An efficient nanoscale-based synthesis is used to form photocatalytically active slurries of titanium oxynitride compounds responsive to activation by visible photons and readily amenable to the surface deposition. The photocatalysts were synthesized in seconds at room temperature via direct nitridation of anatase TiO2 nanostructures with alkyl ammonium salts. With TiO2 nanoparticle agglomeration, TiO2-xNx anatase structured particles were obtained whose absorption onset extends well into the visible region at lambda similar to 550 nm. The introduction of a small quantity of palladium as PdCl2 or Pd(NO3)(2) extends absorption to near-infrared region and enhances the photocatalytic activity of the nanoparticles. Tests in a stop-flow quartz reactor of concentric tubular configuration were run at room temperature (25 degrees C), in a water-free environment and the reactants and products were detected using a mass spectrometer. The catalyzed ethylene oxidation process was observed in the stop-flow reactor in response to excitation provided by UV and incandescent lamps, and the catalyst response to visible light excitation was quantified. Extensive tests performed under a variety of conditions demonstrate photocatalytic activity in the order TiO2-xNx + Pd(NO3)(2) >= TiO2-xNx + PdCl2 > TiO2-xNx > Colloidal TiO2 for nanoparticle assembled sites under visible light illumination. An increase in coating thickness enhances the photocatalysis under UV light illumination, but does not show as pronounced an effect when visible light is used for excitation. The synthesized photocatalysts exhibit excellent long-term stability, which is essential for their practical application. (c) 2004 Elsevier B.V. All rights reserved.