ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

UV–visible-near-IR characterization of MoO₃ catalyzed photodegradation of lambda-cyhalothrin pesticide

Seth O. Osumba, John O. Adongo, and Josiah O. Omolo

Chemistry Department, Njoro Campus, Egerton University, Njoro, Kenya

E-mail: jadongo@egerton.ac.ke

Received: 22 January 2024  Accepted: 9 May 2024

Abstract:

This study investigated UV-induced photodegradation of cyhalothrin (Cy) and elucidated the photocatalytic effect of molybdenum(VI) oxide (MoO₃). Cyhalothrin was exposed to MoO₃ (in the dark): [Cy. + MoO₃-dark], to ultraviolet (UV) irradiation: [Cy + UV-irrad.], and UV irradiation in the presence of MoO₃: [Cy. + MoO₃ + UV-irrad.]. The intensity and nature of the absorption bands were monitored by time-dependent UV–vis-NIR wavelength scan spectroscopic measurements (190–1100 nm) and used to characterize photodegradation and photocatalytic activities. The kinetic analysis of the experiments: [Cy. + UV-irrad.] and [Cy. + MoO₃ + UV-irrad.] showed that the average pseudo-first-order photodegradation rate constants (k_av.) increased by a factor of between 2.27 and 2.56 in the presence of MoO₃, hence indicating photocatalytic activity_. The control experiment [Cy. + MoO₃-dark], with no UV irradiation, showed no change in the absorbance of Cy molecules over the same period. The results showed that MoO₃ exhibits optimal photocatalytic activity at typical operating conditions of UV = 254 nm, 766–775 mmHg, 273–275 K; and 1:2 molar ratio [MoO₃]:[Cy]. The photodegradation kinetic data best fitted the Boltzmann equations (R² = 099). Time-dependent near-infrared (NIR) wavelength scans characterized the formation of reactive intermediates, Mo-complexes, and by-products in the photodegradation catalytic cycles during the [Cy. + MoO₃ + UV-irrad.] experiment. These results show that MoO₃ can be used to enhance the UV photodegradation of Cy residues for environmental remediation purposes.

Graphical abstract

Keywords: Cyhalothrin; Photodegradation; Molybdenum(VI); Photocatalysis; Kinetics

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-024-03513-3

Chemical Papers 78 (9) 5683–5695 (2024)