Photochemical degradation of triazineherbicides – comparison of homogeneous and heterogeneous photocatalysis

Abstract

Photochemical degradation of atrazine under different conditions was studied and compared, namely degradation via photocatalysis on TiO₂, UV C photolysis, and homogeneous photocatalysis in the presence of added ferric ions. The reaction rate constants in heterogeneous photocatalytic reactions on TiO₂ and of photolytic degradation by means of UV C light are similar, 0.018 min⁻¹ and 0.020 min⁻¹, respectively. The reaction rate constants in homogeneous photocatalytic reactions with Fe(III) added depend strongly on the Fe(III) concentration, 0.0017 min⁻¹ for 1.6 × 10⁻⁶ mol l⁻¹ Fe(III) to 0.105 min⁻¹ for 3.3 × 10⁻⁴ mol l⁻¹ Fe(III). In all types of reactions, dechlorination was observed; in homogeneous photocatalytic reactions and in UV C (250–300 nm) photolysis, dechlorination proceeds with a 1 : 1 stoichiometry to atrazine degradation, in photocatalytic reactions on TiO₂, dechlorination measured as chloride ion release reaches only 1/5 of the substrate degradation. In photocatalytic reactions on TiO₂, mineralisation of 40% carbon was observed.