다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Films and powders of TiO 2- x N x have revealed an improvement over titanium dioxide (TiO 2 ) under visible light (wavelength 2 has proven to be indispensable for band-gap narrowing and photocatalytic activity, as assessed by first-principles calculations and x-ray photoemission spectroscopy.

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Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides

Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

The surface science of titanium dioxide

Photocatalysis Using ZnO Thin Films and Nanoneedles Grown by Metal–Organic Chemical Vapor Deposition

Photocatalytic nanodiodes for visible-light photocatalysis

High efficiency solar photocatalysis requires an effective separation of photogenerated charge carriers and their rapid transport to the semiconductor interface. The mechanisms and kinetics of charge separation and interfacial/interparticle charge transfers (CT) are significantly influenced by both the bulk and surface properties of the semiconductor. The surface properties are particularly important because the photocatalysis should be driven by the interfacial CT. The most popular and the most investigated semiconductor photocatalyst is based on bare and modified TiO2. This article highlights the interfacial and interparticle CTs under the bandgap excitation of TiO2 particles, visible light-induced photochemical processes via either dye-sensitization or ligand-to-metal CTs at surface modified TiO2 particles, and the applications of the photo-processes to pollutant degradation and simultaneous hydrogen production. While a variety of surface modification techniques using various nanomaterials and chemical reagents have been developed and tested so far, their effects are very diverse depending on the characteristics of the applied photocatalytic systems and even contradictory in some cases. Better understanding of how the modification influences the photoinduced CT events in semiconductors is required, particularly for designing hybrid photocatalysts with controlled CTs, which is sought-after for practical applications of photocatalysis.

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Photoinduced charge transfer processes in solar photocatalysis based on modified TiO2

Platinum-ion-doped TiO2 (Ption-TiO2) was synthesized by a sol-gel method, and its visible light photocatalytic activities were successfully demonstrated for the oxidative and reductive degradation of chlorinated organic compounds. Ption-TiO2 exhibited a yellow-brown color, and its band gap was lower than that of undoped TiO2 by about 0.2 eV. The flat band potential of Ption-TiO2 was positively shifted by 50 mV compared with that of undoped TiO2. X-ray absorption spectroscopy and X-ray photoelectron spectroscopy analyses showed that the Pt ions substituted in the TiO 2 lattice were present mainly in the Pt(IV) state with some Pt(II) on the sample surface. Ption-TiO2 exhibited higher photocatalytic activities than undoped TiO 2 under UV irradiation as well. The visible light activity of Pt ion-TiO2 was strongly affected by the calcination temperature and the concentration of Pt ion dopant, which were optimal at 673 K and 0.5 atom %, respectively. Under visible irradiation, Pt ion-TiO2 degraded dichloroacetate and 4-chlorophenol through an oxidative path and trichloroacetate via a reductive path. The activity of Pt ion-TiO2 was not reduced when used repeatedly under visible light. However, visible-light-illuminated Pt ion-TiO2 could not degrade substrates such as tetramethylammonium and trichloroethylene, which are degraded with UV-illuminated TiO2. The characteristics and reactivities of Ption-TiO2 as a new visible light photocatalyst were investigated in various ways and discussed in detail.

Visible light active platinum-ion-doped TiO2 photocatalyst.

The multidimensional aspects of the photocatalytic activity were investigated in a systematic way. The photocatalytic activities of eight commercial TiO2 samples were quantified by employing 19 test substrates (phenols, organic acids, amines, chlorohydrocarbons, dyes, inorganic ions, etc.) in terms of their degradation or conversion rates in water. The measured activities exhibited a complex behavior that depends on the test substrate. The photocatalytic activities are roughly correlated only among structurally related compounds. The photocatalytic activities can be represented in many different ways, and even the relative activity order among the tested photocatalysts depends on what substrate is used. Each TiO2 (among eight samples) showed the best activity for at least one test-substrate. This highly substrate-specific activity of TiO2 photocatalysts hinders the straightforward comparison of which catalyst is better than others. Even the common belief that anatase is more photoactive than rutile cannot be fully supported on the basis of the present data set. Although there seems to be no simple correlation between the activity and the common physicochemical parameters of photocatalysts, the substrate-specific activity was analyzed and discussed in terms of various parameters such as surface area, crystallinity, surface charge, and substrate adsorption. Finally, the multivalue photocatalytic activity test in relation with water treatment application was proposed to take the substrate-specificity into account.

Wonyong Choi

Papers

Photocatalysis Using ZnO Thin Films and Nanoneedles Grown by Metal–Organic Chemical Vapor Deposition

Photocatalytic nanodiodes for visible-light photocatalysis

Photoinduced charge transfer processes in solar photocatalysis based on modified TiO2

Visible light active platinum-ion-doped TiO2 photocatalyst.

Substrate-specific photocatalytic activities of TiO2 and multiactivity test for water treatment application.