All three GO types exhibited similar FTIR spectra, despite small differences between us-GO and the other 2 materials (Figure ). In particular, the lower intensities of the bands around 1725cm -1 and 1195cm -1 suggest that us-GO might have a slightly lower abundance of carbonyls and phenols, respectively, which could explain the minor differences observed by ζ-potential measurements (Figure ). However, these minor differences need to be quantitatively analysed to better understand whether and how the chemical micro-environment has changed with sonication to yield us-GO from l-GO, compared to s-GO.