Kinetics and mechanisms of EDTA photocatalytic degradation with TiO2

A complete study on the photocatalytic degradation of ethylenediaminetetraa cetic acid (EDTA) over TiO2 has been initiated, to establish the influence of several parameters on the reaction rate, the nature of the intermediates and the kinetic regime. TiO2 (Degussa P25) suspensions containing EDTA at pH 3 at different concentrations were irradiated under near UV light. A Lan gmuirian behavior was observed, from which kinetic constants have been obta ined. Experiments with 5.0 mM EDTA (zero order kinetic regime) were perform ed for 3 hours irradiation under different conditions. Under N-2 bubbling, depletion of EDTA was very low. Under O-2 bubbling, the concentration of ED TA decreased around 90%. However, the corresponding decrease of TOC ranged only between 4.5% and 9%. A higher TOC reduction (22% or more) was obtained by keeping the pH constant by HClO4 addition, or by hydrogen peroxide addi tion. Addition of 0.5 mM Fe(III) caused a dramatic increase on the initial rate of EDTA depletion and approximately a 32% TOC decrease. Analysis of th e filtered solution was performed by ion chromatography and capillary elect rophoresis to monitor the disappearance of EDTA and the formation of degrad ation products after different irradiation times. So far, glycine, ethylene diamine, formic acid, ammonium, iminodiacetic acid, oxalic acid and glyoxyl ic acid have been identified.