A lanthanum-chitosan composite film modified carbon-based electrode, a preparation method thereof and an electric field assisted deep phosphorus removal method

Abstract

The present application relates to water treatment and electrochemical separation technical field, disclose a kind of lanthanum-chitosan composite membrane modified carbon-based electrode and its preparation method and electric field auxiliary deep phosphorus removal method, the carbon-based electrode includes carbon-based substrate and the lanthanum-chitosan composite membrane layer covered on its surface, lanthanum species in composite membrane layer and chitosan matrix synergistically provide selective binding site to phosphate.The preparation method includes: substrate cleaning and alkali activation, lanthanum salt and chitosan solution are mixed and ultrasonic dispersion, fractionally drop coating load, vacuum drying film and hot pressing / light pressure densification.The electrode is used as anode, unmodified carbon cloth as cathode to construct flow-by CDI device, and under the condition of circulating flow, external voltage can be applied, minutes level rapid deep phosphorus removal can be realized under high chlorine background, and it has reversible regeneration performance, and removal rate is close to 100%.

Description

Technical Field

[0001] This invention relates to the field of water treatment and electrochemical separation technology, and particularly to a carbon-based electrode modified with a lanthanum-chitosan composite membrane and its preparation method, and to a method for achieving electric field-assisted deep phosphorus removal of the electrode in a flow-by CDI system. Background Technology

[0002] Eutrophication and algal blooms are closely related to dissolved phosphorus input, and scenarios such as advanced urban wastewater treatment and non-point source runoff management place higher demands on the efficient removal of low-concentration phosphates. Existing processes such as chemical precipitation, adsorption, and membrane separation often face problems such as high reagent consumption, difficult regeneration, insufficient selectivity, or high operating costs in the low-concentration range.

[0003] Electrochemical separation technologies (such as capacitive deionization, CDI) have attracted attention in the field of low-concentration ion removal due to their advantages such as electroregeneration and good device integration. However, in cases of low-concentration phosphate and the presence of coexisting anions (such as Cl-), further challenges remain. - NO3 - HCO3 - SO4 2- Phosphate removal still faces certain challenges under aquatic conditions. This is because: firstly, coexisting anions compete with phosphate ions for migration and adsorption under an electric field, affecting the selective enrichment of phosphate; secondly, phosphate ions can exhibit different ionic forms (such as H₂PO₄) under different pH conditions. - HPO4 2- The differences between its interface mass transfer behavior and binding behavior further increase the difficulty of stable and efficient capture.

[0004] Furthermore, existing electrode materials have limitations in terms of the number of active sites, the degree of site exposure, and interfacial mass transfer efficiency, which can easily lead to slow deep removal kinetics. During continuous cyclic operation, performance may also degrade due to factors such as site occupancy, interfacial passivation, or insufficient regeneration. Increasing the applied voltage or extending the operating time to achieve a higher removal rate may also increase operating energy consumption.

[0005] Therefore, it remains necessary to develop an electrode and its operating method that are suitable for continuous flow (e.g., flow-by CDI) configurations, have high selectivity for phosphate under coexisting anion conditions, fast removal kinetics, and good cycle stability, in order to meet the requirements for deep removal of low-concentration phosphate. Summary of the Invention

[0006] Given that existing flow-type CDI systems often suffer from insufficient phosphate selectivity, slow deep removal kinetics, and susceptibility to cyclic operation in water treatment scenarios with low phosphate concentrations and coexisting anions, and that pursuing higher removal rates may result in increased operating energy consumption, this invention aims to provide a lanthanum-chitosan composite membrane-modified carbon-based electrode with a relatively simple structure, scalable fabrication, and suitable for flow-type CDI systems, along with its operating method, to achieve electric field-assisted deep phosphorus removal while maintaining operational stability.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a carbon-based electrode modified with a lanthanum-chitosan composite film, comprising the following steps:

[0008] S1. Cleaning and alkaline activation of the carbon-based substrate, wherein the carbon-based substrate is activated carbon cloth or carbon cloth;

[0009] S2. Lanthanum salt, chitosan solution, and deionized water are mixed and ultrasonically dispersed to obtain a composite coating liquid;

[0010] S3. Using a coating method, the composite coating liquid is uniformly loaded onto the surface of the alkali-activated carbon-based substrate, dried under vacuum to form a film, and then subjected to hot pressing to obtain a carbon-based electrode modified with a lanthanum-chitosan composite film.

[0011] Specifically, the alkali activation step is used to pretreat the surface of the carbon-based substrate to remove surface impurities and improve surface wettability and composite film adhesion conditions, thereby facilitating the uniform loading of the subsequent composite coating liquid.

[0012] Specifically, in the composite coating solution formed by the lanthanum salt and chitosan, chitosan serves as a film-forming matrix and adhesion carrier to improve the dispersibility and immobilization of lanthanum species on the carbon-based substrate surface, and to construct a composite film layer containing lanthanum active binding sites on the electrode surface, thereby enhancing the selective binding / capture capability of phosphate.

[0013] As a further preferred embodiment of the present invention, the cleaning and alkaline activation of the carbon-based substrate specifically includes:

[0014] The carbon-based substrate was first rinsed with deionized water, then ultrasonically cleaned in ethanol, and finally placed in a solution of 0.5–3 mol·L⁻¹. -1 The surface is activated by soaking in NaOH solution and then rinsed with deionized water until the washing solution is neutral (pH = 7 ± 0.5).

[0015] As a further preferred embodiment of the present invention, the lanthanum salt is at least one of chloride, nitrate, sulfate, and acetate.

[0016] As a further preferred embodiment of the present invention, the ratio of the lanthanum salt to the chitosan solution is 1 g:(1~10) mL. More preferably, the concentration of the chitosan solution is 0.1~2% (w / v). More preferably, the composite coating solution is applied to the carbon-based substrate surface in equal amounts multiple times, with the number of applications being 2~10. More preferably, after application, the substrate is vacuum dried at 30~80 °C.

[0017] In this invention, hot pressing is used to improve the density of the composite film and its adhesion strength to the carbon-based substrate, reduce the risk of film detachment, cracking, or local peeling during operation, and stabilize the interface structure. After hot pressing, the electrode can obtain stable and effective phosphorus removal performance; this is a necessary process step. Preferably, the hot pressing process involves covering the dried carbon-based substrate surface with a smooth medium at 50-120 °C and applying pressure for hot pressing for 1-10 minutes.

[0018] According to a second aspect of the present invention, a carbon-based electrode modified with a lanthanum-chitosan composite film is also provided, which is prepared by the above-described preparation method. The carbon-based electrode comprises a carbon-based substrate and a lanthanum-chitosan composite film layer covering the surface of the carbon-based substrate.

[0019] According to a third aspect of the present invention, the present invention also provides an application of a lanthanum-chitosan composite membrane-modified carbon-based electrode in the selective adsorption and regeneration of phosphates in solution under an applied electric field and a reverse electric field desorption. Specifically, under the action of an applied electric field, the carbon-based electrode, acting as the anode, selectively adsorbs phosphates in the solution, and desorbs the adsorbed phosphates when the carbon-based electrode acts as the cathode; this adsorption-desorption process is reversible. In a specific embodiment, the applied electric field is preferably 0.3-1.5 V for the selective adsorption of phosphates.

[0020] According to a fourth aspect of the present invention, the present invention also provides an electric field-assisted deep phosphorus removal method, which employs a flow-by CDI configuration, uses a carbon-based electrode modified with a lanthanum-chitosan composite membrane as the anode, and an unmodified carbon cloth as the cathode, and applies an external voltage under circulating flow conditions to remove phosphates from the solution.

[0021] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0022] 1) This invention is based on a high chlorine background (Cl... - Under the conditions of 1 g / L and an initial phosphorus concentration of 1.0 mg / L, rapid deep phosphorus removal can be achieved in minutes: when running at 1.2 V for 10 min, the phosphorus concentration in the solution can be reduced to near the detection limit, and the removal rate is close to 100%.

[0023] 2) This invention utilizes an external electric field to significantly enhance kinetics: compared to the uncharged condition, the phosphorus adsorption rate increases by approximately 4.3 times under the charged condition (example data: 38.2 vs 8.8 mmol·m). -2 ·h -1 The energy consumption and selectivity performance are good: the energy consumption in the example is approximately 26.4 kWh·kg. -1 P was significantly lower than that of the unmodified electrode system; in the examples, the selectivity index SP / Cl was approximately 5.9, and Cl... - Concentration fluctuations have little impact on the removal rate.

[0024] 3) The system of this invention has a certain tolerance to pH and coexisting anions: it can maintain near-complete removal of phosphorus within the pH range of 7-11; and it can also remove NO3-. - HCO3 - SO4 2- Even with coexisting anions, a high removal rate can still be maintained (Example >98%).

[0025] 4) This invention features reversible regeneration and multi-cycle stability: it can achieve multiple cycles in adsorption / desorption cycle mode, and subsequent cycles still maintain a high removal rate and selectivity. Attached Figure Description

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0027] Figure 1 This is a schematic diagram of a flow-by CDI device, where (a) is a schematic diagram of the overall circulation system and (b) is a schematic diagram of a partially enlarged reactor structure.

[0028] Figure 2 This is a schematic diagram of the structure of a carbon-based electrode modified with a lanthanum-chitosan composite film (LaC-CC).

[0029] Figure 3 This is a schematic diagram of the preparation and phosphorus removal process of the LaC-CC electrode.

[0030] Figure 4This is a comprehensive comparative chart showing the phosphorus removal / desalination behavior, kinetics, selectivity, energy consumption, and mechanism of different electrode systems under electric field off / on conditions. Specifically: (a) shows the phosphorus concentration in the effluent over time under different conditions (ordinate: phosphorus concentration, mg / L; abscissa: time, min), with comparison groups including: CC / electric field off, CC / electric field on, LaC-CC / electric field off, and LaC-CC / electric field on; (b) shows the Cl⁻ concentration in the effluent over time under different conditions (ordinate: Cl⁻ concentration, mg / L; abscissa: time, min), with comparison groups the same as (a); (c) shows a bar chart comparing phosphorus removal rates under different conditions (ordinate: phosphorus removal rate, %), with the abscissa representing each comparison group: CC / electric field off, CC / electric field on, LaC-CC / electric field off, and LaC-CC / electric field on); and (d) shows a bar chart comparing phosphorus adsorption rates under different conditions (ordinate: phosphorus adsorption rate, mmol·m⁻¹). -2 ·h -1 (a) The horizontal axis represents the comparison groups: CC / electric field off, CC / electric field on, LaC-CC / electric field off, LaC-CC / electric field on); (e) The current-time variation curves of different electrode systems under the condition of electric field on (energized) (vertical axis: current, A; horizontal axis: time, s), with CC and LaC-CC as the comparison objects; (f) The selectivity coefficient and energy consumption comparison graph of different electrode systems, where the left vertical axis represents the selectivity coefficient. The right vertical axis represents energy consumption (EC), and the horizontal axis represents CC and LaC-CC; (g) is a schematic diagram of the ion mass transfer mechanism under no electric field condition, showing that phosphate ions and competing anions mainly migrate at the electrode interface through ion diffusion; (h) is a schematic diagram of the ion mass transfer mechanism under electric field condition, showing that under the action of an applied electric field, ions undergo directional electromigration in addition to diffusion, and indicating the anode direction of the electrode and the direction of the electric field; (i) is a radar chart of the comprehensive performance of CC / electric field on and LaC-CC / electric field on under electric field on condition, used to compare the overall performance of the two systems in multiple dimensions.

[0031] Figure 5 The diagram shows the effect of pH on phosphorus removal performance, including (a) a graph showing the change of effluent phosphorus concentration over time under different pH conditions, (b) a bar chart comparing phosphorus removal rates under different pH conditions, (c) a bar chart comparing phosphorus adsorption rate / removal rate under different pH conditions, and (d) the distribution of phosphate species (H3PO4, H2PO4) under different solution pH conditions. - HPO4 2- PO4 3- ) Schematic diagram of pH variation.

[0032] Figure 6 The diagram shows the effect of applied voltage on phosphorus removal performance, including (a) a graph showing the change of phosphorus concentration in effluent over time under different applied voltage conditions; (b) a bar chart comparing phosphorus removal rates under different applied voltage conditions; (c) a bar chart comparing phosphorus adsorption rate / removal rate under different applied voltage conditions; and (d) a bar chart comparing system energy consumption (EC) under different applied voltage conditions.

[0033] Figure 7 The graphs and bar charts show the effects of coexisting anions on phosphorus removal performance. (a) is a bar chart comparing phosphorus removal efficiency under different coexisting anion conditions (control group and Cl). - SO4 2- HCO3 - NO3 - (a) Comparison of coexistence conditions); (b) Schematic bar chart comparing the system selectivity coefficients under different coexisting anions (in Cl... - SO4 2- NO3 - HCO3 - Selective performance in a coexisting context.

[0034] Figure 8 This diagram illustrates the changes in removal rate, adsorption rate, and selectivity during a multi-cycle adsorption-desorption process. (a) is a graph showing the change in effluent phosphorus concentration over operating time at different cycle numbers (cycle = 1–4 for comparison); (b) is a bar chart comparing phosphorus removal rates at different cycle numbers; (c) is a bar chart comparing phosphorus adsorption rate / removal rate at different cycle numbers; and (d) is the selectivity coefficient at different cycle numbers (e.g., ...). A schematic diagram of the changes and comparisons using a bar chart.

[0035] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0036] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0037] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0038] Example 1: Preparation of LaC-CC carbon-based electrode modified with lanthanum-chitosan composite film

[0039] 1) Take a 5cm × 5cm activated carbon cloth (ACC) as the carbon-based substrate, rinse it with deionized water, then ultrasonically clean it in ethanol for 10 min, and then place it in 1 mol·L⁻¹ water. -1 Soak the surface in NaOH solution for 30 minutes to activate it; finally, rinse repeatedly with deionized water until the washing solution is close to neutral, and set aside for later use.

[0040] 2) Weigh 1.0 g of La(NO3)3·6H2O, add 4 mL of 0.75% (w / v) chitosan solution and 2 mL of deionized water, mix and ultrasonically disperse for 30 min, gently shaking intermittently during the dispersion process; shake thoroughly again before use to obtain the composite coating solution.

[0041] 3) Take 1.0 mL of the composite coating solution and evenly drop it onto the substrate surface in 5 equal portions; vacuum dry at 50 ℃ for about 30 min to form the initial film layer; then place it on a 75 ℃ hot plate, cover it with a clean glass slide and gently press for about 5 min to enhance the film layer density and adhesion; cool to room temperature to obtain the LaC-CC electrode. The electrode size is 5cm × 5cm, and it can be cut to the required size in actual applications.

[0042] In this embodiment, the La element content in the LaC-CC electrode was determined (e.g., by ICP) and characterized as total amount or by area / mass normalization. The total La element content was found to be 0.27 g.

[0043] Example 2: Electric field-assisted deep phosphorus removal method in flow-by CDI, the device construction is as follows Figure 1 As shown

[0044] 1) The reactor was constructed using a flow-by CDI configuration, with a cavity flow channel between the two electrode chambers and an insulating mesh for support to prevent short circuits. The LaC-CC electrode prepared in Example 1 was used as the anode, and unmodified carbon cloth was used as the cathode. An anion exchange membrane (AEM) was covered on the cathode surface.

[0045] 2) Prepare a phosphate solution using K₂HPO₄ and KH₂PO₄ to achieve an initial P concentration of 1.0 mg / L, and prepare a background Cl solution using NaCl. - The concentration was 1 g / L; the total volume of the solution was 250 mL and remained constant during the experiment; phosphorus adsorption was carried out by a peristaltic pump (30 rpm, the flow rate can be calibrated according to the pump tube specifications), and the pH of the influent aqueous solution was 7.

[0046] 3) Using the Shanghai Chenhua electrochemical workstation, the system was run at a constant voltage of 1.2 V for 10 min. Samples were taken at 0, 1, 2, 3, 5, 7, 8, and 10 min. The concentration of P was determined at 700 nm using ammonium molybdate spectrophotometry, and the concentration of Cl was determined using ion chromatography. - concentration.

[0047] Appendix Figure 1 -Appendix Figure 3 This is used to illustrate the structure of the phosphorus removal device, the electrode structure, and the phosphorus removal process in this embodiment.

[0048] like Figure 1 As shown, this invention employs a flow-by CDI cyclic reaction system, mainly comprising: reactor shell / electrode chamber 1; anode 2 (LaC-CC); cathode 3 (unmodified carbon cloth); flow channel / cavity channel 4; anion exchange membrane 5; insulating mesh / support 6; inlet 7; outlet 8; circulating liquid bottle 9; peristaltic pump 10; electrochemical workstation / power supply 11; and sampling port 12. During operation, under the action of an applied voltage, the water to be treated circulates through the reactor driven by the peristaltic pump, achieving electric field-assisted phosphorus removal.

[0049] like Figure 2 As shown, the LaC-CC electrode includes a carbon-based substrate 21 and a lanthanum-chitosan composite film 22 coated on its surface. The composite film 22 provides lanthanum-containing active sites, while the carbon-based substrate 21 provides conductivity and support, forming a composite functional electrode structure.

[0050] like Figure 3 As shown, the LaC-CC electrode fabrication process includes steps such as carbon-based substrate pretreatment, composite coating solution preparation, multiple drop-coating loading, drying to form a film, and hot-pressing / hot-plate light-pressing densification treatment. Among these, the hot-pressing / hot-plate light-pressing densification treatment is a necessary step to improve the film adhesion stability and phosphorus removal effectiveness.

[0051] Comparative Example 1: Control test of unmodified electrode

[0052] The device construction and operating conditions are the same as in Example 2, except that the anode uses an unmodified carbon cloth electrode (CC), that is, the electrode does not contain a lanthanum-chitosan composite film layer.

[0053] Comparative Example 2: Control experiment without electric field (0 V)

[0054] The device is constructed in the same way as in Example 2, except that no external voltage (0 V) is applied during operation, while all other conditions remain the same.

[0055] Comparative Example 3: Control test with unmodified electrode and no electric field (0 V)

[0056] The device was constructed the same as Comparative Example 1, except that no external voltage (0 V) was applied during operation, while all other conditions remained the same.

[0057] To fully illustrate the application effect of the lanthanum-chitosan composite film modified carbon-based electrode (LaC-CC) described in this invention in the flow-by CDI system, the following is in conjunction with the appendix. Figure 4 -Appendix Figure 8 Explanation will be provided. (Attached) Figure 4 -Appendix Figure 8 This invention is used to illustrate the experimental results and technical effects under different operating conditions. The results show that the electrode of this invention can achieve rapid and deep removal of low-concentration phosphates under an applied electric field, maintain high selectivity under coexisting anion conditions, and exhibit certain cycle stability. Specifically:

[0058] 1) Comparative analysis of phosphorus removal performance of different electrodes under conditions with and without an applied electric field, such as... Figure 4 As shown.

[0059] Figure 4 The phosphorus concentration change curve over time shows that in Example 2, the LaC-CC electrode under an applied electric field (LaC-CC / E On) removed phosphorus significantly faster than the other control groups. The phosphorus concentration in the influent decreased rapidly and approached zero in a short time, demonstrating a significant rapid and deep phosphorus removal capability. In contrast, the unmodified carbon cloth electrode (CC) removed phosphorus weakly under both electric field and non-electric field conditions (Comparative Example 3), indicating that relying solely on the electric double layer effect of ordinary carbon-based electrodes is insufficient to achieve efficient removal of low-concentration phosphates. Although the LaC-CC electrode in Comparative Example 2 showed some improvement compared to CC under conditions without an applied electric field (LaC-CC / E Off), its removal rate and final removal depth were still significantly lower than under the applied electric field conditions. This indicates that the technical effect of this invention stems from the synergistic effect between the "lanthanum-chitosan composite membrane layer" and the "applied electric field," rather than a single adsorption effect.

[0060] Secondly, from Figure 4 The results of chloride ion concentration changes and selectivity / energy consumption show that the changes in background chloride ion concentrations in each system are relatively limited, while the removal of phosphorus by the LaC-CC electro-addition system is significantly enhanced. This indicates that the system of the present invention is not a simple non-selective electro-adsorption, but has a stronger directional enrichment and selective capture ability for phosphate. Figure 4 Selectivity indicators shown (such as) The energy consumption of phosphorus removal is significantly higher in the LaC-CC system than in the unmodified electrode system, while the energy consumption per unit of phosphorus removal is significantly reduced, indicating that the present invention achieves deep removal while taking into account energy consumption control.

[0061] also, Figure 4The comparison of adsorption rates further shows that the apparent adsorption rate of the LaC-CC electrode is significantly improved under the action of an external electric field (significantly improved compared to the condition without an electric field), indicating that the external electric field promotes the migration of phosphate to the anode side and interfacial mass transfer, thereby effectively alleviating the kinetic limitations under low concentration conditions.

[0062] In summary, it is demonstrated that lanthanum-chitosan composite membrane modification combined with external electric field enhancement is a key technology combination for achieving minute-level rapid deep phosphorus removal, high selectivity, and low energy consumption operation.

[0063] 2) Analysis of the effect of solution pH on phosphorus removal performance and its applicable scope, such as... Figure 5 As shown.

[0064] The experimental conditions were the same as in Example 2, except that the pH of the solution was adjusted to 3, 5, 7, 9 and 11 with HCl and NaOH respectively and run for 10 min.

[0065] from Figure 5 The phosphorus concentration-time curves show that under neutral to weakly alkaline conditions (e.g., pH 7-11), the system removes phosphorus rapidly, reducing the phosphorus concentration to a low level in a short time. Under weakly acidic conditions (e.g., pH 5), a high removal rate can still be achieved, but the kinetics are somewhat slowed down. Under strongly acidic conditions (e.g., pH 3), the decrease in phosphorus concentration slows down significantly, resulting in a lower final removal efficiency. These results indicate that the system of this invention is more conducive to achieving rapid and deep phosphorus removal within the neutral and weakly alkaline range.

[0066] In addition, from Figure 5 The bar chart of removal rate and adsorption rate further shows that the removal efficiency and adsorption rate are higher near pH 7, while they decrease significantly under pH 3 conditions, indicating that the acidic environment weakens the interfacial capture and reaction efficiency.

[0067] Combination Figure 5 As shown in the schematic diagram of phosphorus species distribution, the main forms of phosphoric acid in the phosphoric acid system change under different pH conditions. Within the preferred operating range of this invention, the phosphate ions in the solution are more likely to migrate to the electrode interface under the action of an electric field and interact selectively with lanthanum active sites, thereby achieving a faster phosphorus removal process.

[0068] Therefore, it can be seen that the method of the present invention has a certain degree of adaptability to pH, and performs better under neutral to weakly alkaline conditions. It is suitable for common deep phosphorus removal scenarios in water bodies and demonstrates good adaptability to operating conditions.

[0069] 3) Analysis of the impact of applied voltage on phosphorus removal performance and energy consumption, such as... Figure 6 As shown.

[0070] The test conditions were the same as in Example 2, except that the applied voltage was set to 0, 0.3, 0.6, 0.9, and 1.2 V and run for 10 minutes respectively.

[0071] from Figure 6 The phosphorus concentration change curve shows that under no voltage applied (0 V), the phosphorus concentration decreases slowly, indicating that relying solely on the adsorption of the electrode material itself is insufficient to achieve efficient phosphorus removal in a short time. When an external voltage is applied (e.g., 0.3-1.2 V), the phosphorus concentration decreases significantly faster and can reach a high removal level in a short time, indicating that the external electric field can effectively enhance the migration and enrichment process of phosphate ions to the electrode interface.

[0072] Figure 6 The results of the removal rate and adsorption rate further show that the phosphorus removal efficiency and adsorption rate of the system after applying voltage are significantly higher than those under 0 V conditions; within a certain voltage range, increasing the voltage helps to improve the kinetic performance, especially to shorten the time required to achieve deep removal.

[0073] at the same time, Figure 6 The energy consumption results show that the energy consumption per unit of phosphorus removal increases with increasing applied voltage. This result indicates that there is a balance between "phosphorus removal speed / depth" and "energy consumption" in the parameter selection of the system of this invention: higher voltage is beneficial for obtaining faster kinetics, but it will increase energy consumption; lower voltage is beneficial for energy-saving operation. Therefore, a suitable voltage range can be selected according to the actual application scenario, provided that the effluent requirements are met. The preferred voltage range of this invention (e.g., 0.9-1.2V) can take into account both rapid and deep phosphorus removal requirements; in scenarios where energy consumption is the priority, lower voltage operation can also be used.

[0074] In conclusion, Figure 6 This demonstrates that applying an external electric field is one of the necessary operating conditions for achieving the rapid phosphorus removal effect of this invention, and that voltage parameters can be used to regulate removal efficiency, kinetics, and energy consumption.

[0075] 4) Analysis of anti-interference and selectivity under coexisting anion conditions, such as... Figure 7 As shown.

[0076] In this competitive ion experiment, the initial P was maintained at 1 mg / L, and NO3 was added separately. - HCO3 - Cl - or SO4 2- (Only one ingredient is added at a concentration of 1 g / L each time), and the other conditions are the same as in Example 2.

[0077] from Figure 7The removal rate results show that, compared with the control without coexisting anions in Example 2, the overall removal efficiency of phosphorus in the system after adding the above-mentioned coexisting anions has little change and remains at a high level. This indicates that the electrode of the present invention has a strong preferential capture ability for phosphate and is not easily significantly ineffective due to competition from common anions.

[0078] Figure 7 The selectivity results further indicate that the selectivity of the system of the present invention for phosphorus varies to some extent with respect to different coexisting anions, but overall maintains a good level of selectivity. The high selectivity for some anion systems suggests that the present invention still has practical application potential in high-salt or multi-anion coexistence scenarios. Even in coexistence systems with relatively low selectivity, the phosphorus removal efficiency remains high, indicating that the method of the present invention has strong adaptability to operating conditions and stable removal capability.

[0079] In conclusion, Figure 7 This demonstrates that the method of the present invention can still maintain high efficiency and good selectivity in complex ionic backgrounds, making it suitable for practical deep water treatment scenarios.

[0080] 5) Stability and regeneration performance analysis during multi-cycle adsorption-desorption processes, such as... Figure 8 As shown.

[0081] Based on the phosphorus removal device of Example 2, a cycle stability experiment was conducted. Four consecutive cycles were performed, each cycle consisting of 10 min of adsorption (1.2 V) and 10 min of desorption (-1.2 V). In the desorption phase, the voltage was applied in reverse, i.e., LaC-CC was the cathode and CC was the anode during desorption. In addition, the circulation pump was turned off during the desorption phase, and the solution volume was always 250 mL.

[0082] from Figure 8 The phosphorus concentration change curve during the cyclic process shows that as the number of cycles increases, the final phosphorus concentration of the system increases to some extent within the same operating time, indicating that the electrode performance degrades to a certain degree; correspondingly, Figure 8 The removal rate and adsorption rate results also showed that the phosphorus removal efficiency and apparent adsorption rate gradually decreased with increasing cycle number. This phenomenon indicates that during multiple cycles, the availability of electrode active sites may decrease, or the interfacial state may change, thereby affecting subsequent adsorption / reaction processes.

[0083] despite this, Figure 8 The selectivity results show that the system of this invention maintains a high selectivity for phosphorus relative to background ions even after multiple cycles, indicating that its core interface recognition and selective capture mechanism remains effective. In other words, although the kinetics and removal depth of the electrode of this invention decrease to some extent after multiple runs, it has not completely failed and still has practical application value.

[0084] therefore, Figure 8 This demonstrates that the electrode of the present invention has the potential for reversible regeneration and multi-cycle operation; further optimization of regeneration conditions, membrane structure or operating parameters is expected to further improve long-term cycle stability.

[0085] In summary, combining Figures 4-8 Analysis of the experimental data shows that, under the action of an applied electric field, the system of the present invention can achieve rapid and deep removal of low-concentration phosphates; simultaneously, it maintains high removal efficiency and good selectivity under different pH conditions and in the presence of coexisting anions, and has a certain ability to be recycled. These results indicate that the present invention can effectively improve the problems of slow kinetics, insufficient selectivity, and limited adaptability to complex water qualities in existing CDI systems for low-concentration phosphorus removal, and has good application potential.

[0086] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A method for preparing a carbon-based electrode modified with a lanthanum-chitosan composite film, characterized in that, Includes the following steps: S1. Cleaning and alkaline activation of the carbon-based substrate, wherein the carbon-based substrate is activated carbon cloth or carbon cloth; S2. Lanthanum salt, chitosan solution, and deionized water are mixed and ultrasonically dispersed to obtain a composite coating liquid; S3. Using a coating method, the composite coating liquid is uniformly loaded onto the surface of the alkali-activated carbon-based substrate, dried under vacuum to form a film, and then subjected to hot pressing to obtain a carbon-based electrode modified with a lanthanum-chitosan composite film.

2. The method for preparing the carbon-based electrode modified with lanthanum-chitosan composite film according to claim 1, characterized in that, The cleaning and alkaline activation of the carbon-based substrate specifically includes: The carbon-based substrate was first rinsed with deionized water, then ultrasonically cleaned in ethanol, and finally placed in a solution of 0.5–3 mol·L⁻¹. -1 The surface is activated by soaking in NaOH solution and then rinsed with deionized water until the washing solution is neutral.

3. The method for preparing the carbon-based electrode modified with lanthanum-chitosan composite film according to claim 1, characterized in that, The lanthanum salt is at least one of chloride, nitrate, sulfate, and acetate.

4. The method for preparing the carbon-based electrode modified with lanthanum-chitosan composite film according to claim 1, characterized in that, The ratio of the lanthanum salt to the chitosan solution is 1 g: (1~10) mL; and / or the concentration of the chitosan solution is 0.1~2% (w / v).

5. The method for preparing a carbon-based electrode modified with a lanthanum-chitosan composite film according to claim 1 or 5, characterized in that, The composite coating liquid is applied to the surface of the carbon-based substrate in equal amounts in multiple applications, with the number of applications being 2 to 10. After application, the substrate is vacuum dried at 30 to 80 °C.

6. The method for preparing the carbon-based electrode modified with lanthanum-chitosan composite film according to claim 1, characterized in that, The hot pressing process involves applying pressure to the surface of the dried carbon-based substrate by covering it with a smooth medium at 50~120 ℃.

7. A carbon-based electrode modified with a lanthanum-chitosan composite film, characterized in that, The preparation method according to any one of claims 1-7 is used to prepare the product, which includes a carbon-based substrate and a lanthanum-chitosan composite film layer covering the surface of the carbon-based substrate.

8. The application of the carbon-based electrode modified with the lanthanum-chitosan composite membrane as described in claim 7 in the selective adsorption of phosphate in solution and regeneration by desorption under a reverse electric field under an applied electric field.

9. The application according to claim 8, characterized in that, The voltage of the applied electric field is 0.3-1.5 V.

10. An electric field-assisted deep phosphorus removal method, characterized in that, Using a flow-by CDI configuration, a carbon-based electrode modified with the lanthanum-chitosan composite membrane as described in claim 7 is used as the anode, and unmodified carbon cloth is used as the cathode. An external voltage is applied under circulating flow conditions to remove phosphate from the solution.

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