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N-doped nanocrystalline titania microspheres with controlled visible light absorption were obtained by a new route utilizing a heterogeneous hydrolysis of TiCl 4 vapor with reactive droplets of aqueous aerosols, followed by instant calcination of the products in a preheated flow reactor. Thus prepared separate microspheres with a diameter of 0.5-3 microns were found to consist of anatase or rutile nanocrystals, depending on the parameters of the synthesis. Doped titania samples with different nitrogen contents were synthesized using water solutions with various concentrations of urea in the hydrolyzing aerosols. N À species were found to be a major form of nitrogen impurity. A plausible mechanism for the incorporation of nitrogen into titanium dioxide was proposed. The photocatalytic activity of the obtained powders under UV-visible or visible illumination was found to have a complex dependence on the calcination temperature and the titania doping level. ExperimentalThe experimental setup consists of two main parts, the rst for vaporized TiCl 4 hydrolysis with a water-based aerosol, and the

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