A high-capacitance and ion-broad-spectrum flow electrode, a preparation method and application thereof

Abstract

This invention discloses a high-capacitance and broad-spectrum ion-distribution flow electrode, its preparation method, and its application, belonging to the field of capacitive deionization technology. The flow electrode comprises a carbon nanoparticle solution formed from carbon nanoparticles derived from biomass materials and a solvent, wherein the mass concentration of the biomass-derived carbon nanoparticles is 1-6 mg / mL. The preparation method includes the following steps: dispersing pulverized biomass materials in a solvent for a hydrothermal reaction, followed by vacuum filtration, and dialysis of the resulting solution to obtain the carbon nanoparticle solution, which is the flow electrode. This solution can be used in capacitive deionization to remove cations and anions. The carbon nanoparticle solution prepared by this invention is a zero-dimensional material with good flowability, hydrophilicity, conductivity, and capacitance performance. Furthermore, the preparation method of this invention is simple, convenient, uses abundant raw materials, and has low production costs, showing good application prospects and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of capacitive deionization technology, specifically to a high-capacitance and broad-spectrum ion flow electrode, its preparation method, and its application. Background Technology

[0002] Traditional capacitive deionization (FCDI) technology operates by flowing between electrodes, requiring the electrodes to be coated onto a current collector. Electrode fabrication necessitates the addition of binders and conductive additives, making the process cumbersome and limiting adsorption capacity. When the electrode becomes saturated, it needs to be short-circuited or a reverse voltage applied to regenerate it. In contrast, Flow Electrode Capacitive Deionization (FCDI), as an emerging electrochemical ion separation technology, enables continuous regeneration of the flow electrode, exhibiting a pseudo-"unlimited" adsorption capacity. Therefore, FCDI holds immense potential in brine separation applications such as seawater desalination and lithium extraction. During FCDI, charged ions in the aqueous solution pass through the ion exchange membrane under electrostatic driving force and are subsequently adsorbed by the active electrode material in the flow electrode, completing the ion extraction process. Subsequently, the flow electrode adsorbing cations and anions mix outside the FCDI device, causing charge neutralization of the active electrode material. At this point, the salt ions originally adsorbed on the active electrode material are released into the electrolyte. Thus, the electroadsorption capacity of the flow electrode is regenerated. Currently used flow electrode materials are mostly conductive solid materials, such as activated carbon, carbon nanotubes, carbon black, MOF-derived carbon, and graphite. These materials need to be dispersed in deionized water to obtain flow electrode slurry. However, due to the poor hydrophilicity of the above carbon materials, slurry preparation takes a long time and is costly, which is not conducive to large-scale production and application. Summary of the Invention

[0003] Purpose of the invention: The present invention aims to provide a high-capacitance and broad-spectrum ion-specific flow electrode with good fluidity, hydrophilicity, conductivity, simple preparation process, low cost, and easy mass production. The present invention also provides a preparation method and application of the above-mentioned flow electrode.

[0004] Technical solution: The high-capacitance and broad-spectrum ion flow electrode provided by the present invention comprises a carbon nanodot solution formed by carbon nanodots derived from biomass materials and a solvent, wherein the mass concentration of the carbon nanodots derived from biomass is 1-6 mg / mL, preferably 2-6 mg / mL.

[0005] Furthermore, the carbon nanodots are nitrogen-doped carbon nanodots; the solvent is water.

[0006] Furthermore, the biomass material is broad bean shells, pea shells, corn stalks, grass, or leaves; preferably, broad bean shells are naturally nitrogen-doped carbon materials.

[0007] The present invention also provides a method for preparing the above-mentioned high-capacitance and broad-spectrum ion flow electrode, comprising the following steps: dispersing pulverized biomass material in a solvent for hydrothermal reaction, filtering under reduced pressure after the reaction, and dialysis of the resulting solution to obtain a carbon nanoparticle solution, which is the flow electrode.

[0008] Furthermore, the ratio of the biomass material to the solvent is 1g:10-20mL.

[0009] Furthermore, the hydrothermal reaction conditions are: hydrothermal treatment at 150-200℃ for 24-60 hours.

[0010] The present invention also provides the application of the above-mentioned high-capacitance and broad-spectrum ion flow electrode in flow electrode capacitive deionization.

[0011] Furthermore, the flowing electrode capacitor deionization is used to remove or recover cations or anions in the water.

[0012] Furthermore, the cation includes Na. + Ca 2+ Mg 2+ Pb 2+ Cd 2+ Hg 2+ Li + Cu 2+ Co 2+ .

[0013] Furthermore, the anion includes HPO4. 2- H2PO4 - ,HAsO4 2- H2AsO4 - PtCl6 2- .

[0014] Invention Principle: This invention utilizes flow capacitance deionization (FCDI) technology to remove harmful metals or recover precious metals from heavy metal-contaminated water bodies, saline water, brackish water, seawater, salt lake brine, or waste battery solutions. The core component of the FCDI device is the flow electrode material; therefore, to fundamentally solve the problem of efficient extraction of charged ions from water, it is necessary to design an electrode material with stable structure, excellent conductivity, and uniform dispersion in solution.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) Using biomass materials as carbon source, a carbon nanodot solution with good conductivity is prepared by a one-step hydrothermal method as a flow electrode. The flow electrode has good rheological properties, excellent dispersibility and hydrophilicity, which is conducive to the transfer of electrons and ions, thereby achieving excellent FCDI performance. Electrochemical tests show that compared with solid electrodes, the biomass-derived carbon nanodot flow electrode has better capacitance and impedance characteristics, reduces charge transfer resistance and enhances ion diffusion; (2) The emergence of biomass-derived carbon nanodots has enriched the types of flow electrode materials, making them directly usable as electrode slurry or conductive additives, thereby promoting the development of FCDI technology in electron / ion transfer; (3) The present invention uses inexpensive and abundant biomass materials as raw materials, resulting in low production costs, green economy, simple process, convenient operation, and easy industrial production. It is conducive to further research on flow capacitance deionization technology and also provides a new choice and new idea for the design of electrode materials for flow capacitance deionization technology. Attached Figure Description

[0016] Figure 1 A schematic diagram of the FCDI device for testing the capacitive adsorption ion performance of the flow electrode prepared in Example 1;

[0017] Figure 2 Morphological and structural characterization of the biomass-derived carbon nanodot material in the flow electrode prepared in Example 1: (a) Transmission electron microscopy (TEM) image; (b) XRD pattern; (c) Infrared spectroscopy curve.

[0018] Figure 3 Elemental composition characterization of the biomass-derived carbon nanodot material in the flow electrode prepared in Example 1: (a) total X-ray photoelectron spectroscopy; (b) high-resolution C1s spectrum; (c) high-resolution O1s spectrum; (d) high-resolution N1s spectrum.

[0019] Figure 4 The graph shows a comparison of the extraction performance of biomass-derived carbon nanoparticle materials in the flow electrode prepared in Example 1. In this graph, N-CNs represents biomass-derived nanoparticle materials, AC represents commercially purchased activated carbon, and H2O represents pure water as the electrode slurry.

[0020] Figure 5 The lithium extraction performance of the flow electrode prepared in Example 1 was tested under different voltages: (a) conductivity versus time curve, (b) mass adsorption amount versus time curve, (c) Kim-Yoon curve, (d) average adsorption rate and charge efficiency under different voltages. Detailed Implementation

[0021] The present invention will now be further described in conjunction with specific embodiments and accompanying drawings.

[0022] Example 1: The high-capacitance and broad-spectrum ionic flow electrode provided in this example comprises a carbon nanodot solution formed from carbon nanodots derived from broad bean shells and water.

[0023] The preparation method of the aforementioned flow electrode specifically includes the following steps: Fresh nitrogen-rich broad bean shells are used as biomass material. After cleaning, they are dried in an oven at 60℃ for 12 hours, and then pulverized into powder to obtain biomass powder. 3g of biomass powder is placed in a 100mL reaction vessel, 50mL of H2O is added, and the mixture is stirred evenly. The reaction vessel is then placed in an oven at 180℃ for 15 hours. After the reaction is complete, the mixture is naturally cooled to room temperature. The resulting solution is filtered through a 0.2µm cellulose membrane and then dialyzed for 48 hours to remove other impurities, finally yielding an orange-yellow N-doped carbon nanodot solution, named N-CNs. The concentration of the N-CNs solution is 3.0 mg / mL. -1 (With a mass fraction of 0.2%), this indicates that the yield of nanodots is approximately 5%.

[0024] The following tests were performed on the prepared N-doped carbon nanodot solution for the flow electrode:

[0025] (1) Adopting as follows Figure 1 The FCDI testing apparatus shown was used to test the lithium extraction performance of the N-doped carbon nanodot solution prepared in Example 1; its current collector is made of a graphite plate with etched serpentine channels. The effective contact area between the ion exchange membrane and the flow electrode is 7.228 cm². 2 Silicone gaskets are used between the cation exchange membrane (CEM), anion exchange membrane (AEM), water channel plate, and current collector to prevent liquid leakage. The outer end of the current collector is protected by an acrylic sheet of the same type. All components are bolted together to prevent leakage. To avoid short circuits, a nylon insulating post is placed at the bolt hole of one of the current collectors.

[0026] (2) The morphology of the N-doped carbon nanodots derived from broad bean shells prepared in this embodiment was observed using a JEOL 2010 high-resolution transmission electron microscope, such as... Figure 2 As shown in (a), nitrogen-doped carbon nanodot solution was successfully prepared after high-temperature hydrothermal treatment. The solution has a diameter of about 5 nm and an inter-plane distance of 0.33 nm, which corresponds to the (002) crystal plane of graphite carbon. Figure 2 (b) is the X-ray diffraction pattern of the nitrogen-doped carbon nanodot material derived from broad bean shells prepared in Example 1 of the present invention (the horizontal axis represents the angle and the vertical axis represents the intensity). It shows that N-CNs has a prominent diffraction peak at 2θ = 26°, which corresponds to the (002) plane of the carbon material. This is consistent with the high-resolution transmission results. Figure 2 (c) is the infrared curve of the nitrogen-doped carbon nanodot material derived from broad bean shells prepared in Example 1 of this invention, at 3410 cm⁻¹. -1The corresponding tensile vibration of OH is 2960 cm. -1 The peak value corresponds to the tensile vibration of NH; 1620cm -1 1400cm -1 and 1120cm -1 The absorption peaks correspond to the vibrational absorption peaks of HO and C=O / C=N and the bending absorption peak of CO / CN, respectively, indicating that the N-CNs extracted from broad bean shells contain abundant nitrogen and oxygen functional groups on their surface, which is beneficial to enhancing their hydrophilicity and conductivity.

[0027] (3) The structure and composition of the nitrogen-doped carbon nanodot material derived from broad bean shells prepared in Example 1 were tested using an ESCALAB 250 X-ray photoelectron spectroscopy (XPS) system. Figure 3 As shown, its elemental composition includes C, O, and N. Peaks corresponding to CC, CO, C=O, and CN can be observed in the C1s spectrum. The O1s spectrum further confirms the presence of C=O, COC, and C-OH. Simultaneously, the N1s spectrum reveals three distinct nitrogen types: pyridine-N, pyrrole-N, and graphitic-N.

[0028] (4) The nitrogen-doped carbon nanodot flow electrode derived from broad bean shells prepared in Example 1 of this invention was subjected to lithium extraction testing using an FCDI apparatus, and compared with a 2% (w / w) activated carbon AC aqueous solution slurry, thereby obtaining the following results: Figure 4 The performance test graphs shown indicate that when the electrode slurry contains no electrode material, it is classified as an electrodialysis (ED) process. For AC and N-CNs flowing electrode slurries, the conductivity of the LiCl solution decreases significantly, with ASRR values ​​of 0.49 and 0.62 μmol cm⁻¹, respectively. -2 min -1 This explains the Li in the two types of FCDI batteries. + The extraction capabilities are constantly improving. The lithium extraction capability of an N-CNs electrode solution with a mass fraction of 0.2% can rival that of an AC electrode material with a mass fraction of 2%, which has a mass fraction that is ten times smaller, and is even slightly higher than that of the AC electrode material.

[0029] (5) The nitrogen-doped carbon nanodot flow electrode derived from broad bean shells prepared in Example 1 of the present invention was subjected to lithium extraction tests at different voltages using an FCDI device. Figure 5 Figure (a) shows that the solution conductivity decreases with time under different operating voltages, and the decrease is more pronounced at higher voltages. This indicates that increasing the operating voltage of FCDI significantly enhances the driving force for ion adsorption, thereby improving the conductivity of Li. + Recovery rate; Figure 5 (b) in the text represents Li +The GAC variation curves clearly show that, under different operating voltages, the adsorption capacity gradually increases with increasing adsorption time. After 120 minutes of FCDI operation at 3.0V, the capacity reached 175 mg g / L. -1 ; Figure 5 (c) in the figure is the Kim-Yoon curve. The curve gradually extends to the upper right, further confirming that the N-CNs flowing electrode has superior Li-Yoon properties at higher operating potentials. + Extraction performance; such as Figure 5 As shown in (d), the ASRR value is highest at a working voltage of 3V, which is 1.42 μmol cm⁻¹. -2 min -1 The CE results showed that the highest CE (97%) was achieved at an operating voltage of 2.5V. These results indicate that while higher operating voltages lead to greater adsorption capacity and rate, they also significantly increase the operating current, resulting in decreased charge efficiency.

[0030] (6) The nitrogen-doped carbon nanodot flow electrode derived from broad bean shells prepared in Example 1 of this invention was subjected to sodium extraction testing using an FCDI apparatus. The test results showed that the nitrogen-doped carbon nanodot solution derived from broad bean shells obtained in Example 1, at a voltage of 3.0V, yielded sodium... + The removal capacity is 188 mg g -1 At 2.5V, the charge efficiency is 98%.

[0031] (7) The nitrogen-doped carbon nanodot flow electrode derived from broad bean shells prepared in Example 1 of this invention was subjected to copper extraction testing using an FCDI device. The test results showed that the Cu content of the nitrogen-doped carbon nanodot solution derived from broad bean shells obtained in Example 1 was [missing value] at a voltage of 3.0V. 2+ Recovery capacity is 167 mg g -1 At 2.5V, the charge efficiency is 92.5%.

[0032] (8) Arsenate extraction was performed on the nitrogen-doped carbon nanodot flow electrode derived from broad bean shells prepared in Example 1 of this invention using an FCDI apparatus. The test showed that the nitrogen-doped carbon nanodot solution derived from broad bean shells obtained in Example 1, at a voltage of 3.0V, contained HAsO4. 2- The removal capacity is 165 mg g -1 At 2.5V, the charge efficiency is 92%.

[0033] (9) The nitrogen-doped carbon nanodot flow electrode derived from broad bean husks prepared in Example 1 of this invention was subjected to lead extraction testing using an FCDI apparatus. The test results showed that the nitrogen-doped carbon nanodot solution derived from broad bean husks obtained in Example 1, at a voltage of 3.0V, contained Pb. 2+ The removal capacity was 141 mg g.-1 At 2.5V, the charge efficiency is 79%.

[0034] As can be seen from the above, the flow electrode prepared in Example 1 has a good removal effect on both cations and anions. Because carbon nanodots are zero-dimensional carbon materials, carbon nanodot solutions can be directly obtained through hydrothermal methods. By utilizing their double-layer capacitance characteristics and combining them with FCDI technology, effective electro-adsorption of charged ions in water can be achieved.

[0035] Example 2: The high-capacitance and broad-spectrum ionic flow electrode provided in this example comprises a carbon nanodot solution formed from carbon nanodots derived from broad bean shells and water.

[0036] The preparation method of the aforementioned flow electrode specifically includes the following steps: Fresh nitrogen-rich broad bean shells are used as biomass material. After cleaning, they are dried in an oven at 60℃ for 12 hours, and then pulverized into powder to obtain biomass powder. 3g of biomass powder is placed in a 100mL reaction vessel, 30mL of H2O is added, and the mixture is stirred evenly. The reaction vessel is then placed in an oven at 150℃ for 15 hours. After the reaction is complete, the mixture is naturally cooled to room temperature. The resulting solution is filtered through a 0.2µm cellulose membrane and then dialyzed for 48 hours to remove other impurities, finally yielding an orange-yellow N-doped carbon nanodot solution, named N-CNs. The concentration of the N-CNs solution is 2.0 mg / mL. -1 This indicates that the yield of nanodots is 2%.

[0037] The nitrogen-doped carbon nanodot flow electrode derived from broad bean shells, prepared in Example 2 of this invention, was subjected to lithium extraction testing using an FCDI apparatus. The test results showed that the Li extraction capacity of the nitrogen-doped carbon nanodot solution derived from broad bean shells obtained in Example 2 was 118.5 mg g at a voltage of 3.0 V. -1 .

[0038] Example 3: The high-capacitance and broad-spectrum ionic flow electrode provided in this example comprises a carbon nanodot solution formed from carbon nanodots derived from broad bean shells and water.

[0039] The preparation method of the aforementioned flow electrode specifically includes the following steps: Fresh nitrogen-rich broad bean shells are used as biomass material. After cleaning, they are dried in an oven at 60℃ for 12 hours, and then pulverized into powder to obtain biomass powder. 3g of biomass powder is placed in a 100mL reaction vessel, 60mL of H2O is added, and the mixture is stirred evenly. The reaction vessel is then placed in an oven at 180℃ for 15 hours. After the reaction is complete, the mixture is naturally cooled to room temperature. The resulting solution is filtered through a 0.2µm cellulose membrane and then dialyzed for 48 hours to remove other impurities, ultimately yielding an orange-yellow N-doped carbon nanodot solution, named N-CNs. The concentration of the N-CNs solution is 2.6 mg / mL. -1This indicates that the yield of nanodots was 5.2%.

[0040] The nitrogen-doped carbon nanodot flow electrode derived from broad bean shells, prepared in Example 3 of this invention, was subjected to lithium extraction testing using an FCDI apparatus. The test results showed that the nitrogen-doped carbon nanodot solution derived from broad bean shells obtained in Example 3 exhibited a Li extraction capacity of 135 mg g at a voltage of 3.0 V. -1 .

[0041] Example 4: The high-capacitance and broad-spectrum ionic flow electrode provided in this example comprises a carbon nanodot solution formed from carbon nanodots derived from broad bean shells and water.

[0042] The preparation method of the aforementioned flow electrode specifically includes the following steps: Fresh nitrogen-rich broad bean shells are used as biomass material. After cleaning, they are dried in an oven at 60℃ for 12 hours, and then pulverized into powder to obtain biomass powder. 3g of biomass powder is placed in a 100mL reaction vessel, 50mL of H2O is added, and the mixture is stirred evenly. The reaction vessel is then placed in an oven at 200℃ for 12 hours. After the reaction is complete, the mixture is naturally cooled to room temperature. The resulting solution is filtered through a 0.2µm cellulose membrane and then dialyzed for 48 hours to remove other impurities, ultimately yielding an orange-yellow N-doped carbon nanodot solution, named N-CNs. The concentration of the N-CNs solution is 2.3 mg / mL. -1 This indicates that the yield of nanodots was 3.8%.

[0043] The lithium extraction capacity of the nitrogen-doped carbon nanodot flow electrode derived from broad bean shells, prepared in Example 4 of this invention, was tested using an FCDI apparatus. The test results showed that the Li extraction capacity of the carbon nanodot solution derived from broad bean shells obtained in Example 4 was 126 mg g at a voltage of 3.0 V. -1 .

[0044] Example 5: The high-capacitance and broad-spectrum ionic flow electrode provided in this example comprises a carbon nanodot solution formed from carbon nanodots derived from broad bean shells and water.

[0045] The preparation method of the aforementioned flow electrode specifically includes the following steps: Fresh nitrogen-rich broad bean shells are used as biomass material. After cleaning, they are dried in an oven at 60℃ for 12 hours, and then pulverized into powder to obtain biomass powder. 3g of biomass powder is placed in a 100mL reaction vessel, 50mL of H2O is added, and the mixture is stirred evenly. The reaction vessel is then placed in an oven at 200℃ for 15 hours. After the reaction is complete, the mixture is naturally cooled to room temperature. The resulting solution is filtered through a 0.2µm cellulose membrane and then dialyzed for 48 hours to remove other impurities, ultimately yielding an orange-yellow N-doped carbon nanodot solution, named N-CNs. The concentration of the N-CNs solution is 4.0 mg / mL. -1This indicates that the yield of nanodots was 5.3%.

[0046] The nitrogen-doped carbon nanodot flow electrode derived from broad bean husks, prepared in Example 5 of this invention, was subjected to lithium extraction testing using an FCDI apparatus. The test results showed that the Li extraction capacity of the broad bean husk-derived carbon nanodot solution obtained in Example 5 was 163 mg g at a voltage of 3.0 V. -1 .

[0047] Example 6: The difference from Example 1 is that the concentration of the N-CNs solution is approximately 5 mg / mL. -1 The lithium extraction capacity of the nitrogen-doped carbon nanodot flow electrode derived from broad bean shells prepared in Example 6 was tested using an FCDI apparatus. The test results showed that the Li extraction capacity of the carbon nanodot solution derived from broad bean shells obtained in Example 6 was 141 mgg at a voltage of 3.0 V. -1 .

[0048] Example 7: The difference from Example 1 is that the concentration of the N-CNs solution is approximately 6 mg / mL. -1 The lithium extraction capacity of the nitrogen-doped carbon nanodot flow electrode derived from broad bean shells prepared in Example 7 was tested using an FCDI apparatus. The test results showed that the Li extraction capacity of the carbon nanodot solution derived from broad bean shells obtained in Example 7 was 131 mgg at a voltage of 3.0 V. -1 .

[0049] Analysis of Examples 2-7 shows that changing the hydrothermal conditions affects the yield of carbon nanodots. The lower the yield of carbon nanodots, the lower the concentration of carbon nanodots in the corresponding flow electrode, which reduces its conductivity, increases the solution impedance, and weakens its electroadsorption capacity as a flow electrode.

[0050] Comparative Example 1: The difference from Example 1 is that the concentration of the N-CNs solution is approximately 8 mg / mL. -1 The lithium extraction capacity of the nitrogen-doped carbon nanodot flow electrode derived from broad bean shells prepared in Comparative Example 1 was tested using an FCDI apparatus. The results showed that the Li extraction capacity of the carbon nanodot solution derived from broad bean shells obtained in Comparative Example 1 was 10⁴ mg / g at a voltage of 3.0 V. -1 .

[0051] Analysis of Comparative Example 1 shows that when the concentration of carbon nanodots is changed, the electroadsorption performance decreases when the concentration is too high. This is because the high concentration leads to the aggregation of carbon nanodots, which in turn increases the solution resistance of the flow electrode and reduces the electroadsorption performance.

Claims

1. The application of a high-capacitance and broad-spectrum ionic flow electrode in capacitive deionization of flow electrodes, characterized in that, The flow electrode comprises a carbon nanodot solution formed from carbon nanodots derived from biomass materials and a solvent, wherein the mass concentration of the carbon nanodots derived from biomass is 1-6 mg / mL, and the carbon nanodots are nitrogen-doped carbon nanodots; the preparation method of the high-capacitance and broad-spectrum ion flow electrode comprises the following steps: dispersing pulverized biomass materials in a solvent for hydrothermal reaction, filtering under reduced pressure after the reaction, and dialysis of the resulting solution to obtain a carbon nanodot solution, which is the flow electrode.

2. The application according to claim 1, characterized in that, The flow electrode capacitor deionization is used to remove or recover cations or anions from water.

3. The application according to claim 2, characterized in that, The cation includes Na. + Ca 2+ Mg 2+ Pb 2+ Cd 2+ Hg 2+ Li + Cu 2+ Co 2+ .

4. The application according to claim 2, characterized in that, The anions include HPO4. 2- H2PO4 - ,HAsO4 2- H2AsO4 - PtCl6 2- .

5. The application according to claim 1, characterized in that, The biomass material is broad bean shells, pea shells, corn stalks, grass, and leaves; the solvent is water.

6. The application according to claim 1, characterized in that, The ratio of biomass material to solvent is 1g:10-20mL.

7. The application according to claim 1, characterized in that, The hydrothermal reaction conditions are: hydrothermal treatment at 150-200℃ for 12h or 15h.

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