Comparative analysis of biological versus chemical synthesis of palladium nanoparticles for catalysis of chromium (VI) reduction

Abstract

The discharge of hexavalent chromium [Cr(VI)] from several anthropogenic activities leads to environmental pollution. In this study, we explore a simple yet cost effective method for the synthesis of palladium (Pd) nanoparticles for the treatment of Cr(VI). The presence of elemental Pd [Pd(0)] was confirmed by scanning electron microscope (SEM), electron dispersive spectroscopy and X-ray diffraction (XRD). We show here that the biologically synthesized nanoparticles (Bio-PdNPs) exhibit improved catalytic reduction of Cr(VI) due to their size being smaller and also being highly dispersed as compared to chemically synthesized nanoparticles (Chem-PdNPs). The Langmuir–Hinshelwood mechanism was successfully used to model the kinetics. Using this model, the Bio-PdNPs were shown to perform better than Chem-PdNPs due to the rate constant (kbio = 6.37 mmol s−1 m−2) and Cr(VI) adsorption constant (KCr(VI),bio = 3.11 × 10−2 L mmol−1) of Bio-PdNPs being higher than the rate constant (kchem = 3.83 mmol s−1 m−2) and Cr(VI) adsorption constant (KCr(VI),chem = 1.14 × 10−2 L mmol−1) of Chem-PdNPs. In addition, product inhibition by trivalent chromium [Cr(III)] was high in Chem-PdNPs as indicated by the high adsorption constant of Cr(III) in Chem-PdNPs of KCr(III),chem = 52.9 L mmol−1 as compared to the one for Bio-PdNPs of KCr(III),bio = 2.76 L mmol−1.