Methods for purifying carbon materials

Abstract

Methods of purifying samples are provided that are capable of removing carbonaceous and noncarbonaceous impurities from a sample containing a carbon material having a selected structure. Purification methods are provided for removing residual metal catalyst particles enclosed in multilayer carbonaceous impurities in samples generate by catalytic synthesis methods. Purification methods are provided wherein carbonaceous impurities in a sample are at least partially exfoliated, thereby facilitating subsequent removal of carbonaceous and noncarbonaceous impurities from the sample. Methods of purifying carbon nanotube-containing samples are provided wherein an intercalant is added to the sample and subsequently reacted with an exfoliation initiator to achieve exfoliation of carbonaceous impurities.

1 . A method of purifying a sample containing a carbon material having a selected structure said method comprising the steps of:
 providing said sample containing said carbon material having a selected structure and impurities comprising carbonaceous impurities, wherein said carbonaceous impurities comprising one or more carbon layers having a structure different than that of said selected structure;   exfoliating at least a portion of the carbon layers of said carbonaceous impurities, thereby generating exfoliated carbonaceous material; and   removing said impurities, thereby purifying said sample containing a carbon material having a selected structure.   
     
     
         2 . The method of  claim 1  wherein said step of removing said impurities comprises oxidizing the exfoliated carbonaceous material. 
     
     
         3 . The method of  claim 1  wherein said step of removing said impurities comprises preferentially oxidizing said exfoliated carbonaceous material such that the carbon material having a selected structure is not substantially oxidized. 
     
     
         4 . The method of  claim 1  wherein said step of removing said impurities comprises oxidizing said exfoliated carbonaceous materials in air at a temperature selected from the range of about 250 degrees Celsius to about 450 degrees Celsius. 
     
     
         5 . The method of  claim 4  wherein said step of removing said impurities comprises oxidizing said exfoliated carbonaceous materials in the presence of air having a relative humidity selected from the range of about 50 percent to about 100 percent. 
     
     
         6 . The method of  claim 1  wherein said impurities comprise metal particles, wherein said metal particles are at least partially enclosed by a plurality of said carbon layers, wherein said step of exfoliating at least a portion of said multilayer carbonaceous impurities exfoliates at least a portion of said carbon layers enclosing said metal particles, thereby exposing the surface of said metal particles. 
     
     
         7 . The method of  claim 6  wherein said step of removing said impurities comprises oxidizing said metal particles, thereby generating oxidized metal particles, wherein the volume of said metal particles increases upon oxidation, thereby disrupting said carbon layers enclosing said metal particles further exposing said metal surface of said oxidized metal particles. 
     
     
         8 . The method of  claim 6  wherein said step of removing said impurities comprises dissolving said metal particles. 
     
     
         9 . The method of  claim 6  wherein said step of removing said impurities comprises dissolving said metal particles into an acidic solution. 
     
     
         10 . The method of  claim 9  wherein said step of dissolving said metal particles into an acidic solution comprises refluxing said sample in concentrated hydrochloric acid. 
     
     
         11 . The method of  claim 6  wherein said metal particles comprise one or more transition metals. 
     
     
         12 . The method of  claim 6  wherein said metal particles comprise one or more metals selected from the group consisting of:
 nickel;   yttrium;   iron;   molybdenum;   palladium   copper;   molybdenum; and   cobalt.   
     
     
         13 . The method of  claim 1  wherein said step of exfoliating at least a portion of the carbon layers of said carbonaceous impurities comprises adding an intercalant to said sample. 
     
     
         14 . The method of  claim 13  wherein said intercalant inserts into interstitial sites in between multiple carbon layers comprising said carbonaceous impurities, interstitial sites between carbon layers comprising said carbonaceous impurities and said carbon material having a selected structure or both, thereby generating intercalated carbon layers. 
     
     
         15 . The method of  claim 14  wherein said carbon layers comprise a material selected from the group consisting of:
 graphene layers;   graphite layers; and   amorphous carbon layers.   
     
     
         16 . The method of  claim 14  wherein said step of exfoliating at least a portion of the carbon layers of said carbonaceous impurities further comprises increasing the temperature of said sample. 
     
     
         17 . The method of  claim 13  wherein said intercalant is an electron donor intercalant. 
     
     
         18 . The method of  claim 17  wherein said electron donor intercalant is an alkali metal. 
     
     
         19 . The method of  claim 13  wherein said intercalant is an electron acceptor intercalant. 
     
     
         20 . The method of  claim 19  wherein said electron acceptor intercalant is selected from the group consisting of:
 a halogen;   a metal chloride;   nitric acid;   perchloric acid;   sulfuric acid; and   formic acid.