Modification of electrodes with nanostructured films containing dirhodium-substituted polyoxometalates

Layer-by-layer (LBL) electrostatic assembly was used to prepare films comprising generation-4 polyamidoamine dendrimers (G4-PAMAM) and dirhodium polyoxometalates (Rh2POMs) on glassy carbon (GC) electrodes. To employ the propensity of P2Mo18O626- (PMo) to directly adsorb on glassy carbon, a new compound, Rh2PMo, was synthesized and characterized. The behavior was compared to that of a previously reported Rh2POM prepared from PW12O403- (PW). The LBL assembly of (G4-PAMAM, Rh2PW)(n) bilayers on GC pretreated by formation of a monolayer of 4-aminobenzoic acid was studied by doing a linear least-squares fit of peak current to n (n=5); the result gave an r(2) of only 0.90. With Rh2PMo, the analogous experiments with n=7 gave an r(2)=0.995. Strong adsorption of Rh2PMo onto GC allowed the assembly of Rh2PMoadsorbed|(G4-PAMAM, Rh2PMo)(n) on conventional GC and on a 10-mum carbon fiber. The latter was used to demonstrate the bifunctional electrocatalytic property of these films through reduction of nitrite and the oxidation of arsenite.