Hierarchically Porous ZnO/g-C3N4 S-Scheme Heterojunction Photocatalyst for Efficient H2O2 Production.

The design of photocatalysts with hierarchical pore sizes is an effective method to improve mass transport, enhance light absorption, and increase specific surface area. Moreover, the construction of a heterojunction at the interface of two semiconductor photocatalysts with suitable band positions plays a crucial role in separating and transporting charge carriers. Herein, ZIF-8 and urea are used as precursors to prepare hierarchically porous ZnO/g-C3N4 S-scheme heterojunction photocatalysts through a two-step calcination method. This S-scheme heterojunction photocatalyst shows high activity toward photocatalytic H2O2 production, which is 3.4 and 5.0 times higher than that of pure g-C3N4 and ZnO, respectively. The mechanism of charge transfer and separation within the S-scheme heterojunction is studied by Kelvin probe, in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS), and electron paramagnetic resonance (EPR). This research provides an idea of designing S-scheme heterojunction photocatalysts with hierarchical pores in efficient photocatalytic hydrogen peroxide production.