“…In the Fourier transform infrared (FT-IR) spectra in Figure 1c, the RF resins displayed individual bands stemming from resorcinols, linkers, and residual groups, which fully confirmed the precise synthesis of RF [26]. The broad peak at 2900~3300 cm −1 is the stretching vibration of resorcinol, and the peak at 1650 cm −1 belongs to the stretching vibration mode of C=O, which is due to hydrothermal treatment at high temperature, which can produce quinoid groups [27]. Simultaneously, the sharp peaks at 1618 and 1400 cm −1 are caused by the C=C vibrations of the aromatic ring and the C-H vibration of the methylene linker, while the broad peak in the region of 1100~1300 cm −1 is attributed to the C-O vibration of resorcinol and methylol [28].…”