New strategy for the in situ synthesis of single-crystalline MnWO4/TiO2 photocatalysts for efficient and cyclic photodegradation of organic pollutants

Abstract

MnWO₄ nano photocatalysts with plate shapes and in high yields are in situ synthesized on the surface of a porous TiO₂ film by the conventional plasma electrolytic oxidation (PEO) method combined with a subsequent ambient annealing process. Transmission electron microscopy (TEM) analysis shows that the MnWO₄ nano photocatalysts are single crystals free of structural defects and scanning electron microscopy (SEM) observation on the cross-section reveals that these MnWO₄ nano photocatalysts are in situ grown on the porous TiO₂ film surface with strong adhesion. The morphology and dimension size can be selectively tailored through controlling the reaction time, showing the simplicity and versatility of the proposed method. In addition, the photodegradation of methylene blue (MB) solution using the MnWO₄/TiO₂ photocatalysts demonstrated the superior photocatalytic performance with high efficiency and excellent photostability. A high photodegradation rate of MB solution of over 90% in 60 min has been achieved and a superior cyclic capability is also obtained. The superior photocatalytic performance of MnWO₄/TiO₂ photocatalysts can be mainly attributed to the good crystallinity, all-surface covering and strong mechanical properties of the MnWO₄ nanostructures with TiO₂ film. The prevailing advantage of the PEO method in combination with the ambient annealing process will open up more opportunity for the rational synthesis of a wide range of oxide photocatalysts ranging from tungstate to titanate, molybdate and vanadate for promising catalytic applications in diverse fields.