Highly efficient Z-scheme WO 3–x quantum dots/TiO 2 for photocatalytic hydrogen generation

Z-scheme semiconductors are a promising class of photocatalysts for hydrogen generation. In this work, Z-scheme semiconductors composed of WO3–x quantum dots supported on TiO2 (WO3–x QDs/TiO2) were fabricated by solvothermal and hydrogen-reduction methods. Characterization by transmission electron microscopy and X-ray diffraction indicated that the amount and size of the WO3–x QDs could be tuned by modulating the addition of the W precursor. Evidence from X-ray photoelectron spectroscopy and photoluminescence spectroscopy suggested that the hydrogen reduction of the composite induced the formation of oxygen vacancy (W5+/VO) defects in WO3. These defects led to ohmic contact between WO3-x and TiO2, which altered the charge-transfer pathway from type II heterojunction to Z-scheme, and maintained the highly reductive and oxidative ability of TiO2 and WO3–x, respectively. Therefore, the Z-scheme sample showed 1.3-fold higher photoactivity than pure TiO2 in hydrogen generation. These results suggest that the formation of W5+/VO defects at the interface is highly beneficial for the fabrication of Z-scheme photocatalysts.