Fabrication of Ag2O/WO3 p–n heterojunction composite thin films by magnetron sputtering for visible light photocatalysis

Abstract

Semiconductor-based nanostructures which are photo-catalytically active upon solar light irradiation were extensively used for environmental remediation due to the potential decomposition of various kinds of pollutants. In this work, we report the preparation of a sustainable thin film composite, i.e. Ag₂O/WO₃ p–n heterojunction, and investigation of its photocatalytic activity. To achieve the composite structure, WO₃/Ag–WO₃ layers were deposited over a quartz substrate by magnetron sputtering at room temperature and subsequently annealed at 823 to 923 K. The thin film structure, morphology, and chemical states were thoroughly characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron spectroscopy, and X-ray photoelectron spectroscopy. The obtained results revealed that the amorphous Ag-doped WO₃ was crystallized into monoclinic WO₃ and Ag₂O, in which nanocrystalline Ag₂O was diffused towards the surface of WO₃. Optical transmittance spectra recorded by UV-vis-NIR spectroscopy revealed that the WO₃/Ag–WO₃ films became transparant in the visible region after annealing at high temperature (873 K and 923 K). The Ag₂O/WO₃ p–n heterojunction composite thin films showed high photocatalytic activity (0.915 × 10⁻³ min⁻¹) under visible light irradiation, which is attributed to the efficiency of effective photogenerated charge-carrier formation and the reduced recombination rate of photogenerated electron–hole pairs. Unlike the powder-based photocatalysts, the reported thin film-based heterojunction photocatalyst could be very sustainable, and cost-effective.