Photocatalysis, which can convert solar power to chemical energy, offers a green sustainable route for resolving the serious energy crisis and environmental pollutions. In the photocatalytic process, semiconductor materials called photocatalysts play a decisive role in the photocatalytic system because they are responsible for light absorption, the generation and transmission of photogenerated carriers, and the redox reaction.
Compared with the molecular-based semiconductor materials, solid photocatalysts offer superior photostability, recyclability and straightforward separation process as outstanding advantages for practical and continuous application in the chemical industry. However, improving photocatalytic activity of heterogeneous photocatalysts is still a great challenge.
Two-dimensional covalent organic frameworks (2D-COFs), which are a new type of crystalline porous materials with highly ordered periodic architectures have latterly aroused tremendous interest for promising applications.
Specially, introducing photoactive organic building blocks into 2D-COFs can induce the formation of discrete and periodic columnar π-arrays, which offers a perfect path for rapid pervasion and mobility of the photoinduced electron/hole pairs.
Consequently, 2D-COFs with high crystallinity, large porosity, and good photo-response are strongly expected to function as powerful semiconductor materials. However, in principle, the low wettability of organic frameworks undesirably hampers the diffusion of matter into the pores in water, and unsatisfactory stability of boronate ester or imine linkages in water reduces the reusability of the frameworks.
These undesirable features are a bottleneck for the development of COF-based photocatalysts with high photocatalytic performance in water for practical applications.
Recently, a research team led by Prof. Xiaoming Liu from Jilin University, China reported a generic tactic for devising and developing 2D-COFs as high-performance solid photocatalysts by the implementation of a multi-synergistic approach. Two amide-linked 2D-COFs with rich triazine building units are synthesized by oxidizing imine-linked 2D-COFs via a post-synthetic method.
The amide linkage increases the hydrophilicity of the framework and also improves the stability of the COF in water. On one hand, the synergistic effect of the good wettability and inherent porosity can enhance the adsorption capacity of the COFs for dyes in water, thus leading to unprecedented improvement of their photocatalytic activity under visible light.
On the other hand, the high crystallinity works in coordination with good stability to ensure satisfactory recyclability for the resulting COFs.
Indeed, the amide-linked COF-JLU19 with an electron donor-acceptor structure exhibits an outstanding photocatalytic activity and recyclability in water under visible-light illumination. Interestingly, an electrospinning membrane based on the amide-linked COF-JLU19 is prepared to simulate the practical application, where the membrane still displays superior photocatalytic activity and reusability for the photodegradation of Rhodamine B (RhB) in water upon irradiation with sunlight.
Source: http://english.dicp.cas.cn/