Solvent-Induced Deposition of Cu-Ga-In-S Nanocrystals onto a Titanium Dioxide Surface for Visible-Light-Driven Photocatalytic Hydrogen Production

In this paper, copper-gallium-indium-sulfide (CGIS) nanocrystals with different Ga/In ratios, i.e., CuGaxIn5-xS8, where x = 0, 1, 2, 3, 4 and 5, were synthesized and investigated for visible-light-driven hydrogen (H2) evolution from aqueous solutions that contain sulfide/sulfite ions. The synthesized CGIS nanocrystals were characterized by diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). With 1.0 wt.% Ru as a co-catalyst, the H2 evolution rate on CuGa2In3S8 (CGIS hereafter) showed the highest activity. The CGIS nanocrystals were deposited onto a TiO2 surface via a unique solvent-induced deposition method. The CGIS/TiO2 photocatalyst showed comparable activity to that obtained using bare CGIS nanocrystals when the photocatalyst amount was sufficient in the photoreactor system, suggesting that TiO2 remains intact in terms of photocatalytic activity. The quantity of CGIS nanocrystals, however, required to achieve the rate-plateau condition at saturation was much lower in the presence of TiO2. The enhanced activities at low CGIS loadings observed in the presence of TiO2 were explained by the improved dispersion of the powder suspension and optical path in the photoreactor. This TiO2 supported photocatalyst lowers the required amount of photocatalyst, which is beneficial from an economic point of view.