Photocatalytic Composition for Water Purification

Abstract

The present invention refers to lightweight and settable photocatalytic compositions and solid composites; methods of preparing the compositions and solid composites; and their use in water purification. The compositions are comprised of photocatalysts such as titanium dioxide (TiO 2 ) and zinc oxide (ZnO), lightweight glass bubbles, and a hydraulic cementing binder. The lightweight and settable photocatalytic compositions can be formed into lightweight photocatalytic solid composites and/or structures by mixing with water and moist curing. This invention also describes relatively simple, fast, and cost effective methodologies to photodope the TiO 2 —ZnO compositions and composites with silver (Ag), to enhance and extend the photocatalytic activity from the ultraviolet into the visible light spectrum. The lightweight and settable TiO 2 —ZnO and Ag—TiO 2 —ZnO compositions are used in making solids, structures, coatings, and continuous or semi-continuous water purification panels for purifying contaminated water.

I claim: 
     
         1 . A lightweight and settable photocatalytic composition comprising photocatalysts such as TiO 2  and ZnO, glass bubbles, and a settable hydraulic cementing binder; method for preparing the composition; and its use in water purification. 
     
     
         2 . A composition according to  claim 1 , wherein the photocatalyst may be a single photocatalyst or combination of photocatalysts which are selected from materials such as TiO 2 , ZnO, WO 3 , Cu 2 O, SnO 2 , SiO 2 , RuO 2 , SrTiO 3 , Fe 2 O 3 , NiO, SiC, and the like, and may also include non-metals and metals such as N, C, S, P, B, F, I, Cu, Ag, Pt, Pd, Mn, Wo, Ni, Sn, Fe, V and the like, or their oxides as dopants, to enhance and extend its photocatalytic activity from the ultraviolet into the visible light spectrum. 
     
     
         3 . A composition according to  claim 1 , in which the glass bubbles are transparent to UV and visible light, hollow and lightweight, with median particle size ranging from 15 to 70 microns and densities ranging from 0.1 to 0.7 g/cc. 
     
     
         4 . A composition according to  claim 1 , in which the settable hydraulic cementing binder commonly comprises of all types of Portland cements, blended hydraulic cements, performance based hydraulic cements, special cements, and combinations thereof. 
     
     
         5 . A combination of photocatalysts according to  claim 2 , wherein the photocatalysts are TiO 2  and ZnO. 
     
     
         6 . A composition according to  claim 1 , in which the proportions by weight of ZnO:TiO 2 :glass bubbles:cementing binder, is in the ratio of 1:4:25:100, or in various other mixing ratios that retain the photocatalytic properties of the composition. 
     
     
         7 . A method for preparing lightweight and settable TiO 2 —ZnO and Ag—TiO 2 —ZnO photocatalytic compositions comprising:
 a. proportioning, mixing and blending the photocatalysts in a pre-determined ratio, such as a ratio of ZnO:TiO 2  of 1:4; 
 b. adding pre-determined amounts of lightweight glass bubbles, and mixing by mechanical means such as hand agitation or rolling in a horizontal ball mill, wherein the glass bubbles also act as tiny balls in the rotating ball mill, resulting in a homogenous mixture of photocatalysts and glass bubbles; 
 c. adding pre-determined amounts of hydraulic cementing binder and mixing by mechanical means for 5 to 10 minutes, until a homogenous lightweight and settable TiO 2 —ZnO photocatalytic composition is formed; 
 d. photodoping the lightweight and settable photocatalytic composition with dopants such as Ag by mixing or coating the photocatalysts and/or photocatalytic composition with a metal salt solution, such as 0.1 M silver nitrate, exposing it to the sun, and calcining the photodoped photocatalysts and/or photocatalytic composition at temperatures between 200° C. and 500° C. for a period of 1 to 3 hours to form a lightweight and settable Ag—TiO 2 —ZnO photocatalytic composition. 
 
     
     
         8 . A lightweight and settable photocatalytic composition according to  claim 7 , in which the photocatalytic composition further comprises additives or admixtures for rapid hardening, improve workability, air entrainment, or color. 
     
     
         9 . A wet mortar formulation comprising the photocatalytic composition of  claim 7 , for coating applications and/or for binding aggregates in the preparation of lightweight photocatalytic concrete. 
     
     
         10 . A method for preparing lightweight TiO 2 —ZnO and Ag—TiO 2 —ZnO photocatalytic solid composites and/or structures by:
 a. preparing lightweight TiO 2 —ZnO photocatalytic solid composite by mixing with water at the appropriate water-cement ratio and compacting in molds of any desired shape or form; 
 b. coating the surface of the said TiO 2 —ZnO photocatalytic solid composite with 0.1M silver nitrate, exposing it to the sun, and calcining the photodoped composite at temperatures between 200° C. and 500° C. for a period of 1 to 3 hours thereby creating a lightweight Ag—TiO 2 —ZnO photocatalytic solid composites. 
 
     
     
         11 . A method of casting lightweight TiO 2 —ZnO and Ag—TiO 2 —ZnO photocatalytic solid composites according to  claim 10 , into solid spheres, cubes, cylinders or of any regular or irregular size, shape or form, that may be placed in contact with water and exposed to sunlight or artificial light, until the contaminated water is purified by photocatalysis. 
     
     
         12 . A water vessel containing the lightweight TiO 2 —ZnO and Ag—TiO 2 —ZnO photocatalytic solid composites of  claim 10 , for purifying water. 
     
     
         13 . A water purification panel containing the lightweight TiO 2 —ZnO and Ag—TiO 2 —ZnO photocatalytic solid composites of  claim 10 , and its use in water purification, comprising:
 a. tubes transparent to sunlight or artificial light, containing the lightweight TiO 2 —ZnO and Ag—TiO 2 —ZnO photocatalytic solid composites; 
 b. parabolic trough reflectors to concentrate sunlight or artificial light on the lightweight TiO 2 —ZnO and Ag—TiO 2 —ZnO photocatalytic solid composites contained in the tubes; 
 c. filling the tubes with contaminated water and exposing to sunlight or artificial light until the water is purified. 
 
     
     
         14 . A method of purifying contaminated water inside a lightweight reinforced concrete water tanks, constructed or coated with the lightweight and settable TiO 2 —ZnO and Ag—TiO 2 —ZnO photocatalytic compositions according to  claim 7 .