Unveiling the role of Cr-doping in modulating the textural and optical properties of sol-gel derived TiO2 nanomaterials for photocatalytic activity

This research presents a systematic investigation into the sol-gel engineering of pure and high-concentration Chromium (Cr)-doped TiO 2 nanomaterials (5 wt% and 10 wt%) for enhanced visible-light photocatalysis. X-ray diffraction (XRD) and Raman spectroscopy confirmed the successful substitutional incorporation of Cr 3 + ions into the anatase lattice, inducing significant grain refinement from 18.5 nm to 14.2 nm and increasing structural defects such as oxygen vacancies. Morphological analysis via SEM and TEM revealed a highly porous, hierarchical sponge-like nanostructure with a BET specific surface area of 57.6 m 2 /g for the optimal 5% Cr-doped sample. Optical studies through UV-Vis DRS demonstrated a substantial bandgap narrowing from 3.12 eV (pure TiO 2 ) to 2.67 eV (5% Cr-TiO 2 ), significantly extending the light-harvesting capability into the visible spectrum. Photoluminescence (PL) spectra indicated that 5% Cr-doping effectively inhibits charge carrier recombination by creating optimal trapping centers. The photocatalytic efficiency was evaluated through the degradation of Methylene Blue (MB) under visible light, where the 5% Cr-TiO 2 catalyst exhibited superior performance, achieving 80% degradation within 80 min following pseudo-first-order kinetics (k = 0.013 min −1 ). The enhanced activity is attributed to the synergistic effect of improved textural properties, narrowed bandgap, and efficient separation of photogenerated electron-hole pairs. These findings establish a comprehensive correlation between dopant-induced electronic states and accelerated mineralization of organic pollutants. Furthermore, the optimized 5% Cr-TiO 2 composite demonstrated excellent reusability, retaining 90% of its initial efficiency after three consecutive cycles under visible light. This outstanding stability highlights its potential for practical environmental remediation.