Ionic Liquid-based Cross-Linked Polymeric Nanoparticles: Preparation And Its Application In The CO₂ Fixation

In recent years, ionic liquids (ILs) have attracted considerable attention due to their unique advantages, such as almost undetectable vapor pressure, wide liquid temperature range, excellent chemical stability, high thermal stability, and strong solvent power for a wide range of organic, inorganic and polymeric molecules. More recently, it was demonstrated that some ILs were active and selective catalysts for the cycloaddition of CO₂ to epoxides. The combination of ILs as versatile reaction media with suitable catalyst, such as acid, base, nanostructures or metal-complex, may result in a more diverse and flexible platform to establish a highly effective and easily separable catalytic system. Although the immobilization of ILs onto polymers has been studied, the design and preparation of highly effective heterogeneous catalysts are still desirable. In this study, the progress of CO₂ fixation, ionic liquids, nanoparticles, especially CO₂ fixation by ionic liquids, are reviewed. The main contents include the following:1. Highly cross-linked polymeric nanoparticles were prepared via novel one-step synthesis by copolymerizing ethylene glycol dimethacrylate (EGDMA) and the ionic liquid, 1-vinyl-3-(2-methoxyl-2-oxyl ethyl) imidazolium halide ([VMIM]X). The results indicated that nanoparticles with the mean size of about 350 nm could be obtained conveniently through the cross-linking copolymerization. The nanoparticles were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), FT-IR, thermo gravimetric analyzer (TGA), element analysis and X-ray diffraction (XRD) techniques. Moreover, the cross-linked polymeric nanoparticles were highly active and selective catalysts for the cycloaddition reaction of carbon dioxide to epoxides. The effects of reaction time, reaction temperature, CO₂ pressure and amount of catalyst on yield of the products were investigated. The results revealed that cyclic carbonates with high yield and selectivity could be produced on the condition of 0.1 g catalyst, 5 MPa CO₂, 160°C and 12 h. In addition, the catalysts could be recovered by filtration and reused several times with only slight loss of catalytic activity.2. Highly cross-linked polymeric nanoparticles (CLPN) were explored via a facile one-step synthesis as effective catalyst for CO₂ cycloaddition to epoxides. In this study, CLPN was synthesized by radical copolymerization of 4-vinylbenzyl-tributylphosphorous chloride (PIL) and ethylene glycol dimethacrylate (EGDMA) in selective solvent, such as low molecular weight alcohols. The results illustrated that spherical nanoparticles with the mean diameter range of 10–100 nm could be prepared in these alcohols, and the size of CLPN could be facilely tuned by the feed ratio of EGDMA to PIL. CLPN were characterized using dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), thermo gravimetric analysis (TGA), atom absorbance spectrograph, and Fourier transform infrared (FT-IR) spectrum techniques. In addition, CLPN can be exploited as highly active and selective catalysts for the cycloaddition of CO₂ to epoxides. The effects of parameters, such as reaction temperature, pressure, reaction time, and catalyst amount, on the cycloaddition reaction were investigated. As a result, excellent yield (100%) and selectivity (100%) of cyclic carbonates could be achieved at mild conditions (0.1 g CLPN, 3.0 MPa CO₂, 140 ?C and 3 h) without the addition of any solvents or co-catalysts. Unexpectively, CLPN could be dispersed well enough in the products to form homogeneous solution, which resulted in the extremely high activity and selectivity. At the same time, CLPN could be easily separated by filtration after pouring the reaction mixture into toluene. CLPN could be recycled for six times with only less than 1.5% loss of catalytic activity.3. Highly cross-linked polymeric nanoparticles were prepared via novel one-step synthesis by copolymerizing ethylene glycol dimethacrylate (EGDMA) or divinylbenzene (DVB) and the ionic liquid, [BIM]X. Moreover, the cross-linked polymeric nanoparticles were highly active and selective catalysts for the cycloaddition reaction of carbon dioxide to epoxides. The nanoparticles were characterized using FT-IR, thermo gravimetric analyzer (TGA) and scanning electron microscopy (SEM). As a result, excellent yield (97.51%) and selectivity (99.98%) of cyclic carbonates could be achieved at mild conditions (0.1 g CLPN, 3.0 MPa CO₂, 160 ?C and 7 h) without the addition of any solvents or co-catalysts. the catalysts could be recovered by filtration and reused five times with only slight loss of catalytic activity.