Reversible Construction Of Hydrogen Bonds Networks For Efficient Ammonia Absorption

Ammonia?NH₃?is one of typical gaseous pollutant for our social environment and human health,on the other hand,NH₃ is widely applied in industrial production.thus,it is extremely important to recycle waste NH₃from industrial gases.In this work,we designed a series of amidine-based and pyridine-based ionic liquid with high NH₃ absorption capacity and energy-saving desorption.We also further investigated sigmoidal isotherm absorption in ionic networks with cooperative hydrogen bonds?CHBs?.At the end,regulated threshold pressure of reversibly sigmoidal NH₃ absorption isotherm with ionic liquids by tuning the strengths of cooperative hydrogen bonds to highly efficient capture NH₃ at different concentration.ILs with reversible construction of ionic networks,which mainly consist of cooperative hydrogen bonds were designed for sigmoidal ammonia?NH₃?absorption isotherm,which leads to efficient absorption,energy-saving desorption,and high reversibility.Combined with NH₃ absorption-desorption experiments,spectroscopic investigations,NH₃-TPD measurement,and quantum-chemical calculations,NH₃ absorption mechanism was proposed as the hydrogen bond interaction with ILs by overcoming the heat for disorganizing ionic networks,including CHBs breakage and the phase change of ILs from solid to liquid.Reversely,the NH₃ desorption would be promoted by the heat release for the reformation of ionic networks.Thereinto,[BzAm][Tf₂N] with ionic networks showed NH₃ absorption with threshold pressure at 280 mbar and NH₃ capacity of 2.80 mol NH₃/mol ILs at 1 bar as well as be desorpted completely just through pressure swing,calorimetric test indicated the exothermic reformation of ionic networks provided 31.8% of energy for NH₃ desorption from [BzAm][Tf₂N].Furthermore,the ammonia capacity as well as the threshold pressure would be changed by varying the CHBs interaction in ILs,that [2NH₂-PyH][Tf₂N] with weaker interaction of CHBs indicating decreased threshold pressure at 40 mbar and enhanced NH₃ capacity of 3.80 mol NH₃/mol ILs at 1 bar.We believe this highly efficient and reversible process by reversible construction of absorbents can provide a potential alternative for NH₃ as well as other gas absorption.Furthermore,The weaker flexible hydrogen-bonded frameworks composed of amino pyridinium-based protic ionic liquids?ILs?marked as [xNH₂-PyH][Tf₂N]?x=2,3,4?were designed as NH₃ absorption agents.Interestingly,NH₃ absorption isotherm of these ILs present sigmoidal isotherm absorption,and the threshold pressure?TP?decreases from 75 to 6 mbar with the tunable of hydrogen bonded frameworks by varying the substituted group xNH₂.Combined with XRD characterizations,Fourier transform infrared and ¹H NMR spectroscopies,thermometric analyses,and theory calculations,it indicates NH₃ fixed by these ILs via acid-base interaction as well as hydrogen bonding based on the activation of sites through the fracture of the hydrogen-bonded frameworks,which would reform along with heat release when NH₃ desorption.Therefore,S mode NH₃ absorption with [3NH₂-PyH][Tf₂N] presents low TP of 6 mbar?6000 ppm?at 30 °C,and its NH₃ capacity increases sharply and followed by a continuous increase to 3.85 mol/mol ILs?175 mg/g ILs?at 1.0 bar,which is higher than that of the reported ILs.The fixed NH₃ could be desorbed completely in vacuum at 80 °C and 10 mbar.[3NH₂-PyH][Tf₂N] maintained its high capacity within 20 time recycles.The sigmoidal NH₃ absorption would be considered as one of the potential approaches for its simultaneous efficient absorption and energy-saving separation at low concentrations.In conclusion,a series of amidine-based and pyridine-based ionic liquids were designed for NH₃ sigmoidal isotherm absorption due to fracture of cooperative hydrogen bonds,which leads to highly efficient absorption,energy-saving desorption.Threshold pressure was regulated by tuning the strengths of cooperative hydrogen bonds to highly efficient capture NH₃ at different concentration.