Aiming for the enhanced photocatalytic activity of titanium dioxide (TiO2), we probe various co-doping pairs of impurity atoms in TiO2 in search of the right co-dopants which can reduce the bandgap without creating recombination centers. To confirm the band edges and the relative positions of impurity levels, we perform first-principles density-functional-theory calculations within the local density approximation as well as the hybrid functional approach. From the analysis of the bandgaps of doped-TiO2 and the defect levels, we propose that the vanadium-nitrogen (V-N) pair is a suitable passivated co-dopant in TiO2. By doping TiO2 with the V-N pair, the bandgap of TiO2 is reduced; enhancing the visible light absorption. The calculated band edges after doping also matches the redox potentials of hydroxyl radical ((OH)-O-center dot) and superoxide anion (O-2(center dot-)); enhancing the photocatalytic activity for the degradation of organic pollutants and acting as antibacterial agents as well. (C) 2016 Elsevier B.V. All rights reserved.