Bandgap engineering of oxinitride nanowires for water splitting and hydrogen generation

z-scheme solar water splitting using semiconductor electrodes and photocatalysts is exciting approach for hydrogen generation.As many oxide photocatalysts only respond to UV radiation for watersplitting and under visible light the number of photocatalysts are limited.It is important to develop visible light driven photocatalyst materials for solar water splitting via suitable bandgap engineering.The bandgap of visible light driven photocatalyst should be less than 3.00 eV(λ>415nm).TiN nanowires are converted very controllably to TiN_1-xO_x by bringing a trace amount of oxygen during the growth.TNO is semiconducting whose bandgap is a function of oxygen.By controlling oxygen content in TNO,we are able to tune its bandgap,where absorption of visible light is strong to generate hydrogen and oxygen from splitting of water.When N atoms in TiN are partially substituted by O atoms in TNO, the top of the valence band shifts higher compared to the corresponding metal oxide (TiO₂) without affecting the level of the bottom of the conduction band.The potential of the HOMO for the oxinitride is located at higher potential energy than that for the corresponding oxide due to the contribution of N 2p orbitals, making the bandgap energy sufficiently small to respond to visible solar light (< 3eV)