Supercritical CO₂ Assisted Preparation Of Mesoporous Poly?Ionic Liquid?s And Their Applications

Poly?ionic liquid?s?PILs?,known as the polymerized ionic liquids,are polyelectrolytes that comprise a polymeric backbone and ionic liquid?IL?species in monomer repeating units.PILs combine the advantages of ILs and polymers,therefore are widely used in catalysis,adsorption,electrochemical,analytical chemistry and other fields.Abundant mesoporous structure endows PILs with excellent textural properties,including high specific surface area,high pore volume,as well as large pore size,and finally makes mesoporous poly?ionic liquid?s?MPILs?possess more excellent performance.This study innovatively applied supercritical CO2 technology to the preparation of novel MPILs which were further applied to the CO2 capture and conversion,and the dichromate(Cr₂O₇^2-)removal from water.From the design,preparation and applications of the novel MPILs in the study,all meet the requirements of green chemistry.The main research works and creative results in this dissertation are described as follows.?1?A series of novel crosslinked quaternary ammonium-based MPILs featured with rich exposed anion and large surface area were successfully prepared by free-radical polymerization and subsequent supercritical CO2 drying?SCD?.It was discovered that the SCD treatment was vital to form the abundant mesopores of MPILs,which facilitated the high CO2 adsorption and accelerated their cycloaddition process.Among these MPILs,poly?N,N'-?methylene?bis?N,N-dimethyl-l-?4-vinyl-phenyl?methanaminium?chloride?with halogen anion-enriched skeleton displayed the best catalytic performance for CO2 cycloaddition with various epoxides under mild conditions,i.e.1 atm,90?,solvent-free,metal-free and additive-free conditions.The density functional theory?DFT?calculations showed lower activation energy in the rate-determining epoxy ring-opening step by using the quaternary ammonium monomer than that by using the imidazolium monomer,accounting for the lower CO2 cycloaddition temperature with the quaternary ammonium-based MPIL.Moreover,the catalyst can be separated easily and reused with high stability.?2?A family of hypercrosslinked imidazolium-based MPILs with different ionic densities were successfully prepared by free-radical polymerization and subsequent SCD.Among these MPILs,PVIm-6-SCD from the monomer which was produced from the reaction of 1-vinyl-1H-imidazole with 1,2,3,4,5,6-hexakis?bromomethyl?-benzene and has the highest ionic density?six ionic pairs?displayed unprecedented high CO2 adsorption:3.60 mmol·g-1 at 273 K and 1 atm.What's more,PVIm-6-SCD,revealed as one of the most efficient catalysts compared to those reported in the literature,can efficiently convert CO2 with various epoxides into cyclic carbonates at atmospheric pressure,even at relatively low temperature,solvent-free,metal-free and additive-free conditions because of its abundant mesopores for large specific surface area,high ionic density for rich exposed bromide anions as the active sites,as well as high CO2 adsorption capacity.Moreover,it can be easily separated with stable reusability.This work highlights the hypercrosslinked MPILs as a versatile platform to reach efficient CO2 capture and conversion under mild conditions.?3?A family of hypercrosslinked imidazolium-based PILs with different anion contents,crosslinker lengths and textural properties were successfully prepared by free-radical polymerization and subsequent different drying methods?SCD,VD and AD?for Cr₂O₇^2-removal.Subsequently,the anion contents of MPILs and the textural properties of PILs on their adsorption kinetics and adsorption thermodynamics towards Cr₂O₇^2-adsorption were studied systematically.The results showed that the anion content of PILs played a decisive role in their adsorption capacities towards Cr₂O₇^2-;The MPILs?PVBIm-6-SCD?prepared by polymerization of six cationic monomers with a longer crosslinking length and subsequent SCD displayed excellent textural properties such as high specific surface area,large pore volume,and abundant mesoporous structure.It facilitates the exposure of active sites?Br-?in PVBIm-6-SCD,thereby speeding up the mass transfer during anion exchange and accelerating the adsorption rate to Cr₂O₇^2-;The MPILs?PVIm-6-SCD?,also with high specific surface area,large pore volume,and rich mesoporous structure but a higher anion content,showed a very high Cr₂O₇^2-adsorption?628.3 mg·g-1,25??,which is more than twice the adsorption capacity of the reported adsorbent to Cr₂O₇^2-.Remarkably,PVIm-6-SCD exhibits good selectivity for Cr₂O₇^2-in the presence of disturbing anions including chloride?Cl-?,bromide?Br-?,nitrate?NO3-?and sulphate?SO42-?.Moreover,the prepared PVIm-6-SCD has good water and thermal stability,and reusability,showing potential industrial application prospects.The results of this study provide new material design ideas for the treatment of wastewater containing Cr₂O₇^2-.?4?A family of imidazolium-based PILs with high anion content?Cl-?and different textural properties were successfully prepared by free-radical polymerization of dicationic ILs monomer N,N'-methylene-bis?1-?3-vinylimidazolium??chloride?DVIm-CI?and subsequent different drying methods?SCD,VD and AD?.Subsequently,the textural properties of PILs on their adsorption kinetics and adsorption thermodynamics towards Cr₂O₇^2-adsorption were studied systematically.The results showed that all the prepared PILs showed much higher Cr₂O₇^2-adsorption capacity than the literature reported adsorbents,among them,PDVIm-CI-SCD from SCD displayed unprecedented high Cr₂O₇^2-removal capacity of 928.5 mg·g-1 and fast adsorption kinetics because of its abundant mesopores contributed for large specific surface area,as well as high anion content for rich exposed chloride anions as the exchange sites.Moreover,PDVIm-CI-SCD is reusable and capable for Cr₂O₇^2-removal even in the presence of disturbing anions including Cl-,Br-,NO3-and SO42-.This study further expands the application of MPILs in the treatment of wastewater containing Cr₂O₇^2-.