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.
Highlights
Subscripts an Anode Bio-PdNP Biologically synthesized palladium nanoparticle cat Cathode Cr(VI) Hexavalent chromium Cr(III) Trivalent chromium exp Experimental HCOO− Formate o Initial Chem-PdNP Chemically synthesized palladium nanoparticle react Reactor sim Simulation
The synthesis of the nanoparticles for experiments with and without microbial cells at both acidic and basic conditions resulted in low Pd(II) removal (Fig. 1a)
Since this study shows that microbial cells can serve as stabilizing agents due to the Bio-PdNPs being less aggregated, it means that the microbial cells can be used as a substitute to the costly stabilizing agents that are utilized during the synthesis of nanoparticles
Summary
Subscripts an Anode Bio-PdNP Biologically synthesized palladium nanoparticle cat Cathode Cr(VI) Hexavalent chromium Cr(III) Trivalent chromium exp Experimental HCOO− Formate o Initial Chem-PdNP Chemically synthesized palladium nanoparticle react Reactor sim Simulation. Other previously synthesized nanoparticles for catalytic Cr(VI) reduction included silver (Ag)[13], magnetic iron oxide ( Fe3O4)[14] and palladium (Pd) n anoparticles[15] Among those synthesized catalysts, Pd has been explored extensively due to its high selectivity and activity in the oxidation of smaller organic compounds such as formate and lactate[16]. Pd has been explored extensively due to its high selectivity and activity in the oxidation of smaller organic compounds such as formate and lactate[16] The latter method is more favorable as it uses lower cost electron donors and is exempt from Cr(VI) toxicity at higher loading than a purely biological Cr(VI) r eduction[15]
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