Direct Z-scheme TiO2–ZnIn2S4 nanoflowers for cocatalyst-free photocatalytic water splitting

Constructing direct Z-scheme heterojunction (DZH) is significant in improving the efficiency and stability of catalysts for photocatalytic water splitting (PWS). In this work, ultrathin TiO2 nanosheets were integrated into the growth of ZnIn2S4 to produce TiO2–ZnIn2S4 heterostructure nanoflowers. Both the matched energy band and (−)TiO2/(+)ZnIn2S4 internal electric field promote the formation of DZH. The prepared heterojunction holds the highest redox potential in the system, avoids the charge consumption from occurring in the electron mediator, and suppresses the recombination of photogenerated charges, leading to more separated electrons and holes. The formed DZH can consume residual photogenerated holes of ZnIn2S4 and enable water oxidation to occur solely at the TiO2 site, improving the overall stability of the system. The optimized DZH nanoflowers show enhanced PWS activity (214.9 μmol g−1 h−1 for H2 evolution and 81.7 μmol g−1 h−1 for O2 evolution without any cocatalyst and sacrificial agent) and excellent stability (50 h).