Fabrication of Ta 3 N 5 ZnO direct Z-scheme photocatalyst for hydrogen generation

Abstract Based on the Z-scheme mechanism, the combination of two semiconductors with suitable bandgaps can reduce the recombination rate of electrons and holes in a single material to enhance photocatalytic hydrogen evolution. Ta 3 N 5 with suitable band gap positions is a potentially promising material for photocatalysis. In order to raise the hydrogen production rate, ZnO nanocrystals were deposited by atomic layer deposition (ALD) on Ta 3 N 5 to form a direct Z-scheme structure, ZnO@Ta 3 N 5 . The ALD cycle number varied from 200 to 500. All of the direct Z-scheme samples exhibited much higher hydrogen evolution efficiencies than Ta 3 N 5 , ZnO, and the indirect Z-scheme, with the order of ZnO300@Ta 3 N 5 >ZnO200@Ta 3 N 5 >ZnO400@Ta 3 N 5 >ZnO500@Ta 3 N 5 . Because of the uniform distribution, discrete particles, and proper size of ZnO, ZnO300@Ta 3 N 5 showed the highest hydrogen evolution rate, being about 500 μmol/g-h. With 400 or 500 ALD cycles, the larger particles of ZnO would overlap with each other to form a continuous layer on Ta 3 N 5 , thus reducing the exposure of Ta 3 N 5 to the light and water for producing hydrogen.