Synthesis of reactive nano-Fe/Pd bimetallic system-impregnated activated carbon for the simultaneous adsorption and dechlorination of PCBs

Synthesis and use of reactive metal particles have shown significant environmental implications for the remediation of groundwater and sediment contaminated with chlorinated compounds. Herein, we have developed an effective strategy, employing a series of innovative granular activated carbon (GAC) composites incorporated with iron/palladium (Fe/Pd) bimetallic nanoparticles. The physical adsorption of polychlorinated biphenyls (PCBs) to GAC and their electrochemical dechlorination by Fe/Pd bimetal on the GAC could be simultaneously achieved. The novel synthesis approaches and targets to achieve in this study are (i) introduction of mesoporous GAC for Fe/Pd bimetal placement, (ii) in situ formation and incorporation of Fe particles in the GAC pores, (iii) modification of Fe surface with a discontinuous layer of noble metal Pd, and (iv) nanoscaling of Fe and Pd particles. Fe was imbedded in 7-40 nm mesoporous GAC via an incipient wetness impregnation method employing Fe(NO3)(3). Heat-treated GAC/Fe (as Fe2O3) at 300 degrees C was reduced to GAC/zerovalent iron (ZVI) using NaBH4 solution, and,then Pd was reductively deposited to the ZVI surface from Pd(CH3CO2)(2). The resulting GAC/ZVI/Pd had high surface area of 358 m(2)/g and pore volume of 0.352 cm(3)/g for PCBs adsorption and 14.4% Fe and 0.68% Pd contents for PCBs dechlorination. The confinement of Fe crystal growth in the mesopores of GAC resulted in small 6-12 nm Fe nanoparticles on which 2-3 nm Pd nanoislands were well-distributed. Fe and Pd particles were mechanically stable (negligible leaching) due to a strong Fe-GAC metal-support interaction during calcination and Fe-Pd corrosion cell formation during Pd deposition. The GAC/ZVI/Pd system exhibited an efficient dechlorination of 2-chlorobiphenyl (2-C1BP) at 90% after 2 days and complete adsorption of 2-C1BP remaining, and the dechlorination product, biphenyl, formed.