Porous TiO2 adsorbed with squaraine dye as visible-light-responsive photocatalyst

Color Change of Indole Squaraine between Blue and Yellow with Golden Luster

Color change of materials by external stimulus has attracted much attention for various applications. We synthesized 1,3-bis(3,3-dimethyl-2-methylene indolenine)squaraine (ISQ), which was a yellow powder with golden luster (ISQ(gold)) and whose color changed to blue (ISQ(blue)) by being ground using mortar and pestle. Scanning electron microscopy indicated that ISQ(gold) consisted of laminated plate-like crystals with a large flat surface, which was attributable to (2 0-2) facets of monoclinic crystals. Measurements of the diffuse reflectance spectra revealed that J- and H-type aggregates of ISQ were formed by increasing the weight percent of ISQ(blue) in the mixture with BaSO4. A thin film, which was prepared by a spin-coating of ethanol with dissolved ISQ(blue) on glass substrates, looked blue on a white paper, whereas it looked yellowish on a black paper. By repeating the coating process, the film thickness increased, and the thick film exhibited yellow with golden luster regardless of the background color. These results indicate that the color depends on whether the transmitted light through ISQ or the reflected light on the ISQ surface mainly contributes to color vision. To neglect the effect of the transmitted light and intensify the reflection on the surface, a pellet with a smooth surface was prepared by pressing ISQ(gold) or ISQ(blue) at 20 kg/cm2. The ISQ(blue) pellet consisted of the laminated sheets and was dark blue-green. However, under light irradiation, the ISQ(blue) pellet exhibited a yellow color with golden luster, whose specular reflection spectrum was similar to that of the ISQ(gold) pellet. Our results indicate that the color of ISQ is tunable by controlling the transmission and the reflection of the light, including the specular and diffuse reflections.

NCQDs active sites as effective collectors of charge carriers towards enhanced photocatalytic activity of porous Co3O4

In this work, different proportions of N-doped carbon quantum dots/porous Co3O4 (NCQDs/p-Co3O4) NCQDs/Co3O4 composite photocatalysts were prepared by a simple self-assembly method. It was demonstrated by a series of characterizations that 50% NCQDs/Co3O4 has a good visible light response and low electrochemical impedance. The photocatalytic degradation of TC was investigated by the 50% NCQDs/p-Co3O4 composite photocatalyst, and the results showed that the degradation effect of TC reached 81.2% within 120 min. The higher photocatalytic activity of 50% NCQDs/p-Co3O4 was analyzed probably because NCQDs can improve the separation efficiency of photogenerated electron-hole pairs and p-Co3O4 can provide a larger specific surface area and thus has more active sites. This study provides a new strategy for improving the photodegradation activity of Co3O4 photocatalysts.