Biogenic synthesis of Fe and NiFe nanoparticles using Terminalia bellirica extracts for water treatment applications

•Biogenic Fe and NiFe nanoparticles prepared using Terminalia bellirica extracts.•Biogenic Fe and NiFe nanoparticle sizes lower than chemically synthesized nanoparticles.•Polyphenols in the plant extract played both a reducing and capping agent role.•Cr (VI) removal and dye discoloration equal or higher with biogenic nanoparticles, when compared to chemogenic nanoparticles. In this study, we present a facile method for synthesizing biogenic B-Fe and B-NiFe nanoparticles using Terminalia bellirica extract. GC–MS analysis of the extract showed that n-hexadecanoic acid (24%) and octadecanoic acid (13.5%) were the predominant biomolecules. The as-synthesized B-Fe and B-NiFe nanoparticles were characterized using UV–Vis, FE-SEM with EDS, TEM, DLS based particle size analysis, and XRD. The surface morphology of the biogenic nanoparticles was compared to chemically synthesized Fe (C-Fe) and NiFe (C-NiFe) nanoparticles. FE-SEM and TEM images indicated that particles were nanosized, however agglomeration was observed in aqueous medium. Particle sizes using DLS method followed the order: B-Ni-Fe > B-Fe > C-Fe > C-NiFe. Fe2O3 and NiFe2O4 were the predominant crystal phases in the biogenic and chemogenic nanoparticles. The biogenic Fe and NiFe nanoparticles showed higher adsorptive capacity for Cr (VI), and faster rate kinetics for methylene blue degradation in a catalyst – peroxygen assisted oxidation process, when compared to the chemogenic nanoparticles.