sub>O<sub>9.7</sub>N<sub>0.2</sub>]<sup>−</sup> nanosheets
exhibited photocatalytic activity for H<sub>2</sub> evolution from
water under visible light irradiation. In contrast, CsCa<sub>2</sub>Ta<sub>3</sub>O<sub>9.7</sub>N<sub>0.2</sub> exhibited very low photocatalytic
activity for H<sub>2</sub> 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 [Ca<sub>2</sub>Ta<sub>3</sub>O<sub>9.7</sub>N<sub>0.2</sub>]<sup>−</sup> nanosheets restacked with protons
exhibited photocatalytic activity for H<sub>2</sub> and O<sub>2</sub> evolution from pure water under UV-light irradiation. The ratio
of H<sub>2</sub>/O<sub>2</sub> 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 Ta<sub>2</sub>O<sub>5</sub> has been successfully synthesized by a one-pot route
using P-123 as the structure directing agent (SDA). A series of crystalline
mesoporous Ta<sub>2</sub>O<sub>5</sub> 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 Ta<sub>2</sub>O<sub>5</sub> were characterized by XRD, TG-DTA, SEM, TEM, and N<sub>2</sub> sorption techniques. The photocatalytic activity of the as-synthesized
mesoporous Ta<sub>2</sub>O<sub>5</sub> with the cocatalyst NiO<sub><i>x</i></sub> for overall water splitting under ultraviolet
(UV) light irradiation was systematically evaluated. The photocatalytic
activity of crystalline mesoporous Ta<sub>2</sub>O<sub>5</sub> showed
about 3 times that of commercial Ta<sub>2</sub>O<sub>5</sub> powder
and 22 times that of amorphous mesoporous Ta<sub>2</sub>O<sub>5</sub>
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)Âsilylethynyl-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><sup><b>•–</b></sup> (550–1100 nm). The
DFT computation results suggested that the radical states of lowest
energy transitions occurred primarily from π to π<sub>SOMO</sub> or from π<sub>SOMO</sub> to π*
Visible-Light-Driven Photocatalytic Hydrogen Generation on Nanosized TiO<sub>2</sub>‑II Stabilized by High-Pressure Torsion
Photocatalytic
activity of pure TiO<sub>2</sub> is limited to ultraviolet
(UV) light due to the wide bandgap of anatase and rutile phases. The
bandgap of high-pressure phases of TiO<sub>2</sub> can theoretically
coincide with visible light, but these phases are unstable at ambient
pressure. In this work, the high-pressure TiO<sub>2</sub>-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 TiO<sub>2</sub>-II enhanced the hydrogen generation efficiency
under visible light, and the efficiency improved after removing the
oxygen vacancies by annealing