Towards the detection of 2,4,6-trinitrotoluene with ionic liquid/poly(ionic liquid) membranes

In this work, we explore a range of membranes based on ionic liquids (ILs) and poly(ionic liquid)s (poly(IL)s), with varying cation/anion combinations, for the electrochemical detection of 2,4,6-trinitrotoluene (TNT) using gold thin-film electrodes. The influence of the IL anion/cation structure, as well as the incorporation of a polycation, on the TNT reduction behaviour was systematically examined through cyclic voltammetry (CV) measurements. Among the studied systems, [C₂mim][TFSI]:p[DADMA][TFSI] and [C₄mim][TFSI]:p[DADMA][TFSI], where [C₂mim]⁺ = 1-ethyl-3-methylimidazolium, [C₄mim]⁺ = 1-butyl-3-methylimidazolium, [TFSI]^- = bis(trifluoromethylsulfonyl)imide and p[DADMA]⁺ = poly(diallyldimethylammonium), demonstrated an optimal balance between excellent electrochemical performance and high mechanical integrity, maintaining quasi-reversible TNT reduction with distinct three-step cathodic features. Environmental studies under controlled oxygen (0-25 vol %) and humidity (up to 95 % RH) environments revealed that the TNT response in real conditions is dependent on the membrane composition. These results highlight how ion-pair selection and environmental conditions jointly govern the charge transport and electrochemical behaviour in IL/poly(IL) membranes, providing key design principles for electrolytes in next-generation portable explosive sensors. The analytical performance of the sensing platform was evaluated using [C₂mim][TFSI]:p[DADMA][TFSI] and [C₄mim][TFSI]:p[DADMA][TFSI] membranes employing an 'electrode surface-loaded with analyte' detection strategy in which defined masses of TNT were deposited onto the electrode via solvent evaporation prior to electrochemical measurement.