Bioelectrochemical systems (BESs) enable simultaneous wastewater treatment and energy/resource recovery by coupling microorganisms with electrodes. However, sluggish extracellular electron transfer (EET) at the biotic-electrode interface, remains a major bottleneck limiting power output, startup, and long-term stability. This review summarizes the current mechanistic understanding of direct and mediated EET pathways and translates these insights into interface design principles. With primary emphasis on anodic interfaces, we discuss three complementary engineering strategies: structural engineering to construct hierarchical porous architectures for biofilm accommodation and mass transport; chemical modification to regulate conductivity, redox properties, and catalytic sites; and surface functionalization to optimize wettability, charge, microbial adhesion, and interfacial contact. We further compare electrochemical and system-level metrics used to evaluate modified electrodes and relate performance gains to specific interfacial bottlenecks across different BES configurations. Finally, we outline future priorities, including standardized evaluation, mixed-community systems, multiscale design, and integration with synthetic biology and advanced materials. This review provides a mechanism-guided framework for designing high-performance microbial electrodes for sustainable energy and environmental applications.

Hematite, a predominant iron oxide in tropical and subtropical soils and sediments, plays a pivotal role in regulating the biogeochemical cycling of contaminants and nutrients. Its reactivity varies substantially with crystallographic facets; however, the facet-dependent mechanisms underlying sulfidation, a representative surface-mediated process in anaerobic settings (e.g., paddy fields, mangroves, and tidal flats), remain poorly understood. Here, we synthesized hematite nanoparticles with dominant (001), (110), and (214) faces (denoted HNP, HNR, and HBI) and probed their sulfidation pathways under anoxic conditions. Combining aqueous chemistry with surface/bulk characterization, we show that despite identical final sulfidation products, the underlying mechanisms differ markedly among facets. HNP consumed dissolved S(-II) 14-19 times faster than HNR and HBI, due to its undulating and rugged morphology and a higher free-corrosion potential that provides abundant reactive hydroxyl sites and promotes electron uptake. In contrast, HNR and HBI show rapid initial pyrite formation via the ferric-hydroxide-surface (FHS) pathway but suffer from passivation by dense FeSx layers, limiting long-term conversion. HNP sustains reactivity through continuous ferrihydrite regeneration and the absence of a passivation layer, achieving the highest overall hematite conversion (similar to 63% vs. similar to 41%-42%) and pyrite production (similar to 24% vs. similar to 18%-21%). These findings challenge the simplistic view that high-energy facets always dominate reactivity, highlighting instead the importance of defect-mediated surface chemistry and longterm sustainability. This study has implications for importance in predicting iron-sulfur interactions and the bioavailability and mobility of associated elements in redox-fluctuating environments.

The valorization of industrial iron-rich sewage sludge into biochar catalyst (BC) for Fenton-like reaction presents a sustainable route for both safe sludge disposal and resource recovery. Hitherto, proof-of-concept studies have been performed upon recycling sludge-derived Fe-rich BC for decontamination of waste streams from the identical industry. To further specify the construction of functionally tailored sludge BC for eliminating recalcitrant electron-rich pollutant, we report the subtle exogenous nitridation-regulated preparation of Fe-S-N co-doped textile dyeing sludge BC for catalyzing nonradical oxidation purpose. Albeit the negligible endogenous N, exogenous nitridation regulates the interfacial structure of N-doped sludge-derived biochar (NBC) by introducing extra sites (FexN and conjugated N) and optimizing physicochemical properties (e.g. similar to 1.4-fold higher surface area, similar to 1.3-fold higher defective degree of carbon). Such NBC achieves similar to 2.4-fold higher apparent rate constant and similar to 1.3-fold higher oxidation capacity of electron-rich aniline (AN, characteristic pollutant in textile dyeing wastewater), as compared to pristine counterpart. Active species trapping, electron paramagnetic resonance, and fluorescent probe elucidate the predominant contribution of O-1(2) (similar to 74.6 %) and electron-transfer process (similar to 15.1 %) in AN oxidation, which heavily relies on surface-activated PDS (PDS* complex). A Pearson correlation analysis screens FexN and defective carbon near conjugated N as core active centers, and surface equivalent to Fe(II) and S-2(2-) as subcritical sites. This dual nonradical oxidation-dominant framework enables the biodegradability enhancement of electron-rich phenol, 2,4-dichlorophenol, rhodamine B, and tetracycline. Overall, the findings from this work not only displays environmental interests in industrial sludge valorization, but also offers insights for sustainable development-oriented wastewater treatment.

Per- and polyfluoroalkyl substances (PFAS) pose a major challenge to global water security due to their persistence, low environmental concentrations, structural diversity, amphiphilic nature, and high mobility. Recent advances in electrically assisted processes (EAPs) have demonstrated great promise for enhancing PFAS treatment; however, current understanding of these processes remains fragmented and poorly elucidated. This review provides a critical synthesis of EAPs, involving non-destructive (electrosorption and electrocoagulation) and destructive (electrochemical oxidation and reduction) processes for removal of diverse PFAS. We systematically evaluate their removal performance, kinetics, and energy consumption, emphasizing the governing influences of electrode materials, PFAS molecular structures, water matrices, and operating parameters. For non-destructive processes, electrosorption primarily utilizing carbonized electrodes, redox-copolymer electrodes, or MXene electrodes achieves excellent PFAS removal capacity (the maximum value: 1.7 × 103 mg/g), but generally lower than electrocoagulation (the maximum value: 3.6 × 103 mg/g). For destructive processes, electrochemical oxidation (ECO) mainly using Ti4O7 or boron-doped diamond anodes remains dominant, with performance dependent upon electrode materials, PFAS molecular structure, applied bias, degradation intermediates, water matrices, all of which have been discussed in detail. Further comparative analysis reveals that the EAPs outperforms non-electrically assisted processes in terms of regeneration, energy consumption, and removal performance, and the energy consumption for electrosorption is far lower than that for ECO (by 1–4 orders of magnitude). This review establishes a science-based framework for selecting optimal EAPs according to treatment objectives, water characteristics, and target PFAS species. Finally, we identify key challenges and propose future directions to enhance selectivity, stability, and process integration, advancing the rational design of next-generation EAPs for PFAS treatment.

Exogenous ferrous ion dosing allows depassivation of aged zerovalent iron (ZVI) for industrial wastewater treatment, while sustaining the persistent existence of Fe(II) species for continuous depassivation throughout decontamination remains challenging. To tackle this dilemma, pre-oxidized microscale ZVI (poZVI(bm)) is proposed via ball milling with peroxydisulfate (PDS) solids, for tailoring an "continuous self-driven depassivation" scenario with Fe-0/Fe(II) symbiosis. The poZVI(bm) exhibits a 4.4 similar to 19.0 times higher equilibrated adsorption capacity for hexavalent chromium (Cr(VI)) than the referenced ball milled ZVI (ZVI(bm)) and other benchmarked mZVI composites (e.g. oxalated ZVI(bm), sulfidized ZVI(bm), and nanoscale ZVI), following a chemisorption-reduction process. It also demonstrates a 4.5 similar to 18.7 folds faster surface area-normalized removal rate for nitrobenzene (NB) than all these counterparts, mediated by reductive transformation. Cr(VI) removal and NB reduction depend on the dissolved and surface-sorbed Fe(II), respectively, which can be optimized by regulating pre-oxidation degree of poZVI(bm). The "continuous self-driven depassivation" of poZVI(bm) starts with the local microenvironment acidification due to the adsorption of abundant dissolvable Fe(II) over surface-located Fe(III), which drives continuous dissolution of Fe-0 core to create more reactive Fe(II), and therefore repeats the above procedure. Owing to wide pH adaptability (pH 3 similar to 9) and impressive corrosion behavior of poZVI(bm), these findings inspire the intimate integration of Fe-0/Fe(II) component for high-efficient remediation of multicomponent industrial wastewater.

Nanocatalysts-catalyzed heterogeneous advanced oxidation process offers a promising option for decentralized wastewater treatment, whereas free reactive oxygen species (ROS) suffer from ultrashort lifetime and self-quenching effect. Herein, bimetallic CoFe-layered double hydroxide nanorods are synthesized over three-dimensional conductive nickel foam (CoFe-LDHs/NF) to achieve high proportion of surface-localized ROS by peroxymonosulfate (PMS) activation. The Fe incorporation motivates electron redistribution of Co-Fe dual metal sites in stoichiometrically-optimized Co2Fe1-LDHs/NF, and promotes the binding affinity of Co sites for surface complexed PMS and ROS. The introduced Fe2+/Fe3+ couple also facilitates Co2+/Co3+ redox cycle for PMS activation. The monolithic Co2Fe1-LDHs/NF catalyst demonstrates 20 % enhancement in catalytic efficiency than pure Co3-LDHs/NF for sulfisoxazole oxidation. Additionally, it exhibits 1.45 to 7.47-fold higher apparent rate constant than Co3-LDHs/NF for benzoic acid oxidation with extending premixing period of catalyst and PMS (from 0 to 15 min), largely attributed to 64.9 % surface-localized ROS. Electron paramagnetic resonance, radical scavenging test, and probe experiment validate surface-localized SO4- as predominant key species. A continuous flow-through Co2Fe1-LDHs/NF catalytic system achieves >85 % BA removal over 900 min via single-pass operation, with electro-assisted regeneration at appropriate bias voltage. The proposed strategy provides new insights on designing oriented near-surface oxidation mode for long-term stable decontamination.

Although the worldwide spike in the production of dyeing sludge offers a tantalizing resource to be harnessed, effective waste-to-wealth strategies remain elusive due to its intricate toxic organic matter and metallic elements. Here, we developed a temperature-rebuilding strategy to transform discarded dyeing sludge into an iron-based catalyst with favorable charge transfer for the highly efficient and sustainable Fenton-like catalytic degradation of ppm-level contaminants in wash-tank water. Using X-ray diffraction, X-ray photoelectron spectroscopy, and synchrotron X-ray absorption spectroscopy, we could precisely track and identify the gradual formation of inherent sites (i.e., Fe2(SO4)3, FeOOH, and Fe1-xS) towards active sites (i.e., FeS and Fe0) at crystal, surface, and atomic levels. Benefiting from the reconstruction of iron sites, BC-800 effectively decomposed peroxymonosulfate into multiple radicals and nonradicals through electronic structure modulation, which enabled nearly 100 % degradation and over 60 % mineralization rate of common aromatic compounds within 30 min via ring-opening and dechlorination/substitution pathways. More delightedly, the BC-800 maintained excellent Fenton-like activity across a broad pH or multiple anions coexisted, and its device allowed extended parachlorophenol degradation for over 1 d. This work proposes a feasible "waste control by waste" approach to the reutilization of dyeing sludge, encouraging a potential solution for sustainable wastewater treatment.

Fe-based metal organic frameworks (Fe MOFs) offer a promising opportunity to drive chemical oxidation for efficient organic pollutant degradation, but conventional MOFs synthesis consumes analytical grade reagents, while crystalline MOFs lacks enough active sites. Here we report a low-crystalline MIL-101(Fe) based on terephthalic acid-enriched waste textile white mud (denoted as MIL-101(Fe)-W) that can activate H2O2 to proceed Fenton-like reaction with satisfactory center dot OH production and wide pH range (4 similar to 10). Specifically, the low level of impurities (e.g. ethylene alcohol and undecomposed oligoesters) within textile white mud endows MIL-101(Fe)-W with plentiful coordinatively unsaturated Fe-II/Fe-III centers (Fe-II/Fe-III CUCs). MIL-101(Fe)-W triggers a 'two-stage' heterogeneous Fenton-like reaction, where the release of numerous protons due to surface complexation between Fe-II/Fe-III CUCs and H2O2 in the sluggish stage boosts the subsequent rapid oxidation stage. Towards the removal of biorefractory 4-chlorophenol (4-CP), MIL-101(Fe)-W not only demonstrates 2.5-fold higher apparent rate constant than that of MIL-101(Fe) reference, but also outcompetes benchmarked Fe-based catalysts and homogeneous Fenton reaction. Active species identification, surface acidity analysis, and electrochemical techniques confirm the formation of enhanced surface H2O2 complex over MIL-101(Fe)-W, which results in the strengthened center dot OH-induced oxidation. Importantly, this novel catalyst exhibits favorable reusability and resistance to coexisting components within actual wastewater matrix for 4-CP removal. This work provides a proof-of-concept design on efficient valorization of typical industrial solid waste to high-performance MOFs catalyst, which gives a good example on rational design of waste-derived environmental functional materials for sustainable wastewater treatment.

Upcycling iron-rich industrial sludge into Fe-enriched biochar for triggering Fenton-like reaction is proposed as a 'waste control by waste' idea. However, the structure-activity relationship between biochar and its decontamination performance remains largely unclear. Herein, with primary sludge (from a textile dyeing industry) derived biochar (PSDB) as a representative, we unveil that the activation of H2O2 (6 mM) by PSDB (1 g L-1) for 4-chlorophenol (4-CP) removal highly depends on the iron speciation and carbon phase. With rising pyrolysis temperature, Fe minerals in PSDB undergo valence change from amorphous tri- and divalent Fe oxides (PSDB-400) to crystalline Fe3O4 (PSDB-600), Fe0 (PSDB-800), and partially evolve to iron phosphide and sulfide (PSDB-1000). Correspondingly, aliphatic labile fraction and dissolved carbon phase in PSDB-400 evolve into aromatic stable fraction and undissolved phase in PSDB-1000, as suggested by 83.5% reduction in dissolved organic carbon, and 50.1% increase in aromatic carbon proportion. PSDB-400/PSDB-600 tends to degrade 4-CP by leached Fe2+mediated homogeneous Fenton reaction, while PSDB-800/PSDB-1000 achieves rapid 4-CP adsorption and subsequent oxidation through homogeneous/heterogeneous H2O2 activation. Reusability test confirms the potential of PSDB-400 as sustaining Fe2+ donors for H2O2 activation, and the robustness of PSDB-1000 for multiple adsorption-oxidation cycles. This study provides guidance on designing sludge-derived engineered biochar for wastewater purification.

Carbon-based adsorbents used to remove recalcitrant water contaminants, including perfluoroalkyl substances (PFAS), are often regenerated using energy-intensive treatments that can form harmful byproducts. We explore mechanisms for sorbent regeneration using hydrated electrons (e(aq) -) from sulfite ultraviolet photolysis (UV/sulfite) in water. We studied the UV/sulfite treatment on three carbon-based sorbents with varying material properties: granular activated carbon (GAC), carbon nanotubes (CNTs), and polyethylenimine-modified lignin (lignin). Reaction rates and defluorination of dissolved and adsorbed model perfluorocarboxylic acids (PFCAs), perfluorooctanoic acid (PFOA) and perfluorobutanoic acid (PFBA), were measured. Monochloroacetic acid (MCAA) was employed to empirically quantify e(aq) - formation rates in heterogeneous suspensions. Results show that dissolved PFCAs react rapidly compared to adsorbed ones. Carbon particles in solution decreased aqueous reaction rates by inducing light attenuation, e(aq) - scavenging, and sulfite consumption. The magnitude of these effects depended on adsorbent properties and surface chemistry. GAC lowered PFOA destruction due to strong adsorption. CNT and lignin suspensions decreased e(aq )- formation rates by attenuating light. Lignin showed high e(aq) - quenching, likely due to its oxygenated functional groups. These results indicate that desorbing PFAS and separating the adsorbent before initiating PFAS degradation reactions will be the best engineering approach for adsorbent regeneration using UV/sulfite.

To address the increasingly severe oil spill accidents and water contamination, the development of super-wetting membranes with high oil/water separation efficiency is in great demand but remains challenging. The critical challenge lies in the rational design and fabrication of robust rough surface with hierarchical micro/nano-structure. In this study, biomimetic super-wetting polyacrylonitrile composite membrane was developed through in-situ synthesis and synchronous integration of zeolitic imidazolate framework nanoleaves (ZIF-Ls). Thorough investigation was conducted to assess the effect of the ZIF-Ls growth time on membrane morphology and surface wetting property. Incorporating the nanoleaf-like ZIF-Ls onto the surface of the membrane provided the surface with micro/nano rough structure and superamphiphilic/superlyophobic features. The prepared membrane showed great separation capability toward various O/W and W/O emulsions, and could be easily regenerated by employing a simple rinsing and drying procedure with high separation efficiency sustained even after multiple separation cycles. Moreover, the membrane with ZIF-Ls demonstrated outstanding catalytic performance in the Knoevenagel condensation. This study achieves advancements in the development of super-wettable membranes with outstanding performance in separating emulsions and the as-prepared membranes have the potential to serve as promising candidates for practical oily mixture treatment.

To avoid severe aggregation and synergistically utilize the intrinsic and photocatalytic reducibility, pyrite (FeS2) was loaded onto N-doped reduced graphene oxides (N-rGO) to fabricate a novel FeS2/N-rGO heterojunction catalyst for enhanced chromium (Cr(VI)) reduction in oxic condition to simultaneously investigate the specific effect and role of dissolved oxygen (DO). Characterization results showed that strong interaction and combination of FeS2 and N-rGO not only achieved the uniform distribution of FeS2, but also increased the defects, and exposed more functional groups. Meanwhile, the Type II heterojunction was formed in FeS2/N-rGO, which facilitated the separation efficiency of photo-generated carriers and electrons, endowing FeS2/N-rGO a superior photocatalytic activity. Cr(VI) was almost completely reduced via FeS2/N-rGO within 60 min under irradiation (Cr(VI) = 10 mg/L, dosage = 0.2 g/L), 3 times that of pristine FeS2 (18.7 %). Trapping and Electron Spin Resonance (ESR) experiments indicated that photo-generated e and derived center dot O-2(-) species from photoactivation of dioxygen (DO) were the key reactive species for the enhancement of photo-assisted Cr(VI) reduction, rather than reductive Fe2+ and S22 species. Although the photocatalysis of FeS2/N-rGO cannot directly generate hydroxyl radicals (center dot OH), the oxidative center dot OH ascribed to superoxide radicals (center dot O-2), photo-induced holes and free DO preferentially consumed by Fe2+ and S22 with stronger reducibility. Hence, as compared to the anoxic condition, the reduction rate of Cr(VI) was slightly decreased, but still could be totally removed within 60 min in the oxic conditions. Due to the excessive amount of FeS2/N-rGO, Cr(III) after reduction would not be influenced by oxidative species and maintain stability under oxic condition. This study provided a facile modification strategy for FeS2 based composites and uncovered its working mechanism for Cr(VI) decontamination.

Electrocatalytic hydrodechlorination (ECH) based on Pd-modifiedNi foam electrodes offers a sustainable approach for decontaminatinghalogenated chlorinated organics, but the synthesis of Pd/Ni foamis always poorly controlled. In this work, with clofibric acid (emergingas a typical pharmaceutical) as a probe contaminant, we show thatthe ECH performance of Pd/Ni foam is highly dependent on the impregnationtime during its preparation. During preparation, the dissolved Ni2+ can combine with aqueous OH- to form insitu Ni(OH)(2) coatings on Pd/Ni foam. By prolonging theimpregnation time, continuous deposition of Ni(OH)(2) graduallyincreases the anti-corrosive property and the electrochemically activesurface area of the electrode. However, such covered Ni(OH)(2) coatings promote the interfacial charge transfer resistance andhinder the atomic H* adsorption by Pd, which is detrimental to ECH.This work provides a novel strategy for the synthesis of Pd/Ni foamelectrodes with an enhanced ECH property for electroreductive remediationof chlorinated pharmaceutical compounds.

Mechanochemical (MC) remediation with zero-valent iron (ZVI) as co-milling agent enables the non-combustion and solvent-free disposal of solid halogenated organic pollutants (HOPs) via solid-phase reaction, but suffers from incomplete dechlorination (especially for less chlorinated chemicals). Herein, a reduction-oxidation coupling strategy using ZVI and peroxydisulfate as synergistic (ZVI-PDS) co-milling agents was investigated, with 2,4-dichlorophenol (2,4-DCP) as probe contaminant. By revisiting the MC destruction process of 2,4-DCP by ZVI, the contribution of both reductive and oxidative routes is confirmed, and the inefficient •OH generation is addressed. With ball-to-material and reagent-to-pollutant mass ratios of 30:1 and 13:1, respectively, ZVI-PDS achieves higher dechlorination ratio (86.8%) for 2,4-DCP within 5 h, outcompeting sole ZVI (40.3%) or PDS (33.9%), due to the accumulation of numerous SO4•-. As suggested by a two-compartment kinetic model, the optimal ZVI/PDS molar ratio of 4:1 is determined, which balances the relative contribution of reductive/oxidative routes and leads to a maximum mineralization efficiency of 77.4%. The analysis on product distribution verifies the generation of dechlorinated, ring-opening and minor coupling products (with low acute toxicity). This work validates the necessity to couple reduction with oxidation in MC destruction for solid HOPs, and may provide information on reagent formulation.

Zero-valent iron (Fe) is commonly employed as an additive for the mechanochemical destruction (MCD) of organic pollutants. The poly- and perfluoroalkyl substances (e.g., perfluorooctane sulfonate, PFOS) are a class of toxic environmental pollutants that are difficult to effectively degrade due to their thermodynamic and chemical stability. In this study, magnetite (Fe3O4) was applied to improve the milling performance of Fe to PFOS and its promoting mechanisms were emphatically explored. The desulfurization rate was in ahead of the defluorination rate because the C-S bond is less stable than the C-F bonds in PFOS. Fe3O4 had an excellent reinforcement effect on the milling performance of Fe, which was mainly through accelerating the electron transfer as a conductor, reacting with Fe to produce FeO, and facilitating the formation of HO●. During the MCD of PFOS with Fe/Fe3O4 as an additive, HO● played a dominant role in the defluorination process (accounting for >67%). After the elimination of sulfonate group (-SO3-), the produced radical (C7F15CF2●) continued to react through two main pathways: one was the stepwise defluorination after hydrogenation, and the other one was oxidation reaction after alcoholization to yield the corresponding aldehydes and carboxylic acids. The optimum Fe fraction (MFe) was 30%, and air atmosphere was more effective than oxygen and nitrogen conditions. This study helps to comprehensively understand the role of Fe3O4 in defluorination and fills the gap of Fe/Fe3O4 application in the MCD of PFASs.

The ubiquitous heavy metal(loid)s (HMs) contamination has triggered great concern about food safety, while sequestration and separation of trace HMs from herbal extracts still calls for appropriate sorbent materials. In this work, gum acacia was modified by cysteine to form a cysteine-acacia intermolecular complex (Cys-GA complex) via facile mechanochemical synthesis, aiming at capturing multiple HMs simultaneously. Preliminary screening confirms the superiority of Cys-CA complex for both cationic and anionic HMs, and determines an optimum Cys/GA mass ratio of 9:1 to achieve high removal capacities for Pb(II) (938 mg g−1), Cd(II) (834 mg g−1), As(V) (496 mg g−1), and Cr(VI) (647 mg g−1) in simulated aqueous solution. The analysis on HMs-exhausted Cys-GA complex indicates that Pb(II), As(V), and Cr(VI) tend to be removed through chelation, electrostatic attraction, and reduction, while Cd(II) can only be chelated or adsorbed by electrostatic interaction. The batch experiments on commercial herbal (e.g. Panax ginseng, Glycine max, Sophora flavescens, Gardenia jasminoides, Cyclocarya paliurus, and Bamboo leaf) extracts indicate that Cys-GA complex can reduce HMs concentration to attain acceptable level that comply with International Organization for Standardization, with negligible negative effect on its active ingredients. This work provides a practical and convenient strategy to purify HMs-contaminated foods without introducing secondary pollution.

Pd-catalyzed electrochemical hydrodechlorination (HDC), as a key process before discharge and biological treatment, is an effective strategy for the in-situ conversion of low concentration chlorinated aromatic pollutants (CAPs) in wastewater or polluted water. However, its application has been greatly hindered by the low Pd utilization and operation efficiency. Herein, we developed an electrocatalytic HDC method using Pd nano-particles modified nickel foam (Pd NPs/Ni) as cathode and alkaline aqueous solution as catholyte, and applied it to convert high concentration CAPs to value-added chemicals. The results showed that the reaction efficiency and selectivity of the developed HDC method mainly depend on the cathode material, pH and cathode potential. The HDC method can convert CAPs (4 categories) with various high concentrations (0.05 -1 M) into a single value-added chemical (picolinic acid, phenoxyacetic acid, benzoic acid or phenol) with very high yield (>95 %) and chemo-selectivity (>97 %). Compared with the conventional Pd-catalyzed HDC methods, the new patterned one can greatly improve Pd utilization and operation efficiency (The Pd mass activity and the area activity of cathode increased by 16 -685 times). In addition, the underlying reaction pathway and catalytic mechanism of the developed HDC system has also been studied using 3,6-dichloropicolinic acid (3,6-D) as the model CAPs. The HDC of 3,6-D on the Pd NPs/Ni in a stepwise fashion with 3-chloropicolinic acid (3-ClPA) as the main inter-mediate product is suggested, and it follows the indirect HDC mechanism with electrochemically adsorbed H as the reductant. The end product (picolinic acid) of the HDC could be further reduced to pipecolinic acid at very negative potentials following direct hydrogenation mechanism, which would significantly lower the selectivity of HDC.

To achieve the precision removal of trace florfenicol (FLO) with presence of various high-concentration interferents in water matrices, an oxygen vacancy engineered molecular imprinted TiO2 (MI-TiO2-x) cathode material was customized rationally. Benefiting from the increased recognition and the accelerated interfacial charge transfer contributed by molecular imprinted sites and oxygen vacancy, respectively, MI-TiO2-x deeply dehalogenates 10 mg L-1 FLO via direct electron transfer with the degradation rate constant of 0.021 min-1. Such electrode material outperforms most of the recent electrocatalysts, and show resistance to co-existing interferents (e.g. reduced sulfur species). In an electro-reductive and biological coupling system, MI-TiO2-x removes the antibacterial activity of 2 mg L-1 FLO in swine wastewater and thus eliminates the abundance of FLO resistance genes. This study provides insights into not only rational design of the noble-metal-free electrocatalyst for preferential remediation of low-concentration organic halides, but also the significance of mitigating ecological risk by dehalogenation treatment.

Cathodic reduction is a green and promising remediation strategy for reducing the antibacterial activity of antibiotic contaminants and increasing their biodegradability. However, the lack of cost-effective electrocatalysts has restricted its application. In this study, we upcycled textile white mud by separating 1,4-dicarboxybenzene (BDC) and fabricating MIL-125(Ti)-derived amorphous TiO2@C (TiO2@C-W) as a functional electrocatalyst. The separated BDC from white mud shows lower crystallinity than BDC chemicals, but the resulting TiO2@C-W features a much higher degree of oxygen vacancies and a 25-fold higher specific surface area than that of TiO2@C derived from BDC chemicals. With florfenicol (FLO) as a probe, TiO2@C-W exhibits similar cathodic reductive activity (0.017 min−1) as commercial Pd(3 wt.%)/C (0.018 min−1) does, which was 1.4 and 3.7 times higher than that of oxygen vacancy-engineered TiO2 and TiO2@C, respectively. The as-fabricated TiO2@C-W could not easily remove FLO via the oxygen reduction reaction-based pathway with the applied bias for cathodic reduction. Though the activity of TiO2@C-W undergoes a slight decline with continuous running, more than 80% of 20 mg L−1 FLO can still be reduced in the eighth run. Water chemistry studies suggest that a lower initial solution pH boosts the cathodic reduction process, while common co-existing anions such as Cl−, NO3−, HCO3−, and SO32− show a limited negative impact. Finally, TiO2@C-W shows reductive activity against several representative antibiotics, including nitrofurazone, metronidazole, and levofloxacin, clarifying its potential scope of application for antibiotics (e.g., molecules with structures like furan rings, nitro groups, and halogens). This study couples the upcycling of textile white mud with the remediation of antibiotics by developing functional electrocatalysts, and offers new insights for converting wastes from the printing and dyeing industry into value-added products.

Mechanochemical destruction of obsolete halogenated persistent organic chemicals (especially polychlorinated aromatics) has been documented as a safe non-combustion technology, but the smooth implementation of such a system still calls for an appropriate and sustainable co-milling agent. As an example, we show that Na2SO3 as a co-milling agent not only achieves faster degradation rate for hexachlorobenzene (HCB) than calcium oxide (1.4-fold) and reduced iron powders (2.9-fold) with equal mass but also enables high dechlorination ratio (97.4%) after 4 h of milling in a planetary mill. With the input of mechanical energy, the mechanistic study suggests that sulfite salts suffer partial melt to generate SO32- species on fresh surfaces, which attack HCB molecules via the one-electron-transfer mechanism. Detection on intermediates and characterization on milled samples demonstrate that HCB undergoes dechlorination, polymerization, and hydrogenation and finally converts to amorphous and graphitic carbons. Correlation analysis indicates that the degradation reactivity of a specific polychlorinated aromatic compound in such a system is strongly dependent on its molecular structure (e.g., substituent groups and degree of chlorination). This work provides a new insight for utilizing sulfite for green disposal of halogenated wastes.