Preparation method and application of MXene / carboxymethylxylan nanofluidic membrane for salt difference energy conversion

Abstract

The present invention discloses a method for preparing and applying a MXene / carboxymethylxylan nanofluidic membrane for salt gradient energy conversion. The MXene / carboxymethylxylan nanofluidic membrane has a typical two-dimensional layered structure with a thickness of 5-20 μm, an interlamellar spacing of 1.2-2.0 nm, and high mechanical strength. During reverse electrodialysis power generation, the nanofluidic membrane exhibits low internal resistance and high ion selectivity. The membrane shows promising application prospects in the field of reverse electrodialysis.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a MXene / carboxymethylxylan nanofluidic membrane for salt difference energy conversion, belonging to the field of membrane material preparation. Background Art

[0002] As human society rapidly develops, it consumes vast quantities of fossil fuels such as oil, coal, and natural gas. The combustion of these fuels produces carbon monoxide, carbon dioxide, sulfur dioxide, soot, and other substances that pose serious health risks and pollute the natural environment, prompting the search for environmentally friendly, abundant, and clean energy sources. Salinity energy, derived from the salinity gradient at the interface between seawater and rivers, is renewable, readily available, and environmentally friendly. According to calculations, major river estuaries worldwide could generate approximately 2.6 terawatts of electricity, making it considered a plentiful clean energy source.

[0003] Membrane-based reverse electrodialysis (RED) technology can directly convert the electrochemical potential difference between salinity gradients into electric current, which has important practical significance. Nanofluidic membranes formed by self-assembly of two-dimensional materials (such as MXene) have high ion selectivity and are regarded as important materials for capturing salt difference energy. However, nanofluidic membranes composed entirely of two-dimensional materials are expensive, have low mechanical strength, and poor water stability. They are easily damaged during the reverse electrodialysis process, which leads to the failure of the RED process. Therefore, there is an urgent need to develop a two-dimensional composite nanofluidic membrane material with low cost, high mechanical strength, and high salt difference energy conversion efficiency. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies and theories by proposing a method for preparing and applying a MXene / carboxymethylxylan nanofluidic membrane for salinity-induced energy conversion. The MXene / CMX nanofluidic membrane is prepared by etherifying and modifying industrial xylan, a common waste product in the pulp and paper industry, and then composited with the two-dimensional material MXene to form the MXene / CMX nanofluidic membrane. The composite membrane for salinity-induced energy conversion provided by the present invention has the following characteristics:

[0005] (1) Preferably, the MXene / CMX nanofluidic membrane has a two-dimensional layered structure with a thickness of 5-20 μm and a single-layer interlayer spacing of 1.2-2.0 nm.

[0006] (2) It should be noted that there is a gap between each single layer in the laminar structure of the flow control membrane, which provides a movement path for ion transport across the membrane.

[0007] (3) It should be noted that the nanochannels of the MXene / CMX nanofluidic membrane carry negative charges. When anions and cations in a high-concentration salt solution migrate to a low-concentration salt solution driven by the salt difference, the composite membrane selectively allows cations to pass through and blocks anions in the concentrated salt solution.

[0008] (4) It should be noted that during the reverse electrodialysis power generation process, the selective transport of cations by the membrane promotes the directional migration of a large number of cations, forming a directional movement of charges, thereby generating current and realizing the conversion of salt difference energy into electrical energy.

[0009] (5) Preferably, the interlayer spacing of the composite membrane, which allows for selective ion passage, is 1.2-2.0 nm, and this interlayer spacing can be controlled by controlling the amount of CMX added. A smaller interlayer spacing improves the selectivity of the composite membrane for cations. Therefore, the composite membrane provided by the present invention has enhanced ion selectivity while having a lower membrane resistance.

[0010] (6) It should be noted that, in the reverse electrodialysis power generation process of the composite membrane, the reverse electrodialysis module does not require an anode pool and a cathode pool, and the cathode and anode electrodes do not need to be set in the cathode pool and the anode pool.

[0011] (7) The carboxymethyl xylan provided by the present invention is prepared according to the method disclosed in the document Fabrication of flexible composite film based on xylan from pulping process for packaging application. INT J BIOL MACROMOL. 173, 285-292 (2021).

[0012] (8)MXene is composed of M n+1 AX n Phase precursor is etched, wherein M represents a transition metal element; A represents a main group element; and X represents carbon or nitrogen.

[0013] (9) The etching solution contains a mixture of hydrochloric acid and lithium fluoride. After etching, the solution is washed with water until the pH is neutral. Ultrasonic stripping is used to strip the etched multilayer MXene into a few layers or a single layer to form a MXene aqueous solution.

[0014] (10) The MXene provided by the present invention is based on the literature Guidelines for Synthesis and Processing of Two-Dimensional Titanium Carbide (Ti3C2T xMXene). It was prepared by the method disclosed in Chem. Mater. 29, 7633-7644 (2017).

[0015] (11) Preferably, the MXene is Ti3C2T x , where T is a terminal oxygen, hydroxide or fluorine, and x is the number of Ts.

[0016] (12) Carboxymethyl xylan was added to the MXene aqueous solution in a certain proportion and stirred on a magnetic stirrer for 12-24 h, followed by vacuum filtration to obtain a MXene / CMX nanofluidic membrane. The stirrer speed was set to 350 rpm / min, but not limited thereto.

[0017] (13) Preferably, during the reverse electrodialysis power generation process, the molar concentration of the high-concentration salt solution is 0.1-1 mol / L, the molar concentration of the low-concentration salt solution is 0.0001-0.01 mol / L, and the molar concentration ratio of the high-concentration salt solution to the low-concentration salt solution is 1:(0.001-0.1)

[0018] (14) Preferably, the salt solution used in the reverse electrodialysis power generation process can be a sodium chloride solution, a potassium chloride solution, or a calcium chloride solution. The high-concentration salt solution and the low-concentration salt solution use the same salt type.

[0019] (15) Preferably, the electrode used in the process of the present invention is a silver / silver chloride electrode with a salt bridge. In the specific implementation process, the anode electrode reaction is: AgCl → Ag + e - +Cl - , the cathode electrode reaction is Ag+e - +Cl - →AgCl.

[0020] (16) The salt difference energy conversion device used in the present invention is a closed system, such as Figure 6 As shown in the figure, the device mainly consists of four parts: silver / silver chloride electrode, MXene / CMX nanofluidic membrane, high concentration sodium chloride solution, low concentration sodium chloride solution, and external picoammeter and rheostat. The MXene / CMX nanofluidic membrane is placed between the high concentration sodium chloride solution and the low concentration sodium chloride solution. Driven by the concentration difference, the sodium ions on the high concentration side pass through the MXene / CMX nanofluidic membrane into the low concentration side to form an internal current. The internal current is in the same direction as the migration of sodium ions. The anode electrode on the high concentration sodium chloride solution side reacts AgCl→Ag+e - +Cl - The generated electrons are transferred to the cathode electrode on the low concentration sodium chloride solution side through the external circuit, thus forming an external current

[0021] (17) The present invention provides a method for preparing and applying a composite membrane material for salinity-difference energy conversion. The MXene / CMX composite membrane is inexpensive and has a denser two-dimensional layered structure with a thickness of 5-20 μm and a single-layer interlayer spacing of 1.2-2.0 nm. During reverse electrodialysis power generation, it exhibits enhanced ion conductivity, reduced membrane internal resistance, and high power generation efficiency, showing promising application prospects in the field of salinity-difference energy conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 SEM photos of industrial xylan (left) and carboxymethyl xylan (right) in the examples of the present invention

[0023] Figure 2 TEM image of MXene prepared in the embodiment of the present invention

[0024] Figure 3 Optical image of the nanofluidic membrane prepared in Example 3 of the present invention

[0025] Figure 4 This is a cross-sectional SEM image of the MXene / carboxymethyl xylan nanofluidic membrane prepared in Example 3 of the present invention.

[0026] Figure 5 Comparison of mechanical properties of the MXene / carboxymethyl xylan nanofluidic membrane prepared in the embodiment of the present invention and comparative example 1

[0027] Figure 6 Schematic diagram of reverse electrodialysis for MXene / CMX nanofluidic membrane

[0028] Figure 7 The cation migration number and energy conversion efficiency of the MXene / carboxymethyl xylan nanofluidic membrane prepared in Example 3 of the present invention at different salinity differences are shown in FIG.

[0029] Figure 8 This is the relationship between the power generation density, current density and external resistance of the MXene / carboxymethyl xylan nanofluidic membrane prepared in Example 3 of the present invention under a 1000-fold salt difference.

[0030] Figure 9 Comparison of the power generation density of the MXene / carboxymethyl xylan nanofluidic membrane prepared in Example 3 of the present invention and the MXene membrane prepared in Comparative Example 1 under a 1000-fold salt difference DETAILED DESCRIPTION

[0031] The following examples are only provided to further illustrate the technical solutions of the present invention, but are not intended to limit the technical solutions of the present invention.

[0032] Example 1

[0033] (1) Before filtration, the total mass of MXene and carboxymethyl xylan was 36 mg, and the mass of carboxymethyl xylan was equivalent to 50% of the total mass. Carboxymethyl xylan was added to the MXene aqueous solution and stirred on a magnetic stirrer at 350 rpm / min for 12 h.

[0034] (2) The mixed solution obtained in step (1) was filtered for 3.5 hours. After the filtration, it was placed in air for drying to obtain a MXene / CMX nanofluidic membrane.

[0035] Example 2

[0036] (1) Before filtration, the total mass of MXene and carboxymethyl xylan was 36 mg, and the mass of carboxymethyl xylan was equivalent to 33% of the total mass. Carboxymethyl xylan was added to the MXene aqueous solution and stirred on a magnetic stirrer at 350 rpm / min for 12 h.

[0037] (2) Same as Example 1

[0038] Example 3

[0039] (1) Before filtration, the total mass of MXene and carboxymethyl xylan was 36 mg, and the mass of carboxymethyl xylan was equivalent to 25% of the total mass. Carboxymethyl xylan was added to the MXene aqueous solution and stirred on a magnetic stirrer at 350 rpm / min for 12 h.

[0040] (2) Same as Example 1.

[0041] Example 3

[0042] (1) Before filtration, the total mass of MXene and carboxymethyl xylan was 36 mg, and the mass of carboxymethyl xylan was equivalent to 20% of the total mass. Carboxymethyl xylan was added to the MXene aqueous solution and stirred on a magnetic stirrer at 350 rpm / min for 12 h.

[0043] (2) Same as Example 1.

[0044] Comparative Example 1

[0045] (1) The total mass of MXene before filtration was 36 mg. No carboxymethyl xylan was added. The MXene solution was stirred on a magnetic stirrer at a speed of 350 rpm / min for 12 h.

[0046] (2) Same as Example 1

[0047] It should be noted that the molar concentration of the high concentration sodium chloride solution used in the salt difference energy conversion test of the examples and comparative examples is fixed at 0.1 mol / L, and the molar concentration of the low concentration sodium chloride solution is 0.0001-0.01 mol / L.

[0048] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the implementation methods of the present invention. Those skilled in the art should understand that other different forms of changes can be made based on the above description, and obvious modifications or changes to the technical solutions of the present invention should be included in the scope of protection of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. An application of a MXene / carboxymethylxylan nanofluidic membrane for salt gradient energy conversion, characterized by: During the reverse electrodialysis process, a salt difference is formed between the high-concentration salt solution and the low-concentration salt solution. The MXene / carboxymethylxylan nanofluidic membrane converts the salt difference into electrical energy. The molar concentration ratio of the high-concentration salt solution to the low-concentration salt solution is 1:(0.001-0.1). The MXene / carboxymethylxylan nanofluidic membrane is obtained by adding carboxymethylxylan to a MXene aqueous solution, stirring for 12 to 24 hours, and then vacuum filtering. The MXene / carboxymethyl xylan nanofluidic membrane has a two-dimensional layered structure with a thickness of 5-20 μm and a single layer interlayer spacing of 1.2-2.0 nm; The salt solution is sodium chloride solution, potassium chloride solution or calcium chloride solution.

2. The use according to claim 1, characterized in that The mass of the carboxymethyl xylan before filtration accounts for 20%-50% of the total mass.

3. The use according to claim 1, characterized in that The MXene is Ti3C2T x , where T is a terminal oxygen, hydroxide or fluorine, and x is the number of Ts.

4. The use according to claim 1, characterized in that The molar concentration of the high-concentration salt solution is 0.1-1 mol / L, and the molar concentration of the low-concentration salt solution is 0.0001-0.01 mol / L.

5. The use according to claim 1, characterized in that The type of salt in the high-concentration salt solution is the same as that in the low-concentration salt solution.

6. The use according to claim 1, characterized in that The electrodes used in the reverse electrodialysis process are silver / silver chloride electrodes.

Images