CHARACTERIZATIONS OF IRON-RICH CLAY-MODIFIED ELECTRODES AND THEIR APPLICATIONS IN OPTICAL RECOGNITION

Optical recognition was studied with modified electrodes based on iron -rich clays. According to energy-dispersive X-ray spectroscopy (EDX). several clay minerals including montmorillonite K10 (mont. K10) contai n a lot of iron. Cyclic voltammetry suggested that electrochemically a ctive iron species exist in most iron-rich clays and are likely to res ide at different sites. The associated electrochemical activity is str ongly pH-dependent and photosensitive. Under UV irradiation (lambda le ss than or equal to 420 nm), these iron species were activated, and a pronounced photocurrent resulted. When these electrodes were flow-inje cted with 2-pyridylcarboxylic acids (lambda(ab, max) = 260 nm), the or iginally monotonic photocurrent could be modulated into a more recogni zable a.c. pattern and the 260 nm optical signal became distinguishabl e. The photoresponse was highly reproducible, and the response time (t (90)) was less than 10 s. (C) 1997 Elsevier Science S.A.