Electrochemical methods of making nanostructures

Abstract

Electrochemical methods for making nanostructures, for example, titanium oxide (TiO 2 ) nanostructures are described. The morphology of the nanostructures can be manipulated by controlling reaction parameters, for example, solution composition, applied voltage, and time. The methods can be used at ambient conditions, for example, room temperature and atmospheric pressure and use moderate electric potentials. The methods are scalable with a high degree of controllability and reproducibility.

1 . A method of making nanostructures, the method comprising:
 providing an electrolytic cell, which comprises an anode and a cathode disposed in an electrolyte comprising a hydroxide, wherein the anode or the cathode comprise a surface exposed to the electrolyte; and   applying an electrical potential to the electrolytic cell for a period of time sufficient to obtain nanostructures on the surface of the anode or the cathode exposed to the electrolyte.   
     
     
         2 . The method according to  claim 1 , wherein the surface of the anode or the cathode exposed to the electrolyte comprises a metal oxide, a mixed metal oxide, a metal, a mixed metal, a metal alloy, a metal alloy oxide, or combinations thereof. 
     
     
         3 . The method according to  claim 1 , wherein the nanostructures comprise a metal oxide, a mixed metal oxide, a metal, a mixed metal, a metal alloy, a metal alloy oxide, a metal hydroxide, or combinations thereof. 
     
     
         4 . The method according to  claim 3 , wherein the nanostructures further comprise a borate, a phosphate, a carbonate, a boride, a phosphide, a carbide, an intercalated alkali metal, an intercalated alkali earth metal, an intercalated hydrogen, a sulfide, a nitride, or combinations thereof. 
     
     
         5 . The method according to  claim 1 , wherein the anode and the cathode each comprise a surface exposed to the electrolyte. 
     
     
         6 . The method according to  claim 1 , wherein the hydroxide is selected from sodium hydroxide, potassium hydroxide, and combinations thereof. 
     
     
         7 . The method according to  claim 6 , wherein the electrolyte further comprises one or more additives. 
     
     
         8 . The method according to  claim 7 , wherein the additives are selected from boric acid, phosphoric acid, carbonic acid, sodium sulfate, potassium sulfate, sodium sulfite, potassium sulfite, sodium sulfide, potassium sulfide, sodium phosphate, potassium phosphate, sodium nitrate, potassium nitrate, sodium nitrite, potassium nitrite, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, a sodium halide, a potassium halide, a surfactant, and combinations thereof. 
     
     
         9 . The method according to  claim 8 , wherein the surfactant is ionic, nonionic, biological, or combinations thereof. 
     
     
         10 . The method according to  claim 6 , wherein the electrolyte is at a concentration of from 1 molar to 10 molar. 
     
     
         11 . The method according to  claim 1 , wherein the anode and cathode independently comprise a material selected from a uniform metal, a metal layer, a metal foil, a metal alloy, multiple metal layers, a mixed metal layer, multiple mixed metal layers and combinations thereof. 
     
     
         12 . The method according to  claim 11 , wherein the material is disposed on a conductive support, a non-conductive support, or combinations thereof. 
     
     
         13 . The method according to  claim 12 , wherein the conductive support comprises a material selected from a metal, a metal alloy, nickel, stainless steel, indium tin oxide (ITO), copper, and combinations thereof. 
     
     
         14 . The method according to  claim 12 , wherein the non-conductive support comprises a material selected from a polymer, plastic, glass, and combinations thereof. 
     
     
         15 . The method according to  claim 1 , wherein the potential is greater than 0.0 volts. 
     
     
         16 . The method according to  claim 1 , wherein the potential is 5.0 volts or less. 
     
     
         17 . The method according to  claim 1 , wherein the potential is applied continuously for 1 minute or more. 
     
     
         18 . The method according to  claim 1 , wherein the potential is applied for 24 hours or less. 
     
     
         19 . The method according to  claim 1 , further comprising cleaning the anode and cathode prior to contacting the electrolyte. 
     
     
         20 . The method according to  claim 1 , further comprising cleaning the anode and the cathode after obtaining the nanostructures. 
     
     
         21 . The method according to  claim 20 , wherein cleaning comprises acid washing. 
     
     
         22 . The method according to  claim 21 , wherein the acid is selected from hydrochloric, sulfuric, nitric, and combinations thereof. 
     
     
         23 . The method according to  claim 1 , which comprises making the nanostructures in a batch process. 
     
     
         24 . The method according to  claim 1 , which comprises making the nanostructures in a continuous process. 
     
     
         25 . The method according to  claim 1 , further comprising heating the electrolyte to a temperature of from 20 degrees Celsius to 80 degrees Celsius. 
     
     
         26 . A method of making titania nanostructures, the method comprising:
 providing an electrolytic cell, which comprises an anode and cathode disposed in an electrolyte, wherein the anode or the cathode comprise a titanium surface exposed to the electrolyte; and   applying an electrical potential to the electrolytic cell for a period of time sufficient to obtain titania nanostructures on the titanium surface of the anode or the cathode exposed to the electrolyte.