Effect of Dual-Cocatalyst Surface Modification on Photodegradation Activity, Pathway, and Mechanisms with Highly Efficient Ag/BaTiO3/MnOx

Cocatalyst surface-loading has been regarded as an effective strategy to promote solar-energy-conversion efficiency. However, the potential influence of surface modification with cocatalysts on the photodegradation pathway and the underlying mechanisms is still unclear. Herein, we have used ferroelectric BaTiO3 as the substrate, and both the reduction cocatalyst Ag and the oxidation cocatalyst MnOx have been successfully loaded onto BaTiO3 simultaneously by a one-step photodeposition method as evidenced by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). The influence of dual-cocatalyst surface-loading on photodegradation of rhodamine B has been systematically investigated for the first time. First, the dual-cocatalyst-modified BaTiO3 outperformed over the single-cocatalyst-loaded BaTiO3, and the photodegradation rate of Ag/BaTiO3/MnOx is about 3 times and 12 times as high as that of Ag/BaTiO3 and BaTiO3/MnOx, respectively. The credit is given to the synergistic effect between the reduction and oxidation cocatalysts, prompting charge carrier separation and migration as verified by the transient photocurrent, electrochemical impedance, and photoluminescence (PL) spectrum investigation. Second, in addition to the boosted photodegradation activity, the photodegradation pathway is found to be altered as well when using Ag/BaTiO3/MnOx. High-performance liquid chromatography (HPLC) analysis indicated that a highly selective stepwise deethylation process predominates over chromophore cleavage in the Ag/BaTiO3/MnOx system, while it is reverse for the Ag/BaTiO3 system. This phenomenon is attributed to the different dye molecule adsorption modes. Furthermore, the radical trapping experiment shows that holes play a major role in the degradation process, and the recycle test proves the excellent stability of Ag/BaTiO3/MnOx. Our findings may add another layer of understanding depth to cocatalyst surface modification in photodegradation applications.