Enhanced Hydrosaturation Selectivity and Electron Transfer for Electrocatalytic Chlorophenols Hydrogenation on Ru Sites

Boosted chlorate hydrogenation reduction via continuous atomic hydrogen

Chlorate (ClO3-) is a common toxic oxyanion pollutant from various industrial processes, and hydrogenation reduction of ClO3- by atomic hydrogen (H*) is a promising and effective method. Therefore, more efforts are needed to rationalize the design of catalytic active sites for H2 activation to boost ClO3- hydrogenation reduction. In this work, superior H2 activating capabilities were achieved for efficient ClO3- reduction on a porous graphene-based bimetallic catalyst (RuPd/PG). Edge sites and porosity structures on porous graphene promote the anchoring and confinement of Ru and Pd NPs (Nanoparticles), forming abundant Pd-Ru bonding interfaces and highly dispersed NPs. Based on DFT analysis, the ample Pd-Ru interfaces and highly dispersed Ru NPs are the main active sites, simultaneously boosting H* generation and reactant activation for rapid ClO3- reduction. The defective layer of Ru NPs on the Pd surface provides intermediates with accessibility to the inner Pd NPs, thereby avoiding ClO3- regeneration on Ru. Therefore, ClO3- hydrogenation reduction was significantly enhanced on RuPd/PG with an initial turnover frequency (TOF0) of 27.2 min-1, possessing superior robustness in recycling tests and actual water samples. Undoubtedly, this work provides new insights into H* generation and reactant activation to optimize ClO3- hydrogenation reduction applicable for water treatment.

Electronic structure modulation on PdCo bimetal for enhanced atomic hydrogen mediated electro-dehalogention of 2,4,6-trichlorophenol

Atomic hydrogen (H*)-mediated indirect electrochemical reduction has regarded as a highly effective strategy for halogenated organic pollutants (HOPs) removal in wastewater. The efficient generation and prompt utilization of H* are critical factors which directly determine the degradation performance. This study presented a new strategy for the electro-reduction of a typical HOP-2,4,6-trichlorophenol (2,4,6-TCP), achieved by modulating the electronic structure of a PdCo bimetal electrode (Pd1Co1/CP). Through characterizations and density functional theory (DFT) analysis, ZIF-67 as the Co source could effectively improve the uniform distribution of Pd and Co, which exposed more active sites for H* on-demand generation. Meanwhile, the introduction of Co atoms and the optimum of Pd/Co ratios modulated the electronic structure of Pd sites. In 120 min, 92 % 2,4,6-TCP (initial concentration 10 mg/L) was degradated with a reaction rate constant (kobs) of 0.103 min-1, which was 2.1 times higher than that of Pd/CP electrode. Lower Gibbs free energy for hydrogen adsorption (-0.477 eV) was found in Pd1Co1/CP which benefited the surface-adsorbed H* stability for enhanced utilization. The degradation pathway of 2,4,6-TCP was further studied. These findings highlight the critical role of modulating the electronic structure of the electrode to optimize the utilization of surface-adsorbed active intermediates, presenting a novel and promising approach for advancing wastewater treatment technologies.

Electrochemical reduction for chlorinated hydrocarbons contaminated groundwater remediation: Mechanisms, challenges, and perspectives

Electrochemical reduction technology is a promising method for addressing the persistent contamination of groundwater by chlorinated hydrocarbons. Current research shows that electrochemical reductive dechlorination primarily relies on direct electron transfer (DET) and active hydrogen (H⁎) mediated indirect electron transfer processes, thereby achieving efficient dechlorination and detoxification. This paper explores the influence of the molecular charge structure of chlorinated hydrocarbons, including chlorolefin, chloroalkanes, chlorinated aromatic hydrocarbons, and chloro-carboxylic acid, on reductive dechlorination from the perspective of molecular electrostatic potential and local electron affinity. It reveals the affinity characteristics of chlorinated hydrocarbon pollutants, the active dechlorination sites, and the roles of substituent groups. It also comprehensively discusses the current progress on electrochemical reductive dechlorination using metal, carbon-based, and 3D electrode catalysts, with an emphasis on the design and optimization of electrode materials and the impact of catalyst microstructure regulation on dechlorination performance. It delves into the current application status of coupling electrochemical reduction technology with biodegradation and electrochemical circulating well technology for the remediation of groundwater contaminated by chlorinated hydrocarbons. The paper discusses practical application challenges such as electron transfer, electrode corrosion, water chemistry environment, and aquifer heterogeneity. Finally, considerations are presented from the perspectives of environmental impact and sustainable application, along with a summary and analysis of potential future research directions and technological prospects.

Humic acid promotes pathway of chloronitrobenzene cathodic reduction shunting from atomic H* to direct electron transfer

Progress mechanism of humic acid (HA) interacting with chloronitrobenzenes (ClNBs) and affecting their reduction and degradation was investigated. A two-stage chamber with graphite felt as cathode and anode was constructed, and 2,4-dichloronitrobenzene (2,4-DCNB) was target pollutant. Result showed that HA increased 36.15 % of 2,4-DCNB removal efficiency at pH 5.0 after 4-h cathodic reduction, while at pH 7.0 and 10.0, it showed much less effect. Meanwhile, HA reduced cathodic H2 and atomic H* production via competing electron with H+. Combined with result of HA alleviating inhibition of tert‑butyl alcohol on 2,4-DCNB removal, it was supposed that HA shunted dominant pathway of cathodic reduction of 2,4-DCNB from atomic H* to direct electron transfer (DET). This was proved by HA increasing electron transfer efficiency (k) of 2,4-DCNB reduction from 0.50±0.01 to 0.63±0.01, which indicated rate-limiting step of 2,4-DCNB reduction changed from electron transfer (ET) to bond breaking kinetics. HA-mediated DET pathway initially reduced nitro group, followed by dechlorination, while atomic H* pathway was randomly dechlorinated and nitro reduced. The pH significantly affected agglomeration of HA and 2,4-DCNB. Molecular dynamics simulation showed that hydrogen bond and Van der Waals force dominated agglomeration of HA and 2,4-DCNB in acidic condition, while electrostatic force was main driving force in alkaline condition. Less effect of HA on 2,4-DCNB removal efficiency at high pH could be related to its reduced conductivity and weaker molecular interactions with 2,4-DCNB. This study provides comprehensive insight into role and impact of HA in remediation of ClNBs-contaminated sediment and water by (bio)electrochemical technology.

Insights into Electrochemical Nitrate Reduction to Nitrogen on Metal Catalysts for Wastewater Treatment

Electrocatalytic nitrate reduction reaction (NO3RR) to harmless nitrogen (N2) presents a viable approach for purifying NO3--contaminated wastewater, yet most current electrocatalysts predominantly produce ammonium/ammonia (NH4+/NH3) due to challenges in facilitating N-N coupling. This study focuses on identifying metal catalysts that preferentially generate N2 and elucidating the mechanistic origins of their high selectivity. Our evaluation of 16 commercially available metals reveals that only Pb, Sn, and In demonstrated substantial N2 selectivity (79.3, 70.0, and 57.0%, respectively, under conditions of 6 h electrolysis, a current density of 10 mA/cm2, and an initial NO3--N concentration of 100 mg/L), while others largely favored NH4+ production. Comprehensive experimental and theoretical analyses indicate that NH4+-selective catalysts (e.g., Co) exhibited high water activity that enhances •H coverage, thereby promoting the hydrogenation of NO3- to NH4+ through the hydrogen atom transfer mechanism. In contrast, N2-selective catalysts, with their lower water activity, promoted the formation of N-containing intermediates, which likely undergo dimerization to form N2 via the proton-coupled electron transfer mechanism. Enhancing NO3- adsorption was beneficial to improve N2 selectivity by competitively reducing •H coverage. Our findings highlight the crucial role of water activity in NO3RR performance and offer a rational design of electrocatalysts with enhanced N2 selectivity.

Efficient Electrocatalytic Hydrodechlorination and Detoxification of Chlorophenols by Palladium-Palladium Oxide Heterostructure

Electrocatalytic hydrodechlorination is a promising approach for simultaneous pollutant purification and valorization. However, the lack of electrocatalysts with high catalytic activity and selectivity limits its application. Here, we propose a palladium-palladium oxide (Pd-PdO) heterostructure for efficient electrocatalytic hydrodechlorination of recalcitrant chlorophenols and selective formation of phenol with superior Pd-mass activity (1.35 min-1 mgPd-1), which is 4.4 times of commercial Pd/C and about 10-100 times of reported Pd-based catalysts. The Pd-PdO heterostructure is stable in real water matrices and achieves selective phenol recovery (>99%) from the chlorophenol mixture and efficient detoxification along chlorophenol removal. Experimental results and computational modeling reveal that the adsorption/desorption behaviors of zerovalent Pd and PdO sites in the Pd-PdO heterostructure are optimized and a synergy is realized to promote atomic hydrogen (H*) generation, transfer, and utilization: H* is efficiently generated at zerovalent Pd sites, transferred to PdO sites, and eventually consumed in the dechlorination reaction at PdO sites. This work provides a promising strategy to realize the synergy of Pd with different valence states in the metal-metal oxide heterostructure for simultaneous decontamination, detoxification, and resource recovery from halogenated organic pollutants.

Co(PO3)2@CoP Heterojunction in CoPO/GC/NF Nanoarrays Modulate Proton Hydrogen-Promoted Electrocatalytic Hydrodechlorination

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.

Utilizing an Integrated Flow Cathode-Membrane Filtration System for Effective and Continuous Electrochemical Hydrodechlorination

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.

Copper-based electro-catalytic nitrate reduction to ammonia from water: Mechanism, preparation, and research directions

Global water bodies are increasingly imperiled by nitrate pollution, primarily originating from industrial waste, agricultural runoffs, and urban sewage. This escalating environmental crisis challenges traditional water treatment paradigms and necessitates innovative solutions. Electro-catalysis, especially utilizing copper-based catalysts, known for their efficiency, cost-effectiveness, and eco-friendliness, offer a promising avenue for the electro-catalytic reduction of nitrate to ammonia. In this review, we systematically consolidate current research on diverse copper-based catalysts, including pure Cu, Cu alloys, oxides, single-atom entities, and composites. Furthermore, we assess their catalytic performance, operational mechanisms, and future research directions to find effective, long-term solutions to water purification and ammonia synthesis. Electro-catalysis technology shows the potential in mitigating nitrate pollution and has strategic importance in sustainable environmental management. As to the application, challenges regarding complexity of the real water, the scale-up of the commerical catalysts, and the efficient collection of produced NH3 are still exist. Following reseraches of catalyst specially on long term stability and in situ mechanisms are proposed.

Aqueous Electrocatalytic Reduction as a Low‐Carbon and Green Route for Chemical Synthesis and Environmental Remediation

The green electricity‐driven electrocatalytic reduction of organic compounds in aqueous solution has merged as a sustainable and green platform for organic electrosynthesis, upcycling of chemical waste, and environmental remediation. Compared with the thermocatalytic hydrogenation process, the electrocatalytic reduction of organic compounds uses water as a proton source, which enables its operation at ambient conditions with simplified reaction schemes and significantly reduces operation cost and energy consumption. Most studies have demonstrated the development of electrocatalysts to boost the current efficiency, conversion, and product selectivity of the electrocatalytic reduction processes. Still, little attention has been paid to the mechanism (e. g., electron/proton transfer route) and related energetics behind the electrocatalytic reduction process. This Concept overviews the recent development of the electrocatalytic reduction systems for environmental remediation, pollutant upcycling, and valorization of biomass‐derived chemicals. This Concept highlights the underlying mechanisms and aims to provide instructive guidance on designing efficient and selective electrocatalytic systems.

Nanostructured electrocatalysts for organic synthetic transformations

Organic chemists have made and are still making enormous efforts toward the development of novel green catalytic synthesis. The necessity arises from the imperative of safeguarding human health and the environment, while ensuring efficient and sustainable chemical production. Within this context, electrocatalysis provides a framework for the design of new organic reactions under mild conditions. Undoubtedly, nanostructured materials are under the spotlight as the most popular and in most cases efficient platforms for advanced organic electrosynthesis. This Minireview focuses on the recent developments in the use of nanostructured electrocatalysts, highlighting the correlation between their chemical structures and resulting catalytic abilities, and pointing to future perspectives for their application in cutting-edge areas.

Size-dependent influences of nanoplastics on microbial consortium differentially inhibiting 2, 4-dichlorophenol biodegradation

Nanoplastics (NPs), as a type of newly emerging pollutant, are ubiquitous in various environmental systems, one of which is coexistence with organic pollutants in wastewater, potentially influencing the pollutants' biodegradation. A knowledge gap exists regarding the influence of microbial consortium and NPs interactions on biodegradation efficiency. In this work, a 2,4-dichlorophenol (DCP) biodegradation experiment with presence of polystyrene nanoplastics (PS-NPs) with particle sizes of 100 nm (PS100) or 20 nm (PS20) was conducted to verify that PS-NPs had noticeable inhibitory effect on DCP biodegradation in a size-dependent manner. PS100 at 10 mg/L and 100 mg/L both prolonged the microbial stagnation compared to the control without PS-NPs; PS20 exacerbated greater, with PS20 at 100 mg/L causing a noticeable 6-day lag before the start-up of rapid DCP reduction. The ROS level increased to 1.4-fold and 1.8-fold under PS100 and PS20 exposure, respectively, while the elevated LDH under PS20 exposure indicated the mechanical damage to cell membrane by smaller NPs. PS-NPs exposure also resulted in a decrease in microbial diversity and altered the niches of microbial species, e.g., they decreased the abundance of some functional bacteria such as Brevundimonas and Comamonas, while facilitated some minor members to obtain more proliferation. A microbial network with higher complexity and less competition was induced to mediate PS-NPs stress. Functional metabolism responded differentially to PS100 and PS20 exposure. Specifically, PS100 downregulated amino acid metabolism, while PS20 stimulated certain pathways in response to more severe oxidative stress. Our findings give insights into PS-NPs environmental effects concerning microflora and biological degradation.