Application of Cr-doped ZnO for photocatalytic degradation of organic pollutants from aqueous solutions

Abstract

During the water treatment process, some by-products could be produced by combining the disinfectant with the organic compounds. For example, chlorine can effectively convert humic acid derivatives to trihalomethane. Trihalomethanes are important organohalogen compounds with a hazardous effect on human health. In the present research, Cr-doped ZnO nano-photocatalyst was synthesized using a microwave-assisted solution combustion method, and its ability to degradation of trihalomethane, humic acid and fulvic acid were evaluated by an advanced oxidation process. To investigate the structural morphology and characterization of the synthesized nano-photocatalyst, field emission scanning electron microscopy, X-ray diffraction and diffuse reflectance spectroscopy analysis were used. The influence of various factors such as nano-photocatalyst dosage, pollutant initial concentration, reaction time and pH was evaluated to obtain an optimum condition for degradation. Also, isotherms, kinetic and thermodynamic studies were carried out in the optimum condition. According to the results, the removal process of fulvic acid and humic acid follows the Langmuir and Freundlich isotherm models and second-order kinetic equation. Also, the thermodynamic parameters such as entropy (> 0) and enthalpy (> 0) confirmed a higher degradation efficiency for fulvic acid in comparison with humic acid using the developed method due to less require energy. Isotherms and kinetic studies were carried out in the case of trihalomethane, and the results showed that trihalomethane photodegradation was followed the Langmuir–Hinshelwood isotherm model and more fitted by the first-order kinetic.