Design And Synthesis Of Ordered Ionic Liquid-Functionalized Mesoporous Polymers For Efficient Chemical Fixation Of CO₂

There is a growing awareness that carbon dioxide (CO2) emissions associated with global warming should be reduced as CO2 is a major greenhouse gas. However, carbon dioxide is expected to be a potentially abundant, cheap, non-toxic and renewable carbon resource. From the viewpoint of environmental protection and resource utilization, worldwide efforts have been devoted to developing new technologies for CO2 capture, storage and utilization, which play an important role in green carbon science.Ordered mesoporous materials have received considerable attention owing to their tunable mesostructure, large specific surface area and pore volume as well as adjustable aperture, which opens up rapid development in adsorption and separation, energy storage,electrochemistry. It has been demonstrated that ordered mesoporous materials has a wide application prospect and practical value in macromolecular catalysis. Recently, ionic liquid functionalized mesoporous silica could employed as efficient catalysts in the synthesis of cyclic carbonates through the CO2 coupling reaction, which recognized as an effective strategy for the fixation of CO2 in the viewpoint of green chemistry and atom economy. Cyclic carbonates are widely useful in polymer, textile, printing and dyeing, battery and drug intermediates etc.In comparison with conventional mesosilica-based materials, mesoporous polymers have showed promising potential applications because of their outstanding features of both mesoporous material and polymer. However, the fabrication of mesoporous polymers using in chemical fixation of CO2 had not been reported, there is still remains a great challenge.Herein, we have prepared a series of ordered imidazolium-based ionic liquid-functionalized mesoporous polymers for efficient chemical fixation of carbon dioxide. The mesoporous polymer catalysts share the advantages of the interfacial mass/energy transfer, high stability of organic polymers and catalytic performance of ionic liquids. Additionally, the abundant phenolic hydroxyl groups in mesoporous polymers are expected to promote the cycloaddition reaction of epoxides with CO2 due to hydrogen bonding. The thesis is mainly made up of following sections:(1) We have prepared a series of FDU-15 mesopolymer supported imidazolium-based ionic liquids by using rational chemical modification processes. They proved to be efficient heterogeneous catalysts for the cycloaddition of CO2 with epoxides without the use of any organic solvent and co-catalyst. The catalysts were separated by simple filtration and reused more than five times without significant loss of activity. Various techniques including low-angle XRD, TEM and N2 adsorption—desorption were used to testified that a well-ordered mesostructures were precisely maintained. Additionally, the samples were further characterized by FT-IR spectra, EDX spectroscopy and solid state 13C MAS NMR spectra, which confirmed a successful functionalization with imidazolium-based ionic liquids. Compared with polystyrene and SBA-15, the phenolic hydroxyl groups played an important role in accelerating the CO2 cycloaddition reaction through hydrogen bonding. The plausible reaction mechanisms were also deduced on the results in our study.(2) Considering the multistep post-modification method mentioned above, which will inevitably suffer from a low loading of imidazolium-based ionic liquids and inhomogeneously distributed active sites as well as block the pore channels. We first reported a facile one-step synthetic route to synthesize a series of controllable imidazolyl-functionalized ordered mesoporous polymer (IM-MPs) with tunable surface areas, large pore volumes and uniform pore size. This was readily achieved by using an inexpensive and commercially available IMP, phenol and formaldehyde as precursors, ampliphilic triblock copolymer F127 as a structure directing agent via evaporation-induced self-assembly (EISA) method. The TEM, SAXS, and N2 adsorption-desorption clearly shown a well ordered 2D hexagonal structure with the p6mm space group, the successful incorporation of imidazolyl group into the mesoporous polymer framework has also been confirmed by TG, XPS, FT-IR spectra and 13C MAS NMR spectra. Obviously, the obtained IM-MPs can be easily functionalized by with bromoethane and employed as highly efficient and recyclable catalyst for the cycloaddition of CO2. A TON of 280 could be achieved by the IM-MPs-20%-EtBr exhibited the highest catalytic activity, which was higher than that of previously reported catalysts. In addition, the influence of the loading of imidazolium-based ionic liquids and surface area were investigated in this study.