Transparent, stable titanium dioxide sols

Abstract

A method of preparing stable, transparent photocatalytic titanium dioxide sots is disclosed which involves thermal treatment of a suspension of amorphous titanium dioxide in the presence of certain alpha-hydroxy acids. The sots comprise titanium dioxide particles in the anatase form having a crystallite size less than about 10 nm and exhibit excellent stability and transparency at basic, neutral, and acid pH.

1 . A method for preparing a stable, transparent photocatalytic titanium dioxide sol, comprising:
 (i) providing a solution comprising a titanium containing compound;   (ii) precipitating hydrous titanium dioxide from said solution of a titanium containing compound;   (iii) forming an aqueous dispersion of said precipitated hydrous titanium dioxide; and   (iv) mixing said aqueous dispersion in the presence of one or more alpha-hydroxy carboxylic acids.   
     
     
         2 . The method of  claim 1 , wherein said titanium containing compound is selected from the group consisting of titanium alkoxide, titanium oxychloride, titanyl sulfate, and titanyl acetylacetonate. 
     
     
         3 . The method of  claim 2 , wherein said titanium containing compound is titanium isopropoxide. 
     
     
         4 . The method of  claim 1 , wherein said one or more alpha-hydroxy carboxylic acids include an alpha-hydroxy carboxylic acid selected from the group consisting of lactic acid, tartaric acid, malic acid, citric acid, and combinations thereof. 
     
     
         5 . The method of  claim 4 , wherein said one or more alpha-hydroxy carboxylic acids include lactic acid. 
     
     
         6 . The method of  claim 4 , wherein said one or more alpha-hydroxy carboxylic acids include tartaric acid. 
     
     
         7 . The method of  claim 4 , wherein said one or more alpha-hydroxy carboxylic acids include citric acid. 
     
     
         8 . The method of  claim 1 , wherein step (iv) is carried out without an intervening neutralization step between steps (iii) and (iv). 
     
     
         9 . The method of  claim 1 , further comprising the step of neutralizing the resultant sol with a base. 
     
     
         10 . The method of  claim 1 , wherein said sol comprises titanium dioxide crystallites having an average particle size of less than about 5 nm. 
     
     
         11 . The method of  claim 1 , wherein said sol comprises titanium dioxide crystallites, at least 90% of which are in the anatase form.