Defluorination Mechanism Research Articles

Constructing LiF-Dominated Interphases with Polymer Interwoven Outer Layer Enables Long-Term Cycling of Si Anodes.

Constructing a robust solid electrolyte interphase (SEI) is extremely critical to developing high-energy-density silicon (Si)-based lithium-ion batteries. However, it is still elusive how to accurately manipulate the chemical composition and structure of the SEI layer. Herein, a LiF-dominated SEI film intertwined by a highly elastic polymer is achieved by regulating the defluorination mechanism of the fluorinated carbonate additive on the Si electrode surface. The experimental and computational results confirm that the decomposition route of trans-difluoroethylene carbonate (DFEC) molecules can be significantly altered in the presence of lithium difluoro(oxalato)borate (LiDFOB) additive. The induction of direct defluorination of DFEC step by LiDFOB, as opposed to the breaking of C-O bonds without LiDFOB addition, is crucial in ensuring the exclusive formation of LiF-dominated SEI and maintaining the cyclic structure of DFEC. The defluorinated DFEC easily polymerizes to form poly(vinylene carbonate), enhancing the elasticity of the SEI. The resulting LiF-dominated SEI film with a polymer interwoven outer layer shows enhanced ionic conductivity and mechanical stability, which can effectively accelerate electrode reaction kinetics and maintain the structural stability of the Si electrode. As a result, the Si electrode with the electrolyte containing the designed dual-additive exhibits superior cycling stability and excellent rate performance, delivering a high reversible capacity of 1487.3 mAh g-1 after 1000 cycles at 2 A g-1.

Dechlorination Helps Defluorination: Insights into the Defluorination Mechanism of Florfenicol by S-nZVI and DFT Calculations on the Reaction Pathways.

Defluorination is essential to eliminate the antibiotic resistance and detrimental effects of florfenicol (C12H14Cl2FNO4S, FF), which is achievable by sulfidated nanoscale zerovalent iron (S-nZVI), yet a comprehensive understanding of the mechanism is lacking. Herein, we used experimental data and density functional theory calculations to demonstrate four dechlorination-promoted defluorination pathways of FF, depending on S-nZVI or not. FF was defluorinated in a rapid and then slow but continuous manner, accompanying a consecutive dechlorination to deschloro (dFF) and dideschloro FF (ddFF). Unexpectedly, the predominant defluorination occurs by spontaneous hydrolysis of ddFF to form the hydrolyzed byproduct (HO-ddFF), i.e., independent of S-nZVI, which is initiated by intramolecular attack from carbonyl O to alkyl F and is thus limited for FF and dFF owing to the diminished nucleophilicity by electron-withdrawing Cl. The removal of Cl also makes the reductive defluorination of ddFF by S-nZVI amenable. The other two minor but more rapid defluorination pathways occur in synergy with the dechlorination of FF and dFF, which are mediated by the reactive carbanion intermediates and generate HO-dFF and HO-ddFF, respectively. The reliability of these dechlorination-facilitated defluorination pathways was verified by the consistency of theoretical calculations with experimental data, providing valuable insights into the degradation of fluorinated contaminants.

Defluorination of perfluorooctanoic acid and perfluorooctane sulfonic acid by heterogeneous catalytic system of Fe-Al2O3/O3: Synergistic oxidation effects and defluorination mechanism

In this study, catalytic ozonation by Fe-Al2O3 was used to investigate the defluorination of PFOA and PFOS, assessing the effects of different experimental conditions on the defluorination efficiency of the system. The oxidation mechanism of the Fe-Al2O3/O3 system and the specific degradation and defluorination mechanisms for PFOA and PFOS were determined. Results showed that compared to the single O3 system, the defluorination rates of PFOA and PFOS increased by 2.32- and 5.92-fold using the Fe-Al2O3/O3 system under optimal experimental conditions. Mechanistic analysis indicated that in Fe-Al2O3, the variable valence iron (Fe) and functional groups containing C and O served as important reaction sites during the catalytic process. The co-existence of 1O2, OH, O2− and high-valence Fe(IV) constituted a synergistic oxidation system consisting of free radicals and non-radicals, promoting the degradation and defluorination of PFOA and PFOS. DFT theoretical calculations and the analysis of intermediate degradation products suggested that the degradation pathways of PFOA and PFOS involved Kolbe decarboxylation, desulfonation, alcoholization and intramolecular cyclization reactions. The degradation and defluorination pathways of PFOA and PFOS consisted of the stepwise removal of -CF2-, with PFOS exhibiting a higher defluorination rate than PFOA due to its susceptibility to electrophilic attack. This study provides a theoretical basis for the development of heterogeneous catalytic ozonation systems for PFOA and PFOS treatment.

Degradation of fluoride in groundwater by electrochemical fixed bed system with bauxite: performance and synergistic catalytic mechanism.

Fluoride pollution in water has garnered significant attention worldwide. The issue of fluoride removal remains challenging in areas not covered by municipal water systems. The industrial aluminum electrode and natural bauxite coordinated defluorination system (IE-BA) have been employed for fluoride removal. The experiment investigated the effects of pH, current density, and inter-electrode mineral layer thickness on the defluorination process of IE-BA. Additionally, the study examined the treatment efficiency of IE-BA for simulated water with varying F- concentrations and assessed its long-term performance. The results demonstrate that the defluorination efficiency can reach 98.4% after optimization. Moreover, irrespective of different fluoride concentrations, the defluorination rate exceeds 95.2%. After 72 hours of continuous operation, the defluorination rate reached 91.9%. The effluent exhibited weak alkalinity with a pH of around 8.0, and the voltage increased by 2.0 V compared to the initial moment. By analyzing the characterization properties of minerals and flocs, this study puts forward the possible defluorination mechanism of the IE-BA system. The efficacy of the IE-BA system in fluoride removal from water was ultimately confirmed, demonstrating its advantages in terms of defluorination ability under different initial conditions and resistance to complex interference. This study demonstrates that the IE-BA technology is a promising approach for defluorination.

Efficient defluorination of perfluorooctanoic acid enabled by single-atom Cu/reduced graphene oxide electrocatalytic anode and peroxymonosulfate activation

In this study, an electrocatalytic system using reduced graphene oxide supported single-atom copper (SA-Cu/rGO) anode was constructed for perfluorooctanoic acid (PFOA) defluorination. The successful doping of SA-Cu elevated the oxygen evolution potential and electrochemical active surface area of the anode and provided high electrocatalytic properties. Under optimum initial conditions with a peroxymonosulfate (PMS) concentration of 10 mM, a current density of 15 mA·cm−2, and an unadjusted pH of 7.75, the SA-Cu/rGO system achieved 98.8% removal ratio, 92.5% defluorination, and 94.4% mineralization of 20 mg·L-1 PFOA in 120 min. Kinetic studies indicate PFOA degradation following a pseudo-first-order model, with a rate constant of 4.7 × 10−2 min−1. The presence of PMS in the electrocatalytic system significantly improved the degradation rate and defluorination ratio. Radical trapping and quenching experiments confirmed that both ·OH and ·SO4- radicals contributed to PFOA degradation, with ·SO4- playing a more important role in defluorination. The system show high flexibility in initial PFOA concentrations (0.2–20 mg·L−1) and environmental pH values (3.0–10.0), as well as good durability. The electrocatalytic degradation mechanism of PFOA was proposed through determination of intermediates and density functional theory (DFT) calculation. The total short-chain perfluorocarboxylic acids (PFCAs) intermediates generated throughout the degradation were far from sufficient recovery of the PFOA loss, indicating that apart from the ·OH mediated decarboxylation-hydroxylation-elimination-hydrolysis (DHEH) pathway, the ·SO4- mediated decarboxylation-hydroxylation-oxidation-decarbonyl fluoride (DHOD) pathway may play a significant role in the near-complete defluorination and mineralization of PFOA. Moreover, DFT calculations suggest that the DHOD pathway is energetically favorable over DHEH. This study provides a further understanding of the defluorination mechanism of PFOA in electrocatalytic systems and demonstrates that electrochemical degradation with single-atom copper catalyst is an promising method for PFOA remediation in aqueous environment.

Ultra-rapid fluoride removal by magnetic calcium-doped layered yttrium hydroxides at environmental-relevant concentrations

Currently, there is still a lack of strategies for rapid removal of fluoride at environmental-relevant concentrations. In this study, in which several magnetic calcium doped layered yttrium hydroxides (γ-Fe2O3/Ca-Y LRHs) modified with γ-Fe2O3 were synthesized and used for fluoride removal. The magnetic and adsorption properties analysis indicated γ-Fe2O3/4Ca-Y LRHs demonstrated performance of magnetism and adsorption ability. According to the pseudo-second-order and Langmuir models, the equilibrium time and maximum monolayer adsorption capacity of γ-Fe2O3/4Ca-Y LRHs was 2 min and 43.98 ± 2.34 mg/g, respectively. The adsorption and desorption studies revealed electrostatic and ion exchange interactions are involved in the defluorination mechanism, and chloride and oxygenated groups in interlayer spaces were the main ligands for fluoride exchanged. The potential applications on surface water demonstrate that the ability of γ-Fe2O3/4Ca-Y LRHs to remove fluoride at environmental-relevant concentrations. These findings are expected to facilitate the process of rapid removal of fluoride contamination in the aqueous environment.

Zinc oxide nanosheet decorated self-supporting hierarchical porous wood carbon electrode for efficient capacitive deionization defluorination

Excessive fluoride in water is severe harm to human health and has become a global public health problem. However, there is a lack of efficient and affordable defluorination technology, especially for fluoride removal from low concentration F- wastewater. Herein, zinc oxide nanosheet decorated self-supporting hierarchical porous wood carbon (ZnO/HPWC) was prepared as electrode for membrane capacitive deionization (MCDI) and used for defluorination. The used activator of ZnCl2 would not only manufacture hierarchical pore structure of wood carbon, but also allow in-situ vertical growth of uniform ZnO nanosheets on HPWC. A high F- removal (94.52%) was achieved at 5 mg L-1 of F− solution by the ZnO/HPWC-based MCDI, as well as its improved electrosorption capacity (31.25 mgF- g-1ZnO/HPWC). Excellent defluorination performance of ZnO/HPWC was also achieved at real wastewater (F-, 6.25 mg L-1), of which the final F- concentration (1.32 mg L-1) can meet the WHO standard of drinking water (<1.5 mg L-1). The defluorination mechanism was studied and discussed, which proved the high defluorination performance of ZnO/HPWC was due to the chemical interaction between F- and ZnO nanosteets, and diffusion capacitance (pseudocapacitance) offered by ZnO nanosheets dominated over the surface capacitance (electric double layer capacitance) by HPWC.

"Blockchain-Like" MIL-101(Cr)/Carbon Black Electrodes for Unprecedented Defluorination by Capacitive Deionization.

Metal-organic frameworks (MOF) have attracted extensive attention due to their ultra-high specific surface area and tunable structure, the mechanism of direct utilization for capacitive deionization (CDI) defluorination remains undefined. Here, MIL-101(Cr) with ultra-high specific surface area, high water stability, and open metal sites (OMSs) is prepared by a hydrothermal method for defluorination of CDI. Carbon black is used as a "chain" to connect F-stored in the holes of MIL-101(Cr) (Cr-MOF)as "blocks" to enhance the conductivity and ion storage capacity of MIL-101(Cr)/carbon black electrodes (Cr-MOF electrodes). This simple construction method avoids the process complexity of in situ synthesis and performs better. These easily constructed "blockchain-like" Cr-MOF electrodes exhibit excellent defluorination capacity (39.84 mgNaF gelectrodes -1 ), low energy consumption (1.2kWh kgNaF -1 ), and good stability. The coupling of the electrochemical redox reaction of Cr3+ /Cr4+ with confined water is investigated using in situ and ex situ analysis methods combined with density functional theory (DFT), resulting in an unprecedented defluorination mechanism for Cr-MOF electrodes. This study opens up new ideas for the application of MOF in CDI, clarifies the removal mechanism of MOF, and lays a foundation for further promoting the application of raw materials with poor conductivity in the field of CDI.

Photocatalytic degradation of GenX in water using a new adsorptive photocatalyst

GenX, the ammonium salt of hexafluoropropylene oxide dimer acid, has been used as a replacement for perfluorooctanoic acid. Due to its widespread uses, GenX has been detected in waters around the world amid growing concerns about its persistence and adverse health effects. As relevant regulations are rapidly evolving, new technologies are needed to cost-effectively remove and degrade GenX. In this study, we developed an adsorptive photocatalyst by depositing a small amount (3 wt.%) of bismuth (Bi) onto activated-carbon supported titanate nanotubes, Bi/TNTs@AC, and tested the material for adsorption and subsequent solid-phase photodegradation of GenX. Bi/TNTs@AC at 1 g/L was able to adsorb GenX (100 µg/L, pH 7.0) within 1 h, and then degrade 70.0% and mineralize 42.7% of pre-sorbed GenX under UV (254 nm) in 4 h. The efficient degradation also regenerated the material, allowing for repeated uses without chemical regeneration. Material characterizations revealed that the active components of Bi/TNTs@AC included activated carbon, anatase, and Bi nanoparticles with a metallic Bi core and an amorphous Bi2O3 shell. Electron paramagnetic resonance spin-trapping, UV-vis diffuse reflectance spectrometry, and photoluminescence analyses indicated the superior photoactivity of Bi/TNTs@AC was attributed to enhanced light harvesting and generation of charge carriers due to the UV-induced surface plasmon resonance effect, which was enabled by the metallic Bi nanoparticles. •OH radicals and photogenerated holes (h+) were responsible for degradation of GenX. Based on the analysis of degradation byproducts and density functional theory calculations, photocatalytic degradation of GenX started with cleavage of the carboxyl group and/or ether group by •OH, h+, and/or eaq−, and the resulting intermediates were transformed into shorter-chain fluorochemicals following the stepwise defluorination mechanism. Bi/TNTs@AC holds the potential for more cost-effective degradation of GenX and other per- and polyfluorinated alkyl substances.

Defluorination mechanism related to the activity of hydroxyl groups: A combined density functional theory calculations and experimental study

Aluminum-based (Al-based) materials are of great significance to solve the global fluoride pollution problem. Hydroxylation modification is one of the effective methods to improve the surface activity and defluorination performance of aluminum matrix materials. However, the lack of in-depth understanding of the role of hydroxyl gourp at the molecular level restricts the preparation and application of Al-based adsorbents. In this work, based on the interface of Al-based two-dimensional materials, the effects of anionic ligands, doped metals and solution H+ on the structural activity of surface hydroxyl groups were explored by DFT theoretical calculation and experimental design. Simultaneously, quantitative analysis of the contribution of each possible mechanism in the defluorination process was carried out. Both anionic exchange reaction and chemical co-adsorption determined the defluorination process. The high polarizability and more negative charge of anionic ligands was found to facilitate reducing the activity of hydroxyl groups in weak acid environment. H+ can enhance the activity of hydroxyl, and thereby strengthening the hydrogen bond (H-bond) effect, but it will have a synergistic effect with anionic ligands. Metal doping will change the electron density on O atoms, which will affect the F- adsorption effect of hydroxyl via H-bond. Compared with the existing research, we carefully studied the influence of hydroxyl group activity on the defluorination performance of aluminum matrix materials, which can provide a feasible basis for structural design of the subsequent adsorbents.

Discovery of a P450-Catalyzed Oxidative Defluorination Mechanism toward Chiral Organofluorines: Uncovering a Hidden Pathway

While the enzymatic oxidative cleavage of C–F bonds at achiral centers catalyzed by P450 monooxygenases has been studied extensively, less is known about the oxidative defluorination mechanism of chiral substrates with fluorine being at chirality centers. Here, we report that the use of ethyl 2-fluoro-2-phenylacetate as a stereochemical probe enabled us to discover two oxidative defluorination paths catalyzed by P450-BM3: α-site hydroxylation and hydroxylation at the remote phenyl group. By means of intermediate identification and capture, chemical mimics, key intermediate derivatization, and deuterium insertion experiments as well as QM theoretical calculations, we succeeded in demonstrating an unusual mechanism in which these two oxidative defluorination routes occur in a P450 monooxygenase. This work presents valuable insights into the oxidative degradation of organofluorines and provides a convenient method for remote C–F bond activation.

Enhanced fluoroglucocorticoid removal from groundwater in a bio-electrochemical system with polyaniline-loaded activated carbon three-dimensional electrodes: Performance and mechanisms

This study aimed to investigate the removal performance and mechanisms of dexamethasone (DEX), a representative fluoroglucocorticoid (FGC), from micro-polluted oligotrophic groundwater in a bio-electrochemical system amended with polyaniline-loaded activated carbon (PANI@AC) as three-dimensional particle electrodes (BES-3D). The BES-3D achieved a DEX removal efficiency of 95.7%, which was 39.0% and 14.1% higher than that of a single biological system (SBIO) and two-dimensional bio-electrochemical system (BES-2D), respectively. The preliminary metabolic mechanism of defluorination accounted for 53.5%, 41.1%, and 16.3% in BES-3D, BES-2D, and SBIO, respectively, which was accompanied by demethylation, side-chain fracture, and hydroxyl oxidation for ketone formation and final-ring opening. The main mechanism by which removal was improved in BES-3D was the enrichment of functional microbes and enhancement of the expression of dehalogenation genes. The relative abundance of functional microbes with electron transfer ability and reductive dehalogenating genera, i.e., Pseudomonas, Methylotenera, Desulfuromonas, Sphingomonas, and Microbacterium, in BES-3D was 3.7–6.1 times higher and the copy number of functional genes was 1.9 times higher than those of SBIO, which contributed to the high DEX removal.

Adsorption and solid-phase photocatalytic degradation of perfluorooctane sulfonate in water using gallium-doped carbon-modified titanate nanotubes

Perfluorooctane sulfonate (PFOS) has drawn increasing attention due to its omnipresence and adverse health effects. We prepared a new adsorptive photocatalyst, Ga/[email protected], based on activated carbon and TiO2, and tested the adsorption and subsequent solid-phase photodegradation of PFOS. Ga/[email protected] showed faster adsorption kinetics and higher affinity for PFOS than the parent AC, and could degrade 75.0% and mineralize 66.2% of pre-sorbed PFOS within 4-h UV irradiation. The efficient PFOS photodegradation also regenerates Ga/[email protected], allowing for repeated uses without invoking chemical regenerants. The superior photoactivity is attributed to the oxygen vacancies, which not only suppressed recombination of the e−/h+ pairs, but also facilitated O2− generation. Both h+ and O2− played critical roles in the PFOS degradation, which starts with cleavage of the sulfonate group and converts it into PFOA that is then decarboxylated and defluorinated following the stepwise defluorination mechanism. Ga/[email protected] holds the potential for more cost-effective PFOS degradation.

Nanoscale Defluorination Mechanism and Solid Electrolyte Interphase of a MgF2 Anode in Fluoride-Shuttle Batteries

Fluoride-shuttle batteries using fluoride ion transfer have been extensively investigated for developing post-lithium-ion batteries. One of the key issues hampering the development is the low capac...

Removal of fluoride ions from ZnSO4 electrolyte by amorphous porous Al2O3 microfiber clusters: Adsorption performance and mechanism

Amorphous porous Al2O3 microfiber clusters (AP-Al2O3-MCs) are developed by combining hydrothermal and roasting methods, which are applied to remove F− from the ZnSO4 electrolyte. Comprehensive characterization of AP-Al2O3-MCs is performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) analysis, and other techniques. The equilibrium F− removal efficiency and adsorption capacity of AP-Al2O3-MCs are 66.35% and 10.823 mg·g −1, respectively, with an adsorbent dose of 7.0 g·L−1 at 313 K in a pH of 5 for 45 min. The isotherm study found that the Langmuir isotherm model fits the experimental data well. The theoretical maximum adsorption capacity of F− is 14.96 mg·g−1. Adsorption kinetics can be more appropriately to described by the pseudo-second-order kinetic model. The thermodynamic data is indicative of spontaneous, exothermic, and entropy-decreasing reaction at 313 K. The defluorination mechanism is proposed, which includes the interaction of F− with Al and O on the surface of the AP-Al2O3-MCs, as well as ion-exchange by -OH groups and F−. The estimated dosage and preparation cost of the AP-Al2O3-MCs show a suitable application potential. As a result, AP-Al2O3-MCs are an ideal adsorbent for the removal of F− from the ZnSO4 electrolyte.

Ternary NiFeMn layered metal oxide (LDO) compounds for capacitive deionization defluoridation: The unique role of Mn

Fluoride (F–) contamination in drinking water or groundwater due to natural and human activities has been recognized as one of the major problems to human health. In this work, the novel capacitive deionization (CDI) defluorination was proposed and offered satisfactory results especially with the layered metal oxide (LMO) electrode. The NiFe-LMO, NiMn-LMO and NiFeMn-LMO electrodes were prepared and characterized. NiFeMn-LMO was used as the CDI anode, nitric acid treatment AC as the cathode, and the asymmetric module (H-AC//NiFeMn-LMO) was assembled for defluorination test. The NiFeMn-LMO defluoridation capacity can reach 16.7 mg/g at the initial NaF concentration of 500 mg/L and the voltage of 1.4 V, and it can keep 93.3% of the initial capacity after 30 cycles at the voltage of 1.0 V. CDI defluorination mechanism of LMO was analyzed. It was found that Mn tended to transform from low state to high state in the process of CDI defluorination and the introduction of Mn improved the pseudcapacitive behavior of materials, thus enabling the ternary NiFeMn-LMO to have excellent CDI defluorination performance. This provides a new idea for the development of high-performance CDI defluorinated electrode materials.

First-Principles Study for Fluorination/Defluorination Reaction Mechanism in Fluoride-Shuttle Batteries

INTRODUCTIONRechargeable batteries with energy densities higher than those of the present Li-ion batteries (LIBs) are required for electric vehicles. We focus on fluoride-ion (F−) transfer batteries whose electrodes are composed of metal/metal fluoride (M|MF n ) combinations. Electrochemical charge-transfer reactions occur during the discharge/charge processes at the two electrodes. Defluorination of the metal fluoride MF n and fluorination of another metal M’ occurs at the positive and negative electrodes, respectively, during the discharging process asM1/n F + e− → M1/n + F− (1),M’1/m + F− → M’1/m F + e− (2).This type of battery is called a fluoride-shuttle battery (FSB), which is expected to produce high voltage and have large capacity.1 In 2017, Okazaki et al. fabricated a Bi|BiF3 electrode with a liquid electrolyte prepared by dissolving an organic fluoride in an ionic liquids (ILs) at room temperature. 2 In 2018, Davis et al. reported another type of liquid electrolyte composed of a simple organic solvents (OSs) with F−conductivity greater than 1 mS/cm.3 From the development of these liquid electrolytes, the F− conductivity has been dramatically increased in recent years. After improvement of the electrolyte conductivity, the fluorination and defluorination reactions at the electrodes are considered to be the rate-determining steps in FSBs. However, the mechanism of the fluorination and defluorination reactions in FSBs has not been clarified in contrast to the well-investigated Li-intercalation reaction in LIBs.METHODSIn this study, we classify the fluorination and defluorination reactions into two possible reaction pathways from a thermodynamic point of view: reaction through the solid-solution state and reaction through the two-phase state. It is possible to find which reaction pathway is realized from the free energy difference. Selection of these reaction pathways can be determined from the enthalpies of all of the intermediate states, since the entropy term in the free energy is fairly cancelled when we consider the difference of free energies. Selection rule for the fluorination and defluorination reactions in FSBs is schematically illustrated in Figure 1. The solid-solution states of M1/n F x for x ≈ 0 and for x ≈ 1 are assumed to be formed by introducing an interstitial and a vacancy defect, respectively. In this case, the free energy relation for the selection can be described as G ss(x) < G tp(x) → H I(M1/n ) < H(M1/n F) or H(M1/n F) < −H V(M1/n F) (3),where G ss(x), G tp(x), H (M1/n F), H I(M1/n F) , H V(M1/n F) are the free energy of the solid-solution state of M1/n F x , that of two-phase state, the formation enthalpy of M1/n F, that of interstitial defect in M1/n , and that of vacancy defect in M1/n F, respectively. We use the energies from first-principles calculations for the enthalpy differences, whose accuracy is validated by comparing them with experimentally obtained thermodynamic enthalpy data.4 The first-principles calculations were performed with the configurations of the bulk crystal systems using Quantum Espresso package.5 The crystal data were taken from the AtomWork database.6 RESULTSThe relative formation enthalpies of typical, transition, and relativistic metal fluorides are well reproduced by first-principles calculations within 0.1, 0.2, and 0.4 eV, respectively. By comparing the formation enthalpies of H, H V, and H I, the relation H I > H > −H V is always satisfied in all of the calculated metal and metal-fluoride combinations (M = Li, Mg, Ca, Al, Co, Ni, Cu, Pb, Bi). Thus, the selection rule of eq. (3) strongly suggests that fluorination and defluorination in FSB electrodes occur by two-phase reaction.7 This fluorination and defluorination mechanism will be useful to clarify the rate-determining step in FSBs.AcknowledgmentsThis work was supported by the Research and Development Initiative for Scientific Innovation of New Generation Batteries 2 Project (RISING2) administrated by the New Energy and Industrial Technology Development Organization (NEDO).REFERENCES1) F. Gschwind, G. Rodriguez-Garcia, D. Sandbeck, A. Gross, M. Weil, M. Fichtner, N. Hörmann, J. Fluorine Chem. 182, 76 (2016).2) K.-I. Okazaki, Y. Uchimoto, T. Abe, Z. Ogumi, ACS Energy Lett. 2, 1460 (2017).3) V. K. Davis et al., Science 362, 1144 (2018).4) Handbook of Chemistry: Pure Chemistry, 5th ed.5) P. Giannozzi et al., J. Phys.: Condens. Matter. 29, 465901 (2017).6) National Institute for Materials Science (NIMS) AtomWork <http://crystdb.nims.go.jp/>7) J. Haruyama, K.-I. Okazaki, Y. Morita, H. Nakamoto, E. Matsubara, T. Ikeshoji, M. Otani, “Two-Phase Reaction Mechanism for Fluorination and Defluorination in Fluoride-Shuttle Batteries: A First-Principles Study” in revision. Figure 1. Two reaction pathways considered in this study. In the fluorination and defluorination reactions, the solid-solution (M1/n F x , 0 < x< 1) and two-phase (M1/n and M1/n F) states are considered to be possible intermediate states. Figure 1

Enhanced reductive defluorination and inhibited infiltration of fluoroglucocorticoids in a river receiving reclaimed water amended by nano zero-valent iron-modified biochar: Performance and mechanisms

The main aim of this study was to investigate the effect of a nano zero-valent iron-modified biochar-amended composite riverbed (nZVI@BC-R) on inhibited infiltration and enhanced biodegradation of fluoroglucocorticoids (FGCs) in a river receiving reclaimed water. The results demonstrated that the removal efficiency of triamcinolone acetonide (TA), a representative FGC, increased from 38.40% and 77.91% to 91.60% in the nZVI@BC-R compared with that of a natural soil riverbed (S-R) and biochar-amended soil riverbed (BC-R). The main removal mechanismwas attributedto adsorption and biodegradation, of which the contribution rates were 32.2% and 59.4% in nZVI@BC-R, 18.9% and 19.5% in S-R, and 24.4% and 53.5% in BC-R, respectively. The removal process could be described by a two-compartment, first-order dynamic model with decay rate constants for adsorption and biodegradation of 4.02700, 22.44400, and 29.07300 d−1 and 0.00286, 0.01562, and 0.03484 d−1 in the S-R, BC-R and nZVI@BC-R, respectively. The mechanism of defluorination accounted for 42.2% of biodegradation in the nZVI@BC-R, which was accompanied by side-chain rupture, oxidation, and ringopening. Functional microbes with iron oxidizing ability and reductive dehalogenating genera, namely Pseudoxanthomonas, Pedobacter, and Bosea, contributed to the high removal rate of TA, particularly in the nZVI@BC-R. Overall, the nZVI@BC-R provided an effective method to inhibit glucocorticoids infiltration into groundwater.

Two-Phase Reaction Mechanism for Fluorination and Defluorination in Fluoride-Shuttle Batteries: A First-Principles Study.

Fluoride-shuttle batteries (FSBs), which are based on fluoride-ion transfer, have attracted attention because of their high theoretical energy densities. The fluorination and defluorination reactions at the electrodes are the possible rate-determining steps in FSBs, and understanding the mechanism is important to achieve smooth charge/discharge. In this study, we discuss the thermodynamically favored pathways for the fluorination and defluorination reactions and compare the reactions through the solid-solution and two-phase-coexistent states by density functional theory (DFT) calculations. The free energies of the solid-solution and two-phase states approximate the energies calculated by DFT, and their accuracy was validated by comparison with experimental formation enthalpies and free energies. The relative formation enthalpies of typical, transition, and relativistic metal (Tl, Pb, and Bi) fluorides are well reproduced by DFT calculations within 0.1, 0.2, and 0.4 eV, respectively. We also show that the reaction pathway can be determined by comparing the formation enthalpies of the metal fluoride H, a fluorine vacancy HV, and an interstitial fluorine defect HI from the simple selection rule. The enthalpy relation of HI > H > -HV observed in all the calculations strongly suggests that fluorination and defluorination in FSB electrodes occur by a two-phase reaction. This fluorination and defluorination mechanism will be useful to clarify the rate-determining step in FSBs.

Harnessing fluoroacetate dehalogenase for defluorination of fluorocarboxylic acids: in silico and in vitro approach

Widely distributed fluorocarboxylic acids have aroused worldwide environmental concerns due to its toxicity, persistence, and bioaccumulation. Enzyme-based eco-friendly biodegradation techniques have become increasingly important in treating fluorocarboxylic acids. Here we utilized in silico and in vitro approaches to investigate the defluorination mechanism of fluoroacetate dehalogenase (FAcD) toward monofluoropropionic acids at atomic-level. The experimentally determined kcat and kM for defluorination of 2-fluoropropionic acid are 330 ± 60 min−1 and 6.12 ± 0.13 mM. The in silico results demonstrated positive/negative correlations between activation barriers and structural parameters (e.g. distance and angle) under different enzymatic conformations. We also screened computationally and tested in vitro (enzyme assay and kinetic study) the catalytic proficiency of FAcD toward polyfluoropropionic acids and perfluoropropionic acids which are known to be challenging for enzymatic degradation. The results revealed potential degradation activity of FAcD enzyme toward 2,3,3,3-tetrafluoropropionic acids. Our work will initiate the development of a new “integrated approach” for enzyme engineering to degrade environmentally persistent fluorocarboxylic acids.