A carbon nanotube / polypyrrole / MoS 2 Composite electrode materials, their preparation methods, and their application in CDI desalination.

Abstract

This invention provides a carbon nanotube / polypyrrole / MoS 2 Composite electrode materials and their preparation methods, along with their application in CDI desalination, first employ in-situ polymerization to construct a 3D conductive interconnect structure from multi-walled carbon nanotubes and polypyrrole as a growth substrate, and then anchor MoS2 on its surface via a hydrothermal reaction. 2 Nanosheets to alleviate MoS2 2 Stacking of nanosheets. 3D conductive carbon nanotubes / polypyrrole improve the wettability of the composite material, provide a convenient movement path, accelerate charge transport rate, and promote ion diffusion. MoS 2 The enhanced dispersion and expanded layer space of the nanosheets provide ample intercalation sites for ion capture and rapid transfer. The tight chemical coupling of the Mo-N-C bonds ensures the structural stability of the composite electrode material. Therefore, the composite electrode material of this invention exhibits excellent adsorption capacity, ultrafast deionization rate, strong stability, and regenerability, making it a valuable reference and research material for the development of novel, high-efficiency desalination electrode materials.

Description

A carbon nanotube / polypyrrole / MoS2 composite electrode material, its preparation method, and its application in CDI desalination. Technical Field

[0001] This invention belongs to the field of CDI desalination technology, and relates to a desalination electrode material, specifically a ternary carbon nanotube / polypyrrole / MoS2 composite electrode material and its preparation method, as well as its application in CDI desalination. Background Technology

[0002] With population and economic growth and the scarcity of freshwater resources, converting brackish water or seawater into freshwater through separation technology has become an effective way to solve the water crisis. Capacitive deionization (CDI) is an electrochemically controlled method that offers advantages such as energy saving, economy, environmental protection, and high recovery rate compared to traditional desalination methods (distillation, electrodialysis, reverse osmosis, etc.). The desalination capacity of the CDI process mainly depends on the physicochemical properties of the electrode materials. However, traditional carbon-based CDI, which uses the electric double layer (EDL) ion storage principle, typically suffers from inherent limitations such as co-ion repulsion, insufficient ion capture capacity (10–15 mg / g), slow adsorption rate, and low charge efficiency. To address these issues, an optimized electrode configuration was considered, and a hybrid CDI (HCDI) system was constructed by introducing Faraday intercalation materials as cathodes. This system has proven to be far superior to electric double layer-based CDI. However, a significant kinetic mismatch exists between the carbon electrode and the Faraday electrode in HCDI, greatly inhibiting the overall desalination rate of the system. Furthermore, most types of intercalation materials can only capture either cations or anions. It is worth noting that layered two-dimensional (2D) intercalated materials capable of capturing cations and anions have been used as electrodes in the field of pseudocapacitive energy storage. Therefore, it is feasible to construct a symmetric CDI system by using structurally stable 2D intercalated materials as both cathode and anode to solve the dynamic mismatch problem.

[0003] Molybdenum disulfide (MoS2), a graphene-like material, is considered a suitable candidate for CDI electrodes as a typical 2D layered intercalation material. Its flexible and tunable S-Mo-S sandwich structure, abundant accessible sites, and high theoretical capacity have attracted widespread attention from researchers. Furthermore, MoS2 with different morphologies can be used as desalination electrode materials, with ion capture capabilities ranging from 8.81 to 24.6 mg / g. However, the inherent poor conductivity of MoS2 severely inhibits desalination kinetics. Numerous studies have shown that combining carbon-based materials with MoS2 can effectively overcome this deficiency. Zhang et al. constructed a 3D flower-like molybdenum disulfide / graphene composite material as an intercalation electrode (MoS2 / rGO), achieving high desalination capacity (16.82 mg / g) and good cycling stability. Zhang et al. combined nitrogen-doped highly ordered mesoporous carbon with molybdenum disulfide (MoS2 / NOMC), exhibiting enhanced hydrophilicity, conductivity, and pseudocapacitive contributions, with an ion removal capacity reaching 28.82 mg / g. Furthermore, the aggregation tendency and small interlayer spacing of the original MoS2 nanosheets hinder the effective utilization of accessible embedding sites and suppress charge transport processes, resulting in low ion removal capacity and rate. Wang et al. used a well-dispersed thin layer of MoS2 combined with a 3D support network composed of CNTs and carbon spheres as an electrode material (MoS2@CNT-CS), which produced a considerable desalination capacity (25.35 mg / g) and an enhanced desalination rate (3.9 mg / g / min). Therefore, combining MoS2 with carbonaceous materials to construct MoS2-based composite electrode materials with unique conductive structures can enhance the overall conductivity and hydrophilicity of the material while increasing the interlayer spacing of MoS2 to improve the desalination performance of CDI. Summary of the Invention

[0004] To overcome the limitations of MoS2's unsatisfactory conductivity, low removal rate, and repackaging tendency, as well as to address the kinetic mismatch problem associated with HCDI, this invention provides a ternary carbon nanotube / polypyrrole / MoS2 (CNT / PPy / MoS2) composite electrode material and its preparation method. This material connects CNTs and PPy to construct a 3D conductive network, then anchors MoS2 nanosheets on its surface via a hydrothermal reaction. PPy acts as a conductive bridge connecting the MoS2 nanosheets and CNTs, improving the overall conductivity and specific capacitance of the composite material. The unique 3D interconnected structure of CNT / PPy, serving as a growth substrate, reduces the stacking of MoS2 nanosheet layers while providing convenient charge transfer channels.

[0005] To achieve the above objectives, the CNT / PPy / MoS2 composite electrode material provided by the present invention is prepared by the following method:

[0006] Step 1: Multi-walled carbon nanotubes were ultrasonically dispersed in ethanol. Sodium dodecylbenzenesulfonate and ammonium persulfate were added under ice-water bath and continuous stirring. Then, pyrrole was added dropwise. The reaction was carried out for 10-12 hours. The precipitate was washed with deionized water and anhydrous ethanol in sequence and then dried to obtain carbon nanotube / polypyrrole composite material.

[0007] Step 2: Disperse the carbon nanotube / polypyrrole composite material in deionized water, then add ammonium molybdate and thiourea, stir evenly, and transfer the resulting mixture into a high-pressure reactor. Perform hydrothermal reaction at 180-220℃ for 12-24 hours. Wash the resulting precipitate with deionized water and anhydrous ethanol in sequence and then dry to obtain the carbon nanotube / polypyrrole / MoS2 composite electrode material.

[0008] In step 1 above, the preferred mass ratio of multi-walled carbon nanotubes to sodium dodecylbenzenesulfonate, ammonium persulfate, and pyrrole is 1:0.5 to 1:10 to 12:3 to 4.

[0009] In step 2 above, the preferred mass ratio of carbon nanotube / polypyrrole composite material to ammonium molybdate and thiourea is 1:20-25:40-45.

[0010] In step 2 above, it is further preferred to perform a hydrothermal reaction at 200°C for 24 hours.

[0011] This invention also provides the use of carbon nanotube / polypyrrole / MoS2 composite electrode material as a symmetrical electrode in CDI desalination.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] This invention utilizes in-situ polymerization and hydrothermal methods to prepare CNT / PPy / MoS2 composite electrode materials. The material uses a 3D conductive interconnect structure constructed from multi-walled carbon nanotubes and polypyrrole as a growth substrate to reduce the stacking of MoS2 nanosheets. The 3D conductive CNT / PPy improves the wettability of the composite material, providing a convenient movement path. Its excellent conductivity facilitates charge transport, accelerates the charge transport rate, and promotes ion diffusion. The enhanced dispersibility and expanded layer space of the MoS2 nanosheets provide ample intercalation sites for ion trapping and rapid transfer. Furthermore, the formation of Mo-NC coordination bonds ensures the structural stability of the composite electrode material. CNT / PPy / MoS2 exhibits a significant specific capacitance of 160.83 F / g (5 mV / s), which is 4.33 times and 1.41 times that of MoS2 (37.17 F / g) and CNT / PPy (113.97 F / g), respectively. The internal resistance (2.65Ω), charge transfer resistance (0.74Ω), and diffusion resistance of CNT / PPy / MoS2 are all lower than those of MoS2 and CNT / PPy. Furthermore, in a 500 mg / L NaCl solution at 1.2 V, the symmetrical CDI electrode configuration effectively overcomes the HCDI kinetic mismatch problem, achieving a maximum adsorption capacity of 24.8 mg / g and a maximum adsorption capacity of 5.24 mg / g. / The composite electrode material exhibits an ultra-high deionization rate of 92.7%. Even after 25 adsorption / desorption cycles, the ion removal capacity remains at 92.7%. This demonstrates that the composite electrode material of this invention possesses excellent adsorption capacity, ultra-fast deionization rate, strong stability, and regenerability, making it a valuable reference and research material for the development of novel, high-efficiency desalination electrode materials. Attached Figure Description

[0014] Figure 1 shows scanning electron microscope (SEM) and transmission electron microscope (TEM) images of CNT / PPy, MoS2, and CNT / PPy / MoS2 prepared in Example 1.

[0015] Figure 2 shows the X-ray diffraction patterns of CNT / PPy, MoS2, and CNT / PPy / MoS2 prepared in Example 1.

[0016] Figure 3 shows the Raman spectra of CNT / PPy, MoS2, and CNT / PPy / MoS2 prepared in Example 1.

[0017] Figure 4 shows the N2 adsorption / desorption curves of CNT / PPy, MoS2, and CNT / PPy / MoS2 prepared in Example 1.

[0018] Figure 5 shows the pore size distribution of CNT / PPy, MoS2, and CNT / PPy / MoS2 prepared in Example 1.

[0019] Figure 6 shows the full X-ray photoelectron spectra of CNT / PPy, MoS2, and CNT / PPy / MoS2 prepared in Example 1.

[0020] Figure 7 shows the hydrophilicity analysis of CNT / PPy, MoS2, and CNT / PPy / MoS2 prepared in Example 1.

[0021] Figure 8 shows the CV curves of CNT / PPy, MoS2, and CNT / PPy / MoS2 prepared in Example 1.

[0022] Figure 9 shows the EIS curves of CNT / PPy, MoS2, and CNT / PPy / MoS2 prepared in Example 1.

[0023] Figure 10 shows the CDI desalination apparatus for CNT / PPy, MoS2, and CNT / PPy / MoS2 prepared in Example 1.

[0024] Figure 11 is a schematic diagram of the CDI module for desalination testing of CNT / PPy, MoS2 and CNT / PPy / MoS2 prepared in Example 1. In the figure, 1 and 1' are plexiglass, 2 and 2' are silicone gaskets, 3 and 3' are nickel foam, 4 is active material, 5 is silicone separator, and 6 is insulating mesh.

[0025] Figure 12 shows the relationship between NaCl concentration and conductivity in CNT / PPy, MoS2, and CNT / PPy / MoS2 prepared in Example 1 for CDI desalination testing.

[0026] Figure 13 shows a comparison of the ion removal capacity and removal rate of the CNT / PPy / MoS2 composite electrode material prepared in Example 1 as a symmetric electrode with those of the reported MoS2-based CDI system.

[0027] Figure 14 shows a comparison of the ion removal rate operating parameters of the CNT / PPy / MoS2 composite electrode material prepared in Example 1 as a symmetric electrode with those of the reported MoS2-based CDI system. Detailed Implementation

[0028] 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.

[0029] This invention consists of two steps. First, a 3D conductive structure CNT / PPy is prepared by in-situ polymerization. Second, a CNT / PPy / MoS2 composite electrode material is prepared by anchoring MoS2 nanosheets onto the CNT / PPy surface through a simple hydrothermal reaction.

[0030] Example 1

[0031] Step 1: Place 0.2 g of multi-walled carbon nanotubes (MWCNTs) in 40 mL of ethanol and sonicate for 30 minutes to ensure uniform dispersion; under continuous stirring in an ice-water bath, add 0.15 g of sodium dodecylbenzenesulfonate and 2.28 g of ammonium persulfate to the resulting dispersion in sequence, and then add 0.7 mL of pyrrole (PPy) dropwise. Stir the reaction at room temperature for 12 hours; wash the resulting precipitate with deionized water and anhydrous ethanol in sequence, and then dry it in a 60 °C oven for 10 hours to obtain carbon nanotube / polypyrrole composite material (CNT / PPy).

[0032] Step 2: Disperse 40 mg CNT / PPy in 40 mL of deionized water, then add 0.93 g ammonium molybdate tetrahydrate and 1.71 g thiourea. After stirring for 30 minutes, transfer the resulting mixture to a 100 mL high-pressure reactor and hydrothermally react at 200 °C for 24 hours. After the reaction is complete, wash the resulting precipitate with deionized water and anhydrous ethanol in sequence, and then dry it in an oven at 60 °C for 12 hours to obtain the CNT / PPy / MoS2 composite electrode material.

[0033] The microstructures of MoS2 (prepared according to step 2 above, but without CNT / PPy) and the CNT / PPy and CNT / PPy / MoS2 prepared in this embodiment were examined by SEM and TEM. Figures 1a-b show that CNT / PPy has a channel-like 3D network morphology with uniform diameter. Furthermore, polymer PPy nanoparticles are uniformly coated on the surface of the single tube. In Figure 1c, pure MoS2 forms 3D flower-like microspheres through the self-assembly of petal-like sheets. Unlike monomeric MoS2, the surface of CNT / PPy / MoS2 exhibits relatively smooth sheets (Figures 1d-e), meaning that thin MoS2 nanosheets are loosely covering the CNT / PPy surface. Meanwhile, the TEM image (Figure 1f) shows that the 0.68 nm interlayer lattice fringes correspond to the (002) crystal plane of MoS2, which is larger than that of the original MoS2 (approximately 0.62 nm), indicating that the introduction of CNT / PPy can effectively induce the stacking of MoS2 sheets. Elemental mapping of CNT / PPy / MoS2 (Fig. 1g-l) shows a uniform distribution of C, N, O, Mo, and S elements, with the presence of additional N confirming the presence of PPy. SEM and TEM images confirm that the PPy-loaded CNT monotubes are interconnected to form a 3D conductive structure. Subsequently, well-dispersed MoS2 nanosheets are anchored on the CNT / PPy surface.

[0034] As shown in Figure 2, the characteristic diffraction peaks of CNT / PPy at 25.66° and 44.13° match the (002) and (101) crystal planes of the carbonaceous material, respectively. The XRD diffraction of CNT / PPy / MoS2 shows distinct peaks at 13.95°, 33.45°, 39.52°, 49.22°, and 59.07°, corresponding to the (002), (101), (103), (105), and (110) crystal planes of the 2H phase MoS2, respectively. Notably, the (002) peak at 2θ = 14.24° in MoS2 shifts to 2θ = 13.95° in CNT / PPy / MoS2, verifying the extended layer space of MoS2.

[0035] The Raman spectroscopy results in Figure 3 show that, due to the addition of CNT / PPy, a defect-induced D band (1356 cm⁻¹) appears in the spectrum of CNT / PPy / MoS₂. -1 ) and graphite-induced G-band (1584 cm) -1 Two typical peaks were observed at 382.4 cm⁻¹. -1 and 407.0cm -1 The strong peaks at these locations correspond to the E1 2g (in-plane) and A of the 2H phase MoS2, respectively. 1g (Out-of-plane) vibration correlation. Similarly, A of CNT / PPy / MoS2. 1g The peak shifted to the left to 404.4 cm. -1 This further confirms the increased interlayer spacing of MoS2.

[0036] As shown in Figure 4, under higher relative pressures, all samples exhibited a type IV isotherm and an H3 hysteresis loop, indicating the presence of abundant mesopores. Specific surface area (SSA) increased in the following order: MoS2 (7.751 m² / m³). 2 / g) <CNT / PPy / MoS2(12.622m 2 / g) <CNT / PPy(98.993m 2 / g). Furthermore, as shown in Figure 5, the pore size distributions of MoS2, CNT / PPy, and CNT / PPy / MoS2 are concentrated in the range of 2–25 nm, and the pore volume follows the pattern of MoS2 (0.039 cm³ / g). 3 / g) <CNT / PPy / MoS2(0.072cm 3 / g) <CNT / PPy(0.5420cm 3 / g).

[0037] The XPS spectrum of CNT / PPy / MoS2 (Figure 6) showed the presence of C, Mo, S, O, and N elements, further confirming the successful composite of CNT, PPy, and MoS2. Contact angle testing was used to evaluate the hydrophilicity of CNT / PPy, MoS2, and the CNT / PPy / MoS2 composite (Figure 7). Compared to the original MoS2 (78°), the lower contact angle of CNT / PPy / MoS2 (61°) indicates enhanced hydrophilicity of the composite.

[0038] Electrochemical performance tests showed that CNT / PPy / MoS2 exhibited a significant specific capacitance of 160.83 F / g (5 mV / s), which was 4.33 times and 1.41 times that of MoS2 (37.17 F / g) and CNT / PPy (113.97 F / g), respectively (Figure 8). The internal resistance (2.65 Ω), charge transfer resistance (0.74 Ω), and diffusion resistance of CNT / PPy / MoS2 were all lower than those of MoS2 and CNT / PPy (Figure 9).

[0039] Example 2

[0040] In step 2 of this embodiment, the amount of CNT / PPy used is 20mg, and the other steps are the same as in Example 1, to obtain the CNT / PPy / MoS2-20 composite electrode material.

[0041] Example 3

[0042] In step 2 of this embodiment, the amount of CNT / PPy used is 60mg, and the other steps are the same as in Example 1, to obtain the CNT / PPy / MoS2-60 composite electrode material.

[0043] Example 4

[0044] Application of CNT / PPy / MoS2 prepared in Example 1 as a symmetrical electrode in CDI desalination

[0045] Desalination tests were conducted using a circulating mode. The desalination device included a CDI module, a computer, a conductivity meter, a multimeter, a peristaltic pump, and a DC power supply, as shown in Figure 10. A symmetrical CDI module (Figure 11) was constructed using CNT / PPy / MoS2 as the cathode and anode, respectively, to evaluate ion removal capacity. The cathode and anode were separated by a 1 mm thick silicone gasket, with an insulating mesh placed in the center to prevent short circuits. 100 mL of a NaCl aqueous solution with a concentration of 100–500 mg / L was pumped into the CDI module at a flow rate of 20 mL / min. Furthermore, changes in conductivity and current were monitored online using a conductivity meter (DDS-308F) and a multimeter (VC8265), respectively. The relationship between NaCl concentration and conductivity is shown in Figure 12.

[0046] The desalination capacity of CNT / PPy / MoS2 was compared with that of various reported MoS2-based CDI systems, and the results are shown in Figures 13-14. As can be seen from the figures, CNT / PPy / MoS2 exhibits competitive desalination capacity, especially excellent maximum deionization rate. In a 1.2V voltage and 500mg / L NaCl solution, the symmetrical CDI electrode configuration effectively overcomes the kinetic mismatch problem of HCDI, achieving a maximum adsorption capacity of 24.8mg / g and a maximum adsorption rate of 5.24mg / g. / The ultra-high deionization rate of min exceeds that reported in the literature for MoS2 / MXene / / AC (Z. Chen, X. Xu, Y. Liu, J. Li, K. Wang, Z. Ding, F. Meng, T. Lu, L. Pan, Ultra-durable and highly-efficient hybrid capacitive deionization by MXeneconfinedMoS2heterostructure, Desalination 528 (2022), 115616.), MoS2@CNT-CS / / CNT-CS (Y. Cai, W. Zhang, R. Fang, D. Zhao, Y. Wang, J. Wang, Well-dispersed few-layered MoS2connected with robust 3D conductive architecture for rapidcapacitivedeionization process andits specific ion selectivity, Desalination 520 (2021), 115325.), MoS2 / rGO / / AC (L. Gao, Q. Dong, S. Bai, S. Liang, C. Hu, J. Qiu, Graphene oxide-tuned MoS2with an expanded interlayer for efficient hybrid capacitivedeionization, ACS Sustain.Chem.Eng. 8 (2020) 9690-9697.), MoS2@MXene / / AC (Y. Cai, Y. Wang, L. Zhang, R. Fang, J. Wang, 3D heterostructure constructed by few-layeredMXenes with a MoS2layer as the shielding shell for excellent hybridcapacitive deionization and enhanced structural stability, ACSAppl.Mater.Interfaces 14 (2022) 2833-2847.), MoS2 / PDA / / AC (Q. Wang, F. Jia, S. Song, Y.Li, Hydrophilic MoS2 / polydopamine (PDA) nanocomposites as the electrode for enhanced capacitive deionization, Sep. Purif. Technol. 236 (2020), 116298.), MoS2 / g-C3N4 / / MoS2 / g-C3N4 (S. Tian, X. Zhang, Z. Zhang, Capacitive deionization with MoS2 / g-C3N4 electrodes, Desalination 479 (2020), 114348.), MoS2 / NOMC / / MoS2 / NOMC (S. Tian, X. Zhang, Z. Zhang, Novel MoS2 / NOMC electrodes with enhanced capacitive deionization performances, Chem. Eng. J. 409 (2021), 128200.), 3D flower-like MoS2 / rGO / / AC (W. Peng, W. Wang, G. Han, Y. Huang, Y. Zhang, Fabrication of 3D flower-like MoS2 / graphene composite as high-performance electrode for capacitive deionization, Desalination 473 (2)020), 114191.) and MoS2-graphene / / AC (J. Han, T. Yan, J. Shen, L. Shi, J. Zhang, D. Zhang, Capacitive deionization of saline water by using MoS2-Graphene hybrid electrodes with high volumetric adsorption capacity, Environ. Sci. Technol. 53 (2019) 12668-12676.), and after 25 adsorption / desorption cycles, the ion removal ability still remained at 92.7%.

Claims

1. A carbon nanotube / polypyrrole / MoS2 composite electrode material, characterized in that, The material constructs a 3D conductive network by connecting carbon nanotubes and polypyrrole, and then anchors MoS2 nanosheets on its surface through a hydrothermal reaction. Polypyrrole acts as a conductive bridge connecting the MoS2 nanosheets and carbon nanotubes. The material is prepared by the following steps: Step 1: Multi-walled carbon nanotubes are ultrasonically dispersed in ethanol. Sodium dodecylbenzenesulfonate and ammonium persulfate are added under ice-water bath and continuous stirring. Then, pyrrole is added dropwise. The reaction is carried out for 10-12 hours. The resulting precipitate is washed with deionized water and anhydrous ethanol and then dried to obtain a carbon nanotube / polypyrrole composite material. Step 2: The carbon nanotube / polypyrrole composite material is dispersed in deionized water. Then, ammonium molybdate and thiourea are added. After stirring evenly, the resulting mixture is transferred to a high-pressure reactor and hydrothermally reacted at 180-220°C for 12-24 hours. The resulting precipitate is washed with deionized water and anhydrous ethanol and then dried to obtain a carbon nanotube / polypyrrole / MoS2 composite electrode material.

2. The carbon nanotube / polypyrrole / MoS2 composite electrode material according to claim 1, characterized in that, In step 1, the mass ratio of the multi-walled carbon nanotubes to sodium dodecylbenzenesulfonate, ammonium persulfate, and pyrrole is 1:0.5 to 1:10 to 12:3 to 4.

3. The carbon nanotube / polypyrrole / MoS2 composite electrode material according to claim 1, characterized in that, In step 2, the mass ratio of the carbon nanotube / polypyrrole composite material to ammonium molybdate and thiourea is 1:20-25:40-45.

4. The carbon nanotube / polypyrrole / MoS2 composite electrode material according to claim 1, characterized in that, In step 2, the hydrothermal reaction is carried out at 200°C for 24 hours.

5. The use of the carbon nanotube / polypyrrole / MoS2 composite electrode material according to claim 1 as a symmetrical electrode in CDI desalination.

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