Method for preparing metal nanocube with controlled corner sharpness index

A method for preparing a plurality of metal nanocubes, the method comprising:

• (a) selecting an edge length, a surface area (in nm2), and a corner sharpness of the metal nanocubes to be prepared, wherein the corner sharpness is defined by a corner radius (CR) value, a corner sharpness index (CSI) value, or both,
• wherein the edge length (EL) is the shortest distance from one point of a flat surface of a metal nanocube to a point on another parallel surface,
• wherein the corner radius (CR) value is the size (in nm) of a radius of a circle that perfectly matches a curvature of a corner of the metal nanocube,
• wherein the corner sharpness index (CSI) value is defined by Equation 1, below—
• CSI
• ≡
• EL
• -
• 2
• ⁢
• ⁢
• CR
• EL
• Equation
• ⁢
• ⁢
• 1
• wherein the edge length selected is in the range of from 15 to 300 nm, and
• wherein the metal is gold (Au);
• (b) mixing a first surfactant, a surface-protecting agent, and gold metal nanoparticles together to provide a mixed aqueous solution,
• wherein the surface-protecting agent is NaBr and the amount of NaBr used to form the mixed aqueous solution is determined based on the surface area of the metal nanocubes to be prepared selected in step (a) and the corner radius (CR) value or the corner sharpness index (CSI) value of the metal nanocubes to be prepared selected in step (a),
• wherein, when the CR value selected in step (a) is less than 5 nm or the CSI value selected in step (a) is 0.70 or higher, the mixing of step (b) comprises adding an amount of NaBr so that the ratio of bromine atoms in the mixed aqueous solution to the surface area of the metal nanocubes to be prepared selected in step (a) is in the range of from 200 to 700,
• wherein, when the CR value selected in step (a) is 5 nm or higher or the CSI value selected in step (a) is less than 0.70, the mixing of step (b) comprises adding an amount of NaBr so that the ratio of bromine atoms in the mixed aqueous solution to the surface area of the metal nanocubes to be prepared selected in step (a) is less than 200 or is in the range of greater than 700 to 10,000,
• wherein the first surfactant is added to the mixed aqueous solution in an amount in the range of from 30 mM to 70 mM, based on the total volume of the mixed aqueous solution, and
• wherein the gold metal nanoparticles added to the mixed aqueous solution have an average diameter of from 3 nm to 30 nm;
• wherein the gold metal nanoparticles added to the mixed aqueous solution have an average diameter of 3 nm to 30 nm;
• (c) adding a metal ion precursor solution and a reducing agent to the mixed aqueous solution formed in step (b) to provide a reaction solution,
• wherein the reducing agent is ascorbic acid and wherein the reducing agent is added to the reaction solution in an amount in the range of from 0.1 mM to 0.5 mM, based on the total volume of reaction solution,
• wherein the precursor solution comprises gold metal ions,
• wherein the surface-protecting agent binds specifically to a (100) facet of a metal nanocube so as to control its crystal growth from a corresponding surface;
• (d) centrifuging the reaction solution formed in step (c) to provide a solid precipitate and redispersing at least a portion of the solid precipitate in another solvent to form a second solution;
• and
• (e) adding a second surfactant to the second solution to provide a final solution and centrifuging the final solution to obtain an aggregate of gold metal nanocubes.