Monoethanolamine-enabled electrochemical detection of H2S in a hydroxyl-functionalized ionic liquid

There is much interest in developing electrochemical sensors for H2S detection using room temperature ionic liquids as electrolytes. To this end, this study compared the electrochemical behavior at a Pt-microdisk electrode of H2S in [Bmim]BF4, [C3OHmim]BF4, and MEA-[C3OHmim]BF4 (1:6.2 M ratio) using cyclic voltammetry. In both [Bmim]BF4 and [C3OHmim]BF4, the electrochemical oxidation/reduction of H2S requires too high/low a potential (about 1.5/− 1.6 V vs. Ag/Ag+), and these ionic liquids are therefore unsuitable for H2S detection. Addition of monoethanolamine (MEA) to [C3OHmim]BF4 significantly increases the H2S absorption capacity through the chemical reaction between MEA and H2S. This chemical absorption enhances the electrochemical response of H2S, in particular generating electroactive HS− ions that lead to an additional and independent anodic peak at around − 0.4 V vs Ag/Ag+ which is suitable for H2S sensing. There is a good linear relationship between the peak current and H2S content in the tested range (60-210 ppm). Moreover, electroactive ambient gases such as CO2 and SO2 show no response at the potentials of HS− oxidation, so do not interfere with H2S detection. Our findings reveal a new kind of ionic liquid electrolyte for the detection of H2S gas with high sensitivity and selectivity.