A self-supporting composite film, its preparation method and application

Abstract

The present invention belongs to the technical field of self-supporting thin film electrodes, and particularly relates to a self-supporting composite thin film, a preparation method thereof, and an application thereof. In the present invention, molybdenum disulfide, multilayer Ti3C2T x MXene, and graphene oxide are compounded to prepare a self-supporting composite thin film, which solves the problem that two-dimensional materials are prone to stacking. The constructed heterojunction structure has an extremely high adsorption specific capacity, which can reach 51.1 mg / g, and has a great adsorption rate. The self-supporting composite thin film provided by the present invention has good flexibility, toughness, and electrical conductivity, and is an ideal electrode material, especially suitable for the field of capacitive deionization technology, and has great application prospects in devices such as supercapacitors, lithium ion batteries, and sodium ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of self-supporting thin film electrodes, and particularly relates to a self-supporting composite thin film, a preparation method thereof, and an application thereof. Background Art

[0002] Self-supporting electrodes can be directly used as electrodes without additional binders, conductive agents, and current collectors, and have good mechanical properties, higher specific capacitance, and energy density, which are widely favored by researchers.

[0003] MXene is a new type of two-dimensional material composed of alternating arrangements of transition metals and carbides / nitrides. It is usually produced by removing the "A" layer from MAX phase materials. The general formula of the MAX phase is M n+1 AX n (n = 1, 2, 3), where "M" represents a transition metal (M = Ti, Nb, V, Ta, etc.), "A" represents Al or Si, and "X" represents C and N or C and N. The general formula of MXene formed by selectively etching away the A phase from the MAX phase is M n+1 X n T x , where "T x " represents the terminal groups on its surface (such as -O, -OH, -F, etc.), and the subscript "x" represents the number of terminal groups, generally satisfying 0 < x < 2.

[0004] Taking Ti3C2T x as an example, Ti3C2T x MXene is composed of alternating embedded arrangements of transition metal atomic layers and carbon atomic layers, and its surface is coated with various functional terminal groups. This special structural composition endows it with advantages such as adjustable interlayer spacing, excellent metallic conductivity, surface electronegativity, and good hydrophilicity, which makes it different from other two-dimensional materials. Structurally, Ti3C2T x MXene is considered to be an accordion-like two-dimensional sheet material formed by stacking nanosheets with adjustable spacing. This structure can provide fast ion insertion or diffusion channels. Compared with carbon-based materials, Ti3C2T x MXene shows pseudocapacitive behavior with higher energy density in the redox reactions and intercalation Faraday reactions between its interlayers and on its surface. However, Ti3C2T x MXene has the problem of being prone to re-stacking. The original MXene has a small interlayer spacing and a thick sheet layer, which are the results of MXene re-stacking.

[0005] Graphene is a two-dimensional carbon material with a single atomic thickness. Due to its special structural characteristics, it has excellent electron mobility (15000 cm 2V -1 s -1 )、 an extremely low resistivity (10 -6 Ωcm -1 ) and an extremely high theoretical specific surface area (2620 m 2 g -1 ), but it also has the disadvantage of being extremely prone to stacking.

[0006] Molybdenum disulfide is a special layered metal sulfide and the main component of molybdenite. It has a large interlayer spacing and thermal stability and has been widely used in electrochemical energy storage. However, like other two-dimensional materials, molybdenum disulfide is extremely prone to stacking. During the growth of molybdenum disulfide, under the action of electrostatic force, molybdenum disulfide nanosheets are arranged in an interlaced manner and self-assembled to form molybdenum disulfide nanoflowers. This results in a large number of molybdenum disulfide nanosheets stacking together, reducing its effective surface area and active sites, and leading to a sharp decline in its adsorption performance.

[0007] In summary, how to solve the problem of easy stacking of two-dimensional materials and thereby improve their adsorption performance is an urgent problem to be solved in this field. Summary of the Invention

[0008] The purpose of the present invention is to provide a self-supporting composite film, its preparation method and application. The self-supporting composite film provided by the present invention solves the problem of easy stacking of two-dimensional materials and has an extremely high adsorption specific capacity.

[0009] To achieve the above purpose, the present invention provides the following technical solutions:

[0010] The present invention provides a preparation method of a self-supporting composite film, comprising the following steps:

[0011] (1) Mix graphene oxide, molybdenum disulfide, multi-layer Ti3C2T x MXene and water to obtain a molybdenum disulfide / multi-layer Ti3C2T x MXene / graphene oxide dispersion;

[0012] (2) Filter the molybdenum disulfide / multi-layer Ti3C2T x MXene / graphene oxide dispersion by suction filtration to form a wet film;

[0013] Subject the wet film to pre-cooling, freeze-drying and thermal reduction in sequence to obtain a self-supporting composite film.

[0014] Preferably, the mass ratio of graphene oxide to molybdenum disulfide is 1 to 16:4;

[0015] The mass ratio of the multi-layer Ti3C2T x MXene to molybdenum disulfide is 1 to 16:4;

[0016] The mass ratio of the graphene oxide to water is 0.1 - 0.4:1.

[0017] Preferably, the temperature of the thermal reduction is 300 - 350 °C, the heating rate is 2 - 5 °C / min, and the heat preservation time is 2 - 3 h.

[0018] Preferably, the temperature of the precooling is -18 - -24 °C, and the heat preservation time is 2 - 4 h;

[0019] The temperature of the freeze-drying is -40 - -53 °C, and the heat preservation time is 12 - 24 h.

[0020] Preferably, the preparation method of the molybdenum disulfide includes the following steps: performing a hydrothermal reaction on a molybdenum source, water, and a sulfur source, collecting the precipitate, and centrifuging, washing, and drying the obtained precipitate in sequence to obtain molybdenum disulfide.

[0021] Preferably, the sulfur source is thiourea, and the molybdenum source is ammonium molybdate.

[0022] Preferably, the temperature of the hydrothermal reaction is 180 - 200 °C, and the heat preservation time is 12 - 24 h.

[0023] Preferably, the preparation method of the multi-layer Ti3C2T x MXene includes the following steps: etching a Ti3AlC2 powder and a hydrofluoric acid solution, centrifuging, then washing the obtained reaction solution until the pH = 6 - 7, collecting the precipitate and drying it to obtain the multi-layer Ti3C2T x MXene.

[0024] The present invention also provides a self-supporting composite film obtained by the preparation method described in the above solution, including multi-layer Ti3C2T x MXene and molybdenum disulfide and reduced graphene oxide distributed between and on the surfaces of the multi-layer Ti3C2T x MXene layers.

[0025] The present invention also provides an application of the self-supporting composite film described in the above solution as an electrode material.

[0026] The present invention provides a preparation method of a self-supporting composite film. The present invention compositely prepares molybdenum disulfide, multi-layer Ti3C2T x MXene, and graphene oxide into a self-supporting composite film, solves the problem that two-dimensional materials are prone to stacking, and the constructed heterojunction structure has an extremely high adsorption specific capacity, which can reach 51.1 mg / g, and has a great adsorption rate. The preparation mechanism of the present invention is described below:

[0027] First, MoS2 enters the multilayer Ti3C2T during the mixing process. x In the MXene layer, multilayer Ti3C2T x The MXene sheets have a certain pillaring effect, and the evenly dispersed molybdenum disulfide is wrapped by graphene oxide, which reduces the problem of active material shedding caused by volume change during the cycle and improves the cycle stability. Molybdenum disulfide itself has good electrochemical properties, can provide a large adsorption specific capacity, and can also increase the active sites of the material;

[0028] Secondly, there are a large number of oxygen-containing functional groups on the surface of graphene oxide, which can easily adhere to the surface of other materials. Graphene oxide acts as an adhesive to evenly bond multilayer Ti3C2T x MXene wrapped with molybdenum disulfide, multilayer Ti3C2T x The graphene oxide between the MXene layers releases gas during the thermal reduction process, which converts the multilayer Ti3C2T x The MXene flakes are further peeled off, increasing the interlayer spacing and improving the ion diffusion rate. The interconnected graphene oxide forms a good conductive path after high-temperature reduction, which increases the conductivity of the material. In turn, the internal multilayer Ti3C2T x MXene and molybdenum disulfide support graphene oxide, preventing the restacking of graphene oxide and increasing the specific surface area. Graphene oxide acts as both an adhesive and an intercalation agent, effectively increasing the number of multilayer Ti3C2T x The interlayer spacing of MXene; in addition, the graphene oxide that wraps and connects the other two together can provide flexible support for the material, so that the film material has a larger adsorption capacity and a shorter desorption time, and also reduces the impact of the volume change of molybdenum disulfide during the cycle on the cycle performance;

[0029] Third, multilayer Ti3C2T x MXene is accordion-shaped and has the characteristics of large spacing, which provides a fast ion transmission channel for the electrode and improves the adsorption rate. Its surface electronegativity can provide additional adsorption capacity for the electrode when used as a negative electrode. The preparation method provided by the present invention has simple steps, is easy to operate, and has good application prospects.

[0030] The present invention also provides a self-supporting composite film obtained by the preparation method described in the above scheme, with a thickness of 12 to 16 μm. The self-supporting composite film provided by the present invention has extremely high adsorption specific capacity and maximum adsorption rate, has a shorter desorption time, and has good cycle stability and electrochemical performance, and has good flexibility, toughness and conductivity.

[0031] The present invention also provides an application of the self-supporting composite film described in the above solution as an electrode material. The self-supporting composite film prepared by the present invention is particularly suitable for the field of capacitive deionization technology, and is an ideal electrode material, having great application prospects in devices such as supercapacitors, lithium-ion batteries, and sodium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0033] Figure 1 SEM images of multilayer Ti3C2T x MXene (A) and molybdenum disulfide (B) prepared in Example 1 of the present invention;

[0034] Figure 2 SEM image of the self-supporting composite film prepared in Example 1 of the present invention;

[0035] Figure 3 Capacitive deionization adsorption capacity diagram of the self-supporting composite film prepared in Example 1 of the present invention under different voltages;

[0036] Figure 4 Capacitive deionization adsorption rate diagram of the self-supporting composite film prepared in Example 1 of the present invention under different voltages;

[0037] Figure 5 Capacitive deionization adsorption capacity comparison diagram of the self-supporting composite films prepared in Examples 1, 2, and 3 of the present invention and the graphene oxide self-supporting film prepared in Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The present invention provides a method for preparing a self-supporting composite film, comprising the following steps:

[0039] (1) Mix graphene oxide, molybdenum disulfide, multilayer Ti3C2T x MXene and water to obtain a molybdenum disulfide / multilayer Ti3C2T x MXene / graphene oxide dispersion;

[0040] (2) Filter the molybdenum disulfide / multilayer Ti3C2T x MXene / graphene oxide dispersion by suction filtration to form a wet film;

[0041] Pre-cool, freeze-dry, and thermally reduce the wet film to obtain a self-supporting composite film.

[0042] The present invention mixes graphene oxide, molybdenum disulfide, multi-layer Ti3C2T x MXene with water to obtain a molybdenum disulfide / multi-layer Ti3C2T x MXene / graphene oxide dispersion. In the present invention, the preparation method of the multi-layer Ti3C2T x MXene preferably includes the following steps: etching a Ti3AlC2 powder with a hydrofluoric acid solution and then centrifuging, and then washing the obtained reaction solution until the pH = 6-7, collecting the precipitate and drying it to obtain the multi-layer Ti3C2T x MXene. In the present invention, the mixing of the Ti3AlC2 powder and the hydrofluoric acid solution is preferably: slowly adding the Ti3AlC2 powder to the hydrofluoric acid solution and continuously stirring; the volume percentage of the hydrofluoric acid solution is preferably 10-40%, more preferably 10-20%; the mass ratio of the Ti3AlC2 powder to the hydrofluoric acid solution is preferably 1:50-70, more preferably 1:60; the etching reaction is preferably carried out under stirring conditions; the temperature of the etching reaction is preferably room temperature, the reaction time is preferably 12-48 h, more preferably 24-36 h; the cleaning reagent is preferably deionized water; the drying is preferably vacuum drying, the temperature of the vacuum drying is preferably 60-80 °C, more preferably 65-75 °C, and the heat preservation time is preferably 12-24 h, more preferably 15-20 h; the graphene oxide is preferably prepared by a modified Hummers method.

[0043] In the present invention, the preparation method of molybdenum disulfide preferably comprises the following steps: performing hydrothermal reaction on a molybdenum source, water and a sulfur source, collecting the precipitate, centrifuging, washing and drying the obtained precipitate in sequence to obtain molybdenum disulfide; the molybdenum source is preferably ammonium molybdate; the ammonium molybdate is preferably ammonium molybdate tetrahydrate; the sulfur source is preferably thiourea; the water is preferably deionized water; the molar ratio of sulfur in the sulfur source to molybdenum in the molybdenum source is preferably 1:1 to 8, more preferably 1:6 to 8; the concentration of molybdenum atoms in the mixed solution obtained by mixing the molybdenum source, water and sulfur source is preferably 0.02 to 0.1 mol / L, more preferably 0.04 to 0.05 mol / L; the mixing of the molybdenum source, water and sulfur source is preferably as follows: adding the sulfur source into deionized water for first magnetic stirring, then adding the molybdenum source for second magnetic stirring, transferring to a hydrothermal reaction kettle after complete dissolution, and placing it in a blast drying oven; the time of the first magnetic stirring is preferably 10 to 15 min, more preferably 12 to 14 min; the time of the second magnetic stirring is preferably 20 to 30 min, more preferably 24 to 27 min; the temperature of the hydrothermal reaction is preferably 180 to 220 °C, more preferably 190 to 210 °C, and the heat preservation time is preferably 12 to 24 h, more preferably 18 to 22 h; the washing is preferably: centrifuging the product liquid and washing it alternately with deionized water and ethanol; the number of centrifugation is preferably 3 to 9 times, more preferably 6 to 9 times; the number of washing is preferably the same as that of centrifugation; the drying is preferably vacuum drying, the temperature of the vacuum drying is preferably 60 to 80 °C, more preferably 65 to 75 °C, and the heat preservation time is preferably 12 to 24 h, more preferably 16 to 20 h. The molybdenum disulfide prepared by the above method is molybdenum disulfide with lattice defects, and the lattice defects can improve the ion capture ability of molybdenum disulfide and increase its electrochemical activity.

[0044] In the present invention, the molybdenum disulfide / multi-layer Ti3C2T x The concentration of graphene oxide in the graphene oxide / multi-layer Ti3C2T x MXene / graphene oxide dispersion is preferably 0.1 to 0.5 mg / mL, more preferably 0.1 to 0.2 mg / mL; the mass ratio of graphene oxide to multi-layer Ti3C2T x MXene is preferably 1:1 to 4, more preferably 1:2 to 3; the mass ratio of multi-layer Ti3C2T x MXene to molybdenum disulfide is preferably 1 to 16:4, more preferably 3 to 12:4, and further preferably 5 to 9:4. In a specific embodiment of the present invention, the volume of the molybdenum disulfide / multi-layer Ti3C2T x MXene / graphene oxide dispersion is preferably 50 to 100 mL, more preferably 50 to 60 mL.

[0045] In the present invention, the graphene oxide, molybdenum disulfide, multi-layer Ti3C2Tx The mixing of MXene and water is preferably as follows: graphene oxide is added to deionized water and then subjected to a first ultrasonic treatment to obtain a graphene oxide dispersion; molybdenum disulfide is added to the graphene oxide dispersion and then subjected to a second ultrasonic treatment to obtain a molybdenum disulfide / graphene oxide dispersion; multi-layer Ti3C2T x MXene is added to the molybdenum disulfide / graphene oxide dispersion, and after introducing a protective gas for 30 min, a third ultrasonic treatment is carried out to obtain a molybdenum disulfide / Ti3C2T x MXene / graphene oxide dispersion; the frequency of the first ultrasonic treatment is preferably 30 - 50 kHz, more preferably 45 - 50 kHz, and the ultrasonic time is preferably 1 - 2 h, more preferably 1 - 1.5 h; the frequency of the second ultrasonic treatment is preferably 30 - 50 kHz, more preferably 45 - 50 kHz, and the ultrasonic time is preferably 1 - 2 h, more preferably 1 - 1.5 h; the frequency of the third ultrasonic treatment is preferably 30 - 50 kHz, more preferably 45 - 50 kHz, and the ultrasonic time is preferably 1 - 2 h, more preferably 1 - 1.5 h; the protective gas is preferably argon.

[0046] To obtain a molybdenum disulfide / multi-layer Ti3C2T x MXene / graphene oxide dispersion, in the present invention, the molybdenum disulfide / multi-layer Ti3C2T x MXene / graphene oxide dispersion is filtered by suction to form a wet film; the wet film is sequentially pre-cooled, freeze-dried, and thermally reduced to obtain a self-supporting composite film. In the present invention, the suction filtration is preferably vacuum suction filtration, the filter membrane used for the vacuum suction filtration is preferably a mixed cellulose ester filter membrane, the pore size of the mixed cellulose ester filter membrane is preferably 0.22 μm, and the diameter is preferably 40 mm; the temperature of the pre-cooling is preferably -18 to -24 °C, more preferably -19 to -22 °C, further preferably -20 to -21 °C, and the heat preservation time is preferably 2 - 4 h, more preferably 3 h; the temperature of the freeze-drying is preferably -40 to -53 °C, more preferably -45 to -50 °C, and the heat preservation time is preferably 12 - 24 h, more preferably 15 - 20 h; the equipment for the freeze-drying is preferably a freeze-dryer; after the freeze-drying is completed, the obtained film is preferably separated from the filter membrane used for the suction filtration; the thermal reduction is preferably annealing treatment of the product obtained by freeze-drying in a tube furnace by programmed heating; the programmed heating preferably rises from room temperature to the temperature of the thermal reduction, keeps warm for a period of time and then cools to room temperature; the temperature of the thermal reduction is preferably 300 - 350 °C, more preferably 310 - 340 °C, further preferably 320 - 330 °C, the heat preservation time is preferably 2 - 3 h, more preferably 2.5 h, and the heating rate from room temperature to the temperature of the thermal reduction is preferably 2 - 5 °C / min, more preferably 4 - 5 °C / min; the thermal reduction is preferably carried out in a nitrogen atmosphere.

[0047] The present invention also provides a self-supporting composite film obtained by the preparation method described in the above solution, including multiple layers of Ti3C2T x MXene and molybdenum disulfide and reduced graphene oxide distributed between and on the surface of the multiple layers of Ti3C2T x MXene. In the present invention, the thickness of the self-supporting composite film is preferably 12-16 μm, more preferably 12-13 μm, and further preferably 12 μm.

[0048] The present invention also provides an application of the self-supporting composite film described in the above solution as an electrode material.

[0049] In the present invention, the application preferably includes the following steps: cutting the self-supporting composite film into a required shape, and then directly using it as a negative electrode material.

[0050] To further illustrate the present invention, the solutions of the present invention will be described in detail below with reference to the drawings and embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0051] Example 1

[0052] Preparation of molybdenum disulfide: Add 0.2207 g of ammonium molybdate tetrahydrate to 25 mL of deionized water, stir magnetically until fully dissolved, then add 0.7612 g of thiourea, continue to stir magnetically until the drugs are fully dissolved, transfer the solution to a 50 mL hydrothermal reaction kettle with a polytetrafluoroethylene inner lining, and then place the reaction kettle in a forced air drying oven and react at 200 °C for 24 h. After the reaction ends and the reaction kettle cools to room temperature, wash the reaction precipitate with deionized water and ethanol by centrifugation repeatedly 3 times, and finally place it in a vacuum drying oven and dry it at 60 °C under vacuum for 24 h to obtain molybdenum disulfide powder with lattice defects;

[0053] Preparation of multiple layers of Ti3C2T x MXene: Slowly add 2 g of Ti3AlC2 powder to 120 mL of a 10% by volume hydrofluoric acid solution and stir continuously, then stir magnetically for 24 h. Wash the reaction precipitate with deionized water by centrifugation repeatedly for many times until the pH of the suspension is close to 6, centrifuge to collect the precipitate, and place it in a vacuum oven and dry it at 60 °C under vacuum for 24 h to obtain multiple layers of Ti3C2T x MXene powder;

[0054] Preparation of a self-supporting composite film with lattice defects: Add 10 mg of molybdenum disulfide to 50 mL of a graphene oxide dispersion solution with a concentration of 1 mg / mL, and introduce argon as a protective gas, control the water temperature below 30 °C, ultrasonically disperse for 1 h, and then add 5 mg of multiple layers of Ti3C2T xMXene powder, continue to introduce argon protective gas, continue to control the water temperature below 30 °C, after ultrasonic dispersion for 1 h, use a mixed cellulose ester filter membrane with a pore diameter of 0.22 μm and a diameter of 40 mm, and filter it into a film by vacuum-assisted suction filtration. Dry the film using freeze-drying technology, then separate the film from the filter membrane, put the film into a tubular furnace and introduce nitrogen protective gas, and control the programmed heating as follows: heat from room temperature to 350 °C, with a heating rate of 5 °C / min, hold for 2 h, and then cool to room temperature to obtain a self-supporting composite film with lattice defects (lattice defects of molybdenum disulfide), denoted as dr-MoS2 / Ti3C2T x MXene / rGO-10-5-5.

[0055] Example 2

[0056] Adjust the dosage of molybdenum disulfide in Example 1 to 5 mg, and the dosage of multi-layer Ti3C2T x The dosage of MXene is adjusted to 10 mg, and the remaining steps are the same as in Example 1 to obtain a self-supporting composite film with lattice defects, denoted as dr-MoS2 / Ti3C2T x MXene / rGO-5-10-5.

[0057] Example 3

[0058] Adjust the dosage of molybdenum disulfide in Example 1 to 7.5 mg, and the dosage of multi-layer Ti3C2T x The dosage of MXene is adjusted to 7.5 mg, and the remaining steps are the same as in Example 1 to obtain a self-supporting composite film with lattice defects, denoted as dr-MoS2 / Ti3C2T x MXene / rGO-7.5-7.5-5.

[0059] Comparative Example 1

[0060] As a control experiment, without adding molybdenum disulfide and multi-layer Ti3C2T x The dosage of MXene and graphene oxide is adjusted to 20 mg, and the remaining steps are the same as in Example 1 to obtain a graphene oxide self-supporting film, denoted as rGO.

[0061] Use a scanning electron microscope to observe the structural morphology of the multi-layer Ti3C2T x MXene and molybdenum disulfide prepared in Example 1 of the present invention. The results are as follows Figure 1 shown, where Figure 1 Figure A in it is the SEM image of the multi-layer Ti3C2T x MXene prepared in Example 1 of the present invention, Figure 1 Figure B in it is the SEM image of molybdenum disulfide prepared in Example 1 of the present invention. According to Figure 1As shown in Figure A, the original Ti3C2T x MXene has smaller interlayers and thicker layers, which are all due to Ti3C2T x The result of MXene restacking; according to Figure 1 As shown in Figure B, during the growth process of MoS2 synthesized by the hydrothermal method, under the action of electrostatic force, MoS2 nanosheets grow in an interlaced manner and self-assemble to form MoS2 nanoflowers, which causes a large number of MoS2 nanosheets to stack together, reducing their effective surface area and active sites, resulting in a sharp drop in the adsorption performance of MoS2.

[0062] The morphology of the self-supporting composite film prepared in Example 1 of the present invention was observed using a scanning electron microscope. Figure 2 As shown, Figure 2 Figures A and B in the figure are SEM images of different parts of the self-supporting composite film prepared in Example 1 of the present invention. Figure 2 It can be seen that MoS2 enters the multilayer Ti3C2T during the mixing process. x In the MXene layer, multilayer Ti3C2T x The MXene sheets have a certain pillaring effect, and the evenly dispersed molybdenum disulfide is wrapped by graphene oxide; multilayer Ti3C2T x The MXene sheets are peeled off, effectively adding multiple layers of Ti3C2T x The interlayer spacing of MXene; the interconnected graphene oxide forms a good conductive path after high-temperature carbonization, and the internal multilayer Ti3C2T x MXene and molybdenum disulfide support graphene oxide, preventing the restacking of graphene oxide and increasing the specific surface area; the accordion-shaped multilayer Ti3C2T x MXene has the characteristic of large spacing, and the resulting self-supporting composite film has an extremely high adsorption specific capacity.

[0063] The self-supporting composite films prepared in Examples 1 to 3 of the present invention and the graphene oxide self-supporting film prepared in Comparative Example 1 were used as self-supporting electrode materials, and the capacitive deionization adsorption and desorption performance of the films was tested. The adsorption and desorption test was performed in a constant voltage mode. The self-supporting composite film was used as the negative electrode. The preparation steps of the positive electrode were as follows: activated carbon, super C and polyvinylidene fluoride were added to N-methyl-2-pyrrolidone in a mass ratio of 7:1:2, and magnetic stirring was performed for 24 hours to form a uniform black slurry, and then the obtained black slurry was scraped on graphite paper, and finally placed in a vacuum oven at 80°C for vacuum drying for 24 hours to obtain a positive electrode, which was recorded as AC;

[0064] Before the test, deionized water was continuously circulated through the assembled capacitive deionization test module using a peristaltic pump, and the positive and negative electrodes were short-circuited with wires for film washing treatment. After 7 hours of film washing, constant voltage capacitive deionization adsorption and desorption tests were carried out;

[0065] The process parameters of the capacitive deionization test are as follows: the test voltages are 0.8V, 1.0V, and 1.2V in sequence, and the test salt solution used is 40 mL of NaCl solution with an initial conductivity of 1000 μS cm -1 The results are as Figures 3 to 5 shown, where Figure 3 is the capacitive deionization adsorption capacity diagram of the self-supporting composite film prepared in Example 1 of the present invention at different voltages, Figure 4 is the capacitive deionization adsorption rate diagram of the self-supporting composite film prepared in Example 1 of the present invention at different voltages, Figure 5 is the comparative diagram of the capacitive deionization adsorption capacity of the self-supporting composite film prepared in Examples 1-3 of the present invention and the graphene oxide self-supporting film prepared in Comparative Example 1.

[0066] According to Figure 3 it can be seen that the highly electrochemically active molybdenum disulfide uniformly dispersed in the self-supporting composite film electrode prepared in Example 1 of the present invention provides a larger adsorption specific capacity, and the adsorption specific capacity increases with the increase of voltage. The optimal adsorption specific capacity is exhibited at a test voltage of 1.2V, and the adsorption specific capacity is higher than 50 mg / g; moreover, the self-supporting composite film electrode prepared in Example 1 of the present invention has a larger average adsorption rate while maintaining a high adsorption amount.

[0067] According to Figure 4 it can be seen that the self-supporting composite film electrode prepared in Example 1 of the present invention exhibits a great average adsorption rate. When the adsorption specific capacity is 10 mg / g, the average adsorption rate of the self-supporting composite film electrode is greater than 10 mg g - 1 min -1 and the maximum adsorption rate can reach 10.8 mg g -1 min -1 This is due to the large interlayer spacing of the accordion-like multi-layer Ti3C2T x MXene, which provides a fast ion transport channel, while the reduced graphene oxide that wraps and connects the other two together provides flexible support and an electron transport path for the electrode, increasing the conductivity and self-supporting performance of the electrode.

[0068] According to Figure 5It can be seen that, compared with the pure reduced graphene oxide thin film electrode prepared in Comparative Example 1, at a voltage of 1.2 V, the self-supporting composite thin film electrodes prepared in Examples 1 to 3 of the present invention all exhibit extremely high adsorption specific capacities. Among them, the adsorption specific capacity of the self-supporting composite thin film electrode in Example 1 can reach 51.1 mg / g.

[0069] As can be seen from the above examples, the self-supporting composite thin film provided by the present invention has extremely high adsorption specific capacity and extremely high adsorption rate. At a voltage of 1.2 V, the maximum adsorption specific capacity can reach 51.1 mg / g, and the maximum adsorption rate can reach 10.8 mg -1 min -1 , while the cycle stability and electrochemical performance are good, and it has good flexibility, toughness and conductivity.

[0070] Although the above embodiments have made a detailed description of the present invention, they are only a part of the embodiments of the present invention, rather than all embodiments. Other embodiments can also be obtained according to these embodiments without creative work, and these embodiments all belong to the protection scope of the present invention.

Claims

1. A method for preparing a self-supporting composite film, characterized in that, It includes the following steps: (1) Mix graphene oxide, molybdenum disulfide, multi-layer Ti3C2T x MXene and water to obtain a molybdenum disulfide / multi-layer Ti3C2T x MXene / graphene oxide dispersion; (2) Filter the molybdenum disulfide / multi-layer Ti3C2T x MXene / graphene oxide dispersion to form a wet film; Successively pre-cool, freeze-dry and thermally reduce the wet film to obtain a self-supporting composite film; The temperature of the freeze-drying is -40 to -53 °C, and the heat preservation time is 12 to 24 h.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the graphene oxide to the molybdenum disulfide is 1 to 16:4; The multi-layer Ti3C2T x The mass ratio of MXene to molybdenum disulfide is 1 to 16:4; The mass ratio of the graphene oxide to the water is 0.1 to 0.4:

1.

3. The preparation method according to claim 1, characterized in that, The temperature of the thermal reduction is 300 to 350 °C, the heating rate is 2 to 5 °C / min, and the heat preservation time is 2 to 3 h.

4. The preparation method according to claim 1, characterized in that, The temperature of the pre-cooling is -18 to -24 °C, and the heat preservation time is 2 to 4 h.

5. The preparation method according to claim 1 or 2, characterized in that, The preparation method of the molybdenum disulfide includes the following steps: performing a hydrothermal reaction on a molybdenum source, water and a sulfur source, collecting the precipitate, and successively centrifuging, washing and drying the obtained precipitate to obtain molybdenum disulfide.

6. The preparation method according to claim 5, characterized in that The sulfur source is thiourea, and the molybdenum source is ammonium molybdate.

7. The preparation method according to claim 5, characterized in that, The temperature of the hydrothermal reaction is 180 to 200 °C, and the heat preservation time is 12 to 24 h.

8. The preparation method according to claim 1, characterized in that, The multi-layer Ti3C2T x The preparation method of MXene comprises the following steps: performing an etching reaction on Ti3AlC2 powder and hydrofluoric acid solution, centrifuging, then washing the obtained reaction solution until the pH = 6-7, collecting the precipitate and drying it to obtain multi-layer Ti3C2T x MXene.

9. The self-supporting composite film obtained by the preparation method according to any one of claims 1 to 8, comprising multiple layers of Ti3C2T x MXene and molybdenum disulfide and reduced graphene oxide distributed between and on the surfaces of the multiple layers of Ti3C2T x MXene.

10. Application of the self-supporting composite film according to claim 9 as an electrode material.

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