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

Abstract

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 H2 generation (∼100 mmol h–1 g–1) with an apparent quantum yield of 6.3% compared to pure NBT (∼7 mmol h–1 g–1) under visible light. The photoelectrochemical measurements reveal that the NBT/reduced graphene oxide exhibits ∼32 times enhancement in photocurrent density due to a significant increase in the charge-carrier concentration (1.8 × 1017 cm–3) of the heterostructure as compared to bare NBT (3.4 × 1016 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 H2 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.