Gravity-driven membrane for treating acidic arsenic-containing wastewater as well as preparation method and application of gravity-driven membrane

Abstract

The invention discloses a gravity-driven membrane for acidic arsenic-containing wastewater treatment and a preparation method and application thereof.The preparation method of the gravity-driven membrane for acidic arsenic-containing wastewater treatment comprises the following steps that polyacrylonitrile and polyethyleneimine are dissolved in an N, N-dimethylformamide solution, and a spinning solution is obtained after the polyacrylonitrile and the polyethyleneimine are completely dissolved; and putting the spinning solution into an electrostatic spinning machine to prepare a nanofiber membrane, and obtaining the gravity-driven membrane for treating the acidic arsenic-containing wastewater according to the nanofiber membrane. According to the gravity-driven membrane for treating the acidic arsenic-containing wastewater as well as the preparation method and the application of the gravity-driven membrane, high flux can be realized in a dynamic adsorption filtration system, and meanwhile, efficient and rapid removal of arsenic can be ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental governance, and in particular to a gravity-driven membrane for treating acidic arsenic-containing wastewater, and a preparation method and application thereof. Background Art

[0002] Arsenic is a highly toxic element that is widely present in metal ores, coal, and geothermal fluids. In industries such as metal mining, chemical production, and metallurgical processing, it is often released with acidic wastewater to form highly toxic acidic arsenic-containing wastewater (pH=1-4). This type of wastewater not only causes serious damage to the ecological environment, but also accumulates through the food chain, threatening human health. In addition, long-term exposure to an arsenic-containing environment can lead to diseases such as skin cancer and lung cancer. The high toxicity, persistence, and bioaccumulation of arsenic make it a global environmental health threat. Developing efficient and low-cost treatment technologies for acidic arsenic pollution in industrial wastewater is an urgent need for environmental protection and public safety.

[0003] Conventional treatment methods for acidic arsenic-containing wastewater mainly include chemical precipitation, adsorption, ion exchange, membrane separation, etc. Adsorption is one of the most commonly used methods in the field of arsenic removal. It is widely used in the treatment of arsenic pollution in groundwater, industrial wastewater and drinking water because of its simple operation, low cost and applicability to a variety of water quality conditions. However, it still faces challenges such as low removal efficiency of low-concentration arsenic, long adsorption process, and decreased adsorption performance under acidic conditions. Membrane separation has the advantages of efficient arsenic removal, no need to add chemical agents, simple operation, and low energy consumption. It shows great application potential in the treatment of arsenic-containing wastewater. However, membrane separation usually uses nanofiltration or reverse osmosis devices. When treating arsenic, it still faces challenges such as low flux, easy corrosion or degradation of membrane materials under acidic conditions, and limited treatment effect on low-concentration arsenic.

[0004] The disclosure of the above background technology content is only used to assist in understanding the concept and technical solution of the present invention. It does not necessarily belong to the prior art of this patent application. In the absence of clear evidence that the above content has been disclosed on the filing date of this patent application, the above background technology should not be used to evaluate the novelty and creativity of the present application. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a gravity-driven membrane for treating acidic arsenic-containing wastewater and a preparation method and application thereof, which can achieve high flux in a dynamic adsorption filtration system while ensuring efficient and rapid removal of arsenic.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: In the first aspect, the present invention discloses a method for preparing a gravity-driven membrane for treating acidic arsenic-containing wastewater, comprising the following steps: dissolving polyacrylonitrile and polyethyleneimine in an N,N-dimethylformamide solution and completely dissolving them to obtain a spinning solution; placing the spinning solution into an electrospinning machine to obtain a nanofiber membrane, and obtaining a gravity-driven membrane for treating acidic arsenic-containing wastewater based on the nanofiber membrane.

[0007] Preferably, the mass ratio of polyacrylonitrile to polyethyleneimine is (1-3):1.

[0008] Preferably, when polyacrylonitrile and polyethyleneimine are dissolved in N,N-dimethylformamide solution, the mass fraction of polyacrylonitrile in the N,N-dimethylformamide solution is 7.5% to 11.25%, and the mass fraction of polyethyleneimine in the N,N-dimethylformamide solution is 3.75% to 7.5%.

[0009] Preferably, after polyacrylonitrile and polyethyleneimine are dissolved in the N,N-dimethylformamide solution, they are further isolated from air and heated in a water bath and stirred until they are completely dissolved to obtain the spinning solution.

[0010] Preferably, the water bath heating temperature is 50° C. to 70° C., and the water bath heating and stirring time is 3 h to 4 h.

[0011] Preferably, the spinning solution is subjected to ultrasonic treatment for 20 min to 30 min before being placed into the electrospinning machine.

[0012] Preferably, when the spinning solution is placed in an electrospinning machine to obtain the nanofiber membrane, the parameters of the electrospinning machine include: a positive voltage of 16KV to 18KV, a negative voltage of 0 to 1KV, and a propulsion speed of 0.08mm / min to 0.1mm / min.

[0013] Preferably, when the spinning solution is placed in an electrospinning machine to obtain the nanofiber membrane, the ambient temperature is 30°C to 40°C, the relative humidity is 20% to 40%, and on the electrospinning machine, tin foil is used to cover the metal roller as a collection device for the nanofiber membrane.

[0014] Preferably, the nanofiber membrane material is placed in an oven for drying to obtain a gravity-driven membrane for treating acidic arsenic-containing wastewater, wherein the temperature of the oven is 50° C. to 70° C., and the drying time is 20 min to 30 min.

[0015] In a second aspect, the present invention discloses a gravity-driven membrane for treating acidic arsenic-containing wastewater, which is prepared by the preparation method of the gravity-driven membrane for treating acidic arsenic-containing wastewater described in the first aspect.

[0016] In a third aspect, an application of the gravity-driven membrane of the second aspect for treating acidic arsenic-containing wastewater is provided, wherein the gravity-driven membrane is used to treat acidic arsenic-containing wastewater with a pH value of 1 to 5.

[0017] Compared with the prior art, the invention has the following beneficial effects: the gravity-driven membrane for treating acidic arsenic-containing wastewater disclosed in the invention and its preparation method and application increase the adsorption sites by preparing a nanofiber structure with a high specific surface area, wherein polyacrylonitrile (PAN) with high strength, good elasticity and acid resistance is used as the substrate to make the membrane acid-resistant, and polyethyleneimine (PEI) is introduced because its molecular chain is rich in amino groups ( ) and imino groups ( ), these polar groups form strong hydrogen bonds with water molecules, which can significantly improve the surface hydrophilicity and increase the membrane flux. ), the amino group of polyethyleneimine is protonated to , further enhancing the electrostatic attraction to water molecules; experiments show that under the low-pressure gravity drive of 0.98 kPa, the flux can reach Here, the amino group of polyethyleneimine is more easily protonated in an acidic environment, generating a large amount of ammonium ions ( ), effectively reacting with arsenate ions ( ) through electrostatic interaction and coordination bond combination, the adsorption capacity of microgram level arsenic (V) is improved. The gravity-driven membrane prepared by this scheme can achieve high flux in the dynamic adsorption filtration system (under 0.98kPa low pressure and low energy consumption) while ensuring efficient and rapid removal of arsenic (V); the dynamic adsorption filtration method makes it possible to remove arsenic (V) in wastewater. The water flows through the dense membrane pores under the action of gravity, repeatedly contacting the functional adsorption sites on the nanofibers, effectively improving the adsorption capacity of the membrane material. Arsenic (V) in acidic wastewater can be adsorbed and removed within a dozen seconds of contact with the membrane. In addition, the membrane preparation materials are low-cost PAN and PEI, and the process mainly relies on electrospinning technology, which is simple and convenient.

[0018] In addition to the above beneficial effects, the present invention also has the following beneficial effects: (1) Polyethyleneimine (PEI) was successfully introduced into the nanofiber membrane as a functional component. Its rich amino groups ( ) When treating acidic arsenic wastewater ( ) is protonated ( ), and arsenate ions ( ) significantly improves the membrane's adsorption capacity and selectivity for arsenic (V) in solution through electrostatic interaction and coordination bonding, and overcomes the problem of low efficiency of traditional adsorbents in low pH environments.

[0019] (2) The present invention uses electrospinning technology to make a mixed solution of polyethyleneimine and polyacrylonitrile with a large specific surface area, high porosity, and strong hydrophilicity. The arsenic removal research is carried out in a gravity filtration device to obtain a high-throughput ( ) and high arsenic removal capacity (effectively degrading 3 L of 100 ppb pentavalent arsenic solution to below 10 ppb), effectively solving the problem of low permeability flux of traditional filtration membranes.

[0020] (3) The present invention uses cheap polyacrylonitrile (PAN) and polyethyleneimine (PEI) as membrane materials, which will not release harmful substances during use, thus avoiding the risk of secondary pollution. The membrane material is prepared by a simple electrospinning process, which does not require complex equipment and is suitable for large-scale production and application. The cost is much lower than that of traditional adsorbents (such as nano iron oxide). BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A flow chart of a method for preparing a gravity-driven membrane for treating acidic arsenic-containing wastewater according to a preferred embodiment of the present invention; Figure 2a is a schematic diagram of the gravity-driven filtration experimental apparatus; Figure 2b This is a schematic diagram of the filtering principle of the nanofiber membrane; Figure 3 is a physical picture of the nanofiber membrane prepared in Example 3; Figure 4 The nanofiber membranes prepared in Examples 1, 2, 3 and Comparative Example are Schematic diagram of the degradation effect of arsenic-containing wastewater; Figure 5 is a scanning electron microscope (SEM) image of the nanofiber membrane prepared in the comparative example; Figure 6 is a scanning electron microscope (SEM) image of the nanofiber membrane prepared in Example 3; Figure 7 It is a schematic diagram of the water contact angle results of the nanofiber membranes prepared in Examples 1, 2, 3 and the comparative example; Figure 8 It is the Fourier transform infrared spectrum (FTIR) graph of the nanofiber membrane prepared in Examples 1, 2, 3 and the comparative example. DETAILED DESCRIPTION

[0022] The following is a detailed description of the embodiments of the present invention. It should be emphasized that the following description is only exemplary and is not intended to limit the scope and application of the present invention.

[0023] It should be noted that when a component is referred to as being "fixed to" or "disposed on" another component, it can be directly on the other component or indirectly on the other component. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, connection can be used for both fixing and circuit / signal communication.

[0024] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0025] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0026] In view of the difficulties in treating acidic arsenic (V)-containing wastewater due to the low removal efficiency of low-concentration arsenic by adsorption, the long adsorption process, the decreased adsorption performance under acidic conditions, and the low flux of membrane separation method, the present invention optimizes the ratio of polyacrylonitrile (PAN) and polyethyleneimine (PEI) in the spinning solution to provide a high-efficiency, stable, low-cost, simple preparation process, high-flux, and high-removal rate nanofiber membrane. The acidic arsenic (V)-containing wastewater can be treated quickly and efficiently under a low-pressure (0.98 kPa) and low-energy consumption gravity-driven filtration device, providing a practical solution for the treatment of acidic arsenic (V)-containing wastewater by membrane adsorption separation method.

[0027] Membrane adsorption separation is an efficient water treatment technology that combines membrane separation technology with adsorption function. It achieves physical interception and chemical adsorption of pollutants simultaneously through membrane materials with specific functional groups. This method uses the high specific surface area and precise pore size distribution of the membrane to achieve the screening and interception of particulate pollutants. At the same time, the pollutants are allowed to pass through the membrane pores quickly with the water flow under external pressure, and repeatedly contact with the modified active groups (such as amino groups, thiol groups, etc.) in the membrane to produce specific adsorption. It is particularly suitable for the deep removal of low-concentration heavy metal ions (such as arsenic, lead, etc.). Compared with traditional adsorption and membrane separation methods, membrane adsorption separation has the advantages of high treatment efficiency, good selectivity, low operating pressure, and integration. It shows broad application prospects in the fields of drinking water purification and industrial wastewater treatment.

[0028] like Figure 1 As shown, a preferred embodiment of the present invention discloses a method for preparing a gravity-driven membrane for treating acidic arsenic-containing wastewater, comprising the following steps: S1: dissolving polyacrylonitrile (PAN) and polyethyleneimine (PEI) in N,N-dimethylformamide (DMF) solution to obtain a spinning solution; Wherein, step S1 comprises: S11: dissolving polyacrylonitrile and polyethyleneimine in N,N-dimethylformamide solution; The drug parameters used are polyacrylonitrile with an average molecular weight of 150,000 and linear polyethyleneimine with a molecular weight of 10,000.

[0029] Specifically, the mass ratio of polyacrylonitrile to polyethyleneimine is (1-3):1, such as 3:1, 2:1, 1:1. Further, the mass fraction of polyacrylonitrile in the N,N-dimethylformamide solution is 7.5%-11.25%, and the mass fraction of polyethyleneimine in the N,N-dimethylformamide solution is 3.75%-7.5%; for example, the obtained spinning solution.

[0030] S12: Heat in a water bath and stir in an air-tight manner until the spinning solution is completely dissolved to obtain a spinning solution; Specifically, the water bath heating temperature is 50° C. to 70° C., and the water bath heating and stirring time is 3 h to 4 h, wherein the stirring is performed by magnetic stirring, for example.

[0031] S2: The spinning solution is placed in an electrospinning machine to obtain a nanofiber membrane, and a gravity-driven membrane for treating acidic arsenic-containing wastewater is obtained through the nanofiber membrane.

[0032] Wherein, step S2 comprises: S21: ultrasonically treating the spinning solution for 20 min to 30 min to remove bubbles in the spinning solution.

[0033] S22: taking out the spinning solution after ultrasonic treatment with a syringe, adjusting the voltage of the high-voltage electrospinning machine, the distance from the spinneret to the receiving device, the spinning solution injection rate and other parameters to spin the nanofiber membrane material.

[0034] Among them, the parameters of the electrospinning machine are: positive voltage is 16KV~18KV, negative voltage is 0~1KV, propulsion speed is 0.08mm / min~0.1mm / min, collection distance is 20cm, translation speed is 90mm / min, translation distance is 100mm, roller receiving speed is 10r / min, ambient temperature is 30℃~40℃, relative humidity is 20%~40%, and tin foil is used to cover the metal roller as a collection device.

[0035] S23: placing the obtained nanofiber membrane into an oven for drying to obtain a dried nanofiber membrane sheet, which is a gravity-driven membrane for treating acidic arsenic-containing wastewater.

[0036] The temperature of the oven is 50°C to 70°C, and the time is 20min to 30min.

[0037] The preferred embodiment of the present invention further discloses a gravity-driven membrane for treating acidic arsenic-containing wastewater, which is prepared by the preparation method of the gravity-driven membrane for treating acidic arsenic-containing wastewater disclosed in the above preferred embodiment.

[0038] The following is a further test of the effect of the gravity-driven membrane for treating acidic arsenic-containing wastewater in Example 2 of the present invention on treating acidic arsenic-containing wastewater. The specific test steps include: A1: Cut the middle part of the prepared nanofiber membrane into 4×4 cm 2 The two membranes are stacked and placed as Figure 2a The effective filtration area of ​​the gravity-driven filtration device shown is 3.14 × 1.5 × 1.5 cm 2 , membrane adsorption filtration experiments were carried out.

[0039] in, Figure 2a The gravity-driven filtration device shown in the figure specifically lifts the acidic arsenic-containing wastewater 20 into the pipe column 30 through the water pump 10 and combines it with the reflux pipe 60 to form a constant 10 cm high water head in the pipe column 30, and a nanofiber membrane 40 is placed under the pipe column 30. The acidic arsenic-containing wastewater 20 passes through the nanofiber membrane 40 by gravity to achieve a filtering effect; after filtering every 90 ml of the acidic arsenic-containing wastewater, the concentration of residual arsenic (V) in the obtained filtrate 50 is detected by a detection device. Figure 2b The schematic diagram of the filtering principle of the nanofiber membrane 40 of the present invention is shown. Under the condition of pH=4±0.1, arsenic (V) is dissolved in water at The nanofiber membrane 40 (PAN@PEI nanofiber membrane) carries a large amount of positive charge on its surface, which filters and adsorbs negatively charged particles in water through pore size screening and charge adsorption effect. , to achieve the effect of removing arsenic (V).

[0040] A2: The wastewater with pH=4±0.1 and arsenic (V) concentration of 100 ppb is passed through the membrane material at a head height of 10 cm by a pump for gravity filtration.

[0041] A3: Record the time for every 100 ml of water sample filtered, and collect 10 ml of sample (filtrate 50) for every 90 ml of wastewater filtered.

[0042] A4: The collected sample (filtrate 50) is tested for arsenic concentration. The testing instrument achieves high-sensitivity and high-precision detection of arsenic concentration in water through high-temperature plasma ionization, mass analyzer separation and detector signal amplification. It is suitable for arsenic concentration determination at the ppb (Parts Per Billion) or even ppt (Parts Per Trillion) level.

[0043] The preferred embodiment of the present invention also discloses an application of a gravity-driven membrane for treating acidic arsenic-containing wastewater. The gravity-driven membrane for treating acidic arsenic-containing wastewater in the above preferred embodiment is used to treat acidic arsenic-containing wastewater with a pH value of 1 to 5.

[0044] The preferred embodiment of the present invention proposes a nanofiber membrane based on a composite material of polyacrylonitrile (PAN) and polyethyleneimine (PEI) for treating acidic arsenic-containing wastewater. The membrane material is based on PAN and has strong acid resistance; PEI is introduced into the nanofiber membrane as a functional component, and its rich amino groups ( ) is protonated when treating acidic arsenic-containing wastewater (pH=4±0.1) ), and arsenate ions ( ) significantly improves the adsorption capacity and selectivity of the membrane for arsenic (V) in solution through electrostatic interaction and coordination bond combination, and overcomes the problem of low efficiency of traditional adsorbents in low pH environments. Experiments show that the arsenic (V) concentration can be reduced from 100 ppb to below 10 ppb by gravity-driven filtration mode (under 0.98 kPa pressure), while having high flux ( ), low cost, and simple preparation. The present invention provides an efficient and feasible solution to solve the technical bottleneck in the treatment of acidic arsenic-containing wastewater, which has important environmental and social significance. Among them, the preparation method of the gravity-driven membrane provided by the present invention is simple and has both high flux and high removal rate of arsenic (V) under acidic conditions. Thanks to the presence of PEI, a large number of amino groups are introduced, which greatly improves the hydrophilicity of the material. At the same time, it is easy to be protonated under acidic conditions to produce a large amount of Arsenic (V) is usually present in acidic water. The two exist in different forms, and they can be efficiently combined through the dual effects of electrostatic attraction and coordination bonds in a dynamic adsorption filtration system.

[0045] The following is a further description of the effect of the gravity-driven membrane for treating acidic arsenic-containing wastewater with a pH value of 1 to 5 according to the present invention in conjunction with specific examples.

[0046] Example 1

[0047] The method for preparing the nanofiber membrane for treating acidic arsenic-containing wastewater disclosed in this embodiment comprises the following specific steps: B1: Dissolve 4.5 g of polyacrylonitrile (average molecular weight 150,000) powder in 34 g of N,N-dimethylformamide solution (purity 99.5%), and add 1.5 g of linear polyethyleneimine (average molecular weight 10,000, purity 99%).

[0048] B2: The above solution was isolated from air and placed on a magnetic stirrer and heated at 60°C in a water bath for 4 hours until it was completely dissolved to obtain a spinning solution.

[0049] B3: The spinning solution was cooled to room temperature and ultrasonicated for 30 minutes.

[0050] B4: Take out 10 ml of spinning solution with a syringe and place it on the electrospinning machine. Set the parameters as follows: positive voltage 18 KV, negative voltage 1 KV, propulsion speed 0.09 mm / min, collection distance 20 cm, translation speed 90 mm / min, translation distance 100 mm, roller receiving speed 10 r / min, ambient temperature 35 ℃, relative humidity 30%, use tin foil to cover the metal roller as a collecting device to obtain a nanofiber membrane.

[0051] B5: Remove the tin foil loaded with nanofiber membrane, place it in an oven set at 60 °C and dry it for 20 minutes to obtain a weight of , a nanofiber membrane with a thickness of about 0.5 mm.

[0052] B6: Conduct gravity-driven membrane filtration to remove arsenic: Cut the middle part of the prepared membrane material and cut it into 4×4 The two membranes are stacked and placed as Figure 2a In the gravity-driven filter device shown, the effective filtration area is , and conduct membrane filtration experiments. Wastewater containing 100 ppb As (V) was controlled to pass through the membrane material at a head height of 10 cm for gravity filtration. The time was recorded every time 100 ml of water sample was filtered, and 10 ml of sample was collected every time 90 ml of wastewater was filtered for residual arsenic detection.

[0053] Example 2

[0054] The preparation method of the nanofiber membrane for treating acidic arsenic-containing wastewater disclosed in this embodiment is different from that in Example 1 only in that the mass of polyacrylonitrile added to the N,N-dimethylformamide solution in step B1 is 4 g, and the mass of polyethyleneimine is 2 g. , the thickness of the nanofiber membrane is about 0.55 mm. The same filtration experiment as in Example 1 was carried out.

[0055] Example 3

[0056] The preparation method of the nanofiber membrane for treating acidic arsenic-containing wastewater disclosed in this embodiment is different from that in Example 1 only in that the mass of polyacrylonitrile and the mass of polyethyleneimine added to the N,N-dimethylformamide solution in step B1 are 3 g and 3 g, respectively. , the thickness of the nanofiber membrane is about 0.6 mm, such as Figure 3 The figure shows the actual image of the nanofiber membrane obtained in this example. The same filtration experiment as in Example 1 was carried out.

[0057] Comparative Example The difference between this comparative example and Example 1 is that 6 g of polyacrylonitrile is used in the preparation of the spinning solution without adding polyethyleneimine, and the weight of the obtained spinning solution is , a nanofiber membrane with a thickness of about 0.4 mm. The same filtration experiment as in Example 1 was carried out.

[0058] like Figure 4 The figure is a schematic diagram of the degradation effect of the nanofiber membranes prepared in Examples 1, 2, 3 and the comparative example on arsenic-containing wastewater with a pH of 4±0.1. The nanofiber membrane prepared in Example 1 (PAN:PEI=3:1) The nanofiber membrane prepared in Example 2 (PAN:PEI=2:1) ​​can effectively degrade 3 L of acidic wastewater (pH=4±0.1) containing 100 ppb arsenic (V) to below 20 ppb at a flux of 3 L of acidic wastewater (containing 100 ppb arsenic (V)) was effectively converted to ) was degraded to a concentration below 20 ppb; the nanofiber membrane prepared in Example 3 (PAN:PEI=1:1) could 3 L of acidic wastewater (containing 100 ppb arsenic (V)) was effectively converted to ) was degraded to a concentration below 10 ppb; however, the nanofiber membrane prepared in the comparative example (100% PAN) could not effectively treat the acidic wastewater containing arsenic (V) with a concentration of 100 ppb ( ), the removal rate is only about 5%. Therefore, compared with the 100% PAN nanofiber membrane prepared in the comparative example under acidic conditions ( ) cannot effectively remove arsenic (V). The membrane materials prepared by introducing different proportions of PEI can effectively treat arsenic (V). The nanofiber membranes prepared in Example 1 (PAN:PEI=3:1) and Example 2 (PAN:PEI=2:1) ​​can effectively remove arsenic (V) in 1.5-2.5L acidic wastewater ( ) can be effectively degraded to a concentration below 10 ppb (WHO safety standard concentration). In addition, the nanofiber membrane prepared in Example 3 (PAN:PEI=1:1) can effectively degrade 3 L of acidic wastewater (pH=4±0.1) containing arsenic (V) with a concentration of 100 ppb to a concentration below 10 ppb (WHO safety standard concentration), and has a higher adsorption capacity.

[0059] like Figure 5 As shown in FIG. 1 , it is a SEM image of a 15wt% pure PAN nanofiber membrane in a comparative example, from which it can be seen that the fibers of the nanofiber sheet in the comparative example are uniform and have a diameter of about 300nm; Figure 6 As shown, it is the SEM image of the nanofiber membrane obtained in Example 3 (PAN:PEI=1:1), the fibers are uniform, the diameter is 350nm~450nm, and the fiber surface is convex; Figure 5 and Figure 6 It can be seen that the introduction of PEI affects the rheology and curing process of the spinning solution, making the fibers thicker and the surface convex; the thickening of the fibers can further increase the pore size of the nanofiber membrane and the flux; the convex surface can increase the contact area between the pollutants and the membrane and increase the adsorption capacity of the membrane.

[0060] Figure 7The figure shows that the water contact angle of the nanofiber membranes prepared in Examples 1, 2, 3 and the comparative example was tested using a contact angle / surface tension meter. It can be seen that the water contact angle of the nanofiber membrane prepared in the comparative example (100% PAN) is 133°, the water contact angle of the nanofiber membrane prepared in Example 1 (PAN:PEI=3:1) is 35°, the water contact angle of the nanofiber membrane prepared in Example 2 (PAN:PEI=2:1) ​​is 33°, and the water contact angle of the nanofiber membrane prepared in Example 3 (PAN:PEI=1:1) is 27°. It can be seen that the introduction of PEI in Examples 1, 2, and 3 successfully modifies the nanofiber membrane material into a hydrophilic material.

[0061] Figure 8 The Fourier transform infrared spectroscopy (FTIR) images shown in the figure show that the nanofiber membranes prepared by adding PEI in Examples 1, 2, and 3 have secondary amide characteristic peaks (1557 cm -1 、1658 cm -1 、3263 cm -1 ), while the nanofiber membrane prepared in the comparative example (100% PAN) did not show the characteristic peak of secondary amide. Specifically, the infrared spectra of the nanofiber membranes prepared in Example 1 (PAN:PEI=3:1), Example 2 (PAN:PEI=2:1), and Example 3 (PAN:PEI=1:1) showed a peak at 3263 cm -1 There is an amino characteristic peak at ) are introduced into the nanofiber membrane. These groups are the adsorbents of arsenate ( ) and at 3263 cm -1 The broad absorption peak at 1557 cm-1 indicates that the PEI amino group forms a hydrogen bond network and can be efficiently protonated under acidic conditions, providing high-density active sites for arsenate adsorption; -1 Possibly Bending vibration indicates that the PEI amino group has been partially protonated during preparation or storage, indicating that the material can quickly start adsorption in an acidic environment; 1658 cm -1 There is an amide bond or amino vibration peak at the PAN fiber, indicating that PEI is successfully loaded and the PAN fiber structure is intact. However, the comparative example (100% PAN) does not have an amino characteristic peak, indicating that the PAN material itself does not have amino-related functional groups and cannot effectively adsorb arsenate ions ( ).

[0062] The above experiment shows that compared with the comparative example, after adding PEI in Examples 1, 2, and 3, the Fourier infrared spectroscopy ( Figure 8 ) It can be seen that amino groups were successfully introduced into the membrane, which improved the hydrophilicity ( Figure 7). The flux of the nanofiber membrane (PAN: PEI = 1:1) prepared according to Example 3 reached At the same time, it has the ability to efficiently filter and remove arsenic, and can effectively reduce 100 ppb of As (V)-containing wastewater to below the WHO safety standard of 10 ppb. Among them, the nanofiber membrane prepared in the embodiment of the present invention can obtain the above experimental results, thanks to the successful introduction of polyethyleneimine (PEI) as a functional component into the nanofiber membrane, and its rich amino groups ( ) When treating acidic arsenic wastewater ( ) is protonated ( ), and arsenate ions ( ) through electrostatic interaction and coordination bond combination, the membrane's adsorption capacity and selectivity for arsenic (V) in water are significantly improved. At the same time, the dynamic adsorption filtration method makes the wastewater Following the water flow under the action of gravity, it passes through the dense membrane pores and repeatedly contacts the functional adsorption sites on the nanofibers, effectively improving the adsorption capacity of the membrane material.

[0063] The background section of the present invention may contain background information about the problem or environment of the present invention, rather than describing the prior art by others. Therefore, the content contained in the background section is not an admission by the applicant that the prior art is available.

[0064] The above content is a further detailed description of the present invention in combination with specific / preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, it can also make several substitutions or modifications to these described embodiments, and these substitutions or modifications should be regarded as belonging to the protection scope of the present invention. In the description of this specification, the description of reference terms "an embodiment", "some embodiments", "preferred embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily target the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, in the absence of mutual contradiction, the technical personnel in this field can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and modifications can be made herein without departing from the scope defined by the attached claims.

Claims

1. A method for preparing a gravity-driven membrane for treating acidic arsenic-containing wastewater, characterized in that: The following steps are involved: Polyacrylonitrile and polyethyleneimine are dissolved in N,N-dimethylformamide solution and completely dissolved to obtain a spinning solution; the spinning solution is placed in an electrostatic spinning machine to obtain a nanofiber membrane, and a gravity-driven membrane for treating acidic arsenic-containing wastewater is obtained based on the nanofiber membrane.

2. The method for preparing a gravity-driven membrane for treating acidic arsenic-containing wastewater according to claim 1, characterized in that: The mass ratio of polyacrylonitrile to polyethyleneimine is (1-3):

1.

3. The method for preparing a gravity-driven membrane for treating acidic arsenic-containing wastewater according to claim 1, characterized in that: When polyacrylonitrile and polyethyleneimine are dissolved in N,N-dimethylformamide solution, the mass fraction of polyacrylonitrile in the N,N-dimethylformamide solution is 7.5% to 11.25%, and the mass fraction of polyethyleneimine in the N,N-dimethylformamide solution is 3.75% to 7.5%.

4. The method for preparing a gravity-driven membrane for treating acidic arsenic-containing wastewater according to claim 1, characterized in that: After polyacrylonitrile and polyethyleneimine are dissolved in the N,N-dimethylformamide solution, the solution is isolated from air and heated to 50° C. to 70° C. in a water bath and stirred for 3 h to 4 h until they are completely dissolved to obtain the spinning solution.

5. The method for preparing a gravity-driven membrane for treating acidic arsenic-containing wastewater according to claim 1, characterized in that: The spinning solution is also subjected to ultrasonic treatment for 20 minutes to 30 minutes before being placed into the electrospinning machine.

6. The method for preparing a gravity-driven membrane for treating acidic arsenic-containing wastewater according to claim 1, characterized in that: When the spinning solution is placed in an electrospinning machine to obtain the nanofiber membrane, the parameters of the electrospinning machine include: a positive voltage of 16KV to 18KV, a negative voltage of 0 to 1KV, and a propulsion speed of 0.08mm / min to 0.1mm / min.

7. The method for preparing a gravity-driven membrane for treating acidic arsenic-containing wastewater according to claim 1, characterized in that: When the spinning solution is placed in an electrospinning machine to obtain the nanofiber membrane, the ambient temperature is 30°C to 40°C, the relative humidity is 20% to 40%, and on the electrospinning machine, tin foil is used to cover a metal roller as a collection device for the nanofiber membrane.

8. The method for preparing a gravity-driven membrane for treating acidic arsenic-containing wastewater according to claim 1, characterized in that: The nanofiber membrane material is placed in an oven for drying to obtain a gravity-driven membrane for treating acidic arsenic-containing wastewater, wherein the temperature of the oven is 50° C. to 70° C. and the drying time is 20 min to 30 min.

9. A gravity-driven membrane for treating acidic arsenic-containing wastewater, characterized in that: The membrane is prepared by the method for preparing a gravity-driven membrane for treating acidic arsenic-containing wastewater according to any one of claims 1 to 8.

10. Use of the gravity-driven membrane for treating acidic arsenic-containing wastewater according to claim 9, characterized in that: The gravity-driven membrane is used to treat acidic arsenic-containing wastewater with a pH value of 1 to 5.

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