The effects of KOH concentration (10-30 M) on the morphology of KNbO3 produced from Nb2O5 by hydrothermal synthesis have been investigated. High purity KNbO3 nanocubes have been obtained using 30 M KOH at 200 degrees C. The KNbO3 nanocubes can be readily doped with nitrogen by heating with urea at 425 degrees C without significant change in morphology. The band gap of KNbO3 decreases from 3.13 to 2.76 eV as a result of N-doping, the surface area also increases substantially. The photocatalytic activity of the N-doped KNbO3 nanocubes has been evaluated by photodegradation of four organic contaminants (rhodamine B, orange G, bisphenol A and pentachlorophenol) as well as water splitting under visible light irradiation. The results show that the photocatalytic activity of N-doped KNbO3 is significantly higher than that of pure KNbO3 nanocubes and Degussa TiO2 P25 under visible light irradiation. (C) 2013 Published by Elsevier B.V.