Fig. 3: Structural characterization of 3D-Sp-COFs by different microscopic techniques.

a FE-SEM images. b TEM images, 72 h (1)–(4) represents 3D-Sp-COF@72 h synthesized from different experimental batches. c SEM-energy-dispersive spectrum (EDS) elemental mapping images: solid sphere (left), full hollowing sphere (middle), and homogeneous core–shell sphere (right).