Synthesis and characterization of Ppy/Bi₂MoO₆ heterojunction with enhanced photodegradation efficiency of Cr(VI)

To effectively degrade heavy metal ion Cr(VI), Bi2MoO6 and Ppy/Bi2MoO6 composite photocatalyst were successfully prepared using simple solvothermal and in-situ polymerization deposition methods. Compared with pure Bi2MoO6, the Ppy/Bi2MoO6 exhibited dramatically improved photocatalytic activity. The larger specific surface area and higher electronic conductivity of Ppy improve the photocatalytic performance of Bi2MoO6. Especially when the addition amount of Ppy is 0.5 mmol, the degradation rate of 5 mg/L Cr(VI) solution can reach 93.4% after 70min of illumination, and the corresponding degradation reaction rate constant is 0.03893min(-1), which is 3.32 times higher than that of pure Bi2MoO6 and 12.56 times higher than that of pure Ppy. At the same time, the photocatalytic activity of the 0.5Ppy/Bi2MoO6 photocatalyst was 0.33mg/(g center dot min), and the composite photocatalyst exhibited excellent photocatalytic activity. In addition, the deposition of Ppy narrowed the band gap of the composite material and broadened the light absorption range. The electrochemical impedance spectra demonstrated that the introduction of Ppy nanoparticles on the surface of Bi2MoO6 could effectively accelerate the separation of electron and hole pairs. Analyzing the catalytic mechanism, it is speculated that a traditional type-II or Z-scheme heterojunction may have been formed between Ppy and Bi2MoO6, establishing a photo-generated electron and hole transfer channel, hindering the recombination of charge carriers and improving the separation rate, and facilitating the photocatalytic reaction. This work indicated that construction Ppy/Bi2MoO6 composite photocatalysts is an effective approach to improve photocatalytic activity for degradation of Cr(VI).