Polyacrylonitrile fiber membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of precious metal resource recovery and separation, and discloses a polyacrylonitrile fiber membrane and a preparation method and application thereof.The preparation method comprises the following preparation steps that polyacrylonitrile is added into a solvent, then an amido modifier is added, a cyclodextrin modifier is added after heating and stirring, stirring is continued for a reaction, and the polyacrylonitrile fiber membrane is obtained; the modified polyacrylonitrile contains an amino group obtained through modification by an amino modifier and a cyclodextrin group obtained through modification by a cyclodextrin modifier; and carrying out electrostatic spinning on the modified polyacrylonitrile solution, collecting polyacrylonitrile fibers in an adamantane aqueous solution, and carrying out hot pressing to obtain the polyacrylonitrile fiber membrane. The polyacrylonitrile fiber membrane prepared through the method can effectively prevent impurity metal ions from interfering the palladium ion adsorption efficiency, and the palladium ion adsorption capacity is improved.

Description

Technical Field

[0001] This application relates to the field of precious metal resource recovery and separation technology, and in particular to a polyacrylonitrile fiber membrane, its preparation method, and its application. Background Technology

[0002] Palladium, a key platinum group metal, is widely used in automotive exhaust catalysts, electronics, petrochemicals, jewelry, and emerging hydrogen fuel cell catalysts due to its unique physicochemical properties, including excellent catalytic activity, high-temperature stability, corrosion resistance, and good electrical conductivity. However, palladium's abundance in the Earth's crust is extremely low (approximately 0.015 ppm), making it a highly scarce strategic resource. Its primary mineral supply is concentrated and limited, and its mining and refining processes are energy-intensive and environmentally stressful. Therefore, the efficient and economical recovery of palladium ions from secondary resources, particularly from the commonly found low-concentration palladium-containing solutions, is of paramount strategic importance for ensuring the security of critical resource supply chains, reducing production costs, promoting a circular economy, and protecting the environment.

[0003] In existing technologies, methods for recovering palladium from palladium-containing solutions mainly include solvent extraction, electrodeposition, and adsorption. However, solvent extraction requires large amounts of organic solvents and is prone to secondary pollution; electrodeposition has low current efficiency and high energy consumption in dilute solutions; while adsorption is often considered the preferred method due to its simple equipment, convenient operation, low energy consumption, and suitability for low-concentration systems. However, in practical applications, palladium-containing wastewater has an extremely complex composition, containing a large number of coexisting competing metal ions (such as Cu). 2+ Ni 2+ Fe 3+ Zn 2+ Cr 6+ (e.g., ions) are often much higher in concentration than palladium ions. These ions are similar to palladium ions in terms of charge properties, ionic radius, and coordination ability. They will compete fiercely with palladium ions for the limited active sites on the adsorbent surface, which will seriously weaken the specific recognition and capture ability of palladium, resulting in low adsorption efficiency and low adsorption capacity in the adsorption method. Summary of the Invention

[0004] The technical problem to be solved by this invention is to propose a polyacrylonitrile fiber membrane and its preparation method and application, which aims to solve the problem that excessive impurity metal ions interfere with the adsorption efficiency of palladium ions and result in low palladium ion adsorption capacity during the adsorption process of palladium-containing solutions.

[0005] To address the aforementioned technical problems, this invention proposes a method for preparing a polyacrylonitrile fiber membrane, which includes the following preparation steps: S1. Add polyacrylonitrile to a solvent, then add an amine modifier first, heat and stir, then add a cyclodextrin modifier, and continue stirring to obtain a modified polyacrylonitrile solution. The modified polyacrylonitrile contains amine groups modified by the amine modifier and cyclodextrin groups modified by the cyclodextrin modifier. S2. The modified polyacrylonitrile solution is electrospun and the polyacrylonitrile fibers are collected in an aqueous adamantane solution and hot-pressed to obtain a polyacrylonitrile fiber membrane.

[0006] In some embodiments, the solvent in step S1 includes N,N-dimethylformamide and / or dimethyl sulfoxide, the amine modifier includes at least one of ethylenediamine, tetraethylenepentamine, and diethylenetriamine, and the cyclodextrin modifier includes mono-(6-epoxypropyl)-6-deoxy-β-cyclodextrin and / or mono-(6-p-toluenesulfonyl)-β-cyclodextrin.

[0007] In some embodiments, step S1 includes: S1.1 Dissolve polyacrylonitrile and alkaline catalyst in a solvent and stir at 70~80℃ for 1~2h to obtain an activated polyacrylonitrile solution, wherein the concentrations of polyacrylonitrile and alkaline catalyst in the solvent are 10~15wt% and 0.4~0.5wt%, respectively, and the alkaline catalyst includes at least one of triethylamine, tetramethylguanidine, and diazabicyclononene. S1.2 Add an amine modifier to the activated polyacrylonitrile solution, and in an inert atmosphere, heat to 100~120℃ and react for 3~5 hours. Then cool to 70~80℃, add a cyclodextrin modifier, and keep warm and stir for 1~2 hours to obtain a modified polyacrylonitrile solution. The mass ratio of polyacrylonitrile to amine modifier is 1:(1.5~3.0), and the molar ratio of amine modifier to cyclodextrin modifier is (6~8):1.

[0008] In some embodiments, step S1 further includes: S1.1 Dissolve polyacrylonitrile and alkaline catalyst in a solvent and stir at 70~80℃ for 1~2h to obtain an activated polyacrylonitrile solution, wherein the concentrations of polyacrylonitrile and alkaline catalyst in the solvent are 10~15wt% and 0.4~0.5wt%, respectively, and the alkaline catalyst includes at least one of triethylamine, tetramethylguanidine, and diazabicyclononene. S1.2 Add an amine modifier to the activated polyacrylonitrile solution, and in an inert atmosphere, heat to 100~120℃ and react for 3~5 hours. Then cool to 70~80℃, add a cyclodextrin modifier, and keep warm and stir for 1~2 hours to obtain a polymerization solution. The mass ratio of polyacrylonitrile to amine modifier is 1:(1.5~3.0), and the molar ratio of amine modifier to cyclodextrin modifier is (6~8):1. S1.3 After the polymerization solution is cooled to 50~60℃, add the alcohol-soluble pore-forming agent, keep warm and stir for 10~20min to obtain the modified polyacrylonitrile solution. The alcohol-soluble pore-forming agent includes at least one of polymethyl methacrylate, cellulose acetate and polyethylene oxide. The mass ratio of polyacrylonitrile to alcohol-soluble pore-forming agent is 1:(0.1~0.3).

[0009] In some embodiments, step S2 includes: S2.1 Add a stabilizer to the modified polyacrylonitrile solution, stir, and then electrospin, collecting the fibers in an adamantane aqueous solution to obtain polyacrylonitrile fibers. The concentration of the stabilizer in the modified polyacrylonitrile solution is 1-3 wt%, and the stabilizer includes at least one of polyethylene glycol, polyethylene oxide, and polycaprolactone. The adamantane aqueous solution contains 1-adamantane methanol and / or 1-adamantane carboxylic acid, and the concentration of adamantane is 1-5 wt%. The electrospinning voltage is 18-22 kV, the feeding speed is 0.018-0.022 mm / s, the distance between the nozzle and the surface of the adamantane aqueous solution is 7-9 cm, and the diameter of the injection needle is 21-23 G. S2.2. Polyacrylonitrile fibers are hot-pressed at 120~150℃ and 5~10MPa for 3~5min to obtain polyacrylonitrile fiber membrane.

[0010] In some embodiments, step S2.2 further includes: S2.2. Immerse polyacrylonitrile fibers in an alcohol solution, dry them, and then hot-press them at 120~150℃ and 5~10MPa for 3~5min to obtain a polyacrylonitrile fiber membrane with pores. The alcohol solution includes at least one of methanol, ethanol, and isopropanol.

[0011] In some embodiments, prior to the electrospinning operation in step S2.1, a step of adjusting the modified polyacrylonitrile solution to a preset viscosity is further included; Adjusting the modified polyacrylonitrile solution to a preset viscosity specifically includes: Test whether the modified polyacrylonitrile solution reaches the preset range; If so, then perform electrospinning. If not, the viscosity of the modified polyacrylonitrile solution is adjusted using a viscosity modifier, and the step of detecting whether the modified polyacrylonitrile solution has reached the preset range is performed. The viscosity modifier includes polyvinylpyrrolidone for increasing viscosity and N,N-dimethylformamide for decreasing viscosity.

[0012] In addition, a polyacrylonitrile fiber membrane is provided, which is prepared by the method described above for preparing a polyacrylonitrile fiber membrane.

[0013] In addition, an application of polyacrylonitrile fiber membrane for the recovery of palladium ions in palladium-containing solutions is also provided. This polyacrylonitrile fiber membrane is one of the aforementioned types, and the specific application process is as follows: Add 3-4M hydrochloric acid and 0.5-2.0wt% reducing agent to the palladium-containing solution, stir for 8-12 min to obtain a pretreated solution, then pass the pretreated solution through a polyacrylonitrile fiber membrane at a flow rate of 0.8-1.2 mL / min and collect the filtrate. Repeat the above operation 4-6 times with the collected liquid to obtain the final filtrate, thus completing the recovery of palladium ions.

[0014] In some embodiments, the reducing agent includes at least one of ascorbic acid, sodium sulfite, and hydrazine hydrate.

[0015] The beneficial effects of this invention are: First, under high-concentration hydrochloric acid conditions, palladium stabilizes as a planar square anionic complex [PdCl4]. 2- They exist in various forms, and the main competing ions that coexist are Cu. 2+ Ni 2+ Zn 2+ They still mainly exist in cationic or neutral complex form, and can bind Cr ions with the same color as palladium ions. 6+ Converted to Cr 3+ To avoid affecting the adsorption of palladium ions by the polyacrylonitrile fiber membrane; at the same time, by adding an appropriate amount of reducing agent to the system, the strong interfering substance Fe is reduced. 3+ Pre-reduction to Fe, which does not form stable chloride anions 2+ This pre-emptively eliminates most competing adsorbed ions at the solution chemistry level. Secondly, the amine-modified fiber membrane undergoes full protonation of the amine groups in a strongly acidic environment, resulting in a strongly positively charged membrane surface that specifically captures [PdCl4] through strong electrostatic interactions. 2- Anions are electrostatically repelled by impurities in cationic form. Finally, an adamantane aqueous solution is used as the collecting liquid in the electrospinning process. Adamantane molecules can rapidly incorporate the cyclodextrin groups on the fiber surface, forming a stable molecular cross-linking network. This process not only immediately fixes the fiber morphology during the fiber collection stage, improving the mechanical stability of the fiber membrane, but also promotes supramolecular bonding between fibers during subsequent hot pressing, optimizing the membrane's structural compactness and long-term stability. Through this synergistic system, high selectivity and high capacity adsorption of palladium ions are achieved, while significantly reducing competition from impurity ions, thus effectively overcoming the problems of poor selectivity and low capacity of traditional adsorbents in complex solutions. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of a method for preparing a polyacrylonitrile fiber membrane according to an embodiment of the present invention; Figure 2A , Figure 2B This is a scanning electron microscope image of the polyacrylonitrile fiber membrane prepared in Example 1. Figure 3A , Figure 3B The images show the state of the palladium-containing solution before and after treatment in Application Example 1, respectively. Figure 4A , Figure 4B The images show the state of the polyacrylonitrile fiber membrane before and after use in Application Example 1. Detailed Implementation

[0017] In the description of this application, it should be noted that, unless specific conditions are specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0018] Please refer to Figure 1 This invention provides a method for preparing a polyacrylonitrile fiber membrane, which includes the following preparation steps: S1. Add polyacrylonitrile to a solvent, then add an amine modifier, heat and stir, then add a cyclodextrin modifier, and continue stirring to obtain a modified polyacrylonitrile solution. The modified polyacrylonitrile contains amine groups modified by the amine modifier and cyclodextrin groups modified by the cyclodextrin modifier.

[0019] The solvent in step S1 includes N,N-dimethylformamide and / or dimethyl sulfoxide, the amine modifier includes at least one of ethylenediamine, tetraethylenepentamine, and diethylenetriamine, and the cyclodextrin modifier includes mono-(6-epoxypropyl)-6-deoxy-β-cyclodextrin and / or mono-(6-p-toluenesulfonyl)-β-cyclodextrin.

[0020] In a strongly acidic environment, the amine groups of the amine-modified fiber membrane are fully protonated, giving the membrane surface a strong positive charge. This allows for the specific capture of [PdCl4] through strong electrostatic interactions. 2- Anions, on the other hand, electrostatically repel impurities in the form of cationic forms.

[0021] Step S1 includes: S1.1 Dissolve polyacrylonitrile and alkaline catalyst in a solvent and stir at 70~80℃ for 1~2h to obtain an activated polyacrylonitrile solution, wherein the concentrations of polyacrylonitrile and alkaline catalyst in the solvent are 10~15wt% and 0.4~0.5wt%, respectively, and the alkaline catalyst includes at least one of triethylamine, tetramethylguanidine, and diazabicyclononene. A suitable polyacrylonitrile concentration ensures that the solution has sufficient reactive site density and appropriate viscosity, which is beneficial for subsequent processing. The use of an alkaline catalyst at a low concentration can effectively promote the hydrolysis or nucleophilic activation of nitrile groups on the polyacrylonitrile molecular chain at a mild temperature and in a short time, forming active groups such as imides, laying the foundation for subsequent crosslinking or functionalization reactions. At the same time, it avoids the excessive degradation or gelation of polymers that may be caused by strong alkali or high temperature treatment for a long time, ensuring the stability and controllability of the solution.

[0022] S1.2 Add an amine modifier to the activated polyacrylonitrile solution, and in an inert atmosphere, heat to 100~120℃ and react for 3~5 hours. Then cool to 70~80℃, add a cyclodextrin modifier, and keep warm and stir for 1~2 hours to obtain a modified polyacrylonitrile solution. The mass ratio of polyacrylonitrile to amine modifier is 1:(1.5~3.0), and the molar ratio of amine modifier to cyclodextrin modifier is (6~8):1.

[0023] The reaction was carried out at 100-120℃ for a relatively long time under an inert atmosphere to ensure that the active sites on the activated polyacrylonitrile and the amine modifier could fully undergo grafting reactions such as aminolysis and amidation. The high feed mass ratio is conducive to introducing abundant amine functional groups on the molecular chain, laying the foundation for the subsequent introduction of cyclodextrin and enhancing the hydrophilicity or reactivity of the material. Subsequently, the temperature was lowered to 70-80℃ and the cyclodextrin modifier was added. This mild temperature can promote further reaction between the active groups on the cyclodextrin and the grafted amines, while avoiding the decomposition or side reactions of cyclodextrin that may be caused by high temperature. By controlling the high molar ratio of amine modifier to cyclodextrin modifier, it is ensured that the cyclodextrin can be effectively grafted and that enough free amines are retained on the polymer chain, finally obtaining a homogeneous modified solution with controllable structure and integrated function.

[0024] In one embodiment, step S1 further includes: S1.1 Dissolve polyacrylonitrile and alkaline catalyst in a solvent and stir at 70-80°C for 1-2 hours to obtain an activated polyacrylonitrile solution. The concentrations of polyacrylonitrile and alkaline catalyst in the solvent are 10-15 wt% and 0.4-0.5 wt%, respectively. The alkaline catalyst includes at least one of triethylamine, tetramethylguanidine, and diazabicyclononene.

[0025] S1.2 Add an amine modifier to the activated polyacrylonitrile solution, and in an inert atmosphere, heat to 100~120℃ and react for 3~5 hours. Then cool to 70~80℃, add a cyclodextrin modifier, and keep warm and stir for 1~2 hours to obtain a polymerization solution. The mass ratio of polyacrylonitrile to amine modifier is 1:(1.5~3.0), and the molar ratio of amine modifier to cyclodextrin modifier is (6~8):1.

[0026] S1.3 After the polymerization solution is cooled to 50~60℃, add the alcohol-soluble pore-forming agent, keep warm and stir for 10~20min to obtain the modified polyacrylonitrile solution. The alcohol-soluble pore-forming agent includes at least one of polymethyl methacrylate, cellulose acetate and polyethylene oxide. The mass ratio of polyacrylonitrile to alcohol-soluble pore-forming agent is 1:(0.1~0.3).

[0027] In this step, adding the alcohol-soluble pore-forming agent at a lower temperature and briefly stirring effectively controls the solution viscosity and prevents premature decomposition or excessive phase separation of the pore-forming agent at high temperatures. The selected alcohol-soluble pore-forming agent has good compatibility with the modified polyacrylonitrile solution, forming a uniformly dispersed blend system during subsequent film formation or molding processes. This blend is then selectively removed during final processing, resulting in a porous structure within the material. The appropriate mass ratio of polyacrylonitrile to the alcohol-soluble pore-forming agent ensures that the pore-forming agent content is sufficient to introduce significant porosity to enhance the specific surface area of ​​the material, while avoiding excessive addition that could lead to a significant decrease in mechanical strength or structural collapse. This results in a modified polyacrylonitrile solution with a uniform structure and controllable porosity, laying the foundation for the preparation of polyacrylonitrile fiber membranes.

[0028] S2. The modified polyacrylonitrile solution is electrospun and the polyacrylonitrile fibers are collected in an aqueous adamantane solution and hot-pressed to obtain a polyacrylonitrile fiber membrane.

[0029] In step S2, the electrospinning voltage is 18~22kV, the feeding speed is 0.018~0.022mm / s, the distance between the nozzle and the surface of the adamantane aqueous solution is 7~9cm, and the diameter of the injection needle is 21~23G.

[0030] The electrospinning process uses adamantane aqueous solution as the collecting liquid. Adamantane molecules can quickly incorporate the cyclodextrin groups on the fiber surface to form a stable molecular cross-linking network. This process can not only fix the fiber morphology in time during the fiber collection stage and improve the mechanical stability of the fiber membrane, but also promote supramolecular bonding between fibers in the subsequent hot pressing process, thereby optimizing the structural compactness and long-term stability of the membrane.

[0031] Step S2 includes: S2.1 Add a stabilizer to the modified polyacrylonitrile solution, stir, and then electrospin, collecting the fibers in an adamantane aqueous solution to obtain polyacrylonitrile fibers. The concentration of the stabilizer in the modified polyacrylonitrile solution is 1-3 wt%, and the stabilizer includes at least one of polyethylene glycol, polyethylene oxide, and polycaprolactone. The adamantane aqueous solution contains 1-adamantane methanol and / or 1-adamantane carboxylic acid, and the concentration of adamantane is 1-5 wt%. The electrospinning voltage is 18-22 kV, the feeding speed is 0.018-0.022 mm / s, the distance between the nozzle and the surface of the adamantane aqueous solution is 7-9 cm, and the diameter of the injection needle is 21-23 G. The addition of stabilizers primarily enhances the thermal stability of the fibers, enabling them to withstand certain temperatures and pressures during subsequent hot-pressing processes without excessive melting or degradation, thus maintaining the fiber's basic morphology and porous structure. Secondly, optimized electrospinning parameters ensure sufficient and stable stretching and solidification of the jet, forming fibers with uniform diameter and good continuity, providing a foundation for constructing a uniform fiber mat. Finally, collection in an adamantane aqueous solution utilizes the host-guest inclusion interaction between adamantane derivatives and cyclodextrin in the fibers. Adamantane molecules rapidly incorporate cyclodextrin groups on the fiber surface, forming a stable molecular cross-linking network. This process not only instantly fixes the fiber morphology during collection, improving the mechanical stability of the fiber membrane, but also promotes supramolecular bonding between fibers during subsequent hot-pressing, optimizing the membrane's structural density and long-term stability. Overall, the synergistic effect of these parameters aims to prepare a fiber precursor with good thermal stability and uniform morphology, laying a crucial foundation for obtaining a structurally complete and high-performance fiber membrane through hot pressing.

[0032] In one embodiment, to ensure that the modified polyacrylonitrile solution can be successfully electrospun, the viscosity of the modified polyacrylonitrile solution should be adjusted to within 800~2000 mPa·s. Adjusting the modified polyacrylonitrile solution to the preset viscosity specifically includes: Test whether the modified polyacrylonitrile solution reaches the preset range; If so, then perform electrospinning. If not, the viscosity of the modified polyacrylonitrile solution is adjusted using a viscosity modifier, and the step of detecting whether the modified polyacrylonitrile solution has reached the preset range is performed. The viscosity modifier includes polyvinylpyrrolidone for increasing viscosity and N,N-dimethylformamide for decreasing viscosity.

[0033] S2.2. Polyacrylonitrile fibers are hot-pressed at 120~150℃ and 5~10MPa for 3~5min to obtain polyacrylonitrile fiber membrane.

[0034] This temperature range allows the fiber surface to soften and melt moderately without damaging the overall shape. Combined with a moderate pressure of 5-10 MPa, it can promote effective melting and bonding of the softened fibers at the contact points, forming strong weld points between the fiber networks, thereby significantly improving the mechanical strength and structural integrity of the fiber membrane. At the same time, the short treatment time of 3-5 minutes can ensure uniform heat conduction and sufficient bonding, while avoiding excessive fiber collapse, loss of pore structure, or thermal degradation caused by overheating or excessive pressure time.

[0035] In one embodiment, step S2.2 further includes: S2.2. Immerse polyacrylonitrile fibers in an alcohol solution, dry them, and then hot-press them at 120~150℃ and 5~10MPa for 3~5min to obtain a polyacrylonitrile fiber membrane with pores. The alcohol solution includes at least one of methanol, ethanol, and isopropanol.

[0036] The process involves leaching with an alcohol solution, which effectively removes alcohol-soluble pore-forming agents from within the fibers through permeation, thereby creating abundant nanoscale pores within and between individual fibers. This integrated process synergistically achieves multi-scale control from macroscopic membrane structure to nanoscale pores, ultimately yielding polyacrylonitrile fiber membranes with excellent mechanical properties, high specific surface area, and interconnected nanopores.

[0037] In addition, this application also provides a polyacrylonitrile fiber membrane, which is prepared by the polyacrylonitrile fiber membrane preparation method described above.

[0038] In addition, this application also provides an application of a polyacrylonitrile fiber membrane for recovering palladium ions in a palladium-containing solution. The polyacrylonitrile fiber membrane is one of the aforementioned polyacrylonitrile fiber membranes, and the palladium-containing solution also contains 3-4M hydrochloric acid and 0.5-2.0wt% reducing agent.

[0039] Under high concentrations of hydrochloric acid, palladium is stabilized as a planar square anionic complex [PdCl4]. 2- They exist in various forms, and the main competing ions that coexist are Cu. 2+ Ni 2+ Zn 2+ Cr 6+ These compounds, primarily in cationic or neutral complex form, cannot be adsorbed onto polyacrylonitrile fiber membranes. It is also important to note that Cr... 6+ Meanwhile, by adding an appropriate amount of reducing agent to the system, the strong interfering substance Fe... 3+ Pre-reduction to Fe, which does not form stable chloride anions 2+ This allows for the pre-elimination of most competing adsorbed ions at the solution chemistry level.

[0040] For example, the present invention provides the following specific embodiments to illustrate the specific preparation method: Example 1 S1.1. Polyacrylonitrile and triethylamine are dissolved in a solvent and stirred at 75°C for 1.5 h to obtain an activated polyacrylonitrile solution, wherein the concentrations of polyacrylonitrile and triethylamine in the solvent are 12 wt% and 0.45 wt%, respectively. S1.2 Add tetraethylenepentamine to the activated polyacrylonitrile solution, heat to 110℃ and react for 4 h in an inert atmosphere, then cool to 75℃, add mono-(6-p-toluenesulfonyl)-β-cyclodextrin, keep warm and stir for 1.5 h to obtain a modified polyacrylonitrile solution, wherein the mass ratio of polyacrylonitrile to tetraethylenepentamine is 1:2.2, and the molar ratio of tetraethylenepentamine to mono-(6-p-toluenesulfonyl)-β-cyclodextrin is 7:1; S2.1. Polyethylene glycol was added to the modified polyacrylonitrile solution. After stirring, the viscosity of the solution was measured to be 3182 mPa·s using a viscometer. N,N-dimethylformamide was added to reduce the viscosity to 1835 mPa·s. Electrospinning was then performed, and the fibers were collected in a 1-adamantane-methanol aqueous solution to obtain polyacrylonitrile fibers. The concentration of polyethylene glycol in the modified polyacrylonitrile solution was 2 wt%, the concentration of 1-adamantane-methanol in the adamantane aqueous solution was 3 wt%, the electrospinning voltage was 20 kV, the feed speed was 0.020 mm / s, the distance between the nozzle and the surface of the adamantane aqueous solution was 8 cm, and the diameter of the injection needle was 22 G. S2.2. Polyacrylonitrile fibers were hot-pressed at 135℃ and 8MPa for 4 minutes to obtain a polyacrylonitrile fiber membrane as shown in Figure 2.

[0041] Example 2 S1.1. Polyacrylonitrile and triethylamine are dissolved in a solvent and stirred at 75°C for 1.5 h to obtain an activated polyacrylonitrile solution, wherein the concentrations of polyacrylonitrile and triethylamine in the solvent are 12 wt% and 0.45 wt%, respectively. S1.2 Add tetraethylenepentamine to the activated polyacrylonitrile solution, heat to 110℃ and react for 4 hours in an inert atmosphere, then cool to 75℃, add mono-(6-p-toluenesulfonyl)-β-cyclodextrin, and stir for 1.5 hours to obtain a polymerization solution, wherein the mass ratio of polyacrylonitrile to tetraethylenepentamine is 1:2.2, and the molar ratio of tetraethylenepentamine to mono-(6-p-toluenesulfonyl)-β-cyclodextrin is 7:1; S1.3 After the polymerization solution is cooled to 55°C, polymethyl methacrylate is added, and the mixture is stirred for 15 minutes to obtain a modified polyacrylonitrile solution, wherein the mass ratio of polyacrylonitrile to polymethyl methacrylate is 1:0.2. S2.1. Polyethylene glycol was added to the modified polyacrylonitrile solution. After stirring, the viscosity of the solution was measured to be 3596 mPa·s using a viscometer. N,N-dimethylformamide was added to reduce the viscosity to 1958 mPa·s. Electrospinning was then performed, and the fibers were collected in a 1-adamantane-methanol aqueous solution to obtain polyacrylonitrile fibers. The concentration of polyethylene glycol in the modified polyacrylonitrile solution was 2 wt%, the concentration of 1-adamantane-methanol in the adamantane aqueous solution was 3 wt%, the electrospinning voltage was 20 kV, the feed speed was 0.020 mm / s, the distance between the nozzle and the surface of the adamantane aqueous solution was 8 cm, and the diameter of the injection needle was 22 G. S2.2. After placing the polyacrylonitrile fiber in ethanol and letting it stand for 10 minutes, dry it, and then hot-press it at 135℃ and 8MPa for 4 minutes to obtain a polyacrylonitrile fiber membrane with pores.

[0042] Comparative Example 1 This is essentially the same as Example 1, except that triethylamine was not used to activate the polyacrylonitrile. Before electrospinning, the viscosity of the modified polyacrylonitrile solution was measured to be 2864 mPa·s using a viscometer. N,N-dimethylformamide was added to reduce the viscosity to 1729 mPa·s before electrospinning.

[0043] Comparative Example 2 This is essentially the same as Example 1, except that no amine modifier was used to modify the polyacrylonitrile. Before electrospinning, the viscosity of the modified polyacrylonitrile solution was measured to be 2464 mPa·s using a viscometer. N,N-dimethylformamide was added to reduce the viscosity to 1818 mPa·s before electrospinning was performed.

[0044] Unless otherwise specified, the concentrations of each metal ion in the palladium-containing solutions used below are as follows: 15.23Pb 2+ 20.08Cu 2+ 10.71Ni 2+ 8.56Zn 2+ 5.39Cr 6+ 25.54Fe 3+ 2.17Fe 2+ ; Application Examples 1-4 Add 3.5M hydrochloric acid and 1wt% reducing agent to a palladium-containing solution, stir for 10 min to obtain a pretreatment solution, then pass the pretreatment solution through a polyacrylonitrile fiber membrane at a flow rate of 1 mL / min and collect the filtrate. Repeat the above operation 5 times with the collected liquid to obtain the final filtrate. In application example 1, the polyacrylonitrile fiber membrane of example 1 is used; in application example 2, the polyacrylonitrile fiber membrane of example 2 is used; in application example 3, the polyacrylonitrile fiber membrane of comparative example 1 is used; and in application example 4, the polyacrylonitrile fiber membrane of comparative example 2 is used. In Application Example 1, the states of the palladium-containing solution before and after treatment are shown in Figure 3, and the states of the polyacrylonitrile fiber membrane used before and after use are shown in Figure 4.

[0045] Application Example 5 It is basically the same as Application Example 1, except that ascorbic acid was not added to the palladium-containing solution.

[0046] Application Example 6 It is basically the same as Application Example 1, except that the concentration of hydrochloric acid in the palladium-containing solution is 1M.

[0047] Application Example 7 It is basically the same as Application Example 1, except that the concentration of hydrochloric acid in the palladium-containing solution is 1M and no ascorbic acid is added.

[0048] The various metal ions contained in the final filtrate were detected, and the palladium ion recovery rate was calculated as follows: Palladium ion recovery rate = (Palladium ions in palladium-containing solution - Palladium ions in final filtrate) / Palladium ions in palladium-containing solution * 100%; The results of the detection of the content of each metal ion in the final filtrate are shown in Table 1, and the palladium ion recovery rate is shown in Table 2.

[0049] Table 1. Metal ion content of the final filtrate (unit: mg / L) Table 2 Palladium ion recovery rate As shown in Tables 1 and 2, compared with Application Examples 3-4, the polyacrylonitrile fiber membranes used in Application Examples 1-2 have a good recovery rate for palladium ions. Application Example 2 shows even better results because the surface area of ​​the polyacrylonitrile fiber membrane increases further after dissolution with the alcohol-soluble pore-forming agent, thereby further increasing the adsorption capacity of palladium ions. Further observation of Tables 1, Application Example 1, and Application Examples 5-7 shows that when the concentration of hydrochloric acid in the palladium-containing solution is reduced and / or ascorbic acid is not used, the Cr content in the final filtrate is reduced. 2+ Fe 3+The content of [certain substances] also decreased simultaneously, meaning that the polyacrylonitrile fiber membrane not only contains palladium ions but also Cr [certain substances]. 2+ and Fe 3+ Therefore, it can be seen that the concentration of hydrochloric acid and the content of reducing agent in the palladium-containing solution also affect the specific adsorption of palladium ions by the polyacrylonitrile fiber membrane.

[0050] The above embodiments are preferred embodiments of this application, but the implementation of this application is not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of this application shall be considered equivalent substitutions and shall be included within the protection scope of this application.

Claims

1. A method for preparing a polyacrylonitrile fiber membrane, characterized in that, The preparation method includes the following steps: S1. Add polyacrylonitrile to a solvent, then add an amine modifier first, heat and stir, then add a cyclodextrin modifier, and continue stirring to obtain a modified polyacrylonitrile solution. The modified polyacrylonitrile contains amine groups modified by the amine modifier and cyclodextrin groups modified by the cyclodextrin modifier. S2. The modified polyacrylonitrile solution is electrospun and the polyacrylonitrile fibers are collected in an aqueous adamantane solution and hot-pressed to obtain a polyacrylonitrile fiber membrane.

2. The method for preparing a polyacrylonitrile fiber membrane according to claim 1, characterized in that, The solvent in step S1 includes N,N-dimethylformamide and / or dimethyl sulfoxide, the amine modifier includes at least one of ethylenediamine, tetraethylenepentamine, and diethylenetriamine, and the cyclodextrin modifier includes mono-(6-epoxypropyl)-6-deoxy-β-cyclodextrin and / or mono-(6-p-toluenesulfonyl)-β-cyclodextrin.

3. A method for preparing a polyacrylonitrile fiber membrane according to claim 1 or 2, characterized in that, Step S1 includes: S1.1 Dissolve polyacrylonitrile and alkaline catalyst in a solvent and stir at 70~80℃ for 1~2h to obtain an activated polyacrylonitrile solution, wherein the concentrations of polyacrylonitrile and alkaline catalyst in the solvent are 10~15wt% and 0.4~0.5wt%, respectively, and the alkaline catalyst includes at least one of triethylamine, tetramethylguanidine, and diazabicyclononene. S1.2 Add an amine modifier to the activated polyacrylonitrile solution, and in an inert atmosphere, heat to 100~120℃ and react for 3~5 hours. Then cool to 70~80℃, add a cyclodextrin modifier, and keep warm and stir for 1~2 hours to obtain a modified polyacrylonitrile solution. The mass ratio of polyacrylonitrile to amine modifier is 1:(1.5~3.0), and the molar ratio of amine modifier to cyclodextrin modifier is (6~8):

1.

4. The method for preparing a polyacrylonitrile fiber membrane according to claim 3, characterized in that, Step S1 also includes: S1.1 Dissolve polyacrylonitrile and alkaline catalyst in a solvent and stir at 70~80℃ for 1~2h to obtain an activated polyacrylonitrile solution, wherein the concentrations of polyacrylonitrile and alkaline catalyst in the solvent are 10~15wt% and 0.4~0.5wt%, respectively, and the alkaline catalyst includes at least one of triethylamine, tetramethylguanidine, and diazabicyclononene. S1.2 Add an amine modifier to the activated polyacrylonitrile solution, and in an inert atmosphere, heat to 100~120℃ and react for 3~5 hours. Then cool to 70~80℃, add a cyclodextrin modifier, and keep warm and stir for 1~2 hours to obtain a polymerization solution. The mass ratio of polyacrylonitrile to amine modifier is 1:(1.5~3.0), and the molar ratio of amine modifier to cyclodextrin modifier is (6~8):

1. S1.3 After the polymerization solution is cooled to 50~60℃, add the alcohol-soluble pore-forming agent, keep warm and stir for 10~20min to obtain the modified polyacrylonitrile solution. The alcohol-soluble pore-forming agent includes at least one of polymethyl methacrylate, cellulose acetate and polyethylene oxide. The mass ratio of polyacrylonitrile to alcohol-soluble pore-forming agent is 1:(0.1~0.3).

5. The method for preparing a polyacrylonitrile fiber membrane according to claim 1, characterized in that, Step S2 includes: S2.1 Add a stabilizer to the modified polyacrylonitrile solution, stir, and then electrospin, collecting the fibers in an adamantane aqueous solution to obtain polyacrylonitrile fibers. The concentration of the stabilizer in the modified polyacrylonitrile solution is 1-3 wt%, and the stabilizer includes at least one of polyethylene glycol, polyethylene oxide, and polycaprolactone. The adamantane aqueous solution contains 1-adamantane methanol and / or 1-adamantane carboxylic acid, and the concentration of adamantane is 1-5 wt%. The electrospinning voltage is 18-22 kV, the feeding speed is 0.018-0.022 mm / s, the distance between the nozzle and the surface of the adamantane aqueous solution is 7-9 cm, and the diameter of the injection needle is 21-23 G. S2.

2. Polyacrylonitrile fibers are hot-pressed at 120~150℃ and 5~10MPa for 3~5min to obtain polyacrylonitrile fiber membrane.

6. The method for preparing a polyacrylonitrile fiber membrane according to claim 4, characterized in that, Step S2.2 also includes: S2.

2. Immerse polyacrylonitrile fibers in an alcohol solution, dry them, and then hot-press them at 120~150℃ and 5~10MPa for 3~5min to obtain a polyacrylonitrile fiber membrane with pores. The alcohol solution includes at least one of methanol, ethanol, and isopropanol.

7. The method for preparing a polyacrylonitrile fiber membrane according to claim 1, characterized in that, Before the electrospinning operation in step S2.1, the modified polyacrylonitrile solution is adjusted to a preset viscosity. Adjusting the modified polyacrylonitrile solution to a preset viscosity specifically includes: Test whether the modified polyacrylonitrile solution reaches the preset range; If so, then perform electrospinning. If not, the viscosity of the modified polyacrylonitrile solution is adjusted using a viscosity modifier, and the step of detecting whether the modified polyacrylonitrile solution has reached the preset range is performed. The viscosity modifier includes polyvinylpyrrolidone for increasing viscosity and N,N-dimethylformamide for decreasing viscosity.

8. A polyacrylonitrile fiber membrane, characterized in that, The polyacrylonitrile fiber membrane is prepared by any one of the polyacrylonitrile fiber membrane preparation methods according to claims 1-7.

9. The application of polyacrylonitrile fiber membranes in the recovery of palladium ions from palladium-containing solutions, characterized in that, The polyacrylonitrile fiber membrane is the polyacrylonitrile fiber membrane according to claim 8, and the specific application process is as follows: Add 3-4M hydrochloric acid and 0.5-2.0wt% reducing agent to the palladium-containing solution, stir for 8-12 min to obtain a pretreated solution, then pass the pretreated solution through a polyacrylonitrile fiber membrane at a flow rate of 0.8-1.2 mL / min and collect the filtrate. Repeat the above operation 4-6 times with the collected liquid to obtain the final filtrate, thus completing the recovery of palladium ions.

10. The application of the polyacrylonitrile fiber membrane according to claim 9 in the recovery of palladium ions from palladium-containing solutions, characterized in that, The reducing agent includes at least one of ascorbic acid, sodium sulfite, and hydrazine hydrate.

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