CN-122006520-A - Montmorillonite-based nanofiltration membrane with host-guest identification function and preparation method thereof

CN122006520ACN 122006520 ACN122006520 ACN 122006520ACN-122006520-A

Abstract

A montmorillonite-base nano-filter film with host-guest identification function is prepared through pretreating raw montmorillonite, ultrasonic stripping to obtain uniform and stable montmorillonite nano-sheet dispersion liquid, ultrasonic mixing tannic acid with crown ether, vacuum suction filtering to aid self-assembly on porous substrate, immersing film layer in aqueous solution of ferric chloride, and drying. The invention creatively utilizes phenolic hydroxyl groups rich in tannic acid as a molecular connecting agent, and fixes crown ether molecules with a main and guest identification function between montmorillonite layers in situ through hydrogen bond and chemical adsorption, and the montmorillonite, the tannic acid and the crown ether are mutually matched to form a selective transmission layer with regular two-dimensional channels and molecular identification sites. The composite membrane breaks through the bottleneck of poor stability of the traditional lamellar membrane, can effectively realize the efficient screening of monovalent/divalent ions, and has wide application prospects in the fields of sea water desalination, salt lake lithium extraction and the like.

Inventors

LI FANG
XU XIANGMIN
ZHANG WEI
SHEN CHENSI
LI YUNWEI
ZHANG XINGRAN

Assignees

东华大学

Dates

Publication Date: 20260512
Application Date: 20260331

Claims (10)

1. The preparation method of the montmorillonite-based nanofiltration membrane with the host-guest identification function is characterized by comprising the following steps of: dispersing original montmorillonite powder in deionized water, removing coarse particle impurities comprising quartz through a multi-stage screening and natural sedimentation process, adding saturated sodium salt into suspension, adjusting pH to neutral or weak alkalinity, performing ion exchange reaction under a constant temperature condition, performing centrifugal separation, repeating a salt adding-exchanging-centrifuging process to ensure that interlayer cations are completely replaced by sodium ions, repeatedly washing a product by deionized water until the conductivity of supernatant meets the requirement, and performing vacuum drying, grinding and sieving for later use; dispersing the sodium montmorillonite powder obtained in the step 1 in a solvent, and performing high-power ultrasonic stripping in a low-temperature environment, then performing low-speed gradient centrifugation on the dispersion liquid to remove thick-layer particles which are not completely stripped, and taking supernatant to obtain a montmorillonite nano-sheet dispersion liquid which has a single-layer/few-layer structure, uniform size and a Tyndall effect; Step 3, accurately weighing crown ether and tannic acid in a specific mass ratio, and directly adding the crown ether and the tannic acid into a plurality of volumes of montmorillonite nano-sheet dispersion liquid obtained in the step 2; Step 4, under the constant temperature airtight condition, the mixed system obtained in the step 3 is subjected to controlled stirring, tannin-crown ether assembly is induced to be adsorbed and intercalated between montmorillonite nano-sheets and on the surface, after stirring, standing is carried out for a period of time, and crown ether molecules are fixed on the surface and between the montmorillonite by utilizing the interfacial adhesion of tannic acid, so that a montmorillonite-tannin-crown ether ternary functional modified mixed dispersion liquid with main guest recognition sites is formed; step 5, selecting a hydrophilic microfiltration membrane as a support substrate, and flatly loading the support substrate into a vacuum suction filtration device after deionized water activation treatment; Step 6, starting a vacuum system, adjusting to constant negative pressure, adding a certain volume of the 'functional modified' mixed dispersion liquid obtained in the step 4 into a funnel, discharging solvent through a substrate under the dual effects of negative pressure driving and fluid shearing force, enabling functional montmorillonite nano sheets to be stacked layer by layer on the surface of the substrate, and controlling the solid content and the volume of a filtrate to regulate a membrane layer, so that a composite separation layer containing regular two-dimensional sub-nano channels is constructed; Preparing a low-concentration ferric chloride aqueous solution, immersing the membrane obtained in the step 6, and constructing a metal-polyphenol network in situ between montmorillonite sheets by utilizing a rapid coordination reaction between Fe & lt3+ & gt and interlayer tannic acid, so as to physically lock crown ether molecules in interlayer regions and fix interlayer spacing at an Emi level size to obtain a target nanofiltration membrane; And 8, after the reaction is finished, cleaning the surface of the membrane with deionized water, stopping the reaction, naturally drying in a controlled humidity environment, and obtaining the montmorillonite-based nanofiltration membrane with high structural stability and specific host and guest identification function after irreversible solidification and shaping of the membrane layer structure.
2. The method for preparing the montmorillonite-based nanofiltration membrane with the host-guest identification function according to claim 1, wherein in the step 1, the original montmorillonite is one or more of sodium montmorillonite, calcium montmorillonite and magnesium montmorillonite, the particle size range is 1-25 μm, the sieving/sedimentation process is carried out in a clean container, the concentration range of saturated NaCl solution is 3-5 mol/L, the pH range of a system is adjusted to 6.5-7.5, the ion exchange temperature is 60-90 ℃, the single stirring reaction time is 2-5 h, the repetition frequency of the exchange process is 2-5, the washing is carried out until the conductivity of filtrate is less than 10 mu S/cm, and the vacuum drying temperature is 40-80 ℃.
3. The method for preparing the montmorillonite-based nanofiltration membrane with the host-guest identification function according to claim 1, wherein in the step 2, the mass concentration range of the montmorillonite nano-sheet dispersion liquid is 0.1 wt-1.5-wt%, the environmental temperature is controlled to be less than 30 ℃ in the ultrasonic process, the ultrasonic stripping power range is 100-500 and W, the ultrasonic stripping time range is 0.5-5 and h, the dispersion liquid is deionized water or a mixed solvent of deionized water and ethanol, the dispersion liquid is qualified without obvious precipitation after ultrasonic treatment, and the storage is required to be sealed in a 4 ℃ refrigeration environment.
4. The preparation method of the montmorillonite-based nanofiltration membrane with the host-guest identification function according to claim 1, wherein in the step 3, crown ether is a functional modified derivative, the functional modified derivative comprises one or more of 12-crown-4, 15-crown-5, 18-crown-6 and benzo crown ether derivatives, crown ether and tannic acid are weighed in a dry environment, dispersion liquid is rapidly added after weighing, the feeding mass ratio of crown ether to montmorillonite nano sheets is 1:5-1:30, and the feeding mass ratio of tannic acid to montmorillonite nano sheets is 1:2-1:10.
5. The method for preparing montmorillonite-based nanofiltration membrane with host-guest identification function according to claim 1, wherein in the step 4, the rotation speed of the stirring dispersion liquid is 200-500 rpm, the stirring process is carried out in a sealed container, the stirring time is 0.5-3 h, the temperature is 20-60 ℃, the standing balance is 2-5 h, and the standing environment is kept constant at room temperature.
6. The method for preparing montmorillonite-based nanofiltration membrane with host-guest identification function according to claim 1, wherein in the step 5, the hydrophilic microfiltration membrane is made of one or more of polytetrafluoroethylene, mixed cellulose ester, polyether sulfone or polyvinylidene fluoride, and the pore diameter is 0.22-0.45 μm.
7. The method for preparing montmorillonite-based nanofiltration membrane with host-guest identification function according to claim 1, wherein in the step 6, the surface density of the composite separation layer is controlled to be 0.1-1.0 mg/cm2, the vacuum negative pressure is in the range of-0.06 MPa to-0.09 MPa, and the negative pressure is maintained to be 5-10 min after the membrane is formed.
8. The method for preparing the montmorillonite-based nanofiltration membrane with the host-guest identification function according to claim 1, wherein in the step 7, the ferric chloride aqueous solution is prepared at present to avoid iron ion hydrolysis failure, the concentration of the ferric chloride aqueous solution is 0.05-0.2 mol/L, the pH range of the solution is controlled to be 2-3, deionized water is used for preparing the montmorillonite-based nanofiltration membrane, the concentration is controlled accurately, the deviation is not more than +/-0.01 mol/L, the membrane layer is ensured to be completely immersed in the solution in the soaking process, no bubbles are attached to the surface of the membrane, the soaking time is 1-10 min, and the temperature range is constant at room temperature.
9. The method for preparing the montmorillonite-based nanofiltration membrane with the host-guest identification function according to claim 1, wherein in the step 8, gentle water flow is adopted during flushing to avoid direct flushing of the surface of the membrane, flushing is performed until filtrate is yellow, the removal of superfluous Fe 3+ is ensured to be clean, the natural drying time range is 12-24 h, and the drying environment is kept ventilated and the humidity is controlled below 40%.
10. A montmorillonite-based nanofiltration membrane with a host-guest recognition function prepared based on the method of any one of claims 1-9.

Description

Montmorillonite-based nanofiltration membrane with host-guest identification function and preparation method thereof Technical Field The invention belongs to the technical field of membrane material preparation, and particularly relates to a montmorillonite-based nanofiltration membrane with a host-guest identification function and a preparation method thereof. Background Along with the rapid increase of the global demand for new energy and water resource recycling, the efficient ion separation technology plays an increasingly important role in the fields of salt lake lithium extraction, sea water desalination, wastewater reclamation and the like. Particularly in the monovalent/divalent cation separation process, the membrane separation technology has gradually become a key technology for replacing the traditional solvent extraction and chemical precipitation method due to the advantages of low energy consumption, simple and convenient operation, small occupied area and the like. Among the numerous membrane materials, two-dimensional layered membrane materials represented by Graphene Oxide (GO), MXene, and montmorillonite (MMT) have shown great potential in the field of precision ion screening due to their unique sub-nanoscale two-dimensional channels. Among them, montmorillonite, which is a naturally occurring layered silicate clay mineral, has the inherent advantages of being abundant in reserves, low in cost, environmentally friendly, and easy to be exfoliated into single-layer nano sheets, and is regarded as an ideal substrate for preparing next-generation high-performance separation membranes. However, the direct stacking and preparation of pure montmorillonite nano sheets into films still faces significant technical bottlenecks in achieving high-precision ion screening. Traditional montmorillonite membranes rely primarily on size sieving of the interlaminar channels and Donnan rejection for separation. Since many key target ions have very close hydration radii to the coexisting ions (e.g., the difference in hydration radii between li+ and mg2+ is very small), it is difficult to achieve high selective permeation of monovalent ions by only physical screening mechanisms. Meanwhile, the lack of chemical affinity sites for specific ions in the natural montmorillonite channels can not promote the preferential transmission of the specific ions through chemical potential difference, so that the membrane material is often limited by Trade-off effect which is difficult to reconcile between ion permeability and selectivity, and the application of the membrane material in the field of high-end separation is limited. In order to improve the selectivity of the membrane, the introduction of a group having a molecular recognition function becomes an effective strategy. Crown ether is taken as a typical macrocyclic polyether compound, has a unique 'cavity structure', and can specifically capture specific metal cations matched with the cavity size of the crown ether through a host-guest recognition mechanism, so that the crown ether can be accurately separated. Although prior art CN110171817a has disclosed related preparation methods of crown ether functionalized graphene and the like, challenges remain with respect to how to construct stable and efficient crown ether transport channels in montmorillonite layered films. In the prior researches, crown ether is often introduced by a simple physical doping mode, so that uniform and regular recognition sites are difficult to form between montmorillonite layers, and the crown ether is extremely easy to run off during long-term running of the membrane, so that the separation performance is attenuated with time. Based on the above-mentioned problems, there is a need to develop a novel modified montmorillonite base film capable of firmly fixing the host-guest recognition sites between montmorillonite layers, thereby breaking through the trade-off between ion permeability and selectivity of the conventional layered film, and a preparation method thereof. Disclosure of Invention The invention aims to overcome the technical defects that the prior montmorillonite membrane is limited in selectivity due to simple dependence on physical aperture screening, and functional molecules are not firmly combined between layers and are easy to run off, and provides a montmorillonite-based nanofiltration membrane with a host-guest identification function and a preparation method thereof. The invention uses excellent interface adhesiveness and chemical reactivity of tannic acid as a 'molecular bridge', and stably fixes crown ether molecules between and on the surface of montmorillonite nano-sheets in situ on the premise of not damaging the layered structure of montmorillonite. The method not only realizes uniform distribution of recognition sites, but also effectively solves the problem of loss of functional molecules in long-term operation, and remarkably improves the affinity and transmission