(328g) Synthesis, Characterization, and Optimization of Carboxyl-Rich Oxidized Graphene Nanoplatelets Via a Simplified Hummer’s Method

Graphene oxide (GO) is widely synthesized from graphite using the modified Hummer’s method.¹ However, this method yields a high oxidation level and large hydroxyl-to-carboxyl ratio that may not be suitable for certain applications. Moreover, defects are introduced onto the graphene sheets during oxidation that deteriorate their superior mechanical properties. Over the years, variants of the Hummer’s method have been developed that have made it simpler and/or greener to synthesize GO. Simplified Hummer’s method,² where the KMnO₄ oxidizing agent is not present in the reaction, is one such technique. In this method, GO with 4-20 wt.% oxygen content and low platelet defects can be obtained. Herein, we used the simplified Hummer’s method to synthesize oxidized graphene nanoplatelets (ox-GNPs) with the aim of identifying the most suitable GNP average nanoparticle size/surface area and reaction conditions to yield maximum carboxyl functional group content in the final reaction product. For this purpose, we used an I-optimal (integrated variance) response surface design to investigate the effects of three factors, i.e., reaction time (3-18 hours), GNP grade (R-25, M-15, C-300, and C-750, provided by XG Sciences, with a range of nanoparticle sizes and surface areas), and H₂SO₄/HNO₃ ratio (0:1, 1:3, 2:3, and 1:0) on the chemistry and thermophysical properties of the resulting ox-GNPs. Our main target was to maximize the carboxyl group weight percentage in the reaction product since such groups act as reaction sites for the grafting of amino functional groups to the GNPs. To fully characterize the ox-GNPs, we are currently determining the functional groups using Fourier-transform infrared spectroscopy (FTIR), atomic and functional group weight percentages using X-ray photoelectron spectroscopy (XPS), the ratio of the intensity of D/G bands in the ox-GNPs using Raman spectroscopy, and mass loss data using thermogravimetric analysis (TGA). Finally, we are determining the interlayer spacing in the ox-GNPs using X-ray diffraction (XRD). The statistical design consists of 34 experimental runs that are currently being completed. Once completed, we will analyze the data to obtain a predictive model for the ox-GNP synthesis. We will finally identify the optimal factor levels to maximize the carboxyl functional group content in ox-GNP.

References:

(1) Zaaba, N. I.; Foo, K. L.; Hashim, U.; Tan, S. J.; Liu, W.-W.; Voon, C. H. Synthesis of Graphene Oxide Using Modified Hummers Method: Solvent Influence. Procedia Eng. 2017, 184, 469–477.

(2) Kudus, M. H. A.; Zakaria, M. R.; Akil, H. M.; Ullah, F.; Javed, F. Oxidation of Graphene via a Simplified Hummers’ Method for Graphene-Diamine Colloid Production. J. King Saud Univ. - Sci. 2020, 32 (1), 910–913.