A biodegradable wood-based heterogeneous structure composite film, preparation method and application thereof

Abstract

A biodegradable wood-based heterostructured composite membrane, preparation method, and application thereof, belonging to the fields of development and application of forest-derived materials and wastewater purification and separation technology. The present invention adopts a strategy of heterostructure hybrid connection to prepare a biodegradable wood-based heterostructured composite membrane. The prepared composite membrane is composed of an original wood membrane, a COF (covalent organic framework) active layer, and a polymer optimization layer. It can be used to separate dyes, inorganic salts, and mixtures of dyes and inorganic salts. The dyes are one or more of methylene blue, methyl orange, crystal violet, Congo red, methyl blue, and bengal, and the inorganic salts are one or more of sodium chloride, sodium sulfate, magnesium chloride, and magnesium sulfate. The composite membrane has certain operational stability, good antifouling properties, and soil degradability. Overall, the present invention enables the design and manufacture of nanofiltration membranes to be extracted from nature and used in nature, thereby achieving efficient and sustainable water purification applications.

Description

Technical Field

[0001] The present invention belongs to the field of development and application of forest-derived materials and wastewater purification and separation technology, and specifically relates to a biodegradable wood-based heterogeneous structure composite membrane, a preparation method and application thereof. Background Art

[0002] With the rapid development of industrialization and urbanization, wastewater discharge continues to increase, posing a serious threat to the environment and human health. Dyeing wastewater is one of the major hazardous industrial wastewaters, primarily originating from the production of dyes and dye intermediates. Among the numerous wastewater treatment technologies, advanced nanofiltration membranes are indispensable in many fields, including seawater desalination, wastewater treatment, dye recovery, and pharmaceutical desalination. It is undeniable that membrane materials, as the key to membrane structure and membrane separation performance, are closely related to membrane performance, with the two mutually reinforcing factors. Applying appropriate materials and developing effective strategies are one of the pathways to achieving high-performance membranes.

[0003] Currently, water treatment separation membranes dominate the global separation membrane market. With the deepening of the concept of sustainable development, environmental protection, resource utilization, and new energy development are placing higher demands on separation technologies. High-performance membrane materials are also listed as one of the new chemical materials products encouraged for development in my country, and they can make a significant contribution to promoting the implementation of the sustainable development strategy. However, since the vast majority of water treatment separation membranes are currently made from non-renewable petroleum-based polymers extracted from fossil resources, the acquisition of membrane materials, the traditional membrane preparation process, and the disposal of discarded membranes all generate large amounts of difficult-to-treat waste, causing certain pollution to the ecological environment. In view of this, the green, low-carbon and sustainable development of membrane separation technology are gaining increasing attention.

[0004] In order to achieve environmental friendliness in membrane separation technology, researchers usually choose greener chemical reagents and preparation methods or choose to develop more environmentally friendly membrane substrate materials. The survey found that using bio-based materials to replace non-renewable petroleum-based materials has become the main means for researchers to develop environmentally friendly materials. Cellulose has become a strong candidate to replace petroleum-based materials due to its abundant reserves in nature, versatility, and green sustainability. However, the current choice of cellulose is relatively limited, and there is also the problem of selecting cheap and green solvents to achieve ultra-fast cellulose dissolution and the construction of orderly and robust cellulose membranes. In comparison, directly designing natural wood rich in cellulose may bring a series of opportunities. Currently, there are few reports on the invention of wood-based separation membranes.

[0005] In summary, the invention of a method for preparing naturally degradable wood-based heterostructured composite membranes and the exploration of their separation performance are of great significance for the future research and development of systematically constructed wood-based nanofiltration membranes. Selecting appropriate membrane materials, optimizing operating conditions, and utilizing energy recovery and system integration can further enhance the energy-saving performance of membrane separation technology. It is anticipated that the structural design and innovative selection of membrane substrates presented in this invention will provide a simple and effective approach for the development of next-generation wood-based heterostructured composite membranes with excellent separation performance and environmental friendliness, offering significant development potential and broad application prospects. Summary of the Invention

[0006] The present invention aims to provide a biodegradable wood-based heterostructured composite membrane, a preparation method, and its application to address the aforementioned problems of the prior art. The present invention utilizes a heterostructure hybrid connection strategy to prepare the biodegradable wood-based heterostructured composite membrane. The resulting composite membrane consists of a raw wood membrane, a COF (covalent organic framework) active layer, and a polymer-optimized layer. The biodegradable wood-based heterostructured composite membrane prepared by the present invention has important application value in the separation of inorganic salts and dyes.

[0007] The method for preparing a biodegradable wood-based heterogeneous structure composite film according to the present invention comprises the following steps:

[0008] 1) After planing the log, a long strip of wood of a certain thickness is obtained, and then the long strip of wood is evenly cut into the same size. The impurities on the surface are cleaned with deionized water, and the original wooden mold is obtained after natural drying;

[0009] 2) preparing a sodium periodate aqueous solution of a certain volume and molar concentration as an oxidizing solution, ultrasonically dissolving the solution, and then adding glacial acetic acid to adjust the oxidizing solution to acidity; immersing the original wood film obtained in step 1) therein, and conducting an oxidation reaction at room temperature in the dark, so that after the reaction, an oxide layer with a thickness of 0.005 to 0.02 μm is obtained on the surface of the original wood film, i.e., an oxidized wood film is obtained; after the reaction, the original wood film is removed and rinsed with distilled water 3 to 5 times; the rinsed original wood film is immersed in a 1,4-dioxane solution containing p-phenylenediamine, so that the solution quickly changes from colorless to reddish brown, reacting for a period of time at room temperature, removing the film, and drying the film to obtain a Pa layer with a thickness of 0.01 to 0.03 μm on the surface of the oxidized wood film, i.e., a Pa-wood film, which appears black;

[0010] 3) ultrasonically dissolving the aldehyde compound and the amine compound in dimethyl sulfoxide to induce a Schiff base reaction, obtaining a uniform solution through ultrasonic dissolution, and then allowing the solution to stand at room temperature to obtain an iCOF colloidal solution, wherein the yellow color of the colloidal solution gradually deepens as the reaction proceeds; then immersing the original wood film obtained in step 2) in the iCOF colloidal solution, and reacting at room temperature to obtain an iCOF layer with a thickness of 0.01 to 0.03 μm on the surface of the Pa-wood film, thereby obtaining an iCOF-wood film;

[0011] 4) dissolving the polymer in dimethyl sulfoxide and stirring the reaction in a water bath to obtain a uniform light yellow polymer solution; the polymer solution is evenly coated on the surface of the iCOF-wood film obtained in step 3), and then placed in an oven for drying after being left at room temperature to form a solid polymer layer with a thickness of 0.02 to 0.05 μm on the surface of the iCOF-wood film, thereby obtaining the biodegradable wood-based heterogeneous structure composite membrane (SPEEK-Na@iCOF-wood film).

[0012] Preferably, the log in step 1) is pine scale, and the size of the original wood film is 20-30 mm (length) × 20-30 mm (width) × 0.2-0.6 mm (thickness);

[0013] Preferably, in step 2), 80 to 120 mL of a sodium periodate aqueous solution with a molar concentration of 0.05 to 0.2 mol / L is prepared as the oxidizing solution, and the ultrasonic dissolution time is 2 to 5 minutes; the mass of the original wood film added is 1.5 to 5 g;

[0014] Preferably, in step 2), glacial acetic acid is used to adjust the pH of the oxidation solution to 2-5, the oxidation reaction temperature is 20-30° C., and the oxidation reaction time is 20-30 h;

[0015] Preferably, in step 2), the molar concentration of p-phenylenediamine in the 1,4-dioxane solution is 0.005 to 0.02 mol / L, the reaction temperature of the oxidized wood film therein is 20 to 30° C., and the reaction time is 20 to 30 h;

[0016] Preferably, in step 3), the molar ratio of the amine compound to the aldehyde compound is 0.2 to 1:0.75, the amine compound is triaminoguanidine hydrochloride, and the aldehyde compound is terephthalaldehyde;

[0017] Preferably, in step 4), the polymer is SPEEK-Na, the concentration of the polymer solution is 20-65 mg / mL, the dissolution temperature is 60-80°C, and the dissolution time is 3-6 hours; the water bath temperature is 50-70°C, the water bath stirring time is 3-6 hours, the standing time at room temperature is 1-3 hours, and the drying temperature is 50-80°C.

[0018] The biodegradable wood-based heterogeneous structure composite membrane of the present invention is prepared by the above method.

[0019] The biodegradable wood-based heterogeneous structure composite membrane prepared by the present invention can be used in separating dyes, and the dye is one or more of methylene blue, methyl orange, crystal violet, Congo red, methyl blue and bengal.

[0020] The biodegradable wood-based heterogeneous structure composite membrane prepared by the present invention can be used in separating inorganic salts, and the inorganic salt is one or more of sodium chloride, sodium sulfate, magnesium chloride and magnesium sulfate.

[0021] The biodegradable wood-based heterogeneous structure composite membrane prepared by the present invention can be used in separating a mixture of inorganic salts and dyes, wherein the inorganic salts are one or more of sodium chloride, sodium sulfate, magnesium chloride, and magnesium sulfate, and the dyes are one or more of methylene blue, methyl orange, crystal violet, Congo red, methyl blue, and bengal.

[0022] The principle of the present invention is to prepare a biodegradable wood-based heterostructure composite membrane by sequentially growing iCOF and SPEEK-Na on a wood substrate using an in-situ symbiotic method. The method first involves completely dissolving an amine compound and an aldehyde compound in a dimethyl sulfoxide solvent, then uniformly mixing them to produce a Schiff base reaction. After standing at room temperature, a uniformly dispersed iCOF colloidal solution is obtained. The iCOF colloidal solution is then assembled onto the treated wood membrane using a simple in-situ growth strategy. The synthesized cationic imine covalent organic framework (CFO) coats the surface of the pretreated wood membrane. The CFO and the negatively charged wood membrane support layer interact electrostatically, resulting in a tight bond between the CFO active layer and the wood membrane support layer. This modifies the wood membrane support layer, altering its surface physicochemical properties and avoiding the problem of membrane performance degradation caused by unstable membrane separation from the support layer in practical applications. When the negatively charged SPEEK-Na is introduced, the SPEEK-Na can tightly bond to the wood-based membrane through electrostatic interactions, hydrogen bonds, and π-π interactions, thereby forming a stable hybrid heterostructure.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] The present invention aims to invent an environmentally friendly biodegradable membrane with certain salt-dye separation ability to replace non-degradable petroleum-based material membranes. The biodegradable wood-based heterogeneous structure composite membrane prepared by this method has certain application value in salt and dye separation.

[0025] The wood-based heterogeneous structure composite membrane prepared by the present invention has high dye removal rate (>97%), low salt removal rate (<10%) and high permeation flux (172.34L m-2 h -1 bar -1 ), outperforming many reported dye / salt separation membrane materials. Furthermore, the composite membrane exhibits moderate operational stability, good antifouling properties, and soil degradability. Overall, this work enables the design and fabrication of nanofiltration membranes that can be extracted from and used in nature, enabling efficient and sustainable water purification applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 (a) is the ATR-FTIR spectrum of SPEEK-Na@iCOF-wood membrane and the products of each step in Example 1, Figure 1 (b) is the liquid ATR-FTIR spectrum of the colloidal solution in Example 1, Figure 1 (c) is the particle size curve in the colloidal solution;

[0028] Figure 2 (ac) are cross-sectional SEM images of the original wood film, iCOF-wood film, and SPEEK-Na@iCOF-wood film in Example 1, respectively. Figure 2 (df) are the surface scanning electron micrographs of the original wood film, iCOF-wood film, and SPEEK-Na@iCOF-wood film in Example 1. Figure 2 (gi) AFM images of the original wood film, iCOF-wood film, and SPEEK-Na@iCOF-wood film in Example 1;

[0029] Figure 3 (a) is a bar graph showing the separation performance of different dyes using the iCOF-wood membrane and SPEEK-Na@iCOF-wood membrane in Example 1. Figure 3 (b) is a bar graph showing the separation performance of bengal red dye using original wood membrane, iCOF-wood membrane, and SPEEK-Na@iCOF-wood membrane. Figure 3 (c) is a bar chart showing the separation performance of four inorganic salts, NaCl, Na2SO4, MgCl2, and MgSO4, using SPEEK-Na@iCOF-wood membrane. Figure 3 (d) is a bar graph showing the separation performance of a mixture of four inorganic salts, NaCl, Na2SO4, MgCl2, and MgSO4, and bengal dye using SPEEK-Na@iCOF-wood membrane. Figure 3(e) Bar graph showing the separation performance of SPEEK-Na@iCOF-wood membrane for different concentrations of bengal red dye and sodium chloride salt.

[0030] Figure 4 (a) is the anti-pollution performance curve of the iCOF-wood membrane and SPEEK-Na@iCOF-wood membrane in Example 1, Figure 4 (b) is a bar graph showing the anti-pollution performance of iCOF-wood membrane and SPEEK-Na@iCOF-wood membrane. Figure 4 (c) is a bar graph showing the separation and recycling capability of SPEEK-Na@iCOF-wood membrane for bengal red dye. Figure 4 (d) is a graph showing the long-term stability test of tiger red dye using SPEEK-Na@iCOF-wood membrane;

[0031] Figure 5 (ab) are photos of the degradation of activated sludge and normal soil by five membrane materials (NF1, NF6, original wood membrane, iCOF-wood membrane and SPEEK-Na@iCOF-wood membrane) before and after degradation. Figure 5 (cd) are the weight loss curves of five membrane materials (NF1, NF6, original wood membrane, iCOF-wood membrane and SPEEK-Na@iCOF-wood membrane) buried in activated sludge and normal soil for 90 days. Figure 5 (e) Actual photos of the degradation of five membrane materials (NF1, NF6, original wood membrane, iCOF-wood membrane and SPEEK-Na@iCOF-wood membrane) buried in activated sludge and normal soil for 90 days.

[0032] Table 1: Parameter data of composition differences between activated sludge and normal soil

[0033] DETAILED DESCRIPTION

[0034] Exemplary embodiments of the present invention will now be described in detail. This description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0036] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0037] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the present invention. The present description and examples are intended to be illustrative only.

[0038] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0039] It should be noted that, unless otherwise specified, % in Examples and Comparative Examples is based on mass.

[0040] The raw materials required in the embodiments of the present invention are all purchased from commercial sources.

[0041] The cross-flow filtration devices used in the separation tests in the embodiments of the present invention all used small membrane flat plate testing machines (TYLG-17) purchased from Shandong Bona Group.

[0042] Example 1: Preparation method of a biodegradable wood-based heterogeneous structure composite membrane

[0043] 1) Planing a pine log to obtain a long strip of wood with a thickness of 440 μm, and then evenly cutting the long strip of wood into original wood films of 25 mm (length) × 25 mm (width); cleaning the surface impurities with deionized water, and naturally drying it for use;

[0044] 2) Prepare 100 mL of a 0.1 mol / L sodium periodate aqueous solution as an oxidizing solution, sonicate for 2 minutes, then add glacial acetic acid to adjust the pH of the oxidizing solution to 3; weigh 2.00 g (approximately 18 pieces) of the original wood film obtained in step 1) and immerse it in the solution. Oxidation reaction is carried out at 25°C in the dark for 24 hours, resulting in an oxide layer (oxidized wood film) with a thickness of 0.01 μm on the surface of the original wood film; after the reaction is completed, remove the oxidized wood film and rinse it three times with distilled water; then immerse the entire 2.00 g of the oxidized wood film in 50 mL of a 1,4-dioxane solution containing 0.01 mmol of p-phenylenediamine (Pa). The solution quickly changes from colorless to reddish brown. After reaction at room temperature for 24 hours, remove the film, and obtain a 0.015 μm thick Pa layer (Pa-wood film) on the surface of the oxidized wood film, which is then placed in deionized water for later use; the reaction formula is as follows:

[0045]

[0046] 3) 0.75 mmol of terephthalaldehyde and 0.5 mmol of triaminoguanidine hydrochloride were dissolved in 30 mL of dimethyl sulfoxide to undergo a Schiff base reaction. The solution was ultrasonically dissolved for 20 minutes to obtain a homogeneous solution. As the reaction proceeded, the yellow color of the colloidal solution was observed to gradually deepen. The homogeneous solution was allowed to stand at room temperature for 24 hours to obtain an iCOF colloidal solution. The reaction formula is as follows:

[0047]

[0048] Then, the Pa-wood film obtained in step 2) was immersed in a COF colloid solution and reacted at room temperature for 24 hours to obtain an iCOF layer (iCOF-wood film) with a thickness of 0.015 μm on the surface of the Pa-wood film;

[0049] 4) 50 mg / mL of SPEEK-Na solid was dissolved in dimethyl sulfoxide and stirred in a 60°C water bath for 4 hours to obtain a uniform light yellow liquid; a certain amount of SPEEK-Na solution was taken and evenly coated on the surface of the iCOF-wood membrane obtained in step 3), and the mixture was left at room temperature for 2 hours and then dried in an oven at 60°C until a solid polymer layer with a thickness of approximately 0.03 μm was formed on the surface of the iCOF-wood membrane; thereby, the biodegradable wood-based heterogeneous structure composite membrane, designated as SPEEK-Na@iCOF-wood membrane, was obtained, with a total thickness of 440.07 μm.

[0050] Figure 1 (a) is the infrared spectra (ATR-FTIR) of the log, oxidized wood film, Pa-wood film, iCOF-wood film, and SPEEK-Na@iCOF-wood film in Example 1. ATR-FTIR shows that after the wood is oxidized, the -1The C=O stretching vibration peak appeared at 1640 cm, which confirmed that sodium periodate successfully oxidized the -OH group in the wood cellulose molecules to form aldehyde groups. -1 The characteristic peak of C=N appeared at 1024 cm, indicating that the aldehyde group generated on the wood matrix can react with the p-phenylenediamine monomer and the amino group of iCOF to form an imine bond, which shows that the reaction between the aldehyde group and the amino group occurred successfully. When SPEEK-Na was introduced into the iCOF-wood film, the spectrum showed that the peak at 1024 cm -1 and 1080cm -1 The characteristic absorption peaks at correspond to the symmetric and asymmetric stretching vibrations of the sulfonic acid group (O=S=O), which proves the successful growth of SPEEK-Na; Figure 1 (b) ATR-FTIR spectrum at 1640 cm -1 A new characteristic peak appeared at , which corresponds to the C=N characteristic peak after 24h of mixed reaction of triaminoguanidine hydrochloride and terephthalaldehyde monomer, and an obvious Tyndall effect was observed, confirming the successful formation of iCOF colloidal solution. Figure 1 (c) shows the specific particle size values ​​of the colloidal solution before and after the reaction in Example 1. The average particle size increases from 55 nm to 78 nm, confirming the growth behavior of iCOF within 24 h.

[0051] Figure 2 (ac) are cross-sectional SEM images of the original wood film, iCOF-wood film, and SPEEK-Na@iCOF-wood film prepared in Example 1. Figure 2 (df) is the surface scanning electron microscope image, Figure 2 (gi) is an atomic force microscope image, from Figure 2 From (ac), we can see that the cross-sectional morphology of the original wood film presents a clear layered structure, and the iCOF layer mainly grows on the wood surface. When SPEEK-Na is added, a dense coating appears on the surface of the iCOF-wood film. Figure 2 (df) It can be seen that compared with the untreated original wood film, the surface of the iCOF wood presents a rough sponge-like structure, which is observed under a high-power microscope ( Figure 2 (e) Inset), solid particles can be observed on the surface of the iCOF-wood film. After the introduction of SPEEK-Na, a dense coating was observed on the surface of the iCOF-wood film. SPEEK-Na evenly covered the surface of the iCOF-wood film, making its surface smoother. In addition, the high-magnification scanning electron microscopy image ( Figure 2 The inset in (f) shows that SPEEK-Na chains form nodule-like structures on the surface of iCOF-wood film. Atomic force microscopy image ( Figure 2(gi)) reflects that the surface roughness of the membrane is 23.4nm, 68.9nm and 2.15nm, respectively, showing a state of reduced roughness, which is conducive to the increase of permeation flux.

[0052] Example 2: Separation performance test

[0053] The separation performance of the biodegradable wood-based heterostructure composite membrane prepared in Example 1 was determined by a circulating cross-flow filtration method using a 5 mg / L rose bengal aqueous solution. The separation performance of the membrane was measured at a pressure of 0.5 bar using 5 mg / L (aqueous solution) of dyes (Rose Bengal (negatively charged, 1072.8 Da), methyl blue (negatively charged, 799.8 Da), Congo red (Congo Red, 2 negatively charged, 696.66 Da), crystal violet (positively charged, 407.99 Da), methylene blue (positively charged, 319.9 Da) and methyl orange (negatively charged, 327.3 Da)) or 1 g / L inorganic salt solution (aqueous solution) (sodium chloride, magnesium chloride, sodium sulfate and magnesium sulfate) as the feed solution.

[0054] like Figure 3 As shown in (a), the iCOF-wood membrane's separation of dyes shows a decreasing retention rate and increasing permeation flux as the molecular weight of the dye decreases. For crystal violet, the dye retention rate shows the opposite trend, which is due to the electrostatic repulsion between the positively charged crystal violet and the positively charged iCOF layer containing triaminoguanidine hydrochloride monomers. Therefore, crystal violet (positively charged) exhibits a better repulsion effect than Congo red (negatively charged). For the positively charged methylene blue dye, due to its smaller molecular weight, its repulsion effect is similar to that of Congo red. The SPEEK-Na@iCOF-wood membrane has a retention rate of over 90% for bengal, methyl blue, and Congo red. Based on the Donnan effect, it shows that the introduction of negatively charged polymers gives the wood-based heterostructure membrane good repulsion performance for negatively charged dyes. However, due to its small molecular weight and linear molecular formula, methyl orange easily passes through the wood-based heterostructure membrane, resulting in a lower rejection rate. Figure 3 (b) More intuitively reflects the rejection rate and permeation flux of the original wood membrane, iCOF-wood membrane, and SPEEK-Na@iCOF-wood membrane for bengalensis dye. The rejection rate of SPEEK-Na@iCOF-wood membrane for bengalensis dye is 97%, and the permeation flux is 220 L h -1 m -2 bar -1 , indicating good separation performance.

[0055] Figure 3(c) reflects the rejection of the membrane to four inorganic salts. The results show that the rejection rate of different inorganic salts is Na2SO4 (8.66%) > MgSO4 (8.41%) > MgCl2 (5.21%) > NaCl (2.86%). Specifically, compared with chloride salts, the higher rejection of sulfate by SPEEK-Na@iCOF-wood membrane is due to the negative charge of the membrane repelling high-valent anions. In addition, the divalent anion SO4 2- (0.38nm) than the monovalent anion Cl - The larger hydration radius (0.33 nm) also contributes to this difference in repulsion. In addition, the negatively charged membrane has a stronger stabilizing electrostatic interaction with divalent cations than with monovalent cations, which explains why the rejection of MgSO4 is lower than that of Na2SO4. However, due to the divalent cation Mg 2+ The hydration radius (0.43 nm) is larger than that of the monovalent cation Na + (0.36 nm), resulting in a higher retention rate for MgCl₂ than for NaCl. In summary, the SPEEK-Na@iCOF-wood membrane's screening of inorganic salts is influenced by the synergistic effects of Donnan repulsion, electrostatic interactions, and steric repulsion. The SPEEK-Na@iCOF-wood membrane effectively facilitates the transport of a variety of salts.

[0056] Four types of salts (1 g / L, aqueous solution) were mixed with RB dye (10 mg / L, aqueous solution) in equal volumes, and the biodegradable wood-based heterogeneous structure composite membrane prepared in Example 1 was further subjected to salt-dyeing separation test. Figure 3 (d) shows the performance results of the SPEEK-Na@iCOF-wood membrane for the removal of RB from solutions containing Na2SO4, MgSO4, NaCl, or MgCl2. It can be observed that the SPEEK-Na@iCOF-wood membrane exhibits good RB molecule removal efficiency in solutions containing all four salts, with the RB rejection rate remaining above 95%.

[0057] Different concentrations (5, 10, 15, 20 mg / L) of Bengal Red solution were mixed with 1 g / L NaCl to study the effect of dye concentration on salt separation. Figure 3As can be seen from (e), changing the dye concentration has little effect on salt separation, and the rejection rate of NaCl remains relatively constant. When the concentration of rose bengal solution reaches 20 mg / L, the rejection rate drops to 90%. This may be because under higher concentration conditions, the electronegativity of the rose bengal solution increases, and the negative charges on the surface of the SPEEK-Na@iCOF-wood membrane are not sufficient to repel the aggregated rose bengal molecules with higher electronegativity, resulting in partial penetration of rose bengal molecules and a decrease in the rejection rate. In addition, various factors such as dye hydration, aggregation, steric barrier effect, concentration polarization, ion competitive permeation, and electrostatic repulsion may all cause changes in the selectivity of the membrane for dyes and salts. In summary, the above results indicate that the SPEEK-Na@iCOF-wood membrane has potential application value in dye / salt separation.

[0058] Example 3: Anti-fouling and stability tests

[0059] Using the biodegradable wood-based heterostructure composite membrane prepared in Example 1, a cross-flow filtration device was used to evaluate the anti-fouling and stability of the membrane. Figure 4 (a) is a line graph of the water flux change with pure water and bovine serum albumin (BSA) alternately used as the feed solution; Figure 4 (b) is a bar graph of the flux recovery rate (PRR), reversible fouling rate (Rr), irreversible fouling rate (Rir), and total fouling rate (Rt) of the membrane calculated after the test. In Figure 4 (b), the pattern in front of the character "iCOF-wood membrane" represents 240 min, and the pattern behind represents 420 min; the pattern in front of the character "SPEEK-Na@iCOF-wood membrane" represents 240 min, and the pattern behind represents 420 min.

[0060] The calculation formulas are as follows:

[0061] PRR% = F w,2 / F w,1 × 100% (1)

[0062] Rr% = (F w,2 - F P ) / F w,1 × 100% (2)

[0063] Rir% = (F w,1 - F w,2 ) / F w,1 × 100% (3)

[0064] Rt% = Rr% + Rir% = (F w,1 - F p [[ID=w,1 × 100% (4)

[0065] Where, F w,1 is the water flux after pre-pressing with pure water as feed, F p is the water flux when the bovine serum albumin aqueous solution replaces pure water as feed, F w,2 It is the water flux when the membrane contaminated with bovine serum albumin is washed with water and then fed with pure water again.

[0066] Figure 4 (a) When BSA was fed through the membrane, the pure water flux of all membranes decreased. After 60 minutes of permeation of pure water with BSA as the feed solution, the permeability of the iCOF-wood membrane decreased significantly, from 290.81 Lh -1 m -2 bar -1 Down to 247.77Lh -1 m -2 bar -1 Similarly, the permeability of SPEEK-Na@iCOF-wooden mold was significantly reduced from 247.43 L h - 1 m -2 bar -1 Down to 178.54L h -1 m -2 bar -1 The main reasons for the decrease in permeability are the accumulation of BSA on the membrane surface to form a fouling layer and the occurrence of concentration polarization. In order to accurately compare the anti-fouling capabilities of iCOF-wood membrane and SPEEK-Na@iCOF-wood membrane, we further calculated relevant indicators. Figure 4 (b) After 210 minutes of filtration (first cycle), the SPEEK-Na@iCOF-wood membrane achieved a water flux recovery of 96.41%, a reversible fouling rate of 27.0%, an irreversible fouling rate of 3.59%, and a total fouling rate of 30.59%. The flux recovery (96.41%) was superior to that of the iCOF-wood membrane (92.93%). Furthermore, after the second fouling cycle, the water flux recovery of the SPEEK-Na@iCOF-wood membrane remained relatively good, demonstrating that the biodegradable wood-based heterostructured composite membrane prepared in Example 1 possesses excellent fouling resistance.

[0067] In addition to anti-fouling performance, stability is also an important factor affecting the service life of composite membranes. Figure 4 (c) shows that after 5 cycles of testing, the rejection rate of SPEEK-Na@iCOF-wood membrane for bengalensis solution remains at around 90%. Figure 4(d) It can be seen that after 500 minutes of continuous filtration, the permeation flux of SPEEK-Na@iCOF-wooden mold is basically stable, and the retention rate of bengalensis solution is about 90%. This shows that the membrane has good stability.

[0068] Example 4: Biodegradation Experiment

[0069] Biodegradation experiments were conducted using the biodegradable wood-based heterostructure composite membrane prepared in Example 1 and a commercial nanofiltration membrane.

[0070] The specific operation is as follows: cut the membrane into a size of 25mm×25mm×0.44mm and store it at 60℃ for 12h. Then measure the initial dry weight m1. Prepare two soil environments: activated sludge and normal soil (see Table 1 for specific parameter differences). After stabilization in the greenhouse for 24h, measure and record the relevant parameters of the two soil environments. During the entire test, the temperature and humidity of the soil were maintained at a relatively stable level. Each group of three parallels, bury the cut membrane in the soil at a depth of 10 cm. According to the experimental phenomena, select the appropriate time to record the degradation. Before quality testing, carefully collect the membrane samples from the soil and clean the decomposed samples with a soft brush. Rinse the soil attached to the surface of the sample with distilled water, dry it at 60℃ for 12h, and weigh it as m2. Record the soil biodegradation rate according to the following formula (5):

[0071]

[0072] After each sampling, the soil was gently stirred to maintain a certain aerobic condition. Two commercially available nanofiltration membranes, NF-1 (polyamide material) and NF-6 (polyethersulfone material), were used as control inspection groups.

[0073] Figure 5 (ab) Digital photos visually show the degradation of all membranes after being buried in activated sludge / normal soil for about 90 days (from left to right in the picture are NF1, NF6, original wood membrane, iCOF-wood membrane and SPEEK-Na@iCOF-wood membrane). It can be seen that over time, due to the degradability of cellulose and hemicellulose in wood, the original wood mold, iCOF-wood membrane and SPEEK-Na@iCOF-wood membrane gradually lost their original luster and showed cracking and fragmentation. This shows that wood showed a certain degradation ability in both soil environments. Figure 5 (cd) Detailed data on membrane weight loss and detailed digital photos within 90 days Figure 5(e) It can further support the degradation ability of the wood-based membrane. After approximately 90 days of continuous changes in ambient temperature and relative humidity, the SPEEK-Na@iCOF-wood membrane was observed to degrade by approximately 80% in activated sludge and by approximately 60% in normal soil. This degradation phenomenon is primarily due to the SPEEK-Na@iCOF-wood membrane's enhanced hydrophilicity and porous structure, which are more conducive to microbial growth and accelerate the degradation process. The difference in organic matter content between the two soil environments is the primary factor contributing to the difference in soil degradation. Activated sludge exhibits a higher organic matter content, resulting in more pronounced degradation of the SPEEK-Na@iCOF-wood membrane than normal soil over the same period. Under identical conditions, both commercial membranes exhibit lower soil degradation ability due to their primary composition of non-hydrolyzable -C-C and -C-H covalent bonds, coupled with the large spatial barriers formed by the macromolecular segments. Therefore, the SPEEK-Na@iCOF-wood membrane prepared by this invention is a sustainable green material that can be buried in the soil for biodegradation and returned to nature without causing white pollution.

[0074] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a biodegradable wood-based heterogeneous structure composite membrane, comprising the following steps: 1) Planing the logs to obtain long strips of wood, which were then cut into uniform sizes. The wood was then cleaned of impurities on the surface with deionized water and dried naturally to obtain the original wood film. The original wood film had a length of 20-30 mm, a width of 20-30 mm, and a thickness of 0.2-0.6 mm. 2) Prepare 80-120 mL of sodium periodate aqueous solution with a molar concentration of 0.05-0.2 mol / L as an oxidizing solution. Ultrasonicate the solution for 2-5 minutes, then add glacial acetic acid to adjust the oxidizing solution to a pH of 2-5. Immerse 1.5-5 g of the original wood film obtained in step 1) in the solution. The oxidation reaction was carried out at 20-30°C in the dark for 20-30 hours. After the reaction, an oxide layer with a thickness of 0.005-0.02 μm was formed on the surface of the original wood film, namely the oxidized wood film. After the reaction, the original wood film was removed and rinsed with distilled water 3-5 times. The rinsed original wood film was immersed in a 1.4-dioxane solution containing p-phenylenediamine. The solution quickly changed from colorless to reddish-brown. After a period of reaction at room temperature, the film was removed and dried to form a Pa layer with a thickness of 0.01-0.03 μm on the surface of the oxidized wood film, namely the Pa-wood film, which appeared black. Wherein Pa represents p-phenylenediamine. 3) ultrasonically dissolving the aldehyde compound and the amine compound in dimethyl sulfoxide to induce a Schiff base reaction, obtaining a uniform solution through ultrasonic dissolution. The solution was then allowed to stand at room temperature to obtain an iCOF colloidal solution, with the yellow color of the colloidal solution gradually deepening as the reaction proceeded. The Pa-wood film obtained in step 2) was then immersed in the iCOF colloidal solution. After reaction at room temperature, an iCOF layer with a thickness of 0.01 to 0.03 μm was obtained on the surface of the Pa-wood film, thereby obtaining an iCOF-wood film. 4) dissolving the polymer SPEEK-Na in dimethyl sulfoxide and stirring the reaction in a water bath to obtain a uniform light yellow polymer solution; the polymer solution is evenly coated on the surface of the iCOF-wood membrane obtained in step 3), and then placed in an oven for drying after being left at room temperature to form a solid polymer SPEEK-Na layer with a thickness of 0.02-0.05 μm on the surface of the iCOF-wood membrane, thereby obtaining the biodegradable wood-based heterogeneous structure composite membrane.

2. The method for preparing a biodegradable wood-based heterogeneous structure composite film according to claim 1, wherein: In step 2), the molar concentration of p-phenylenediamine in the 1,4-dioxane solution is 0.005-0.02 mol / L, the reaction temperature of the oxidized wood film is 20-30° C., and the reaction time is 20-30 h.

3. The method for preparing a biodegradable wood-based heterogeneous structure composite membrane according to claim 1, wherein: In step 3), the molar ratio of the amine compound to the aldehyde compound is 0.2-1:0.75, the amine compound is triaminoguanidine hydrochloride, and the aldehyde compound is terephthalaldehyde.

4. The method for preparing a biodegradable wood-based heterogeneous structure composite membrane according to claim 1, wherein: In step 4), the concentration of the polymer solution is 20-65 mg / mL, the dissolution temperature is 60-80°C, and the dissolution time is 3-6 h; the water bath temperature is 50-70°C, the water bath stirring time is 3-6 h, the placement time at room temperature is 1-3 h, and the drying temperature is 50-80°C.

5. A biodegradable wood-based heterogeneous structure composite film, characterized by: The invention is prepared by the preparation method according to any one of claims 1 to 4.

6. Use of a biodegradable wood-based heterogeneous structure composite membrane according to claim 5 in dye separation, characterized in that: The dye is one or more of methylene blue, methyl orange, crystal violet, Congo red, methyl blue and carmine bengal.

7. Use of a biodegradable wood-based heterogeneous composite membrane according to claim 5 in separating inorganic salts, characterized in that: The inorganic salt is one or more of sodium chloride, sodium sulfate, magnesium chloride and magnesium sulfate.

8. Use of the biodegradable wood-based heterostructure composite membrane according to claim 5 in separating a mixture of an inorganic salt and a dye, characterized in that: The inorganic salt is one or more of sodium chloride, sodium sulfate, magnesium chloride, and magnesium sulfate; the dye is one or more of methylene blue, methyl orange, crystal violet, Congo red, methyl blue, and bengal.

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