A three-dimensional graphene / metal oxide composite microsphere, its preparation method and application

Abstract

This invention relates to the field of materials, and discloses a three-dimensional graphene / metal oxide composite microsphere, its preparation method, and its application fields. The three-dimensional graphene / metal oxide composite microsphere comprises graphene microspheres and metal oxides loaded on the graphene microspheres; wherein the specific surface area of ​​the three-dimensional graphene / metal oxide composite microspheres is 50-500 m². 2 / g. In the three-dimensional graphene / metal oxide composite microspheres obtained by this invention, the metal oxide is uniformly loaded on the surface of the graphene microspheres, and the microspheres have a rich porous structure, which is beneficial for applications such as gas sensing, catalysis, and energy storage.

Description

Technical Field

[0001] This invention relates to the field of materials, specifically to a three-dimensional graphene / metal oxide composite microsphere, its preparation method, and its application. Background Technology

[0002] In recent years, graphene, as a two-dimensional nanosheet material, has demonstrated excellent performance, particularly in terms of its superior electrical conductivity (reaching 10⁸ S·m). -1 Thermal conductivity (thermal conductivity can reach 5300 W·m) -1 K -1 It also boasts superior mechanical properties (Young's modulus reaches 1 TPa) and a large specific surface area (2630 m²). 2 ·g -1 With its extremely high transmittance (absorbance of only 2.3%), graphene can be applied to a variety of fields: preparing conductive and thermally conductive composite materials, high-strength composite materials, catalytic electrode materials, aerogel materials, etc., making it one of the hot topics in the research of nano-gas-sensitive materials.

[0003] Common graphene materials can be classified according to their dimensionality into one-dimensional nanofibers, two-dimensional nanofilms, and three-dimensional porous graphene materials. The porous structure of three-dimensional graphene is highly advantageous for improving its adsorption, energy storage, and gas-sensing properties: First, the three-dimensional structure effectively reduces the stacking between graphene sheets, helping to maintain graphene's high specific surface area and increasing the number of active sites for reactions; second, the interconnected channels allow molecules to diffuse more easily into the material's interior, improving its sensitivity; finally, the three-dimensional graphene framework not only provides support sites for the loading of other nanomaterials but also accelerates the flow of electrons within the material, enhancing its conductivity. Nanoscale metal oxides, including nano-ferric oxide (Fe₂O₃), tin dioxide (SnO₂), tungsten trioxide (WO₃), molybdenum trioxide (MoO₃), copper oxide (CuO), and zinc oxide (ZnO), have wide applications in catalysis, energy storage, and sensing due to their unique crystal structures, morphological compositions, and physicochemical properties. Combining three-dimensional graphene with nano-metal oxides can achieve complementary advantages between the two, while further enhancing their performance and expanding their application range by utilizing heterojunctions and synergistic effects.

[0004] However, current methods for preparing three-dimensional graphene / metal oxide composites fall into two categories: one involves directly adding nano-metal oxides to a graphene oxide solution, forming a three-dimensional structure through hydrothermal or chemical reduction; the other involves directly adding a metal oxide precursor to a graphene oxide solution, generating metal oxides simultaneously with the formation of the three-dimensional structure. The former method relies solely on physical interactions between the metal oxides and graphene, resulting in poor stability and electrochemical properties. The latter method requires stringent reaction conditions for forming a three-dimensional structure, is only suitable for small-scale metal oxide composites, and involves complex processes. Furthermore, the three-dimensional graphene / metal oxide composites prepared by both methods are mostly cylindrical, which is unfavorable for assembling sensor devices and consequently affects the stability and electrical performance of these devices. Millimeter-spherical three-dimensional graphene / metal oxide composites are also relatively rare. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem that existing technologies cannot prepare millimeter-sized three-dimensional graphene / metal oxide composite microspheres with high specific surface area, and to provide a three-dimensional graphene / metal oxide composite microsphere, its preparation method and application. The three-dimensional graphene / metal oxide composite microsphere has a rich pore structure inside, which is beneficial for applications such as gas sensing, catalysis, and energy storage.

[0006] To achieve the above objectives, the present invention provides a three-dimensional graphene / metal oxide composite microsphere, wherein the three-dimensional graphene / metal oxide composite microsphere comprises graphene microspheres and metal oxides loaded on the graphene microspheres;

[0007] The specific surface area of ​​the three-dimensional graphene / metal oxide composite microspheres is 50-500 m². 2 / g.

[0008] Preferably, the three-dimensional graphene / metal oxide composite microspheres have a multi-level porous structure with an average pore diameter of 0.1-50 nm.

[0009] Preferably, the diameter of the three-dimensional graphene / metal oxide composite microspheres is 0.5-5 mm.

[0010] Preferably, the metal oxide is selected from one or more of WO3, CuO, ZnO, Co3O4, MoO3 and SnO2.

[0011] A second aspect of this invention provides a method for preparing the above-mentioned three-dimensional graphene oxide / metal oxide composite microspheres, the method comprising the following steps:

[0012] (1) Mix graphene oxide, sodium alginate and water, then sonicate and heat to obtain a mixed dispersion;

[0013] (2) The mixed dispersion is dripped into a solution containing Ca using an injection pump. 2+ The graphene oxide / sodium alginate hydrogel was obtained by soaking in an aqueous solution. The graphene oxide / sodium alginate hydrogel was then washed to obtain graphene oxide microspheres.

[0014] (3) The graphene oxide microspheres, metal salt and water are mixed to obtain a mixture;

[0015] (4) The mixture is subjected to a hydrothermal reaction, followed by solid-liquid separation, washing, freeze drying, and sintering.

[0016] Preferably, in step (1), the weight ratio of the graphene oxide, sodium alginate and water is 1-15:0.1-50:1000, more preferably 5-10:0.1-40:1000.

[0017] Preferably, in step (1), the ultrasound duration is 10-120 min.

[0018] Preferably, in step (1), the heating conditions include: a temperature of 70-95°C and a time of 3-6 hours.

[0019] Preferably, in step (2), the flow rate of the syringe pump is 10-200 μL / min.

[0020] Preferably, in step (2), the substance containing Ca 2+ Ca in aqueous solution 2+ The concentration is 1-10% by weight.

[0021] Preferably, in step (2), the soaking time is 1-24 hours.

[0022] Preferably, in step (2), the washing process includes rinsing the graphene oxide / sodium alginate hydrogel with water and then soaking it in water for 12-48 hours.

[0023] Preferably, in step (3), the metal salt is selected from one or more of tungstate, copper salt, cobalt salt, zinc salt, molybdate and tin salt.

[0024] Preferably, the metal salt is selected from one or more of sodium tungstate, copper sulfate, zinc nitrate, cobalt nitrate, ammonium molybdate, and stannous chloride.

[0025] Preferably, in step (3), the weight ratio of the graphene oxide microspheres, metal salt and water is 1:1-20:2000-2600.

[0026] Preferably, in step (4), the hydrothermal reaction is a microwave hydrothermal reaction.

[0027] Preferably, the conditions for the microwave hydrothermal reaction include: a temperature of 150-220℃, a time of 0.5-6h, and a microwave power of 400-800W.

[0028] Preferably, in step (4), the freeze-drying conditions include a temperature of 25-60°C and a time of 12-48h.

[0029] Preferably, in step (4), the sintering conditions are: temperature of 200-700℃, time of 1-5h, and atmosphere of inert atmosphere.

[0030] A third aspect of the present invention provides an application of the above-mentioned three-dimensional graphene / metal oxide composite microspheres in the fields of gas sensing, adsorption, or energy storage.

[0031] This invention presents a two-step method for preparing three-dimensional graphene / metal oxide composite microspheres. First, graphene oxide millispheres are prepared using a micro-injection method. Then, a metal salt is mixed with the graphene oxide millispheres, and the mixture is subjected to microwave-assisted hydrothermal treatment, freeze-drying, and high-temperature sintering to obtain the three-dimensional graphene / metal oxide composite microspheres. The metal oxide is uniformly loaded on the surface of the graphene microspheres, and the microspheres possess a rich porous structure, which is beneficial for applications such as gas sensing, catalysis, and energy storage. Attached Figure Description

[0032] Figure 1 It is an optical scanning image of three-dimensional graphene / WO3 composite microspheres;

[0033] Figure 2 Images show the nitrogen adsorption and desorption properties of three-dimensional graphene / WO3 composite microspheres.

[0034] Figure 3 These are scanning electron microscope images of three-dimensional graphene / WO3 composite microspheres;

[0035] Figure 4 These are scanning electron microscope (SEM) images of three-dimensional graphene / CuO composite microspheres and freeze-dried microspheres. Detailed Implementation

[0036] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0037] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0038] The present invention provides a three-dimensional graphene / metal oxide composite microsphere, wherein the three-dimensional graphene / metal oxide composite microsphere comprises graphene microspheres and metal oxides loaded on the graphene microspheres;

[0039] The specific surface area of ​​the three-dimensional graphene / metal oxide composite microspheres is 50-500 m². 2 / g.

[0040] Preferably, the three-dimensional graphene / metal oxide composite microspheres have a multi-level porous structure with an average pore diameter of 0.1-50 nm, for example, 0.1 nm, 1 nm, 5 nm, 20 nm, 30 nm, 40 nm or 50 nm.

[0041] Preferably, the diameter of the three-dimensional graphene / metal oxide composite microspheres is 0.5-5 mm.

[0042] In this invention, in order to ensure that the three-dimensional graphene / metal oxide composite microspheres possess good gas-sensing properties, the specific surface area of ​​the three-dimensional graphene / metal oxide composite microspheres needs to be controlled within the aforementioned range in a preferred embodiment. In a specific embodiment, the specific surface area of ​​the three-dimensional graphene / metal oxide composite microspheres can be 50 m². 2 / g, 100m 2 / g, 150m 2 / g、200m 2 / g、250m 2 / g, 350m 2 / g or 500m 2 / g.

[0043] Preferably, the metal oxide is selected from one or more of WO3, CuO, ZnO, Co3O4, MoO3 and SnO2.

[0044] A second aspect of this invention provides a method for preparing the above-mentioned three-dimensional graphene oxide / metal oxide composite microspheres, the method comprising the following steps:

[0045] (1) Mix graphene oxide, sodium alginate and water, then sonicate and heat to obtain a mixed dispersion;

[0046] (2) The mixed dispersion is dripped into a solution containing Ca using an injection pump. 2+ The graphene oxide / sodium alginate hydrogel was obtained by soaking in an aqueous solution. The graphene oxide / sodium alginate hydrogel was then washed to obtain graphene oxide microspheres.

[0047] (3) The graphene oxide microspheres, metal salt and water are mixed to obtain a mixture;

[0048] (4) The mixture is subjected to a hydrothermal reaction, followed by solid-liquid separation, washing, freeze drying, and sintering.

[0049] In this invention, graphene oxide, as a monolayer material peeled from graphene oxide, can exist stably in aqueous solutions and polar solvents due to the introduction of numerous oxygen-containing groups on its surface and edges. After oxidation treatment, graphene oxide retains the layered structure of graphite, but many oxygen-containing functional groups are introduced into each graphene monolayer. The introduction of these oxygen-containing functional groups makes the structure of a single graphene very complex. Given the importance of graphene oxide in the field of graphene materials, many scientists have attempted to provide a detailed and accurate description of its structure to facilitate further research on graphene materials. Although computer simulations, Raman spectroscopy, and nuclear magnetic resonance have been used to analyze its structure, the precise structure of graphene oxide remains undetermined due to various reasons (different preparation methods, experimental conditions, and different graphite sources all have a certain influence on the structure of graphene oxide). The generally accepted structural model is that hydroxyl and epoxy groups are randomly distributed on the graphene oxide monolayer, while carboxyl and carbonyl groups are introduced at the edge of the monolayer. However, related theoretical analysis shows that the surface functional groups of graphene oxide are not randomly distributed, but have a high degree of correlation.

[0050] Sodium alginate is a byproduct of the extraction of iodine and mannitol from brown algae such as kelp or Sargassum. Its molecule is composed of β-D-mannuronic acid (M) and α-L-guluronic acid (G) linked by (1→4) bonds. Sodium alginate aqueous solutions have high viscosity and readily form gels under mild conditions. When Ca... 2+ 、Sr 2+ When cations are present, Na on the G unit + It undergoes an ion exchange reaction with divalent cations, and the G units stack up to form a cross-linked network structure, thereby forming a hydrogel.

[0051] In the preparation method described in this invention, to facilitate the formation of graphene / sodium alginate hydrogels and obtain graphene microspheres with better performance, it is necessary to rationally control the dosage ranges of graphene oxide, sodium alginate, and water. The addition of sodium alginate can increase the viscosity and strength of the dispersion, preventing the dispersion from dripping from the injection pump into the Ca... 2+ In solution, it deforms due to low strength; however, the amount of sodium alginate should not be too high, as excessive sodium alginate will lead to excessive viscosity of the dispersion and blockage of the injection pump.

[0052] Therefore, in a preferred embodiment, in step (1), the weight ratio of the graphene oxide, sodium alginate and water is 1-15:0.1-50:1000, and more preferably 5-10:0.1-40:1000.

[0053] In a specific implementation, in step (1), the weight ratio of graphene oxide to water can be 5:1000, 6:1000, 7:1000, 8:1000, 9:100 or 10:1000, and the weight ratio of sodium alginate to water can be 0.1:1000, 1:1000, 5:1000, 10:1000, 15:1000, 20:1000, 25:1000, 30:1000, 35:1000 or 40:1000.

[0054] In the method described in this invention, in step (1), since the viscosity of the entire system increases due to the addition of sodium alginate, it is necessary to completely disperse the graphene oxide by ultrasound. The ultrasound time can be adjusted according to the amount of sodium alginate added. Preferably, in step (1), the ultrasound time is 10-120 min, specifically 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, or 120 min.

[0055] In this invention, in step (1), the heating operation can completely dissolve sodium alginate and prevent agglomeration. The heating time is related to the amount of sodium alginate added. In a preferred case, the heating conditions include a temperature of 70-95°C and a time of 3-6 hours.

[0056] In a specific implementation, in step (1), the heating temperature can be 70°C, 75°C, 80°C, 85°C, 90°C or 95°C, and the heating time can be 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h.

[0057] Preferably, in step (2), the flow rate of the syringe pump is 10-200 μL / min, specifically 10 μL / min, 30 μL / min, 50 μL / min, 70 μL / min, 90 μL / min, 110 μL / min, 130 μL / min, 150 μL / min, 180 μL / min or 200 μL / min.

[0058] In the method described in this invention, step (2) contains Ca. 2+ In an aqueous solution, if Ca 2+ If the concentration of Ca is too low, the resulting gel strength will be too low; if the concentration of Ca is too low, the gel strength will be too low. 2+ If the concentration is too high, too much will remain in the gel, affecting its structure and performance. Therefore, in a preferred embodiment, preferably, in step (2), the Ca-containing... 2+ Ca in aqueous solution 2+ The concentration is 1-10% by weight, specifically 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight or 10% by weight.

[0059] In the method described in this invention, the substance containing Ca 2+ An aqueous solution can be obtained by mixing water with various water-soluble calcium salts conventionally used in the art. In one specific embodiment, the Ca-containing... 2+ The aqueous solution is calcium chloride aqueous solution.

[0060] In step (2) of the present invention, for the substance containing Ca 2+ There are no special requirements for the amount of aqueous solution used; it is sufficient to completely soak the mixed dispersion dripped in by the syringe pump.

[0061] In the method described in this invention, in step (2), the soaking time is calculated from the time the dripping is completed until the soaking ends. Preferably, in step (2), the soaking time is 1-24 hours, more preferably 6-24 hours. Specifically, the soaking time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 2 hours, or 24 hours.

[0062] In the method described in this invention, in order to fully remove calcium ions from the hydrogel, the product can be washed by rinsing and soaking. Therefore, in a preferred embodiment of step (2), the washing process includes: rinsing the graphene oxide / sodium alginate hydrogel with water, and then soaking it in water for 12-48 hours. The specific soaking time can be 12 hours, 16 hours, 18 hours, 20 hours, 24 hours, 30 hours, 32 hours, 36 hours, 40 hours, or 48 hours.

[0063] Preferably, in step (2), the number of rinsings during the washing process is 1-5 times, specifically 1 time, 2 times, 3 times, 4 times or 5 times.

[0064] In step (3) of the present invention, the metal salt is selected from one or more of tungstate, copper salt, cobalt salt, zinc salt, molybdate and tin salt, and is more preferably a soluble salt.

[0065] In a preferred embodiment of the present invention, the tungstate is used to provide tungsten and can be a soluble tungstate commonly used in the art, such as one or more of potassium tungstate, sodium tungstate, and ammonium tungstate.

[0066] In a preferred embodiment of the present invention, the copper salt is used to provide copper element and can be a soluble copper salt commonly used in the art, such as one or more of copper chloride, copper sulfate and copper nitrate.

[0067] In a preferred embodiment of the present invention, the cobalt salt is used to provide cobalt element and can be a soluble cobalt salt commonly used in the art, such as one or more of cobalt chloride, cobalt carbonate, cobalt sulfate and cobalt nitrate.

[0068] In a preferred embodiment of the present invention, the zinc salt is used to provide zinc element and can be a soluble zinc salt commonly used in the art, such as one or more of zinc chloride, zinc sulfate and zinc nitrate.

[0069] In a preferred embodiment of the present invention, the molybdate is used to provide molybdenum and can be a soluble molybdate commonly used in the art, such as one or more of potassium molybdate, ammonium molybdate, and sodium molybdate.

[0070] In a preferred embodiment of the present invention, the tin salt is used to provide tin element and can be a soluble tin salt commonly used in the art.

[0071] Preferably, in step (3), the metal salt is selected from one or more of sodium tungstate, copper sulfate, zinc nitrate, cobalt nitrate, ammonium molybdate, and stannous chloride.

[0072] Preferably, in step (3), the weight ratio of the graphene oxide microspheres, metal salt and water is 1:1-20:2000-2600.

[0073] In the specific implementation of step (3), the weight ratio of the graphene oxide microspheres to the metal salt can be 1:1, 1:5, 1:10, 1:15 or 1:20, and the weight ratio of the graphene oxide microspheres to water can be 1:2000, 1:2100, 1:2200, 1:2300, 1:2400, 1:2500 or 1:2600.

[0074] In step (3) of the present invention, due to the different metal salts used, a certain amount of acid or alkali needs to be added to adjust the pH value to a suitable range in order to form a stable and dispersed hydrosol, thereby ensuring uniform growth into nano metal oxides during the heating process.

[0075] Therefore, in a specific embodiment of the present invention, when the metal salt is sodium tungstate, the specific process of step (3) includes: mixing the graphene oxide microspheres, the metal salt and water, and then adding a 2 mol / L hydrochloric acid solution dropwise under stirring to adjust the pH value to 1.5-2.5, and then obtaining the mixture, wherein the dropwise addition time of the hydrochloric acid solution is controlled to be 10-30 min; wherein there are no special requirements for the dropwise addition rate of the hydrochloric acid solution, it is sufficient to add it within the limited time.

[0076] In a specific embodiment of the present invention, when the metal salt is copper sulfate, the specific process of step (3) includes: mixing the graphene oxide microspheres, the metal salt and water, and then adding a sodium hydroxide solution with a concentration of 2 mol / L dropwise under stirring, adjusting the pH value to 9.5-10.5, and then obtaining a mixture, wherein the dropwise addition time of the sodium hydroxide solution is controlled to be 10-30 min; wherein there are no special requirements for the dropwise addition rate of the sodium hydroxide solution, it is sufficient to complete the dropwise addition within the limited time.

[0077] In a specific embodiment of the present invention, when the metal salt is zinc nitrate, the specific process of step (3) includes: mixing the graphene oxide microspheres, the metal salt and water, and then adding a sodium hydroxide solution with a concentration of 2 mol / L dropwise under stirring, adjusting the pH value to 9.5-10.5, and then obtaining a mixture, wherein the dropping time of the sodium hydroxide solution is controlled to be 10-30 min; wherein there are no special requirements for the dropping rate of the sodium hydroxide solution, and it is sufficient to drop it completely within the limited time.

[0078] In a specific embodiment of the present invention, when the metal salt is cobalt nitrate, the specific process of step (3) includes: mixing the graphene oxide microspheres, the metal salt and water, and then adding a 2 mol / L sodium hydroxide solution dropwise under stirring to adjust the pH value to 9.5-10.5, and then obtaining the mixture. The dropwise addition time of the sodium hydroxide solution is controlled to be 10-30 min. There are no special requirements for the dropwise addition rate of the sodium hydroxide solution, as long as it is added within the specified time.

[0079] In a specific embodiment of the present invention, when the metal salt is ammonium molybdate, the specific process of step (3) includes: mixing the graphene oxide microspheres, the metal salt and water, and then adding a nitric acid solution with a concentration of 2 mol / L dropwise under stirring, adjusting the pH value to 1.5-2.5, and then obtaining a mixture, wherein the dropping time of the nitric acid solution is controlled to be 10-30 min; wherein there are no special requirements for the dropping rate of the nitric acid solution, and it is sufficient to drop it completely within the limited time.

[0080] In a specific embodiment of the present invention, when the metal salt is stannous chloride, stannous chloride can hydrolyze on its own and form a stable dispersed hydrosol, so there is no need to add acid or alkali. Therefore, when the metal salt is stannous chloride, the specific process of step (3) includes: mixing the graphene oxide microspheres, the metal salt and water, and then stirring for 10-30 minutes to obtain a mixture.

[0081] In a specific embodiment of the present invention, in step (3), when sodium hydroxide solution, hydrochloric acid solution or nitric acid solution is added, the amount of water used is calculated as the total amount of water added and the water contained in the added solution. When the water content in the added sodium hydroxide solution, hydrochloric acid solution or nitric acid solution meets the ratio requirements of the amount of graphene oxide microspheres, metal salt and water, no additional water needs to be added.

[0082] In a preferred embodiment, the hydrothermal reaction in step (4) is a microwave hydrothermal reaction. Using a microwave hydrothermal method is beneficial for obtaining nanomaterials with more uniform size distribution, improving material stability, and significantly shortening the reaction time.

[0083] Preferably, the conditions for the microwave hydrothermal reaction include: a temperature of 150-220℃, a time of 0.5-6h, and a microwave power of 400-800W.

[0084] In the specific implementation of step (4), the temperature of the microwave hydrothermal reaction can be 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃ or 220℃, the time of the microwave hydrothermal reaction can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, and the microwave power can be 400W, 500W, 600W, 700W or 800W.

[0085] In a preferred embodiment, in step (4), when washing the solid phase obtained from solid-liquid separation, anhydrous ethanol and deionized water are used in sequence.

[0086] More preferably, the washing is performed 2-5 times with anhydrous ethanol and 2-5 times with deionized water.

[0087] In the method described in this invention, the freeze-drying method used in step (4) can prevent the collapse of the pore structure of the gel and preserve the three-dimensional structure of its microspheres to the greatest extent.

[0088] Therefore, preferably, in step (4), the freeze-drying conditions include: a temperature of 25-60°C and a time of 12-48h.

[0089] In the specific implementation of step (4), the freeze-drying temperature can be 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C or 60°C, and the freeze-drying time can be 12h, 18h, 24h, 30h, 36h, 42h or 48h.

[0090] In step (4) of the present invention, the sintering operation can remove sodium alginate on the one hand, and reduce graphene oxide on the other hand, thereby improving its electrical conductivity and mechanical properties, while improving the crystal structure of the metal oxide.

[0091] Therefore, preferably, in step (4), the sintering conditions are: temperature of 200-700℃, time of 1-5h, and atmosphere of inert atmosphere. Specifically, the sintering temperature can be 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃ or 700℃, and the sintering time can be 1h, 2h, 3h, 4h or 5h.

[0092] More preferably, in step (4), the inert atmosphere may be provided by one or more gases selected from nitrogen, helium, neon, argon, krypton and xenon.

[0093] A third aspect of the present invention provides an application of the above-mentioned three-dimensional graphene / metal oxide composite microspheres in the fields of gas sensing, adsorption, or energy storage.

[0094] Compared with existing technologies, the main advantages of this patent are:

[0095] 1. The obtained three-dimensional graphene / metal oxide composite microspheres have controllable size and structure and high specific surface area;

[0096] 2. The metal oxides are uniformly dispersed on the surface of the microspheres and can be used to prepare gas-sensitive materials, adsorbent materials, and electrode materials.

[0097] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0098] All room temperatures mentioned below refer to 25°C.

[0099] Example 1

[0100] (1) Disperse 50mg of graphene oxide into 10ml (10g) of deionized water, add 0.1g of sodium alginate, and stir evenly. The weight ratio of graphene oxide, sodium alginate and deionized water is 5:10:1000. Then sonicate for 30min to completely peel off the graphene oxide sheets and disperse them evenly in water. Then heat at 70℃ for 4h to obtain a mixed dispersion.

[0101] (2) Add the mixed dispersion to a micro-injection pump, controlling the pump flow rate at 30 μL / min, so that the mixed dispersion drops evenly into the calcium chloride aqueous solution (Ca). 2+ The graphene oxide / sodium alginate hydrogel was formed by soaking in deionized water at a concentration of 5% by weight for 12 hours. The graphene oxide / sodium alginate hydrogel was rinsed three times with deionized water and then soaked in deionized water for 24 hours to obtain graphene oxide microspheres.

[0102] (3) Add 0.1g of graphene oxide microspheres to a 500mL beaker, then add 190mL (190g) of deionized water, and then add 1.06g of sodium tungstate. Under the conditions of room temperature and stirring, add hydrochloric acid solution with a concentration of 2mol / L dropwise to adjust the pH value to 2. The dropwise addition time of hydrochloric acid solution is controlled to be 30min to obtain a mixture. The weight ratio of graphene oxide microspheres, sodium tungstate and water is 1:10.6:2400 (at this time, the amount of water used is the amount of deionized water plus the water content in the hydrochloric acid solution). At this time, the mixture is a uniform suspension.

[0103] (4) Transfer the mixture to a hydrothermal reactor and then place it in a microwave synthesizer. Microwave (800W power) assisted hydrothermal treatment at 180°C for 0.5h. After naturally cooling to room temperature, wash the solid obtained from solid-liquid separation three times with anhydrous ethanol and deionized water respectively. Then freeze-dry at 25°C for 24h to obtain freeze-dried microspheres. Then sinter at 500°C for 2h under nitrogen protection to obtain three-dimensional graphene / WO3 composite microspheres.

[0104] Example 2

[0105] The method of Example 1 was followed, except that step (3) was performed as follows: 0.1 g of graphene oxide microspheres were added to a 500 mL beaker, followed by 220 mL (220 g) of deionized water, and then 0.55 g of copper sulfate. A 2 mol / L sodium hydroxide solution was added dropwise at room temperature and with stirring. The pH was adjusted to 10, and the addition time of the sodium hydroxide solution was controlled to be 30 min. A mixture was then obtained, in which the weight ratio of graphene oxide microspheres, copper sulfate and water was 1:5.5:2400 (at this time, the amount of water used was the amount of deionized water plus the water content in the sodium hydroxide solution); finally, three-dimensional graphene / CuO composite microspheres were obtained.

[0106] Example 3

[0107] The method of Example 1 was followed, except that step (3) was performed as follows: 0.1 g of graphene oxide microspheres were added to a 500 mL beaker, followed by 220 mL (220 g) of deionized water, and then 1.428 g of zinc nitrate was added. A 2 mol / L sodium hydroxide solution was added dropwise at room temperature and with stirring. The pH was adjusted to 10, and the dropping time of the sodium hydroxide solution was controlled to be 30 min. A mixture was then obtained, in which the weight ratio of graphene oxide microspheres, zinc nitrate and water was 1:14.28:2400 (at this time, the amount of water used was the amount of deionized water plus the water content in the sodium hydroxide solution); finally, three-dimensional graphene / ZnO composite microspheres were obtained.

[0108] Example 4

[0109] The method of Example 1 was followed, except that step (3) was performed as follows: 0.1 g of graphene oxide microspheres were added to a 500 mL beaker, followed by 220 mL (220 g) of deionized water, and then 1.164 g of cobalt nitrate was added. A 2 mol / L sodium hydroxide solution was added dropwise at room temperature and with stirring. The pH was adjusted to 10, and the dropwise addition time of the sodium hydroxide solution was controlled to be 30 min. A mixture was then obtained, in which the weight ratio of graphene oxide microspheres, cobalt nitrate and water was 1:11.64:2400 (at this time, the amount of water used was the amount of deionized water plus the water content in the sodium hydroxide solution); finally, three-dimensional graphene / Co3O4 composite microspheres were obtained.

[0110] Example 5

[0111] The method was implemented according to Example 1, except that step (3) was performed as follows: 0.1g of graphene oxide microspheres were added to a 500mL beaker, followed by 220mL (220g) of deionized water, and then 1.76g of ammonium molybdate was added. Under the conditions of room temperature and stirring, a 2mol / L nitric acid solution was added dropwise to adjust the pH value to 2 and control the dropwise addition time of the nitric acid solution to 30min. Then a mixture was obtained, and the weight ratio of graphene oxide microspheres, ammonium molybdate and water was 1:17.6:2400 (at this time, the amount of water used is the amount of deionized water plus the water content in the nitric acid solution); finally, three-dimensional graphene / MoO3 composite microspheres were obtained.

[0112] Example 6

[0113] The method of Example 1 was implemented, except that step (3) was performed as follows: 0.1g of graphene oxide microspheres were added to a 500mL beaker, followed by 240mL (240g) of deionized water, and then 1.2g of stannous chloride was added. The weight ratio of graphene oxide microspheres, stannous chloride and deionized water was 1:12:2400. The mixture was stirred at room temperature for 30min to obtain a mixture. Finally, three-dimensional graphene / SnO2 composite microspheres were obtained.

[0114] Example 7

[0115] The method is implemented according to Example 1, except that step (1) is performed as follows:

[0116] 50 mg of graphene oxide was dispersed in 5 mL of deionized water, and 0.1 g of sodium alginate was added and stirred until homogeneous. The weight ratio of graphene oxide, sodium alginate and water was 10:20:1000. The mixture was then sonicated for 100 min to completely exfoliate the graphene oxide sheets and disperse them uniformly in water. The mixture was then heated at 70 °C for 4 h to obtain a mixed dispersion. Finally, three-dimensional graphene / WO3 composite microspheres were obtained.

[0117] Example 8

[0118] The method is implemented according to Example 1, except that step (2) is performed as follows:

[0119] The mixed dispersion was added to a micro-injection pump, and the flow rate of the pump was controlled at 100 μL / min, so that the mixed dispersion was evenly dropped into the calcium chloride aqueous solution (Ca). 2+ The graphene oxide / sodium alginate hydrogel was formed by soaking the sample in a solution of 10% by weight for 12 hours. The graphene oxide / sodium alginate hydrogel was then rinsed three times with deionized water and soaked in deionized water for 24 hours to obtain graphene oxide microspheres. Finally, three-dimensional graphene / WO3 composite microspheres were obtained.

[0120] Example 9

[0121] The method is implemented according to Example 1, except that step (4) is performed as follows:

[0122] The mixture was transferred to a hydrothermal reactor and then placed in a microwave synthesizer. It was then subjected to microwave-assisted hydrothermal treatment at 200°C (800W power) for 3 hours. After naturally cooling to room temperature, the solid obtained from solid-liquid separation was washed three times with anhydrous ethanol and deionized water, respectively. It was then freeze-dried at 50°C for 24 hours and sintered at 500°C for 4 hours under nitrogen protection to obtain three-dimensional graphene / WO3 composite microspheres.

[0123] Example 10

[0124] The method was carried out according to Example 1, except that in step (4), the sintering temperature was 200°C to obtain three-dimensional graphene / WO3 composite microspheres.

[0125] Comparative Example 1

[0126] The method of Example 1 was implemented, except that step (3) was performed as follows: 0.1g of graphene oxide microspheres were added to a 500mL beaker, then 240mL of deionized water was added, followed by 0.5g of WO3. The mixture was stirred at room temperature for 30min to obtain a mixture; finally, three-dimensional graphene / WO3 composite microspheres were obtained.

[0127] Comparative Example 2

[0128] The method was carried out in Comparative Example 1, except that WO3 was replaced with an equal weight of CuO, and three-dimensional graphene / CuO composite microspheres were finally obtained.

[0129] Comparative Example 3

[0130] The method was carried out in Comparative Example 1, except that WO3 was replaced with an equal weight of ZnO, and three-dimensional graphene / ZnO composite microspheres were finally obtained.

[0131] Comparative Example 4

[0132] The method was carried out in Comparative Example 1, except that WO3 was replaced with an equal weight of Co3O4, and three-dimensional graphene / Co3O4 composite microspheres were finally obtained.

[0133] Comparative Example 5

[0134] The method was carried out in Comparative Example 1, except that WO3 was replaced with an equal weight of MoO3, and three-dimensional graphene / MoO3 composite microspheres were finally obtained.

[0135] Test Example 1

[0136] The morphology of the graphene / metal oxide composite microspheres obtained in Examples 1-10 and Comparative Examples 1-5 was tested using scanning electron microscopy. The results are shown in Table 1. The morphology of the graphene / WO3 composite microspheres obtained in Example 1 is shown in the figure below. Figure 1 As shown, from Figure 1 As can be seen, the obtained graphene / WO3 composite microspheres are uniform spheres with a diameter of 1.78 mm.

[0137] Test Example 2

[0138] The specific surface area and pore structure of the graphene / metal oxide composite microspheres obtained in Examples 1-10 and Comparative Examples 1-5 were tested using the nitrogen adsorption-desorption method (BET method). The results are shown in Table 1. The graphene / WO3 composite microspheres obtained in Example 1 are as follows: Figure 2 As shown, from Figure 2 The graphene / WO3 composite microspheres have a specific surface area of ​​206 m². 2 / g, with a very high specific surface area and multi-level channels ranging from 2 nanometers to 100 nanometers, with an average channel diameter of 10.38 nm.

[0139] Table 1

[0140]

[0141]

[0142] Test Example 3

[0143] The morphology of the graphene / WO3 composite microspheres obtained in Example 1 was tested using scanning electron microscopy, such as... Figure 3 As shown, from Figure 3 As can be seen, WO3 nanosheets were successfully loaded onto the surface of graphene microspheres using the in-situ loading method, and the WO3 nanosheets were uniformly distributed on the surface of the graphene microspheres.

[0144] Test Example 4

[0145] The morphology of the three-dimensional graphene / CuO composite microspheres obtained in Example 2 and the freeze-dried microspheres obtained after freeze-drying were tested using scanning electron microscopy. Figure 4 As shown, where Figure 4 Images B1, B2, and B3 are three-dimensional graphene / CuO composite microspheres, while images A1, A2, and A3 show the morphology of the freeze-dried microspheres. Figure 4As can be seen, the material grown on the surface of the freeze-dried microspheres is a cluster of CuO nanorods with a length of about 500 nm. After sintering at 500 °C, the CuO nanorods disappear and crystal particles with a size of about 1 μm appear. At the same time, a large number of CuO particles with a size of about 50 nm are uniformly distributed on the surface of the graphene microspheres. This indicates that the high-temperature sintering treatment in this invention is beneficial to improving the crystallinity of the nano-oxide and to improving the gas-sensitive response of the three-dimensional graphene / metal oxide composite microspheres.

[0146] The results above show that the three-dimensional graphene / metal oxide composite microspheres obtained by this invention have a high specific surface area and abundant nanopores, which are beneficial for the adsorption of gas and liquid molecules on the surface and promote the transport of gas and liquid molecules in the internal pores. At the same time, the composite material surface has a large number of active sites, which can accelerate the physicochemical reaction on the surface. It can be widely used in the fields of gas sensing, adsorption or energy storage.

[0147] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing three-dimensional graphene / metal oxide composite microspheres, characterized in that, The three-dimensional graphene / metal oxide composite microspheres include graphene microspheres and metal oxides loaded on the graphene microspheres; The specific surface area of ​​the three-dimensional graphene / metal oxide composite microspheres is 188-500 m². 2 / g; The three-dimensional graphene / metal oxide composite microspheres have a hierarchical porous structure with an average pore diameter of 0.1-20 nm. The diameter of the three-dimensional graphene / metal oxide composite microspheres is 0.9-5 mm; The metal oxide is selected from one or both of WO3 and MoO3; The preparation method includes the following steps: (1) Mix graphene oxide, sodium alginate and water, then sonicate and heat to obtain a mixed dispersion; (2) The mixed dispersion is dripped into a solution containing Ca using an injection pump. 2+ The graphene oxide / sodium alginate hydrogel was obtained by soaking in an aqueous solution. The graphene oxide / sodium alginate hydrogel was then washed to obtain graphene oxide microspheres. (3) The graphene oxide microspheres, metal salt and water are mixed to obtain a mixture; (4) The mixture is subjected to a hydrothermal reaction, followed by solid-liquid separation, washing, freeze drying and sintering in sequence; The weight ratio of graphene oxide, sodium alginate and water is 5-10:0.1-40:1000, and the weight ratio of graphene oxide to sodium alginate is 1:

2. In step (1), the heating conditions include: a temperature of 70-95°C and a time of 3-6 hours; In step (2), the flow rate of the syringe pump is 10-200 μL / min; In step (3), the weight ratio of the graphene oxide microspheres, metal salt and water is 1:1-20:2000-2600; In step (4), the hydrothermal reaction is a microwave hydrothermal reaction, and the conditions of the microwave hydrothermal reaction include: temperature of 150-220℃, time of 0.5-6h, and microwave power of 400-800W; the conditions of the sintering are: temperature of 200-700℃, time of 1-5h, and inert atmosphere.

2. The preparation method according to claim 1, characterized in that, In step (1), the ultrasound duration is 10-120 min.

3. The preparation method according to claim 1, characterized in that, In step (2), the substance containing Ca 2+ Ca in aqueous solution 2+ The concentration is 1-10 by weight.

4. The preparation method according to claim 1, characterized in that, In step (2), the soaking time is 1-24 hours.

5. The preparation method according to claim 1 or 4, characterized in that, In step (2), the washing process includes rinsing the graphene oxide / sodium alginate hydrogel with water and then soaking it in water for 12-48 hours.

6. The preparation method according to claim 1, characterized in that, In step (3), the metal salt is selected from one or both of tungstate and molybdate.

7. The preparation method according to claim 6, characterized in that, The metal salt is selected from one or both of sodium tungstate and ammonium molybdate.

8. The preparation method according to claim 1, characterized in that, In step (4), the freeze-drying conditions include a temperature of 25-60°C and a time of 12-48h.

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