Two-dimensional composite confined MnO2.0.3H2O@MC film, preparation method thereof and application thereof in seawater lithium extraction

Abstract

The application belongs to the technical field of lithium recovery in seawater, and provides a two-dimensional composite confined MnO2·0.3H2O@MC film, a preparation method thereof and application of the film in lithium extraction from seawater, to solve the problems of existing lithium ion sieve in powder form, low recovery, low utilization rate and low adsorption rate. 1.33 Mn 1.67 O4; acid washing Li 1.33 Mn 1.67 O4 to obtain MnO2·0.3H2O; Ti, Al and TiC powders are mixed and calcined to synthesize MAX powders, and then LiF-HCl solution is added to prepare MXene; MnO2·0.3H2O is dispersed in deionized water, a cellulose solution is added, then MXene solution is added, and finally the film is obtained by suction filtration, which is MnO2·0.3H2O@MC film. Both the adsorption capacity and the problem of powder not easy to recover are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium recovery in seawater, and specifically relates to a two-dimensional composite confined MnO2·0.3H2O@MC membrane and its preparation method and application in lithium extraction from seawater. The MnO2·0.3H2O@MC membrane prepared by the present invention uses MnO2·0.3H2O as Li + The imprinted sites were prepared by selecting different substrate materials, and the obtained MnO2·0.3H2O@MC membrane had high utilization rate and excellent Li recovery performance. Background Art

[0002] Due to the wide application of lithium resources in ceramics, batteries, medicine and other fields, the market demand for lithium resources is growing rapidly. Many studies have focused on finding other potential sources of lithium, such as seawater, which is estimated to contain 2.5×10 14 kg lithium.

[0003] However, Li in seawater + The concentration is very low, about 0.17 mg / L -1 , while other cations such as Na + , Ca 2+ Mg 2+ and K + The concentration of spinel lithium manganese oxide ion sieve is relatively high due to its large adsorption capacity and selective capture of Li + Lithium ion sieves are considered promising green materials for extracting lithium from seawater due to their ability to be extracted. However, powdered lithium ion sieves are difficult to handle and difficult to recycle due to their high loss during continuous recovery processes. Currently, lithium ion sieves are not economically or environmentally suitable for lithium recovery applications in seawater. Summary of the Invention

[0004] In order to solve the problems of existing lithium ion sieves being in powder form, difficult to recycle, low utilization rate and low adsorption rate, the present invention provides a two-dimensional composite confined MnO2·0.3H2O@MC membrane and its preparation method and application in lithium extraction from seawater.

[0005] The present invention is achieved by the following technical solutions: a method for preparing a two-dimensional composite confined MnO2·0.3H2O@MC film, wherein MnCO3 and Li2CO3 are mixed at a lithium / manganese molar ratio of 1.33 / 1.67 and then heat-treated to prepare Li 1.33 Mn 1.67 O4; then pickled Li 1.33 Mn 1.67O4 was used to obtain MnO2·0.3H2O; Ti, Al and TiC powders were mixed and calcined in a molar ratio of Ti:Al:C=3.0:1.2:1.8 to synthesize MAX powder, which was then added to a LiF–HCl solution to prepare MXene; MnO2·0.3H2O was dispersed in deionized water, cellulose solution was added, and then MXene solution was added, and finally the membrane was filtered to form the MnO2·0.3H2O@MC membrane.

[0006] The specific steps are as follows:

[0007] (1) Preparation of Li 1.33 Mn 1.67 O4: MnCO3 and Li2CO3 were uniformly mixed and ground in proportion for 30 min, placed in a muffle furnace, and heat treated at 500℃ for 4 h in air to obtain Li 1.33 Mn 1.67 O4;

[0008] (2) Preparation of MnO2·0.3H2O: Li obtained in step (1) 1.33 Mn 1.67 O4 was acid-washed with 0.5 M HCl for 24 h, washed repeatedly with deionized water until neutral, and dried at 60 °C overnight to obtain MnO2·0.3H2O;

[0009] (3) Preparation of single-layer MXene: Ti, Al, and TiC powders were mixed in proportion and ground for 4 h to obtain a uniform powder mixture; the prepared powder mixture was then calcined at 1350 °C for 3 h under an argon atmosphere to synthesize MAX. After cooling to room temperature, the obtained powder was ground to obtain MAX powder with a particle size of less than 40 μm;

[0010] Slowly add MAX powder to the LiF–HCl solution and stir at 35°C for 24 h to obtain a MXene dispersion with a controlled MXene:HCl ratio of 7.5 M:6.0 M.

[0011] The obtained MXene dispersion was repeatedly washed with deionized water, and then the MXene dispersion was centrifuged continuously at 5000 rpm for 30 min until the pH value was ≥6. The supernatant in the dispersion was collected to obtain a monolayer MXene.

[0012] (4) Obtaining MnO2·0.3H2O@MC membrane: MnO2·0.3H2O was dispersed in 1-5 mL of deionized water according to the mass fraction of MnO2·0.3H2O in the final MnO2·0.3H2O@MC membrane of 55%, 65%, 75%, and 85%, and a concentration of 2.5 mg mL -12.5-5 mL of cellulose solution was shaken for 20-50 min; after shaking, the prepared cellulose solution with a concentration of 6 mg mL was added. -1 2.5-5 mL of MXene solution was added and shaken for 20-50 min; finally, the membrane was filtered and dried in vacuum at 60 °C to obtain MnO2·0.3H2O@MC membrane.

[0013] The present invention also provides a two-dimensional composite confined MnO2·0.3H2O@MC film prepared by the above method.

[0014] The present invention also provides the application of the two-dimensional composite confined MnO2·0.3H2O@MC membrane in extracting lithium from seawater. The specific method is: preparing a two-dimensional composite confined MnO2·0.3H2O@MC membrane containing different ions (Li + 、Na + , Ca 2+ , K + Mg 2+ ) simulated seawater solution, and oscillated adsorption was performed at 200 rpm in a constant temperature shaker at 25°C. The lithium ion concentration in the solution at different times was measured by inductively coupled plasma optical emission spectrometry (ICP-OES). The concentrations of different ions in the simulated artificial seawater were: (0.17 mg L -1 Li + 、10554 mg L -1 Na + 、403.5 mg L -1 Ca 2+ 、391 mg L -1 K + 、1267.5 mg L -1 Mg 2+ ).

[0015] Compared with the prior art, the two-dimensional composite confined MnO2·0.3H2O@MC membrane of the present invention showed high adsorption efficiency in the first 9 h, and then slowly reached the adsorption equilibrium state (21.6 mg g −1 ); In addition, the utilization rate of MnO2·0.3H2O reached 96%. The adsorption results in a simulated artificial seawater environment showed that the efficiency of 75% MnO2·0.3H2O@MC membrane in extracting Li+ from artificial seawater was 98.11%, which was significantly higher than that of other ions (Na + , Ca 2+ , K + Mg 2+, maximum extraction efficiency <4%). Compared with other lithium ion sieve composite material preparation methods including freeze drying, electrospinning, and scraper method, the preparation process of the present invention is simple. The MnO2·0.3H2O@MC membrane with a content of 75% can still maintain a stable structure through folding, soaking, etc., and even if the proportion of MnO2·0.3H2O reaches 75%, it can still maintain good flexibility. Therefore, the two-dimensional composite membrane prepared by the present invention solves both the problem of adsorption capacity and the problem of difficult powder recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 FESEM surface images of MnO2·0.3H2O@MC films with different mass fractions;

[0017] Figure 2 FESEM cross-sectional images of MC membrane and MnO2·0.3H2O@MC membrane with a mass fraction of 75%. a and b are MC membranes, c is MnO2·0.3H2O@MC membrane with a mass fraction of 75% before adsorption, and d is MnO2·0.3H2O@MC membrane with a mass fraction of 75% after adsorption;

[0018] Figure 3 This is a physical photo of the MnO2·0.3H2O@MC membrane with a mass fraction of 75%;

[0019] Figure 4 The adsorption kinetics experimental curves of MnO2·0.3H2O particles and 75% mass fraction MnO2·0.3H2O@MC membrane;

[0020] Figure 5 The cyclability of 75%MnO2·0.3H2O@MC membrane;

[0021] Figure 6 The artificial seawater selectivity of 75%MnO2·0.3H2O@MC membrane. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0023] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and the disclosure and materials cited therein are hereby incorporated by reference.

[0024] Technical equivalents to the specific embodiments described that are apparent to those skilled in the art using no more than routine experimentation are intended to be encompassed by this application.

[0025] The experimental methods in the following examples, unless otherwise specified, are all conventional methods. The instruments and equipment used in the following examples, unless otherwise specified, are all conventional laboratory instruments and equipment; the experimental materials used in the following examples, unless otherwise specified, are all purchased from conventional biochemical reagent stores.

[0026] Example 1: The preparation method of the MnO2·0.3H2O@MC membrane for lithium extraction from seawater in this example is achieved by the following steps:

[0027] 1. Li 1.33 Mn 1.67 Preparation of O4: MnCO3 and Li2CO3 were uniformly mixed and ground at a lithium / manganese molar ratio of 1.33 / 1.67 for 30 minutes, placed in a muffle furnace, and heat treated in air (500℃, 4 h) to prepare Li 1.33 Mn 1.67 O4;

[0028] 2. Preparation of MnO2·0.3H2O: Acid wash with 0.5 M HCl for 24 h, washing and drying to obtain MnO2·0.3H2O;

[0029] Preparation of MXene: First, Ti, Al, and TiC powders were mixed to obtain a powder mixture with a molar ratio of Ti:Al:C = 3.0:1.2:1.8, which was then ground for 4 h to obtain a uniform powder mixture. Subsequently, the prepared powder mixture was calcined at 1350 °C for 3 h under an argon atmosphere to synthesize MAX. After cooling to room temperature, the resulting powder was ground to obtain MAX powder with a particle size of less than 40 μm. MXene was prepared by adding MAX powder to a LiF–HCl solution (MXene:HCl = 7.5 M: 6.0 M). MAX was slowly added to the solution and stirred at 35 °C for 24 h to obtain a MXene dispersion. After repeated washing with deionized (DI) water, the MXene dispersion was continuously centrifuged at 5000 rpm for 30 min until the pH value was ≥6. Finally, the supernatant of the dispersion was collected to obtain a monolayer MXene.

[0030] 4. MnO2·0.3H2O@MC membrane: Disperse MnO2·0.3H2O in 1-5 mL of deionized water, add 2.5-5 mL of cellulose solution (2.5 mg mL -1) and shake for 20-50 min. After shaking, add 2.5-55 mL of MXene solution (6 mg mL -1 ) and shake for 20-50 min. After filtering the membrane using a suction filtration device, vacuum drying was performed at 60°C to obtain a MnO2·0.3H2O@MC membrane.

[0031] The mass ratio of MnO2·0.3H2O powder to MC membrane in step 4 is 1.06-4.93:0.87. The lithium ion sieve powder (MnO2·0.3H2O) is compounded with the tough MC membrane material.

[0032] Example 2: This example differs from Example 1 in that deionized (DI) water is used in step 2 for washing until a neutral pH is reached. The remaining methods are the same as in Example 1.

[0033] Example 3: The difference between this example and Example 1 is that the mass ratio of MnO2·0.3H2O powder to MC film in step 3 is 2.61:0.87. The rest of the method is the same as that of Example 1.

[0034] Example 4: The preparation method of the MnO2·0.3H2O@MC membrane for lithium extraction from seawater in this example is carried out according to the following steps:

[0035] Disperse 67.35 mg of MnO2·0.3H2O in 1-5 mL of deionized water and add 2.5-5 mL of cellulose solution (2.5 mg mL -1 ) and shake for 20 min. After shaking, add 2.5-5 mL of MXene solution (6 mg mL -1 ) and shake for 20 minutes. After filtering the membrane using a suction filtration device, vacuum drying was performed at 60°C to obtain a MnO2·0.3H2O@MC membrane. The remaining procedures were the same as those described in Example 1.

[0036] The prepared MnO2·0.3H2O@MC film was observed by field emission scanning electron microscopy. The FESEM surface image is shown in Figure 2. Figure 1 As shown in the figure, the MC membrane exhibits a tightly overlapped micro-wrinkled layered structure, similar to the graphite structure. It not only provides a large specific surface area, but also increases the adsorption active sites of the adsorbent. As the mass fraction of MnO2·0.3H2O in the composite material gradually increases, it is observed that the surface begins to become rough and pores are found inside. Until the content reaches 85%, as shown in the attached figure, the surface of the membrane becomes rough and pores are found inside. Figure 1In the red-framed area, MnO2·0.3H2O accumulates severely, causing it to fall off during adsorption. Despite this, the 75% mass fraction of MnO2·0.3H2O in the 75% MnO2·0.3H2O@MC membrane still far exceeds that of other lithium-ion sieve composites, preventing MnO2·0.3H2O aggregation while ensuring its maximum loading capacity.

[0037] The FESEM cross-sectional images of the MC membrane and the MnO2·0.3H2O@MC membrane with a mass fraction of 75% are shown in Figure 2. Figure 2 As shown, Figure 2 Figures a and b show cross-sections of MC, clearly showing the structural edges of the different layers, and the distinct wrinkles indicating its multilayered structure. After doping with MnO2·0.3H2O, the cross-section changes, revealing that the MnO2·0.3H2O particles are embedded within the MC film, while the structure retains the layered structure of MC. Figure d shows a FESEM image after adsorption, showing that the MnO2·0.3H2O particles are firmly embedded within the MC, while the structure also retains a clearly discernible layered structure.

[0038] The actual photo of MnO2·0.3H2O@MC membrane with a mass fraction of 75% is shown in the figure. Figure 3 As shown, the MnO2·0.3H2O@MC membrane with a content of 75% can still maintain a stable structure through folding, soaking, etc., and even if the proportion of MnO2·0.3H2O reaches 75%, it can still maintain good flexibility, ensuring that the composite material has the mechanical properties that should be possessed by adsorption in a real seawater environment.

[0039] Figure 4 The graph of the adsorption of lithium ions by MnO2·0.3H2O particles and 75% MnO2·0.3H2O@MC membrane over time shows that MnO2·0.3H2O particles rapidly adsorb Li within the first 10 h of adsorption. + After that, the absorption rate decreased and finally reached equilibrium after 50 h (23.63 mg g −1 The 75% MnO2·0.3H2O@MC membrane also showed high adsorption efficiency in the first 9 h and then slowly reached the adsorption equilibrium state (21.6 mg g −1 ); in addition, the utilization rate of MnO2·0.3H2O reached 96%. The results showed that the two-dimensional composite membrane maintained the high adsorption rate and adsorption capacity of MnO2·0.3H2O particles and the short adsorption time.

[0040] By 25 mg L -1After adsorption in LiCl solution for 24 h, it was transferred to 0.5 M HCl solution for desorption for 24 h to complete an adsorption cycle. The adsorption and desorption performance of the material was tested for 5 cycles. The results are as follows Figure 5 As shown in the figure, although the adsorption performance of 75% MnO2·0.3H2O@MC membrane decreases with the increase of cycle number, the adsorption amount is close to the previous desorption amount, which shows that the MC membrane has good lithium transport performance and will not lead to the blockage of lithium diffusion channels due to the increase of cycle number. The lower desorption amount than the adsorption amount may be caused by the lithiation of the lithium ion sieve itself.

[0041] The present invention also studied the 75% MnO2·0.3H2O@MC membrane in simulated artificial seawater (0.17 mg L -1 Li + 、10554mg L -1 Na + 、403.5 mg L -1 Ca 2+ 、391 mg L -1 K + 、1267.5 mg L -1 Mg 2+ ) in the adsorption selectivity, the results are as follows Figure 6 , as shown in Table 1.

[0042] Table 1: Artificial seawater selectivity data for 75% MnO2·0.3H2O@MC membrane

[0043]

[0044] Li + The distribution coefficient K d It is 27833.33, which is significantly higher than K + (17.11), Ca 2+ (9.28), Mg 2+ (7.72) and Na + (0.95), indicating that the 75% MnO2·0.3H2O@MC film has excellent Li + Select adsorption performance. + The results are consistent with the distribution coefficient, separation factor and separation efficiency of coexisting ions. Therefore, the research results show that 75% MnO2·0.3H2O@MC membrane can selectively separate Li + It has huge application potential.

[0045] Different ions have different adsorption efficiencies; 75% MnO2·0.3H2O@MC membrane extracts Li from artificial seawater +The efficiency is 98.11%, which is significantly higher than other ions (Na + , Ca 2+ , K + Mg 2+ , the maximum extraction efficiency is <4%). This is because Li + The radius is smaller than Na + , K + and Ca 2+ The radius of the vacancies provided by the 75% MnO2·0.3H2O@MC film is only allowed to be less than or equal to the radius of Li + ions enter. However, Mg 2+ He Li + The radius of Mg is similar, but its separation efficiency is still low because Mg 2+ The hydration energy (−455 kcal mol -1 ) is higher than Li + (−122 kcal mol -1 ). Therefore, the two-dimensional composite membrane prepared by the present invention solves both the problem of adsorption capacity and the problem of difficult powder recovery.

[0046] The high adsorption selectivity of the 75% MnO2·0.3H2O@MC membrane comes from the MnO2·0.3H2O material with specific recognition sites, the interception effect of the MXene material on divalent metal ions and potassium ions with larger ionic radius, and the coordination effect of the hydroxyl functional groups on the cellulose surface with other ions. These interactions weaken the interaction between other ions and Li + competition among them, thus promoting the + The diffusion in the composite material makes the 75% MnO2·0.3H2O@MC membrane have a shorter equilibrium adsorption time. Therefore, the use of MC composite membrane two-dimensional confined composite lithium ion sieve is an effective strategy to solve the problems of difficult recovery, low adsorption capacity and adsorption rate in the process of lithium ion sieve seawater lithium extraction.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a two-dimensional composite confined MnO2·0.3H2O@MC film, characterized by: MnCO3 and Li2CO3 were mixed with a lithium / manganese molar ratio of 1.33 / 1.67 and then heat-treated to prepare Li 1.33 Mn 1.67 O4; then pickled Li 1.33 Mn 1.67 O4 was used to obtain MnO2·0.3H2O; Ti, Al and TiC powders were mixed and calcined in a molar ratio of Ti:Al:C=3.0:1.2:1.8 to synthesize MAX powder, which was then added to a LiF–HCl solution to prepare MXene; MnO2·0.3H2O was dispersed in deionized water, cellulose solution was added, and then MXene solution was added, and finally the membrane was filtered to form the MnO2·0.3H2O@MC membrane.

2. The method for preparing a two-dimensional composite confined MnO2·0.3H2O@MC film according to claim 1, characterized in that: The specific steps are as follows: (1) Preparation of Li 1.33 Mn 1.67 O4: MnCO3 and Li2CO3 were uniformly mixed and ground in proportion for 30 min, placed in a muffle furnace, and heat treated at 500℃ for 4 h in air to obtain Li 1.33 Mn 1.67 O4; (2) Preparation of MnO2·0.3H2O: Li obtained in step (1) 1.33 Mn 1.67 O4 was acid-washed with 0.5 M HCl for 24 h, washed repeatedly with deionized water until neutral, and dried at 60 °C overnight to obtain MnO2·0.3H2O; (3) Preparation of single-layer MXene: Ti, Al, and TiC powders were mixed in proportion and ground for 4 h to obtain a uniform powder mixture; the prepared powder mixture was then calcined at 1350 °C for 3 h under an argon atmosphere to synthesize MAX. After cooling to room temperature, the obtained powder was ground to obtain MAX powder with a particle size of less than 40 μm; Slowly add MAX powder to the LiF–HCl solution and stir at 35°C for 24 h to obtain a MXene dispersion with a controlled MXene:HCl ratio of 7.5 M:6.0 M. The obtained MXene dispersion was repeatedly washed with deionized water, and then the MXene dispersion was centrifuged continuously at 5000 rpm for 30 min until the pH value was ≥6. The supernatant in the dispersion was collected to obtain a monolayer MXene. (4) Obtaining MnO2·0.3H2O@MC membrane: MnO2·0.3H2O was dispersed in 1-5 mL of deionized water according to the mass fraction of MnO2·0.3H2O in the final MnO2·0.3H2O@MC membrane of 55%, 65%, 75%, and 85%, and a concentration of 2.5 mg mL -1 2.5-5 mL of cellulose solution was shaken for 20-50 min; after shaking, the prepared cellulose solution with a concentration of 6 mg mL was added. -1 2.5-5 mL of MXene solution was added and shaken for 20-50 min; finally, the membrane was filtered and dried in vacuum at 60 °C to obtain MnO2·0.3H2O@MC membrane.

3. A two-dimensional composite confined MnO2·0.3H2O@MC film prepared by the method according to claim 1 or 2.

4. The use of the two-dimensional composite confined MnO2·0.3H2O@MC membrane according to claim 3 in lithium extraction from seawater, characterized in that: The specific method is: prepare different ions: Li + 、Na + , Ca 2+ , K + Mg 2+ The simulated seawater solution was shaken and adsorbed at 200 rpm in a constant temperature shaker at 25°C, and the lithium ion concentration in the solution at different times was determined by inductively coupled plasma optical emission spectrometry (ICP-OES).

5. The use according to claim 4, characterized in that: The concentration of different ions in the simulated artificial seawater is: 0.17 mg L -1 Li + 、10554 mg L -1 Na + 、403.5 mg L -1 Ca 2+ 、391 mg L -1 K + 、1267.5 mg L -1 Mg 2+ .

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