Surfactant-intercalated clay films for electrochemical catalysis. Reduction of trichloroacetic acid

Abstract

Composite films made from insoluble dialkyldimethylammonium surfactants and clay colloids were evaluated for electrochemical catalysis. When cast on pyrolytic graphite (PG) electrodes from chloroform, the films act as charge-transfer barriers toward multivalent electroactive ions in solution. They take up ions with hydrophobic ligands, e.g. tris-(2,2'-bipyridyl)cobalt(II). To make catalytic electrodes, water-insoluble cobalt and iron phthalocyanines (CoPc and FePc) were dissolved in surfactant-clay dispersions in chloroform and cast on PG. Films containing CoPc were 35-fold more active than FePc films for catalytic reduction of trichloroacetic acid. CoPc films decreased overpotential for reduction of trichloroacetic acid by about 0.5 V compared to 0.05 V for FePc. These MPc films gave stable catalytic currents for at least 10 days. Catalytic current vs temperature plots for reduction of trichloroacetic acid showed linear branches with intersection points close to reported gel-to-liquid crystal-phase transition temperatures. Charge transport was faster in the liquid crystal than the gel phase of the films. Observation of phase transitions suggests a multibilayer structure.