Je Seung Lee

Ether-functionalized ionic liquids as highly efficient SO2 absorbents

Room temperature ionic liquids (RTILs), ether-functionalized imidazolium methanesulfonates, exhibit extremely high SO2 solubility, at least 2 moles of SO2 per mole of RTIL at 30 °C and at atmospheric pressure. The solubility of SO2 in these RTILs increases with increasing number of tethered ether oxygen atoms and also with the pressure rise. FT-IR spectroscopic and quantum mechanical calculation results show that such high SO2 solubility is originated from the combined interactions of SO2 with methanesulfonate anion and ether oxygen atom or atoms on the imidazolium ring. The absorbed SO2 gas can be readily and completely desorbed from the RTILs by heating at 100 °C in a N2 flow, thereby allowing the RTILs to be reused up to 5 cycles without loss of their initial capacity.

Steric hindrance-induced zwitterionic carbonates from alkanolamines and CO2: highly efficient CO2 absorbents

Sterically hindered amines such as 2-[(1,1-dimethylethyl)amino]ethanol (TBAE) and 1-[(1,1-dimethylethyl)amino]-2-propanol (TBAP) were found to reversibly interact with CO2 in a 1 : 1 molar ratio exclusively through the hydroxyl group, producing zwitterionic carbonate species, which lose CO2 at considerably lower temperatures than the CO2-adducts of other alkanolamines including monoethanolamine and diethanolamine. The formation of zwitterionic carbonate species from TBAE and TBAP was supported by spectroscopic and computational studies.

CO2 Absorption and Desorption in an Aqueous Solution of Heavily Hindered Alkanolamine: Structural Elucidation of CO2-Containing Species

The pathways for the CO2 absorption and desorption in an aqueous solution of a heavily hindered alkanolamine, 2-(t-butylamino)ethanol (TBAE) were elucidated by X-ray crystallographic and (13)C NMR spectroscopic analysis. In the early stage of the CO2 absorption, the formation of carbonate species ([TBAEH]2CO3) was predominant, along with the generation of small amounts of zwitterionic species. With the progress of the absorption, the carbonate species was rapidly transformed into bicarbonate species ([TBAEH]HCO3), and the amounts of the zwitterionic species increased gradually. During desorption at elevated temperature in the absence of CO2, [TBAEH]HCO3 was found to transform into [TBAEH]2CO3, where CO3(2-) strongly interacts with two [TBAEH](+) via hydrogen bondings.

Nitrile-functionalized tertiary amines as highly efficient and reversible SO2 absorbents.

Three different types of nitrile-functionalized amines, including 3-(N,N-diethylamino)propionitrile (DEAPN), 3-(N,N-dibutylamino)propionitrile (DBAPN), and N-methyl-N,N-dipropionitrile amine (MADPN) were synthesized, and their SO2 absorption performances were evaluated and compared with those of hydroxy-functionalized amines such as N,N-diethyl-N-ethanol amine (DEEA), N,N-dibutyl-N-ethanol amine (DBEA), and N-methyl-N,N-diethanol amine (MDEA). Absorption-desorption cycle experiments clearly demonstrate that the nitrile-functionalized amines are more efficient than the hydroxy-functionalized amines in terms of absorption rate and regenerability. Computational calculations with DBEA and DBAPN revealed that DBEA bearing a hydroxyethyl group chemically interacts with SO2 through oxygen atom, forming an ionic compound with a covalently bound OSO2(-) group. On the contrary, DBAPN bearing a nitrile group physically interacts with SO2 through the nitrogen and the hydrogen atoms of the two methylene groups adjacent to the amino and nitrile functionalities.

Role of alkyl group in the aromatic extraction using pyridinium-based ionic liquids.

The performance of N-alkylpyridinium-based ionic liquids with a SCN anion (PyILs) was evaluated for the selective extraction of aromatics from aliphatic hydrocarbons. The aromatic extraction ability of PyILs was greatly enhanced by the presence of a methyl group on the pyridinium ring at the 3- or 4-position, whereas the solubility of the aromatics in the PyILs decreased with increasing the number of methyl groups on the benzene ring. The FT-IR studies revealed that the solubility of an aromatic compound in a PyIL is closely correlated with the degree of aromatic C-H bending frequency shift observed during the dissolution of the aromatic compound in the PyIL: the larger the shift, the higher the solubility. The computational calculations on the dispersion interactions between aromatics and PyILs demonstrated that the anion-aromatic interaction is much more important than the cation-aromatic interaction in determining the aromatic solubility in PyILs, and such anion-aromatic interaction can be enhanced by introducing a methyl group at the carbon atom of the pyridinium ring.

Tailoring chemically converted graphenes using a water-soluble pyrene derivative with a zwitterionic arm for sensitive electrochemiluminescence-based analyses

We report a method to tailor chemically converted graphenes (CCGs) using a water-soluble pyrene derivative (1) with a zwitterionic arm, and the feasibility of the tailored CCGs to sensitive electrochemiluminescence (ECL)-based analyses. The compound 1 serves the dual purpose of improving the dispersion of the CCGs in aqueous solutions and further tailoring the catalytic activity of the CCGs with dendrimer-encapsulated catalytic nanoparticles. As a model system, we conjugated dendrimer-encapsulated Pt nanoparticles to the 1-functionalized CCGs on indium tin oxide (ITO) electrodes. The resulting ITOs exhibited significantly increased ECL emission of the luminol/H2O2 ECL system; i.e. two orders-of-magnitude enhancement in the ECL compared to that obtained from bare ITOs, which allowed a ca. 154 times more sensitive ECL-based analysis of cholesterol using the modified ITOs compared with the use of bare ITOs.

Ionic cellulose-stabilized gold nanoparticles and their application in the catalytic reduction of 4-nitrophenol

A novel strategy for the synthesis of highly stable gold nanoparticles (GNPs) was designed by reducing HAuCl4 with NaBH4 in an aqueous solution of water-soluble ionic cellulose composed of dimethylimidazolium cations and phosphite-bound cellulose anions. NMR and UV-Vis analysis along with the measurement of the zeta potential suggest that the exceptionally high stability of GNPs originates from the strong interaction of GNPs with the phosphite groups of the ionic cellulose. The thus prepared GNPs exhibit excellent catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol, a model hydrogenation reaction.

Highly Efficient Non-Catalytic Carboxylation of Diamines to Cyclic Ureas Using 2-Pyrrolidone as a Solvent and a Promoter

Carboxylation reactions of diamines were found to proceed rapidly and non-catalytically, producing corresponding cyclic ureas in excellent yields and selectivities when 2-pyrrolidone (2-PY) was used as a solvent. A similar promoting effect with 2-PY was also observed for the carboxylation of monoamines by carbon dioxide (CO2). Most notably, the carboxylation reactions of monoand diamines conducted in 2-PY afforded 2–4 times higher yields of corresponding dialkyl ureas and cyclic ureas compared with those in Nmethyl-2-pyrrolidone (NMP). Such a dramatic promoting effect using 2-PY is believed to be associated with the multiple hydrogen bonding interactions between 2-PY and the CO2-containing species of amines. Due to such favorable interactions, carboxylation reactions seem to be more facilitated in 2-PY than in NMP.