Construction of a 3D/2D Z-Scheme Heterojunction for Promoting Charge Separation and Augmented Photocatalytic Hydrogen Evolution

Fabrication of multidimensional heterogeneous photocatalysts combining two-dimensional (2D) and three-dimensional (3D) nanostructures is crucial for efficient solar energy conversion at the 3D/2D interface. Herein, a direct Z-scheme heterostructure has been developed by modification of the wide band gap Na0.5Bi0.5TiO3 (NBT, 3.10 eV) with graphene nanosheets via a facile hydrothermal method which demonstrated a 14-fold increase in H-2 generation (similar to 100 mmol h(-1) g(-1)) with an apparent quantum yield of 6.3% compared to pure NBT (similar to 7 mmol h(-1) g(-1)) under visible light. The photoelectrochemical measurements reveal that the NBT/reduced graphene oxide exhibits similar to 32 times enhancement in photocurrent density due to a significant increase in the charge-carrier concentration (1.8 x 10(17) cm(-3)) of the heterostructure as compared to bare NBT (3.4 x 10(16) cm(-3)). Remarkably, the formation of a direct Z-scheme heterojunction at the interface of graphene and NBT induces an in-built electric field and facilitates the vectorial transfer of the photogenerated charge carriers, which improves the rate of H-2 generation without using noble metal-based cocatalysts. Moreover, waste-derived NBT/reduced graphene oxide from the graphite powder reclaimed from spent Li-ion batteries shows excellent photocatalysis performance comparable to natural resources. This suggests the potential for large-scale photocatalysts production from waste-derived carbon source for solar fuel generation.