Structural Design Of Novel Functionalized Ionic Liquids For Tuning The Capture Of Acidic Gas

Human beings have realized that climate change would bring a catastrophe to social society if no action is taken.It is well-known that carbon dioxide(CO2)emissions are mainly responsible for global warming,sea level rise and more severe weather patterns.As a matter of fact,accumulation of anthropogenic CO2 in the atmosphere has reached to an unprecedented level at around 400 part per million(ppm)principally due to the soaring consumption of fossil fuels.Therefore,it is highly essential to develop effective carbon capture and storage(CCS)technologies for the mitigation of CO2 crisis.In this regard,ionic liquids(ILs)are state-of-the art solvents by taking advantage of their unique properties,including negligible vapour pressure,high thermal stability,non-flammability,wide liquid temperature range,virtually unlimited tunability and excellent CO2 affinity.In this dissertation,we focus on the synthesis of functionalized ILs for tuning the absorption performance of CO2.In the first part,?-electron-conjugated structures are employed into the anion of IL to achieve reversible CO2 capture,originating from the formation of dynamic covalent carbon-oxygen bonds.These large ?-electron-conjugated anions offer dual functions:?-electron delocalization through charge dispersion improves the CO2 desorption,and the anion aggregation strengthens the formed dynamic C-O bonds during the uptake process.The dual-tuning role is supported by Absorption experiments,spectroscopic investigations,quantum chemical caculations,and thermogravimetric analysis results.Notably,no-deuterium NMR spectroscopy(No-D NMR)exhibits a significant enhancement of the absorbed CO2 signal and provides an effective in situ strategy for the determination of the mechanism of the interaction between the IL and CO2.These ILs show good thermal stability,high absorption,and excellent desorption for CO2 capture,revealing the important role of dynamic covalent bonds in eliminating CO2 crisis.In the second part,we have designed a series of amino-functionalized pyridine-based ILs,which exhibit improved CO2 uptake through intramolecular proton transfer reaction.Our strategy is that an alkaline group(a deprotonated hydroxide group)is introduced as a proton acceptor to avoid intermolecular proton transfer from one amine group to another during CO2 uptake,resulting in an enhanced absorption capacity of CO2 and controllable viscosity change.Very significantly,in contrast to previous reported amino-functionalized ILs where large viscosity increases are an issue,the viscosity of[P66614][2-NH2-3-O-Py]decreases by around 40%after CO2 absorption,indicating self-promoted absorption kinetics.As a result,these amino-functionalized ILs exhibit robust,fast,water-tolerant,and reversible CO2 absorption.In the third part,we have constructed a series of novel anion-functionalized light-responsive ILs by tailoring an azobenzene group to the phosphonium cation and using 1,2,4-triazole as the anion.Different from previous reports on light-responsive ionic liquids,functionalized anion(1,2,4-triazole)is first employed into light-responsive IL by an anion exchange method,and the neat cis state of the IL is obtained by two approaches.One way is that the trans-IL is dissolved in THF solvent,followed by UV irradiation,and subsequently removal of THF solvent,giving rise to the cis-IL.The other way is that the cis-IL is obtained by direct irradiation on the thin film of the corresponding trans-IL with UV light.The reversible trans-cis isomerization of IL occurs both in solution and on the film by alternating irradiation of UV light and blue light.The effect of geometrical transformation on the absorption of CO2 in the IL is underway in our lab.In the forth part,we have reported the gas-induced cis to trans isomerization of the azobenzene-containing ILs in the first time.Sulfur dioxide(SO2)gas,in contrast to nitrogen(N2)or carbon dioxide(CO2),can selectively trigger a complete cis-to-trans transformation,which is supported by NMR spectra,UV-vis spectroscopy,and FT-IR methods.Furthermore,logical experments based on NMR data reveal high physical absorption of SO2 is mainly responsible for this geometrical change.Meanwhile,the photo-isomerization process of trihexyl-(tetradecyl)phosphonium(E)-4-(phenyldiazenyl)benzoate([P66614][azo-COO])is remarkably hindered after the uptake of SO2 as indicated by the photoisomerization rate constants.We anticipate this work would provide some inspiration to the design of stimuli-responsive materials for gas sensor.All in all,we hope novel concepts or strategies are emerged and introduced to the field of ionic liquids for CO2 capture.We also appreciate new findings or discoveries during the process of solving scientific problems.One word should be reminded that "Please break the thinking boundary,and build an interdisciplinary thinking pattern,which help to obtain some original findings or discoveries."...