Design of a p–n heterojunction in 0D/3D MoS2/g-C3N4 composite for boosting the efficient separation of photogenerated carriers with enhanced visible-light-driven H2 evolution

Constructing a 0D/3D p–n heterojunction is a feasible strategy for accelerating photo-induced charge separation and promoting photocatalytic H₂ production. In this study, a 0D/3D MoS₂/g-C₃N₄ (0D/3D-MCN) photocatalyst with a p–n heterojunction was prepared via a facile light-assisted deposition procedure, and the 3D spongy-like g-C₃N₄ (3D-CN) was synthesized through simple thermolysis of NH₄Cl and melamine mixture. For comparison, 2D-MoS₂ nanosheets were also embedded in 3D-CN by a solution impregnation method to synthesize a 2D/3D-MCN photocatalyst. As a result, the as-prepared 0D/3D-MCN-3.5% composite containing 3.5 wt% 0D-MoS₂ QDs exhibited the highest photocatalytic H₂ evolution rate of 817.1 μmol h⁻¹ g⁻¹, which was 1.9 and 19.4 times higher than that of 2D/3D-MCN-5% (containing 5 wt% 2D-MoS₂ nanosheets) and 3D-CN, respectively. The results of XPS and electrochemical tests confirmed that a p–n heterojunction was formed in the 0D/3D-MCN-3.5% composite, which could accelerate the electron and hole movement in the opposite direction and retard their recombination; however, it was not found in 2D/3D-MCN-5%. This study revealed the relationship among the morphologies of MoS₂ using g-C₃N₄ as a substrate, the formation of a p–n heterojunction, and the H₂ evolution activity; and provided further insights into fabricating a 3D g-C₃N₄-based photocatalyst with a p–n heterojunction for photocatalytic H₂ evolution.

A 0D/3D p–n heterojunction was formed in the MoS₂/g-C₃N₄ composite, which could promote the separation of electrons and holes efficiently.