The surface chemistry of graphene oxide (GO) can be modified by the chemical reduction of oxygen-containing groups using L-ascorbic acid (L-AA). Being able to "tune" the surface hydrophobicity of GO in a controlled manner, with a well-defined level of reduction, provides a valuable tool for understanding and controlling interactions with hydrophobic surfaces. Numerous analytical and chemical methods have been used to determine the extent of reduction in chemically reduced graphene oxide (CRGO) samples. However, many of these methods are limited by their laborious nature, cost, or lack of sensitivity in resolving oxygen content in samples that have only been reduced for short periods of time, making them inappropriate for rapid use with multiple samples. Here, we have used ultraviolet (UV), Raman, and attenuated total reflection infrared (ATR-IR) spectroscopy to monitor the chemical reduction of GO. These three techniques are simple, rapid, nondestructive, accurate, and widely available. The data set from each technique has been correlated and modeled against a reference data set (carbon to oxygen ratio obtained from elemental analysis) using partial least squares regression (PSLR). Using this approach, the chemical reduction of GO was quantified from UV (r2 = 0.983, RMSECV = 0.049), Raman (r2 = 0.961, RMSECV = 0.073) and ATR-IR (r2 = 0.993, RMSECV = 0.032) data. ATR-IR enabled identification of the different oxygen-containing groups on GO, and coupled with chemometric modeling, provides an excellent approach for the routine quantitative analysis of the chemical reduction of GO.
Keywords: CRGO; Chemically reduced graphene oxides; GO; PLSR; chemometric; graphene oxide; partial least squares regression; surface hydrophobicity.