Hummers' method
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Hummer's MethodCite error: There are <ref> tags on this page without content in them (see the help page).
The Hummers' method is a chemical process that can be used to generate graphite oxide through the addition of potassium permanganate to a solution of graphite, sodium nitrate, and sulfuric acid.
Method
The Hummers' Method[1] was developed in 1958 as a safer, faster and more efficient method of producing graphite oxide. Before the method was developed, the production of graphite oxide was slow and hazardous to make, involving the use of concentrated sulfuric and nitric acid. The Staudenmeier-Hoffman-Hamdi method[2] involved the addition of potassium chlorate, introducting more hazards and produced one gram of graphite oxide to ten grams of potassium chlorate.
William S. Hummers and Richard E. Offeman introduced their method as an alternative to the above methods after noting the hazards they poised to workers at the The National Lead Company. Their approach was similar in that it involved adding graphite to a solution of concentrated acid. However, they simplified it to just graphite, concentrated sulfuric acid, sodium nitrate, and potassium nitrate. They also did not have to use temperatures above 98°C and avoided most of the explosive risk of the Staudenmeier-Hoffman-Hamdi Method.
The procedure starts with 100g graphite and 50g of sodium nitrate in sulfuric acid at 66°C which is then cooled to 0°C. 300g of potassium permanganate is then added to the solution and stirred. Water is then added in increments until the solution is approximately 32 liters.
The final solution contains about 0.5% of solids to then be cleaned of impurities and dehydrated with phosphorus pentoxide.
Chemical Equations and Efficiency
The basic chemical reaction involved in the Hummers' method is the oxidation of graphite, introducing molecules of oxygen to the pure carbon graphene. The reaction occurs between the graphene and the concentrated sulfuric acid with the potassium permanganate and sodium nitrate acting as catalysts. The process is capable of yielding approximately 188g of graphite oxide to 100g of graphite used. The ratio of carbon to oxygen produced is within the range of 1 to 2.1-2.9 that is characteristic of graphite oxide. The contaminants are determined to be mostly ash and water. Unfortunately toxic gases such as N2O4 and NO2 are evolved in the process. The final product is typically 47.06% carbon, 27.97% oxygen, 22.99% water, and 1.98% ash with a carbon to oxygen ratio of 2.25. All of these results are comparable to the methods that preceded them.
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Graphite Oxide
Graphite Oxide is a compound of carbon, oxygen, and hydrogen where the there is a ratio between 2.1 to 2.9 of carbon to oxygen. Graphite Oxide is typically a yellowish solid. It is also known as graphene oxide when used to form monomolecular sheets.
Modern Variations
Graphite oxide has recently captured the attention of the scientific community after the discovery of graphene in 2004. Many teams are looking into ways of using graphite oxide as a shortcut to mass production of graphene. So far, the materials produced by these methods have shown to have more defects than those produced directly from graphite. The Hummers' method remains a key point of interest because it is an easy method of producing large quanitities of graphite oxide.
Besides graphene, the Hummer's method has recently become a point of interest in photocatalysts. Recent approaches in the field have involved the use of graphite oxide to bolster the speed of the reactions. The most common method for producing the graphite oxide in these experiments has been the Hummers' Method.
Other groups have been focused on making improvements to the Hummers' method to make it more efficient and environmentally friendly. On such process is eliminating the use of NaNO3 from the process.[3] The process was found by discovering stubborn ions in the solution used and finding an alternative in phosphoric acid. This is advantageous as it stops the production of gasses such as NO2 and N2O4.
See Also
References
- ^ Hummers, William S.; Offeman, Richard E. (March 20, 1958). "Preparation of Graphitic Oxide". Journal of the American Chemical Society. 80 (6): 1339. doi:10.1021/ja01539a017.
{{cite journal}}:|access-date=requires|url=(help) - ^ Ojha, Kasinath; Anjaneyulu, Oruganti; Ganguli, Ashok (10 August 2014). "Graphene-based hybrid materials: synthetic approaches and properties" (PDF). Current Science. 107 (3): 397–418. Retrieved 7 November 2014.
- ^ Chen, Ji; Yao, Bowen; Li, Chun; Shi, Gaoquan (November 2013). "An improved Hummers method for eco-friendly synthesis of graphene oxide". Carbon. 64: 225–229. doi:10.1016/j.carbon.2013.07.055.