Zr4+ doped nano titania was prepared by sol-gel method using titanium(IV) isopropoxide and zirconium nitrate as precursors. The materials were characterized by XRD, BET, UV-vis, Fr-IR, SEM-EDX and TEM techniques. The nanoparticles of pure TiO2 contained both anatase and rutile phases together but Zr4+ doped TiO2 gave anatase phase only. The framework substitution of Zr4+ in TiO2 was established by XRD, SEM-EDX and FT-IR techniques. The band gap value of Zr4+ doped TiO2 was higher than the parent nano TiO2. TEM observations confirmed the nanocrystalline nature of Zr4+ doped TiO2. The presence of dopants therefore could suppress the growth of TiO2 grains, increase the surface area, decrease the anatase-rutile phase transformation and accelerate the surface hydroxylation. These properties resulted higher photocatalytic activity for Zr4+ doped nano TiO2 than undoped nano TiO2 The presence of anatase type structure in TiO2 with high crystallinity and high phase stability, even after annealing at 800 degrees C substantially indicated that the dopants might inhibit densification and crystallite growth by providing dissimilar boundaries. The photocatalytic activity in the degradation of 4-chlorophenol was found to be higher for Zr4+ doped TiO2 than both nano TiO2 and commercial TiO2 (Degussa P25). The experimental parameters such as initial concentration of 4-chlorophenol, catalyst loading, pH and light intensity were optimized for maximum degradation efficiency. (c) 2006 Elsevier B.V. All rights reserved.