CN106185893B - A kind of application for breathing graphene film in light stability is detected - Google Patents

Abstract

The invention discloses an application of a breathable graphene film in detecting light intensity stability. The application is realized by detecting the electromagnetic shielding performance of the breathable graphene film. The lower the electromagnetic shielding performance data of the breathable graphene film Stable, the lower the light intensity stability. The breathable graphene film with thermal conductivity (1800‑2600 W/mK) expands rapidly under light irradiation, and the shielding effect is improved. High-sensitivity detection of light intensity stability can be realized through the graphene film.

Description

Application of a breathable graphene membrane in detecting light intensity stability

technical field

The invention relates to the application of novel heat conduction, wave absorption and electromagnetic shielding materials, in particular to the application of a breathable graphene film in the detection of light intensity stability.

Background technique

In 2010, two professors Andre GeiM and Konstantin Novoselov from the University of Manchester won the Nobel Prize in Physics for their first successful separation of stable graphene, which set off a wave of research on graphene around the world. Graphene has excellent electrical properties (electron mobility up to 2×10 ⁵ cM ² /Vs at room temperature), outstanding thermal conductivity (5000W/(MK), extraordinary specific surface area (2630 M ² /g), and its poplar Modulus (1100GPa) and breaking strength (125GPa). The excellent electrical and thermal conductivity of graphene completely exceeds that of metals. At the same time, graphene has the advantages of high temperature resistance and corrosion resistance, and its good mechanical properties and low density make it more The potential to replace metals in the field of electrothermal materials.

Graphene films with macroscopically assembled graphene oxide or graphene nanosheets are the main application forms of nanoscale graphene. Through further high-temperature treatment, the defects of graphene can be repaired, and the electrical conductivity and thermal conductivity of the graphene film can be effectively improved. It can be widely used in portable electronics with high heat dissipation requirements such as smartphones, smart portable hardware, tablet computers, and notebook computers. device.

At present, the application of graphene films is limited to independent functional materials, such as thermally conductive films, conductive films, wave absorbing films, and shielding films. A single function obviously cannot meet the complex needs of future technological progress. To this end, we designed a breathable graphene film using super-large pieces of fragment-free graphene as the substrate, and completed the function conversion between thermal conduction and wave-absorbing shielding between exhalation and inhalation. It provides new ideas for the design of multifunctional devices.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide an application of a breathable graphene film in detecting light intensity stability.

The purpose of the present invention is achieved through the following technical solutions: a kind of application of breathable graphene film in detecting light intensity stability, said application is realized by detecting the electromagnetic shielding performance of breathable graphene film, breathable graphene The more unstable the electromagnetic shielding performance data of the film, the lower the light intensity stability. The breathable graphene film is composed of planarly oriented graphene sheets with an average size larger than 100 μm, which are overlapped by ππ conjugation. It contains a graphene structure composed of 1-4 layers of graphene sheets. And the graphene sheet has very few defects, and its I _D /T _G <0.01.

Further, the preparation method of the breathable graphene film is as follows:

(1) Graphene oxide with an average size greater than 100 μm is formulated into a graphene oxide aqueous solution with a concentration of 6 to 30 mg/mL, and an auxiliary agent with a mass fraction of 0.1-5% is added in the solution (that is, the mass fraction of the auxiliary agent in the solution is 0.1-5%), the additives are inorganic salts, organic small molecules or macromolecules; after ultrasonic dispersion, pour it on the mold plate and dry it into a graphene oxide film, and then reduce it with a reducing agent;

(2) Heating the reduced graphene film to 500-700°C at a rate of 0.1-0.5°C/min in an inert gas atmosphere, and keeping it warm for 0.5-2h;

(3) Raise the temperature to 1000-1200°C at a rate of 1-3°C/min in an inert gas atmosphere, and keep it warm for 0.5-3h;

(4) Raise the temperature to 2500-3000°C at a rate of 5-8°C/min in an inert gas atmosphere, keep it warm for 0.5-4h, and naturally cool down to obtain a porous breathable graphene film.

Described inorganic salt is selected from ammonium bicarbonate, urea, thiourea, azodicarbonamide; Small organic molecule is selected from glycerol, polyethylene glycol 200, polyethylene glycol 400; Macromolecule is selected from cellulose, gelatin, Chitosan, water-based polyurethane, acrylic emulsion, etc.

The graphene oxide with an average size greater than 100 μm in the step 1 is obtained by the following method:

(1) After diluting the reaction solution of the graphite oxide sheet obtained by the Modified-Hummer method, filter at 140 mesh sieves to obtain a filter product;

(2) After mixing the filtered product obtained in step 1 with ice water according to the volume ratio of 1:10, let it stand for 2 hours, and add hydrogen peroxide (H ₂ O ₂ mass fraction is 30%) dropwise until the color of the mixed solution changes. Change again (that is, the potassium permanganate in the mixed solution has been completely removed);

(3) Add concentrated hydrochloric acid (concentration is 12mol/L) dropwise in the mixed solution after step 2 treatment, until the flocculent graphite oxide disappears, then filter out the graphite oxide wafer with 140 mesh screens;

(4) Place the graphite oxide wafer obtained in step 3 in a shaking table, 20 to 80 rpm, shake and wash, so that the graphite oxide wafer is peeled off, and a large sheet of graphene oxide without fragments is obtained, with an average size greater than 100 μm, The distribution coefficient is between 0.2-0.5.

The Modified-Hummer method in the step 1 is specifically: at -10°C, fully dissolve potassium permanganate in concentrated sulfuric acid with a mass fraction of 98%, add graphite, stir at 60 rpm for 2 hours, and then stop stirring. React at low temperature (-10-20°C) for 6-48h to obtain a wide distribution of graphite oxide flake reaction solution; the mass volume ratio of graphite, potassium permanganate and concentrated sulfuric acid is: 1g: 2-4g: 30- 40ml, the particle size of graphite is greater than 150μm.

The mesh screen is an acid-resistant mesh screen such as titanium alloy.

In the step 1, the reaction solution of the graphite oxide sheet is diluted with a diluent such as concentrated sulfuric acid, and the volume of the diluent is 1-10 times the volume of the reaction solution.

The present invention describes a new application of a multifunctional graphene film that can switch between thermal conductivity and electromagnetic shielding performance, and the graphene film is composed of planarly oriented graphene sheets with an average size greater than 100 μm interacting through ππ conjugation Lap made. The large conjugated structure ensures the smooth passage between graphene, and the introduction of the graphene structure composed of 1-4 layers of graphene sheets greatly improves the electrical conductivity of the material; A cavity is formed between the sheet and the sheet. When the graphene film is placed under high-intensity light, the graphene conducts heat rapidly, causing the gas in the cavity to heat up and expand rapidly. On the other hand, at high temperatures, the folds themselves tend to stretch, and at the same time , Under the action of gas expansion, the folds of the cavity wall are stretched by the gas and gradually become smooth; the large cavity and smooth cavity wall are assisted by good electrical conductivity, so that the film has a strong electromagnetic shielding performance. The higher the light intensity, the better the electromagnetic shielding performance. When it needs to be reused, the micro-airbag can be compressed under high pressure.

Description of drawings

Figure 1 shows graphite oxide crystals before filtration (left), and graphite oxide crystals after filtration (right).

Figure 2 shows graphene oxide before filtration (left) and graphene oxide after filtration (right).

Figure 3 is graphene oxide obtained by reaction at 50 degrees.

Figure 4 shows the size distribution of graphene oxide obtained by reaction at 50 degrees (left), and the size distribution of graphene oxide obtained by reaction at 20 degrees (right).

Fig. 5 is a cross-sectional view of the breathable graphene membrane in the breathing and breathing state.

Fig. 6 is a curve diagram of electromagnetic shielding under illumination with different powers.

detailed description

The present invention forms a film by using super large sheets of graphene oxide, in which graphene sheets with an average size of plane orientation greater than 100 μm play an important role in the process of forming the graphene film of the present invention. Before the graphite oxide crystals are washed with water, the present invention uses a mesh screen The method of separation is to separate the fragments. And use more than 10 times the volume of ice water to dilute, so that the wafer will not be damaged by the heat of dissolution of sulfuric acid. Further use of a shaker to shake and wash, so that the graphene oxide sheet avoids mechanical crushing when it is peeled off. Further, the present invention also prepares graphene sheets by low temperature conditions. At low temperatures, potassium permanganate has relatively weak oxidizing properties, and its self-decomposition produces oxygen at a relatively slow rate, so the fragmentation effect of gas on graphite oxide crystals is very weak. This allows large sheets of graphene oxide to be preserved. Moreover, there is no vigorous stirring and ultrasonic process in the reaction process and the cleaning process, so the sheet is basically not broken. Based on the above points, we obtained a super-large sheet of non-fragmented graphene oxide, with an average size greater than 87 μm, a distribution coefficient between 0.2-0.5, and a fragment content of less than 1%.

The present invention will be further described below in conjunction with the accompanying drawings and embodiments. This embodiment is only used to further illustrate the present invention, and should not be understood as limiting the protection scope of the present invention. Those skilled in the art make some non-essential changes and adjustments according to the content of the above invention, which all belong to the protection scope of the present invention .

Example 1: Preparation of Graphene Oxide without Fragmentary Super Large Sheets

Example 1-1

(1) Slowly add potassium permanganate into the rapidly stirring concentrated sulfuric acid at -10°C. After fully dissolving, add graphite, stir slowly at 60 rpm for 2 hours, then stop stirring. React 6h, obtain the graphite oxide crystal of wide distribution respectively; As shown in Figure 1, all there are more fragments in the graphite oxide wafer that obtains under two kinds of temperatures, this makes its corresponding graphene oxide have a lot of fragments equally (Fig. 2).

(2) the reaction solution obtained in step 1 is diluted with concentrated sulfuric acid (the dilution factor can be any multiple, and the present embodiment has diluted about 10 times), and the graphite oxide crystal is filtered with a titanium alloy mesh sieve with a 150 μm aperture (140 orders) out (recovery of the reaction solution), and slowly pour into rapidly stirred ice water 10 times the volume of the filtered product, let it stand for 2 hours, slowly add H ₂ O ₂ , to remove excess potassium permanganate in the reaction, add an appropriate amount of Hydrochloric acid until the flocculent graphite oxide disappears, and then filter the graphite oxide wafer with a titanium alloy mesh sieve (140 mesh); the shaking table is slowly oscillating and washed to obtain a large sheet of graphene oxide without fragments (the average size is 87 μ m, and the distribution coefficient is 0.5 ). The mass volume ratio of graphite, potassium permanganate and concentrated sulfuric acid is: 1g:2g:40ml, and the particle size of graphite is 200μm.

As shown in Figure 3, the graphite oxide wafer separated after the reaction at a high temperature of 50 degrees is separated and the graphene oxide obtained after washing has a lot of fragments; The size distribution of graphene oxide is more uniform and concentrated, and the fragment content is very small.

Example 1-2

Slowly add potassium permanganate into the rapidly stirring concentrated sulfuric acid at -10°C. After fully dissolving, add graphite, stir slowly at 60 rpm for 2 hours, stop stirring, and react at low temperature (0°C,) for 48 hours. Obtain the reaction solution; the reaction solution is diluted with concentrated sulfuric acid with a mass fraction of more than 98% and dilute sulfuric acid with a mass fraction of 10% respectively, and then the graphite oxide crystals are filtered out with a titanium alloy mesh sieve with a pore size of 150 μm (recovery of the reaction solution) , and slowly poured into rapidly stirred ice water 10 times the volume of the filtered product, let it stand for 2 hours, slowly added H ₂ O ₂ , to remove excess potassium permanganate in the reaction, and added an appropriate amount of hydrochloric acid until flocculent graphite oxide Disappeared, and then filtered out the graphite oxide wafers with a titanium alloy sieve; the shaker was slowly oscillating and washed to obtain the reaction product. The mass volume ratio of graphite, potassium permanganate and concentrated sulfuric acid is: 1:4g:30ml; the particle size of graphite is 500μm.

Diluted with concentrated sulfuric acid, the reaction obtained non-fragmented super large graphene oxide (average size is 98 μm, distribution coefficient at 0.4), and diluted with dilute sulfuric acid, the obtained product contains a large number of fragments, and the size distribution coefficient exceeds 100% . This is due to the large amount of heat released during the dilution process of dilute sulfuric acid, which destroys the graphite oxide crystals.

Example 1-3

Slowly add potassium permanganate into the rapidly stirring concentrated sulfuric acid at -10°C. After fully dissolving, add graphite, stir slowly at 60 rpm for 2 hours, stop stirring, and react at low temperature (20°C) for 28 hours to obtain Widely distributed graphite oxide crystals; the reaction solution is diluted with concentrated sulfuric acid and the graphite oxide crystals are filtered out (reaction solution recovery) with a titanium alloy mesh screen with a pore size of 150 μm, and slowly poured into rapidly stirring 5 times the volume of the filtered product , 8 times the volume, 10 times the volume of ice water, let it stand for 2 hours, slowly add H ₂ O ₂ , to remove excess potassium permanganate in the reaction, add an appropriate amount of hydrochloric acid until the flocculent graphite oxide disappears, and then use a titanium alloy mesh Graphite oxide wafers were filtered out by sieve; the shaker was shaken and washed slowly to obtain the reaction product; the mass volume ratio of graphite, potassium permanganate and concentrated sulfuric acid was 1:5g:34ml, and the particle size of graphite was 2mm.

Experimental results show that 5 times the volume and 8 times the volume of ice water cannot obtain graphene sheets with uniform size, and only 10 times the volume can obtain graphene oxide with no fragments and super large sheets (the average size is 92 μ m, and the distribution coefficient is in 0.2). It can be seen that if the amount of ice water is too low, the heat of mixing will be released intensively and the crystal structure will be destroyed.

Embodiment 2: Using the non-fragmented super large sheet of graphene oxide prepared in embodiment 1 to prepare a breathable graphene film.

Graphene oxide with an average size greater than 100 μm is prepared into a concentration of 28mg/mL graphene oxide aqueous solution, adding mass fraction 5.4% urea in the solution, after ultrasonic dispersion, it is poured on the mold plate and dried to form a graphene oxide film, and then Reduction with a hydrogen iodide reducing agent; the reduced graphene film is subjected to three-step heat treatment in an inert gas atmosphere according to the heat treatment methods shown in Table 1 to Table 3; after natural cooling, a porous graphene film with a thickness of 1mm can be obtained . The graphene film is pressed under high pressure to obtain an ultra-flexible and highly thermally conductive graphene film. The pressure of the pressing process is 200MP, and the time is 300h.

The graphene film obtained above was pressed at a high pressure of 50 MP for 2 hours; its thermal conductivity was measured; the pressed graphene film was placed in an environment of 400 degrees, and its electromagnetic shielding performance was measured to obtain a high thermal conductivity. The parameters of the graphene film with high rate and high sensitivity; as shown in Table 1-3. Figure 5 is an electron micrograph of the respiration process of the respirable graphene membrane. During the respiration process under the action of external force, the graphene membrane is flattened, and the breathing pores are preserved in the form of folds; during the respiration process under the action of light and heat, The folds are stretched by the gas and gradually become smooth.

Table 1: The heat treatment method of the first step

Table 2: The heat treatment method of the second step

Table 3: The heat treatment method of the third step

It can be seen from Table 1 to Table 3 that the performance of this material is mainly determined by three aspects. One is the repair of the graphene oxide sheet structure inside the material, that is, the loss of functional groups and the repair of the carbon conjugated structure at high temperature. Second, the continuity of the three-dimensional orientation structure inside the material, that is, the connectivity of the internal lamellar structure. Third, the formation of micro-air pockets can ensure the flexibility of the material and the existence of the graphene sheet structure. All three work together to increase the performance of graphene membranes.

As can be seen from Table 1, comparing A1, B1, C1, D1, and E1, the temperature of A1 is too low to remove most of the easily degradable functional groups, resulting in a large amount of rapid gas generation in the second high-temperature process. Split layer structure; E1 temperature is too high, gas is generated too fast, and the internal structure of the material will be torn in large quantities, both of which will make the material performance worse. Only at B1, C1, and D1 temperatures, the functional groups will be removed slowly and completely to ensure the performance of the material. Comparing C1, F1, G1, and H1, the heating rate of F1 is too low, and the gas release is too slow, which cannot form through holes inside the material, which is not conducive to the formation of micro-air pockets in the subsequent heating process; the heating process of H1 is too fast, and the gas release Too fast will tear the internal structure of the material, which is not conducive to the formation of transmission channels. Only at the heating rate of CG can both the formation of micro-air pockets and the integrity of the channel be guaranteed. Comparing C1, I1, J1, K1, L1, and M1, the holding time of I1 is too short, which cannot guarantee the degradation of most functional groups; the holding time of M1 is too long, which will absorb the tar in the furnace, which is not conducive to the improvement of performance. C1, J1, K1, L1 just avoid the above two.

It can be seen from Table 2 that, comparing A2, B2, C2, D2, and E2, the heating rate of A2 is too low to form a tiny void structure, so that the film cannot form micro-air pockets, which seriously affects the electromagnetic shielding performance. If the heating rate of E2 is too high, the interlayer structure of graphene will be torn, making the linkability of graphene film worse, and the heat conduction and electromagnetic shielding performance will be worse. Only at the heating rates of B2, C2, and D2 can it be possible to ensure both the micro-airbag structure and the continuity inside the graphene membrane. Comparing C2, I2, J2, K2, L2, and M2, the holding time of I2 is too short, and the stable functional groups cannot be fully detached; the holding time of M2 is too long, the graphene film is easy to absorb tar, which is not conducive to the improvement of film performance; while C2, J2, Under the conditions of K2 and M2, it can not only ensure the sufficient shedding of stable functional groups, but also avoid the trouble of tar.

As can be seen from Table 3, comparing A3, B3, C3, D3, and E, the heating rate of A3 is too low, and the most stable functional group falls off too slowly, which is not enough to support the formation of microairbags in the process of forming microairbags; E3 heating process Too fast, gas release and high temperature expansion are too fast, easily destroying the formation of micro air pockets. Only in the case of B3, C3, and D3, the micro-air pockets can be formed stably, and the structure on the graphene can be repaired slowly. Comparing C3, F3, G3, H3, and I3, the end temperature of F3 is too low, and the repair of graphene structure is not perfect, so various performances are poor; the end temperature of I3 is too high, graphene will be vaporized; C3, G3, H3 Only at a high temperature can the repair of the graphene structure be guaranteed without being vaporized. Comparing C3, J3, K3, L3, and M3, the holding time of J3 is too low, the graphene structure cannot be fully repaired, and the holding time of M3 is too long, which will also cause the tar in the furnace to be adsorbed and affect the performance of the membrane.

Embodiment 3: Graphene film is used for detecting light intensity.

First, the breathable graphene membrane is prepared as follows

(1) Graphene oxide with an average size greater than 100 μm is formulated into a graphene oxide aqueous solution with a concentration of 6 mg/mL, and glycerin with a mass fraction of 5% is added to the solution; after ultrasonic dispersion, it is poured on a mold plate and dried to form graphene oxide film, and then reduced with a reducing agent;

(2) Heat the reduced graphene film to 700°C at a rate of 0.5°C/min in an inert gas atmosphere, and keep it warm for 1h;

(3) Raise the temperature to 1200°C at a rate of 2°C/min under an inert gas atmosphere, and keep it warm for 1h;

(4) In an inert gas atmosphere, the temperature was raised to 2500 °C at a rate of 7 °C/min, kept for 1 h, and a porous breathable graphene film was obtained after natural cooling.

Then, the prepared graphene films were respectively placed in dark environments I-VII, and each dark environment was illuminated with the same series of lasers. The laser power in dark environments I-VII is shown in the table below.

I II III IV V VI VII 5×10 ³ lux 80×10 ³ lux 150×10 ³ lux 220×10 ³ lux 300×10 ³ lux 400×10 ³ lux 500×10 ³ lux

After 10 minutes of light, the measured electromagnetic shielding data are shown in Figure 6.

It can be seen from Figure 6 that the graphene film has ultra-high thermal conductivity, basically completes the heat conduction work within 1 minute, and has high sensitivity. In addition, the electromagnetic shielding performance of the graphene film under different light powers is significantly different, indicating that different lighting environments can be identified. The greater the light intensity, the greater the electromagnetic shielding performance. Therefore, light intensity stability can be efficiently evaluated.

Claims (7)

1. An application of a breathable graphene film in detecting light intensity stability, characterized in that, the application is realized by detecting the electromagnetic shielding performance of the breathable graphene film, and the electromagnetic shielding performance data of the breathable graphene film The more unstable, the lower the light intensity stability; the breathable graphene film is formed by overlapping graphene sheets with a planar orientation and an average size greater than 100 μm through ππ conjugation. A cavity is formed between the sheet and the cavity, and there are wrinkles on the wall of the cavity; and it contains a graphene structure composed of 1-4 layers of graphene sheets; and the graphene sheet has very few defects, and its I _D / _IG <0.01. 2. application according to claim 1, is characterized in that, the preparation method of described breathable graphene film is as follows: (1) Graphene oxide with an average size greater than 100 μm is formulated into a graphene oxide aqueous solution with a concentration of 6-30 mg/mL, and an auxiliary agent with a mass fraction of 0.1-5% is added to the solution, and the auxiliary agent is an inorganic salt, an organic small Molecules or polymers; after ultrasonic dispersion, pour it on the mold plate and dry it to form a graphene oxide film, and then reduce it with a reducing agent; (2) Heating the reduced graphene film to 500-700°C at a rate of 0.1-0.5°C/min in an inert gas atmosphere, and keeping it warm for 0.5-2h; (3) Raise the temperature to 1000-1200°C at a rate of 1-3°C/min in an inert gas atmosphere, and keep it warm for 0.5-3h; (4) Raise the temperature to 2500-3000°C at a rate of 5-8°C/min in an inert gas atmosphere, keep it warm for 0.5-4h, and naturally cool down to obtain a porous breathable graphene film. 3. application according to claim 2, is characterized in that, described inorganic salt is selected from ammonium bicarbonate; Small organic molecule is selected from glycerin, gelatin, acrylic acid, urea, thiourea, azodicarbonamide, polymer Selected from cellulose, chitosan, water-based polyurethane, polyethylene glycol 200, polyethylene glycol 400. 4. application according to claim 2, is characterized in that, in described step 1, the graphene oxide that average size is greater than 100 μ m obtains by following method: (1) After diluting the reaction solution of the graphite oxide sheet obtained by the Modified-Hummer method, filter at 140 mesh sieves to obtain a filter product; (2) After mixing the filtered product obtained in step 1 with ice water according to the volume ratio of 1:10, let it stand for 2 hours, and add hydrogen peroxide with a mass fraction of 30% drop by drop until the color of the mixed solution does not change; (3) adding concentration dropwise to the mixed solution after step 2 is 12mol/L concentrated hydrochloric acid, until flocculent graphite oxide disappears, then filter out the graphite oxide wafer with 140 mesh screens; (4) Place the graphite oxide wafer obtained in step 3 in a shaking table, 20 to 80 rpm, shake and wash, so that the graphite oxide wafer is peeled off, and a large sheet of graphene oxide without fragments is obtained, with an average size greater than 100 μm, The distribution coefficient is between 0.2-0.5. 5. The application according to claim 4, characterized in that the Modified-Hummer method in the step 1 is specifically: at -10°C, fully dissolving potassium permanganate in concentrated sulfuric acid with a mass fraction of 98% , add graphite, stir at 60 rpm for 2 hours, stop stirring, and react at a low temperature of -10-20°C for 6-48 hours to obtain a wide-distributed graphite oxide flake reaction solution; the graphite, potassium permanganate and concentrated The mass volume ratio of sulfuric acid is: 1g: 2-4g: 30-40ml, and the particle size of graphite is greater than 150μm. 6. The application according to claim 4, characterized in that the mesh screen is a titanium alloy acid-resistant mesh screen. 7. The application according to claim 4, characterized in that, in the step 1, the reaction solution of the graphite oxide sheet is diluted by a concentrated sulfuric acid diluent, and the volume of the diluent is 1-10 times the volume of the reaction solution.