Femtosecond to second time-resolved visible to mid-infrared absorption spectroscopy was applied to investigate the behavior of photogenerated electrons and holes on a Pt- or CoO x -loaded LaTiO2N photocatalyst. CoO x -loaded catalyst exhibits the highest activity for water oxidation under visible light (<600 nm) excitation, and the quantum efficiency reaches up to ∼30%. Transient absorption spectra suggest that most of the photoexcited electrons in LaTiO2N lose activity by deep trapping in the mid-gap states created at 0.74 eV (6000 cm–1) below the conduction band. In this case, Pt loading was not so effective for H2 evolution because the loaded Pt could not effectively capture the trapped electrons from LaTiO2N. The electron transfer was slow, proceeding in 0–100 μs, and was thus ineffective. However, in the case of CoO x loading, we have clearly observed, for the first time, that the holes are captured rapidly by CoO x in a few picoseconds, and the lifetimes of electrons are dramatically prolonged to the second region. This implies that the photogenerated holes and electrons are separated effectively in CoO x and LaTiO2N, respectively. Furthermore, the electron trap becomes shallower, its depth decreasing from 0.74 eV (6000 cm–1) to 0.49 eV (4000 cm–1) upon CoO x loading, suggesting that the reactivity of the trapped electrons increases. These perturbations of electrons and holes are what cause the dramatic increase in photocatalytic activity. We expected that coloading of Pt and CoO x would further increase the activity, but it was significantly reduced. It was demonstrated that the undesirable process of recombination is accelerated under high loading and coloading.

New semiconductors and host materials are expected to be found among newly synthesized boron/carbon/nitrogen (B/C/N) materials based on the graphite network. The synthesis, structure, and properties of such materials, including solid solutions, more‐ordered B/C/N hybrids, and compounds (e.g., BC3, C5N, BC2N, BC3N, BC4N, BC6N2H3), are reviewed. Particular attention is paid to their electrical properties, luminescenc characteristics, and intercalation chemistry, together with the application of B/C/N materials as a battery electrode matrix.

which are described as BCN(H) and BC 3 N(H), have been prepared by the interaction of acetonitrile with boron trichloride in a hydrogen and nitrogen atmosphere and acrylonitrile with boron trichloride, respectively. X-ray and electron diffraction analyses indicate that these materials have hexagonal structures similar to that of graphite. ESCA spectra and the possible chemical bonds suggest that the ideal structure of BCN is made of the unit structure of BC 2 N + BN, while BC 3 N is composed of BC 3 N + BNC 3 . A BCN(H) plate has a basal-plane conductivity of 1.28 (Ω cm) -1 at room temperature, while a BC 3 N(H) plate has that of 88.5 (Ω cm) -1 . Thermoelectric measurements indicate that both materials behave as p-type semiconductors and a BCN(H) plate has a high Seebeck coefficient of 300 µV/°K at room temperature in air.

The effects of defects on the behavior of photogenerated charge carriers in SrTiO3 (STO) are studied by time-resolved absorption spectroscopy from the visible to mid-IR region. In the case of defect-free single-crystalline STO, free and shallowly trapped electrons are dominant, but they recombine within 50 ns. By contrast, in the case of defect-rich powder STO, the electron lifetime is much longer than 1 ms. The transient absorption spectra show that most of the charge carriers in powder STO are trapped in the defects, which elongates their lifetime. We found that these trapped carriers are nevertheless reactive toward O2 or CH3OH that depends on the trap depth. The steady-state photocatalytic activity is strongly correlated with the lifetime and the reactivity of the trapped charge carriers: the energy state of electrons can be deduced from the spectral shape, especially in the mid-IR region.

Regularly coiled carbon filaments have been obtained by the catalytic pyrolysis of acetylene at 350–750 °C using Ni plate and powder as a catalyst. Morphology and extension characteristics of the obtained coiled filaments were examined in some detail. The regularly coiled filaments have generally a 0.1–0.3 μm thickness, a 2–8 μm coil diameter, and a 0.1–5 mm coil length. The coiled filaments were always formed by the entwistness of two pair coils which grew in the same direction simultaneously from a diamond-shaped Ni seed. We have found that the coiled filaments could be elastically extended up to about three times versus the original coil length.

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A B S T R A C TThe effects of the morphology-change of SrTiO 3 particles on the behavior of photogenerated charge carriers are studied by time-resolved absorption (TA) spectroscopy from the visible to mid-IR region. In the case of as-purchased defect-rich commercial SrTiO 3 particles, most of the charge carriers are deeply trapped, showing a transient absorption peak at 11,000 cm À1 . Scanning electron microscopy reveals that the irregular-shaped primary particles are heavily aggregated and that the photocatalytic activity for the water splitting reaction is negligibly small. However, when this powder is flux-treated by SrCl 2 , fine cubic SrTiO 3 crystals exposing well-defined surfaces are formed and the photocatalytic activity is greatly improved. TA measurements show that the spectral shape is changed dramatically: the number of deeply trapped electrons is reduced, and that of shallowly trapped electrons producing the absorption band at 2500 cm À1 is increased. The change in electron trap depth, observed upon flux treatment, is due to the decrease in the number of defects. We also found that further flux treatment in an Al 2 O 3 crucible (i) induces Al doping into SrTiO 3 , (ii) enhances the photocatalytic activity, (iii) changes the spectral shape, and (iv) prolongs the lifetime of shallowly trapped electrons. The increase in photocatalytic activity is presumably due to the change in lifetime.

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