Fig. 2: Characterization of the chemical structure and morphology.

a FTIR spectra of linker monomers and COFs. b 13C ss-NMR spectra of Obq-COF and Ace-COF. SEM images of c CuSA/Obq-COF and d CuSA/Ace-COF; the insets show the corresponding TEM and EDS elemental mapping images. AC-HAADF-STEM images of e CuSA/Obq-COF and f CuSA/Ace-COF, with the yellow circle highlighting the single-atom Cu feature.