Construction
of Layer-Blocked Covalent Organic Framework
Heterogenous Films via Surface-Initiated Polycondensations with Strongly
Enhanced Photocatalytic Properties
Imine-linked covalent organic frameworks (COFs) usually
show high
crystallinity and porosity, while vinyl-linked COFs have excellent
semiconducting properties and stability. Therefore, achieving the
advantages of imine- and vinyl-linkages in a single COF material is
highly interesting but remains challenging. Herein, we demonstrate
the fabrication of a layer-blocked COF (LB-COF) heterogeneous film
that is composed of imine- and vinyl-linkages through two successive
surface-initiated polycondensations. In brief, the bottom layer of
imine-linked COF film was constructed on an amino-functionalized substrate
via Schiff-base polycondensation, in which the unreacted aldehyde
edges could be utilized for initiating aldol polycondensation to prepare
the second layer of vinyl-linked COF film. The resultant LB-COF film
displays excellent ordering due to the crystalline templating effect
from the bottom imine-linked COF layer; meanwhile, the upper vinyl-linked
COF layer could strongly enhance its stability and photocatalytic
properties. The LB COF also presents superior performance in photocatalytic
uranium extraction (320 mg g–1), which is higher
than the imine-linked (35 mg g–1) and the vinyl-linked
(295 mg g–1) counterpart. This study provides a
novel surface-initiated strategy to synthesize layer-blocked COF heterogeneous
films that combine the advantages of each building block