"Fabrication and Characterization of ZnO/TiO₂ Nanocomposites for Enhanced Photocatalytic Degradation of Organic Pollutants "

Abstract

The increasing contamination of water resources by synthetic organic dyes has created significant environmental and public health concerns worldwide. This study investigates the fabrication and characterization of ZnO/TiO₂ nanocomposites synthesized through the sol-gel method for enhanced photocatalytic degradation of methylene blue (MB) and rhodamine B (RhB) dyes. Nanocomposites with ZnO:TiO₂ molar ratios of 1:0, 3:1, 1:1, 1:3, and 0:1 were prepared and calcined at 500°C for 2 hours. Structural analysis using X-ray diffraction confirmed the successful formation of wurtzite ZnO and anatase TiO₂ phases, with crystallite sizes ranging from 14.3 to 18.7 nm. The optimized 1:1 ZnO/TiO₂ nanocomposite exhibited a crystallite size of 16.2 nm and the highest BET surface area of 78.4 m² g⁻¹, representing a 73.1% increase over pure ZnO. UV–Visible diffuse reflectance spectroscopy revealed bandgap reduction from 3.25 eV for ZnO and 3.20 eV for TiO₂ to 3.02 eV for the 1:1 composite, resulting in enhanced light absorption. Photocatalytic experiments demonstrated that the 1:1 ZnO/TiO₂ nanocomposite achieved 98.7% degradation of methylene blue within 60 minutes and 95.3% degradation of rhodamine B within 90 minutes under 36 W UV irradiation. The corresponding pseudo-first-order rate constants were 6.84 × 10⁻² min⁻¹ for MB and 3.41 × 10⁻² min⁻¹ for RhB, significantly higher than those of pure ZnO and TiO₂. Total organic carbon removal reached 82.6%, confirming substantial mineralization of pollutants. Reusability studies showed only 6.8% activity loss after five cycles. The enhanced photocatalytic performance was attributed to Type-II heterojunction formation, improved electron-hole separation, increased surface area, and efficient generation of hydroxyl and superoxide radicals. The findings demonstrate that ZnO/TiO₂ nanocomposites are promising photocatalysts for sustainable wastewater treatment and environmental remediation applications.