TIN(IV) OXIDE GRAFTED ON A SILICA-GEL SURFACE AS A CONDUCTING SUBSTRATE BASE FOR CUPRIC HEXACYANOFERRATE

Tin(IV) oxide grafted on a silica gel surface, ( = SiO)(n)Sn(OH)4-n, was used as a conducting substrate base for cupric hexacyanoferrate electroactive species. The film adhered strongly to the surface and exhibited good chemical stability. The mid-point potential of the redox reaction ST-Cu[Fe(III)(CN)6] + M+ + e- half-arrow-right-over-half-arrow-left ST-MCu[Fe(II)(CN)6] where M = K+, NH4+, Na+, Li+ and ST denotes tin(IV) oxide substrate on silica gel surface, is related to the facility that the cation moves into and out of the film during reduction and oxidation respectively. The cyclic voltammetry waves for Li+ and Na+ were broadened, suggesting that the diffusion of these cations at the film-solution interface is hindered due to the larger hydrated ionic radii of these cations compared with those of K+ and NH4+. The symmetry of the cyclic voltammetry waves with respect to the potential axis indicated a highly reversible character of the redox reactions: I(pa)/I(pc) almost-equal-to 1, where I(pa) and I(pc) are the anodic and cathodic peak currents respectively. The film behavior was quasi-Nernstian since the slope of the straight line obtained by plotting - log (electrolyte concentration) against the mid-point potential was 46 mV per decade change of concentration of electrolyte.