Degradation kinetics of iron(III) cyanocomplexes in irradiated systems

摘要

The degradation of iron(III) cyanocomplexes in an aqueous medium under UV or near-UV radiation was investigated both in homogeneous and heterogeneous systems. For the experiments carried out in the heterogeneous system, polycrystalline TiO2 (anatase) was used as the photocatalyst. The influence of the 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 cyanocomplexes 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 cyanocomplexes 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 allowed the oxidation of cyanide to cyanate via a heterogeneous photocatalytic pathway which was predominant with respect to the homogeneous photochemical one. A simple kinetic model is proposed for the photodegradation of cyanocomplexes and the quantum yields and extinction coefficients for this process are calculated. References: 27