Graphene oxide (GO) is a very promising material because it is easy to process, water soluble, and chemically versatile due to the presence of oxygenated groups on its surface. Oxygenated groups like ?COOH, ?C=O, and ?OH are important for the GO reactivity and for further functionalization. During preparation of GO sheets by exfoliating graphite with a mixture of potassium permanganate and concentrated sulfuric acid (modified Hummers method [1]), complex mixtures of highly oxidized polyaromatic carboxylated fragments ? oxidative debris (OD) ? are produced. While these debris, that are strongly bound to GO surface [2], act as surfactant and help stabilizing aqueous GO suspensions, they also change GO surface properties such as the capacity of adsorbing molecules by noncovalent functionalization. This capacity is specially important for remediating environmental pollutants. Here we study the role of OD on the GO capacity to adsorb organic pollutants. Single-layered GO was synthesized by a modified Hummers method (as-produced GO ? aGO) and chemically treated to yield to debris-free GO (dfGO). We used the Salmonella typhimurium mutagenicity assay (Ames test [3]) to indirectly probe the GO adsorption capacity by looking at bacteria growth caused by non-adsorbed testing molecules (pollutants) on GO surfaces. We selected two important organic pollutants produced from incomplete combustion of fossil fuels (1-nitropyrene (1NP) and 3-nitrobenzanthrone (3NBA)) as the testing molecules. We observed that GO samples without oxidative debris were found to be 75% more effective to adsorb 1NP than samples with debris which indicates that OD reduce the GO adsorption capacity [4]. Molecular dynamics simulations indicated that the resulting weak interaction between 1NP and 3NBA molecules and aGO surfaces is not sufficient to trap these molecules. Our results suggest that OD with size comparable to the the size of 1NP and 3NBA molecules (~1 nm) are responsible for preventing adsorption sites on GO surfaces from being reached by potentially adsorbate molecules. We acknowledge the financial support from INOMAT, CNPq, CAPES and FAPESP.

References:

[1] W. S. Hummers and R. E. Offeman, J. Am. Chem. Soc. 80 (1958) 1339.

[2] J. P. Rourke, P. A. Pandey, J. J. Moore, M. Bates, I. A. Kinloch, R. J. Young, N. R. Wilson, Angew. Chem. 123 (2011) 3231-3235.

[3] K. Mortelmans and E. Zeiger, Mutat. Res. 455 (2000) 29-60.

[4] V. R. Coluci, D. S. T. Martinez, J. G. Honrio, A. F. de Faria, D. A. Morales, M. S. Skaf, O. L. Alves, G. A. Umbuzeiro, J. Phys. Chem. C 118 (2014) 2187?2193.

Vitor Coluci

School of Technology, University of Campinas?UNICAMP

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