Method for generating hydrated electrons by amphoteric metal cathode and application thereof in degrading perfluorooctanoic acid

Abstract

The application discloses a method for generating hydrated electrons by amphoteric metal cathode and application thereof in degrading perfluorooctanoic acid, and belongs to the technical field of electrochemical wastewater treatment. aq ‑ Efficient electro-reduction of PFOA and other fluorine-containing organic matters is realized under local alkaline conditions, which is also the first attempt to produce e aq ‑ .

Description

Technical Field

[0001] This invention belongs to the field of electrochemical wastewater treatment technology, specifically relating to a method for electrogenerating hydrated electrons using an amphoteric metal cathode and its application in the degradation of perfluorooctanoic acid. Background Technology

[0002] Perfluorooctanoic acid (PFOA) is a class of compounds containing a CF bond, formed by fluorine atoms replacing some or all of the hydrogen atoms on a carbon atom. Since its synthesis in the 1940s, PFOA has been widely used in textiles, food packaging, fire-fighting foams, protective coatings, and related industrial fields due to its high heat resistance, chemical stability, hydrophobicity, and oleophobicity. PFOA is known for its neurotoxicity, genotoxicity, reproductive toxicity, and potential carcinogenicity. In recent years, PFOA has been frequently detected in industrial wastewater, groundwater, and surface water. Therefore, developing efficient technologies for the removal of PFOA from water is crucial.

[0003] However, due to the strong electronegativity of fluorine and the high structural stability of the carbon-fluorine bond (bond energy of 485.3 kJ·mol⁻¹), -1 However, the degradation of PFOA remains a technical challenge. PFOA is susceptible to biodegradation, chemical oxidation, and even ·OH (k = 2.6 × 10⁻⁶). 5 M-1·s -1 ) and SO4 ·- (2.59×10 5 M -1 ·s -1 Advanced oxidation processes of PFOA are highly resistant. Thermodynamically, reduction reactions may be more favorable than oxidation reactions for PFOA cleavage. Theoretically, a potential of at least +2.2V (relative to the standard hydrogen electrode, SHE) is required to initiate dissociative electron transfer (DET) of the CF bond via oxidation, while only -1.1V vs SHE is needed to trigger PFAS reduction. The most commonly used PFAS reduction methods include zero-valent iron (ZVI), photocatalysis, electrochemistry, and hydrated electron-based reduction (electron-dependent reduction) methods. aq - Advanced Reduction Procedures (ARPs). aq - Considered the strongest reducing agent (E θ = -2.87V vs SHE), capable of reacting nonselectively with most compounds under thermodynamically feasible and kinetically rapid conditions (10 6 -10 10 L·mol -1 ·s -1 In addition, e aq - It possesses high nucleophilicity, enabling it to subsequently react with halogen atoms involved in organic molecules. Therefore, based on eaq - Advanced reduction techniques have attracted considerable attention from researchers for their efficient removal of PFOA.

[0004] To date, e aq - Mainly through UV excitation of photosensitizers (such as I) - and SO3 2- Electron beam / gamma-ray irradiation of water and alkali metals dissolved in liquid ammonia solution generates e.g., .e., e is produced via a UV / sulfite process. aq - It is a simple strategy, its e aq - The yield is relatively high, but due to (i) secondary pollution caused by the addition of sulfites, (ii) e aq - The high pH dependence of the generated material (pH > 9.2), and the light-shielding effect caused by the coexisting anions and natural organic matter (iii), pose challenges to the environmental applications of this technology. Therefore, there is an urgent need to develop more manageable, universal, and efficient strategies to obtain e- for PFOA reduction. aq - . Summary of the Invention

[0005] To address the above problems, this invention provides a method for generating hydrated electrons using an amphoteric metal cathode and its application in the degradation of perfluorooctanoic acid.

[0006] Fundamentally, e aq - H2 can be produced through a rapid dimerization reaction, with a second-order rate constant as high as k = 1.1 × 10⁻⁶. 10 M -1 ·s -1 (Equation 1). If there exists a path through e aq - The dimerization reaction involves hydrogen evolution (Equation 1), rather than the traditional proton substitution (M+H). + →M + +H2) and water decomposition (H2O→H2+O2), then based on this reaction equation, develop e aq - Alternative methods for their formation are feasible. Based on classical chemical principles, amphoteric metals can be generated independently of H... + Displacement reaction, but with OH - The reaction produces H2 (Equation 2, taking Al as an example), e aq -This occurs during the dissolution of aluminum (Equation 3). Generally, alkaline conditions are achieved by adding alkaline chemicals to obtain an alkaline solution, but maintaining strongly alkaline conditions in water purification is unlikely to be optimal in most cases. This invention, however, uses electrolysis to create a locally highly alkaline microenvironment near the amphoteric metal acting as the cathode, thereby releasing OH-. - , generate e aq - (Equation 3, taking Al as an example). Electrochemical-chemical tandem electrogeneration can be achieved by generating a locally strong alkaline environment through electrochemical Al cathode electrolysis and in-situ inducing Al dissolution. aq - The process, and to achieve e aq - Mediated PFOA reduction and removal.

[0007] e aq - +e aq - →H2+OH - (1)

[0008] Al + OH- → Al(OH)4 - +H2 (2)

[0009] Al + 4OH - →Al(OH)4 - +3e aq - (3)

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] One of the technical solutions of this invention is to provide a method for electrogenerating hydrated electrons using an amphoteric metal cathode, comprising the following steps:

[0012] A diaphragm electrolytic cell is constructed using amphoteric metals as cathode materials, and hydrated electrons are generated in the cathode chamber when electricity is applied.

[0013] The membrane electrolyzer constructed in this invention creates a locally alkaline environment around the amphoteric cathode after being energized, generating a locally high concentration of OH-. - It reacts with amphoteric metals to produce e aq - Taking aluminum as an example, OH - It reacts with aluminum to form tetrahydroxyaluminate ions [Al(OH)4] - ] and e aq - .

[0014] Preferably, the amphoteric metal is aluminum.

[0015] The membrane used in the membrane electrolyzer constructed in this invention can be a proton exchange membrane, the anode can be a platinum electrode, and the electrolyte in the electrolyte solution can be Na2SO4.

[0016] The second technical solution of the present invention provides an application of the above-mentioned method for generating hydrated electrons by a zwitterionic metal cathode in the degradation of perfluorooctanoic acid.

[0017] The third technical solution of the present invention provides an application of the above-mentioned method for electro-generating hydrated electrons by a zwitterionic metal cathode in the degradation of fluorine-containing organic compounds.

[0018] Fourth technical solution of the present invention: A method for the degradation of perfluorooctanoic acid mediated by electro-generated hydrated electrons from an amphoteric metal cathode, comprising the following steps:

[0019] A membrane electrolytic cell is constructed using an amphoteric metal as the cathode material and an electrolyte containing at least perfluorooctanoic acid (PFOA) as the cathode chamber electrolyte. The degradation of PFOA can be achieved by passing electricity through the cell.

[0020] Preferably, the amphoteric metal is aluminum.

[0021] Fifth technical solution of the present invention: A method for the degradation of fluorine-containing organic matter mediated by electro-generated hydration electrons from an amphoteric metal cathode, comprising the following steps:

[0022] A membrane electrolytic cell is constructed using a zwitterionic metal as the cathode material and an electrolyte containing at least fluorinated organic compounds as the cathode chamber electrolyte. The degradation of fluorinated organic compounds can be achieved by passing an electric current through the cell.

[0023] Preferably, the amphoteric metal is aluminum.

[0024] The beneficial technical effects of the present invention are as follows:

[0025] e aq - As one of the most reactive reducing species, it has broad application prospects in the reductive decomposition of recalcitrant PFOA in water treatment. aq - Typically, this is achieved through ultraviolet light excitation of photosensitizers and electron beam / gamma-ray radiolysis, which increases operating costs, separation complexity, and efficiency. This invention, for the first time, demonstrates the generation of e-elements through electrolysis using an amphoteric metal as the cathode in a membrane electrolyzer. aq - This study demonstrates the efficient electroreduction of PFOA and other fluorinated organic compounds under locally alkaline conditions, marking the first attempt to produce fluorinated compounds without requiring significant energy input or additional chemical reagents. aq - This will make the reduction and removal of PFOA more efficient, easier to manage, and more sustainable. Attached Figure Description

[0026] Figure 1 The effect of different current densities on PFOA degradation in Example 1 is shown, where a represents the change of PFOA degradation over time, and b represents the change of defluorination rate over time.

[0027] Figure 2 The current density in Example 1 is 25 mA·cm. -2 SEM and AFM images of the original aluminum cathode, the aluminum cathode after one electrolytic cycle (4h), and the aluminum cathode after 10 electrolytic cycles (40h) are shown. In the image, a is the SEM image of the original aluminum cathode, d and g are the AFM images of the original aluminum cathode, b is the SEM image of the aluminum cathode after one cycle, e and h are the AFM images of the aluminum cathode after one cycle, c is the SEM image of the aluminum cathode after 10 cycles, and f and i are the AFM images of the aluminum cathode after 10 cycles.

[0028] Figure 3 The current density in Example 1 is 25 mA·cm. -2 XPS full spectrum of the original aluminum cathode, the aluminum cathode after 1 electrolytic cycle (4h), and the aluminum cathode after 10 electrolytic cycles (40h).

[0029] Figure 4 The current density in Example 1 is 25 mA·cm. -2 Al 2p spectra of the original aluminum cathode, the aluminum cathode after one electrolytic cycle (4h), and the aluminum cathode after 10 electrolytic cycles (40h).

[0030] Figure 5 The current density in Example 1 is 25 mA·cm. -2 XRD patterns of the original aluminum cathode, the aluminum cathode after one electrolytic cycle (4h), and the aluminum cathode after 10 electrolytic cycles (40h).

[0031] Figure 6 The current density in Example 1 is 25 mA·cm. -2 EIS spectra of the original aluminum cathode, the aluminum cathode after one electrolytic cycle (4h), and the aluminum cathode after 10 electrolytic cycles (40h).

[0032] Figure 7 The LSV curves (a) of the original aluminum cathode, the aluminum cathode after 1 electrolysis cycle (4h), and the aluminum cathode after 10 electrolysis cycles (40h) at a current density of 25mA·cm-2 in Example 1, the LSV curves of the original aluminum cathode and the Ti cathode (b), the degradation rate of PFOA by the original aluminum cathode and the Ti cathode (c), and the degradation kinetic fitting curves of PFOA degradation by the original aluminum cathode and the Ti cathode (d) are shown.

[0033] Figure 8 This indicates the inhibitory effect of H* scavenger on the degradation of PFOA on aluminum cathodes during quenching experiments.

[0034] Figure 9 ESR signal (a) obtained using DMPO as a free radical scavenger, e aq - The inhibitory effect of the cleaning agent on the degradation of PFOA in the aluminum cathode system (b), the change of ECL signal of luminol as a probe over time under different conditions (c), and the theoretically calculated local pH value (d).

[0035] Figure 10 The figure shows the degradation kinetic fitting curves of PFOA degradation in the aluminum cathode ARP system under different NaNO3 concentrations during the quenching experiment.

[0036] Figure 11 The following figures illustrate the changes in PFOA removal rate over time in the aluminum cathode ARP system during 10 consecutive experiments: (a), (b) removal rate of OFX and FLO in the aluminum cathode ARP system, (c) degradation rate of PFOA in the aluminum and zinc cathode reduction system, and (d) defluorination rate of PFOA in the aluminum and zinc cathode reduction system.

[0037] Figure 12 For the electro-generated hydrated electrons based on the Al cathode system aq - A schematic diagram of the PFOA degradation mechanism. Detailed Implementation

[0038] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0039] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0040] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0041] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0042] Example 1

[0043] Laboratory construction of a membrane electrolyzer for PFOA degradation based on Al cathode electrogenerated hydration electrons:

[0044] The experiment was conducted in an H-type reactor, with two compartments separated by a DuPont proton exchange membrane (Nafion 117), and 50 mM Na₂SO₄ solution as the supporting electrolyte. A commercially available aluminum electrode (30 mm × 40 mm) was immersed in 50 mL of PFOA solution (concentration 5.0 mg·L⁻¹) in the cathode chamber. -1 The anode chamber contained a platinum electrode and 50 mL of Na₂SO₄ solution. The applied current densities were set to 10, 25, and 40 mA cm⁻¹, respectively. -2 .

[0045] Subsequent analysis and testing methods:

[0046] The concentrations of PFOA and its related degradation intermediates were analyzed using an ultra-high performance liquid chromatography-triple quadrupole tandem mass spectrometer equipped with an ACQUITY BEH C18 column (2.1 mm × 100 mm, 1.7 μm, Waters). Reaction rate constants (k, min) were also analyzed. -1 The value was calculated by linearly fitting ln(C0 / C) with reaction time, assuming that the degradation of PFOA is a pseudo-first-order reaction, where C0 and C are the initial and reaction concentrations of PFOA, respectively. The concentration of fluoride ions was determined by ion chromatography, and the defluorination rate was calculated using equation (4).

[0047]

[0048] In equation (4), [F - [] represents the concentration of fluoride ions in the system after the reaction, [PFOA]0 represents the initial concentration of PFOA, 414 represents the molecular mass of PFOA, and 285 represents the total atomic mass of all fluoride atoms in PFOA.

[0049] Electron spin resonance (ESR, Bruker A300, Germany) was used to detect the generation of atomic hydrogen (H*). During electrolysis, a trapping agent, 5,5-dimethyl-1-pyrrolidone-N-oxide (DMPO, 50 mmol / L), was added. -1The electrode was immersed in the electrolyte, and the power was immediately turned off. Subsequently, ESR analysis was performed by carefully sampling at points near the cathode surface using a capillary tube. The ESR measurement parameters were: center field 3510 G, scan width 100 G, microwave frequency 9.87 GHz, modulation frequency 100 GHz, and power 18.11 mW. The morphology, surface roughness, and metallic valence state of the electrode before and after use were measured and analyzed using a ZEISS Sigma 300 scanning electron microscope (SEM, Germany), a Bruker Dimension Icon atomic force microscope (AFM, Germany), a Rigaku Miniflex 600 X-ray diffractometer (XRD, Japan), and a Thermo Scientific K-Alpha X-ray photoelectron spectrometer (XPS, USA). The electrochemical performance of the aluminum electrode was characterized in a three-electrode H-cell using an electrochemical workstation (CHI760E, Chenhua Instruments Co., China), with an Ag / AgCl (3M NaCl) reference electrode placed near the working electrode. Electrochemiluminescence (ECL) signals were recorded on an LK5100 instrument (LK5100, Lanlike Co., China) using luminol as a probe (ECL emission wavelength approximately 425 nm). aq - With the participation of luminol, the luminescent probe is activated and exhibits an electrochemiluminescent signal.

[0050] Analysis results:

[0051] The effect of different current densities on PFOA degradation in Example 1 is shown in the figure. Figure 1 Where a represents the change of PFOA degradation over time, and b represents the change of defluorination rate over time.

[0052] Figure 1 As shown in Figure a, the current densities are 40, 25, and 10 mA·cm⁻¹. -2 At that time, the degradation rates were 99.1%, 97.4%, and 80.9%, respectively, with corresponding first-order kinetic constants (k... obs The values ​​were 0.0169 min. -1 0.0125min -1 and 0.0039min -1 The defluorination rate is calculated based on the concentration of fluoride ions in the cathode chamber at different times and formula (4), such as... Figure 1 As shown in Figure b, the current densities are 40, 25, and 10 mA·cm⁻¹. -2At the specified times, the defluorination rates were 95.3%, 85.2%, and 40.7%, respectively. The lower defluorination rate compared to the degradation rate may be attributed to the generated fluorine intermediates. This indicates that the aluminum cathode-based electrochemical reduction system can effectively decompose PFOA, and the high defluorination rate is due to the electron-triggered reduction process responsible for PFOA removal. Considering PFOA removal and energy consumption factors, a 25 mA·cm² energy level was selected. -2 This serves as the optimal current density for subsequent electrolysis tests.

[0053] During electrolysis, the morphology of the aluminum cathode was characterized by SEM and AFM (25 mA·cm⁻¹). -2 SEM and AFM images of the original aluminum cathode, the aluminum cathode after one electrolytic cycle (4h), and the aluminum cathode after ten electrolytic cycles (40h) are shown below. Figure 2 In the figure, a is the SEM image of the original aluminum cathode, d and g are the AFM images of the original aluminum cathode, b is the SEM image of the aluminum cathode after 1 cycle, e and h are the AFM images of the aluminum cathode after 1 cycle, c is the SEM image of the aluminum cathode after 10 cycles, and f and i are the AFM images of the aluminum cathode after 10 cycles.

[0054] like Figure 2 As shown in Figure a, the original aluminum cathode surface contained nanoparticles caused by the preparation process (rolling and annealing). After one electrolytic cycle (4 h), compared to its original state, the number of nanoparticles decreased, and micropores were formed. Figure 2 (b) After 10 electrolytic cycles (40 h), significant corrosion was observed on the electrode surface, manifested as the formation of more nanoscale pores. Figure 2 (c) Figure 2 The AFM images of the electrode further illustrate the surface changes before and after use, showing that the surface roughness gradually increases with continuous electrolysis. For example, the average roughness of the original electrode surface was 33.0 nm, increasing to 49.4 nm after one cycle, and further increasing to 109.0 nm after 10 cycles. This corrosion phenomenon is likely due to the localized enrichment of OH groups on the aluminum and aluminum electrode. - The result of the reaction.

[0055] To assess the chemical state of the aluminum electrode during electrolysis, XPS analysis was performed after SEM and AFM characterization. The full XPS spectrum is shown below. Figure 3 The Al 2p spectrum is shown below. Figure 4 .

[0056] like Figure 3 As shown, the aluminum electrode spectra before and after use are almost identical, indicating that the aluminum electrode has a uniform composition and high purity. Furthermore, there is no evidence of new element formation on the electrode surface, ruling out PFOA or F... - Adsorption potential on aluminum cathodes.

[0057] like Figure 4 As shown, the Al 2p spectrum of the original electrode exhibits characteristic peaks, representing Al₂O₃ and Al (metallic) bonds at 73.48 eV and 75.08 eV, respectively. In contrast, the used aluminum electrode after 1 and 10 cycles only shows Al₂O₃ peaks, indicating that the aluminum electrode is partially oxidized, and the used electrode has undergone significant elemental changes. During electrolysis, the formed Al₂O₃ layer interacts with localized OH groups. - The reaction converts it into AlO2. - without affecting OH - Dissolution of Al. Further evidence is found in high-resolution O1s spectra ( Figure 3 In the study, it was observed that the initial aluminum electrode exhibited a double peak at 531.98 eV and 533.38 eV, representing CO and O-Al bonds from the relevant preparation process. In contrast, the used aluminum electrode mainly contained O-Al bonds, with the exception of CO bonds, indicating that OH groups were destroyed during electrolysis. - Ion etching.

[0058] Following SEM and AFM characterization, this invention also underwent XRD analysis, the results of which are shown below. Figure 5 .

[0059] like Figure 5 As shown, the four significant peaks at 38.49°, 44.80°, 65.17°, and 78.30° are characteristic XRD signals of Al, belonging to the (111), (200), (220), and (311) crystal planes, respectively. The disappearance of the (111) peak and the weakening of the intensities of the (200), (220), and (311) crystal planes indicate that the aluminum electrode is affected by OH-. - Additional evidence of corrosion is consistent with the results of SEM, AFM, and XPS characterization.

[0060] To better characterize the electrochemical properties of the aluminum electrode, electrochemical impedance spectroscopy (EIS) measurements were performed after SEM and AFM characterization. The measurement results are shown below. Figure 6 .

[0061] Figure 6 The results show that the original aluminum electrode exhibited the lowest charge transfer resistance (Rct, 114.3 ohms), which increased slightly to 118.0 ohms after one cycle and further increased to 127.7 ohms after 10 cycles. This indicates that the charge transfer characteristics of the aluminum cathode remain relatively stable as the electrolysis process progresses, which is beneficial for PFOA degradation cycling under long-term operating conditions.

[0062] Fundamentally, the electrochemical reduction and decomposition of organic pollutants can be achieved through dissociation electron transfer (DET) at the cathode or indirectly through electrochemically generated reduction intermediates. Although PFOA removal is theoretically thermodynamically feasible at potentials below -1.2 V vsAg / AgCl, DET-mediated PFOA defluorination reactions are rarely reported, primarily due to the electrostatic repulsion between PFOA in aqueous solution and the cathode. For example, linear sweep voltammetry (LSV)... Figure 7 As shown in a), the applied cathode potentials are -1.7V and -1.9V vsAg / AgCl, corresponding to current densities of 10 mA·cm⁻¹. -2 and 25mA·cm -2 Despite a slight difference in cathode potential (0.2V), the PFOA removal rate differed significantly, being 0.0039 min at -1.7V. -1 At -1.9V, the time is 0.0125 min. -1 From a thermodynamic perspective, such a small difference in cathode potential is unlikely to have a significant impact on PFOA removal.

[0063] Therefore, this invention further compares the degradation of PFOA by titanium (Ti), a commonly used cathode material in electrochemical systems (current density 25 mA·cm). -2 The LSV curves of the original aluminum cathode and the Ti cathode are shown in [reference needed]. Figure 7 Figure b shows the Ti cathode potential as -2.8V vs. Ag / AgCl, which is 0.9V higher than that of the aluminum cathode. The degradation rates of PFOA by the original aluminum and Ti cathodes are shown in [Figure b]. Figure 7 As shown in Figure c, the degradation efficiency of the Ti cathode is 21.4%, far lower than that of the aluminum cathode (97.4%). This is consistent with... Figure 7 The degradation rate constant of the corresponding fitted curve shown in Figure d is 0.0010 min. -1 (Ti cathode) and 0.0125 min -1 (Al cathode).

[0064] The significant difference in degradation efficiency and rate between aluminum and titanium cathodes clearly demonstrates that PFOA decomposition is independent of DET cathode reduction.

[0065] To identify free radicals that may be involved in PFOA degradation, tert-butanol (TBA) was added as a H* scavenger and NO3 scavenger. - As e aq - Quenching experiments were conducted using the scavenging agent. ECL / CL measurements were then performed, using luminol (LH2) under alkaline conditions as the luminescent agent to measure the electron emission generated on the aluminum cathode. aq -Provide direct evidence. Since luminol has a pKa1 of 6.7 and a pKa2 of 15.1, it primarily exists in a single deprotonated form as LH. - Yes. The chemiluminescent pathway of luminol typically begins with hydrogen atom extraction (Equation 5) or rapid deprotonation of LH· radicals formed through single-electron oxidation (Equation 6). In O2 ·- When used as an oxidizing agent, LH- generates L... ·- Then, in the strong reducing agent e aq - Under the influence of [equations 7-9], luminescence conditions are achieved (Equations 7-9). When the rate of the protonation reaction (Equation 10) is faster than that of the de-excitation reaction (Equation 9), the emitting species is considered to be LH. - *

[0066] LH - +O2 ·- →L ·- +HO x (5)

[0067] LH - +O2 ·- →L ·- +H + +O x - (6)

[0068] e aq - +O2→O2 ·- (7)

[0069] L ·- +e aq - →L 2-* (8)

[0070] L 2-* →L 2- +hv (9)

[0071] L 2- +H₂O→LH - +OH - (10)

[0072] pH(OH - Concentration) is the concentration of Al producing e aq - Essential conditions. To study the pH changes at the aluminum cathode, this invention detected OH- ions near the aluminum cathode during electrolysis. - Concentration. Due to the technical difficulty of experimentally measuring local pH values, the local [OH] concentration on the Al cathode boundary layer was limited. - Theoretical calculations were performed. Based on Faraday's law, assuming 100% coulombic efficiency and no consumption of the generated OH...- And it is uniformly mixed in the boundary layer, theoretically maximizing the local [OH] - The boundary layer thickness (δ, m) and electrolysis time (t, s) can be calculated using Equations 11 and 12.

[0073]

[0074] Where It is the current (A), z is the number of electrons transferred in the reaction (z=1), and F is the Faraday constant 96485 (C·mol⁻¹). -1 S is the cathode (S = 0.0012 m) 2 The area of ​​the boundary layer is δ, where δ is the thickness of the boundary layer (m).

[0075] Similar to PFOA, other fluorinated compounds are also known as recalcitrant pollutants and pose a high risk to aquatic ecosystems. To assess the applicability of decomposing other fluorinated compounds, this invention also investigated the degradation of ofloxacin (OFX) and florfenicol (FLO) using an aluminum cathode ARP system.

[0076] To confirm that Al generates e aq - In addition to studying the important role of zinc in the process, this invention also investigates the degradation of PFOA using zinc (Zn), another typical amphoteric metal, as the cathode.

[0077] The inhibition of PFOA degradation by H* scavenger on aluminum cathodes is shown in the figure. Figure 8 .

[0078] ESR signals (a) and (e) obtained using DMPO as a free radical scavenger aq - The inhibitory effect of the scavenger on PFOA degradation in the aluminum cathode system (b), the change of ECL signal of luminol as a probe over time under different conditions (c) ([luminol] = 0.1 μM, pH = 11.0), and the theoretically calculated local pH value (d) are shown in the figure. Figure 9 , Figure 9 The inset of d in the figure shows the catholyte [OH] measured. - ]value.

[0079] The degradation kinetic fitting curves of PFOA degradation in the aluminum cathode ARP system under different NaNO3 concentrations are shown in the figure. Figure 10 .

[0080] The following data were collected in 10 consecutive experiments: the removal rate of PFOA in the aluminum cathode ARP system over time (a); the removal rates of OFX and FLO in the aluminum cathode ARP system (b); the degradation rate of PFOA in the aluminum and zinc cathode reduction systems (c); and the defluorination rate of PFOA in the aluminum and zinc cathode reduction systems (d). Figure 11 .

[0081] When different concentrations of TBA were added to the catholyte to quench H*, the PFOA degradation rate decreased slightly, by approximately 10%, as the TBA concentration increased from 0 mM to 100 mM. Figure 8 As shown in the ESR data ( Figure 9 In section a), the presence of H* was verified by observing nine characteristic peaks of the DMPO-H adduct on the aluminum electrode. Combined with ESR and Figure 8 As a result, H* is unlikely to be the major reducing species responsible for PFOA degradation.

[0082] like Figure 9 As shown in Figure c, no CL signal was observed in the blank group, which rules out the possibility of luminol self-luminescence at pH = 11.0. No CL signal was also observed in the titanium cathode reference group in alkaline aqueous solution. Notably, a significant luminescence signal was detected on the aluminum cathode, clearly demonstrating the presence of luminescence on the aluminum cathode. aq - The generation of, and e aq - It favors the CL of luminol in alkaline solutions. Furthermore, at 25 mA cm⁻¹... -2 ECL measurements were also performed on the aluminum cathode at a current density of [value missing]. Notably, the ECL signal strength increased sharply when the aluminum cathode was powered by electrolysis, followed by a sharp decrease after 600 seconds of power-off. The CL / ECL measurements together provide insights into the generation of electrons in the alkaline microenvironment adjacent to the aluminum cathode. aq - Direct evidence.

[0083] For the initial bulk PFOA solution, a pH of ~4.0 was observed. Figure 9 (Illustration of d in the middle), and then increased to ~11.0 at an electrolysis time of 0.5 h, and then showed slight changes as electrolysis continued, resulting in [OH] - From 1×10 -10 Increased to 0.0013 mol L -1 (pH 4.0~11.0). Theoretical calculation results ( Figure 9 d) shows that local [OH] - The thickness of the boundary layer on the Al cathode is negatively correlated with the boundary layer thickness. Assuming a maximum boundary layer thickness of 1 mm, theoretically, after 30 minutes of electrolysis, lg[OH]... - The value is 0.7, and after electrolysis for 240 min, lg[OH] - The value is 1.6, corresponding to [OH] - [The concentrations reached as high as 4.7 mol / L] -1 and 37.3 mol L -1 In fact, at the Al cathode where hydrogen evolution occurs during water electrolysis, if the boundary layer is thin, local [OH]- [Possibly higher. That is, HER is a local OH.] - The enrichment of [a substance] creates suitable conditions for its reaction with Al to produce e. aq - This is the key reduction intermediate responsible for the local decomposition of PFOA.

[0084] like Figure 11 As shown in Figure a, after 10 consecutive cycles of testing, the degradation rate of PFOA can be maintained at ~95%, indicating that the aluminum cathode ARP system has good reusability under long-term operation.

[0085] like Figure 11 As shown in Figure b, when the electrolysis times were 0.5 and 3.0 h, respectively, FLO and OFX were 100% degraded by the ARP system based on the Al cathode.

[0086] like Figure 11 As shown in Figures c and d, with Zn as the cathode, the degradation rate of PFOA was 36.5% after 4 hours of electrolysis, and only 42.8% after 12 hours of electrolysis. These values ​​are much lower than those with an Al cathode, which can be well explained by the fact that Al and Zn react with OH... - The difference in reactivity during the reaction. This further explains the formation of e- by the dissolution of amphoteric metals in alkaline solutions. aq - The degradation of PFOA provides evidence.

[0087] Based on Al cathode system for electro-hydration electrons e aq - A schematic diagram of the PFOA degradation mechanism is shown below. Figure 12 .

[0088] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for electrogenerating hydrated electrons using an amphoteric metal cathode, characterized in that, The steps are as follows: A membrane electrolytic cell is constructed using an amphoteric metal as the cathode, and hydrated electrons are generated in the cathode chamber when electricity is applied; the amphoteric metal is aluminum. The experiment was conducted in an H-type reactor, with two compartments separated by a DuPont Nafion 117 proton exchange membrane. A 50 mM Na₂SO₄ solution was used as the supporting electrolyte. A 30 mm × 40 mm commercial aluminum electrode was immersed in 50 mL of 5.0 mg·L⁻¹ sodium hydroxide solution in the cathode chamber. −1 The anode chamber contained a perfluorooctanoic acid solution, a platinum electrode, and 50 mL of Na₂SO₄ solution; the applied current density was set to 25 or 40 mA·cm⁻¹, respectively. −2 .

2. The application of the method for electrogenerating hydrated electrons by a zwitterionic metal cathode as described in claim 1 in the degradation of perfluorooctanoic acid.

3. The application of the method for electrogenerating hydrated electrons by a zwitterionic metal cathode as described in claim 1 in the degradation of fluorine-containing organic compounds.

Images