MSL membrane capable of enhancing permeation energy conversion and preparation method of MSL membrane

Abstract

The invention relates to an MSL membrane for enhancing permeation energy conversion and a preparation method thereof, and belongs to the technical field of composites.The preparation method comprises the steps that SL is dissolved in water and stirred at the room temperature, and an SL solution is obtained; the MXene nanosheet solution and EGDE are added into the SL solution to be mixed, the mixture is stirred in nitrogen and then centrifuged and repeatedly washed until supernate is neutral, precipitates are re-dispersed to obtain uniform MSL nanosheets, and then the two-dimensional channel MSL membrane is obtained. According to the invention, SL with abundant functional groups is combined with MXene, so that not only is the problem of water stability of 2D MXene solved, but also large surface charges are provided to realize selective ion transmission, and an ordered skeleton channel of MXene provides a shorter permeation path for rapid ion transmission, so that the MSL film has ultralow resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials, and particularly relates to an MSL membrane for enhancing osmotic energy conversion and a preparation method thereof. Background Art

[0002] Two-dimensional (2D) materials have shown great potential in obtaining osmotic energy due to their high membrane selectivity, but the high resistance of the tortuous channels of 2D nanofluid membranes still hinders the further improvement of output performance.

[0003] MXene is a new type of 2D layered material and is considered a candidate material for reverse electrodialysis (RED) membranes because the laminated MXene nanochannels with charged functional groups can provide excellent ion selectivity and conductivity. However, due to the poor binding force between nanosheets, MXene-based ion exchange membranes have weak mechanical properties and are unstable in water, thus limiting their RED performance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an MSL membrane for enhancing osmotic energy conversion and a preparation method thereof.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: a preparation method of an MSL membrane for enhancing osmotic energy conversion, comprising the following steps: S1. Dissolve sulfonated lignin (SL) in water and stir at room temperature to obtain an SL solution; S2. Add an MXene nanosheet solution and a drop of ethylene glycol diglycidyl ether (EGDE) into the SL solution and mix. After the mixture is stirred under nitrogen, centrifuge and wash repeatedly until the acidity and alkalinity of the supernatant reach neutrality, then redisperse the precipitate to obtain uniform MSL nanosheets (i.e., MXene-SL nanosheets); S3. Assemble the MSL nanosheets into a regular two-dimensional channel MSL membrane by vacuum-assisted filtration.

[0006] Further, in step S2, the preparation method of the MXene nanosheet solution is: etch the Al layer in Ti3AlC2 powder by HF in-situ generated by the reaction of HCl and LiF, and then ultrasonically exfoliate and disperse it in water to obtain an MXene nanosheet solution, i.e., a Ti3C2Tx nanosheet suspension.

[0007] Further, in step S3, the vacuum-assisted filtration method is: dilute the aqueous solution of MSL nanosheets, then pour it into a filtration device containing an MCE membrane, and after standing, perform vacuum filtration under pressure.

[0008] Another object of the present invention is to provide an MSL membrane for enhancing osmotic energy conversion.

[0009] Due to the above technical solution, the beneficial effects of the present invention are as follows: The present invention prepares an ultra-low resistance 2D MSL (MXene-SL) layered membrane, which can achieve efficient osmotic energy generation.

[0010] The present invention adds sulfonated lignin with rich functional groups, that is, combines SL with rich functional groups with MXene, which not only solves the water stability problem of 2D MXene, but also provides a large surface charge to achieve selective ion transport. The ordered skeleton channels of MXene provide a shorter penetration path for rapid ion transport, thus making the MSL membrane have ultra-low resistance.

[0011] Therefore, by mixing artificial seawater and river water, the MSL membrane can reach an ultra-high power output of about 22.15 W / m 2 , which is 6.78 times higher than that of the original MXene membrane. In addition, in terms of output power and internal resistance (9.3 kΩ), the MSL membrane is superior to all reported osmotic generators based on single-layer 2D nanosheets under the same experimental conditions.

[0012] It can be seen that the present invention proposes a reliable strategy for stabilizing 2D MXene membranes in electrolytes, opening up new ways for designing promising 2D nanofluidic membranes to achieve efficient blue energy harvesting (the blue osmotic energy existing in the ocean is a new type of clean "zero-carbon" energy with extremely rich reserves and sustainability. The present invention can convert the chemical energy generated by the salinity gradient between natural seawater and river water into electrical energy, and then realize the efficient collection and utilization of blue osmotic energy) and ion devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will be specifically described below with reference to the drawings and examples. The advantages and implementation manners of the present invention will become more obvious. The content shown in the drawings is only used for the explanation of the present invention and does not constitute any limitation to the present invention. In the drawings: Figure 1 is the surface SEM image of Ti3AlC2 nanosheets and Ti3C2T x nanosheets of the present invention.

[0014] Figure 2 is the SEM image of the MXene membrane, MSL membrane, cross-section of the MXene membrane and cross-section of the MSL membrane of the present invention.

[0015] Figure 3 is the XPS spectrum of the MXene membrane and MSL membrane of the present invention.

[0016] Figure 4 is the deconvolution map of the C1s spectrum of the MXene membrane and MSL membrane of the present invention.

[0017] Figure 5 These are the FTIR spectra of the MXene film, MSL film, and SL of the present invention.

[0018] Figure 6 These are the XRD patterns of the Ti3AlC2 nanosheets and Ti3C2T x nanosheets of the present invention.

[0019] Figure 7 These are the XRD patterns of the MXene film, MSL1 film, MSL2 film, and MSL3 film of the present invention.

[0020] Figure 8 These are the I-V curves of the MSL film of the present invention in neutral KCl electrolytes with different concentrations.

[0021] Figure 9 These are the graphs showing the relationship between the transmembrane ionic conductivity of a single MSL1 film and the KCl concentration in the present invention.

[0022] Figure 10 These are the I-T curves of the MSL1 film in 10 -2 MKCl solution in the present invention.

[0023] Figure 11 These are the graphs of the current density and voltage of the MSL film in a 50-fold KCl concentration gradient in the forward and reverse diffusion directions in the present invention.

[0024] Figure 12 These are the schematic diagrams showing the influence of the SL content on the output current density in the present invention.

[0025] Figure 13 These are the schematic diagrams showing the influence of the SL content on the output power density in the present invention.

[0026] Figure 14 These are the schematic diagrams showing the change of the output power density of the MSL film with the increase of the external resistance at 5, 50, and 500-fold concentration gradients in the present invention. Detailed implementation manners

[0027] In order to enable those skilled in the art of the present technology to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with the best embodiments.

[0028] A preparation method of an MSL film for enhancing osmotic energy conversion includes the following steps: S1. Dissolve (SL) 5 mg of sulfonated lignin in ml of water, and stir at room temperature for 1 h to obtain an SL solution; S2. Add 5 ml of the MXene nanosheet solution and a drop of ethylene glycol diglycidyl ether (EGDE) to the SL solution and mix. After stirring the mixture under nitrogen for 36 h, centrifuge and wash repeatedly until the supernatant reaches neutral pH of 7.0, then redisperse the precipitate to obtain uniform MSL1 nanosheets (i.e., MXene-SL nanosheets). S3. Assemble the MSL1 nanosheets into a regular two-dimensional channel MSL1 membrane by vacuum-assisted filtration method.

[0029] Among them, in step S2, the preparation method of the MXene nanosheet solution is: etch the Al layer in the Ti3AlC2 powder by HF in-situ generated by the reaction of HCl and LiF, and then ultrasonically exfoliate and disperse it in water to obtain the MXene nanosheet solution, that is, the Ti3C2Tx nanosheet suspension.

[0030] Among them, in step S3, the vacuum-assisted filtration method is: dilute the aqueous solution of MSL1 nanosheets, then pour it into a filtration device containing a MCE membrane, and after standing, perform vacuum filtration under pressure. The filtration process lasts for more than 1 h to ensure proper compaction of the MSL1 membrane.

[0031] Among them, when 10 mg of SL is used, a uniform MSL2 membrane is obtained through steps S1 to S3.

[0032] Among them, when 15 mg of SL is used, a uniform MSL3 membrane is obtained through steps S1 and S2.

[0033] In the subsequent examples, the MSL membrane specifically refers to the MSL2 membrane.

[0034] Another object of the present invention is to provide a MSL membrane for enhancing osmotic energy conversion.

[0035] As Figure 1 shown, characterize the Ti3AlC2 nanosheets and Ti3C2T x nanosheets. Figure 1 (a) is the surface SEM image of the Ti3AlC2 nanosheets; Figure 1 (b) is the surface SEM image of the Ti3C2T x nanosheets.

[0036] As Figure 2 shown, characterize the MXene membrane, the MSL membrane, the cross-section of the MXene membrane and the cross-section of the MSL membrane. Figure 2 (a) is the surface SEM image of the MXene membrane; Figure 2 (b) is the surface SEM image of the MSL membrane; Figure 2 (c) is the SEM image of the cross-section of the MXene membrane; Figure 2(d) is the SEM image of the cross-section of the MSL film.

[0037] As Figure 3 shown, in the XPS full spectrum, there are significant differences in the peak positions of C1s between the MXene film and the MSL film.

[0038] As Figure 4 and Figure 5 shown, Figure 4 (a) is the deconvolution of the C1s spectrum of the MXene film; Figure 4 (b) is the deconvolution of the C1s spectrum of the MSL film. By comparing the energy spectra of C1s, it is found that the C1s of the MXene film can be decomposed into 4 peaks, at 282.03 eV, 284.71 eV, 286.11 eV, and 288.62 eV respectively, corresponding to C-C, C-O, C=O, and O-C=O. The C1s of the MSL film can be decomposed into 4 peaks, at 282.03 eV, 284.69 eV, 286.12 eV, and 288.67 eV respectively, corresponding to C-C, C-O, C=O, and O-C=O. Among them, the peak position difference between C-O and C=O is the largest. The results show that a strong hydrogen bond network is formed between MXene and SL. In addition, the change in the FTIR spectrum also proves that the MXene nanosheets are successfully modified by SL. The FTIR spectrum proves that the addition of SL not only enhances the interlayer binding force between the MXene sheets but also promotes the formation of a continuous and defect-free composite film; the synergistic effect of these functional groups effectively reduces the energy barrier for proton transport, thus significantly improving the proton conductivity of the film.

[0039] As Figure 6 shown, the diffraction peaks of Ti3AlC2 nanosheets and Ti3C2T x nanosheets are shown. It can be seen that the diffraction peak characteristics of Ti3C2T x nanosheets are significantly different from those of Ti3AlC2 nanosheets. Ti3C2T x nanosheets have a strong (002) peak in the low-angle region, while the peaks at other angles are relatively weak or not obvious. This diffraction peak characteristic is related to its layered structure and surface functional groups T x (such as -OH, -F, -O, etc.). Its strong (002) peak is associated with structural information such as the interlayer distance, reflecting the influence of its layered structure and surface functional groups on diffraction.

[0040] As Figure 7 shown, there are differences in the diffraction peak positions between the MSL1 film, the MSL2 film, the MSL3 film, and the MXene film. The diffraction peak position is related to structural parameters such as the crystal plane spacing of the crystal, indicating that the crystal structures of these materials are different, that is, the crystal plane spacing of the MSL1 film > the crystal plane spacing of the MSL2 film > the crystal plane spacing of the MSL3 film > the crystal plane spacing of the MXene film.

[0041] The transmembrane ionic diffusion characteristics of the MSL film were evaluated by measuring the current-voltage (I-V) curve. Since the ionic mobilities and volumes of K + and Cl - are very similar, KCl was chosen as the probe electrolyte.

[0042] As Figure 8 shown, in the KCl electrolyte, the I-V curves of the MSL1 film, MSL2 film, and MSL3 film showed linear Ohmic behavior, and the ionic current rectification was negligible, indicating the presence of permanent conductance channels and the symmetric structure of the composite film.

[0043] As Figure 9 shown, according to the I-V curve, the ionic conductivity of the MSL film was calculated. The ionic conductance of the MSL film showed two different characteristic behaviors. In the high-concentration region (>10 -3 M), the ionic conductance of the MSL film followed the bulk rule and showed a linear relationship; when the KCl concentration was lower than 10 -3 M, the ionic conductance of the MSL film gradually deviated from the bulk value and tended to a plateau, indicating that the transport of ions in the MSL film was mainly controlled by the surface charge of the nanochannels.

[0044] As Figure 10 shown, the ionic transport stability of the MSL film was examined by applying an alternating external voltage of +0.2 and -0.2 V and measuring the I-T curve. Each cycle lasted for 16 min, and a total of 8 cycles were carried out continuously. The negative current and positive current after each voltage polarity switch remained at the same level, indicating that the MSL film had excellent ionic transport stability.

[0045] By measuring the current density and voltage curve of the MSL film under different salt concentration gradients, the ionic transport mechanism was further explored. Due to the anion-selective transport characteristics of the MSL film, Cl - preferentially transported from the high-concentration side to the low-concentration side, generating diffusion current and diffusion potential. The KCl concentration in the low-concentration electrolyte cell was fixed at IS of 10 -2 M, and the concentration gradient was 50 times. Therefore, the values of the diffusion current and diffusion potential were equal to the short-circuit current (I SC ) and open-circuit voltage (V OC ) in the corresponding current density and voltage curves. As Figure 11 shown, the current density and voltage curve of the MSL film (SL content of 1:2) at a 50-fold concentration gradient (10 -2 M / 0.5 M KCl). Similar ionic transport behaviors were observed under the reverse concentration gradient, indicating that the MSL film had a symmetric structure and no preferential direction of ionic diffusion.

[0046] To evaluate the application prospects of the MSL membrane nanofluid system, standard artificial seawater (0.5 M NaCl) and river water (0.01 M NaCl) systems were selected for salinity gradient energy conversion tests. Considering the diversity of actual application scenarios, the output current density and power density of the MSL membrane under different SL contents were explored (i.e., MXene:SL = 1:1, 1:2, and 1:3), as Figure 12 and Figure 13 shown. When the SL contents were 1:1, 1:2, and 1:3 respectively, the maximum output power densities of the MSL1 membrane, MSL2 membrane, and MSL3 membrane were 12.71 Wm -2 , 22.15 Wm -2 , and 19.89 Wm -2 respectively. As the SL content increased, the power output density of the MSL1 membrane, MSL2 membrane, and MSL3 membrane showed a trend of first increasing and then decreasing significantly at each load resistance, indicating that the MSL membrane performed better when the SL content was 1:2.

[0047] As Figure 14 shown, the present invention also conducted energy conversion tests with 5-fold and 500-fold salinity gradients, and the maximum output power densities were 0.51 Wm -2 and 34.54 Wm -2 respectively.

[0048] The above has described the embodiments of the present invention in detail, but the content described is only the preferred embodiments of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope covered by the present invention.

Claims

1. A preparation method of an MSL membrane for enhancing osmotic energy conversion, characterized in that: Including the following steps: S1. Dissolve sulfonated lignin in water and stir to obtain an SL solution; S2. Add the MXene nanosheet solution and ethylene glycol diglycidyl ether to the SL solution and mix. After stirring the mixture under nitrogen, centrifuge and wash repeatedly until the supernatant is neutral in acidity and alkalinity, and then redisperse the precipitate to obtain uniform MSL nanosheets; S3. Assemble the MSL nanosheets into a regular two-dimensional channel MSL membrane by vacuum-assisted filtration method.

2. The preparation method of the MSL film for enhancing osmotic energy conversion according to claim 1, characterized in that: In step S2, the preparation method of the MXene nanosheet solution is as follows: etch the Al layer in Ti3AlC2 powder by HF in-situ generated by the reaction of HCl and LiF, and then ultrasonically exfoliate and disperse it in water to obtain the MXene nanosheet solution.

3. The preparation method of the MSL film for enhancing osmotic energy conversion according to claim 1, characterized in that: In step S3, the vacuum-assisted filtration method is as follows: dilute the aqueous solution of MSL nanosheets, and then pour it into a filtration device containing an MCE membrane. After standing, perform vacuum filtration under pressure.

4. An MSL membrane for enhancing osmotic energy conversion, characterized in that: Prepared by the preparation method of the MSL membrane for enhancing osmotic energy conversion according to any one of claims 1 to 3.

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