We synthesised a sulfonated covalent organic framework (COF-SO3H) via a hydrothermal method following a previous report (Figure ). In brief, 2,5-diaminobenzenesulfonic acid (DASA), 1,3,5-triformylphloroglucinol (Tp) and p-toluenesulfonic acid (PTSA) were dissolved in water and mixed thoroughly for 20 min using a vortex shaker. The resulting orange mixture was transferred to a Teflon-lined autoclave and heated at 120 °C for 24 h under static conditions, yielding COF-SO3H as a dark red powder. A more detailed synthesis description can be found in the SI. The successful formation of COF-SO3H was confirmed using Fourier-transform infrared spectroscopy (FTIR). The FTIR spectrum of COF-SO3H (Figure ) confirmed the complete conversion of the starting materials, evidenced by the absence of the characteristic N-H stretching vibrations (3425 and 3335 cm -1 ) and the -CH=O band (2923 cm -1 ), corresponding to free diamine in DASA and free aldehyde in Tp, respectively. Furthermore, characteristic signals ascribed to the formation of the β-ketoenamine-linked framework were observed at 1653 cm -1 (C=O), 1574 cm -1 (C=C), and 1225 cm -1 (C-N), respectively. The presence of -SO3H groups was verified by the appearance of distinctive signals at 1435 cm -1 , 1080 cm -1 , 1024 cm -1 , and 986 cm -1 , assigned to S=O and S-OH stretching vibrations.