Characterisation of an RuO2·xH2O colloid and evaluation of its ability to mediate the oxidation of water
Abstract
A colloid of RuO2·xH2O supported by polybrene was prepared, characterised and assessed as an O2 catalyst. Thermal analysis (t.g.a. and d.t.g.a.) of RuO2·xH2O precipitated from the colloid indicated the presence of both weakly and tightly bound water. Dynamic light scattering indicated that the coagulated colloidal particles were large (d= 825 nm) and positively charged. Transmission electron microscopy demonstrated that the colloidal particles were themselves aggregates of crystallites too small ( < 10 nm) to be clearly resolved. The colloid proved unstable towards coagulation under conditions of high electrolyte concentration ( 10–3 mol dm–3) even when the electrolyte was H2SO4. In the presence of CeIV ions the colloid did show some activity as an O2 catalyst (O2 yield = 73%) but also underwent some anodic corrosion to RuO4(27%). At low concentrations of CeIV ions (4.5 × 105 mol dm–3) and colloid ([RuO2]= 0.02–0.00125 g dm–3) the colloid appeared to mediate the oxidation of polybrene over that of water by the CeIV ions. Kinetic studies performed under these conditions and in the presence of a high constant background concentration of polybrene (0.015 g dm–3) showed the kinetics to be biphasic with an initial fast step (associated with charging of the catalyst) followed by a second step which was proportional to the concentrations of both CeIV ions and colloid. Under conditions where no extra polybrene was added to dilutions of the colloid some O2 evolution was observed (ca. 20%) and the kinetics of CeIV disappearance once again appeared biphasic, although more complicated and difficult to interpret.