Preparation method of composite nanofiber for adsorption treatment of heavy metal wastewater

Abstract

The invention discloses a preparation method of composite nanofibers for adsorption treatment of heavy metal wastewater, which comprises the following steps: step 1, dissolving ferric trichloride hexahydrate and 1, 2, 4, 5-pyromellitic acid in N, N-dimethylformamide by using a solvothermal method to obtain (COOH) 2-MIL-101 (Fe) powder; step 2, dispersing the powder obtained in the step 1 into a prepared PAN / DMF homogeneous solution so as to obtain a (COOH) 2-MIL-101 (Fe) coated PAN spinning solution; step 3, preparing a multi-carboxyl modified MIL-101 (Fe) / polyacrylonitrile composite nanofiber by adopting electrostatic spinning; and step 4, drying the composite nanofiber obtained in the step 3. The problems of high technical energy consumption, high cost, insufficient water stability of the adsorbent and difficulty in regeneration in the prior art are solved.

Description

Technical Field

[0001] This invention belongs to the technical field of water heavy metal adsorption materials, specifically relating to a method for preparing composite nanofibers for heavy metal wastewater adsorption treatment. Background Technology

[0002] Adsorption has become the most effective method for treating water pollutants due to its advantages such as simple operation, high cost-effectiveness, excellent performance, environmentally friendly entire adsorption process, and recyclable adsorbents. Adsorption mainly utilizes adsorbent materials or adsorbents with high porosity, high surface activity, and large specific surface area to adsorb pollutants in water. It involves using substances with a large specific surface area and adsorption capacity to adsorb pollutants in the water, thereby achieving the purpose of purifying the water.

[0003] MIL-101(Fe) possesses a large cell volume, high specific surface area, high porosity, excellent thermal stability, and numerous unsaturated active sites. It also exhibits abundant Fe-O and excellent water stability, making it a subject of extensive research in water pollution remediation, particularly showing promising applications in the reduction of hexavalent chromium and the removal of organic pollutants from water through advanced oxidation. Wu et al. discovered that MIL-101(Fe) primarily adsorbs As(III) through the coordination of the central metal Fe with arsenite, achieving a maximum adsorption capacity of 211.42 mg·g⁻¹. -1 Zhang et al. found that MIL-101 (Fe) mainly adsorbs complexed Cr(III) through the coordination of Fe(III) with the -COOH group in EDTA-Cr(III), and the adsorption capacity for EDTA-Cr(III) can reach 120.48 mg. g -1 Chen et al. discovered that the MIL-101 (Fe) / GO nanofiber membrane mainly utilizes Fe... 3+ The adsorption of Pb(II) is achieved through coordination with heavy metal ions and complexation with oxygen-containing groups on the GO surface, with a maximum adsorption capacity of 126 mg. g -1 However, existing materials for the adsorption of heavy metals in water suffer from problems such as limited adsorption performance, difficulty in separating and easily losing adsorbents, unstable material properties, and poor renewability. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing composite nanofibers for the adsorption and treatment of heavy metal wastewater, thereby solving the problems of high energy consumption, high cost, insufficient water stability of adsorbents, and difficulty in regeneration in the existing technology.

[0005] To achieve the above objectives, the technical solution adopted in this invention is: a method for preparing composite nanofibers for heavy metal wastewater adsorption treatment, specifically implemented according to the following steps:

[0006] Step 1: Ferric chloride hexahydrate and 1,2,4,5-pyromellitic acid are dissolved in N,N-dimethylformamide using a solvothermal method to obtain (COOH)2-MIL-101(Fe) powder. Step 2: Disperse the powder obtained in Step 1 in the prepared homogeneous PAN / DMF solution to obtain (COOH)2-MIL-101(Fe)@PAN spinning solution; Step 3: Prepare multi-carboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofibers by electrospinning; Step 4: Dry the composite nanofibers obtained in Step 3.

[0007] As a preferred technical solution of the present invention, in step 1, the specific preparation method of (COOH)2-MIL-101(Fe) powder is as follows: First, ferric chloride hexahydrate and 1,2,4,5-pyromellitic acid are dissolved in N,N-dimethylformamide (DMF), with each 15 mL-45 mL of N,N-dimethylformamide (DMF) corresponding to 0.187 g-0.748 g of ferric chloride hexahydrate and 0.264 g-1.054 g of 1,2,4,5-pyromellitic acid; after stirring, the solution is transferred to a polytetrafluoroethylene reactor, and after heat treatment in an oven, the obtained (COOH)2-MIL-101(Fe) crystals are washed 2-5 times each with DMF and anhydrous ethanol, and then dried under vacuum.

[0008] As a preferred technical solution of the present invention, in step 1: the solution is transferred to a polytetrafluoroethylene reactor after being stirred for 0.5 h - 1.5 h.

[0009] As a preferred technical solution of the present invention, in step 1, the product is subjected to heat treatment in an oven at 120 ℃-180 ℃ for 12 h-24 h.

[0010] As a preferred technical solution of the present invention, in step 1, the product is dried in a vacuum environment of 50 ℃ - 70 ℃.

[0011] As a preferred technical solution of the present invention, in step 2, the preparation method of (COOH)2-MIL-101(Fe)@PAN spinning solution is as follows: First, a 10 wt% homogeneous PAN / DMF solution is prepared, and then the (COOH)2-MIL-101(Fe) powder in step 1 is dispersed in the PAN / DMF homogeneous solution at 3 wt% - 12 wt%, and stirred magnetically for 20 min - 40 min at room temperature for 0.5 h - 1.5 h, and then ultrasonically treated for later use.

[0012] As a preferred embodiment of the present invention, in step 3, the preparation method of the polycarboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofibers is specifically as follows: Inject the (COOH)2-MIL-101(Fe)@PAN spinning solution prepared in step 2 into the reservoir of the textile nozzle of the electrospinning machine. Connect the injection pump to a power supply. Place the textile nozzle on the left side of the receiving device of the electrospinning machine and control the flow rate of the spinning solution through the injection pump. Place tin foil on the receiving cylinder of the receiving device of the electrospinning machine, turn on the receiving cylinder rolling switch, and then start the single needle spinning to spin the spinning solution in the reservoir. A uniform layer of multi-carboxyl modified MIL-101(Fe) / polyacrylonitrile composite nanofibers can be obtained on the surface of the tin foil in the receiving cylinder. The concentration of the spinning solution was 3 wt% - 12 wt%, the spinning voltage was 16 KV - 22 KV, the spinning distance was 20 cm, the feeding rate was 0.5 mL / h - 1.5 mL / h, and the collection time was 120 min - 360 min.

[0013] As a preferred embodiment of the present invention, the post-processing stage in step 4 comprises the following steps: The composite nanofibers obtained in step 3 were vacuum dried at 50 ℃ - 70 ℃ for 8 h - 12 h to obtain the highly efficient heavy metal adsorption polycarboxylic acid MIL-101(Fe) composite nanofibers.

[0014] The beneficial effects of this invention are as follows: This invention provides a method for preparing composite nanofibers for heavy metal wastewater adsorption treatment. It utilizes polycarboxylated MIL-101(Fe) composite nanofibers to efficiently adsorb low concentrations of various forms of heavy metals in water, exhibiting superior stability compared to conventional materials. This invention is simple to operate, low in cost, and the adsorption material is easily separated, exhibiting high water stability and easy regeneration, thus overcoming, to some extent, the application problems of existing MIL-101(Fe) materials. Attached Figure Description

[0015] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of a device for preparing composite nanofibers for heavy metal wastewater adsorption treatment according to the present invention. Figure 2 This is a scanning electron microscope (SEM) diagram of (COOH)2-MIL-101(Fe) of the present invention; Figure 3 This is a scanning electron microscope (SEM) schematic diagram of a composite nanofiber for heavy metal wastewater adsorption treatment according to the present invention. In the diagram, 1. Voltage power supply; 2. Injection pump; 3. Spinning nozzle; 4. Receiving device. Detailed Implementation

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] Example 1 The present invention discloses a method for preparing composite nanofibers for heavy metal wastewater adsorption treatment, which is specifically implemented according to the following steps: Step 1: Ferric chloride hexahydrate and 1,2,4,5-pyromellitic acid are dissolved in N,N-dimethylformamide using a solvothermal method to obtain (COOH)2-MIL-101(Fe) powder, specifically: First, 0.187 g of ferric chloride hexahydrate and 0.264 g of 1,2,4,5-pyromellitic acid were dissolved in 15 ml of N,N-dimethylformamide (DMF). After stirring for 0.5 h, the solution was transferred to a polytetrafluoroethylene reactor and heat-treated in an oven at 120 ℃ for 24 h. The resulting (COOH)2-MIL-101(Fe) crystals were washed twice each with DMF and anhydrous ethanol, and then dried under vacuum at 50 ℃. Step 2 involves dispersing the powder obtained in Step 1 in a prepared homogeneous PAN / DMF solution to obtain (COOH)2-MIL-101(Fe)@PAN spinning solution, specifically as follows: First, prepare a 10 wt% homogeneous PAN / DMF solution. Then, disperse the (COOH)2-MIL-101(Fe) powder from step 1 at 3 wt% in the homogeneous PAN / DMF solution. Stir magnetically for 40 min at room temperature for 0.5 h, and then sonicate for later use. Step 3: Prepare multi-carboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofibers by electrospinning, specifically as follows: like Figure 1As shown, the (COOH)2-MIL-101(Fe)@PAN spinning solution prepared in step 2 is injected into the storage tank of the spinning nozzle 3 of the electrospinning machine. The injection pump 2 is connected to the power supply 1. The spinning nozzle 3 is placed on the left side of the receiving device of the electrospinning machine, and the flow rate of the spinning solution is controlled by the injection pump 2. Tin foil is placed on the receiving tank of the receiving device 4 of the electrospinning machine. The rolling switch of the receiving tank is turned on, and then the single needle spinning is started to spin the spinning solution in the storage tank. A uniform layer of polycarboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofibers can be obtained on the surface of the tin foil in the receiving tank. The concentration of the spinning solution is 3 wt%, the spinning voltage is 16 KV, the spinning distance is 20 cm, the feeding rate is 0.5 mL / h, and the collection time is 120 min. Step 4, the post-processing stage, specifically involves drying the composite nanofibers obtained in Step 3 under vacuum at 50 °C for 12 h to obtain highly efficient heavy metal adsorption polycarboxylic acid MIL-101(Fe) composite nanofibers.

[0018] Example 2 The present invention discloses a method for preparing composite nanofibers for heavy metal wastewater adsorption treatment, which is specifically implemented according to the following steps: Step 1: Ferric chloride hexahydrate and 1,2,4,5-pyromellitic acid are dissolved in N,N-dimethylformamide using a solvothermal method to obtain (COOH)2-MIL-101(Fe) powder, specifically: First, 0.748 g of ferric chloride hexahydrate and 1.054 g of 1,2,4,5-pyromellitic acid were dissolved in 45 mL of N,N-dimethylformamide (DMF). After stirring for 1.5 h, the solution was transferred to a polytetrafluoroethylene reactor and heat-treated in an oven at 180 ℃ for 12 h. The resulting (COOH)2-MIL-101(Fe) crystals were washed five times each with DMF and anhydrous ethanol, and then dried under vacuum at 70 ℃. Step 2 involves dispersing the powder obtained in Step 1 in a prepared homogeneous PAN / DMF solution to obtain (COOH)2-MIL-101(Fe)@PAN spinning solution, specifically as follows: First, prepare a 10 wt% homogeneous PAN / DMF solution. Then, disperse the (COOH)2-MIL-101(Fe) powder from step 1 at 12 wt% in the homogeneous PAN / DMF solution. Stir magnetically for 20 min at room temperature for 1.5 h, and then sonicate for later use. Step 3: Prepare multi-carboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofibers by electrospinning, specifically as follows: like Figure 1As shown, the (COOH)2-MIL-101(Fe)@PAN spinning solution prepared in step 2 is injected into the storage tank of the spinning nozzle 3 of the electrospinning machine. The injection pump 2 is connected to the power supply 1. The spinning nozzle 3 is placed on the left side of the receiving device of the electrospinning machine, and the flow rate of the spinning solution is controlled by the injection pump 2. Tin foil is placed on the receiving tank of the receiving device 4 of the electrospinning machine. The rolling switch of the receiving tank is turned on, and then the single needle spinning is started to spin the spinning solution in the storage tank. A uniform layer of polycarboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofibers can be obtained on the surface of the tin foil in the receiving tank. The concentration of the spinning solution is 12wt%, the spinning voltage is 22 KV, the spinning distance is 20 cm, the feeding rate is 1.5 mL / h, and the collection time is 120 min. Step 4, the post-processing stage, specifically involves drying the composite nanofibers obtained in Step 3 under vacuum at 70 °C for 8 hours to obtain highly efficient heavy metal adsorption polycarboxylic acid MIL-101(Fe) composite nanofibers.

[0019] Example 3 The present invention discloses a method for preparing composite nanofibers for heavy metal wastewater adsorption treatment, which is specifically implemented according to the following steps: Step 1: Ferric chloride hexahydrate and 1,2,4,5-pyromellitic acid are dissolved in N,N-dimethylformamide using a solvothermal method to obtain (COOH)2-MIL-101(Fe) powder, specifically: First, 0.4675 g of ferric chloride hexahydrate and 0.659 g of 1,2,4,5-pyromellitic acid were dissolved in 30 mL of N,N-dimethylformamide (DMF). After stirring for 1 h, the solution was transferred to a polytetrafluoroethylene reactor and heat-treated in an oven at 150 ℃ for 18 h. The resulting (COOH)2-MIL-101(Fe) crystals were washed three times each with DMF and anhydrous ethanol, and then dried under vacuum at 60 ℃. Step 2 involves dispersing the powder obtained in Step 1 in a prepared homogeneous PAN / DMF solution to obtain (COOH)2-MIL-101(Fe)@PAN spinning solution, specifically as follows: First, prepare a 10 wt% homogeneous PAN / DMF solution. Then, disperse the (COOH)2-MIL-101(Fe) powder from step 1 at 7.5 wt% in the homogeneous PAN / DMF solution. Stir magnetically for 30 min at room temperature for 1 h, and then sonicate for later use. Step 3: Prepare multi-carboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofibers by electrospinning, specifically as follows: like Figure 1As shown, the (COOH)2-MIL-101(Fe)@PAN spinning solution prepared in step 2 is injected into the storage tank of the spinning nozzle 3 of the electrospinning machine. The injection pump 2 is connected to the power supply 1. The spinning nozzle 3 is placed on the left side of the receiving device of the electrospinning machine, and the flow rate of the spinning solution is controlled by the injection pump 2. Tin foil is placed on the receiving tank of the receiving device 4 of the electrospinning machine. The rolling switch of the receiving tank is turned on, and then the single needle spinning is started to spin the spinning solution in the storage tank. A uniform layer of polycarboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofibers can be obtained on the surface of the tin foil in the receiving tank. The concentration of the spinning solution is 7.5 wt%, the spinning voltage is 19 KV, the spinning distance is 20 cm, the feeding rate is 1 mL / h, and the collection time is 240 min. Step 4, the post-processing stage, specifically involves drying the composite nanofibers obtained in Step 3 under vacuum at 60 °C for 10 h to obtain highly efficient heavy metal adsorption polycarboxylic acid MIL-101(Fe) composite nanofibers.

[0020] Example 4 The present invention discloses a method for preparing composite nanofibers for heavy metal wastewater adsorption treatment, which is specifically implemented according to the following steps: Step 1: Ferric chloride hexahydrate and 1,2,4,5-pyromellitic acid are dissolved in N,N-dimethylformamide using a solvothermal method to obtain (COOH)2-MIL-101(Fe) powder, specifically: First, 0.468 g of ferric chloride hexahydrate and 0.659 g of 1,2,4,5-pyromellitic acid were dissolved in 25 mL of N,N-dimethylformamide (DMF). After stirring for 0.8 h, the solution was transferred to a polytetrafluoroethylene reactor and heat-treated in an oven at 130 ℃ for 14 h. The resulting (COOH)2-MIL-101(Fe) crystals were washed four times each with DMF and anhydrous ethanol, and then dried under vacuum at 55 ℃. Step 2 involves dispersing the powder obtained in Step 1 in a prepared homogeneous PAN / DMF solution to obtain (COOH)2-MIL-101(Fe)@PAN spinning solution, specifically as follows: First, prepare a 10 wt% homogeneous PAN / DMF solution. Then, disperse the (COOH)2-MIL-101(Fe) powder from step 1 at 5 wt% in the homogeneous PAN / DMF solution. Stir magnetically for 25 min at room temperature for 0.8 h, and then sonicate for later use. Step 3: Prepare multi-carboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofibers by electrospinning, specifically as follows: like Figure 1As shown, the (COOH)2-MIL-101(Fe)@PAN spinning solution prepared in step 2 is injected into the storage tank of the spinning nozzle 3 of the electrospinning machine. The injection pump 2 is connected to the power supply 1. The spinning nozzle 3 is placed on the left side of the receiving device of the electrospinning machine, and the flow rate of the spinning solution is controlled by the injection pump 2. Tin foil is placed on the receiving tank of the receiving device 4 of the electrospinning machine. The rolling switch of the receiving tank is turned on, and then the single needle spinning is started to spin the spinning solution in the storage tank. A uniform layer of polycarboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofibers can be obtained on the surface of the tin foil in the receiving tank. The concentration of the spinning solution is 5 wt%, the spinning voltage is 17 KV, the spinning distance is 20 cm, the feeding rate is 0.8 mL / h, and the collection time is 150 min. Step 4, the post-processing stage, specifically involves drying the composite nanofibers obtained in Step 3 under vacuum at 55 °C for 9 h to obtain highly efficient heavy metal adsorption polycarboxylic acid MIL-101(Fe) composite nanofibers.

[0021] Example 5 The present invention discloses a method for preparing composite nanofibers for heavy metal wastewater adsorption treatment, which is specifically implemented according to the following steps: Step 1: Ferric chloride hexahydrate and 1,2,4,5-pyromellitic acid are dissolved in N,N-dimethylformamide using a solvothermal method to obtain (COOH)2-MIL-101(Fe) powder, specifically: First, 0.374 g of ferric chloride hexahydrate and 0.527 g of 1,2,4,5-pyromellitic acid were dissolved in 15 ml of N,N-dimethylformamide (DMF). After stirring for 1.2 h, the solution was transferred to a polytetrafluoroethylene reactor and heat-treated in an oven at 170 ℃ for 22 h. The resulting (COOH)2-MIL-101(Fe) crystals were washed twice each with DMF and anhydrous ethanol, and then dried under vacuum at 60 ℃. Step 2 involves dispersing the powder obtained in Step 1 in a prepared homogeneous PAN / DMF solution to obtain (COOH)2-MIL-101(Fe)@PAN spinning solution, specifically as follows: First, prepare a 10 wt% homogeneous PAN / DMF solution. Then, disperse the (COOH)2-MIL-101(Fe) powder from step 1 at 8 wt% in the homogeneous PAN / DMF solution. Stir magnetically for 20 min at room temperature for 0.5 h, and then sonicate for later use. Step 3: Prepare multi-carboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofibers by electrospinning, specifically as follows: like Figure 1As shown, the (COOH)2-MIL-101(Fe)@PAN spinning solution prepared in step 2 is injected into the storage tank of the spinning nozzle 3 of the electrospinning machine. The injection pump 2 is connected to the power supply 1. The spinning nozzle 3 is placed on the left side of the receiving device of the electrospinning machine, and the flow rate of the spinning solution is controlled by the injection pump 2. Tin foil is placed on the receiving tank of the receiving device 4 of the electrospinning machine. The rolling switch of the receiving tank is turned on, and then the single needle spinning is started to spin the spinning solution in the storage tank. A uniform layer of multi-carboxyl modified MIL-101(Fe) / polyacrylonitrile composite nanofibers can be obtained on the surface of the tin foil in the receiving tank. The concentration of the spinning solution is 8wt%, the spinning voltage is 22 KV, the spinning distance is 20 cm, the feeding rate is 1.5 mL / h, and the collection time is 60 min. Step 4, the post-processing stage, specifically involves drying the composite nanofibers obtained in Step 3 under vacuum at 50 °C for 8 hours to obtain highly efficient heavy metal adsorption polycarboxylic acid MIL-101(Fe) composite nanofibers.

[0022] Example 6 The present invention discloses a method for preparing composite nanofibers for heavy metal wastewater adsorption treatment, which is specifically implemented according to the following steps: Step 1: Ferric chloride hexahydrate and 1,2,4,5-pyromellitic acid are dissolved in N,N-dimethylformamide using a solvothermal method to obtain (COOH)2-MIL-101(Fe) powder, specifically: First, 0.281 g of ferric chloride hexahydrate and 0.396 g of 1,2,4,5-pyromellitic acid were dissolved in 45 mL of N,N-dimethylformamide (DMF). After stirring for 1.5 h, the solution was transferred to a polytetrafluoroethylene reactor and heat-treated in an oven at 180 ℃ for 24 h. The resulting (COOH)2-MIL-101(Fe) crystals were washed five times each with DMF and anhydrous ethanol, and then dried under vacuum at 70 ℃. Step 2 involves dispersing the powder obtained in Step 1 in a prepared homogeneous PAN / DMF solution to obtain (COOH)2-MIL-101(Fe)@PAN spinning solution, specifically as follows: First, prepare a 10 wt% homogeneous PAN / DMF solution. Then, disperse the (COOH)2-MIL-101(Fe) powder from step 1 at 12 wt% in the homogeneous PAN / DMF solution. Stir magnetically for 40 min at room temperature for 1.5 h, and then sonicate for later use. Step 3: Prepare multi-carboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofibers by electrospinning, specifically as follows: like Figure 1As shown, the (COOH)2-MIL-101(Fe)@PAN spinning solution prepared in step 2 is injected into the storage tank of the spinning nozzle 3 of the electrospinning machine. The injection pump 2 is connected to the power supply 1. The spinning nozzle 3 is placed on the left side of the receiving device of the electrospinning machine, and the flow rate of the spinning solution is controlled by the injection pump 2. Tin foil is placed on the receiving tank of the receiving device 4 of the electrospinning machine. The rolling switch of the receiving tank is turned on, and then the single needle spinning is started to spin the spinning solution in the storage tank. A uniform layer of polycarboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofibers can be obtained on the surface of the tin foil in the receiving tank. The concentration of the spinning solution is 12 wt%, the spinning voltage is 22 KV, the spinning distance is 20 cm, the feeding rate is 1.5 mL / h, and the collection time is 360 min. Step 4, the post-processing stage, specifically involves drying the composite nanofibers obtained in Step 3 under vacuum at 70 °C for 12 h to obtain highly efficient heavy metal adsorption polycarboxylic acid MIL-101(Fe) composite nanofibers.

[0023] Figure 2 This is a scanning electron microscope (SEM) diagram of the preparation of (COOH)2-MIL-101(Fe)@PAN composite nanofibers in the present invention. Figure 3 This is a scanning electron microscope (SEM) image of the (COOH)2-MIL-101(Fe)@PAN composite nanofibers prepared according to Example 3 of the preparation method of this invention. The SEM image shows that the PAN loaded with carboxyl-modified MIL-101(Fe) has a uniform fibrous structure; the fibers are thin and without bending. The protrusions on the fiber surface are a normal phenomenon after loading MOFs, indicating that the MOFs material has been successfully incorporated into the fibers, enhancing the adsorption capacity of the nanofibers and giving them excellent performance in the water purification field. Using multi-carboxyl MIL-101(Fe) composite nanofibers for efficient adsorption of low concentrations of various forms of heavy metals in water exhibits superior stability compared to conventional materials. This invention is simple to operate, low in cost, the adsorbent material is easy to separate, has high water stability, and is easy to regenerate, thus overcoming to some extent the application problems of existing MIL-101(Fe).

[0024] This invention employs electrospinning technology to prepare a multi-carboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofiber that can be used for efficient adsorption of various forms of heavy metals in water. It has the advantages of simple preparation method, low cost, easy separation of adsorption materials, high water stability, and easy regeneration. It achieves a removal rate of 87% for free Cr(III) in water and a removal rate of up to 96% for complexed Cr(III) in water rich in organic matter, thus overcoming to some extent the application problems of existing MIL-101(Fe).

[0025] The foregoing description illustrates and describes several preferred embodiments of the invention. However, as previously stated, it should be understood that the invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the invention should be within the protection scope of the appended claims.

Claims

1. A method for preparing composite nanofibers for the adsorption treatment of heavy metal wastewater, characterized in that, The specific steps are as follows: Step 1: Ferric chloride hexahydrate and 1,2,4,5-pyromellitic acid are dissolved in N,N-dimethylformamide using a solvothermal method to obtain (COOH)2-MIL-101(Fe) powder. Step 2: Disperse the powder obtained in Step 1 in the prepared homogeneous PAN / DMF solution to obtain (COOH)2-MIL-101(Fe)@PAN spinning solution; Step 3: Prepare multi-carboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofibers by electrospinning; Step 4: Dry the composite nanofibers obtained in Step 3.

2. The method for preparing composite nanofibers for heavy metal wastewater adsorption treatment according to claim 1, characterized in that, In step 1, the specific preparation method of (COOH)2-MIL-101(Fe) powder is as follows: First, ferric chloride hexahydrate and 1,2,4,5-pyromellitic acid are dissolved in N,N-dimethylformamide (DMF). Each 15 ml-45 mL of N,N-dimethylformamide (DMF) corresponds to 0.187 g-0.748 g of ferric chloride hexahydrate and 0.264 g-1.054 g of 1,2,4,5-pyromellitic acid. After stirring, the solution is transferred to a polytetrafluoroethylene reactor and heat-treated in an oven. The resulting (COOH)2-MIL-101(Fe) crystals are then washed 2-5 times each with DMF and anhydrous ethanol, and dried under vacuum.

3. The method for preparing composite nanofibers for heavy metal wastewater adsorption treatment according to claim 2, characterized in that, In step 1: the solution is stirred for 0.5 h - 1.5 h and then transferred to a polytetrafluoroethylene reactor.

4. The method for preparing composite nanofibers for heavy metal wastewater adsorption treatment according to claim 3, characterized in that, In step 1, the product undergoes heat treatment in an oven at 120 ℃-180 ℃ for 12 h - 24 h.

5. The method for preparing composite nanofibers for heavy metal wastewater adsorption treatment according to claim 4, characterized in that, In step 1, the product is dried in a vacuum environment of 50°C - 70°C.

6. The method for preparing composite nanofibers for heavy metal wastewater adsorption treatment according to claim 5, characterized in that, In step 2, the preparation method of (COOH)2-MIL-101(Fe)@PAN spinning solution is as follows: First, prepare a 10 wt% homogeneous PAN / DMF solution. Then, disperse the (COOH)2-MIL-101(Fe) powder from step 1 at 3 wt% - 12 wt% in the homogeneous PAN / DMF solution. Stir magnetically for 20 min - 40 min at room temperature for 0.5 h - 1.5 h. After ultrasonic treatment, it is ready for use.

7. The method for preparing composite nanofibers for heavy metal wastewater adsorption treatment according to claim 6, characterized in that, In step 3, the preparation method of the polycarboxyl-modified MIL-101(Fe) / polyacrylonitrile composite nanofibers is as follows: The (COOH)2-MIL-101(Fe)@PAN spinning solution prepared in step 2 is injected into the storage tank of the textile nozzle (3) of the electrospinning machine. The injection pump (2) is connected to the voltage power supply (1). The textile nozzle (3) is placed on the left side of the receiving device of the electrospinning machine and the flow rate of the spinning solution is controlled by the injection pump (2). Tin foil is placed on the receiving tank of the receiving device (4) of the electrospinning machine. The receiving tank rolling switch is turned on. Then, the single needle spinning is started to spin the spinning solution in the storage tank. A uniform layer of multi-carboxyl modified MIL-101(Fe) / polyacrylonitrile composite nanofibers can be obtained on the surface of the tin foil in the receiving tank. The concentration of the spinning solution was 3 wt% - 12 wt%, the spinning voltage was 16 KV - 22 KV, the spinning distance was 20 cm, the feeding rate was 0.5 mL / h - 1.5 mL / h, and the collection time was 120 min - 360 min.

8. The method for preparing composite nanofibers for heavy metal wastewater adsorption treatment according to claim 7, characterized in that, In step 4, the specific steps of the post-processing stage are as follows: The composite nanofibers obtained in step 3 were vacuum dried at 50 ℃ - 70 ℃ for 8 h - 12 h to obtain the highly efficient heavy metal adsorption polycarboxylic acid MIL-101(Fe) composite nanofibers.

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