Structural Design and Photocatalytic Performance Study of Binary and Ternary Photocatalysts Based on ZnO, TiO2, and SiO2 Oxides for Azo Dye Degradation

Semiconductor photocatalysis offers a promising approach for degradation of organic dye contaminants from industrial effluent; however, rapid charge-carrier recombination and limited optical absorption in single-component photocatalysts often reduce degradation efficiency. To overcome these limitations, this study focuses on developing binary and ternary oxide composites with tailored structures and optimized compositions to enhance UV-assisted photocatalysis. The metal oxides were synthesized in ZnO/TiO2, TiO2/SiO2, ZnO/SiO2, and ZnO/TiO2/SiO2 combinations by using a sol–gel method. The prepared metal oxide composites were characterized for band-gap energy, morphology, and structural properties and then used to degrade MB and MO dyes in solution. The photocatalytic degradation experiments were performed under UV irradiation using a 36 W discharge lamp with an emission wavelength range of 300–400 nm. Comparative photocatalytic experiments were conducted using an initial dye concentration of 10 mg/L, a catalyst loading of 5.0 g/L, a reaction time of 180 min, and a solution pH of 6.5. The ZnO/TiO2 showed 98.44% and 97.69% removal efficiency against MB and MO dyes, respectively. The high degradation efficiency is possibly due to improved charge separation, a low electron–hole recombination rate, and an extended lifetime of the electrons within the photocatalyst structure.