A comparative study for the removal of imidacloprid insecticide from water by chemical-less UVC, UVC/TiO₂ and UVC/ZnO processes

Background

Chloronicotinic insecticide are a class of pesticides that are commonly used as insecticides. Among the frequently used chloronicotinic pesticide, imidacloprid (IM) was developed in 1986. The residual of this insecticide or any pesticides may have serious public health threats.

Methods

Both degradation and mineralization of the imidacloprid (IM) in aqueous solution was studied under various experimental conditions using different advanced oxidation processes namely, ultraviolet C (UVC), UVC + TiO₂, and UVC + ZnO. All the experiments were performed using a lab-scale batch photoreactor with a working volume of 100 mL equipped with low-pressure mercury vapor lamp (9 W, 18 cm long, Philips Co.), emitting UV radiation with maximum intensity at 254 nm. The possible intermediates and a reaction pathway for photocatalytic degradation of the IM were also evaluated.

Results

It was observed that under optimal condition for UVC/TiO₂ process (C₀ = 100 mg/L, pH = 7.5, t = 20 min, TiO₂ dose = 100 mg/L), IM was effectively degraded (88.15%) and followed the first order kinetics model. The degradation efficiency increased with increasing of illumination time and is more favorable in alkaline pH compared to acidic pH. Degradation of the IM in photocatalytic process was compared with photolysis showing a significant synergy effect in the case of the photocatalytic degradation process, leading at 20 min illumination time to a 36.7% increase of the IM removal efficiency in comparison to the single UVC. The GC/MS chromatograms before and after treatment confirmed the effectiveness of the UVC/TiO₂ process in simplifying the nature of IM and its conversion to more simple and degradable compounds.

Conclusion

The heterogeneous UVC/TiO₂ process was found to be an efficient chemical-less method that is appropriate for degradation of IM from aqueous phase.