A method for preparing carbon nanotubes from decommissioned photovoltaic modules and carbon nanotubes

Abstract

The present application belongs to the technical field of photovoltaic module recycling, and provides a method for preparing carbon nanotubes from decommissioned photovoltaic modules and carbon nanotubes. The method comprises: disassembling the decommissioned photovoltaic module to obtain a photovoltaic laminate; subjecting the photovoltaic laminate to microwave pyrolysis to produce pyrolysis gas; sequentially subjecting the pyrolysis gas to condensation and purification treatment to obtain raw material gas; and using the raw material gas as a carbon source gas to perform chemical vapor deposition reaction. The present application uses the non-condensed pyrolysis gas produced by microwave pyrolysis of the decommissioned photovoltaic module as a carbon source, and through microwave pyrolysis and pyrolysis gas regulation, the complex pyrolysis gas is used as a carbon source gas for chemical vapor deposition to prepare carbon nanotubes; through condensation and purification treatment, the pyrolysis gas is regulated and treated to improve the applicability of the pyrolysis gas as a carbon source, and carbon nanotubes with more obvious tubular structure characteristics can be obtained, which have good uniformity of morphology, good structural integrity, high purity and high graphitization degree, and reduce irregular deposition on the surface.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic module recycling technology, and in particular to a method for preparing carbon nanotubes from retired photovoltaic modules and the carbon nanotubes themselves. Background Technology

[0002] Carbon nanotubes possess excellent electrical and thermal conductivity, mechanical properties, and chemical stability, making them promising candidates for applications in conductive composite materials, energy storage devices, electromagnetic shielding, catalyst supports, and sensing. Currently, the main methods for preparing carbon nanotubes include arc discharge, laser ablation, and chemical vapor deposition (CVD). Among these, CVD has become the mainstream method due to its relatively simple equipment, easily controllable reaction conditions, and ease of continuous and large-scale production.

[0003] Current chemical vapor deposition (CVD) methods typically use small-molecule hydrocarbons such as methane, ethylene, and acetylene as carbon sources, and maintain the reaction temperature through external heating. However, CVD for carbon nanotube preparation still has certain shortcomings: on the one hand, traditional fossil-based carbon sources are relatively singular, limiting resource utilization; on the other hand, conventional external heating methods mainly rely on furnace wall heat transfer, which suffers from slow heating rates, uneven temperature distribution within the reactor, and difficulty in stably controlling the carbon source decomposition process. Under certain conditions, this can easily lead to increased amorphous carbon deposition and decreased regularity of the tubular structure, thus affecting the quality of carbon nanotubes.

[0004] With the rapid development of the photovoltaic industry, a large number of waste photovoltaic modules will continue to enter the end-of-life stage. During pyrolysis, the organic components in these modules can release small-molecule hydrocarbons and some oxygen-containing organic components, which have the potential to serve as carbon source precursors for the preparation of carbon nanotubes via chemical vapor deposition. Therefore, utilizing the gases generated from the pyrolysis of waste photovoltaic modules to prepare carbon nanotubes provides a new approach for the high-value utilization of these modules.

[0005] However, unlike conventional single carbon sources, the pyrolysis gas from waste photovoltaic modules has a more complex composition. Besides the gaseous organic components usable for subsequent growth, it contains condensable heavy components, acidic gases, and fluorine-containing impurities. Directly using this type of pyrolysis gas in catalytic chemical vapor deposition (CVD) processes can negatively impact catalyst activity, carbon source decomposition behavior, and deposition stability, thereby affecting the growth behavior and product morphology of carbon nanotubes. Therefore, effectively regulating and adapting the pyrolysis gas to its compositional characteristics and ensuring its stable use for subsequent carbon nanotube catalytic growth has become a pressing technical problem in this field. Microwave heating, with its volumetric heating, rapid temperature rise, and selective heating characteristics, is advantageous compared to conventional external heating methods in promoting the rapid decomposition of polymer encapsulation materials in waste photovoltaic modules and provides conditions for the separation, regulation, and utilization of non-condensable gases in the subsequent pyrolysis gas.

[0006] Based on this, we developed a microwave pyrolysis, gas regulation, and catalytic deposition method for non-condensable gases from waste photovoltaic modules. This method is of great significance for realizing the high-value conversion of complex pyrolysis gases from waste photovoltaic modules into carbon nanotubes. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing carbon nanotubes from decommissioned photovoltaic modules and the carbon nanotubes themselves, aiming to solve the problems of complex pyrolysis gas composition, numerous impurities, and difficulty in directly using it as a carbon source for catalytic chemical vapor deposition.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing carbon nanotubes from decommissioned photovoltaic modules, comprising the following steps: 1) Disassemble retired photovoltaic modules to obtain photovoltaic laminates; 2) Microwave pyrolysis of the photovoltaic laminate generates pyrolysis gas; 3) The pyrolysis gas is sequentially condensed and purified to obtain the raw material gas; 4) Using the raw material gas as the carbon source gas, a chemical vapor deposition reaction is carried out to obtain carbon nanotubes.

[0009] Preferably, the microwave pyrolysis temperature in step 2) is 400~900℃, the microwave pyrolysis frequency is 500~3000MHz, the microwave pyrolysis power is 0.5~20kW, and the microwave pyrolysis time is 1~120min.

[0010] Preferably, the microwave pyrolysis in step 2) is carried out in an air atmosphere, an inert atmosphere, an oxygen atmosphere, or a hydrogen atmosphere.

[0011] Preferably, the condensation temperature in step 3) is 25~200℃ and the condensation time is 30~600s.

[0012] Preferably, the purification process in step 3) is an alkaline treatment, wherein the alkaline solution is a sodium hydroxide solution with a mass fraction of 5-20%.

[0013] Preferably, the carrier gas for the chemical vapor deposition reaction in step 4) is nitrogen or a nitrogen-hydrogen mixture.

[0014] Preferably, in the chemical vapor deposition reaction described in step 4), the volume ratio of the feed gas to the carrier gas is 1:1~2, and the total gas flow rate of the feed gas and the carrier gas is 100~400mL / min.

[0015] Preferably, the temperature of the chemical vapor deposition reaction in step 4) is 700~900℃, and the time of the chemical vapor deposition reaction is 10~240min.

[0016] Preferably, the catalyst used in the chemical vapor deposition reaction in step 4) is a transition metal nanocatalyst.

[0017] The present invention also provides carbon nanotubes prepared by the method.

[0018] The beneficial effects of this invention are: This invention uses the non-condensable pyrolysis gas generated from the microwave pyrolysis of retired photovoltaic modules as a carbon source. By constructing a microwave pyrolysis system and regulating the pyrolysis gas, the complex pyrolysis gas generated from the microwave pyrolysis of retired photovoltaic modules can be used as a carbon source gas for chemical vapor deposition to prepare carbon nanotubes, realizing the high-value conversion of organic components of waste photovoltaic modules into carbon nanotubes. Through condensation and purification treatment, the condensable heavy components and fluorine-containing impurities in the pyrolysis gas are regulated to reduce the adverse effects of impurities on chemical vapor deposition, improve the applicability of the pyrolysis gas as a carbon source, and obtain carbon nanotubes with more obvious tubular structure characteristics, good morphological uniformity, good structural integrity, high purity and graphitization degree, and reduced surface irregular deposition. The liquid phase product obtained after condensation (condensable heavy components) can be used for subsequent recovery of valuable metals. Attached Figure Description

[0019] Figure 1 This is a schematic flowchart of the method of the present invention; Figure 2 The image shows a scanning electron microscope (SEM) image of the Ni / Fe co-supported Al2O3 catalyst used in the example. Figure 3 Scanning electron microscope image of the carbon nanotubes prepared in Example 1; Figure 4 The image shows the analysis of organic components in the pyrolysis gas of Example 1. Figure 5 Scanning electron microscope image of the carbon nanotubes prepared in Example 2; Figure 6 Scanning electron microscope image of the carbon nanotubes prepared in Example 3; Figure 7 Scanning electron microscope image of the carbon nanotubes prepared in Comparative Example 1; Figure 8 Scanning electron microscope image of the carbon nanotubes prepared in Comparative Example 2; Figure 9 The image shows a scanning electron microscope (SEM) image of the carbon nanomaterials prepared in Comparative Example 3. Detailed Implementation

[0020] This invention provides a method for preparing carbon nanotubes from decommissioned photovoltaic modules, comprising the following steps: 1) Disassemble retired photovoltaic modules to obtain photovoltaic laminates; 2) Microwave pyrolysis of the photovoltaic laminate generates pyrolysis gas; 3) The pyrolysis gas is sequentially condensed and purified to obtain the raw material gas; 4) Using the raw material gas as the carbon source gas, a chemical vapor deposition reaction is carried out to obtain carbon nanotubes.

[0021] In this invention, the disassembly in step 1) preferably includes removing the junction box and the aluminum frame.

[0022] In this invention, the microwave pyrolysis temperature in step 2) is preferably 400~900℃, more preferably 500~800℃, and even more preferably 600~700℃; the microwave pyrolysis frequency is preferably 500~3000MHz, more preferably 1000~2500MHz, and even more preferably 1500~2000MHz; the microwave pyrolysis power is preferably 0.5~20kW, more preferably 3~15kW, and even more preferably 5~10kW; and the microwave pyrolysis time is preferably 1~120min, more preferably 15~90min, and even more preferably 30~60min.

[0023] In this invention, the microwave pyrolysis in step 2) is preferably carried out in an air atmosphere, an inert atmosphere, an oxygen atmosphere, or a hydrogen atmosphere.

[0024] In this invention, the microwave pyrolysis in step 2) preferably decomposes the polymer encapsulation material in the photovoltaic laminate; The polymer encapsulation material preferably comprises an EVA film. During microwave pyrolysis, the EVA film generates a gas containing small-molecule hydrocarbons and some oxygen-containing organic components.

[0025] In this invention, the pyrolysis gas in step 2) is preferably a gas containing small molecule organic acids such as acetic acid.

[0026] In this invention, the inert atmosphere preferably comprises nitrogen and / or argon; The oxygen content in the oxygen atmosphere is preferably 1-50%, more preferably 5-40%, and even more preferably 10-30%. The hydrogen content in the hydrogen atmosphere is preferably 1-20%, more preferably 5-15%, and even more preferably 10%.

[0027] In this invention, the condensation temperature in step 3) is preferably 25~200℃, more preferably 50~150℃, and even more preferably 100℃; the condensation time is preferably 30~600s, more preferably 180~480s, and even more preferably 360s.

[0028] In this invention, the purification treatment in step 3) is preferably an alkaline treatment, wherein the alkaline solution is preferably a sodium hydroxide solution, and the mass fraction of the alkaline solution is preferably 5-20%, more preferably 10-18%, and even more preferably 12-15%. The purification treatment can remove hydrofluoric acid and other fluorine-containing components from the pyrolysis gas, reducing the adverse effects of impurities on the chemical vapor deposition reaction.

[0029] In this invention, after the condensation in step 3) is completed, condensable components and non-condensable gas are obtained. The non-condensable gas is purified to obtain raw material gas. The condensable component is preferably a liquid-phase product containing organic acids. The condensable component can be used for subsequent resource utilization.

[0030] In this invention, the carrier gas for the chemical vapor deposition reaction in step 4) is preferably nitrogen or a nitrogen-hydrogen mixture.

[0031] In this invention, in the chemical vapor deposition reaction described in step 4), the volume ratio of the feed gas to the carrier gas is preferably 1:1 to 2, more preferably 1:1.2 to 1.8, and even more preferably 1:1.5; the total gas flow rate of the feed gas and the carrier gas is preferably 100 to 400 mL / min, more preferably 200 to 300 mL / min, and even more preferably 250 mL / min.

[0032] In this invention, the temperature of the chemical vapor deposition reaction in step 4) is preferably 700~900℃, more preferably 750~850℃, and even more preferably 800℃; the time of the chemical vapor deposition reaction is preferably 10~240min, more preferably 60~200min, and even more preferably 120~180min.

[0033] In this invention, the catalyst used in the chemical vapor deposition reaction in step 4) is preferably a transition metal nanocatalyst.

[0034] In this invention, the transition metal in the transition metal nanocatalyst preferably includes iron and / or nickel.

[0035] The present invention also provides carbon nanotubes prepared by the method.

[0036] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0037] The retired photovoltaic modules used in the embodiments and comparative examples of this invention are derived from retired photovoltaic panels from crystalline silicon photovoltaic power plants. The catalyst used in the chemical vapor deposition reaction is a Ni / Fe co-supported Al2O3 catalyst, with a total Ni / Fe loading of 20%, wherein the Ni to Fe loading ratio is 1:1. The Ni / Fe co-supported Al2O3 catalyst is prepared by a chemical impregnation loading method. Figure 2 The image shows a scanning electron microscope (SEM) image of the Ni / Fe co-supported Al2O3 catalyst used in the example.

[0038] Example 1

[0039] Retired photovoltaic modules are mechanically disassembled, and the aluminum frame and junction box are removed to obtain a photovoltaic laminate composed of glass plate / EVA / cell / EVA / backsheet. The photovoltaic laminate is then cut and placed in a microwave pyrolysis apparatus for microwave pyrolysis treatment in air atmosphere. The microwave pyrolysis treatment temperature is 600℃, frequency is 1000MHz, power is 3kW, and time is 30min. During microwave pyrolysis, the polymer encapsulation materials (EVA film, etc.) in the photovoltaic laminate undergo pyrolysis, producing pyrolysis gas containing small molecule organic acids such as acetic acid. Simultaneously, the adhesion between the layers in the photovoltaic laminate weakens, making the photovoltaic laminate easier to separate and recycle. The pyrolysis gas is passed into a condenser and condensed at 25℃ for 30s, causing the condensable heavy components in the pyrolysis gas to condense and collecting the liquid phase products for resource utilization. The remaining non-condensable gas after condensation is purified by alkaline washing with a 10% sodium hydroxide solution to remove hydrofluoric acid and other fluorine-containing components, yielding raw material gas. Using raw gas as the carbon source gas and nitrogen as the carrier gas, with a volume ratio of 4:6 and a total gas flow rate of 200 mL / min, the carbon source gas and carrier gas were mixed and then passed into a tubular reactor containing a Ni / Fe co-supported Al2O3 catalyst. The chemical vapor deposition reaction was carried out at 700 °C for 180 min to obtain carbon nanotubes.

[0040] Figure 3 This is a scanning electron microscope (SEM) image of the carbon nanotubes prepared in Example 1. Figure 3 It can be seen that carbon nanotubes exhibit a relatively obvious tubular structure, with some areas showing continuously elongated tubular morphology.

[0041] Figure 4 This is an analytical diagram of the organic components in the pyrolysis gas of Example 1.

[0042] Example 2

[0043] Retired photovoltaic modules are mechanically disassembled, and the aluminum frame and junction box are removed to obtain a photovoltaic laminate composed of glass plate / EVA / solvent cells / EVA / backsheet. The photovoltaic laminate is then cut and placed in a microwave pyrolysis apparatus for microwave pyrolysis treatment in an oxygen atmosphere (10% oxygen by mass, the remainder nitrogen). The microwave pyrolysis treatment temperature is 700℃, frequency is 2000MHz, power is 10kW, and time is 20min. During microwave pyrolysis, the polymer encapsulation materials (EVA film, etc.) in the photovoltaic laminate undergo pyrolysis, producing pyrolysis gas containing small-molecule organic acids such as acetic acid. Simultaneously, the bonding between the layers in the photovoltaic laminate weakens, making the photovoltaic laminate easier to separate and recycle. The pyrolysis gas is then passed into a condenser and condensed at 100℃ for 360s, causing the condensable heavy components in the pyrolysis gas to condense and collecting the liquid products for resource utilization. The remaining non-condensable gas after condensation is purified by alkaline washing with a 15% sodium hydroxide solution to remove hydrofluoric acid and other fluorine-containing components, yielding the raw material gas. Using raw gas as the carbon source gas and nitrogen as the carrier gas, with a volume ratio of 4:6 and a total gas flow rate of 300 mL / min, the carbon source gas and carrier gas were mixed and then passed into a tubular reactor containing a Ni / Fe co-supported Al2O3 catalyst. The chemical vapor deposition reaction was carried out at 800 °C for 150 min to obtain carbon nanotubes.

[0044] Figure 5 This is a scanning electron microscope (SEM) image of the carbon nanotubes prepared in Example 2. Figure 5 It can be seen that carbon nanotubes exhibit a relatively obvious tubular structure, with some areas showing entangled tubular morphology, and some tube walls having relatively clear outlines and high morphological uniformity.

[0045] Example 3

[0046] Retired photovoltaic modules are mechanically disassembled, and the aluminum frame and junction box are removed to obtain a photovoltaic laminate composed of glass plate / EVA / solvent cells / EVA / backsheet. The photovoltaic laminate is then cut and placed in a microwave pyrolysis apparatus for microwave pyrolysis treatment in an oxygen atmosphere (18% oxygen by mass, the remainder nitrogen). The microwave pyrolysis treatment temperature is 800℃, frequency is 3000MHz, power is 15kW, and time is 15min. During microwave pyrolysis, the polymer encapsulation materials (EVA film, etc.) in the photovoltaic laminate undergo pyrolysis, producing pyrolysis gas containing small-molecule organic acids such as acetic acid. Simultaneously, the bonding between the layers in the photovoltaic laminate weakens, making the photovoltaic laminate easier to separate and recycle. The pyrolysis gas is passed into a condenser and condensed at 50℃ for 240s, causing the condensable heavy components in the pyrolysis gas to condense and collecting the liquid phase products for resource utilization. The remaining non-condensable gas after condensation is purified by alkaline washing with a 20% sodium hydroxide solution to remove hydrofluoric acid and other fluorine-containing components, yielding raw material gas. Using raw gas as the carbon source gas and nitrogen as the carrier gas, with a volume ratio of 4:6 and a total gas flow rate of 400 mL / min, the carbon source gas and carrier gas were mixed and then passed into a tubular reactor containing a Ni / Fe co-supported Al2O3 catalyst. The chemical vapor deposition reaction was carried out at 900 °C for 120 min to obtain carbon nanotubes.

[0047] Figure 6 This is a scanning electron microscope (SEM) image of the carbon nanotubes prepared in Example 3. Figure 6 It can be seen that carbon nanotubes with obvious tubular structures can still be obtained at relatively high microwave pyrolysis temperatures and chemical vapor deposition temperatures. Combined with... Figure 3 , Figure 5 and Figure 6 This indicates that the pyrolysis gas from the microwave pyrolysis of retired photovoltaic modules, after condensation and purification, can be used as a raw material gas for catalytic vapor deposition to prepare carbon nanotubes, and is beneficial for the formation of tubular carbon materials.

[0048] Comparative Example 1

[0049] The difference from Example 2 is that the remaining non-condensed gas after condensation is used as the carbon source gas and nitrogen is used as the carrier gas. The volume ratio of the carbon source gas to the carrier gas is 4:6, and the total gas flow rate is 300 mL / min. After the carbon source gas and the carrier gas are mixed, they are introduced into a tubular reactor containing a Ni / Fe co-supported Al2O3 catalyst. The chemical vapor deposition reaction is carried out at 800°C for 150 min to obtain carbon nanotubes.

[0050] Figure 7 This is a scanning electron microscope (SEM) image of the carbon nanotubes prepared in Comparative Example 1. Figure 7 It can be seen that the tubular structure of carbon nanotubes is not obvious, and the morphological uniformity is poor, with a lot of irregular deposition on the surface.

[0051] Comparative Example 2

[0052] The difference from Example 2 is that pyrolysis gas is used as the carbon source gas and nitrogen is used as the carrier gas. The volume ratio of carbon source gas to carrier gas is 4:6 and the total gas flow rate is 300 mL / min. After the carbon source gas and carrier gas are mixed, they are introduced into a tubular reactor containing a Ni / Fe co-supported Al2O3 catalyst. Chemical vapor deposition reaction is carried out at 800°C for 150 min to obtain carbon nanotubes.

[0053] Figure 8 This is a scanning electron microscope (SEM) image of the carbon nanotubes prepared in Comparative Example 2. Figure 8 It can be seen that the tubular structure of carbon nanotubes is not obvious, and the tubular structure is weaker than that of Comparative Example 1. Furthermore, the morphological uniformity is worse, and the irregular deposition phenomenon on the surface is more obvious.

[0054] Comparative Example 3

[0055] Retired photovoltaic modules are mechanically disassembled, and the aluminum frames and junction boxes are removed to obtain a photovoltaic laminate composed of a glass plate, EVA, solar cells, and a backsheet. The photovoltaic laminate is then cut and placed in a pyrolysis apparatus, which is heated externally by a resistance furnace at 700°C for 20 minutes to generate pyrolysis gas. This pyrolysis gas is then passed into a condensation device and condensed at 200°C for 300 seconds, allowing condensable heavy components to condense and collecting the liquid products for resource utilization. The remaining non-condensable gas is then purified by alkaline washing with a 15% sodium hydroxide solution to remove hydrofluoric acid and other fluorine-containing components, yielding a feed gas. Using raw gas as the carbon source gas and nitrogen as the carrier gas, with a volume ratio of 4:6 and a total gas flow rate of 300 mL / min, the carbon source gas and carrier gas were mixed and then introduced into a tubular reactor containing a Ni / Fe co-supported Al2O3 catalyst. The chemical vapor deposition reaction was carried out at 800 °C for 150 min to obtain carbon nanomaterials.

[0056] Figure 9 This is a scanning electron microscope (SEM) image of the carbon nanomaterials prepared in Comparative Example 3. Figure 9 It can be seen that carbon nanomaterials have no obvious tubular structure features, poor morphological uniformity, and obvious irregular deposition on the surface.

[0057] As can be seen from the above embodiments, the present invention provides a method for preparing carbon nanotubes from decommissioned photovoltaic modules. The photovoltaic laminates after the decommissioned photovoltaic modules are disassembled are subjected to microwave pyrolysis to generate pyrolysis gas. After condensation and purification, the pyrolysis gas can be used as a carbon source gas for chemical vapor deposition to prepare carbon nanotubes. The carbon nanotubes obtained have obvious tubular structure characteristics, good morphological uniformity, high purity and high degree of graphitization, and no obvious irregular deposition on the surface.

[0058] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing carbon nanotubes from decommissioned photovoltaic modules, characterized in that, It includes the following steps: 1) Disassemble retired photovoltaic modules to obtain photovoltaic laminates; 2) Microwave pyrolysis of the photovoltaic laminate generates pyrolysis gas; 3) The pyrolysis gas is sequentially condensed and purified to obtain the raw material gas; 4) Using the raw material gas as the carbon source gas, a chemical vapor deposition reaction is carried out to obtain carbon nanotubes.

2. The method for preparing carbon nanotubes from decommissioned photovoltaic modules according to claim 1, characterized in that, Step 2) The microwave pyrolysis temperature is 400~900℃, the microwave pyrolysis frequency is 500~3000MHz, the microwave pyrolysis power is 0.5~20kW, and the microwave pyrolysis time is 1~120min.

3. The method for preparing carbon nanotubes from decommissioned photovoltaic modules according to claim 1 or 2, characterized in that, Step 2) The microwave pyrolysis is carried out in an air atmosphere, an inert atmosphere, an oxygen atmosphere, or a hydrogen atmosphere.

4. The method for preparing carbon nanotubes from decommissioned photovoltaic modules according to claim 3, characterized in that, Step 3) The condensation temperature is 25~200℃, and the condensation time is 30~600s.

5. The method for preparing carbon nanotubes from decommissioned photovoltaic modules according to claim 4, characterized in that, Step 3) The purification process involves treatment with an alkaline solution, which is a sodium hydroxide solution with a mass fraction of 5-20%.

6. The method for preparing carbon nanotubes from decommissioned photovoltaic modules according to claim 4 or 5, characterized in that, Step 4) The carrier gas for the chemical vapor deposition reaction is nitrogen or a nitrogen-hydrogen mixture.

7. The method for preparing carbon nanotubes from decommissioned photovoltaic modules according to claim 6, characterized in that, In step 4), the volume ratio of feed gas to carrier gas in the chemical vapor deposition reaction is 1:1~2, and the total gas flow rate of feed gas and carrier gas is 100~400mL / min.

8. The method for preparing carbon nanotubes from decommissioned photovoltaic modules according to claim 7, characterized in that, Step 4) The temperature of the chemical vapor deposition reaction is 700~900℃, and the time of the chemical vapor deposition reaction is 10~240min.

9. The method for preparing carbon nanotubes from decommissioned photovoltaic modules according to claim 7 or 8, characterized in that, Step 4) The catalyst used in the chemical vapor deposition reaction is a transition metal nanocatalyst.

10. Carbon nanotubes prepared by the method according to any one of claims 1 to 9.

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