Facile Synthesis of Oxygen-Deficient CeVO4/Bi/Bi2MoO6 Ternary Heterostructures with Bi-Mediated Switching from Type-I to Z-Scheme Mechanism for O2 and N2 Photoreductions

The rapid assembly of ternary heterostructures with robust solar light absorption and high redox potential of photogenerated charged species is a pragmatic approach for achieving photocatalytic activation of tenacious atmospheric molecules. In the current study, a novel CeVO4/Bi/Bi2MoO6 ternary heterostructure was fabricated by in situ deposition of CeVO4 over one-pot-synthesized Bi/Bi2MoO6 binary composite. The effect of the salt precursor and reaction duration on the morphology and crystal structure of Bi/Bi2MoO6 was studied in detail. The initial formation of Bi2MoO6 nanoplates and their subsequent disintegration to nanorods upon prolonged reaction time was observed due to concurrent leaching and reduction of Bi3+ ions to plasmonic Bi0 metal. The salt precursors also crucially influenced the reaction kinetics for the formation of Bi/Bi2MoO6 heterostructures. The CeVO4/Bi/Bi2MoO6 ternary heterostructure demonstrated a uniform deposition of CeVO4 nanoparticles (10–20 nm) over Bi2MoO6 nanorods that are embedded with ultrasmall Bi0 nanodots (2–5 nm). The ternary composites displayed improved surface area, porosity, surface hydrophilic character, strong absorption in the entire UV–visible region, and enhanced space charge separation property. The enhancement in optoelectronic feature is ascribed to the creation of surface oxygen vacancies and plasmonic nature of Bi nanodots. The optimized ternary photocatalyst exhibited encouraging photocatalytic activity for H2O2 generation (953 μM/g/h) and NH4+ production (131 μmol/g/h) with reaction kinetics 7–20 and 4–5 times greater than those of pure semiconductors and CeVO4/Bi2MoO6 binary heterostructure. The apparent conversion efficiencies for O2 and N2 reduction were found to be 0.9% and 3.7%, respectively. Energy band structure analysis and spectroscopic investigation of in situ generated radicals indicated a switching of charge migration route from Type-I in CeVO4/Bi2MoO6 to Bi0-mediated all-solid-state Z-scheme for the CeVO4/Bi/Bi2MoO6 composite, which accounted for its improved photocatalytic activity.