A composite membrane for heavy metal pollution treatment and a preparation method thereof

Abstract

The application provides a preparation method of a two-dimensional layered silicate mineral film treated by a reducing modifier, which comprises the following steps: firstly, organic modification of a two-dimensional layered silicate mineral by a reducing ionic liquid; then, loading of the reducing modifier into the interlayer of the two-dimensional layered silicate mineral; and finally, construction of a two-dimensional channel by vacuum filtration to prepare a film with a thickness of 5-20 microns. The two-dimensional layered silicate mineral film obtained by the method has a large surface area and can effectively treat heavy metal Cr(VI). The construction of the two-dimensional channel provides a limited space for the reducing modifier to prevent oxidation and provides abundant sites for the oxidation-reduction reaction in the nanopore channel, and solves the problems of desorption difficulty and secondary pollution caused by the traditional adsorption method for treating heavy metals.

Description

Technical Field

[0001] This invention belongs to the fields of two-dimensional layered silicate mineral membrane materials and water heavy metal pollution control, specifically relating to a composite membrane for water heavy metal pollution control and its preparation method. Background Technology

[0002] With the improvement of socio-economic levels and rapid industrial development, environmental issues have become a common problem facing the world. Among the many environmental problems, water pollution is the most serious. Due to the easy accumulation, difficulty in metabolism, and high toxicity of heavy metals, the treatment of heavy metal pollution in water has gradually become a focus of attention.

[0003] Heavy metals in wastewater originate from a wide range of sources, including both natural sources and anthropogenic emissions. Anthropogenic heavy metal emissions can be further categorized into industrial / agricultural emissions and domestic emissions. Industrial emissions refer to heavy metal waste generated during product manufacturing and processing, as well as during mineral development and smelting. Agricultural emissions are heavy metal pollution generated during agricultural activities (such as fertilization). These wastes enter water bodies through direct discharge or rainwater runoff, becoming a major source of heavy metal pollution in water, primarily containing elements such as Cd, Pb, Fe, Cu, Hg, and As. Domestic emissions mainly refer to heavy metal emissions generated through household waste (such as used batteries or other everyday activities), including elements such as Cd, Pb, Cr, Ni, Cu, As, and Zn.

[0004] When heavy metal pollution in water bodies reaches a certain level, it will have a detrimental impact on organisms living in and dependent on the polluted water. Furthermore, due to the food chain, heavy metal pollution in water bodies can also seriously harm human health. Related studies show that when heavy metals accumulate to a certain level in plants, they will exhibit certain symptoms, such as slowed growth, reduced enzyme activity, and loss of some plant functions. Animals with a certain amount of heavy metals in their bodies will also experience slowed growth and other symptoms. Besides plants and animals, the accumulation of heavy metals will also have a certain impact on humans. Humans absorb heavy metals mainly through drinking water and daily food intake. When the heavy metal content reaches the ppm level, it will cause harm to the human body. The harm of heavy metals to the human body mainly manifests as chronic poisoning or acute poisoning. For example, heavy metals with carcinogenic effects include Cd, Cr, Ni, Se, and Co. In addition, some heavy metals also have teratogenic effects, causing slowed growth or impaired physiological functions.

[0005] Among the many hazards posed by heavy metals, chromium (Cr) is the most prevalent and serious. Cr exists in the environment primarily in two states: Cr(III) and Cr(VI). Cr(III) is a trace element necessary for human metabolism, while Cr(VI) is highly toxic, a carcinogen and mutagen. Even trace amounts can pose potential harm to the ecological environment and human health. Cr(VI) in the environment enters the human body through the respiratory tract, digestive tract, and skin, causing harm to health. Studies have shown that the accumulation of Cr(VI) can lead to systemic poisoning, causing adverse physiological reactions and potentially causing cell carcinogenesis. When it enters the body through the digestive tract, it can cause loss of taste and smell and damage organs such as the stomach. Skin contact with Cr(VI) can cause allergic reactions, dermatitis, and may even lead to chromocytosis. When it enters the body through the respiratory tract, it can cause nasal septum perforation, pneumonia, and even more serious nasopharyngeal carcinoma. Due to the extreme toxicity and carcinogenicity of Cr(VI), the World Health Organization has classified it as a Group 1 carcinogen.

[0006] To date, methods for treating heavy metals in wastewater include precipitation, physicochemical methods, electrochemical methods, and biochemical methods. Precipitation often requires the addition of a precipitant, which is convenient, but the addition of a precipitant can easily cause secondary pollution of the water body, and the quality of the effluent is also greatly affected by the precipitant. Ion exchange, adsorption, membrane separation, and extraction are all physicochemical methods. Membrane separation is highly efficient and energy-saving, but membrane fouling is a significant concern. Electrochemical methods consume a lot of electricity and are not suitable for large-scale treatment. Biological treatment methods include biological pond purification, microbial and algal treatment, and phytoremediation, but their application is somewhat limited.

[0007] Generally, membrane separation technology is defined as using membrane materials as the intermediate medium and the pressure and concentration difference across the membrane as the driving force to achieve filtration. Membrane separation technology has a wide range of applications, and has been extensively studied in areas such as seawater desalination, food purification, and energy regeneration. Membrane separation technology is also receiving increasing attention from researchers worldwide.

[0008] In recent years, two-dimensional (2D) membranes have gradually developed, attracting increasing attention due to their ease of expansion, precise and tunable channel size, ease of modification, and high ion flux. Compared with traditional membranes, 2D membranes exhibit superior separation performance. Graphene oxide, transition metal dihydrides, graphitic carbonitrides, MXene, and metal-organic frameworks are typical examples of 2D membranes. 2D membranes are formed by the recombination of nanosheets with a two-dimensional layered structure. The layered structure provides abundant nanochannels for small molecules, while large molecules are excluded. By adjusting the interlayer spacing between adjacent nanosheets, some molecules can be trapped while others can pass through. Currently, graphene oxide membranes are the most studied, as this material possesses good film-forming properties, flexibility, and hydrophilicity. However, graphene oxide contains polar oxygen-containing functional groups. Due to the hydrophilicity of these functional groups and the strong electrostatic repulsion between adjacent graphene oxide nanosheets, graphene oxide membranes swell significantly in water due to the hydration of these oxygen-containing functional groups, posing numerous challenges to its development.

[0009] In water treatment, two-dimensional membranes can be used for water softening, decolorization, removal of organic matter, removal of heavy metals, and separation of organic solvents, greatly reducing the cost of membrane materials and improving resource utilization. In gas, two-dimensional membranes also have excellent gas separation capabilities. In addition, two-dimensional membranes can also be used as separators in batteries.

[0010] Two-dimensional layered silicate mineral nanosheets have attracted widespread attention in the construction of high-performance ion exchange membranes due to their hydrophilicity, high cation exchange capacity, and large specific surface area. Montmorillonite and vermiculite are among the most common layered silicate minerals, with a 2:1 crystal structure. Each unit crystal structure consists of two layers of silicon-oxygen tetrahedra and one layer of aluminum-oxygen octahedra. Interlayer cation insertion balances the charge, and the layered silicate minerals exhibit weak cation interactions between the interlayer sheets, thus possessing strong cation exchange capacity and a large cation exchange efficiency. Two-dimensional layered silicate mineral channel arrays are constructed by bottom-up recombination of mineral monolayers, obtained by liquid-phase exfoliation of their layered crystals. The interstitial spaces created between these monolayers are uniform, providing nanoscale transport channels for ions. By exfoliating their crystalline precursors in the liquid phase, it is easier to obtain two-dimensional layered silicate nanosheets in monolayer form. Furthermore, two-dimensional layered silicate mineral nanoparticles are frequently used as filler materials for constructing composite polymer membranes due to their excellent stability, hydrophilicity, low cost, mechanical strength, and unique charge properties. Although mineral materials have been widely used in the treatment of heavy metals in wastewater, most are used as adsorbents or modifiers, with few studies and reports focusing on the construction of two-dimensional layered silicate mineral membranes. Research indicates that the recombination of two-dimensional layered silicate mineral nanosheets facilitates the uncontrolled creation of layered structures with two-dimensional nanofluidic channels. This allows the two-dimensional mineral membrane to not only possess better separation performance but also to utilize Na+... + Crosslinking exhibits good stability in water.

[0011] Traditional chemical reduction methods for treating hexavalent chromium involve reducing hexavalent chromium to trivalent chromium with a suitable reducing agent, then adjusting the pH to an appropriate range to precipitate the trivalent chromium as chromium hydroxide, which is then collected. However, if Fe is added to wastewater containing hexavalent chromium... 2+ This introduces impurity ions into the wastewater system, making it impossible to directly recover the target element during later precipitation and collection, thus hindering the comprehensive resource utilization of certain elements. In recent years, nano-zero-valent iron has been increasingly used as a reducing agent to treat oxidizing and toxic substances such as As(V) and Cr(V) in the environment. However, its huge specific surface area and extremely high surface energy, coupled with the magnetism of iron, make nano-zero-valent iron particles prone to agglomeration. Agglomeration affects the fluidity and reactivity of the particles in the aquifer, thus limiting its application in groundwater treatment. To overcome the agglomeration problem of nano-zero-valent iron, preparing supported zero-valent iron using activated carbon, various clays, pumice, etc., has become a current research hotspot. Membrane treatment of heavy metals is a simple process with high separation efficiency and no sludge production, making it a key technology for achieving near-zero emissions.

[0012] Numerous reports have documented the use of Fe(II)-modified silicate minerals for treating heavy metal ions in wastewater. For example, the research group of Wu Honghai at South China Normal University added Fe(II) and ascorbic acid to a montmorillonite dispersion, sealed and stirred under nitrogen, and aged it to obtain antioxidant Fe(II)-modified montmorillonite. The addition of ascorbic acid inhibited the oxidation of Fe(II) to Fe(III). Compared to directly modifying montmorillonite with Fe(II) without adding ascorbic acid, the addition of ascorbic acid in the antioxidant Fe(II)-modified montmorillonite protects Fe(II), making it less susceptible to oxidation by dissolved oxygen, resulting in better removal of heavy metal ions from water. It is speculated that in addition to the protective effect on Fe(II), there is also a process of reduction followed by adsorption and fixation of Cr(III), which more stably reduces and transfers heavy metal chromium pollutants from the aqueous phase to the solid phase. However, this patent requires a large amount of ascorbic acid, and its protective effect is only effective in the initial stage. After a period of storage or use, when the ascorbic acid is depleted, it still cannot achieve the goal of improving the treatment of chromium-containing wastewater with montmorillonite.

[0013] Another method involves intercalating mineral materials with long-chain alkyl quaternary ammonium salts. After intercalation, the interlayer spacing of the mineral materials increases, thereby increasing their adsorption capacity, as reported in CN112237901A.

[0014] Besides quaternary ammonium salts, there are other reports on the modification of mineral materials by organic modifiers. For example, the use of 8-hydroxyquinoline citrate to modify mineral materials has been found to increase the removal efficiency of heavy metals.

[0015] The aforementioned existing technologies all focus on modifying two-dimensional layered silicate minerals to improve their removal efficiency for heavy metal ions in water. However, research on modifying two-dimensional layered silicate mineral membranes to confine oxidation-reduction techniques within nano / sub-nanometer-scale two-dimensional channels for heavy metal removal remains unexplored. Nevertheless, this technology offers advantages such as low cost, simple operation, good removal efficiency, and avoidance of secondary pollution, making it a promising approach for industrial application. However, two-dimensional layered silicate mineral membranes lack skeletal support and sufficient mechanical strength, preventing direct application in water treatment. Generally, a substrate membrane is required to support the membrane. Furthermore, if it were possible to simultaneously regenerate the oxidized reducing agent during heavy metal treatment using two-dimensional layered silicate mineral membranes, the removal efficiency for heavy metal ions would be further improved. For example, by introducing advanced oxidation technologies into two-dimensional layered silicate mineral membranes. Summary of the Invention

[0016] To address the shortcomings of existing mineral-based technologies in removing heavy metal ions from water, which are not yet satisfactory, this invention proposes a modified two-dimensional layered silicate mineral membrane and its application in heavy metal pollution control. This invention first modifies the two-dimensional layered silicate mineral membrane with a reducing ionic liquid, followed by further modification with a reducing inorganic substance. The two-dimensional layered silicate mineral obtained through this two-step modification method (organic-inorganic modification) exhibits excellent removal efficiency of heavy metal ions from water. The reduction reaction of high-valence heavy metal ions occurs within the membrane rather than in the treated water, separating the reducing agent from the treated heavy metals, facilitating subsequent treatment and utilization of the reducing agent. Adding the reducing agent to the membrane after wastewater filtration allows the oxidized reducing modifier to be re-reduced, thus enabling the two-dimensional layered silicate mineral membrane provided by this invention to be repeatedly recycled. This invention combines two-dimensional layered silicate minerals with a reduction system, effectively leveraging their respective advantages while mitigating some of their disadvantages, thus maximizing their effectiveness. To achieve the above objectives, the following specific technical solutions are adopted:

[0017] A composite membrane for the treatment of heavy metal pollution in water includes a base membrane and a modified two-dimensional layered silicate mineral membrane. The modified two-dimensional layered silicate mineral membrane is attached to the surface of the base membrane. The modified two-dimensional layered silicate mineral membrane is obtained by sequentially modifying two-dimensional layered silicate with a reducing ionic liquid and an iron-containing reducing modifier.

[0018] Furthermore, the two-dimensional layered silicate mineral is selected from at least one of montmorillonite, vermiculite, and mica; the reducing ionic liquid is obtained by reacting triethylamine with iodoethanol, and then reacting the intermediate product with sodium borohydride; the iron-containing reducing modifier is selected from at least one of ferrous salt and nano-zero valent iron; even further, the ferrous salt is selected from at least one of ferrous sulfate and ferrous chloride.

[0019] Furthermore, the thickness of the base film is 10-20 μm, and the pore size is 0.1-1 μm, preferably 0.3-0.5 μm; the thickness of the modified two-dimensional layered silicate mineral film is 5-20 μm.

[0020] This invention uses two-dimensional layered silicate minerals, which are first modified by reducing ionic liquids and then by iron-containing reducing modifiers. This organic-inorganic composite modification method significantly enhances the removal effect of heavy metal ions in the resulting composite membrane. It can be used to treat heavy metals such as Cr(VI) and Pb(II) in water, and can be recycled repeatedly, making it suitable for the rapid treatment of wastewater containing heavy metal ions.

[0021] The present invention also provides a method for preparing the composite membrane for the treatment of heavy metal pollution in water, comprising the following steps:

[0022] (S1) Preparation of reducing ionic liquid: Triethylamine and iodoethanol are mixed and reacted at 90-105℃ for 8-12h. Water is added to disperse the mixture, and sodium borohydride is slowly added at 0-6℃. The reaction is carried out for 10-30min to obtain the reducing ionic liquid.

[0023] (S2) Organic modification: Under a nitrogen atmosphere, two-dimensional layered silicate minerals are added to the reducing ionic liquid obtained in step (S1), ultrasonically dispersed, heated and stirred for 0.5-1 h, centrifuged, washed, and dried to obtain organically modified two-dimensional layered silicate minerals.

[0024] (S3) Inorganic modification: Under nitrogen atmosphere, the organically modified two-dimensional layered silicate minerals obtained in step (S2) and the iron-containing reducing modifier are dispersed in ethanol and stirred for 10-15 h to obtain a modified two-dimensional layered silicate mineral dispersion.

[0025] (S4) Membrane composite: The modified two-dimensional layered silicate mineral dispersion is poured into a funnel covered with a base membrane and vacuum filtered until no residue is left, to obtain a composite membrane composed of the base membrane and the modified two-dimensional layered silicate mineral.

[0026] Further, in step (S1), the molar ratio of triethylamine, iodoethanol, and sodium borohydride is 1:1-1.2:1.1-1.5. The amount of water added is sufficient to fully disperse the intermediate product obtained from ethylamine and iodoethanol, generally 5-8 times the mass of triethylamine. Sodium borohydride is added slowly over 1-2 hours.

[0027] Furthermore, in step (S2), ultrasonic dispersion is performed at 80-100 Hz for 0.5-1 h.

[0028] Further, in step (S2), the mass ratio of the two-dimensional layered silicate mineral to the reducing ionic liquid obtained in step (S1) is 3-4:10, the heating and stirring are carried out at 160-200℃ for 1-2 hours, the washing is carried out with deionized water and anhydrous ethanol in sequence, and the drying is carried out under vacuum at 50-80℃.

[0029] Furthermore, in step (S3), the mass ratio of the organically modified two-dimensional layered silicate mineral to the iron-containing reducing modifier is 1:1-2; the amount of ethanol used is 100-200 times that of the organically modified two-dimensional layered silicate mineral.

[0030] Furthermore, in step (S4), the vacuum degree of vacuum filtration is 0.09-0.10 MPa, and the filtration time is not particularly limited. Filtration is carried out until there is no residual liquid, and the filtration time is generally 2-5 minutes.

[0031] The preferred two-dimensional layered silicate mineral is montmorillonite, with a lateral dimension of 200-400 nm, obtained by chemical-mechanical exfoliation of montmorillonite. Montmorillonite is a common layered clay mineral, belonging to aluminosilicates, and its crystal structure is of the 2:1 type. Each unit crystal layer of montmorillonite consists of two layers of silicon-oxygen tetrahedra and one layer of aluminum-oxygen octahedra, with interlayer cations (Na₂O₃, Na ... + and Ca 2+ The insertion of Fe to balance the charge, the weak cation-cation interactions between the layered montmorillonite crystals between the interlayered thin sheets, and therefore their strong cation exchange capacity, make them suitable for Fe exchange. 2+ Exchanging interlayer cations is very easy to achieve. Furthermore, montmorillonite is relatively easy to exfoliate into monolayers. We will use Fe... 2+ The exchanged montmorillonite, after being peeled off and then rearranged through filtration to construct two-dimensional channels, is also easily achievable. However, we found that... 2+ Although exchanged montmorillonite can form a two-dimensional montmorillonite membrane, it has poor affinity with the basement membrane and its ability to remove heavy metals is limited. The inventors unexpectedly discovered that by first organically modifying montmorillonite with a reducing ionic liquid before Fe(II) modification, and then inorganically modifying it with Fe(II) ion exchange, this combination of organic and inorganic modification results in a composite membrane with superior overall performance. This increases the removal efficiency of heavy metal ions, and the addition of a reducing agent after use revitalizes the composite membrane, allowing it to be repeatedly used for the removal of heavy metal ions from water.

[0032] The present invention also provides a method for removing heavy metals from water, comprising the following steps: passing water containing heavy metal ions through the composite membrane for treating heavy metal pollution in water; wherein the heavy metal ions are selected from Cr(VI) and Pb(II).

[0033] Furthermore, the method for removing heavy metals from water also includes a step of recycling the composite membrane: adding the composite membrane that has adsorbed heavy metal ions into a solution containing a reducing agent for treatment. The reducing agent is selected from strong reducing reagents such as sulfites.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] The composite membrane based on a modified two-dimensional layered silicate mineral membrane of the present invention first modifies the two-dimensional layered silicate mineral membrane with a reducing ionic liquid, and then uses Fe as the interlayer cation. 2+Zero-valent iron nanoparticles are subjected to ion exchange or adsorption. The resulting modified two-dimensional layered silicate minerals are then dispersed in a solvent to form a dispersion. The dispersion is then deposited onto a filter membrane using vacuum filtration under controlled vacuum conditions, ultimately forming a composite membrane consisting of a modified two-dimensional layered silicate mineral membrane and a substrate membrane. The two-dimensional channels of the modified two-dimensional layered silicate mineral membrane have a large specific surface area, and the two-dimensional channels are constructed using Fe... 2+ The nano-zero-valent iron provides a site for the reaction with heavy metal ions such as Cr(VI). The construction of two-dimensional channels increases the path of ions flowing through the two-dimensional membrane and increases the reaction time, enabling efficient treatment of heavy metal ions. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a photograph illustrating the construction of a two-dimensional channel for montmorillonite using a Buchner funnel vacuum filtration method according to the present invention.

[0037] Figure 2 This is a photograph of the composite film obtained in Example 1;

[0038] Figure 3 These are SEM images of the composite membrane obtained in Example 1;

[0039] Figure 4 These are photos of potassium dichromate solution before and after filtration through the composite membrane in Example 1. Detailed Implementation

[0040] The present invention will be further described below with reference to specific embodiments, but is not limited to the contents of the specification. All reagents used are commercially available in the art.

[0041] Montmorillonite was purchased from NANOCOR, USA, and originated in Wyoming, USA. Its specifications are shown in Table 1 below.

[0042] Table 1

[0043]

[0044] The main oxide contents of montmorillonite are shown in Table 2 below:

[0045] Table 2

[0046]

[0047] Example 1

[0048] (S1) Preparation of reducing ionic liquid: 1 mole of triethylamine and 1 mole of iodoethanol are mixed and reacted at 105℃ for 8 hours. Water is added to disperse the mixture. Sodium borohydride is slowly added at 0-4℃ and added completely within 1 hour. The reaction is maintained at 0-4℃ for 10-30 minutes to obtain the reducing ionic liquid.

[0049] (S2) Organic modification: Under a nitrogen atmosphere, 30 parts by mass of montmorillonite (200 nm) were added to 100 parts by mass of the reducing ionic liquid prepared in step (S1), and ultrasonically dispersed at 100 Hz for 1 h. Then, the mixture was heated to 200 °C, stirred for 1 h, centrifuged, washed with deionized water and anhydrous ethanol in sequence, and vacuum dried at 60 °C to obtain organically modified montmorillonite.

[0050] (S3) Ferrous sulfate and organically modified montmorillonite were added to anhydrous ethanol at a mass ratio of 1:1 to 100 times the mass of organically modified montmorillonite. The mixture was stirred for 12 hours under a nitrogen atmosphere to obtain a modified montmorillonite dispersion.

[0051] (S4) Construction of the two-dimensional channel: The modified montmorillonite dispersion obtained in step (S3) is poured into a Buchner funnel covered with a PTFE filter membrane with a pore size of 0.3 μm. Vacuum filtration is performed at a vacuum degree of 0.10 MPa until no residual liquid remains in the funnel. The membrane removed from the funnel is the composite membrane, which is composed of a PTFE base membrane and a modified montmorillonite two-dimensional membrane. The thickness of the PTFE base membrane is 20 μm, and the amount of dispersion is controlled to make the thickness of the modified montmorillonite two-dimensional membrane 5 μm.

[0052] Figure 1 This is a schematic diagram of the construction of montmorillonite two-dimensional channels using a Buchner funnel vacuum filtration method, specifically, the obtaining of a composite membrane through vacuum filtration using a Buchner funnel. This invention does not require complex equipment; only conventional laboratory vacuum filtration devices such as Buchner funnels are needed to construct the montmorillonite two-dimensional channels. For scale-up production, suitable industrial vacuum filtration equipment, such as a belt vacuum filter, can be used.

[0053] Figure 2 This is the composite membrane obtained in Example 1. Its size is determined by the size of the vacuum filtration equipment, such as a Buchner funnel.

[0054] Figure 3 The image shows an SEM image of the composite membrane obtained in Example 1. It can be seen that the modified montmorillonite two-dimensional membrane forms a layered structure with a thickness of approximately 5 μm through stacking, and together with the base membrane, constitutes the composite membrane. The base membrane imparts a certain mechanical strength to the modified montmorillonite two-dimensional membrane. When immersed in water, the modified montmorillonite two-dimensional membrane does not peel, break, or crack, and can maintain its intact shape in water for a long time. Therefore, it can be used for wastewater treatment containing heavy metal ions.

[0055] Example 2

[0056] The rest is the same as in Example 1, except that the amount of montmorillonite in step (S2) is changed from 30 parts by mass to 40 parts by mass.

[0057] Example 3

[0058] The rest is the same as in Example 1, except that the mass ratio of ferrous sulfate to organically modified montmorillonite is 2:1.

[0059] Comparative Example 1

[0060] The rest is the same as in Example 1, except that steps (S1) and (S2) are omitted, and step (S3) is performed directly: unmodified montmorillonite and ferrous sulfate are added to ethanol at a mass ratio of 1:1. That is, the montmorillonite in the resulting composite membrane has not been modified by a reducing ionic liquid.

[0061] Comparative Example 2

[0062] The rest is the same as in Example 1, except that step (S3) is omitted, and the organically modified montmorillonite obtained in step (S2) is dispersed in ethanol under ultrasonic conditions. The resulting dispersion is then subjected to step (S4). That is, the montmorillonite in the resulting composite membrane has not undergone Fe(II) inorganic modification.

[0063] Comparative Example 3

[0064] The rest is the same as in Example 1, except that step (S1) is omitted and step (S2) is replaced by: under a nitrogen atmosphere, 30 parts by mass of montmorillonite (200 nm) is added to 500 parts by mass of 10 wt% hexadecyltrimethylammonium chloride aqueous solution, ultrasonically dispersed at 100 Hz for 1 h, then heated to 60 °C, stirred for 1 h, centrifuged, washed with anhydrous ethanol, and vacuum dried at 60 °C to obtain organically modified montmorillonite. In the resulting composite membrane, the organic modification of montmorillonite is replaced by long-chain alkyl quaternary ammonium salt intercalation modification instead of a reducing ionic liquid.

[0065] Application Example 1

[0066] A potassium dichromate solution with a concentration of 10 mg / L and a Cr(VI) concentration of 3.54 mg / L was prepared. The potassium dichromate solution was then filtered using the membranes prepared in the examples and comparative examples. Figure 4 The images show photos of potassium dichromate solutions before and after filtration. As can be seen from the images, the membrane becomes darker after filtration, while the potassium dichromate solution becomes lighter after membrane treatment, indicating that the membrane has a treatment effect on the potassium dichromate solution.

[0067] The composite membranes prepared in the above examples and comparative examples were used to filter a 10 mg / L potassium dichromate solution. The change in Cr(VI) concentration before and after filtration was measured by ultraviolet spectrophotometry. The filtered composite membranes were activated by soaking in H₂O₂ for 30 min and then used again to filter a 10 mg / L potassium dichromate solution. This process was repeated 30 times. The removal efficiency of the composite membrane for Cr(VI) after 30 cycles was tested. The results are shown in Table 3 below. Furthermore, using the composite membrane prepared in Example 1 to filter a Cr(VI) concentration of 3.54 mg / L solution repeatedly for 30 cycles, the reduction rate increased from approximately 50% to about 65%, and remained essentially unchanged after 6 cycles.

[0068] Table 3

[0069]

[0070] As can be seen, the composite membrane based on the modified montmorillonite two-dimensional membrane prepared by this invention can effectively remove heavy metal ions, such as Cr(VI), from water, significantly reducing the Cr(VI) concentration simply through filtration. To achieve a suitable heavy metal ion content in the water, only multiple filtrations in series are required. This eliminates the problem of requiring prolonged stirring to reach saturated adsorption of montmorillonite, which prevents continuous processing, and also avoids secondary environmental pollution caused by heavy metal leaching from the adsorbent. Furthermore, the composite membrane based on the modified montmorillonite two-dimensional membrane prepared by this invention can regain its ability to treat heavy metal ions through simple reduction treatment, maintaining a satisfactory level even after 30 cycles. A comparison of Example 1 and Comparative Example 1 reveals that without organic modification with a reducing ionic liquid, the Cr(VI) treatment effect decreases slightly, and after 30 cycles, the effect significantly diminishes, making recycling difficult. A comparison of Example 1 and Comparative Example 2 shows that organic modification without Fe(II) modification results in a poor Cr(VI) treatment effect in the composite membrane. A comparison of Example 1 and Comparative Example 3 shows that replacing the organic modification with a long-chain alkyl quaternary ammonium salt significantly improves the Cr(VI) removal effect of the composite membrane, but recycling remains difficult. These findings demonstrate that the present invention's two-step composite modification—organic modification of montmorillonite with a reducing ionic liquid and inorganic modification of Fe(II)—and the method of obtaining a composite membrane based on a modified montmorillonite two-dimensional membrane for treating heavy metal ions in water through simple filtration, are successful.

Claims

1. A composite membrane for heavy metal pollution remediation of water bodies, characterized in that, The composite membrane comprises a base membrane and a modified two-dimensional layered silicate mineral membrane, the modified two-dimensional layered silicate mineral membrane is attached to the surface of the base membrane, and the modified two-dimensional layered silicate mineral membrane is obtained by sequentially modifying a two-dimensional layered silicate mineral with a reducing ionic liquid and an iron-containing reducing modifier; the two-dimensional layered silicate mineral is at least one selected from montmorillonite, vermiculite and mica; the reducing ionic liquid is obtained by reacting triethylamine with iodoethanol first, and then reacting the obtained intermediate product with sodium borohydride; the iron-containing reducing modifier is at least one selected from ferrous salt and nano zero-valent iron; the ferrous salt is at least one selected from ferrous sulfate and ferrous chloride.

2. The composite film according to claim 1, characterized by, The base membrane has a thickness of 10-20 μm and a pore size of 0.1-1 μm; and the modified two-dimensional layered silicate mineral membrane has a thickness of 5-20 μm.

3. The composite film of claim 1, wherein, The base membrane has a pore size of 0.3-0.5 μm.

4. The method for preparing the composite membrane for the treatment of heavy metal pollution in water bodies according to any one of claims 1-3, characterized in that, The method comprises the following steps: (S1) Preparation of the reducing ionic liquid: triethylamine is mixed with iodoethanol, and reacted at 90-105 ℃ for 8-12 h; water is added, and sodium borohydride is slowly added under temperature control of 0-6 ℃, and reacted for 10-30 min to obtain the reducing ionic liquid; (S2) Organic modification: under a nitrogen atmosphere, the two-dimensional layered silicate mineral is added into the reducing ionic liquid prepared in step (S1), ultrasonic dispersion is performed, and then heating and stirring are performed for 0.5-1 h; centrifugation, washing and drying are performed to obtain the organically modified two-dimensional layered silicate mineral; (S3) Inorganic modification: under a nitrogen atmosphere, the organically modified two-dimensional layered silicate mineral obtained in step (S2) and the iron-containing reducing modifier are dispersed in ethanol, and stirring is performed for 10-15 h to obtain a modified two-dimensional layered silicate mineral dispersion; (S4) Membrane compounding: the modified two-dimensional layered silicate mineral dispersion is poured into a funnel covered with the base membrane, and vacuum filtration is performed until no residual liquid is left to obtain a composite membrane compounded by the base membrane and the modified two-dimensional layered silicate mineral.

5. The preparation method according to claim 4, characterized in that, In step (S1), the molar ratio of triethylamine, iodoethanol and sodium borohydride is 1:1-1.2:1.1-1.5; the sodium borohydride is slowly added within 1-2 h.

6. The preparation method according to claim 4, characterized in that, In step (S2), the ultrasonic dispersion is performed under 80-100 Hz for 0.5-1 h.

7. The production method according to claim 6, wherein In step (S2), the ultrasonic dispersion is performed under 80-100 Hz for 0.5-1 h.

8. The preparation method according to claim 4, characterized in that, In step (S3), the mass ratio of the organically modified two-dimensional layered silicate mineral and the iron-containing reducing modifier is 1:1-2; and the amount of ethanol is 100-200 times that of the organically modified two-dimensional layered silicate mineral.

9. The preparation method according to claim 4, characterized in that, In step (S4), the vacuum degree of the vacuum filtration is 0.09-0.10 MPa, and the filtration time is 2-5 min.

10. A method of removing heavy metals from water, characterized by, The method comprises the following steps: Water containing heavy metal ions is passed through the composite membrane for heavy metal pollution treatment of water bodies according to any one of claims 1-3 or prepared by the method according to any one of claims 4-8; and the heavy metal ions are selected from Cr(VI) and Pb(II).

11. The method of claim 10, wherein, Also included is a step of recycling the composite membrane by adding the composite membrane having the heavy metal ions adsorbed thereto to a solution containing a reducing agent.

12. The method of claim 11, wherein, The reducing agent is selected from the group consisting of sulfites.

Images