Covalent organic frameworks (COFs) are a class of crystalline porous polymer that allows the atomically precise integration of organic units into extended structures with periodic skeletons and ordered nano pores. One important feature of COFs is that they are designable; that is, the geometry and dimensions of the building blocks can be controlled to direct the topological evolution of structural periodicity. The diversity of building blocks and covalent linkage topology schemes make COFs an emerging materials platform for structural control and functional design, which are promising for handling environmental issues. We have realized tuning the physicochemical properties of COFs by tailoring the building blocks via molecular design and precise construction, which significantly improves the performance of COFs as adsorbents or photo catalysts for enrichment or photo-degradation of organic pollutants.

Fig. 1. The influence of structural control on the photocatalytic performance of imine-linked COFs

1) Novel bouquet-shaped magnetic porous nano compositeis fabricated via graftinga COF (TpPa-1) onto the surface-modified Fe3O4 nanoparticles (Fe3O4 NPs). The magnetic TpPa-1 contains clusters of core-shell magnetic nanoparticles and interconnected porous TpPa-1 nanofibers.Due to this particular morphology, it possesses larger specific surface area, higher porosity, and super magnetism, making it an ideal sorbent for enrichment of trace analytes. This work has been published at ACS Applied Materials &Interfaces (2017, 9 (3), 2959–2965).

2) A COF inlaid with C3N4 building block is synthesized from 1,3,5-triformylphloroglucinol (Tp) and melamine (MA), which is employed as a high-performance metal-free photo catalyst with visible light response. Three functional factors inducing photocatalytic ability are artfully integrated in the COF skeleton, where triazine units serves as photoactive centers, cyclic ketone units a selectron-withdrawing moieties, and conjugated structure as a photoelectron shift platform, respectively. This COF with segregated donor-acceptor alignments exhibits an excellent visible-light photocatalytic capacity for organic pollutant decomposition. This work has been published in Chemical Communication (2017, 53, 9636-9639).

3) We have synthesized a series of imine-linked COFs from the same aldehyde and three different monomers of nitrogen-containing functional groups, and investigated the translation of chemical and structural variation in the precursors to photo electric properties of the resulting COFs, with the consequent influence on photo catalytic degradation. We find that the visible-light photocatalytic performances an enhanced with increasing density of active centers and conjugation degree in the networks, which provides a forceful basis for the systematic fine-tuning of their structural and physicochemical properties thus broadening the applications of COFs in photo catalysis. We further have prepared series of novel metal-organic framework/covalent organic framework(MOF/COF) hybrid materials by encapsulating MOF with highly stable TTB-TTA COF. These hybrids inherit the merits of high crystallinity, large surface area, outstanding visible-light response and tunable bandgaps from MOFs and COFs. These studies have been published in Applied Catalysis B: Environmental (2018, 239, 147–15) and Applied Catalysis B: Environmental (2019, 247, 49–56).

The above-mentioned studies are undertaken by Sijing He PhD. Owning to these excellent works, she has been awarded the title of outstanding graduates in 2019 and got the grant of Special Foundation of President of the Chinese Academy of Sciences.

Paper 1：https://doi.org/10.1021/acsami.6b13643

Paper 2：https://doi.org/10.1039/C7CC04515H

Paper 3：https://doi.org/10.1016/j.apcatb.2018.08.005

Paper 4：https://doi.org/10.1016/j.apcatb.2019.01.078