Highly crystalline multi-layered WO3 sheets for photodegradation of Congo red under visible light irradiation

• WO3 multi- layered sheets were successfully synthesized by simple thermal decomposition method.
• Phase transformation of sintered WO3 occurred from monoclinic to orthorhombic structure.
• Few-to-multi layered WO3 sheets are formed by the oriented attachment (OA)-self-assembly (SA).
• Photodegradation mechanism of WO3 sheets is elucidated and discussed.
• Synthetic procedure may open up an opportunity to tailor the morphologies of semiconductors.

We report a simple synthetic method for few- to multi-layered tungsten oxide (WO3) sheets through complexation of a sodium tungstate dihydrate precursor by 1-propanol, sulfuric acid and urea. The formation of tungsten oxo-clusters and their organized transformation into few-to-multi-layered WO3 sheets occurs during the hydrolysis stage, and crystallization occurs during the post-sintering process. XRD results exhibited a phase transformation from monoclinic to orthorhombic β-WO3 due to post-sintering effects. The as-prepared material appears as self-organized few- to multi-layered WO3 sheets. The as-prepared and sintered samples are used for the photodegradation of Congo red (CR) under visible light irradiation. A sample sintered at 300 °C (S-300) shows much higher photocatalytic activity than the as-prepared WO3 and those sintered at 180 °C and 400 °C. The S-300 photocatalyst has the optimal performance in the removal of CR, which is due to high specific surface area and patches of crystalline sites on the photocatalyst surface. These sites can suppress the recombination of electrons and holes by accelerating the charge carrier transformation within the photocatalyst.

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