CN117534062B - Preparation and application of one-dimensional vanadium oxide based nano rod material synergistic composite two-dimensional graphene sheet conductive sensing material - Google Patents

Abstract

The present invention relates to the preparation and application _of a conductive sensing material composed of a one-dimensional vanadium oxide nanorod material and a composite two-dimensional graphene sheet. First, vanadium pentoxide particles are added to an acetic acid solution and stirred thoroughly to prepare a _V2O5 suspension; then _{the V2O5} suspension is mixed with a GO dispersion, and a composite material _VO2 @RGO of reduced graphene oxide nanosheets loaded with vanadium dioxide nanorods is obtained through hydrothermal reaction and freeze drying; finally, the composite material _VO2 @RGO is annealed with ammonia to obtain a one-dimensional/two-dimensional composite sensing material VOx _@ RGO of graphene sheets loaded with vanadium oxide nanorods. The controllable construction of the one-dimensional/two-dimensional composite material of the present invention is conducive to improving the sensitivity and sensing range of the sensor under strain, and realizing a comprehensive improvement in sensing performance. The preparation method of the entire composite sensing material is simple, low in cost, low in energy consumption, and easy to be industrially mass-produced and applied in flexible strain sensors.

Description

Preparation and application of conductive sensing material based on one-dimensional vanadium-based nanorods and composite two-dimensional graphene sheets

Technical Field

The invention relates to the preparation and application of a one-dimensional/two-dimensional composite sensing material of graphene sheets loaded with vanadium oxide nanorods, belonging to the technical field of functional nanomaterials.

Background technique

In recent years, the global manufacturing industry has rebounded, and the market capacity of strain sensors has also grown accordingly. As an important component of wearable electronic devices, strain sensors have flourished in the fields of motion monitoring, human-machine interface, electronic skin, and medical rehabilitation, and have good application prospects. In order to meet the use requirements of these advanced wearable devices, sensors should have high sensitivity and a wide working range. Therefore, the preparation of flexible strain sensors that meet application requirements by optimizing the selection of active material systems and designing composites of materials of different dimensions has become a research hotspot.

Strain sensors can sense mechanical deformation by measuring changes in electrical signals. To date, researchers have proposed many methods to develop flexible strain sensors, such as using nanomaterials such as carbon black (CB), carbon nanotubes (CNTs), graphene, metal particles, nanowires, etc. as sensing elements, combined with elastic polymers as flexible and stretchable substrates. At present, common strain sensors can be roughly divided into four types according to their sensing mechanism: resistive, capacitive, piezoelectric, and triboelectric. Among them, in terms of the stability of the sensing process, the sensitivity of the sensing signal, and the reliability of the sensor, the resistive strain sensor is undoubtedly a simple and easy-to-integrate design. To achieve high sensitivity of resistive strain sensors, the device requires obvious separation of the conductive layer during the stretching process, while the wide sensing range requires that the electrical contact and integrity of the conductive layer be maintained under large strains.

Graphene is a new material with a two-dimensional honeycomb lattice structure composed of a single layer of carbon atoms tightly packed together. Its honeycomb structure is composed of carbon atoms connected by ^sp2 hybridization. Graphene has excellent electrical conductivity, and its electron mobility is as high as ^15000cm2 /(V·s) at room temperature. It has been proven to be a highly sensitive sensing element. However, for pure graphene sheets, the mechanism of increased resistance during strain is that stretching causes the graphene lattice structure to be distorted, and the band structure and the electron transmission efficiency near the Fermi level change, thereby increasing the resistance response signal. When the strain exceeds a certain range, the conductive path of the stretched graphene sheet will not be able to recover because the excessive strain intensity destroys the hexagonal honeycomb structure of graphene, resulting in plastic deformation of graphene. Therefore, strain sensors designed based on graphene can achieve high sensitivity, but cannot obtain a wide sensing range.

At present, there have been many reports on the research of strain sensors based on the composite of graphene and other conductive media. The literature (Lin, Y.; Yin, Q.; Wang, J.; Jia, H.; Yuan, G.; Wang, J., Sensitivity Enhanced, Highly Stretchable, and Mechanically Robust Strain Sensors Based on Reduced Graphene Oxide-Aramid Nanofibers Hybrid Fillers. Chemical Engineering Journal 2022, 443, 136468.) designed a graphene material mixed with aramid nanofibers as a sensing material self-assembled around natural rubber. Graphene sheets themselves are very prone to irreversible agglomeration or even accumulation, and aramid nanofibers have a conjugated structure similar to graphene, which easily leads to strong π-π interactions between the two. Aramid nanofibers, as a bridge connecting RGO nanosheets, can effectively avoid the agglomeration of graphene sheets and form a unique interconnected network. The strain sensor of this composite material shows significantly improved sensitivity (GF up to 870) in a wider sensing range (0-226%). The literature (Zhang, H.; Han, W.; Xu, K.; Lin, H.; Lu, Y.; Liu, H.; Li, R.; Du, Y.; Nie, Z.; Xu, F.; Miao, L.; Zhu, J.; Huang, W., Stretchable and Ultrasensitive Intelligent Sensors for Wireless Human–Machine Manipulation. Advanced Functional Materials 2021, 31, 2009466.) designed oxygen-doped two-dimensional metal vanadium nitride nanosheets (VNO) as a single sensing material. Thanks to the ultra-high conductivity of transition metal nitride nanosheets, the oxygen-doped VNO nanosheets not only have excellent conductive properties but also have a high specific surface area. The strain sensor assembled based on VNO nanosheets shows high sensitivity (GF up to 2667) within the sensing range (0-100%), which greatly exerts the advantage of the high sensitivity of two-dimensional nanosheet materials, but its sensing range is narrow.

However, there are few studies on the composite of graphene and one-dimensional metal materials as sensing materials. The fast resistance strain response of strain sensors assembled based on two-dimensional graphene sheets originates from the slip and fracture mechanism of graphene sheets, and usually exhibits a narrow sensing range. In order to solve the above problems, the present invention designs a one-dimensional/two-dimensional composite sensing material of graphene sheets loaded with vanadium oxide nanorods.

Summary of the invention

The purpose of the present invention is to solve the problem of the deficiency of existing single graphene materials as conductive materials for sensors, and propose a method of converting zero-dimensional particles with poor conductivity into one-dimensional highly conductive nanorods through hydrothermal reaction, and at the same time composite two-dimensional graphene nanosheets to construct a richer conductive network. The preparation method is simple and controllable, and the strain sensor assembled with the one-dimensional/two-dimensional composite material can simultaneously achieve excellent sensing performance with high sensitivity and wide sensing range. The controllable construction of the one-dimensional/two-dimensional composite material improves the sensitivity and sensing range of the sensor under strain, and achieves a comprehensive improvement in sensing performance.

The present invention verifies that the sensor assembled with the composite material VO _x @RGO prepared at an annealing temperature of 600°C and a mass ratio of hydrothermal precursor liquid V ₂ O ₅ :GO of 3:7 has better performance than the same type of sensors. It can not only maintain a high sensitivity (GF of 1143) under large strain (sensing range of 0-457%), but also has good mechanical durability and stability (4000 cycles of strain).

In order to solve the technical problem of the present invention, the composite material prepared by the present invention is realized by the following technical scheme:

A method for preparing a one-dimensional/two-dimensional composite sensing material of graphene sheets loaded with vanadium oxide nanorods, characterized in that the preparation method comprises the following steps:

a. Dissolve a certain amount of commercial vanadium pentoxide (V ₂ O ₅ ) particles in an acetic acid (CH ₃ COOH) solution diluted with an appropriate amount of deionized water, and stir thoroughly to prepare an orange-yellow V ₂ O ₅ suspension.

b. Mix a certain amount of graphene oxide (GO) dispersion with the V ₂ O ₅ suspension obtained in step a to prepare a hydrothermal precursor solution, stir and mix evenly, and then transfer to a stainless steel reactor containing polytetrafluoroethylene for hydrothermal reaction. After the reaction is completed, cool to room temperature, place the sample in a freeze drying oven for freeze drying, and obtain a composite material of one-dimensional vanadium dioxide nanorods loaded with two-dimensional reduced graphene oxide nanosheets, VO ₂ @RGO.

c. The composite material VO ₂ @RGO obtained in step b is subjected to high-temperature thermal reduction treatment in a tube furnace through an annealing process to obtain a one-dimensional/two-dimensional composite sensing material VO _x @RGO of graphene sheets loaded with vanadium oxide nanorods.

Preferably, the concentration of the CH ₃ COOH solution after dilution in step a is 1 mg mL ^-1 , the mass concentration of the V ₂ O ₅ suspension after mixing is 9 mg mL ^-1 , and the stirring condition is stirring at room temperature for ≥12 h.

Preferably, the mass concentration of the GO dispersion in step b is 13.73 mg mL ^-1 , the total mass of V ₂ O ₅ and GO in the hydrothermal precursor is 384 mg, wherein the mass ratio of V ₂ O ₅ :GO is 1:1, the stirring conditions are stirring at room temperature for ≥ 12 h; the hydrothermal temperature is 200°C, the hydrothermal time is 72 h, and the freeze-drying time is 36-48 h. The hydrothermal reaction realizes the phase transformation of the V ₂ O ₅ particles with poor conductivity into one-dimensional VO ₂ nanorods with metallic properties.

Preferably, in step c, the gas in the tube furnace is ammonia (NH ₃ ), the heating rate during the annealing process is 5° C. min ^-1 , the annealing temperature is 400-700° C., and the holding time is 3 hours.

Preferably, a certain amount of commercial V ₂ O ₅ particles is dissolved in a 1 mg mL ^-1 CH ₃ COOH solution, and stirred at room temperature for 12 h to prepare an orange-yellow V ₂ O ₅ suspension with a mass concentration of 9 mg mL ^-1 .

The total mass of V ₂ O ₅ and GO in the hydrothermal precursor solution was kept at 384 mg. According to the mass ratio of V ₂ O ₅ :GO of 7:3, the prepared V ₂ O ₅ suspension was mixed with a GO dispersion with a mass concentration of 13.73 mg mL ^-1 to prepare a hydrothermal precursor solution. After stirring at room temperature for 12 h to mix evenly, the mixture was transferred to a stainless steel reactor containing polytetrafluoroethylene and subjected to hydrothermal reaction at 200 °C for 72 h. After cooling to room temperature, the sample was placed in a freeze drying oven for freeze drying for 36-48 h.

Finally, the composite material VO ₂ @RGO was transformed into a one-dimensional/two-dimensional composite material VO _0.9 @RGO of graphene sheets loaded with vanadium oxide nanorods by high-temperature annealing in ammonia at 600 ° ^C for 3 h at a heating rate of 5 °C min -1 .

Another technical solution of the present invention: the one-dimensional/two-dimensional composite sensing material VO _x @RGO loaded with graphene sheets can be used as a conductive material for strain sensors.

Preferably, the method for preparing the one-dimensional/two-dimensional composite material VO _x @RGO as a conductive material for a strain sensor comprises the following steps:

a. The composite material VO _x @RGO was placed in a centrifuge tube filled with ethanol solution and subjected to ultrasonic treatment to obtain a VO _x @RGO suspension.

b. Apply the VO _x @RGO suspension obtained in step a to the elastic double-sided tape VHB substrate, and then place the whole under a far-infrared light source to accelerate drying. After drying, copper wires are drawn out from both ends of the material as electrodes and fixed with conductive silver glue. After the silver glue is dried, a VHB substrate of the same size is attached to the side coated with the active material to obtain a VO _x @RGO strain sensor with a certain load.

c. The VO _x @RGO strain sensor was controlled by a universal material testing machine (HY-0350, Shanghai Hengyi Precision Co., Ltd.) and the resistance change of the sensor was recorded in real time by a digital current source meter (Keithley 2450) to test the performance of the VO _x @RGO strain sensor.

d. After testing, the sensing performance of the VO _x @RGO strain sensor was optimized by successively adjusting the temperature during the ammonia annealing process of the composite material VO ₂ @RGO and the mass ratio of V ₂ O ₅ to GO in the hydrothermal precursor solution.

Preferably, the mass concentration of the VO _x @RGO suspension in step a is 5 mg mL ^-1 ; and the ultrasonic treatment time in step a is 2 h.

Preferably, the size of the VHB substrate in step b is 3 cm×3 cm; the area ratio of the VHB substrate to the active material drop-coated region in step b is 4:1; and the loading amount of the VO _x @RGO strain sensor in step b is 0.5 mg cm ^-2 .

Preferably, the annealing temperature in step d is regulated at 400°C, 500°C, 600°C and 700°C respectively. The strain sensor assembled with the composite material VO _x @RGO prepared at an annealing temperature of 600°C achieves a wider strain range (0-348%) and higher sensitivity (492).

Preferably, in step d, the total mass of V ₂ O ₅ and GO in the hydrothermal precursor solution is maintained at 384 mg, and the mass ratio of V ₂ O ₅ :GO is adjusted to 7:3, 1:1, 3:7 and 1:9 respectively. Among them, the strain sensor assembled with the composite material VO _x @RGO prepared at an annealing temperature of 600°C and a mass ratio of the hydrothermal precursor solution of 3:7 achieves a wider strain range (0-457%) and higher sensitivity (1143).

Beneficial effects:

The hydrothermal reaction of the present invention successfully realizes the transformation of _V2O5 particles with poor conductivity into _VO2 nanorods _with metallic properties, and the annealing treatment causes the _VO2 nanorods to undergo in-situ deoxidation reaction, further improving the conductivity of the composite material. The _VOx nanorods are evenly dispersed between the RGO nanosheets, and can act as a "bridge" to connect the nanosheets to form a _VOx -RGO- _VOx conductive network, so that the entire composite material continues to maintain or reconstruct the "surface-surface" and "line-surface" conductive networks.

Compared with other graphene composite sensing materials, the preparation method of the present invention for selecting graphene sheets to load vanadium oxide nanorods is efficient and suitable for industrial-scale production. First, the V ₂ O ₅ particles with poor conductivity are transformed into one-dimensional VO ₂ nanorods with metallic properties through hydrothermal and freeze-drying treatment steps, and are loaded on two-dimensional reduced graphene oxide (RGO) nanosheets to obtain a composite material VO ₂ @RGO. Then, the VO ₂ nanorods are in-situ deoxidized and converted into VO _x nanorods through high-temperature annealing treatment to obtain the composite material VO _x @RGO.

Graphene is a carbon nanomaterial with a two-dimensional honeycomb lattice structure composed of a single layer of carbon atoms tightly stacked together. Its two-dimensional ^sp2 hybrid structure allows electrons to move sub-micrometer distances without scattering, which is the quantum Hall effect. It has excellent electrical properties and good flexibility, and has been proven to be a highly sensitive sensing element.

The vanadium pentoxide selected by the present invention has the advantage of adjustable morphology, and at the same time constructs a composite structure of two-dimensional RGO nanosheets loaded with one-dimensional VO _x nanorods, which effectively improves the overall performance of the sensor. Due to its own characteristics, graphene sheets usually exist in the form of sheet-like aggregates, and the contact area between the sheets is small. Therefore, the strain effect of the "RGO-RGO" surface-to-surface conductive structure formed by the graphene sheets is weak.

Although the sensor assembled based on a single RGO nanosheet as a sensing material in the present invention has a high sensitivity (1767), its sensing range is very limited (0-179%). After loading VO _x nanorods, the performance of the entire sensor is improved. VO _x nanorods are uniformly loaded on the RGO sheets and between adjacent RGO sheets, forming a "RGO-VO _x -RGO" line-surface-line conductive structure. When the RGO sensor is stretched, the "surface-surface" conductive structure established between the sheets will be first destroyed due to the increase in the spacing between adjacent RGO sheets. For the VO _x @RGO sensor, the load of VO _x nanorods can act as a "bridge" when the sensor is stretched, and continue to maintain or reconstruct the "surface-line" and "surface-surface" conductive structures between the entire material. As the tensile strain increases, the "surface-line" and "surface-surface" conductive structures will slip and break, resulting in a gradual reduction in the effective conductive path of the sensor and a decrease in the conductivity of the composite material. Therefore, the addition of VO _x nanorods can play a buffering role, effectively improve the tensile strain capacity of the sensor, and greatly improve the performance of the sensor.

The one-dimensional/two-dimensional composite materials VO _0.9 @RGO (denoted as VR _0.5 , VR _0.3 , VR _0.7 and VR _0.9 ) prepared in Examples 3, 7, 8 and 9 and the pure two-dimensional nanosheet material RGO prepared in Example 10 were selected to assemble strain sensors according to the steps in Example 5 and perform performance tests. The sensor performance test results in Figure 7a and b show that the strain sensor assembled with pure RGO material has the highest sensitivity (1767) due to the slippage of RGO nanosheets during the strain process, but the conductive path is destroyed after the pure RGO nanosheets are broken, resulting in the narrowest sensing range of the RGO sensor (0-179%). Similarly, for strain sensors assembled based on composite materials VR _0.3 , VR _0.5 , VR _0.7 and VR _0.9 , as the GO content increases, the sensitivity of the sensor (respectively: 480, 1045, 1143 and 1085) shows a trend of increasing first and then decreasing. At the same time, due to the connection of VO _x nanorods between adjacent RGO nanosheets, the sensing range of the sensor (respectively: 0-236%, 0-304, 0-457%, 0-292%) also shows a trend of increasing first and then decreasing. Therefore, the sensor assembled based on the composite material VR _0.7 shows the widest sensing range (0-457%) and the relatively highest sensitivity (1143). At the same time, as shown in Figures 9 and 10, it has good dynamic stability and long cycle ability (4000 cycles of strain).

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described below in conjunction with the accompanying drawings.

FIG1 is a scanning electron microscope image of the commercial V ₂ O ₅ particle material in Example 1 of the present invention;

FIG2 is a scanning electron microscope image of the composite material VO ₂ @RGO in Example 1 of the present invention;

FIG3 is an XRD spectrum of the composite material VO ₂ @RGO in Example 1 of the present invention;

FIG4 is an XRD spectrum of the composite material VO _x @RGO after annealing at different temperatures in Example 5 of the present invention;

FIG5 is a current-voltage (IV) curve of a strain sensor assembled with the composite material VO _x @RGO after annealing at different temperatures in Example 5 of the present invention;

6 is a performance diagram of the strain sensor assembled from the composite material VO _x @RGO after annealing at different temperatures in Example 5 of the present invention, wherein relative resistance change ΔR/R ₀ (ΔR＝RR ₀ , R: instantaneous resistance, R ₀ : initial resistance), sensitivity (GF＝(ΔR/R ₀ )/ε, ε＝LL ₀ /L ₀ , L: length after stretching, L ₀ : initial length);

FIG7a is a performance diagram of a strain sensor assembled from a composite material VO _0.9 @RGO and pure RGO material after adjusting the mass ratio of the hydrothermal precursor (VR _0.3 , VR _0.5 , VR _0.7 , VR _0.9 ) in Example 11 of the present invention, and FIG7b is a comparison diagram of the corresponding maximum sensitivity performance and sensing range performance;

FIG8 is a scanning electron microscope image of the best composite material VO _0.9 @RGO in Example 11 of the present invention;

FIG9 is a diagram showing the resistance response variation of the strain sensor VR _0.7 in Example 11 of the present invention under different strain conditions at a frequency of 0.2 Hz;

FIG10 is a long cycle test diagram of the strain sensor VR _0.7 in Example 11 of the present invention;

FIG. 11 is a flow chart of the composite material VO _x @RGO of graphene sheets loaded with vanadium oxide nanorods of the present invention.

Detailed ways

The technical solution of the present invention is further described below in conjunction with the embodiments. These embodiments should not be construed as limiting the technical solution.

1. Preparation of V ₂ O ₅ suspension

A certain amount of commercial vanadium pentoxide (V ₂ O ₅ ) particles were dissolved in an appropriate amount of acetic acid (CH ₃ COOH) solution, and the mixture was stirred at room temperature for 12 h to prepare an orange-yellow V ₂ O ₅ suspension.

2. Preparation of VO _x @RGO composites

The hydrothermal precursor solution was prepared by mixing graphene oxide (GO) dispersion with different contents with the V ₂ O ₅ suspension obtained above, and the total mass of V ₂ O ₅ and GO in the hydrothermal precursor solution was kept at 384 mg. After stirring at room temperature for 12 hours and mixing evenly, the mixture was transferred to a stainless steel reactor with polytetrafluoroethylene and hydrothermally reacted at 200°C for 72 hours. After cooling to room temperature, the sample was placed in a freeze drying oven for freeze drying for 36-48 hours to obtain the composite material VO ₂ @RGO. Finally, the composite material VO ₂ @RGO was converted into a one-dimensional/two-dimensional composite sensing material VO _x @RGO of graphene sheets loaded with vanadium oxide nanorods by high-temperature annealing with ammonia at different temperatures for 3 hours.

3. Preparation of VO _x @RGO strain sensor

The composite material VO _x @RGO was placed in a centrifuge tube filled with ethanol solution and ultrasonically treated for 2 hours to obtain a VO _x @RGO suspension. The VO _x @RGO suspension obtained above was then drop-coated on a 3cm×3cm elastic double-sided tape VHB substrate (active material area: 1.5cm×1.5cm), and then the whole was placed under a far-infrared light source to accelerate drying. After drying, copper wires were drawn out from both ends of the material as electrodes and fixed with conductive silver glue. After the silver glue was dried, a VHB substrate of the same size was attached to the side coated with the active material to obtain a VO _x @RGO strain sensor with a loading of 0.5mg cm ^-2 .

Example 1

A certain amount of commercial V ₂ O ₅ particles was dissolved in a 1 mg mL ^-1 CH ₃ COOH solution and stirred at room temperature for 12 h to prepare an orange-yellow V ₂ O ₅ suspension with a mass concentration of 9 mg mL ^-1 .

The total mass of V ₂ O ₅ and GO in the hydrothermal precursor solution was kept at 384 mg. According to the mass ratio of V ₂ O ₅ :GO of 1:1, the prepared V ₂ O ₅ suspension was mixed with a GO dispersion with a mass concentration of 13.73 mg mL ^-1 to prepare a hydrothermal precursor solution. After stirring at room temperature for 12 hours and mixing evenly, the mixture was transferred to a stainless steel reactor with polytetrafluoroethylene and hydrothermally reacted at 200°C for 72 hours. After cooling to room temperature, the sample was placed in a freeze drying oven for freeze drying for 36-48 hours. The scanning electron microscope images in Figures 1 and 2 and the XRD spectrum in Figure 3 confirm that the hydrothermal reaction successfully transformed the commercial V ₂ O ₅ particles with poor conductivity into one-dimensional VO ₂ nanorods with metallic properties to obtain the composite material VO ₂ @RGO.

Finally, the composite material VO ₂ @RGO was subjected to high temperature annealing treatment at 400°C for 3 h at a heating rate of 5°C min ^-1 . The XRD spectrum in FIG4 shows that the composite material VO 2 @RGO was converted into a one-dimensional/two-dimensional composite material VO ₂ @RGO of graphene sheets loaded with vanadium oxide nanorods.

Example 2

A certain amount of commercial V ₂ O ₅ particles was dissolved in a 1 mg mL ^-1 CH ₃ COOH solution and stirred at room temperature for 12 h to prepare an orange-yellow V ₂ O ₅ suspension with a mass concentration of 9 mg mL ^-1 .

The total mass of V ₂ O ₅ and GO in the hydrothermal precursor solution was kept at 384 mg. According to the mass ratio of V ₂ O ₅ :GO of 1:1, the prepared V ₂ O ₅ suspension was mixed with a GO dispersion with a mass concentration of 13.73 mg mL ^-1 to prepare a hydrothermal precursor solution. After stirring at room temperature for 12 hours and mixing evenly, the mixture was transferred to a stainless steel reactor with polytetrafluoroethylene and hydrothermally reacted at 200°C for 72 hours. After cooling to room temperature, the sample was placed in a freeze drying oven for freeze drying for 36-48 hours. The scanning electron microscope images in Figures 1 and 2 and the XRD spectrum in Figure 3 confirm that the hydrothermal reaction successfully transformed the commercial V ₂ O ₅ particles with poor conductivity into one-dimensional VO ₂ nanorods with metallic properties to obtain the composite material VO ₂ @RGO.

Finally, the composite material VO ₂ @RGO was subjected to high temperature annealing treatment in ammonia at a temperature of 500°C for 3 h at a heating rate of 5°C min ^-1 . The XRD spectrum in FIG4 shows that the composite material VO 2 @RGO was converted into a one-dimensional/two-dimensional composite material V ₂ O ₃ @RGO of graphene sheets loaded with vanadium oxide nanorods.

Example 3

A certain amount of commercial V ₂ O ₅ particles was dissolved in a 1 mg mL ^-1 CH ₃ COOH solution and stirred at room temperature for 12 h to prepare an orange-yellow V ₂ O ₅ suspension with a mass concentration of 9 mg mL ^-1 .

The total mass of V ₂ O ₅ and GO in the hydrothermal precursor solution was kept at 384 mg. According to the mass ratio of V ₂ O ₅ :GO of 1:1, the prepared V ₂ O ₅ suspension was mixed with a GO dispersion with a mass concentration of 13.73 mg mL ^-1 to prepare a hydrothermal precursor solution. After stirring at room temperature for 12 hours and mixing evenly, the mixture was transferred to a stainless steel reactor with polytetrafluoroethylene and hydrothermally reacted at 200°C for 72 hours. After cooling to room temperature, the sample was placed in a freeze drying oven for freeze drying for 36-48 hours. The scanning electron microscope images in Figures 1 and 2 and the XRD spectrum in Figure 3 confirm that the hydrothermal reaction successfully transformed the commercial V ₂ O ₅ particles with poor conductivity into one-dimensional VO ₂ nanorods with metallic properties to obtain the composite material VO ₂ @RGO.

Finally, the composite material VO ₂ @RGO was annealed in ammonia at 600°C for 3 h at a heating rate of 5°C min ^-1 . The XRD spectrum in FIG4 shows that the composite material VO 2 @RGO was converted into a one-dimensional/two-dimensional composite material VO _0.9 @RGO of graphene sheets loaded with vanadium oxide nanorods.

Example 4

A certain amount of commercial V ₂ O ₅ particles was dissolved in a 1 mg mL ^-1 CH ₃ COOH solution and stirred at room temperature for 12 h to prepare an orange-yellow V ₂ O ₅ suspension with a mass concentration of 9 mg mL ^-1 .

The total mass of V ₂ O ₅ and GO in the hydrothermal precursor solution was kept at 384 mg. According to the mass ratio of V ₂ O ₅ :GO of 1:1, the prepared V ₂ O ₅ suspension was mixed with a GO dispersion with a mass concentration of 13.73 mg mL ^-1 to prepare a hydrothermal precursor solution. After stirring at room temperature for 12 hours and mixing evenly, the mixture was transferred to a stainless steel reactor with polytetrafluoroethylene and hydrothermally reacted at 200°C for 72 hours. After cooling to room temperature, the sample was placed in a freeze drying oven for freeze drying for 36-48 hours. The scanning electron microscope images in Figures 1 and 2 and the XRD spectrum in Figure 3 confirm that the hydrothermal reaction successfully transformed the commercial V ₂ O ₅ particles with poor conductivity into one-dimensional VO ₂ nanorods with metallic properties to obtain the composite material VO ₂ @RGO.

Finally, the composite material VO ₂ @RGO was subjected to high temperature annealing treatment at 700°C for 3 h at a heating rate of 5°C min ^-1 . The XRD spectrum in FIG4 shows that the composite material VO 2 @RGO was converted into a one-dimensional/two-dimensional composite material VO _0.9 /VN@RGO of graphene sheets loaded with vanadium oxide nanorods.

Example 5

The one-dimensional/two-dimensional composite materials prepared by annealing temperatures of 400°C, 500°C, 600°C and 700°C in Examples 1-4 of the present invention are VO ₂ @RGO, V ₂ O ₃ @RGO, VO _0.9 @RGO and VO _0.9 /VN@RGO (collectively referred to as VO _x @RGO), which can be used as conductive materials to assemble strain sensors. The composite materials are placed in a centrifuge tube filled with an ethanol solution and subjected to ultrasonic treatment for 2 hours to obtain a VO _x @RGO suspension with a mass concentration of 5 mg mL ^-1 . The VO _x @RGO suspension obtained above is then drop-coated on a 3cm×3cm elastic double-sided tape VHB substrate (active material area: 1.5cm×1.5cm), and then the whole is placed under a far-infrared light source to accelerate drying. After drying, copper wires are drawn out from both ends of the material as electrodes and fixed by conductive silver glue. After the silver glue is dried, a VHB substrate of the same size is attached to the side coated with the active material to obtain a VO _x @RGO strain sensor with a loading of 0.5 mg cm ^-2 .

The current-voltage (IV) curve test and sensing performance of the VO _x @RGO strain sensor were tested by applying strain to the strain sensor using a universal material testing machine (HY-0350, Shanghai Hengyi Precision Co., Ltd.) and using a digital current source meter (Keithley 2450) to record the resistance change of the sensor in real time. After data recording, data processing was performed using Excel software and graphing and analysis was performed using Origin software.

Example 6

The IV curve graph of Figure 5 shows that for the strain sensors assembled with VO _x @RGO composite materials in Examples 1-4 with annealing temperatures of 400°C, 500°C, 600°C and 700°C, respectively, the slope of the IV curve of the sensor gradually increases with the increase of annealing temperature, confirming that the increase of annealing temperature can effectively improve the conductivity of the composite material VO _x @RGO.

The sensor performance diagram in Figure 6 shows that the sensitivity value (GF) of the strain sensor assembled with the VO _x @RGO composite material of Examples 1-4 with annealing temperatures of 400°C, 500°C, 600°C and 700°C, respectively, shows a trend of first increasing and then decreasing with the increase of annealing temperature. The sensor shows the highest GF value (2661) at 500°C, GF values of 299 and 1045 at 400°C and 600°C, respectively, and the lowest GF value (229) at 700°C. The sensing range shows a trend of gradually widening with the increase of annealing temperature. The widest sensing range of 0-395% is achieved at 700°C, and the sensing ranges at 400°C, 500°C and 600°C are 0-200%, 0-261% and 0-304%, respectively. Because, the VO _x @RGO sensor assembled from the composite material (mass ratio of V ₂ O ₅ :GO is 1:1) with annealing temperature of 600°C can achieve both a wide sensing range (0-304%) and high sensitivity (1045).

Example 7

Example 6 The optimal annealing temperature was determined to be 600°C, and the mass ratio of V ₂ O ₅ :GO in the hydrothermal precursor solution was regulated according to the preparation steps in Example 4. A certain amount of commercial V ₂ O ₅ particles was dissolved in 1 mg mL ^-1 CH ₃ COOH solution, and an orange-yellow V ₂ O ₅ suspension with a mass concentration of 9 mg mL ^-1 was prepared by stirring at room temperature for 12 h.

The total mass of V ₂ O ₅ and GO in the hydrothermal precursor solution was kept at 384 mg. According to the mass ratio of V ₂ O ₅ :GO of 7:3, the prepared V ₂ O ₅ suspension was mixed with a GO dispersion with a mass concentration of 13.73 mg mL ^-1 to prepare a hydrothermal precursor solution. After stirring at room temperature for 12 hours and mixing evenly, the mixture was transferred to a stainless steel reactor with polytetrafluoroethylene and hydrothermally reacted at 200 °C for 72 hours. After cooling to room temperature, the sample was placed in a freeze drying oven for freeze drying for 36-48 hours to obtain a composite material VO ₂ @RGO. Finally, the composite material VO 2 @RGO was annealed at 600 °C for 3 hours at a heating rate of 5 °C min ^-1 , and the composite material VO ₂ @RGO was converted into a one-dimensional/two-dimensional composite material VO _0.9 @RGO with graphene sheets loaded with vanadium oxide nanorods.

Example 8

The mass ratio of V ₂ O ₅ :GO in the hydrothermal precursor solution was regulated according to the preparation steps in Example 4. A certain amount of commercial V ₂ O ₅ particles was dissolved in 1 mg mL ^-1 CH ₃ COOH solution, and stirred for 12 h at room temperature to prepare an orange-yellow V ₂ O ₅ suspension with a mass concentration of 9 mg mL ^-1 .

The total mass of V ₂ O ₅ and GO in the hydrothermal precursor solution was kept at 384 mg. According to the mass ratio of V ₂ O ₅ :GO of 3:7, the prepared V ₂ O ₅ suspension was mixed with a GO dispersion with a mass concentration of 13.73 mg mL ^-1 to prepare a hydrothermal precursor solution. After stirring at room temperature for 12 hours and mixing evenly, the mixture was transferred to a stainless steel reactor with polytetrafluoroethylene and hydrothermally reacted at 200 °C for 72 hours. After cooling to room temperature, the sample was placed in a freeze drying oven for freeze drying for 36-48 hours to obtain a composite material VO ₂ @RGO. Finally, the composite material VO 2 @RGO was annealed at 600 °C for 3 hours at a heating rate of 5 °C min ^-1 , and the composite material VO ₂ @RGO was converted into a one-dimensional/two-dimensional composite material VO _0.9 @RGO with graphene sheets loaded with vanadium oxide nanorods.

Example 9

The mass ratio of V ₂ O ₅ :GO in the hydrothermal precursor solution was regulated according to the preparation steps in Example 4. A certain amount of commercial V ₂ O ₅ particles was dissolved in 1 mg mL ^-1 CH ₃ COOH solution, and stirred for 12 h at room temperature to prepare an orange-yellow V ₂ O ₅ suspension with a mass concentration of 9 mg mL ^-1 .

The total mass of V ₂ O ₅ and GO in the hydrothermal precursor solution was kept at 384 mg. According to the mass ratio of V ₂ O ₅ :GO of 1:9, the prepared V ₂ O ₅ suspension was mixed with a GO dispersion with a mass concentration of 13.73 mg mL ^-1 to prepare a hydrothermal precursor solution. After stirring at room temperature for 12 hours and mixing evenly, the mixture was transferred to a stainless steel reactor with polytetrafluoroethylene and hydrothermally reacted at 200 °C for 72 hours. After cooling to room temperature, the sample was placed in a freeze drying oven for freeze drying for 36-48 hours to obtain a composite material VO ₂ @RGO. Finally, the composite material VO 2 @RGO was subjected to high temperature annealing at 600 °C for 3 hours at a heating rate of 5 °C min ^-1 , and the composite material VO ₂ @RGO was converted into a one-dimensional/two-dimensional composite material VO _0.9 @RGO with graphene sheets loaded with vanadium oxide nanorods.

Example 10

According to the mass of GO of 384 mg, a pure GO dispersion was prepared as a hydrothermal precursor, and the mixture was stirred at room temperature for 12 hours and then transferred to a stainless steel reactor with polytetrafluoroethylene for hydrothermal reaction at 200°C for 72 hours. After cooling to room temperature, the sample was placed in a freeze drying oven for freeze drying for 36-48 hours, and finally annealed at 600°C for 3 hours with ammonia at a heating rate of 5°C min ^-1 to obtain a comparative sample material RGO.

Embodiment 11

The one-dimensional/two-dimensional composite materials VO _0.9 @RGO (denoted as VR _0.5 , VR _0.3 , VR _0.7 and VR _0.9 ) prepared in Examples 3, 7, 8 and 9 and the pure two-dimensional nanosheet material RGO prepared in Example 10 were selected to assemble strain sensors according to the steps in Example 5 and perform performance tests. The sensor performance test results in Figure 7a and b show that the strain sensor assembled with pure RGO material has the highest sensitivity (1767) due to the slippage of RGO nanosheets during the strain process, but the conductive path is destroyed after the pure RGO nanosheets are broken, resulting in the narrowest sensing range of the RGO sensor (0-179%). Similarly, for strain sensors assembled based on composite materials VR _0.3 , VR _0.5 , VR _0.7 and VR _0.9 , with the increase of GO content, the sensitivity of the sensors (480, 1045, 1143 and 1085, respectively) shows a trend of first increasing and then decreasing. At the same time, due to the connection of VO _x nanorods between adjacent RGO nanosheets, the sensing range of the sensors (0-236%, 0-304, 0-457%, 0-292%, respectively) also shows a trend of first increasing and then decreasing.

Therefore, the sensor assembled based on the composite material VR _0.7 exhibits the widest sensing range (0-457%) and the relatively highest sensitivity (1143). As shown in Figures 9 and 10, it has good dynamic stability and long cycle capability (4000 cycles of strain).

The present invention is not limited to the specific technical solutions described in the above embodiments, and all technical solutions formed by equivalent replacement are within the protection scope required by the present invention.

Claims (4)

1. The preparation method of the one-dimensional vanadium oxide nano rod material synergistic composite two-dimensional graphene sheet conductive sensing material is characterized by comprising the following steps of:

a. Dissolving a certain amount of commercial vanadium pentoxide particles in an acetic acid solution diluted by a proper amount of deionized water, and preparing an orange-yellow V ₂O₅ suspension by fully stirring;

b. Mixing a certain amount of graphene oxide dispersion liquid with the V ₂O₅ suspension liquid obtained in the step a to prepare a hydrothermal precursor liquid, uniformly stirring and mixing the hydrothermal precursor liquid, then transferring the hydrothermal precursor liquid into a stainless steel reaction kettle of polytetrafluoroethylene to perform hydrothermal reaction, cooling the reaction to room temperature after the reaction is finished, and placing a sample into a freeze drying box to perform freeze drying treatment to obtain a composite material VO ₂ @RGO of a one-dimensional vanadium dioxide nano rod and a two-dimensional reduced graphene oxide nano sheet;

c. C, performing high-temperature thermal reduction treatment on the composite material VO ₂ @RGO obtained in the step b in a tubular furnace at the annealing temperature of 600 ℃ through an annealing process to obtain a one-dimensional/two-dimensional composite sensing material VO _0.9 @RGO of the graphene sheet-loaded vanadium oxide nanorod;

The concentration of the diluted CH ₃ COOH solution in the step a is 1 mg/mL, the mass concentration of the mixed V ₂O₅ suspension is 9 mg/mL, and the stirring condition is that stirring is more than or equal to 12 h at room temperature; the mass concentration of the GO dispersion liquid in the step b is 13.73 mg/mL, the total mass of V ₂O₅ and GO in the hydrothermal precursor liquid is 384 mg, the mass ratio of V ₂O₅ to GO is 3:7, and the stirring condition is that stirring is more than or equal to 12 h at room temperature; the hydrothermal temperature is 200 ℃, the hydrothermal time is 72 h, the freeze-drying time is 36-48 h, and the hydrothermal reaction realizes that the V ₂O₅ particle phase with poor conductivity is converted into a one-dimensional VO ₂ nano rod with metal property;

in the step c, ammonia gas is used as the gas in the tubular furnace, the heating rate in the annealing treatment process is 5 ℃/min, and the heat preservation time is 3 h.

2. The application of the one-dimensional vanadium oxide based nano rod material synergistic composite two-dimensional graphene sheet conductive sensing material prepared by the method according to claim 1 is characterized in that: the one-dimensional/two-dimensional composite material VO _0.9 @RGO is used as a strain sensor conductive material.

3. The use according to claim 2, characterized in that: the method for using the one-dimensional/two-dimensional composite material VO _0.9 @RGO as the conductive material of the strain sensor comprises the following steps:

a. placing the composite material VO _0.9 @RGO in a centrifuge tube filled with ethanol solution for ultrasonic treatment to obtain VO _0.9 @RGO suspension;

b. C, coating the VO _0.9 @RGO suspension obtained in the step a on an elastic double-sided tape VHB substrate in a liquid manner, then integrally placing the substrate under a far infrared ray light source for accelerating drying, leading out copper wires at two ends of the material after the drying is finished to serve as electrodes, fixing the electrodes through conductive silver colloid, and attaching the VHB substrate with the same size on one side coated with an active material after the silver colloid is dried to obtain the VO _0.9 @RGO strain sensor with a certain load.

4. A use according to claim 3, characterized in that: the mass concentration of the VO _0.9 @RGO suspension in the step a is 5 mg/mL; the ultrasonic treatment time in the step a is 2 h; the VHB substrate size in step b is 3 cm x 3 cm; the area ratio of the VHB substrate area to the active material dripping area in the step b is 4:1; and in the step b, the load capacity of the VO _0.9 @RGO strain sensor is 0.5 mg/cm ².