Because of its high specific surface area and good stability, and its structure can be designed and simulated and then directionally synthesized, it has a certain degree of controllability [1], so POFS has been widely studied and applied by researchers in the past ten years. However, in addition to these advantages, it is still necessary to develop and design new pore structures and materials that are composite with the main body framework while maintaining the structural integrity, so as to ensure that POFs materials have broader application prospects in the fields of gas adsorption, heterogeneous catalysis, photoluminescence, and energy conversion [2-4]. Compared with metal-organic framework materials that have been developed for decades, the research on the composite and functionalization of porous organic framework materials is still in its infancy, but its excellent stability and porosity undoubtedly have great application potential.
Fig. 1 Porous materials can be defined by structure or function, but their function determines the scope of practical application [3].
Porous organic framework compoundsMetal nanoparticle composites
The combination of POFs and metal nanoparticles (MNPs) has greatly improved the gas adsorption, gas separation and heterogeneous catalysis of POFs materials.
Due to its high specific surface area and porosity, POFs exhibit ideal adsorption and storage effects for hydrogen, carbon dioxide, methane and other gases. However, other nanofunctional groups modified in their pores or on the walls of their pores can effectively improve their selectivity and storage for specific gases. POFS is an ideal storage material for hydrogen and carbon dioxide. On the one hand, the framework of POFs is composed of light elements and has a high specific surface area, which has great adsorption potential for hydrogen and carbon dioxide. On the other hand, the presence of nanoparticles such as Ni, Mn, and Li in the pores of POFs can effectively enhance the adsorption effect of polymers on hydrogen and carbon dioxide.
In 2009, Froudakis et al. [5] carried Li atoms in the COF-105 channel, which enabled the adsorption capacity of hydrogen at 77 K and 100 bar to reach 22 wt%, which was much higher than that of pure Cof-105 under the same conditions (6 wt%). In 2014, MA et al. [6] further modified Ag nanoparticles on the basis of PAF-1-SO3H to form PAF-1-SO3AG composites, which exhibited excellent selectivity in the separation of ethylene ethane. In addition, Zhu et al. [7] prepared X-PAF-50 (x = f, cl, br, i) in a PAF-50 framework by carrying different non-metallic particles, achieving a pair of pore sizes from 3Precise control of 4 to 7 separates hydrogen, oxygen, nitrogen, methane and carbon dioxide one by one through the sieving of the pores.
Figure 2 Structure of X-PAF-50 and GC chromatograms of the separation of H2, N2, O2, CH4, and CO2 gas mixtures on CL-PAF-50 and 2I-PAF-50 linkages [7].
There are also many studies on the use of MNPS and POFs as heterogeneous catalysts, in which the high specific surface area and good structural stability of POFs make them very suitable as nanoreactors for catalytic reactions. In 2009, Schüch et al. [8] introduced the metal salt precursor of PT into the CTF pore to generate PT-CTF through presynthesis and in-situ synthesis, which greatly improved the molar reaction rate in the catalytic oxidation of methane to formaldehyde. Wang et al. [9] (2014) published that pd@cpp-1 and pd@cpp-2 materials were obtained by carrying PD NPS in the porous polymers CPP-1 and CPP-2 pores, and found that they have strong catalytic activity for the reduction of nitrobenzene to aniline.
Porous organic framework compoundsPolyoxometalate composites
In 2016, Ma et al. [10] synthesized the composite EB-COF:PW12 by exchanging polyoxometalate pw12O403 into the pores of the ionic framework COF material by ion exchange method, and carried out proton conduction studies. The experimental results show that the composite exhibits good chemical and thermal stability, and at the same time, the pores of the original COF material are well retained during ion exchange, and the proton conduction rate of the synthesized composite EB-COF:PW12 is 332 10 3 s cm1, higher than all reported COFS material.
Fig.3 Schematic diagram of the synthetic composite EB-COF:PW12 [10].
3.Porous organic framework compoundsOrganic polymer composites
Since its inception in 2009, the OFS material G-C3N4 has been extensively studied by researchers due to its strong catalytic properties of photolysis of water, high specific surface area and stable structural framework. When researchers used G-C3N4 to perform experiments on photocatalytic removal of nitric oxide, they found that it was difficult to completely oxidize NO, and its catalytic active center was easily inactivated, so Dong et al. [11] in 2016 combined polyimide (Pi) and G-C3N4 through heterogeneous cross-linking reaction to form a new composite material PI-G-C3N4, and the addition of PI functional materials significantly improved the photocatalytic activity of G-C3N4. At the same time, it effectively reduces the inactivation effect of the catalyst during the reaction.
Porous organic framework compoundsCarbon nanotube composites
DU et al. [12] (2015) reported the synthesis of porous cobalt porphyrin framework compounds (COP) N-MWCNTs on multilayer carbon nanotubes and tested the catalytic activity of the water electrolysis reaction. The experimental results show that the new composite has good cycling stability. At the same time, the composites have a lower oxidation potential than the monomer (COP) N-Tips and the pure substrate MWCNTs, which proves that the catalyst of the composites has better catalytic performance, and the Faraday efficiency of the oxygen evolution reaction can exceed 86%.
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