Gallium-doped TiO2 for enhanced azo dye removal: Insights from combined experimental and theoretical investigations

Abstract

This study explores the inflence of gallium (Ga) doping on the structural and adsorption properties of TiO2 nanoparticles toward methyl orange (MO). Ga-doped TiO2 with several metal contents was synthesized and characterized, while its adsorption performance was evaluated in batch experiments under controlled aqueous conditions. DFT calculations complemented the experimental fidings by modeling MO adsorption on pristine, Ga-doped anatase, and β-Ga2O3 surfaces, considering that the majority of the dopant is present as an oxide at high Ga levels. The results show that 1 wt.% Ga doping maximizes adsorption effiiency, outperforming undoped TiO2, as a consequence of increased surface roughness and defect generation due to isomorphic substitutions. At higher Ga contents, the formation of a signifiant amount of Ga oxide smooths the surface and reduces the removal capacity. Computational simulations reveal that the sulfonate group of MO drives adsorption through hydrogen bonding and coordination with surface Ti or substitutional Ga sites, with β- and dimethylaminoprotonated forms being the most stable. The formation of such complexes on β-Ga2O3, however, seems not to enhance adsorption thermodynamics, in accordance with experimental data. The inflence of interfering specieson the adsorption performance was analyzed and discussed. Ga-doped TiO2 demonstrated high effectiveness over successive reuse cycles.