Neutral, stable and transparent photocatalytic titanium dioxide sols

Abstract

A method for preparing a neutral, stable and transparent photocatalytic titanium dioxide sol is provided. The method comprises (1) contacting an alkaline titanium dioxide sol with an alkaline peptizing agent to provide a peptized alkaline titanium dioxide sol; (2) neutralizing the peptized alkaline titanium dioxide sol; and (3) obtaining or collecting the neutral, stable and transparent photocatalytic titanium dioxide sol. The titanium dioxide sol is stable and transparent over a range of pH of about 7.0 to about 9.5. The titanium dioxide sol may include crystallites of titanium dioxide having an average particle size of less than about 10 nm with at least 90% of the crystallites being in the anatase form.

1 - 64 . (canceled) 
     
     
         65 . A method for preparing a photocatalytic titanium dioxide sol, the method comprising:
 peptizing a titanium dioxide material by reacting with an alkaline peptizing agent to provide a titanium dioxide sol; and   neutralizing the titanium dioxide sol with a concentrated acid;   wherein the titanium dioxide sol has a TiO 2  concentration of at least 18% by weight; and   wherein the titanium dioxide sol has been washed to have a calcium ion concentration of less than about 71 ppm.   
     
     
         66 . The method according to  claim 65 , wherein the alkaline peptizing agent is selected from the group consisting of an alkylamine, a quaternary ammonium hydroxide, and combinations thereof. 
     
     
         67 . The method according to  claim 66 , wherein the alkaline peptizing agent is a tetraalkylammonium hydroxide. 
     
     
         68 . The method according to  claim 66 , wherein the alkaline peptizing agent is selected from the group consisting of diethylamine (DEA), tetramethylammonium hydroxide (TMAOH), and combinations thereof. 
     
     
         69 . The method according to  claim 65 , wherein the titanium dioxide sol has been washed to a filtrate conductivity of equal to or less than 500 μs. 
     
     
         70 . The method according to  claim 65 , wherein the concentrated acid comprises phosphoric acid. 
     
     
         71 . The method according to  claim 65 , wherein the titanium dioxide sol has a TiO 2  concentration of about 30% to about 40% by weight. 
     
     
         72 . The method according to  claim 65 , wherein, after said neutralizing, the titanium dioxide sol has a pH of about 8 to about 9. 
     
     
         73 . The method according to  claim 65 , wherein the titanium dioxide sol comprises TiO 2  crystallites having an average particle size of less than about 50 nm, at least 90% of which are in the anatase form. 
     
     
         74 . The method according to  claim 65 , wherein the titanium dioxide sol is doped with a metal. 
     
     
         75 . The method according to  claim 74 , wherein the doping metal is selected from the group consisting of Ag, Zn, Mg, Sn, Fe, Co, Ni, Se, Ce, Cu, and combinations thereof. 
     
     
         76 . The method according to  claim 65 , wherein the viscosity of the titanium dioxide sol is less than about 100 centipoise after at least 4 weeks at room temperature. 
     
     
         77 . The method according to  claim 65 , wherein said peptizing comprises addition of the titanium dioxide material to a solution of the alkaline peptizing agent. 
     
     
         78 . A photocatalytic titanium dioxide sol prepared according to the method of  claim 65 . 
     
     
         79 . A titanium dioxide sol comprising titanium dioxide at a concentration of about 30% to about 40% by weight and having pH of about 8 to about 9. 
     
     
         80 . The titanium dioxide sol of  claim 79 , wherein the titanium dioxide sol is doped with a metal. 
     
     
         81 . The titanium dioxide sol of  claim 80 , wherein the doping metal is selected from the group consisting of Ag, Zn, Mg, Sn, Fe, Co, Ni, Se, Ce, Cu, and combinations thereof. 
     
     
         82 . The titanium dioxide sol of  claim 79 , wherein the viscosity of the titanium dioxide sol is less than about 100 centipoise after at least 4 weeks at room temperature. 
     
     
         83 . The titanium dioxide sol of  claim 79 , wherein the titanium dioxide sol comprises TiO 2  crystallites having an average particle size of less than about 50 nm, at least 90% of which are in the anatase form.