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Structural regulation of Pd-based electrocatalytic hydrodechlorination (EHDC) catalyst for constructing high-efficient cathode materials with low noble metal content and high atom utilization is crucial but still challenging. Herein, a support electron inductive effect of Pd-Mn/Ni foam catalyst was proposed via in-situ Mn doping to optimize the electronic structure of the Ni foam (NF), which can inductive regulation of Pd for improving the EHDC performance. The mass activity and current efficiency of Pd-Mn/NF catalyst are 2.91 and 1.34 times superior to that of Pd/NF with 2,4-dichlorophenol as model compound, respectively. The Mn-doped interlayer optimized the electronic structure of Pd by bringing the d-state closer to the Fermi level than Pd on the NF surface, which optimizied the binding of EHDC intermediates. Additionally, the Mn-doped interlayer acted as a promoter for generating H* and accelerating the EHDC reaction. This work presents a simple and effective regulation strategy for constructing high-efficient cathode catalyst for the EHDC of chlorinated organic compounds.

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Cobalt phosphide has received much attention as an efficient catalyst for electrocatalytic hydrodechlorination (EHDC). However, the active species proton hydrogen (H*) is consumed by the hydrogen evolution reaction (HER). Herein, we report a crystal regulation strategy for cobalt phosphate/graphitic nanocarbon/nickel foam (CoPO/GC/NF) catalysts applied for the EHDC of 2,4-dichlorophenoxyacetic acid (2,4-D). Characterization revealed that during the high-temperature phosphatization process, CoPO/GC/NF catalysts developed Co(PO3)2@CoP heterojunctions, enhancing charge transfer at the electrolyte-catalyst interface and water dissociation. The interaction between Co(PO3)2 and CoP induced the reconstitution of CoP into the Co-OH species, which facilitated the production of H* by accelerating the Volmer step, enhancing EHDC activity. Furthermore, Co(PO3)2 species improve the catalyst tolerance, with CoPO/GC/NF(450) maintaining over 71% yield of phenoxyacetic acid (PA) in continuous testing for up to 80 h under high-salt conditions. This work clarifies the surface transformation process of CoP/GC/NF during hydrodechlorination and demonstrates great potential for chlorophenol wastewater remediation.

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Hydrodechlorination has emerged as a promising technique for detoxifying chlorophenols (CPs) in wastewater, but it suffers from sluggish reaction kinetics and limited durability due to the lack of effective and stable catalysts. Herein, a composite filter consisting of melamine-sponge (MS), chitin fiber (CF) and ultrafine PdAu nanoparticles (PdAu/CF-MS) has been designed for continuous hydrodechlorination of CPs by using formic acid as a H-donor and sodium formate as a promoter. Benefitting from the dense active sites, rich porosity, and synergetic interaction of Pd/Au, the PdAu/CF-MS filter exhibits excellent hydrodechlorination performance (∼ 100 % conversion) towards 4-chlorophenol (1 mM, fluxes below 6100 mL·h-1·g-1) and outstanding durability (over 500 h at 61 mL·h-1·g-1), surpassing most reported counterparts (usually deactivated within 200 h or several cycles). Moreover, other CPs can also be effectively dechlorinated by the PdAu/CF-MS filter. The catalytic system proposed herein will provide a promising candidate for the detoxification of wastewater containing toxic CPs.

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Pd-based electrodes are recognized to facilitate effective electrochemical hydrodechlorination (EHDC) as a result of their superior capacity for atomic hydrogen (H*) generation. However, challenges such as electrode stability, feasibility of treating complex matrices, and high cost associated with electrode synthesis hinder the application of Pd-based electrodes for EHDC. In this work, we investigated the feasibility of degrading 2,4-dichlorophenol (2,4-DCP) by EHDC employing Pd-loaded activated carbon particles, prepared via a simple wet-impregnation method, as a flow cathode (FC) suspension. Compared to other Pd-based EHDC studies, a much lower Pd loading (0.02-0.08 mg cm-2) was used. Because of the excellent mass transfer in the FC system, almost 100% 2,4-DCP was hydrodechlorinated to phenol within 1 h. The FC system also showed excellent performance in treating complex water matrices (including hardness ion-containing wastewater and various other chlorinated organics such as 2,4-dichlorobenzoic acid and trichloroacetic acid) with a relatively low energy consumption (0.26-1.56 kW h m-3 mg-1 of 2,4-DCP compared to 0.32-7.61 kW h m-3 mg-1 of 2,4-DCP reported by other studies). The FC synthesized here was stable over 36 h of continuous operation, indicating its potential suitability for real-world applications. Employing experimental investigations and mathematical modeling, we further show that hydrodechlorination of 2,4-DCP occurs via interaction with H*, with no role of direct electron transfer and/or HO•-mediated processes in the removal of 2,4-DCP.

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The confinement effect of catalytic nanoreactors containing metal catalysts within nanometer-sized volumes has attracted significant attention for their potential to enhance reaction rate and selectivity. Nevertheless, unregulated catalyst loading, aggregation, leaching, and limited reusability remain obstacles to achieving an efficient nanoreactor. A robust and durable catalytic membrane nanoreactor prepared by incorporating palladium nanocatalysts within a 3D-continuous nanoporous covalent framework membrane is presented. The reduction of palladium precursor occurs on the pore surface within 3D nanochannels, producing ultrafine palladium nanoparticles (Pd NPs) with their number density adjustable by varying metal precursor concentrations. The precise catalyst loading enables controlling the catalytic activity of the reactor while preventing excess metal usage. The facile preparation of Pd NP-loaded free-standing membrane materials allows hydrodechlorination in both batch and continuous flow modes. In batch mode, the catalytic activity is proportional to the loaded Pd amount and membrane area, while the membrane retains its activity upon repeated use. In continuous mode, the conversion remains above 95% for over 100 h, with the reactant solution passing through a single 50 µm-thick Pd-loaded membrane. The efficient nanoporous film-type catalytic nanoreactor may find applications in catalytic reactions for small chemical devices as well as in conventional chemistry and processes.

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Palladized iron (Pd/Fe) represents one of the most common modification strategies for nanoscale zero-valent iron (nZVI). Most studies prepared Pd/Fe by reducing iron salts and depositing Pd species on the surface of pre-synthesized nZVI, which can be called the two-step method. In this study, we proposed a one-step method to obtain Pd/Fe by the concurrent formation of Fe0 and Pd0 and investigated the effects of these two methods on 4-chlorophenol (4-CP) removal, with carboxymethylcellulose (CMC) coated as a surface modifier. Results indicated that the one-step method, not only streamlined the synthesis process, but also Pd/Fe-CMCone-step, synthesized by it, exhibited a higher 4-CP removal rate (97.9%) compared to the two-step method material Pd/Fe-CMCtwo-step (82.4%). Electrochemical analyses revealed that the enhanced activity of Pd/Fe-CMCone-step was attributed to its higher electron transfer efficiency and more available reactive species, active adsorbed hydrogen species (Hads*). Detection of intermediate products demonstrated that, under the influence of Pd/Fe-CMCone-step, the main route of 4-CP was through hydrodechlorination (HDC) to form phenol and H* was the main active specie, supported by EPR tests, quenching experiments and product analysis. Additionally, the effects of initial 4-CP concentration, initial pH, O2 concentration, anions such as Cl-, SO42-, HCO3-, and humic acid (HA) were also investigated. In conclusion, the results of this study suggest that Pd/Fe-CMCone-step, synthesized through the one-step method, is a convenient and efficient nZVI-modifying material suitable for the HDC of chlorinated organic compounds.

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Efficient water dissociation to atomic hydrogen (H*) with restrained recombination of H* is crucial for improving the H* utilization for electrochemical dechlorination, but is currently limited by the lack of feasible electrodes. Herein, we developed a monolithic single-atom electrode with Co single atoms anchored on the inherent oxide layer of titanium foam (Co1-TiOx/Ti), which can efficiently dissociate water into H* and simultaneously inhibit the recombination of H*, by taking advantage of the single-atom reverse hydrogen spillover effect. Experimental and theoretical calculations demonstrated that H* could be rapidly generated on the oxide layer of titanium foam, and then overflowed to the adjacent Co single atom for the reductive dechlorination. Using chloramphenicol as a proof-of-concept verification, the resulting Co1-TiOx/Ti monolithic electrode exhibited an unprecedented performance with almost 100 % dechlorination at -1.0 V, far superior to that of traditional indirect reduction-driven commercial Pd/C (52 %) and direct reduction-driven Co1-N-C (44 %). Moreover, its dechlorination rate constant of 1.64 h-1 was 4.3 and 8.6 times more active than those of Pd/C (0.38 h-1) and Co1-N-C (0.19 h-1), respectively. Our research sheds light on the rational design of hydrogen spillover-related electrocatalysts to simultaneously improve the H* generation, transfer, and utilization for environmental and energy applications.

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PdNi nanoalloy catalysts were prepared by a carbon-promoted galvanic replacement method. Characterizations and control experiments show the increased replacement rate of metal Ni with Pd2+ ion can be attributed to the higher electrode potential and smaller crystalline sizes caused by carbon doping. Introduction of carbon (C) into Ni particles not only accelerates the formation process of PdNi nanoalloys, but also enables C atoms to successfully enter the lattice interstices of PdNi nanoalloys. C regulates the surface electronic properties of PdNi nanoalloys by the electron transfer between different elements and improves their activity. The PdNi@C-650 exhibits extraordinary activity and long-term stability for hydrogenation reduction of hexavalent chromium (Cr (VI)) and hydrodechlorination of chlorophenols in comparison with PdNi/CNTs (carbon nanotubes) and commercial Pd/C. Density functional theory calculations together with investigations of mechanism reveal that the high electron-deficient PdNi nanoalloys from the redistribution of electron between Ni, Pd and C of the PdNi@C-650 promote the surface adsorption of substrate molecules and H2, which accordingly enhances the hydrogenation activity. This study brings a new method for the design and preparation of high active noble metal nanoalloy.

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Polychlorinated biphenyls (PCBs) is a group of persistent organic pollutants that still requires remediation and reduction long after the production is discontinued. Aroclor 1232 is a commercial PCB mixture that has been much less studied. To address this void, this paper presented catalytic hydro-dechlorination (HDC) of Aroclor 1232 using palladium on activated carbon (Pd/AC) at atmospheric pressure. Experimental variables studied including three mild temperatures, 22.5 °C, 50 °C, and 80 °C, and four different co-catalyst loadings. This batch of Aroclor 1232 constituted of more than 83% of mono-, di-, and tri-, chlorinated biphenyls (CB), in addition to biphenyl, tetra- and penta CBs. HDC efficiency increased with temperature, and reached 99.9% within 4 h of reaction at 80 °C. HDC efficiency also increased with co-catalyst loading. HDC efficiencies followed the trend of para > meta > ortho positions among isomers. The increase of temperature and Et3N dosage are especially effective in dechlorination at ortho and meta positions. The apparent activation energy of Aroclor 1232 HDC was estimated as 25.57 kJ/mol based on pseudo-first order assumption, indicating that the reaction may be diffusion limited. Given the modest reaction conditions used, the HDC of Aroclor 1232 can potentially be a low-cost process.

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Electrocatalytic hydrogenation is acknowledged as a promising strategy for chlorophenol dechlorination. However, the widely used Pd catalysts exhibit drawbacks, such as high costs and low selectivity for phenol hydrosaturation. Herein, we demonstrate the potential and mechanism of Ru in serving as a Pd substitute using 2,4,6-trichlorophenol (TCP) as a model pollutant. Up to 99.8% TCP removal efficiency and 99% selectivity to cyclohexanol, a value-added compound with an extremely low toxicity, were achieved on the Ru electrode. In contrast, only 66% of TCP was removed on the Pd electrode, with almost no hydrosaturation selectivity. The superiority of Ru over Pd was especially noteworthy in alkaline conditions or the presence of interfering species such as S2-. The theoretical simulation demonstrates that Ru possesses a hydrodechlorination energy barrier of 0.72 eV, which is comparable to that on Pd. Meanwhile, hydrosaturation requires an activation energy of 0.69 eV on Ru, which is much lower than that on Pd (0.92 eV). The main reaction mechanism on Ru is direct electron transfer, which is distinct from that on Pd (indirect pathway via atomic hydrogen, H*). This work thereby provides new insights into designing cost-effective electrocatalysts for halogenated phenol detoxification and resource recovery.

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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.

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The effect of ionic liquids on the separation of chlorinated anionic dyes such as Mordant Blue 9 (MB9) or Acid Yellow 17 (AY17) via ion exchange has been investigated in model aqueous solutions that simulate wastewater from the textile dyeing industry. The effect of ionic liquids chemical nature on the separation efficiency of mentioned dyes has been compared. It was found that especially ionic liquid based on quaternary ammonium salts comprising two or three long alkyl chains bound to the quaternary ammonium nitrogen (typically benzalkonium chloride or Aliquat 336) are very effective for the separation of both studied MB9 and AY17 from aqueous solution. In addition, the innovative technique has been developed for the reactivation of spent ionic liquids which is based on the chemical reduction of the formed ion pairs using NaBH4/NiSO4, NaBH4/Na2S2O5 or Raney Al-Ni alloy/NaOH. Thus, only NaBH4/NiSO4 in co-action with Al-Ni alloy enables both effective reduction of the azo bond and subsequent hydrodechlorination of emerging chlorinated aromatic amines. The efficiency of tested dyes separation or regeneration of ion pairs was evaluated by determination of the absorbance at wavelength of the maximum absorbance, of the Chemical Oxidation Demand (COD), and of the Adsorbables Organically bound Halogens (AOX). The formation of ion pairs or products of reduction and hydrodechlorination of these ion pairs has been studied using the 1H NMR and LC-MS techniques.

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The application of electrochemical hydrodechlorination has been impeded due to the low utilization and activity of Pd catalyst. Herein, a series of Pd catalysts were prepared via the controllable evolution of Zn state during the pyrolysis of ZIF-8 nanosheet. Various forms of Pd with different chemical surroundings were generated upon the combined use of galvanic displacement and ion exchange process. Electrocatalytic hydrodechlorination of 4-chlorophenol was performed and the electrocatalytic hydrodechlorination efficiency of Pd/CN reaches 100% within 3 h at extra low Pd concentration. The coexistence of zero-valent Pd (Pd0) and nitrogen coordinated Pd (Pd-N) was verified by XAFS which provide multiple active sites for focusing on adsorbing H* and cracking C-Cl respectively. The synergetic effect between different chemical state of Pd for efficient hydrodechlorination of chloroaromatics and scheme for dexterous preparation of Pd based electrocatalyst are proposed and discussed.

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Photocatalytic hydrodechlorination (HDC) is a promising method for eliminating chlorinated organic compounds (COCs) from water, but it requires catalysts with excellent water activation ability. Defect engineering is a feasible way to enhance the catalytic performance of photocatalysts by improving light adsorption, charge carrier dynamics, and surface reactions. Herein, a well-designed 0D/2D S-scheme heterojunction with favorable band structures and defective interfaces was constructed via defect tailoring on TiO2 quantum dots (QDs) and the interface structure. The optimized catalyst Ni-TiO2-x/g-C3N4 with 1% Ni doping after thermal treatment at 300 °C under nitrogen resulted in superior visible-light-driven activity in trichloroethylene (TCE) photocatalytic HDC, approximately an 18.2-fold increase as compared with g-C3N4. Ni doping and thermal-induced oxygen vacancies were verified to synergistically endow the catalyst with improved visible-light absorption efficiency, ameliorated charge separation and migration, and enhanced redox potential. Experimental and theoretical results showed that the synergy of multifold defects in promoting visible-light harvesting was mainly due to the characteristic multiple midgap states, in terms of different intermediate energy levels and narrowed bandgap. Furthermore, the contradicting effects of midgap states on photogenerated charge carrier dynamics were mediated by the defective S-scheme heterojunction, where the detrimental charge recombination relating to excessive defects was considerably inhibited via superior spatial charge separation and promoted surface redox reactions. The design of defect-engineered heterojunctions and the role of controlled defects in adjusting band structures provide valuable insights for creating highly efficient artificial photosystems in the visible region.

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The upgrading of wasted chloroform in hydrodechlorination for the production of olefins such as ethylene and propylene is studied by employing four catalysts (PdCl/CNT, PdCl/CNF, PdN/CNT, and PdN/CNF) prepared by different precursors (PdCl2 and Pd(NO3)2) supported on carbon nanotubes (CNT) or carbon nanofibers (CNF). TEM and EXAFS-XANES results confirm that Pd nanoparticle size increases in the order: PdCl/CNT < PdCl/CNF âˆ¼ PdN/CNT < PdN/CNF, descending the electron density of Pd nanoparticles in the same order. It illustrates that PdCl-based catalysts show donation of electrons from support to Pd nanoparticles, which is not observed in PdN-based catalysts. Moreover, this effect is more evident in CNT. The smallest and well-dispersed Pd nanoparticles (NPs) on PdCl/CNT with high electron density favor an excellent and stable activity and a remarkable selectivity to olefins. In contrast, the other three catalysts show lower selectivity to olefins and lower activities which suffer strong deactivation due to the formation of Pd carbides on their larger Pd nanoparticles with lower electron density, compared to PdCl/CNT.

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Degradation of Chlorine-containing disinfection by-products(Cl-DBPs) on surface by electrocatalytic hydrodechlorination (EHDC) is considered a promising advanced water treatment method. Cl-DBPs have ecological toxicity and health risks so that it is urgent to degrade DBPs. We designed and verified the degradation performance of the EHDC of 18 kinds of DBPs (TAAs, TANs, TALs, TNMs, TAcAms, THMs) with different substituents led by the Ti3C2X2(X = O/OH) system by the first-principles. On the surface of Ti3C2(OH)2, DBPs react with atomic hydrogen (*H) by a direct-indirect continuous reduction mechanism to eliminate the Cl atom in turn. Dissociative adsorption of DBPs on the surface of Ti3C2(OH)2 simultaneously realizes the first electron transfer step and forms H vacancy, which makes its electrocatalytic activity superior to that of Ti3C2O2. Removing the six types of DBPs only needs to add -0.1 V of applied potential. In addition, we investigated the impact of substituents and chlorination degree on the reactivity of DBPs removal. The strong electron-withdrawing group is more conducive to the dechlorination reaction. Dehalogenation is much favorable in thermodynamics as the increase in chlorination degree. This study provides important insights and efficient catalysts for the degradation of DBPs and shows the potential of MXenes in eliminating chloride in water.

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Hydrodechlorination (HDC) is a reaction that involves the use of hydrogen to cleave the C-Cl bond in chlorinated organic compounds such as chlorophenols and chlorobenzenes, thus reducing their toxicity. In this study, a palladium (Pd) catalyst, which is widely used for HDC due to its advantageous physical and chemical properties, was immobilized on alumina (Pd/Al) and graphene-based materials (graphene oxide and reduced graphene oxide; Pd/GO and Pd/rGO, respectively) to induce the HDC of 4-chlorophenol (4-CP). The effects of the catalyst dosage, initial 4-CP concentration, and pH on 4-CP removal were evaluated. We observed that 4-CP was removed very rapidly when the HDC reaction was induced by Pd/GO and Pd/rGO. The granulation of Pd/rGO using sand was also investigated as a way to facilitate the separation of the catalyst from the treated aqueous solution after use, which is to improve practicality and effectiveness of the use of Pd catalysts with graphene-based support materials in an HDC system. The granulated catalyst (Pd/rGOSC) was employed in a column to induce HDC in a continuous flow reaction, leading to the successful removal of most 4-CP after 48 h. The reaction mechanisms were also determined based on the oxidation state of Pd, which was observed using X-ray photoelectron spectroscopy. Based on the results as a whole, the proposed granulated catalyst has the potential to greatly enhance the practical applicability of HDC for water purification.

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Chlorinated nitroaromatic antibiotic chloramphenicol (CAP) is a persistent pollutant that is widely present in environments. A H2 transfer membrane biofilm reactor (H2-MBfR) and short-term batch tests were setup to investigate the co-removal of CAP and NO3-. Results showed that the presence of CAP (<10 mg L-1) has no effect on the denitrification process while 100% removal efficiency of CAP can be obtained when nitrate was absent. Nitroaromatic reduction and completely dechlorination were successfully realized when CAP was removed. The CAP transformation product p-aminobenzoic acid (PABA) was detected and batch tests revealed that the hydroxy carboxylation was far faster than nitroaromatic reduction when p-nitrobenzyl alcohol (PNBOH) was conversed to p-aminobenzoic acid (PABA). The path way of CAP degradation was proposed based on the intermediate's analysis. Microbial community analysis indicated that Pleomorphomonadaceae accounts for the dechlorination of CAP.

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Soil contamination by PCBs is still known as a serious problem across the world, and the development of new technologies or the improvement of existing ones (e.g. higher efficiency, shorter processing time, lower input energy) are more and more important. Moreover, understanding the chemistry of the entire process, from a mechanistic point of view, can accelerate the process of improvement. In these circumstances, we attempted a clarification of the highly efficient degradation of PCBs by nano-sized particle of metallic Ca in CaO ("nCa") at 250 °C in dry solid state conditions. The reaction involved the hydrodechlorination, simple reduction, reductive coupling and hydroxylation processes. The detoxification efficiency reached over 99%. A tentative pathway and mechanism is proposed for explaining the final reactions products. Finally, the process was applied to real PCBs-contaminated soil, containing various amounts of PCBs, with a total success in completely eliminating the toxic polychlorinated compounds.

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Chlorine- and nitrogen-containing carbon nanofibers (CNFs) were obtained by combined catalytic pyrolysis of trichloroethylene (C2HCl3) and acetonitrile (CH3CN). Their efficiency in the adsorption of 1,2-dichlorobenzene (1,2-DCB) from water has been studied. The synthesis of CNFs was carried out over self-dispersing nickel catalyst at 600 °C. The produced CNFs possess a well-defined segmented structure, high specific surface area (~300 m2/g) and high porosity (0.5-0.7 cm3/g). The addition of CH3CN into the reaction mixture allows the introduction of nitrogen into the CNF structure and increases the volume of mesopores. As a result, the capacity of CNF towards adsorption of 1,2-DCB from its aqueous solution increased from 0.41 to 0.57 cm3/g. Regardless of the presence of N, the CNF samples exhibited a degree of 1,2-DCB adsorption from water-organic emulsion exceeding 90%. The adsorption process was shown to be well described by the Dubinin-Astakhov equation. The regeneration of the used CNF adsorbent through liquid-phase hydrodechlorination was also investigated. For this purpose, Pd nanoparticles (1.5 wt%) were deposited on the CNF surface to form the adsorbent with catalytic function. The presence of palladium was found to have a slight effect on the adsorption capacity of CNF. Further regeneration of the adsorbent-catalyst via hydrodechlorination of adsorbed 1,2-DCB was completed within 1 h with 100% conversion. The repeated use of regenerated adsorbent-catalysts for purification of solutions after the first cycle of adsorption ensures almost complete removal of 1,2-DCB.