Synthesis of ZnO-TiO₂-WO₃ tertiary heterojunction for improved photocatalytic degradation of dyes using visible light

A ZnO-TiO2-WO3 tertiary heterojunction was synthesized using the facile sol gel and calcination methods from Zn (II), Ti (IV) and W (VI) precursors. The ZnO-TiO2-WO3 material exhibits remarkable photocatalytic performance, settling the obstacles of the pristine ZnO, TiO2, and WO3 materials. The results indicate that the composite material possesses a nanoparticle morphology alongside individual component phases. Inclusion of WO3 expands the absorption range of the composite material towards the visible region and reduces the recombination of photogenerated electron-hole pairs compared to single-phase ZnO and TiO2, where ZnO doping reduces the conduction band potential, while WO3 enhances the valence band potential, helping to convert H2O and OH into free radicals. Photocatalytic activity reveals a 92% degradation of methylene blue (20 mg/L) after 120 minutes of illumination, increased by 2 to 3 times compared to single-phase materials. An optimal Zn:Ti:W molar ratio of 6.4:5.5:1.0 was identified, which improves the hold of photogenerated electron-hole pairs. Furthermore, the ZnO-TiO2-WO3 material also demonstrates robustness over four usage cycles, maitaining methylene blue degradation above 84% in visible light. These findings indicate that the ZnO-TiO2-WO3 tertiary heterojunction has been shown to be highly effective in the degradation of dye in wastewater, offering a promising approach to environmental remediation.