CN113548661A

CN113548661A - Preparation method of graphene-loaded iron oxide, composite material and application of composite material

Info

Publication number: CN113548661A
Application number: CN202110828266.5A
Authority: CN
Inventors: 朱守圃; 孟晓茹; 黄景瑞; 林孟昌
Original assignee: Shandong University of Science and Technology
Current assignee: Shandong University of Science and Technology
Priority date: 2021-07-22
Filing date: 2021-07-22
Publication date: 2021-10-26

Abstract

The invention belongs to the technical field of graphene material compounding, and discloses a method for preparing graphene-supported iron oxide, a composite material and application thereof, wherein the method is simple, safe and environment-friendly. The oxygen content in the graphene is greatly improved by heat treatment to more than 10 wt.%, and the precursor of the iron oxide is uniformly attached to the surface of the graphene in the form of nanoparticles or ions, and the content can be as high as 75 wt.%. The graphene iron oxide-loaded composite material obtained by the method is used in a lithium ion battery, can obviously improve the cycle capacity, and still maintains higher coulombic efficiency and better cycle stability.

Description

Preparation method of graphene-loaded iron oxide, composite material and application of composite material

Technical Field

The invention belongs to the technical field of material preparation, relates to a graphene material compounding technical process, and particularly relates to a preparation method for compounding graphene and iron oxide.

Background

After water pollution, air pollution, noise pollution and solid waste pollution, electromagnetic radiation which is invisible, inaudible and untouchable becomes the fifth pollution, the electromagnetic radiation not only brings harm to the health of human bodies, but also influences the normal function and the service life of electronic equipment, in addition, the leakage of confidential information is caused, and the problems of exposure of targets such as military airplanes, equipment and the like can also occur due to the reflection of the emitted electromagnetic wave. Therefore, the development of electromagnetic compatibility technology has become an urgent need. Based on the characteristics of high electronic conductivity, low density, corrosion resistance, high temperature resistance, large specific surface area, good mechanical property and the like of graphene, the graphene has been widely researched and focused in the field of electromagnetic compatibility. Magnetic nanoparticles are loaded on graphene with a lamellar structure, so that the composite material has high magnetic loss capacity, and a better electromagnetic compatibility characteristic is obtained through a synergistic effect of dielectric loss and magnetic loss and an interface effect. The magnetic iron oxide has the advantages of environmental friendliness, low price, abundant reserves and the like. The composite material combining the graphene and the iron oxide with the wave-absorbing property has the magnetic and dielectric properties, and improves the magnetic attenuation, so that the microwave absorption efficiency is improved, and higher electromagnetic shielding efficiency is obtained. Chinese patent CN 107418513B discloses that GO is prepared by using Hummer's method, and then graphene foam-supported Fe is prepared by hydrothermal reaction₃O₄A method for compounding a wave-absorbing material with magnetic particles. Chinese patent CN 106118594B discloses that Fe is prepared by heating and ultrasonically dispersing GO dispersion liquid and ferrous iron source salt solution and adjusting the pH value of the dispersion liquid₃O₄the/GO compound is used for wave-absorbing materials.

In addition, in the field of lithium ion batteries, iron oxides have a relatively high theoretical capacity (1000 mA h g)^-1) However, the huge volume change between iron oxide and iron atoms during charge and discharge generates a very large volume stress, resulting in a broken crystal structure, capacity loss and shortened cycle life. The graphene with excellent electronic conductivity and high specific surface of the iron oxide is compounded, so that on one hand, the graphene can make up for the defect of iron oxidation conductivity and also can buffer the volume change in the charging and discharging processes, and better electrochemical performance is obtained. Chinese patent CN 109461599 discloses a method for preparing Fe by preparing GO through an improved Hummer's method, drying the GO, fully grinding the GO, an iron salt precursor and a nitrogen precursor in a container, transferring the mixture to a tubular furnace, and calcining the mixture at high temperature in the presence of atmosphere protection₃O₄A/nitrogen doped graphene composite electrode material. Chinese patent CN 106997954B discloses that GO prepared by Hummer's method is doped with nitrogen by taking urea as nitrogen source, and then is secondarily oxidized by concentrated sulfuric acid and concentrated nitric acid, and then is subjected to hydrothermal reaction with ferrous ions to prepare Fe₂O₃A graphene composite electrode.

However, in the above preparation methods, GO is prepared from graphite by using strong acid and strong oxidizing reagent, and then iron oxide is loaded, so that a large amount of highly corrosive strong acid such as sulfuric acid, nitric acid and hydrochloric acid, and highly oxidizing reagent such as potassium permanganate are required in the process, which not only makes the experimental process have certain danger, but also brings adverse effect to the environment, and is not beneficial to large-scale preparation.

Disclosure of Invention

The invention aims to overcome the defects in the prior art, and provides a simple, safe and environment-friendly method for preparing graphene-supported iron oxide, a composite material and application thereof.

In order to achieve the above object, a first aspect of the present invention provides a method for preparing graphene-supported iron oxide, the method comprising the steps of:

(1) firstly, carrying out thermogravimetric analysis on graphene powder in an oxygen atmosphere at a heating rate of 5-10 ℃/min to determine the initial weight loss temperature;

(2) putting graphene powder into a high-temperature furnace, introducing oxygen-containing atmosphere of 0.01-5 mL/min, heating to the initial weight loss temperature or slightly exceeding the initial weight loss temperature at the heating rate of 1-10 ℃/min, and maintaining for several hours at the temperature, so that a certain amount of oxygen-containing functional groups are attached to the surface of graphene, and the graphene attached with oxygen-containing groups is obtained;

(3) under the condition of adding or not adding a surfactant, uniformly dispersing graphene attached with oxygen-containing groups in a polar solvent under the assistance of ultrasound, then adding an iron oxide precursor into the graphene, and stirring and standing the mixture to enable the iron oxide precursor to be adsorbed on the surface of the graphene;

(4) according to the type of the prepared target iron oxide and the reduction degree requirement of the graphene, a reducing agent and a pH regulator are optionally added into the step (3), and a precursor of the iron oxide is converted into the iron oxide in situ through a liquid phase reaction to obtain a compound of the graphene attached to the iron oxide;

(5) according to the requirements of the reduction degree of the graphene and the crystallinity of the iron oxide in the prepared target product, the subsequent calcination in an inert atmosphere is further carried out to further reduce the graphene, so that the conductivity of the composite material is improved, the crystallinity of the iron oxide is improved, and the graphene-loaded iron oxide composite material is obtained.

In a second aspect, the present invention provides a graphene iron oxide-loaded composite material prepared by the above method.

The third aspect of the invention provides an application of the graphene loaded iron oxide composite material in electromagnetic compatibility and lithium ion batteries, especially in lithium ion batteries.

Through the technical scheme, the invention has the following beneficial effects:

the oxygen-containing group attached to the graphene is obtained by specific heat treatment in an oxygen-containing atmosphere, and the oxygen exists in a form mainly including a carbon-oxygen double bond connecting aromatic carbons, a carbon-oxygen single bond connecting aliphatic carbons, and a carbon-oxygen single bond connecting aromatic carbons. Further, the oxygen content in the graphene is greatly improved through heat treatment, and the mass fraction of oxygen in the graphene attached with the oxygen-containing group reaches more than 10 wt.%.

The oxygen-containing groups on the surface of the graphene are helpful for loading iron oxide, the precursor of the iron oxide is uniformly attached to the surface of the graphene in the form of nanoparticles or ions, and then the precursor is converted into the iron oxide in situ, and the content of the attached iron oxide can be as high as 75 wt.%.

Furthermore, when the graphene-loaded iron oxide composite material obtained by the method is used in a lithium ion battery, the cycle capacity can be obviously improved, and higher coulombic efficiency and better cycle stability are still maintained. The iron oxide is firmly adsorbed on the graphene after heat treatment, and the graphene and the iron oxide have a synergistic effect, so that the graphene loaded with the iron oxide and attached with the oxygen-containing group can buffer the volume change of the iron oxide in the charging and discharging processes, and the graphene attached with the oxygen-containing group can make up the deficiency of the conductivity of the iron oxide.

According to the invention, the graphene-loaded iron oxide compound is prepared innovatively, and the use of strong acid and strong oxidant is avoided based on the method for attaching oxygen-containing groups through heat treatment of graphene in an oxygen-containing atmosphere; has the advantages of simple process, safe operation, environmental protection, suitability for large-scale preparation and the like.

The graphene loaded iron oxide composite material subjected to heat treatment can be widely applied to the fields of lithium ion batteries, electromagnetic compatibility and the like.

Description of the drawings:

FIG. 1 is a thermogravimetric analysis plot of a single-layer graphene used in example 1 of the present invention;

FIG. 2 is an X-ray photoelectron spectroscopy (XPS) chart of the oxygen-containing group-attached monolayer graphene prepared in example 1 of the present invention and its raw material;

fig. 3 is a photograph of graphene to which an oxygen-containing group is attached, uniformly dispersed in water, prepared in example 1 of the present invention;

FIG. 4 shows that the graphene attached with oxygen-containing groups prepared in example 1 of the present invention supports Fe (OH)₃Scanning Electron Microscope (SEM) pictures of the composite;

FIG. 5 shows that the raw material graphene prepared in example 1 of the present invention supports Fe₂O₃(a) And heat treated graphene supported Fe₂O₃(b) SEM picture of (a);

FIG. 6 shows Fe supported by heat treated graphene prepared in example 1 of the present invention₂O₃A Transmission Electron Microscope (TEM) picture of (a);

FIG. 7 shows Fe supported by heat treated graphene prepared in example 1 of the present invention₂O₃X-ray diffractometer (XRD) pictures of (c);

FIG. 8 shows the raw material graphene and the heat-treated graphene loaded Fe prepared in example 1 of the present invention₂O₃Thermogravimetric analysis of (A) and (B);

FIG. 9 shows that raw material graphene loaded Fe prepared in example 1 of the present invention₂O₃Composite and heat-treated graphene-supported Fe₂O₃The cycle capacity curve of the composite for a lithium button cell;

FIG. 10 shows that the graphene prepared in example 2 of the present invention supports Fe₃O₄SEM picture of (a);

FIG. 11 shows Fe supported on heat treated graphene prepared in example 2 of the present invention₃O₄Composite, Fe₃O₄XRD pictures of nanoparticles and heat-treated graphene;

FIG. 12 shows Fe loaded on heat-treated graphene prepared in example 8 of the present invention₂O₃SEM picture of (a);

FIG. 13 shows Fe loaded on heat-treated graphene prepared in example 8 of the present invention₂O₃Thermogravimetric plot of;

FIG. 14 shows Fe loading of heat-treated graphene prepared in example 8 of the present invention₂O₃The composite is used for the positive electrode of a button lithium battery and has a voltage ranging from 0.01 to 3V (relative to lithium)Electrode) cycling capacity plot at 0.5A/g current density.

Detailed Description

The following examples further illustrate the details of the present invention.

The invention provides a preparation method of graphene-loaded iron oxide, which comprises the following steps:

(2) putting graphene powder into a high-temperature furnace, introducing oxygen-containing atmosphere at a flow rate of 0.01-5 mL/min, heating to an initial weight loss temperature or slightly exceeding the initial weight loss temperature at a heating rate of 1-10 ℃/min, and carrying out heat treatment at the temperature for several hours, so that a certain amount of oxygen-containing functional groups are attached to the surface of graphene, and graphene attached with oxygen-containing groups is obtained;

(3) uniformly dispersing graphene attached with oxygen-containing groups and a surfactant in a polar solvent under the assistance of ultrasound, then adding an iron oxide precursor into the polar solvent, and stirring and standing the mixture to enable the iron oxide precursor to be adsorbed on the surface of the graphene;

(4) according to the type of the prepared target iron oxide and the requirement of the reduction degree of the graphene, optionally adding a reducing agent and a pH regulator into the step (3), and converting a precursor of the iron oxide into the iron oxide in situ through a liquid phase reaction to obtain the graphene loaded iron oxide composite material;

(5) according to the requirements of the reduction degree of graphene and the crystallinity of the iron oxide in the prepared target product, the subsequent calcination in the inert atmosphere further reduces the graphene, so that the conductivity of the composite material is improved, and the crystallinity of the iron oxide is improved.

In the step (2), the amount of the graphene powder is 0.03-0.3 g, the oxygen-containing atmosphere comprises air, oxygen, a mixed gas of air and an inert atmosphere and a mixed gas of oxygen and an inert atmosphere, and the inert atmosphere is nitrogen and argon; the heat treatment is maintained for 0.1-5 h.

In the invention, the temperature of the heat treatment is the initial weight loss temperature or slightly exceeds the initial weight loss temperature, wherein slightly exceeding the initial weight loss temperature means the temperature range from the initial weight loss temperature to 130 ℃ at most exceeding the initial weight loss temperature, and the temperature is required to be more than 10 ℃ lower than the initial temperature of the weight loss finishing platform. Under the condition of lower than the initial weight loss temperature, graphene is difficult to react with oxygen, so that oxygen-containing groups are difficult to generate on the surface of the graphene; when the initial weight loss temperature is exceeded, the reaction rate of graphene and oxygen is very high, so that the reaction condition is difficult to control, the difficulty in selecting gas flow is increased, the carbon material is easy to be completely converted into gaseous oxycarbide, and the morphology of graphene is difficult to maintain; the heat treatment can be carried out slowly under the condition of small oxygen-containing atmosphere flow, and a large number of oxygen-containing groups are attached to the surface of the graphene while the morphology of the graphene is maintained.

In the invention, the inventor researches and discovers that the oxygen-containing group attached to the graphene is obtained by heat treatment in an oxygen-containing atmosphere, and the existence form of oxygen mainly comprises a carbon-oxygen double bond connecting aromatic carbon, a carbon-oxygen single bond connecting aliphatic carbon and a carbon-oxygen single bond connecting aromatic carbon.

Further, the oxygen content in the graphene can be greatly improved through heat treatment, and the mass fraction of oxygen in the graphene attached with the oxygen-containing groups reaches more than 10 wt.%, and can reach 19 wt.%.

In the step (3), the surfactant is selected from one of polyvinylpyrrolidone, sodium dodecyl benzene sulfonate or cetyl trimethyl ammonium bromide;

the polar solvent is selected from one of water, N-dimethylformamide and N-methylpyrrolidone;

the iron oxide precursor is selected from Fe (OH)₃Sol, ferric nitrate, ferric acetate, FeCl₃、FeCl₂One or a mixture of two of them;

the dosage ratio of the graphene attached with the oxygen-containing group, the surfactant, the iron oxide precursor and the polar solvent is 30-60 mg: 0-200 mg: 20-200 mg: 20-40 mL;

the ultrasonic power is 300-1000W, and the ultrasonic dispersion time is 30-100 min;

stirring and standing are carried out at normal temperature, the stirring and standing are carried out to enable the iron oxide precursor to be better attached to the surface of the graphene, the stirring rotating speed is 50-200 revolutions per minute, the stirring time is 1-5 min, and the standing time is 2-10 min.

In step (4) of the present invention, the reducing agent comprises adding Fe³⁺Reduction to Fe²⁺The reducing agent A is selected from ascorbic acid or trisodium citrate, and/or the reducing agent B is selected from hydrazine hydrate or ethylene glycol;

the pH regulator is selected from one of ammonia water, sodium hydroxide and sodium bicarbonate;

the dosage of the reducing agent A is 0.5-2 times of the molar weight of the iron oxide precursor, and the dosage of the reducing agent B is 3-30 vol.% of the total volume of the solvent; adding a pH regulator to regulate the pH value of the reaction solution to about 11;

the liquid phase reaction is a hydrothermal reaction or a coprecipitation reaction, the hydrothermal reaction is carried out for 10-14 h at 120-180 ℃, and the coprecipitation reaction is carried out for 2-5 min at 80 ℃.

According to the present invention, a reducing agent and a pH adjusting agent are also added to the solution of the iron oxide precursor. The pH of the reaction solution is adjusted to be alkaline so as to provide OH needed by an intermediate of an iron oxide target product^-Ions; the auxiliary agent for reducing the oxygen-containing groups on the surface of the graphene reduces the graphene to a certain extent, so that the conductivity of the graphene is increased; mixing Fe³⁺Conversion of ions to Fe²⁺The ionic reducing agent will cause the iron oxide finally produced to be Fe₃O₄。

According to the invention, the iron oxide precursor attached to the surface of the graphene is converted into the iron oxide in situ through a subsequent liquid phase reaction, wherein the iron oxide is Fe₂O₃Or Fe₃O₄Or a mixture of the two. The liquid phase reaction mainly comprises the steps that the iron oxide precursor and ions in a liquid phase are subjected to chemical reaction under the liquid phase reaction condition of a certain temperature, and finally the iron oxide precursor is converted into the iron oxide in situ; or iron oxide precursorWhich does not chemically react with ions in the liquid phase, is itself converted in situ to iron oxide and water under liquid phase reaction conditions at a certain temperature.

In the step (5), the calcination temperature is 400-500 ℃, and the calcination time is 0.5-5 h.

The graphene of the invention refers to non-oxidized graphene which is commercially produced on a large scale.

In the invention, the inventor researches and discovers that iron oxide is uniformly attached to the surface of graphene in the form of nanoparticles, the content of the attached iron oxide can reach 75 wt.%, and the graphene without heat treatment is only loaded with a small amount of iron oxide nanoparticles, and the weight of the graphene is less than 10 wt.%. This confirms that the oxygen-containing group on the surface of graphene supports Fe thereon₃O₄The importance of (c). In addition, the inventor researches and discovers that the content of oxygen-containing groups on the surface of graphene has an important influence on loading iron oxide, the oxygen content is too low to load effectively, and the mass fraction of oxygen in the graphene attached with the oxygen-containing groups obtained by adopting the heat treatment method is more than 10 wt%, which is enough to form effective load.

Example 1:

the preparation process of the embodiment comprises the following steps:

(1) the raw material is single-layer graphene powder (purity: 98%, model: GR0991, manufacturer: Shenzhen panicle equilibrium graphene science and technology Limited), and the thermal gravimetric test is carried out on the single-layer graphene powder, and the initial weight loss temperature is determined to be 580 ℃, which is shown in figure 1; then weighing about 0.1g of raw materials, placing the raw materials in a quartz boat, placing the quartz boat in a tube furnace, introducing air at the flow rate of 0.5mL/min, heating to 700 ℃ at the heating rate of 5 ℃/min, maintaining for 3 hours, cooling, and taking out to obtain graphene attached with oxygen-containing groups;

(2) weighing 30mg of graphene attached with oxygen-containing groups, adding the graphene into 20mL of deionized water, carrying out ultrasonic dispersion for 30min, and then adding 15mL of graphene containing about 50mg of Fe (OH)₃Fe (OH) of colloidal particles₃Stirring the aqueous solution for 3-5 min at the rotation speed of 100-;

(3) then ammonia water is used for adjusting the pH value of the reaction solution to about 11, and then hydrothermal reaction is carried out at 180 DEG CTaking the reaction solution for 12 hours, and obtaining the graphene-loaded Fe after centrifuging, washing and drying₂O₃And (c) a complex.

Further, the prepared graphene is loaded with Fe₂O₃And (4) assembling the button lithium battery by using the composite material, and testing the charge and discharge capacity.

Example 2:

this example is the same as example 1 except that 80mg ascorbic acid was added in step (3) and the iron oxide precursor was converted into iron oxide Fe in situ by liquid phase reaction₃O₄Obtaining graphene loaded Fe₃O₄The compound of (1), wherein Fe₃O₄The mass ratio of (A) is about 53 wt.%.

Example 3:

this example is the same as example 1 except that 120mg of trisodium citrate is further added in step (3) to convert the iron oxide precursor into iron oxide Fe in situ by liquid phase reaction₃O₄Obtaining graphene loaded Fe₃O₄The compound of (1), wherein Fe₃O₄The mass ratio of (A) is about 53 wt.%.

Example 4:

this example is the same as example 1 except that no Fe (OH) precursor was added₃An equimolar amount of FeCl is added in a 1:1 molar ratio₃And FeCl₂Obtaining graphene loaded Fe₃O₄The compound of (1), wherein Fe₃O₄Is about 51 wt.%.

Example 5:

the method is the same as the step of example 1, except that ammonia water is not added, 1.25mL of hydrazine hydrate is added, the added hydrazine hydrate has the effects of adjusting the pH value and reducing graphene, and the graphene-loaded Fe is obtained₃O₄The compound of (1), wherein Fe₃O₄The mass ratio of (a) is about 56 wt.%.

Example 6:

this embodiment is the same as embodiment 4 except for the difference that step (A)3) The liquid phase reaction non-hydrothermal method used in the method is a coprecipitation method, and the specific preparation process comprises the following steps: then ammonia water is used for adjusting the pH value of the reaction solution to about 11, the reaction solution is heated to 80 ℃ under stirring, the reaction solution is continuously stirred for 3min at the temperature, and graphene-loaded Fe is prepared after centrifugation, washing and drying₃O₄Composite of Fe₃O₄Is about 50 wt.%.

Example 7:

this example was carried out in the same manner as in example 1, except that 0.02g of polyvinylpyrrolidone (type K30, manufactured by Kogyo Kaishu reagent, national medicine) was added as a dispersant, and the prepared composite was a graphene-supported Fe₂O₃In which Fe₂O₃The mass ratio of (a) is about 56 wt.%.

Example 8:

the method is the same as the step of the embodiment 1, except that the used raw material graphene powder is different, the type of the graphene powder used in the embodiment is XF001W, the manufacturer is Nanjing Xiancheng nanometer material science and technology Co., Ltd, the initial weight loss temperature is 400 ℃, the used heat treatment temperature is 425 ℃, the heat treatment time is 3h, the heat treatment atmosphere is air, and the flow rate is 1 mL/min;

the product prepared by hydrothermal reaction is graphene loaded Fe₂O₃A complex;

Example 9:

this example is the same as example 2 except that an equimolar amount of FeCl is added₃In place of the iron oxide precursor Fe (OH)₃The prepared iron oxide is Fe₃O₄Obtaining graphene loaded Fe₃O₄The compound of (1), wherein Fe₃O₄Is about 50 wt.%.

Example 10:

this example is the same as example 2 except that it will be preparedGraphene supported Fe₃O₄Calcining the compound for 2 hours in an argon atmosphere at 500 ℃ to ensure that the reduction degree of the heat-treated graphene in the compound is higher, and Fe₃O₄The crystallinity is better, and the graphene-loaded Fe is obtained₃O₄Composite of Fe₃O₄The mass ratio of (A) is about 58 wt.%.

Comparative example 1:

in the same way as example 1, the raw material graphene supported Fe was prepared by directly performing the steps (2) and (3) without performing the heat treatment of the step (1)₂O₃And (c) a complex.

Fig. 2 is an XPS diagram of the monolayer graphene with oxygen-containing groups attached and the raw material thereof prepared in example 1 of the present invention, and fig. 2 shows that the oxygen content of the monolayer graphene is greatly increased from 0.97 wt.% to 10.96 wt.% after the monolayer graphene is heat-treated in an air atmosphere at 700 ℃ for 3 hours, which indicates that a large amount of oxygen-containing groups are attached to the graphene during the heat-treatment in the air;

fig. 3 is a photograph of the heat-treated graphene uniformly dispersed in water prepared in step (1) of example 1 of the present invention, and it can be seen from fig. 3 that the single-layer graphene attached with the oxygen-containing group is uniformly dispersed in water, which provides an advantage in that it attaches the positively charged support precursor to the surface thereof by electrostatic force;

fe (OH) loaded on the graphene to which the oxygen-containing group is attached prepared in step (2) of example 1 by a Scanning Electron Microscope (SEM)₃The morphology of the composite is shown in FIG. 4, and it can be seen from FIG. 4 that a large amount of Fe (OH) is attached to the surface of the graphene after the heat treatment₃Nanoparticles (precursors of iron oxide), which provide conditions for their subsequent in situ conversion to iron oxide to form graphene-supported iron oxide composites;

fe-loaded graphene prepared in step (3) of example 1 by SEM₂O₃The compound is subjected to morphology characterization, and is loaded with Fe compared with the raw material graphene of comparative example 1₂O₃For comparison, the result is shown in fig. 5, from which it is apparent that the heat-treated graphene prepared in example 1 supports Fe₂O₃Is far superior to the raw material graphene because the oxygen content of the thermally treated graphene prepared in example 1 is far higher than that of the raw material;

FIG. 6 shows that the graphene loaded Fe prepared in example 1 of the present invention₂O₃A Transmission Electron Microscope (TEM) picture of the composite, the morphology of which is substantially in accordance with fig. 5 b; fe-loaded graphene prepared in example 1 by X-ray diffractometer (XRD)₂O₃The composite was characterized, and the results are shown in fig. 7, from which it can be seen that the graphene surface-supported nanoparticles obtained by heat treatment were Fe₂O₃Position of diffraction peak and Fe₂O₃Corresponds one to one, and diffraction peaks at 24.1 °, 33.1 °, 35.6 °, 40.8 °, 49.5 °, 54.1 °, 57.6 °, 62.4 °, 64.0 ° and 72.3 ° of 2 θ respectively correspond to cubic α -Fe₂O₃The (012), (104), (110), (113), (024), (116), (018), (214), (300), and (119) crystal planes of (c); and the peak around 2 θ of 26.4 ° corresponds to the (002) crystal plane of the graphite layer structure of graphene.

Fe-loaded graphene prepared in example 1 by thermogravimetric analysis₂O₃Amount of composite and Fe loading of raw graphene of comparative example 1₂O₃The amount of the composite was characterized and compared with the raw material graphene, and the results are shown in fig. 8. It can be seen from the figure that the raw material graphene of comparative example 1 supports Fe₂O₃Fe in composites₂O₃Is only 7.7 wt.%, whereas the example 1 heat treated graphene is Fe-loaded₂O₃In the composite, Fe₂O₃Up to 55.5 wt.%;

fe is loaded on the raw material graphene prepared in comparative example 1 of the invention₂O₃Composite and example 1 heat treated graphene supported Fe₂O₃The composite is used for the assembly of lithium button cells, in which the active substance: conductive additive (carbon black): the mass ratio of the binder (polyvinylidene fluoride) is 8: 1:1 LiPF with electrolyte of 1M₆The solvent is a solvent with the volume ratio of 1: 1:1 ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate. By passingThe cycle capacity of the Newwei battery test system (model: CT-3008W, manufacturer: Shenzhen, New Wille electronics Limited) is tested and characterized, the result is shown in FIG. 9, and the graph shows that the graphene loaded Fe subjected to heat treatment in example 1₂O₃The charge-discharge specific capacity of the compound is obviously higher than that of the raw material graphene loaded Fe in comparative example 1₂O₃Complex, mainly due to Fe₂O₃High theoretical capacity and heat-treated graphene-supported Fe₂O₃The loading capacity is higher, and 1126.9mAh g is still kept after 280 charge-discharge cycles in the charge-discharge voltage range of 0.01 to 3V and the current density of 0.5A/g^-1The discharge specific capacity of the graphene can buffer Fe in the charge and discharge process₂O₃On the other hand, the graphene can compensate for Fe₂O₃Insufficient conductivity. Better charge-discharge cycle performance shows that Fe₂O₃The adhesion on the heat-treated graphene is stronger. And raw material graphene loaded Fe₂O₃The corresponding specific discharge capacity is only 393.9mAh g^-1This is Fe supported by the graphene as a raw material₂O₃Less in the amount of (c).

An SEM image of the composite of graphene-supported iron oxide prepared in example 2 is shown in fig. 10, and it can be seen that the surface of the graphene heat-treated in example 2 is supported by a large amount of Fe₃O₄A nanoparticle; FIG. 11 shows Fe supported on heat treated graphene prepared in example 2 of the present invention₃O₄Composite, Fe₃O₄XRD patterns of nanoparticles and heat-treated graphene, it can be seen from fig. 11 that the heat-treated graphene supported Fe₃O₄Contains Fe₃O₄And diffraction peaks of the heat-treated graphene. Diffraction peaks at 2 θ of 18.3 °, 30.1 °, 35.4 °, 56.9 ° and 62.5 ° respectively correspond to Fe₃O₄The (111), (220), (311), (511) and (440) crystal planes of (a). The diffraction peaks at 26.4 °, 44.4 ° and 54.4 ° 2 θ correspond to the (002), (101) and (004) crystal planes of the graphite layer.

Example 8 the resulting Heat-treated StoneSEM image of graphene-iron oxide-attached composite is shown in fig. 12, from which it can be seen that a large amount of Fe is attached to the surface of the heat-treated graphene₂O₃And (3) nanoparticles.

Fe-loading of graphene obtained in example 8 by thermogravimetric analysis₂O₃The amount of (b) is characterized, and the result is shown in fig. 13, from which it can be seen that the graphene obtained in example 8 is loaded with Fe₂O₃Fe in composites₂O₃Was 74.6 wt.% (during thermogravimetric analysis the graphene substrate in the composite was converted to gaseous carbon oxides, the remaining species was Fe₂O₃). The graphene heat-treated in this example was loaded with Fe₂O₃The composite was used for assembling lithium button cells according to the above method, and the test results are shown in fig. 14, and it can be seen from fig. 14 that the graphene prepared in example 8 is loaded with Fe₂O₃The composite still maintains 753.8mAh g after 150 charge-discharge cycles in the charge-discharge voltage range of 0.01 to 3V and the current density of 0.5A/g^-1Specific discharge capacity of (2). Example 8 graphene supported Fe₂O₃The first-turn discharge capacity of the compound is up to 2011.6mAh g^-1And only 1514.4mAh g at turn 2^-1This is because the number of graphene layers used in example 10 is small and the specific surface area is relatively large, and therefore a relatively large amount of solid electrolyte interface film is generated during the first discharge cycle, and this portion of the capacity is irreversible, so the coulombic efficiency of the first charge and discharge cycle is only 72.6%.

Claims

1. A preparation method of graphene-loaded iron oxide is characterized by comprising the following steps:

(4) according to the type of the prepared target iron oxide and the reduction degree requirement of the graphene, a reducing agent and a pH regulator are optionally added in the step (3), and a precursor of the iron oxide is converted into the iron oxide in situ through a liquid phase reaction, so that the graphene-supported iron oxide composite material is obtained.

2. The method for preparing graphene-supported iron oxide according to claim 1, wherein in the step (2), the oxygen-containing atmosphere comprises air, oxygen, a mixture of air and an inert atmosphere, and a mixture of oxygen and an inert atmosphere, and the inert atmosphere is nitrogen and argon;

the slightly exceeding initial weightlessness temperature is a temperature range from the initial weightlessness temperature to 130 ℃ at most exceeding the initial weightlessness temperature, and is required to be more than 10 ℃ lower than the initial temperature of the weightlessness ending platform;

the heat treatment is maintained for 0.1-5 h.

3. The method for preparing graphene-supported iron oxide according to claim 1, wherein the oxygen-containing group attached to the graphene is obtained by heat treatment in an oxygen-containing atmosphere, and the oxygen exists in a form mainly comprising a carbon-oxygen double bond connecting aromatic carbons, a carbon-oxygen single bond connecting aliphatic carbons, and a carbon-oxygen single bond connecting aromatic carbons;

the mass fraction of oxygen in the graphene attached with the oxygen-containing group reaches more than 10 wt.%, and can reach 19 wt.%.

4. The method for preparing graphene-supported iron oxide according to claim 1, wherein in the step (3), the surfactant is selected from one of polyvinylpyrrolidone, sodium dodecylbenzenesulfonate or cetyltrimethylammonium bromide;

the dosage ratio of the graphene attached with the oxygen-containing group, the surfactant, the iron oxide precursor and the polar solvent is 30-60 mg: 0-200 mg: 20-200 mg: 20-40 mL.

5. The preparation method of the graphene-supported iron oxide according to claim 1, wherein the ultrasonic power is 300-1000W, and the ultrasonic dispersion time is 30-100 min;

stirring and standing are carried out at normal temperature, the rotating speed of stirring is 50-200 revolutions per minute, the stirring time is 1-5 min, and the standing time is 2-10 min.

6. The method for preparing graphene-supported iron oxide according to claim 1, wherein in the step (4), the reducing agent comprises Fe³⁺Reduction to Fe²⁺The reducing agent A is selected from ascorbic acid or trisodium citrate, and/or the reducing agent B is selected from hydrazine hydrate or ethylene glycol;

the dosage of the reducing agent A is 0.5-2 times of the molar weight of the iron oxide precursor, and the dosage of the reducing agent B is 3-30 vol.% of the total volume of the solvent; adding a pH regulator to regulate the pH value of the reaction solution to about 11.

7. The method for preparing graphene-supported iron oxide according to claim 1, wherein a liquid phase reaction is a hydrothermal reaction or a coprecipitation reaction, the hydrothermal reaction is carried out at 120-180 ℃ for 10-14 h, and the coprecipitation reaction is carried out at 80 ℃ for 2-5 min.

8. The method for preparing graphene-supported iron oxide according to claim 1, further comprising a step (5) of, according to the reduction degree of graphene in the prepared target product and the requirement of the crystallinity of iron oxide, subsequently calcining in an inert atmosphere to further reduce graphene so as to improve the conductivity of the composite material and improve the crystallinity of iron oxide;

the calcination temperature is 400-500 ℃, and the calcination time is 0.5-5 h.

9. The graphene-iron oxide-loaded composite material prepared by the method of any one of claims 1-8, wherein the iron oxide is Fe₂O₃Or Fe₃O₄Or a mixture of the two;

the iron oxide is uniformly attached to the surface of the graphene in the form of nanoparticles, and the content of the attached iron oxide can reach 75 wt.%.

10. The graphene iron oxide-loaded composite material of claim 9 is applied to electromagnetic compatibility, lithium ion batteries and medicines, and particularly to lithium ion batteries.