1,3-Dimethylurea Tetrabutylphosphonium Bromide Ionic Liquids for NO Efficient and Reversible Capture

To explore environmentally friendly and benign solvents to capture NO gas, a series of ionic liquids was newly synthesized by 1,3-dimethylurea and tetrabutylphosphonium bromide with different mole ratios (1:1, 2:1, and 3:1). In addition, their NO absorption and desorption properties were studied at a temperature from 30 to 70 °C and atmospheric pressure for the first time. These synthesized ionic liquids exhibited excellent reversibility and high NO solubility, such as 1.173 mol of absorbed NO/mol of ionic liquids (3:1) at 40 °C and 101.3 kPa. The solubility of NO in these synthesized ionic liquids increased with the increase of the mole ratios of 1,3-dimethylurea in ionic liquids and also with the decrease of the temperature. The studies of Fourier transform infrared spectroscopy (FTIR) and 1H and 13C nuclear magnetic resonance (NMR) spectra revealed that it is a reversible chemical process for these ionic liquids to capture NO gas; therefore, we proposed a reversible chemical absorption mechanism. These reversible and benign ionic liquids potentially offer a new opportunity to absorb NO gas.