The author and coworkers focused on the fabrication of composite photocatalysts and charge transfer between composite constituents for increased activity and sensitivity to visible light, aiming at ...developing materials for environmental preservation through the oxidative decomposition of organic pollutants and clean energy production through water splitting for hydrogen generation. Cu2+ ion-grafted titanium dioxide (TiO2) was designed on the basis of visible-light-induced interfacial charge transfer from the valence band (VB) of TiO2 to Cu2+, generating high oxidative decomposition activity owing to the utilization of photogenerated holes in the VB of TiO2. Cu+ produced by electron injection was converted back to Cu2+ by oxygen (O2) reduction through multi-electron O2 reduction reaction. As for water splitting, zinc rhodium oxide (ZnRh2O4) and bismuth vanadate (Bi4V2O11) as H2 and O2 evolution photocatalysts, respectively, were connected with silver (Ag), acting as a solid-state electron mediator, to prepare a composite photocatalyst that is sensitive to red light. The key function of the heterojunction photocatalyst is the transfer of photoexcited electrons from the conduction band (CB) of Bi4V2O11 to the VB of ZnRh2O4 via Ag. Thus, the photoexcited electrons in the CB of ZnRh2O4 and the holes in the VB of Bi4V2O11 effectively reduced and oxidized water, respectively, thereby splitting water and liberating H2 and O2 at a stoichiometric ratio.
Through the use of a strategy that involves narrowing the TiO2 band gap by shifting its conduction band positively and utilizing the catalytic activity of photoproduced Cu(I) for oxygen reduction, a ...novel visible-light-sensitive TiO2 photocatalyst, Cu(II)-grafted Ti1−3x W x Ga2x O2, was designed and synthesized. The Cu(II)/Ti1−3x W x Ga2x O2 photocatalyst produced high activity under visible-light irradiation. In fact, it decomposed 2-propanol to CO2 via acetone under visible light (>400 nm) with a high quantum efficiency of 13%. The turnover number for this reaction exceeded 22, indicating that it functioned catalytically.
Abstract
Magnetic Weyl semimetals have novel transport phenomena related to pairs of Weyl nodes in the band structure. Although the existence of Weyl fermions is expected in various oxides, the ...evidence of Weyl fermions in oxide materials remains elusive. Here we show direct quantum transport evidence of Weyl fermions in an epitaxial 4
d
ferromagnetic oxide SrRuO
3
. We employ machine-learning-assisted molecular beam epitaxy to synthesize SrRuO
3
films whose quality is sufficiently high to probe their intrinsic transport properties. Experimental observation of the five transport signatures of Weyl fermions—the linear positive magnetoresistance, chiral-anomaly-induced negative magnetoresistance, π phase shift in a quantum oscillation, light cyclotron mass, and high quantum mobility of about 10,000 cm
2
V
−1
s
−1
—combined with first-principles electronic structure calculations establishes SrRuO
3
as a magnetic Weyl semimetal. We also clarify the disorder dependence of the transport of the Weyl fermions, which gives a clear guideline for accessing the topologically nontrivial transport phenomena.
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For the efficient and stable electrochemical reduction of carbon dioxide (CO2), we fabricated bimetallic catalysts composed of palladium (Pd) nanoparticles covered with copper (Cu) ...atomic layers. While a monometallic Pd nanoparticle catalyst has high activity toward the reduction of CO2 to formate, it has been reported to be readily subjected to self-poisoning by carbon monoxide (CO), which is produced as a minor byproduct of CO2 reduction. Cu layers prepared by underpotential deposition induced charge transfer from Pd to Cu and a downward shift of the average d-band center of the catalyst relative to the Fermi level. As a result, the Cu-modified Pd catalyst demonstrated improved CO tolerance and an increase in Faradaic efficiency for formate production without sacrificing CO2 reduction activity.
Photocatalytic degradation of organic compounds requires photoexcited holes with strong oxidative power in the valence band (VB) of semiconductors. Although numerous types of doped semiconductors, ...such as nitrogen-doped TiO2, have been studied as visible-light-sensitive photocatalysts, the quantum yields of these materials were very low because of the limited oxidation power of holes in the nitrogen level above the VB. Recently, we developed visible-light-sensitive Cu(II) and Fe(III) nanocluster-grafted TiO2 using a facile impregnation method and demonstrated that visible-light absorption occurs at the interface between the nanoclusters and TiO2, as electrons in the VB of TiO2 are excited to the nanoclusters under visible-light irradiation. In addition, photogenerated holes in the VB of TiO2 efficiently oxidize organic contaminants, and the excited electrons that accumulate in nanoclusters facilitate the multielectron reduction of oxygen. Notably, Cu(II) and Fe(III) nanocluster-grafted TiO2 photocatalyst has the highest quantum yield among reported photocatalysts and has antiviral, self-cleaning, and air purification properties under illumination by indoor light fixtures equipped with white fluorescent bulbs or white light-emitting diodes.
We have prepared a TiO2-based novel visible-light-sensitive photocatalyst, in which Fe(III) species were grafted on a rutile TiO2 surface (denoted as Fe(III)/TiO2). With use of X-ray absorption fine ...structure analysis, the grafted iron species were determined to be in the 3+ state and adopt an amorphous FeO(OH)-like structure. Fe(III)/TiO2 displayed optical absorption in the visible light range over 400 nm, which was assigned to the interfacial charge transfer from the valence band of TiO2 to the surface Fe(III) species. Its photocatalytic activity was evaluated by the decomposition of gaseous 2-propanol under visible light (400−530 nm), which revealed a high quantum efficiency (QE) of 22%. Monochromatic light experiments indicated that the effective wavelength region was extended as far as 580 nm while maintaining a QE of greater than 10%. On the basis of the analogy to Cu(II)-grafted TiO2 photocatalyst (Irie, H.; et al. Chem. Phys. Lett. 2008, 457, 202), we speculate that the high performance of the present photocatalyst is derived from the photoproduced holes that are generated in the valence band of TiO2 and contribute to the oxidative decomposition of 2-propanol, and the catalytic reduction of oxygen (presumably multielectron reduction) by photoproduced Fe(II) species on TiO2.
The utilization of a support material has been an effective method for the management of proton transfer on catalytic active centers. Previous studies showed that the large overpotential of α-Fe2O3 ...for the oxygen evolution reaction (OER) resulted from the sequential transfer of electrons and protons. Here, by combining α-Fe2O3 with La2O3, which functions as a solid proton acceptor, concerted proton–electron transfer (CPET) was induced. The induction of CPET facilitated the formation of intermediate species, leading to the OER activity enhancement at neutral pH. This work may provide useful insight for the design of promising OER catalysts, which is pivotal for energy conversion.
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