The influence of polychromatic light on methomyl degradation in TiO₂ and ZnO aqueous suspension

Abstract

The photocatalytic degradation of the insecticide methomyl in water using TiO₂ Merck Eusolex® T (anatase) under Osram ultra-vitalux® lamp light (315–400 nm, 300 W) was studied. The effect of the operational parameters, such as initial concentration of catalyst, initial methomyl concentration, initial salt concentration (NaCl), and pH, was studied. The optimal concentration of catalyst was found to be 2.0 g/L. Using the Langmuir–Hinshelwood mechanism as a base, a pseudo-first-order kinetic model was illustrated and the adsorption equilibrium constant and the rate constant of the surface reaction were calculated (K_MT = 0.079 L/mg and k_C = 0.134 mg/L min, respectively). The photodegradation rate was higher in acidic than in alkaline conditions. The presence of Cl^– ions significantly affected the photodegradation of the pollutant. The rate of photodecomposition of methomyl was measured using UV spectroscopy and high performance liquid chromatography, while its mineralization was followed using ion chromatography and total organic carbon analysis. In addition, several photocatalysts were used: ZnO (Merck), TiO₂ P-25 (Degussa), TiO₂ Merck (anatase), and TiO₂ Merck R-706 (rutile), and were compared with TiO₂ Merck Eusolex® T (anatase).

Keywords:

• Photocatalytic degradation
• Methomyl
• Titanium dioxide
• Zinc oxide
• Water remediation

Acknowledgments

The authors are grateful to the Ministry of Education and Science of the Republic of Serbia for financial support (Project Nos. III 46008 and 172013). They also wish to thank Mr Aleksandar F. Tomaši for technical assistance. The authors wish to thank also DuPont de Nemours, USA, for their analytical standard of methomyl, received as a present.