Removal of Cr(VI) from aqueous solutions via reduction and absorption by green synthesized iron nanoparticles

Iron-based nanoparticles (Fe-NPs) were successfully green synthesized using eucalyptus leaf extracts. Subsequently Fe-NPs were used to remove Cr(VI) from aqueous solution under varying experimental conditions, including temperature, pH, initial Cr(VI) concentration and Fe-NPs loading. Under optimal experimental conditions, 84.6% of total chromium and 98.6% of Cr(VI) were removed. The removal efficiency of Cr(VI) was still relatively high (55.7%) even after reusing the material four times. Nanoparticles were characterized using a range of techniques such as DLS, EDS, FTIR, SEM and XRD both before and after interaction with Cr. This characterization revealed the existence of chromium and its oxide or complex on the surface of Fe-NPs, indicating that adsorption of Cr(VI) was occurring and a mechanism of Cr(VI) removal was proposed. Batch experiments revealed that the reduction kinetics followed a pseudo-second order rate model whereas adsorption was best fitted to the Langmuir model (R2 = 0.999) with qm = 20.5 mg g−1 and b = 3.6 L mg−1.