Ultrasonically-assisted synthesis of CeO2 within WS2 interlayers forming type II heterojunction for a VOC photocatalytic oxidation

Here, we investigate the band structure, density of states, photocatalytic activity, and heterojunction mechanism of WS₂ with CeO₂ (CeO₂@WS₂) as a photoactive heterostructure. In this heterostructure, CeO₂'s growth within WS₂ layers is achieved through ultrasonicating WS₂ and intercalating CeO₂'s precursor within the WS₂ interlayers, followed by hydrothermal treatment. Through a set of density functional calculations, we demonstrate that CeO₂ and WS₂ form an interface through a covalent bonding that can be highly stable. The electrochemical impedance spectroscopy (EIS) found that the CeO₂@WS₂ heterostructure exhibits a remarkably higher conductivity (22.23 mS cm^-2) compared to either WS₂ and CeO₂, assignable to the interface in CeO₂@WS₂. Furthermore, in a physically mixed CeO₂-WS₂ where the interaction between particles is noncovalent, the resistance was significantly higher (0.67 mS cm^-2), confirming that the heterostructure in the interface is covalently bonded. In addition, Mott-Schottky and the bandgap measurements through Tauc plots demonstrate that the heterojunction in CeO₂ and WS₂ is type II. Eventually, the CeO₂@WS₂ heterostructure indicated 446.7 µmol g ^-1 CO₂ generation from photocatalytic oxidation of a volatile organic compound (VOC), formic acid, compared to WS₂ and CeO₂ alone.