Fig. 5. Structural characterization of TAFs, CUg and CUb, isolated from the reaction product of the thermal reaction of citric acid and urea: (a) 1H-, 13C-, and 15N-NMR spectra of CUb recorded in DMSO-d6; for the 15N-NMR spectrum, samples were enriched with 15N; (b) 1H-, 13C-, and 15N-NMR spectra of CUg recorded in DMSO-d6; for the 15N-NMR spectrum, samples were enriched with 15N; (c) solid state FT-IR spectra of CUb and CUg; (d) thermogravimetric analysis of CUg; (e) thermogravimetric analysis of CUb.
