Photocatalytic degradation of a widely used insecticide Thiamethoxam in aqueous suspension of TiO2: Adsorption, kinetics, product analysis and toxicity assessment

• TiO2 P25 is a more efficient photocatalyst than UV100 & PC500 for degradation of Thiamethoxam.
• Low H2O2 dosages enhance degradation whereas overdose retards it.
• Toxicity of Thiamethoxam decreases with the increase in irradiation time.
• Eight intermediate products have been identified using GC–MS analysis technique.

This paper deals with the study of photocatalyzed degradation of an insecticide, Thiamethoxam in aqueous suspension of TiO2. The adsorption of Thiamethoxam on TiO2 surface under dark conditions was also investigated in order to find out equilibrium adsorption constant. The degradation kinetics was studied using spectrophotometric method under various conditions such as substrate concentration, type of catalyst, catalyst dosage, pH, and in the presence of electron acceptors such as hydrogen peroxide, potassium bromate, and ammonium persulphate under continuous purging of atmospheric oxygen, and the degradation rates were found to be strongly influenced by these parameters. The results manifested that the photocatalysis of Thiamethoxam follows pseudo-first-order kinetics. The toxicity assessments of the irradiated samples were carried out using human erythrocytes as a model system under in vitro conditions. GC–MS study showed the formation of several intermediate products which were characterised based on their molecular mass and mass fragmentation pattern. A probable mechanism for the formation of various products formed during the photocatalytic process of Thiamethoxam was also proposed.

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