Palladium nanoparticles for catalytic reduction of Cr(VI) using formic acid

Cr(VI), a leading contaminant in most hazardous waste sites, is acutely toxic, a proven mutagen and a carcinogen whereas Cr(III) is believed to be an essential element. We describe a one-pot synthesis and characterization of palladium nanoparticles (PdNPs) using transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and 13C nuclear magnetic resonance (NMR). The resulting PdNPs were used as catalyst to demonstrate a new concept for the reduction of Cr(VI) to Cr(III) using formic acid as a reducing agent. Percentage decrease in the concentration of Cr(VI) as a function of time was monitored using UV/vis spectroscopy at a fixed wavelength of 350 nm. Results showed that the reduction follows first-order reaction kinetics with respect to initial concentrations of Cr(VI) and HCOOH. The leveling off in reaction rate with respect to PdNPs loading confirms the importance of surface reaction as the rate-controlling step. The rate of Cr(VI) reduction was found to be dependent on temperature, pH, amount of PdNPs and formic acid concentrations, with the optimum at 45 °C under acidic conditions. For every 0.1 M increment in formic acid concentration, there was a corresponding 18.4% enhancement in the reduction rate. Consequently, it took 5 min for the PdNPs to catalyze the reduction of a 7.14 mM concentration of Cr(VI) at 99.8% efficiency. Subsequent practical application in environmental samples indicates a complete elimination of Cr(VI) from the tested soil and aqueous media.