Synthesis and Photocatalytic Properties of Single Crystalline (Ga1-xZnx)(N1-xOx) Nanotubes

Recently, (Ga1-xZnx)(N1-xOx) has gained widespread attention as a comparatively high efficiency photocatalyst for visible-light-driven overall water splitting. Despite significant gains in efficiency over the past several years, a majority of the photogenerated carriers recombine within bulk powders. To improve the photocatalytic activity, we used an epitaxial casting method to synthesize single-crystalline, high surface area (Ga1-xZnx)(N1-xOx) nanotubes with ZnO compositions up to x=0.10. Individual nanotubes showed improved homogeneity over powder samples due to a well defined epitaxial interface for ZnO diffusion into GaN. Absorption measurements showed that the ZnO incorporation shifts the absorption into the visible region with a tail out to 500 nm. Gas chromatography (GC) was used to compare the solar water splitting activity of (Ga1-xZnx)(N1-xOx) nanotubes (x=0.050.10) with similar composition powders. Cocatalyst decorated samples were dispersed in aqueous solutions of CH3OH and AgO2CCH3 to monitor the H+ reduction and H2O oxidation half reactions, respectively. The nanotubes were found to have approximately 1.52 times higher photocatalytic activity than similar composition powders for the rate limiting H+ reduction half reaction. These results demonstrate that improvements in homogeneity and surface area using the nanotube geometry can enhance the photocatalytic activity of GaN:ZnO for solar water splitting.