Hybrid methyl green/cobalt-polyoxotungstate nanostructured films: Self-assembly, electrochemical and electrocatalytic properties

Abstract Hybrid multilayer films were prepared by alternately depositing cationic dye methyl green (MG) and anionic sandwich-type polyoxometalate K 10 [Co 4 (H 2 O) 2 (PW 9 O 34 ) 2 ] (Co(PW 9 ) 2 ) via electrostatic layer-by-layer (LbL) self-assembly method. Film build-up was monitored by UV–vis spectroscopy which showed a regular stepwise growth. X-ray photoelectron spectroscopy data confirmed the successful fabrication of the hybrid films with MG-Co(PW 9 ) 2 composition and scanning electron microscopy images revealed a completely covered surface with a non-uniform distribution of the molecular species. Electrochemical characterization of films by cyclic voltammetry revealed two tungsten-based reduction processes in the potential range between −0.9 and −0.5 V due to W VI → W V in Co(PW 9 ) 2 . Studies with the redox probes, [Fe(CN) 6 ] 3−/4− and [Ru(NH 3 ) 6 ] 3+/2+ , revealed that not only the electrostatic attractions or repulsions have effects on the kinetics of the probe reactions, but also the film thickness. Additionally, the {MG/Co(PW 9 ) 2 } n multilayer films exhibit efficient W-based electrocatalytic activity towards reduction of nitrite and iodate.