Highly Efficient and Reversible Nitric Oxide Capture by Functionalized Ionic Liquids through Multiple-Site Absorption

Abstract

A series of basicity-tunable ionic liquids with carboxylate and sulfonate anion were designed, prepared, and applied in NO capture. Both high absorption capacity and low desorption residue were achieved through tuning the basicity of the anion, leading to a superhigh working capacity of more than 6 mol per mol ionic liquid, which is superior to that of traditional absorbents. Through a combination of absorption experiments, quantum chemical calculations, and spectroscopic investigations, the results indicated that such a high absorption capacity was originated from multiple sites interaction between oxygen atoms of carboxylate or sulfonate anion and NO, while the reduced interaction induced by the decreased basicity of the O-site ionic liquid led to excellent desorption. We show that the highly efficient and reversible NO capture by these tunable ionic liquids provides a new strategy for improving gas capture and utilization, which is also important for some other fields such as material, biology, and medicine.

Combined Experimental and Theoretical Study of the Competitive Absorption of CO2 and NO2 by a Superbase Ionic Liquid

“…The interest in ILs stems from the ability to alter their physiochemical properties, such as thermal stability or CO 2 absorption capacity, through changing the combination of cation and anion, which enables the tuning of their properties for specific applications. , For example, the amount of CO 2 absorbed by a particular IL has been shown to have a strong dependence on the anion, with conventional anions only physically absorbing small quantities of CO 2 , , compared with task-specific ILs that incorporate amine functionality and chemically absorb up to 1 n CO 2 : n IL. , Superbase ILs (SBILs) containing an aprotic heterocyclic anion (AHA) were developed to minimize the increase in viscosity observed in amine-functionalized ILs, and they can reversibly capture a greater than equimolar amount of CO 2 . − Extensive studies into the absorption of other acidic gases such as SO 2 and NO by SBILs have found that irreversible absorption was observed in many cases, often on multiple active sites within the IL, affecting the recyclability of the system. − …”

Sorbents for the Capture of CO2 and Other Acid Gases: A Review

“…Ionic liquids have been studied widely as an emerging class of acid gas sorbent. ,,, These materials consist of [cation]­[anion] pairs and are typically liquids at temperatures less than 100 °C. A large number of possible such cation–anion pairs creates a substantial material design space and enables tunability of the sorbents for specific properties. , This permits both physical ,, and chemical , interactions for the reversible capture and release of CO 2 , − SO x , ,− NO x , − and H 2 S. , There has been some success in handling mixtures, − although often the presence of contaminants reduces performance, , and requires sorbent recovery . This is a problem for these high cost materials, partially offset by the negligible vapor pressure of ionic liquids, , which eliminates losses to the gas phase.…”

Investigation on Protic Ionic Liquids as Physical Solvents for Absorption of NO at Low Pressures

“…To better understand the interaction of [TETAH] [PhO] with NO on the molecular level, density functional theory (DFT) calculations were carried out to examine the interaction of the [TETAH] cation and the [PhO] anion with NO, and their optimized structures are shown in Figure 6. As for the [PhO] anion, it has been previously pointed out that the negative O-site on the [PhO] anion played the primary role in interacting with NO; 35,38 therefore, the contribution of other Interestingly, the binding energies of NO with the free secondary amine (−9.77 kJ/mol) and the primary amine (−10.59 kJ/mol) were much less negative than that of NO with the −NH 2 + − group. This phenomenon might be attributed to the fact that the alkalinity of the N-site on the cation was reduced due to the presence of H proton, so that the interaction strength of NO with the N-site was weakened.…”

“…In view of this situation, Wang et al proposed a new strategy to design the IL with an O-site to replace the N-site and further tune the interaction between the anion and NO via basicity. 38 They designed a series of ILs with carboxylate and sulfonate as the anions for NO capture with the absorption capacity of more than 6 mol NO/mol IL (conditions: 303.2 K and 1 bar). Such a high absorption capacity resulted from the chemical interaction between NO and the O-site on the anion.…”