Graphite oxide powder, method for producing same and use thereof
阅读说明：本技术 石墨的氧化物粉末、其制备方法及其应用 (Graphite oxide powder, method for producing same and use thereof ) 是由 杜宁 杨扬 吴祯琪 陈桥 川崎学 于 2019-08-28 设计创作，主要内容包括：本发明提供了一种石墨的氧化物、其制备方法、含有该石墨氧化物的膜以及其在海水淡化领域中的应用。通过调节石墨的氧化条件控制石墨氧化物的层间距,形成可以使水分子通过同时截留离子的层间距,使其达到海水脱盐的要求。该石墨的氧化物亲水性好,同时具有抗菌性,适用于海水淡化领域。(The invention provides an oxide of graphite, a preparation method thereof, a membrane containing the graphite oxide and application thereof in the field of seawater desalination. The interlayer spacing of the graphite oxide is controlled by adjusting the oxidation condition of the graphite, so that the interlayer spacing which can enable water molecules to pass through and simultaneously trap ions is formed, and the seawater desalination requirement is met. The graphite oxide has good hydrophilicity and antibacterial property, and is suitable for the field of seawater desalination.)
1. An oxide powder of graphite, characterized in that: the graphite oxide has an interlayer spacing of 0.4nm or more and less than 0.6nm, and the oxygen atom concentration at the inner edge portion of a single sheet of the graphite oxide is 5% to 64% higher than that at the central portion.
2. The oxide powder of graphite according to claim 1, characterized in that: in the single sheet of graphite oxide, the atomic ratio of oxygen to carbon at the edge part is 0.38-0.46, and the atomic ratio of oxygen to carbon at the central part is 0.28-0.36.
3. The oxide powder of graphite according to claim 1, characterized in that: the specific surface area of the graphite oxide powder is 15-150m2/g。
4. The oxide powder of graphite according to claim 1, characterized in that: raman spectrum I of the graphite oxideD/IGIs 0.6-0.9.
5. A method for preparing the graphite oxide powder according to any one of claims 1 to 4, comprising the steps of:
step (1): adding 100-180 parts by mass of concentrated sulfuric acid into 1 part by mass of graphite under the ice-water bath condition, and mixing for 5-20 minutes to realize partial intercalation of the concentrated sulfuric acid into graphite layers;
step (2): adding 1.5-2 parts by mass of potassium permanganate, heating to 20-45 ℃, and keeping for 1-2 hours;
and (3): 150-250 parts by mass of deionized water is dropwise added, and then 10-20 parts by mass of hydrogen peroxide is dropwise added;
and (4): and (4) repeatedly washing and drying the product obtained in the step (3) to obtain the graphite oxide powder.
6. A film, characterized by: the film comprises the oxide powder of graphite according to any one of claims 1 to 4 and a binder.
7. Use of the graphite oxide powder according to any one of claims 1 to 4 in the field of desalination of sea water.
8. Use of the membrane of claim 6 in the field of desalination of sea water.
Technical Field
The invention relates to the field of graphite materials, in particular to graphite oxide powder and a preparation method thereof, a film containing the graphite oxide powder, and application of the graphite oxide powder and the film in the field of seawater desalination.
Background
Earth water resources are abundant, but fresh water resources account for only 3% of the total earth water, wherein surface water accounts for only 0.3% of the total fresh water, and as the demand for water increases year by year, the problem of water resource shortage which can be developed and utilized by human beings has become a non-competitive fact. In order to utilize seawater resources, seawater desalination is a major issue facing human beings.
The key step in desalination of sea water is desalination, and the most difficult of various salts to remove are various monovalent ions, usually less than 10 a in diameter-3And (3) micron. The most commonly used method of desalination of sea water at present is to filter out dissolved ions in sea water by means of RO membranes. However, RO membranes also present problems in use due to the materials used. Because the RO membrane material has no antibacterial property, the RO membrane material is easy to generate membrane pollution and has to be replaced regularly, which brings inconvenience to users and increases the use cost. Meanwhile, due to the hydrophobicity of the membrane material, high pressure needs to be added in order to maintain high water flux in use, so that the problems of high working pressure, low treatment rate and high energy consumption exist. Therefore, in order to realize efficient desalination of seawater, it is necessary to develop a new material having excellent properties such as antibacterial property and hydrophilicity.
One of the more popular research directions in recent years is the preparation of graphene by a redox method. Graphite oxide and graphene, which are carbon materials, have excellent antibacterial properties, and this property has been verified by many studies. Particularly, graphite oxide has a strong hydrophilicity because it contains a large amount of oxygen-containing groups. The original interlayer spacing of the graphite can be increased by a violent oxidation method in the preparation process of the graphite oxide, namely, the interlayer spacing is increased from 0.34nm to about 0.9nm, which is a basic and common method for stripping the graphite into the graphene and is also one of means for forming the desalting water-permeable channel. Many examples of the application of graphite oxide to water treatment have been developed in recent years. For example, in the document Yue-Heng Xi, et al, graphene-based membranes with uniform 2D nanochannels for precipitation of mono-/multi-equivalent methods volume 550, (2018): 208-. The result shows that the membrane can realize interception on ions with the hydrated ionic radius larger than 0.8nm, but can not realize interception on K+、Na+、Li+And removing monovalent metal ions.
In order to remove ions dissolved in seawater, particularly monovalent metal ions having a small hydrated ionic radius, it is required to control the interlayer spacing of graphite oxide to 0.6nm or less. In order to adjust the interlayer spacing of graphite oxide, many efforts have been made in the related art. For example, patent document CN105214607A discloses that the interlayer spacing of graphite is adjusted by introducing an intercalation agent, and the interlayer spacing range of the reduced graphene oxide with a layered porous nano structure is 0.413-0.89nm, and the reduced graphene oxide with a layered porous nano structure is applied to the field of wastewater treatment. Patent CN108137415A, prepares an integrated highly oriented halogenated graphene monolithic film by introducing halogen on the surface of graphene, and the distance between the multiple halide planes in the integrated layer is 0.35-1.2 nm. Patent CN103693637A discloses an expanded graphite containing an interlayer material obtained by inserting an interlayer material between graphenes of a graphene laminated body, wherein XRD test results show that the expanded graphite has a diffraction peak in a range of 18 ° to 24 ° 2 θ, and the interlayer spacing of the expanded graphite is 0.37 to 0.49nm as calculated by bragg equation. However, in the techniques disclosed in the above patent documents, the purpose of controlling the interlayer distance is achieved by introducing a new group or an intercalator into the interlayer of graphite, and the obtained substance is not a pure graphite oxide, so that in the application of seawater desalination, the water permeability is low due to poor hydrophilicity, the applied water pressure is high, and the problems of high energy consumption and low treatment efficiency are caused.
In addition, in patent document CN106882801A, graphene oxide having different interlayer spacings is prepared by controlling the degree of reduction. Since the central part of the graphene oxide is highly oxidized, and the reduction process is gradually performed from the edge of the graphene oxide to the center, the obtained graphene oxide has poor hydrophilicity at the edge, is not favorable for water molecules to pass through, and cannot be applied to the field of water treatment.
Disclosure of Invention
In view of the above prior art, an object of the present invention is to provide an oxide powder of graphite which can pass water molecules therebetween while retaining monovalent metal ions, and a method for preparing the same, and also to provide a membrane having high water permeability, antibacterial properties and filterability, which comprises the oxide powder of graphite.
The present invention provides an oxide powder of graphite having an interlayer spacing of 0.4nm or more and less than 0.6nm, and an oxygen atom concentration at an inner edge portion of a single sheet of the oxide powder of graphite is 5% to 64% higher than that at a central portion.
The graphite oxide powder has a graphite-like layered structure, which is capable of specifically trapping monovalent metal ions by having an interlayer spacing of 0.4nm or more and less than 0.6 nm. The interlayer distance can be calculated by reading the (002) peak diffraction angle of the graphite oxide powder from its XRD curve and by the bragg equation.
In order to clarify the characteristics of the graphite oxide powder of the present invention, it is necessary to specify the specific positions of the edge portion and the central portion. According to optical microscope characterization, the graphite of the present invention has most of its oxides irregular shape, and its maximum and minimum sheet diameters are relatively close. The center and edge portions of the graphite oxide in the present invention are defined as follows: the central part is the region of the longest sheet diameter of the graphite oxide sheet from the midpoint position of the longest sheet diameter of the graphite oxide sheet by less than 10% of the longest sheet diameter, and the edge part is the region of the longest sheet diameter of the graphite oxide sheet from the boundary by less than 10% of the longest sheet diameter.
The oxygen atom concentration at the edge portion and the center portion in a single sheet of the graphite oxide of the present invention can be measured by the following method: and respectively measuring the atomic percentages of oxygen and carbon elements on the surface of the oxide of the graphite by adopting high-precision EDX (enhanced data X), and representing the oxygen atom concentration by using the ratio of oxygen atoms to the total number of atoms. According to the invention, the oxygen atom concentration of the edge part in the single sheet of the graphite oxide is 5-64% higher than that of the central part, and more hydrophilic groups can be introduced, so that the hydrophilicity of the edge part in the single sheet of the graphite oxide is improved, the entry of water molecules is facilitated, the hydrophobicity of the central part is kept, and the rapid elimination of the water molecules is facilitated, therefore, a rapid channel structure of the water molecules is formed, and the high water passing rate can be realized without additional high water pressure.
The graphite oxide in the present invention may be any size. In order to maximize the volume of the effective interlayer distance portion for effective application, the size of the graphite oxide is preferably 2000 mesh or less, and more preferably 500 mesh or less. In order to ensure consistent oxidation of the individual pieces of graphite oxide, a narrowly sized distribution of graphite oxide, i.e., an oxide of graphite having a difference between D90 and D10 of less than 20 microns, is preferred.
In the present invention, in view of adjusting the interlayer distance of the graphite oxide, it is preferable that the atomic ratio of oxygen to carbon in the edge portion is 0.38 to 0.46 and the atomic ratio of oxygen to carbon in the center portion is 0.28 to 0.36 in the single sheet of the graphite oxide. When the oxygen/carbon atomic ratio is too low in the center portion and the edge portion, the oxidation of the graphite oxide tends to be insufficient, and the interlayer distance tends to be too small, thereby impairing the water permeability. When the oxygen-carbon atomic ratio is too high, it tends to excessively oxidize the oxide of graphite, resulting in too large interlayer spacing to trap monovalent metal ions.
In the present invention, it is preferable that the specific surface area of the graphite oxide powder is 15 to 150m from the viewpoint of controlling the degree of oxidation of the graphite oxide and adjusting the interlayer distance2(ii) in terms of/g. Because the specific surface area reflects the dispersion degree of graphite oxide and the condition that the interlayer is stretched, when the value of the specific surface area is in the range, excessive oxidation caused by overhigh specific surface area can be avoided, the interlayer spacing is overlarge, and monovalent metal ions can not be intercepted; meanwhile, the insufficient surface oxidation caused by the excessively low specific surface area is avoided, and the interlayer spacing is excessively small, so that the water permeability is damaged.
The graphite oxide of the invention maintains the ordered structure of the graphite to a certain extent, and can specifically pass through I of a Raman spectrumD/IGAnd (5) characterizing. In the present invention, I of Raman spectrum of the oxide of graphite is preferableD/IGIs 0.6-0.9. The reason for this is thatD/IGToo high a value indicates that too much oxidation introduces too many defects, while too low a value indicates that the structure is closer to the original structure of graphite due to insufficient oxidation.
The graphite oxide powder can be obtained by introducing oxygen-containing groups into the edge of graphite by adopting a milder oxidation method compared with the traditional oxidation method, so that the graphite oxide is partially oxidized, and the obtained graphite oxide has the interlayer spacing of more than or equal to 0.4nm and less than 0.6 nm. The preparation method can be specifically used for preparing the material by adopting the following steps:
step (1): adding 100-180 parts by mass of concentrated sulfuric acid into 1 part by mass of graphite under the ice-water bath condition, and mixing for 5-20 minutes to realize partial intercalation of the concentrated sulfuric acid into graphite layers;
step (2): adding 1.5-2 parts by mass of potassium permanganate, heating to 20-45 ℃, and keeping for 1-2 hours;
and (3): 150-250 parts by mass of deionized water is dropwise added, and then 10-20 parts by mass of hydrogen peroxide is dropwise added;
and (4): and (4) repeatedly washing and drying the product obtained in the step (3) to obtain the graphite oxide powder.
In order to control the oxidation degree of the graphite oxide, not only ensuring the oxidation of the edge region of the graphite, but also ensuring that the central region is not excessively oxidized to increase the interlayer spacing, relative to 1 part by mass of the graphite, the amount of the concentrated sulfuric acid in the step (1) is preferably 110-170 parts by mass, and is further preferably 120-160 parts by mass, the amount of the potassium permanganate in the step (2) is preferably 1.6-1.8 parts by mass, and is further preferably 1.65-1.75 parts by mass, the amount of the deionized water in the step (3) is preferably 150-220 parts by mass, and the amount of the hydrogen peroxide is preferably 13-18 parts by mass. The washing of the product in the step (4) can be realized by a filtration or centrifugation method, and the drying can be realized by vacuum drying or freeze drying.
The graphite oxide powder of the present invention can achieve the effect of removing monovalent ions having a small hydrated ion radius in the application of seawater desalination by virtue of its specific structure. Accordingly, the present invention also provides a film comprising the oxide powder of graphite as described above and a binder. The binder can be any conventional binder, and in view of applicable cost, one of polyvinylidene fluoride, epoxy resin, sodium carboxymethylcellulose and styrene butadiene rubber is preferred. The film-forming method may be a vacuum filtration method, a doctor blade method, a leveling method, or a spin coating method, and among them, a doctor blade method is preferably used in order to increase the water permeability of the film.
According to the present invention, the oxide powder of graphite and the film comprising the same and a binder can be applied to the field of seawater desalination.
Advantageous effects
The graphite oxide provided by the invention has the interlayer spacing of more than or equal to 0.4nm and less than 0.6nm, which is lower than the interlayer spacing of the traditional graphite oxide, so that the removal of monovalent ions in seawater is possible. On the other hand, the edges of the graphite oxide have good hydrophilicity due to the presence of a large number of oxygen-containing groups at the edges. The relatively central part has low oxidation degree and hydrophobicity, so that water entering the oxide layers of the graphite can be rapidly discharged. Therefore, the graphite oxide having this structure can efficiently realize the desalting effect on seawater. In addition, the graphite oxide retains the antibacterial property of graphite oxide, and can effectively improve the pollution resistance. Therefore, the graphite oxide in the invention overcomes many problems of RO membrane, and is suitable for application in seawater desalination field.
The preparation method of the graphite oxide provided by the invention is different from the traditional preparation method of graphite oxide, so that dangerous high-temperature reaction is avoided, the reaction condition is mild and safe, and the industrial large-scale production is easier to realize.
Drawings
FIG. 1 is an electron micrograph of a single piece of the graphite oxide powder obtained in example 3.
FIG. 2 is an optical micrograph of a single piece of the graphite oxide powder obtained in example 3.
Fig. 3 is an XRD curve of the graphite oxide powder obtained in example 2.
Detailed Description
The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples.
Specific chemicals and their suppliers involved in the present invention:
high-purity natural graphite: 150 mesh, 325 mesh, 500 mesh, available from Qingdao Tian and Dagraphi, Inc.
Concentrated sulfuric acid (98%, AR), potassium permanganate (AR), and hydrogen peroxide (30%, AR) were purchased from national drug group chemical reagents, Inc.
Polyvinylidene fluoride: HSV-900, purchased from Ashoma China.
The methods of characterization of properties involved in the present invention are shown below.
A. Characterization of the graphite oxide powder:
(A-1) interlayer spacing
The oxide powders of graphite of examples and comparative examples were measured for diffraction angle by an X-ray diffractometer (XRD, Bruker D8 ADVANCE Da Vinci) under conditions of a tube voltage of 40kV and a tube current of 150mA, a scanning rate of 5 DEG/min, and (002) interlayer spacing of the oxide of graphite was calculated by the Bragg equation.
(A-2) oxygen atom concentration
The surface morphology of the oxide powders of graphite of examples and comparative examples was characterized by an electron microscope (SEM, hitachi S4800), and the edge/center positions thereof were determined. The proportion of oxygen atoms and carbon atoms at the center and the edge of the monolithic graphite oxide is respectively measured by using a high-precision EDX accessory, and the oxygen atom concentration is represented by the ratio of the oxygen atoms to the total number of atoms. The oxygen atom concentration difference was calculated as [ (edge site-center site)/center site ]. 100%. (A-3) specific surface area
The specific surface area of the oxide powders of graphite of examples and comparative examples was measured using a nitrogen adsorption apparatus (BEL Japan Belsorp II mini).
(A-4) Raman spectrum ID/IG
The oxide powders of graphite of examples and comparative examples were measured for their Raman spectra using a Raman spectrometer (INVia Qntor), and the peak intensity ratio I of the D peak and the G peak was calculatedD/IG。
B. The characteristic parameters of the films comprising the graphite oxide powder and the binder were tested as follows:
(B-1) salt Water filtration Rate and desalination Rate
An aqueous solution of 20 wt% NaCl was used as the salt solution. The filtrate produced per unit filtration time was collected by passing brine through the graphite oxide membrane plane parallel to the brine flow direction under a vacuum of 0.09MPa using a reduced pressure filtration method, and the volume of the filtrate and the salt concentration were measured. The volume of the filtrate divided by the filtration time is the filtration rate of the brine. The salt amount retained by the membrane can be simply calculated according to the salt amount in the filtrate, and the salt amount in the original brine is divided to obtain the desalting rate.
(B-2) antibacterial Properties
The antibacterial properties of the oxide films of graphite were tested with the characterization standard being ISO2073:2013, and the test bacteria being Escherichia coli ATCC 8739, concentration 2.5 x 105CFU/mL, incubation time 24hr, test method: plate count method. The antibacterial property is characterized by an antibacterial value, and when the antibacterial value is more than 3, the antibacterial property is good.
The above test results are shown in table 1 below and in fig. 1-3.
< preparation of oxide powder of graphite >
Example 1
Step (1): adding 100g of concentrated sulfuric acid into 1g of 325-mesh natural graphite under the ice-water bath condition, and mixing for 10 minutes;
step (2): adding 1.5g of potassium permanganate into the mixture obtained in the step (1), heating to 35 ℃, and mixing for 1.5 hours;
and (3): dropwise adding 200g of deionized water into the mixture obtained in the step (2), and then dropwise adding 15g of hydrogen peroxide;
and (4): and (4) repeatedly washing the product obtained in the step (3) until the pH value is 7, and freeze-drying to obtain graphite oxide powder.
Example 2
Step (1): adding 100g of concentrated sulfuric acid into 1g of 325-mesh natural graphite under the ice-water bath condition, and mixing for 10 minutes;
step (2): adding 1.65g of potassium permanganate into the mixture obtained in the step (1), heating to 35 ℃, and mixing for 1 hour;
and (3): dropwise adding 200g of deionized water into the mixture obtained in the step (2), and then dropwise adding 15g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
Since the graphite oxide is less oxidized than conventional graphite oxide, the XRD profile of the product shows a diffraction peak in the vicinity of 2 θ ═ 20 ° simultaneously in addition to a diffraction peak in the vicinity of 2 θ ═ 10 °.
Example 3
Step (1): adding 100g of concentrated sulfuric acid into 1g of 325-mesh natural graphite under the ice-water bath condition, and mixing for 10 minutes;
step (2): adding 1.65g of potassium permanganate into the mixture obtained in the step (1), heating to 35 ℃, and mixing for 1.5 hours;
and (3): dropwise adding 200g of deionized water into the mixture obtained in the step (2), and then dropwise adding 15g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
The electron microscope photo shows that the graphite oxide keeps the shape of the natural graphite raw material, and the edge part is whitish compared with the central part due to high oxidation degree and poor conductivity.
The optical micrograph shows that the graphite oxide has an irregular shape, and the maximum and minimum sheet diameters are relatively close.
Example 4
Step (1): adding 100g of concentrated sulfuric acid into 1g of 325-mesh natural graphite under the ice-water bath condition, and mixing for 10 minutes;
step (2): adding 1.65g of potassium permanganate into the mixture obtained in the step (1), heating to 35 ℃, and mixing for 2 hours;
and (3): dropwise adding 200g of deionized water into the mixture obtained in the step (2), and then dropwise adding 15g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
Example 5
Step (1): adding 100g of concentrated sulfuric acid into 1g of 325-mesh natural graphite under the ice-water bath condition, and mixing for 10 minutes;
step (2): adding 2g of potassium permanganate into the mixture obtained in the step (1), heating to 35 ℃, and mixing for 1.5 hours;
and (3): dropwise adding 200g of deionized water into the mixture obtained in the step (2), and then dropwise adding 15g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
Example 6
Step (1): adding 140g of concentrated sulfuric acid into 1g of 325-mesh natural graphite under the ice-water bath condition, and mixing for 10 minutes;
step (2): adding 1.65g of potassium permanganate into the mixture obtained in the step (1), heating to 35 ℃, and mixing for 1.5 hours;
and (3): dropwise adding 200g of deionized water into the mixture obtained in the step (2), and then dropwise adding 15g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
Example 7
Step (1): adding 180g of concentrated sulfuric acid into 1g of 325-mesh natural graphite under the ice-water bath condition, and mixing for 10 minutes;
step (2): adding 1.65g of potassium permanganate into the mixture obtained in the step (1), heating to 35 ℃, and mixing for 1.5 hours;
and (3): dropwise adding 200g of deionized water into the mixture obtained in the step (2), and then dropwise adding 15g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
Example 8
Step (1): adding 100g of concentrated sulfuric acid into 1g of 500-mesh natural graphite under the ice-water bath condition, and mixing for 10 minutes;
step (2): adding 1.65g of potassium permanganate into the mixture obtained in the step (1), heating to 35 ℃, and mixing for 1.5 hours;
and (3): dropwise adding 200g of deionized water into the mixture obtained in the step (2), and then dropwise adding 15g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
Example 9
Step (1): adding 100g of concentrated sulfuric acid into 1g of 150-mesh natural graphite under the ice-water bath condition, and mixing for 10 minutes;
step (2): adding 1.65g of potassium permanganate into the mixture obtained in the step (1), heating to 35 ℃, and mixing for 1.5 hours;
and (3): dropwise adding 200g of deionized water into the mixture obtained in the step (2), and then dropwise adding 15g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
Example 10
Step (1): adding 100g of concentrated sulfuric acid into 1g of 325-mesh natural graphite under the ice-water bath condition, and mixing for 5 minutes;
step (2): adding 1.65g of potassium permanganate into the mixture obtained in the step (1), heating to 35 ℃, and mixing for 1.5 hours;
and (3): dropwise adding 200g of deionized water into the mixture obtained in the step (2), and then dropwise adding 15g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
Example 11
Step (1): adding 100g of concentrated sulfuric acid into 1g of 325-mesh natural graphite under the ice-water bath condition, and mixing for 20 minutes;
step (2): adding 1.65g of potassium permanganate into the mixture obtained in the step (1), heating to 35 ℃, and mixing for 1.5 hours;
and (3): dropwise adding 200g of deionized water into the mixture obtained in the step (2), and then dropwise adding 15g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
Example 12
Step (1): adding 100g of concentrated sulfuric acid into 1g of 325-mesh natural graphite under the ice-water bath condition, and mixing for 10 minutes;
step (2): adding 1.65g of potassium permanganate into the mixture obtained in the step (1), controlling the temperature to be 20 ℃, and mixing for 1.5 hours;
and (3): dropwise adding 200g of deionized water into the mixture obtained in the step (2), and then dropwise adding 15g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
Example 13
Step (1): adding 100g of concentrated sulfuric acid into 1g of 325-mesh natural graphite under the ice-water bath condition, and mixing for 10 minutes;
step (2): adding 1.65g of potassium permanganate into the mixture obtained in the step (1), heating to 45 ℃, and mixing for 1.5 hours;
and (3): dropwise adding 200g of deionized water into the mixture obtained in the step (2), and then dropwise adding 15g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
Example 14
Step (1): adding 100g of concentrated sulfuric acid into 1g of 325-mesh natural graphite under the ice-water bath condition, and mixing for 10 minutes;
step (2): adding 1.65g of potassium permanganate into the mixture obtained in the step (1), heating to 35 ℃, and mixing for 1.5 hours;
and (3): dropwise adding 150g of deionized water into the mixture obtained in the step (2), and then adding 15g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
Example 15
Step (1): adding 100g of concentrated sulfuric acid into 1g of 325-mesh natural graphite under the ice-water bath condition, and mixing for 10 minutes;
step (2): adding 1.65g of potassium permanganate into the mixture obtained in the step (1), heating to 35 ℃, and mixing for 1.5 hours;
and (3): dropwise adding 250g of deionized water into the mixture obtained in the step (2), and then dropwise adding 15g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
Example 16
Step (1): adding 100g of concentrated sulfuric acid into 1g of 325-mesh natural graphite under the ice-water bath condition, and mixing for 10 minutes;
step (2): adding 1.65g of potassium permanganate into the mixture obtained in the step (1), heating to 35 ℃, and mixing for 1.5 hours;
and (3): dropwise adding 200g of deionized water into the mixture obtained in the step (2), and then dropwise adding 10g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
Example 17
Step (1): adding 100g of concentrated sulfuric acid into 1g of 325-mesh natural graphite under the ice-water bath condition, and mixing for 10 minutes;
step (2): adding 1.65g of potassium permanganate into the mixture obtained in the step (1), heating to 35 ℃, and mixing for 1.5 hours;
and (3): dropwise adding 200g of deionized water into the mixture obtained in the step (2), and then adding 20g of hydrogen peroxide;
and (4): the product was washed repeatedly until the pH was 7, and freeze-dried to obtain graphite oxide powder.
Comparative example 1
Step (1): under the condition of ice-water bath, 22ml of concentrated sulfuric acid, 0.35g of sodium nitrate and 2.1g of potassium permanganate are sequentially added into 1g of 500-mesh natural graphite and mixed for 1 hour;
step (2): heating the mixture obtained in the step (1) to 35 ℃, and reacting for 4 hours;
and (3): adding 50g of deionized water into the mixture obtained in the step (2), and heating to 90 ℃ for reaction for 15 minutes;
and (4): adding 60g of deionized water and 5g of hydrogen peroxide into the mixture obtained in the step (3), and reacting for 5 minutes to obtain a product;
and (5): and repeatedly washing the product until the pH value is 7, and freeze-drying to obtain graphite oxide.
< preparation of oxide film of graphite >
The graphite oxide powder obtained from the products of examples 1 to 17 or the graphite oxide powder prepared in comparative example 1 was mixed with 10 parts by weight of a 10 wt% polyvinylidene fluoride/NMP solution, and then a wet film was prepared by a doctor blade method, and the film was dried at 80 ℃ for 2 hours to obtain a graphite oxide film.