We investigate anatase TiO 2 doping with Au to determine the change in the band gap energy and optoelectronic properties using experimental and theoretical analysis. The structural analysis using XRD patterns revealed that the synthesized materials primarily exhibited an anatase phase of TiO 2 , with no impurity peaks observed. However, as the concentration of Au increased, additional diffraction peaks corresponding to Au crystalline phases were detected, indicating successful doping. Furthermore, the crystallite size was found to decrease with increasing Au concentration. We observe that the band gap reduces through substitution of Au into the TiO 2 lattice from 3.09 eV to 2.78 eV, demonstrating the feasibility of bandgap tuning of the TiO 2 system. A redshift for Au doped TiO 2 is observed from absorption spectroscopy and optical absorption intensity using hybrid density functional theory, facilitating visible light absorption, although with potential electron-hole recombination limitations. To enhance a visible light photocatalytic activity for water splitting, we extend our work to explore the impact of N and Au codoping into TiO 2 lattice. It reveals that the combination between N and Au leads to a suitable reduction in the band gap width of pure TiO 2. Interestingly, Au-N codoping may decrease the effect of photogenerated carriers, produce a new optical absorption feature in the visible region, and enhance the photocatalytic performance of TiO 2. This codoping configuration is also a promising photocatalyst for the decomposition of water using visible light without inducing unoccupied states.