Photocatalytic degradation of reactive black 5 from synthetic and real wastewater under visible light with TiO coated PET photocatalysts.

The photocatalytic removal of Reactive Black 5 (RB5) was investigated using a titanium dioxide-polyethylene terephthalate (TiO-PET) catalyst under visible (VIS) light. The sol-gel method was employed for the fabrication of the TiO-coated PET catalyst, which was then characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and elemental mapping (MAP) analysis. This study examined the reaction kinetics using the one-factor-at-a-time (OFAT) approach and evaluates the effects of various parameters, including pH (3-11), catalyst dosage (0.1-1 g L), contact time (15-120 min), RB5 concentration (10-50 mg L), hydrogen peroxide (HO) content (2-100 mM), purging gases, organic compound types, and ionic strength, on the photocatalytic removal of RB5. Under optimal conditions (pH= 3, [RB5]= 20 mg L, nanocatalyst dosage= 0.5 g L), 99.99% of the dye was removed after 120 min. Increasing the RB5 concentration (10-50 mg L) resulted in a decrease in the observed reaction rate constant (k) from 0.052 to 0.0017 min, while the calculated electrical energy per order (EEO) increased from 11.08 to 338.82 kWh m. Furthermore, the total operating cost of the light emitting diode (LED)/TiO-PET process (3 USD kg) was lower than that of other photocatalytic processes, including LED/TiO (4.73 USD kg), LED/PET (40 USD kg), and LED (63.16 USD kg). The removal of RB5 was negatively affected by the presence of HO, O and N gases, organic compounds, and ionic species. Radical quenching experiments confirmed that hydroxyl radicals (OH) were the dominant reactive species responsible for RB5 degradation. The RB5 removal efficiency using the LED/TiO-PET method (99.99%) was significantly higher than that of the LED/TiO method (63.42%). Desorption experiments demonstrated excellent catalyst stability, maintaining catalytic activity for up to five sequential cycles. GC-MS analysis identified several intermediate degradation products, including 1,2-benzenedicarboxylic acid, benzoic acid (2-amino-, methyl ester), benzene [(methylsulfonyl) methyl], phenol, 4-naphthalenedione, acetic acid, and propionic acid. Moreover, the removal efficiency in drinking water samples was approximately 63.31%, whereas for real textile wastewater samples, it reached 96.66%. Toxicity tests conducted on the final treated solutions confirmed no toxicity toward Daphnia magna, demonstrating the effectiveness of the LED/TiO-PET method in degrading both RB5 dye and its toxic by-products.