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

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 ɣ-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.