Environmentally benign chemical oxidation method of producing graphite intercalation compound, exfoliated graphite, and nano-scaled graphene platelets
A method of producing exfoliated graphite, flexible graphite, or nano-scaled graphene platelets. The method comprises: (a) forming a graphite intercalation compound by a chemical oxidation reaction which uses a combination of a carboxylic acid and hydrogen peroxide as an intercalate source; and (b) rapidly heating the graphite intercalation compound to a desired temperature for a length of time sufficient for producing exfoliated graphite. The method may further comprise a step of subjecting the exfoliated graphite to a mechanical shearing treatment to produce nano-scaled graphene platelets. Alternatively, the method may further comprise a step of compressing the exfoliated graphite to form a flexible graphite product. The exfoliation step in the instant invention does not involve the evolution of undesirable species, such as NO x and SO x , which are common by-products of exfoliating conventional sulfuric or nitric acid-intercalated graphite compounds. The nano-scaled platelets are candidate reinforcement fillers for polymer nanocomposites. Nano-scaled graphene platelets are much lower-cost alternatives to carbon nano-tubes or carbon nano-fibers.
1 . A method of producing an exfoliated graphite product from a layered graphite material wherein said product comprises exfoliated graphite, flexible graphite, or nano-scaled graphene platelets; said method comprising:
a) forming a graphite intercalation compound by a chemical oxidation reaction which uses a combination of a carboxylic acid and hydrogen peroxide as an intercalate source; and
b) rapidly heating said graphite intercalation compound to a desired temperature for a length of time sufficient for producing exfoliated graphite.
2 . The method of claim 1 , further comprising a step of subjecting said exfoliated graphite to a mechanical shearing treatment to produce nano-scaled graphene platelets.
3 . The method of claim 1 , further comprising a step of compressing said exfoliated graphite to form a flexible graphite product.
4 . The method of claim 1 wherein said layered graphite material is selected from natural graphite, synthetic graphite, highly oriented pyrolytic graphite, graphite fiber, graphitic nano-fiber, graphite oxide, graphite fluoride, chemically modified graphite, exfoliated graphite, or a combination thereof.
5 . The method of claim 1 wherein said carboxylic acid is selected from the group consisting of aromatic carboxylic acid, aliphatic or cycloaliphatic carboxylic acid, straight chain or branched chain carboxylic acid, saturated and unsaturated monocarboxylic acids, dicarboxylic acids and polycarboxylic acids that have 1-10 carbon atoms, alkyl esters thereof, and combinations thereof.
6 . The method of claim 1 wherein said carboxylic acid is selected from the group consisting of saturated aliphatic carboxylic acids of the formula H(CH 2 ) n COOH, wherein n is a number of from 0 to 5, including formic, acetic, propionic, butyric, pentanoic, and hexanoic acids, anhydrides thereof, reactive carboxylic acid derivatives thereof, and combinations thereof.
7 . The method of claim 2 wherein said mechanical shearing treatment comprises using air milling, air jet milling, ball milling, rotating-blade mechanical shearing, ultrasonication, or a combination thereof.
8 . The method of claim 1 wherein the combination comprises a mixture of a carboxylic acid and hydrogen peroxide at a weight ratio of 100:1 to 100:50.
9 . The method of claim 1 wherein step (b) comprises heating said intercalated graphite to a temperature in the range of 300-800° C. for a period of 15 seconds to 2 minutes.
10 . The method of claim 1 , further comprising additional steps of intercalating said exfoliated graphite to obtain a further intercalated graphite compound and exfoliating said further intercalated graphite compound to produce thinner graphite flakes or nano-scaled graphene platelets.
11 . The method of claim 2 , further comprising additional steps of intercalating said nano-scaled graphene platelets to obtain a further intercalated compound and exfoliating said further intercalated compound to produce thinner nano-scaled graphene platelets.
12 . A method of producing ultra-thin, nano-scaled graphene platelets with an average thickness smaller than 2 nm or 5 graphene sheets from a layered graphite material, said method comprising:
a) forming a graphite intercalation compound by a chemical oxidation reaction which uses a combination of a carboxylic acid and hydrogen peroxide as an intercalate source;
b) rapidly heating said graphite intercalation compound to a desired temperature to produce exfoliated graphite;
c) re-intercalating said exfoliated graphite by repeating step (a), using a combination of a carboxylic acid and hydrogen peroxide as an intercalate source, to produce a further-intercalated graphite compound; and
d) rapidly heating said further intercalated graphite compound to a desired temperature for further exfoliating said further intercalated compound and optionally subjecting a further exfoliated graphite compound to a mechanical shearing treatment to produce said ultra-thin, nano-scaled graphene platelets.
13 . The method of claim 12 wherein said layered graphite material is selected from natural graphite, synthetic graphite, highly oriented pyrolytic graphite, graphite fiber, graphitic nano-fiber, graphite oxide, graphite fluoride, chemically modified graphite, or a combination thereof.
14 . The method of claim 12 wherein said carboxylic acid is selected from the group consisting of aromatic carboxylic acid, aliphatic or cycloaliphatic carboxylic acid, straight chain or branched chain carboxylic acid, saturated and unsaturated monocarboxylic acids, dicarboxylic acids, and polycarboxylic acids that have 1-10 carbon atoms, alkyl esters thereof, and combinations thereof.
15 . The method of claim 12 wherein said carboxylic acid is selected from the group consisting of saturated aliphatic carboxylic acids of the formula H(CH 2 ) n COOH, wherein n is a number of from 0 to 5, including formic, acetic, propionic, butyric, pentanoic, and hexanoic acids, anhydrides thereof, reactive carboxylic acid derivatives thereof, and combinations thereof.
16 . The method of claim 12 wherein said mechanical shearing treatment comprises using air milling, air jet milling, ball milling, rotating-blade mechanical shearing, ultrasonication, or a combination thereof.
17 . The method of claim 12 wherein the combination in step (a) or step (c) comprises a mixture of a carboxylic acid and hydrogen peroxide at a weight ratio of 100:1 to 100:50.
18 . The method of claim 12 wherein said step (b) or (d) comprises heating said intercalated graphite to a temperature in the range of 300-800° C. for a period of 15 seconds to 2 minutes.
19 . The method of claim 12 wherein said ultra-thin, nano-scaled graphene platelets comprise single graphene-sheet and/or double graphene-sheet platelets.