Fig. 2: Characterizations of COF-LZU1 films.

a SEM image of the surface of COF-LZU1 films (insert is the digital image of COF-LZU1 films). b Cross-sectional SEM images of COF-LZU1 films. c AFM image of the surface of the COF-LZU1 films. d XRD spectrum of the surface of COF-LZU1 films.