Preparation method of carbon nano tube with ultra-large tube diameter

Abstract

The invention relates to the technical field of preparation of carbon nanotube materials, and provides a preparation method of an ultra-large-diameter carbon nanotube, which comprises the following steps of: adhering an active substance and an accelerant on the surface of fumed silica to form a catalyst precursor, performing high-temperature annealing treatment, adding the catalyst into a fluidized bed or a CVD (Chemical Vapor Deposition) tubular furnace reactor for reaction, and performing vacuum drying to obtain the ultra-large-diameter carbon nanotube. And after the reaction is completed, carrying out pre-oxidation treatment, and finally, carrying out acid pickling purification to obtain the high-purity ultra-large-diameter carbon nanotube. According to the method, the particle size of the catalyst is regulated and controlled by controlling the concentration of ammonium carbonate, so that the pipe diameter is spanned from a traditional carbon nanotube to an ultra-large pipe diameter. The problems of catalyst particle aggregation, environmental pollution and the like in a traditional method are solved, the ammonium carbonate concentration scheme is optimized, the optimal catalyst complexing condition is realized, and an efficient and controllable process scheme is provided for preparation of the ultra-large-diameter carbon nanotube.

Description

Technical Field

[0001] The invention relates to the technical field of carbon nanotube material preparation, and in particular to a method for preparing ultra-large diameter carbon nanotubes. Background Art

[0002] Carbon is one of the most abundant elements in nature. Carbon atoms can form complex cross-linked network structures, which are essential for the existence of organic chemistry and life. Carbon material is a special material that can exist in nature in zero-dimensional to three-dimensional forms. In addition, carbon allotropes have different physical and chemical properties. From superhard material diamond to soft material graphite, from insulating material diamond to semiconductor material graphite to conductive material carbon nanotubes, carbon allotropes play an important role. Although carbon allotropes have different structures and properties, there is a magical carbon allotrope that occupies a unique and special position in the field of materials, which is carbon nanotubes. Carbon nanotubes have great advantages in the fields of biosensors, lithium-ion batteries, drug delivery materials, composite materials, etc.

[0003] Large-diameter carbon nanotubes are a type of carbon-based nanomaterial with a diameter ranging from 100 nanometers to microns. Compared with conventional materials, large-diameter carbon nanotubes have better conductivity than vapor-grown carbon fibers, mechanical properties with tensile strength >4GPa, and better dispersion (low specific surface area reduces agglomeration). Large-diameter carbon nanotubes show broad prospects in new energy, composite materials, electronic devices and other fields. Studies have shown that as a conductive additive for lithium batteries, they can increase energy density by more than 20%, and can reduce weight by 30% and enhance structural strength when used in aerospace composites. They are also irreplaceable in chip heat dissipation, flexible sensors and bio-drug delivery systems. They fill the performance gap between nanomaterials and macroscopic materials, solve the pain points of high cost and difficult dispersion of traditional carbon fibers, and are expected to become a core component of the next generation of high-performance materials, promoting technological innovation in multiple fields.

[0004] In the preparation process of large-diameter carbon nanotubes, the core breakthrough direction is to achieve a leap in tube diameter from traditional carbon nanotubes (<100nm) to carbon fiber scale (>1μm) through catalyst design and dynamic process control (staged carbon source introduction, gradient annealing).

[0005] As the application publication number CN103721750B discloses a catalyst for preparing large-diameter carbon nanotubes, which is prepared from raw materials with the following weight percentages: lanthanum nitrate 5.6% - 47.8%, cobalt nitrate 2.3% - 39.5%, iron nitrate 1.7% - 46.7%, calcium nitrate 2.7% - 41.6%, citric acid 2.7% - 41.6%, and ethylenediaminetetraacetic acid 2.7% - 41.6%. This patent also discloses a preparation method for the catalyst of large-diameter carbon nanotubes. Adding large-diameter carbon nanotubes to the positive electrode of the battery has significantly better performance than traditional graphite and small-diameter carbon nanotubes. The lower resistivity is significantly helpful for reducing the internal resistance of the battery electrode sheet, that is, it can improve the cycle life of the battery and the energy density of the battery. The smaller specific surface area makes it easier to disperse carbon nanotubes.

[0006] Although this method can achieve the preparation of large-diameter carbon nanotubes, the tube diameters are basically distributed below 150 nm, which is difficult to meet the application scenarios that require larger-diameter carbon nanotubes. Moreover, the preparation method uses sol-gel, which causes greater environmental pollution, and the auxiliary agent EDTA used has greater harm to the environment and the human body. The loose bulk density of the catalyst prepared by this method is small and fluffy, and there are relatively large problems in practical applications.

[0007] The present invention prepares high-quality ultra-large-diameter carbon nanotubes through a special catalyst preparation process. The tube diameters are distributed between 180 - 380 nm. Using the corresponding reactor process, the tube diameter can reach 500 nm. Further treatment can be used as the final product, maximizing the retention of its good structure to ensure the performance. It can be applied as a conductive additive for various materials and has excellent heat conduction and strengthening effects. Summary of the Invention

[0008] To solve the problems in the background technology, the present invention provides a preparation method for ultra-large-diameter carbon nanotubes, including the following steps:

[0009] S1. Attach active substances and promoters on the surface of fumed silica to make a catalyst precursor;

[0010] S2. Filter and dry the precursor solution;

[0011] S3. Perform high-temperature annealing treatment on the dried precursor;

[0012] S4. Add the precursor completed with high-temperature annealing treatment as a catalyst into a fluidized bed or a CVD tube furnace reactor for reaction;

[0013] S5. Perform pre-oxidation treatment after the reaction is completed to obtain ultra-large-diameter carbon nanotube raw powder;

[0014] S6. Purify the carbon nanotube raw powder by pickling to obtain high-purity ultra-large-diameter carbon nanotubes.

[0015] In a preferred embodiment, the specific process of step S1 includes: soaking the fumed silica with a nickel nitrate solution of 0.2 - 0.5 g / ml, titrating with an ammonium carbonate solution of 0.02 - 0.06 g / ml, and carrying out a sufficient reaction.

[0016] In a preferred embodiment, the specific process of step S1 includes: soaking the fumed silica with a nickel nitrate solution of 0.2 - 0.5 g / ml for 20 min, titrating with an ammonium carbonate solution of 0.04 g / ml, and carrying out a sufficient reaction for 30 min.

[0017] In a preferred embodiment, in step S2, after filtration, it is dried at 120 °C for 180 min.

[0018] In a preferred embodiment, in step S3, after drying, it is added to a double-chamber heating furnace for high-temperature annealing treatment. The heating rate is 10 °C / min for the first 500 °C, and the heating rate increases by 5 °C / min from 500 - 900 °C until the heating rate reaches 55 °C / min, then it is heated at a constant rate to 900 °C and held at a constant temperature for 30 min, and then naturally cooled to room temperature.

[0019] In a preferred embodiment, in step S4, the step S41 of using the precursor after high-temperature annealing treatment as a catalyst and adding it to a fluidized bed reactor for reaction is as follows:

[0020] S411. Reactor preheating: Under a nitrogen protection atmosphere, the fluidized bed reactor is heated to 660 °C; the low-temperature preheater is heated to 500 °C to preheat hydrogen and propylene gases; the high-temperature preheater is heated to 850 °C to fully crack the carbon source gas.

[0021] S412. Catalyst addition and fluidization: The precursor after high-temperature annealing is used as a catalyst and added to the fluidized bed reactor; nitrogen is introduced to make the catalyst particles in a suspended fluidized state.

[0022] S413. Reduction reaction: Hydrogen is introduced, and the metal oxide in the catalyst is reduced to active elemental form at 660 °C until the reduction is completed; during this process, the carbon source is introduced in stages; in the first 5 minutes: propylene is used as the carbon source and introduced at a flow rate of 10 L / min to initiate the nucleation of carbon nanotubes; in the middle 10 minutes: the propylene flow rate is increased to 35 L / min to promote the rapid growth of carbon tubes; in the last 5 minutes: the propylene flow rate is reduced to 20 L / min to optimize the wall structure integrity; the total reaction time is 20 minutes, and hydrogen is introduced as the reducing gas throughout the process; after the reaction is completed, the supply of propylene is stopped, and nitrogen is introduced for 5 minutes to remove the residual gas in the reactor.

[0023] In a preferred embodiment, in step S4, the step S42 of adding the precursor after high-temperature annealing treatment as a catalyst into the CVD tube furnace reactor for reaction is as follows:

[0024] S421. Reactor preheating: Under a nitrogen protection atmosphere, heat the CVD tube furnace reactor to 660 °C; heat the low-temperature preheater to 500 °C for preheating hydrogen and propylene gases; heat the high-temperature preheater to 850 °C to fully crack propylene into active carbon atoms.

[0025] S422. Catalyst loading: Use the precursor after high-temperature annealing as a catalyst and evenly spread it on the quartz boat, and place it in the constant-temperature zone of the reaction tube.

[0026] S423. Reduction reaction: Introduce hydrogen and nitrogen, and complete the reduction of the catalyst at 660 °C. During this process, the carbon source is introduced in stages; in the first 5 minutes: propylene is introduced at a flow rate of 10 L / min, which is the nucleation stage of the carbon tube; in the middle 10 minutes: the flow rate of propylene is increased to 35 L / min, which is the main growth stage; in the last 5 minutes: the flow rate of propylene is reduced to 20 L / min, which is the structure optimization stage; the total reaction time is 20 minutes, and hydrogen is introduced throughout the process; after the reaction is completed, stop the supply of propylene and continue to introduce nitrogen for 5 minutes to purge the gas in the reaction tube.

[0027] In a preferred embodiment, the specific process of step S5 includes: Under positive nitrogen pressure protection, transport the product of step S4 to the pre-oxidation equipment; mix nitrogen and air in a volume ratio of 1:1 and oxidize at 500 °C for 20 minutes, and then transfer it to the storage tank after completion.

[0028] In a preferred embodiment, the specific process of step S6 includes:

[0029] S61. Put the pre-oxidized product into the configured acidic solution with a specific concentration to remove the residual reaction metal while stripping the product, and wash and filter it twice.

[0030] S62. Put the product obtained after filtration into the acidic solution with a specific concentration for a second time for impurity removal.

[0031] S63. Wash the product after impurity removal and filtration. After the pH is close to 7.0, filter and dry it.

[0032] In a preferred embodiment, in S61, the mass ratio of the product to the acidic components in the acidic solution with a specific concentration is set according to the following ratio:

[0033] Product: Hydrochloric acid: Nitric acid: Hydrofluoric acid = 1:2:1:0.5;

[0034] In S62, the mass ratio of the product to the acidic components in the acidic solution with a specific concentration is set according to the following ratio:

[0035] Product: Hydrochloric acid:Nitric acid:Hydrofluoric acid = 1:1:0.5:0.25.

[0036] The beneficial effects achieved by the present invention are as follows:

[0037] First, the present invention uses fumed silica as a catalyst support, and forms uniformly dispersed nickel active particles through the complexation reaction of nickel nitrate and ammonium carbonate. Compared with the traditional sol-gel method (such as the use of EDTA in the background technology), harmful chemical substances are avoided, and by controlling the concentration of ammonium carbonate (0.02 - 0.06 g / ml), the size of catalyst particles is regulated, achieving a pipe diameter of 180 - 380 nm (fluidized bed process) to 520 nm (CVD process), far exceeding the prior art (<150 nm in the background technology).

[0038] Second, by adding the ammonium carbonate solution (0.02 - 0.06 g / ml) in stages, the complexation equilibrium of nickel ions and carbonate ions is accurately regulated to form a stable soluble complex, rather than directly generating a precipitate. This process is verified by Example 12, solving the problem of catalyst particle agglomeration in the traditional process.

[0039] Third, the double-chamber heating furnace adopts a staged heating strategy (10 °C / min for the first 500 °C, and the heating rate is gradually increased to 55 °C / min from 500 - 900 °C), realizing the lattice reorganization of catalyst particles and the formation of high-active sites. Compared with the traditional constant heating rate process, the thermal stability and activity of the catalyst are significantly improved.

[0040] Fourth, in the fluidized bed / CVD reactor, the propylene flow rate is regulated in three stages (nucleation stage: 10 L / min, growth stage: 35 L / min, optimization stage: 20 L / min), corresponding to the nucleation, rapid growth, and structure optimization of carbon nanotubes. Compared with the traditional single-stage feeding, the generation of amorphous carbon is reduced, and the crystallinity of the tube wall is improved. The parallel selection of the fluidized bed and the CVD tube furnace realizes high yield through the fluidized bed and an ultra-large pipe diameter (520 nm) through CVD, flexibly meeting different application requirements.

[0041] Fifth, pre-oxidation with a nitrogen-air mixture (500 °C) is used to remove amorphous carbon, combined with two-stage pickling (Hydrochloric acid:Nitric acid:Hydrofluoric acid = 1:2:1:0.5 → 1:1:0.5:0.25), while removing metal impurities, the structural integrity of the carbon tubes is retained. Compared with the traditional single pickling, the metal residue rate is reduced to <0.5 wt%.

[0042] Sixth, through the regulation of ammonium carbonate concentration (0.02 - 0.06 g / ml) in the present invention, the tube diameter shows predictable changes (such as 0.02 g / ml → 240 nm, 0.04 g / ml → 380 nm), meeting the requirements of different application scenarios. Through a large number of experiments, the technical solution of selecting 0.04 g / ml ammonium carbonate concentration is obtained in the present invention, achieving the maximum tube diameter of 380 nm, and the BET specific surface area is 43.23 m 2 / g, providing the optimal complexation conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Flow chart showing the preparation method of super-large diameter carbon nanotubes.

[0044] Appendix Figure 2 Showing the macroscopic morphology and microscopic structure (scanning electron microscope image) of the super-large diameter carbon nanotubes prepared in Example 1, presenting the basic morphology of the carbon nanotubes.

[0045] Appendix Figure 3 Showing the microscopic structure of the product of Example 2, which is an enlarged image of the sampling area, showing a more detailed tube diameter distribution. Figure 2 Showing the microscopic structure of the product of Example 2, which is an enlarged image of the sampling area, showing a more detailed tube diameter distribution.

[0046] Appendix Figure 4 Showing the microscopic structure (scanning electron microscope image) of the product of Example 3, demonstrating the morphology of the carbon nanotubes after adjustment with different concentrations of ammonium carbonate.

[0047] Appendix Figure 5 Showing the microscopic structure (scanning electron microscope image) of the product of Example 4, presenting the tube diameter and length distribution of the carbon nanotubes.

[0048] Appendix Figure 6 Showing the microscopic structure (scanning electron microscope image) of the product of Example 5, demonstrating the morphology of the carbon nanotubes under the condition of higher concentration of ammonium carbonate.

[0049] Appendix Figure 7 Showing the microscopic structure (scanning electron microscope image) of the product of Example 6, presenting the morphology and distribution of short and thick carbon nanotubes.

[0050] Appendix Figure 8 Showing the microscopic structure (scanning electron microscope image) of the product of Example 7, demonstrating the morphology of the carbon nanotubes under the condition of high concentration of ammonium carbonate.

[0051] Appendix Figure 9 Showing the microscopic structure (scanning electron microscope image) of the product of Example 8, presenting the morphology of the product under the condition of low concentration of ammonium carbonate.

[0052] Appendix Figure 10 Showing the microscopic structure (scanning electron microscope image) of the product of Example 9, demonstrating the morphology of carbon-coated particles under the condition of extremely low concentration of ammonium carbonate.

[0053] Appendix Figure 11 Showing the microstructure of the product of Example 10 (scanning electron microscope image), the morphology of carbon nanotubes after replacing fumed silica with magnesium nitrate.

[0054] Appendix Figure 12 Showing the microstructure of the product of Example 11 (scanning electron microscope image), the morphology of carbon nanotubes prepared using a CVD tube furnace reactor.

[0055] Appendix Figure 13 is Figure 2 An enlarged view of the microstructure of ultra-large diameter carbon nanotubes;

[0056] Appendix Figure 14 is the diagram of the reactant state during the reaction process in Example 12. Detailed implementation manners

[0057] Next, in combination with the accompanying drawings in the present invention, the technical solutions in the present invention will be clearly and completely described. In addition, the forms of the various structures described in the following embodiments are merely examples, and the present invention is not limited to the various structures described in the following embodiments. All other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0058] Referring to Figure 1 , the present invention designs a preparation method for ultra-large diameter carbon nanotubes, including the following steps:

[0059] S1. Attach active substances and promoters to the surface of fumed silica to produce a catalyst precursor; the specific process of step S1 includes: soaking fumed silica with a nickel nitrate solution of 0.2 - 0.5 g / ml, and then titrating with an ammonium carbonate solution of 0.02 - 0.06 g / ml, and reacting fully. The preferred specific process of step S1 is: soaking fumed silica with a nickel nitrate solution of 0.2 - 0.5 g / ml for 20 min, then titrating with an ammonium carbonate solution of 0.02 - 0.06 g / ml, and reacting fully for 30 min.

[0060] S2. Filter and dry the precursor solution; in step S2, after filtration, dry at a temperature of 120 °C for 180 min.

[0061] S3. Perform high-temperature annealing treatment on the dried precursor; in step S3, after drying, add it to a double-chamber heating furnace for high-temperature annealing treatment. The heating rate in the first 500 °C is 10 °C / min, and the heating rate increases by 5 °C / min from 500 - 900 °C until the heating rate reaches 55 °C / min, then heat up to 900 °C at a constant speed, keep the temperature constant for 30 min, and then cool naturally to room temperature.

[0062] S4. Add the precursor after high-temperature annealing treatment as a catalyst into a fluidized bed or a CVD tube furnace reactor for reaction; in step S4, the steps of adding the precursor after high-temperature annealing treatment as a catalyst into a fluidized bed reactor for reaction, i.e., S41, are as follows:

[0063] S411. Reactor preheating: Under a nitrogen protection atmosphere, heat the fluidized bed reactor to 660 °C; heat the low-temperature preheater to 500 °C to preheat hydrogen and propylene gases; heat the high-temperature preheater to 850 °C to fully crack the carbon source gas.

[0064] S412. Catalyst addition and fluidization: Add the precursor after high-temperature annealing as a catalyst into the fluidized bed reactor; introduce nitrogen to keep the catalyst particles in a suspended fluidized state.

[0065] S413. Reduction reaction: Introduce hydrogen and reduce the metal oxide in the catalyst to active elemental form at 660 °C until the reduction is completed; during this process, the carbon source is introduced in stages; in the first 5 minutes: Propylene is introduced as the carbon source at a flow rate of 10 L / min to initiate the nucleation of carbon nanotubes; in the middle 10 minutes: The flow rate of propylene is increased to 35 L / min to promote the rapid growth of carbon tubes; in the last 5 minutes: The flow rate of propylene is reduced to 20 L / min to optimize the structural integrity of the tube wall; total reaction time: 20 minutes, hydrogen is introduced throughout as the reducing gas; after the reaction is completed, stop the supply of propylene and continue to introduce nitrogen for 5 minutes to remove the residual gas in the reactor.

[0066] In step S4, the steps of adding the precursor after high-temperature annealing treatment as a catalyst into a CVD tube furnace reactor for reaction, i.e., S42, are as follows:

[0067] S421. Reactor preheating: Under a nitrogen protection atmosphere, heat the CVD tube furnace reactor to 660 °C; heat the low-temperature preheater to 500 °C for preheating hydrogen and propylene gases; heat the high-temperature preheater to 850 °C to fully crack propylene into active carbon atoms.

[0068] S422. Catalyst loading: Evenly lay the precursor after high-temperature annealing as a catalyst in a quartz boat and place it in the constant temperature zone of the reaction tube.

[0069] S423. Reduction reaction: Introduce hydrogen and nitrogen and complete the reduction of the catalyst at 660 °C; during this process, the carbon source is introduced in stages; in the first 5 minutes: Propylene is introduced at a flow rate of 10 L / min, which is the carbon tube nucleation stage; in the middle 10 minutes: The flow rate of propylene is increased to 35 L / min, which is the main growth stage; in the last 5 minutes: The flow rate of propylene is reduced to 20 L / min, which is the structure optimization stage; the total reaction time is 20 minutes, and hydrogen is introduced throughout; after the reaction is completed, stop the supply of propylene and continue to introduce nitrogen for 5 minutes to remove the gas in the reaction tube.

[0070] S5. After the reaction is completed, pre-oxidation treatment is carried out to obtain the original powder of ultra-large-diameter carbon nanotubes. The specific process of step S5 includes: under the protection of positive nitrogen pressure, the product of step S4 is transported to the pre-oxidation equipment; nitrogen and air are mixed at a volume ratio of 1:1 and oxidized at 500 °C for 20 minutes, and then transferred to a storage tank after completion.

[0071] S6. The original powder of carbon nanotubes is purified by acid washing to obtain high-purity ultra-large-diameter carbon nanotubes. The specific process of step S6 includes:

[0072] S61. The pre-oxidized product is put into a configured acidic solution with a specific concentration to remove the residual reaction metals while stripping the product, and then washed and filtered twice with water;

[0073] S62. The product obtained after filtration is put into the acidic solution with a specific concentration again for impurity removal;

[0074] S63. The product after impurity removal and filtration is washed with water. After the pH is close to 7.0, it is filtered and dried.

[0075] In S61, the mass ratio of the product to the acidic components in the acidic solution with a specific concentration is set according to the following ratio:

[0076] Product: Hydrochloric acid: Nitric acid: Hydrofluoric acid = 1:2:1:0.5;

[0077] In S62, the mass ratio of the product to the acidic components in the acidic solution with a specific concentration is set according to the following ratio:

[0078] Product: Hydrochloric acid: Nitric acid: Hydrofluoric acid = 1:1:0.5:0.25;

[0079] Example 1: A method for preparing ultra-large-diameter carbon nanotubes in this example includes the following steps:

[0080] Step 1: Preparation of the precursor. Select a nickel nitrate solution with a concentration of 0.2 g / ml, a total of 2 L of the solution, soak 10 g of fumed silica, and after 20 minutes, titrate with an ammonium carbonate solution with a concentration of 0.02 g / ml, add 0.2 L, and react for 30 minutes after the titration is completed;

[0081] Step 2: Filter the solution after the reaction is completed, and dry the attached catalyst precursor at 120 °C for 180 minutes;

[0082] Step 3: After drying, put it into a double-chamber heating furnace for high-temperature annealing treatment. The heating rate in the first 500 °C is 10 °C / min, and the heating rate from 500 to 900 °C increases by 5 °C / min until the heating rate reaches 55 °C / min, then heat up to 900 °C at a constant speed, keep the temperature constant for 30 minutes, and naturally cool down to room temperature to obtain the catalyst;

[0083] Step 4: After the completion of the treatment, the fluidized bed reactor is heated to 660 °C while introducing a protective gas, the low-temperature preheater is heated to 500 °C, and the high-temperature preheater is heated to 850 °C. After the temperature rise is completed, 10 g of catalyst is added, and then a carrier gas, a reducing gas, and a carbon source are quantitatively introduced for reaction (the reduction reaction is carried out first, and then the carbon source is introduced after the end). The quantitative amount of the carrier gas is 80 L / min, the quantitative amount of the reducing gas is 40 L / min, and the quantitative amount of the carbon source is 10 L / min in the first 5 min, 35 L / min in the middle 10 min, and 20 L / min in the last 5 min. The reaction time is 20 min. The carbon source gas is propylene, the reducing gas is hydrogen, and the protective gas and the carrier gas are nitrogen. After the reaction is completed, the supply of the carbon source gas is stopped. After the carrier gas is introduced for 5 min, positive pressure feeding to the pre-oxidation equipment is started to complete this preparation, and the next preparation is started;

[0084] Step 5: After the material is transported to the pre-oxidation equipment, pre-oxidation treatment is started. Nitrogen:Air = 1:2, temperature 500 °C, time 20 min. After pre-oxidation is completed, it is transported to the storage tank to obtain 117 g of the product;

[0085] Step 6: The pre-oxidized product is put into a configured acidic solution with a specific concentration (product:hydrochloric acid:nitric acid:hydrofluoric acid = 1:2:1:0.5) to remove the residual reaction metals while stripping the product, and it is washed and filtered twice; the product obtained after filtration is put into an acidic solution with a specific concentration (product:hydrochloric acid:nitric acid:hydrofluoric acid = 1:1:0.5:0.25) for impurity removal; after impurity removal and filtration, the product is washed with water. After the pH is close to 7.0, it is filtered and dried to obtain 105 g of the product, that is, high-purity ultra-large-diameter carbon nanotubes. (See the attached Figure 2 )

[0086] Example 2: The difference between this example and Example 1 is that the concentration of ammonium carbonate in Step 1 is increased from 0.02 g / ml to 0.03 g / ml. Other steps and parameters are the same as those in Example 1. After the reaction is completed, 140 g of the product before purification and 125 g of the product after purification are obtained. See the attached Figure 3 。

[0087] Example 3: The difference between this example and Example 1 is that the concentration of ammonium carbonate in Step 1 is increased from 0.02 g / ml to 0.04 g / ml. Other steps and parameters are the same as those in Example 1. After the reaction is completed, 195 g of the product before purification and 177 g of the product after purification are obtained. See the attached Figure 4 。

[0088] Example 4: The difference between this example and Example 1 is that the concentration of ammonium carbonate in Step 1 is increased from 0.02 g / ml to 0.05 g / ml. Other steps and parameters are the same as those in Example 1. After the reaction, 121 g of the product before purification and 101 g of the product after purification are obtained. The micro-structure is shown in the appendix Figure 5 。

[0089] Example 5: The difference between this example and Example 1 is that the concentration of ammonium carbonate in Step 1 is increased from 0.02 g / ml to 0.06 g / ml. Other steps and parameters are the same as those in Example 1. After the reaction, 82 g of the product before purification and 69 g of the product after purification are obtained. The micro-structure is shown in the appendix Figure 6 。

[0090] Example 6: The difference between this example and Example 1 is that the concentration of ammonium carbonate in Step 1 is increased from 0.02 g / ml to 0.07 g / ml. Other steps and parameters are the same as those in Example 1. After the reaction, 45 g of the product before purification and 39 g of the product after purification are obtained. The micro-structure is shown in the appendix Figure 7 。

[0091] Example 7: The difference between this example and Example 1 is that the concentration of ammonium carbonate in Step 1 is increased from 0.02 g / ml to 0.08 g / ml. Other steps and parameters are the same as those in Example 1. After the reaction, 31 g of the product before purification and 19 g of the product after purification are obtained. The micro-structure is shown in the appendix Figure 8 。

[0092] Example 8: The difference between this example and Example 1 is that the concentration of ammonium carbonate in Step 1 is decreased from 0.02 g / ml to 0.01 g / ml. Other steps and parameters are the same as those in Example 1. After the reaction, 22 g of the product before purification and 15 g of the product after purification are obtained. The micro-structure is shown in the appendix Figure 9 。

[0093] Example 9: The difference between this example and Example 1 is that the concentration of ammonium carbonate in Step 1 is decreased from 0.02 g / ml to 0.005 g / ml. Other steps and parameters are the same as those in Example 1. After the reaction, 13 g of the product before purification and 8 g of the product after purification are obtained. The micro-structure is shown in the appendix Figure 10 。

[0094] Example 10: The difference between this example and Example 1 is that the fumed silica in Step 1 is replaced by magnesium nitrate. Other steps and parameters are the same as those in Example 1. After the reaction, 55 g of the product before purification and 41 g of the product after purification are obtained. The micro-structure is shown in the appendix Figure 11 。

[0095] Example 11: The difference between this example and Example 3 is that the fluidized bed reactor in Step 4 is replaced with a CVD tube furnace reactor. Other steps and parameters are the same as those in Example 3. After the reaction, 225 g of the product before purification and 200 g of the product after purification are obtained. The microstructure is shown in the appendix Figure 12 . The specific process is as follows:

[0096] Step S1: Preparation of catalyst precursor;

[0097] First, prepare 2 L of nickel nitrate solution with a concentration of 0.2 g / ml, immerse 10 g of fumed silica in it, and continuously soak for 20 minutes to allow the carrier to fully adsorb the active component. Subsequently, titrate 0.2 L (the same concentration as in Example 3) with ammonium carbonate solution at a concentration of 0.04 g / ml. During the titration process, slow stirring is required to ensure uniform reaction. After the titration is completed, continue to react for 30 minutes to allow the nickel ions to fully combine with ammonium carbonate to form a stable catalyst precursor complex.

[0098] Step S2: Filtration and drying of the precursor;

[0099] After the reaction, separate the solution and the solid carrier loaded with the catalyst through a filtration device to remove the unreacted residual liquid. Place the filtered precursor in an oven at 120 °C and continuously dry for 180 minutes to ensure that the catalyst precursor is completely dry and avoid structural defects caused by residual moisture during the subsequent high-temperature annealing process.

[0100] Step S3: High-temperature annealing treatment;

[0101] Transfer the dried precursor to a double-chamber heating furnace and perform heat treatment in stages. In the initial stage, heat up to 500 °C at a rate of 10 °C / min; subsequently, increase the heating rate by 5 °C / min for every 100 °C increase until the heating rate reaches 55 °C / min and then maintain a constant speed until finally heating up to 900 °C. Keep the temperature constant at 900 °C for 30 minutes to promote the crystallization of the catalyst particles and form high-active sites, and then naturally cool to room temperature to obtain a catalyst with a stable structure.

[0102] Step S4: CVD tube furnace reaction process;

[0103] Reactor preheating: Under nitrogen protection, heat the CVD tube furnace to 660 °C; a low-temperature preheater (500 °C) is used to preheat hydrogen and propylene gases, and a high-temperature preheater (850 °C) ensures that propylene is fully cracked into active carbon atoms. Catalyst loading: Evenly spread the annealed catalyst in a quartz boat and place it in the constant-temperature zone of the reaction tube. Carbon source introduction in stages: Introduce propylene at 10 L / min for the first 5 minutes to initiate carbon tube nucleation; increase it to 35 L / min for the middle 10 minutes to accelerate growth; finally, reduce it to 20 L / min for the last 5 minutes to optimize the tube wall structure. The total reaction time is 20 minutes, and hydrogen is introduced throughout the process to assist in reduction. Post-reaction treatment: After stopping the supply of propylene, continuously introduce nitrogen for 5 minutes to remove residual gases and avoid side reactions.

[0104] Step S5: Pre-oxidation treatment;

[0105] Transfer the reaction product to a pre-oxidation device under positive nitrogen pressure protection, introduce a mixed gas of nitrogen and air (volume ratio 1:1), and oxidize it at 500 °C for 20 minutes. This process removes amorphous carbon impurities and enhances the surface activity of the carbon nanotubes. After the pre-oxidation is completed, 225 g of carbon nanotube raw powder (product before purification) is collected and temporarily stored in a sealed storage tank.

[0106] Step S6: Pickling and purification;

[0107] First pickling: Immerse the raw powder in a mixed acid solution (product: hydrochloric acid: nitric acid: hydrofluoric acid = 1:2:1:0.5) to remove residual metal catalysts, and wash and filter twice to separate the acid solution from the product. Second pickling: Use a diluted acid solution (product: hydrochloric acid: nitric acid: hydrofluoric acid = 1:1:0.5:0.25) for further impurity removal, and wash with water until the pH of the filtrate is close to 7.0. The filtered product is dried at 120 °C to obtain 200 g of high-purity carbon nanotubes with super-large diameters, whose diameter distribution is uniform and the structure is complete (the microscopic morphology is as shown in the attachment Figure 12 shown).

[0108] The specific surface area of carbon nanotubes refers to the total surface area per unit mass or unit volume of carbon nanotubes, usually expressed in square meters per gram (m 2 / g). Its value is jointly determined by the inner and outer tube wall surface areas of carbon nanotubes. Among them, the theoretical specific surface area of single-walled carbon nanotubes (SWCNT) can be as high as 1315 m 2 / g, while multi-walled carbon nanotubes (MWCNT) have a relatively lower specific surface area due to the superposition of multiple layers. In actual preparation, due to the easy bundling and aggregation of carbon nanotubes and the low opening rate, the measured specific surface area is usually significantly lower than the theoretical value.

[0109] The specific surface area of carbon nanotubes is negatively correlated with the tube diameter. Theoretically, a decrease in the tube diameter will significantly increase the proportion of surface atoms per unit mass. For example, when the diameter of single-walled carbon nanotubes decreases by 1 nm, the specific surface area can increase by about 200 m2 / g. This law has also been verified in experiments: For carbon nanotubes with fine tube diameters (such as samples with a diameter of 2 nm) prepared through catalyst design and process optimization, their specific surface area can reach over 600 m 2 / g.

[0110] Although the fine tube diameter brings the advantage of a high specific surface area, an overly small tube diameter (such as <5 nm) will cause an increase in the length-to-diameter ratio of carbon nanotubes, an elevation of surface energy, and an exacerbation of the agglomeration phenomenon. For example, carbon nanotubes with a tube diameter of 2 nm, due to their overly large specific surface area (>80 m 2 / g), are prone to dispersion difficulties due to agglomeration in conductive slurries, resulting in a decline in actual conductivity. Therefore, in industrial applications, a balance needs to be struck between the tube diameter and dispersibility.

[0111] For the samples obtained in Examples 1 - 11, a NOVA series Quantachrome specific surface area analyzer was used. Based on the Brunauer - Emmett - Teller (BET) theory, the nitrogen adsorption method was used to measure the specific surface area of each sample.

[0112] Sample pretreatment: Place approximately 0.1 - 0.3 g of carbon nanotube samples in a sample tube, heat them to 200 - 300 °C in a vacuum or flowing nitrogen environment for 2 - 4 hours for degassing treatment to thoroughly remove adsorbed moisture, gases, and impurities on the surface, ensuring that the samples are clean and dry before testing.

[0113] Nitrogen adsorption experiment: Immerse the sample tube in liquid nitrogen (-196 °C) to maintain a low temperature, gradually adjust the nitrogen pressure through a precision flow controller, and record in real time the nitrogen adsorption amount of the sample at different pressures to generate an adsorption - desorption isotherm.

[0114] BET equation calculation: Based on the adsorption isotherm data, use the BET equation to fit the monolayer adsorption capacity, combine the cross - sectional area of nitrogen molecules (0.162 nm 2 ) and the sample mass, and calculate the specific surface area through the formula to directly reflect the correlation between the total surface area of the material and the tube diameter and pores.

[0115] Data verification and optimization: Repeat the measurement of each group of samples 3 times, remove outliers, take the average value, and verify the contribution of micropores / mesopores by comparing with theoretical models (such as the t - plot method) to ensure the accuracy and repeatability of the specific surface area data.

[0116] Select the samples obtained in Examples 1 - 11, measure the average tube diameter, and proceed as follows:

[0117] Disperse the carbon nanotube sample in an ethanol solution and ultrasonically treat it for 10 - 20 minutes to break up the agglomerates and ensure that individual carbon nanotubes are fully dispersed. Subsequently, drop the dispersion onto the surface of a silicon wafer covered with conductive glue, and after drying, enhance the conductivity of the sample by sputtering gold (or carbon) to avoid image distortion caused by charge accumulation during SEM imaging.

[0118] Use a scanning electron microscope (SEM) to capture the morphology of carbon nanotubes in high - resolution mode at an acceleration voltage of 5 - 20 kV, selecting multiple representative regions. Through the secondary electron signal (SE) or backscattered electron (BSE) mode, clearly present the surface structure and details of the carbon nanotube diameter.

[0119] Randomly select at least 100 carbon nanotubes in the SEM image and use the image analysis software ImageJ to measure the diameter of a single carbon nanotube along the direction perpendicular to the axial direction of the carbon nanotube. Record the data through manual scale or automatic recognition function, excluding broken, overlapping, or contaminated areas to ensure that the measurement object is a complete and independent carbon nanotube.

[0120] Calculate the arithmetic mean and standard deviation of all valid measurement values to generate a diameter distribution histogram. For key samples (such as ultra - thick diameter tubes), supplement with local high - precision retesting using transmission electron microscopy (TEM) to verify the accuracy of the SEM data, and finally obtain the average diameter result and mark the error range. The specific surface area and average diameter measurement results of the samples in Examples 1 - 11 are shown in Table 1.

[0121] Table 1. Summary of experimental data for Examples 1 - 11

[0122]

[0123]

[0124] Example 1 (using fumed silica), large - diameter carbon nanotubes with an average diameter of more than 200 nm appeared in the product (attached Figure 2 ). Example 10 (replaced with magnesium nitrate): Only fine carbon nanotubes with a diameter < 50 nm were generated (attached Figure 11 ), and no large - diameter products were formed, indicating that fumed silica is a key condition for the formation of large - diameter carbon nanotubes. Fumed silica has a porous, high - specific - surface - area silica (SiO2) structure, which can uniformly load nickel (Ni) active substances to form dispersed catalyst particles, providing uniform nucleation sites for carbon nanotubes. Active substances in existing technologies such as magnesium nitrate lack a porous structure and have insufficient surface active sites, resulting in agglomeration of catalyst particles, forming small - sized particles and only generating fine - diameter carbon nanotubes.

[0125] The specific surface area of Example 10 (83.13 m 2 / g) is significantly higher than that of Example 1 (54.37 m 2 / g), indicating that the number of carbon nanotubes with a fine diameter is large and the porosity is high, indirectly verifying the diameter difference. The growth of carbon nanotubes with a large diameter requires larger catalyst particles. Fumed silica stabilizes and disperses Ni particles to a size above 200 nm, thus supporting the growth of large-diameter carbon nanotubes. Magnesium nitrate cannot inhibit particle agglomeration, and the catalyst particle size is small (<50 nm), only capable of generating carbon nanotubes with a fine diameter.

[0126] The concentration of ammonium carbonate is a key factor in regulating the diameter. Low concentration (0.005 - 0.01 g / mL): The product is catalyst particles coated with carbon, and no carbon nanotubes are formed (Examples 8 - 9).

[0127] Medium concentration (0.02 - 0.04 g / mL): Large-diameter carbon nanotubes (100 - 380 nm) are generated, and the diameter first increases and then decreases with the increase in concentration (Examples 1 - 3). High concentration (0.06 - 0.08 g / mL): The carbon nanotubes gradually disappear, and the product is short and thick carbon nanotubes or amorphous carbon (Examples 6 - 7).

[0128] The complexation equilibrium between nickel nitrate and ammonium carbonate is crucial. When ammonium carbonate is insufficient, NiCO3 precipitates (the particles are too large), and an active catalyst cannot be formed, resulting in carbon-coated particles without carbon nanotubes (Examples 8 - 9). The formation of soluble 2- complex [Ni(CO3)2] provides uniformly dispersed Ni nanoparticles (50 - 300 nm), supporting the growth of large-diameter carbon nanotubes. Excessive ammonium carbonate causes NH4 + hydrolysis to form Ni(OH)2 precipitate, destroying the complex structure and forming small-sized catalyst particles (<50 nm), only generating short and thick carbon nanotubes.

[0129] Carbon-coated particles (Examples 8 - 9), the particle surface is covered with amorphous carbon, and no carbon nanotubes are formed (Appendix Figures 9 - 10 ). The specific surface area is small (<10 m 2 / g), and due to the lack of pores between particles, the gas molecule adsorption capacity is low. Short and thick carbon nanotubes (Examples 6 - 7); short carbon nanotubes (length <1 μm) are closely packed, and the porosity is low (Appendix Figures 7 - 8 ); the specific surface area is low (15 - 21 m 2 / g), because short carbon nanotubes cannot form an open pore network. In summary, as can be seen from Table 1:

[0130] The key carrier for catalyst nucleation, namely fumed silica, is used as a catalyst nucleation carrier to control the particle size of the basic catalyst active substances, ensure the presence of a suitable catalyst during the growth of carbon nanotubes, and maintain the most basic particle size of the large-diameter carbon nanotube catalyst.

[0131] An appropriate concentration of ammonium carbonate, too low or too high will not produce large-diameter carbon nanotubes.

[0132] Example 12. To further determine the reasons for the influence of the change in ammonium carbonate concentration on carbon nanotubes with large diameters, in this example, nickel nitrate solution and ammonium carbonate solution were selected to design an experiment. Using the 0.2 g / ml nickel nitrate solution in Example 1 as the base solution, ammonium carbonate was gradually added, and the reaction changes were observed. The reactions at the experimental nodes are as Figure 14 shown. After the addition of ammonium carbonate, a green precipitate (No. 1) first appears. As ammonium carbonate continues to be added, the precipitate disappears and the whole becomes a green colloid (No. 2). When ammonium carbonate is continuously added, the colloid disappears and a green precipitate appears again (No. 3).

[0133] When ammonium carbonate is added dropwise to the nickel nitrate solution, the phenomenon of first forming a precipitate, then the precipitate disappearing, and then a precipitate appearing again has the following mechanistic reasons:

[0134] 1. First, a precipitate is formed;

[0135] Nickel nitrate Ni(NO3)2 reacts with ammonium carbonate (NH4)2CO3 to form nickel carbonate NiCO3 precipitate. The ionic equation is Ni 2+ +CO3 2- = NiCO3 precipitate. At this time, the pH value of the solution is about 7. Because the ammonium carbonate solution is slightly alkaline and the nickel nitrate solution is slightly acidic, the pH approaches neutrality after the two are mixed.

[0136] 2. The precipitate disappears;

[0137] When ammonium carbonate is continuously added dropwise, due to the increase in the concentration of carbonate ions CO3 2- , it will react with the formed nickel carbonate precipitate to form a soluble [Ni(CO3)2] 2- complex ion, dissolving the precipitate. The ionic equation is NiCO3 + CO3 2- = [Ni(CO3)2] 2- . During this process, the pH value of the solution will increase because the concentration of carbonate ions increases and the alkalinity of the solution increases, and the pH value rises to about 8 - 9.5.

[0138] 3. A precipitate appears again;

[0139] When a large amount of ammonium carbonate is in excess, the concentration of ammonium ions NH4 + in the solution also increases significantly, and it will undergo a hydrolysis reaction with carbonate ions, generating a large amount of bicarbonate ions HCO3 - and hydroxide ions OH - . When the concentration of hydroxide ions increases to a certain extent, it will react with nickel ions to form nickel hydroxide Ni(OH)2 precipitate. The ionic equation is Ni 2+ + 2OH -= Ni(OH)2 precipitate. At this time, the pH value of the solution continues to rise and may reach above 9.5, and nickel hydroxide precipitate is formed.

[0140] Combined with the fluctuating change of ammonium carbonate and the corresponding microscopic structure and specific surface properties of the product, we can conclude that when nickel nitrate solution is dropped into ammonium carbonate solution, a precipitate is first formed to coat the nucleation carrier, but carbon nanotubes cannot grow (Example 8 / Example 9). When ammonium carbonate is dropped in excess, a precipitate is also formed to coat the nucleation carrier, and large-diameter carbon nanotubes cannot grow (Example 6 / Example 7). Only during the formation of the complex (Examples 1-5) can large-diameter carbon nanotubes grow. As ammonium carbonate continues to be added, the complex begins to decrease, and the large-diameter carbon nanotubes also decrease. This complex is the key to preparing large-size catalysts, that is, an appropriate concentration of ammonium carbonate. According to the results in Table 1, the selection of 0.04 g / ml ammonium carbonate concentration in the present invention is the optimal choice and has achieved unexpected results.

[0141] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing carbon nanotubes with an ultra-large diameter, characterized in that, It includes the following steps: S1. Attach active substances and promoters to the surface of fumed silica to produce a catalyst precursor; S2. Filter and dry the precursor solution; S3. Perform high-temperature annealing treatment on the dried precursor; S4. Use the precursor after high-temperature annealing treatment as a catalyst and add it to a fluidized bed or a CVD tube furnace reactor for reaction; S5. Perform pre-oxidation treatment after the reaction is completed to obtain ultralarge-diameter carbon nanotube raw powder; S6. Purify the carbon nanotube raw powder by pickling to obtain high-purity ultralarge-diameter carbon nanotubes.

2. The preparation method of the super-large diameter carbon nanotubes according to claim 1, characterized in that, The specific process of step S1 includes: soaking fumed silica with a nickel nitrate solution of 0.2 - 0.5 g / ml, then titrating with an ammonium carbonate solution of 0.02 - 0.06 g / ml, and carrying out a full reaction.

3. The preparation method of the super-large diameter carbon nanotubes according to claim 1, characterized in that, The specific process of step S1 includes: soaking fumed silica with a nickel nitrate solution of 0.2 - 0.5 g / ml for 20 min, then titrating with an ammonium carbonate solution of 0.04 g / ml, and carrying out a full reaction for 30 min.

4. The method for preparing super-large diameter carbon nanotubes according to claim 1, characterized in that, In step S2, after filtration, dry at 120 °C for 180 min.

5. The preparation method of the ultra-large diameter carbon nanotubes according to claim 1, characterized in that, In step S3, after drying, add it to a double-chamber heating furnace for high-temperature annealing treatment. The heating rate is 10 °C / min for the first 500 °C, and the heating rate increases by 5 °C / min from 500 - 900 °C until the heating rate reaches 55 °C / min, then heat up to 900 °C at a constant speed, keep the temperature constant for 30 min, and then cool naturally to room temperature.

6. The preparation method of super-large diameter carbon nanotubes according to claim 1, characterized in that In step S4, the following is step S41 of using the precursor after high-temperature annealing treatment as a catalyst and adding it to a fluidized bed reactor for reaction: S411. Reactor preheating: Under a nitrogen protection atmosphere, heat the fluidized bed reactor to 660 °C; heat the low-temperature preheater to 500 °C to preheat hydrogen and propylene gases; heat the high-temperature preheater to 850 °C to fully crack the carbon source gas; S412. Catalyst addition and fluidization: Use the precursor after high-temperature annealing as a catalyst and add it to the fluidized bed reactor; introduce nitrogen to keep the catalyst particles in a suspended fluidized state; S413. Reduction reaction: Introduce hydrogen and reduce the metal oxide in the catalyst to active elemental form at 660 °C until the reduction is completed; During this process, the carbon source is introduced in stages; in the first 5 minutes: propylene is used as the carbon source and introduced at a flow rate of 10 L / min to initiate the nucleation of carbon nanotubes; in the middle 10 minutes: the propylene flow rate is increased to 35 L / min to promote the rapid growth of carbon tubes; in the last 5 minutes: the propylene flow rate is reduced to 20 L / min to optimize the integrity of the tube wall structure; total reaction time: 20 minutes, hydrogen is introduced throughout as the reducing gas; after the reaction is completed, stop the supply of propylene and continue to introduce nitrogen for 5 minutes to remove the residual gas in the reactor.

7. The preparation method of super-large diameter carbon nanotubes according to claim 1, characterized in that, In step S4, the following is step S42 of using the precursor after high-temperature annealing treatment as a catalyst and adding it to a CVD tube furnace reactor for reaction: S421. Reactor preheating: Under a nitrogen protection atmosphere, heat the CVD tube furnace reactor to 660 °C; heat the low-temperature preheater to 500 °C for preheating hydrogen and propylene gases; heat the high-temperature preheater to 850 °C to fully crack propylene into active carbon atoms; S422. Catalyst loading: The precursor after high-temperature annealing is used as the catalyst and evenly spread on the quartz boat, which is placed in the constant-temperature zone of the reaction tube. S423. Reduction reaction: Hydrogen and nitrogen are introduced, and the catalyst reduction is completed at 660 °C. During this process, the carbon source is introduced in stages. In the first 5 minutes: Propylene is introduced at a flow rate of 10 L / min, which is the nucleation stage of the carbon tube. In the middle 10 minutes: The flow rate of propylene is increased to 35 L / min, which is the main growth stage. In the last 5 minutes: The flow rate of propylene is reduced to 20 L / min, which is the structure optimization stage. The total reaction time is 20 minutes, and hydrogen is introduced throughout the process. After the reaction is completed, the supply of propylene is stopped, and nitrogen is continuously introduced for 5 minutes to purge the gas in the reaction tube.

8. The preparation method of the super-large diameter carbon nanotubes according to claim 1, wherein, The specific process of step S5 includes: Under the protection of positive nitrogen pressure, the product of step S4 is transported to the pre-oxidation equipment; nitrogen and air are mixed at a volume ratio of 1:1 and oxidized at 500 °C for 20 minutes, and then transferred to the storage tank after completion.

9. The method for preparing super-large diameter carbon nanotubes according to claim 1, wherein The specific process of step S6 includes: S61. Put the pre-oxidized product into the prepared acidic solution with a specific concentration. While removing the residual reaction metal, the product is peeled off, and it is washed and filtered twice. S62. Put the product obtained after filtration into the acidic solution with a specific concentration for a second time for impurity removal. S63. The product after impurity removal and filtration is washed with water. After the pH is close to 7.0, it is filtered and dried.

10. The method for preparing super-large-diameter carbon nanotubes according to claim 9, characterized in that: In S61, the mass ratio of the product to the acidic components in the acidic solution with a specific concentration is set as follows: Product: Hydrochloric acid: Nitric acid: Hydrofluoric acid = 1:2:1:0.5; In S62, the mass ratio of the product to the acidic components in the acidic solution with a specific concentration is set as follows: Product: Hydrochloric acid: Nitric acid: Hydrofluoric acid = 1:1:0.5:0.25.

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