Catalytic peroxygen activation by biosynthesized iron nanoparticles for enhanced degradation of Congo red dye

•Biogenic Fe NPs were synthesized using Terminalia Bellirica plant extracts.•The NPs were composed of FeO/Fe2O3 and used to generate sulfate radicals.•Congo red degradation followed the order: C-Fe-PMS > B-Fe-PMS > C-Fe-PS > B-Fe-PS.•Absence of intermediates in treated water indicated mineralization of contaminant.•Alkaline pH, low oxidant/catalyst loading negatively affected degradation kinetics.