Photocatalytic diphenhydramine degradation under different radiation sources: Kinetic studies and energetic comparison

The degradation of diphenhydramine hydrochloride (DPH) by TiO2 photocatalysis was studied under different radiation sources: UVC, black blue lamps (BLB), simulated solar radiation (SB, Solarbox) and solar radiation (CPCs, Compound Parabolic Concentrators) at lab and pilot plant scales. Results indicated that photolysis showed an important role in the DPH abatement under UVC radiation (32.5% of DPH conversion), being negligible in all other cases. Different TiO2 concentrations (0.05, 0.1 and 0.4 g/L) were used in SB device and the best results were obtained for 0.4 g/L: 35.7% of DPH conversion, after 60 min of irradiation. For comparison purposes, concentration of 0.4 g/L TiO2 was used in all the devices. The best results obtained after 60 min of irradiation using only TiO2 were 44.8% of DPH degradation in BLB and 9.0% of mineralization in SB. The addition of H2O2 improves the photocatalytic process (without H2O2) and the best results obtained were when UVC was used obtaining 100% DPH degradation and 28.6% TOC reduction. Concerning the removal efficiencies to the energy used, the best results were obtained for UVC with H2O2 (4492 mg DPH/kWh and 2246 ppm DPH/kWh), being also the corresponding cheapest costs (2.89 × 10−5 €/mg DPH and 5.79 × 10−5 €/ppm DPH). In terms of efficiency between 380 and 400 nm (absorption range for TiO2), BLB presents the best results. Kinetic constants were also estimated referred to the irradiation time (h−1) or the accumulated energy (kJ−1), the highest values correspond to UVC with hydrogen peroxide (7.64 h−1 and 0.493 kJ−1). Finally, toxicity and reaction intermediates were identified and DPH photo-degradation pathway was proposed.