Silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode materials for capacitive deionization and their preparation and application

Abstract

The present invention belongs to the technical field of capacitive deionization and desalination, and relates to the preparation and application of a mesoporous carbon zinc-based MOF ternary composite porous carbon electrode material for capacitive deionization. The preparation comprises: first preparing SBA-15 mesoporous carbon precursor by a hydrothermal method under acidic conditions using P123 and ethyl orthosilicate; then dispersing the SBA-15 mesoporous carbon precursor, carbon nanotubes and zinc nitrate hexahydrate in anhydrous methanol to obtain solution A; dissolving dimethylimidazole in anhydrous methanol to obtain solution B; then adding solution B to solution A, stirring and standing thoroughly, and obtaining a silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material precursor after suction filtration and drying; finally, calcining at high temperature under an inert atmosphere, and then drying after acid oxidation etching. The preparation method of the present invention is simple, environmentally friendly, and has excellent effects in capacitive deionization and desalination applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of capacitive deionization and desalination, and in particular relates to a silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material for capacitive deionization, and its preparation and application. Background Art

[0002] In today's world of extreme water scarcity, metal-organic frameworks (MOFs) and their derivatives have been widely studied and applied in capacitive deionization (CDI) desalination technology, primarily due to their high specific surface area and ability to control pore size. However, the pore size of most MOF materials is relatively microporous, which makes it easy for ions to clog the pores during CDI adsorption, resulting in a reduction in the effective pore size, a decrease in adsorption efficiency after repeated use, and the inability to regenerate the electrodes. To address this limitation of MOF materials, scientists have explored various methods to improve the situation, including increasing the sintering temperature and performing an acidification treatment. A Chinese patent document (application number 201710504003.2) discloses a MOF-structured porous carbon material. The preparation method includes: compounding a metal-organic framework material onto the surface of carbon nanotubes to form a carbonized precursor; and heating the carbonized precursor to 700-1000°C in a protective atmosphere to obtain the MOF-structured porous carbon material. The prepared material has the following defects: the wettability of the obtained electrode surface is insufficient, the contact area between the electrode and the solution to be adsorbed is small, which is not conducive to the adsorption and desorption of ions; the specific surface area of ​​the composite electrode material is too small and the surface pore size is too large, which is not conducive to the transmission and storage of ions, resulting in poor adsorption performance of the electrode material. Summary of the Invention

[0003] Research has found that Zn-MOF has an excessive number of microporous structures and a small average pore size. This can cause salt ions to block the pores during adsorption, reducing the effective pore size. To overcome this technical problem, the present invention provides a silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material for capacitive deionization, as well as its preparation and application.

[0004] To achieve the purpose of the present invention, the technical solution adopted is: a method for preparing a silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material for capacitive deionization, characterized by:

[0005] The method comprises the following steps: (1) preparing SBA-15 mesoporous carbon precursor by hydrothermal reaction of P123 and tetraethyl orthosilicate under acidic conditions;

[0006] (2) adding the SBA-15 mesoporous carbon precursor, carbon nanotubes, and zinc nitrate hexahydrate in step (1) to anhydrous methanol in a certain mass ratio, stirring evenly and allowing for sufficient adsorption to obtain solution A; adding the required amount of dimethylimidazole to anhydrous methanol to obtain solution B;

[0007] (3) adding the solution B in step (2) to the solution A, stirring until fully reacted, and then filtering to obtain a silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite material precursor;

[0008] (4) calcining the silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite material precursor in step (3) under inert atmosphere to obtain derived carbon, then oxidizing and etching the derived carbon with nitric acid, and vacuum drying to obtain a silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material;

[0009] The mass ratio of zinc in SBA-15 mesoporous carbon precursor, carbon nanotubes, and zinc nitrate is calculated to be 0.2-0.6: 0.15-0.3: 1.85-1.95;

[0010] In step (4), the high-temperature calcination adopts a step-by-step calcination method, first heating to 500-550°C at 2-4°C / min, and calcining at this temperature for 4-5 hours; then continuing to heat to 950-1000°C at 5-8°C / min, and calcining at this temperature for 2-3 hours; the nitric acid concentration is 4-8M, the etching temperature is 90-100°C, and the reaction time is 4-6 hours.

[0011] The structure of the silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material for capacitive deionization prepared by the above method includes SBA mesoporous carbon, Zn-MOF-derived carbon attached to the SBA mesoporous carbon, and carbon nanotubes uniformly interspersed and connected in the gaps between the SBA mesoporous carbon and the Zn-MOF-derived carbon. The structure is formed by the following method: uniformly dispersed SBA-15 mesoporous carbon precursor and carbon nanotubes in situ composite organic metal framework Zn-MOF, and then calcined and carbonized under inert atmosphere protection;

[0012] The average pore size of the electrode material is 7.5 to 10 nm, and the specific surface area is ≥500 m 2 / g, pore volume 0.3~6cm 3 / g, equivalent series resistance ≤ 0.7Ω, and water contact angle no more than 102°.

[0013] Furthermore, in step (2), the mass ratio of zinc to dimethylimidazole in the zinc nitrate is 1:7.8-8.5.

[0014] Furthermore, in step (2), the stirring time is 6 to 8 hours;

[0015] Furthermore, in step (4), the high-temperature calcination adopts a step-by-step calcination method, which is divided into two calcination processes. The calcination temperature of the first stage is 550°C, the heating rate is 2°C / min, and the calcination time is 4h; the calcination temperature of the second stage is 950°C, the heating rate is 5°C / min, and the calcination time is 2h;

[0016] An application of the silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material for capacitive deionization prepared by the above method includes the following steps: the silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material can be prepared into a CDI electrode using a general method.

[0017] For example, silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite-derived carbon, acetylene black and polytetrafluoroethylene emulsion (60wt%) (PTFE) are mixed in a mass ratio of 8:1:1, anhydrous ethanol is added dropwise until it becomes viscous, and after high-temperature mixing, a roller press is used to press it into a carbon film to obtain a CDI electrode.

[0018] Compared with the prior art, the present invention achieves the following beneficial effects:

[0019] 1) The present invention uses an in-situ growth method to prepare a silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material, a simple and low-cost method. After high-temperature carbonization, nitric acid is used for oxidative etching, effectively improving the pore structure and increasing the number of active sites for ion adsorption. Simultaneously, oxygen-containing functional groups are introduced, improving the hydrophilicity of the carbon material (the water contact angle of the composite electrode material does not exceed 102°), increasing the contact area between the solution and the electrode, and improving the electrode's adsorption of salt ions.

[0020] 2) The silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material of the present invention adds an appropriate amount of carbon nanotubes, so that the carbon nanotubes are interspersed and connected between and inside the MOF crystals and mesoporous carbon to form a three-dimensional structure, which can prevent the carbon nanotubes from agglomerating, thereby improving the conductivity of the derived carbon material, facilitating the rapid transmission of ions, and having good effects in capacitive deionization and desalination applications.

[0021] 3) The silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material of the present invention is prepared by introducing SBA-15 silicon-based mesoporous carbon with rich mesopore volume to prepare a precursor, and using a step-by-step temperature sintering process to prepare PCNT / SBA-derived carbon, thereby further improving the pore structure of the electrode material, realizing more ion transmission channels and storage active sites, and further improving the adsorption performance of MOF-based composite materials in salt solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a scanning electron microscope image of the PCNT0.03-derived carbon in Example 1;

[0023] Figure 2 is a scanning electron microscope image of the PCNT / SBA0.02-derived carbon in Example 2;

[0024] Figure 3 is a scanning electron microscope image of the PCNT / SBA0.04-derived carbon in Example 3;

[0025] Figure 4 is a scanning electron microscope image of the PCNT / SBA0.06-derived carbon in Example 4;

[0026] Figure 5 is a transmission electron micrograph of the PCNT / SBA0.04-derived carbon in Example 3;

[0027] Figure 6 The XPS graphs of the PCNT, PCNT / SBA0.06, PCNT / SBA0.04 and PCNT / SBA0.02 derived carbon electrode materials and the fine spectrum of the PCNT / SBA0.04 derived carbon electrode material in Examples 1 to 4 are shown;

[0028] Figure 7 The XRD spectra of the ZIF-8 / CNT0.03, ZCNT / SBA0.02, ZCNY / SBA0.04 and ZCNT / SBA0.06 precursors in Examples 1 to 4, and the XRD spectra of the PCNT0.03, PCNT / SBA0.02, PCNT / SBA0.04 and PCNT / SBA0.06 derived carbon electrode materials;

[0029] Figure 8 The nitrogen adsorption-desorption isotherms and pore size distributions of the PCNT0.03, PCNT / SBA0.02, PCNT / SBA0.04, and PCNT / SBA0.06 derived carbon electrode materials in Examples 1 to 4 are shown;

[0030] Figure 9 are Raman spectra of PCNT0.03, PCNT / SBA0.02, PCNT / SBA0.04 and PCNT / SBA0.06 derived carbon electrode materials in Examples 1 to 4;

[0031] Figure 10 Graphs of water contact angles of PCNT0.03, PCNT / SBA0.02, PCNT / SBA0.04, and PCNT / SBA0.06 derived carbon electrode materials in Examples 1 to 4;

[0032] Figure 11The constant current charge-discharge graphs of the PCNT0.03, PCNT / SBA0.02, PCNT / SBA0.04 and PCNT / SBA0.06 derived carbon electrode materials in Examples 1 to 4 at a current density of 1 A / g, a voltage range of -1 to -0.2 V, and an electrolyte of 6 M KOH;

[0033] Figure 12 are AC impedance diagrams of PCNT0.03, PCNT / SBA0.02, PCNT / SBA0.04, and PCNT / SBA0.06 derived carbon electrode materials in Examples 1 to 4;

[0034] Figure 13 The CDI curves, electrosorption kinetics curves and Kim-Yoon curves of the PCNT0.03, PCNT / SBA0.02, PCNT / SBA0.04 and PCNT / SBA0.06 derived carbon electrode materials in Examples 1 to 4 at an operating voltage of 1.2 V are shown;

[0035] Figure 14 These are (a) CDI curves (b) electrosorption kinetics curves (c) Kim-Yoon curves of the PCNT / SBA0.04-derived carbon electrode material at different voltages in Example 4; (d) electrosorption kinetics curves (e) Kim-Yoon curves of the PCNT / SBA0.04-derived carbon electrode in NaCl solutions of different concentrations; and adsorption-desorption cycle diagrams of the PCNT / SBA0.04-derived carbon electrode at an operating voltage of 1.2 V and a 500 mg / L NaCl solution. DETAILED DESCRIPTION

[0036] In order to further understand the purpose, content and advantages of the present invention, now specific embodiments of the present invention are described in detail below, but can not be limited to the following examples, and will be freely matched according to actual conditions. The endpoints and any values ​​of the scope disclosed in this article are not limited to this accurate scope and value. For numerical ranges, between the endpoint values ​​of each scope, between the endpoint values ​​of each scope and a separate point value, and between the separate point value, can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered as specifically disclosed in this article.

[0037] The present invention provides an example of preparing a dual MOF-derived porous carbon / nitrogen-sulfur co-doped graphene composite electrode material for capacitive deionization, comprising the following steps:

[0038] (1) SBA-15 mesoporous carbon precursor was prepared by hydrothermal reaction of P123 and tetraethyl orthosilicate under acidic conditions;

[0039] (2) adding the SBA-15 mesoporous carbon precursor, carbon nanotubes, and zinc nitrate hexahydrate in step (1) to anhydrous methanol in a certain mass ratio, stirring evenly and allowing for sufficient adsorption to obtain solution A; adding the required amount of dimethylimidazole to anhydrous methanol to obtain solution B;

[0040] (3) adding the solution B in step (2) to the solution A, stirring until fully reacted, and then filtering to obtain a silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite material precursor;

[0041] (4) calcining the silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite material precursor in step (3) under inert atmosphere to obtain derived carbon, then oxidizing and etching the derived carbon with nitric acid, and vacuum drying to obtain a silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material;

[0042] The mass ratio of zinc in SBA-15 mesoporous carbon precursor, carbon nanotubes, and zinc nitrate is calculated to be 0.2-0.6: 0.15-0.3: 1.85-1.95;

[0043] In step (4), the high-temperature calcination adopts a step-by-step calcination method, first heating to 500-550°C at 2-4°C / min, and calcining at this temperature for 4-5 hours; then continuing to heat to 950-1000°C at 5-8°C / min, and calcining at this temperature for 2-3 hours; the nitric acid concentration is 4-8M, the etching temperature is 90-100°C, and the reaction time is 4-6 hours.

[0044] The structure of the silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material for capacitive deionization prepared by the above method includes SBA mesoporous carbon, Zn-MOF-derived carbon attached to the SBA mesoporous carbon, and carbon nanotubes uniformly interspersed and connected in the gaps between the SBA mesoporous carbon and the Zn-MOF-derived carbon. The average pore size of the obtained composite electrode material is 7.5-10nm, and the specific surface area is ≥500m 2 / g, pore volume 0.3~6cm 3 / g, equivalent series resistance ≤ 0.7Ω, and water contact angle no more than 102°.

[0045] In a preferred embodiment, in order to efficiently obtain SBA-15 mesoporous carbon precursor, a specific method for preparing SBA-15 mesoporous carbon precursor is given, including: adding hydrochloric acid to a P123 aqueous solution, adding ethyl orthosilicate dropwise under heating conditions (the purpose of heating is to facilitate mixing, not exceeding the reaction temperature, preferably 40°C to 50°C), magnetically stirring for 4 to 6 hours, adding to an autoclave, hydrothermally reacting at 100 to 110°C for 10 to 12 hours, and then washing and drying to obtain an SBA-15 mesoporous carbon precursor.

[0046] In a more specific embodiment, the mass ratio of P123, ethyl orthosilicate, deionized water and concentrated hydrochloric acid is 1:1.96:26.25:4, and the mass concentration of concentrated hydrochloric acid is 36-38%.

[0047] In one preferred embodiment, the mass ratio of the SBA-15 mesoporous carbon precursor, carbon nanotubes, and zinc in the zinc nitrate in step (2) is calculated to be 0.3-0.5:0.18-0.25:1.85-1.95. This optimization can further optimize the specific surface area and pore size, while also increasing the nitrogen content and reducing the equivalent series resistance, providing the necessary conditions for further increasing the salt adsorption content of the electrode material.

[0048] The amount of dimethylimidazole used is generally aimed at consuming all zinc ions as much as possible to form an organic framework. From an economic perspective, in the above embodiment, the mass ratio of zinc to dimethylimidazole in the zinc nitrate is 1:1.8-2.0.

[0049] The present invention is further described in detail below in conjunction with the embodiments:

[0050] Example 1:

[0051] Step 1: Weigh 200 mg of carbon nanotubes and 8.8 g of zinc nitrate hexahydrate into 200 mL of methanol solution and stir for 30 min to obtain solution A. Add 15.4 g of dimethylimidazole into 200 mL of methanol to obtain solution B.

[0052] Step 2: The B solution in step 1 was quickly added to the A solution, stirred for 6 hours and then allowed to stand for 12 hours. The product was collected by filtration and vacuum dried at 60°C for 12 hours (drying reduces the humidity before calcination and reduces the risk of cracking the crucible and clogging the furnace ventilation pipe. The vacuum drying temperature is generally 60-80°C and the time is 12-15 hours) to obtain a ZnMOF / carbon nanotube precursor, which is recorded as ZCNT;

[0053] Step 3: The ZnMOF / carbon nanotube precursor obtained in step 2 was calcined at 950°C for 2h under argon protection with a heating rate of 5°C / min. The carbonized product was washed with 2M hydrochloric acid, filtered, washed to neutrality and dried. The obtained product was oxidized and etched with 6M nitric acid at 90°C for 4h, washed to neutrality, and vacuum dried to obtain a Zn-MOF-derived carbon / carbon nanotube composite electrode material. According to the proportion of carbon nanotubes in the total mass (3%), the electrode material was recorded as PCNT0.03.

[0054] Through FE-SEM test, we can see that Figure 1, PCNT0.03 derived carbon presents a polyhedral structure with a particle size of 100nm. At the same time, it can be observed that carbon nanotubes are interspersed and connected between the crystal particles and are distributed relatively evenly. In XPS analysis, PCNT0.03 derived carbon has three characteristic peaks of C1s, N1s and O1s at the binding energies of 284.8eV, 399.7eV and 531.8eV, and the peak shape is relatively obvious. The nitrogen content is 18.9% and the oxygen content is 5.6%. In Raman test, the I of PCNT0.03 derived carbon is 18.9%. D / I G The value is 1.10, indicating a high degree of graphitization. In the nitrogen adsorption-desorption (BET) analysis, the nitrogen adsorption-desorption curve of the electrode material is a type IV curve. The pore size distribution diagram further confirms that the specific surface area of ​​the derived carbon electrode material is 575.04 m 2 / g, pore volume 0.35cm 2 / g, with an average pore size of 5.58nm. Further investigation of its electrochemical performance: The electrochemical working electrode was prepared by ultrasonically dispersing the electrode active material, conductive carbon black, and polytetrafluoroethylene (binder) in a mass ratio of 8:1:1 in an ultrasonic machine. When the final paste-like form was obtained, it was evenly coated on graphite paper. The sample was placed in a vacuum oven and dried at 60°C for 6 hours. After cooling to room temperature, the test electrode was obtained. In galvanostatic charge-discharge (GCD) tests, the charge-discharge curves exhibited a symmetrical triangular shape at a current density of 1 A / g, a voltage window of -1 to -0.2 V, and a 6 M KOH electrolyte. The specific capacitance was 195.5 F / g. In electrochemical impedance spectroscopy (EIS), the equivalent series resistance (Rs) of the derived carbon electrode material was 0.726 Ω. In desalination performance tests, the CDI electrode was prepared by mixing the electrode material, acetylene black, and polytetrafluoroethylene (PTFE) emulsion (60 wt%) in a mass ratio of 8:1:1, adding anhydrous ethanol dropwise until viscous, and then pressing the mixture at high temperature to form a carbon film using a roller press. In the desalination performance test, a voltage of 1.2 V was applied across the electrodes. The electrolyte was a 50 mL volume, 500 mg / L NaCl aqueous solution. The electrosorption capacity of the derived carbon electrode material was 9.18 mg / g.

[0055] Based on Example 1, the carbon nanotube dosage was adjusted to 100 mg, resulting in an electrode material designated PCNT0.02. FE-SEM analysis revealed a small amount of CNTs intercalated between Zn-MOF particles, while the PCNT0.02-derived carbon particles maintained the same size as the Zn-MOF.

[0056] The nitrogen content of PCNT0.02 derived carbon is 15.4%. This nitrogen comes from the doping effect of organic ligands during high temperature cracking and the addition of appropriate amounts of carbon nanotubes. In the Raman test, the I D / I G The value is 1.08, and the degree of graphitization has decreased. In the nitrogen adsorption-desorption (BET) analysis, the nitrogen adsorption-desorption curve of the derived carbon electrode material is a type IV curve. The pore size distribution diagram further confirms that the specific surface area of ​​the electrode material is 507.47 m 2 / g, pore volume 0.33cm 3 / g, with an average pore size of 4.65nm. Further research on its electrochemical properties: In the constant current charge-discharge (GCD) test, the current density was 1A / g, the voltage window was -1 to -0.2V, and the electrolyte was 6M KOH. The charge-discharge curve was symmetrically triangular, and the tested specific capacitance was 135.9F / g; in the electrochemical impedance spectroscopy (EIS) test of the electrode material, the equivalent series resistance (Rs) value of the derived carbon electrode material was 0.734Ω; in the desalination performance test, the voltage applied across the electrode was 1.2V, the electrolyte was a 50ml, 500mg / L NaCl aqueous solution, and the electrical adsorption capacity of the derived carbon electrode material was 7.82mg / g.

[0057] Based on Example 1, the amount of carbon nanotubes was adjusted to 300 mg, and the electrode material was recorded as PCNT0.04. FE-SEM analysis showed that the morphology and structure of the PCNT0.04-derived carbon became disordered, with a large amount of agglomeration. The nitrogen content of the PCNT0.02-derived carbon was 13.9%. In Raman analysis, the I D / I G The value is 1.09, and the degree of graphitization has decreased. In the nitrogen adsorption-desorption (BET) analysis, the nitrogen adsorption-desorption curve of the electrode material is a type IV curve. The pore size distribution diagram further confirms that the specific surface area of ​​the electrode material is 505.85m 2 / g, pore volume 0.34cm 3 / g, with an average pore size of 3.80nm. Further research on its electrochemical properties: In the constant current charge-discharge (GCD) test, the current density was 1A / g, the voltage window was -1 to -0.2V, and the electrolyte was 6M KOH. The charge-discharge curve was symmetrically triangular, and the tested specific capacitance was 160.5F / g; in the electrochemical impedance spectroscopy (EIS) test of the electrode material, the equivalent series resistance (Rs) value of the derived carbon electrode material was 0.728Ω; in the desalination performance test, the voltage applied across the electrode was 1.2V, the electrolyte was a 50ml, 500mg / L NaCl aqueous solution, and the electrical adsorption capacity of the derived carbon electrode material was 8.40mg / g.

[0058] Example 2

[0059] Step 1: Dissolve 4 g of P123 in 105 mL of deionized water and stir for 5 h to obtain solution A. Then weigh 20 mL of concentrated HCl (mass concentration of 36-38%) and add it to solution A to obtain solution B.

[0060] Step 2: Place solution B in step 1 in an oil bath at 40°C, add 9.1 mL of ethyl orthosilicate dropwise, react under magnetic stirring for 4 hours, place in a hydrothermal reactor, react at 100°C for 24 hours, filter and wash, and place in a vacuum oven at 60°C for 12 hours to obtain a silicon-based mesoporous carbon precursor (denoted as SBA);

[0061] Step 3: Add 200 mg of the silicon-based mesoporous carbon precursor, 200 mg of carbon nanotubes, and 8.8 g of zinc nitrate hexahydrate from step 2 to 200 mL of methanol and stir for 6 h to obtain solution C. Add 15.4 g of dimethylimidazole to 200 mL of methanol to obtain solution D.

[0062] Step 4: Solution D in step 3 was quickly added to solution C, stirred for 12 hours and then allowed to stand, the product was collected by filtration, and vacuum dried at 60°C for 12 hours (drying was used to reduce the humidity before calcination and reduce the risk of cracking the crucible and clogging the furnace ventilation pipe. The vacuum drying temperature was generally 60-80°C and the time was 12-15 hours) to obtain a silicon-based mesoporous carbon / Zn-MOF / carbon nanotube composite precursor, recorded as ZCNT / SBA0.02;

[0063] Step 5. The silicon-based mesoporous carbon / Zn-MOF / carbon nanotube composite precursor obtained in step 4 is first calcined at 550°C for 4 hours under argon protection at a heating rate of 2°C / min; then the temperature is continued to be raised to 950°C and calcined for 2 hours at a heating rate of 3°C / min. The carbonized product is washed with 2M hydrochloric acid and filtered to neutrality and dried. The obtained product is oxidized and etched with 6M nitric acid at 90°C for 4 hours and then washed to neutrality. It is vacuum dried to obtain a silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material, which is recorded as PCNT / SBA0.02.

[0064] Through FE-SEM test, we can see that Figure 2, PCNT / SBA0.02 derived carbon presents a polyhedral structure, a large number of MOF derived carbon particles are attached to the surface of SBA mesoporous carbon, forming a core-shell structure, and a large number of carbon nanotubes are connected and interspersed in the gaps between the crystals and the mesoporous carbon; in the XPS spectrum, PCNT0.03 and PCNT / SBA0.02 derived carbon both found three characteristic peaks of C1s, N1s and O1s at binding energies of 284.8eV, 399.7eV and 531.8eV, and the peak shape is relatively obvious, which shows that the introduction of mesoporous carbon does not have a significant effect on the Zn-MOF crystal, of which the nitrogen content is 17.7% and the oxygen content is 10.0%; in the XRD diagram, the main diffraction peak of the precursor is consistent with the diffraction peak position of the Zn-MOF precursor, which also shows that the addition of SBA mesoporous carbon does not cause much change in the crystal surface of the precursor; in the Raman test, the I D / I G The value is 1.07, indicating a high degree of graphitization. In the nitrogen adsorption-desorption (BET) analysis, the nitrogen adsorption-desorption curve of the electrode material is a type IV curve. The pore size distribution diagram further confirms that the specific surface area of ​​the electrode material is 523.02 m 2 / g, pore volume 0.34cm 2 / g, with an average pore size of 7.64nm. Further investigation of its electrochemical properties revealed that in a galvanostatic charge-discharge (GCD) test, the charge-discharge curves exhibited a symmetrical triangular shape at a current density of 1A / g, a voltage window of -1 to -0.2V, and a 6M KOH electrolyte. The specific capacitance measured was 210.0F / g. In an electrochemical impedance spectroscopy (EIS) test of the electrode material, the equivalent series resistance (Rs) of the electrode material was 0.678Ω. In a desalination performance test, a voltage of 1.2V was applied across the electrode, and the electrolyte was a 50ml, 500mg / L NaCl aqueous solution. The electrosorption capacity of the electrode material was 9.54mg / g.

[0065] Example 3

[0066] The main difference compared with Example 2 is that the amount of silicon-based mesoporous carbon (SBA) added in step 3 is 400 mg, and the remaining steps are the same as Example 2.

[0067] The product of this example, the silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material, is denoted as PCNT / SBA0.04.

[0068] Through FE-SEM test, we can see that Figure 3Due to the increase in SBA content, the attachment of Zn-MOF crystals on the surface of mesoporous carbon becomes dispersed and no longer aggregates, which exposes more pores inside the mesoporous carbon, and carbon nanotubes are more evenly interspersed in the Zn-MOF crystals and mesoporous carbon, while connecting the gaps between the two; in the XPS spectrum, through the O1s spectrum of PCNT / SBA0.04, it can be found that the three characteristic peaks that appear correspond to three different forms of C=O, CO and OC=O, respectively. The appearance of these peaks indicates that oxygen-containing functional groups have been successfully introduced into the surface of the material, which is beneficial to increase the hydrophilicity of the electrode surface. The nitrogen content is 14.9% and the oxygen content is 12.4%; in the XRD diagram, the main diffraction peaks of the precursor are consistent with the diffraction peaks of the ZIF-8 precursor, which also shows that the addition of SBA mesoporous carbon does not cause much change in the crystal surface of the precursor; in the Raman test, the I D / I G The value is 1.12, indicating a high degree of graphitization. In the nitrogen adsorption-desorption (BET) analysis, the nitrogen adsorption-desorption curve of the electrode material is a type IV curve. The pore size distribution diagram further confirms that the specific surface area of ​​the electrode material is 590.06 m 2 / g, pore volume 0.36cm 2 / g, with an average pore size of 8.77nm. Further investigation of its electrochemical properties revealed that in the galvanostatic charge-discharge (GCD) test, the current density was 0.5A / g, the voltage window was -1 to -0.2V, and the electrolyte was 6M KOH. The charge-discharge curve was symmetrically triangular, and the tested specific capacitance was 235.0F / g. In the electrochemical impedance spectroscopy (EIS) test of the electrode material, the equivalent series resistance (Rs) value of the electrode material was 0.654Ω. In the desalination performance test, the voltage applied across the electrode was 1.2V, the electrolyte was a 50ml, 500mg / L NaCl aqueous solution, and the electrosorption capacity of the electrode material was 10.25mg / g.

[0069] Example 4

[0070] The main difference compared with Example 2 is that the amount of silicon-based mesoporous carbon (SBA) added in step 3 is 600 mg, and the remaining steps are the same as Example 3.

[0071] The product of this example, the silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material, is denoted as PCNT / SBA0.06.

[0072] Through FE-SEM test, we can see that Figure 4, when the SBA content increased to 0.6g, the number of Zn-MOF crystals on the surface of PCNT / SBA0.06 derived carbon decreased significantly, and the number of carbon nanotubes interpenetrating and connecting inside the derived carbon also decreased significantly; in the XPS spectrum, when the SAB mesoporous carbon content increased to 0.6g, the nitrogen and oxygen contents of the PCNT / SBA0.06 derived carbon increased, the carbon content decreased to 67%, the nitrogen content was 15.1%, and the oxygen content was 17.8%; in the XRD diagram, the main diffraction peak of the precursor was consistent with the diffraction peak position of the ZIF-8 precursor, which also shows that the addition of SBA mesoporous carbon did not cause much change in the crystal surface of the precursor; in the Raman test, the I D / I G The value is 1.08, indicating a high degree of graphitization. In the nitrogen adsorption-desorption (BET) analysis, the nitrogen adsorption-desorption curve of the electrode material is a type IV curve. The pore size distribution diagram further confirms that the specific surface area of ​​the electrode material is 543.22 m 2 / g, pore volume 0.57cm 3 / g, with an average pore size of 7.54nm. Further research on its electrochemical properties showed that in the galvanostatic charge-discharge (GCD) test, the current density was 0.5A / g, the voltage window was -1 to -0.2V, and the electrolyte was 6M KOH. The charge-discharge curve was symmetrically triangular, and the tested specific capacitance was 161.8F / g. In the electrochemical impedance spectroscopy (EIS) test of the electrode material, the equivalent series resistance (Rs) value of the electrode material was 0.668Ω. In the desalination performance test, the voltage applied across the electrode was 1.2V, the electrolyte was a 50ml, 500mg / L NaCl aqueous solution, and the electrosorption capacity of the electrode material was 9.85mg / g.

[0073] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who can make equivalent replacements or changes based on the technical solutions and concepts of the present invention, should be covered by the scope of protection of the present invention.

[0074] Table 1 Test results of the embodiment

[0075]

[0076] The present invention combines silicon-based mesoporous carbon with a high specific surface area and average pore size with a Zn-MOF / carbon nanotube composite material with good hydrophilicity, and uses a step-by-step temperature sintering process to prepare PCNT / SBA-derived carbon. The introduction of an appropriate amount of SBA mesoporous carbon does not affect the arrangement of Zn-MOF crystals and carbon nanotubes, but instead effectively increases the average pore size of the derived carbon. The carbon nanotubes also intersperse between MOF crystals and between MOF and mesoporous carbon, acting as a link, giving the carbon electrode material a three-dimensional structure. Through step-by-step high-temperature pyrolysis and acid etching, the pore size is effectively expanded while introducing more oxygen-containing groups, improving the wettability of the electrode surface and paving the way for increasing the electrode material's electrical adsorption capacity and desalination efficiency.

Claims

1. A method for preparing a silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material for capacitive deionization, characterized by: The following steps are involved: (1) SBA-15 mesoporous carbon precursor was prepared by hydrothermal reaction of P123 and tetraethyl orthosilicate under acidic conditions; (2) adding the SBA-15 mesoporous carbon precursor, carbon nanotubes, and zinc nitrate hexahydrate in step (1) to anhydrous methanol in a certain mass ratio, stirring evenly and allowing for sufficient adsorption to obtain solution A; adding the required amount of dimethylimidazole to anhydrous methanol to obtain solution B; (3) adding the solution B in step (2) to the solution A, stirring until fully reacted, and then filtering to obtain a silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite material precursor; (4) calcining the silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite material precursor in step (3) under inert atmosphere to obtain derived carbon, then oxidizing and etching the derived carbon with nitric acid, and vacuum drying to obtain a silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material; The mass ratio of zinc in SBA-15 mesoporous carbon precursor, carbon nanotubes, and zinc nitrate is calculated to be 0.2-0.6: 0.15-0.3: 1.85-1.95; In step (4), the high-temperature calcination adopts a step-by-step calcination method, first heating to 500-550°C at 2-4°C / min, and calcining at this temperature for 4-5 hours; then continuing to heat to 950-1000°C at 5-8°C / min, and calcining at this temperature for 2-3 hours; the nitric acid concentration is 4-8M, the etching temperature is 90-100°C, and the reaction time is 4-6 hours.

2. The method for preparing the silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material for capacitive deionization according to claim 1, characterized in that: The specific steps of step (1) include adding hydrochloric acid to the P123 aqueous solution, adding ethyl orthosilicate dropwise under heating conditions, magnetically stirring for 4 to 6 hours, adding it to an autoclave, hydrothermally reacting at 100 to 110° C. for 10 to 12 hours, and then washing and drying to obtain an SBA-15 mesoporous carbon precursor.

3. The method for preparing the silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material for capacitive deionization according to claim 1, characterized in that: In step (2), the mass ratio of the SBA-15 mesoporous carbon precursor, the carbon nanotubes, and the zinc in the zinc nitrate is calculated to be 0.3-0.5: 0.18-0.25: 1.85-1.

95.

4. The method for preparing the silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material for capacitive deionization according to claim 1, characterized in that: In step (2), the stirring time of solution A is 6 to 8 hours.

5. The method for preparing the silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material for capacitive deionization according to claim 1, characterized in that: The stirring time in step (3) is 10 to 12 hours.

6. A composite electrode material, characterized in that: It is prepared according to the preparation method of the silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material for capacitive deionization according to any one of claims 1 to 5.

7. Use of the composite electrode material according to claim 6 in capacitive deionization and desalination, characterized in that: The method comprises preparing a silicon-based mesoporous carbon / MOF-derived carbon / carbon nanotube composite electrode material into a CDI electrode.

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