Catalytic efficiency of laterite-based FeNPs for the mineralization of mixture of herbicides in water

In this work, low cost, locally available laterite-based iron nanoparticles were synthesized using Tectona Grandis extract (Teak extract) with an average size of 75 nm. The synthesized FeNPs were applied as a heterogeneous Fenton catalyst for the oxidation of mixture herbicides, namely ametryn, dicamba and 2,4-D in water. The FeNPs were characterized for various analytical methods (field emission scanning electron microscopy-X-ray energy-dispersive spectrophotometer, XRD, FTIR and BET) and the effect of different variables (FeNPs dosage, H₂O₂, pH) was studied using the responses surface methodology. The initial herbicide concentration was considered as 25, 3.5 and 94 mg L⁻¹ for 2,4-D, ametryn and dicamba, respectively, with the COD value of 172 mg L⁻¹. The 100% degradation and mineralization was achieved in 135 min and >85% in 45 min (optimum dosage: FeNPs = 25.29 mg L⁻¹, H₂O₂= 430 mg L⁻¹ and pH = 5). The degradation kinetics were performed for both pseudo-first order and second order, it was observed that first-order kinetics (R²> 0.85) was well fitted in the treatment process. Recycling of FeNPs in five cycles was performed at optimum conditions and 10–40% of reduction in degradation efficiency was achieved. Finally, the whole treatment process was validated with a contour overlay plot and analysis of variance.