Carbon-chlorine Bond Research Articles

A Two-Phase Hydrogenation Membrane for Contaminants Reduction at High Hydrogen Reagent Utilization Efficiency.

Heterogeneous hydrogenation is surging as a promising strategy for selective removal of water pollutants, yet numerous efforts rely on catalyst design to advance catalytic activity. Herein, we enhanced the mass transfer and the utilization of hydrogen reagent through construction of a two-phase flow-through membrane reaction device (Pd/SiC-MR). Pd/SiC-MR displays high efficiency and selectivity toward removal of multiple pollutants. For instance, rapid (∼0.35 s) and exclusive hydrogenation (>99%) of carbon-chlorine bond in organohalogens were realized at high water flux (220 L/m2/h). More importantly, the two-phase Pd/SiC-MR reaction system achieved 31.4% utilization of hydrogen reagent, 1-3 orders of magnitude higher than those by classical slurry or fixed-bed reactor. The high hydrogenation performance is attributed to the close proximity of the hydrogen source, reactive hydrogen atom, and pollutant under high molecular collision frequency in membrane pores. Our study opens an approach for improved hydrogen reagent utilization while reserving the high pollutant removal efficiency through altering operating conditions, beyond complex material design limitations in hydrogenation water purification.

Vibrational Frequencies of Tetrachloroethylene using Lie Algebraic Framework

This study employs a sophisticated computational approach to predict tetrachloroethylene's higher overtone vibrational frequencies (C2Cl4) up to the fourth overtone. We utilize a Lie algebraic framework within the context of the vibrational Hamiltonian. The method involves replacing tetrachloroethylene's carbon-chlorine (C-Cl) bonds with unitary Lie algebras. The resulting Hamiltonian is written in terms of Casimir and Majorana's invariant operators and parameters. The derived Hamiltonian operator effectively characterizes the stretching vibrations inherent to the molecular structure. This approach enhances our understanding of the vibrational dynamics of tetrachloroethylene at higher overtones, offering valuable insights for applications in diverse scientific and technological fields.

Insights into the inhibitory effects of trichloroisocyanuric acid disinfectant on the phototransformation of polypropylene microplastics

The chemical components in the natural aquatic environment have the potential to be involved in phototransformation of microplastics (MPs). Little information is available regarding the mediation effects of artificially introduced chemicals on MP phototransformation, especially those used in aquaculture water that are vulnerable to human interference. Herein, this study investigated the phototransformation process and mechanism of polypropylene microplastic (PP MPs) in presence of trichloroisocyanuric acid (TCCA) disinfectant with unique properties unlike the conventional inorganic chlorine disinfectants. The results showed that the presence of TCCA inhibited the surface photooxidation of PP MPs. Analysis of PP MP surface and reaction filtrate indicated that the inhibitory effects were likely derived from TCCA derivatives and the weakening in promoting effect of polypropylene microplastic-derived dissolved organic matter (PP-DOM) as photolytic byproducts, with the more important role of free chlorine in initial period and that of other chlorine species (i.e., the adsorbed chloride ions (Cl−), newly formed carbon-chlorine (CCl) bonds, chlorinated cyanurates, and chlorinated products) in middle and later period. The study highlights for the first time the important role of chlorine species derived from TCCA in phototransformation process of co-existed PP MPs and proposes a previously unrecognized phototransformation pathway, which will provide a new understanding and knowledge for the environmental behavior of MPs in aquaculture environment.

Catalytic Enantioselective Nucleophilic α-Chlorination of Ketones with NaCl.

Catalytic enantioselective α-chlorination of ketones is a highly desirable process. Different from the conventional approaches that employ corrosive electrophilic chlorination reagents, the process disclosed here employs nucleophilic chloride, aqueous NaCl solution, and even seawater, as green inexpensive chlorine sources. This mechanistically distinct and electronically opposite approach provides facile access to diverse highly enantioenriched acyclic α-chloro ketones that are less straightforward by conventional approaches. With a chiral thiourea catalyst, a range of racemic α-keto sulfonium salts underwent enantioconvergent carbon-chlorine bond formation with high efficiency and excellent enantioselectivity under mild conditions. The sulfonium motif plays a crucial triple role by permitting smooth dynamic kinetic resolution to take place via a chiral anion binding mechanism in a well-designed phase-transfer system. This protocol represents a new general platform for the asymmetric nucleophilic α-functionalization of carbonyl compounds.

EVALUATION OF THE THERMAL-OXIDATIVE STABILITY OF A HALOGEN-CONTAINING PLASTICIZER-FIRE RETARDANT

The importance of assessing the indicators of thermal-oxidative stability of plasticizers that are part of polymer compositions for ensuring high performance indicators during their processing and operation of finished products is noted. When using brominated organic compounds of the aromatic series, a short burning time of polymer compositions and a significant smoldering time have been established. The use of flame retardants containing a halogen in the aliphatic radical leads to a decrease in the smoldering time and an increase in the duration of combustion due to a decrease in the thermal stability of the material at the stage of decomposition. It is indicated that bromine-containing compounds give the best inhibition effect compared to chlorine-containing compounds due to a decrease in the carbon-bromine bond breaking energy compared to the carbon-chlorine bond energy. The decomposition parameters of the brominated plasticizer-fire retardant have been established. It is shown that the thermal decomposition of the brominated plasticizer occurs in two stages, corresponding to the elimination of bromine from the aliphatic radical in the temperature range 473 K – 573 K and the decomposition of phthalic acid esters in the range 603 K – 623 K. The beginning of intensive decomposition corresponds to 443 K. The maximum of the first stage of decomposition is at the point corresponding to 501 K, the second - 606-623 K. It was noted that the bromine-free plasticizer decomposes intensively, starting from 503 K and reaches the maximum decomposition rate at 611 K. The maximum loss of the bromine-free plasticizer was established at 27%, brominated - 50.9% of the mass of the sample. It has been confirmed that the presence of bromine atoms in the plasticizer adversely affects its thermal stability. The influence of the degree of halogenation of an unsaturated plasticizer on the nature of its thermal-oxidative degradation in the temperature range corresponding to the technological parameters of processing polymeric materials at elevated temperatures of 413-443 K has been studied. It is shown that an increase in the content of bromine in the plasticizer when performing technological operations for the processing of polymer compositions in the specified temperature range and the duration of exposure to elevated temperatures within one hour does not significantly affect the mass fraction of bromine in the plasticizer. A kinetic equation for the reaction of thermal decomposition of a bromine-containing plasticizer-flame retardant of the phthalate type, accompanied by the elimination of hydrogen bromide, is proposed. The activation parameters of the hydrogen bromide evolution reaction were determined for the temperature range of maximum decomposition of a brominated phthalate plasticizer with a bromine content in the range of 5% – 25%. It is shown that the activation energy of hydrogen bromide elimination depends on the bromine content in the plasticizer and decreases by 23% with an increase in the degree of bromination. It is shown that the temperature range of maximum decomposition of the brominated fire retardant plasticizer, corresponding to 473 K – 573 K, allows using it as a secondary plasticizer for polyvinyl chloride without reducing the thermal stability of the base.

(Invited) Surface and Structural Dependent Reactivity of Alkylphosphonic Acids-Modified Titanium Oxide Nanostructures with 2-Chloroethyl Ethyl Sulfide Under Visible Light Excitation

Synthesizing novel TiO2 nanomaterials are valuable for heterogeneous reactivity to address toxic chemical remediation. Titanium oxide nanoflowers (comprising assemblies of nanorods) and nanowires have been synthesized in which photocatalytic reactivity with 2-chloroethyl ethyl sulfide (2-CEES) has been significantly enhanced under visible light (1000 nm > λ > 400 nm) excitation. Enhancement of photooxidation with reaction rates of 99 and 168 µmol/g/h (quantum yields of 5.07 x 10-4 and 8.58 x 10-4 molecules/photon) were observed for TiO2 synthesized in the presence of two different alkylphosphonic acids (C14H29PO3H2 and C9H19PO3H2). Additionally, H2Ti2O5‧H2O nanowires were synthesized and capable of highly efficient hydrolysis of the carbon-chlorine (C-Cl) bond of 2-CEES without light at a reaction rate of 279.2 µmol/g/h due to high surface area and chemical nature of the titanate structure. These observations are correlated with: 1) generation of new surface defects/states (i.e. oxygen vacancies) as a result of TiO2 grafting by alkyl phosphonic acid that may serve as reaction active sites; 2) better light absorption by assemblies of nanorods in comparison to individual nanorods, 3) surface area differences, and 4) the exclusion of OH groups due to the formation surface functionalization with alkylphosphonic acids via Ti-O-P bonds on the TiO2. These robust materials can be used for highly efficient surface decontamination.

Liquid Metal Interfacial Engineering Strategy to Synthesize All-Carbon-Linked Porous Aromatic Frameworks for the Cycloaddition of CO2 with Epoxides.

This study explores the room-temperature synthesis of porous materials and the immobilization of CO2 without the use of metals. The porous aromatic frameworks synthesized at room temperature retain the important functional group structure, and the abundance of carbon-chlorine bonds creates an excellent environment for imidazole linkage. Consequently, a catalyst conducive to the cycloaddition of carbon dioxide is obtained. Hexachloro-p-xylene is explored as the precursor, and a catalyst conducive to carbon dioxide cycloaddition is obtained. The functionalized porous aromatic frameworks (PAF-280-I/B) possess a conversion of 99.6% with a selectivity of 98.9% toward styrene carbonate (SC). The findings of this study can help mitigate the impact of greenhouse gases and enable the production of organic compounds in the circular carbonate platform, turning waste into valuable resources.

Palladium Single-Atom (In)Stability Under Aqueous Reductive Conditions.

Here, we investigate the stability and performance of single-atom Pd on TiO2 for the selective dechlorination of 4-chlorophenol. A challenge inherent to single atoms is their high surface free energy, which results in a tendency for the surface migration and aggregation of metal atoms. This work evaluates various factors affecting the stability of Pd single-atoms, including atomic dispersion, coordination environment, and substrate properties, under reductive aqueous conditions. The transition from single atoms to clusters vastly enhanced dechlorination kinetics without diminishing carbon-chlorine bond selectivity. X-ray absorption spectroscopy analysis using both in situ and ex situ conditions followed the dynamic transformation of single atoms into amorphous clusters, which consist of a unique unsaturated coordination environment and few nanometer diameter. The intricate relationship between stability and performance underscores the vital role of detailed characterization to properly determine the true active species for dehalogenation reactions.

Chlorination-Mediated π-π Stacking Enhances the Photodynamic Properties of a NIR-II Emitting Photosensitizer with Extended Conjugation.

NIR-II-emitting photosensitizers (PSs) have attracted great research interest due to their promising clinical applications in imaging-guided photodynamic therapy (PDT). However, it is still challenging to realize highly efficient PDT on NIR-II PSs. In this work, we develop a chlorination-mediated π-π organizing strategy to improve the PDT of a PS with conjugation-extended A-D-A architecture. The significant dipole moment of the carbon-chlorine bond and the strong intermolecular interactions of chlorine atoms bring on compact π-π stacking in the chlorine-substituted PS, which facilitates energy/charge transfer and promotes the photochemical reactions of PDT. Consequently, the resultant NIR-II emitting PS exhibits a leading PDT performance with a yield of reactive oxygen species higher than that of previously reported long-wavelength PSs. These findings will enlighten the future design of NIR-II emitting PSs with enhanced PDT efficiency.

In-situ surface chlorination strategy enables highly efficient metal-support catalyst toward chlorophenols pollutants degradation

Heterogeneous advanced oxidation processes (AOPs) by metal-support catalysts have been developed to water or wastewater treatment, however several critical issues hampered their real application, including aggregation and loss of catalysts, and the low mass transfer efficiency of radicals. To address these, the surface sonochemical chlorination strategy is proposed to defy the activity-stability trade-off of metal-support catalyst, taking the ZnO supported nanosilver (AgNPs) catalyst (Ag/ZnO) as model, which is controllably evolved into AgCl/Ag/ZnO heterostructure. Their sonocatalysis degradation performance and activity-stability on chlorophenols (CPs) micropollutants are demonstrated. The results show that the cleavage of organic carbon-chlorine (C-Cl) bonds leads to the in-situ generation of AgCl layer on AgNPs, and the produced AgCl/Ag/ZnO heterostructure exhibits a sustained and enhanced sonocatalytic activity for CPs removal. Specifically, AgCl/Ag/ZnO heterostructure really resists to the Ag+ release from AgNPs, and showing advantage for synergistic reduction–oxidation degradation of CPs. This work demonstrates that the in-situ surface chlorination strategy is promising to solve the activity-stability riddle of metal-support catalysts for environmental remediation.

Effect of lanthanum on thermal and mechanical properties of modified polyvinyl chloride film

Polyvinyl chloride (PVC) hybrid film containing cerium, tin and folic acid modified nano titanium dioxide is a new functional material with good compatibility, light resistance and heat resistance. In this work, the PVC hybrid film was prepared by replacing cerium with lanthanum. The hybrid film was characterized by thermogravimetric infrared spectroscopy, dynamic mechanical analysis, atomic force microscopy, x-ray photoelectron spectroscopy, scanning electron microscopy, tensile strength and thermal aging. The results show that the initial thermal stability of the hybrid film containing lanthanum is slightly higher than that of the control sample (conversion α < 1.9%). For the same gaseous component plasticizer, the peak intensity of the ester based infrared characteristic group is higher than that of the hybrid film containing lanthanum, indicating that the intermolecular force between lanthanum and plasticizer is greater than that of cerium. In the range of 350 °C–575 °C and the wave number range of 2850–3100 cm−1, the peak height of the lanthanum containing film is significantly higher than that of the control sample, which may be due to the difference of the outer layer electrons. The peak intensity of O and C atoms on the surface of the hybrid film containing lanthanum is significantly lower than that of the control sample, indicating that the surface relative concentration of lanthanum atoms is lower than that of cerium atoms. The surface roughness RMS of the hybrid film containing lanthanum is significantly lower than that of the organic tin film, which is the result of the attraction between folic acid modified TiO2, lanthanum and tin and the carbon chlorine bond in PVC. It has the function of a potential ultrafiltration membrane. In addition, the hybrid film containing 1phr lanthanum shows good energy storage modulus and low temperature resistance. The prepared hybrid film shows the characteristics of a potential multi-functional material.

Bifunctional solvent-driven hydrodechlorination of 1,2-dichlorohexafluorocyclopentene and mechanism study

The hydrodechlorination of 1,2-dichlorohexafluorocyclopentene (F6) with Zn in the mixed solvents of water and amide was taken into investigation. It was proposed that the hydrodechlorination reaction involved the following steps: (1) the reaction of Zn insertion into carbon-chlorine bond of F6 in amide; (2) the hydrolysis reaction of 2-chlorohexafluorocyclopentenyl zinc chloride with water into 1-chloro-3,3,4,4,5,5-hexafluorocyclpentene (F6E-1Cl); (3) A small amount of F6E-1Cl could undergo the above-mentioned hydrodechlorination reaction similar to F6, thereby generating 3,3,4,4,5,5-hexafluorocyclopentene (F6E). Besides, it was also found when the molecular polarity index (MPI) of the amide was greater than or equal to 11.94 kcal/mol, it was conducive to the hydrodechlorination reaction, and the conversion was close to 100%. The molecular electrostatic potential (ESP) analysis results showed that F6 was easier to hydrolyze than F6E-1Cl, which was consistent with the experimental results and was beneficial to improve the selectivity of F6E-1Cl.

Photocatalytic dechlorination of unactivated chlorocarbons including PVC using organolanthanide complexes.

Simple lanthanide cyclopentadienyl (Cp) complexes can photochemically cleave the sp3 carbon-chlorine bond of unactivated chlorinated hydrocarbons including polyvinyl chloride (PVC). The excited state lifetimes of these simple complexes are among the longest observed for cerium complexes (175 ns for [(CpMe4)2Ce(μ-Cl)]2) and the light absorption by the Cp ligand is efficient, so photocatalytic reactivity is enhanced for cerium and now also made possible for neighboring, normally photoinactive, lanthanide congeners.

Metaproteomics reveals methyltransferases implicated in dichloromethane and glycine betaine fermentation by 'Candidatus Formimonas warabiya' strain DCMF.

Dichloromethane (DCM; CH2Cl2) is a widespread pollutant with anthropogenic and natural sources. Anaerobic DCM-dechlorinating bacteria use the Wood-Ljungdahl pathway, yet dechlorination reaction mechanisms remain unclear and the enzyme(s) responsible for carbon-chlorine bond cleavage have not been definitively identified. Of the three bacterial taxa known to carry out anaerobic dechlorination of DCM, 'Candidatus Formimonas warabiya' strain DCMF is the only organism that can also ferment non-chlorinated substrates, including quaternary amines (i.e., choline and glycine betaine) and methanol. Strain DCMF is present within enrichment culture DFE, which was derived from an organochlorine-contaminated aquifer. We utilized the metabolic versatility of strain DCMF to carry out comparative metaproteomics of cultures grown with DCM or glycine betaine. This revealed differential abundance of numerous proteins, including a methyltransferase gene cluster (the mec cassette) that was significantly more abundant during DCM degradation, as well as highly conserved amongst anaerobic DCM-degrading bacteria. This lends strong support to its involvement in DCM dechlorination. A putative glycine betaine methyltransferase was also discovered, adding to the limited knowledge about the fate of this widespread osmolyte in anoxic subsurface environments. Furthermore, the metagenome of enrichment culture DFE was assembled, resulting in five high quality and two low quality draft metagenome-assembled genomes. Metaproteogenomic analysis did not reveal any genes or proteins for utilization of DCM or glycine betaine in the cohabiting bacteria, supporting the previously held idea that they persist via necromass utilization.

Electroanalytical sensing of trichloroacetic acid based on activated self-supported porous silver wire prepared by voltammetric etching with trichloroacetic acid as etchant

• Self-supporting highly active porous silver electrodes fabricated by a simple voltammetric etching method. • Increase in electrode active sites by creating a molecular imprinting-like effect during preparation. • Interfacial contact failure caused by excessive dissolution is blocked by the embedding of TCA molecules in micro-nanostructures. • The electrode exhibits good electrocatalytic activity and enables the electrochemical detection of TCA. A novel approach has been designed using trichloroacetic acid as etching molecule to prepare a highly activated self-supporting porous silver electrode for electrochemical detection of trichloroacetic acid. By analyzing the molecular structure, it contains three carbon-chlorine bonds, which can be controlled to form and break the silver-chlorine bonds. It is speculated that trichloroacetic acid molecules can be embed into micro-nano structures through Ag-Cl 3 CCOOH bonding, thus blocking the interface contact failure caused by excessive dissolution of AgCl and displaying the gate effect of imprinted trichloroacetic acid molecules. The performance of the electrochemical sensor constructed by trichloroacetic acid etching are significantly improved. Under the optimal conditions, the determination of TCA was performed with a linear range of 0.05 – 313.20 μmol·L −1 and a detection limit of 0.035 μmol·L −1 . The electrochemical sensor has good reproducibility and stability with relative standard deviations of 4.5% and 3%, respectively, and still achieve 95% of the initial current value after two weeks.

Difluoromethylation of Unactivated Alkenes Using Freon-22 through Tertiary Amine-Borane-Triggered Halogen Atom Transfer.

The application of abundant and inexpensive fluorine feedstock sources to synthesize fluorinated compounds is an appealing yet underexplored strategy. Here, we report a photocatalytic radical hydrodifluoromethylation of unactivated alkenes with an inexpensive industrial chemical, chlorodifluoromethane (ClCF2H, Freon-22). This protocol is realized by merging tertiary amine-ligated boryl radical-induced halogen atom transfer (XAT) with organophotoredox catalysis under blue light irradiation. A broad scope of readily accessible alkenes featuring a variety of functional groups and drug and natural product moieties could be selectively difluoromethylated with good efficiency in a metal-free manner. Combined experimental and computational studies suggest that the key XAT process of ClCF2H is both thermodynamically and kinetically favored over the hydrogen atom transfer pathway owing to the formation of a strong boron-chlorine (B-Cl) bond and the low-lying antibonding orbital of the carbon-chlorine (C-Cl) bond.

Liquid Na/K Alloy Interfacial Synthesis of Functional Porous Carbon at Ambient Temperature.

The functional groups in porous carbon generally suffer a severe loss during the high-temperature carbonization. Instead, the low-temperature synthesis of carbon featuring porous structures and abundant functional groups is not only a solution that evades the pitfalls of pyrolysis but also is of significance for the development of synthetic methodology. Herein, a liquid metal interfacial engineering strategy is reported for the synthesis of porous carbon using CCl4 as the carbon precursor and sodium-potassium alloy (NaK) as the reducing agent, which is superior to traditional synthetic methods because it enables the engineering of a highly active liquid metal alloy microemulsion to directly generate porous carbon at ambient temperature. As synthesized porous carbon featured abundant carbon-chlorine bonds can be tandem-grafted with imidazole and 1,2-dibromoethane to achieve a CO2 cycloaddition catalyst, which exhibits excellent catalytic activity, in addition to exceptional stability.

Kinetic isotope effects of C and N indicate different transformation mechanisms between atzA- and trzN-harboring strains in dechlorination of atrazine.

Compound-specific stable isotope analysis provides an alternative method to insight into the biotransformation mechanisms of diffuse organic pollutants in the environment, e.g., the endocrine disruptor herbicide atrazine. Biotic hydrolysis process catalyzed by chlorohydrolase AtzA and TrzN plays an important role in the detoxification of atrazine, while the catalytic mechanism of AtzA is still speculative. To investigate the catalytic mechanism of AtzA and answer whether both enzymes catalyze hydrolytic dechlorination of atrazine by the same mechanism, in this study, apparent kinetic isotope effects (AKIE) for carbon and nitrogen were observed by three atzA-harboring bacterial isolates and their membrane-free extracts. The AKIEs obtained from atzA-harboring bacterial isolates (AKIEC = 1.021 ± 0.010, AKIEN = 0.992 ± 0.003) were statistically different from that of trzN-harboring strains (AKIEC = 1.040 ± 0.006, AKIEN = 0.983 ± 0.006), confirming the different activation mechanisms of atrazine preceding to nucleophilic aromatic substitution of Cl atom in actual enzymatic reaction catalyzed by AtzA and TrzN, despite the limitation of variable dual-element isotope plots. The lower degree of normal carbon and inverse nitrogen isotope fractionation observed from atzA-harboring strains, suggesting AtzA catalyzing hydrolytic dechlorination of atrazine by coordination of Cl and one aromatic N to the Fe2+ drawing electron density from carbon-chlorine bond that facilitating the nucleophilic attack, rather than in TrzN case that protonation of aromatic N increasing nucleophilic substitution of Cl atom. This study suggests considering the potential influences of phylogenetic diversity of bacterial isolates and evolution of enzymes on the applications of CSIA method in future study.

Surface- and Structural-Dependent Reactivity of Titanium Oxide Nanostructures with 2-Chloroethyl Ethyl Sulfide under Ambient Conditions.

Robust materials capable of heterogeneous reactivity are valuable for addressing toxic chemical clean up. Synthetic manipulations for generating titanium oxide nanomaterials have been utilized to alter both photochemical (1000 nm > λ > 400 nm) and chemical heterogeneous reactivity with 2-chloroethyl ethyl sulfide (2-CEES). Synthesizing TiO2 nanomaterials in the presence of long-chain alkylphosphonic acids enhanced the visible light-driven oxidation of the thioether sulfur of 2-CEES. Photooxidation reaction rates of 99 and 168 μmol/g/h (quantum yields of 5.07 × 10-4 and 8.58 × 10-4 molecules/photon, respectively) were observed for samples made with two different alkylphosphonic acids (C14H29PO3H2 and C9H19PO3H2, respectively). These observations are correlated with (i) generation of new surface defects/states (i.e., oxygen vacancies) as a result of TiO2 grafting by alkylphosphonic acid that may serve as reaction active sites, (ii) better light absorption by assemblies of nanorods and nanowires in comparison to individual nanorods, (iii) surface area differences, and (iv) the exclusion of OH groups due to the surface functionalization with alkylphosphonic acids via Ti-O-P bonds on the TiO2. Alternatively, nanowire-form H2Ti2O5·H2O was produced and found to be capable of highly efficient hydrolysis of the carbon-chlorine (C-Cl) bond of 2-CEES in the dark with a reaction rate of 279.2 μmol/g/h due to the high surface area and chemical nature of the titanate structure.

Electrocatalytic activation of organic chlorides via direct and indirect electron transfer using atomic vacancy control of palladium-based catalyst

Electrocatalytic dehalogenation (EDH) is a promising green technology for the breakage of strong carbon-chlorine (C-Cl) bonds that have fundamental importance in organic chemistry and environmental remediation. The lack of fundamental understanding and practical issues such as potential secondary pollution, side reactions (e.g., hydrogen-evolution reaction), deficiency in catalytic activity, and/or stability have limited the adoption of EDH technology. Here, we address these problems by designing a palladium-based nanocatalyst with precise control of atomic vacancies to exploit the combination of direct and indirect EDH. Experimental and theoretical investigations show that atomic vacancies can promote electron transfer on the catalyst surface to enhance the generation/storage capacity of atomic hydrogen and to simultaneously facilitate dissociative electron transfer to C-Cl bond. Our work guides the design of atomic-vacancy-rich palladium-based electrocatalysts and provides a new strategy for efficient electro-dehalogenation in water and fundamental insights into the relationship of different dehalogenation mechanisms for accurate quantitative prediction.