A dual-ion selective HCDI system induced by pseudocapacitive behavior of MoS2 / PPy / / Ag@PANI / AC and its application.

Abstract

The application discloses a kind of based on MoS2 / PPy / / Ag@PANI / AC pseudocapacitance behavior induced dual-ion selective HCDI system and application, MoS2 / PPy as Na + Interlayer cathode, Ag modified polyaniline modified activated carbon (Ag@PANI / AC) as Cl-capture anode. In this system, hollow PPy nanotube is anchored by ultrathin MoS2 nanosheet, as a conductive chain to connect loose MoS2 nanoflower, forming a three-dimensional flower chain network. Ag@PANI / AC is synthesized by modifying Ag particles on the 3D electron conducting substrate formed by coupling PANI and AC. MoS2 / PPy / / Ag@PANI / AC realizes excellent adsorption capacity of 25.1 mg·g ‑1 ‑1 ·min ‑1 ), good cycle stability (97.7% retention rate) and improved charge efficiency (56.2%), providing a feasible method for more energy-saving HCDI, which can be used for seawater desalination and water purification desalination.​

Description

Technical Field

[0001] This invention relates to a dual-ion selective HCDI system and its application based on pseudocapacitive behavior induced by MoS2 / PPy / / Ag@PANI / AC. Background Technology

[0002] With global population growth and industrial expansion, the freshwater crisis is increasingly impacting societal progress. The use of unconventional water resources (such as seawater, brackish water, and mine water) is crucial for meeting daily freshwater needs. Capacitive deionization (CDI), an emerging electrochemical control technology, has attracted widespread attention in water purification processes due to its environmental friendliness, ease of operation, and low energy consumption. However, the physical charge adsorption based on the electric double layer (EDL) mechanism limits the improvement of desalination capacity, and conventional CDI with porous carbon electrodes faces bottlenecks in future development. Hybrid capacitive deionization (HCDI), the most promising derivative of CDI, consists of a Faraday cathode and a carbon anode and has found widespread application in electrochemical desalination. Specifically, the Faraday electrode material selectively removes ions through ion intercalation or interaction with ions via surface redox reactions, thereby achieving high desalination capacity. Based on this, a series of Faraday electrode materials have been proposed, such as transition metal oxides (TMO), transition metal carbides / nitrides, transition metal dichalcogenides (TMDs), conductive polymers, Prussian blue (PB) and its analogues (PBAs) (cathode materials) and Ag and Bi (anode materials).

[0003] Among these Faraday electrode materials, graphene-like molybdenum disulfide (MoS2), as a typical two-dimensional (2D) layered intercalation material, has attracted considerable interest from researchers due to its flexible and tunable interlayer space, abundant active sites, and high theoretical capacity. However, pure MoS2 is prone to aggregation and structural collapse, and its poor conductivity hinders its application in electrochemical fields. Combining MoS2 with carbonaceous materials (such as g-C3N4, graphene, and carbon nanotubes) provides a feasible strategy to overcome these limitations, with reported adsorption capacities (SAC) ranging from 16.8 to 24.5 mg·g⁻¹. -1 Furthermore, the potential volume expansion during MoS2 ion intercalation still limits its further applications. Exploring the use of 2D / 3D conductive materials as growth substrates to alleviate interlayer aggregation of MoS2 nanosheets while improving their conductivity and stability may be an ideal solution. Conductive polymers, such as polyaniline (PANI) and polypyrrole (PPy), contain abundant amine and imine functional groups, possess good conductivity, are easy to synthesize, and have high pseudocapacitance properties, which hold promise for improving the CDI performance of MoS2. Excitingly, nanotubular PPy with a hollow conductive structure facilitates the construction of conductive networks, and its unique hollow structure allows for the formation of conductive networks in Na+.+ The volumetric strain of MoS2 is buffered during the embedding / removal process, which is considered an ideal scaffold for supporting and stabilizing MoS2.

[0004] Currently, almost all research on HCDI-related systems focuses on Na. + Development of trapping electrode materials. For Cl - The exploration of high-performance adsorption anode materials has been largely neglected. Porous carbon, a commonly used cathode material, exhibits low Cl- content. - Removal capacity, due to its low capacitance, is limited to 5 to 10 mg·g⁻¹ for SAC. -1 In MoS2-based HCDI systems, the unbalanced module structure inevitably leads to severe performance mismatches, limiting desalination capacity and ion removal rates. Typically, anion exchange membranes are placed on the carbon electrode to mitigate co-ion repulsion effects in order to achieve high charge efficiency. To address these issues, metal-loaded carbon-based materials are considered a promising approach for selectively capturing Cl-. - This method achieves high removal efficiency. Recently, Vengtesan et al. developed a method for capturing Na+. + Sepiolite intercalated graphene (GS) capacitor electrode and a method for selectively capturing Cl - The silver-doped GS (AGS) Faraday electrode provided 20.7 mg·g. -1 Excellent SAC value and high charge efficiency of 87.1%. Subsequently, Mittal et al. designed a dual-ion HCDI system using 3D MnO2@graphene / CNT (MGG) and Ag@graphene / CNT (AGG) redox active materials as the anode and cathode, respectively. The MGG / / AGG system achieved a SAC value of 62.4 mg·g⁻¹. -1 It possesses high desalination capability and a charge efficiency of up to 95%. However, during cycling, the non-conductive nature of the formed AgCl hinders the desalination of Cl. - Further diffusion and electron transport affect the deionization performance of the Ag / AgCl electrode. Summary of the Invention

[0005] To overcome the limitations of MoS2's undesirable conductivity, low removal rate, and re-accumulation tendency, and to address the dynamic mismatch problem in HCDI, this invention provides a dual-ion selective HCDI system based on pseudocapacitive behavior induced by MoS2 / PPy / / Ag@PANI / AC.

[0006] The dual-ion selective HCDI system based on pseudocapacitive behavior induced by MoS2 / PPy / / Ag@PANI / AC provided by this invention uses a MoS2 / PPy composite material with a three-dimensional flower chain network structure formed by polypyrrole nanotubes and MoS2 nanoflowers as the cathode, and a heterostructure Ag@PANI / AC composite material formed by Ag particles modifying polyaniline-modified activated carbon as the anode.

[0007] The preparation method of the above-mentioned MoS2 / PPy composite material is as follows: ammonium molybdate and thiourea are dissolved in deionized water, then polypyrrole nanotubes are added, and after ultrasonic treatment, the mixture is transferred to a high-pressure reactor and reacted at 160-220°C for 20-30 hours. The resulting black powder is washed with deionized water and anhydrous ethanol by centrifugation and then vacuum dried to obtain the MoS2 / polypyrrole composite material, i.e., the MoS2 / PPy composite material. Preferably, the mass ratio of the polypyrrole nanotubes to ammonium molybdate and thiourea is 1:1.5-2:2.5-3.5. More preferably, the reaction is carried out at 190-200°C for 24 hours.

[0008] The preparation method of the above-mentioned polypyrrole nanotubes is as follows: methyl orange is ultrasonically dissolved in deionized water, and then pyrrole and ferric chloride aqueous solution are added under stirring conditions. The mixture is then subjected to in-situ polymerization under dark ice bath conditions for 20–24 hours. After the reaction is complete, the precipitate is collected by filtration, washed with deionized water and ethanol, and dried to obtain polypyrrole nanotubes. Preferably, the mass ratio of methyl orange to pyrrole to ferric chloride is 1:2–2.5:5–5.5.

[0009] The preparation method of the above Ag@PANI / AC composite material is as follows: Polyaniline-modified activated carbon is dispersed in deionized water, silver nitrate aqueous solution is added and stirred for 1-2 hours, then ascorbic acid aqueous solution is added and stirring continues for 2-4 hours. Finally, the reaction product is washed with deionized water and dried to obtain Ag-supported polyaniline-modified activated carbon with a heterostructure, i.e., Ag@PANI / AC composite material. Preferably, the mass ratio of the polyaniline-modified activated carbon to silver nitrate and ascorbic acid is 1:0.12-0.14:0.13-0.15.

[0010] The preparation method of the above-mentioned polyaniline-modified activated carbon is as follows: aniline and activated carbon are added to a 1M HCl aqueous solution, ultrasonically treated for 1-2 hours, then ammonium persulfate aqueous solution is added, and the mixture is continuously stirred at room temperature for 20-24 hours. The resulting precipitate is washed with deionized water and ethanol until the pH of the filtrate is neutral, and then vacuum dried to obtain polyaniline-modified activated carbon. Preferably, the mass ratio of aniline to activated carbon and ammonium persulfate is 1:0.9-1.2:1.3-1.5.

[0011] This invention also provides the application of the above-mentioned pseudocapacitive behavior-induced dual-ion selective HCDI system based on MoS2 / PPy / / Ag@PANI / AC in water desalination. In this system, hollow PPy nanotubes are anchored by ultrathin MoS2 nanosheets, acting as conductive chains to connect loose MoS2 nanoflowers, forming a 3D flower chain network. PPy, as a growth substrate, can alleviate the stacking of MoS2 nanosheet layers while providing convenient charge transfer channels. Ag@PANI / AC is synthesized by modifying Ag particles on a 3D electronically conductive substrate formed by the coupling of PANI and AC, and by reacting with Cl... - A conversion reaction occurs, achieving selective removal of Cl-. Unique electrode material structure design and optimized module configuration enable excellent desalination performance.

[0012] This invention constructs an advanced pseudocapacitive behavior-induced dual-ion selective HCDI system (denoted as the Di-CDI system) based on MoS2 / PPy / / Ag@PANI / AC, which removes Na+ by introducing Faraday reactions at the two electrodes. + and Cl - In the Di-CDI system, the PPy conductive network serves as a growth framework to mitigate the aggregation of MoS2 nanosheets, providing enhanced conductivity and a shortened ion diffusion path. Simultaneously, hollow PPy nanotubes are encapsulated by MoS2 nanosheets to form a core-shell structure, acting as conductive chains to connect loosely arranged MoS2 nanoflowers, constructing a unique flower-chain network. The improved dispersion and expanded interlayer spacing of the MoS2 nanosheets are comparable to Na... + The insertion and extraction of PPy nanoflowers provide abundant accessible sites. The interconnected conductive channels enable convenient electron transfer paths and rapid charge transport. Charge redistribution at the heterojunction interface catalyzes a strong local electric field, leading to accelerated ion diffusion dynamics. The highly interwoven conductive network enables rapid electron transfer between MoS2 nanoflowers, further enhancing the stability of the heterostructure. As a cathode material, it can achieve Na... + High-efficiency transmission and capture. Regarding Cl - The material was captured, and a 3D conductive structure was constructed by coupling polyaniline (PANI) and activated carbon (AC) through in-situ polymerization. Then, Ag particles were modified on its surface by chemical reduction to synthesize a heterostructure Ag@PANI / AC composite material. This composite material is compatible with Cl... -A conversion reaction occurs to produce AgCl. The doped PANI and Ag provide abundant pseudocapacitive reaction sites, contributing to the generation of additional storage capacity. This structural design compensates for the low conductivity of AgCl while providing fast performance and high desalination capability, thus achieving rapid electroadsorption motive force. Therefore, the Di-CDI system exhibits superiority over most publicly disclosed MoS2-based CDI systems. In particular, the ion removal mechanism was revealed through in-situ characterization and density functional theory (DFT) calculations. The MoS2 / PPy electrode, in synergy with the 3D conductive PPy substrate, induces Na... + Intercalation behavior. Furthermore, through the synergistic effect of redox-active Ag, the Faraday pseudocapacitive reaction from PAIN, and the EDL electroadsorption from AC, Cl... - It is electrochemically adsorbed onto the Ag@PANI / AC electrode.

[0013] The beneficial effects of this invention are as follows:

[0014] 1. This invention uses MoS2 / PPy as Na + Intercalated cathode, Ag-supported polyaniline modified activated carbon (Ag@PANI / AC) is Cl - By capturing the anode, an asymmetric dual-ion selective capacitive deionization (Di-CDI) system induced by pseudocapacitive behavior was constructed, which effectively solved the performance mismatch problem and further improved the desalination performance.

[0015] 2. This invention uses a core-shell structured MoS2 / PPy as a conductive chain to connect loosely packed MoS2 nanoflowers, constructing a unique flower-chain network. This highly cross-linked conductive network enables rapid electron transfer between MoS2 nanoflowers, while further enhancing the stability of the heterostructure.

[0016] 3. This invention constructs a 3D conductive structure by coupling polyaniline (PANI) and activated carbon (AC) through in-situ polymerization, and synthesizes an Ag@PANI / AC heterostructure by loading Ag particles onto its surface through chemical reduction. This structure compensates for the low conductivity of AgCl, thereby improving the overall conductivity and structural stability of the structure, and obtaining an electrode with ion selectivity, high rate performance, and desalination capability.

[0017] 4. The Di-CDI system MoS2 / PPy / / Ag@PANI / AC constructed in this invention exhibits a concentration of 25.1 mg·g⁻¹. -1 Excellent adsorption capacity and outstanding desalination rate (5.88 mg·g⁻¹) -1 ·min -1 It exhibits good cycle stability (97.7% retention) and improved charge efficiency (56.2%).

[0018] 5. In the Di-CDI system constructed in this invention, the MoS2 / PPy electrode induces Na under the synergistic effect of the 3D conductive PPy substrate. + Intercalation behavior. Furthermore, through the synergistic effect of the Faraday pseudocapacitive reaction of redox-active Ag with PAIN and the electric double layer (EDL) adsorption of AC, Cl... - It is electrochemically adsorbed onto the Ag@PANI / AC electrode. Attached Figure Description

[0019] Figure 1 Here are SEM images of MoS2 (a); SEM and TEM (inset) images of PPy nanotubes (b); SEM (c, d), TEM (e), and HRTEM (f) images of MoS2 / PPy (inset: SAED diffraction); elemental mapping of MoS2 / PPy (g-l).

[0020] Figure 2 The images show the XRD patterns (a), Raman spectra (b), N2 adsorption / desorption isotherms (c), and pore size distribution (d) of MoS2, PPy nanotubes, and MoS2 / PPy.

[0021] Figure 3 SEM images of AC(a) and PANI / AC(b); SEM image of Ag@PANI / AC-1.2 (c) and corresponding element maps (d-g).

[0022] Figure 4 These are the XRD patterns of AC, PANI / AC, and Ag@PANI / AC-1.2.

[0023] Figure 5 The CV curves (5 mV s) for MoS2, PPy nanotubes, and MoS2 / PPy are shown. -1 (a) Corresponding specific capacitance (5~100mV s) -1 (b) GCD curve (1A g) -1 (c) Corresponding discharge specific capacitance (0.5~5A g) -1 (d), Nyquist diagram (illustration: equivalent circuit) (e), and the charging resistance of the electrodes (f).

[0024] Figure 6 The CV curves (5 mV s) of the AC, PANI / AC, Ag@PANI / AC-1, Ag@PANI / AC-1.2, and Ag@PANI / AC-1.4 electrodes are shown. -1 (a) Corresponding specific capacitance (5~100mV s) -1 (b) GCD curve (1A g) -1(c) Corresponding discharge specific capacitance (0.5~5A g) -1 )(d).

[0025] Figure 7 These are Nyquist plots of the AC, PANI / AC, and Ag@PANI / AC-1.2 electrodes.

[0026] Figure 8 The table shows the SAC and charge efficiency (a) of modules MoS2 / / AC, MoS2 / / Ag@PANI / AC, and MoS2 / PPy / / Ag@PANI / AC at different voltages (0.8–1.4 V), the change of SAC over time at 1.4 V (b), the corresponding Kim-Yoon plot (c), and the results at different NaCl concentrations (100–500 mg·L⁻¹). -1 SACs(d) under )

[0027] Figure 9 The SAC variation of the module MoS2 / PPy / / Ag@PANI / AC over the entire concentration range is shown in (a) and the corresponding Kim-Yoon plot is shown in (b).

[0028] Figure 10 It is the cyclic stability of the module MoS2 / PPy / / Ag@PANI / AC within 10 adsorption / desorption cycles.

[0029] Figure 11 This is a comparison of the deionization performance (a) and ion removal rate (b) of the Di-CDI system MoS2 / PPy / / Ag@PANI / AC with the reported MoS2-based CDI system. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0031] Example 1

[0032] 1. Preparation of MoS2 / PPy composite materials

[0033] Step 1: 1.5 g of methyl orange (MO) was placed in 400 mL of deionized water and dissolved completely by sonication. Then, 3.5 g of pyrrole (Py) was added dropwise under stirring. Subsequently, 13.5 g of FeCl3·6H2O was completely dissolved in 50 mL of deionized water and slowly poured into the resulting Mo / Py solution. The polymerization reaction was carried out in an ice bath in the dark with stirring for 24 h. Finally, the precipitate was collected by filtration, washed with deionized water and ethanol to remove MO, and dried at 60 °C to obtain polypyrrole (PPy) nanotubes.

[0034] Step 2: Add 0.93g of (NH4)6Mo7O 24 • 4H2O and 1.71 g of thiourea were dissolved in 40 mL of deionized water, and then 0.56 g of PPy nanotubes were added. After sonication for 60 min, the mixture was transferred to a high-pressure reactor and kept at 200 °C for 24 h. The cooled black powder was washed three times by centrifugation with deionized water and anhydrous ethanol, and then vacuum dried at 60 °C to obtain a 3D flower-chain network structured MoS2 / PPy composite material.

[0035] In addition, flower-shaped pure MoS2 was synthesized without PPy nanotubes using the same method.

[0036] 2. Preparation of Ag@PANI / AC composite materials

[0037] Step 1: Disperse 1.0 g aniline (PANI) and 1.0 g activated carbon (AC) in 100 mL of 1 M HCl aqueous solution and sonicate for 2 h. Then, add 1.46 g ammonium persulfate dissolved in 10 mL of deionized water dropwise to the above solution. After stirring continuously at 25 °C for 24 h, filter out the black precipitate and wash repeatedly with deionized water and ethanol until the pH of the filtrate is close to 7. The final product is vacuum dried at 60 °C to obtain polyaniline modified activated carbon (PANI / AC).

[0038] Step 2: Disperse 1.2g PANI / AC in 40mL of deionized water, add 9.3mL of 0.1M AgNO3 aqueous solution and stir vigorously for 2h, then add 10mL of 0.1mol·L⁻¹ -1 L-ascorbic acid aqueous solution, continue stirring for 3 hours to reduce Ag + Finally, the reaction product was thoroughly washed with deionized water to remove unreacted chemicals, and dried at 60°C to obtain Ag@PANI / AC (denoted as Ag@PANI / AC-1.2).

[0039] In this embodiment, the amount of PANI / AC added in step 4 was changed to obtain samples containing different amounts of PANI / AC (1, 1.2 and 1.4 mg), which were labeled as Ag@PANI / AC-x, where x represents the content of PANI / AC.

[0040] like Figure 1 As shown in figure a, the original MoS2 exhibits dense flower-like microspheres formed by stacks of many interwoven nanosheets. Figure 1 As can be seen from b, the PPy nanotubes prepared in this embodiment are cross-linked to form a 3D framework structure. It is worth noting that for a single PPy nanotube ( Figure 1Further observation (see illustration b) reveals that it possesses a relatively smooth surface, and in particular, its unique hollow structure provides a large specific surface area (SSA) for rapid ion migration and mitigates the effects of Na+. + Changes in overall volume caused by insertion / extraction. Figure 1 d shows that the ultrathin MoS2 nanosheets with good dispersibility have been successfully anchored on and around the nanotube-shaped PPy. Furthermore, TEM observations ( Figure 1 e) It was confirmed that the flower-like MoS2 nanosheets are interconnected as shells, while the individual PPy nanotubes, which act as the core, are wrapped by the MoS2 nanosheets, forming a unique core-shell tubular structure. Figure 1 f shows a high-resolution TEM image of MoS2 nanosheets loaded on PPy, exhibiting clear lattice fringes with an interlayer spacing (0.69 nm) corresponding to the expansion of the (002) crystal plane. The inset shows the electron diffraction pattern (SAED) of a selected region, indicating that MoS2 / PPy exhibits polycrystalline properties with five diffraction rings. EDS image ( Figure 1 e to Figure 1 (j) reveals that C, N, O, Mo, and S are uniformly distributed throughout the heterostructure. The additional N element clearly confirms the presence of PPy. In this structure, PPy nanotubes encapsulated in MoS2 nanosheets act as conductive chains for electron transfer between well-dispersed MoS2 nanoflowers. Figure 1 c). A 3D interconnected flower chain network structure is formed by the interweaving of core-shell tubular PPy and MoS2 nanoflowers.

[0041] exist Figure 2 In a, the broad peak at 2θ = 26.0° in PPy nanotubes corresponds to amorphous PPy. Typical peaks of 2H-MoS2 were observed in MoS2 / PPy, located at 14.3°, 33.6°, 39.6°, 49.7°, and 59.2°, denoted as (002). 2H (101) 2H (103) 2H (105) 2H and (110) 2H (JCPDS No. 37-1492). The (002) peak at 2θ = 14.25° in MoS2 shifts to the left to 13.7° in MoS2 / PPy, demonstrating that the interlayer spacing is increased due to the interaction between MoS2 and PPy. In addition, the broadening of the (002) and (101) diffraction peaks in the heterostructure spectrum indicates that the PPy nanotubes reduce the crystallinity of MoS2. Figure 2 The Raman spectra of b show that for MoS2 / PPy and PPy, the two significant peaks correspond to the sp values ​​of carbonaceous materials, respectively. 3 Hybrid D band (1356 cm) -1 ) and sp2 Hybrid G-band (1584cm) -1 The intensity ratio of the D and G peaks of MoS2 / PPy (I) D / I G =0.87) is higher than the intensity ratio of PPy (0.41), indicating that an increased number of structural defects, acting as active sites, are formed in the MoS2 / PPy heterostructure. Regarding MoS2 / PPy and MoS2, at 381.2 and 407 cm⁻¹... -1 The main peaks are respectively with E 1 2g and A 1g Related. E 1 2g The band reflects the in-plane transfer of Mo-S, while A 1g It is produced by out-of-plane symmetric transfer of S atoms. The A atoms in MoS2 / PPy... 1g The peak shifted to the left at 403cm -1 This proves that the interlayer spacing of MoS2 increases. From Figure 2 The results from c show that all samples exhibited a Type IV isotherm with an H3-type hysteresis loop, indicating that mesoporous structures dominate the pore structure. The specific surface area order is MoS2 (7.8 m² / m³). 2 g -1 ) <MoS2 / PPy(25.3m 2 g -1 ) <PPy(55.9m 2 g -1 ). Figure 2 d shows that all three samples exhibit both mesoporous and macroporous characteristics, with the pore volume order being MoS2 (0.04 cm⁻¹). 3 g -1 ) <MoS2 / PPy(0.14cm 3 g -1 ) <PPy(0.30cm 3 g -1 The results show that the introduction of PPy nanotubes and dispersed layered MoS2 nanosheets endow the heterostructure with higher SSA and pore volume than the original MoS2.

[0042] like Figure 3 As shown in figure a, AC exhibits a relatively smooth, stone-like morphology with irregular shapes. The in-situ polymerization growth of PANI on the surface of AC particles reveals a nanowire-like external morphology, resembling conductive wires that connect individual AC particles together to form a 3D interconnected porous structure. Figure 3 b). Figure 3 c and the corresponding element diagram ( Figure 3 d to Figure 3 g) The results reflect the successful modification of Ag particles on the PANI / AC plane.

[0043] like Figure 4 The XRD pattern shows that the two broad peaks of AC at 23.9° and 42.4° are associated with the (002) and (101) crystal planes of the carbonaceous material, respectively. After in-situ polymerization of PANI on the AC surface, the PANI / AC composite material overlaps with the 42.4° peak of AC, while the three additional peaks at 14.9°, 20.6°, and 25.2° are associated with the (011), (020), and (200) crystal planes of PANI, respectively. For Ag@PANI / AC-1.2, in addition to the typical peaks of PANI, new peaks at 38.1°, 44.3°, 64.4°, and 77.5° are associated with the Ag crystal planes, respectively. 0 The (111), (200), (220), and (311) crystal planes of (JCPDS No. 04-0783) are matched. The presence of these diffraction peaks indicates that Ag was successfully doped into the heterostructure by chemical reduction.

[0044] Figure 5 a reacted at 5mV·s -1 CV curves for MoS2, PPy, and MoS2 / PPy electrodes at scan rates. Note that MoS2 / PPy exhibits the largest CV integral area, with a corresponding calculated specific capacitance of 105.22 F·g. -1 It exceeds MoS2 (37.17 F·g) -1 ) and PPy(86.90F·g -1 In addition, through 5–100 mV·s -1 Comparative analysis of CV curves within the sweep speed range ( Figure 5 b) reveals that the specific capacitance of the three electrodes decreases significantly with increasing scan rate, and MoS2 / PPy consistently maintains the highest capacitance characteristic. The GCD curves of the three electrodes are observed ( Figure 5 c) In 1A·g -1 At the current density, the discharge time of MoS2 / PPy is significantly longer than that of the other two electrodes. Figure 5 d depicts the relationship between discharge specific capacitance and current density. The charge / discharge time varies with current density (0.5–5 A·g). -1 The pseudocapacitive properties of the MoS2 / PPy electrode gradually decrease with increasing density. MoS2 / PPy maintains its advantage across all density ranges, consistent with CV results. These findings suggest that the introduction of PPy nanotubes improves the pseudocapacitive electrochemical performance of the MoS2 / PPy electrode. The impedance characteristics of the three electrodes were investigated using AC impedance spectroscopy. Based on equivalent circuit simulations, R... s (Interface resistance) and R ct (charge transfer resistance) Figure 5 (Illustration of e). R of MoS2, PPy and MoS2 / PPy electrodes sThe values ​​are 2.89Ω, 2.55Ω, and 2.48Ω, respectively. Additionally, R... ct (MoS2 / PPy)=1.76Ω <R ct (PPy) = 2.08Ω <R ct (MoS2) = 5.03 Ω. In Figure 5 In the f-type, compared with MoS2 and PPy electrodes, the MoS2 / PPy electrode exhibits a lower charging resistance, further verifying that the unique 3D flower chain network structure of MoS2 / PPy can promote charge transfer and ultimately induce rapid Na+ charging. + storage.

[0045] Electrodes AC, PANI / AC, Ag@PANI / AC-1, Ag@PANI / AC-1.2, and Ag@PANI / AC-1.4 at 5 mV s -1 The CV curve at the sweep speed is as follows Figure 6 As shown in Figure a, Ag@PANI / AC-1.2 has the largest enclosed area, and its specific capacitance is calculated to be 192.06 F·g. -1 It was significantly higher than AC (120.48 F·g). -1 ), PANI / AC (151.41F·g) -1 ), Ag@PANI / AC-1(180.21F·g -1 ) and Ag@PANI / AC-1.4 (169.72 F·g -1 In Ag@PANI / AC-x, another pair of strong redox peaks appear near -0.05 and 0.21 V, representing Ag / Ag + Reversible electrochemical transitions. For example... Figure 6 As shown in b, the specific capacitance of all five electrodes decreases significantly with increasing scan rate. At any scan rate, the specific capacitance of Ag@PANI / AC-x is consistently higher than that of PANI and AC. In particular, Ag@PANI / AC-1.2 exhibits the best performance across the entire scan rate range. The GCD curves of the five electrodes (…) Figure 6 In c), it was clearly observed that charging and discharging times increased with increasing current density (0.5–5 A·g). -1 The discharge time of Ag@PANI / AC-1.2 is significantly longer than that of AC, PANI / AC, Ag@PANI / AC-1, and Ag@PANI / AC-1.4, indicating its advantage in charge release and storage capacity. Meanwhile, the specific capacitance of Ag@PANI / AC-1.2 remains superior across all density ranges. Figure 6 d). By fitting the equivalent circuit ( Figure 7 ), R of AC, PANI / AC and Ag@PANI / AC-1.2 electrodes sThe values ​​are 3.58Ω, 3.08Ω, and 3.06Ω, respectively. Furthermore, R... ct (Ag@PANI / AC-1.2)=0.64Ω <R ct (PANI / AC) = 0.95Ω <R ct (AC) = 5.81Ω. This indicates that appropriate Ag loading helps reduce the ion transport resistance at the interface between the Ag@PANI / AC-1.2 heterostructure and the electrolyte, thereby improving the conductivity of the electrode and achieving the desired ion diffusion capability.

[0046] Based on electrochemical performance comparisons, Ag@PANI / AC-1.2 was selected as the optimal electrode for assembly into the Di-CDI system. Three asymmetric desalination systems were configured, including an HCDI system constructed from MoS2 / / AC and two Di-CDI systems: MoS2 / / Ag@PANI / AC and MoS2 / PPy / / Ag@PANI / AC. The effect of operating voltage on deionization performance was first investigated at 500 mg·L⁻¹. -1 Evaluation was conducted in NaCl solution. Figure 8 a) As the voltage increased from 0.8V to 1.4V, the SAC of the MoS2 / PPy / / Ag@PANI / AC system consistently showed an advantage over the other two systems. The charge efficiency of all three systems decreased with increasing voltage. At 0.8V, the maximum charge efficiencies of MoS2 / PPy / / Ag@PANI / AC and MoS2 / / Ag@PANI / AC were 56.2% and 50.8%, respectively, both higher than the maximum charge efficiency of MoS2 / / AC (42.7%). Figure 8 In step b, MoS2 / PPy / / Ag@PANI / AC reached adsorption equilibrium with the fastest removal rate, yielding the maximum SAC (25.1 mg·g⁻¹). -1 ), namely MoS2 / / Ag@PANI / AC (18.2 mg·g -1 ) and MoS2 / / AC (13.9 mg·g -1 1.38 and 1.81 times that of ). Figure 8 In the Kim-Yoon plot of c, the relationship between adsorption rate (SAR) and SAC intuitively describes the ion removal performance. Clearly, at 1.4 V, the curve for MoS2 / PPy / / Ag@PANI / AC occupies the upper right quadrant, indicating the highest SAC (25.1 mg·g⁻¹). -1 ) and the fastest SAR (5.88 mg·g -1 ·min -1Comparing the two Di-CDI systems, MoS2 / PPy / / Ag@PANI / AC exhibited better deionization capability than MoS2 / / Ag@PANI / AC. Based on the comparison results of SAC, the optimal voltage was determined to be 1.4V. (The last part, "100 to 500 mg L," appears to be an error and is left untranslated.) - 1 Comparison of SAC values ​​of MoS2 / PPy / / Ag@PANI / AC within the NaCl concentration range. Figure 8 d). As observed, the SAC of MoS2 / PPy / / Ag@PANI / AC gradually increased from 11.3 to 15.2, 17.4, 21.0, and 25.1 mg·g, respectively. -1 At any concentration, the SAC of this system was higher than that of the other two systems. As the concentration increased, the SAC of all three systems showed an increasing trend. Figure 9 This study revealed that the SAC of MoS2 / PPy / / Ag@PANI / AC exhibited the same trend under different NaCl concentrations, increasing significantly in the initial stage, then rising slowly until approaching saturation, and the corresponding Kim-Yoon plots showed... Figure 9 Given in b. Clearly, 500 mg·L - 1 The NaCl curve is located in the upper right corner, indicating the best ion removal capability.

[0047] The cycling stability of MoS2 / PPy / / Ag@PANI / AC was measured at 1.4V and 300mg·L⁻¹. -1 The experiment was conducted in NaCl solution. The conductivity change curve was used to... Figure 10 It can be seen that after 10 consecutive charge / discharge cycles, the adsorption capacity is still maintained at 97.7%, indicating that the Di-CDI system has significant cyclic performance. The desalination capacity of MoS2 / PPy / / Ag@PANI / AC is compared with various previously reported MoS2-based CDI systems. Figure 11 (a and 11b). The Di-CDI system MoS2 / PPy / / Ag@PANI / AC exhibits competitive SAC performance, especially its ultrafast rate capability, which surpasses other reported MoS2-based HCDI and symmetric CDI systems.

[0048] In summary, this invention constructs a Di-CDI system comprising a 3D interconnected flower chain network MoS2 / PPy as Na + The trap electrode, a 3D conductive structure Ag@PANI / AC as Cl - The capture electrode, thanks to its unique electrode material design and optimized module configuration, exhibits superior desalination capacity (25.1 mg·g⁻¹).-1 ), and an extremely high maximum ion removal rate (5.88 mg·g⁻¹). -1 ·min -1 It exhibits good desalination retention (97.7% after 10 cycles). The MoS2 / PPy electrode, in synergy with the 3D conductive PPy substrate, induces Na+ desalination. + Intercalation behavior. Similarly, through the synergistic effect of redox-active Ag, the Faraday pseudocapacitive reaction from PAIN, and the EDL electroadsorption from AC, Cl... - The MoS2 / PPy composite material and the Ag@PANI / AC composite material prepared in this invention are promising candidates for seawater desalination and can be used to construct Di-CDI systems for water purification.

Claims

1. A dual-ion selective HCDI system based on pseudocapacitive behavior induced by MoS2 / PPy / / Ag@PANI / AC, characterized in that: The HCDI system uses a MoS2 / PPy composite material with a three-dimensional flower chain network structure formed by polypyrrole nanotubes and MoS2 nanoflowers as the cathode, and a heterostructure Ag@PANI / AC composite material formed by Ag particles modifying polyaniline-modified activated carbon as the anode. The preparation method of the MoS2 / PPy composite material is as follows: ammonium molybdate and thiourea are dissolved in deionized water, then polypyrrole nanotubes are added, and after ultrasonic treatment, the mixture is transferred to a high-pressure reactor and reacted at 160-220°C for 20-30 hours. The resulting black powder is washed with deionized water and anhydrous ethanol by centrifugation and then vacuum dried to obtain the MoS2 / polypyrrole composite material, i.e., the MoS2 / PPy composite material. The preparation method of the Ag@PANI / AC composite material is as follows: polyaniline modified activated carbon is dispersed in deionized water, silver nitrate aqueous solution is added and stirred for 1 to 2 hours, then ascorbic acid aqueous solution is added and stirred for another 2 to 4 hours. Finally, the reaction product is washed with deionized water and dried to obtain Ag-supported polyaniline modified activated carbon with a heterostructure, namely Ag@PANI / AC composite material.

2. The dual-ion selective HCDI system based on pseudocapacitive behavior induced by MoS2 / PPy / / Ag@PANI / AC according to claim 1, characterized in that: In the preparation method of the MoS2 / PPy composite material, the mass ratio of polypyrrole nanotubes to ammonium molybdate and thiourea is 1:1.5-2:2.5-3.

5.

3. The dual-ion selective HCDI system based on pseudocapacitive behavior induced by MoS2 / PPy / / Ag@PANI / AC according to claim 1, characterized in that: In the preparation method of the MoS2 / PPy composite material, the reaction is carried out at 190-200℃ for 24 hours.

4. The dual-ion selective HCDI system based on pseudocapacitive behavior induced by MoS2 / PPy / / Ag@PANI / AC according to any one of claims 1 to 3, characterized in that: The preparation method of the polypyrrole nanotubes is as follows: methyl orange is ultrasonically dissolved in deionized water, and then pyrrole and ferric chloride aqueous solution are added under stirring conditions. The reaction is carried out in situ under dark ice bath conditions for 20-24 hours. After the reaction is completed, the precipitate is collected by filtration, washed with deionized water and ethanol, and dried to obtain polypyrrole nanotubes.

5. The dual-ion selective HCDI system based on pseudocapacitive behavior induced by MoS2 / PPy / / Ag@PANI / AC according to claim 4, characterized in that: In the preparation method of the polypyrrole nanotubes, the mass ratio of methyl orange to pyrrole to ferric chloride is 1:2-2.5:5-5.

5.

6. The dual-ion selective HCDI system based on pseudocapacitive behavior induced by MoS2 / PPy / / Ag@PANI / AC according to claim 1, characterized in that: In the preparation method of the Ag@PANI / AC composite material, the mass ratio of polyaniline modified activated carbon to silver nitrate and ascorbic acid is 1:0.12-0.14:0.13-0.

15.

7. The dual-ion selective HCDI system based on pseudocapacitive behavior induced by MoS2 / PPy / / Ag@PANI / AC according to claim 1 or 6, characterized in that: The preparation method of the polyaniline modified activated carbon is as follows: aniline and activated carbon are added to a 1M HCl aqueous solution, ultrasonically treated for 1-2 hours, then ammonium persulfate aqueous solution is added, and the mixture is continuously stirred at room temperature for 20-24 hours. The resulting precipitate is washed with deionized water and ethanol until the pH of the filtrate is neutral, and then vacuum dried to obtain polyaniline modified activated carbon.

8. The dual-ion selective HCDI system based on pseudocapacitive behavior induced by MoS2 / PPy / / Ag@PANI / AC according to claim 7, characterized in that: In the preparation method of polyaniline modified activated carbon, the mass ratio of aniline to activated carbon and ammonium persulfate is 1:0.9-1.2:1.3-1.

5.

9. The use of the dual-ion selective HCDI system based on pseudocapacitive behavior induced by MoS2 / PPy / / Ag@PANI / AC as described in claim 1 in water desalination.

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