Method of making mesoporous carbon from natural wood and mesoporous carbon hollow tubes made thereby
In various embodiments, the present invention provides a relatively low cost and substantially chemical free method of making high surface area mesoporous carbon (as well as novel mesoporous carbon hollow tube (MCHT) structures made thereby) utilizing the cellulose framework found in natural wood and/or other plant fibers to make porous carbon structures. In some embodiments, the present invention will provide porous carbon structures having higher surface area than porous carbon structures made using prior art template methods, higher adsorption capacity than commercial activated carbon, and, in some embodiments, excellent electrochemical capacitance and storage capabilities. These new carbon materials may be adapted for a wide variety of uses including such things as removal of both inorganic and organic toxic pollutants from water, energy storage/conversion, supercapacitor electrodes for electrochemical energy storage, adsorption, and catalysis.
1. A method for making a porous carbon material comprising the steps of:
A. carbonizing a naturally occurring cellulose framework containing lignin to form a carbonized structure containing carbonized cellulose and carbonized lignin, said step of carbonizing including heating the cellulose framework and lignin in the absence of oxygen at a temperature and for a time sufficient to convert said cellulose and at least a portion of said lignin to carbon;
B. cooling said carbonized structure; and,
C. after said step of cooling, oxidizing said carbonized lignin by heating said carbonized structure in the presence of oxygen to a temperature of from about 200° C. to about 500° C. and for a time sufficient to volatilize, and thus remove, at least a portion of said carbonized lignin to provide a porous carbon structure.
2. The method of claim 1 wherein the naturally occurring cellulose framework containing lignin comprises a plant material selected from the group consisting of soft woods, hard woods, switchgrass, cotton, bamboo, walnut shell, peanut shell, rattan, luffa, sugar cane, and combinations thereof.
3. The method of claim 1 wherein said step of carbonizing comprises heating the cellulose framework to a temperature of from about 500° C. to about 1,500° C.
4. The method of claim 1 wherein said step of carbonizing comprises heating said cellulose framework to a temperature of from about 750° C. to about 850° C.
5. The method of claim 1 wherein the step of carbonizing comprises heating said cellulose framework to a temperature of from about 600° C. to about 1500° C. for a period of from about 1 hour to about 6 hours.
6. The method of claim 1 wherein said step of oxidizing includes heating said carbonized structure to an initial temperature of from about 25° C. to about 50° C. and then gradually increasing the temperature to a second temperature from about 200° C. to about 500° C. at a rate of from about 1° C./min to about 20° C./min.
7. The method of claim 1 wherein said step of oxidizing comprises increasing the surface area of the carbonized structure by continuing to heat the cellulose framework after substantially all of said carbonized lignin has been oxidized.
8. The method of claim 1 wherein the porous carbon structure comprises pores having a mean diameter of from 2 nm or more to 30 nm or less.
9. The method of claim 1 , wherein, after said step of oxidizing, the method further comprises the step of chemically etching said porous carbon structure thereby increasing its surface area.
10. The method of claim 9 wherein the step of etching comprises contacting said carbonized structure with an oxidizer.
11. The method of claim 9 wherein the step of etching comprises contacting said carbonized structure with potassium hydroxide.
12. The method of claim 1 , wherein, after said step of oxidizing, the method further comprises thermally annealing said carbonized structure.
13. The method of claim 12 wherein the step of thermally annealing comprises heating said carbonized structure in an inert atmosphere to a temperature of between 600° C. or more and 1500° C. or less for a period of between 1 hours and 6 hours.