The present work reports on the soft precipitation synthesis of Bi doped and Bi-N co-doped anatase TiO2 nanoparticles that exhibit superior photocatalytic activity under visible light illumination. The photo-oxidative properties of the doped and co-doped TiO2 nanoparticles have been evaluated with Acid Red 85 - a fabric azo dye. The influence of physio-chemical parameters such as, solution pH, dopant stoichiometry, dye concentration, catalyst quantity, electron acceptors, illumination time and light intensity, has been investigated to study the extent of dye photocatalytic degradation. The modified TiO2 particles are found to exhibit faster degradation time (≤0.33 h for Bi-TiO2 and ≤0.16 h for Bi-N-TiO2), using 20 g/L of the photocatalyst materials. The photocatalysts are characterized using, XRD, SEM, TEM, EDAX, SAED, XPS, UV-vis-DRS, PLS, TGA, and BET analysis. The band gap measurements for the TiO2, Bi-TiO2 and Bi-N-TiO2 particles reveal values of 3.15, 3.01 and 2.88 eV, respectively. The synergetic combination of Bi and N co-doping plays a significant role in the narrowing the band gap energy of the photocatalysts, thereby resulting in superior visible light photocatalytic activity. © 2016 Elsevier Ltd. All rights reserved.