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

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 (kav.) 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.