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

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 (k(bio) = 6.37 mmol s(−1) m(−2)) and Cr(VI) adsorption constant (K(Cr(VI),bio) = 3.11 × 10(−2) L mmol(−1)) of Bio-PdNPs being higher than the rate constant (k(chem) = 3.83 mmol s(−1) m(−2)) and Cr(VI) adsorption constant (K(Cr(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 K(Cr(III),chem) = 52.9 L mmol(−1) as compared to the one for Bio-PdNPs of K(Cr(III),bio) = 2.76 L mmol(−1).