BACKGROUND: The aim of this study was to investigate improvement of the photocatalytic activity of visible-light driven nitrogen-modified TiO2 (N-TiO2) powder toward methyl blue (MB) and direct blue-86 (DB-86) dyes. The Taguchi method with an L9 orthogonal array was applied to plan the synthesis parameters, i.e. nitrogen sources, nitrogen source concentrations, stirring time and calcined temperatures. 95% confirmation experiments were undertaken to verify the effectiveness of the Taguchi method. RESULTS: All N-TiO(2) photocatalysts were shifted toward the visible light region with the optical band gap ( Eg). Nitrogen source concentrations were significant parameters for the photocatalytic decolorization rate constants ( k values). In comparison with pure TiO(2), the photodecolorization behavior of N-TiO(2) toward DB-86 was superior with a reaction rate constant of 1.68 x 10(-3) min(-1), and a 4 h photodecolorization efficiency of 34%. CONCLUSION: The Taguchi method was reported to alter the surface properties of commercial Degussa P25 TiO(2), which could then be used as a visible-light driven photocatalyst. The visible-light-driven photocatalyst was investigated to determine material characteristics. Greater photodecolorization of MB and DB-86 dye pollutants using optimally-prepared N-TiO(2) under visible light irradiation was successfully obtained. (C) 2011 Society of Chemical Industry