ABSTRACT
Frequent occurrence of pharmaceutical compounds in aquatic environments and drinking water has raised a concern about their potential effects on environment and human health. Advanced oxidation processes (AOPs) including heterogeneous photocatalysis have proved to be one of the most effective methods for water treatment. The coupling of TiO2 and ZnFe2O4 semiconductors results in a composite having high photocatalytic activity under solar and/or visible light irradiation. Thus, ZnFe2O4-TiO2 composite was synthesized using microwave assisted combustion method. The ZnFe2O4-TiO2 composite was characterized using XRF, XRD and SEM techniques. Adsorption of acetaminophen in the dark onto the ZnFe2O4-TiO2 composite nicely fitted pseudo second-order kinetic model and the Langmuir isotherm model. The maximum adsorption capacity of the ZnFe2O4-TiO2 composite was 26.88 mgg�’1. Control experiments showed that the percentage removal of acetaminophen via adsorption in the dark, photolysis (irradiation with visible light) and photocatalysis were 35%, 4% and 88%, respectively. The kinetics of photocatalytic degradation of acetaminophen under visible light irradiation using the ZnFe2O4-TiO2 composite obeys pseudo-first order approximation of the Langmuir-Hinshelwood kinetic model. Quadratic model equations that adequately describe photocatalytic degradation and mineralization of acetaminophen were developed using RSM (response surface methodology). The significant photocatalytic process parameters were: initial concentration of acetaminophen, dosage of ZnFe2O4-TiO2 composite (photocatalyst) and irradiation time. Numerical optimization of the process parameters was carried out for photocatalytic degradation and mineralization of acetaminophen. The predicted optimum conditions for photocatalytic degradation of acetaminophen were initial acetaminophen concentration of 11.0 mg/l, photocatalyst dosage of 0.6 g/L and irradiation time of 42.0 min. The predicted optimum conditions for photocatalytic mineralization of acetaminophen were initial acetaminophen concentration of 11.2 mg/l, photocatalyst dosage of 1.0 g/L and irradiation time of 28.7 min. Under the predicted optimum conditions, photocatalytic degradation and mineralization of acetaminophen were 91.5% and 96.3% respectively. The validated experiments for photocatalytic degradation and mineralization of acetaminophen were 90.9% and 95.9 %, respectively.