In situ synthesis of n-n Bi2MoO6 & Bi2S3 heterojunctions for highly efficient photocatalytic removal of Cr(vi)

Exploiting novel photocatalysts with high efficiency and durability for reduction of hexavalent chromium (Cr(vi)) has gained attention from fundamental science and industrial research. In this work, we synthesized novel two-dimensional (2D) n-n Bi2MoO6 & Bi2S3 heterojunctions by a facile in situ anion exchange process for remarkably efficient removal of Cr(vi). Results show that Bi2MoO6 & Bi2S3 heterojunctions with core-shell structures are formed through the intimate contact of Bi2MoO6 core and Bi2S3 shell. The prepared Bi2MoO6 & Bi2S3 heterojunctions exhibit unprecedented photocatalytic activity for reduction of Cr(vi) under visible light irradiation. The optimized BMO-S1 heterojunction displays the highest reduction efficiency ((app) = 0.164 min(-1)) for Cr(vi) reduction. To the best of our knowledge, it is one of the highest reduction rate achieved among reported photocatalysts for Cr(vi) reduction under visible-light irradiation. Detailed studies show that strong selective adsorption for Cr(vi) enhances this unprecedented photocatalytic activity. Moreover, the intimate heterojunction between Bi2MoO6 core and Bi2S3 shell can efficiently deteriorate the charge carrier recombination and Bi2S3 content can boost visible light harvesting, thereby contributing to the remarkable photocatalytic catalytic activity, which were proven by PL, EIS and transient photocurrent responses. Characterization of Mott-Schottky plots and DRS prove that the Bi2MoO6 & Bi2S3 heterojunctions established a type-II band alignment with intimate contact, accounting for the efficient transfer and separation of photogenerated carriers. This work provides a simple route for facial synthesis of heterojunction photocatalysts for Cr(vi) reduction in industrial applications.