Method for preparation of nanometer cerium-based oxide particles

Abstract

The invention comprises novel undoped and doped nanometer-scale CeO 2 particles as well as a novel semi-batch reactor method for directly synthesizing the novel particles at room temperature. The powders exhibited a surface area of approximately 170 m 2 /g with a particle size of about 3-5 nm, and are formed of single crystal particles that are of uniform size and shape. The particles' surface area could be decreased down to 5 m 2 /g, which corresponds to a particle size of 100 nm, by thermal annealing at temperatures up to 1000° C. Control over the particle size, size distribution and state of agglomeration could be achieved through variation of the mixing conditions such as the feeding method, stirrer rate, amount of O2 gas that is bubbled through the reactor, the temperature the reaction is carried out at, as well as heating the final product at temperatures ranging from 150° to 1000° C.

1 . A process for the production of cerium dioxide crystals comprising: 
 (a) providing a first solution of a water-soluble cerium salt solution;    (b) providing a second aqueous solution of an alkali metal or ammonium hydroxide;    (c) mixing said first and second solutions together to form a reactant solution;    (d) agitating said reactant solution under turbulent flow conditions while concomitantly passing gaseous oxygen through said reactant solution; and    (e) precipitating cerium dioxide particles having a predominant particle size within the range of 3-100 nanometers.    
     
     
         2 . The method of  claim 1  wherein said cerium salt is cerous nitrate.  
     
     
         3 . The method of  claim 1  wherein said second solution is an aqueous solution of ammonium hydroxide.  
     
     
         4 . The method of  claim 3  wherein the ammonium hydroxide solution ranges from 0.1 mol/l to 1.5 mol/l.  
     
     
         5 . The process of  claim 1  wherein the agitation of said reactor solution is carried out within a reactor vessel to which one of said first and second solutions is added followed by the addition of the other said first and second solutions.  
     
     
         6 . The method of  claim 5  wherein the other first and second solution is added to the reactor at a rate of from 0.5 ml/min to 10 ml/min.  
     
     
         7 . The method of  claim 5  wherein the first solution is added to the reactor vessel followed by the addition of the second solution to the reactor.  
     
     
         8 . The method of  claim 5  wherein the second solution is added to the reactor followed by the addition of the first solution to the reactor.  
     
     
         9 . The method of  claim 8  wherein said cerium salt is cerous nitrate, said solution is an aqueous solution of ammonium hydroxide, the first solution is added to the reactor at a rate within the range of 0.5 ml/min to 10 ml/min, said agitating step is accomplished by stirring the solution with an impeller at a rate within the range of 100-5000 rpm during the mixing step, and wherein the oxygen is passed through said reactant solution at a rate from 1 ml/min to 500 ml/min.  
     
     
         10 . The method of  claim 1  wherein distilled water is added to the reactor followed by the simultaneous addition of the first and second solutions to the reactor.  
     
     
         11 . The method of  claim 1  wherein the agitating step is accomplished by stirring the solution with an impeller at a rate within the range of 100-5000 rpm during the mixing step.  
     
     
         12 . The method of  claim 1  wherein the oxygen is passed through said reactant solution at a rate within the range of 1 ml/min to 500 ml/min.  
     
     
         13 . The method of  claim 1  that further comprises mixing a dopant precursor solution comprised of the nitrate or acetate form of a lanthanide series metal with the first and second solutions.  
     
     
         14 . The method of  claim 13  wherein the dopant precursor solution is mixed with the first solution prior to mixing with the second solution.  
     
     
         15 . The method of  claim 13  wherein the reactor is maintained at room temperature.  
     
     
         16 . The doped cerium oxide formed by the method of  claim 13 .  
     
     
         17 . The method of  claim 1  further comprising the step of vacuum drying the synthesized powders.  
     
     
         18 . The method of  claim 1  further comprising the step of heating the precipitate to result in the growth of the particles to a desired size.  
     
     
         19 . The method of  claim 1  wherein each of the cerium dioxide particles are a single crystal.  
     
     
         20 . The cerium dioxide particles formed by using the method of  claim 1 .  
     
     
         21 . The cerium dioxide particles of  claim 20  wherein the particle size is further controlled within the range of 3 to 10 nanometers.  
     
     
         22 . The cerium dioxide particles of  claim 20  wherein the particle size and shape are uniform.  
     
     
         23 . A cerium dioxide composition comprising single crystal cerium dioxide particles that are smaller than 100 nanometers in size.  
     
     
         24 . The cerium dioxide composition of  claim 23  wherein the particles are smaller than 10 nanometers in size.  
     
     
         25 . The cerium dioxide composition of  claim 23  wherein the particles are predominantly of a uniform size and shape.  
     
     
         26 . A doped cerium dioxide composition comprising cerium dioxide particles that are doped with a lanthanide series metal and have a particle size less than 100 nanometers.  
     
     
         27 . The doped cerium dioxide particles of  claim 26  wherein the particle size is less than 10 nanometers.  
     
     
         28 . The doped cerium dioxide particles of  claim 26  wherein the particle size is within the range of 3-5 nanometers.  
     
     
         29 . The doped cerium dioxide particles of  claim 26  wherein each particle is a single crystal.  
     
     
         30 . The doped cerium dioxide particles of  claim 26  wherein the particles are predominantly of uniform shape and size.  
     
     
         31 . A cerium dioxide composition comprising cerium dioxide particles having a predominant particle size within the range of 3 to 100 nanometers produced by the process of: 
 (a) mixing together a first solution of a water-soluble cerium salt solution and a second aqueous solution of an alkali metal or ammonium hydroxide to form a reactant solution    (b) agitating said reactant solution under turbulent flow conditions while concomitantly passing gaseous oxygen through said reactant solution; and    (c) precipitating said cerium dioxide particles having a predominant particle size within the range of 3 to 100 nanometers.    
     
     
         32 . The composition of  claim 31  wherein said cerium dioxide particles have a predominant particle size within the range of 3 to 10 nanometers.  
     
     
         33 . The composition of  claim 31  wherein said cerium dioxide particles are predominantly of uniform particle size and shape.  
     
     
         34 . A cerium dioxide composition comprising single crystal cerium dioxide particles that are smaller than 100 nanometers in size.  
     
     
         35 . The cerium dioxide composition of  claim 34  wherein said particles are smaller than 10 nanometers in size.  
     
     
         36 . The cerium dioxide composition of  claim 34  wherein said particles are predominantly of a uniform size and shape.  
     
     
         37 . A doped cerium dioxide composition comprising cerium dioxide particles that are doped with a lanthanide series metal and have a particle size less than 100 nanometers.  
     
     
         38 . The doped cerium dioxide particles of  claim 37  wherein said cerium dioxide particles have a particle size of less than 10 nanometers.  
     
     
         39 . The doped cerium dioxide particles of  claim 37  wherein said cerium dioxide particles have a particle size within the range of 3 to 5 nanometers.  
     
     
         40 . The doped cerium dioxide particles of  claim 37  wherein each particle is a single crystal.  
     
     
         41 . The doped cerium dioxide particles of  claim 37  wherein said particles are predominantly of uniform shape and size.  
     
     
         42 . The doped cerium dioxide composition of  claim 37  wherein said lanthanide series metal is selected from the group consisting of lanthanum, samarium and gadolinium.  
     
     
         43 . The doped cerium dioxide composition of  claim 42  wherein said lanthanide series metal is samarium.  
     
     
         44 . A cerium dioxide composition comprising doped cerium dioxide particles having a predominant particle size within the range of 3 to 100 nanometers produced by the process of: 
 (a) mixing together a first solution of a water-soluble cerium salt solution and a second aqueous solution of an alkali metal or ammonium hydroxide to form a reactant solution;    (b) mixing a dopant precursor solution comprised of the nitrate or acetate form of a lanthanide series metal with at least one of said first and second solutions and said reactant solution;    (c) agitating said reactant solution under turbulent flow conditions while concomitantly passing gaseous oxygen through said reactant solution; and    (d) precipitating said doped cerium dioxide particles having a predominant particle size within the range of 3 to 100 nanometers.    
     
     
         45 . The cerium dioxide composition of  claim 43  wherein said doped cerium dioxide particles are produced by the process of mixing said dopant precursor solution with said cerium salt solution.  
     
     
         46 . The cerium dioxide composition of  claim 44  wherein said lanthanide series metal is selected from the group consisting of lanthanum, samarium and gadolinium  
     
     
         47 . The cerium dioxide composition of  claim 45  wherein said lanthanide series metal is samarium.