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The degradation of gallic acid and imidacloprid with supported Millennium PC500 and Degussa P25 Ti[O.sub.2] is reported. Ti[O.sub.2] particles were immobilized using a titanium solsolution and direct deposition on glass supports. The film characterization was done by x-ray diffraction, scanning electron microscopy, and atomic force microscopy, and degradation of organic compounds was monitored by high-performance liquid chromatography, total organic carbon analyzer, and ion chromatography. The experiments were performed under sunlight in compound parabolic collector plants with flat supports inside the glass tubes. Photocatalytic activity of the films was compared and identified. Although sol-gel coatings had better mechanical properties, mineralization was observed to be approximately five times slower than paste-deposited films. Photoactivity of the films decreased with silver deposition due to the nature of the organic compounds. The rate constants were calculated to be between 2 x [10.sup.-1] and 6 x [10.sup.-2] mg [m.sup.2]/kJ for organic compounds, and 6 X [10.sup.-2] and 6 x [10.sup.-3] for total organic carbon. [DOI: 10.1115/1.2210494] Keywords: photocatalysis, supported catalyst, silver deposition, sol-gel film

The technical feasibility and performance of photocatalytic degradation of four water-soluble pesticides (diuron, imidacloprid, formetanate and methomyl) have been studied at pilot scale in two well-defined systems which are of special interest because natural-solar UV light can be used for them: heterogeneous photocatalysis with titanium dioxide and homogeneous photocatalysis by photo-Fenton. The pilot plant is made up of compound parabolic collectors specially designed for solar photocatalytic applications. The initial concentration tested with imidacloprid, formetanate and methomyl was 50 and 30 mg/l with diuron, and the catalyst concentrations were 200 mg/l and 0.05 mM with Ti[O.sub.2] and iron, respectively. Total disappearance of the parent compounds, 90% mineralisation and toxicity reduction below the threshold (E[C.sub.50]) have been attained with all pesticides tested. All these results have contributed to an evaluation of photocatalytic treatment capacity and comments on the main parameters of Ti[O.sub.2] and Fe separation from the treated water.