Noble metal superparticles and methods of preparation thereof

1. A method, comprising:

heating an aqueous solution of colloidal silver particles;

adding a soluble noble metal halide salt to the aqueous solution, the noble metal halide salt undergoing a redox reaction on a surface of the colloidal silver particles to form at least one of noble metal/silver halide superparticles, noble metal halide/silver halide superparticles and noble metal oxide/silver halide superparticles on the surface of the silver particles;

maintaining the heat for a predetermined time to consume the silver particles and release the at least one of the noble metal/silver halide superparticles, the noble metal halide/silver halide superparticles and noble metal oxide/silver halide superparticles into the aqueous solution;

cooling the aqueous solution; and

separating the at least one of the noble metal/silver halide superparticles, the noble metal halide/silver halide superparticles and noble metal oxide/silver halide superparticles from the aqueous solution.

2. The method of claim 1 , wherein the noble metal is platinum or palladium.

3. The method of claim 2 , wherein the noble metal is platinum, and wherein the superparticles comprise platinum/silver halide superparticles.

4. The method of claim 3 , wherein the method further comprises:

dissolving silver halide from the platinum/silver halide superparticles in an aqueous ammonia solution to produce platinum superparticles,

wherein, a surface of the platinum superparticles is free of organic ligands.

5. The method of claim 2 , wherein the noble metal is palladium, and wherein the superparticles comprise palladium/palladium oxide/silver halide superparticles.

6. The method of claim 5 , further comprising:

dispersing the palladium/palladium oxide/silver halide superparticles in an aqueous ammonia solution to dissolve the silver halide and produce palladium/palladium oxide superparticles; and

reducing the palladium oxide in the palladium/palladium oxide superparticles in a solution to produce palladium superparticles,

wherein, a surface of the palladium superparticles is free of organic ligands.

7. The method of claim 1 , further comprising:

optionally, adding a soluble halide salt to the aqueous solution.

8. The method of claim 7 , wherein the noble metal is selected from a group consisting of rhodium and iridium.

9. The method of claim 8 , wherein the noble metal is rhodium and the superparticles comprise rhodium halide/silver halide superparticles, the method further comprising:

reducing the rhodium halide/silver halide superparticles in an aqueous solution of sodium borohydride to produce rhodium/silver superparticles.

10. The method of claim 9 , further comprising:

solvothermally annealing the rhodium/silver superparticles in a solvent to produce rhodium superparticles,

wherein, a surface of the rhodium superparticles is free of organic ligands.

11. The method of claim 8 , wherein the noble metal comprises iridium and the superparticles comprise iridium halide/silver halide superparticles, the method further comprising:

reducing the iridium halide/silver halide superparticles in an alcohol based solution to produce iridium/silver halide superparticles,

wherein, a surface of the iridium/silver halide superparticles is free of organic ligands.

12. The method of claim 1 , wherein halide anions are absorbed on the surface of the at least one of the noble metal/silver halide superparticles, the noble metal halide/silver halide superparticles and noble metal oxide/silver halide superparticles, the halide anions producing a negative charge to prevent the at least one of the noble metal/silver halide superparticles and the noble metal halide/silver halide superparticles and noble metal oxide/silver halide superparticles from coalescing.

13. The method of claim 1 , wherein the at least one of the noble metal/silver halide superparticles and the noble metal halide/silver halide superparticles and noble metal oxide/silver halide superparticles have a diameter of greater than 20 nm.

14. The method of claim 1 , wherein the silver particles include at least one of a silver nanospheres, irregular silver particle aggregates, silver nanowires, gold core silver shell nanoparticles, silver nanosheets and silver microspheres.

15. The method of claim 1 , wherein the surface of the silver particles exhibits non-uniform reactivity.

16. A method of fabricating platinum superparticles comprising a plurality of platinum nanoparticles arranged in three-dimensional structure having a hemispherical dome shape with a flat bottom, a hollow interior and a plurality of pores defined between the platinum nanoparticles, the method comprising:

heating an aqueous solution of colloidal silver particles;

adding a soluble platinum halide salt to the aqueous solution, the platinum halide salt undergoing a redox reaction on a surface of the silver particles to form a plurality of platinum/silver halide superparticles disposed on the surface of the silver particles;

maintaining the heat for a predetermined time to consume the silver particles and release the platinum/silver halide superparticles in the aqueous solution, the platinum/silver halide superparticles including a plurality of platinum nanoparticles interspersed with silver halide nanoparticles;

cooling the aqueous solution;

separating the platinum/silver halide superparticles from the aqueous solution; and

incubating the platinum/silver halide superparticles in an aqueous ammonia solution to dissolve the silver halide and produce the platinum superparticles.

17. The method of claim 16 , wherein a surface of the platinum superparticles is free of organic ligands.

18. The method of claim 16 , wherein the platinum superparticles have a negative zeta potential of lower than −20 eV.

19. The method of claim 16 , wherein the platinum superparticles have a diameter of greater than 20 nm.

20. The method of claim 16 , wherein the soluble platinum halide salt is Na 2 PtCl 4 .

21. The method of claim 16 , wherein the silver particles include at least one of a silver nanospheres, irregular silver particle aggregates, silver nanowires, gold core silver shell nanoparticles, silver nanosheets and silver microspheres.

22. The method of claim 16 , wherein at least a portion of a surface of the silver particles is coated with a surfactant.

23. A catalyst, comprising:

noble metal superparticles comprising a plurality of noble metal nanoparticles arranged in a three-dimensional structure, a surface of the noble metal superparticles being free of organic ligands, the noble metal superparticles having a zeta potential sufficient to prevent the noble metal superparticles from aggregating.

24. The catalyst of claim 23 , wherein the noble metal is selected from a group consisting of platinum, palladium, rhodium and iridium.

25. The catalyst of claim 24 , wherein the noble metal is platinum and the superparticles include platinum superparticles, the platinum superparticles including a plurality of platinum nanoparticles arranged in three-dimensional structure having a hemispherical dome shape with a flat bottom, a hollow interior and a plurality of pores defined between the platinum nanoparticles.

26. The catalyst of claim 25 , wherein the platinum superparticles have a negative zeta potential of lower than −20 eV.

27. The catalyst of claim 25 , wherein the platinum superparticles have a catalytic conversion efficiency of greater than 80%.

28. The catalyst of claim 24 , wherein the noble metal includes iridium and the noble metal superparticles include iridium nanoparticles interspersed with silver halide nanoparticles.