Fig. 4. (a) The FTIR spectra for GO, GO–CNT10, and GO–CNT15 presented in transmittance. The left panel shows the broad OH stretch band in the region from 3700–2400 cm^–1 containing contributions from H₂O and the functional groups (COOH and C–OH). The right panel depicts the region from 1950–550 cm^–1 providing information on the vibrational modes for the C O stretch (1850–1720 cm^–1), water scissor (1650–1620 cm^–1), sp² C C stretch (1500–1600 cm^–1), OH in-plane bending (1400 cm^–1 and 1385 cm^–1), C–O stretch (1223 cm^–1, 1055 cm^–1 and 1003 cm^–1), and C–O–C bending (831 cm^–1). (b) The transmittance difference spectra obtained after subtracting the spectrum of GO showing the region from 3800 cm^–1 to 2400 cm^–1. The positive (upper part) and negative (lower part) values refer to the relative decrease and increase of the GO–CNT signals with respect to GO. A horizontal line marks the zero reference value throughout the wavenumber range. The zones for loosely bound water (3800–3420 cm^–1), the overlap region for the OH water and oxygen functional groups from GO and oCNTs (3420–2800 cm^–1), and the cooperatively strengthened OH···O C hydrogen bonds between GO and oCNTs (2800–2400 cm^–1) are separated by vertically dashed lines. (c) The transmittance difference spectra showing the region from 1900–550 cm^–1. The different vibrational modes or respective zones are indicated.