Photocatalytic oxidation of Reactive Black 5 with UV-A LEDs

• Photocatalytic RB5 decolourization with UV-A LEDs/TiO2.
• UV-A LEDs/TiO2 attains a decolourization of 89% with 40 W/m2 and 1.0 g/L of TiO2.
• UV-A LEDs/TiO2 process reaches an EEO of only 220 kWh/m3/order.

The effectiveness of UV-A Light emitting diodes (UV-A LEDs) for decolourization of Reactive Black 5 (RB5) solutions in a continuous photoreactor and the effect of different operational parameters on the photocatalytic decolourization of RB5 were investigated in the present work. The operational parameters included catalyst load, initial dye concentration, irradiance and solution flowrate. Photocatalytic experiments were conducted in a self-designed photoreactor with a matrix of 96 UV-A LEDs (375 nm) and Evonik P-25 TiO2 was used as a photocatalyst. The optimum experimental conditions that allowed the highest decolourization of RB5 (89%) were an irradiance of 40 W/m2, 1.0 g/L of TiO2, 50 mg/L of RB5 and a flowrate of 0.8 mL/min.A continuous stirred tank reactor (CSTR) design equation, subsequently simplified to a pseudo-first order rate equation, was used to analyse the kinetics of the experimental results. From the kinetics it is possible to observe that high TiO2 concentrations (1.0 g/L) and light irradiances (40 W/m2) positively affect the reaction rate (r, 2.483 × 10−7 mol/L min) and the reaction rate constants (k, 7.351 × 10−3 min−1).The figure-of-merit electrical energy per order (EEO) was calculated for the photoreactor, and values of 220 kWh/m3/order were reached for an electric power consumption of 0.0129 kW and a solution flowrate of 4.8 × 10−6 m3/h. Results demonstrated that a UV-A LED/TiO2 process can effectively decolourize RB5 dye solutions within the selected optimum conditions.

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