Carboxyl-modified resin composite electrode and preparation method and application thereof

Abstract

The application discloses a carboxyl-modified resin composite electrode and a preparation method and application thereof, and aims at solving the problems of poor ion selectivity of a carbon-based CDI electrode, poor conductivity of an ion exchange resin, slow adsorption kinetics and the like. The preparation method comprises the following steps: dispersing the ion exchange resin in deionized water, adding an initiator and acrylic acid under the protection of inert gas, and performing graft copolymerization reaction at 60-80 DEG C to obtain a carboxyl-modified ion exchange resin; and the carboxyl-modified ion exchange resin, a conductive agent and a binder are mixed in an organic solvent, uniformly stirred to form a composite slurry, the composite slurry is coated on a conductive porous current collector, and the carboxyl-modified resin composite electrode is obtained after drying. The carboxyl-modified ion exchange resin prepared by the application has both sulfonic acid groups and carboxyl groups, the two functional groups synergistically act, the adsorption mode of "fast capturing-stable locking" is realized, and the adsorption capacity and selectivity of the composite electrode are greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical water treatment and functional materials technology, specifically relating to a composite electrode material for capacitive deionization (CDI) technology, particularly a highly selective electrode based on a composite of carboxyl grafted modified ion exchange resin and conductive carbon material, and its preparation method, as well as the application of this electrode in the treatment of wastewater containing heavy metal ions, especially in the treatment of electroplating rinse water that selectively removes copper (Cu(II)) from a high-concentration nickel (Ni(II)) background. Background Technology

[0002] Electroplating is a vital basic industry, but its wastewater contains high concentrations of heavy metal ions, posing a serious threat to the environment. In processes such as nickel-chromium electroplating, the accumulation of trace copper ion (Cu(II)) impurities can severely affect the coating quality, while nickel ions (Ni(II)) are valuable components that need to be retained. Therefore, selectively removing copper ions from a background of high nickel ion concentration is key to achieving a closed-loop recycling of electroplating wastewater.

[0003] Capacitive deionization (CDI) is an emerging electrochemical water treatment technology that adsorbs ions from water by applying an electrostatic field to the surface of a porous electrode. However, traditional carbon-based CDI electrodes exhibit poor selectivity for ions, making it difficult to distinguish between similar divalent cations. While ion exchange resins possess adsorption capacity, they suffer from poor conductivity and slow adsorption kinetics. Existing technologies have enhanced selectivity for target ions by introducing specific functional groups (such as carboxyl groups) through chemical modification, but the modified materials still face challenges such as insufficient conductivity and the need for further improvement in adsorption efficiency and selectivity in practical wastewater systems. Therefore, developing a composite electrode material that combines high selectivity, high adsorption capacity, and good conductivity is of great significance for the efficient treatment of copper-containing electroplating wastewater. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of poor ion selectivity of carbon-based CDI electrodes, poor conductivity of ion exchange resins, and slow adsorption kinetics, and to provide a carboxyl-modified resin composite electrode, its preparation method, and its application.

[0005] The carboxyl-modified resin composite electrode of the present invention includes a conductive porous current collector and a composite slurry. The composite slurry is formed by mixing carboxyl-modified ion exchange resin, conductive agent and binder in an organic solvent. The composite slurry is coated on the conductive porous current collector and, after drying, forms a composite functional coating on the surface and pores of the conductive porous current collector.

[0006] The preparation method of the carboxyl-modified resin composite electrode of the present invention is carried out according to the following steps:

[0007] I. Synthesis of Carboxyl-Modified Ion Exchange Resins:

[0008] Ion exchange resin was dispersed in deionized water, and under inert gas protection, an initiator and acrylic acid (containing carboxyl monomers) were added. Graft copolymerization was carried out at 60-80°C. After washing and drying, carboxyl modified ion exchange resin (MD001) was obtained.

[0009] II. Preparation of Carboxyl-Modified Resin Composite Electrode:

[0010] Carboxyl-modified ion exchange resin, conductive agent, and binder are mixed in an organic solvent at a mass ratio of (0.6~0.9):(0.05~0.2):(0.05~0.2), stirred evenly to form a composite slurry, and then coated onto a conductive porous current collector. After drying, a carboxyl-modified resin composite electrode is obtained.

[0011] The carboxyl-modified resin composite electrode of this invention is constructed by combining highly selective carboxyl functional groups with highly conductive carbon materials and building a stable three-dimensional porous electrode structure. It aims to achieve high-capacity, highly selective, and rapid electro-adsorption removal of Cu(II) in simulated electroplating rinse water, while maintaining good cycle regeneration stability.

[0012] The application of the carboxyl-modified resin composite electrode of the present invention is to use the carboxyl-modified resin composite electrode as a cathode and use a capacitor deionization process to adsorb and remove copper ions in electroplating wastewater.

[0013] The carboxyl-modified resin composite electrode prepared in this invention removes copper ions from electroplating wastewater through selective electroadsorption enhanced by a synergistic "chemical-electric field" effect. This synergistic effect is manifested in the following three aspects:

[0014] I. Electric Field-Driven Rapid Mass Transfer: The electric field applied by CDI generates a strong electrostatic force, overcoming the mass transfer resistance of Cu(II) ions diffusing from the bulk solution to the adsorbent surface in traditional adsorption, and significantly accelerating the ion migration rate. This is manifested in the adsorption equilibrium time being shortened from tens of hours in traditional chemisorption to less than 7 hours.

[0015] II. Strong selectivity of chemical bonding: Carboxyl groups (-COO) grafted onto the resin surface - ) is a typical "hard base", and it interacts with Cu(II) ions (d) as a "borderline acid". 9 (Electronic configuration) forms stable inner-shell coordination complexes. The Jahn-Teller effect of Cu(II) makes it more inclined to form a planar square chelate structure with the carboxyl group, gaining additional coordination field stabilization energy. Ni(II) (d 8 Cu(II) tends to form octahedral complexes, exhibiting relatively low coordination stability with carboxyl groups. This fundamental difference in coordination chemistry is the root cause of the electrode's excellent selectivity for Cu(II).

[0016] III. Synergistic Capture of Functional Groups: The MD001 resin retains both the sulfonic acid group (-SO3H) and the grafted carboxyl group (-COOH) of the original D001 resin. The sulfonic acid group rapidly binds to Cu(II) through an ion exchange mechanism, while the carboxyl group stabilizes it through a chelation mechanism. The synergistic effect of these two functional groups achieves a "rapid capture-stable locking" adsorption mode, significantly improving adsorption capacity and selectivity. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the synthesis route of the carboxyl-modified D001 resin (MD001) of the present invention;

[0018] Figure 2 This is a schematic diagram of the capacitor deionization (CDI) system of the present invention;

[0019] Figure 3 These are scanning electron microscope (SEM) images of (a) original D001 resin, (b) carboxyl-modified D001 resin, (c) original nickel foam, (d) composite electrode containing only MD001 resin, and (e) MD001 resin / conductive carbon black composite electrode in the examples.

[0020] Figure 4 This is a comparison of the infrared spectra (FTIR) of the original D001 resin and the carboxyl-modified MD001 resin of this invention.

[0021] Figure 5 Examples include (a) a comparison of cyclic voltammetry (CV) curves for different electrodes; and (bd) CV curves for carbon black electrode, D001 composite electrode, and MD001 composite electrode at different scan rates.

[0022] Figure 6 These are (a) electrochemical impedance spectroscopy (EIS) Nyquist plots and (b) magnified high-frequency region plots of different electrodes in the examples;

[0023] Figure 7 The figures shown are (a) initial, (b) middle, and (c) later stages of the MD001 composite electrode during the CDI dynamic adsorption process, and (d) a graph showing the change of copper ion concentration over time.

[0024] Figure 8 The examples show: (a) a comparison of Cu(II) removal efficiency of different electrodes; (b) a test graph showing the effect of pH value on Cu(II) removal; (c) a test graph showing the effect of voltage on Cu(II) removal; and (d) a test graph showing the Cu(II) removal efficiency of the MD001-CB electrode in the presence of competing ion Ni(II).

[0025] Figure 9 These are fitting plots of (a) pseudo-first-order kinetics, (b) pseudo-second-order kinetics, (c) Langmuir isotherm, and (d) Freundlich isotherm of Cu(II) on the D001, MD001, and MD001-CB electrodes in the embodiments;

[0026] Figure 10 The following are the following graphs for the MD001-CB composite electrode in the examples: (a) chronocurrent (it) curve; (b) salt adsorption capacity (SAC) change after 30 cycles; (c) cycle capacity retention rate; and (d) selective adsorption performance test results for Cu(II), Ni(II), Zn(II) and Mg(II).

[0027] Figure 11 The following are the XPS full spectrum of MD001 resin and MD001-CB electrode before and after adsorption in the examples; and the high-resolution XPS spectra of (b) C 1s, (c) O 1s, (d) S 2p and (e) Cu 2p of the electrode after adsorption.

[0028] Figure 12 These are the FTIR spectra of MD001 resin and MD001-CB electrode before and after adsorption in the examples;

[0029] Figure 13 The images shown are SEM images and corresponding EDS elemental distribution maps of Cu(II) adsorbed on the MD001-CB electrode in the examples. Detailed Implementation

[0030] Specific Implementation Method 1: The preparation method of the carboxyl-modified resin composite electrode in this implementation method is carried out according to the following steps:

[0031] I. Synthesis of Carboxyl-Modified Ion Exchange Resins:

[0032] Ion exchange resin was dispersed in deionized water, and under inert gas protection, an initiator and acrylic acid (containing carboxyl monomers) were added. Graft copolymerization was carried out at 60-80°C. After washing and drying, carboxyl modified ion exchange resin (MD001) was obtained.

[0033] II. Preparation of Carboxyl-Modified Resin Composite Electrode:

[0034] Carboxyl-modified ion exchange resin, conductive agent, and binder are mixed in an organic solvent at a mass ratio of (0.6~0.9):(0.05~0.2):(0.05~0.2), stirred evenly to form a composite slurry, and then coated onto a conductive porous current collector. After drying, a carboxyl-modified resin composite electrode is obtained.

[0035] The carboxyl-modified resin in this embodiment is prepared by chemically bonding polyacrylic acid chains (PAA) to the surface of an ion exchange resin matrix using a "surface grafting polymerization" method, and its surface contains a high density of carboxyl (-COOH) active sites.

[0036] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the ion exchange resin mentioned in step one is a strong acid styrene-based cation exchange resin, and the initiator is benzoyl peroxide (BPO).

[0037] In this embodiment, the preferred ion exchange resin is a D001 type macroporous strong acid cation exchange resin, which has excellent mechanical strength and thermal stability.

[0038] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the graft copolymerization reaction time in step 1 is 8-24 hours.

[0039] Specific Implementation Method Four: This implementation method differs from one of the specific implementation methods one to three in that the carboxyl-modified ion exchange resin is ground and then passed through a 200-mesh sieve in step one.

[0040] Specific Implementation Method 5: This implementation method differs from one of the specific implementation methods 1 to 4 in that the mass ratio of ion exchange resin, acrylic acid and initiator in step 1 is (4-8):(1-3):(0.1-0.4).

[0041] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the conductive agent mentioned in step two is conductive carbon black, and the binder is polyvinylidene fluoride (PVDF).

[0042] In this embodiment, the conductive agent is used to construct a three-dimensional conductive network, and the polyvinylidene fluoride binder has good chemical stability and electrode adhesion.

[0043] Specific Implementation Method Seven: This implementation method differs from one of the specific implementation methods one to six in that the conductive porous current collector mentioned in step two is nickel foam with a thickness of 1.0-1.7 mm.

[0044] In this embodiment, the current collector provides a three-dimensional channel for electron transport and ion diffusion.

[0045] Specific Implementation Method Eight: This implementation method differs from one of Specific Implementation Methods One to Seven in that the organic solvent mentioned in step two is N-methylpyrrolidone (NMP).

[0046] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that step two uses a scraping or dipping-coating method to coat the composite slurry onto the conductive porous current collector.

[0047] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 1 to 9 in that the drying described in step 2 is vacuum drying at a temperature of 60°C.

[0048] Example 1: The preparation method of the carboxyl-modified resin composite electrode in this example is carried out according to the following steps:

[0049] I. Synthesis of Carboxyl-Modified Ion Exchange Resins:

[0050] A strong acidic styrene-based cation exchange resin (type D001) was dispersed in deionized water. Under high-purity nitrogen protection, initiator BPO and acrylic acid (containing carboxyl monomers) were added. The mass ratio of ion exchange resin, acrylic acid monomer, and initiator BPO was 5:2:0.2. A graft copolymerization reaction was carried out at 70°C for 12 hours. After the reaction, the product was naturally cooled to room temperature and washed three times alternately with deionized water and anhydrous ethanol to remove unreacted monomers and homopolymers. Finally, the product was dried to constant weight in a vacuum oven at 70°C to obtain a carboxyl-modified ion exchange resin, denoted as MD001.

[0051] II. Preparation of Carboxyl-Modified Resin Composite Electrode:

[0052] Carboxyl-modified ion exchange resin, conductive carbon black, and PVDF binder were mixed in N-methylpyrrolidone at a mass ratio of 8:1:1. The mixture was stirred for 5 hours using a high-speed disperser to form a black viscous composite slurry. The composite slurry was then coated onto porous nickel foam and pre-dried in a 60°C forced-air drying oven for 2 hours. Finally, it was transferred to a 60°C vacuum drying oven and dried for 12 hours to obtain a carboxyl-modified resin composite electrode (denoted as MD001-CB E).

[0053] This embodiment characterizes and verifies the prepared carboxyl-modified resin composite electrode material. In the following text, CB-E represents a single conductive carbon black electrode, and D001-CB E represents a composite electrode of D001 ion exchange resin and conductive carbon black.

[0054] The morphology of the material was observed using a scanning electron microscope (SEM). Figure 3 (a) shows that the original D001 resin consists of smooth, spherical particles with a diameter of approximately 100 μm. Figure 3 (b) shows that the surface of MD001 becomes very rough after carboxyl modification, with a large number of wrinkles and protrusions, which is direct morphological evidence of successful grafting of polyacrylic acid chains. Figure 3 (c) shows the clean three-dimensional porous framework of nickel foam. Figure 3 (e) shows that the resin particles and carbon black of MD001-CB E are uniformly distributed, and the carbon black fills the space between the resin and the nickel foam skeleton, forming a good conductive network.

[0055] The chemical structure was analyzed using Fourier transform infrared spectroscopy (FTIR). Figure 4 The results showed that the carboxyl-modified MD001 had a viscosity of 1690 cm⁻¹. -1 A new strong absorption peak appeared at [location], corresponding to the carboxyl group (-COO). - The C=O stretching vibration of ) at 3400 cm -1 The increased intensity of the nearby broad peak (-OH) confirms successful grafting of the carboxyl group. The original D001 resin at 1150 cm⁻¹... -1 and 1030 cm -1 The characteristic peak is attributed to the sulfonic acid group (-SO3H), and this peak still exists after modification, indicating that the ion exchange skeleton of the resin has not been destroyed.

[0056] This embodiment uses a three-electrode system to perform electrochemical testing on the electrodes. The prepared carboxyl-modified resin composite electrode (1×1 cm⁻¹) was used as the working electrode. 2 The platinum sheet was used as the counter electrode, Ag / AgCl was used as the reference electrode, and the electrolyte was a 0.5 M NaCl solution.

[0057] Cyclic voltammetry (CV) test results ( Figure 5 (a) shows that at a scan rate of 20 mV / s, CB E has the largest integrated area and a calculated specific capacitance of 2.5 F / g. D001-CB E has the smallest integrated area (1.4 F / g), which is attributed to the reduced conductivity due to the addition of insulating resin. The integrated area of ​​MD001-CB E (1.7 F / g) is significantly larger than that of D001-CB E, indicating that the introduction of carboxyl groups improves the electrochemical activity of the electrode.

[0058] Electrochemical impedance spectroscopy (EIS) test results ( Figure 6 The results show that the charge transfer resistance (Rct) of CBE, MD001-CBE, and D001-CBE are 10.85 Ω, 11.8 Ω, and 14.0 Ω, respectively. The charge transfer resistance of MD001-CBE is much lower than that of D001-CBE, proving that the addition of conductive carbon black significantly reduces the charge transfer resistance.

[0059] This embodiment uses a self-assembled CDI system for constant-pressure adsorption experiments. The CDI system consists of multiple MD001-CB composite electrodes as cathodes, separated from the counter electrodes by insulating gaskets, assembled into a "sandwich" structure CDI flow-through module. The electrode pair dimensions are 4×4 cm. 2 The spacing is 5 mm. A 250 mg / L Cu(II) solution is used as the target solution. Figure 10 The competitive ion concentration was disclosed, the pH was adjusted to 5.0, and the adsorption experiment was carried out at a voltage of 0.8 V and a flow rate of 20 mL / min.

[0060] Regeneration process: Once the electrode is saturated with adsorption, stop applying voltage and short-circuit the electrode or apply a reverse voltage (-0.4 to -1.0 V). The captured Cu(II) ions desorb back into the solution under the influence of the loss of electric field force or reverse repulsion force, resulting in a concentrated Cu(II) solution. The electrode can be reused for the next round of adsorption.

[0061] like Figure 8 As shown in (a), under the same conditions, MD001-CB E achieved a Cu(II) removal rate of up to 85%, significantly higher than D001-CB E (approximately 55%) and CBE (approximately 35%). This indicates that the synergistic effect of carboxyl modification and conductive carbon black significantly enhances the Cu(II) adsorption performance. Figure 8 As shown in (b), when pH < 4, H + It competes with Cu(II) for binding sites, resulting in a low adsorption rate; when the pH rises to 5, the degree of carboxyl deprotonation increases (-COOH → -COO). - At pH > 6, electrostatic attraction and coordination are enhanced, leading to a peak adsorption rate. However, at pH > 6, Cu(II) begins to hydrolyze, forming Cu(OH)₂ precipitate, which affects the adsorption process. Therefore, the optimal pH is 5.0. Figure 8 As shown in (c), when the voltage increased from 0 to 0.8 V, the Cu(II) removal rate increased linearly from less than 30% to 85%; when the voltage increased to 1.0 V and 1.2 V, the removal rate no longer increased and even decreased slightly, due to the occurrence of water electrolysis side reactions. Therefore, the optimal voltage is 0.8 V. Different concentrations of Ni(II) (0, 50, 100, 250 mg / L) were added to a solution with an initial Cu(II) concentration of 250 mg / L, and competitive adsorption was carried out under optimal conditions. Figure 8 As shown in (d), even when the Ni(II) concentration is equal to that of Cu(II) (250 mg / L), the removal rate of Cu(II) by MD001-CB E remains above 85%, while the removal rate of Ni(II) remains below 20%. This indicates that the electrode has extremely high selectivity for Cu(II).

[0062] The adsorption capacity was tested over time in a 50 mg / L Cu(II) solution. Figure 9 As shown in (a) and (b), and the quasi-first-order model (R 2 =0.990) and quasi-second-order model (R 2 The goodness of fit of the values ​​(=0.939) is high, indicating that the adsorption process is a complex process involving both physical and chemical adsorption. The equilibrium adsorption capacity calculated by the pseudo-second-order model (165.7 mg / g) is closer to the experimental value (168.5 mg / g).

[0063] Thirty consecutive adsorption-desorption cycles were performed in 250 mg / L Cu(II) solution at 0.8 V (7 hours of adsorption, 2 hours of desorption at -0.8 V). Figure 10 As shown in (b) and (c), the initial adsorption capacity was approximately 168 mg / g. After 30 cycles, the adsorption capacity remained stable between 155 and 170 mg / g, with a capacity retention rate consistently above 93%, demonstrating the electrode's excellent reversibility and long-term stability. This was confirmed by the chronoamperometry curve (…). Figure 10 (a) Integral calculations show that the charge efficiency Λ is 0.63 and the specific energy consumption is 0.331 Wh / g Cu(II), indicating that the electrode maintains low energy consumption while achieving high selective adsorption.

[0064] X-ray photoelectron spectroscopy (XPS) was used to analyze the electrodes before and after adsorption. For example... Figure 11 As shown in (b), the carbon peak of the carboxyl group shifts to a higher binding energy by about 0.4 eV after adsorption, indicating that Cu(II) is coordinated with the oxygen atom in the carboxyl group. Figure 11 In the O 1s spectrum of (c), a new peak appears at 530.5 eV, which is attributed to the Cu-O bond and is direct evidence that Cu(II) forms a coordinate bond with the carboxyl oxygen atom. Figure 11 (e) The Cu 2p spectrum is clearly visible. 3 / 2 (~932.5 eV) and Cu 2p 1 / 2 The characteristic peak (~952.4 eV) and the obvious satellite peaks between 940-945 eV confirm that the adsorbed copper is in the Cu(II) valence state.

[0065] Combined with FTIR ( Figure 12 ) and SEM-EDS ( Figure 13 As a result, it can be determined that the removal mechanism of Cu(II) by the composite electrode of the present invention is: under the enhanced mass transfer of electric field, the coordination chelation of carboxyl groups is the main factor, supplemented by the ion exchange of sulfonic acid groups and the electrostatic attraction of the double layer, forming a synergistic adsorption mechanism.

Claims

1. A carboxyl-modified resin composite electrode, characterized in that... The carboxyl-modified resin composite electrode includes a conductive porous current collector and a composite slurry. The composite slurry is formed by mixing carboxyl-modified ion exchange resin, conductive agent and binder in an organic solvent. The composite slurry is coated on the conductive porous current collector and, after drying, forms a composite functional coating on the surface and in the pores of the conductive porous current collector.

2. The method for preparing the carboxyl-modified resin composite electrode as described in claim 1, characterized in that... The preparation method of the carboxyl-modified resin composite electrode is carried out according to the following steps: I. Synthesis of Carboxyl-Modified Ion Exchange Resins: Ion exchange resin was dispersed in deionized water, and under inert gas protection, an initiator and acrylic acid were added. Graft copolymerization was carried out at 60-80°C. After washing and drying, carboxyl-modified ion exchange resin was obtained. II. Preparation of Carboxyl-Modified Resin Composite Electrode: Carboxyl-modified ion exchange resin, conductive agent, and binder are mixed in an organic solvent at a mass ratio of (0.6~0.9):(0.05~0.2):(0.05~0.2), stirred evenly to form a composite slurry, and then coated onto a conductive porous current collector. After drying, a carboxyl-modified resin composite electrode is obtained.

3. The method for preparing the carboxyl-modified resin composite electrode according to claim 1, characterized in that... The ion exchange resin mentioned in step one is a strong acid styrene-based cation exchange resin, and the initiator is benzoyl peroxide.

4. The method for preparing the carboxyl-modified resin composite electrode according to claim 1, characterized in that... The graft copolymerization reaction in step one takes 8-24 hours.

5. The method for preparing the carboxyl-modified resin composite electrode according to claim 1, characterized in that... In step one, the mass ratio of ion exchange resin, acrylic acid and initiator is (4-8):(1-3):(0.1-0.4).

6. The method for preparing the carboxyl-modified resin composite electrode according to claim 1, characterized in that... The conductive agent mentioned in step two is conductive carbon black, and the binder is polyvinylidene fluoride.

7. The method for preparing the carboxyl-modified resin composite electrode according to claim 1, characterized in that... The conductive porous current collector mentioned in step two is nickel foam with a thickness of 1.0-1.7 mm.

8. The method for preparing the carboxyl-modified resin composite electrode according to claim 1, characterized in that... The organic solvent mentioned in step two is N-methylpyrrolidone.

9. The method for preparing the carboxyl-modified resin composite electrode according to claim 1, characterized in that... In step two, the composite slurry is coated onto the conductive porous current collector using a scraping or dip-coating method.

10. The application of the carboxyl-modified resin composite electrode prepared by the method described in claim 2, characterized in that... A carboxyl-modified resin composite electrode was used as the cathode, and a capacitive deionization process was employed to adsorb and remove copper ions from electroplating wastewater.

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