Direct Z-Scheme charge transfer in heterostructured MoO3/g-C3N4 photocatalysts and the generation of active radicals in photocatalytic dye degradations

Abstract

Photocatalytic degradation is an attractive strategy to purify waste water contaminated by macromolecular organics. Compared with the single-component photocatalysts, heterostructures of different semiconductors have been widely used to improve the photocatalytic performance. In this work, we fabricate a hetero-structured photocatalyst consisting of two-dimensional graphitic carbon nitride (g-C₃N₄) nanosheets and commercial MoO₃ microparticles through a simple mixing and annealing process. The photocatalytic performance was evaluated in various dye degradation reactions, especially Rhodamine (RhB) degradation. The MoO₃/g-C₃N₄ composite shown a significant improvement compared with individual MoO₃ or g-C₃N₄ as well as their physical mixture. By applying electron spin resonance (ESR) spin-trap spectra, radical scavenge experiments and electrochemical analysis, we find that a direct Z-scheme charge transfer between MoO₃ and g-C₃N₄ not only causes an accumulation of electrons in g-C₃N₄ and holes in MoO₃, but also boosts the formation of superoxide radical and hydroxyl radical. The superoxide radical and hole dominate the photocatalytic degradation, while the hydroxyl radical plays a negligible role and its production can be suppressed by lowering the pH value.

Keywords: Dye photodegradation; Graphitic carbon nitride; Molybdenum trioxide; Superoxide radical; Z-Scheme.