Papers by Keyword: Visible Light Absorption

Abstract: In this work, zinc phthalocyanine (ZnPc) was impregnated onto mesoporous carbon nitride (m-C₃N₄) to expand its absorption to longer wavelength. Nitrogen adsorption-desorption isotherm confirmed that the m-C₃N₄ showed type IV of adsorption-desorption isotherm. Transmission electron microscopy (TEM) revealed the presence of both nanosphere and nanoworm structure in the m-C₃N₄. Thermogravimetric analysis (TGA) showed that the synthesized m-C₃N₄ was thermally stable until 723 K. The presence of ZnPc on the m-C₃N₄ was confirmed from the X-ray diffraction (XRD) patterns and diffuse reflectance ultraviolet-visible (DR UV-Vis) spectra. The higher the amount of ZnPc loaded on m-C₃N₄, the higher the intensity of ZnPc peaks in the diffraction patterns. The successful impregnation of ZnPc onto the m-C₃N₄ was also supported by the color changing of the solids from yellow to blue, which can be seen as an additional broad band at 500-900 nm from the absorption spectra. Since the material gives visible light absorption, it is expected that the ZnPc/m-C₃N₄ would be a potential photocatalyst for reactions conducted under visible light irradiation.

Abstract: Visible light absorption of TiO2 can be induced by the addition of transition metal impurities. However, many dissimilar results have been reported about this subject and there are various interpretations about the origin of these absorption features. In this work, samples of chromium-doped titania (TiO2-Cr) with different dopant contents (0.1, 0.5, 1.0 and 5.0 wt. %) were prepared by a sol-gel method. Their particle size was determined by dynamic light scattering and it was on the nanometer scale (18 nm). X-ray powder diffraction and Raman spectroscopy showed only the presence of anatase phase in all samples. X-ray photoelectron spectroscopy reveals that the oxidation state of chromium in the prepared materials is different than in the dopant precursor. This change can be associated to the oxidative gelling conditions used in the materials preparation. UV VIS diffuse reflectance spectroscopy showed that the chromium doping, until 1.0 wt. %, did not effectively narrow the TiO2 band-gap but it induces the visible light absorption probably through the formation of color centers.