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

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.