The plasma treatment method was employed to characterize nitrogen (N)-doped nanoporous TiO2 photocatalysts (N-nTiO(2)) of similar to 18 nm diameter. With respect to the organic dye degradation efficiencies and antibacterial properties after exposure to visible-light irradiation, N-nTiO(2) showed better performance than the alternative commercial 5 nm anatase TiO2 (TiO2), as-grown nanoporous TiO2 (as-grown nTiO(2)), and Ar-plasma-treated nanoporous TiO2 (nTiO(2)) photocatalysts. This was attributed mainly to N-nTiO(2)'s higher anatase/brookite phase crystallinity and large surface area (375.9 m(2) g(-1)). The N doping of N-nTiO(2) was confirmed by a shift of similar to 0.25 degrees toward the higher angles in the XRD patterns and high-resolution X-ray photoelectron spectroscopy (HR-XPS) surface analysis results. Additionally, N-nTiO(2)'s total surface energy was significantly increased. Its photoluminescence (PL) response and apparent quantum yield inhibited the recombination of holes and electrons and decreased the band-gap energy (Eg < 3.2 eV), both of which contribute to activation in an expanded visible-light range. Ultraviolet (UV) and visible-light irradiation of the organic dye model Rhodamine B (Rho B), both of 70 min duration, resulted in rate constants of 3.381 and 4.269 h(-1) for N-nTiO(2), respectively. In contrast, under exposure to visible light, the value for nTiO(2) was 0.395 h(-1). Moreover, the antibacterial activity indicated that similar to 100% of both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were destroyed after 30 min visible-light irradiation while photostability was maintained. Considering all of these results, it was concluded that N-nTiO (2) is an excellent solarlight-activated photocatalyst candidate for water/waste treatment and medical applications. (C) 2014 Elsevier B.V. All rights reserved.