Photodegradation pathway of rhodamine B with novel Au nanorods @ ZnO microspheres driven by visible light irradiation

A series of Au–ZnO photocatalysts were successfully synthesized from ZnO microspheres impregnated with Au nanorods by the seed-mediated method, and their photocatalytic activity of degradation of rhodamine B (RhB) was investigated. The nanocomposite catalyst exhibited high photocatalytic activity and degraded 92% of RhB solution under visible light irradiation in 330 min. The enhancement of photocatalytic effects was mainly ascribed to the surface plasmon resonance effect of Au nanorods; therefore, Au–ZnO spheres can absorb resonant photons and transfer the electron to the conduction band (CB) of ZnO leading to the separation of electrons and holes under visible light. Meanwhile, the photocatalytic performance was beneficial from the flower-like porous structure of ZnO, which enhances adsorption of the dye molecules and dissolved oxygen on the catalyst surface and facilitates the electron/hole transfer. Furthermore, the degradation pathway was proposed on the basis of the intermediates during the photodegradation process using liquid chromatography analysis coupled with mass spectroscopy (LC–MS). The degradation mechanism of pollutant is ascribed to the superoxide radicals (^·O²⁻), which is the main oxidative species for the N-deethylated degradation of RhB. Moreover, the Au–ZnO photocatalysts demonstrated excellent photostability after five cycles. This work provides a facile and effective approach for removal of organic dyes under visible light and thus can be potentially used in the environmental purification.