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

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-CN) nanosheets and commercial MoO microparticles through a simple mixing and annealing process. The photocatalytic performance was evaluated in various dye degradation reactions, especially Rhodamine (RhB) degradation. The MoO/g-CN composite shown a significant improvement compared with individual MoO or g-CN 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 MoO and g-CN not only causes an accumulation of electrons in g-CN and holes in MoO, 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.