Preparation method and application of polyethylene coated carbon nanotube electrode material

Abstract

The invention provides a preparation method and application of a polyethylene-coated carbon nanotube electrode material, and belongs to the technical field of plastic processing, and the preparation method comprises the following steps: collecting waste polyethylene products, chopping, cleaning to remove impurities, filtering, and drying; the method comprises the following steps: adding waste polyethylene fragments into a xylene solution, magnetically stirring and mixing, adding into a Buchner funnel, carrying out suction filtration, and collecting filtrate; weighing a carbon nano tube, adding the carbon nano tube into the filtrate, and continuously heating and mixing to prepare a colloidal solution; dropwise adding the colloidal solution into a cyclohexanone solution, carrying out ultrasonic mixing, separating out powder precipitate, filtering, washing with an ethanol solution, and drying to obtain composite powder; the composite powder and activated carbon are mixed and placed in a ball mill to be ground, electrode powder is prepared, the electrode powder is poured into a round mold, round electrode particles are prepared through pressing under a hydraulic machine, and the round electrode particles are annealed to prepare the polyethylene-coated carbon nanotube electrode. According to the invention, high value-added utilization of polyethylene and greenness and harmlessness of the final product waste can be realized.

Description

Technical Field

[0001] The invention belongs to the technical field of plastic processing, and in particular relates to a preparation method and application of a polyethylene-coated carbon nanotube electrode material. Background Art

[0002] Polyethylene (PE) is one of the most widely used plastics in the world, with production reaching 118 million tons in 2021 alone. In China, more than 2.35 million tons of mulch is used each year, and the residue of agricultural film on the land can lead to reduced crop yields. Although a variety of methods have been developed to recycle PE, including mechanical recycling, chemical recycling, biological recycling and thermal treatment, in the current market recycling methods, making the application of the resulting product reach a profit point and making PE recycling profitable is the key to promoting self-sustaining PE recycling. However, due to the low price of PE, profitable PE recycling methods do not allow the application of complex, expensive and energy-intensive technologies, resulting in the resulting product being easily degraded or polluted, and only suitable for low value-added applications, the so-called "downcycling". Therefore, there are very few methods that can be tried to use recycled PE for high value-added applications, the so-called "upcycling".

[0003] On the other hand, using carbon nanotubes (CNT) to improve polyethylene through melt blending, that is, adding CNT to improve PE conductivity and mechanical strength. However, most studies only add a small amount of CNT to PE. A Chinese patent for a flame-retardant and heat-resistant nano-magnesium oxide-doped polyethylene DC cable composite material (publication number CN105778221A, publication date July 20, 2016) includes 1.2-1.5 multi-walled carbon nanotubes and 90-91 polyethylene, and the ratio of carbon nanotubes to polyethylene does not exceed 10%. Because at high PE content, CNT is embedded in the PE material, and the carbon nanotubes are adhered to each other due to PE, which makes it difficult to fully disperse during application, and it is impossible to effectively achieve an effective balance between the strength and conductivity of the composite material. PE is insoluble in conventional solvents, and it is easy to agglomerate when cooled and solidified. The high crystallinity of PE is prone to interfacial compatibility problems, resulting in large resistance and not suitable for electronic devices with high conductivity requirements. The Chinese patent for a flame-retardant functionalized carbon nanotube-modified polyethylene material (publication number CN119391067A, publication date February 7, 2025) and the Chinese patent for a method for preparing an oxidized carbon nanotube-modified polyvinyl alcohol shape memory fiber (publication number CN112160037A, publication date January 1, 2021) use chemical covalent grafting and other technologies to modify the surface of CNT to improve conductivity, which is technically complex and has poor economic benefits. Therefore, there is an urgent need for a design that allows PE to achieve high added value utilization and green and harmless final product waste. Summary of the invention

[0004] The purpose of the embodiments of the present invention is to provide a preparation method and application of a polyethylene-coated carbon nanotube electrode material, which can achieve high value-added utilization of PE and green and harmless treatment of waste products in the final product, and provide a new systematic path for the upgrading and recycling of PE.

[0005] The technical solution adopted by the present invention is a method for preparing a polyethylene-coated carbon nanotube electrode material, comprising the following steps:

[0006] S1, collect and chop waste polyethylene products, clean and remove impurities, filter and dry;

[0007] S2, weighing waste polyethylene fragments and adding them to the xylene solution, mixing them by magnetic stirring, and after stirring, placing them in a Buchner funnel for suction filtration, and collecting the filtrate after removing insoluble impurities;

[0008] S3, weighing carbon nanotubes and adding them to the filtrate, and continuing to heat and mix to obtain a colloidal solution;

[0009] S4, dripping the colloidal solution into the cyclohexanone solution and mixing by ultrasonication, filtering the precipitated powder and washing it with an ethanol solution, and drying it to obtain a composite powder;

[0010] S5. Weigh the composite powder and activated carbon, mix them, grind them in a ball mill to obtain electrode powder, weigh the electrode powder and pour it into a round mold, press the round mold under a hydraulic press to obtain round electrode particles, and anneal the round electrode particles to obtain a polyethylene-coated carbon nanotube electrode.

[0011] Furthermore, in step S2, the mass of the waste polyethylene fragments is 1 to 1.3 g, the volume of the xylene solution is 25 to 50 mL, and the magnetic stirring is performed at a temperature of 125 to 145° C. for 20 to 30 min.

[0012] Furthermore, in step S2, the Buchner funnel is preheated to 90-95°C in advance.

[0013] Furthermore, in step S3, the mass of the carbon nanotubes is 1-1.2 g, the heating temperature is 125-145° C., and the mixing time is 30-60 min.

[0014] Furthermore, in step S4, the colloidal solution is dripped for 30-60 minutes.

[0015] Furthermore, in step S4, the volume of the cyclohexanone solution is 80-250 ml, and the temperature of the cyclohexanone solution is 50-90°C.

[0016] Furthermore, in step S5, the mass ratio of the composite powder to the activated carbon is 1 to 3:2.

[0017] Furthermore, in step S5, the annealing is to heat the round electrode particles at 140-160° C. for 10 min.

[0018] Another technical solution adopted by the present invention is that the polyethylene-coated carbon nanotube electrode material obtained by the above-mentioned preparation method is used to prepare zinc ion capacitors and desalination water purification devices.

[0019] The beneficial effects of the present invention are:

[0020] (1) The preparation method of the present invention is a one-step method, the preparation process is simple and does not require chemical reaction. When the colloidal solution is dripped into the cyclohexanone solution, PE slowly and evenly precipitates and tightly wraps on the surface of CNT, so that CNT is evenly coated with nano-scale (<2nm) PE, and the good dispersion of the nano-scale makes the compatibility between PE solution and CNT excellent. PE can produce a quantum tunneling effect at the nanoscale, so that charges can pass through the conductive film, thereby improving the overall conductivity of the material, solving the current problem of low conductivity of composite materials at high PE content, and facilitating the good bonding ability of CNT-PE and the activated carbon with energy storage activity, further giving the electrode energy storage effect, and providing a new method for applying PE to high value-added fields.

[0021] (2) The xylene and cyclohexanone solution used in the preparation method of the present invention can be separated and reused by simple distillation, and the recovery rate is higher than 95%. Filtering and recovering the solvent can reduce pollution and emissions in the preparation process. The ultrasonic mixing used in the present invention makes the precipitated powder precipitation very uniform, further improving its dispersion effect.

[0022] (3) Based on the conductivity and high dispersibility of PE-CNT materials, the present invention designs a pressed electrode material with PE-CNT materials as the key material, which has a very high effective active material mass loading, all exceeding 200 mAh g -1 Based on this performance, the application design of zinc ion capacitors and desalination water purification devices was proposed, and the calorific value and ash element composition were proved through combustion tests. The use of ash as fertilizer will not have an adverse effect on plant growth. Based on PE-CNT materials, a fully green plastic recycling and utilization PE technology system that can integrate energy storage, fuel and fertilizer application scenarios was established, demonstrating an innovative method of converting recycled PE into high value-added products. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 It is a transmission electron microscope image of the nano-coating structure of PE-CNT of the present invention.

[0025] Figure 2 It is a SEM picture of the dispersion state of PE-CNT of the present invention.

[0026] Figure 3 This is a graph showing the change in electrical conductivity of the PE-CNT material of the present invention.

[0027] Figure 4 This is a real picture of the polyethylene-coated carbon nanotube electrode prepared by the present invention.

[0028] Figure 5 It is the charge and discharge test curve of the polyethylene coated carbon nanotube electrode prepared by the present invention.

[0029] Figure 6 This is the thermogravimetric curve of the polyethylene-coated carbon nanotube electrode prepared by the present invention.

[0030] Figure 7 This is a thermogravimetric curve of the polyethylene-coated carbon nanotube electrode prepared by the present invention after 20,000 cycles of charge and discharge.

[0031] Figure 8 The element composition of the ash obtained by incinerating the polyethylene-coated carbon nanotube electrode prepared by the present invention after 20,000 cycles of charge and discharge.

[0032] Fig. 9 The ash obtained by burning the polyethylene-coated carbon nanotube electrode prepared by the present invention is used as zinc fertilizer, and the length of corn seedling leaves is counted. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The present invention provides a method for preparing a polyethylene-coated carbon nanotube electrode material, comprising the following steps:

[0035] S1, collect and chop waste polyethylene products, clean and remove impurities, filter and dry;

[0036] S2, weigh 1-1.3g of waste PE fragments and add them to 25-50mL of xylene solution, stir and mix them under magnetic stirring at 125-145℃ for 20-30min, and after stirring, place them in a Buchner funnel preheated to 90-95℃ for suction filtration, remove insoluble impurities and collect the filtrate;

[0037] S3, weighing 1-1.2 g of carbon nanotubes and adding them to the filtrate, continuing to heat to 125-145° C. and mixing for 30-60 min to obtain a colloidal solution;

[0038] S4, dripping the colloidal solution into 80-250 ml of cyclohexanone solution at 50-90° C. and ultrasonically mixing, the dripping time of the colloidal solution is 30-60 min, the ultrasonic power is set to 1200 W, filtering the precipitated powder and washing it with an ethanol solution, and drying it at 60° C. to obtain a composite powder;

[0039] S5. Weigh and mix the composite powder and activated carbon in a mass ratio of 1 to 3:2, grind them in a ball mill at 500 rpm for 8 hours to obtain electrode powder, weigh 70 mg of the electrode powder and pour it into a circular mold with a diameter of 1.3 cm, press the circular mold under a hydraulic press at a pressure of 376 MP (5t pressure) for 5 minutes to obtain circular electrode particles, anneal the circular electrode particles at 140 to 160° C. for 10 minutes to obtain a polyethylene-coated carbon nanotube electrode.

[0040] The present invention selects waste PE plastic bags and film products as raw materials, and cuts them into pieces with a width of 5 to 10 cm with scissors to facilitate cleaning and drying; the present invention preheats the Buchner funnel in advance to avoid premature precipitation of polyethylene; the waste liquid generated by the present invention can be separated by distillation to achieve the recycling of xylene and cyclohexanone solvents, and the solvent recovery rate is greater than 95%.

[0041] Example 1

[0042] S1, collect and chop waste polyethylene products, clean and remove impurities, filter and dry;

[0043] S2, weigh 1g of waste PE fragments and add them to 25mL of xylene solution, mix them under magnetic stirring at 125℃ for 20min, and after stirring, place them in a Buchner funnel preheated to 90℃ for suction filtration, remove insoluble impurities and collect the filtrate;

[0044] S3, weighing 1 g of carbon nanotubes and adding them to the filtrate, continuing to heat to 125° C. and mixing for 30 min to obtain a colloidal solution;

[0045] S4, dripping the colloidal solution into 125 ml of cyclohexanone solution at 80° C. and ultrasonically mixing, the colloidal solution dripping time is 30 min, the ultrasonic power is set to 1200 W, filtering the precipitated powder and washing it with ethanol solution, and drying it at 60° C. to obtain a composite powder;

[0046] S5. Weigh and mix the composite powder and activated carbon in a mass ratio of 3:2, place them in a ball mill and grind them at 500 rpm for 8 hours to obtain electrode powder, weigh 70 mg of electrode powder and pour it into a circular mold with a diameter of 1.3 cm, press the circular mold under a hydraulic press at a pressure of 376 MP (5t pressure) for 5 minutes to obtain circular electrode particles, and anneal the circular electrode particles at 150°C for 10 minutes to obtain a polyethylene-coated carbon nanotube electrode.

[0047] Example 2

[0048] The difference from Example 1 is that in step S3, 1.2 g of carbon nanotubes are weighed; in step S5, the round electrode particles are annealed at 140° C. The remaining steps are the same as in Example 1.

[0049] Example 3

[0050] The difference from Example 1 is that in step S2, 1.2 g of PE fragments are weighed and added to 35 mL of xylene solution, and mixed with magnetic stirring at 135° C. for 25 min; in step S3, heating to 135° C. and mixing for 45 min; in step S5, the round electrode particles are annealed at 160° C. The remaining steps are the same as in Example 1.

[0051] Example 4

[0052] The difference from Example 1 is that in step S2, 1.3 g of PE fragments are weighed and added to 50 mL of xylene solution, and mixed with magnetic stirring at 145° C. for 30 min. After stirring, the solution is added to a Buchner funnel preheated to 95° C. for suction filtration. In step S3, 1.0 g of carbon nanotubes are weighed, and the mixture is heated to 145° C. and mixed for 60 min. The remaining steps are the same as in Example 1.

[0053] Example 5

[0054] The difference from Example 1 is that in step S4, the colloidal solution is dripped into 250 ml of cyclohexanone solution and ultrasonically mixed, and the dripping time of the colloidal solution is 60 minutes. The remaining steps are the same as in Example 1.

[0055] Example 6

[0056] The difference from Example 1 is that in step S4, the colloidal solution is dripped into 100 ml of cyclohexanone solution and ultrasonically mixed, and the dripping time of the colloidal solution is 60 minutes. The remaining steps are the same as in Example 1.

[0057] Example 7

[0058] The difference from Example 1 is that in step S4, the colloidal solution is dripped into 80 ml of cyclohexanone solution and ultrasonically mixed, and the dripping time of the colloidal solution is 60 minutes. The remaining steps are the same as in Example 1.

[0059] Example 8

[0060] The difference from Example 1 is that in step S5, the composite powder and activated carbon are weighed and mixed in a mass ratio of 1:2. The remaining steps are the same as those in Example 1.

[0061] Example 9

[0062] The difference from Example 1 is that in step S5, the composite powder and activated carbon are weighed and mixed in a mass ratio of 1:1. The remaining steps are the same as in Example 1.

[0063] Example 10

[0064] The difference from Example 1 is that in step S5, the colloidal solution is dripped into the cyclohexanone solution at 50° C. and ultrasonically mixed, and the dripping time of the colloidal solution is 40 minutes. The remaining steps are the same as in Example 1.

[0065] Embodiment 11

[0066] The difference from Example 1 is that in step S4, the colloidal solution is dripped into the cyclohexanone solution at 50° C. and ultrasonically mixed, and the dripping time of the colloidal solution is 60 minutes. The remaining steps are the same as in Example 1.

[0067] Comparative Example 1

[0068] The difference from Example 1 is that in step S2, 1.4 g of PE fragments are weighed; in step S3, 0.6 g of carbon nanotubes are weighed, and the remaining steps are the same as in Example 1.

[0069] Comparative Example 2

[0070] The difference from Example 1 is that in step S2, 0.6 g of PE fragments are weighed; in step S3, 1.4 g of carbon nanotubes are weighed, and the remaining steps are the same as in Example 1.

[0071] Step S5: The electrode is difficult to prepare and shape.

[0072] Comparative Example 3

[0073] The difference from Example 1 is that in step S4, the colloidal solution is dripped into 60 ml of cyclohexanone solution and ultrasonically mixed, and the dripping time of the colloidal solution is 60 minutes. The remaining steps are the same as in Example 1.

[0074] Comparative Example 4

[0075] The difference from Example 1 is that in step S4, the colloidal solution is dripped into 60 ml of cyclohexanone solution and ultrasonically mixed, and the dripping time of the colloidal solution is 12 minutes. The remaining steps are the same as in Example 1.

[0076] Comparative Example 5

[0077] The difference from Example 1 is that in step S5, the composite powder and activated carbon are weighed and mixed according to a mass ratio of 1:4. The remaining steps are the same as in Example 1.

[0078] Step S5: The electrode is difficult to prepare and shape.

[0079] Comparative Example 6

[0080] The difference from Example 1 is that in step S5, the composite powder and activated carbon are weighed and mixed in a mass ratio of 4:1. The remaining steps are the same as in Example 1.

[0081] Comparative Example 7

[0082] The difference from Example 1 is that in step S4, the colloidal solution is dripped into the cyclohexanone solution at 40° C. and ultrasonically mixed, and the dripping time of the colloidal solution is 20 minutes. The remaining steps are the same as in Example 1.

[0083] Comparative Example 8

[0084] Waste polyethylene products were collected and chopped, washed to remove impurities, filtered and dried, and 1 g of waste PE fragments and 1 g of carbon nanotubes were weighed and heated and stirred at 150°C for 1 h.

[0085] The obtained product is a mixture of agglomerated masses.

[0086] Comparative Example 9

[0087] Collect and chop waste polyethylene products, wash to remove impurities, filter and dry; weigh 1g of waste PE fragments and add them to 25mL of toluene solution, and mix them under magnetic stirring at 125℃ for 20min.

[0088] Toluene is used to replace xylene. Toluene has a low boiling point and is volatile, so PE cannot be dissolved in it.

[0089] Comparative Example 10

[0090] The difference from Example 1 is that in step S2, the waste PE fragments are weighed and added to 25 mL of trimethylol solution, and the remaining steps are the same as Example 1.

[0091] Trimethylbenzene is used to replace xylene. The boiling point of trimethylbenzene is close to that of cyclohexanone, making it difficult to recover and separate the solvent by distillation in the later stage.

[0092] Comparative Example 11

[0093] The difference from Example 1 is that in step S2, the waste PE fragments are weighed and added to 25 mL of white mineral oil, and the remaining steps are the same as Example 1.

[0094] In step S4, the white mineral oil and cyclohexanone have poor compatibility, the solution is stratified in the later stage of mixing, the composite powder is severely agglomerated, and the electrode is difficult to prepare in step S5.

[0095] Comparative Example 12

[0096] The difference from Example 1 is that in step S4, ultrasonic mixing is not performed, and the remaining steps are the same as Example 1.

[0097] The precipitated powder is precipitated into solid agglomerates, and the electrode in step S5 is difficult to prepare and shape.

[0098] Comparative Example 13

[0099] The difference from Example 1 is that in step S4, the colloidal solution is dripped into 125 ml of 80° C. butanone solution and ultrasonically mixed. The remaining steps are the same as in Example 1.

[0100] The prepared composite powder is severely agglomerated, and the electrode in step S5 is difficult to prepare and form.

[0101] Comparative Example 14

[0102] Waste polyethylene products were collected and shredded, washed to remove impurities, filtered and dried; waste PE fragments, CNT, and activated carbon AC were mixed in a mass ratio of 3:3:4, and then the mixture was ground in a ball mill at 500 rpm for 8 hours to obtain a mixed powder. 70 mg of the mixed powder was weighed and poured into a circular mold with a diameter of 1.3 cm, and the circular mold was pressed under a hydraulic press at a pressure of 376 MP (5t pressure) for 5 minutes.

[0103] The produced electrodes are fragile and cannot be formed, and their strength cannot meet the use requirements.

[0104] like Figure 1 The figure shows a transmission electron microscope image of the PE-CNT colloidal solution prepared in Example 1 of the present invention, showing that the CNT is coated with nano-scale PE; Figure 2 The SEM image of the PE-CNT colloidal solution prepared in Example 1 of the present invention shows that it has good dispersibility; Figure 3 As shown in Figure 2, CNTs have excellent electrical conductivity when coated with nanoscale (<2 nm) PE; Figure 4 As shown in the actual picture of the polyethylene-coated carbon nanotube electrode prepared by the present invention, compared with a 5-cent coin, its size is slightly smaller and its surface is smooth.

[0105] The performance test was performed on the tablets prepared from the composite powders obtained in step S4 of Examples 1 to 4 of the present invention and Comparative Examples 1 to 2. 30 mg of the composite powder was weighed to make tablets with a diameter of 1 cm. The conductivity of the tablets was measured by linear voltammetry on an electrochemical workstation as shown in Table 1:

[0106] Table 1 Conductivity of different PE / CNT ratios

[0107] Example / Comparative Example PE to CNT ratio Conductivity Example 1 1:1 2S / m Example 2 1:1.2 2.3S / m Example 3 1.2:1 1.9S / m Example 4 1.3:1 1.3S / m Comparative Example 1 1.4:0.6 0.07S / m Comparative Example 2 0.6:1.4 4.7S / m

[0108] As can be seen from Table 1, the conductivity of the polyethylene-coated carbon nanotube electrode prepared by compounding a high content of CNT and PE in the embodiment of the present invention meets the requirements for application in electronic devices, while the conductivity of the pressed sheet prepared in Comparative Example 1 is greatly reduced due to the excessively high PE content. Although the conductivity of Comparative Example 2 can be improved by adding a high proportion of CNT, the CNTs cannot be fully dispersed due to adhesion caused by PE due to the excessively high CNT content, resulting in the inability to form the electrode.

[0109] The polyethylene-coated carbon nanotube electrodes prepared in the examples of the present invention and the comparative examples were tested at 0.1 mA cm -2 The capacitance was tested under current density, and the test results are shown in Table 2:

[0110] Table 2 Capacitance test comparison table

[0111]

[0112]

[0113] As shown in Table 2, the capacitance of the embodiment of the present invention reaches 200 mAh g by designing the ratio of PE to CNT. -1 As mentioned above, if the PE content is too high, the material capacitance will drop extremely fast. If the CNT content is too high, the material will stick together and the electrode cannot be prepared. The present invention has concluded through experiments that the colloidal solution needs to have enough volume in the process of dripping into the cyclohexanone solution so that the polyethylene can be fully precipitated. If the volume of cyclohexanone is too small, the precipitated powder will be poorly dispersed, not uniform and fluffy, resulting in a decrease in capacitance; and it can be known that the temperature of the cyclohexanone solution and the dripping time also have a great influence on the polyethylene precipitation time. If the temperature is too low, the polyethylene precipitation rate is too fast to produce serious agglomeration. If the temperature is too high, the cyclohexanone volatilizes too fast. The present invention does not set a comparative example; if the dripping time is too fast, the polyethylene cannot be fully precipitated in the cyclohexanone solution, resulting in agglomeration. The present invention prepares electrodes by composite powder and activated carbon. It is found that if the activated carbon content is too high, the electrode particles cannot be formed during the pressing process, and if the activated carbon content is too low, its capacitance is greatly reduced. The present invention selects xylene as a polyethylene solvent and cyclohexanone as a precipitation solvent through multiple experiments. Other solvents cannot prepare electrodes.

[0114] The polyethylene-coated carbon nanotube electrode prepared in Example 1 of the present invention was used as the cathode, the metal zinc was used as the anode, and the mass concentration of the electrolyte was selected to be 2 mol L -1 ZnCl2 solution was used to prepare zinc ion capacitors at 0.1 mA cm -2 Under the current density, the battery charge and discharge test system is used to test the capacity. The test results are as follows: Figure 5 As shown, it can be seen that in 1Ah g -1 The capacity showed no attenuation after 30,000 cycles of charge and discharge at the same current density.

[0115] like Figure 6 and Figure 7 As shown in FIG. 1 , the thermal stability test of the polyethylene-coated carbon nanotube electrode before and after the cyclic charge and discharge is carried out, and it can be seen that the electrode prepared by the present invention has good thermal stability; the electrode after the cyclic charge and discharge weighs 5.5 g, and the ash obtained by combustion is 0.6 g. The combustion heat release test in the air atmosphere shows that its calorific value is 29 MJ kg -1 .

[0116] The elemental composition of the ash was analyzed, such as Figure 8 As shown, it can be seen that the Zn content in the electrode after cyclic charge and discharge is greatly increased. The ash was dissolved in 10mL of concentrated hydrochloric acid, and then added to 600ml of commercially available plant complete nutrient solution without zinc ions to prepare a hydroponic nutrient solution doped with electrode ash. Corn kernels were placed in the hydroponic box and covered with quartz sand to avoid the introduction of other ions. A complete nutrient solution and a zinc-deficient nutrient solution were set as control groups, and they were cultivated under the same conditions, and the number and length of leaves were counted to observe and evaluate the leaf development status. Fig. 9 As shown, it can be seen that the corn plants and leaf development status added with electrode ash are significantly better than the other two reference groups, and the corn leaf length is increased by 10-20% compared with the control group, proving that the polyethylene-coated carbon nanotube electrode prepared by the present invention will not pollute plants and can be used as a zinc fertilizer.

[0117] The polyethylene-coated carbon nanotube electrodes prepared in Example 1 of the present invention were used as the positive and negative electrodes of the desalination and water purification device. Ten pieces of each were used to adsorb and desorb salt ions in 50 mL of 0.1 M NaCl salt water. The adsorption voltage was 0.5 to 1.5 V. During desalination, a voltage of 1.2 V was applied to the electrode. The current during the desorption process was 10 to 20 mA, and the cut-off voltage was 0 V. The salinity in the salt solution decreased accordingly, and the changes were monitored by a salt meter. When the salinity decrease ratio reached 10% of the initial salinity, it tended to stabilize. It can be seen that the polyethylene-coated carbon nanotube electrodes prepared by the present invention have excellent effects when applied to desalination and water purification devices.

[0118] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for preparing a polyethylene-coated carbon nanotube electrode material, characterized in that: The following steps are involved: S1, collect and chop waste polyethylene products, clean and remove impurities, filter and dry; S2, weighing waste polyethylene fragments and adding them to the xylene solution, mixing them by magnetic stirring, and after stirring, placing them in a Buchner funnel for suction filtration, and collecting the filtrate after removing insoluble impurities; S3, weighing carbon nanotubes and adding them to the filtrate, and continuing to heat and mix to obtain a colloidal solution; S4, dripping the colloidal solution into the cyclohexanone solution and mixing by ultrasonication, filtering the precipitated powder and washing it with an ethanol solution, and drying it to obtain a composite powder; S5. Weigh the composite powder and activated carbon, mix them, grind them in a ball mill to obtain electrode powder, weigh the electrode powder and pour it into a round mold, press the round mold under a hydraulic press to obtain round electrode particles, and anneal the round electrode particles to obtain a polyethylene-coated carbon nanotube electrode.

2. The method for preparing a polyethylene-coated carbon nanotube electrode material according to claim 1, characterized in that: In step S2, the mass of the waste polyethylene fragments is 1 to 1.3 g, the volume of the xylene solution is 25 to 50 mL, and the magnetic stirring is performed at a temperature of 125 to 145° C. for 20 to 30 min.

3. The method for preparing a polyethylene-coated carbon nanotube electrode material according to claim 1, characterized in that: In step S2, the Buchner funnel is preheated to 90-95°C in advance.

4. The method for preparing a polyethylene-coated carbon nanotube electrode material according to claim 1, characterized in that: In step S3, the mass of the carbon nanotubes is 1-1.2 g, the heating temperature is 125-145° C., and the mixing time is 30-60 min.

5. The method for preparing a polyethylene-coated carbon nanotube electrode material according to claim 1, characterized in that: In step S4, the colloidal solution is dripped for 30-60 minutes.

6. The method for preparing a polyethylene-coated carbon nanotube electrode material according to claim 1, characterized in that: In step S4, the volume of the cyclohexanone solution is 80-250 ml, and the temperature of the cyclohexanone solution is 50-90°C.

7. The method for preparing a polyethylene-coated carbon nanotube electrode material according to claim 1, characterized in that: In step S5, the mass ratio of the composite powder to the activated carbon is 1 to 3:

2.

8. The method for preparing a polyethylene-coated carbon nanotube electrode material according to claim 1, characterized in that: In step S5, the annealing is to heat the round electrode particles at 140-160° C. for 10 minutes.

9. A polyethylene-coated carbon nanotube electrode material obtained by the preparation method according to any one of claims 1 to 8, which is used for preparing zinc ion capacitors and desalination water purification devices.

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