Degradation kinetics of iron(III) cyanocomplexes in irradiated systems

The degradation of iron(III) cyanocomplexes in an aqueous medium under UV o r near-UV radiation was investigated both in homogeneous and heterogeneous systems. For the experiments carried out in the heterogeneous system, polyc rystalline TiO2 (anatase) was used as the photocatalyst. The influence of t he following operative parameters on the photodegradation rate was studied: (i) initial concentration of cyanocomplex; (ii) presence of oxygen in the reacting mixture; (iii) photon energy. The photodegradation of cyanocomplex es to cyanide ions occurred by means of a homogeneous photochemical process . The presence of TiO2 was found to be detrimental to the photodegradation process owing to the fact that the catalyst particles competed with cyanoco mplexes for photon absorption. In the homogeneous system cyanide ions were photochemically oxidized to cyanates only in the presence of UV radiation ( lambda=254 nm) and O-2. In the heterogeneous system the presence of TiO2 al lowed the oxidation of cyanide to cyanate via a heterogeneous photocatalyti c pathway which was predominant with respect to the homogeneous photochemic al one. A simple kinetic model is proposed for the photodegradation of cyan ocomplexes and the quantum yields and extinction coefficients for this proc ess are calculated.