TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Methods: Compound (II) comprises tetra-alkyl orthotitanates and orthosilicates, especially tetra-ethyl orthotitanate. Polymer particles (III) are obtained by radical polymerisation of unsaturated monomers to form the core particles followed by grafting of polyelectrolyte side chains. Suitable monomers comprise 1-20C alkyl esters of alpha , beta -unsaturated mono- and di-carboxylic acids, unsaturated nitriles, vinyl esters of 1-30C monocarboxylic acids, vinyl and vinylidene halides, 2-8C mono-olefins and/or non-aromatic hydrocarbons with at least two conjugated double bonds, especially styrene or a styrene-containing monomer mixture. Before the grafting stage, the core particles are subjected to surface-functionalisation, preferably by copolymerisation with an unsaturated photoinitiator, especially 2-(4-(2-hydroxy-2-methylpropionyl)-phenoxy)-ethyl methacrylate. The second stage (grafting) involves using alpha . beta -unsaturated monomers with a radically-polymerisable double bond and at least one ionogenic and/or ionic group, preferably sodium styrene-4-sulfonate. M1 involves (a) preparation of a dispersion of polymer particles (III) in a mixture of water and water-miscible organic solvent(s) (preferably an alkanol corresponding to the alkyl group in (II)) with a water/solvent ratio such that the mol ratio of water to (II) is (2:1)-(50:1), preferably (2.1:1)-(25:1) and (b) adding compound (II) at not above 60 (preferably not above 40) degrees C and at a rate of not more than 5 (preferably not more than 2) % of the total amount of (II) per minute to give a composition (I) containing TiO2 nano-particles associated with dispersed particles (III). Further stages involve (c) purification and/or drying and/or solvent exchange (preferably drying after optional purification) and (d) calcination at 200-800 (preferably 300-600) degrees C in inert atmosphere or in an oxidising atmosphere, or in an inert atmosphere and then in an oxidising atmosphere. Preferred Compositions: Compositions (I) in the form of carbon-modified TiO2 compositions with a porous structure, obtained by the above method, preferably using an oxidising atmosphere for calcination, at least in the second stage. These compositions contain a network of TiO2 nano-particles with a mesoporous and macroporous structure, especially crystalline TiO2 in the anatase form, preferably containing macropores and mesopores with average pore diameters (by FESEM) analysis) of 50-200 (preferably 75-150) nm and 2-30 (preferably 5-20) nm respectively; the composition shows a BET surface of at least 50 (preferably at least 60) m2/g. Emulsion polymers used in the binder compositions are derived from monomers as above and/or mono-unsaturated carboxylic or sulfonic acids, phosphorus-containing monomers, esters of unsaturated mono- and di-carboxylic acids with 2-30C alkanediols, amides of similar acids with 2-30C aminoalcohols with prim. or sec. amino groups, prim. amides of unsaturated mono-acids and their N-alkyl and N,N-dialkyl derivatives, N-vinyl-lactams, N-vinylamides, allyl esters of 1-30C mono-acids, esters of unsaturated mono- or di-acids with aminoalcohols, amides of these acids with diamines with at least one prim. or sec. amino group, N,N-diallyl-amines, N,N-diallyl-N-alkylamines, vinyl- and allyl-substituted nitrogen heterocycles, vinyl ethers, polyether-(meth)acrylates and/or monomers with urea groups. Preferred monomer compositions comprise at least 40 (preferably at least 80) wt.% monomer(s) selected from 1-20C alkyl esters of unsaturated mono- or di-acids, vinylaromatics, vinyl esters of 1-30C mono-acids, unsaturated nitriles, vinyl halides and/or vinylidene halides, and up to 60 (preferably up to 20) wt.% monomer(s) selected from unsaturated mono- and di-acids, anhydrides and half-esters of unsaturated di-acids, (meth)acrylamides, 1-10C hydroxyalkyl (meth)acrylates and/or 1-10C hydroxy-(meth)acrylamides. Preferred Substrates: Plastics, metal, wood, paper or mineral substrates. EXAMPLE - A mixture of 2.07 g sodium dodecyl sulfate, 820 ml water and 208 g styrene was treated with 0.44 g potassium perdisulfate in 20 ml water, heated for 1 hour at 80 degrees C, cooled to 70 degrees C, treated with a solution of 10.64 g HMEM (2-(4-(2-hydroxy-2-methylpropionyl)-phenoxy)-ethyl methacrylate) in 9 ml acetone and purified by ultrafiltration in the dark. The resulting dispersion was diluted to a solid content of 2.5% with water, treated with sodium 4-styrene-sulfonate (30 mol% based on styrene), polymerised for 1 hour at 25 degrees C with UV light and worked up by dialysis against pure water (cellulose nitrate membrane) followed by dialysis against ethanol (regenerated cellulose membrane). The product (solid content 4.62 wt.%; 1.09 g polystyrene core with polyelectrolyte side chains) was treated with 32 ml ethanol followed by 0.15 ml water and then a solution of 0.15 ml tetraethyl orthotitanate in 8 ml ethanol at 0.08 ml/min. After reaction, the mixture was stirred for a further 2 hours and the TiO2 alkosol was purified 3 times with ethanol and water by repeated centrifugation and then redispersed in water. The titanium dioxide nano-composite particles obtained showed a diameter of 12 plus minus 2 nm (by SEM analysis), a TiO2 content of 19.8 wt.% (by TGA analysis) and a crystallite size of 3 nm (anatase form; by XRD analysis). Highly-porous TiO2 was obtained by thermolysis of the product in air at 500 degrees C; BET analysis of this material showed a pore diameter of 12.3 nm (mesopores) and a surface area of 64.25 m2/g, compared with 34.61 m2/g before calcination. A mixture of 0.5 ml composite particle solution (solid content 0.2 wt.%) and 20 ml aqueous Rhodamine B solution (2 x 10-5 mol/l) was stirred for 30 minutes in the dark and then irradiated with UV light, taking UV/VIS spectra for the sample in the range 400-650 nm. The rate constant for the photocatalytic decomposition of Rhodamine B (obtained from the signal strength of the peak at 552 nm) was 9.41 x 10-3 min-1m-2.l, compared with 7.44 x 10-4 min-1m-2.l for Degussa P25 (RTM: TiO2 particles; d = 40 nm).