Wednesday, March 12, 2008

Graphene oxide papers modified by divalent ions- enhancing mechanical properties via chemical cross-linking

Graphene oxide papers modified by divalent ions- enhancing mechanical properties via chemical cross-linking

Sungjin Park, Kyoung-Seok Lee, Gulay Bozoklu, Weiwei Cai, SonBinh T. Nguyen, and Rodney S. Ruoff

ACS Nano, 2008 (still ASAP)

DOI: 10.1021/nn700349a

ACS Nano is a journal that started accepting papers in April of last year, and as far as I can tell, it's complimentary to Nano Letters, carrying mostly papers and reviews on nanostuff. The paper I'm reviewing in this post can be entirely summarized in the graphic from the abstract, which I'd love to post but Blogger won't let me include the picture. Click through for the picture.

So let me first describe how you make graphene oxide paper:
1. Get a graphene oxide dispersion from oxidized graphite using the techniques detailed in the previous posts
2. Filter it

Yeah, that's pretty much it. In this paper, Ruoff (who's kind of a big deal in this graphene oxide stuff) runs a solution of divalent cations (Mg and Ca) through the filtered graphene oxide paper. The paper gets stronger after this treatment, but if you rinse the paper after you run the ions into it, you get a material with mechanical strength somewhere between the treated paper and the untreated paper. Big deal, I guess.

The interesting part of this paper is that they theorize that the divalent ions are coordinated with the carboxylic acids on seperate graphene sheets, giving a metal-mediated cross linking which increases the mechanical strength. They also theorize that some of the ions get stuck between the sheets and weakly coordinate to the epoxides and phenols on the oxidized graphene. These intercalated ions are removed after a rinse, giving a material that's a bit weaker than before but still has the metal-carboxylic acid interaction to hold the sheets together. Since this is insoluble muck, they use XRD, energy dispersive X-ray (EDX) fluorescent mapping, and XPS to characterize the samples. Using IR, they see a decrease in the C=O peak and in increase in the C-O peak in the treated material, further suggesting that the divalent metals are coordinating to the carbonyls.

In summary, this paper details a way to make stronger graphene oxide paper. You can't use the stuff for electrical applications, which is what I'm interested in, so this paper made me yawn. However, if you think graphene-based materials are going to end up in airplane wings and carbon fiber car hoods, check it out.

Park, S., Lee, K., Bozoklu, G., Cai, W., Nguyen, S.T., Ruoff, R.S. (2008). Graphene Oxide Papers Modified by Divalent Ions—Enhancing Mechanical Properties via Chemical Cross-Linking. ACS Nano DOI: 10.1021/nn700349a