CN107163686B - Preparation method and application of graphene composite conductive ink - Google Patents
Preparation method and application of graphene composite conductive ink Download PDFInfo
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Abstract
The invention discloses a preparation method and application of graphene composite conductive ink, which comprises the following steps: (1) preparing graphite oxide by a Hummers method; (2) soaking the original graphene nanoplatelets and the multi-walled carbon nanotubes by using dilute nitric acid to graft a small amount of oxygen-containing functional groups on the original graphene nanoplatelets and the multi-walled carbon nanotubes; (3) and (3) dispersing the material obtained in the step (2), the graphite oxide obtained in the step (1) and a thickening agent into a mixed solvent, and fully grinding and mixing to obtain the graphene composite conductive ink. The graphene composite conductive ink prepared by the invention has high concentration and excellent stability, and can be applied to the fields of ink-jet printing, conductive circuit and conductive film preparation and the like.
Description
Technical Field
The invention belongs to the technical field of graphene application, and particularly relates to a preparation method and application of graphene composite conductive ink.
Background
In 2004, adelim-gomer (Geim) and comastatin norvoschoff (Novoselov) as professors of physics at manchester university in the uk successfully exfoliated and observed a single layer of graphene crystals by a simple micromechanical exfoliation method, i.e., a tape method. Graphene is a polymer made of carbon atoms in sp2The hybridized orbitals form a hexagonal crystal thin film material in a honeycomb lattice, the arrangement of carbon atoms of the crystal thin film material is the same as that of a graphite monoatomic layer, each carbon atom is bonded with the surrounding carbon atoms to form a regular hexagon, the regular hexagon is actually similar to a benzene ring, each carbon atom in the structure contributes to an unbonded electron, and the length of a carbon-carbon bond in graphene is about 0.142 nm. Single-layered graphene crystals are the basic units for building other-dimensional carbonaceous materials, whose decomposition can form zero-dimensional fullerenes, curling can form one-dimensional carbon nanotubes, and stacking can form three-dimensional graphite.
The particular structure of graphene determines its unique properties. On a molecular level, of carbon atoms in grapheneMost of the properties are similar to those of carbon atoms on benzene rings. However, since graphene is composed of an infinite number of six-membered rings, and its edge hydrogen atoms contribute much less to the molecule than benzene rings, graphene has many unique properties. On the macroscopic level, graphene is a single layer of graphite, so its edge properties are similar to those of graphite to some extent. That is, graphene has the chemical properties of both polycyclic aromatic hydrocarbons and graphite. The rich electron cloud around the graphene carbon skeleton causes it to easily undergo pi-pi stacking, thereby forming a multilayer graphite structure from which many of the excellent properties of graphene are obtained. Firstly, graphene has an ultra-large specific surface area, up to 2630m2(ii)/g; secondly, the graphene also has excellent photoelectric properties, the light transmittance of the single-layer graphene is as high as 97.7%, and the carrier mobility of the single-layer graphene is as high as 2 multiplied by 105cm2V.S; it also has extraordinary thermal and mechanical properties, its thermal conductivity coefficient is up to 5000W/m.K, Young's modulus is up to 1 TPa; in addition, graphene also has a series of unique properties such as perfect quantum tunneling effect, half-integer quantum Hall effect and room-temperature ferromagnetism. Due to the unique properties, the graphene has great potential application value in the fields of composite materials, energy storage materials, adsorption materials, photoelectric materials and the like. The graphene has great application potential in the fields of conductive ink and thin films due to the excellent conductivity and ultrahigh light transmittance of the graphene.
The conductive ink is a conductive composite material consisting of conductive filler, binder, solvent and auxiliary agent. In the conductive ink, numerous conductive particles are uniformly dispersed in a binder and a solvent and are in an insulating state, and after drying, the solvent is volatilized, so that a printed product has conductivity. With the rapid development of nanotechnology and the increasing maturity of printed electronic technology, nanoscale conductive ink is receiving more and more attention in scientific research and industrial fields at home and abroad, and the application of nanoscale conductive ink in the fields of printed circuit boards, conductive coatings, radio frequency identification and the like is increasing day by day. Therefore, the method has great practical significance and industrial value for the research and preparation of the nano conductive ink. The nano conductive ink which is widely used at present comprises metal nano conductive ink, inorganic semiconductor conductive ink, conductive polymer conductive ink, graphite, carbon fiber conductive ink and the like. However, conductive inks prepared from these nanomaterials have advantages and disadvantages. The metal nano conductive ink generally uses gold, silver and copper nano ions as conductive fillers, the gold nanoparticles and the silver nanoparticles have excellent conductive performance, but the cost is high, and the silver nanoparticles are easy to cause silver migration to cause precipitation of silver particles. Although the cost of copper nanoparticle inks is reduced, they have poor conductivity, poor stability, are not easily dispersed, and are easily oxidized when exposed to air. Inorganic semiconductor inks are generally used in the fields of thin film transistors, solar cells, and the like, but have poor conductivity. Although conductive polymers are soluble, they are poor in stability and conductivity. The graphite and carbon fiber conductive ink has low cost, but has poor conductivity and solvent resistance, and can only be used for printing products with low conductivity requirements. Therefore, it is important to develop a conductive ink with more excellent comprehensive properties.
Recently, the application of graphene nanoplatelets in conductive ink is receiving more and more attention, theoretically, graphene can be used as an effective and economical conductive filler in the conductive ink, and the prepared conductive ink can be applied to touch screens, electronic paper, sensors, radio frequency identification tags, photovoltaic cells, solar cells, conductive circuits and the like. Compared with nano metal particles, the graphene has excellent conductivity and obvious cost advantage. Compared with traditional graphite and carbon fiber conductive ink, the graphene conductive ink is superior in conductivity and can be suitable for technologies such as 3D printing and ink-jet printing. On the other hand, the application of graphene in transparent conductive thin films is also receiving more and more attention of researchers, and in view of the excellent electrical conductivity, light transmittance, thermal conductivity and flexibility of graphene, the graphene transparent conductive thin films are expected to replace the conventional ITO thin films to be applied to the photoelectric fields of liquid crystal displays, solar cells, organic light emitting diodes, smart windows, touch screens and the like, and become the next generation conductive thin film material. Although the unique and attractive properties of graphene have attracted many researchers to research, the application of graphene in conductive inks and conductive films has many excellent results, but there are still many problems to be overcome.
In the field of graphene conductive ink, due to the special two-dimensional structure and the ultra-large specific surface area of graphene and the strong van der waals attraction among graphene micro-sheets, graphene is difficult to disperse well in a solvent and a polymer matrix. Graphene oxide can be dispersed in most solvents, but has low conductivity, and can only recover partial conductivity even after reduction, so that the requirement of printed electronics on conductivity cannot be met. At present, the preparation research on graphene conductive ink generally focuses on the synthesis and dispersion of conductive fillers, most preparation methods are complicated in steps, waste of raw materials is caused, the cost is high, and a large amount of toxic solvents such as DMF, NMP, acetone, tetrahydrofuran, isophorone and the like are used in the process. The prepared graphene conductive ink is added with more resin and auxiliary agent, and the organic solvent has higher boiling point and is difficult to volatilize, so that the ink can not be cured at lower temperature and in shorter time in the printing process, and the application of the ink in the field of printed electronics is limited.
In the field of graphene conductive films, although quite abundant results are obtained in the aspects of structure, performance, preparation and the like, the preparation of large-area high-transparency and high-conductivity films has certain challenges. At present, the preparation methods of graphene conductive films mainly include Chemical Vapor Deposition (CVD), vacuum filtration, spin coating, drop coating, spray coating, self-assembly, roll-to-roll, inkjet printing, and the like, and these preparation methods can be basically divided into two categories: CVD method and post-treatment method of liquid phase dispersion. The cost for preparing the graphene transparent conductive film by the CVD method is high, the uniformity and the like of the graphene transparent conductive film are to be improved, and the graphene film is easy to damage in the transfer process. However, the graphene film prepared by the solution method is generally based on an oxidation-reduction method, and defects introduced in the oxidation process are difficult to completely recover, so that the conductivity of the prepared graphene conductive film is difficult to be compared with that of the traditional material, and if the conductivity of the film is to be improved, noble metal nanoparticles such as Au and Ag need to be introduced in the preparation process, so that the process is complex and the cost is high, and the graphene conductive film cannot be applied in a large scale.
Therefore, a formula which is green, efficient, low in cost and free of an insulating polymer auxiliary agent needs to be developed, the graphene composite conductive ink and the graphene composite conductive film are prepared on a large scale through a simple and easy process, the preparation of the conductive ink and the preparation of the graphene composite conductive film are combined, and the practical application process of the graphene in the photoelectric field is promoted.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a preparation method of graphene composite conductive ink.
The invention also aims to provide a preparation method of the graphene composite conductive film.
The theoretical basis of the invention is as follows:
graphene and carbon nanotubes are typical two-dimensional and one-dimensional carbon nanomaterials and have excellent electrical conductivity, mechanical properties, thermal conductivity, light transmittance, and the like. Therefore, they have received a wide range of attention from researchers since their advent. If the two materials are simultaneously used as conductive fillers for preparing the graphene composite conductive ink, the two-dimensional graphene nanoplatelets and the one-dimensional carbon nanotubes are complementary in structure and property, a synergistic effect can be generated between the two materials, and respective advantages are fully exerted, so that various physical and chemical properties of the conductive ink are enhanced, and the conductive ink has more excellent technological properties and use properties. The product coated and printed by the composite conductive ink also has a more perfect conductive network structure and more excellent conductivity. After the composite conductive ink is coated on a substrate, in the formed conductive film, the carbon nano tube can make up the discontinuity of the graphene nanoplatelets, and the graphene nanoplatelets can repair the gaps of the carbon nano tube network structure. However, since graphene and carbon nanotubes have a high specific surface area to thickness ratio and strong van der waals attraction forces, they tend to aggregate together and settle, and thus, how to stably disperse them in a solvent is a key factor in preparing a graphene composite conductive ink. Can be good at presentThe solvents for well dispersing the carbon nano materials such as graphene and the like only comprise organic solvents with high toxicity such as NMP, DMF, acetone, isophorone and the like, the solvents have high boiling points and are difficult to volatilize, and the prepared ink can not be cured at a low temperature in a short time in the printing and coating process. Therefore, the method uses a more green, safe and effective solvent to prepare the graphene conductive ink and the graphene conductive film. According to the principle of similar compatibility, the surface tension of the solvent can be matched with the surface free energy of graphene (46 mJ/m at room temperature)2) When the graphene nanoplatelets are matched and balanced with each other, the graphene nanoplatelets can be well dispersed in a solvent. The surface tension of water is 72.86mN/m and the surface tension of ethanol is 21.97mN/m at room temperature, so that the surface tension of the obtained mixed solvent can be balanced with the surface free energy of materials such as graphene after the water and the ethanol are mixed according to a certain proportion, the purpose of similar compatibility is achieved, and the mixed solvent is low in boiling point and environment-friendly. Certainly, the method is not enough to prepare the graphene composite conductive ink with high concentration and high stability, and a proper dispersing auxiliary agent is required to be added to assist carbon materials such as graphene to perform good dispersion, and the dispersing auxiliary agent commonly used at present is an insulating polymer surfactant, and the polymer auxiliary agent is difficult to remove from a finished product, so that the conductivity of the graphene conductive ink and the film is influenced to a great extent. Since GO contains more oxygen-containing functional groups and has excellent hydrophilicity, it should also be considered as a dispersant to replace the totally non-conductive polymeric surfactant. Grafting a small amount of oxygen-containing functional groups on the surfaces of graphene and multi-wall carbon nanotubes, and dispersing the oxygen-containing functional groups and a trace amount of GO in a mixed solvent for grinding and mixing. Oxygen-containing groups carried by trace GO can be partially grafted on the surfaces of graphene and multi-walled carbon nanotubes, and the rest oxygen-containing groups are dispersed in a solvent phase to play a role in assisting dispersion and prevent the graphene and the multi-walled carbon nanotubes from agglomerating and settling, so that the prepared graphene composite conductive ink has more excellent conductivity. And because GO is used as a dispersing aid, the addition amount is very small, a coating and a film with excellent conductivity can be obtained even if the ink is not subjected to reduction treatment after being cured, and the conductivity of the film can be obtained after the ink is reducedThe performance is further improved, so that whether reduction is carried out or not can be selected according to application requirements.
The technical scheme of the invention is as follows:
a preparation method of graphene composite conductive ink comprises the following steps:
(1) preparing Graphite Oxide (GO) by a Hummers method;
(2) soaking original Graphene Nanoplatelets (GNP) and multi-walled carbon nanotubes (MWCNTs) by dilute nitric acid to graft a small amount of oxygen-containing functional groups on the original Graphene Nanoplatelets (GNP) and the multi-walled carbon nanotubes (MWCNTs); the number of the original graphene nanoplatelets is 1-10, the sheet diameter is 0.1-5um, and the initial conductivity is 10000-20000S/m; the length of the multi-wall carbon nanotube is 10-30um, the inner diameter is 10-20nm, and the initial conductivity is 300-600S/m;
(3) dispersing the material obtained in the step (2), the graphite oxide obtained in the step (1) and a thickening agent into a mixed solvent, and fully grinding and mixing to obtain the graphene composite conductive ink;
the thickening agent is at least one of hydroxypropyl methyl cellulose, acrylic resin, ethyl cellulose, polyvinyl alcohol and terpineol, the mixed solvent is composed of ethanol and water in a volume ratio of 1-10: 1-10, the mass ratio of the original graphene nanoplatelets soaked by dilute nitric acid, the multi-walled carbon nanotubes soaked by dilute nitric acid, graphite oxide, the thickening agent and the mixed solvent is 1-4: 0.1-2: 0.1-1: 0-1: 310-380.
In a preferred embodiment of the invention, the graphite oxide in step (1) is prepared from 8000-mesh crystalline flake graphite as a raw material by using KMnO4And concentrated sulfuric acid as strong oxidant to perform oxidation intercalation on the original flake graphite.
In a preferred embodiment of the present invention, the pristine graphene nanoplatelets are prepared by a mechanical exfoliation method.
In a preferred embodiment of the present invention, the step (2) is: and soaking the original graphene nanoplatelets and the multi-walled carbon nanotubes for 1-6 hours by using dilute nitric acid so as to graft a small amount of oxygen-containing functional groups on the original graphene nanoplatelets and the multi-walled carbon nanotubes, then carrying out suction filtration and washing on the obtained material, and drying for later use.
In a preferred embodiment of the present invention, the grinding and mixing in step (3) is performed by using a sand mill or a basket mill, the grinding speed is set to 2000-3000 rpm, the grinding and mixing time is 3-24 h, and the grinding medium is 0.2-2 mm zirconia beads.
The other technical scheme of the invention is as follows:
the preparation method of the graphene composite conductive film is characterized in that the graphene composite conductive ink is used as a precursor to be coated and reduced.
In a preferred embodiment of the present invention, the coating is performed by a drop coating method or a spin coating method.
In a preferred embodiment of the present invention, the reduction treatment is HI reduction or high temperature annealing reduction.
The invention has the beneficial effects that:
1. the formula of the graphene composite conductive ink is green and safe, the cost is low, the micro GO replaces an insulating high-molecular surfactant, and the ethanol and the water are used as mixed solvents, so that the prepared graphene composite conductive ink is environment-friendly, high in applicability and wide in application range;
2. the preparation process is simple and easy to implement, has high efficiency, enables the conductive fillers to have good interaction directly through simple one-step grinding and mixing, and prepares the graphene composite conductive ink with stable dispersion and high performance.
3. The graphene composite conductive ink prepared by the invention has high concentration and excellent stability, and can be applied to the fields of ink-jet printing, conductive circuit and conductive film preparation and the like.
4. The graphene composite conductive ink prepared by the invention is used as a precursor, a graphene conductive film with excellent performance can be prepared by a simple dripping coating method and a spin coating method, the preparation of the graphene conductive film and the preparation of the graphene conductive ink are closely linked, and the application process of graphene is further promoted.
5. The graphene conductive film prepared by the invention has excellent conductive performance, can be directly attached to a substrate, can be peeled off without damage, and can meet the requirements of different application fields.
Drawings
FIG. 1 is a process flow diagram for preparing graphene composite conductive ink and films according to the present invention;
fig. 2 is a specific schematic diagram of the graphene composite conductive ink used in example 1 of the present invention, where a is an apparent diagram of the graphene composite conductive ink product prepared in example 1 of the present invention, and b is a microscopic action mechanism diagram of each raw material in the graphene composite conductive ink of the present invention;
fig. 3 is a photograph of the graphene conductive film prepared in the embodiment of the present invention, where a is an appearance image of the graphene conductive film prepared in the embodiment 1 of the present invention, b is an appearance image of the graphene conductive film prepared in the embodiment 2 of the present invention, c is the graphene conductive film obtained in the embodiment 1 of the present invention suspended in a HI solution, and d is the graphene conductive film prepared in the embodiment 3 of the present invention; e is the graphene conductive film prepared in embodiment 4 of the present invention, and f is the independent unsupported graphene conductive film obtained in embodiment 1 of the present invention;
fig. 4 is an SEM characterization diagram of the graphene conductive film prepared in example 1 of the present invention, where a is an SEM characterization diagram of a fracture surface of the graphene conductive film obtained in example 1 of the present invention, and b is a planar SEM characterization diagram of the graphene conductive film obtained in example 1 of the present invention;
FIG. 5 is a TEM representation of the graphene composite conductive ink prepared in example 1 of the present invention;
fig. 6 is an EDS comparison graph of the graphene conductive film prepared in example 2 before and after reduction, wherein a is an EDS test result graph of the graphene conductive film prepared in example 2 before reduction, and b is an EDS test result graph of the graphene conductive film prepared in example 2 after HI reduction;
fig. 7 is a comparison graph of raw material components before and after treatment in the examples of the present invention, where a is an infrared spectrum comparison of original graphene nanoplatelets before and after dilute nitric acid treatment in all the examples of the present invention, b is an infrared spectrum comparison of original multiwall carbon nanotubes before and after dilute nitric acid treatment in all the examples of the present invention, c is an infrared spectrum comparison of GO obtained by a conventional Hummers method and mechanically exfoliated graphene nanoplatelets in the present invention, and d is an infrared spectrum comparison of graphene conductive thin films obtained in example 2 of the present invention before and after reduction;
fig. 8 is a Raman comparison of the graphene conductive film of example 2 of the present invention before and after reduction;
fig. 9 is an XRD comparison graph of the graphene conductive film prepared in example 2 before and after reduction, where a is an XRD characterization graph of the graphene conductive film in example 2 before reduction, and b is an XRD characterization graph of the graphene conductive film in example 2 after reduction.
Detailed Description
The technical solution of the present invention will be further illustrated and described below with reference to the accompanying drawings by means of specific embodiments.
As shown in fig. 1, a preparation method of graphene composite conductive ink includes the following steps:
(1) preparing graphite oxide by a Hummers method;
(2) soaking the original graphene nanoplatelets and the multi-walled carbon nanotubes by using dilute nitric acid to graft a small amount of oxygen-containing functional groups on the original graphene nanoplatelets and the multi-walled carbon nanotubes; the number of the original graphene nanoplatelets is 1-10, the sheet diameter is 0.1-5um, and the initial conductivity is 10000-20000S/m; the length of the multi-wall carbon nanotube is 10-30um, the inner diameter is 10-20nm, and the initial conductivity is 300-600S/m;
(3) dispersing the material obtained in the step (2), the graphite oxide obtained in the step (1) and a thickening agent into a mixed solvent, and fully grinding and mixing to obtain the graphene composite conductive ink;
the thickening agent is at least one of hydroxypropyl methyl cellulose, acrylic resin, ethyl cellulose, polyvinyl alcohol and terpineol, the mixed solvent is composed of ethanol and water in a volume ratio of 1-10: 1-10, the mass ratio of the original graphene nanoplatelets soaked by dilute nitric acid, the multi-walled carbon nanotubes soaked by dilute nitric acid, graphite oxide, the thickening agent and the mixed solvent is 1-4: 0.1-2: 0.1-1: 0-1: 310-380.
In the step (1), the preparation of Graphite Oxide (GO) by using the traditional Hummers method takes 8000-mesh flake graphite as a raw material and KMnO4And concentrated sulfuric acid is used as a strong oxidant to carry out oxidation intercalation on the original flake graphite. The specific process flow of the step is as follows: firstly, accurately weighing 2g of scale graphite powder, and measuring 100ml of concentrated H2SO4Mixing in a beaker, and stirring and mixing in an ice-water bath; ② weighing 11-12g potassium permanganate powder, slowly adding into the mixture containing original crystalline flake graphite and concentrated H2SO4Keeping the beaker in an ice water bath for 30 min; thirdly, after ice-water bath is carried out for 30min, stirring for 2h under normal temperature water bath, and then slowly adding 150ml of distilled water into the beaker to release a large amount of heat in the process; fourthly, after the temperature is reduced to the room temperature, a proper amount of 30 percent H by mass is added into the beaker2O2Carrying out oxidation-reduction reaction with a strong oxidant, and neutralizing the strong oxidant until the solution turns golden yellow; fifthly, standing the obtained product for 24 hours, removing supernatant, and repeatedly washing and centrifuging the sediment at the bottom by using distilled water until the pH value of the product is neutral (the pH value is more than or equal to 6); sixthly, collecting the solid product, and freeze-drying for later use; seventhly, repeating the processes of the first step and the sixth step; and (3) preparing sufficient GO, and applying the sufficient GO to preparation research of graphene composite conductive ink and thin films.
And infrared spectrum characterization comparison is carried out on GO and the mechanically exfoliated graphene nanoplatelets, and the result is shown in fig. 7 c. It can be seen that the infrared spectrum of GO clearly contains more characteristic peaks of oxygen-containing groups such as hydroxyl groups, carbonyl groups and the like, while the graphene nanoplatelets mechanically exfoliated do not contain these oxygen-containing functional groups.
In the step (2), the original graphene nanoplatelets are prepared by a mechanical stripping method, the number of the layers is 1-10, the sheet diameter is 0.1-5um, and the initial conductivity is 10000-20000S/m. The length of the multi-wall carbon nano-tube is 10-30um, the inner diameter is 10-20nm, and the initial conductivity is 300-600S/m. The dilute nitric acid treatment is to soak the original graphene and the multi-walled carbon nano-tubes in a dilute nitric acid solution for reaction for 1-6h, then perform suction filtration and washing, and dry the graphene and the multi-walled carbon nano-tubes for later use. The specific process flow of the step is as follows: weighing 10g of original graphene and multi-wall carbon nanotube powder respectively, and pouring the powder into two wide-mouth brown reagent bottles respectively; adding equivalent and sufficient diluted nitric acid solution into the two wide-mouth brown reagent bottles to fully submerge the solid powder; thirdly, after soaking and reacting for 1-6 hours, removing the dilute nitric acid solution by suction filtration, washing and suction filtering the solid powder for many times by using distilled water until the PH value of the filtrate is neutral, collecting the solid product, and drying for later use; and fourthly, repeating the process flows of the first step and the third step to prepare enough amount of graphene and multi-walled carbon nanotubes with trace oxygen-containing functional groups, and applying the graphene and multi-walled carbon nanotubes to preparation research of graphene composite conductive ink and films.
Compared with the prior art, the graphene composite conductive ink and the film have the advantages that GO is used as a dispersing auxiliary agent, the addition of an insulating polymer auxiliary agent can be effectively avoided, a good dispersing effect is obtained, and the conductivity of the graphene composite conductive ink and the film can be improved to a certain extent. In addition, the step (1) and the step (2) can be carried out simultaneously, the process is simple and convenient, and the operation and industrialization are easy.
The infrared spectrum characterization analysis was performed on the graphene nanoplatelets and the multi-walled carbon nanotubes before and after the dilute nitric acid treatment, and the results are shown in fig. 7 (a-b). It can be seen that the original GNP did not carry any oxygen-containing functional groups, whereas the-OH groups (3735 cm) were successfully grafted after soaking in dilute HNO3-1) C ═ O group (1794 cm)-1) Part of the double bond structure in the benzene ring is broken to form a C-H single bond (2923 cm)-1) And C-C group (1384 cm)-1). The original MWCNTs already have a small number of hydroxyl groups on the surface (3416 cm)-1) After soaking with diluted HNO3, the surface was successfully grafted with C ═ O groups (1654 cm)-1). Therefore, through simple dilute nitric acid soaking treatment, a small amount of oxygen-containing functional groups can be grafted on the surfaces of GNP and MWCNTs, and the oxygen-containing groups can react with partial oxygen-containing functional groups on GO in the grinding and mixing process, so that the hydrophobic GNP and MWCNTs can be stably dispersed in an aqueous solvent, and the graphene composite conductive ink is prepared.
After a sufficient amount of conductive filler is prepared through the steps (1) and (2), different formulas and preparation processes are tried to prepare the graphene composite conductive ink and the graphene composite conductive film.
Example 1
According to the technical scheme disclosed by the invention, the following proportioning and operation are carried out:
(1) taking the following materials in parts by mass: 3 parts of graphene micro-sheets treated by dilute nitric acid, 0.75 part of multiwall carbon nanotubes treated by dilute nitric acid, 0.75 part of GO, 100 parts of ethanol and 260 parts of water are mixed, and the mixture is put into a basket grinder to be ground and mixed for 4 hours after ultrasonic pre-dispersion, wherein the rotating speed is set to 2000rpm, so that the graphene composite conductive ink without any high-molecular auxiliary agent is prepared;
(2) coating the prepared graphene composite conductive ink on a glass slide by a dripping method, and heating to evaporate a solvent to obtain a uniform and continuous graphene conductive film on a glass slide substrate;
(3) taking one piece of the obtained graphene conductive film, equally dividing into three equal parts for comparison test: one part is not treated, the other part is reduced in HI, and the other part is annealed and reduced at a high temperature of 300 ℃;
(4) and testing the resistivity of the three graphene films subjected to different treatments after the uniform division by using a four-probe tester, and representing the micro-morphology of the graphene composite conductive ink and the film by using a field emission scanning electron microscope and a transmission electron microscope.
As shown in fig. 2, the graphene composite conductive ink prepared by the embodiment of the invention can be stably dispersed and has a high concentration. The microscopic action mechanism among the conductive raw materials in the graphene composite conductive ink is shown in fig. 2b, and after the original GNP and MWCNTs are soaked in dilute nitric acid, a very small amount of oxygen-containing functional groups are attached to the surfaces of the original GNP and MWCNTs. In the process of grinding and mixing, the oxygen-containing functional groups can react with partial oxygen-containing functional groups on GO, so that the surfaces of GNP and MWCNTs are connected with extremely hydrophilic GO micro-sheets, the hydrophobic GNP and MWCNTs are effectively prevented from self-aggregation and sedimentation, and finally the stably dispersed graphene composite conductive ink is prepared. As shown in fig. 3a, the graphene conductive film prepared in the embodiment of the present invention is uniform and smooth, and the graphene composite conductive ink obtained in the present invention has a high concentration, so that the formed conductive film is thick and opaque. When the HI is used for reducing the graphene conductive film, the graphene conductive film deposited and loaded on the glass slide can be peeled off intact and suspended on the surface of the HI solution, as shown in fig. 3c, and then the peeled graphene conductive film can be transferred to other target substrates for application, or directly dried to obtain an independent unsupported graphene conductive film, as shown in fig. 3 f. After the graphene conductive film prepared by the embodiment of the invention is subjected to different reduction treatments, the surface sheet resistance of the graphene conductive film can be obviously reduced, and the table 1 shows. The results indicate that the film prepared from the graphene composite conductive ink can meet the requirements of different fields on the form and the conductivity of the conductive film, and has very wide application prospects. Fig. 4 and 5 are SEM and TEM characterization result diagrams of the graphene composite conductive ink and the graphene composite conductive film prepared in the embodiment of the present invention, and it can be seen that good composite overlapping can be performed between the conductive fillers to form a continuous conductive network structure (fig. 4a), and the structure formed by MWCNTs is sandwiched between the layers of the graphene platelet stack to play a supporting role (fig. 4 b). The MWCNTs can not only serve as bridge joints for the graphene nanoplatelets that are not in contact with each other (fig. 5a), but also can be wound and overlapped with each other to form a network structure, and serve as a base layer scaffold for the graphene nanoplatelets that are stacked and overlapped with each other, and meanwhile, a part of the MWCNTs are loaded on the graphene nanoplatelets (fig. 5 b-d). The lapping modes are all beneficial to improving the comprehensive properties of the graphene film and enlarging the application range of the graphene composite conductive ink.
Example 2
According to the technical scheme disclosed by the invention, the following proportioning and operation are carried out:
(1) taking the following raw materials in parts by mass: 1 part of graphene micro-sheets treated by dilute nitric acid, 0.2 part of multiwall carbon nanotubes treated by dilute nitric acid, 0.25 part of GO, 100 parts of ethanol and 260 parts of water are mixed, subjected to ultrasonic pre-dispersion, put into a basket grinder to be ground for 4 hours at the rotating speed of 2000rpm, and graphene composite conductive ink without any high-molecular auxiliary agent is prepared;
(2) coating the prepared graphene composite conductive ink on a glass slide by a dripping method, and heating to evaporate a solvent to obtain a uniform and continuous graphene conductive film on a glass slide substrate;
(3) taking one piece of the obtained graphene conductive film, equally dividing into three equal parts for comparison test: one part is not treated, the other part is reduced in HI, and the other part is annealed and reduced at a high temperature of 300 ℃;
(4) and testing the resistivity of the three graphene thin films subjected to different treatments after the uniform division by using a four-probe tester, and performing EDS (electronic discharge spectroscopy), infrared spectroscopy, Raman and XRD (X-ray diffraction) test characterization on the graphene conductive thin films before and after the reduction treatment.
The apparent morphology of the graphene conductive film prepared by the embodiment of the invention is shown in fig. 3b, and the resistivity of the graphene conductive film is greatly reduced after reduction treatment. As shown in fig. 6, after the graphene conductive film prepared by the embodiment of the present invention is subjected to HI reduction treatment, the oxygen content of the graphene conductive film is significantly reduced, which indicates that the reduction method of the present invention is feasible, and the oxygen-containing functional groups in the film can be effectively removed, and the surface sheet resistance of the film is further reduced due to the reduction of the oxygen content in the film. As shown in fig. 7d, after the graphene conductive film is subjected to the reduction treatment, infrared spectrum absorption peaks of hydroxyl groups and carbonyl groups disappear, which indicates that the reduction treatment can effectively remove oxygen-containing functional groups in the film to a certain extent. The microstructure changes of the graphene conductive film before and after reduction treatment are characterized through Raman and XRD, and the influence of the reduction treatment on the microstructure of the graphene conductive film is researched and analyzed according to the result. Fig. 8 is a Raman characterization comparison graph of the graphene conductive film prepared in the embodiment of the present invention before and after reduction treatment, and it can be seen that after the graphene conductive film is subjected to HI reduction treatment, the intensity ratio I of the D peak to the G peak in the Raman spectrum thereofD/IGIs significantly increased. The reduction method used in the invention can effectively remove oxygen-containing groups in the graphene film, the added GO is reduced into rGO, and the added GO is thin in the reduction processSp in film structure3Conversion of hybridized carbon atoms to sp2The carbon atoms are hybridized, and the order degree of the microstructure of the film is reduced to a certain extent. In addition, in the reduction process, due to the disappearance of oxygen-containing groups such as hydroxyl, carboxyl and the like, chemical bonds at certain parts on the sheet layer can be broken, so that the defects in the microstructure of the conductive film are increased, and therefore I of the reduced graphene filmD/IGThe value increases. An XRD characterization result of the graphene conductive film obtained in the embodiment of the present invention before and after reduction is shown in fig. 9, and a sharp and strong characteristic diffraction peak is present at 26.26 ° of a film prepared from the graphene composite conductive ink with trace GO assistance in dispersion, which indicates that the arrangement between layers in the microstructure of the graphene conductive film is dense and ordered, and the crystallinity is relatively high. However, after the reduction treatment, the intensity of the characteristic diffraction peak of the graphene conductive film at the position is obviously reduced, because in the reduction process, the bond fracture occurs in the microstructure of the film, so that the defects on the surface of the conductive filler are increased, the plane size of the graphene micro-sheet is also reduced, and after the oxygen-containing group in the film is removed, the combination between the sheet layers is looser, the distance between the sheet layers is increased, and the microstructure of the film becomes disordered. As can also be seen from the inset in fig. 9, a diffraction peak with weak intensity appears at 11.92 ° in the thin film prepared from the graphene composite conductive ink with micro GO auxiliary dispersion, and the peak is a characteristic diffraction peak of GO. However, after the graphene conductive film is subjected to reduction treatment, the characteristic diffraction peak of GO is obviously disappeared, and a weaker diffraction peak appears at 23.70 degrees instead, as shown in fig. 3b, which again strongly proves that trace GO in the film is successfully reduced to rGO, and the peak is obviously weaker in intensity compared with the characteristic diffraction peak of graphene.
Example 3
According to the technical scheme disclosed by the invention, the following proportioning and operation are carried out:
(1) taking the following raw materials in parts by mass: mixing 4 parts of graphene nanoplatelets treated by dilute nitric acid, 2 parts of multiwalled carbon nanotubes treated by dilute nitric acid, 1 part of GO, 1 part of hydroxypropyl methylcellulose, 205 parts of ethanol and 130 parts of water, performing ultrasonic pre-dispersion, and then putting the mixture into a basket grinder to grind for 4 hours at the rotating speed of 2000rpm to prepare the graphene composite conductive ink with high viscosity;
(2) coating the prepared graphene composite conductive ink on a glass slide by a dripping method, and heating to evaporate a solvent to obtain a uniform and continuous graphene conductive film on a glass slide substrate;
(3) taking one piece of the obtained graphene conductive film, equally dividing into three equal parts for comparison test: one part is not treated, the other part is reduced in HI, and the other part is annealed and reduced at a high temperature of 300 ℃;
(4) and testing the resistivity of the three graphene films subjected to different treatments after the uniform division by using a four-probe tester.
The apparent morphology of the graphene conductive film prepared by the embodiment is shown in fig. 3d, and the resistivity of the graphene conductive film is greatly reduced after reduction treatment.
Example 4
According to the technical scheme disclosed by the invention, the following proportioning and operation are carried out:
(1) taking the following raw materials in parts by mass: mixing 2 parts of graphene micro-sheets treated by dilute nitric acid, 1 part of multiwall carbon nanotubes treated by dilute nitric acid, 0.2 part of GO, 60 parts of ethanol and 310 parts of water, performing ultrasonic pre-dispersion, putting the mixture into a basket type grinder to grind for 4 hours at the rotating speed of 2000rpm, and preparing the graphene composite conductive ink without any macromolecular auxiliary agent;
(2) coating the prepared graphene composite conductive ink on a glass slide by a dripping method, and heating to evaporate a solvent to obtain a uniform and continuous graphene conductive film on a glass slide substrate;
(3) taking one piece of the obtained graphene conductive film, equally dividing into three equal parts for comparison test: one part is not treated, the other part is reduced in HI, and the other part is annealed and reduced at a high temperature of 300 ℃;
(4) and testing the resistivity of the three graphene films subjected to different treatments after the uniform division by using a four-probe tester.
The apparent morphology of the graphene conductive film prepared by the embodiment is shown in fig. 3e, and the resistivity of the graphene conductive film is greatly reduced after reduction treatment.
In summary, the test results of the sheet resistance of the surface of the graphene conductive film in table 1 are combined to show that the graphene composite conductive ink and the film preparation method based on the trace amount of graphite oxide assisted dispersion are feasible. GO is first prepared by the traditional Hummers method, by simple dilute HNO3A small amount of oxygen-containing groups are grafted on original GNP and MWCNTs successfully, the oxygen-containing groups and trace GO are mixed and dispersed in a mixed solvent of ethanol and water, and in the grinding and mixing process, part of the oxygen-containing groups on GO can interact with the GNP and the MWCNTs, so that a good dispersion-assisting effect is achieved, and finally the graphene composite conductive ink which is stable, uniform and high in concentration is prepared. The prepared graphene composite conductive ink can be used for preparing a uniform, continuous and good-conductivity graphene conductive film by a dripping method regardless of the addition of a thickening agent, and the obtained graphene conductive film can be completely and nondestructively peeled off from a glass slide when being reduced in a HI solution, so that the film can be conveniently applied subsequently. The MWCNTs in the graphene conductive film can play a bridge lapping role for graphene sheets which are not in contact with each other, and can also form a support type conductive network structure between the stacked graphene layers. Most of oxygen-containing groups and impurities in the film can be effectively removed through reduction treatment, the process can have certain influence on the microstructure of the graphene conductive film, and the conductivity of the film is improved.
TABLE 1
The above description is only a preferred embodiment of the present invention, and therefore should not be taken as limiting the scope of the invention, which is defined by the appended claims.
Claims (8)
1. A preparation method of graphene composite conductive ink is characterized by comprising the following steps: the method comprises the following steps:
(1) preparing graphite oxide by a Hummers method;
the specific process flow for preparing the graphite oxide by the Hummers method in the step (1) is as follows: firstly, accurately weighing 2g of scale graphite powder, and measuring 100ml of concentrated H2SO4Mixing in a beaker, and stirring and mixing in an ice-water bath; ② weighing 11-12g potassium permanganate powder, slowly adding into the mixture containing original crystalline flake graphite and concentrated H2SO4Keeping the beaker in an ice water bath for 30 min; thirdly, after ice-water bath is carried out for 30min, stirring for 2h under normal temperature water bath, and then slowly adding 150ml of distilled water into the beaker to release a large amount of heat in the process; fourthly, after the temperature is reduced to the room temperature, a proper amount of 30 percent H by mass is added into the beaker2O2Carrying out oxidation-reduction reaction with a strong oxidant, and neutralizing the strong oxidant until the solution turns golden yellow; fifthly, standing the obtained product for 24 hours, removing supernatant, and repeatedly washing and centrifuging the sediment at the bottom by using distilled water until the pH value of the product is more than or equal to 6; sixthly, collecting the solid product, and freeze-drying for later use;
(2) soaking the original graphene nanoplatelets and the multi-walled carbon nanotubes by using dilute nitric acid to graft a small amount of oxygen-containing functional groups on the original graphene nanoplatelets and the multi-walled carbon nanotubes; the number of the original graphene nanoplatelets is 1-10, the sheet diameter is 0.1-5um, and the initial conductivity is 10000-20000S/m; the length of the multi-wall carbon nanotube is 10-30um, the inner diameter is 10-20nm, and the initial conductivity is 300-600S/m;
the specific process steps of soaking and treating the original graphene nanoplatelets and the multi-walled carbon nanotubes by using dilute nitric acid in the step (2) are as follows: weighing 10g of original graphene and multi-wall carbon nanotube powder respectively, and pouring the powder into two wide-mouth brown reagent bottles respectively; adding equivalent and sufficient diluted nitric acid solution into the two wide-mouth brown reagent bottles to fully submerge the solid powder; thirdly, after the soaking reaction is carried out for 1 to 6 hours, removing the dilute nitric acid solution by suction filtration, washing and carrying out suction filtration on the solid powder for many times by using distilled water until the pH value of the filtrate is neutral, collecting the solid product, and drying for later use;
(3) dispersing the material obtained in the step (2), the graphite oxide obtained in the step (1) and a thickening agent into a mixed solvent, and fully grinding and mixing to obtain the graphene composite conductive ink;
the thickening agent is at least one of hydroxypropyl methyl cellulose, acrylic resin, ethyl cellulose, polyvinyl alcohol and terpineol, the mixed solvent is composed of ethanol and water in a volume ratio of 1-10: 1-10, the mass ratio of the original graphene nanoplatelets soaked by dilute nitric acid, the multi-walled carbon nanotubes soaked by dilute nitric acid, graphite oxide, the thickening agent and the mixed solvent is 1-4: 0.1-2: 0.1-1: 0-1: 310-380.
2. The method of claim 1, wherein: the graphite oxide in the step (1) is prepared by taking 8000-mesh crystalline flake graphite as a raw material and KMnO4And concentrated sulfuric acid as strong oxidant to perform oxidation intercalation on the original flake graphite.
3. The method of claim 1, wherein: the pristine graphene nanoplatelets are prepared by a mechanical exfoliation method.
4. The method of claim 1, wherein: the step (2) is as follows: and soaking the original graphene nanoplatelets and the multi-walled carbon nanotubes for 1-6 hours by using dilute nitric acid so as to graft a small amount of oxygen-containing functional groups on the original graphene nanoplatelets and the multi-walled carbon nanotubes, then carrying out suction filtration and washing on the obtained material, and drying for later use.
5. The method of claim 1, wherein: the grinding and mixing equipment in the step (3) is a sand mill or a basket type grinder, the grinding rotating speed is set to be 2000-3000 rpm, the grinding and mixing time is 3-24 hours, and the grinding medium is zirconia beads with the thickness of 0.2-2 mm.
6. A preparation method of a graphene composite conductive film is characterized by comprising the following steps: coating and reducing the graphene composite conductive ink as claimed in any one of claims 1 to 5 as a precursor.
7. The method of claim 6, wherein: the coating adopts a dripping coating method or a spin coating method.
8. The method of claim 6, wherein: the reduction treatment is HI reduction or high-temperature annealing reduction.
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| CN112254850B (en) * | 2020-08-28 | 2022-01-11 | 苏州烯时代材料科技有限公司 | Conductive carbon paste for flexible pressure sensor, preparation method thereof and pressure sensor |
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