Ionic liquid/poly(ionic liquid) membranes as non-flowing, conductive materials for electrochemical gas sensing.

Ionic liquids (ILs) are highly promising, tuneable materials that have the potential to replace volatile electrolytes in amperometric gas sensors in a 'membrane-free' sensor design. However, the drawback of removing the membrane is that the liquid ILs can readily leak or flow from the sensor device when moved/agitated in different orientations. A strategy to overcome the flowing nature of ILs is to mix them with polymers to stabilise them on the surface in the form of membranes. In this research, the room temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][NTf2]), has been mixed with the poly(ionic liquid) (poly(IL), poly(diallyldimethylammonium bis(trifluoromethylsulfonyl)imide), poly[DADMA][NTf2]) to form stable membranes on miniaturised, planar electrode devices. Different mixing ratios of the IL/poly(IL) have been explored to find the optimum membrane that gives both high robustness (non-flowing material) and adequate conductivity for measuring redox currents, with the IL/poly(IL) 60/40 wt% proving to give the best responses. After assessing the blank potential windows on both platinum and gold electrodes, followed by the kinetics of the cobaltocenium/cobaltocene redox couple, the voltammetry of oxygen, sulfur dioxide and ammonia gases have been studied. Not only were the membranes highly robust and non-flowing, but the analytical responses towards the gases were excellent and highly reproducible. The presence of the poly(IL) negatively affected the sensitivity, however the electron transfer kinetics and the limit of detection were actually improved for O2 and SO2, combined with the poly(IL) experiencing less reference potential shifting. These promising results show that membranes containing conductive poly(IL)s mixed with ionic liquids could be used as new 'designer' gas sensor materials in robust membrane free amperometric gas sensor devices.

Salt-tolerance of alkyl-glyceryl ether carboxylates hydrotropes and surfactants. Dramatic effect of the methylation of the glyceryl spacer.

HYPOTHESIS: The insertion of polyether spacers between the anionic head and the alkyl chain of ionic surfactants significantly improves their salt-tolerance. The aim of this work is to study whether the petro-based polyethoxy spacer can be replaced by a glyceryl ether group for high salinity applications. EXPERIMENTS: A series of amphiphilic sodium salts of alkyl glyceryl ether carboxylates are synthesized with different alkyl chain lengths from 4 to 12 and various spacers between the glyceryl and the carboxylate groups. Their aggregation behavior is studied by tensiometry and their amphiphilicities are assessed by the PIT-slope method. The dramatic effect of the methylation of the glyceryl spacer on the salt-tolerance is highlighted, and rationalized by DFT calculations and molecular dynamics. FINDINGS: In contrast to the corresponding sodium soap, n-C6H13-CO2Na, and to the non-methylated counterpart, the sodium salt of 1-pentyl-3-methyl glyceryl ether methylene carboxylate ([5.0.1]-CH2CO2Na) exhibits an excellent salt-tolerance since it remains water-soluble with NaCl or CaCl2 concentrations greater than 20 wt% at 25 °C. Amphiphiles with short alkyl chains (

Detection of sulfur dioxide at low parts-per-million concentrations using low-cost planar electrodes with ionic liquid electrolytes.

Sulfur dioxide (SO2) is a toxic gas at low parts-per-million (ppm) concentrations, with a permissible exposure limit (PEL) of 2 ppm. Its detection is mandatory, particularly in the fields of occupational health and safety, and environmental pollution. In this work, ppm concentration detection of sulfur dioxide was performed in six room temperature ionic liquids (RTILs), as well as on two different electrode materials - platinum and gold - and with two different electrode geometries, i.e. macro thin-film electrodes (TFEs) and microarray thin-film electrodes (MATFEs). Calibration curves were established for 10-200 ppm SO2 using cyclic voltammetry to determine the optimum combination of RTIL, electrode surface and geometry for the sensing. The RTIL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonium)imide ([C4mpyrr][NTf2]) with a platinum thin-film electrode was found to give the best response due to the relatively low viscosity of the RTIL combined with the high sensitivity and a clean blank response. On MATFEs, deposited sulfur particles - confirmed using scanning electron microscopy (SEM) coupled to an energy dispersive spectrometer - were found to passivate and block some of the microholes, leading to unstable long-term chronoamperometric responses. To the best of our knowledge, this is the first observation of sulfur deposition from SO2 reduction in aprotic ionic liquids. Consecutive additions of 2 ppm SO2 were studied in [C4mpyrr][NTf2] on a TFE using long-term chronoamperometry, showing excellent reproducibility upon successive additions. This demonstrates that small volumes of RTILs can be combined with miniaturized, low-cost TFEs and applied for the reliable and continuous monitoring of sulfur dioxide gas at concentrations lower than the permissible exposure limit of 2 ppm.