Electrochemical Reduction Dehalogenation Catalyzed By Rhodium, Rhodium-Silver And Single Atom Cobalt

The electrochemical reduction dehalogenation reaction of halogenated organic compounds is one of the most important reaction types in organic electrochemistry.This reaction has important applications in organic synthesis and the treatment of environmental pollutants.In recent years,due to the large-scale production and widespread use of fluorinated organics,environmental problems caused by fluorinated organics have received widespread attention worldwide.At the same time,the use of chlorinated organic substances is gradually increasing,and it has also become a type of pollutant widely concerned by society.The toxicity of halogenated organic pollutants mainly comes from the halogen,and dehalogenation is a key step in the treatment of halogenated pollutants.Therefore,the development of an efficient and convenient electrochemical reduction dehalogenation method to convert the carbon-halogen bond(C-R)in a halogenated organic compound to a carbon-hydrogen bond(C-H)can greatly increase its biodegradability.In order to improve the defluorination method of fluorinated organic compounds and the dechlorination method of chlorinated organic compounds,the main contents are as folows:(1)We studied the defluorination performance of rhodium-modified foamed nickel(Rh/Ni)catalytic electrode for high-concentration fluorophenol.First,electrodeposition method was used to prepare Rh/Ni catalytic electrodes loaded with rhodium metal content,the surface morphology and phase composition of the electrode were characterized by field emission scanning electron microscope(SEM)and XRD;Second,We study on the effects of liquid composition and operating parameters on the electrocatalytic hydrogenation defluorination(HDF)of 4-fluorophenol(4-FP)in the aqueous solution and the defluorination reaction path of 4-FP;Finally,under optimized conditions,the feasibility and technical and economic indicators of electrocatalytic HDF of high concentration 4-FP are described.To the best of our knowledge,studies on electrocatalytic HDF treatment of high-concentration fluorinated organic pollutants have not been reported.(2)We investigated the feasibility of selective defluorination of pentafluorophenol(PFP)with a rhodium-silver bimetallic modified catalytic electrode.First,we prepared a rhodium-silver bimetallic catalytic electrode loaded with different metal contents by electrodeposition,characterized the surface morphology and phase composition of the electrode by SEM and XRD;Then we used constant current electrolysis to study the effect of silver and rhodium bimetal modified catalytic electrode on the defluorination performance of PFP;Finally,we systematically studied the feasibility of its selective defluorination.(3)We prepared a nitrogen-doped graphene anchored metal Co single atom catalyst(A-Co-NG),and used high-resolution transmission electron microscope(TEM),corrected scanning transmission electron microscope(HAADF-STEM),X-ray difffraction(XRD)and high resolution X-ray photoelectron spectroscopy(XPS)to characterize the prepared single atom catalyst,which confirmed that the catalytically active metal was indeed dispersed in the form of single atoms on the surface of the carrier.We selected chloroacetic acid(CAAs)as the model molecule,the constant current electrolysis experiment showed that A-Co-NG has excellent dechlorination performance.Combined with cyclic voltammetry(CV)and constant current electrolysis experiments,it was proved that the electrochemical reduction and dechlorination of trichloroacetic acid(TCAA)on A-Co-NG modified carbon paper electrode(A-Co-NG/CP)followed a direct dechlorination mechanism,the dechlorination path is mainly TCAA?dichloroacetic acid(DCAA)?monochloroacetic acid(MCAA)?acetic acid(AA);The order of the dechlorination process from difficult to easy is:MCAA>DCAA>TCAA.The first electron transfer of TCAA in the process of electrochemical reduction and dechlorination to DCAA and the breaking of carbon-chlorine(C-Cl)bond are carried out in steps,and the first electron transfer in this process is speed control.In the step,the product DCAA produced by reduction is further dechlorinated to produce MCAA.In this process,the first electron transfer and the breaking of the C-Cl bond occur synergistically,and the desorption of the Cl-group occurs throughout the electroreductive dechlorination process.Cl~-desorption were not rate-determining steps(RDS)during the dechlorination process.