Synthesis of metallic nanoshells on porphyrin-stabilized emulsions
View Patent ↗Metal nanostructures formed by photocatalytic interfacial synthesis using a porphyrin-stabilized emulsion template and the method for making the nanostructures. Catalyst-seeded emulsion droplets are employed as templates for hollow-nanoshell growth. The hollow metal nanospheres may be formed with or without inclusions of other materials.
1. A method for making metal nanoshells, the method comprising:
forming an emulsion comprising lipoporphyrin-stabilized nanodroplets, wherein the emulsion comprises a photocatalytic lipoporphyrin, water, and an organic liquid wherein a concentration of the organic liquid is less than or equal to approximately an order of magnitude greater than a solubility limit of the organic liquid in water and wherein a solubility of the photocatalytic lipoporphyrin in water and a solubility of the photocatalytic lipoporphyrin in the organic liquid are sufficient to position the photocatalytic lipoporphyrin at a water/organic liquid interface of the lipoporphyrin-stabilized nanodroplets;
adding a seed metal ion and an electron donor species to the emulsion;
illuminating the emulsion with light of a wavelength that causes electronic excitation of the photocatalytic lipoporphyrin to form an excited photocatalytic lipoporphyrin;
reacting the excited photocatalytic lipoporphyrin with the electron donor species to form a reduced photocatalytic lipoporphyrin
reducing the seed metal ion by reaction with the reduced photocatalytic lipoporphyrin to form a seed metal nanoparticle at the water/organic liquid interface;
adding a shell metal ion to the emulsion; and
reducing the shell metal ion catalytically using the seed metal nanoparticle to form a metallic nanoshell.
2. The method of claim 1 , wherein the photocatalytic lipoporphyrin is a metalloporphyrin comprising a hydrophilic head and a hydrophobic tail.
3. The method of claim 2 , wherein the hydrophilic head comprises a hydrophilic substituent segment selected from the group consisting of a hydroxyl group, an amide group, a carboxyl group, a pyridyl group, a sulfonate group, a phosphate group, and an amine group, and wherein the hydrophobic tail comprise a hydrocarbon moiety containing between 5 and 20 carbon atoms.
4. The method of claim 1 , wherein the photocatalytic lipoporphyrin is a metalloporphyrin selected from the group consisting of a tin(IV) lipoporphyrin and tin(IV) meso-tetra(N-octadecyl-4-pyridyl)porphyrin chloride.
5. The method of claim 1 , wherein the electron donor species is selected from a group consisting of ascorbic acid, triethanolamine, ethylenediamine tetraacetic acid and the salts thereof, methanol, and ethanol.
6. The method of claim 1 , wherein the seed metal ion is Pt.
7. The method of claim 1 , wherein the shell metal is selected from the group consisting of Pt, Pd, Au, and Ag.
8. The method of claim 1 , wherein the organic liquid has a solubility in water suitable for forming an emulsion that is stable for a time required to form the metallic nanoshell.
9. The method of claim 1 , wherein the organic liquid is selected from the group consisting of benzene, chloroform, dichloromethane.
10. The method of claim 1 , the step of forming the emulsion further comprising incorporating an inclusion particle in a droplet of the emulsion.
11. The method of claim 10 , wherein the inclusion particle is selected from the group consisting essentially of Fe 3 O 4 , Fe 2 O 3 , TiO 2 , Au, Ag, FePt, Ni, Co, semiconductor quantum dots, metal particles, metal alloy particles, and solubilized versions thereof made soluble by surface modification with a material that facilitates solubilization.
12. The method of claim 1 , further comprising
collecting the metallic nanoshell;
suspending the metallic nanoshell in an aqueous solution comprising a second shell metal ion and a second electron donor species;
reducing the second shell metal ion on the metallic nanoshell to form a layered metallic nanoshell.