Dechlorination of chloroacetic acids by Pd/Fe nanoparticles: Effect of drying method on metallic activity and the parameter optimization

Two kinds of dry Pd/Fe nanoparticles (Pd/Fe-1 and Pd/Fe-2) were obtained by drying the laboratory synthesized wet Pd/Fe nanoparticles with direct oven drying method and solvent replacement oven drying method, respectively. A comparison was made between the two drying methods, concerning the effects of the washing reagents used during the drying process on the physicochemical properties and the activities of Pd/Fe nanoparticles for catalytic dechlorination of chloroacetic acids. Pd/Fe nanoparticles prepared by impregnation of iron nanoparticles with an aqueous solution of potassium hexachloropalladate were washed with different reagents (deionized water and organic solvents), followed by vacuum drying in an oven at 100 °C. The prepared dry Pd/Fe-1 and Pd/Fe-2 nanoparticles were characterized in terms of specific surface area (BET-N₂), morphology (SEM), surface elemental distribution (EDS), and particle size (TEM). The catalytic activities of Pd/Fe-1 and Pd/Fe-2 nanoparticles were evaluated via dechlorination reaction of chloroacetic acids including trichloroacetic acid (TCAA), dichloroacetic acid (DCAA), and monochloroacetic acid (MCAA). The removal efficiencies of chloroacetic acids by Pd/Fe-2 were about 58.5-22.7% greater than that achieved by Pd/Fe-1. The optimal Pd content, the amount of metal loading, and the initial pH value of reaction system for higher removal efficiency of chloroacetic acids were determined. The variation of pH value, dechlorination pathway and kinetics of chloroacetic acids were also investigated. The removal efficiencies of chloroacetic acids followed the order of TCAA > DCAA > MCAA with observed reaction rate constant (k_obs) values of 1.113 × 10^-1, 1.278 × 10^-2, and 1.900 × 10^-3 min^-1, respectively.