Preparation method and application of MOF modified cellulose acetate membrane material

Abstract

The invention discloses a preparation method and application of an MOF modified cellulose acetate membrane material. According to the invention, ZIF-8 is grown on nanofibers by using an in-situ growth method, so that a stable ion selective channel is constructed, and osmotic energy power generation is realized in an environment with external concentration difference. The preparation method comprises the following steps: firstly, adding dimethylimidazole into a spinning solution of cellulose acetate, immersing an electrospun film into a methanol solution of zinc nitrate, carrying out in-situ growth for 4 hours, and then drying to obtain the ZIF-8 / CA film. The long-term stability and economic benefits of the ion-selective membrane can be improved when the ion-selective membrane is applied to osmotic energy collection. The method is simple in process and high in repeatability, and a new thought is provided for designing an osmotic energy collecting membrane with high economic benefit and high stability.

Description

Technical Field

[0001] The invention belongs to the field of osmotic energy collection, and specifically relates to a preparation method of a MOF-modified cellulose acetate membrane material and an application thereof. Background Art

[0002] The energy crisis caused by the continuous depletion of fossil fuels is one of the pressing issues facing our modern society. In this context, scientists and engineers are focusing on the development of alternative renewable energy sources, such as wind, geothermal, biomass, and solar energy. Osmotic energy, also known as "blue energy," is a promising renewable energy source for power generation extracted from the chemical potential difference between high-salinity seawater and low-salinity river water. The mixing of ion solutions of different concentrations releases Gibbs free energy, which can be harvested and converted into electrical energy.

[0003] It is predicted that the total amount of osmotic energy available worldwide is about 1TW. Membrane-based reverse electrodialysis, first proposed in 1954, is a key technology for capturing this blue energy. However, commonly used ion exchange membranes are subject to some limitations, such as insufficient mass transfer and high membrane resistance, resulting in low power density, which is insufficient for effective energy conversion. But with the rise of nano-ion channels, lower membrane internal resistance and efficient transmission have greatly improved the conversion efficiency. When ions pass through nano-ion channels with certain selectivity, a net current will be generated due to the different mobility of positive and negative ions. By collecting this current, the conversion of osmotic energy into electrical energy can be completed. In nature, electric eels can generate voltages up to 600V through sodium or potassium ion concentration gradients. Its neuronal fibrils can generate stimulation signals that prompt ions in resting cells to pass through nano-ion channels on the cell membrane to generate transcellular potentials.

[0004] Among the osmotic energy collection membranes at the current cutting-edge level of science and technology, the design of ion selective membranes with good performance mainly considers three aspects: the first is its ion selectivity. High ion selectivity means that charges are carried on both sides of the nanochannel, and ions with opposite charges are allowed to pass through the ion double layer model to generate a net potential and output current. The second is that it needs to have a high ion flux to ensure that it has a good ion pass rate and output power. The third is that it needs an asymmetric channel structure to improve the overall ion rectification and eliminate the influence of concentration polarization. In order to achieve high ion flux and good ion selectivity, most membranes are designed with complex nanofluid channels. Considering the actual economic effects of power generation, most membranes do not have the potential for large-scale power generation. Summary of the invention

[0005] In order to solve the problems existing in the above background, the present invention provides a preparation method of MOF-modified cellulose acetate membrane material and its application. Through a new preparation method with simple process, the porous MOF material is in situ grown on the cellulose acetate electrospinning film. The prepared film has high ion flux and low raw material cost with high economic effect, reaching a commercial 5W / m 2 The standard provides a new idea and method for realizing concentration gradient power generation.

[0006] The technical solution proposed by the present invention is:

[0007] The present invention discloses a preparation method of a MOF-modified cellulose acetate membrane material and its application, comprising the following steps:

[0008] (1) Weigh cellulose acetate (CA) and add it to N,N-dimethylacetamide (DMAc). Add acetone to the mixed solution and stir well.

[0009] (2) Add 2-methylimidazole to the solution in step (1), heat and stir to obtain a spinning precursor solution.

[0010] (3) Adding the transparent and uniform spinning precursor solution in step (2) into the electrospinning syringe for electrospinning.

[0011] (4) The spun fiber membrane is placed in a watch glass, zinc nitrate methanol solution is added, and then 2-methylimidazole methanol solution is added, and the ZIF-8 is grown in situ.

[0012] (5) The grown membrane was washed three times with ethanol and water, and then dried to obtain a MOF-modified cellulose acetate membrane.

[0013] As a preferred solution, the content of CA in step (1) is 10-15 wt%, DMAc:acetone=3:2; more preferably, the ratio is 12 wt% cellulose acetate;

[0014] As a preferred solution, the content of 2-methylimidazole in step (2) is 3-6wt%, the heating temperature is 50-60°C, and the heating time is 2-3h; more preferably, the ratio is 5wt% 2-methylimidazole, the heating temperature is 50°C, and the heating time is 2h;

[0015] As a preferred solution, the electrospinning parameters in step (3) are 18 kV and a pushing speed of 0.001 mm / s;

[0016] As a preferred solution, the concentration of the zinc nitrate methanol solution in step (4) is 0.15 mol / L, and the concentration of the 2-methylimidazole methanol solution is 0.6 mol / L. The in-situ growth temperature is room temperature and the time is 4 hours;

[0017] As a preferred solution, the drying temperature in step (5) is 60° C. and the drying time is 0.5 h;

[0018] Compared with the prior art, the advantages of the technology of the present invention are:

[0019] (1) The present invention has the advantages of simple process and low raw material cost. Compared with the osmotic energy collection film with the same power, it has better application potential and proposes a new idea for osmotic energy collection;

[0020] (2) The film prepared by the present invention reaches the commercial standard of 5W / m 2 , and has strong structural stability;

[0021] (3) The method of in situ growth of MOF on fiber proposed in the present invention has strong binding force and uniformity; BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the process of preparing the osmotic energy collection film according to Example 1 of the present invention.

[0023] Figure 2 The scanning electron microscope images of the osmotic energy collection film prepared in Example 1 of the present invention before and after modification.

[0024] Figure 3 XRD and FT-IR diagrams of the osmotic energy collection film prepared in Example 2 of the present invention.

[0025] Figure 4 Schematic diagram of membrane permeability energy collection tested in Example 2 of the present invention.

[0026] Figure 5 The conductivity curves of the film tested in Example 3 of the present invention in KCl solutions of different concentrations.

[0027] Figure 6 This is a diagram of the power generation efficiency of the thin film simulated seawater or river water concentration and different ions tested in Example 4 of the present invention.

[0028] Figure 7 This is a stability test diagram of the film tested in Example 4 of the present invention. DETAILED DESCRIPTION

[0029] The present invention is described more fully below in conjunction with specific embodiments and drawings, but the present invention is not limited thereto.

[0030] The experimental methods in the following examples are all conventional methods unless otherwise specified.

[0031] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0032] Example 1

[0033] Preparation of 2-methylimidazole modified cellulose acetate film

[0034] This embodiment 1 provides a method for preparing a 2-methylimidazole-modified cellulose acetate film, comprising the following steps:

[0035] (1) 1.2 g of cellulose acetate (CA) with a molecular weight of 50,000 was dissolved in 4.98 g of N,N-dimethylacetamide (DMAc) and 3.32 g of acetone solution, and stirred in a 50°C water bath for 2 h to obtain a uniform and transparent solution. 0.5 g of 2-methylimidazole was added to the solution and dissolved for ten minutes to obtain a uniform and transparent dimethylimidazole-modified cellulose acetate spinning precursor solution.

[0036] (2) The solution obtained in (1) was sucked into a 5 mL syringe, and the electrospinning machine parameters were adjusted to 18 kV, a pushing time of 0.001 mm / s, a room temperature environment, a relative humidity of 40%, and a spinning time of 8 h.

[0037] (3) The fiber membrane in (2) is placed in an oven for 0.5 h to obtain a 2-methylimidazole-modified cellulose acetate membrane.

[0038] Please see attached Figure 1 , is a schematic diagram of the preparation of this embodiment, see the attached Figure 2 a is a scanning electron microscope image of this embodiment, from which it can be seen that the spun nanofibers are evenly distributed and the modified 2-methylimidazole is wrapped in the fibers.

[0039] Example 2

[0040] In situ growth of ZIF-8 on cellulose acetate nanofibers.

[0041] Example 2 provides a method for in-situ growth of ZIF-8 on cellulose acetate nanofibers, comprising the following steps:

[0042] (1) 1.34 g of zinc nitrate hexahydrate was added to 30 mL of methanol solution and completely dissolved to obtain a 0.15 mol / L zinc nitrate methanol solution. 1.48 g of 2-methylimidazole was weighed and added to 30 mL of methanol solution and completely dissolved to obtain a 0.6 mol / L 2-methylimidazole methanol solution.

[0043] (2) Cut a 3 cm × 3 cm piece of the film obtained in Example 1 and immerse it in 15 mL of the zinc nitrate methanol solution in step 1. After the film is completely soaked, add 15 mL of the 2-methylimidazole methanol solution in step 1. At room temperature, the solution slowly becomes turbid and is allowed to grow in situ for 4 h.

[0044] (3) The film obtained in (2) was rinsed three times with a mixed solution of deionized water and ethanol, and then placed in an oven for drying for 1 hour to obtain a cellulose acetate film with ZIF-8 grown in situ.

[0045] Please refer to the attached Figure 1 , is a schematic diagram of the preparation of this embodiment; please refer to the attached Figure 2 b is a scanning electron microscope image of this example, from which it can be seen that the in-situ grown ZIF-8 crystals are uniformly wrapped on the surface of the nanofibers.

[0046] XRD test was performed on ZIF-8@CA membrane, such as Figure 3 As shown in a, the characteristic peak of ZIF-8 is obvious and the diffraction peak intensity is high. The BET test of ZIF-8@CA membrane is carried out, such as Figure 3 As shown in b, the average pore size of the membrane is concentrated at 3.9 nm.

[0047] Example 3

[0048] In this Example 3, the ion transport properties of the obtained MOF modified film were tested. Figure 4 Schematic diagram of the osmotic energy collection device.

[0049] The ZIF-8 modified cellulose acetate film was cut into 3mm×3mm pieces and placed between the experimental devices. The test area was 0.01mm 2 , KCl solutions of different concentrations were added to both sides of the film, the scanning speed was 0.01V / s, and a scanning voltage of -0.5V to 0.5V was applied to both ends of the solution through the Ag / AgCl electrode using an electrochemical workstation to obtain a linear curve, and the conductivity of different concentrations was calculated using Ohm's law. Figure 5 As shown, in low concentration solutions, the deviation of transmembrane conductivity from the bulk value is more significant, indicating that surface charge controls the ion transport behavior.

[0050] Example 4

[0051] In Example 4, the obtained MOF modified film was subjected to a permeation energy collection test. Figure 4 Schematic diagram of the osmotic energy collection device.

[0052] The concentration difference between seawater and river water was artificially simulated in the experimental device. 0.01 mol / L NaCl solution was added to the left end to simulate river water, and 0.5 mol / L NaCl solution was added to the right end to simulate seawater. An electrochemical workstation was used to apply a scanning voltage of -0.5 V to 0.5 V at both ends of the solution through Ag / AgCl electrodes. The scanning speed was 0.01 V / s, and the IV curve under 50 times NaCl salt difference was obtained as shown in the figure. Figure 6 As shown in a. Add 50 times CaCl in the experimental device 2 、KCl、LiCl、MgCl2 The power density collected by the film for different ion penetration can be measured by the above method, such as Figure 6 b. The film was tested for a long time, and it maintained a relatively stable permeability output capacity during the long test. Figure 7 shown.

Claims

1. The present invention provides a method for preparing a MOF-modified cellulose acetate membrane material and its application, characterized in that: The following steps are involved: (1) Weigh cellulose acetate (CA) and add it to N,N-dimethylacetamide (DMAc). Add acetone to the mixed solution and stir well. (2) Add 2-methylimidazole to the solution in step (1), heat and stir to obtain a spinning precursor solution. (3) Adding the transparent and uniform spinning precursor solution prepared in step (2) into the electrospinning syringe for electrospinning. (4) The spun fiber membrane is placed in a watch glass, zinc nitrate methanol solution is added, and then 2-methylimidazole methanol solution is added, and the ZIF-8 is grown in situ. (5) The grown membrane was washed three times with ethanol and water, and then dried to obtain a MOF-modified cellulose acetate membrane.

2. The present invention according to claim 1 discloses a method for preparing a MOF-modified cellulose acetate membrane material and its application, characterized in that: In the step (1), the content of CA added is 10-15 wt%, and the ratio of DMAc to acetone is 3:

2.

3. The present invention according to claim 2 discloses a method for preparing a MOF-modified cellulose acetate membrane material and its application, characterized in that: In the step (2), 3-6 wt% of 2-methylimidazole is added, the heating temperature is 50-60° C., and stirring is performed for 2-4 hours.

4. The present invention according to claim 3 discloses a method for preparing a MOF-modified cellulose acetate membrane material and its application, characterized in that: In the step (3), the parameters of the electrospinning are 18 kV, a pushing speed of 0.001 mm / s, and a spinning volume of 5 ml.

5. The present invention according to claim 4 discloses a method for preparing a MOF-modified cellulose acetate membrane material and its application, characterized in that: In the step (4), the concentration of the zinc nitrate methanol solution is 0.15-0.2 mol / L, and the concentration of the 2-methylimidazole methanol solution is 0.6-0.8 mol / L. The in-situ growth temperature is room temperature and the time is 4-6 hours.

6. The ZIF-8@cellulose acetate membrane obtained by the preparation method according to any one of claims 1 to 5, characterized in that: Dimethylimidazole was added to the nanofibers in advance, and ZIF-8 was grown in situ at room temperature to construct ion-selective channels, thereby preparing a long-term stable and economically efficient film and realizing osmotic energy collection.

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