Effect of Yttrium Co-Doping on the Microstructure, Optical Properties, and Photocatalytic Activity of Al-Doped TiO2 Nanostructures

This study reports the synthesis and comprehensive characterization of aluminum-doped titanium dioxide nanostructures co-doped with yttrium at 0.5 and 1% levels prepared using a sol–gel method followed by supercritical ethanol drying. X-ray diffraction analysis confirmed the formation of a pure anatase phase with successful yttrium incorporation, causing slight lattice distortions and reduced crystallinity without significantly affecting the crystallite size. Yttrium doping modestly increased the specific surface area. Fourier transform infrared spectroscopy revealed titanium–oxygen lattice vibrations and surface hydroxyl groups, with a subtle redshift in the titanium–oxygen bands upon yttrium addition, corroborating the induced lattice distortion. Scanning electron microscopy images showed that yttrium incorporation densified the microstructure, reducing porosity and smoothing surface features. Optical reflectance measurements indicated a slight narrowing of the optical bandgap (from 3.25 to 3.22 eV), attributed to lattice strain and defect states, while maintaining the anatase structure. Photoluminescence spectroscopy displayed enhanced ultraviolet emission intensity with yttrium incorporation, reflecting a lower defect density and improved optical quality. Photocatalytic degradation experiments at alkaline pH demonstrated that undoped aluminum-doped titanium dioxide exhibited superior methylene blue degradation efficiency under both ultraviolet and visible light irradiation compared to yttrium-doped samples, where doping reduced activity likely due to enhanced charge recombination. Overall, yttrium co-doping modifies the structural and optical properties of aluminum-doped titanium dioxide but detrimentally affects its photocatalytic performance.