CN110104650B - An ultrathin MXenes two-dimensional material with tunable surface functional groups and transition metal valence states and its preparation method - Google Patents

Abstract

The invention discloses an ultra-thin MXenes two-dimensional layered material with adjustable surface functional groups and transition metal valence states and a preparation method thereof, including an ultra-thin MXenes two-dimensional material with adjustable surface functional groups and an ultra-thin MXenes two-dimensional material with controllable transition metal valence states. MXenes 2D materials and ultrathin MXenes 2D materials with both tunable simultaneously. The ultrathin two-dimensional layered materials include MXenes, graphene, black phosphorus, silicene, ultrathin metals, ultrathin metal oxides, layered transition metal sulfides, layered transition metal selenides, layered transition metal tellurium compound, boron nitride, layered hydroxide. Compared with the prior art, the present invention adopts the physical peeling method to open the metal bond and peel off the layered material, without using corrosive acid, and simultaneously realize the synchronous regulation of the surface functional group type and the metal valence state, and the equipment is simple, the operation is convenient, and it is beneficial to a large number of The advantages of preparing two-dimensional ultra-thin materials, etc., are low in preparation cost, green, safe and non-toxic.

Description

A two-dimensional ultrathin MXenes material with tunable surface functional groups and transition metal valence states and preparation method thereof

technical field

The invention relates to ultrathin MXenes with adjustable surface functional groups and transition metal valence states and a preparation method thereof, in particular to the preparation of ultrathin MXenes two-dimensional layered materials by physical exfoliation method opening metal bonds.

Background technique

Compared with bulk metals, nanomaterials have the characteristics of larger specific surface area, specific crystal face exposure, special size effect, etc., thus showing higher activity, so nanomaterials have made great progress in most application fields. Among the numerous nanomaterials, two-dimensional nanomaterials have attracted much attention in recent years because their thicknesses have been reduced from three-dimensional bulk to monolayer or few-layer nanoscales, producing unique electronic structures and exposing more active sites. The research of two-dimensional materials such as ultrathin metals, ultrathin metal oxides, layered metal chalcogenides, hexagonal boron nitride, layered hydroxides and other systems has attracted increasing attention. Layered transition metal carbides (MXenes) are a new type of graphite-like two-dimensional hot material with rich chemical composition and high carrier mobility. Researchers at home and abroad have carried out theoretical and experimental studies on MXenes phase materials and found that It has a unique two-dimensional lamellar structure, large specific surface area and good electrical conductivity, which is expected to be widely used in energy storage, catalysis, adsorption, hydrogen storage, sensors, and new polymer-reinforced matrix composites.

In the MAX phase of the precursor of MXenes, the M-X atomic layers are mainly covalent bonds and ionic bonds, and the M-A atomic layers are mainly connected by metal bonds. The M-A bond energy is weaker than that of the M-X atomic layer. Vander Waals is strong. Therefore, ordinary physical-mechanical exfoliation methods cannot open metal bonds to achieve ultrathin structures. Compared with the M-X bond, the M-A bond is weaker, so the atomic reactivity of the A layer is relatively high, which can be peeled off by etching, thus obtaining MXenes with a layered structure. People usually use acid chemical liquid-phase etching to strip A-layer atoms to prepare MXenes ultra-thin layers, but this method has three major characteristics: First, MXenes obtained by HF etching are easy to adsorb hydrophilic functional groups such as -F, -O, -OH, etc. Most related studies reported that the types of surface functional groups of MXenes prepared by chemical etching method significantly affect the electrocatalytic performance, lithium-ion battery capacity, electrochemical capacity, energy band structure, electron transport properties and light absorption properties. Secondly, the low-coordination transition metal ions exposed on the surface during the corrosion process are easily oxidized, resulting in the disappearance of a large number of active sites; and the higher the corrosion temperature, the more serious the oxidation, resulting in a decrease in the conductivity of the material, and the theoretically predicted semi-metallic properties are no longer an advantage. , thereby reducing the activity; in addition, transition metal oxidation also affects the structural stability of MXenes. Surface adsorption of functional groups and transition metal oxidation are the keys to restrict the potential applications of 2D layered MXenes in many fields, which are also crucial issues for MXenes in material preparation and performance research. Third, the HF solution used in the experiment is more toxic and corrosive, and has certain dangers in actual operation. Therefore, the traditional acid etching method for interlayer peeling has the above disadvantages. In view of the above, finding a green and safe preparation method that can prevent the oxidation of low-valence metals on the surface during the layered exfoliation process of the precursor and at the same time effectively control the surface functional groups has become an urgent problem facing MXenes.

SUMMARY OF THE INVENTION

In order to overcome the above shortcomings and deficiencies of the prior art, one of the objectives of the present invention is to provide an ultra-thin MXenes two-dimensional material with adjustable surface functional groups and transition metal valence states, which has the functions of surface functional group regulation and transition metal valence state adjustment, etc. advantage. The second purpose of the present invention is to provide a method for preparing the above-mentioned ultra-thin MXenes two-dimensional layered material, which has the advantages of simple equipment, convenient operation, easy control of functional groups and transition metal valence states, and is conducive to mass preparation of two-dimensional ultra-thin materials, etc. The preparation cost is low, and it is green and non-toxic.

The object of the present invention is achieved through the following technical solutions:

An ultrathin MXenes two-dimensional material with tunable surface functional groups and transition metal valence states, including an ultrathin MXenes two-dimensional material with tunable surface functional groups, an ultrathin MXenes two-dimensional material with controllable transition metal valence, and both At the same time tunable ultrathin MXenes two-dimensional material; the ultrathin MXenes two-dimensional material is directly prepared by one-step low temperature and ultrahigh pressure physical exfoliation method.

Further, the ultrathin two-dimensional materials prepared by the above preparation method also include graphene, black phosphorus, silicene, ultrathin metals, layered transition metal oxides, layered transition metal sulfides, and layered transition metal selenides. , Layered transition metal telluride, boron nitride, layered hydroxide.

A method for preparing ultrathin MXenes two-dimensional materials with adjustable surface functional groups and transition metal valence states, comprising the following steps:

( ₁ ) Using layered precursors (such as MAX: _Ti3AlC2 , etc.) as raw materials, ultrasonically dispersing the layered precursors in a solvent of a certain concentration, and by changing the functional group types and redox properties of the solvent, the surface adsorption of functional groups is realized. Control of species and metal valence;

(2) Pour the precursor dispersed in the solvent in step (1) into the container of the low temperature and ultra-high pressure continuous flow crusher at a low speed, and use the low temperature and ultra-high pressure physical exfoliation method to directly prepare the ultra-thin two-dimensional MXenes material in one step. Water bath temperature, ultra-high pressure conditions, peeling times and concentration, physical peeling of layered precursors to obtain a homogeneous solution with a certain concentration, then adding an appropriate amount of deionized water for centrifugation, washing several times, vacuum freeze-drying, and the final step to directly prepare surface adsorption functional groups Two-dimensional ultrathin MXenes with simultaneously tunable valence states of metals.

Further, in the method for preparing an ultra-thin MXenes two-dimensional material with adjustable surface functional groups and transition metal valence, the particle diameter of the layered precursor in step (1) is below 100um to avoid blocking the valve outlet; the functional group of the solvent The types are various functional groups, which can realize the regulation of surface adsorption functional groups; the properties of the solvent include oxidizing, neutral, and reducing properties, so as to realize the regulation of the high and low valence states of transition metals in the process of physical exfoliation.

Further, in the preparation method of the ultra-thin MXenes two-dimensional material with adjustable surface functional groups and transition metal valence states, the process parameters of the continuous flow crusher in step (2) are as follows, low temperature circulating water bath: 1-4°C, ultra-high pressure Conditions: 50-200MPa; peeling times: 2-10 times; concentration: 0.001-1 mg/ml.

Further, the preparation method of the ultrathin MXenes two-dimensional material with adjustable surface functional groups and transition metal valence states, the preparation method is used to prepare ultrathin two-dimensional materials with specific surface functional groups and transition metal valence states, including MXenes, Graphene, black phosphorus, silicene, ultrathin metals, layered transition metal oxides, layered transition metal sulfides, layered transition metal selenides, layered transition metal tellurides, boron nitride, layered hydroxides .

Compared with the prior art, the present invention has the following advantages and beneficial effects:

(1) In the present invention, ultrathin MXenes are prepared by physically exfoliating layered precursors by a low temperature and ultrahigh pressure method. The traditional chemical etching method not only has high toxicity in the HF solution used in the experiment, but also the obtained MXene has two characteristics: the surface contains functional groups such as hydroxyl and fluoride ions; meanwhile, the low-valent transition metals are easily oxidized. This greatly restricts the display of excellent properties and the expansion of application fields of 2D ultrathin MXenes. Ultra-thin materials can be prepared in large quantities by the low-temperature and ultra-high pressure method, and this method is simple and convenient. The reaction is carried out in a low-temperature circulating water bath, and the ultra-high pressure energy is used to make the sample nano-sized under the action of shearing, cavitation, and collision. It still maintains the activity of the original substance. The strong shock wave generated by cavitation under ultra-high pressure can easily open the M-A metal bond, and achieve the energy required to peel off the precursor MAX to achieve the peeling of the layered material. This eliminates the need for the use of corrosive acids, while achieving thinning and increasing productivity. This method provides a new idea for the preparation and synthesis of hot spot materials MXenes and other two-dimensional layered materials.

(2) The present invention uses a low-temperature and ultra-high pressure method to physically exfoliate the layered precursor to prepare ultra-thin MXenes, without using corrosive acids and further surface chemical modification steps to achieve synchronous regulation of MXenes surface functional groups and transition metal valence states. By changing the type and redox properties of the processing solvent, not only can the types of surface adsorption functional groups be designed, but also the valence state of metal ions can be adjusted to maintain their activity, and finally the surface structure and properties of MXenes can be adjusted, which is very important for the realization of specific functions. The application of 2D materials is of great significance.

(3) Ultra-thin MXenes are a class of international hot materials, and their applications involve materials science, chemistry, physics, biology, sensing and energy and other disciplines. The research on related scientific issues is related to each other. Therefore, this method is used to prepare ultra-thin materials. Its research can promote the development of multiple disciplines, especially the development of ultrathin MXenes with specific surface structures, and also provide feasibility for designing specific application-oriented 2D layered materials.

Description of drawings

FIG. 1 is a schematic flow chart of the preparation of ultrathin MXenes according to the present invention.

FIG. 2 is the XPS image of the ultrathin MXenes prepared by the present invention.

FIG. 3 is a SEM image of the ultrathin MXenes prepared by the present invention.

FIG. 4 is an AFM image of the ultrathin MXenes prepared by the present invention.

Detailed ways

The present invention will be further described in detail below with reference to the examples and accompanying drawings, but the embodiments of other two-dimensional layered materials of the present invention are not limited thereto.

Example 1

The preparation method of low temperature and ultra-high pressure physical exfoliation of Ti ₃ C ₂ material in ultra-thin MXenes of the present embodiment includes the following steps:

(1) The layered precursor Ti ₃ AlC ₂ is used as the raw material, and the particle diameter is below 100um. The Ti ₃ AlC ₂ is ultrasonically dispersed in a solvent with a certain concentration, and the solvent is selected from tetramethylamine hydroxide, which has a reducing property and a concentration of 0.001 mg/ml.

(2) One-step direct preparation of ultra-thin 2D MXenes by low-temperature and ultra-high pressure physical exfoliation method: The Ti ₃ AlC ₂ solution dispersed in tetramethylammonium hydroxide in step (1) was poured into a low-temperature ultra-high pressure continuous flow crusher at a low speed In the container, the process parameters of the continuous flow crusher are as follows, low temperature circulating water bath: 4 ℃, ultra-high pressure condition: 200MPa; peeling times: 2 times; concentration: 0.001mg/ml.

(3) After the peeling is completed, an appropriate amount of deionized water is added for centrifugation, washed twice, and then vacuum freeze-dried. The final step is to directly prepare a _two -dimensional ultra-thin _Ti3C2 material with surface adsorption of methyl and nitrogen-containing functional groups and low-valent titanium.

FIG. 1 is a flow chart of the preparation of ultra-thin MXenes by a low-temperature and ultra-high pressure physical exfoliation method according to the present invention, including a layered precursor 11 , different kinds of solvents 21 , and an ultra-thin MXenes material 31 prepared by the exfoliation method. The layered precursors are exfoliated into ultrathin MXenes under the action of cavitation shear force.

FIG. 2 is a comparison diagram of XPS test of ultra-thin Ti ₃ C ₂ prepared by the method of the present invention and the traditional HF etching method. The XPS spectra of characteristic elements Ti, C, N and O were obtained by testing, and it was found that the surface of ultra-thin Ti ₃ C ₂ obtained by HF chemical etching method was rich in -O and -OH functional groups, and a large amount of low-coordination metal Ti was oxidized to TiO ₂ . The ultra-thin Ti ₃ C ₂ surface obtained by stripping Ti ₃ AlC ₂ in a reducing solvent (TMAH) at low temperature and ultra-high pressure was detected to be free of F elements, but rich in N groups and adsorbed a small amount of oxygen-containing groups at the same time. The method can effectively control the adsorption of functional groups on the surface of MXene; the most important thing is that the low-coordination metal Ti still maintains the original valence of +2 and +3, and even metal Ti atoms appear, which further shows that the low-temperature and ultra-high pressure exfoliation method can synchronously control the transition metal valence state. It can be seen that the low temperature and ultra-high pressure method can simultaneously change the surface functional groups and control the valence state of Ti metal in one step.

FIG. 3 is a SEM image of the ultra-thin Ti ₃ C ₂ prepared by the present invention. It can be seen from the figure that the size of the layered precursor Ti ₃ AlC ₂ raw material is about 8 μm, and the size of the Ti ₃ C ₂ nanosheet is about 1-2 μm.

FIG. 4 is an AFM test chart of the ultra-thin Ti ₃ C ₂ prepared by the present invention. It can be seen from the figure that when the pressure is 200MPa, Ti ₃ C ₂ nanosheets with a thickness of about 3.5 nm and a size of 1-2 μm can be obtained by peeling off the Ti ₃ AlC ₂ solution three times. If the processing pressure and times are increased, thinner Ti ₃ C ₂ can be obtained.

Example 2

The preparation method of the two-dimensional ultrathin SnSe ₂ (MoS ₂ and WSe ₂ , etc.) physical exfoliation in which surface functional groups and transition metal valence states can be synchronously controlled in this embodiment includes the following steps:

(1) The layered bulk SnSe ₂ is used as the raw material, and the particle diameter is below 100um. The bulk SnSe ₂ was ultrasonically dispersed in a solvent with a certain concentration, and the solvent was water, which was neutral, and the concentration was 1 mg/ml.

(2) Direct preparation of ultrathin two-dimensional SnSe ₂ materials by low temperature and ultra-high pressure physical exfoliation method: Pour the SnSe ₂ solution dispersed in water in step (1) into the container of a low temperature and ultra-high pressure continuous flow crusher at a low speed, and the continuous flow crusher The process parameters are as follows, low temperature circulating water bath: 1°C, ultra-high pressure condition: 50MPa; peeling times: 10 times; concentration: 1 mg/ml.

(3) After the peeling is completed, an appropriate amount of deionized water is added for centrifugation, washed three times, and then vacuum freeze-dried. In the final step, a two-dimensional ultrathin SnSe ₂ material with a surface adsorption of hydroxyl functional groups and +4 valence tin and a thickness of about 2 nm is directly prepared.

Example 3

The preparation method of the two-dimensional ultra-thin metal Zn physical exfoliation in which the surface functional groups and the transition metal valence state can be synchronously controlled in this embodiment, includes the following steps:

(1) The layered bulk Zn is used as the raw material, and the particle diameter is below 100um. The layered graphite is ultrasonically dispersed in a solvent with a certain concentration, and the solvent is sodium sulfite solution, which is reducing, and the concentration is 0.1 mg/ml.

(2) Direct preparation of ultrathin two-dimensional Zn nanosheets by low temperature and ultrahigh pressure physical exfoliation method: Pour the layered bulk Zn solution dispersed in neutral water in step (1) into the container of a low temperature and ultrahigh pressure continuous flow crusher at a low speed , Continuous flow crusher process parameters are as follows, low temperature circulating water bath: 3 ℃, ultra-high pressure conditions: 100MPa; peeling times: 6 times; concentration: 0.1mg/ml.

(3) After the peeling is completed, an appropriate amount of deionized water is added, centrifuged for 3 times, and then vacuum freeze-dried. The final step is to directly prepare two-dimensional ultrathin Zn nanosheets with a thickness of about 2 nm adsorbing a small amount of hydroxyl and sulfhydryl groups on the surface.

Example 4

The preparation method of the two-dimensional ultra-thin layered transition metal oxide molybdenum oxide (Ni, Co, Mn, Mo, Fe, etc.) physical exfoliation in which the surface functional groups and the valence state of the transition metals can be synchronously controlled in this embodiment, includes the following steps:

(1) The layered block MoO ₃ is used as the raw material, and the particle diameter is below 100um. The bulk MoS ₂ was ultrasonically dispersed in a solvent with a certain concentration, and the solvent was ethanol, which was neutral, and the concentration was 0.01 mg/ml.

(2) Direct preparation of ultrathin two _- dimensional MoO3 materials by low temperature and ultrahigh pressure physical exfoliation method: Pour the MoO3 solution dispersed in neutral ethanol in step ( ₁ ) into the container of a low temperature and ultrahigh pressure continuous flow crusher at a low speed, continuously The process parameters of the flow crusher are as follows, low temperature circulating water bath: 2°C, ultra-high pressure condition: 150MPa; peeling times: 4 times; concentration: 0.5mg/ml.

(3) After the peeling is completed, add an appropriate amount of deionized water, centrifuge and wash 3 times, and then vacuum freeze-drying. In the final step, a two-dimensional ultra-thin layer with a surface rich in hydroxyl functional groups and +6-valent molybdenum and a thickness of about 2.5 nm is directly prepared. Molybdenum double hydroxide LDH.

Example 5

The preparation method of the two-dimensional ultra-thin graphene physical exfoliation in which the surface functional groups and the transition metal valence state can be controlled synchronously in the present embodiment, includes the following steps:

(1) Using graphite as raw material, the diameter is below 100um. The graphite is ultrasonically dispersed in a solvent with a certain concentration, and the solvent is ammonia water, which is reducible, and the concentration is 0.1 mg/ml.

(2) The ultrathin two-dimensional graphene material is directly prepared by the low temperature and ultrahigh pressure physical exfoliation method: the layered graphite solution dispersed in the neutral ethanol in step (1) is poured into the container of the low temperature ultrahigh pressure continuous flow crusher at a low speed, The process parameters of the continuous flow crusher are as follows, low temperature circulating water bath: 2°C, ultra-high pressure condition: 150MPa; peeling times: 8 times; concentration: 0.5mg/ml.

(3) After the peeling is completed, an appropriate amount of deionized water is added for centrifugation, washed three times, and then vacuum freeze-dried. In the final step, two-dimensional ultrathin graphene with a surface rich in amine groups and a small amount of hydroxyl functional groups and a thickness of about 1.5 nm is directly prepared.

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the described embodiments, and any other changes, modifications, substitutions, and combinations made without departing from the spirit and principle of the present invention , simplification, all should be equivalent replacement modes, and are all included in the protection scope of the present invention.

Claims (3)

1. A method for preparing an ultra-thin MXenes two-dimensional material, characterized in that it includes an ultra-thin MXenes two-dimensional material with tunable surface functional groups, an ultra-thin MXenes two-dimensional material with a controllable transition metal valence state, and a Tuned ultrathin MXenes 2D materials; The preparation method of the ultra-thin MXenes two-dimensional material is a one-step method of low temperature and ultra-high pressure physical exfoliation, which includes the following steps: 1) Using layered precursors as raw materials, ultrasonically dispersing the layered precursors in a solvent of a certain concentration, and by changing the types of functional groups and redox properties of the solvent, the types of surface adsorption functional groups and the regulation of metal valence states are realized; 2) Pour the precursor dispersed in the solvent in step 1) into the container of the low temperature and ultra-high pressure continuous flow crusher at a low speed, and use the low temperature and ultra-high pressure physical exfoliation method to directly prepare the ultra-thin two-dimensional MXenes material in one step, by controlling the temperature of the circulating water bath , ultra-high pressure conditions, peeling times and concentration, physical peeling of layered precursors to obtain a homogeneous solution with a certain concentration, and then adding an appropriate amount of deionized water for centrifugation, washing several times, vacuum freeze drying, and finally directly preparing the surface adsorption functional groups and metal valences Two-dimensional ultrathin MXenes with simultaneously tunable states; The process parameters of the continuous flow breaker in step 2) are as follows, low temperature circulating water bath: 1-4°C, ultra-high pressure condition: 50-200MPa; peeling times: 2-10 times; concentration: 0.001-1mg/ml. 2. The method for preparing an ultra-thin MXenes two-dimensional material according to claim 1, wherein the functional group types of the solvent in step 1) are various functional groups, which can all realize the regulation of surface adsorption functional groups, and the functional group properties of the solvent. Including oxidation, neutrality, and reduction, so as to realize the regulation of high and low valence states of transition metals in the process of physical exfoliation. 3. The method for preparing an ultra-thin MXenes two-dimensional material according to claim 1, wherein the particle diameter of the layered precursor in step 1) is below 100um.

Images