| As is well known,organochlorine compounds,especially the chlorinated phenols（CPs）,have been one of the primary pollutants of water and soil resources due to their broad applications in agriculture and industry.It is generally believed that CPs are usually of high carcinogenicity,mutagenicity and toxicity,which is associated with the presence of chlorine atoms.Moreover,due to the chlorine atoms inhabiting the activity of benzene ring lyase and the stable chlorine-carbon bonds,the degradation of CPs is a strong resistant in the ecosystem.It is constantly driving research attention to detoxify the CPs in water with high efficiency and no secondary pollution.The significant advantage provided by the electroreductive dechlorination are electron donator reagent as well as second pollution free and limited consumption of electrode material compared with the common processing techniques.In order to realize the electrocatalytic dechlorination reduction process of CPs in water,the synthesis of electrocatalysts with high dechlorination activity is a key research focus and hot topic in this field.In this study,two kinds of palladium（Pd）-based ternary catalysts,phosphorus-doped palladium-nickel ternary composite nanoparticles（Pd/Ni P）and atomic vacancy modified palladium-copper-silver trimetallic defective alloy（v-Pd Cu Ag）,were prepared.The morphology,valence and other physical or chemical properties of the composites were analyzed by typical characterization techniques such as transmission electron microscopy（TEM）,field emission scanning electron microscopy（SEM）and x-ray diffractometer（XRD）,et al.And 4-chlorophenol（4-CP）was chosen as model organohalide,whose catalytic activity and dechlorination mechanism of electrocatalytic dechlorination reduction of 4-CP in water were discussed.The main research contents and related conclusions are as follows:（1）Phosphorus doped Pd Ni nanoparticles were prepared by one-pot synthesis method,which were carefully characterized by TEM,SEM and x-ray photoelectron spectroscopy（XPS）methods,showing an ultrafine particle size with diameter at 4.4±1.0 nm.Cyclic voltammetry study demonstrated this material exhibited an excellent electrochemical property with an electrochemically active surface area（ECSA）of Pd at 42.11 m2/g,which was 1.5times higher than its commercial Pd/C counterparts.Results indicated that the synergistic effect of trimetallic alloy and the compressive strain caused by the doping of Ni and P atoms markedly promoted the generation and retainment capacities of the adsorbed atomic hydrogen（H*ads）and the absorbed atomic hydrogen（H*abs）,and effectively inhibited the hydrogen evolution reaction,thereby enhancing the electrocatalytic dechlorination efficiency.A big driving force for growth for the electrocatalytic reduction dechlorination efficiency.Electrolyses of 2 mmol/L 4-CP showed that catalyzed by the Pd/Ni P nanoparticles（1.02 mg）,87.5%of 4-CP could be completely dechlorinated within 360 min with an apparent rate constant of 0.0057/min,demonstrating an excellent dechlorination performance of the developed material.（2）In this part,we established a general approach to make a defective alloy with abundant atomic vacancies,e.g.,v-Pd Cu Ag nanoparticles with an ultrasmall size of 4.1±0.8nm by using N,N-dimethylformamide（DMF）as both solvent and metaldispersant with the addition of ascorbic acid as reductant and etchant.The existence of atomic vacancies was confirmed by the aberration corrected high-resolution transmission electron microscopy（AC-HRTEM）.The v-Pd Cu Ag nanoparticles with vacancy showed excellent electrocatalytic activity and stability toward the reductive dechlorination of 4CP.Specifically,the ECSA of v-Pd Cu Ag nanoparticles was 45.88 m2/g,which is 1.81 times higher than that of Pd Cu Ag nanoparticles counterpart.Meanwhile,this catalyst showed by far the best dehalogenation performance with the highest mass activity[12.11/min/(g Pd)]and apparent rate constant（0.0097/min）.The experimental investigations showed that the atomic vacancies in v-Pd Cu Ag nanoparticles can largely promote the electron transfer on the catalyst surface to enhance the generation and storage capacity of H*species and simultaneously facilitate the dissociative electron transfer（DET）to C-Cl bond,thereby greatly boosting the electrocatalytic dehalogenation performance.（3）More importantly,both Pd/Ni P nanoparticles and v-Pd Cu Ag nanoparticles showed a remarkable electrocatalytic dechlorination activity,in which direct electron transfer and indirect atomic hydrogen mediated electron transfer simultaneously occurred during the dehalogenation process of 4-CP aqueous solution.The results of cyclic voltammetry experiments consistently showed that the two kinds of Pd-based ternary composite nanoparticles have excellent abilities to generate and store atomic hydrogen（H*）,and all three hydrogen species such as H*ads,H*abs and hydrogen molecules（H2）contributed to the indirect electrocatalytic hydrodechlorination process within a certain range.Meanwhile,voltammetric analyses showed that the electron transfer coefficients（k）were much smaller than 0.5,suggesting the DET to C-Cl bond of 4-CP following the concerted DET mechanism with the electron transfer process as the velocity control step.And both direct electrochemical reduction processes were simultaneously controlled by the combined electron transfer and substance transfer,while the diffusion control of 4-CP from the solution to the electrode surface played a dominant role in this process.In summary,this work provides the general attractive strategies to prepare Pd-based ternary nanoparticles（Pd/Ni P）,even with abundant vacancy defects Pd-based ternary nanoparticles on the exterior surface（v-Pd Cu Ag）.Moreimportantly,it paves the way for efficiently performing electroreductive dehalogenation in water and provides the steps toward the fabrication of new types of electrocatalysts for potential use in organic synthesis,environmental remediation,catalysis and mechanistic investigations. |
