Direct Electrochemical Sensing of Water‐Soluble Dyes in Hyperporous Carbon: Analyte Concentration by Micropore Absorption

Electrochemical sensing of water‐soluble small organic molecules provides a facile method for monitoring water quality in different water streams. In this report, we demonstrate the crucial role played by micropores in a highly porous carbon electrode (surface area 2543 m ² /g) in facilitating direct sensing of such water‐soluble molecules. The micropores of the electronically conductive porous carbon facilitate adsorptive pre‐concentration of the water‐soluble molecules at the pores of the electrode, in effect enhancing the effective concentration at the electrode–electrolyte interface, thus enhancing the detection limit of such soluble molecules. Moreover, as the sensing mechanism relies on direct redox reactions of the target molecules over the carbon surface, selective sensing of such materials was readily observed, with an excellent level of detection reaching down to 25–65 ppb. This is in contrast with previous reports utilizing catalytic action of several nanomaterials, mostly metal oxides, for indirect sensing of water‐soluble molecules. The versatility of this approach is outlined through electrochemical sensing of four anionic dyes, namely phenol red, eosin yellow, methyl orange, eriochrome black T, and two cationic dyes, methylene blue and malachite green.