Abstract
Modification effects of porphyrin dyes on the photocatalytic activity of tantalum (oxy)nitride (TaON) were investigated. The nitrogen content in tantalum (oxy)nitride was increased by increasing the heat treatment period. The optimized nitridation conditions were found to be calcination at 800 °C for 14 h under a NH3 gas flow (25 mL min−1). Among the porphyrin dyes examined, pentamethylene bis[4-(10,15,20-triphenylporphine-5-yl) benzoate]-dizinc (II) (Zn-TPPD) showed the most positive effect on the photocatalytic activity of TaON for H2 production from Na2S aqueous solution. From the results of the photocatalytic reaction using various combinations of catalyst components, it was found that the modification dye and PtOx co-catalysts were necessary to achieving photocatalytic H2 formation. In the PtOx/Zn-TPPD/TaON photocatalyst, the expected charge transfer mechanism was a two-step excitation of both TaON and Zn-TPPD, and the oxidation and reduction sites were TaON and PtOx co-catalyst, respectively. These results indicate that dye modification has the potential to improve the photocatalytic activity of various (oxy)nitride photocatalysts.
Highlights
The production of alternative and renewable energy sources is a significant challenge for sustaining the development of human society
We focused on the modification effect of organic dyes on the photocatalytic activity of inorganic compounds such as
Crystal structures ofnitride samples were determined by X-ray diffraction (XRD)
Summary
The production of alternative and renewable energy sources is a significant challenge for sustaining the development of human society. Various metal oxide semiconductors, especially Ta-based oxides, have been reported as highly active photocatalysts for water splitting [1,2,3,4,5,6,7,8] These compounds have wide band gaps, which is a disadvantage for solar energy harvesting. Tantalum oxynitride (TaON) is a good candidate for a water splitting photocatalyst due to its stability, suitable conduction and valence band energies [11,12]. The reduction potential of the photo-excited electron was increased from the conduction band level of KTaO3 to the LUMO level of the porphyrin dyes. The tantalum (oxy)nitrides were modified with five different types of porphyrin dyes, and the influence of adsorption states (physical adsorption and covalent attachment) and the photocatalytic activities of each were investigated
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