Transition metal dopants have been used to decrease the band gap energy of TiO2 for visible light photocatalytic purposes. Fe3+ is a good dopant candidate owing to its capability to decrease the band gap energy and enhance the electron/hole trapping. However, in previous studies the photocatalytic activity of Fe-TiO2 was around 40-50% for a reaction time of similar to 300 min. Herein, using HRTEM it was found out that the photocatalytic activity of Fe-TiO2 is limited by an amorphous contamination layer on the surface of the Fe-TiO2 nanoparticles. The contamination layer was determined to be composed of iron oxide by XPS surface analysis. The contamination layer was successfully removed using an acid treatment process comprising of HCl solution. Using the cleaned Fe-TiO2 nanoparticles, the photocatalytic activity measured utilizing a solution of 20 mg L-1 methyl orange (MO) was significantly increased from 24% to 98% within 60 min of reaction time under visible light illumination. (C) 2017 Elsevier B.V. All rights reserved.