(253d) Ionic Liquids and Ionic Liquid-Functionalized Carbons for Sorption of Gaseous Toxins

Highly efficient and selective adsorption systems are needed for gas masks and security-sensitive buildings to protect against exposure to warfare toxins. Ionic liquids (ILs), molten salts with melting points below 100°C composed only of anions and cations, offer an opportunity to enhance adsorption of low-concentration warfare toxins and improve selectivity compared to traditionally-used activated carbons. By tuning the IL, the properties of sorption can be controlled. ILs can be functionalized on the surface of carbons to utilize the unique sorption properties, while creating a filter-stable system. Additionally, the minimal vapor pressure of ILs will not create air quality concerns post-filtration, which is an added benefit compared to other possible chemical modifiers.

To test the feasibility of ionic liquids to capture warfare toxins, dimethyl methylphosphonate (DMMP) was used as a model simulant. Equilibrium absorption capacities for DMMP were measured in neat ILs to identify basic structure-property relationships between absorption and IL anions and cations. Imidazolium, pyridinium and cholinium-based ILs with dicyanamide and bis(trifluoromethylsulfonyl) imide anions were investigated. It was found that both the anion and cation impacted the equilibrium absorption capacity. Promising ILs were tethered to activated carbons (AC) to investigate DMMP adsorption on to AC-ILs. AC-ILs were synthesized by physical adsorption of the IL to the AC from a solvent, followed by drying under vacuum. Characterization of the AC-ILs was performed using X-ray Photoelectron Spectroscopy (XPS) and thermal analysis techniques. Adsorption of DMMP on the AC-ILs was performed to determine breakthrough and equilibrium capacities.