Lower-energy process for preparing passivated inorganic nanoparticles

Abstract

The disclosure is directed to a method for reducing the chemical activity and photo activity of titanium dioxide nanoparticles comprising adding an amorphous alumina-stabilizing agent, specifically an anion, such as citric acid, to an aqueous slurry of the titanium dioxide nanoparticles; treating the aqueous slurry with a source of alumina, such as a solution of sodium aluminate, to form alumina-treated titanium dioxide nanoparticles; recovering the alumina-treated inorganic nanoparticles, wherein the nanoparticles have a particle size of about 50 to about 300 nm; and milling the nanoparticles to form nanoparticles having a particle size about 15% smaller than silica-treated inorganic nanoparticles milled under similar conditions. The titanium dioxide nanoparticles described herein are useful in cosmetic, coating and thermoplastic compositions.

1 . A process for making alumina-treated inorganic nanoparticles, comprising: 
 (a) forming a slurry of inorganic nanoparticles by mixing the nanoparticles with water;    (b) contacting the slurry of inorganic nanoparticles with an amorphous alumina-stabilizing agent;    (c) contacting the slurry with a source of alumina to form alumina-treated inorganic nanoparticles;    (d) recovering the alumina-treated inorganic nanoparticles by filtering the slurry to form a wet cake;    (e) liquefying the wet cake and jet milling the liquefied wet cake to form a milled slurry;    (f) drying the milled slurry to form a powder and    (g) micronizing the powder to form alumina-treated inorganic nanoparticles in which 5% or less of the particles, based on the volume particle size distribution within a range of 6 nm to 6000 nm, have a diameter greater than 220 nm.    
     
     
         2 . The process of  claim 1  wherein the inorganic nanoparticle is selected from metal oxide, mixed metal oxides, metal hydroxide, metal sulfide, metal carbonate, metal sulfate, silica, and mixtures thereof.  
     
     
         3 . The process of  claim 2  wherein the metal is selected from Ca, Mg, Ti, Ba, Zn, Zr, Mo, Ce, and Al.  
     
     
         4 . The process of  claim 2  wherein the inorganic nanoparticle comprises titanium dioxide.  
     
     
         5 . The process of  claim 1  wherein the amorphous alumina-stabilizing agent is an anion.  
     
     
         6 . The process of  claim 5  wherein the anion is selected from the group of citrate ions, phosphate ions, sulfate ions, and fluoride ions  
     
     
         7 . The process of  claim 1  further comprising contacting the slurry of inorganic nanoparticles with sodium aluminate prior to step (b).  
     
     
         8 . The process of  claim 1  wherein the source of alumina is sodium aluminate.  
     
     
         9 . The process of  claim 1  wherein micronizing is accomplished in a jet mill.  
     
     
         10 . (canceled)  
     
     
         11 . (canceled)  
     
     
         12 . The process of  claim 1  wherein the treated inorganic nanoparticles are silanized.  
     
     
         13 . The process of  claim 1  further comprising contacting the treated inorganic nanoparticle with an organic composition wherein the organic composition comprises at least one of octyltriethoxysilane, aminopropyltriethoxysilane, polyhydroxystearic acid, and polyhydroxy siloxide.  
     
     
         14 . The process of  claim 5  wherein the source of the anion comprises citric acid.  
     
     
         15 . The process of  claim 5  wherein the source of the anion comprises phosphoric acid.  
     
     
         16 . The process of  claim 5  wherein the source of the anion comprises sodium sulfate.  
     
     
         17 . The process of  claim 5  wherein the source of the anion comprises potassium fluoride.  
     
     
         18 . A composition for screening ultra violet radiation comprising inorganic nanoparticles made by the process of  claim 1  dispersed in an organic or aqueous medium.  
     
     
         19 . The composition of  claim 18  wherein the inorganic nanoparticle comprises titanium dioxide.  
     
     
         20 . A thermoplastic composition comprising inorganic nanoparticles made by the process of  claim 1  dispersed in a thermoplastic material.  
     
     
         21 . The thermoplastic composition of  claim 20  wherein the inorganic nanoparticle comprises titanium dioxide.  
     
     
         22 . A process for making alumina-treated inorganic nanoparticles, comprising: 
 (a) forming a slurry of inorganic nanoparticles by mixing the nanoparticles with water;    (b) contacting the slurry of inorganic nanoparticles with an amorphous alumina-stabilizing agent;    (c) contacting the slurry with a source of alumina to form alumina-treated inorganic nanoparticles;    (d) recovering the alumina-treated inorganic nanoparticles by filtering the slurry to form a wet cake;    (e) liquefying the wet cake and milling the liquefied wet cake to form a milled slurry; and    (f) dry grinding the milled slurry in a drier-grinder apparatus to form a dry powder of alumina-treated inorganic nanoparticles in which 5% or less of the particles, based on the volume particle size distribution within a range of 6 nm to 6000 nm, have a diameter greater than 220 nm.    
     
     
         23 . The process of  claim 22  wherein the drier grinder-apparatus is a single unit operation spray drier and in-line jet mill.