Photoassisted electrochemical incineration of selected organic compounds

The decrease in chemical oxygen demand (COD) of mildly acidic (pH 3.5) aque ous solutions of phenol, aniline, n-propanol, and acetic acid was observed to be significantly larger at PbO2(s)-coated Pt electrodes ("PbO2/Pt") in c omparison to bare Pt electrodes in a flow-through reactor. Furthermore, the rate of CO2(g) production during electrolysis of phenol solutions at PbO2/ Pt electrodes (4.6 cm(2)) also was determined to be significantly larger wh en these electrode surfaces were illuminated by a 14 W UV lamp (254 nm). Th e total amount of CO2(g) produced over a 4 h electrolysis period at an illu minated PbO2/Pt electrode in a Bow-through cell was equal to 90% of the the oretical amount, corresponding to stoichiometric conversion of the phenol t o CO2(g). Elemental analysis of the PbO2(s) films demonstrated that they we re doped slightly with iron, presumably in the Fe(III) state, i.e., Fe(III) /Pb(IV) = 0.010. Thr sourer of Fe(III) was concluded to be the stainless st eel used in construction of the flow-through electrolysis vessel. It is spe culated that the Fe(III) sites in the surfaces of the PbO2(s) films can fun ction as Lewis acid sites for adsorption of reactant molecules via nonbonde d electrons as an initial step in the anodic degradation mechanisms. The ad vantage of preadsorption of reactant molecules is thought to be the result of longer residence times for these molecules within the applied electric f ield at the electrode-solution interfacial region. The observed effect of U V illumination is speculated to be associated with absorption of the photon s within the surface of the PbO2(s) films. (C) 2001 The Electrochemical Soc iety.