Photocatalytic discolouration of Reactive Black 5 by UV-A LEDs and solar radiation

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Rodríguez Chueca,J
José Ramiro Fernandes
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One of the most important disadvantages of photocatalytic treatments is the high cost associated with the use of UV lamps. In this work, the efficiency of two UV-A LEDs (ultraviolet-a light emitting diodes) photosystems as a low cost alternative to conventional UV lamps was tested. The efficiency of the two UV-A LEDs photosystems was compared to that of the most economical UV source - solar radiation. To this end, the oxidative discolouration of Reactive Black 5 (RB5) aqueous solutions was studied using photocatalysis with different concentrations of TiO2 (0.5-1 g/L) and H2O2 (1.76, 4.41, 8.82 and 17.64 mM), exposed to different radiation sources: UV-A LEDs and solar radiation. The use of H2O2 increased the discolouration rate of RB5; however, an excessive dosage reduced the yield of the treatment, and the best results were attained with a concentration of 8.82 mM of H2O2. Strong differences were observed between the use of UV-A LEDs (23 W/m2) and solar radiation. In both cases total discolouration was observed, but the discolouration rate was considerably higher with solar radiation. However, the use of a more powerful UV-A LED photo-system (85 W/m2) allowed the achievement of higher discolouration rates (k = 0.284 min-1) than those obtained with solar radiation (k = 0.189 min-1) using only 0.5 g/L of TiO2. Therefore, UV-A LED radiation is a serious alternative to conventional UV lamps, since they are ecofriendly, have a low operational cost and high energy efficiency. © 2015 Elsevier Ltd.