Nanoparticulate titanium dioxide coatings, and processes for the production and use thereof

Abstract

Nanoparticulate titanium dioxide coating produced by educing flocculates of titanium dioxide nanoparticles from a titanyl sulfate solution and dispersing the nanoparticles in a polar sol-forming medium to make a sol suitable as a coating usable to impart photocatalytic activity, U.V. screening properties, and fire retardency to particles and to surfaces. The photocatalytic material and activity is preferably localized in dispersed concentrated nanoparticles, spots or islands both to save costs and leverage anti-microbial effects.

What is claimed is:  
     
         1 . A process for producing particulate titanium dioxide comprising: 
 a) mixing an alkaline-reacting liquid with an aqueous solution of titanyl sulfate at elevated temperature until the resultant mixture reacts acidically and is neutralized to a pH between 5 and 9, forming flocculates of titanium dioxide nanoparticles;    b) first-isolating the formed titanium dioxide nanoparticle flocculate;    c) first-washing in water the isolated titanium dioxide nanoparticle flocculate;    d) second-washing in an acid or an alkali the isolated and first-washed nanoparticle flocculate,    e) second-isolating as a product of the second-washing an acidic or an alkaline titania concentrate of particulate titanium dioxide.    
     
     
         2 . The process for the producing particulate titanium dioxide according to  claim 1  extended and enlarged to a process of producing a sol of particulate titanium dioxide comprising as a step after the e) second-isolating the further step of: 
 f) dispersing the second-isolated titania concentrate in a polar sol-forming medium to make a sol suitable to serve as a coating in which is present particulate titanium dioxide.  
 
     
     
         3 . The extended and enlarged process of producing both (i) particulate titanium dioxide and (ii) a sol of particulate titanium dioxide according to  claim 2   wherein the a) mixing through f) dispersing makes a sol that is transparent.    
     
     
         4 . The extended and enlarged process of producing both (i) particulate titanium dioxide and (ii) a sol of particulate titanium dioxide according to  claim 2  still further extended and enlarged to use the sol as a coating, the method comprising as a step after the f) dispersing the further step of: 
 g) applying a film of the titania sol to a surface.  
 
     
     
         5 . The process according to  claim 4  further comprising as a step after the g) applying, 
 h) neutralizing the surface with a suitable acidic- or alkaline-reacting compound; and  
 i) washing the surface with water.  
 
     
     
         6 . The process according to  claim 4  wherein the surface is prepared after the g) applying of the film of the titania sol by: 
 coating said surface with 0.1 to 1,000 wt., relative to TiO 2  that is within the titania sol in the g) applying step, of at least one oxide, hydroxide or hydrous oxide compound dawn from the group consisting of aluminum, silicon, zirconium, tin, magnesium, zinc, cerium and phosphorus.  
 
     
     
         7 . The process according to  claim 6  wherein the coating with at least one oxide, hydroxide or hydrous oxide compound is 5 to 200 wt. %, relative to the TiO 2 .  
     
     
         8 . The process according to  claim 5  wherein after the coating the surface is dried.  
     
     
         9 . The process according to  claim 5  wherein after the coating the surface is annealed.  
     
     
         10 . The process according to  claim 1  wherein the mixing is until the resultant mixture reacting acidically is neutralized to a pH between 6.5 and 7.5.  
     
     
         11 . The process according to  claim 1  wherein the mixing is with an alkaline-reacting liquid drawn from the group consisting essentially of aqueous solutions of ammonium hydroxide, sodium hydroxide, and potassium hydroxide.  
     
     
         12 . The process according to  claim 1  wherein the mixing is with an alkaline-reacting liquid drawn from the group consisting essentially of carbonates of sodium, potassium and ammonium.  
     
     
         13 . The process according to  claim 1  wherein the mixing is with an ammonium hydroxide solution having a concentration from 1 to 8 molar NH 4 OH.  
     
     
         14 . The process according to  claim 1  wherein the mixing proceeds at a temperature within the range of 60° C. to 100° C.  
     
     
         15 . The process according to  claim 1  wherein, between the a) and the b) first-isolating transpires the further step of 
 a1) letting cool a mixture created by the a) mixing.  
 
     
     
         16 . The process according to  claim 15  wherein the al) letting cool the mixture comprising: 
 quenching to a temperature below 600° C, for greater than {fraction (1/4)} hour.  
 
     
     
         17 . The process according to  claim 1  wherein the b) first-isolating comprises: 
 separating, by filtering or other method conventionally recognized in the art.  
 
     
     
         18 . The process according to  claim 17  wherein the d) second-washing in the acid or the alkali is with monobasic acid or alkali so as to both (i) remove contaminants from the isolated and first-washed nanoparticle flocculate and (ii) introduce ions necessary for sol formation.  
     
     
         19 . The process according to  claim 18  wherein the d) second-washing is in monobasic acid or alkali 1 to 6 times the weight of the titanium flocculate precipitate.  
     
     
         20 . The process according to  claim 18   wherein the d) second-washing in the acid or the alkali is with hydrochloric acid.    
     
     
         21 . The process according to  claim 20   wherein the d) second-washing in the acid or the alkali is with 3 to 6 molar hydrochloric acid.    
     
     
         22 . The process according to  claim 1   wherein the e) second-isolated acid or alkaline titania concentrate contains 4 to 40 wt. % of TiO 2 , the remainder being any of (i) wash acid or wash alkali, (ii) water moisture and (iii) small quantities of contaminants.    
     
     
         23 . The process according to  claim 2  wherein the f) dispersing of the second-isolated titania concentrate in a polar sol-forming medium is so to make a transparent sol in which TiO 2  is present exclusively as nano-particles having a diameter of between 1 and 100 nm.  
     
     
         24 . The process according to  claim 2  wherein the f) dispersing of the second-isolated titania concentrate is in a polar sol-forming medium consisting essentially of water, or an alcohol containing 1 to 10 carbon atoms and at least one hydroxide group per molecule, or mixtures thereof.  
     
     
         25 . A sol suitable as a coating consisting essentially of titanium dioxide nanoparticles educed from 
 an aqueous titanyl sulfate solution    neutralized with an alkali to    precipitate titania floculates that are    water-washed and then    acid-washed; dispersed in a polar sol-forming medium.    
     
     
         26 . The sol according to  claim 25  wherein the sol is transparent.  
     
     
         27 . The sol according to  claim 25  wherein the aqueous titanyl sulfate solution from which the-titanium dioxide nanoparticles are educed contains sulfuric acid.  
     
     
         28 . The sol according to  claim 25   wherein the titanyl sulfate solution is obtained by    digesting with sulfuric acid material drawn from the group consisting of ilmenite and titanium slag;    dissolving a digestion cake resultant from the digesting in water; and    performing clarification to derive the aqueous titanyl sulfate solution suitable as an educt.    
     
     
         29 . The sol according to  claim 25  wherein the titanyl sulfate undergoing dissolution in water is commercial grade.  
     
     
         30 . The sol according to  claim 25   wherein the titanyl sulfate solution is. obtained by dissolution of titanium dioxide and TiO 2  hydrates, including orthotitanic acid and metatitanic acid, in sulfuric acid (H 2 SO 4 ).    
     
     
         31 . The sol according to  claim 25   wherein the titanyl sulfate solution is obtained by dissolution in H 2 SO 4  of alkali metal and magnesium titanates in hydrous form.    
     
     
         32 . The sol according to  claim 25   wherein the titanyl sulfate solution is obtained by reaction of TiCl 4  with H 2 SO 4  to form TiOSO 4  and HCl.    
     
     
         33 . The sol according to  claim 25  wherein the titanyl sulfate solution contains 100 to 300 g of titanium/l, calculated as TiO 2 .  
     
     
         34 . The sol according to  claim 25  wherein the titanyl sulfate solution contains 170 to 230 g of titanium/l, calculated as TiO 2 .  
     
     
         35 . The sol according to  claim 25  having less than 0.1 wt. % of carbon.  
     
     
         36 . A composite body exhibiting a photocatalytic effect consisting essentially of 
 a core particle consisting essentially of a material without deleterious effect on a photocatalytic reaction; and    a multiplicity of nanoparticles, each less than 33% the diameter of the core particles, of photocatalytic material upon the surface of the core particle, the photocatalytic material being. less than 20% by weight of (i) the combined multiplicity of photocatalytic material nanoparticles and (ii) the core particle.    
     
     
         37 . The composite body according to  claim 36   wherein the core particle is less than 1 centimeter in diameter; and    wherein each of the multiplicity of nanoparticles is of diameter less than 100 nanometers.    
     
     
         38 . The composite body according to  claim 36  wherein the core particle's material without deleterious effect on a photocatalytic reaction consists essentially of 
 a material drawn from the group consisting essentially of silicates and carbonates including silicate and carbonate powders, mineral and mineral composites including calcined clay and wollastonite, metal oxides including zinc oxide, inorganic pigments, and construction aggregates including roofing granules.  
 
     
     
         39 . The composite body according to  claim 36  wherein the core particle consists essentially of 
 a polymer.  
 
     
     
         40 . The composite body according to  claim 39  wherein the core particle's polymer consists essentially of 
 polymer drawn from the group consisting essentially of acrylics, acrylonitriles, acrylamides, butenes, epoxies, fluoropolymers, melamines, methacrylates, nylons, phenolics, polyamids, polyamines, polyesters, polyethylenes, polypropylenes, polysulfides, polyurethanes, silicones, styrenes, terephthalates, vinyls.  
 
     
     
         41 . The composite body according to  claim 39   wherein the polymer core particle is less than 1 centimeter in diameter.    
     
     
         42 . The composite body according to  claim 36   wherein the photocatalytic material of the multiplicity of nanoparticles is drawn from the group of metal compound semiconductors consisting essentially of titanium, zinc, tungsten and iron, and oxides of titanium, zinc, tungsten and iron, and strontium titanates.    
     
     
         43 . The composite body according to  claim 42   wherein the metal compound semiconductor photocatalytic material is combined with a metal or metal compound drawn from the group consisting of vanadium, iron, cobalt, nickel, copper, zinc, ruthenium, rhodium, silicon, tin, palladium, gold, platinum, and silver.    
     
     
         44 . The composite body according to  claim 36   wherein the photocatalytic material is drawn from the group of metal compound semiconductors consisting essentially of anatase titanium dioxide and zinc oxide.    
     
     
         45 . The composite body according to  claim 36   wherein the photocatalytic material consists of particles of a diameter from 1 nanometer to 100 nanometers.    
     
     
         46 . The composite body according to  claim 36   wherein the photocatalytic material consists of particles of diameter from 1 nanometer to 50 nanometers.    
     
     
         47 . The composite body according to  claim 36   wherein the photocatalytic material consists of particles of diameter from 1 nanometer to 10 nanometers.    
     
     
         48 . The composite body according to  claim 36   wherein the core particles consist of particles of diameter from 100 nanometers to 1 centimeter.    
     
     
         49 . The composite body according to  claim 36   wherein weight of the photocatalytic material of the combined multiplicity of nanoparticles is less than 10% of weight of the core particle.    
     
     
         50 . A great multiplicity of composite bodies in accordance with  claim 36  incorporated in amount from 0.001% to 85% by volume within a composition suitable for use as an additive or a coating.  
     
     
         51 . The great multiplicity of composite bodies in accordance with  claim 50  incorporated in a composition that further includes one or more materials from the group of building materials consisting of concrete, cement, ceramic, stucco, hard flooring, masonry, roofing shingles, wall shingles, building siding and swimming pool surfaces.  
     
     
         52 . The great multiplicity of composite bodies in accordance with  claim 50  incorporated in a composition that is effective as an anti-fouling coating.  
     
     
         53 . The composite body according to  claim 36  effective in killing by contact any of algae, bacteria, mold or fungus.  
     
     
         54 . The composite body according to  claim 36  wherein, at a proportion by weight of the photocatalytic material in the composite particle of less than 10%, the efficacy of the photocatalytic material within the composite particle to kill by contact algae, bacteria, mold, and fungus upon the composite particle's surface is at least one-half (0.5) as good as is the efficacy of this same photocatalytic material to kill in purest form, making that at least equal killing effect is realized with a five to one (5:1) reduction in the amount of photocatalytic material when this photocatalytic material is upon the surface of the composite particle.  
     
     
         55 . A method of making composite photocatalytic particles comprising: 
 preparing an aqueous slurry of first particles, consisting essentially of a material without deleterious effect on photocatalytic reaction, having an associated first particle size in the range from 100 nanometers to 1 centimeter diameter;    adding a colloidal suspension of 0.1% to 60% by weight second particles, which second particles consist essentially of photocatalytic material having diameters in the range from 1 to 100 nanometers, the combined weight of second particles in the colloidal suspension being less than 20% of the combined weight of the. first particles that are also within the aqueous slurry;    mixing the aqueous slurry and the colloidal suspension so that the photocatalytic material second particles attach through van der Waals or fusion chemical forces to the nondeleterious material first particles, forming a slurry of composite particles wherein the relatively smaller photocatalytic material second particles (i) are upon the surfaces of the relatively larger nondeleterious material first particles, and (ii) are in weight less than 20% of these first particles.    
     
     
         56 . The method according to  claim 55   wherein the colloidal suspension added is from 0.1% to 60% by weight second particles.    
     
     
         57 . The method according to  claim 56   wherein the colloidal suspension added is of the highest solids concentration at which the suspension is stable, being in the range from 14% to 50% by weight.    
     
     
         58 . The method according to  claim 56  further comprising: 
 adjusting the pH of the mixing so as to move away from, in the same direction, the respective isoelectric points of the photocatalytic material second particles and the nondeleterious material first particles, the isoelectric points being those points at which the particles have a neutral net charge.  
 
     
     
         59 . The method according to  claim 56  further comprising: 
 adjusting the pH of the mixing so that either the photocatalytic material second particles or the nondeleterious material first particles approach their respective isoelectric points, but only when the mixture of both particles have low ionic strength and the pH is such that both particles are above or below their isoelectric points.  
 
     
     
         60 . The method according to  claim 56  further comprising: 
 establishing an opposite electrical charge on the nondeleterious material first particles and the photocatalytic material second particles.  
 
     
     
         61 . The method according to  claim 56  wherein either the adding of the colloidal suspension of second particles, or the mixing of the aqueous slurry and the colloidal suspension, or both the adding and the mixing, transpires in the presence of at least one dispersant.  
     
     
         62 . The method according to  claim 56  further comprising one or more finishing steps drawn from the group consisting of separating, washing and drying the composite photocatalytic particles.  
     
     
         63 . The method according to  claim 56  further comprising 
 drying the slurry of composite photocatalytic particles; and  
 annealing in a kiln the dried composite photocatalytic particles.  
 
     
     
         64 . The method according to  claim 63  that, after the annealing, further comprises: 
 rapidly cooling the annealed composite photocatalytic particles to ambient room temperature within a time period, which time period is necessarily dependent upon the temperature of the annealing and the amount of the composite photocatalytic particles, that is less than six hours.  
 
     
     
         65 . The method according to  claim 64  wherein the rapid cooling of the annealed composite photocatalytic is accomplished by rapid removal of the material from the kiln to a room temperature environment.  
     
     
         66 . A photocatalytic aggregate particle. consisting essentially of 
 an extender particle of material both non-photocatalytic and non-interfering with photocatalytic reaction; with    discrete photocatalytic titanium oxide particles exposed on the surface.    
     
     
         67 . The photocatalytic aggregate particle according to  claim 66  wherein the photocatalytic titanium oxide particles consists essentially of 
 titanium dioxide in the anatase crystalline form.  
 
     
     
         68 . The photocatalytic aggregate particle according to  claim 66  wherein the photocatalytic titanium oxide particles are less than about 20% by weight.  
     
     
         69 . The photocatalytic aggregate particle according to  claim 66  wherein the extender particle is a material drawn from the group consisting essentially of silicates and carbonates including silicate and carbonate powders, mineral and mineral composites including calcined clay and wollastonite, metal oxides including zinc oxide, inorganic pigments, and construction aggregates including roofing granules.  
     
     
         70 . A process of making photocatalytic aggregate particles comprising: 
 mixing an aqueous slurry of 
 extender particles made from material both non-photocatalytic and non-interfering with photocatalytic reactions with  
 a solution of titanyl sulfate; then  
   adding an acid or an alkaline reacting agent to cause discrete microparticles of titanium dioxide to be deposited onto the extender particles.    
     
     
         71 . A process for making photocatalytic aggregate particles comprising: 
 mixing an aqueous slurry of 
 extender particles made from material both non-photocatalytic and non-interfering. with photocatalytic reactions with  
 an alkaline or acidic titania sol containing particles of titanium dioxide.  
   
     
     
         72 . The process for making photocatalytic aggregate particles according to  claim 71  wherein the titanium dioxide particles in the titania sol have an average diameter size within the range of about 1 to about 100 nanometers.  
     
     
         73 . The process for making photocatalytic aggregate particles according to  claim 71  wherein the titanium dioxide particles in the titania sol and the extender particles are both above or below their respective isoelectric points.  
     
     
         74 . The process for making photocatalytic aggregate particles according to  claim 71  wherein discrete particles of the titanium dioxide that is within the titania sol are dispersed onto the surfaces of the extender particles in an amount less than 20 weight % based on aggregate particle weight.