Influence of environmental factors on the electrocatalytic dechlorination of 2,4-dichlorophenoxyacetic acid on nTiN doped Pd/Ni foam electrode

In this study, nanosized titanium nitride (nTiN) doped palladium/nickel (Pd/Ni) foam electrodes were prepared via electroless deposition method for the dechlorination of 2,4-dichlorophenoxyacetic acid (2,4-D). Characterization analyses including field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM) revealed that nTiN was successfully doped onto the electrode surface. 2,4-D was first dechlorinated to intermediate products p-chlorophenoxyacetic acid (p-CPA) or o-chlorophenoxyacetic acid (o-CPA) and then to the final product, phenoxyacetic acid (PA). The effects of environmental factors including initial 2,4-D concentration, current density, reaction temperature and dissolved anions were also studied. High initial 2,4-D concentration increased the efficient utilization of active hydrogen atom [H] by nTiN doped Pd/Ni foam electrodes. Increases in current density promoted better dechlorination efficiency while the hydrogen evolution side reaction was undesirably increased, leading to a lower average current efficiency. Higher reaction temperature was proved to be favorable for the enhancement of dechlorination efficiency. NO3− and reduced sulfur compounds including S2− and SO32− showed negative impacts on Pd catalytic capability, whereas CO32− and Cl− exhibited less adverse effects on dechlorination efficiency. The activation energy (Ea) value of 2,4-D dechlorination by nTiN doped Pd/Ni foam electrode was calculated to be 32.06 kJ mol−1. Two typical stages namely electrode activation and efficient dechlorination procedures occurred in 2,4-D dechlorination by nTiN doped Pd/Ni foam electrodes. The reaction paths of [H] on the electrode were also summarized. The removal efficiency of 2,4-D dechlorination on nTiN doped Pd/Ni foam electrodes was observed to slightly decrease from 100% to 89.95% after 5 consecutive experiments.