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

Abstract

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 (κ_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.