Preparation and modification method of chitosan nanofiltration membrane

Abstract

The application discloses a preparation and modification method of a chitosan nanofiltration membrane, and steps are as follows: step one: completely dissolving CS in an acetic acid solution, standing and defoaming, loading CS on the surface of a PAN membrane by vacuum assistance, drying at normal temperature, then cross-linking by using a TMC organic phase solution to obtain a CS-TMC nanofiltration membrane; step two: soaking the CS-TMC nanofiltration membrane prepared in step one in a PEI aqueous solution for a set time, and then washing with deionized water after taking out; step three: solidification treatment; step four: soaking in deionized water for subsequent use. The positively charged CS-PEI composite nanofiltration membrane is prepared on a PAN base membrane by interfacial polymerization and surface grafting, the membrane obtained by the method has high flux while maintaining high separation performance of metal ions in radioactive nuclear wastewater, and the CS-PEI composite nanofiltration membrane has very important practical significance in the fields of radioactive wastewater treatment and sewage treatment.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology and relates to a method for preparing and modifying chitosan (CS) nanofiltration membranes for the efficient separation of nuclides in radioactive wastewater. Background Technology

[0002] With the rapid increase in global energy demand, nuclear energy, as a sustainable energy source, has become a key area for energy development. Among the various nuclear elements released, nuclear energy stands out due to its high gamma radiation, long half-lives (30.2 years, 28.79 years, and 5.27 years, respectively), and high solubility. 137 Cs, 90 Sr and 60 Co (carbon) is considered the most important element. Radioactive nuclides can gradually accumulate in the human body, leading to anemia, bone cancer, leukemia, metabolic disorders, and even death. Radioactive wastewater can be classified into high, medium, and low-level radioactive wastewater (LLRW) based on its radioactivity intensity. Long-term isolation of radioactive wastewater from the living environment, allowing it to decay naturally, is suitable for all levels of radioactive wastewater. However, leaks can cause serious environmental damage. Therefore, effective treatment technologies for radioactive wastewater are necessary. To date, various physical, chemical, biological, and combined methods have been developed to purify radioactive wastewater. Among these, membrane separation is considered an ideal method due to its advantages such as mild operating conditions, simple equipment, low energy consumption, good effluent quality, high concentration ratio, large decontamination coefficient, and stable and reliable operation. With the continuous development of membrane technology, various new types of membranes have played an important role in the treatment of radioactive wastewater in recent years.

[0003] Hyung-Ju Kim et al. performed radionuclide separation using a commercial polymer membrane at room temperature (298 K). The results showed that the water flux of NF270 was 11.2 Lm. -2 h -1 bar -1 Sr 2+ Cs + and Co 2+ The rejection rates for these three types of components can reach 83%, 78%, and 64%, while XLE-2540 can achieve rejection rates of 99%, 98%, and 96% for these three types, but the flux is only 5.4 Lm. -2 h -1 bar -1 .

[0004] Zhang Xue et al. investigated the effect of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) on the metal salt rejection rate during ultrafiltration. During ultrafiltration of LLRW, as the concentration of CTAB increased from 0 mg / L to 50 mg / L, the Sr...2+ Co 2+ and Ag + The retention rate increased from 24-33% to 92-97% when the concentration of CTAB increased from 0 mg / L to 400 mg / L, and Cs + The retention rate increased from 23% to 54%.

[0005] Lu Yawei et al. prepared zirconium dioxide (TDZ) nanofiltration (NF) membranes doped with titanium dioxide using an improved sol-gel process. When the TDZNF membrane was in a solution with a pH of approximately 6-8, the membrane surface was almost uncharged, achieving only about 20% ion rejection. However, in a solution with a pH of 3, the membrane surface became positively charged, and Co… 2+ 、Sr 2+ and Cs + The retention rates can reach 99.6%, 99.2%, and 75.5%.

[0006] The above research indicates that existing membrane technologies for treating simulated radioactive wastewater have two main problems: first, the membrane flux is relatively low, and high-pressure conditions are required during operation; second, they need to be combined with other processes to achieve higher treatment efficiency, making operation complex and unsuitable for large-scale commercial application.

[0007] Chitosan (CS) is a product formed by the deacetylation of chitin. It is widely found in the cell walls of shrimp, crabs, fungi, etc. It is abundant in nature and can also be extracted from industrial and agricultural waste. It is non-toxic, non-polluting, and biodegradable, and its application prospects are very broad. Summary of the Invention

[0008] (I) Purpose of the Invention

[0009] The purpose of this invention is to address the limitations of existing membrane technologies, such as low flux, the need for integration with other processes, and complex operation. Therefore, this invention proposes a method for preparing and modifying chitosan (CS) nanofiltration membranes to efficiently separate nuclides from radioactive wastewater.

[0010] (II) Technical Solution

[0011] To address the aforementioned technical problems, this invention provides a method for preparing and modifying a chitosan nanofiltration membrane, comprising the following steps:

[0012] Step 1: Preparation of CS-TMC nanofiltration membrane

[0013] CS was completely dissolved in acetic acid solution, allowed to stand to remove bubbles, and then loaded onto the surface of polyacrylonitrile (PAN) membrane with vacuum assistance. After drying at room temperature, it was crosslinked with trimethylolpropionate chloride (TMC) organic phase solution to obtain CS-TMC nanofiltration membrane.

[0014] Step 2: Membrane surface modification treatment

[0015] The CS-TMC nanofiltration membrane prepared in step one was immersed in a polyethyleneimine (PEI) aqueous solution for a set time, and then rinsed with deionized water.

[0016] Step 3: Curing treatment

[0017] The nanofiltration membrane with a cation layer prepared in step two was placed in an oven for curing and drying to obtain a CS-PEI composite nanofiltration membrane.

[0018] Step 4: Remove the dried membrane and soak it in deionized water for later use.

[0019] In step one, the surface-dried membrane is immersed in a 0.1% (w / w) trimethylbenzene chloride organic phase solution for crosslinking for 3-30 minutes.

[0020] In step one, the dosage of CS is 0.005mg-0.1mg.

[0021] In step two, the concentration of the PEI aqueous solution is 1%.

[0022] In step two, the soaking time in the PEI solution is 1-45 minutes.

[0023] In step three, the curing temperature is 60℃ and the curing time is 5 minutes.

[0024] (III) Beneficial Effects

[0025] The preparation and modification method of chitosan nanofiltration membrane provided by the above technical solution obtains a positively charged CS-PEI composite nanofiltration membrane on a PAN base membrane through interfacial polymerization and surface grafting. The membrane obtained by this method maintains high separation performance of metal ions in radioactive nuclear wastewater while also having a high flux. The CS-PEI composite nanofiltration membrane has very important practical significance in the field of radioactive wastewater treatment or sewage treatment. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the principle of the chitosan (CS) nanofiltration membrane preparation and modification method of the present invention for the efficient treatment of radionuclides in radioactive wastewater;

[0027] Figure 2 This is a schematic diagram of the separation performance test process of the CS-PEI composite nanofiltration membrane of the present invention;

[0028] Figure 3 This is a graph showing the changes in separation performance of 0.05 mg CS and TMC crosslinked for different times;

[0029] Figure 4 This is a graph showing the changes in separation performance after 15 minutes of crosslinking different amounts of CS and TMC;

[0030] Figure 5 The graph shows the changes in the separation performance of the CS-PEI composite membranes prepared in Examples 1-7.

[0031] Note: Figures 3 to 5 In the middle, the labels in the upper right corner, from top to bottom, correspond to the results of each set of comparative data from left to right in the diagram. Detailed Implementation

[0032] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0033] This embodiment first determines the interfacial polymerization time and the amount of chitosan used during interfacial polymerization in the preparation and modification methods of chitosan nanofiltration membrane through two processes, thereby obtaining the optimal manufacturing conditions for CS-TMC nanofiltration membrane. Then, the modification time of CS-TMC nanofiltration membrane in PEI aqueous solution is determined.

[0034] The process for determining the timing of interface aggregation is as follows:

[0035] (1) Dissolve 1gCS completely in 50mL of 2% acetic acid aqueous solution using magnetic stirring, and let stand for 4h to remove bubbles.

[0036] (2) Dilute 2.5 μL of the CS solution obtained in step (1) with deionized water to 10 mL, load it onto the surface of the PAN base film with vacuum assistance, and dry at room temperature;

[0037] (3) Then pour a 0.1% (w / w) trimethylbenzene chloride organic phase solution onto a PAN membrane loaded with CS and perform interfacial polymerization for 3-30 min; the optimal interfacial polymerization time can be determined by changing the interfacial polymerization time.

[0038] (4) Remove the TMC solution from the surface and heat-treat the membrane in a 60°C oven for 5 minutes to obtain a nanofiltration membrane.

[0039] To examine the performance of the prepared nanofiltration membrane, the experimental setup and results were as follows: Figure 2 and Figure 3 The operating pressure was 4 bar, and the experimental membrane area was 7.068 cm². 2 The concentrations of NaCl and Na₂SO₄ were both 1000 ppm, and Cs + 、Sr 2+ and Co 2+The concentrations were 7 ppm, 13 ppm, and 1 ppm, respectively. Water flux J = ΔV / (A × T × P), where J is the water flux, ΔV is the pure water permeate volume (L), and A is the effective membrane area of ​​the reverse osmosis membrane (m²). 2 ), T is time (h), and P is the pressure (bar) during the filtration process. Retention rate R = (C p -C f ) / C p ×100%, where C p C represents the concentration of the solute in the original solution. f This represents the concentration of the solute in the permeate.

[0040] The process for determining the amount of client-server (CS) usage during interface aggregation is as follows:

[0041] (1) Dissolve 1gCS completely in 50mL of 2% acetic acid aqueous solution using magnetic stirring, and let stand for 4h to remove bubbles.

[0042] (2) Dilute 0.25μL-5μL of the CS solution obtained in step (1) with deionized water to 10mL, load it onto the surface of the PAN base film with vacuum assistance, and dry it at room temperature; change the amount of CS used during interfacial polymerization to determine the optimal amount of chitosan.

[0043] (3) Then, a 0.1% (w / w) solution of pyromellitic chloride organic phase was poured onto the PAN membrane loaded with CS and interfacial polymerization was carried out for 15 min.

[0044] (4) Remove the TMC solution from the surface and heat-treat the membrane in a 60°C oven for 5 minutes to obtain a nanofiltration membrane.

[0045] To examine the performance of the prepared nanofiltration membrane, the experimental setup and results were as follows: Figure 2 and Figure 4 The operating pressure was 4 bar, and the experimental membrane area was 7.068 cm². 2 The concentrations of NaCl and Na₂SO₄ were both 1000 ppm, and Cs + 、Sr 2+ and Co 2+ The concentrations were 7 ppm, 13 ppm, and 1 ppm, respectively. Water flux J = ΔV / (A × T × P), where J is the water flux, ΔV is the pure water permeate volume (L), and A is the effective membrane area of ​​the reverse osmosis membrane (m²). 2 ), T is time (h), and P is the pressure (bar) during the filtration process. Retention rate R = (C p -C f ) / C p ×100%, where C p C represents the concentration of the solute in the original solution. fThis represents the concentration of the solute in the permeate.

[0046] Based on the determination of the interfacial polymerization time and the amount of chitosan used during interfacial polymerization, the following embodiments were carried out.

[0047] Example 1

[0048] The preparation method of chitosan (CS) nanofiltration membrane includes the following specific steps:

[0049] (1) Dissolve 1gCS completely in 50mL of 2% acetic acid aqueous solution using magnetic stirring, and let stand for 4h to remove bubbles.

[0050] (2) Dilute 2.5 μL of the CS solution obtained in step (1) with deionized water to 10 mL, load it onto the surface of the PAN base film with vacuum assistance, and dry at room temperature;

[0051] (3) Then, a 0.1% (w / w) solution of pyromellitic chloride organic phase was poured onto the PAN membrane loaded with CS and interfacial polymerization was carried out for 15 min.

[0052] (4) Remove the TMC solution from the surface and heat-treat the membrane in a 60°C oven for 5 minutes to obtain the composite matrix nanofiltration membrane TFC.

[0053] To examine the performance of the nanofiltration membranes prepared in the examples, the experimental setup and results were as follows: Figure 2 and Figure 5 The operating pressure was 4 bar, and the experimental membrane area was 7.068 cm². 2 The concentrations of NaCl and Na₂SO₄ were both 1000 ppm, and Cs + 、Sr 2+ and Co 2+ The concentrations were 7 ppm, 13 ppm, and 1 ppm, respectively. Water flux J = ΔV / (A × T × P), where J is the water flux, ΔV is the pure water permeate volume (L), and A is the effective membrane area of ​​the reverse osmosis membrane (m²). 2 ), T is time (h), and P is the pressure (bar) during the filtration process. Retention rate R = (C p -C f ) / C p ×100%, where C p C represents the concentration of the solute in the original solution. f This represents the concentration of the solute in the permeate.

[0054] Example 2

[0055] The preparation and modification method of chitosan (CS) nanofiltration membrane, the specific steps are as follows:

[0056] (1) Dissolve 1gCS completely in 50mL of 2% acetic acid aqueous solution using magnetic stirring, and let stand for 4h to remove bubbles.

[0057] (2) Dilute 2.5 μL of the CS solution obtained in step (1) with deionized water to 10 mL, load it onto the surface of the PAN base film with vacuum assistance, and dry at room temperature;

[0058] (3) Then, a 0.1% (w / w) solution of pyromellitic chloride organic phase was poured onto the PAN membrane loaded with CS and interfacial polymerization was carried out for 15 min.

[0059] (4) Remove the TMC solution from the surface, immerse the membrane in a PEI solution with a mass percentage concentration of 1% for 1 min, then rinse the membrane surface with deionized water to remove the residual PEI on the surface, and finally place the membrane in a 60℃ oven for heat treatment for 5 min to obtain the composite matrix nanofiltration membrane TFC-1.

[0060] To examine the performance of the nanofiltration membranes prepared in the examples, the specific testing process was consistent with that in Example 1, and the experimental setup and results were as follows: Figure 2 and Figure 5 .

[0061] Example 3

[0062] The preparation and modification method of chitosan (CS) nanofiltration membrane, the specific steps are as follows:

[0063] (1) Dissolve 1gCS completely in 50mL of 2% acetic acid aqueous solution using magnetic stirring, and let stand for 4h to remove bubbles.

[0064] (2) Dilute 2.5 μL of the CS solution obtained in step (1) with deionized water to 10 mL, load it onto the surface of the PAN base film with vacuum assistance, and dry at room temperature;

[0065] (3) Then pour the 0.1% TMC solution onto the PAN membrane loaded with CS and perform interfacial polymerization for 15 min;

[0066] (4) Remove the TMC solution from the surface, immerse the membrane in a PEI solution with a mass percentage concentration of 1% for 5 minutes, then rinse the membrane surface with deionized water to remove the residual PEI on the surface, and finally place the membrane in a 60℃ oven for heat treatment for 5 minutes to obtain the composite matrix nanofiltration membrane TFC-2.

[0067] To examine the performance of the nanofiltration membranes prepared in the examples, the specific testing process was consistent with that in Example 1, and the experimental setup and results were as follows: Figure 2 and Figure 5 .

[0068] Example 4

[0069] The preparation and modification method of chitosan (CS) nanofiltration membrane, the specific steps are as follows:

[0070] (1) Dissolve 1gCS completely in 50mL of 2% acetic acid aqueous solution using magnetic stirring, and let stand for 4h to remove bubbles.

[0071] (2) Dilute 2.5 μL of the CS solution obtained in step (1) with deionized water to 10 mL, load it onto the surface of the PAN base film with vacuum assistance, and dry at room temperature;

[0072] (3) Then, a 0.1% (w / w) solution of pyromellitic chloride organic phase was poured onto the PAN membrane loaded with CS and interfacial polymerization was carried out for 15 min.

[0073] (4) Remove the TMC solution from the surface, immerse the membrane in a PEI solution with a mass percentage concentration of 1% for 10 min, then rinse the membrane surface with deionized water to remove the residual PEI on the surface, and finally place the membrane in a 60℃ oven for heat treatment for 5 min to obtain the composite matrix nanofiltration membrane TFC-3.

[0074] To examine the performance of the nanofiltration membranes prepared in the examples, the specific testing process was consistent with that in Example 1, and the experimental setup and results were as follows: Figure 2 and Figure 5 .

[0075] Example 5

[0076] The preparation and modification method of chitosan (CS) nanofiltration membrane, the specific steps are as follows:

[0077] (1) Dissolve 1gCS completely in 50mL of 2% acetic acid aqueous solution using magnetic stirring, and let stand for 4h to remove bubbles.

[0078] (2) Dilute 2.5 μL of the CS solution obtained in step (1) with deionized water to 10 mL, load it onto the surface of the PAN base film with vacuum assistance, and dry at room temperature;

[0079] (3) Then, a 0.1% (w / w) solution of pyromellitic chloride organic phase was poured onto the PAN membrane loaded with CS and interfacial polymerization was carried out for 15 min.

[0080] (4) Remove the TMC solution from the surface, immerse the membrane in a PEI solution with a mass percentage concentration of 1% for 15 min, then rinse the membrane surface with deionized water to remove the residual PEI on the surface, and finally place the membrane in a 60℃ oven for heat treatment for 5 min to obtain the composite matrix nanofiltration membrane TFC-4.

[0081] To examine the performance of the nanofiltration membranes prepared in the examples, the specific testing process was consistent with that in Example 1, and the experimental setup and results were as follows: Figure 2 and Figure 5 .

[0082] Example 6

[0083] The preparation and modification method of chitosan (CS) nanofiltration membrane, the specific steps are as follows:

[0084] (1) Dissolve 1gCS completely in 50mL of 2% acetic acid aqueous solution using magnetic stirring, and let stand for 4h to remove bubbles.

[0085] (2) Dilute 2.5 μL of the CS solution obtained in step (1) with deionized water to 10 mL, load it onto the surface of the PAN base film with vacuum assistance, and dry at room temperature;

[0086] (3) Then, a 0.1% (w / w) solution of pyromellitic chloride organic phase was poured onto the PAN membrane loaded with CS and interfacial polymerization was carried out for 15 min.

[0087] (4) Remove the TMC solution from the surface, immerse the membrane in a PEI solution with a mass percentage concentration of 1% for 30 min, then rinse the membrane surface with deionized water to remove the residual PEI on the surface, and finally place the membrane in a 60℃ oven for heat treatment for 5 min to obtain the composite matrix nanofiltration membrane TFC-5.

[0088] To examine the performance of the nanofiltration membranes prepared in the examples, the specific testing process was consistent with that in Example 1, and the experimental setup and results were as follows: Figure 2 and Figure 5 .

[0089] Example 7

[0090] The preparation and modification method of chitosan (CS) nanofiltration membrane, the specific steps are as follows:

[0091] (1) Dissolve 1gCS completely in 50mL of 2% acetic acid aqueous solution using magnetic stirring, and let stand for 4h to remove bubbles.

[0092] (2) Dilute 2.5 μL of the CS solution obtained in step (1) with deionized water to 10 mL, load it onto the surface of the PAN base film with vacuum assistance, and dry at room temperature;

[0093] (3) Then, a 0.1% (w / w) solution of pyromellitic chloride organic phase was poured onto the PAN membrane loaded with CS and interfacial polymerization was carried out for 15 min.

[0094] (4) Remove the TMC solution from the surface, immerse the membrane in a PEI solution with a mass percentage concentration of 1% for 45 min, then rinse the membrane surface with deionized water to remove the residual PEI on the surface, and finally place the membrane in a 60℃ oven for heat treatment for 5 min to obtain the composite matrix nanofiltration membrane TFC-6.

[0095] To examine the performance of the nanofiltration membranes prepared in the examples, the specific testing process was consistent with that in Example 1, and the experimental setup and results were as follows: Figure 2 and Figure 5 .

[0096] Experimental results:

[0097] from Figure 2 and 4 It can be determined that the optimal dosage of CS is 0.05 mg, and the optimal TMC crosslinking time is 15 min. Figure 5 Figure 3 Figure 5 It can be observed that the pure water flux of the nanofiltration membrane gradually increases from 1 min to 30 min with PEI treatment time, and then tends to decrease after 30 min. Cs after PEI treatment... + 、Sr 2+ and Co 2+ The retention performance was significantly improved; after PEI treatment for 30 minutes, 23.3 Lm -2 h -1 bar -1 Cs + 、Sr 2+ and Co 2+ The retention rates were 61.62%, 94.8%, and 78.63%, respectively.

[0098] As can be seen from the figure, the obtained CS-PEI composite nanofiltration membrane maintains high separation performance of nuclides in simulated radioactive wastewater while also having a high flux. Compared with commercial membranes, the CS-PEI composite nanofiltration membrane has a promising application prospect for treating radioactive wastewater.

[0099] As can be seen from the above technical solution, the present invention has the following significant features:

[0100] 1. The method for preparing and modifying chitosan (CS) nanofiltration membrane according to the present invention involves firstly, CS and TMC polymerizing at the interface of PAN to form a polyamide layer. After interfacial polymerization, unreacted acyl chlorides and carboxylic acids produced by the hydrolysis of acyl chlorides provide a basis for PEI grafting, enabling a large amount of PEI to be successfully grafted onto the negatively charged polyamide layer surface. The synergistic effect of size effect and electrostatic repulsion provides conditions for retaining metal ions in simulated radioactive nuclear wastewater.

[0101] 2. The method for preparing a composite nanofiltration membrane based on chitosan described in this invention introduces a positively charged functional layer through a simple method. The CS-PEI composite nanofiltration membrane obtained by this method maintains high separation performance of metal ions in simulated radioactive nuclear wastewater while also having a high flux. Furthermore, the CS-PEI composite nanofiltration membrane can achieve good treatment results for radioactive nuclear wastewater without additional investment, and has good application prospects.

[0102] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing and modifying a chitosan nanofiltration membrane, characterized in that, Includes the following steps: Step 1: Preparation of CS-TMC nanofiltration membrane CS was completely dissolved in acetic acid solution, allowed to stand to remove bubbles, and then loaded onto the surface of PAN membrane using vacuum assistance. After drying at room temperature, it was cross-linked with TMC organic phase solution to obtain CS-TMC nanofiltration membrane. Step 2: Membrane surface modification treatment The CS-TMC nanofiltration membrane prepared in step one was immersed in PEI aqueous solution for a set time, and then rinsed with deionized water. Step 3: Curing treatment The nanofiltration membrane with a cation layer prepared in step two is placed in an oven for curing and drying to obtain a CS-TMC-PEI composite nanofiltration membrane, abbreviated as CS-PEI composite nanofiltration membrane. Step 4: Take out the dried composite nanofiltration membrane and soak it in deionized water for subsequent use.

2. The method for preparing and modifying the chitosan nanofiltration membrane as described in claim 1, characterized in that, In step one, the surface-dried membrane is immersed in a 0.1% TMC organic phase solution for crosslinking for 3-30 minutes.

3. The method for preparing and modifying the chitosan nanofiltration membrane as described in claim 2, characterized in that, In step one, the dosage of CS is 0.005 mg-0.1 mg.

4. The method for preparing and modifying the chitosan nanofiltration membrane as described in claim 3, characterized in that, In step two, the concentration of the PEI aqueous solution is 1%.

5. The method for preparing and modifying the chitosan nanofiltration membrane as described in claim 4, characterized in that, In step two, the soaking time in the PEI solution is 1-45 minutes.

6. The method for preparing and modifying the chitosan nanofiltration membrane as described in claim 5, characterized in that, In step three, the curing temperature is 60℃ and the curing time is 5 minutes.

7. The method for preparing and modifying the chitosan nanofiltration membrane as described in claim 5, characterized in that, In step two, the soaking time in the PEI solution is 1 min, 5 min, 10 min, 15 min, or 45 min.

8. A chitosan nanofiltration membrane, characterized in that, It is prepared and modified by any one of claims 1-7.

9. An application of the chitosan nanofiltration membrane according to claim 8 in the field of membrane separation technology.

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