NOVELTY - Synthesis of a size homogenous composition of titanium (IV) oxide (titania) nanoparticles comprises synthesizing a titania inorganic crystalline matrix within a sol gel reaction process under conditions that constrain the growth of the matrix, such that a majority of the nanoparticles in the composition does not exceed a maximum diameter of 100 nm.    USE - The method is for synthesizing size homogenous composition of titania nanoparticles for an aqueous titania paste composition for use in coating a substrate or for a photoactive layer for coating a solid substrate. The titania nanoparticles are for thermally treated film for a coated substrate (claimed) (e.g. conductive substrate such as conductive glass, slides, panels, or tiles), useful in the direct conversion of solar energy into electricity, the photocatalytic degradation of organic and biological pollutants (such as organic dyes, phenols, or pesticides) or gas (aromatic hydrocarbons, harmful organics, or oxides of nitrogen), and the development of antibacterial and superhydrophilic surfaces. The film is used in photo-electrodes for use in regenerative solar cells, particularly dye-sensitized solar cells. The aqueous dispersion of nanoparticles is used as additives to paints, treatments, render, cement, plaster, and washes for use in the construction industry. The photoactive catalytic properties of the nanoparticles can be applied to building surfaces. The aqueous nanoparticle suspensions are useful in light mediated cleaning of instruments, articles, and utensils used e.g. in food preparation.    ADVANTAGE - The method provides the benefits including simple and mild reaction conditions; ease of byproduct removal; flexibility over solvent choice (i.e. organic non-polar solvent) and reduction in the amount of solvent required; fine viscosity adjustment; high level of control over nanoparticle size and homogeneity; easy removal of organic load; and option to modify photoactivity of nano-particles to respond in the visible light range. The pastes demonstrate improved rheological and viscosity properties. The paste compositions provide easier low cost reagents that are environmentally friendly and produce products of improved quality. The aqueous dispersion of nanoparticles exhibits long shelf lives. The photoactive catalytic properties of the nanoparticles contribute to the improvement of air quality in the urban environment. The aqueous nanoparticle dispersion is reusable after removal of the cleaned utensils, and reduces the need for detergents or other caustic/chemicals that are damaging to the environment.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a composition comprising an aqueous dispersion of titania nanoparticles, which are of a homogenous size distribution;    (2) an aqueous titania paste composition comprising titania nanoparticles and an organic binder compound; and    (3) a method of coating a solid substrate with a photoactive layer comprising titania nanoparticles, comprising depositing on the substrate, an aqueous composition; and thermally treating the coating to eliminate the aqueous phase and any associated organic load, and to cause sintering of the coating.    DESCRIPTION OF DRAWING(S) - The figure depicts the characteristic hydrodynamic radius (Rh) distribution of modified (nitrogen-containing) titania aqueous suspensions, prepared by applying the sol-gel technique in an aqueous environment.