Natural sunlight induced photocatalytic hydrogen evolution by SrTaO2N/CdS nanocomposites

Abstract

The oxynitride SrTaO₂N is a potential semiconductor for converting solar energy into hydrogen energy due to its visible light absorption capability. However, the catalytic activity is low due to fast electron-hole (e^--h⁺) recombination. Here, we have synthesized SrTaO₂N/CdS heterojunction by using the co-precipitation method to improve the catalytic activity. SrTaO₂N/CdS nanocomposite is studied for photocatalytic H₂ evolution in the presence of Na₂S/Na₂SO₃ under both natural sunlight and artificial light (Xe lamp). Among the synthesized nanocomposites, the 5 % SrTaO₂N/CdS heterojunction exhibits the highest H₂ generation of 40.25 mmol for 5 h under visible light produced by a xenon lamp without utilizing a co-catalyst, and the apparent quantum efficiency of 5 % SrTaO₂N/CdS is found to be 11.8 ± 0.1 % at a wavelength of 400 nm. This is much higher than that of the catalytic activity shown by SrTaO₂N and CdS independently under similar experimental conditions. It is because of the effective e^--h⁺ pair separation in the nanocomposite due to the Z-scheme heterojunction formation between SrTaO₂N and CdS semiconductors with valance, conduction band positions at 2.15, −0.26 eV vs SHE for SrTaO₂N and 1.40, −0.78 eV vs SHE for CdS, respectively. This composite exhibits hydrogen evolution activity of 40.04 mmol for 5 h under natural sunlight, which is a promising step towards practical applications.