Preparation method of two-dimensional inorganic nanomaterial modified quaternary ammonium chitosan-based bipolar membrane anion exchange layer

Abstract

This invention provides a membrane material for a bipolar anion exchange layer modified with two-dimensional inorganic materials, specifically quaternized chitosan-based materials. Two-dimensional MgAl-LDH nanosheets are added to a chitosan (QCS) / polyvinyl alcohol (PVA) mixed matrix to construct an inorganic-organic composite material. The ion exchange capacity and mechanical reinforcing ability of the two-dimensional MgAl-LDH give the modified QCS / PVA mixed matrix better ion transport capacity and mechanical strength. This results in a bipolar membrane with this anion exchange layer exhibiting lower transmembrane voltage and membrane surface resistivity, thus improving water dissociation efficiency. The bipolar anion exchange layer of this invention uses low-cost materials, exhibits good ion transport properties, is simple to operate, and has wide applications.

Description

Technical Field

[0001] This invention belongs to the fields of chemistry and materials science and green energy, and specifically relates to the preparation and application of a two-dimensional inorganic nanomaterial modified quaternized chitosan-based anion exchange layer bipolar membrane. Background Technology

[0002] A bipolar membrane (BPM) is a layered composite ion exchange membrane composed of an anion exchange layer, a cation exchange layer, and an intermediate interface layer. Under the action of a reverse voltage, it can cause water to dissociate and produce hydrogen ions (H+). + ) and hydroxide ions (OH-) - These two ions are transported through cation exchange layers and anion exchange layers, respectively. Bipolar membrane technology can directly generate acids and bases by electrolyzing solutions such as brine without introducing other impurities, achieving in-situ regeneration and recycling. This significantly improves production efficiency, reduces energy consumption and pollutant emissions, and meets the demands of modern industry for highly efficient, energy-saving, and environmentally friendly technologies. However, because OH... - Due to their larger volume, the H+ in the membrane experiences relatively greater migration resistance, resulting in a generally lower transport efficiency compared to H+ in cation exchange layers. + This limits the overall efficiency of the bipolar membrane. Therefore, the anion exchange layer of the bipolar membrane is modified to improve the OH- ion exchange efficiency. - The transmission efficiency is crucial for improving the overall water dissociation efficiency of bipolar membranes.

[0003] Chitosan (CS) is a natural polysaccharide primarily derived from the shells of crustaceans such as shrimp and crab. It is a widely available and readily available natural material. Furthermore, due to the abundance of active groups such as hydroxyl and amino groups in its molecular structure, chitosan can be chemically modified to introduce different functional groups or combined with other substances, thereby endowing it with more special properties. For example, quaternization modification of chitosan can yield quaternized chitosan (QCS) membrane materials with anion exchange capacity. As the degree of quaternization increases, the corresponding OH- transport efficiency also improves. However, a higher degree of quaternization also further increases the water absorption and swelling properties of the resulting QCS membrane material, leading to a decrease in the mechanical strength of the QCS membrane. Utilizing solid ionic conductors as multifunctional additives to construct organic-inorganic composite materials can simultaneously improve both mechanical strength and anionic conductivity, providing an effective and simple method to address the aforementioned problems. Layered double hydroxides (LDHs) are characterized by their unique two-dimensional (2D) nanosheet structure and inherent OH groups. -Its outstanding conductivity stems from the ultra-high aspect ratio and specific surface area of ​​two-dimensional nanosheets, which facilitates the formation of extensive interactions at the interface to strengthen the composite material and promote rapid ion transport. Furthermore, LDH possesses exchangeable interlayer anions, thus exhibiting inherent anionic conductivity. Due to this property, LDH can be directly used as an effective anionic conductor.

[0004] Therefore, this invention aims to improve the water dissociation efficiency of bipolar membranes by preparing a membrane material for a two-dimensional inorganic material-modified quaternized chitosan-based bipolar membrane anion exchange layer. Two-dimensional MgAl-LDH nanosheets are added to a chitosan (QCS) / polyvinyl alcohol (PVA) mixed matrix to construct an inorganic-organic composite material. The ion exchange capacity and mechanical strengthening ability of two-dimensional MgAl-LDH give the modified QCS / PVA mixed matrix better ion transport capacity and mechanical strength. The bipolar membrane anion exchange layer of this invention uses low-cost materials, has good ion transport properties, is simple to operate, and has wide applications. Summary of the Invention

[0005] The purpose of this invention is to prepare a bipolar membrane with a two-dimensional inorganic material modified quaternized chitosan-based anion exchange layer, which solves the problems of high cost, low ion transport rate and low water dissociation efficiency of existing bipolar membrane materials. At the same time, this invention will also provide a method for preparing a bipolar membrane with a two-dimensional inorganic material modified quaternized chitosan-based anion exchange layer.

[0006] To achieve the above and other related objectives, the technical solution of this invention patent is as follows:

[0007] Step 1: Chitosan is dissolved in acetic acid solution, and then the quaternizing agent 2,3-epoxypropyltrimethylammonium chloride is added. After bathing in a water bath at 80°C, quaternized chitosan is obtained. After filtration, drying, and pulverization, quaternized chitosan powder is obtained. In Step 1, the concentration of acetic acid solution is 2 vol%, and the concentrations of chitosan and 2,3-epoxypropyltrimethylammonium chloride are both 20 g / L.

[0008] Step 2 involves dissolving a certain amount of magnesium nitrate nonahydrate, aluminum nitrate hexahydrate, and urea in an ethylene glycol aqueous solution, followed by a hydrothermal reaction at 160°C for 6 hours to obtain two-dimensional nanosheet-like MgAl-LDH. In Step 2, the amounts of magnesium nitrate, aluminum nitrate, and urea are 0.75-0.8 g, 1-1.2 g, and 1.5-2 g, respectively, and the ethylene glycol aqueous solution is 60 mL with a concentration of 90 wt%.

[0009] Step 3: Dissolve the quaternized chitosan obtained in Step 1 in an acetic acid solution to obtain a homogeneous solution. Mix this solution with a polyvinyl alcohol solution of a certain concentration to obtain a uniformly mixed matrix. Add the two-dimensional MgAl-LDH powder obtained in Step 2 to the above quaternized chitosan / polyvinyl alcohol mixed matrix, stir evenly, and then defoam to obtain a casting solution. Cast the casting solution in a glass container and dry it at 60°C to evaporate the solution or obtain an anion exchange layer. Immerse the anion exchange layer in a 1 mol / L KOH solution for 24 hours to ultimately exchange OH-. - Form. The anion exchange layer was hot-pressed with a hydrolyzed polyacrylonitrile cation exchange layer to obtain a two-dimensional modified anion exchange layer bipolar membrane.

[0010] This invention discloses a two-dimensional material-modified quaternized chitosan-based anion exchange layer bipolar membrane material obtained according to the above method, which has the following advantages: First, the polymer matrix used is a natural polymer material that is widely available and regenerable in nature. Second, the polymer matrix is ​​modified with inorganic two-dimensional MgAl-LDH nanosheets with ion exchange capacity, which improves its mechanical strength and ion exchange capacity, and reduces the surface resistance of the bipolar membrane with the cation exchange layer, thereby improving the water dissociation efficiency. Attached Figure Description

[0011] Figure 1 The image shown is an electron microscope image of the anion exchange layer disclosed in Embodiment 1 of the present invention.

[0012] Figure 2 The image shown is an electron microscope image of the anion exchange layer disclosed in Comparative Example 1 of this invention. Detailed Implementation

[0013] The preparation method of the two-dimensional nanosheet material modified quaternized chitosan-based anion exchange layer bipolar film of the present invention will be described in detail below with reference to the embodiments and accompanying drawings. However, the present invention is not limited to the following embodiments.

[0014] Example 1:

[0015] Quaternized chitosan (QCS) was dissolved in 2 vol% acetic acid solution to obtain a 3 wt% QCS acetic acid solution. Polyvinyl alcohol (PVA) was dissolved in pure water at 95℃ to obtain a 10 wt% aqueous solution. 100 g of the QCS acetic acid solution and 20 g of the PVA aqueous solution were placed in a round-bottom flask and stirred evenly at 60℃ to obtain a homogeneous QCS / PVA mixed matrix. 0.015 g of two-dimensional sheet-like nano-MgAl-LDH powder was ultrasonically dispersed in 8 mL of pure water and added to the QCS / PVA mixed matrix, stirred evenly to obtain a casting solution. After defoaming treatment, the casting solution was poured into a glass container and dried at 60℃ for 12 hours to obtain a two-dimensional nano-sheet MgAl-LDH modified quaternized chitosan-based anion exchange layer. Finally, the exchange layer was immersed in a 1 mol / L KOH solution to exchange for OH-. - The final anion exchange layer was obtained after washing with water. This anion exchange layer was then hot-pressed with a hydrolyzed polyacrylonitrile cation exchange layer at 5 MPa and 80°C to obtain the bipolar membrane. The transmembrane voltage of this membrane was measured to be 0.18 V, and the sheet resistivity was 9.1 Ω·cm. 2 .

[0016] Example 2:

[0017] Quaternized chitosan (QCS) was dissolved in 2 vol% acetic acid solution to obtain a 3 wt% QCS acetic acid solution. Polyvinyl alcohol (PVA) was dissolved in pure water at 95℃ to obtain a 10 wt% aqueous solution. 100 g of the QCS acetic acid solution and 20 g of the PVA aqueous solution were placed in a round-bottom flask and stirred evenly at 60℃ to obtain a homogeneous QCS / PVA mixed matrix. 0.045 g of two-dimensional sheet-like nano-MgAl-LDH powder was ultrasonically dispersed in 8 mL of pure water and added to the QCS / PVA mixed matrix and stirred evenly to obtain a casting solution. After defoaming treatment, the casting solution was poured into a glass container and dried at 60℃ for 12 hours to obtain a two-dimensional nano-sheet MgAl-LDH modified quaternized chitosan-based anion exchange layer. Finally, the exchange layer was immersed in a 1 mol / L KOH solution to exchange OH-. - The final anion exchange layer was obtained after washing with water. This anion exchange layer was then hot-pressed with a hydrolyzed polyacrylonitrile cation exchange layer at 5 MPa and 80°C to obtain the bipolar membrane. The transmembrane voltage of this membrane was measured to be 0.14 V, and the sheet resistivity was 2.83 Ω·cm. 2 .

[0018] Example 3:

[0019] Quaternized chitosan (QCS) was dissolved in 2 vol% acetic acid solution to obtain a 3 wt% QCS acetic acid solution. Polyvinyl alcohol (PVA) was dissolved in pure water at 95℃ to obtain a 10 wt% aqueous solution. 100 g of the QCS acetic acid solution and 20 g of the PVA aqueous solution were placed in a round-bottom flask and stirred evenly at 60℃ to obtain a homogeneous QCS / PVA mixed matrix. 0.1 g of two-dimensional sheet-like nano-MgAl-LDH powder was ultrasonically dispersed in 8 mL of pure water and added to the QCS / PVA mixed matrix, and stirred evenly to obtain a casting solution. After defoaming treatment, the casting solution was poured into a glass container and dried at 60℃ for 12 hours to obtain a two-dimensional nano-sheet MgAl-LDH modified quaternized chitosan anion exchange layer. Finally, the exchange layer was immersed in 1 mol / L KOH solution to exchange for OH- ions, and after washing with water, the final anion exchange layer was obtained. The anion exchange layer was then hot-pressed with a hydrolyzed polyacrylonitrile cation exchange layer at 5 MPa and 80°C to obtain the bipolar membrane. The transmembrane voltage of the membrane was measured to be 0.15 V, and the sheet resistivity was 4.24 Ω·cm. 2 .

[0020] Example 4:

[0021] Quaternized chitosan (QCS) was dissolved in 2 vol% acetic acid solution to obtain a 3 wt% QCS acetic acid solution. Polyvinyl alcohol (PVA) was dissolved in pure water at 95℃ to obtain a 10 wt% aqueous solution. 100 g of the QCS acetic acid solution and 20 g of the PVA aqueous solution were placed in a round-bottom flask and stirred evenly at 60℃ to obtain a homogeneous QCS / PVA mixed matrix. 0.2 g of two-dimensional sheet-like nano-MgAl-LDH powder was ultrasonically dispersed in 8 mL of pure water and added to the QCS / PVA mixed matrix and stirred evenly to obtain a casting solution. After defoaming treatment, the casting solution was poured into a glass container and dried at 60℃ for 12 hours to obtain a two-dimensional nano-sheet MgAl-LDH modified quaternized chitosan anion exchange layer. Finally, the exchange layer was immersed in a 1 mol / L KOH solution to exchange for OH-. - The final anion exchange layer was obtained after washing with water. This anion exchange layer was then subjected to hot-pressing at 5 MPa and 80°C with a hydrolyzed polyacrylonitrile cation exchange layer to obtain the bipolar membrane. The transmembrane voltage of this membrane was measured to be 0.16 V, and the sheet resistivity was 5.26 Ω·cm. 2 .

[0022] Comparative Example 1:

[0023] Quaternized chitosan (QCS) was dissolved in 2 vol% acetic acid solution to obtain a 3 wt% QCS acetic acid solution. Polyvinyl alcohol (PVA) was dissolved in pure water at 95°C to obtain a 10 wt% aqueous solution. 100 g of the QCS acetic acid solution and 20 g of the PVA aqueous solution were placed in a round-bottom flask and stirred at 60°C to obtain a homogeneous QCS / PVA mixed matrix casting solution. After defoaming, the casting solution was poured into a glass container and dried at 60°C for 12 hours to obtain an anion exchange layer of quaternized chitosan without 2D nanosheet MgAl-LDH modification. Finally, the exchange layer was immersed in a 1 mol / L KOH solution to exchange for OH-. - The final anion exchange layer was obtained after washing with water. This anion exchange layer was then subjected to hot-pressing at 5 MPa and 80°C with a hydrolyzed polyacrylonitrile cation exchange layer to obtain the bipolar membrane. The transmembrane voltage of this membrane was measured to be 0.22 V, and the sheet resistivity was 15.89 Ω·cm. 2 .

[0024] In summary, this invention prepares modified anion exchange layer bipolar membrane materials with different structures by varying the proportion of inorganic two-dimensional nanosheets MgAl-LDH in the quaternized chitosan matrix. The optimal proportion of MgAl-LDH results in bipolar membranes that possess not only good mechanical strength but also minimal surface resistivity, thereby improving OH- ion exchange capacity. - The transport rate in the anion exchange layer is increased, thereby improving the efficiency of water dissociation in the bipolar membrane.

[0025] The above description is merely a preferred embodiment of the present invention and is illustrative rather than restrictive. Those skilled in the art will understand that many changes, modifications, and even equivalent alterations can be made within the spirit and scope defined by the claims of the present invention, but all such changes will fall within the protection scope of the present invention.

Claims

1. A method for preparing a two-dimensional inorganic nanomaterial-modified quaternized chitosan-based anion exchange layer bipolar membrane, characterized in that, Follow these steps: Step 1: Dissolve chitosan in a 2 vol% acetic acid solution, then add the quaternizing agent 2,3-epoxypropyltrimethylammonium chloride. Quaternized chitosan was obtained by water bath at 80℃, and then filtered, dried and pulverized to obtain quaternized chitosan powder. Step 2: Dissolve a certain amount of magnesium nitrate nonahydrate, aluminum nitrate hexahydrate, and urea in an ethylene glycol aqueous solution, and then perform a hydrothermal reaction at 160°C for 6 hours to obtain two-dimensional nanosheet MgAl-LDH. Step 3: Dissolve the quaternized chitosan obtained in Step 1 in a 2 vol% acetic acid solution to obtain a homogeneous solution. Mix this solution with a polyvinyl alcohol solution of a certain concentration to obtain a uniformly mixed matrix. Add the two-dimensional MgAl-LDH powder obtained in Step 2 to the above quaternized chitosan / polyvinyl alcohol mixed matrix, stir evenly, and then defoam to obtain a casting solution. Cast the casting solution in a glass container and dry it at 60°C for 6 hours to evaporate the solution or obtain an anion exchange layer. Immerse the anion exchange layer in a 1 mol / L KOH solution for 24 hours to finally exchange OH-. - Form. The anion exchange layer was hot-pressed with a hydrolyzed polyacrylonitrile cation exchange layer to obtain a two-dimensional modified anion exchange layer bipolar membrane.

2. The method for preparing a two-dimensional inorganic nanomaterial-modified quaternized chitosan-based anion exchange layer bipolar film according to claim 1, characterized in that, In step 1, the mass of both chitosan and 2,3-epoxypropyltrimethylammonium chloride is 8-10 g.

3. The method for preparing a two-dimensional inorganic nanomaterial-modified quaternized chitosan-based anion exchange layer bipolar film according to claim 1, characterized in that, In step 2, the amounts of magnesium nitrate, aluminum nitrate, and urea are 0.75-0.8g, 1-1.2g, and 1.5-2g, respectively, and the amount of ethylene glycol aqueous solution is 60-80ml with a concentration of 90-95wt%.

4. The method for preparing a two-dimensional inorganic nanomaterial-modified quaternized chitosan-based anion exchange layer bipolar membrane according to claim 1, characterized in that, Two-dimensional MgAl-LDH powder was added to the above-mentioned quaternized chitosan / polyvinyl alcohol mixed matrix in a mass of 0.015-0.2g.

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