Switching charge transfer of C3N4/W18O49 from type-II to Z-scheme by interfacial band bending for highly efficient photocatalytic hydrogen evolution

Z-scheme composite represents an ideal system for photocatalytic hydrogen evolution, but the charge transfer mechanism is still ambiguous, and how to design and construct such system is a big challenge. Herein, we demonstrate that C3N4-W18O49, the type-II composite, can be switched to direct Z-scheme via modulating the interfacial band bending. Experiment and DFT computation results reveal that the adsorption of triethanolamine (TEOA) on C3N4 surface significantly uplifts its Femi level, inverses the continuous interfacial band bending to interrupted one, and thus switches the composite from type-II to Z-scheme, without the assistance of any electron shuttles. Importantly, this Z-scheme C3N4/W18O49 composites exhibit much better photocatalytic H2 activity compared with pure C3N4, and obtain H2 evolution rate of 8597 μmol h−1 g−1 (AQY of 39.1% at 420 nm) with Pt as cocatalyst and TEOA as hole scavenger. Also, using this hypothesis we successfully explain why C3N4/WO3 is inherent Z-scheme composite but the performance is not as good as C3N4/W18O49 and why TEOA is the best hole scavenger for C3N4. This work is expected to give deep insights into understanding the charge transfer in semiconductor composites and rationally designing and constructing Z-scheme photocatalyst for hydrogen evolution.