TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The method comprises adding a visible light-absorbing center precursor molecule to the sol gel reaction process, to generate titania nanoparticles that demonstrate photoactivity in response to irradiation with visible light. Preferred Component: The visible light-absorbing center precursor molecule comprises nitrogen, sulfur, and/or phosphorus. It is urea. The titania inorganic crystalline matrix is synthesized from an organometallic titanium precursor molecule, which is a titanium alkoxide, preferably titanium butoxide or titanium isopropoxide; or from a titanium halide. The titania nanoparticles are spherical. They are in aqueous dispersion. The titania nanoparticles are comprised within a sintered coating applied to a solid substrate. Preferred Parameter: The titania nanoparticles have a hydrodynamic radius of between 0.1-100 nm. greater than or equal to 70, Preferably greater than or equal to 90% of the titania nanoparticles have a diameter of 1-100, preferably of 7-20 nm. greater than or equal to 75% Of titania nanoparticles have size distribution centered around a diameter range of 10-15 nm.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The sol gel reaction process occurs under aqueous conditions in the presence of a complexing reagent, which is a bidentate ligand capable of complexing with a titanium (IV) metal center. Preferred Compound: The complexing reagent is acetylacetone (2,4-pentanedione), EDTA, sodium-EDTA, disodium-EDTA, oxalic acid, or oxamic acid.    TECHNOLOGY FOCUS - POLYMERS - Preferred Method: The sol gel reaction process occurs under non-aqueous conditions in the presence of an organic polymer matrix. It occurs under acidic conditions, where pH of the reaction is between 1-4. The aqueous composition is deposited on the substrate via dip coating, doctor blade technique, spray coating, screen printing, or spin coating. Preferred Compound: The organic polymer is cellulose, ethylated derivative of cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate hydrogenphthalate, cellulose acetate propionate, cellulose acetate trimellitate, cellulose nitrate, cellulose cyanoethylate, or cellulose triacetate. The organic binding agent is from polyethylene glycol and/or methoxy-polyethyleneglycol or their derivatives. EXAMPLE - A solution of titania precursor, tetrabutylorthotitanate (15 v/v%) was added to an acidic (below pH 4) aqueous solution (100 ml) (inorganic acid such as nitric acid (HNO3) or organic such as HCOOH, approximately 1.5 v/v%) under intense stirring. To this solution mixture, visible light absorbing precursor (i.e. urea, up to 30 w/v%) was dissolved to enable production of nitrogen (N)-doped titania microparticle. The dispersed mixture was constantly stirred for 4 hours, resulting in the formation of a colloidal solution. Only after the solution was refined, a second solution containing the complexing agent, acetylacetone (4 v/v%), was added, and the color of the final solution turned to yellow-orange. Under continuous stirring, to the final sol, an amount of a modifier-stabilizer (i.e. polyethylene glycol) was added. The mixture-suspension was stable for many months at room temperature, and size distribution (hydrodynamic radius) of the nanoparticles in the solution exhibited its maximum value in 7-12 nm. The preparation of modified (N-containing) nanostructured titania powders included solvent evaporation followed by thermal treatment of the solid residue at 400-550 degrees C, resulting to the formation of N-doped titanium (IV) oxide nano-structured powders with a specific surface area between 35-70 m2/g.