Defluorination Reaction Research Articles

Degradation of norfloxacin by the synergistic effect of micro-nano bubbles and sodium hypochlorite: kinetics, influencing factors and pathways.

This study thoroughly investigated the degradation of norfloxacin (NOR) under the influence of micro-nanobubbles (MNBs) and sodium hypochlorite (NaClO), focusing on their synergistic effects. The impact of various environmental factors, including NaClO concentration, pH, inorganic anions, and surfactants, on NOR degradation efficiency within the MNBs/NaClO system was systematically assessed. The basic properties of the MNBs/NaClO system and the degradation kinetics of NOR were explored. The degradation products and pathways of NOR were explored to reveal the degradation mechanism of antibiotics in the MNBs/NaClO system by employing density functional theory (DFT) and high-performance liquid chromatography-mass spectrometry (HPLC-MS). The redox potential of the MNBs/NaClO system exhibited significantly superior properties than the single system, with bubble sizes predominantly in the nanoscale. The degradation kinetics of NOR adhered to a pseudo-first-order reaction model, with optimal degradation occurring at a 0.025% NaClO volume concentration. Acidic conditions promoted the degradation of NOR, and alkaline conditions inhibited the degradation of NOR. Inorganic anions PO43-, HCO3-, and CO32- in the water matrix led to strong inhibition of NOR degradation. Cationic surfactants accelerated the degradation process of NOR, while anionic and nonionic surfactants had a consistent inhibitory effect on the degradation of NOR. Based on the degradation behavior, three potential pathways for NOR degradation were proposed: quinolone group transformation, defluorination reaction, piperazine ring cracking and quinolone ring decomposition. This research contributes a novel technical approach for addressing antibiotic pollution and offers a theoretical framework for understanding the fate of antibiotics in the environment.

Efficient recovery of highly pure CaF2 from fluorine-containing wastewater using an icy lime solution.

Developing a feasible and low-cost strategy for the recovery of calcium fluoride efficiently from fluoride-containing wastewater is very essential for the recycle of fluoride resources. Herein, a modified lime precipitation method was employed to recover CaF2 from fluorinated wastewater using a special icy lime solution. Intriguingly, the highest F- removal was greater than 95% under the optimal condition, leaving a fluoride concentration from 200 to 8.64 mg/L, while the lime dosage was much lower than that of industry. Importantly, spherical-shaped CaF2 particles with a 93.47% purity and size smaller than 600 nm were recovered, which has a high potential for the production of hydrofluoric acid. Besides, the precipitation was significantly affected by Ca/F molar ratio, stirring time, temperature, and solution pH. Furthermore, the thermodynamics and kinetics were investigated in detail to reveal the crystallization process. As a result, the defluorination reaction followed the pseudo-second order reaction kinetics model. Also, CO2 in the air adversely influenced the CaF2 purity. Based on this facile method, a high lime utilization efficiency was applied to defluorination, which contributed to protecting the environment and saving costs. This study, therefore, provides a feasible approach for the green recovery of fluorine resources and has significance for related research.

A mechanistic study of the hydrolysis of tetrafluoromethane on γ-alumina

CF4 is one of the representative and environmentally hazardous perfluorinated compounds. Even though their decomposition via a catalytic thermal process is an effective process for dissociating C-F bonds by employing catalysts with Lewis acid sites, the related mechanisms are unclear. Herein, we report a theoretical mechanism for the hydrolysis of tetrafluoromethane (CF4) on an γ-alumina surface via density functional theory calculations. The overall reaction mechanism was divided into two steps: CF2O formation and CO2 formation. After the dissociative adsorption of CF4 to the strongest Lewis acid site on the surface of the catalyst, several pathways of defluorination reaction were investigated considering the presence of water and the order of reaction steps. Regardless of the reaction pathway considered, the rate-determining step of the overall reaction was found to be the first dissociation of the C-F bond in CF4, which has the highest energy barrier of 42.31 kcal/mol. Interestingly, oxygen vacancies were readily formed on the catalyst surface during several reaction pathways following its interaction with the reaction intermediate, and these sites could be replaced by fluorine atoms detached from CF4. Our findings suggest that facile desorption of HF, in addition to the presence of strong acidic sites on the catalyst surface for C-F bond dissociation, is critical for improving the CF4 hydrolysis.

Fast Interfacial Defluorination Kinetics Enables Stable Cycling of Low-Temperature Lithium Metal Batteries.

The development of low-temperature lithium metal batteries (LMBs) encounters significant challenges because of severe dendritic lithium growth during the charging/discharging processes. To date, the precise origin of lithium dendrite formation still remains elusive due to the intricate interplay between the highly reactive lithium metal anode and organic electrolytes. Herein, we unveil the critical role of interfacial defluorination kinetics of localized high-concentration electrolytes (LHCEs) in regulating lithium dendrite formation, thereby determining the performance of low-temperature LMBs. We investigate the impact of solvation structures of LHCEs on low-temperature LMBs by employing tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-MeTHF) as comparative solvents. The combination of comprehensive characterizations and theoretical simulations reveals that the THF-based LHCE featured with a strong solvation strength exhibits fast interfacial defluorination reaction kinetics, thus leading to the formation of an amorphous and inorganic-rich solid-electrolyte interphase (SEI) that can effectively suppress the growth of lithium dendrites. As a result, the highly reversible Li metal anode achieves an exceptional Coulombic efficiency (CE) of up to ∼99.63% at a low temperature of -30 °C, thereby enabling stable cycling of low-temperature LMB full cells. These findings underscore the crucial role of electrolyte interfacial reaction kinetics in shaping SEI formation and provide valuable insights into the fundamental understanding of electrolyte chemistry in LMBs.

Visible Light‐Mediated Defluorination to Access 1,1‐Difluoro‐1,3‐Enynes

Herein, a visible light‐mediated defluorination reaction to access 1,1‐difluoro‐1,3‐enynes is described. Compared with previous studies, this protocol employs more readily accessible acids as a radical precursor under the redox‐neutral conditions. Moreover, the reaction exhibits high compatibility with diverse primary, secondary and tertiary acids, especially natural amino acids and drug‐derived acids. Preliminary mechanism investigations reveal that a radical pathway is involved in the catalytic cycle.

Oxidative C-F Bonds Activation Using Electrochemical Techniques

Fluorinated organic compounds are widely used in diverse areas such as pharmaceuticals, agrochemicals, and materials science, and occupy an important position in modern chemistry.[1] Consequently, there has been a large library of fluorine-containing chemicals. Thus, the evolution of defluorination reactions using abundant fluorinated organic compounds as starting materials is expected to lead to further development in various fields. For example, it is expected to be applied to the synthesis of medical and agrochemical products with new functions using defluorination reactions, as well as to the defluorination process of polyfluorinated organic compounds that are highly persistent in the environment.The inherent challenge of C-F functionalization is the highly stable and strong nature of C-F bond. To tackle this problem, various methods have been proposed to activate C-F bonds using transition metal complexes, and Lewis acids. However, these methods have some issues that using expensive heavy metals and toxic reagents. Recent years have seen a focus on the development of economical and environmentally friendly defluorination reactions, especially C-F bonds activation based on efficient energy input using electrochemical or photochemical methods. As for photochemical methods, Gouverneur and co-workers developed photocatalytic methods for the selective hydrodefluorination and defluoroalkylation of trifluoromethyl(hetero)arenes using 2,4,5,6-tetrakis(diphenylamino)isophthalonitrile as an organophotocatalyst.[2] As for electrochemical methods, Cheng and co-workers reported a defluorinative method to convert α,α,α-trifluoromethyl cinnamates to gem-difluorostyrenes using electrochemical reduction.[3] These methods of defluorination still have limitations in terms of the versatility of the substrates where only substrates with π-system or have electron acceptors like carbonyl groups are suitable for cleaving C-F bonds presumably for the facile single electron reduction. Thus, the activation and functionalization of C-F bonds in the aliphatic backbone by electrochemical or photochemical means still remain a challenge.In this work, we have developed an electrochemical C-F bond activation and functionalization under oxidative conditions. After exploring the reaction conditions, the electrochemical defluorination reaction of 1-fluoroadamantane was found to proceed in weakly coordinating electrolyte composed of 0.1 M Bu4NB(C6F5)4/CH2Cl2. Nucleophiles such as allyltrimethylsilane and 4,4,5,5-tetramethyl-2-(p-tolyl)-1,3,2-dioxaborolane were applicable to affording 1-allyladamantane (72% yield) and p-(1-adamantyl)toluene (52% yield), respectively. In this reaction, the use of a divided cell was found to be necessary, evidencing that the defluorination reaction proceeds oxidatively at the anode.In conclusion, we have successfully developed the first electrochemical defluorinative functionalization system under oxidative conditions, which potentially become a complementary strategy of electro-reductive counterpart of the defluorinative transformation of organic molecules. In the presentation, an exploration of the substrate scope, electrochemical studies, and the mechanistic proposal of the reaction will also be discussed.[1] Y. Ogawa, E. Tokunaga, O. Kobayashi, K. Hirai, N. Shibata, iScience., 2020, 23, 101467–101467.[2] J. B. I. Sap, N. J. W. Straathof, T. Knauber, C. F. Meyer, M. Médebielle, L. Buglioni, C. Genicot, A. A. Trabanco, T. Noël, C. W. am Ende, V. Gouverneur, J. Am. Chem. Soc., 2020, 142, 20, 9181–9187.[3] J. Sheng, N. Wu, X. Liu, F. Liu, S. Liu, W. Ding, C. Liu and X. Cheng, Chin. J. Org. Chem., 2020, 40, 11, 3873–3880. Figure 1

The in vacuo release of Ar and rare gases from minerals: 3. The degassing of He, Ne, Ar, Kr and Xe from irradiated apatite

The mechanisms of in vacuo release of Ar are investigated by bringing them into context with nine other rare gas isotopes and by studying the mineralogical modifications that occur in their host mineral. A 200 mg shard of Durango fluorapatite was step-heated after neutron irradiation. It contained radiogenic 4He from natural U decay and artificially produced major rare gas isotopes: 20Ne from F, 37Ar from Ca, 38Ar from Cl, 80Kr and 82Kr from Br, 128Xe from I, 131Xe from Ba and 134Xe from U. The 4He release rate was compared with that from an unirradiated aliquot.Helium was expected, and observed, to degas at the lowest furnace temperatures, with nearly complete exhaustion by 1300 °C. Neon followed a bimodal degassing pattern, with a peak of the release rate at 1178 °C and a higher one at 1406 °C. Argon degassing showed a similar bimodality. Krypton and xenon were both mostly released in a single, concentrated burst between 1362 and 1460 °C.The two Xe isotopes 128 and 131, produced from I and Ba, respectively, followed exactly the same degassing pattern. The crystallographic site of the target element had no control on the movement of the irradiation-produced rare gas atom.The He release from the irradiated and unirradiated aliquots gave two overlapping alignments in the Arrhenius diagram at temperatures between 450 and 1300 °C. The two slopes are indistinguishable at the 1 sigma level and yield an average activation energy of 62 ± 5 kJ/mol. In the 450–1300 °C temperature interval, all five rare gases showed parallel trends with an activation energy around 62 kJ/mol and release rate constants decreasing from He to Xe by about 4 orders of magnitude. Arrhenian trajectories for the Kr and Xe degassing rate merge and sharply steepen in the 1362 °C step, with a degassing rate in the 1406 °C step about 400 times higher than at lower temperatures and an activation energy of 1.28 MJ/mol. The high-T modes of the bimodal Ar and Ne release also merge on the same steep Arrhenius line, with release rate constants indistinguishable from those of Kr and Xe. This break in Arrhenius slope and the merger of four trajectories that were widely separated below 1300 °C indicate a major, energetically very costly event between 1300 and 1362 °C.The possible structural reordering was investigated with four mineralogical techniques: Raman spectroscopy, X ray diffractometry, transmission electron microscopy, and microchemical analysis by laser induced breakdown spectroscopy. Total loss of F may have transiently modified the apatite structure. Complete outgassing of Ne, Ar, Kr and Xe was only achieved after the defluorination reaction and attending displacive structural reorganization. Like in hydrated minerals, in K-feldspar, and in leucite, degassing of heavy noble gases in apatite occurs by at least two different physical mechanisms. In all of these minerals downslope extrapolation of in vacuo Ar degassing in the laboratory to temperatures of geological interest does not appear warranted.

Removal of fluoride from the mixed Ni-Co-Mn sulfate leach solution of spent lithium ion batteries using polyaluminum sulfate

The mechanism and application of defluorination in a simulated leaching solution of spent lithium-ion batteries (LIBs) using poly‑aluminum sulfate (PAS) were studied. The experimental results indicated that reaction parameters such as the molar ratio of Al to F, pH of the solution, reaction temperature, initial concentration of fluorine, and concentration of lithium and nickel, significantly affected the reaction efficiency. Under the optimum reaction conditions, the percentage of defluorination was 95.5 (wt%). During the defluorination reaction, Al3+, Al(OH)3 reacted with F−, HF to generate AlF3 and AlF(OH)2. The crystallinity of AlF3, AlF(OH)2, and Al(OH)3 and the chemical stability of the precipitates improved with the increase in temperature and pH. The Li+ concentration in the solution increased the defluorination efficiency by forming LiAlF4. At the same time, high concentrations of NiSO4 inhibited the defluorination effect and were lost in association with the solids, NiSO4·6H2O and Ni(OH)2. According to the study of reaction kinetics, the rate equation of the aluminum‑fluorine reaction was -d[F]/dt = 0.0384exp(−8.59/RT) [F0]1.11[Al]0.31. The activation energy of the precipitation reaction was 8.59 kJ/mol, and the reaction rate was relatively high. In the actual defluorination process of the acid-leaching solution of waste battery powder with Ni-Mn-Co chemistry, the F− concentration reduced from 1205 mg/L to 48 mg/L and the loss of valuable metals was <6%, and the Ni, Co, and Mn in the precipitates were predominantly sulfates and hydroxides.

Nickel-Catalyzed Enantioselective Dearomative Heck-Reductive Allylic Defluorination Reaction of Indoles.

Herein, we describe a nickel-catalyzed asymmetric dearomative aryl-difluoroallylation reaction of indoles with α-trifluoromethyl alkenes as an electrophilic coupling partner. The reaction proceeds via a cascade sequence involving dearomative Heck cyclization and reductive allylic defluorination. A series of gem-difluoroallyl substituted indolines are obtained in moderate to good yields (36-77% yield) with excellent enantioselectivity (up to 99% ee). The reaction features broad functional group tolerance, scaled-up synthesis, and late-stage diversification.

Fluorine recovery through alkaline defluorination of polyvinylidene fluoride

The establishment of technological approaches for the defluorination of waste fluoropolymers and recovery of eliminated F– may contribute to the development of fluorine recycling routes. In this study, we investigated the effects of alkalinity, phase transfer catalyst (PTC) concentration, reaction temperature, and solvent types on the defluorination of polyvinylidene fluoride (PVDF) by alkaline wet processing. The rate of defluorination of PVDF in 4.0 M sodium hydroxide (NaOH) and 50 mM tetrabutylammonium bromide (TBAB) under aqueous conditions reached 89.2%. In addition, the defluorination reaction proceeded faster in solvents such as diethylene glycol (DEG) and triethylene glycol (TEG) than in water because of the high affinity between PVDF and these diols. To investigate the feasibility of developing a fluorine recycling route, the defluorination of a photovoltaic (PV) backsheet and subsequent CaF2 precipitation from the eliminated F– was examined. A total of 88.3% of F contained in the PV backsheet was recovered as CaF2, which satisfied the quality standards of commercial fluorspar. This study demonstrated that alkaline wet processing is effective for the defluorination of PVDF and that the establishment of a F recycling route along the F supply chain may be feasible.

Photodegradation fate of different dissociation species of antidepressant paroxetine and the effects of metal ion Mg2+: Theoretical basis for direct and indirect photolysis

Paroxetine (abbreviated as PXT) has been widely used as one of the standard antidepressants for the treatment of depression. PXT has been detected in the aqueous environment. However, the photodegradation mechanism of PXT remains unclear. The present study aimed to use density functional theory and time-dependent density functional theory to study the photodegradation process of two dissociated forms of PXT in water. The main mechanisms include direct and indirect photodegradation via reaction with ·OH and 1O2 and photodegradation mediated by the metal ion Mg2+. Based on the calculations, PXT and PXT-Mg2+ complexes in water are photodegraded mainly indirectly and directly. It was found that PXT and PXT-Mg2+ complexes were photodegraded by H-abstraction, OH-addition and F-substitution. The main reaction of PXT indirect photolysis is OH-addition reaction, while the main reaction of PXT0-Mg2+ complex is H-abstraction. All the reaction pathways of H-abstraction, OH-addition and F-substitution are exothermic. PXT0 reacts more readily with ·OH or 1O2 in water than PXT+. However, the higher activation energy of PXT with 1O2 indicates that the 1O2 reaction plays a minor role in the photodegradation pathway. The direct photolysis process of PXT includes ether bond cleavage, defluorination, and dioxolane ring-opening reaction. In the PXT-Mg2+ complex, the direct photolysis process occurs via a dioxolane ring opening. Additionally, Mg2+ in water has a dual effect on the direct and indirect photolysis of PXT. In other words, Mg2+ can inhibit or promote their photolytic reactions. Overall, PXT in natural water mainly undergo direct and indirect photolysis reactions with ·OH. The main products include direct photodegradation products, hydroxyl addition products and F-substitution products. These findings provide critical information for predicting the environmental behavior and transformation of antidepressants.

Cu-ZnO Heterojunction Catalytic SF6/H2 Gas Conversion Mechanism and Reaction Network Construction

How to treat waste sulfur hexafluoride (SF6) in an environmentally friendly way to alleviate the greenhouse effect caused by it is a global concern. In this article, a catalytic reaction model of the gas–solid reaction interface formed by the main active sites of SF6/H2 and Cu-ZnO heterojunctions was constructed. Subsequently, the thermodynamic properties of SF6 in the process of adsorption, dissociation, and defluorination occurring on the surface of the Cu-ZnO catalyst under the H2 atmosphere were investigated. A defluorination and hydrogenation reaction network of 22 reactions was constructed. To better fit the actual situation in engineering application, the participation of trace water and oxygen was considered. The total reaction heat for the conversion of SF6 to the target reduction product H2S catalyzed by the Cu-ZnO heterojunction is −12.90 eV. Compared to the primary decomposition on the Cu(111) surface, the Cu-ZnO interface reduces the reaction energy of complete defluorination by 297.04%, showing an outstanding catalytic conversion activity. This indicates that ZnO not only plays the reductant carrier but also participates in the catalytic process. This article offers a new method for managing the greenhouse effect problem caused by SF6, proposes a set of catalytic pathways, and analyzes the catalytic mechanism of Cu-ZnO.

Rapidly Constructing Sodium Fluoride-Rich Interface by Pressure and Diglyme-Induced Defluorination Reaction for Stable Sodium Metal Anode.

Sodium (Na) metal is able to directly use as a battery anode but have a highly reductive ability of unavoidably occurring side reactions with organic electrolytes, resulting in interfacial instability as a primary factor in performance decay. Therefore, building stable Na metal anode is of utmost significance for both identifying the electrochemical performance of laboratory half-cells employed for quantifying samples and securing the success of room-temperature Na metal batteries. In this work, weproposean NaF-rich interface rapidly prepared by pressure and diglyme-induced defluorination reaction for stable Na metal anode. Once the electrolyte is dropped into the coin-type cells followed by a slight squeeze, the Na metal surface immediately forms a protective layer consisting of amorphous carbon and NaF, effectively inhibiting the dendrite growth and dead Na. The resultant Na metal anode exhibits a long-term cycling lifespan over 1800 h even under the area capacity of 3.0 mAh cm-2 . Furthermore, such a universal and facile method is readily applied in daily battery assembly regarding Na metal anode.

TiO2 supported on rice straw biochar as an adsorptive and photocatalytic composite for the efficient removal of ciprofloxacin in aqueous matrices

Ciprofloxacin (CIP) is a broad-spectrum antibiotic, but it is widely found in pharmaceutical wastewater, livestock wastewater, domestic sewage, and river sediments. CIP is not easy to be decomposed naturally and has high harm to human body. The development of cheap, environmental-friendly, and efficient biochar materials for antibiotic removal has certain practicability and applicability. The characteristics of rice straw biochar (RSB) and TiO2 modified rice straw biochar (Ti-RSB) were examined by BET, FTIR, UV–vis DRS, LRS, XPS, Zeta potential, SEM, EDS and XRD. Then the ability and mechanism of RSB and Ti-RSB to remove CIP were evaluated through kinetic and isotherm adsorption experiments. The results showed that the adsorption of CIP by RSB is more consistent with BET model. When pH= 5, the maximum adsorption capacity for CIP based on Langmuir model was 747.64 mg/g. The adsorption mechanism includes electrostatic interaction, π-π interaction, and H bond interaction, in which CO is the functional group that plays the main adsorption role. While using TiO2 to functionalize the surface of RSB, increasing the photocatalytic performance of the material, the composite Ti-RSB has a superior removal effect on CIP degradation at a wide pH from 5 to 9. The degradation mechanism belongs to the first defluorination reaction, and then the degradation of the piperazine ring. The recycling of rice straw into biochar and its functional modification into composite materials have application values in the removal of CIP.

Unravelling binder chemistry in sodium/potassium ion batteries for superior electrochemical performances

TiO2 is used as a model to illustrate the binder chemistry in ethers by polyvinylidene difluoride (PVdF) and sodium carboxymethyl cellulose (CMC). The worse performance of PVdF is due to the defluorination reaction and the adhesion loss.

Insight into the defluorination ability of per- and polyfluoroalkyl substances based on machine learning and quantum chemical computations

UV-generated hydrated electrons play a critical role in the defluorination reaction of poly- and perfluoroalkyl substances (PFAS). However, limited experimental data hinder insight into the effects of the structural characteristics of emerging PFAS on their defluorination abilities. Therefore, in this study, we adopted quantity structure−activity relationship models based on machine learning algorithms to develop the predictive models of the relative defluorination ability of PFAS. Five-fold cross-validations were used to perform the hyperparameter tuning of the models, which suggested that the gradient boosting algorithms with PaDEL descriptors as the best model possessed superior predictive performance (R2test = 0.944 and RMSEtest = 0.114). The importance of the descriptor indicated that the electrostatic properties and topological structure of the compounds significantly affected the defluorination ability of the PFAS. For the emerging PFAS the best model showed that most compounds, such as potential alternatives of perfluorooctane sulfonic acid, were recalcitrant to reductive defluorination, whereas perfluoroalkyl ether carboxylic acids had relatively stronger defluorination abilities than perfluorooctanoic acid. The theoretical calculations implied that additional electrons on PFAS could cause molecular deconstruction, such as changes in the dihedral angle involved in the carbon chain, as well as C–F bond and ether C–O bond cleavages. In general, the current computational models could be useful for screening emerging PFAS to assess their defluorination ability for the molecular design of fluorochemical structures.

Ultrafine PdRu Nanoparticles Immobilized in Metal–Organic Frameworks for Efficient Fluorophenol Hydrodefluorination under Mild Aqueous Conditions

Ultrafine PdRu Nanoparticles Immobilized in Metal–Organic Frameworks for Efficient Fluorophenol Hydrodefluorination under Mild Aqueous Conditions

On the Role of the Cathode for the Electro-Oxidation of Perfluorooctanoic Acid

Perfluorooctanoic acid (PFOA), C7F15COOH, has been widely employed over the past fifty years, causing an environmental problem because of its dispersion and low biodegradability. Furthermore, the high stability of this molecule, conferred by the high strength of the C-F bond makes it very difficult to remove. In this work, electrochemical techniques are applied for PFOA degradation in order to study the influence of the cathode on defluorination. For this purpose, boron-doped diamond (BDD), Pt, Zr, and stainless steel have been tested as cathodes working with BDD anode at low electrolyte concentration (3.5 mM) to degrade PFOA at 100 mg/L. Among these cathodic materials, Pt improves the defluorination reaction. The electro-degradation of a PFOA molecule starts by a direct exchange of one electron at the anode and then follows a complex mechanism involving reaction with hydroxyl radicals and adsorbed hydrogen on the cathode. It is assumed that Pt acts as an electrocatalyst, enhancing PFOA defluorination by the reduction reaction of perfluorinated carbonyl intermediates on the cathode. The defluorinated intermediates are then more easily oxidized by HO• radicals. Hence, high mineralization (xTOC: 76.1%) and defluorination degrees (xF−: 58.6%) were reached with Pt working at current density j = 7.9 mA/cm2. This BDD-Pt system reaches a higher efficiency in terms of defluorination for a given electrical charge than previous works reported in literature. Influence of the electrolyte composition and initial pH are also explored.

Defluorination/Fluorination Reaction of BiF3 Nanoparticles Prepared Via Sol–Gel Method for Fluoride Shuttle Battery

Introduction Rechargeable batteries with high energy density have been required for recent applications such as hybrid electric vehicles and large-scale energy storage. Rechargeable batteries based on fluoride shuttle (FSBs) have attracted much attention as a candidate above, owing to their high theoretical energy density by selecting appropriate metal/metal fluoride couples as active materials of negative- and positive-electrode[1-3]. One of the important things of the battery is adoption of the good conductive media for fluoride species, that is, an electrolyte[4]. Another is reversible fluorination/defluorination of active materials at the interface with electrolyte. Previously, we have demonstrated archetypal reversible FSB using a liquid electrolyte containing organic fluoride at room temperature[3]. However, this battery needed to improve the utilization and cyclability of its active material. Since the common metal fluoride shows low electronic- and ionic-conductivity, the active materials should be minified for FSBs. In this study, metal fluoride nanoparticle, e.g. BiF3, was prepared via sol–gel method using a trifluoroacetate precursor for improvement of the charge/discharge reactions in FSB. Bismuth trifluoride having 302 mAh/g in theoretical capacity is considered as a candidate for positive active material[1-6]. Then, we studied reversible defluorination/fluorination reaction of thus prepared BiF3 nanoparticles in a liquid electrolyte of FSB at room temperature, and valence change of bismuth species in the consequent electrode was evaluated using synchrotron ex-situ XANES measurement.Experimental Bismuth trifluoride nanoparticle was prepared from bismuth trifluoroacetate precursor via decarboxylation at 453 K in an oleylamine solution under argon atmosphere. At that time, specific amount of trifluoroacetic acid and/or trifluoroacetic anhydride were added as a supplementary fluorine source. After the nanoparticles were precipitated via addition of toluene and ethanol sequentially, the resulting precipitation was centrifuged and then re-dispersed in toluene containing oleic acid as a dispersant. Finally, nanoparticles were obtained after stripping of ligand using a trimethyloxonium tetrafluoroborate. Size of the resulting nanoparticles can be controlled by precursor concentration, decarboxylation reaction time and its temperature. Electrochemical measurement was carried out using a three-electrode cell with a VSP-300 BioLogic potentiostat/galvanostat in an argon-filled glove box at room temperature. The cell was composed of a carbon cloth as a counter electrode, a silver wire as a quasi-reference electrode, and an ionic liquid containing an organic fluoride as a liquid electrolyte. The liquid electrolyte was prepared by dissolving N-methyl-N-propylpiperidinium fluoride (MPPF) or N,N,N-trimethyl-N-neopentylammonium fluoride (NpF) in N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide (TMPA-TFSA) with molar ratio of 1:10. Nanoparticles-supported carbon cloth electrode as a working electrode was prepared by soaking the cloth in BiF3-nanoparticles/acetonitrile dispersion. The prepared nanoparticles via the sol–gel method and the defluorination/fluorination products in electrochemical measurements were evaluated using XRD, XPS, SEM-EDS, and so on in our laboratory. Furthermore, valence change of bismuth species was evaluated using synchrotron ex-situ XANES measurement at SPring-8, Japan.Results and Discussion Thus obtained nanoparticles via above-mentioned procedure had a few tens of nanometers in diameter and showed low crystallinity. Moreover, it was suggested that small amount of oxygen would be doped into the nanoparticles according to elemental analyses. Then, non-doped BiF3 nanoparticles having hexagonal crystalline structure had been acquired after further fluorination-treatment. Consequent BiF3 nanoparticles-supported carbon cloth showed ca. 240 mAh/g (80%) as an initial discharge capacity, and retained ca. 100 mAh/g for more than five cycles at room temperature. Furthermore, in ex-situ bismuth L3-edge XANES spectra, valence of bismuth species changed from trivalent to zero (metal) during the defluorination reaction and similar reverse change was elucidated in fluorination reaction. In this way, the size of the active material was minified by the preparation method, thereby improving the utilization and cyclability in FSB. This method will be also applied for other positive- and negative-active material having high gravitational theoretical capacity.Acknowledgements This work was supported by the “Research and Development Initiative for Scientific Innovation of New Generation Batteries 2 (RISING2)” of the New Energy and Industrial Technology Development Organization (NEDO), Japan.

A Novel Reduced Graphene Oxide-Attapulgite (RGO-ATP) Supported Fe2O3 Catalyst for Heterogeneous Fenton-like Oxidation of Ciprofloxacin: Degradation Mechanism and Pathway

Ciprofloxacin, a third-generation fluoroquinolones (FQs) antibiotic, is observed to increasingly pollute the environment. In this study, a three-dimensional reduced graphene oxide-attapulgite-based catalyst Fe2O3/RGO-ATP was prepared and used to analyze the degradation of ciprofloxacin in a heterogeneous Fenton reaction. The heterogeneous catalyst Fe2O3/RGO-ATP was prepared by a one-step hydrothermal method, and the samples were characterized using BET(Brunauer-Emmett-Teller) surface area, Raman spectroscopy, X-ray diffraction (XRD), Fourier infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The effect of reaction time, temperature, pH, initial concentration, H2O2 dosage and reuse time on the degradation of ciprofloxacin by the catalyst Fe2O3/RGO-ATP was investigated. The optimum conditions of degradation of ciprofloxacin are observed to be 60 °C, pH 5, H2O2 concentration of 2.9724 mmol/L, and initial ciprofloxacin concentration of 50 mg/L. The catalyst could be reused several times with a decline in catalytic capacity. Fourier-transform ion cyclotron resonance mass spectrometer (FT) was also employed to study the degradation products of ciprofloxacin in the aqueous solution. The results show that the heterogeneous catalyst Fe2O3/RGO-ATP possessed an excellent ability for the catalytic degradation of ciprofloxacin. Direct hydroxyl oxidation is noted to be the main pathway of degradation of ciprofloxacin, and no defluorination reaction is observed during the degradation process.