CN110687169B - A humidity-sensitive carbon nanotube/graphene/organic composite flexible material, humidity sensor and preparation method thereof - Google Patents

Abstract

The invention provides a humidity-sensitive carbon nano tube/graphene/organic composite flexible material, a flexible humidity sensor and a preparation method thereof. The preparation method of the composite flexible material comprises the following steps: dispersing graphene oxide in an organic solvent I to prepare a graphene oxide dispersion liquid; dispersing the carbon nano tube in an organic solvent II to prepare a carbon nano tube dispersion liquid; soaking the flexible substrate in the graphene oxide dispersion liquid, and drying to obtain a flexible substrate coated by graphene oxide; and soaking the flexible substrate coated with the graphene oxide in the carbon nano tube dispersion liquid, and drying to obtain the carbon nano tube/graphene/organic composite flexible material sensitive to humidity. The composite flexible material has high sensitivity to humidity, and the preparation method is simple, low in production cost and high in efficiency, and can realize continuous and large-scale production.

Description

A humidity-sensitive carbon nanotube/graphene/organic composite flexible material, humidity sensor and preparation method thereof

technical field

The invention belongs to the technical field of flexible functional electronic materials and flexible sensors, and particularly relates to a humidity-sensitive carbon nanotube/graphene/organic composite flexible material, a flexible humidity sensor and a preparation method thereof.

Background technique

The working principle of common humidity sensors is to change the dielectric constant or conductivity of organic polymers through the interaction of water molecules and organic polymers, and to reflect changes in humidity by measuring changes in resistance or capacitance. With the increasing diversification of sensor applications in recent years and the development of sensor technology in various countries around the world, humidity sensors have shown broad application prospects in atmospheric monitoring, industrial production, biomedical and other fields. At present, many intelligent detection devices have adopted a large number of various sensors, and their applications have already penetrated into various aspects such as industrial production, marine exploration, environmental protection, medical diagnosis, bioengineering, and smart home. With the increasing application requirements in the information age, the expectations and idealization requirements for various performance parameters such as the range, accuracy and stability of the measured information are gradually increasing. In response to the measurement requirements of humidity in special environments and special signals, new sensor technology has developed to the following trends: developing new materials, new processes and developing new sensors; realizing the integration and intelligence of sensors; realizing sensing technology hardware systems and components of miniaturization. At the same time, it is hoped that the sensor can also be transparent, flexible, extensible, freely bendable or even foldable, easy to carry, and wearable. However, the traditional silicon-based semiconductor humidity sensor cannot be flexible, and the manufacturing cost is high and it is not easy to carry.

The prior art reports a method for preparing a humidity sensor by coating polyimide on silver crossed electrodes using inkjet printing. Although the humidity sensor prepared by this method has a large resistance change with humidity, Limited measurement range and poor humidity sensitivity. The prior art also discloses a method for preparing a humidity sensor by exfoliating WS2 with tert-butyl lithium to synthesize 2D nanomaterials, and then depositing it on an interdigitated electrode of a conductive ceramic platform. Higher, the manufacturing process is complicated and the sensor response time is longer. There are also reports on fabricating humidity sensors on glass fiber substrates based on the principle of mechanical strain induced by carboxymethyl cellulose (CMC) in response to changes in humidity. Although the sensor has high sensitivity, it has a narrow range of applicable humidity, which limits the sensor application.

SUMMARY OF THE INVENTION

In view of the above prior art, the present invention provides a humidity-sensitive carbon nanotube/graphene/organic composite flexible material, based on which a flexible humidity sensor with high sensitivity and rapid response can be prepared.

In order to achieve the above object, the technical solution adopted in the present invention is: a preparation method of a humidity-sensitive carbon nanotube/graphene/organic composite flexible material is provided, comprising the following steps:

S1: Immerse the graphene in a mixed acid prepared from concentrated sulfuric acid and concentrated nitric acid at a material-to-liquid ratio of 1 g:180 to 220 mL, treat at 68 to 75 ° C for 6 to 8 hours, and then perform centrifugation, cleaning and drying in sequence, get graphene oxide;

S2: dispersing graphene oxide and carbon nanotubes in a solvent, respectively, to obtain a graphene dispersion and a carbon nanotube dispersion with a concentration of 3-7 mg/mL;

S3: the flexible substrate is soaked in the graphene dispersion solution and the carbon nanotube dispersion solution in turn to obtain a carbon nanotube/graphene/organic composite flexible material.

On the basis of the above technical solutions, the present invention can also be improved as follows.

Further, the volume ratio of concentrated sulfuric acid and concentrated nitric acid in the mixed acid is 1:1-5.

Further, the graphene is single-layer graphene or multi-layer graphene; and the carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes.

Further, the cleaning solution used for cleaning in S1 is deionized water with pH≥6; the drying temperature is 55-65° C., and the drying time is 12-16 h.

Further, the solvent for dispersing graphene oxide in S2 is ethanol; the solvent for dispersing carbon nanotubes is N,N-dimethylformamide.

Further, the flexible substrate was ultrasonically cleaned with absolute ethanol for 10-30 min before soaking.

Further, the flexible substrate is polypropylene, polyacrylonitrile, polyvinyl formal, polyamide, polyethylene terephthalate, polyamide or cyanoacrylate

Further, the soaking time of the flexible substrate in the graphene dispersion liquid is 4-7 min, after soaking, it is dried at 60 °C for 10 min, then put into the carbon nanotube dispersion liquid for soaking for 3-5 min, and then dried at 150 °C for 0.5 h , to obtain carbon nanotube/graphene/organic composite flexible materials.

Using the above method, a humidity-sensitive carbon nanotube/graphene/organic composite flexible material can be prepared, and the flexible humidity sensor can be obtained after the flexible material is cut and coated with electrodes.

The beneficial effects of the present invention are:

1. In the present invention, graphene oxide and carbon nanotubes are used to prepare the composite flexible layer, because strong hydrogen bonds and van der Waals interaction can be formed between the two, so the carbon nanotube/graphene/organic composite finally prepared is more The resistance of the layer material is small, which brings the advantage of stable performance to the sensor.

2. The characteristic of the humidity sensitive element is that the substrate is covered with a film made of moisture-sensitive material. When the water vapor in the air is adsorbed on the moisture-sensitive film, the resistivity and resistance value of the element change. Humidity can be measured with one feature. When the humidity in the air increases, the concentration of water molecules increases, the moisture-sensitive film absorbs more water molecules, the electrical conductivity increases, the resistivity decreases, and the resistance decreases accordingly. When the water molecules on the surface of the humidity sensitive film fall off, the resistance will return to its original value. However, due to the good hydrophilic properties of graphene oxide itself, the shedding of water molecules takes a long time, and the shedding of water molecules can be accelerated after the surface of graphene oxide is covered with carbon nanotubes. Carbon nanotubes have a tubular structure and are interspersed between graphene sheet structures. Since carbon nanotubes are hydrophobic, when the water molecules adsorbed by graphene come into contact with carbon nanotubes, they will fall off, accelerating the moisture-sensitive film. Responsive recovery. Therefore, the resistance of the humidity-sensitive film can quickly decrease when the humidity change is detected, and when the humidity returns to the original value, the water molecules on the surface of the humidity-sensitive film fall off, and the resistance also recovers quickly. In this way, the humidity sensor has the characteristics of high sensitivity and fast response recovery. The humidity response time of the humidity sensor provided by the invention is less than 2 seconds, and the recovery time is less than 10 seconds.

3. From the perspective of the preparation process of the composite flexible conductive fabric, the adopted dip coating process is simple, the production cost is low, the efficiency is high, and it is easy to realize continuous and large-scale production.

Description of drawings

Fig. 1 is the humidity-resistance fast response characteristic curve of carbon nanotube/graphene/organic composite flexible material;

Figure 2 is the humidity-resistance response recovery time characteristic curve of the carbon nanotube/graphene/organic composite flexible material with the best sensitivity;

Fig. 3 is the surface SEM image of carbon nanotube/graphene/organic composite flexible material;

Fig. 4 is the humidity gradient-resistance characteristic curve of carbon nanotube/graphene/organic composite flexible material;

Figure 5 is the humidity point diagram of carbon nanotube/graphene/organic composite flexible material.

Detailed ways

The materials used in the process of preparing the flexible self-adhesive cloth with pressure/friction sensing function in the present invention are as follows:

1. Graphene: it can be single-layer graphene or multi-layer graphene;

2. Carbon nanotubes: can be single-walled carbon nanotubes or multi-walled carbon nanotubes; preferably multi-walled carbon nanotubes, and the average diameter of the multi-walled carbon nanotubes is 10-20 nm, and the average length is 20 μm.

3. Flexible substrate: The flexible substrate is 2cm wide and 10cm long, and is made of high polymers, such as polypropylene, polyacrylonitrile, polyvinyl formal, polyamide, polyethylene terephthalate, polyethylene amides or cyanoacrylates, etc.

The specific embodiments of the present invention will be described in detail below with reference to the examples.

Example 1

A preparation method of a humidity-sensitive carbon nanotube/graphene/organic composite flexible material, comprising the following steps:

S1: take 150 mL of concentrated sulfuric acid (98%) and 50 mL of concentrated nitric acid (65%), and mix the two to obtain 200 mL of mixed acid; add 1 g of multi-layer graphene to the above mixed acid, stir evenly and heat to 70 ° C to keep the reaction 7h. After the reaction system was cooled, the reaction system was centrifuged at 6000 rpm for 3 min, then washed with deionized water with pH ≥ 6 for 4 times, and then dried at 60 °C for 14 h to obtain graphene oxide;

S2: Disperse the prepared graphene oxide in absolute ethanol to obtain a graphene oxide dispersion liquid with a concentration of 5 mg/mL; disperse the multi-walled carbon nanotubes in N,N-dimethylformamide (DMF) , to obtain a carbon nanotube dispersion with a concentration of 5 mg/mL;

S3: ultrasonically clean both sides of the polypropylene non-woven fabric with absolute ethanol for 10 minutes;

S4: soak the cleaned polypropylene non-woven fabric in the graphene oxide dispersion for 5 min, and then dry at 60° C. for 10 min to obtain a graphene oxide-coated non-woven fabric;

S5: The obtained graphene oxide-coated non-woven fabric was soaked in carbon nanotube dispersion for 20 s, and then dried at 150° C. for 0.5 h to obtain a carbon nanotube/graphene/organic composite multilayer coated Non-woven.

Embodiment 2

A preparation method of a humidity-sensitive carbon nanotube/graphene/organic composite flexible material, the graphene oxide-coated non-woven fabric is soaked in a carbon nanotube dispersion for 1 min, and the rest of the operations are the same as in the embodiment.

Embodiment 3

A preparation method of a humidity-sensitive carbon nanotube/graphene/organic composite flexible material, the graphene oxide-coated non-woven fabric is soaked in a carbon nanotube dispersion liquid for 3 minutes, and the remaining operations are the same as those in the embodiment.

Embodiment 4

A preparation method of a humidity-sensitive carbon nanotube/graphene/organic composite flexible material, the graphene oxide-coated non-woven fabric is soaked in a carbon nanotube dispersion for 10 minutes, and the rest of the operations are the same as in the embodiment.

Embodiment 5

A preparation method of a humidity-sensitive carbon nanotube/graphene/organic composite flexible material, the graphene oxide-coated non-woven fabric is soaked in a carbon nanotube dispersion liquid for 5 minutes, and the rest of the operations are the same as in the embodiment.

Fig. 1 is the humidity-resistance fast response characteristic curve of carbon nanotube/graphene/organic composite flexible material, A to E are respectively the humidity-resistance response characteristic curve of the flexible material obtained in Example 1 to Example 5. It can be seen from Figure 1 that the resistance value of the carbon nanotube/graphene/organic composite flexible material decreases with the increase of relative humidity, and the sensitivity is high; and it can be seen from the curves A to C and E in Figure 1 that, With the prolongation of the soaking time of the graphene oxide-coated non-woven fabric in the carbon nanotube dispersion, its resistance-humidity change sensitivity also increases; it can be seen from the curve D in Figure 1 that the carbon nanotube/graphene/ The resistance value change rate of the organic composite flexible material is greatly reduced, but its resistance-humidity change sensitivity is still increasing. This result shows that the hydrophobicity of the surface of the humidity-sensitive film is already very strong, and the hydrophilicity of the humidity-sensitive film is prolonged by continuing to prolong the soaking time. Sexuality is disrupted and has hydrophobic properties.

Figure 2 shows the carbon nanotube/graphene/organic composite flexible material prepared in Example 5. At this time, the sensitivity of the humidity sensor reaches the best, the response time is 1s, and the recovery time is 7s. The response recovery curve is shown in Figure 2.

3 is a SEM image of the surface of the carbon nanotube/graphene/organic composite flexible material prepared in Example 2. As can be seen from the figure, carbon nanotubes and graphene form a conductive network with certain continuity.

Figure 4 is the humidity gradient-resistance characteristic curve of the carbon nanotube/graphene/organic composite flexible material. It can be seen from the figure that by changing the humidity of the test environment for many times, the resistance value of the humidity-sensitive film resistor at the corresponding humidity does not change much, indicating that the composite humidity-sensitive material has good stability.

Figure 5 is the humidity point diagram of carbon nanotube/graphene/organic composite flexible material. It can be seen from the figure that the sensitivity of the low humidity area is higher than that of the high humidity area, and the resistance change is larger. From 45%RH to 95%RH relative humidity, the resistance drops by 436kΩ for every 1%RH rise on average.

Although the specific embodiments of the present invention have been described in detail with reference to the examples, they should not be construed as limiting the protection scope of the present patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative efforts still belong to the protection scope of this patent.

Claims (8)

1. a preparation method of a humidity-sensitive carbon nanotube/graphene/organic substrate composite flexible material, is characterized in that, comprises the following steps: S1: Immerse the graphene in a mixed acid prepared from concentrated sulfuric acid and concentrated nitric acid at a material-to-liquid ratio of 1 g:180 to 220 mL, treat at 68 to 75 ° C for 6 to 8 h, and then perform centrifugation, cleaning and drying in sequence, get graphene oxide; S2: disperse graphene oxide and carbon nanotubes in a solvent, respectively, to obtain a graphene oxide dispersion liquid and a carbon nanotube dispersion liquid with a concentration of 3-7 mg/mL; wherein, the solvent for dispersing graphene oxide is ethanol; dispersing The solvent of carbon nanotubes is N,N-dimethylformamide; S3: soak the flexible substrate in the graphene oxide dispersion liquid and the carbon nanotube dispersion liquid in turn to obtain a carbon nanotube/graphene oxide/organic substrate composite flexible material; wherein, the flexible substrate is immersed in the graphene oxide dispersion liquid The soaking time is 4~7min. After soaking, it is dried at 60°C for 10min, then put into the carbon nanotube dispersion solution for soaking for 5min, and then dried at 150°C for 0.5h. 2. preparation method according to claim 1, is characterized in that: the volume ratio of vitriol oil and concentrated nitric acid in described mixed acid is 1～5:1. 3. The preparation method according to claim 1, wherein the graphene is a single-layer graphene or a multi-layer graphene; the carbon nanotube is a single-walled carbon nanotube or a multi-walled carbon nanotube. 4. The preparation method according to claim 1, characterized in that: the cleaning solution used for cleaning in S1 is deionized water with pH≥6; the drying temperature is 55~65°C, and the drying time is 12~16h. 5 . The preparation method according to claim 1 , wherein the flexible substrate is ultrasonically cleaned with absolute ethanol for 10-30 min before soaking. 6 . 6. The preparation method according to claim 1 or 5, wherein the flexible substrate is polypropylene, polyacrylonitrile, polyvinyl formal, polyamide or polyethylene terephthalate. 7. The humidity-sensitive carbon nanotube/graphene oxide/organic substrate composite flexible material prepared by the preparation method according to any one of claims 1 to 6. 8. A flexible humidity sensor, comprising the flexible material of claim 7.

Images