Preparation method of MXene-rGO aerogel and floating type hydrogen production system and method

Abstract

The invention discloses a preparation method of MXene-rGO aerogel and a floating type hydrogen production system and method.The preparation method comprises the steps that MXene dispersion liquid and rGO dispersion liquid are mixed and then added into a glucose solution for ultrasonic treatment, then a three-dimensional porous structure is assembled through glucose on the basis of a hydrothermal method, finally thermal reduction treatment is completed in the nitrogen atmosphere, and the MXene-rGO aerogel is obtained; the MXene-rGO aerogel can float on the liquid level of formic acid, expands the light absorption range of solar energy and converts the solar energy into heat energy under the condition of sunlight irradiation, and meanwhile, after the active site MXene adsorbs formic acid, the formic acid hydrogen production catalytic reaction is completed. The three-dimensional structure of the aerogel has a wide light absorption range, and light loss can be avoided; the aerogel floats in formic acid, so that photo-thermal conversion occurs on the upper surface of the aerogel rather than in a solution, and heat consumption of the solution is greatly reduced. In addition, due to the floating state, contact with excessive solution is reduced, and rapid photo-thermal conversion can also be achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen production, and in particular relates to a preparation method of a MXene-rGO aerogel and a floating hydrogen production system and method. Background Art

[0002] Formic acid can release hydrogen at low temperatures through the action of catalysts. At present, the technology for producing hydrogen from formic acid generally adopts heat drive and uses stirring to accelerate the mass transfer rate, resulting in a certain amount of energy consumption. At the same time, this complex operation mode also limits its path for large-scale application. In comparison, solar energy-driven formic acid hydrogen production is expected to solve the energy consumption problem and reduce costs. However, the current research technology is concentrated in the field of photocatalysis, and photothermal catalysis is rarely studied. The absorption range of solar energy by photocatalysis is limited. Although the absorption range of solar energy by photothermal catalysis is wide, the heat is easily dissipated, which reduces the output of hydrogen production. The activation of the catalyst is also closely related to the temperature, and the slow photothermal conversion will also reduce the catalytic activity. In addition, the accelerated mass transfer of formic acid and the recovery of the catalyst require additional energy consumption, which increases the application cost. Therefore, there is an urgent need for a new catalytic material and method to improve the performance of photothermal hydrogen production. Summary of the invention

[0003] In order to overcome the shortcomings of the above-mentioned prior art, the object of the present invention is to provide a method for preparing MXene-rGO aerogel and a floating hydrogen production system and method to solve the problems of insufficient light absorption and slow photothermal conversion in solar hydrogen production.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] In a first aspect of the present invention, a method for preparing a MXene-rGO aerogel is provided, comprising the following steps:

[0006] Step 1, after mixing the MXene dispersion and the rGO dispersion, adding the glucose solution, and ultrasonically treating to obtain a uniformly mixed dispersion;

[0007] Step 2: Based on the hydrothermal method, glucose is used to assemble into a three-dimensional porous structure, and then a thermal reduction treatment is completed under a nitrogen atmosphere to obtain MXene-rGO aerogel.

[0008] In one embodiment, after the MXene dispersion and the rGO dispersion are mixed, the mass ratio of MXene to rGO is 0.2-0.25, and the mass ratio of rGO to water is 1-2; in the uniformly mixed dispersion, the mass ratio of glucose to rGO is 100-200. In addition, the present invention can adjust the mass of MXene according to the volume of the synthesized MXene-rGO aerogel. Generally speaking, the more MXene is used, the larger the volume of the MXene-rGO aerogel.

[0009] In one embodiment, the hydrothermal method is carried out under the conditions of 120°C-140°C for 20-24 hours; and the thermal reduction treatment is carried out under the conditions of 50°C-100°C for 4-6 hours.

[0010] According to a second aspect of the present invention, a floating hydrogen production system is provided, comprising a sealed optically transparent glass reactor, wherein formic acid is contained in the optically transparent glass reactor, and the MXene-rGO aerogel obtained by the preparation method of the MXene-rGO aerogel according to the first aspect is placed in the formic acid. The MXene-rGO aerogel has a smaller density and can automatically float on the formic acid liquid surface.

[0011] In one embodiment, the total cross-sectional area of ​​the MXene-rGO aerogel floating on the formic acid liquid surface is the same as the light-receiving area of ​​the optically transparent glass reactor. In this case, light energy can be better utilized to improve hydrogen production efficiency.

[0012] In one embodiment, the mass ratio of the MXene-rGO aerogel to formic acid is 1-2.

[0013] In one embodiment, after formic acid is placed in the optically transparent glass reactor, there is still space, which is a temporary storage space for the prepared hydrogen. The space has an air inlet and an air outlet, the air inlet is connected to a nitrogen bottle, and the air outlet is connected to a hydrogen gas collection bag. The hydrogen gas collection bag has a sampling port, and the sampling port is connected to a gas chromatograph. The nitrogen bottle can pass nitrogen into the space, which serves to exhaust the air in the space. The hydrogen gas collection bag is used to collect the prepared hydrogen, and the gas chromatograph detects the sampled gas. When no oxygen is detected, that is, after confirming that the air has been exhausted from the above-mentioned space, the reaction is started to collect hydrogen.

[0014] The third aspect of the present invention provides a floating hydrogen production method, which is implemented based on the floating hydrogen production system described in the second aspect. The optically transparent glass reactor is placed in a sunlight irradiation environment. Under sunlight irradiation conditions, the MXene-rGO aerogel can expand the light absorption range of solar energy and convert solar energy into thermal energy. At the same time, the active site MXene adsorbs formic acid to complete the formic acid hydrogen production catalytic reaction.

[0015] In one embodiment, the air inlet and the air outlet are opened before the reaction, and nitrogen is introduced into the space above the formic acid in the optically transparent glass reactor through a nitrogen bottle to prevent the original gas in the reactor from affecting the detection of the reaction. The gas composition in the hydrogen gas collection bag is detected by a gas chromatograph until no oxygen is detected. The nitrogen is stopped, the air inlet is closed, and the air outlet is kept open. The optically transparent glass reactor is placed in a sunlight environment to collect hydrogen.

[0016] In one embodiment, the MXene-rGO aerogel has a continuous photothermal effect and hydrogen production performance, and the hydrogen production rate remains stable in multiple repeated experiments. In addition, after the reaction is completed, the MXene-rGO aerogel is fished out of the formic acid and directly dried at 60°C ± 5°C in a nitrogen atmosphere without filtering or other means, and the MXene-rGO aerogel is quickly and efficiently recovered, and the recovered MXene-rGO aerogel can be directly reused.

[0017] Compared with the traditional formic acid hydrogen production system, which directly puts the catalyst into the reaction solution and relies on continuous heating and stirring to increase the catalytic rate, the floating hydrogen production system based on MXene-rGO aerogel in the present invention uses solar energy to drive, replacing the energy-consuming heat source. Since the three-dimensional structure of the aerogel has a wide light absorption range, it can avoid light loss. More importantly, the specific gravity of the MXene-rGO aerogel allows it to float in formic acid, so that the photothermal conversion occurs on the upper surface of the aerogel instead of in the solution, greatly reducing the solution's heat consumption. In addition, the floating state reduces contact with excess solution and can also achieve rapid photothermal conversion.

[0018] Furthermore, the present invention saves the step of catalyst recovery by loading the catalyst on aerogel, thereby reducing subsequent costs. The stable loading of the catalyst can improve the stability of the catalyst, reduce the loss during recovery, and improve the utilization efficiency of the catalyst.

[0019] In general, the problems of high energy consumption, high cost, high pollution, low catalyst hydrogen production efficiency, and inability to achieve solar thermal drive in traditional systems can all be overcome by the present invention. The present invention has good catalytic effect, improves the utilization efficiency of the catalyst, reduces the application cost of formic acid hydrogen production, and reduces energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a scanning electron micrograph of rGO aerogel.

[0021] Figure 2 is a scanning electron microscope image of the MXene-rGO aerogel of the present invention.

[0022] Figure 3 This is the real object and self-floating picture of MXene-rGO aerogel

[0023] Figure 4 This is the temperature change diagram of MXene-rGO aerogel and traditional input reaction solution system

[0024] Figure 5 It is a schematic diagram of the floating hydrogen production system of the present invention.

[0025] Figure 6It is a schematic diagram of an implementation mode of the floating hydrogen production system of the present invention.

[0026] Figure 7 It is a schematic diagram showing the change of hydrogen production amount over time in the floating hydrogen production method of the present invention. DETAILED DESCRIPTION

[0027] The embodiments of the present invention are described in detail below with reference to the accompanying drawings and examples.

[0028] The present invention first provides a method for preparing a MXene-rGO aerogel. The MXene-rGO aerogel is prepared by the following steps, that is, a catalyst (MXene) is loaded on the aerogel.

[0029] Step 1: Place MXene in deionized water and perform ultrasonic dispersion to obtain a MXene dispersion.

[0030] Step 2, placing rGO into deionized water and performing ultrasonic dispersion to obtain an rGO dispersion.

[0031] Step 3, mixing the MXene dispersion with the rGO dispersion, wherein the mass ratio of MXene to rGO is 0.2-0.25, and the mass ratio of rGO to total deionized water is 1-2.

[0032] Step 4, adding glucose solution to the mixed solution obtained in step 3 and ultrasonically treating it to obtain a uniformly mixed dispersion, wherein the mass ratio of glucose to rGO is 100-200.

[0033] Step 5: Place the uniformly mixed dispersion obtained in step 4 in a reactor for hydrothermal reaction. The recommended hydrothermal conditions are 120° C.-140° C. for 20-24 hours. During the reaction, glucose is used to assemble into a three-dimensional porous structure.

[0034] Step 6, the product obtained in step 5 is subjected to thermal reduction treatment under a nitrogen atmosphere, the recommended conditions are 50°C-100°C, and the time is 4-6h, to obtain the product MXene-rGO aerogel, wherein the amount of MXene and rGO can be adjusted to adjust the volume of the MXene-rGO aerogel, and the larger the volume of the MXene-rGO aerogel, the more MXene and rGO are required. In addition, the MXene-rGO aerogel can be prepared in a controllable volume according to the size of the hydrothermal reactor, and has a broader application value in the hydrogen production system of the present invention.

[0035] In a specific embodiment of the present invention, 5 mg MXene and 20 mg rGO are added to 30 mL water, the dispersion is sonicated for 30 min by ultrasonic method, then 3 g glucose is added and sonicated for 30 min, the dispersion after sonication is added to a reactor, heated at 120 ° C for 20 h by hydrothermal method, and finally reduced in a nitrogen atmosphere at 60 ° C for 5 h to obtain MXene-rGO aerogel.

[0036] Electron microscope image reference of aerogel Figure 1 As shown, the electron microscope image of the MXene-rGO aerogel obtained in this embodiment is shown in FIG. Figure 2 As shown, it can be seen that MXene-rGO aerogel has a porous structure, exhibits a highly connected microporous structure, and has many folds inside, further increasing the surface area.

[0037] The MXene-rGO aerogel obtained in this example is as follows Figure 3 As shown, it can be seen that it has a completely black surface, which is conducive to absorbing sunlight. According to calculations, its density range is about 3-5g / cm 2 When placed in formic acid solution, it can be seen that it has self-floating properties and can automatically float on the liquid surface.

[0038] The MXene-rGO aerogel has excellent light-to-heat conversion properties. After being placed in a formic acid solution, it floats on the liquid surface, and its temperature change characteristics are as follows: Figure 4 As shown, it can be seen that the photothermal conversion of MXene-rGO aerogel is faster and has better photothermal capacity. The photothermal conversion performance of MXene-rGO aerogel is significantly better than that of the traditional system where the catalyst is directly added to the reaction solution.

[0039] Based on the above properties, the present invention further uses the MXene-rGO aerogel for hydrogen production and obtains a floating hydrogen production system, such as Figure 5As shown, it includes a closed optically transparent glass reactor 1, in which formic acid 2 is contained, and the MXene-rGO aerogel 3 of the present invention is put into the formic acid 2. Since the density of the MXene-rGO aerogel 3 is relatively small, it can automatically float on the liquid surface of the formic acid 2, that is, it constitutes the main floating hydrogen production system. For example, the mass ratio of the MXene-rGO aerogel 3 and the formic acid 2 is 1-2, and it is preferable that the total cross-sectional area of ​​the floating MXene-rGO aerogel 3 is the same as the light receiving area of ​​the optically transparent glass reactor 1. The MXene-rGO aerogel 3 can only cover a part of the liquid surface, and adjust the light route or adjust the position of the optically transparent glass reactor 1 so that the light area is exactly equal to the surface area of ​​the entire MXene-rGO aerogel 3. In the figure, for the experiment, a solar simulator 4 is used to simulate the real lighting environment. The solar simulator 4 irradiates downward from the top of the optically transparent glass reactor 1.

[0040] MXene-rGO aerogel 3 is the key to the rapid photothermal conversion and heat loss reduction of the present invention. It has a rapid photothermal conversion capability and can timely convert solar energy into thermal energy and decompose the absorbed formic acid in a timely manner. Specifically, when the sun shines, MXene-rGO aerogel 3 absorbs light energy and converts it into thermal energy, which is transferred to the internal catalyst active sites. While activating the activity, it also uses the porous structure to absorb formic acid 2 from the solution and then decomposes the formic acid 2.

[0041] In order to obtain pure hydrogen and collect it, the hydrogen production system also needs a gas purification and collection component. In the embodiment of the present invention, it is obvious that there is still space after the formic acid is placed in the optically transparent glass reactor, that is, there must be a certain amount of space between the top surface of the floating MXene-rGO aerogel and the top of the optically transparent glass reactor to accommodate hydrogen. Figure 6 As shown, the space has an air inlet 5 and an air outlet 6. The air inlet 5 is connected to a nitrogen bottle 7 through a gas pipeline, which is used to feed nitrogen into the space before starting the reaction to exhaust the air therein for subsequent reactions. The air outlet 6 is connected to a hydrogen gas collecting bag 8 through a gas pipeline. The hydrogen gas collecting bag 8 has a sampling port, which is connected to a gas chromatograph 9. The gas chromatograph 9 analyzes the gas composition in the hydrogen gas collecting bag 8 and displays the results on a display 10 connected thereto. The hydrogen gas collecting bag 8 and the gas chromatograph 9 facilitate the collection and detection of gas.

[0042] According to the hydrogen production method of the above-mentioned floating hydrogen production system, the optically transparent glass reactor 1 loaded with formic acid 2 and MXene-rGO aerogel 3 is directly placed in a sunlight irradiation environment so that the sunlight can irradiate the MXene-rGO aerogel 3 floating on the surface of the formic acid 2. Under the sunlight irradiation conditions, the MXene-rGO aerogel 3 can expand the light absorption range of solar energy and convert solar energy into thermal energy. At the same time, the active site MXene adsorbs formic acid to complete the formic acid hydrogen production catalytic reaction.

[0043] The further specific process can be described as follows:

[0044] Before the reaction, the optically transparent glass reactor 1 is protected from light, the air inlet 5 and the air outlet 6 are opened, and nitrogen is introduced into the space above the formic acid in the optically transparent glass reactor 1 through the nitrogen bottle 7 to prevent the original gas in the reactor from affecting the reaction detection.

[0045] During the process, the gas chromatograph 9 is used to continuously detect the gas composition in the hydrogen gas collecting bag 8 until no oxygen is detected, which means that the air in the above space is basically exhausted. The nitrogen flow is stopped, the air inlet 5 is closed, and the air outlet 6 is kept open.

[0046] Finally, the optically transparent glass reactor 1 is placed in a sunlight irradiation environment, and the MXene-rGO aerogel 3 receives sunlight, completes the photothermal conversion, and transfers the heat to the active site by heat conduction. At the same time, the MXene-rGO aerogel also uses its porous properties to pump the formic acid 2 in the solution to the active site, catalytically decomposes it in the closed reactor to generate hydrogen, and the generated hydrogen is collected in the hydrogen gas collection bag 8.

[0047] The MXene-rGO aerogel of the present invention has a sustained photothermal effect and hydrogen production performance. The hydrogen production rate remains stable in multiple repeated experiments. The light source intensity of the solar simulator is 1000W / m 2 For example, MXene-rGO aerogel 3 receives sunlight through a transparent glass window and converts it into heat energy. The heat then activates the active sites of MXene-rGO aerogel 3, catalyzing the decomposition of the adsorbed formic acid. In order to explore the effect of solar light intensity on the catalytic reaction, an optical power meter and a thermocouple were used to detect the light intensity and temperature, respectively. At the same time, the drainage method was used to record the gas generation rate and the gas chromatography was used to detect the product. It was found that hydrogen production remained stable during the 5 hydrogen production cycles, such as Figure 7 As shown, there is no need to take energy-consuming measures such as filtration during the circulation process, and the catalyst can be directly recovered in one step.

[0048] The specific recycling method is: after the reaction is completed, the MXene-rGO aerogel 3 is directly removed from the formic acid 2 and directly dried at 60°C±5°C under a nitrogen atmosphere. The MXene-rGO aerogel can be recycled quickly and efficiently without filtering or other means.

[0049] In summary, the present invention successfully prepared MXene-rGO aerogel, which has the characteristics of self-floating and excellent light-to-heat conversion effect in formic acid solution, thereby enhancing mass transfer, expanding solar energy absorption, and improving catalyst stability. At the same time, the three-dimensional structure reduces the loss of catalyst. It can be reused, and the recycling method is simple, which can save hydrogen production and production costs, and improve the formic acid hydrogen production performance and application benefits.

[0050] The floating hydrogen production system of the present invention takes the MXene-rGO aerogel as the core, has good light absorption, rapid photothermal conversion and hydrogen production effect, and abandons the shortcomings of the traditional system of directly adding the catalyst to the bulk solution and requiring continuous heating and stirring. In addition, the recovery of the catalyst after the reaction is completed no longer requires multiple steps such as filtration, which solves the problems of slow solar photothermal conversion, large heat loss, high energy consumption and cost, and reduces the steps of reuse.

[0051] The present invention can explore the hydrogen production efficiency under different working conditions by controlling variables, the system has fewer interference factors, and the entire floating hydrogen production system can operate repeatedly and smoothly.

Claims

1. A method for preparing MXene-rGO aerogel, characterized in that: The steps include: Step 1, after mixing the MXene dispersion and the rGO dispersion, adding the glucose solution, and ultrasonically treating to obtain a uniformly mixed dispersion; Step 2: Based on the hydrothermal method, glucose is used to assemble into a three-dimensional porous structure, and then a thermal reduction treatment is completed under a nitrogen atmosphere to obtain MXene-rGO aerogel.

2. The method for preparing the MXene-rGO aerogel according to claim 1, characterized in that: After the MXene dispersion and the rGO dispersion are mixed, the mass ratio of MXene to rGO is 0.2-0.25, and the mass ratio of rGO to water is 1-2; in the uniformly mixed dispersion, the mass ratio of glucose to rGO is 100-200.

3. The method for preparing the MXene-rGO aerogel according to claim 1, characterized in that: The hydrothermal method has the conditions of 120°C-140°C and the time of 20-24h; the thermal reduction treatment has the conditions of 50°C-100°C and the time of 4-6h.

4. A floating hydrogen production system, characterized in that: It comprises a sealed optically transparent glass reactor, wherein formic acid is contained in the optically transparent glass reactor, and the MXene-rGO aerogel obtained by the preparation method of the MXene-rGO aerogel according to any one of claims 1 to 3 is placed in the formic acid, and the MXene-rGO aerogel floats on the formic acid liquid surface.

5. The floating hydrogen production system according to claim 4, characterized in that: The total cross-sectional area of ​​the MXene-rGO aerogel floating on the formic acid liquid surface is the same as the light-receiving area of ​​the optically transparent glass reactor.

6. The floating hydrogen production system according to claim 4, characterized in that: The mass ratio of the MXene-rGO aerogel to formic acid is 1-2.

7. The floating hydrogen production system according to claim 4, characterized in that: After formic acid is placed in the optically transparent glass reactor, there is still space, and the space has an air inlet and an air outlet. The air inlet is connected to a nitrogen bottle, and the air outlet is connected to a hydrogen gas collecting bag. The hydrogen gas collecting bag has a sampling port, and the sampling port is connected to a gas chromatograph.

8. A floating hydrogen production method, implemented based on the floating hydrogen production system according to any one of claims 4 to 7, characterized in that: The optically transparent glass reactor is placed in a sunlight irradiation environment. Under the sunlight irradiation conditions, the MXene-rGO aerogel expands the light absorption range of solar energy and converts solar energy into thermal energy. At the same time, the active site MXene adsorbs formic acid and completes the formic acid hydrogen production catalytic reaction.

9. The floating hydrogen production method according to claim 8, characterized in that: Before the reaction, the air inlet and the air outlet are opened, and nitrogen is introduced into the space above the formic acid in the optically transparent glass reactor through a nitrogen bottle. The gas composition in the hydrogen gas collection bag is detected by a gas chromatograph. The nitrogen is stopped when no oxygen is detected, the air inlet is closed, and the air outlet is kept open. The optically transparent glass reactor is placed in a sunlight environment to collect hydrogen.

10. The floating hydrogen production method according to claim 8, characterized in that: After the reaction is completed, the MXene-rGO aerogel is fished out from the formic acid and directly dried at 60°C±5°C under a nitrogen atmosphere to complete the recovery of the MXene-rGO aerogel.

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