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Nitrogen-substituted TiO2 (N-TiO2) thin film photocatalysts have been prepared by a radio frequency magnetron sputtering (RF-MS) deposition method using a N2/Ar mixture sputtering gas. The effect of the concentration of substituted nitrogen on the characteristics of the N-TiO2 thin films was investigated by UV-vis absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses. The absorption band of the N-TiO2 thin film was found to shift smoothly to visible light regions up to 550 nm, its extent depending on the concentration of nitrogen substituted within the TiO2 lattice in a range of 2.0-16.5%. The N-TiO2 thin film photocatalyst with a nitrogen concentration of 6.0% exhibited the highest reactivity for the photocatalytic oxidation of 2-propanol diluted in water even under visible (lambda > or = 450 nm) or solar light irradiation. Moreover, N-TiO2 thin film photocatalysts prepared on conducting glass electrodes showed anodic photocurrents attributed to the photooxidation of water under visible light, its extent depending on wavelengths up to 550 nm. The absorbed photon to current conversion efficiencies reached 25.2% and 22.4% under UV (lambda = 360 nm) and visible light (lambda = 420 nm), respectively. UV-vis and photoelectrochemical investigations also confirmed that these thin films remain thermodynamically and mechanically stable even under heat treatment at 673 K. In addition, XPS and XRD studies revealed that a significantly high substitution of the lattice O atoms of the TiO2 with the N atoms plays a crucial role in the band gap narrowing of the TiO2 thin films, enabling them to absorb and operate under visible light irradiation as a highly reactive, effective photocatalyst.

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The oxidative coupling of benzylamines proceeds efficiently using salicylic acid derivatives as organocatalysts under an oxygen atmosphere, affording the corresponding N -benzylidenebenzylamines in high yields. Electron-rich salicylic acid derivatives such as 4,6-dimethoxysalicylic acid and 4,6-dihydroxysalicylic acid exhibit excellent catalytic activities for the oxidative coupling of benzylamines to give the corresponding imines. This amine oxidation can also be applied to the synthesis of nitrogen-containing heterocycles such as benzimidazole derivatives. Furthermore, to recycle the catalyst, silica gel supported with 4.7 wt % of 4,6-dihydroxysalicylic acid is prepared, which acts as a recyclable catalyst, oxidizing benzylamine to imine four times successfully.

The effect of chemical etching by HF solution on the photoelectrochemical performance and photocatalytic activity of visible light-responsive TiO 2 (Vis-TiO 2 ) thin films prepared by a radio-frequency magnetron sputtering method has been investigated. It was found that VisTiO 2 thin films treated with HF solution (HF-Vis-TiO 2 ) exhibit a remarkable enhancement of the photoelectrochemical performance not only under UV but also visible light irradiation as compared to untreated Vis-TiO 2 . The incident photon to current conversion efficiencies reached 66 and 9.4% under UV (k = 360 nm) and visible light (k = 420 nm), respectively. The HF-Vis-TiO 2 thin films have a larger surface area and higher donor density than Vis-TiO 2 , indicating that the remarkable increase in the photocurrent may be due to the short diffusion length of the photoformed holes in reaching the solid-liquid interface as well as to the high conductivity. Moreover, the HF-Vis-TiO 2 thin films were found to act as efficient photocatalysts for the decomposition of water with the separate evolution of H 2 and O 2 from H 2 O under visible or sunlight irradiation.