Nitrogen-doped TiO2 nanoparticles were synthesized via plasma assisted metal organic chemical vapor deposition. Nitrogen dopant concentration was varied from 0 to 1.61 at. %. The effect of nitrogen ion doping on visible light photocatalysis has been investigated. Samples were analyzed by various analytical techniques such as x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy, and near-edge x-ray absorption fine structure. Titanium tetraisopropoxide was used as the titanium precursor, while rf-plasma-decomposed ammonia was used as the source for nitrogen doping. The N-doped TiO2 nanoparticles were deposited on stainless steel mesh under a flow of Ar and O-2 gases at 600 degrees C in a tube reactor. The photocatalytic activity of the prepared N-doped TiO2 samples was tested by the degradation of 2-chlorophenol (2-CP), in an aqueous solution using a visible lamp equipped with an UV filter. The efficiency of photocatalytic oxidation of 2-CP was measured using high performance liquid chromatography. Results obtained revealed the formation of N-doped TiO2 samples as TiO2-xNx, and a corresponding increase in the visible light photocatalytic activity. (c) 2006 American Vacuum Society.