Matrix effects on the photocatalytical degradation of dichloroacetic acid and atrazine in water

Abstract

The effect of different organic and inorganic aqueous matrices on the photocatalytical degradation of dissolved atrazine and dichloroacetic acid (DCA) with immobilized TiO 2 was investigated. Two series of experiments were carried out at pH values around 7.1 for the degradation of atrazine and around 5.3 for the degradation of DCA. It is shown that the effects of the water constituents are completely different for the various substances and pH ranges. In pure deionized water 95% of the initial amount p = 1 mg/L of atrazine were degraded within 24 hours. Tap water as matrix led to a distinct lower degradation rate (factor 3). The single additives chloride, sulfate, phosphate, carbonate and DOC showed no decrease in the degradation rate. Especially in the case of phosphate and carbonate there was even a significant promoting effect. DEDIA, the doubly desalkylated and not dechlorinated product, occurred in higher concentrations than in the experiment without additives. In pure deionized water ρ 0 (DCA) = 1 mg/L was completely degraded within 330 min. By addition of any tested substance, organic or inorganic, the degradation rate of DCA, which is strongly dependent on the adsorption on the TiO 2 surface, decreased clearly. In the case of tap water the degradation rate decreased by a factor of 7.5. From the checked inorganic ions phosphate showed the strongest effect followed by sulfate, chloride and carbonate. Added DOC also had a significant influence on the degradation rate.