To use visible-light more efficiently in photocatalytic reactions, nanoporous nitrogen-doped titanium dioxide (N-TiO2) was synthesized at room temperature, without thermal treatment, using modified sol-gel processing and ultrasound irradiation. In addition, the N-TiO2 was irradiated with visible-light to improve the hydrophilicity of its surface. The calculated surface energy of visible-light irradiated N-TiO2 (*N-TiO2) was 69.1% higher than the value of 91.47 mJ m(-2) obtained for N-TiO2. Under visible-light irradiation, the photocatalytic activity for *N-TiO2 ([k] = 4.258 h(-1)) was 22.8 times higher than that for N-TiO2 ([k] = 1.871 h(-1)). The *N-TiO2 photocatalyst was highly recyclable, with a decolorization rate at 92.9% of the initial value after 15 cycles. Interestingly, the *N-TiO2 photocatalysts showed very strong antimicrobial properties against both Gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus), compared to the results for 5 nm anatase TiO2 and TiO2 photocatalysts after visible-light exposure for 3 h. More than similar to 90.2% of E. coil were killed, even after ten cycles of use for the *N-TiO2 photocatalyst. There were large increases in the photocatalytic and antibacterial activities of *N-TiO2 relative to those of N-TiO2; these were the result of the improved surface hydrophilicity of N-TiO2 by visible-light irradiation. The results presented here contribute significantly toward the development of delicate composite photocatalysts for photocatalytic water/air purification and bactericidal agents. (C) 2013 Elsevier B.V. All rights reserved.