Fe / Mn / Zr-CF catalytic electrode and preparation method and application thereof

Abstract

The invention discloses a Fe / Mn / Zr-CF catalytic electrode and a preparation method and application thereof, and belongs to the technical field of heavy metal wastewater treatment. The preparation method of the Fe / Mn / Zr-CF catalytic electrode comprises the following steps: adding an alkaline solution containing carbonate into an aqueous solution containing Fe < 3 + >, Mn < 2 + > and Zr < 4 + >, so that Fe < 3 + >, Mn < 2 + > and Zr < 4 + > form a coprecipitate, drying and grinding the obtained coprecipitate, electrically depositing the coprecipitate on a carbon felt, and calcining to obtain the Fe / Mn / Zr-CF catalytic electrode. The Fe / Mn / Zr-CF catalytic electrode is prepared by using coprecipitation, electrodeposition and calcination methods, and the prepared Fe / Mn / Zr-CF catalytic electrode has good ORR performance and electrochemical performance. When being applied to a BES system, the composite material has a good capability of removing heavy metal ions in sewage.

Description

Technical Field

[0001] This invention belongs to the field of heavy metal wastewater treatment technology, specifically relating to an Fe / Mn / Zr-CF catalytic electrode, its preparation method, and its application. Background Technology

[0002] With the acceleration of industrialization, the amount of heavy metal wastewater generated is increasing. This wastewater comes from diverse sources and is characterized by high toxicity and easy accumulation, making its treatment difficult. Electroplating wastewater, in particular, contains multiple heavy metals, drawing significant attention. Heavy metal wastewater poses substantial threats to the ecological environment, human health, and economic development. Ecologically, it can directly harm aquatic life, potentially impairing the respiratory function of fish. While many common heavy metals are non-essential elements for plants, these heavy metals can still damage plant physiology and even pose a fatal threat. Regarding human health, heavy metals can enter the human body through drinking water and the food chain. Excessive accumulation can damage organs such as the brain, kidneys, and liver; some heavy metals may even be carcinogenic. The treatment of heavy metal wastewater has been extensively studied. Removal methods mainly include coagulation / flocculation, ion exchange, and chemical precipitation. These methods are low-cost, but have drawbacks such as poor removal of heavy metal ions and the generation of toxic sludge. With the development of materials science, membrane technology (nanofiltration, ultrafiltration, reverse osmosis), electrodialysis, and photocatalysis are also gradually being applied. These technologies have disadvantages such as high cost, long treatment time, and low applicable concentration.

[0003] How to remove heavy metal ions from heavy metal wastewater in a simple and efficient way is a practical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0004] The present invention aims to provide a Fe / Mn / Zr-CF catalytic electrode, its preparation method, and its application. Using carbon felt (CF) as a substrate, a catalytic electrode (Fe / Mn / Zr-CF) containing oxides of Fe, Mn, and Zr was prepared via co-precipitation, electrodeposition, and calcination. The oxides of Fe, Mn, and Zr are uniformly dispersed on the CF surface, exhibiting excellent electrochemical performance. The Fe / Mn / Zr-CF electrode coupled with a bioelectrode exchange (BES) is used to treat heavy metal wastewater, demonstrating good removal efficiency for heavy metal ions.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] One of the technical solutions of this invention is to provide a method for preparing a Fe / Mn / Zr-CF catalytic electrode, comprising the following steps:

[0007] To contain Fe 3+ Mn 2+ and Zr 4+Adding an alkaline solution containing carbonate ions to an aqueous solution of Fe... 3+ Mn 2+ and Zr 4+ A coprecipitate is formed, and the resulting coprecipitate is dried, ground, and electrodeposited onto a carbon felt. After calcination, the Fe / Mn / Zr-CF catalytic electrode is obtained.

[0008] Preferably, the Fe 3+ Mn 2+ and Zr 4+ The molar ratio is 1-2:1-2:1, more preferably 1:1:1.

[0009] Preferably, the concentration of carbonate ions in the alkaline solution containing carbonate ions is 1 mol / L.

[0010] Preferably, the Fe 3+ Mn 2+ and Zr 4+ The pH value during coprecipitation is 10.

[0011] Preferably, the carbon felt is pretreated before electrodeposition, and the pretreatment method is acid immersion.

[0012] Preferably, the electrodeposition potential is -0.7V, the time is 500s, and the electrodeposition solution is an aqueous solution containing 25g / L of the coprecipitate and 50g / L of sodium sulfate.

[0013] Preferably, the calcination temperature is 150–300°C, more preferably 250°C.

[0014] The second technical solution of the present invention provides a Fe / Mn / Zr-CF catalytic electrode prepared according to the above-mentioned preparation method of Fe / Mn / Zr-CF catalytic electrode.

[0015] The third technical solution of the present invention provides a bioelectrochemical system based on the above-mentioned Fe / Mn / Zr-CF catalytic electrode, wherein the Fe / Mn / Zr-CF catalytic electrode serves as the cathode of the bioelectrochemical system.

[0016] The fourth technical solution of the present invention provides an application of the above-mentioned bioelectrochemical system in the removal of heavy metal ions from water.

[0017] Bioelectrochemical systems (BES) utilize the self-generated electricity of microorganisms to remove heavy metal ions from water, and have recently attracted widespread attention. It involves multiple disciplines such as biology, electrochemistry, and chemical engineering. BES utilizes microorganisms to react with organic matter in the anode chamber; the generated electrons travel through an external circuit to the cathode chamber, thus producing an electric current. BES suffers from drawbacks such as the high cost of electrode materials, requiring further optimization. The performance of the cathode material largely determines the overall treatment effect of the BES. Highly active catalysts can improve the electron transfer rate, thereby accelerating the oxygen reduction reaction (ORR), making the development of a low-cost catalytic electrode important. Transition metal oxides (TMOs) have good ORR performance and are widely favored due to their advantages such as low synthesis cost, simple synthesis methods, abundant reserves, high catalytic activity, and good stability. The combination of Fe3O4, Fe2O3, and MnO2 has a rich valence state composition (Fe... 2+ Fe 3+ and Mn 3+ Mn 4+ These variable-valence ions can greatly improve the ORR performance of the catalytic electrode. This invention found that the addition of ZrO2 can further improve the overall electrochemical performance.

[0018] The beneficial technical effects of the present invention are as follows:

[0019] This invention utilizes co-precipitation, electrodeposition, and calcination methods to prepare Fe / Mn / Zr-CF catalytic electrodes. The prepared Fe / Mn / Zr-CF catalytic electrodes exhibit excellent ORR (Organic Reduction) and electrochemical performance. When applied to a BES (Boiler Estimate) system, they demonstrate good removal capabilities for heavy metal ions in wastewater. The preparation method provided by this invention is simple, and the Fe / Mn / Zr-CF coupled BES system exhibits good heavy metal ion removal efficiency, showing potential for large-scale application. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the preparation of the Fe / Mn / Zr-CF catalytic electrode according to the present invention.

[0021] Figure 2 This is a schematic diagram of the BES system in Example 2.

[0022] Figure 3 The CV curves (a) of the catalytic electrodes A-CF, B-CF, C-CF, D-CF and E-CF in Example 1, and the CV curves (b), LSV curves (c), afel curves (d), EIS curves (e) and interface charge transfer resistance diagrams (f) of Fe / Mn / Zr-CF obtained at different calcination temperatures.

[0023] Figure 4The images shown are: SME diagram (a) of CF after pretreatment in Example 1; SME diagram (b) of C-CF after electrodeposition; SME diagram (c) of Fe / Mn / Zr-CF at 250℃; EDS diagram (d) of Fe / Mn / Zr-CF at 250℃; TEM diagram (e) and elemental mapping diagram (e1-e3) of Fe / Mn / Zr-CF at 250℃; XRD diagrams (f) of C-CF and Fe / Mn / Zr-CF at 250℃; XPS full spectrum (g), Fe 2p spectrum (g1), Mn 2p spectrum (g2), Zr 3d spectrum (g3), C 1s spectrum (g4), and O 1s spectrum (g5) of Fe / Mn / Zr-CF at 250℃.

[0024] Figure 5 To simulate the effect of wastewater pH on Cu(II) removal rate (a), fitting curve of pseudo-first-order kinetic model (a1) and fitting curve of pseudo-second-order kinetic model (a2); on Zn(II) removal rate (b), fitting curve of pseudo-first-order kinetic model (b1) and fitting curve of pseudo-second-order kinetic model (b2); on Ag(I) removal rate (c), fitting curve of pseudo-first-order kinetic model (c1) and fitting curve of pseudo-second-order kinetic model (c2); and on Ni(II) removal rate (d), fitting curve of pseudo-first-order kinetic model (d1) and fitting curve of pseudo-second-order kinetic model (d2).

[0025] Figure 6 The effects of catalytic cathode area on Cu(II) removal rate (a), fitting curves of pseudo-first-order kinetic model (a1) and pseudo-second-order kinetic model (a2); on Zn(II) removal rate (b), fitting curves of pseudo-first-order kinetic model (b1) and pseudo-second-order kinetic model (b2); on Ag(I) removal rate (c), fitting curves of pseudo-first-order kinetic model (c1) and pseudo-second-order kinetic model (c2); and on Ni(II) removal rate (d), fitting curves of pseudo-first-order kinetic model (d1) and pseudo-second-order kinetic model (d2).

[0026] Figure 7 To simulate the effects of heavy metal ion concentrations in wastewater on Cu(II) removal rate (a), fitting curves of the pseudo-first-order kinetic model (a1) and pseudo-second-order kinetic model (a2), on Zn(II) removal rate (b), fitting curves of the pseudo-first-order kinetic model (b1) and pseudo-second-order kinetic model (b2), on Ag(I) removal rate (c), fitting curves of the pseudo-first-order kinetic model (c1) and pseudo-second-order kinetic model (c2), and on Ni(II) removal rate (d), fitting curves of the pseudo-first-order kinetic model (d1) and pseudo-second-order kinetic model (d2).

[0027] Figure 8 The images show SEM (a) and EDS (b) images of the Fe / Mn / Zr-CF catalytic electrode surface after running the BES system, XRD patterns (c) of the Fe / Mn / Zr-CF catalytic electrode and cathode chamber precipitate after running the BES system, and TEM (d) images and elemental mappings (d1–d7) of the Fe / Mn / Zr-CF catalytic electrode after running the BES system.

[0028] Figure 9 XPS full spectrum of Fe / Mn / Zr-CF catalytic electrode after running BES system (a), Fe 2p spectrum (a1), Mn 2p spectrum (a2), Zr 3d spectrum (a3), Cu 2p spectrum (a4), Zn 2p spectrum (a5), Ag 3d spectrum (a6), Ni 2p spectrum (a7), C 1s spectrum (a8) and O 1s spectrum (a9).

[0029] Figure 10 This is a schematic diagram of the mechanism for recovering heavy metal ions using the BES system in this invention.

[0030] Figure 11 The power density curve and polarization curve (a) collected in Example 2, the effect of intermittent flow and continuous flow modes on the removal rate of different heavy metal ions (b-e), and the fitting curves of the pseudo-first-order and second-order kinetic models for the removal of different heavy metal ions (b1-e1). Detailed Implementation

[0031] 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.

[0032] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] Unless otherwise specified, room temperature or normal temperature in this invention refers to a temperature of 20±10℃.

[0037] The flowchart for preparing the Fe / Mn / Zr-CF catalytic electrode according to this invention is shown below. Figure 1 .

[0038] The carbon felt used in this invention has a thickness of 5 mm.

[0039] Example 1

[0040] Preparation of Fe / Mn / Zr-CF catalytic electrode:

[0041] (1) Pretreatment of carbon felt

[0042] Cut the CF into 2×4cm pieces. Then, soak the cut CF pieces in acetone and anhydrous ethanol for 24 hours to remove impurities from the production process. After soaking, rinse with deionized water and then soak in hydrochloric acid for half an hour to make it easier for the catalytic components to adhere to the CF surface. After soaking, rinse the CF carefully with deionized water and then dry it in a 60℃ oven overnight. Store the pretreated CF in a sealed bag to prevent contamination.

[0043] (2) Preparation of Fe / Mn / Zr-CF:

[0044] Add 3.18 g MnSO4·H2O, 5.56 g FeSO4·7H2O, and 4.66 g ZrCl4 to 120 mL of deionized water (Fe:Mn:Zr = 1:1:1) and stir on a magnetic stirrer at 330 r / min until homogeneous. Then, heat and stir the mixture in an 80 °C water bath for 30 min, and add 1 mol·L⁻¹ water dropwise. -1The sodium carbonate solution was heated until the pH reached 10, and then stirred for 45 minutes. The precipitate was separated using a centrifuge and washed three times with dehydrated ethanol and deionized water to neutralize the washing solution. The washed precipitate was then dried in an oven (60°C) for 24 hours. After drying, it was thoroughly ground in an agate mortar and sieved through a 60-mesh sieve to obtain catalyst powder. By changing the reagent dissolved in the first step while keeping other conditions unchanged, different catalyst powders can be obtained, as detailed in Table 1.

[0045] Table 1 Composition of different catalyst powders

[0046] Catalyst powder <![CDATA[FeSO4·7H2O]]> <![CDATA[MnSO4·H2O]]> <![CDATA[ZrCl4]]> Fe:Mn:Zr A 5.56g 0g 0g 1 B 5.56g 3.18g 0g 1:1 C 5.56g 3.18g 4.66g 1:1:1 D 11.12g 3.18g 4.66g 2:1:1 E 11.12g 6.36g 4.66g 2:2:1

[0047] Electrodeposition experiments were conducted using an electrochemical workstation. The three electrodes of the workstation were configured as follows: a platinum sheet, pretreated CF, and a saturated calomel electrode served as the counter, working, and reference electrodes, respectively. The electrodeposition solution consisted of 2.5 g of A / B / C / D / E powder and 5 g of Na₂SO₄ added to 100 mL of ultrapure aqueous solution. The electrodeposition potential was set to -0.7 V, and the electrodeposition time was controlled to 500 s. The electrodeposited CF was then dried in an oven (60 °C) for 24 hours. The resulting catalytic electrodes were named A-CF, B-CF, C-CF, D-CF, and E-CF, respectively. Among them, C-CF exhibited better electrochemical performance and was selected for the next step of calcination.

[0048] The electrodeposited C-CF was then calcined in a tube furnace at a heating rate of 5 °C / min to 150 °C, 200 °C, 250 °C, and 300 °C, respectively. After heating, the temperature was held for 2 hours, and then cooled to room temperature. These were named Fe / Mn / Zr-CF-150 °C, Fe / Mn / Zr-CF-200 °C, Fe / Mn / Zr-CF-250 °C, and Fe / Mn / Zr-CF-300 °C, respectively.

[0049] Example 2

[0050] Building and running the BES system:

[0051] A schematic diagram of the BES system is shown below. Figure 2 As shown, the BES has a two-chamber configuration, consisting of a cathode chamber, an anode chamber, and a proton exchange membrane (0011PEM, Hangzhou, China). The proton exchange membrane is pretreated before use by immersing it in hydrogen peroxide and dilute sulfuric acid solutions, respectively. The usable area is approximately 40 cm². 2The anode chamber has a volume of 100 mL and is filled with activated carbon and graphite as granular electrodes, with a particle size of 3–5 mm. The activated carbon and graphite particles have high conductivity, effectively collecting electrons generated by electrogenic bacteria in the anode chamber. Specialized electrogenic bacteria (Shewanella) cultured in the laboratory are inoculated, and a few drops of activated sludge are added to enhance the microbial community and improve the system's electrogenic capacity. During the acclimatization stage of the anode microorganisms, a nutrient solution (C6H4O3) prepared with deionized water is used. 12 O6, 200 mg·L -1 K2HPO4·3H2O, 10 mg·L -1 NH4Cl, 120 mg·L -1 MgSO4, 5 mg·L -1 CaCl2·2H2O, 5 mg·L -1 The anode chamber was fed with water in a continuous flow mode and cultured for 10 days. During the culture period, the open-circuit voltage was tested daily with a multimeter. After culture, the open-circuit voltage of the anode chamber gradually stabilized. An 8cm long, 5mm diameter iron nail was used to collect electrons in the anode chamber and served as the anode of the BES. A saturated calomel electrode (SCE) was used as the reference electrode to collect potential data. The cathode chamber of the BES had a volume of 100mL and a prepared catalytic electrode was used as the cathode. The iron nail and Fe / Mn / Zr-CF were connected to the data acquisition system to monitor the potential data of the BES. A suitable resistor was connected between the Fe / Mn / Zr-CF and the iron nail to form a closed loop of the BES system, thus constituting a complete BES system, which operated in a continuous flow mode. Simulated electroplating wastewater containing Cu(II), Zn(II), Ag(I), and Ni(II) was prepared, fed into the anode chamber, passed through the anode chamber into the cathode chamber, and then discharged from the system to test the system's heavy metal ion removal capacity. During the experiment, four identical BES systems were run simultaneously to conduct parallel experiments, with samples taken every three hours to test the concentration of heavy metal ions.

[0052] Analysis method:

[0053] Scanning electron microscopy (FE-SEM, America, Quanta S) and energy dispersive spectroscopy (EDS) were used to image CF and Fe / Mn / Zr-CF during the preparation process. X-ray diffraction (XRD, Germany, Bruker D8 Advance) was used to determine the crystal form of the prepared Fe / Mn / Zr-CF, the Fe / Mn / Zr-CF after BES system operation, and the cathode chamber sludge. X-ray photoelectron spectroscopy (XPS, America, Thermo Fisher Scientific K-Alpha) was used to test FMMO-SS before and after BES system operation to identify elemental composition and crystal morphology, and to determine the morphologies of copper, zinc, silver, and nickel after the reaction. 16S high-throughput sequencing was used to characterize the anode chamber microbial population before and after the reaction. Flame atomic absorption spectrometry was used to determine the concentration of metal elements in the solution. Electrochemical characterization of Fe / Mn / Zr-CF was performed using an electrochemical workstation. A three-electrode system was employed, and its electrochemical performance was evaluated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and Tafel curves. The three-electrode system consisted of a working electrode (10 mm × 10 mm), an auxiliary electrode (platinum sheet, 10 mm × 10 mm), and a saturated calomel electrode (SCE). The three-electrode system was tested at 1 mol·L⁻¹. -1 The measurement was performed in Na₂SO₄. The result was measured at 10 mV·s. -1 The CV was scanned at a speed between -0.8V and 0.8V, and the EIS was subjected to sinusoidal perturbation tests at an amplitude of 10mV from 10,000Hz to 0.01Hz, at a speed of 50mV·s between -0.8V and 0.8V. -1 The LSV was measured.

[0054] Figure 3 The CV curves (a) of the catalytic electrodes A-CF, B-CF, C-CF, D-CF and E-CF in Example 1, and the CV curves (b), LSV curves (c), afel curves (d), EIS curves (e) and interface charge transfer resistance diagrams (f) of Fe / Mn / Zr-CF obtained at different calcination temperatures.

[0055] Figure 3 The results showed that both C-CF and D-CF exhibited significant reduction peaks (a), but the reduction peak of the catalytic electrode C-CF was relatively better. This may be because the addition of a certain proportion of Zr can promote the reduction of Fe. 3+ / Mn 4+ and Fe 2+ / Mn 3+Based on the test results, C-CF was selected for subsequent calcination after mutual conversion between the two processes.

[0056] The CV test results of the catalytic electrodes prepared at different calcination temperatures show that the reduction peak first strengthens and then weakens with increasing calcination temperature. The reduction peak is strongest at 250℃, and also has the largest integral area, indicating the largest capacitance. Compared with other calcination temperatures, the peak of the catalytic electrode at 250℃ is closer to zero potential. The CV test results show that the catalytic electrode calcined at 250℃ has the best electrochemical activity and is more likely to reduce heavy metal ions. The LSV test results show that the catalytic electrode calcined at 250℃ has a better current response than other catalytic electrodes, indicating a faster electron transfer rate at the reduction peak position and better ORR performance. Based on the Tafel test fitting of the exchange current density (i0), the i0 ranking of different catalytic electrodes is: Fe / Mn / Zr-CF-250℃ (1.7×10⁻⁶). -4 A·cm -2 )>Fe / Mn / Zr-CF-150℃(1.55×10 -4 A·cm -2 )>Fe / Mn / Zr-CF-200℃(1.39×10 -4 A·cm -2 )>Fe / Mn / Zr-CF-300℃(7.33×10 -5 A·cm -2 According to the test results, the i0 of Fe / Mn / Zr-CF-250℃ is the largest. Therefore, the electron transfer efficiency and electrochemical performance of the catalytic electrode are the highest at the calcination temperature of 250℃. This indicates that the combination of Fe, Mn and Zr is conducive to the rapid transfer of electrons, giving the catalytic electrode better ORR kinetic performance.

[0057] The formula for calculating the removal rate Re of various heavy metal ions is shown in formula (1):

[0058] Re(%)=(C0-C t ) / C0×100% (1)

[0059] In formula (1), C0 refers to the initial concentration of heavy metal ions, C t It refers to the concentration of heavy metal ions at time t.

[0060] The removal of heavy metal ions under different conditions was fitted by a pseudo-first-order kinetic model (Equation (2)) and a pseudo-second-order kinetic model (Equation (3)).

[0061] C t =C0×e -kt (2)

[0062]

[0063] In formulas (2) and (3), C0 refers to the initial concentration of heavy metal ions, C t It refers to the concentration of heavy metal ions at time t, where k is the rate constant, e is the natural constant, and t is time (h).

[0064] The interfacial charge transfer resistance (Rct) was obtained by fitting the EIS curves of each catalytic electrode using an equivalent circuit diagram. According to the fitting results, the Rct values ​​for different catalytic electrodes were: Fe / Mn / Zr-CF-150℃ (7.61Ω), Fe / Mn / Zr-CF-200℃ (5.41Ω), Fe / Mn / Zr-CF-250℃ (4.06Ω), and Fe / Mn / Zr-CF-300℃ (5.48Ω). According to the fitting results, the Rct obtained by the catalytic electrode Fe / Mn / Zr-CF-250℃ was the smallest. The smaller the Rct, the stronger the electron transfer ability. Electrochemical analysis results show that the catalytic electrode obtained at a calcination temperature of 250℃ has the most obvious reduction peak, the largest i0, and the smallest Rct, indicating that Fe / Mn / Zr-CF at 250℃ can make heavy metal ions easier to reduce and is beneficial to the system's power generation. Therefore, Fe / Mn / Zr-CF with a calcination temperature of 250℃ is selected for subsequent experiments.

[0065] Figure 4 The images shown are: SME diagram (a) of CF after pretreatment in Example 1; SME diagram (b) of C-CF after electrodeposition; SME diagram (c) of Fe / Mn / Zr-CF at 250℃; EDS diagram (d) of Fe / Mn / Zr-CF at 250℃; TEM diagram (e) and elemental mapping diagram (e1-e3) of Fe / Mn / Zr-CF at 250℃; XRD diagrams (f) of C-CF and Fe / Mn / Zr-CF at 250℃; XPS full spectrum (g), Fe 2p spectrum (g1), Mn 2p spectrum (g2), Zr 3d spectrum (g3), C 1s spectrum (g4), and O 1s spectrum (g5) of Fe / Mn / Zr-CF at 250℃.

[0066] Figure 4 The pretreated CF surface is clean and smooth. When magnified (top right corner), tiny cracks can be seen on the surface, indicating that more catalyst attachment points appear on the CF surface after pretreatment, which is beneficial to the subsequent preparation of the catalytic electrode (a). Figure 4 As shown in (b), numerous catalyst particles were uniformly deposited on the CF surface. Magnified analysis revealed that these catalyst particles adhered to the CF surface in a dotted pattern, and the rough CF surface provided more active sites for the deposition of the catalyst particles. Figure 4 As can be seen in (c), the catalyst powder is still uniformly dispersed after calcination at 250℃. The surface area of ​​the catalyst powder increases after calcination, which can enable the catalytic electrode to better reduce heavy metal ions. Furthermore, calcination can make the catalyst more tightly bound to the CF surface, which is beneficial to the operation of the catalytic electrode in the later stage.

[0067] EDS testing results showed that, in addition to carbon (C) from the CF, iron (Fe), manganese (Mn), and zirconium (Zr) from the catalyst powder were also detected on the surface of the catalytic electrode, further confirming the successful loading of the catalyst particles. Elemental mapping images of Fe / Mn / Zr-CF at 250℃ showed the presence of Fe, Mn, and Zr elements on the prepared Fe / Mn / Zr-CF surface, and these elements were uniformly dispersed on the catalytic electrode surface.

[0068] The XRD results of Fe / Mn / Zr-CF before and after calcination showed that the C-CF image had obvious peaks at 25.6° and 51.58°, and the Fe / Mn / Zr-CF image had obvious peaks at 28.1° and 50.6°. These two peaks correspond to the (002) and (112) planes of C (PDF#13-0148). This is because the catalytic electrode is based on CF. The C-CF and Fe / Mn / Zr-CF images clearly show crystalline plane features corresponding to Fe2O3 (PDF#15-0615, PDF#13-0458, PDF#04-0755). The peaks at 36.6°, 45.3°, 54° and 35.56°, 45.4°, 53.6° in these two images indicate the presence of Fe3O4 on the catalytic electrode surface (PDF#01-1111). Furthermore, characteristic crystal planes of MnO2 are present at 42.6°, 52.19° and 40.6°, 59.6° (PDF#14-0644). The remaining diffraction peaks are characteristic crystal planes of ZrO2 (PDF#02-0733). This indicates the presence of well-crystallized Fe2O3, Fe3O4, MnO2, and ZrO2 on the surface.

[0069] XPS characterization results showed the presence of Fe 2p at 711.17 eV and 723.78 eV. 3 / 2 and Fe 2p 1 / 2 The remaining peaks belong to Fe. 2+ and Fe 3+ Mn 2p exists in the Mn 2p spectrum. 3 / 2 and Mn 2p 1 / 2 This confirms the presence of MnO2. Zr3d is present at 182.5 eV and 184.9 eV in the Zr3d spectrum. 5 / 2 and Zr3d 3 / 2Two peaks indicate the presence of ZrO2. C=C and CO are present in both the C1s and O1s spectra.

[0070] Figure 5 To simulate the effect of wastewater pH on Cu(II) removal rate (a), fitting curve of pseudo-first-order kinetic model (a1) and fitting curve of pseudo-second-order kinetic model (a2); on Zn(II) removal rate (b), fitting curve of pseudo-first-order kinetic model (b1) and fitting curve of pseudo-second-order kinetic model (b2); on Ag(I) removal rate (c), fitting curve of pseudo-first-order kinetic model (c1) and fitting curve of pseudo-second-order kinetic model (c2); and on Ni(II) removal rate (d), fitting curve of pseudo-first-order kinetic model (d1) and fitting curve of pseudo-second-order kinetic model (d2).

[0071] Figure 5 The result showed that the infusion contained 10 mg·L⁻¹ -1 Simulated wastewater containing Cu(II), Zn(II), Ag(I), and Ni(II) was introduced into a BES, and the pH of the simulated wastewater was changed (3, 5, 7, 9), and four identical BESs were run. Under these pH conditions, the removal rates of various heavy metal ions were as follows: Cu(II) (66.7%, 87.93%, 98.55%, 99.79%), Zn(II) (71.13%, 82.2%, 98.24%, 98.63%), Ag(I) (98.99%, 99.43%, 98.95%, 99.94%), and Ni(II) (78.81%, 84.74%, 98.92%, 95.82%). It can be seen that the removal rate increases with increasing pH, which is consistent with previous research results. This is mainly attributed to the formation of a galvanic cell between activated carbon / graphite particles and iron nails in the anode chamber. The iron nails release iron ions as crystal nuclei, which can react with hydroxide ions in the solution to form ferric hydroxide. Ferric hydroxide removes heavy metal ions from the wastewater through flocculation. However, it was also observed that the removal rate of Ag(Ⅰ) was relatively high at different pH values, indicating that Ag(Ⅰ) is relatively easy to remove. The removal of heavy metal ions was fitted using pseudo-first-order and pseudo-second-order kinetic models to study the kinetic characteristics of pH value and heavy metal ion removal. Figure 5 (a1-d1) and Figure 5 (a2-d2) represent the fitting results of the pseudo-first-order and second-order kinetic models, respectively. It can be seen that the actual removal results are closer to the pseudo-first-order kinetic model. As the pH value increases, the rate constant of the pseudo-first-order kinetic model also increases, which can be attributed to the fact that flocculation is more likely to occur under alkaline conditions.

[0072] Figure 6The effects of catalytic cathode area on Cu(II) removal rate (a), fitting curves of pseudo-first-order kinetic model (a1) and pseudo-second-order kinetic model (a2); on Zn(II) removal rate (b), fitting curves of pseudo-first-order kinetic model (b1) and pseudo-second-order kinetic model (b2); on Ag(I) removal rate (c), fitting curves of pseudo-first-order kinetic model (c1) and pseudo-second-order kinetic model (c2); and on Ni(II) removal rate (d), fitting curves of pseudo-first-order kinetic model (d1) and pseudo-second-order kinetic model (d2).

[0073] Figure 6 The result showed that the infusion contained 10 mg·L⁻¹ -1 Simulated wastewater containing Cu(II), Zn(II), Ag(I), and Ni(II) was introduced into a BES (Boiler Electrode System). Four identical BES systems were run with varying cathode areas (1×4 cm, 1×3 cm, 1×2 cm, and 1×1 cm). Under these conditions, the removal rate of heavy metal ions increased with increasing cathode area. This is likely because the increased cathode area leads to a larger contact area between the wastewater and the cathode, resulting in more reduction sites for heavy metal ions, which significantly promotes their reduction. Figure 6 (a1-d1) and Figure 6 (a2-d2) represent the fitting results of the pseudo-first-order and second-order dynamic models, respectively. When the size is 1×4cm, Cu(II), Zn(II), Ag(I), and Ni(II) all obtain the maximum velocity constants, which are 0.953h. -1 1.097h -1 1.028h -1 and 0.547h -1 The fitting results clearly show that changing the area of ​​the catalytic electrode can effectively regulate the reduction process of heavy metal ions on the surface of the catalytic electrode.

[0074] Figure 7 To simulate the effects of heavy metal ion concentrations in wastewater on Cu(II) removal rate (a), fitting curves of the pseudo-first-order kinetic model (a1) and pseudo-second-order kinetic model (a2), on Zn(II) removal rate (b), fitting curves of the pseudo-first-order kinetic model (b1) and pseudo-second-order kinetic model (b2), on Ag(I) removal rate (c), fitting curves of the pseudo-first-order kinetic model (c1) and pseudo-second-order kinetic model (c2), and on Ni(II) removal rate (d), fitting curves of the pseudo-first-order kinetic model (d1) and pseudo-second-order kinetic model (d2).

[0075] Figure 7In this study, the pH value of all simulated wastewater was 7, and the concentration of each heavy metal ion was 5 mg·L⁻¹. -1 10 mg·L -1 20 mg·L -1 30 mg·L -1 The results showed that the removal rates of all heavy metal ions were high at low concentrations. However, as the concentration of heavy metal ions increased, the removal rates of all ions decreased to varying degrees. This is because the activity of electrogenic bacteria in the anode chamber significantly decreased with increasing heavy metal ion concentration. This affects the removal of heavy metal ions by microorganisms through phagocytosis and adsorption, and also reduces the electrogenic capacity of the electrogenic bacteria, thus decreasing the reduction of heavy metal ions on the catalytic electrode surface. The removal of heavy metal ions was fitted using pseudo-first-order and pseudo-second-order kinetic models to further investigate the kinetic characteristics of heavy metal ion removal under the influence of initial concentration. The fitting results are shown in the figures below. Figure 7 (a1-d1) and Figure 7 In (a2-d2), R is obtained from the pseudo-first-order dynamic model. 2 R is greater than that obtained from the pseudo-second-order dynamic model 2 The rate constant obtained from the first-order fitting is not linearly related to the concentration. This may be the result of the interaction between two factors: the decrease in the activity of electrogenic bacteria and the increase in the solution conductivity due to the increase in the initial concentration.

[0076] Mechanism analysis of heavy metal ion removal:

[0077] Figure 8 The images show SEM (a) and EDS (b) images of the Fe / Mn / Zr-CF catalytic electrode surface after running the BES system, XRD patterns (c) of the Fe / Mn / Zr-CF catalytic electrode and cathode chamber precipitate after running the BES system, and TEM (d) images and elemental mappings (d1–d7) of the Fe / Mn / Zr-CF catalytic electrode after running the BES system.

[0078] Figure 8The results showed that after running the BES system, the Fe / Mn / Zr-CF surface became significantly rougher. This is due to the oxidation products of the heavy metal ions deposited after the reaction. Magnified (upper right corner), the oxidation products can be seen to be in an aggregated form, irregularly arranged on the catalytic electrode surface. EDS further characterized the elemental composition of the catalytic electrode surface, revealing the presence of the constituent elements of Fe / Mn / Zr-CF (Fe, Mn, Zr, and C), as well as heavy metal elements (Cu, Zn, Ag, and Ni) present in simulated wastewater, and trace elements (Ca and Mg) present during the microbial culture stage in the anode chamber. The elemental mapping image of the Fe / Mn / Zr-CF surface also confirmed that the constituent elements and heavy metal elements of the catalytic electrode were uniformly distributed on the surface, indicating that the catalytic components still exist on the surface of the catalytic electrode after use, and that the heavy metal elements were uniformly deposited on the catalytic electrode surface after reduction.

[0079] XRD analysis was performed on the catalytic electrode after use and the cathode chamber precipitate collected several times. The results showed that characteristic crystal planes of Fe2O3, Fe3O4, MnO2, and ZrO2 remained on the surface of the catalytic electrode after use, indicating that the catalyst powder did not disappear after operation, suggesting a relatively tight bond between the catalyst powder and CF. Various reduction products of heavy metal ions were present in the sludge of the catalytic electrode and cathode chamber, including Cu (42° and 51.7°, 43.34°), CuO (56.16° and 56.44°), Cu2O (32.18° and 31.66°), Zn (34.98° and 34.2°, 53.84°), ZnO (30.14° and 37.5°), and Ni (46.1° and 45.4°). The values ​​of NiO (62.66°, 75.44° and 35.88°), Ag (38.76°, 65.66° and 39.7°, 45.4°, 66.4°, 75.24°) and AgO (33.3°, 38.5° and 34.32°, 38.5°, 44.34°, 27.32°) indicate that these heavy metal ions underwent reduction reactions on the catalyst surface.

[0080] Figure 9 XPS full spectrum of Fe / Mn / Zr-CF catalytic electrode after running BES system (a), Fe 2p spectrum (a1), Mn 2p spectrum (a2), Zr 3d spectrum (a3), Cu 2p spectrum (a4), Zn 2p spectrum (a5), Ag 3d spectrum (a6), Ni 2p spectrum (a7), C 1s spectrum (a8) and O 1s spectrum (a9).

[0081] XPS characterization of the Fe / Mn / Zr-CF catalytic electrode after operation showed that Fe2p was present in the Fe 2p spectrum. 2+ and Fe3+ The peaks at 641.32 eV and 651.45 eV indicate the presence of Fe2O3 and Fe3O4. The peaks at 641.32 eV and 651.45 eV belong to Mn2p, respectively. 3 / 2 and Mn 2p 1 / 2 This indicates that MnO2 still exists after use, and in the Zr 3d spectrum, Zr 3d 5 / 2 and Zr 3d 3 / 2 The 2.4 eV difference is attributed to the presence of ZrO2. This indicates that Fe2O3, Fe3O4, MnO2, and ZrO2 remain well-crystallized on the surface of the catalytic electrode after use. Several peaks of 933.194 eV, 934.624 eV, 9534 eV, 954.74 eV, and 944.4 eV are present in the Cu 2p spectrum, which belong to Cu... 0 Cu 2+ Cu + Cu + and Cu 2+ The satellite peaks indicate the presence of Cu(II) reduction products Cu, CuO, and Cu₂O. The peaks at 1022 eV and 1020.8 eV in the Zn 2p spectrum indicate the presence of ZnO and Zn. The peaks at 3684 eV and 3744 eV in the Ag 3d spectrum indicate the presence of Ag, and that it is relatively pure. The peaks at 856.4 eV and 873.83 eV in the Ni 2p spectrum belong to Ni₂p. 3 / 2 The peaks at 861 and 879.69 eV belong to Ni 2p 1 / 2 This also proves the existence of Ni. 0 and Ni + .

[0082] Based on the above characterization and comprehensive analysis of the removal results of heavy metal ions under the influence of different factors, this invention proposes a reasonable mechanism for the recovery of heavy metal ions (see...). Figure 10 The inventors believe that the removal of heavy metal ions in the BES system of this invention mainly involves three mechanisms: (1) electroreduction; (2) electrocoagulation; and (3) microbial removal. Electrogenic bacteria in the anode chamber decompose organic matter to generate bioelectricity, which is then transferred to the catalytic electrode in the cathode chamber via the external circuit. At this time, heavy metal ions (Mn) in the cathode chamber solution are removed. + The heavy metals are recovered through electroreduction (pathway 1). In the anode chamber, iron nails and activated carbon / graphite particles form a galvanic cell, decomposing iron ions to form ferric hydroxide. Ferric hydroxide acts as a flocculant, forming complexes with heavy metal ions, thus removing them (pathway 2). In addition to generating electricity, microorganisms in the anode chamber can also remove heavy metal ions from wastewater through adsorption and other pathways (pathway 3).

[0083] Comprehensive analysis of the BES system:

[0084] In addition to exploring the system's ability to remove heavy metal ions, this invention also analyzes the system's economic cost table (see Table 2) to explore the system's practical application potential.

[0085] Table 2. Economic Cost Analysis of the BES System

[0086]

[0087] Table 2 shows that the overall cost of the BES system of the present invention is low, at only 76 yuan.

[0088] The BES system of this invention does not introduce external energy when removing heavy metal ions. It relies on electrons generated by electrogenic bacteria to electroreduce heavy metal ions at the catalytic electrode. The inventors plotted power density curves and polarization curves based on data obtained from the data acquisition system. Figure 11 In (a), when Fe / Mn / Zr-CF is used as the cathode, the maximum power density of BES can reach 1332.3 mW·m. -3 This is due, on the one hand, to the fact that the galvanic cell composed of iron nails in the anode chamber and activated carbon / graphite particles promotes current generation, and on the other hand, to the fact that the combination of Fe3O4, Fe2O3, MnO2 and ZrO2 in the prepared catalytic electrode reduces the internal resistance of the catalytic electrode, thereby improving the power generation capacity of the system.

[0089] To further explore the application potential of the BES system of this invention, the removal efficiency of various heavy metal ions in the intermittent flow mode was compared. In this mode, a solution containing 10 mg L of heavy metal ions was injected into the cathode chamber. -1 Simulated wastewater containing Cu(II), Zn(II), Ag(I), and Ni(II) with a pH of 7 was tested using a Fe / Mn / Zr-CF electrode with a size of 1×4cm. Figure 11The figure (be) compares the removal capabilities of intermittent and continuous flow modes. It shows that after 12 hours of treatment, the removal rates of Cu(II), Zn(II), Ag(I), and Ni(II) reached 93.2%, 82.33%, 98.24%, and 48.97%, respectively. Compared with the continuous flow removal effect under the same conditions, the removal efficiency was relatively lower to varying degrees. The removal results of these four heavy metal ions were ranked as Ag(I) > Cu(II) > Zn(II) > Ni(II). The high removal rate of Ag(I) is attributed to the excellent electrochemical properties of the catalytic electrode. The reduction of Ag(I) requires only one electron, and the smaller electron transfer number gives Ag(I) a significant kinetic advantage. Cu(II), Zn(II), and Ni(II) all require two electrons. Ag(I) and Cu(II) have higher reduction potentials, which makes it easier for the bioelectricity generated by electrogenic bacteria in the anode chamber to reduce Ag(I) and Cu(II). Although the reduction potentials of Zn(II) and Ni(II) are lower, the low internal resistance of the catalytic electrode promotes electron exchange on the electrode surface, enabling Zn(II) and Ni(II) to achieve better removal effects. To further investigate the reduction effect of each heavy metal ion under intermittent flow mode, the removal of heavy metal ions was fitted using pseudo-first-order and pseudo-second-order kinetic models. The results are shown in [Figure 1]. Figure 11 The reduction trends of these heavy metal ions (b1-e1) are more consistent with the pseudo-first-order kinetic model. The rate constants obtained from the pseudo-first-order kinetic model are Cu(0.573h) and Cu(b1-e1). -1 ), Zn(0.170h -1 ), Ag(1.005h -1 ), Ni(0.069h -1 The fitting results were consistent with the reduction results. Experimental results show that the reduction effect obtained under intermittent flow is slightly lower than that under continuous flow, but the overall effect is still good. In particular, the removal rates of Cu(II) and Ag(I) can still reach more than 90%, indicating that the BES system of the present invention can achieve good removal effects under multiple modes, further improving the feasibility of subsequent practical applications.

[0090] 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 preparing a Fe / Mn / Zr-CF catalytic electrode, characterized in that, Includes the following steps: To contain Fe 3+ Mn 2+ and Zr 4+ Adding an alkaline solution containing carbonate ions to an aqueous solution of Fe... 3+ Mn 2+ and Zr 4+ A coprecipitate is formed, and the resulting coprecipitate is dried, ground, and electrodeposited onto a carbon felt. After calcination, the Fe / Mn / Zr-CF catalytic electrode is obtained.

2. The method for preparing the Fe / Mn / Zr-CF catalytic electrode according to claim 1, characterized in that, The Fe 3+ Mn 2+ and Zr 4+ The molar ratio is 1~2:1~2:

1.

3. The method for preparing the Fe / Mn / Zr-CF catalytic electrode according to claim 1, characterized in that, The concentration of carbonate ions in the alkaline solution containing carbonate ions is 1 mol / L.

4. The method for preparing the Fe / Mn / Zr-CF catalytic electrode according to claim 1, characterized in that, The Fe 3+ Mn 2+ and Zr 4+ The pH value during coprecipitation is 10.

5. The method for preparing the Fe / Mn / Zr-CF catalytic electrode according to claim 1, characterized in that, The carbon felt is pretreated before electrodeposition by acid leaching.

6. The method for preparing the Fe / Mn / Zr-CF catalytic electrode according to claim 1, characterized in that, The electrodeposition was performed at a potential of -0.7V for 500s, and the electrodeposition solution was an aqueous solution containing 25g / L of the coprecipitate and 50g / L of sodium sulfate.

7. The method for preparing the Fe / Mn / Zr-CF catalytic electrode according to claim 1, characterized in that, The calcination temperature is 150–300°C.

8. A Fe / Mn / Zr-CF catalytic electrode prepared by the method according to any one of claims 1 to 7.

9. A bioelectrochemical system based on the Fe / Mn / Zr-CF catalytic electrode of claim 8, characterized in that, The Fe / Mn / Zr-CF catalytic electrode serves as the cathode of the bioelectrochemical system.

10. The application of the bioelectrochemical system of claim 9 in the removal of heavy metal ions from water.

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