Fourier transform infrared spectra were obtained with a Tensor 27 spectrometer (Bruker, UK), equipped with a 3000 Series High Stability Temperature Controller with RS232 Control (Specac, UK) and a MKII Golden Gate Single Reflection ATR system (Specac, UK) for measurements in ATR mode. The bottom plate of the Golden Gate ATR system was pre-heated at 60ºC to allow the complete evaporation of water from the drops (typically 20 μL) of the original GO dispersions. About 3 min after depositing the dispersions on the plate, the transmittance spectra of GO were recorded by acquiring 32 scans in the 4000-700 cm -1 range, with a resolution of 4 cm -1 .