The oxygen evolution reaction (OER) with a large overpotential is the key step common to artificial photosynthesis. In semiconductor photocatalysts, the light available to the reactions is usually ...limited to UV or visible with wavelengths shorter than the absorption edge of the semiconductors. On the other hand, gold nanoparticle (Au NP)-based plasmonic photocatalysts, particularly hot-electron transfer (HET)-type plasmonic photocatalysts, have the capability to utilize visible-to-near infrared light that makes up most sunlight as a driving force for the energetically uphill reactions. In recent years, experimental and theoretical studies on HET-type plasmonic photocatalysts consisting of Au NPs and a semiconductor have been intensively pursued. This perspective article highlights the fundamentals and recent progress of Au NP-based HET-type plasmonic photocatalysts for OER. After the introduction, the basics for the rational design of plasmonic photocatalysts are treated first. Secondly, the concrete design for the plasmonic photocatalysts is dealt with in the order of semiconductors, Au NPs, and their interface. Thirdly, recent advanced studies on plasmonic photocatalysts for OER are described. Finally, the conclusions are summarized with a direction for future research on plasmonic photocatalysts.
Antimony dopants in tin oxide (SnO2:Sb) occupy part of the Sn sites in the crystal lattice to be dispersed at an atomic level. The resulting generation of conduction band electrons gives rise to high ...electric conductivity and strong optical absorption in the near-infrared region. Chemically, SnO2:Sb possesses electrocatalytic activities for the two-electron oxygen reduction reaction (2e–-ORR) with an extraordinary low affinity for H2O2 and one-electron water oxidation reaction (1e–-WOR). Owing to these unique properties, SnO2:Sb is currently finding its applications for green and sustainable chemistry. This Perspective outlines the fundamentals and applications of SnO2:Sb. The fundamental parts deal with the three-dimensional single-atom-catalyst-like character of SnO2:Sb and the electrocatalytic activities for 2e–-ORR and 1e–-WOR. In the subsequent application parts, SnO2:Sb-catalyzed electrochemical and photocatalytic reactions including hydrogen peroxide synthesis, low-temperature oxidative organic transformations, and decomposition of organic water pollutants are described with the photothermal catalytic reactions. Finally, the conclusions and future prospects are summarized.
Gold nanoparticle‐loaded rutile TiO2 with a bimodal size distribution around 10.6 nm and 2.3 nm (BM‐Au/TiO2) was prepared by the deposition precipitation and chemical reduction (DP‐CR) technique. ...Visible‐light irradiation (λ>430 nm) of the BM‐Au/TiO2 plasmonic photocatalyst yields 35 μm H2O2 in aerated pure water at irradiation time (tp)=1 h, and the H2O2 concentration increases to 640±60 μm by the addition of 4 % HCOOH as a sacrificing electron donor. Further, a carbonate‐modified surface BM‐Au/TiO2 (BM‐Au/TiO2‐CO32−) generates a millimolar level of H2O2 at tp=1 h with a quantum efficiency (Φ) of 5.4 % at λ=530 nm under the same conditions. The recycle experiments confirmed the stable performance of BM‐Au/TiO2.
Solar hydrogen peroxide formation: Hydrogen peroxide was produced from molecular oxygen at millimolar level over bimodal gold‐nanoparticle‐decorated rutile by visible‐light irradiation (see picture). Formic acid was used as electron donor and carbonate molecules were absorbed onto the rutile surface to minimize the simultaneous loss of hydrogen peroxide (LSPR=localized surface plasmon resonance).
Natural photosynthesis, which achieves efficient solar energy conversion through the combined actions of many types of molecules ingeniously arranged in a nanospace, highlights the importance of a ...technique for site-selective coupling of different materials to realize artificial high-efficiency devices. In view of increasingly serious energy and environmental problems, semiconductor-based artificial photosynthetic systems consisting of isolated photochemical system 1 (PS1), PS2 and the electron-transfer system have recently been developed. However, the direct coupling of the components is crucial for retarding back reactions to increase the reaction efficiency. Here, we report a simple technique for forming an anisotropic CdS-Au-TiO2 nanojunction, in which PS1(CdS), PS2(TiO2) and the electron-transfer system (Au) are spatially fixed. This three-component system exhibits a high photocatalytic activity, far exceeding those of the single- and two-component systems, as a result of vectorial electron transfer driven by the two-step excitation of TiO2 and CdS.
The development of environmental catalysts is an urgent subject to be tackled by scientists and engineers all over the world due to the borderless nature of environmental pollution. We named the ...catalyst enabling the decomposition of the pollutants by effectively utilizing the solar energy from ultraviolet to infrared as “solar environmental catalysts”. This Feature Article reviews the recent studies on a novel class of solar environmental catalysts consisting of TiO2 and molecular scale oxides of 3d metals and for comparison d10 (Sn) on the surface (MOs/TiO2). The TiO2 surface modification with MO clusters by the chemisorption–calcination cycle (CCC) technique presents novel band engineering for finely tuning the top of the valence band, while the unique physicochemical and electronic properties of MOs/TiO2 give rise to the outstanding photo- and thermocatalytic activities for the decomposition of organic pollutants. In the first part following the Introduction, the CCC technique for forming extremely small MO clusters on TiO2, the structures, physicochemical properties, and electronic structures of MOs/TiO2 are described. The second part deals with their thermo- and photocatalytic activities for the degradation of model organic pollutants and the essential action mechanisms of the MO clusters. The combination of experiments and first-principles density functional theory simulations shows that Co2O3/TiO2 can be a prototype of the solar environmental catalyst with high levels of photo(UV and visible)- and thermocatalytic activities.
Gold nanoparticle loading has led to a drastic enhancement of TiO2-photocatalized generation of H2O2 from O2 with a unique inversed volcano-type relation between the activity and Au particle size.
A solid-phase photochemical method produces Au-Ag alloy nanoparticles (NPs) with a sharp size distribution and varying composition in AgBr crystals (Au-Ag@AgBr). These features render Au-Ag@AgBr ...promising as a material for the plasmonic photocatalyst further to provide a possibility of elucidating the action mechanism due to the optical tunability. This study shows that the visible-light activity of Au-Ag@AgBr for degradation of model water pollutant is very sensitive to the alloy composition with a maximum at the mole percent of Au to all Ag in AgBr (y) = 0.012 mol%. Clear positive correlation is observed between the photocatalytic activity and the quality factor defined as the ratio of the peak energy to the full width at half maximum of the localized surface plasmon resonance band. This finding indicates that Au-Ag@AgBr works as a local electromagnetic field enhancement-type plasmonic photocatalyst in which the Au-Ag NPs mainly promotes the charge separation. This conclusion was further supported by the kinetic analysis of the light intensity-dependence of external quantum yield.
Among various metal oxide-supported Au nanoparticles, Au/rutile TiO2 exhibits a particularly high level of visible-light activity for aerobic oxidation of amines to yield the corresponding imines on ...a synthetic scale with high selectivity (>99%) at 298 K. Experimental results have suggested that the reaction proceeds via the localized surface plasmon resonance-excited electron transfer from the Au nanoparticle to the TiO2.
This article reviews the semiconductor and metal-based nanohybrid-sensitized photoelectrochemical (PEC) cells for hydrogen generation from water. The nanoscale hybridization of sensitizers in the ...photoanode can enhance light harvesting, interfacial charge transfer, charge separation, and induce a catalytic effect in dependence on the kind of the components and interfacial junction state. Subsequent to the introduction, second and third sections present the basic structure and design of the nanohybrid-sensitized PEC cell. Fourth section deals with the effect of the interfacial bond between quantum dots and TiO2 on the electron injection process. Fifth section mainly describes the formation of heteroepitaxial junction between the components of nanohybrids. In the sixth section, the state-of-the-art nanohybrid-sensitized PEC cells are treated with a particular emphasis placed on the interface state.
Hydrogen peroxide (H2O2) is not only a versatile clean and strong oxidant but also a promising fuel for fuel cells. This Feature Article has shown that gold nanoparticle (NP)-loaded metal oxides ...(Au/MOs) can be promising photocatalysts for H2O2 production via two electron-oxygen reduction reaction (2e–-ORR). The fundamental parts deal with the general requirements for the H2O2 synthesis, electrocatalytic activity of Au NPs for 2e–-ORR, Fermi level control of the Au NP of Au/MOs in the dark and under light irradiation, and the factors for governing the catalytic activity for H2O2 production. Subsequently, an artificial photosynthesis of H2O2 from water and O2 under visible light irradiation at ambient temperature and pressure is described. Finally, the conclusions are summarized with a direction of the future research on the hot topics.
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