Evaluation of the use of free or supported phenalenone based on natural halloysite for phenol photodegradation in aqueous solution

Abstract

Our work has focused on evaluating the use of phenalenone (PN) for phenol photodegradation in aqueous solution. This evaluation was conducted using both free and supported (PN) on halloysite nanotubes (HNTs). The photodegradation study took place in an annular photoreactor with ultraviolet (UV) or visible irradiation, whose emission corresponded to PN absorption wavelength. The influence of operating parameters, namely pH, initial phenol and PN concentrations, light intensity, and type of irradiation (i.e. UV, visible), has been examined. Phenol photodegradation was performed in the presence of sodium azide, propan-2-ol and, lastly, nitrogen (N2) to determine the mechanism pathway. Results reveal pH as the most important parameter affecting phenol photodegradation. A complete phenol transformation could be attained within 120 min under UV irradiation and within 300 min under visible irradiation at pH 12. The PN/phenol ratio alters photodegradation kinetics, especially under UV irradiation. The photodegradation rate was higher with free PN than with a supported photosensitizer. Pseudo-first-order kinetics were observed under both UV and visible irradiation. A type II mechanism proved to be the main pathway in phenol photodegradation, with possible contribution from a type I mechanism.