Synthesis and characterisation of a novel bilayer tungsten trioxide nanojunction with different crystal growth orientation for improved photoactivity under visible light irradiation

Highlights: • Cathodic electrodeposition-annealing synthesis of a bilayer WO₃ nanojunction. • Effect of annealing temperature to obtain various crystal growth orientation of WO₃. • Influences of polycrystalline structure phases of WO₃ for improved photoactivity. The main aim of this study was to prove the concept and elucidate the effect of a bilayer tungsten trioxide (WO₃) nanojunction with different crystal growth orientation for improved photoactivity under visible light irradiation. For the first time, the concept of a bilayer WO₃ nanojunction with different crystal growth orientation was demonstrated. A layer-by-layer assembly for the bilayer WO₃ nanojunction with the same monoclinic -WO₃ crystal structure, but with two different crystal growth orientation of {002} at 600 °C and {200} at 500 °C was synthesized via the controlled electrodeposition-annealing method. Photocurrent measurements showed that the individual photoactivity of WO₃ thin film with {002} crystal growth orientation was higher than that of WO₃ thin film with {200} crystal growth orientation, while the bilayer WO₃ nanojunction with different crystal growth orientation exhibited the highest photoactivity. To further characterise the bilayer WO₃ nanojunction, X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), high resolution-transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and photocurrent density measurements were performed. Based on the findings, a theoretical postulation model was proposed in explaining the transfer of photogenerated charge carriers in bilayer WO₃ nanojunction that leads to improved photoactivity under visible light irradiation.