Highly efficient process for manufacture of exfoliated graphene
View Patent ↗A process for preparing oxidized graphite that provides exfoliated graphene, preferably with high surface area. The process uses considerably less chlorate than previously known systems.
1. A process for manufacturing oxidized graphite, the process comprising:
(a) mixing concentrated sulfuric acid and concentrated nitric acid in a reaction vessel for a time sufficient to generate nitronium ions wherein the ratio of the sulfuric acid to the nitric acid is 1.6:1 to 3:1 (v/v), and wherein neither acid is a fuming acid;
(b) combining the acids from step (a) and graphite to form a first mixture, wherein the acids from (a) are combined with the graphite so that a slight excess of nitronium ion is present;
(c) stirring the first mixture for a time sufficient to form a graphite-nitronium intermediate;
(d) adding aqueous solution comprising NaClO 3 at a concentration of at least 2.5 molar in a ratio of 1:4 to 1:7.17 (graphite:chlorate) to the first mixture at 0-35° C. and thereby forming a second mixture, wherein the chlorate is added so that when it reacts with the graphite-nitronium complex the rate of formation of ClO 2 is minimized;
(f) stirring the second mixture; and
(g) isolating the oxidized graphite from the reaction mixture.
2. A process according to claim 1 , wherein the volume ratio of concentrated sulfuric acid to concentrated nitric acid in the reaction mixture is between 255:100 and 255:150.
3. A process according to claim 1 , wherein the graphite consists essentially of particles having sizes characterized as being −10 mesh or a higher mesh number.
4. A process for manufacturing exfoliated graphene, the process comprising:
providing oxidized graphite prepared according to the process of claim 1 ; and
subjecting the oxidized graphite to an exfoliation step to produce exfoliated graphene.
5. A process according to claim 4 , wherein the exfoliation step comprises heating the oxidized graphite at a temperature of from 250° C. 2000° C. under substantially inert atmosphere.
6. A process according to claim 5 , wherein the exfoliation step comprises heating the oxidized graphite at a temperature of from 500° C. to 1500° C.
7. A process according to claim 1 , wherein the exfoliated graphene is a highly exfoliated graphene having a Brunauer-Emmett-Teller surface area of from 400 meters-squared per gram to 1500 meters-squared per gram.
8. A process for manufacturing exfoliated graphene, the process comprising:
providing oxidized graphite prepared according to the process of claim 1 ; and
subjecting the oxidized graphite to an exfoliation step to produce exfoliated graphene.
9. A process according to claim 1 , wherein the presence of nitronium ion or a nitronium-graphite complex is monitored in the reaction mixture during the reaction by Raman spectroscopy.
10. A process according to claim 1 , wherein the first mixture is stirred for 2 to 4 hours.
11. A process according to claim 1 , wherein the second mixture is stirred for between 4 hours and 50 hours.