Heterostructured Fluorohectorite Clay as an Electrochemical Sensor for the Detection of 2,4-Dichlorophenol and the Herbicide 2,4-D

A mixed-ion, amphiphilic fluorohectorite heterostructure, wherein the galleries are regularly interstratified by hydrophilic inorganic ions (Na + ) and lipophilic onium ions, is shown to be an efficient electrochemical sensor for the specific determination of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and the pollutant 2,4-dicholorophenol (2,4-DCP) when incorporated at the 5 wt % level into a carbon paste electrode (CPE). The clay-modified electrode was substantially less sentive to herbicides that lack the aromatic hydroxyl groups needed for oxidation to a quinone (e.g., Illoxan and Furore). Conventional homoionic organoclays with all galleries exclusively occupied by an onium ion surfactant exhibited a lower electrochemical response to 2,4-D and 2,4-DCP oxidation when incorporated into a CPE. Similarly, low current responses were observed for a CPE modified with a homostructured mixed-ion montmorillonite clay with both inorganic ions and organic onium ions co-occuping each clay gallery. The electrochemical response observed for the mixed-ion fluorohectorite heterostructure was attributed to the ability of this unique clay intercalate to achieve electrical neutrality upon oxidation of the dichlorophenoxy moiety through the facile ejection of sodium ions from the segregated inorganic galleries.