Ceramic granules with a photocatalytic coating and method of making

Abstract

A plurality of photocatalytic coated ceramic granules comprising base ceramic granules, each having an outer surface, and a photocatalytic coating disposed on the outer surface. The photocatalytic coating comprising an inorganic binder and a plurality of photocatalytic particles selected from TiO2, ZnO, Ti(OH)4, doped derivatives thereof and combinations thereof. The photocatalytic particles have a surface area per weight of tire particles of no more than 30 square meters per gram (m2/g). The coated ceramic granules have a Total Solar Reflectance of at least 0.7.

1 . A plurality of coated ceramic granules comprising:
 base ceramic granules, each having an outer surface; and
 a photocatalytic coating disposed on the outer surface, 
 wherein the photocatalytic coating comprises an inorganic binder and a plurality of photocatalytic particles selected from TiO 2 , ZnO, Ti(OH) 4 , doped derivatives thereof, and combinations thereof, 
 wherein the photocatalytic particles have a surface area per weight of the particles of no more than 30 square meters per gram (m 2 /g); and 
 wherein the coated ceramic granules have a Total Solar Reflectance of at least 0.7. 
   
     
     
         2 . The coated ceramic granules of  claim 1  wherein the photocatalytic particles have a surface area per weight of the particles of no more than 25 m 2 /g. 
     
     
         3 . The coated ceramic granules of  claim 1  wherein the plurality of photocatalytic particles comprise TiO 2 . 
     
     
         4 . The coated ceramic granules of  claim 1  wherein the inorganic binder comprises an alkali metal silicate binding agent. 
     
     
         5 . The coated ceramic granules of  claim 4  wherein the alkali metal silicate binding agent is selected from lithium silicate, potassium silicate, sodium silicate, and combinations thereof. 
     
     
         6 . The coated ceramic granules of  claim 5  wherein the alkali metal silicate binding agent is selected from lithium silicate, potassium silicate, and combinations thereof. 
     
     
         7 . The coated ceramic granules of  claim 1  wherein the coating comprises 45 wt-% to 95 wt-% of the plurality of photocatalytic particles, based on the total weight of the coating. 
     
     
         8 . The coated ceramic granules of  claim 1  wherein the coating comprises 5 wt-% to 55 wt-% of the inorganic binder, based on the total weight of the coating. 
     
     
         9 . The coated ceramic granules of  claim 1  wherein the coating further comprises a crosslinker. 
     
     
         10 . The coated ceramic granules of  claim 9  wherein the crosslinker is selected from boric acid, a borate, a silicate, a fluoroaluminate, an aluminosilicate, and combinations thereof. 
     
     
         11 . The coated ceramic granules of  claim 9  wherein the coating comprises 2 wt-% to 10 wt-% of the crosslinker, based on the total weight of the coating. 
     
     
         12 . The coated ceramic granules of  claim 1  wherein the base ceramic granules each comprise a plurality of ceramic particles. 
     
     
         13 . The coated ceramic granules of  claim 12  wherein the base ceramic granules comprise an inorganic core having an outer surface and a shell on and surrounding the outer surface. 
     
     
         14 . The coated ceramic granules of  claim 13  wherein the inorganic core is a solid ceramic core. 
     
     
         15 . The coated ceramic granules of  claim 13  wherein the shell comprises ceramic particles bound together with an inorganic binder. 
     
     
         16 . A method of making photocatalytic coated ceramic granules comprising base ceramic granules, each having an outer surface, and a photocatalytic coating disposed on the outer surface, the method comprising:
 providing a coatable composition containing an inorganic binder and a plurality of photocatalytic particles selected from TiO 2 , ZnO, Ti(OH) 4 , doped derivatives thereof, and combinations thereof, wherein the photocatalytic particles have a surface area per weight of the particles of no more than 30 square meters per gram (m 2 /g);   applying the coatable composition to uncoated base ceramic granules to form intermediate coated granules; and   beating the intermediate coated granules at a temperature of at least 700° C. to produce the photocatalytic coated ceramic granules having a Total Solar Reflectance (TSR) of at least 0.7.   
     
     
         17 . The method of  claim 16  wherein the coatable composition is an aqueous slurry. 
     
     
         18 . The method of  claim 17  wherein the aqueous slurry further comprises a dispersant. 
     
     
         19 . The method of  claim 16  wherein the uncoated base ceramic granules are unfired. 
     
     
         20 . The method of  claim 16  wherein heating the intermediate coated granules occurs at a temperature of up to 900° C.