Carbon nanotube hollow microspheres, and preparation method and application thereof

Abstract

The present application relates to the technical field of micro-nano carbon material, and relates to a carbon nanotube hollow microsphere, a preparation method and application thereof.The particle size of the carbon nanotube hollow microsphere is 5-60 microns; the carbon nanotube hollow microsphere is composed of carbon nanotubes.The surface conductive performance of the carbon nanotube hollow microsphere-PVA system prepared by the present application is much better than that of the carbon nanotube-PVA system, and the surface resistivity of the carbon nanotube hollow microsphere-PVA system can be less than or equal to 0.32 ohm.The performance of the carbon nanotube hollow microsphere-PDMS flexible sensor is also better than that of the carbon nanotube-PDMS flexible sensor.The carbon nanotube hollow microsphere is widely used, for example, as a conductive filler of a composite material, a functional structure of a pressure sensor, a carrier of a catalyst and the like.

Description

Technical Field

[0001] This invention relates to the field of micro and nano carbon materials technology, and more specifically, to a hollow carbon nanotube microsphere, its preparation method, and its application. Background Technology

[0002] Carbon nanotubes are one-dimensional carbon nanomaterials with hollow tubular structures formed from graphene. They possess many excellent properties and have broad potential applications in materials, devices, sensors, microelectronics, and biology. They exhibit good electrical conductivity, with an average conductivity of 1000-2000 S / cm, and a single carbon nanotube can withstand the charge of 10... 6 A / cm 2 With its high current density, carbon nanotubes are ideal nanowires; they are fibrous materials with a large aspect ratio (>1000:1) and can form highly efficient conductive networks in composite materials, making them ideal conductive additives. Furthermore, carbon nanotubes have a Young's modulus exceeding 1 TPa and a tensile strength exceeding 100 GPa, making them ideal reinforcing materials for composite materials. Although carbon nanotubes are one-dimensional materials, their powder is generally disordered, including both individual carbon nanotubes and the spaces between them. This disordered powdered carbon nanotube structure limits many applications, such as the fabrication of functional devices. Therefore, organizing disordered carbon nanotubes into materials with a specific structure is of great significance for the application of carbon nanotubes.

[0003] In existing technologies, the preparation of carbon nanotubes with ordered structures in a certain aspect is generally achieved by controlling factors such as the structure, arrangement, or size of the catalyst during the growth and preparation stage to achieve the desired effect. However, this control method is complex and costly. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, this invention proposes a hollow carbon nanotube microsphere. Specifically, it relates to a hollow carbon nanotube microsphere and its preparation method.

[0005] This invention prepares hollow microspheres composed of carbon nanotubes. The particle size is 5–60 micrometers, preferably 5–50 micrometers. The hollow carbon nanotube microspheres are composed of carbon nanotubes. This application takes into account that, firstly, carbon nanotubes can coat the surface of ultrafine fully vulcanized powdered rubber particles to form composite microspheres. The structure is as follows: carbon nanotubes coat the surface of the secondary particles of fully vulcanized powdered rubber to form a shell; the fully vulcanized powdered rubber forms the core. Then, the internal ultrafine fully vulcanized powdered rubber is pyrolyzed at high temperature, leaving the surface carbon nanotube cages to form a hollow structure. This hollow microsphere composed of carbon nanotubes possesses the excellent properties of carbon nanotubes while combining the containment function of a hollow structure. Hollow carbon nanotube microspheres have wide applications, such as as conductive fillers in composite materials, gas sensors, and catalyst supports.

[0006] One objective of this invention is to provide a hollow carbon nanotube microsphere, which is a hollow microsphere composed of carbon nanotubes with a particle size of 5–60 micrometers, preferably 5–50 micrometers. After imaging the composite microspheres using scanning electron microscopy, optical microscopy, atomic force microscopy, or other imaging equipment, the particle size range of the sample is obtained by randomly measuring more than 100 particles.

[0007] The carbon nanotube hollow microspheres mentioned above, wherein the carbon nanotubes are selected from at least one of multi-walled carbon nanotubes and single-walled carbon nanotubes.

[0008] The second objective of this invention is to provide a method for preparing the aforementioned carbon nanotube hollow microspheres, which may include the following steps: mixing and stirring components including carbon nanotubes and ultrafine fully vulcanized rubber powder, and then heating at high temperature to decompose the ultrafine fully vulcanized rubber powder to obtain carbon nanotube hollow microspheres.

[0009] Specifically, the preparation method may include the following steps:

[0010] 1) Prepare core-shell structured composite microspheres; the core-shell structured composite microspheres include an outer shell and a core; the outer shell includes carbon nanotubes, and the core includes ultrafine fully vulcanized powder rubber;

[0011] Step 1) includes the following steps:

[0012] The components, including carbon nanotubes and ultrafine fully vulcanized powder rubber, are mixed and stirred to obtain ultrafine fully vulcanized powder rubber composite microspheres with carbon nanotubes on the surface, namely core-shell structure microspheres.

[0013] 2) Under an inert atmosphere, the ultrafine fully vulcanized powder rubber is heated at high temperature to decompose it, thereby obtaining the carbon nanotube hollow microspheres.

[0014] in,

[0015] The core-shell structured composite microspheres are composed of components including carbon nanotubes and ultrafine fully vulcanized powdered rubber. The carbon nanotubes, based on 100% of the total mass of the core-shell structured composite microspheres, have a mass content of 5-50%, preferably 5-40%; (for example, it can be 5, 6, 7, 9, 10, 15, 20, 22, 25, 30, 35, 40, 42, 43, 44, 45, 46, 47, 48, 49, 50%, or any value between the above). The mass content of the ultrafine fully vulcanized powder rubber is 50-95%, preferably 60-95% (e.g., it can be 50, 51, 52, 53, 54, 55, 56, 57, 58, 60, 65, 70, 75, 78, 80, 85, 90, 91, 93, 94, 95% or any value between the above values ​​or any two values ​​between the above values, for example, 55-75%).

[0016] Step 1) includes the following steps:

[0017] A core-shell structured composite microsphere is prepared by mixing and stirring components including carbon nanotubes, fully vulcanized powdered rubber, and optional additives. The core-shell structured microspheres have a particle size of 5–60 micrometers, preferably 5–50 micrometers.

[0018] The carbon nanotubes used in this invention include those disclosed in the prior art. One or more types of single-walled carbon nanotubes and multi-walled carbon nanotubes may be selected; there are no specific requirements for the length, diameter, or aspect ratio of the carbon nanotubes.

[0019] The fully vulcanized powder rubber used in this invention does not include ultrafine fully vulcanized powder silicone rubber; the fully vulcanized powder rubber used in this invention can be an ultrafine fully vulcanized powder rubber prepared using the technology disclosed in Chinese Patent 00816450.9. The ultrafine fully vulcanized powder rubber can be selected from at least one of ultrafine fully vulcanized styrene-butadiene powder rubber, ultrafine fully vulcanized carboxyl styrene-butadiene powder rubber, ultrafine fully vulcanized acrylate powder rubber, ultrafine fully vulcanized carboxyl acrylonitrile butadiene powder rubber, and ultrafine fully vulcanized acrylonitrile butadiene powder rubber. This type of ultrafine fully vulcanized powder rubber is prepared by radiation crosslinking and spray drying of the corresponding rubber latex, resulting in the agglomeration of primary rubber particles of approximately 100 nm into secondary particles with a particle size of approximately 10-60 micrometers. The radiation crosslinking technology results in a high degree of crosslinking on the surface of the primary rubber particles, reducing interparticle adhesion.

[0020] In addition, other conventional additives, such as release agents and antioxidants, may be added as needed.

[0021] Step 2) includes the following steps:

[0022] The ultrafine fully vulcanized powder rubber in the core-shell structured composite microspheres is decomposed under a high-temperature inert atmosphere. The high-temperature temperature is 400–800°C, preferably 400–650°C. Nitrogen or argon can be used as the inert gas.

[0023] Specifically, the preparation method includes the following steps: (1) Weighing a set amount of carbon nanotubes and ultrafine fully vulcanized powder rubber and stirring in a high-speed stirrer. The stirrer speed is 100-3000 rpm, preferably 1-2000 rpm, and the dispersion time is ≥20 seconds. Since the surface energy of carbon nanotubes and ultrafine fully vulcanized powder rubber is similar, carbon nanotubes are loaded on the surface of the fully vulcanized powder rubber to form a shell layer, forming a core-shell structured composite microsphere, the structure of which is as follows. Figure 2 As shown. (2) Under a high-temperature inert atmosphere, the ultrafine fully vulcanized powder rubber is decomposed to obtain carbon nanotube hollow microspheres, the structure of which is as follows. Figure 1 As shown.

[0024] A third objective of this invention is to provide applications for the aforementioned hollow carbon nanotube microspheres or the hollow carbon nanotube microsphere products prepared by the aforementioned method.

[0025] The inventors have discovered that carbon nanotubes can be loaded onto the surface of ultrafine fully vulcanized rubber powder to create a unique core-shell structure with carbon nanotubes as the shell and ultrafine fully vulcanized rubber powder as the core. Under high temperature, the internal ultrafine fully vulcanized rubber powder decomposes, leaving a hollow structure formed by the woven carbon nanotubes on the surface. This assembles disordered carbon nanotube powder into hollow carbon nanotube microspheres with a particle size in the range of 5-60 micrometers, transforming them into an ordered structure. The surface conductivity of the carbon nanotube hollow microsphere-PVA system prepared using this method is significantly better than that of the standard carbon nanotube-PVA system, with a surface resistivity ≤0.32 ohms. The performance of the carbon nanotube hollow microsphere-PDMS flexible sensor is also superior to that of the standard carbon nanotube-PDMS flexible sensor. Carbon nanotube hollow microspheres have wide applications, such as as conductive fillers in composite materials, functional structures in pressure sensors, and catalyst supports. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the hollow carbon nanotube microspheres described in this invention;

[0027] Figure 2 This is a schematic diagram of the core-shell structure of the composite microspheres formed by carbon nanotubes coating ultrafine fully vulcanized powder rubber according to the present invention.

[0028] Figure 3 This is a scanning electron microscope image of the composite microspheres of carbon nanotube-coated ultrafine fully vulcanized powder rubber in Example 1;

[0029] Figure 4Scanning electron microscope image of the hollow carbon nanotube microspheres prepared in Example 1;

[0030] Figure 5 This is a scanning electron microscope image of the hollow carbon nanotube microspheres in Example 2;

[0031] Figure 6 This is a scanning electron microscope image of the hollow carbon nanotube microspheres in Example 2. Figure 5 A magnified view of a portion of the image;

[0032] Figure 7 Scanning electron microscope image of the carbon nanotube hollow microspheres prepared in Example 3;

[0033] Figure 8 Scanning electron microscope image of the hollow carbon nanotube microspheres prepared in Example 3 ( Figure 7 A magnified view of a portion of the image; Detailed Implementation

[0034] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0035] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0036] Source of raw materials

[0037] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0038] Example 1

[0039] 3.0 g of carbon nanotubes (Beijing Tiannai Technology Co., Ltd., model FloTube 9000, average diameter 10 nm, average length 11 μm) and 7.0 g of ultrafine fully vulcanized carboxylated nitrile butadiene rubber powder (VP-501, Beijing Yanshan Petrochemical High-Tech Co., Ltd.) were weighed and stirred at 2000 rpm for 40 seconds in a high-speed mixer to obtain composite microspheres with carbon nanotubes coated on the surface of ultrafine fully vulcanized carboxylated nitrile butadiene rubber powder. A small amount was taken for scanning electron microscopy (Phillips, XL-30) to observe its morphology. The scanning electron micrograph is shown in [image missing].Figure 3 .

[0040] The prepared carbon nanotubes were coated onto the surface of ultrafine fully vulcanized carboxylated nitrile butadiene rubber powder to form composite microspheres, which were then placed in a quartz boat and placed in a tube furnace. Nitrogen gas was introduced for one minute and then shut off; followed by vacuuming for one minute. After three cycles, the nitrogen flow rate was adjusted to 10 ml / min, and the mixture was decomposed at 500℃ for 30 minutes to obtain hollow carbon nanotube microspheres. Figure 4 As shown, the particle size of the prepared carbon nanotube hollow microspheres ranges from 5 to 50 micrometers.

[0041] Example 2

[0042] The amount of carbon nanotubes used in Example 1 was changed to 4.0 g, and the amount of ultrafine fully vulcanized carboxylated nitrile butadiene rubber powder was changed to 6.0 g. All other preparation conditions remained the same as in Example 1. The prepared hollow carbon nanotube microspheres are as follows: Figure 5 and Figure 6 As shown, the particle size of the prepared carbon nanotube hollow microspheres ranges from 5 to 50 micrometers.

[0043] Example 3

[0044] The decomposition temperature in Example 1 was set at 600℃, and all other preparation conditions were the same as in Example 1. The prepared carbon nanotube hollow microspheres are as follows: Figure 7 and Figure 8 As shown, the particle size of the prepared carbon nanotube hollow microspheres ranges from 5 to 50 micrometers.

[0045] Example 4

[0046] In Example 1, the ultrafine fully vulcanized carboxylated nitrile butadiene rubber powder was replaced with ultrafine fully vulcanized styrene-butadiene rubber powder (VP-101, Beijing Yanshan Petrochemical High-Tech Co., Ltd.), and all other preparation conditions were the same as in Example 1. The particle size of the prepared nanotube hollow microspheres was 5–50 micrometers.

[0047] Example 5

[0048] Weigh 10.0 g of polyvinyl alcohol (PVA, model 1799, analytical grade, Sinopharm Chemical Reagent Co., Ltd.) and add it to 100 mL of deionized water. Stir at 80 °C until completely dissolved. Then weigh 0.5 g of the carbon nanotube hollow microspheres from Example 1 and add them to the 10.0 g PVA solution. Stir magnetically at low speed for 2 hours to ensure uniform dispersion. Take 2 mL of the mixture and coat it evenly on the surface of a PC sheet using a doctor blade with a gap of 100 μm. Dry the sheet in an 80 °C oven and measure its surface resistivity. The surface resistivity of the carbon nanotube hollow microsphere-PVA system is 0.32 ohms.

[0049] Example 6

[0050] 10.0 g of polyvinyl alcohol (PVA, model 1799, analytical grade, Sinopharm Chemical Reagent Co., Ltd.) was weighed and added to 100 mL of deionized water, and stirred at 80 °C until completely dissolved. Then, 0.5 g of the carbon nanotube hollow microspheres from Example 2 was weighed and added to the 10.0 g PVA solution, and the mixture was magnetically stirred at low speed for 2 hours to ensure uniform dispersion. 2 mL of the mixture was taken and uniformly coated onto the surface of a PC sheet using a doctor blade with a gap of 100 μm. After drying in an 80 °C oven, the surface resistivity was measured. The surface resistivity of the carbon nanotube hollow microsphere-PVA system was 0.21 ohms.

[0051] Comparative Example 1

[0052] 10.0 g of polyvinyl alcohol (PVA, model 1799, analytical grade, Sinopharm Chemical Reagent Co., Ltd.) was weighed and added to 100 mL of deionized water, and stirred at 80 °C until completely dissolved. Then, 0.5 g of carbon nanotubes was weighed and added to the 10.0 g PVA solution, and the mixture was magnetically stirred at low speed for 2 hours to ensure uniform dispersion. 2 mL of the mixture was taken and evenly coated onto the surface of a PC sheet using a doctor blade with a gap of 100 μm. After drying in an 80 °C oven, the surface resistivity was measured. The surface resistivity of the carbon nanotube-PVA system was measured to be 5.4 × 10⁻⁶ ohms.

[0053] As can be seen from the comparison of data from Examples 5 and 6 and Comparative Example 1, the surface conductivity of the carbon nanotube hollow microsphere-PVA system prepared in this application is much better than that of the carbon nanotube-PVA system.

[0054] Example 7

[0055] Take 10g of component A (vinyl-terminated poly(dimethyl-methylhydrosiloxane)) and 1g of component B (poly(dimethyl-methylhydrosiloxane)) of PDMS (DOWCORNING 184, USA) and magnetically stir for 30 minutes at room temperature until uniformly mixed. Then, place the mixture in a vacuum chamber for degassing for 30 minutes to remove air bubbles, obtaining uncured, bubble-free liquid PDMS. Apply a 0.5mm thick PDMS coating to the surface of a glass plate using a scraper. Embed copper foil electrodes at both ends of the coating. Then, place the plate in an oven at 110℃ for curing for 1 hour to obtain a PDMS rubber sheet. After curing, cut the PDMS rubber sheet into strips of 8cm × 2cm.

[0056] Weigh 0.5 g of the carbon nanotube hollow microspheres prepared in Example 3, 0.1 g of dimethyl silicone oil (analytical grade, Sinopharm Chemical Reagent Co., Ltd.), and 0.3 g of sodium dodecyl sulfate (analytical grade, Sinopharm Chemical Reagent Co., Ltd.), and add them to 10 mL of anhydrous ethanol (analytical grade, Sinopharm Chemical Reagent Co., Ltd.). Separately, weigh 0.5 g of carbon nanotubes, 0.1 g of dimethyl silicone oil, and 0.3 g of sodium dodecyl sulfate, add them to 10 mL of anhydrous ethanol, and vibrate in a water bath for 2 hours to uniformly disperse the carbon nanotubes in the anhydrous ethanol. Take 2 mL of each mixture and coat it evenly on the surface of a strip of PDMS using a doctor blade. After the ethanol evaporates, encapsulate it with uncured, bubble-free liquid PDMS. After curing, a carbon nanotube hollow microsphere-PDMS flexible sensor and a control group carbon nanotube-PDMS flexible sensor are obtained.

[0057] Sensitivity, repeatability, and response time are important indicators reflecting the performance of flexible strain sensors, with sensitivity being the most crucial performance parameter. Sensitivity reflects the amplitude of changes in the sensor's intrinsic parameters in response to external stimuli; it is the ratio of the output parameter change to the input signal intensity. The magnitude of sensitivity reflects the sensor's ability to respond to external stimuli. Its calculation formula is S = K / ε, K = (R - R0) / R0, ε = (L - L0) / L0, where: S is sensitivity; K is the rate of change of resistance; ε is strain; R0 and R are the initial resistance and the resistance after strain, respectively; L0 and L are the initial length and the length after strain, respectively. The sensitivity of the carbon nanotube hollow microsphere-PDMS flexible sensor is 1200 at ε = 0.01%. With increasing strain, its sensitivity continuously decreases. When ε = 2%, its sensitivity rapidly decreases from 600 to 30 at ε = 5%, and then the decrease in sensitivity slows down with further increases in ε. The sensitivity of the carbon nanotube-PDMS flexible sensor is 500 at ε = 0.01%. As strain increases, its sensitivity continuously decreases. When ε = 0.5%, its sensitivity rapidly drops from 200 to 10 when ε = 5%, after which the sensitivity decreases more slowly with increasing ε. The sensitivity of the carbon nanotube hollow microsphere-PDMS flexible sensor is consistently higher than that of the nanotube-PDMS flexible sensor, and the ε value at which its sensitivity rapidly decreases is also much larger than that of the carbon nanotube-PDMS flexible sensor. Therefore, the performance of the carbon nanotube hollow microsphere-PDMS flexible sensor is superior to that of the carbon nanotube-PDMS flexible sensor.

Claims

1. A hollow carbon nanotube microsphere having a particle size of 5–60 micrometers; wherein the hollow carbon nanotube microsphere is composed of carbon nanotubes; The aforementioned hollow carbon nanotube microspheres are prepared by a method including the following steps: After mixing the components, including carbon nanotubes and ultrafine fully vulcanized rubber powder, in a high-speed stirrer, core-shell structured microspheres are obtained. After heating at high temperature, hollow carbon nanotube microspheres are obtained. With the total mass of the core-shell structured microspheres as 100%, the mass content of the carbon nanotubes is 5-50%; and the mass content of the ultrafine fully vulcanized powder rubber is 50-95%.

2. The hollow carbon nanotube microspheres according to claim 1 have a particle size of 5 to 50 micrometers.

3. The hollow carbon nanotube microspheres according to claim 1, characterized in that: The carbon nanotubes are selected from at least one of multi-walled carbon nanotubes and single-walled carbon nanotubes.

4. The method for preparing hollow carbon nanotube microspheres according to any one of claims 1 to 3 comprises the following steps: The components, including carbon nanotubes and ultrafine fully vulcanized rubber powder, are mixed and heated at high temperature to obtain hollow carbon nanotube microspheres.

5. The method for preparing hollow carbon nanotube microspheres according to any one of claims 1 to 3 comprises the following steps: 1) Preparation of core-shell structured microspheres; the core-shell structured microspheres comprise an outer shell and a core; the outer shell comprises carbon nanotubes, and the core comprises ultrafine fully vulcanized powder rubber; 2) Under an inert atmosphere, the ultrafine fully vulcanized powder rubber is heated at high temperature to decompose it, thereby obtaining the carbon nanotube hollow microspheres.

6. The method for preparing hollow carbon nanotube microspheres according to claim 5, characterized in that: The ultrafine fully vulcanized powder rubber does not include ultrafine fully vulcanized powder silicone rubber.

7. The method for preparing hollow carbon nanotube microspheres according to claim 6, characterized in that: The ultrafine fully vulcanized powder rubber is selected from at least one of ultrafine fully vulcanized styrene-butadiene powder rubber, ultrafine fully vulcanized carboxylated styrene-butadiene powder rubber, ultrafine fully vulcanized acrylate powder rubber, ultrafine fully vulcanized carboxylated nitrile butadiene powder rubber, and ultrafine fully vulcanized nitrile butadiene powder rubber.

8. The method for preparing hollow carbon nanotube microspheres according to claim 5, characterized in that: With the total mass of the core-shell structured microspheres as 100%, the mass content of the carbon nanotubes is 5-40%; and the mass content of the ultrafine fully vulcanized powder rubber is 60-95%.

9. The method for preparing hollow carbon nanotube microspheres according to claim 5, characterized in that: Step 1) includes the following steps: The components, including carbon nanotubes and ultrafine fully vulcanized powder rubber, are mixed and stirred to obtain the core-shell structured microspheres.

10. The method for preparing hollow carbon nanotube microspheres according to claim 5, characterized in that: Step 2) includes the following steps: The high-temperature heating temperature is 400-800℃.

11. The method for preparing hollow carbon nanotube microspheres according to claim 10, characterized in that: Step 2) includes the following steps: The high-temperature heating temperature is 400–650°C.

12. The carbon nanotube hollow microspheres prepared by the method according to any one of claims 5 to 11.

13. Application of the carbon nanotube hollow microspheres according to any one of claims 1 to 3 or the carbon nanotube hollow microspheres prepared by the preparation method according to any one of claims 4 to 11.

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