Improvement Of Electrochemical Reductive Dechlorination Of 2,4-dichlorophenoxyacetic Acid Using Palladium Catalysts Prepared By A Pulsed Electrodeposition Method

2,4-dichlorophenoxyacetic acid(2,4-D)is a typicalchlorinated organic compounds(COCs)with strong biological activity.It is often used asinhibitor of cereal crop,turfgrass,and broadleaf weeds in prairie.But it has caused serious harm because of their resistance to degradation,tendency towards bioaccumulation and biomagnification throughout the food web,and potential toxicity to humans and the soil or water ecosystems ecosystem.It is of great scientific significance and application to study the dechlorination behavior of 2,4-D in situ remediation of surface or groundwater.In this paper,a nickel-foam,supporting palladium particles(PE-Pd/foam-Ni),was fabricated by pulsed electrodeposition.Different techniques including field emission scanning electron microscopy(FE-SEM),transmission electron microscopy(TEM),X-rayphotoelectron spectroscopy(XPS),X-ray diffraction(XRD),energy dispersive Brunauer-Emmett-Teller(BET)and rough factor(RF)were used for the characterization of PE-Pd/foam-Ni.The PE-Pd/foam-Ni was proven to be a promising electrode for electro-catalytic reductive dechlorination of 2,4-dichlorophenoxyacetic acid(2,4-D)in aqueous solution.Compared to the traditional chemical deposition of palladium on a foam-nickel electrode,the PE-Pd/foam-Ni exhibits markedly improved removal efficiency and current efficiency(CE)for the dechlorination of 2,4-D.Pd/foam-Ni prepared by traditional chemical deposition(CD-Pd/foam-Ni)with 20.31 mg Pd loading get a maximum 2,4-D removal efficiency of 79% and a CE of 10% after 3 h at a current density of 1.5 mA cm-2.As contrast to CD-Pd/foam-Ni,PE-Pd/foam-Niwith 0.67 mg Pd loading could achieve a maximum 2,4-D removal efficiency of 98% and a CE of 14% after 3 h at the same current density.Moreover,the PE-Pd/foam-Ni maintained stable performance throughout three successive recyclability tests,the main reason is the pulsed electrodeposition could avid drop of Pd catalyst..As supported by physical-chemical characterization,the palladium catalysts originated from pulse electrodeposition possess a higher percentage of exposed {111} facets and a higher number of low-coordinated(edge/corner)sites,associated with a smaller particle size,in comparison with catalysts obtained from chemical deposition.Since the palladium atoms located on the edge/corner sites facilitate the catalytic reaction and the exposed {111} facets favor the generation and stabilization of chemisorbed active hydrogen,the enhanced electrocatalytic dechlorination performance of PE-Pd/foam-Ni electrode can be ascribed to the improved intrinsic properties of the Pd catalyst.