Yolk–shell
composites offer a promising platform for integrating
cores into hollow shells to create unique structures and properties.
However, the concomitant functionality and tunability of yolk–shell
nanocomposites is still a great challenge but highly desirable. Herein,
we demonstrate a rational design for the fabrication of yolk–shell-structured
covalent organic framework (COF)@metal–organic framework (MOF)
(YS-COF@MOF) nanocomposites with COF as the external shell and MOF
as the inner yolk. Series of the YS-COF@MOF composites with different
MOF cores and COF shells were readily synthesized via a template-free
solvothermal method. Control experiments showed that the formation
of the hollow cavity between the core and the shell originated from
the amorphous-to-crystalline transformation and the simultaneous shrinkage
of the shell under the pyrrolidine-catalyzed conditions. The resultant
YS-COF@MOF merges the inherent structure tunability and functionality
of both COFs and MOFs. The functions of YS-COF@MOF can be regulated
and optimized by judicious selections of metal ions and organic building
blocks. Representative YS-TpPa@UiO-66-(COOH)2 with spatially
distributed acidic and basic sites exhibited synergistically enhanced
catalytic activity in one-pot deacetalization–Knoevenagel cascade
reactions.
Covalent organic frameworks (COFs) are emerging as a class of photocatalyst for solar energy utilization. The separation of photogenerated excitons in COFs is crucial for their photocatalytic performance. Herein, we report a strategy to tune the electronic structure of COFs by implanting Zn ions within the framework to facilitate the separation and utilization of the photoinduced charges. Zn ions are incorporated within the shell of hollow COF cages (Zn@H-TpPa) by a sacrificial template method with a formation of hollow cages. The implantation of Zn ions within the framework results in a redistribution of electron density and an increment of the polarity of the COF, as evidenced by experimental and computational analyses, and thus contributes to the separation and transport of charge carries. The Zn@H-TpPa shows enhanced photocatalytic H 2 production efficiency as compared to TpPa. The results demonstrate a new way to optimize the electronic structure of COFs for photocatalysis.
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