System and method for preparing graphene oxide and reduced graphene oxide

Abstract

There is provided an industrially scalable system and method for preparing graphene oxide and thereafter reduced graphene oxide, with high yields (generally better than 98 percent), in which the yield and quality are maximized. In certain embodiments of the present method and process, the initial particle size of the graphite charge and the temperature profile are of greater importance to a successful outcome than the reactants themselves. It should be noted that unlike the previous Hummers methods and derivatives, secondary oxidizers and exfoliation agents such as nitric acid, sodium nitrate and similar intercalation agents are not necessary to achieve the desired result.

What is claimed is: 
     
         1 . A method comprising:
 chilling a reaction vessel to a predetermined chill temperature;   intermixing a quantity of two or more acid reactants to fora an intermixed acid mixture;   chilling the intermixed acid mixture to the predetermined chill temperature;   intermixing a quantity of KMnO 4  and a quantity of graphite;   chilling the intermixed KMnO 4  and graphite to the predetermined chill temperature;   placing the chilled intermixed acid mixture into the chilled reaction vessel and initiating a low speed agitation of the acid mixture;   adding the chilled intermixed KMnO 4  and graphite to the chilled reaction vessel to form a graphite suspension;   continuing agitation of the reaction vessel for a predetermined period of cool agitation while maintaining the reaction vessel within a predetermined cool temperature profile;   adding a first volume of warm distilled water during a first period of warm agitation while the graphite suspension is agitated;   adding a second volume of distilled water during a second period of arm agitation while the graphite suspension is agitated;   while agitating, cooling the graphite suspension to a predetermined pre-peroxide temperature;   adding a predetermined amount of hydrogen peroxide to the reaction vessel;   allowing contents of the reaction vessel to cool and settle over a settling period; and   separating colloidal graphene oxide from reaction products within the vessel contents.   
     
     
         2 . The method of  claim 1 , further comprising reducing the graphene oxide by:
 adding ascorbic acid to the colloidal graphene oxide while agitating and maintaining the colloidal graphene oxide/ascorbic acid mixture at a predetermined reduction temperature; and   allowing the colloidal graphene oxide/ascorbic acid mixture to cool to an ambient temperature for a determined reduction period.   
     
     
         3 . The method of  claim 1 , wherein the predetermined chill temperature is approximately 0 degrees C. 
     
     
         4 . The method of  claim 1 , wherein the two or more acid reactants include a quantity of H 2 SO 4  and a quantity of H 3 PO 4 . 
     
     
         5 . The method of  claim 1 , wherein the intermixed acid mixture comprises sulfuric acid and phosphoric acid in a ratio of approximately 75/25 by volume, respectively. 
     
     
         6 . The method of  claim 1 , wherein a ratio of the quantity of KMnO 4  and the quantity of graphite is 3 to 1 by weight, respectively. 
     
     
         7 . The method of  claim 1 , wherein graphite suspension placed into the chilled reaction vessel is in gaseous communication with atmospheric oxygen. 
     
     
         8 . The method of  claim 1 , wherein the predetermined period of cool agitation comprises a period of four to eight hours. 
     
     
         9 . The method of  claim 1 , wherein the predetermined cool temperature profile comprises one or more of:
 maintaining a temperature of the graphite suspension below 50 degrees C. over the first 90 minutes of the predetermined period of cool agitation;   providing a continuously rising temperature profile of the graphite suspension from about zero degrees C. to about 45 degrees C., over an initial 60 to 90 minutes of the predetermined period of cool agitation;   maintaining a temperature profile of the graphite suspension to prevent temperatures from plateauing for more than five minutes during the predetermined period of cool agitation;   maintaining temperature of the graphite suspension between 40 and 45 degrees C. with a PID thermal control loop; and   cooling the graphite suspension during a first 15 to 30 minutes of the predetermined period of cool agitation and thereafter allowing the temperature the graphite suspension to rise to between 40 to 45 degrees C. over about 90 minutes of the predetermined period of cool agitation and then remain at a temperature between 40 to 45 degrees C. a remainder of the predetermined period of cool agitation.   
     
     
         10 . The method of  claim 1 , wherein the first volume of warm distilled water is heated to 50 to 80 degrees C. 
     
     
         11 . The method of  claim 1 , wherein the first period of warm agitation comprises a period of time from 45 to 60 minutes. 
     
     
         12 . The method of  claim 1 , wherein the first volume of warm distilled water is approximately equal to a volume of the intermixed acid mixture. 
     
     
         13 . The method of  claim 1 , wherein the first volume of warm distilled water is added to the reaction vessel at a controlled rate between 2 ml/min and 5 ml/min so as to maintain the temperature of contents of the reaction vessel between 80 and 90 degrees C. 
     
     
         14 . The method of  claim 13 , wherein the reaction vessel further comprises a PID thermal control loop and a heating and/or cooling apparatus interface. 
     
     
         15 . The method of  claim 1 , wherein the second volume of warm distilled water is approximately equal to a volume of the intermixed acid mixture. 
     
     
         16 . The method of  claim 1 , wherein:
 the second volume of war distilled water is heated to one of approximately 90 degrees C.; or   the predetermined pre-peroxide temperature is approximately 50 degrees C.   
     
     
         17 . The method of  claim 1 , wherein:
 a concentration of the hydrogen peroxide is 35% by volume; or   a volume of the hydrogen peroxide is approximately equal to one half an initial volume of H 2 SO 4  used in the intermixed acid mixture.   
     
     
         18 . The method of  claim 1 , wherein the settling period is within the range of 12 to 14 hours. 
     
     
         19 . The method of  claim 2 , wherein the predetermined reduction temperature is within the range of 40 to 50 degrees C. 
     
     
         20 . The method of  claim 2 , wherein the predetermined reduction period ranges from one of:
 1 to 10 hours;   until the graphene oxide/ascorbic acid mixture obtains ambient temperature; or   24 hours.