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Aqueous TiO{sub 2} photocatalysis of metal-EDTA complexes
This report describes the results of experiments performed to determine the viability of titanium dioxide photocatalysis towards the treatment of water contaminated with different metal-EDTA complexes. Both the PB-EDTA and Ni-EDTA complexes were chosen for study, as they represent respectively metals that are and are not capable of photodeposition onto the TiO{sub 2} catalyst during the photoreaction. Batch reactions were carried out in a jacketed glass pot reactor using 300 ml of 50m g/l metal chelated with an equimolar amount of EDTA and 0.1wt% of TiO{sub 2} in the solution. The UV source used was a 100 W low-pressure Hg spot lamp. The two systems were studied using Degussa P-25 titanium dioxide, and Aldrich titanium dioxide loaded with Pt and Au. Around 80% removal of the Ni-EDTA complex was attained after 120 min using both catalysts with no photodeposition of Ni onto the catalyst. However, pH precipitation treatment of the reacted solutions indicated that the Ni was still complexed, probably to complexing agents that were EDTA oxidation products. Apparent zero-order kinetics was observed in the P-25 catalyst reaction, whereas apparent first-order kinetics was observed in the metal-loaded TiO{sub 2} catalyst. In contrast the Pb-EDTA complex was completely removed in 10 min using both catalysts. Also, complete Pb deposition onto the catalyst was attained in 30 min for both catalysts. The Pb deposition seemed to first require the degradation of the complex. Total organic carbon was reduced in the Ni-EDTA system 15--21% using both catalysts, and about 33% in the Pb-EDTA system using both catalysts. No reduction of either metal or metal complex was observed when no catalyst was present and the other conditions held constant.