Z-scheme MgFe2O4/Bi2MoO6 heterojunction photocatalyst with enhanced visible light photocatalytic activity for malachite green removal

A novel heterostructured MgFe₂O₄/Bi₂MoO₆ composites were rationally designed and successfully synthesized firstly by a successive hydrothermal process and in-situ ball-milling followed by high temperature calcination technology. The investigation showed that the MgFe₂O₄ nanoparticles were closely anchored on the surface and edge of Bi₂MoO₆ nanoplates. Under visible-light illumination, the 20 wt% MgFe₂O₄/Bi₂MoO₆ samples showed the highest photocatalytic activity for the degradation of Malachite Green (MG) with 120 min and had the maximum of reaction rate constant (0.0113 min⁻¹), which was approximately 8.07 times than that of pure Bi₂MoO₆ (0.0014 min⁻¹). Moreover, the effects of MG concentration, coexisting ions, and water sources for photocatalytic activity were also investigated. The detection of reactive species demonstrated that the ∙O₂^– and h⁺ were playing important roles during MG removal process. Besides, the Z-scheme transfer mechanism of photoexcited electron-hole over composite were proved by using nitrotetrazolium blue chloride (NBT, ∙O₂^– trapping agent) and terephthalic acid (TA, ∙OH trapping agent) trapping methods. The significant improvement of photocatalytic performance can be predominantly interpreted as enhancing light harvesting ability, increasing charge carriers density as well as the formation of Z-scheme system between Bi₂MoO₆ and MgFe₂O₄ semiconductor.