Construction of Bi2WO6 with double active sites of tunable metallic Bi and oxygen vacancies for photocatalytic oxidation of cyclohexane to cyclohexanone

Abstract

Oxygen-containing organics, which are generated from the selective oxidation of their corresponding hydrocarbons, have high value in the chemical and pharmaceutical industries. However, their oxidation reactions are very challenging as the products are more active than the substrates, especially for the oxidation of cyclohexane (CHA). Herein, we focused on the one-step preparation of Bi₂WO₆ with double active sites of tunable metallic Bi and oxygen vacancies (OV–Bi/Bi₂WO₆) by a facile solvothermal treatment. Then, OV–Bi/Bi₂WO₆ was used as an efficient photocatalyst for the partial oxidation of CHA to cyclohexanone (CHA-one) for the first time in air as an oxidant under solvent-free and room temperature conditions. The Bi : Bi₂WO₆ ratio in the as-prepared OV–Bi/Bi₂WO₆ heterojunction could be tailored from 0.08 to 8.43 by controlling the solvothermal temperature, and the synergistic effect between DMF and EG could increase the reduction of MDF/EG and promote the production of Bi. Moreover, OV–Bi/Bi₂WO₆-160 yielded 4.4 and 8.8 times more CHA-one (128.8 μmol) than pure Bi₂WO₆ and metallic Bi, respectively, and achieved 93.6% selectivity to CHA-one in air as an oxidant under solvent-free conditions. The results revealed that the highly enhanced photocatalytic activity was mainly attributed to the superior specific surface area, outstanding photo-absorption, abundant oxygen vacancies, and efficient electron–hole separation. Moreover, for the unique double active sites in OV–Bi/Bi₂WO₆, oxygen vacancies can enhance the adsorption and activation capacity of Bi₂WO₆ for O₂, while metallic Bi can improve the adsorption and activation capacity of Bi₂WO₆ for CHA. Meanwhile, OV–Bi/Bi₂WO₆ also exhibited excellent durability due to the strong interaction between metallic Bi and Bi₂WO₆. The present work provides a flexible approach for tailoring the Bi : Bi₂WO₆ ratio and outlines an effective method for producing CHA-one from CHA under mild conditions.