Sol-Gel Synthesis of Yb-Er Co-doped TiO₂-ZnO Heterostructures for Enhanced Photocatalytic Degradation of Methylene Blue: Performance and Mechanism

Water pollution is a pressing global issue, and photocatalysis is a promising approach for degrading organic pollutants in printing and dyeing wastewater. Enhancing solar utilization and clarifying reaction mechanisms are core goals of heterogeneous photocatalysis. TiO₂ is limited by its wide bandgap (UV-only activation) and rapid photogenerated charge recombination. Herein, a Yb³⁺/Er³⁺ co-doped TiO₂-ZnO composite was prepared via sol-gel method. Structural/morphological analyses confirmed enlarged specific surface area, narrowed bandgap and improved light absorption, with optimal calcination at 550°C for 2 h. The TiO₂-5%ZnO/1%Yb-1%Er composite achieved 76.31% methylene blue (MB) degradation under visible light for 6 h (vs. 33.20% for pure TiO₂) and 98.58% degradation under UV light for 2 h (vs. 52.82% for pure TiO₂), outperforming P25. This work verifies that rare-earth co-doping effectively boosts the photocatalytic performance of TiO₂ based composites.