CN114560459A

CN114560459A - Method for directly synthesizing graphene nanoribbon by surface catalysis of salt microcrystal

Info

Publication number: CN114560459A
Application number: CN202210061502.XA
Authority: CN
Inventors: 胡宝山; 付长啸; 金燕
Original assignee: Chongqing University
Current assignee: Chongqing University
Priority date: 2022-01-19
Filing date: 2022-01-19
Publication date: 2022-05-31
Anticipated expiration: 2042-01-19
Also published as: CN114560459B

Abstract

The invention discloses a method for directly synthesizing a graphene nanoribbon by surface catalysis of salt microcrystals, which comprises the following steps: preparing salt microcrystal powder; uniformly mixing an organic compound and salt microcrystal powder, wherein the organic compound is an organic compound which can generate naphthalene ring or perylene ring free radicals by pyrolysis at 450-650 ℃; and introducing mixed gas of protective gas and hydrogen, calcining at 450-650 ℃ until the reaction is finished, and purifying the product after the reaction to obtain the graphene nanoribbon. The method breaks through the limitation of the existing method for synthesizing the graphene nanoribbon by using the noble metal substrate, selects NaCl which is large in reserve and easy to obtain as the synthesis substrate and the catalytic inducer, does not need high-vacuum equipment, and has the advantages of environmental friendliness and resource saving; and the method has the advantages of simple raw materials, low cost, good repeatability and high industrial feasibility, and is expected to realize large-scale preparation.

Description

Method for directly synthesizing graphene nanoribbon by surface catalysis of salt microcrystal

Technical Field

The invention belongs to the technical field of carbon nanomaterial preparation, relates to a method for directly synthesizing graphene nanoribbons by surface catalysis of salt microcrystals, and particularly relates to a novel technology for synthesizing graphene nanoribbons at a specified temperature and normal pressure by taking a solid organic compound as a precursor and under the induction catalysis of the salt microcrystals.

Background

Graphene has been discovered by two scientists of K.Novoseov and A.Geim of Manchester university in England in 2004 (Novoseov K S, et al.science,2004,306,666.), which is always the focus and focus of research in the scientific community, and has excellent nanostructure and optical, electrical, thermal and mechanical properties, so that the graphene shows great scientific significance and application value in theoretical and experimental research. However, compared to common semiconductor materials, the band gap of two-dimensional graphene is zero, and it is difficult to directly apply to electronic devices requiring a high on/off ratio. Therefore, several schemes have been proposed to open the band gap of graphene, such as applying mechanical stress (Daniel E.P, et al. Phys. Rev. Lett.,2021,127,027601.), atomic (ion) bombardment (Pradhan J, et al. Carbon,2021,184,322-330.), chemical modification (Zribi B, et al. Carbon,2019,153: 557-564.), adding a vertical electric field (Prasad N, et al. J. Phys. chem.C.,2020,124(39): 21874-21885.) on the surface of bi-layer graphene, and preparing one-dimensional graphene nanostructures (Zhou X H, et al. Adv. Mater.,2020,32(6), 1905957.).

Research has shown that quasi-one-dimensional Graphene Nanoribbons (GNRs) can open up the band gap using quantum confinement effects, and the size of the band gap depends on the edge type of the GNRs (i.e., zigzag or armchair) and the width of the GNRs. The GNRs inherit the excellent physical and chemical properties of graphene, and have better regulation and control performance in the aspect of electronic structures, and the advantages enable the graphene to have wider application prospects. For example, as channel materials, field effect transistors with high performance (high on-off ratio and high field effect mobility) are prepared, silicon-substituted material transistors and doped catalytic materials are applied to the field of electrical (photoelectric) chemistry. In addition, due to its extremely small size and ultra-fast electron transfer rate, which can meet the requirements of high sensitivity and fast response of sensors, GNRs are also expected to be applied to the fields of biological and chemical sensors. Therefore, the large-scale preparation of GNRs and the control of their band gaps have become a research hotspot.

In recent years, various preparation methods have been developed by many research groups at home and abroad aiming at the research on GNRs with controllable edges and widths. Currently, GNRs are prepared in two broad categories, top-down and bottom-up. "Top-down" methods include the usual photolithography (Arjmangdi-Tash H, et al. adv. Mater. Interfaces,2021,8(20),2100293.), decompressed carbon nanotube method (Li H, et al. ACS appl. Mater. Interfaces,2021,13, 52892-52900.), sonochemical method (Yoon W, et al. Carbon,2015,81(1): 629-638.), and metal assisted etching (Saraswat V, et al. J. Phys. chem. C,2019,123,18445-18454.). Such processes produce GNRs that are long, have a relatively narrow bandwidth distribution, but generally have low throughput, are irregular at the edges of the strip, may introduce more defects, and are complex in processing. The "bottom-up" rule is mainly divided into two categories, i.e., solution synthesis (narta a, et al chem. sci.,2019,10,964.) and surface synthesis (Chen Z P, et al adv. mater.,2020,32(45),2001893.), wherein the surface synthesis (On-surface synthesis) technique has attracted extensive attention and research since 2010, and precise control of GNRs edges and bandwidths can be achieved through sophisticated organic precursor molecular design. However, the selected substrate surfaces of Au, Ag and the like have strong interaction with GNR, are relatively difficult to transfer, and the precious metal has high cost and limited reserves, so that large-scale preparation is not easy to realize. In order to overcome the problems and achieve the purposes of environmental friendliness and resource saving, a reaction substrate which has similar functions of Au and Ag and hopefully replaces precious metals such as Au and Ag is urgently needed to be searched, and the efficiency of a surface synthesis strategy is further improved.

The metal salt has the characteristics of simplicity, easiness in obtaining, good water solubility, good thermal stability and the like, shows the advantages of rapidness, high yield and low cost when used for assisting in synthesizing various novel materials, and at present, a method for assisting in synthesizing a carbon material by taking a metal salt crystal as a catalytic template has been reported. For example, Hu et al heated 1, 5-diphenylcarbohydrazide and MgCl₂The mixture of (b) produced two-dimensional porous carbon nanosheets (Hu W, et al. acs susteable chem. eng.,2017,5,8630.) having a mean pore diameter of 8.69 nm. Li et al utilize FeCl₃·6H₂O is used as an activating agent and a structure-oriented template, and a two-dimensional porous nitrogen-doped carbon nano sheet (Li S, et al. adv. Mater.,2017,29,1700707.) is successfully synthesized. Huang et al use 2-methylimidazole and Co (NO)₃)₂·6H₂An ultrathin Co-based organic framework with a thickness of 4.5nm was prepared by pyrolysis with O as precursor and NaCl as salt template (Huang L, et al.J.Mater.chem.A,2017,5, 18610.). These studies provide a new idea for the preparation of carbon materials, in which metal salt crystals play a crucial role, specifically as templating, activating, pairingInduction of the reaction. However, reports of direct synthesis of graphene nanoribbons by the surface catalysis of metal salt crystals have not been found so far.

Disclosure of Invention

In order to develop a method suitable for large-scale industrial production, the invention provides a method for directly synthesizing graphene nanoribbons based on surface catalysis of salt microcrystals. The method is mainly characterized in that cheap and commercially available solid organic compounds, such as 3,4,9, 10-perylenetetracarboxylic dianhydride (PTCDA) and the like, are used as precursors, microcrystals of NaCl, LiCl, KCl and the like which are abundant and easily available are used as reaction substrates, and the graphene nanoribbons can be obtained through a one-step calcination mode under the conditions of normal pressure, specified atmosphere and temperature.

The technical scheme adopted by the invention for solving the technical problems is as follows:

1) salt crystallite powder is prepared. Weighing commercially available NaCl, LiCl or KCl to prepare a saturated solution, slowly dripping a solvent into the saturated solution under the conditions of water bath temperature control and magnetic stirring, controlling the dripping speed, after the dripping of ethanol is finished, carrying out suction filtration on the hot mixed solution, and transferring the product into a vacuum drying oven to dry to obtain the recrystallized salt microcrystal powder. The method comprises the steps of regulating the size distribution of commercial NaCl, LiCl or KCl by recrystallization, controlling crystallization temperature, concentration, rotation speed, ethanol dropping speed and other factors by taking ethanol, liquid ammonia, acetone, DMF or water as a solvent, and realizing the controllable preparation of NaCl, LiCl or KCl particles. Preferably, the solvent may be absolute ethanol in consideration of green and economic factors.

2) The organic compound and the salt microcrystal powder are mixed evenly. The organic compound as a precursor can be mixed with the salt microcrystal powder by adopting a dry mixing mode or a wet mixing mode. The dry mixing method achieves the aim of uniform mixing by mechanically grinding the mixture of the two; the wet mixing is to transfer the mixture into a proper amount of absolute ethyl alcohol, and then to obtain a uniformly mixed mixture through the steps of magnetic stirring, vacuum drying, grinding and the like. For example, dry mixing may include: weighing a certain amount of PTCDA, mixing with a proper amount of NaCl microcrystalline powder prepared in the step 1), placing the mixture in an agate mortar for grinding uniformly, transferring the mixture to a clean porcelain boat for uniformly paving, and covering the porcelain boat with a corundum porcelain boat cover for later use.

3) The organic compound and salt crystallite powder mixture is calcined, for example, it may be placed in a high temperature tube furnace for calcination. Argon gas (100-200 sccm) is used as a protective gas and a carrier gas, hydrogen gas (10-50 sccm) is added to etch and modify the graphene nanoribbon, the temperature is increased to a specified temperature (450-650 ℃) at a heating rate of 5-20 ℃/min, and the temperature is kept constant for 10-240 min, so that the multi-step reaction processes of slow pyrolysis of an organic compound, free radical release, free radical synthesis of the nanoribbon and the like are realized. And cooling to room temperature after the reaction is finished to obtain a mixture of the graphene nanoribbons and the salt. The width of the prepared graphene nanoribbon is distributed in the range of 50-1000 nm, and the graphene nanoribbon has obvious Raman RBLM signals and characteristic peaks such as D, G and 2D. After the cooling to the room temperature is finished, the temperature can be rapidly reduced to the room temperature or naturally reduced to the room temperature, and preferably, the room temperature is reduced by selecting a natural cooling mode. For example, pushing the ceramic boat loaded with the mixture obtained in the step 2) into a quartz tube, placing the quartz tube at the central position of a heating area of the tube furnace, and connecting a device to ensure sealing; introducing Ar gas for a period of time to remove air in the quartz tube, and adjusting Ar (100-200 sccm) and H₂(10-50 sccm) the flow of the mixed gas is stabilized until the reading of the flow meter is stable; setting parameters such as temperature rise time, temperature rise rate, reaction temperature and the like, and calcining the mixture; and after the reaction is finished, naturally cooling to room temperature, taking out the porcelain boat, and collecting a product to obtain the mixture of the graphene nanoribbon and NaCl.

The graphene nanoribbon is synthesized on a metal base template by using a solid organic matter containing a benzene ring as a precursor. In the reaction process, the organic compound plays a role of serving as a raw material and pyrolyzing the self-radical and free radical synthetic belt; the metal salt plays the roles of capturing free radicals, inducing the nucleation of the free radicals and catalyzing the polymerization and growth of the free radicals in the reaction.

Compared with the prior art, the beneficial effects of the invention at least comprise one of the following:

1. compared with gas carbon sources such as methane, ethylene and the like, the invention adopts the cheap solid organic matter as the precursor, can greatly reduce the pyrolysis temperature and reduce the energy consumption.

2. The method selects NaCl as a catalytic reaction growth substrate, does not use a metal catalyst, and has the advantages of large storage capacity, easy acquisition, convenient transfer, easy recycling and low cost.

3. The reactions involved in the invention are all carried out under normal pressure, and expensive high-vacuum equipment is not needed.

Drawings

The invention is further illustrated with reference to the figures and examples.

FIG. 1 is a graph of the temperature versus time for the calcination process of the method of the present invention.

Fig. 2 is an SEM image and a raman spectrum image of the graphene nanoribbon prepared in example 1.

Fig. 3 is an SEM image of graphene nanoribbons prepared in different mixing manners of example 2.

Fig. 4 is an SEM image of graphene nanoribbons prepared from example 3 of mixtures of different mass ratios.

Detailed Description

The invention provides a typical but non-limiting preparation method, and in order to facilitate understanding of the technical scheme of the invention, the invention is described in detail by combining the accompanying drawings and specific examples.

The invention provides a method for directly synthesizing a graphene nanoribbon by surface catalysis of salt microcrystals, which comprises the following steps:

s01, preparing salt microcrystal powder;

the preparation of the salt microcrystalline powder can comprise preparing salt into saturated solution, adding solvent at 20-50 ℃ under stirring, filtering, and drying to obtain the salt microcrystalline powder. The salt may be a metal salt, which may be, for example, NaCl, LiCl or KCl. For example, when the salt is NaCl, a proper amount of commercially available NaCl (0.3-2.0 g) is weighed and placed in a 250ml round-bottom flask to prepare a saturated solution, the temperature of a water bath is set to be 20-50 ℃, anhydrous ethanol (20-100 ml) is slowly dripped into the saturated solution under the stirring of a polytetrafluoroethylene magnetic stirrer (300-700 rpm), and the dripping speed is controlled to uniformly precipitate NaCl particles. And after the absolute ethyl alcohol is dropwise added, continuously maintaining stirring and water bath for 0.5-2 h, filtering the obtained mixed solution while the mixed solution is hot after the stirring is finished, transferring the product into a vacuum drying oven for drying at 60 ℃ to obtain NaCl microcrystalline particles, and grinding the NaCl microcrystalline particles for later use.

S02, mixing the organic compound with the salt microcrystalline powder;

and (3) uniformly mixing the organic compound and the salt microcrystal powder. For example, a proper amount of PTCDA (20-100 mg) is weighed, mixed with NaCl obtained in step S01, and then put into an agate mortar for grinding and mixing. And then transferring the mixture to a clean porcelain boat for uniformly paving, and covering the porcelain boat for later use.

S03, synthesizing a graphene nanoribbon;

the porcelain boat loaded with the mixture obtained in step S02 is pushed into a quartz tube and placed at the center of the heating zone of the tube furnace. The device is then connected to ensure sealing. Introducing Ar for a certain time to remove air in the quartz tube, and then adjusting Ar (100-200 sccm) and H₂(10-50 sccm) until the flow rate of the mixed gas is stabilized, and then calcining at 450-650 deg.C, for example, 500 deg.C.

S04, purifying and collecting the graphene nanoribbons;

and collecting the product obtained in the step S03, putting the product into a 100ml beaker, adding a proper amount of mixed solution of deionized water and absolute ethyl alcohol according to the volume ratio of 1:1, and performing ultrasonic treatment for 10-60 min to uniformly disperse the product. And transferring the dispersion liquid into a 10ml centrifuge tube, removing mixed salt particles in the product through centrifugal washing, and alternately washing 3-5 groups by using deionized water and ethanol. And (3) filtering residual moisture of the product after centrifugal washing through vacuum filtration, transferring the product to a plastic culture dish, and freeze-drying for 12-24 hours to obtain the purified black powder of the graphene nanoribbon.

Further, the organic compound may be an organic compound that is pyrolyzed at 450 to 650 ℃ to generate a naphthalene ring or perylene ring radical, thereby performing a polymerization reaction. For example, the organic compound may be 3,4,9, 10-perylenetetracarboxylic dianhydride (PTCDA), 3,4,9, 10-perylenetetracarboxylic acid, 3,4,9, 10-perylenetetracarboxylic diimine, N-bis (2, 6-xylene) perylene-3, 4,9, 10-tetracarboxylic diimide, 1,4,5, 8-naphthalenetetracarboxylic dianhydride (NTCDA), 1,4,5, 8-naphthalenetetracarboxylic acid, or 1,4,5, 8-naphthalenetetracarboxylic diimide.

Further, the salt microcrystal powder is a cubic system, atoms are stacked in a face-centered cubic manner, and can provide nucleation sites for free radicals. For example, the salt crystallite powder may be NaCl, LiCl and KCl crystallite powders.

Further, after the organic compound is mixed with the salt microcrystal powder by a dry method, the surface of the salt microcrystal powder can be covered with a layer of salt microcrystal powder. For example, the organic compound may be mixed with NaCl and then covered with a thin layer of NaCl; the organic compound may be coated with a thin layer of KCl after mixing with the KCl.

Further, the size of the salt crystallite powder may be 1 μm to 300 μm. The size of the salt microcrystal powder is related to the width of the graphene nanoribbon, and the smaller the size of the salt microcrystal is, the narrower the graphene nanoribbon prepared by the salt microcrystal powder is; the larger the size of the salt microcrystal is, the wider the graphene nanoribbon prepared by the salt microcrystal is. But the size of the salt microcrystal powder is not more than 300 mu m, and graphene nanoribbons may not be obtained after the size is exceeded.

Further, the temperature of calcination was set to 450 ℃ to 650 ℃. Preferably, the calcination temperature of 1,4,5, 8-naphthalene tetracarboxylic dianhydride (NTCDA), 1,4,5, 8-naphthalene tetracarboxylic acid, or 1,4,5, 8-naphthalene tetracarboxylic diimide may be set in the range of 200 to 300 ℃. For example, for the organic compound PTCDA, the sublimation temperature of PTCDA is 450 ℃ and the temperature at which radicals are generated by pyrolysis is between 500 ℃ and 650 ℃. PTCDA cannot be sublimed and pyrolyzed at too low a temperature (<450 ℃), and the reaction of the polymeric tapes cannot occur; too high a temperature (>650 ℃) PTCDA pyrolysis is too rapid, which is not conducive to slow, stable, uniform reactions.

Furthermore, the mass ratio of the organic compound to the salt microcrystal powder is 1 (0.6-7). For example, the mass ratio may be 1:0.8 or 1:3 or 1: 5. Preferably, the mass ratio is 1:1, and the graphene ribbon prepared by the method has the best quality at the mass ratio.

Further, in step S03, the temperature is raised to 450-650 ℃ at a temperature raising rate of 5-20 ℃/min, and the calcination time is 10-240 min. For example, the temperature is raised to 500 ℃ at a temperature raising rate of 15 ℃/min, and the calcination time is 100 min.

Further, in step S03, the temperature-increasing reaction may be performed according to the process shown in fig. 1 after the mixed gas of the protective gas and the hydrogen gas is introduced until the reaction is completed. Specifically, the temperature is raised to the growth temperature (450-650 ℃ C.) at the rate of 5-20 ℃/min in the temperature raising stage, the temperature is maintained for 10-240 min, then the temperature is raised to the annealing temperature (700-800 ℃ C., annealing stage), the reaction is finished, the ceramic boat is naturally cooled to the room temperature (temperature lowering stage), the ceramic boat is taken out, and the product is collected, namely the mixture of the graphene nanoribbon and the salt. The annealing time can be 30 min-120 min. Calcining at 450-650 ℃ to synthesize graphene nanoribbons, and locking the shape of the strip-shaped graphene; by the annealing, the crystallinity of the nano-belt can be further promoted and improved, and the physical and chemical properties such as the conductivity, the electron mobility and the like of the nano-belt can be further improved.

For a better understanding of the present invention, the following further illustrates the contents of the present invention with reference to specific examples, but the contents of the present invention are not limited to the following examples.

Example 1

(1) Weighing 1g of commercially available NaCl, placing the commercially available NaCl in a 250ml round-bottom flask to prepare a saturated solution, setting the water bath temperature to be 30 ℃, slowly dripping 100ml of absolute ethanol into the saturated solution at 500rpm under the stirring of a polytetrafluoroethylene magnetic stirrer, and controlling the dripping speed to uniformly separate NaCl particles. And after the dropwise addition of the ethanol is finished, continuously maintaining stirring and water bath for 1h, filtering the obtained mixed solution while the mixed solution is hot after the stirring is finished, transferring the product into a vacuum drying oven for drying at 60 ℃ to obtain NaCl microcrystalline powder, and grinding the NaCl microcrystalline powder for later use.

(2) Weighing 50mg of PTCDA, mixing with 100mg of NaCl prepared in the step (1), and then placing in an agate mortar for grinding and uniformly mixing. And then transferring the mixture to a clean porcelain boat for uniformly paving, and covering the porcelain boat for later use.

(3) Pushing the porcelain boat loaded with the mixture obtained in the step (2) into a quartz tube, and placing the quartz tube in the central position of a heating area of the tube furnace. Then connecting the device to ensure sealing, introducing Ar for a certain time to remove air in the quartz tube, and then adjusting Ar (150sccm) and H₂(30sccm) the mixed gas flow rate until the flow meter reading stabilizes. Heating to 550 deg.C at a rate of 15 deg.C/min, maintaining for 2 hr, heating to 750 deg.C at a rate of 15 deg.C/min, reacting, naturally cooling to room temperature, taking out the ceramic boat, and collectingAnd collecting the product, wherein the obtained product is a mixture of the graphene nanoribbons and NaCl.

(4) Collecting the product obtained in the step (3), placing the product in a 100ml beaker, and mixing the product according to a volume ratio of 1:1 adding a proper amount of mixed solution of deionized water and absolute ethyl alcohol, and carrying out ultrasonic treatment for 30min to ensure that the mixture is uniformly dispersed. The dispersion was transferred to a 10ml centrifuge tube, and the mixed NaCl in the product was removed by centrifugal washing, and 4 sets of alternate washing with deionized water and ethanol were performed. And filtering residual water of the washed product through vacuum filtration, transferring the product to a plastic culture dish, and freeze-drying for 12 hours to obtain the purified black graphene nanoribbon powder. Fig. 2 shows SEM images (image (a)) and raman spectrum images (image (b)) of the graphene nanoribbons, which indicate that the prepared graphene nanoribbons have widths ranging from 50nm to 1000nm and have significant raman RBLM signals and characteristic peaks such as D, G and 2D.

Example 2: and comparing the influence of different mixing modes of PTCDA and NaCl on the growth of the graphene nanoribbon.

A microcrystalline powder of NaCl was prepared by the procedure (1) of example 1, dried and then ground for use.

50mg of PTCDA and 350mg of NaCl are accurately weighed, are uniformly mixed by respectively selecting a mixing mode I (dry mixing) and a mixing mode II (wet mixing), and are covered by a corundum porcelain boat cover for later use.

Mixing mode I: and mixing the weighed PTCDA and NaCl, placing the mixture in an agate mortar, grinding for 15min, uniformly mixing, and transferring the mixture to a clean porcelain boat for paving.

And (3) a mixing mode II: and (3) dispersing the weighed PTCDA and NaCl in 25ml of absolute ethyl alcohol under the ice-water bath condition, stirring by using a polytetrafluoroethylene magnetic stirrer, controlling the rotating speed at 300rpm, and continuously stirring for 1 h. And (4) carrying out suction filtration on the mixed solution, transferring the mixed solution to a glass culture dish, carrying out vacuum drying for 12h, grinding to obtain a mixture of PTCDA and NaCl, and transferring the mixture to a porcelain boat for paving.

And (4) carrying out a nanobelt growth program according to the step (3). Adjusting Ar flow to 100sccm, H₂The temperature is raised to 525 ℃ at the temperature raising rate of 5 ℃/min at the flow rate of 20sccm, and the temperature is maintained for 60min, so that the PTCDA is promoted to be pyrolyzed and the free radical synthesis belt is promoted. Then heating to 700 ℃ at the heating rate of 5 ℃/min, and maintaining for 90min to promote the graphiteCrystallization of olefinic nanoribbons. And after the reaction is finished, naturally cooling to room temperature, stopping ventilation, disassembling the device, and collecting the product.

Fig. 3 is a field emission Scanning Electron Microscope (SEM) image of in-situ observation of graphene nanoribbons prepared in different mixing manners on NaCl particles. As can be seen from the figure, the graphene ribbons can be grown by both mixing methods, but the dry mixing method has a better induction promoting effect on the growth of the graphene nanoribbons, which is reflected in that the number of ribbons is larger, the coverage is larger, and the morphology is more complete (as shown in fig. 3 (b)). Therefore, preferably, a dry mixing method, which is more suitable for the growth of the graphene nanoribbon, may be used.

Example 3: and comparing the influence of different mass ratios of PTCDA and NaCl on the growth of the graphene nanoribbon.

Accurately weighing 50mg of PTCDA and a certain mass of NaCl, selecting a dry mixing mode, mixing the PTCDA and the NaCl, placing the mixture in an agate mortar, grinding for 15min, and uniformly mixing. The mixture was transferred to a clean porcelain boat and laid flat, and the boat was then covered with a corundum porcelain boat cover for use. This step sets 4 comparative experimental parameters: the weighed NaCl masses are respectively: 15mg, 50mg, 150mg, 350mg, the products being labelled in sequence: GNRs 15 (see fig. 4(d)), GNRs 50 (see fig. 4(c)), GNRs 150 (see fig. 4(b)), and GNRs 350 (see fig. 4 (a)).

And (4) carrying out a nanobelt growth program according to the step (3). Adjusting Ar flow to 100sccm, H₂The temperature is raised to 525 ℃ at the temperature raising rate of 5 ℃/min at the flow rate of 20sccm, and the temperature is maintained for 60min, so that the PTCDA is promoted to be pyrolyzed and the free radical synthesis belt is promoted. And then heating to 700 ℃ at the heating rate of 5 ℃/min, and maintaining for 90min to promote the crystallization of the graphene nanoribbon. And after the reaction is finished, naturally cooling to room temperature, stopping ventilation, disassembling the device, and collecting the product.

Fig. 4 is a field emission Scanning Electron Microscope (SEM) image of in-situ observation of graphene nanoribbons prepared by four control experiments on NaCl particles. It can be seen that the change in mass ratio shows a significant effect on the growth of graphene nanoribbons. The concrete expression is as follows: along with the reduction of the NaCl quality from 350mg to 50mg, the quality (quantity, coverage and appearance) of the grown graphene nanoribbon is greatly improved; there was some degradation in nanobelt quality as the NaCl mass was reduced from 50mg to 15 mg. Therefore, the quality of the graphene nanoribbon can be controlled and optimized by adjusting the mixing ratio of the PTCDA and the NaCl, and the quality of the prepared graphene nanoribbon is the best when the mass ratio of the PTCDA to the NaCl is 1: 1.

Finally, it is noted that the above-mentioned contents are only basic descriptions of the concept of the present invention, the above-mentioned embodiments are only used to illustrate the technical solution of the present invention, and not to limit the above-mentioned method, and any equivalent changes made according to the technical solution of the present invention are within the protection scope and the disclosure of the present invention.

Claims

1. A method for directly synthesizing graphene nanoribbons by surface catalysis of salt microcrystals is characterized by comprising the following steps:

s01, preparing salt microcrystal powder;

s02, uniformly mixing an organic compound and salt microcrystal powder, wherein the organic compound is an organic compound which can generate naphthalene ring or perylene ring free radicals by pyrolysis at the temperature of 450-650 ℃;

and S03, introducing a mixed gas of protective gas and hydrogen, calcining at 450-650 ℃ until the reaction is finished, and purifying the product after the reaction to obtain the graphene nanoribbon.

2. The method for the direct synthesis of graphene nanoribbons by surface catalysis of salt crystallites according to claim 1, characterized in that the organic compound is 3,4,9, 10-perylenetetracarboxylic dianhydride, 3,4,9, 10-perylenetetracarboxylic acid, 3,4,9, 10-perylenetetracarboxylic diimine, N-bis (2, 6-xylene) perylene-3, 4,9, 10-tetracarboxylic acid diimide, 1,4,5, 8-naphthalenetetracarboxylic dianhydride, 1,4,5, 8-naphthalenetetracarboxylic acid or 1,4,5, 8-naphthalenetetracarboxylic diimide.

3. The method for the direct synthesis of graphene nanoribbons by surface catalysis of salt crystallites according to claim 1 or 2, wherein the salt crystallite powder is NaCl crystallite powder, LiCl crystallite powder or KCl crystallite powder.

4. The method for directly synthesizing the graphene nanoribbon by the surface catalysis of the salt microcrystal according to claim 1 or 2, wherein the size of the salt microcrystal powder is 1-300 μm.

5. The method for the surface catalytic direct synthesis of graphene nanoribbons by salt crystallites according to claim 1 or 2, wherein the step of uniformly mixing the organic compound with the salt crystallite powder comprises: the organic compound and the salt crystallite powder are mixed and then mechanically ground to be uniformly mixed, or,

the step of uniformly mixing the organic compound and the salt microcrystal powder comprises the following steps: mixing the organic compound and the salt microcrystal powder, adding the mixture into absolute ethyl alcohol, stirring, drying in vacuum, and grinding to mix uniformly.

6. The method for directly synthesizing the graphene nanoribbon by the surface catalysis of the salt microcrystal according to claim 1 or 2, wherein the mass ratio of the organic compound to the salt microcrystal powder is 1 (0.6-7).

7. The method for directly synthesizing the graphene nanoribbon by the surface catalysis of the salt microcrystal according to claim 6, wherein the mass ratio of the organic compound to the salt microcrystal powder is 1: 1.

8. The method for directly synthesizing the graphene nanoribbon by the salt microcrystal surface catalysis, as recited in claim 1, 2 or 7, is characterized in that the introduction flow rate of the protective gas is 100sccm to 200sccm, and the introduction flow rate of the hydrogen is 10 sccm to 50 sccm.

9. The method for directly synthesizing the graphene nanoribbon by the surface catalysis of the salt microcrystal according to claim 1, 2 or 7, wherein in the step S03, the temperature is raised to 450-650 ℃ at a temperature rise rate of 5-20 ℃/min, and the calcination time is 10-240 min.

10. The method for directly synthesizing the graphene nanoribbon by the surface catalysis of the salt microcrystals according to claim 9, wherein the method further comprises heating to 700-800 ℃ at a heating rate of 5-20 ℃/min after calcination, annealing for 30-240 min, and cooling to room temperature.