Preparation method and application of functional filler particle material kaolinin / CNT

Abstract

The invention provides a preparation method and application of a functional filler particle material kaolinin / CNT. The kaolinite and the carbon nanotubes are mixed and then subjected to high-temperature calcination, a micropore-mesopore hierarchical structure is formed, and meanwhile, a three-dimensional conductive network is constructed, so that the granular material has excellent salt adsorption performance, cycling stability and mechanical strength. Furthermore, the calcining temperature is optimized, so that the crystal structure of kaolinite and the graphitization degree of the carbon nanotubes reach the optimal balance, and the salt adsorption performance and the cycling stability of the material are further improved. In addition, the granular material disclosed by the invention shows excellent mechanical strength and durability in strong acid and strong alkali, and can still keep stable performance after being soaked in a high-temperature environment for 24 hours. The granular material is suitable for multiple fields of wastewater treatment, seawater desalination and the like, and meanwhile, the preparation process is simple, low in cost and suitable for large-scale production and practical engineering application.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental material synthesis, and relates to a preparation method and application of a functional filler particle material kaolin / CNT. Background Art

[0002] With the growth of the global population and the acceleration of the industrialization process, the problems of fresh water shortage and water body pollution have become increasingly severe, posing major environmental and economic challenges that attract global attention. According to statistics, about 98% of the world's water resources are salt water, and the fresh water resources that can be directly used account for less than 2%. Against this background, seawater desalination technology is considered one of the key means to solve fresh water shortage. Currently, the widely used desalination technologies mainly include membrane technologies (such as reverse osmosis, electrodialysis, etc.) and thermal strategy-based distillation technologies (such as multi-stage flash evaporation, etc.). However, these technologies still face problems such as high energy consumption, high cost, equipment scaling, and secondary pollution in practical applications, which are not conducive to popularization and application. In recent years, capacitive deionization (CDI) technology, as an emerging electro-driven desalination technology, has received extensive attention for its advantages such as low energy consumption, simple operation, and low carbon emissions, and has shown remarkable potential in the field of desalination of low to medium salinity water bodies.

[0003] In capacitive deionization technology, the performance of the electrode material directly determines the desalination efficiency and cycle stability. Currently, commonly used electrode materials include conductive polymers, carbon-based materials, MXene, etc., but these materials still have certain limitations in practical applications, such as insufficient stability, limited desalination capacity, short cycle life, and high cost. Therefore, developing electrode materials with both high-efficiency salt adsorption performance, excellent mechanical strength, and good cycle stability has become the core requirement for the further popularization of CDI technology. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art, and provide a preparation method and application of a functional filler particle material kaolin / CNT. The present invention provides a preparation method and application of a functional filler particle material kaolin / CNT. The present invention mixes kaolinite and carbon nanotubes and then performs high-temperature calcination to form a microporous-mesoporous hierarchical structure while constructing a three-dimensional conductive network, enabling the particle material to have excellent salt adsorption performance, cycle stability, and mechanical strength. Further, the calcination temperature is optimized to achieve the best balance between the crystal structure of kaolinite and the graphitization degree of carbon nanotubes, further improving the salt adsorption performance and cycle stability of the material.

[0005] In addition, the granular material of the present invention exhibits excellent mechanical strength and durability in strong acids and strong bases, and can still maintain its stable performance after being soaked in a high-temperature environment for 24 hours. The three-dimensional structure design of the present invention not only reduces the preparation cost, but also improves the application feasibility of the material in the fields of desalination, wastewater treatment, etc., providing a new solution for the development of electroadsorption technology.

[0006] The object of the present invention can be achieved by the following solutions:

[0007] In a first aspect, the present invention provides a preparation method of a functional filler granular material kaolin / CNT, comprising the following steps:

[0008] S1. Mix kaolin powder and carbon nanotube powder evenly to obtain a first uniform powder;

[0009] S2. Mix the binder with the first uniform powder evenly to obtain a second uniform powder;

[0010] S3. Granulate the second uniform powder to obtain a first electroadsorption particle;

[0011] S4. Calcinate the first electroadsorption particle to obtain a second electroadsorption particle;

[0012] S5. Soak the second electroadsorption particle in an acid solution, and obtain the product after drying.

[0013] As an embodiment of the present invention, in step S1, the mass ratio of the kaolin powder to the carbon nanotube powder is 0.8-1.2:1. Preferably, it is 1:1. In some embodiments, the mixing is carried out in a V-type mixer, and the mixing time is 6-8h.

[0014] As an embodiment of the present invention, in step S2, the binder includes polyvinyl alcohol (PVA) particles. Preferably, it is 1799-type polyvinyl alcohol (PVA) particles.

[0015] Furthermore, the binder is obtained by dissolving polyvinyl alcohol particles in deionized water, heating in an oil bath and stirring; wherein, the temperature of the oil bath heating is 70-90°C, the heating time is 3-5h, and the stirring speed is 15-30rpm.

[0016] As an embodiment of the present invention, in step S2, the mass fraction of polyvinyl alcohol particles in the binder is 4-6wt%, and the dosage ratio of the binder to the carbon nanotube powder is 180-220mL:50mg. Preferably, it is 200mL:50mg.

[0017] As an embodiment of the present invention, in step S3, after granulation, polishing is further included to obtain the first electroadsorption particles. In some embodiments, the granulation is carried out in a small pill-making machine, and the size of the shaft cutter used in the small pill-making machine is 3 mm.

[0018] As an embodiment of the present invention, in step S4, before calcination, the first electroadsorption particles are dried; wherein, the drying temperature is 50 - 70 °C, and the drying time is 10 - 15 h.

[0019] As an embodiment of the present invention, in step S4, the calcination temperature is 800 - 850 °C, the heating rate is 4 - 6 °C / min, the calcination time is 1.5 - 3 h, and the calcination atmosphere includes an argon atmosphere. The preferred calcination temperature is 800 °C. In some embodiments, the calcination is carried out in a tube furnace.

[0020] As an embodiment of the present invention, in step S5, the acid solution includes a hydrochloric acid solution with a concentration of 0.3 - 0.8 mol / L; the soaking time is 15 - 30 h.

[0021] As an embodiment of the present invention, in step S5, before drying, the second electroadsorption particles are ultrasonically treated; wherein, the number of ultrasonic treatments is 5 - 7 times, and the ultrasonic time for each time is 10 - 30 min.

[0022] As an embodiment of the present invention, in step S5, the drying temperature is 50 - 65 °C, and the time is 8 - 20 h.

[0023] In the second aspect, the present invention provides a functional filler particle material kaolin / CNT obtained by the above preparation method.

[0024] In the third aspect, the present invention provides an application of the functional filler particle material kaolin / CNT in capacitive deionization desalination.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. In the present invention, kaolinite and carbon nanotubes are mixed and then calcined at high temperature to form a microporous-mesoporous hierarchical structure, providing high active sites and fast ion diffusion channels, enabling the material to efficiently adsorb salt ions, thereby improving its chlorine removal capacity; and the elasticity of CNT relieves the cyclic stress, making the material have high cyclic stability in the electroadsorption of chloride ions; at the same time, after kaolinite is calcined, a mesoporous framework is formed and carbon nanotubes CNT are interspersed therein to construct a three-dimensional conductive network, which not only inhibits the pore closure caused by sintering, optimizes the porous structure, but also enhances the mechanical strength.

[0027] 2. In addition, the calcined kaolinite in the present invention generates stable quartz phases that, together with the inert surface of CNTs, resist acid and alkali erosion. It exhibits excellent stability and adaptability under strong acid, strong alkali, and high-temperature conditions, achieving long-term stability in complex environments. This provides an efficient and durable three-dimensional filler solution for capacitive deionization technology and is suitable for long-term use in actual complex working conditions.

[0028] 3. The present invention further optimizes the calcination temperature. At 800 - 850 °C, the crystallization structure of kaolinite and the graphitization degree of carbon nanotubes reach the best balance. After calcination of kaolinite within this temperature range, the porosity is significantly enhanced, forming a uniform mesoporous distribution, further improving the desalination performance of the material. At the same time, after calcination of kaolinite within this temperature range, a highly stable crystal phase structure is formed, and there is no excessive collapse, maintaining the integrity of the particles. As a result, the material kaolin / CNT shows significant superiority in mechanical strength, and its yield load is much higher than that of uncalcined or under-calcined samples. In addition, the carbon nanotubes have a high degree of graphitization within this temperature range, with good electrical conductivity, improving the cycle stability of the material and providing effective support for electrochemical desalination.

[0029] 4. The particulate material kaolin / CNT of the present invention effectively utilizes the advantages of its three-dimensional structure, breaking through the limitations of the high cost of traditional two-dimensional ion exchange membranes and non-reusability. This excellent cycle stability benefits from the structural stability of the particles and the high electrochemical activity of the carbon nanotubes, enabling the material of the present invention to meet the long-term use requirements in actual wastewater treatment and salt adsorption processes. At the same time, the functional filler particulate material kaolin / CNT of the present invention is applicable to multiple fields such as wastewater treatment and seawater desalination, and has a simple preparation process and low cost, making it suitable for large-scale production and actual engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Other features, objectives, and advantages of the present invention will become more apparent by reading the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0031] Figure 1 XRD patterns of the particulate material kaolin / CNT of functional filler in Example 1 after being ground into powder; among them, the left figure is the XRD pattern of the material before calcination, and the right figure is the XRD patterns of the material after calcination at 700 °C, 800 °C, and 900 °C;

[0032] Figure 2 SEM images of the particulate material kaolin / CNT of functional filler in Example 1 and the particulate material before calcination; among them, a is the SEM image of the material before calcination, b is the SEM image of the material after calcination at 700 °C, c is the SEM image of the material after calcination at 800 °C, and d is the SEM image of the material after calcination at 900 °C;

[0033] Figure 3 It is the variation curve of the conductivity of the functional filler particulate material kaolin / CNT in Example 1 with time under a voltage of 1.4V;

[0034] Figure 4 It is the chlorine ion removal cycle stability diagram of the functional filler particulate material kaolin / CNT (800°C) in Example 1 under a certain voltage;

[0035] Figure 5 It is the mechanical strength diagram of the functional filler particulate material kaolin / CNT (800°C) in Example 1 under strong acid, strong base and high temperature environments; among them, the left figure is the mechanical strength diagram of the material under high temperature environment, the middle figure is the mechanical strength diagram of the material under strong base environment, and the right figure is the mechanical strength diagram of the material under strong acid environment;

[0036] Figure 6 It is the nitrogen adsorption / desorption curve and pore size distribution of the functional filler particulate material kaolin / CNT (800°C) in Example 1 before and after calcination; among them, the left figure is the nitrogen adsorption / desorption curve of the material before and after calcination, and the right figure is the pore size distribution of the material before and after calcination;

[0037] Figure 7 It is the preparation flow chart of the functional filler particulate material kaolin / CNT of the present invention. Detailed implementation mode

[0038] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The following examples are implemented on the premise of the technical solution of the present invention, providing detailed implementation methods and specific operation processes, which will help those skilled in the art to further understand the present invention. It should be noted that the protection scope of the present invention is not limited to the following embodiments. Any several adjustments and improvements made on the premise of the concept of the present invention belong to the protection scope of the present invention.

[0039] Example

[0040] Reference Figure 7 According to the preparation process shown, the preparation method of the functional filler particulate material kaolin / CNT in this example includes the following steps:

[0041] (1) Weigh 50g of kaolinite powder and 50g of carbon nanotube powder, add the two powders to a V-type mixer, and mix for 7h until evenly mixed;

[0042] (2) Dissolve 10g of 1799-type polyvinyl alcohol (PVA) particles in 190mL of deionized water, stir at 20rpm in an oil bath at 80°C for 4h to obtain a binder solution;

[0043] (3) Add 200 mL of the obtained binder solution to the above-mentioned uniformly mixed powder and mix again to obtain a uniformly powdered mixture with the binder added.

[0044] (4) Put the above-mentioned uniformly powdered mixture into a small pelletizer equipped with a 3-mm shaft cutter for granulation and polishing to obtain spherical electroadsorption particles.

[0045] (5) Place the above-mentioned spherical electroadsorption particles in an oven and dry them at 60 °C for 12 h, then place them in a tube furnace and calcine them in an argon atmosphere for 2 h. The heating rate during calcination is 5 °C / min to obtain calcined spherical electroadsorption particles. In fact, in step (5), a crystallization process and a graphitization process occur. Under the action of high-temperature calcination, the crystallization process of kaolinite and the graphitization process of carbon nanotubes occur simultaneously, generating porous three-dimensional filler particles.

[0046] (6) Immerse the above-mentioned calcined spherical electroadsorption particles in a 0.5 mol / L hydrochloric acid solution for 24 h, take them out and ultrasonicate them 6 times, each time for 20 min, and then place them in an oven and dry them at 60 °C for 12 h to obtain the functional filler particle material kaolin / CNT.

[0047] <Experiment>

[0048] Perform the following experiments on the products of the above embodiments respectively.

[0049] <Experiment 1>

[0050] The purpose of this experiment is to characterize the crystal structure and morphology of the functional filler particle material kaolin / CNT.

[0051] As Figure 1As shown in the figure, the calcination temperature has a significant regulatory effect on the crystal structure evolution of carbon nanotube / kaolinite composites. The XRD pattern of the uncalcined sample shows that the main phase is kaolinite (Al2[Si2O5][OH]4, PDF#97-006-8698). When the temperature rises to 700 °C, the characteristic peaks of kaolinite disappear, and only the diffraction peak of the (002) crystal plane of graphite carbon (C, PDF998-000-0231, 2θ≈26.5°) is detected. This phenomenon is consistent with the process of forming an amorphous Al-Si-O intermediate after the dehydroxylation reaction of kaolinite at 400-600 °C, indicating that kaolinite begins to undergo a dehydroxylation reaction but no obvious crystalline phase products are formed. Amorphization leads to the destruction of the long-range ordered crystal structure of kaolinite, manifested as no sharp diffraction peaks in the XRD pattern, only broadened diffuse background signals. It is worth noting that the characteristic peak of the (022) crystal plane of quartz (SiO2, PDF#98-000-0369) (2θ≈54.9°) appears for the first time in the 800 °C sample. Its crystallographic characteristics show that the amorphous intermediate undergoes phase separation at higher temperatures, where free SiO2 begins to recrystallize into the α-quartz phase at 800 °C, and the preferred orientation of the (022) crystal plane may be due to the heterogeneous nucleation effect induced by the carbon nanotube template. The above phase evolution law is consistent with the staged decomposition behavior of kaolinite: dehydroxylation at 400-600 °C generates an amorphous Al-Si-O intermediate, and SiO2 and Al2O3 are gradually precipitated above 700 °C.

[0052] As the temperature further rises to 900 °C, the characteristic peak of the SiO2 crystal plane gradually weakens until it disappears again. Combining with the agglomeration and collapse phenomena observed by SEM, it can be inferred that the amorphous Al-Si-O phase further transforms into a glassy structure with a higher degree of disorder at this time.

[0053] As Figure 2 shown, the SEM test of the functional filler particle material kaolin / CNT prepared by the above method shows that the pore structure significantly increases after calcination. However, since kaolinite is still in the initial stage of amorphization at 700 °C and the interlayer hydroxyl groups are not completely removed, the layered structure of the composite particles obtained at 700 °C does not fully collapse, and a stable mesoporous framework cannot be formed. There are obvious pore structures on the surfaces of the composite particles calcined at 800-900 °C. The pores in the kaolin / CNT calcined at 800 °C are more numerous and evenly distributed, and the porosity is significantly increased; the pore distribution in the kaolin / CNT calcined at 850 °C slightly decreases, but the porosity is still relatively high. In contrast, the pore structure of the composite particles obtained at 900 °C decreases again because the amorphous metakaolinite formed by the kaolinite flake structure at high temperature (>850 °C) undergoes interlayer sintering, resulting in agglomeration, which covers the particle surface in a large area and leads to the reduction of the pore structure again.

[0054] <Experiment 2>

[0055] The purpose of this experiment is to explore the desalination performance and cyclic stability of the functional filler particulate material kaolin / CNT.

[0056] As Figure 3 shown, at a constant voltage of 1.4 V, with the charge-discharge time both being 0.5 h, the electrode obtained at 800 °C has the best salt adsorption capacity, and its chlorine removal capacity is about 0.294 mgCl / g. The electrode obtained at 850 °C has a relatively better salt adsorption capacity, and its chlorine removal capacity is about 0.230 mgCl / g. In comparison, the kaolin / CNT electrode obtained at 700 °C (chlorine removal capacity ~0.124 mgCl / g) and the kaolin / CNT electrode obtained at 900 °C (chlorine removal capacity ~0.135 mgCl / g) are both inferior.

[0057] As Figure 4 shown, at a voltage of 1.4 V, the chlorine removal capacity of the kaolin / CNT electrode obtained at 800 °C can reach ~0.294 mgCl / g. Although the chlorine removal capacity is lower than that of the two-dimensional electrode, the packed particulate electrode has no mass limitation like the two-dimensional coated film electrode. After the three-dimensional electrode device is scaled up, the mass of the filler particulate electrode can increase without limitation, thus achieving the effect that low-adsorption-capacity particles can reach a high total adsorption capacity. At the same time, the functional filler particulate material kaolin / CNT has stable cyclic stability, and the salt adsorption capacity remains above 81.93% of the initial adsorption capacity during 50 desalination cycles. And the kaolin / CNT electrode obtained at 850 °C has the salt adsorption capacity remaining above 77.83% of the initial adsorption capacity during 50 desalination cycles.

[0058] <Experiment 3>

[0059] The purpose of this experiment is to explore the strong acid resistance, strong base resistance and high temperature resistance of the functional filler particulate material kaolin / CNT.

[0060] As Figure 5 shown, after the functional filler particulate material kaolin / CNT obtained at 800 °C is soaked in strong acid (2 mol / L HCl) and strong base (2 mol / L NaOH) solutions for 24 hours, its mechanical strength not only does not decrease, but even slightly increases. This may be because the impurities on the particle surface are removed by the acid-base treatment, and at the same time, the binding force between the particles is further enhanced. In addition, in a high-temperature environment (soaked in water at 55 °C for 24 hours), the mechanical properties of the particles basically remain unchanged, showing its excellent high temperature resistance. Generally speaking, the functional filler particulate material kaolin / CNT exhibits excellent stability and adaptability under strong acid, strong base and high temperature conditions, and is suitable for long-term use in actual complex working conditions.

[0061] <Experiment 4>

[0062] The purpose of this experiment is to explore the pore structure and pore size distribution of the functional filler particulate material kaolin / CNT.

[0063] Figure 6 The nitrogen adsorption-desorption isotherms of the medium particles show that both before and after calcination, the material presents a type-IV isotherm, indicating a pore structure dominated by mesopores. The H3-type hysteresis loop of the 800 °C sample further confirms its slit-shaped mesopore characteristics, which are consistent with the interlayer pores formed after the amorphization of kaolinite. Further combined with the NLDFT pore size distribution, the C-8 particles show a significant micropore peak in the range of 1-2 nm, indicating that after calcination at 800 °C, a rich micropore-mesopore hierarchical structure is formed inside the material, providing high-activity sites and fast diffusion channels for ion adsorption.

[0064] Compared with conventional conductive agents (such as conductive carbon black, graphene, acetylene black, carbon fiber, etc.) and clay materials (such as montmorillonite, diatomite, medaka stone, etc.), the composite system of kaolinite and carbon nanotubes in this invention significantly optimizes the porous structure and cycle stability through a synergistic effect: after calcination at 800-850 °C, kaolinite forms a mesoporous framework, and CNTs are interspersed therein to construct a three-dimensional conductive network, which not only inhibits the pore closure caused by sintering but also enhances the mechanical strength. The combination of the two forms a micropore-mesopore hierarchical structure, providing high-activity sites and fast ion diffusion channels. At the same time, the elasticity of CNTs relieves the cyclic stress, making the capacity retention rate reach over 81.93% after 50 desalination cycles. In contrast, other conductive materials such as conductive carbon black have good conductivity, but the particles are prone to agglomeration, the porosity is low, and there is a lack of long-range structural support, making them prone to pulverization during cycling. Graphene has the disadvantages of high cost, easy stacking of sheet structures, low utilization rate of the actual specific surface area, and significant mechanical brittleness. Other clay materials such as montmorillonite have easily leachable interlayer cations, high structural disorder after high-temperature calcination, broad pore distribution (mainly mesopores > 10 nm), and it is difficult to form a micropore-mesopore hierarchical system. In addition, the stable quartz phase formed by the calcination of kaolinite and the inert surface of CNTs jointly resist acid-base erosion, achieving long-term stability in complex environments and providing an efficient and durable three-dimensional filler solution for capacitive deionization technology.

[0065] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A preparation method of a functional filler particulate material kaolin / CNT, characterized in that, It includes the following steps: S1. Mix kaolinite powder and carbon nanotube powder evenly to obtain a first uniform powder; S2. Mix the binder and the first uniform powder evenly to obtain a second uniform powder; S3. Granulate the second uniform powder to obtain first electro-adsorption particles; S4. Calcinate the first electro-adsorption particles to obtain second electro-adsorption particles; S5. Immerse the second electro-adsorption particles in an acid solution, and obtain the product after drying.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of the kaolinite powder to the carbon nanotube powder is 0.8 - 1.2:

1.

3. The preparation method according to claim 1, characterized in that, In step S2, the binder includes polyvinyl alcohol particles.

4. The preparation method according to claim 3, wherein The binder is obtained by dissolving polyvinyl alcohol particles in deionized water, heating in an oil bath and stirring; wherein, the temperature of the oil bath heating is 70 - 90 °C, the heating time is 3 - 5 h, and the stirring speed is 15 - 30 rpm.

5. The preparation method according to claim 3, characterized in that, In step S2, the mass fraction of polyvinyl alcohol particles in the binder is 4 - 6 wt%, and the dosage ratio of the binder to the carbon nanotube powder is 180 - 220 mL:50 mg.

6. The preparation method according to claim 1, characterized in that In step S4, the calcination temperature is 800 - 850 °C, the heating rate is 4 - 6 °C / min, the calcination time is 1.5 - 3 h, and the calcination atmosphere includes an argon atmosphere.

7. The preparation method according to claim 1, characterized in that, In step S5, the acid solution includes a hydrochloric acid solution with a concentration of 0.3 - 0.8 mol / L; the soaking time is 15 - 30 h.

8. The preparation method according to claim 1, wherein In step S5, the drying temperature is 50 - 65 °C, and the time is 8 - 20 h.

9. A functional filler particle material kaolin / CNT obtained by the preparation method according to any one of claims 1 - 8.

10. An application of the functional filler particle material kaolin / CNT according to claim 9 in capacitive deionization desalination.

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