First Principles Investigation of Niobium and Carbon‐Doped Titanium Dioxide for Enhanced Visible Light Photocatalytic Activity

Abstract This study employs first‐principles density functional theory (DFT) calculations to explore the effects of carbon (C) and niobium (Nb) co‐doping on the structural, electronic, and optical properties of rutile titanium dioxide (TiO 2 ). Results show that C–Nb co‐doping introduces impurity states near the valence and conduction band edges, effectively narrowing the bandgap and enhancing visible light absorption. Optical properties reveal a redshifted absorption edge and improved dielectric response, while formation energy analysis confirms the thermodynamic stability of the co‐doped system. The introduced mid‐gap states facilitate efficient charge separation and reduce electron–hole recombination, suggesting that C–Nb co‐doping is a promising strategy for improving TiO 2 photocatalytic performance under visible light.