Ag/Ag2O/BiNbO4 structure for simultaneous photocatalytic degradation of mixed cationic and anionic dyes

Abstract

In principle, n-type and p-type semiconductors are respectively responsible for photo-catalytic degradation of cationic dyes (e.g., methylene blue) and anionic dyes (e.g., acid red 1), governed by photoelectrons in the former and photo-holes in the later system. Hence, we present a new strategy: design and fabrication of photocatalytic structures to match the redox potentials of mixed basic/acidic dyes as well as the reactive oxygen species (ROS). For the first time Ag/Ag2O/BiNbO4 structure is (1) designed to match the redox potentials of basic/acidic dyes as well as ROS, (2) fabricated using photoreduction to control the Ag/Ag2O/BiNbO4 interfaces, and (3) able to simultaneously degrade 84% methylene blue dye (MB) in 240 min and 88% acid red 1 (AR) in 25 min under LED light irradiation, corresponding to 7 wt% Ag loading. To the best of our knowledge, this is the first photocatalytic degradation study on mixed basic and acidic dyes using a single catalyst. We also tested the new redox potential matching strategy in mixed basic dyes (MB and rhodamine B (RhB)). As expected our experimental results reproduced well our model predictions: in particular, results support our proposed hydroxyl radical (OH) mechanism, which is initiated by photo-holes. Therefore, this new design strategy, which consists of matching band structures of the photocatalyst with redox potentials of dyes and ROS, has immediate implications to general photocatalytic applications beyond dye degradation and water-splitting.