Polyvinyl alcohol-flaxseed gum composite sponge as well as preparation method and application thereof

Abstract

The invention discloses a polyvinyl alcohol-flaxseed gum composite sponge and a preparation method and application, and belongs to the technical field of metal adsorption type environment-friendly materials.The preparation method of the polyvinyl alcohol-flaxseed gum composite sponge comprises the following steps that a flaxseed colloidal solution and a polyvinyl alcohol solution are mixed and stirred, and a mixed system is obtained; adding n-pentane into the mixed system, adding a rotor, sealing with a preservative film, adjusting the speed of a magnetic stirrer to 400 rpm, and starting to stir until the expansion volume of the mixed system is 2 times of the initial volume to obtain a stable foam system; adding an acid solution into the stable foam system, carrying out acid catalysis crosslinking, and adjusting the pH for the first time; then adding a glutaraldehyde aqueous solution, adjusting the pH value again, and carrying out chemical cross-linking curing; and drying to prepare the polyvinyl alcohol-flaxseed gum composite sponge. The polyvinyl alcohol-flaxseed gum composite sponge provided by the invention shows excellent lead ion removal performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal adsorption environmental protection materials, and particularly relates to a polyvinyl alcohol-flaxseed gum composite sponge and a preparation method and application thereof. Background Art

[0002] Heavy metals are a class of toxic metal elements that can migrate in the environment. The sources of heavy metal pollutants are diverse, and the types and contents of pollutants vary greatly in different regions. The waste residues, waste gases and waste waters discharged from industrial production will carry a large amount of heavy metals into water bodies, such as lead, zinc, cadmium, copper, mercury and arsenic, etc.; in agricultural production, the application of pesticides and fertilizers, as well as livestock manure and straw burning, etc. will all lead to the enrichment of heavy metals in water bodies; with the development of social economy, domestic sewage, urban garbage, catering sewage and hospital sewage, etc. have gradually become the sources of heavy metal pollution.

[0003] With the continuous improvement of agricultural production levels, people make less and less use of agricultural and forestry waste. The annual crop waste generated can reach about 500 million tons, most of which are directly discarded or burned in the open air, which not only causes serious waste of green resources, but also pollutes the ecological environment. With the increasingly serious water pollution, while people are looking for efficient and environmentally friendly treatment methods, they turn their attention to crop waste. Crop waste contains a large amount of substances such as cellulose, hemicellulose and lignin, which can provide many active functional groups, such as hydroxyl, carboxyl and phenolic groups, etc. These groups have adsorption characteristics for heavy metal ions. As an important economic crop planting base in the northwest region, the annual output of flaxseed in Xinjiang accounts for about 28% of the total national output, occupying an important position in the oil crop industry. However, in the process of flaxseed oil processing, about 1.5 tons of flaxseed meal waste residue will be generated for every 1 ton of refined oil produced. Calculated according to the annual processing volume in Xinjiang, the annual waste flaxseed meal generated is as high as 150,000 tons. These by-products rich in active ingredients such as crude protein (content up to 32%-38%), dietary fiber (about 12%) and lignans have long been mainly used as extensive animal feed or directly landfilled, which not only causes waste of resources, but also brings serious environmental pressure. The waste residue stacked in the open air is easily washed by rainwater to produce leachate containing cyanide, polluting the soil and groundwater.

[0004] In summary, an adsorption sponge that can reasonably utilize flaxseed meal waste residue is urgently needed to be developed. Summary of the Invention

[0005] The object of the present invention is to provide a polyvinyl alcohol - flaxseed gum composite sponge, a preparation method and an application thereof to solve the problems existing in the above - mentioned prior art. The present invention provides a polyvinyl alcohol - flaxseed gum composite sponge adsorbent constructed by synergistically combining plant - derived components and synthetic polymer materials. It combines the natural porous structure and polymer characteristics of flaxseed gum and polyvinyl alcohol (PVA), and can be effectively used for heavy metal removal in water treatment.

[0006] One of the technical solutions provided by the present invention:

[0007] A preparation method of a polyvinyl alcohol - flaxseed gum composite sponge includes the following steps: mixing and stirring a flaxseed gum colloidal solution and a polyvinyl alcohol solution to obtain a mixed system; adding n - pentane to the mixed system, adding a rotor and then sealing it with plastic wrap, adjusting the magnetic stirrer to 400 rpm and then starting stirring until the expanded volume of the mixed system reaches 2 times the initial volume to obtain a stable foam system; adding an acid solution to the stable foam system for acid - catalyzed cross - linking and adjusting the pH for the first time; then adding an aqueous glutaraldehyde solution, adjusting the pH again for chemical cross - linking and curing; drying to prepare the polyvinyl alcohol - flaxseed gum composite sponge.

[0008] The preparation of the polyvinyl alcohol - flaxseed gum composite sponge realizes the regulation of structure and performance through three key processes: First, the foaming treatment uses n - pentane to gasify under high - temperature stirring to form micro - bubbles. The amphiphilic molecules of PVA and flaxseed gum stabilize the foam by reducing the surface tension, constructing a hierarchical porous structure and increasing the specific surface area. Second, the acid - catalyzed cross - linking protonates the hydroxyl and carboxyl groups with sulfuric acid, triggering intermolecular dehydration condensation and the formation of ester bonds, establishing a primary hydrogen - bond network, shrinking the foam volume and enhancing the shape stability. Finally, the chemical cross - linking and curing uses glutaraldehyde to react with the polymer hydroxyl groups to form a covalently cross - linked three - dimensional network, significantly improving the mechanical strength and thermal stability. Through the synergistic effect of the above three steps, based on the porous framework constructed by physical foaming, the pore structure is optimized through a step - by - step cross - linking strategy of acid - base synergy, providing a theoretical and technological basis for the design of functional adsorbents.

[0009] Further, the volume ratio of the flaxseed gum colloidal solution to the polyvinyl alcohol solution is (15 - 18)∶(2 - 5); and / or, the mass concentration of the polyvinyl alcohol solution is 10%; and / or, the mass concentration of the flaxseed gum colloidal solution is 5%.

[0010] Further, the volume ratio of the n - pentane to the mixed system is 1∶40.

[0011] In the present invention, n-pentane is added to the mixed system formed by polyvinyl alcohol and flaxseed gum, and uniform microbubbles are formed by a physical foaming mechanism. The specific process is as follows: n-pentane (boiling point 36 °C) is rapidly vaporized in a water bath to form tiny bubble nuclei; the hydroxyl groups (-OH) in PVA molecules and the carboxyl groups (-COOH) of flaxseed gum polysaccharides are amphiphilic, adsorbing at the gas-liquid interface to reduce the surface tension and stabilizing the surface activity of the bubbles; the shear force generated by magnetic stirring is combined to break the bubbles into uniform and stable microbubbles.

[0012] By regulating the volume ratio of the mixed system to n-pentane, precise control of the pore structure of the material is achieved. Specifically, when the volume ratio of n-pentane to the mixed system is set to 1:40, a porosity of 70%-85% (calculated based on the Langmuir adsorption model) can be formed during the foaming process. In the foaming stage, after the bubbles are generated in the water bath environment, the system is rapidly cooled to room temperature, and the significant temperature gradient change is utilized to induce a sharp increase in the system viscosity, thereby effectively "freezing" the pore structure and ensuring the stability of the pore morphology.

[0013] Furthermore, the pH is 3.5 - 5.0.

[0014] In the present invention, the structure and properties of the porous material are regulated through an acid-catalyzed crosslinking mechanism. Specifically:

[0015] In the acid-catalyzed crosslinking system, sulfuric acid (H2SO4) serves as a proton donor. By regulating the solution pH to a weakly acidic environment of 3.5 - 5.0, the molecular-level structural reconstruction of the polysaccharide chain and polyvinyl alcohol (PVA) is initiated. First, the strong acidity of sulfuric acid protonates the carboxyl group (-COOH) of the polysaccharide chain to -COOH2 + , significantly enhancing its electrophilic activity; at the same time, the hydroxyl group (-OH) of PVA is partially converted to an oxonium ion (-OH2 + ) under acidic conditions, forming a highly reactive intermediate state. The above protonation process provides a chemical basis for the subsequent condensation reaction.

[0016] In the condensation reaction stage, the protonated groups form a covalent bond network through intermolecular dehydration, that is, the hydroxyl groups (-OH2 + ) of adjacent PVA molecules undergo dehydration condensation to generate an ether bond (-O-), constructing a lateral connection between molecular chains; at the same time, the carboxyl group (-COOH2 +) It undergoes an esterification reaction with the hydroxyl groups (-OH) of PVA under acid catalysis to form ester bonds (-COO-), achieving the chemical crosslinking of the polysaccharide chain and PVA. This dual condensation mechanism (the synergism of ether bonds and ester bonds) significantly enhances the crosslinking density of the material. The direct result of the crosslinking reaction is the significant strengthening of the material structure. The initially formed three-dimensional network structure results in a foam volume shrinkage rate of 40%-50%, indicating the formation of stable steric hindrance between molecular chains. Mechanical property tests show that pre-crosslinking increases the storage modulus (G') of the material by 2-3 orders of magnitude, reflecting stronger constraints on the movement of molecular chains. This structural strengthening effect not only improves the mechanical stability of the material. Through the acid-catalyzed crosslinking mechanism, the present invention realizes the coordinated regulation of the pore structure and mechanical properties of porous materials, providing new ideas for the structural design and functional application of bio-based materials.

[0017] Further, the volume ratio of the glutaraldehyde aqueous solution to the mixed system is (0.1-0.3):4; and / or, the mass concentration of the glutaraldehyde aqueous solution is 25%.

[0018] Further, the time for chemical crosslinking and curing is 30 min; and / or, the pH is adjusted to 3 again.

[0019] In the chemical crosslinking system mediated by glutaraldehyde (OHC-(CH2)3-CHO), its dialdehyde structure undergoes an acetalization reaction with the hydroxyl groups (-OH) of polyvinyl alcohol (PVA) and the polysaccharide chain. By forming a stable six-membered cyclic acetal structure, an intermolecular covalent bond network is constructed, significantly enhancing the network structure stability and mechanical strength of the material. The present invention regulates the crosslinking density through the glutaraldehyde concentration and pH. Specifically, by controlling the glutaraldehyde concentration, the crosslinking point density can reach 1.2×10 - 3 mol / m 3 (measured by the swelling method), and in an acidic environment (pH = 3), the reaction rate increases by 3-5 times (calculated by the Arrhenius equation), thus accelerating the formation of the crosslinking network. In addition, PVA and flaxseed gum form an interpenetrating network (IPN) through the synergistic action of covalent bonds and hydrogen bonds. This structural feature causes the glass transition temperature (Tg) of the material to increase significantly from 45 °C to 85 °C (measured by differential scanning calorimetry DSC), reflecting restricted molecular chain movement and enhanced thermodynamic stability.

[0020] The second technical solution provided by the present invention:

[0021] A polyvinyl alcohol-flaxseed gum composite sponge prepared by the above preparation method.

[0022] The third technical solution provided by the present invention:

[0023] Application of the above polyvinyl alcohol - flaxseed gum composite sponge in the treatment of heavy metal ion - contaminated wastewater.

[0024] Further, the heavy metal ion is a lead ion.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] The polyvinyl alcohol - flaxseed gum composite sponge provided by the present invention exhibits excellent lead ion removal performance. In a lead ion solution with an initial concentration of 10 mg / L, the composite sponge can achieve a removal rate of 86.38% within 10 min, and after 2 h, its removal rate can reach as high as 99.94%. In addition, the composite sponge also has good hydrophilic characteristics, and its water contact angle can drop to 35.67° in only 1 s, which helps it to achieve a better adsorption effect in the field of treating heavy metal ion - contaminated wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0028] Figure 1 Cross - sectional view of the polyvinyl alcohol - flaxseed gum composite sponge prepared for Example 3;

[0029] Figure 2 Infrared spectrum of the polyvinyl alcohol - flaxseed gum composite sponge prepared for Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0030] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0031] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0032] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the said documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0033] Without departing from the scope or spirit of this invention, various modifications and variations can be made to the specific embodiments of the specification of this invention, which will be obvious to those skilled in the art. Other embodiments obtained from the specification of this invention will be obvious to those skilled in the art. The specification and examples of this invention are merely exemplary.

[0034] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0035] The room temperature in this invention refers to 25 ± 2 °C.

[0036] The embodiments of this invention provide a method for preparing a polyvinyl alcohol - linseed gum composite sponge, which specifically includes the following steps:

[0037] I. Preparation of linseed gum powder:

[0038] 1. Raw material pretreatment:

[0039] 1.1 Crushing and sieving: Crush linseed cake (water content ≤ 10%) with a hammer mill and sieve it through an 80 - mesh sieve, and remove crude fiber and impurities through a vibrating sieve to obtain a uniform powder;

[0040] 1.2 Degreasing treatment: If the residual oil content of the raw material of linseed cake > 5%, Soxhlet extraction with n - hexane or petroleum ether (solid - liquid ratio 1:4) is required, reflux at 55 °C for 6 h, and dry it for later use after degreasing.

[0041] 2. Linseed gum extraction

[0042] 2.1 Add cellulase to the degreased linseed cake powder at a mass ratio of 10:1, adjust the pH to 4.5 - 5.0, enzymatically hydrolyze at 50 °C for 1 h to break the cell wall structure and fully dissolve and release the colloid; heat up to 85 - 90 °C and stir and extract at a constant temperature for 2 h;

[0043] 2.2 Centrifugal slag removal: Remove the residue from the extract through a horizontal spiral centrifuge (4000 - 5000 rpm, 15 min), and collect the upper - layer gum solution.

[0044] 3. Dehydration and drying

[0045] 3.1 Centrifuge the upper layer of the glue solution, collect the precipitate, wash it twice with absolute ethanol, and obtain light yellow linseed gum powder by freeze-drying or spray-drying (inlet air temperature 180 °C, outlet air temperature 85 °C).

[0046] II. Preparation of the mixed system

[0047] Mix linseed gum powder and deionized water, heat and stir to obtain a linseed gum colloidal solution (5Wt%).

[0048] Accurately measure 15 - 18 mL of the above linseed gum colloidal solution with a syringe, transfer it to a 50 mL beaker, add 2 - 5 mL of a pre-prepared 10% (mass concentration) aqueous solution of polyvinyl alcohol (PVA1788, degree of polymerization 1700), turn on the timing stirrer, set the rotation speed to 300 rpm, and stir for 5 min to obtain a mixed system.

[0049] III. Foaming treatment

[0050] Add n-pentane (chromatographically pure, boiling point 36 °C) to the mixed system with a micropipette, immediately seal the bottle mouth with a sealing film, set the rotation speed to increase to 400 rpm, and continuously stir until the volume of the system expands to 2 - 3 times the initial volume (about 15 - 20 min) to form a stable foam system.

[0051] IV. Acid-catalyzed crosslinking

[0052] Slowly add a small amount of dilute sulfuric acid (5%) with a pipette, adjust the stirring speed to 400 rpm, and continuously stir until the volume of the system is stable (about 8 - 10 min). During this period, monitor the pH value with pH test paper and it should drop to 3.5 - 5.0.

[0053] V. Chemical crosslinking and curing

[0054] Add an aqueous solution of 25% (mass concentration) glutaraldehyde (analytical pure) with a pipette gun, adjust the pH to 5, stir at room temperature, and immediately stop stirring when the viscosity of the system increases significantly (the rotation speed of the magnetic stirrer decreases by ≥ 30%). Re-seal the bottle mouth and let it stand for curing.

[0055] VI. Preliminary drying treatment

[0056] Transfer the cured sample to a petri dish, spread it into a thickness of 2 - 3 mm, place it in a DHG-9070A type electrothermal blast drying oven for drying, take it out and cool it to constant weight at room temperature, and then transfer it to a -4 °C refrigerator and let it stand overnight (12 ± 0.5 h).

[0057] VII. Freeze-drying

[0058] Precool the FD-1A-50 freeze dryer to -50°C. Place the preliminarily dried sample in the cold trap and quickly freeze it to below -40°C. Turn on the vacuum pump, maintain the pressure ≤ 10 Pa, continue freeze-drying until completely dried, and take out the sample and store it sealed in a desiccator for later use.

[0059] This invention mainly explores the adsorption performance of composite sponges made of flaxseed gum and polyvinyl alcohol (PVA) for heavy metal ions. By optimizing the functional complementarity of flaxseed gum on different materials, its application fields are broadened. The embodiments of this invention have systematically studied various properties during the adsorption process, evaluated the application potential of the prepared polyvinyl alcohol-flaxseed gum composite sponge in environmental pollution control, specifically including the effects of factors such as adsorption performance, pH value, ion concentration, and adsorption time on the adsorption capacity and kinetic characteristics, providing a new solution for the treatment of heavy metal water pollution and opening up a new direction for the development of new bionic sponge functions.

[0060] In the embodiments of this invention, the mass concentration of the flaxseed gum solution used is 5 wt.%.

[0061] "Let stand overnight" in the embodiments of this invention means letting the sample stand in the refrigerator at -3°C for 12 h.

[0062] Example 1 Preparation method of a polyvinyl alcohol-flaxseed gum composite sponge

[0063] S1. Use a 20 mL glass syringe to accurately measure 15 mL of flaxseed gum solution, transfer it to a 50 mL beaker, add 5 mL of a pre-prepared 10 wt.% polyvinyl alcohol aqueous solution, turn on the timing stirrer, set the rotation speed to 300 rpm, and stir for 5 min to obtain a mixed system of polyvinyl alcohol and flaxseed gum. The volume of this mixed system is 20 mL;

[0064] S2. Use a micropipette to accurately add 0.5 mL of n-pentane to the mixed system obtained in S1, immediately seal the bottle mouth with a sealing film, set the rotation speed to increase to 400 rpm, and continuously stir until the volume of the mixed system expands to 40 mL to form a stable foam system;

[0065] S3. Slowly add 1 mL of dilute sulfuric acid (5 wt.%) with a pipette, keep the stirring speed at 400 rpm, and continuously stir until the system volume stabilizes at 30 mL. During this period, monitor the pH value with pH test paper and it should drop to 5.0;

[0066] S4. Use a pipette to add 0.5 mL of 25 wt.% glutaraldehyde aqueous solution to the system obtained in S3, adjust the pH to 3 again, maintain stirring at 400 rpm at room temperature, and immediately stop stirring when the viscosity of the system significantly increases (the rotation speed of the magnetic stirrer decreases by ≥ 30%), re-seal the bottle mouth and let it stand for curing for 30 min;

[0067] S5. Transfer the sample obtained by curing in S4 to a petri dish, spread it into a thickness of 1 cm, place it in a DHG-9070A type electrothermal blast drying oven, dry it at 70 °C for 10 min, take it out and cool it to constant weight at room temperature, then transfer it to a 4 °C refrigerator and let it stand overnight.

[0068] S6. Pre-cool the FD-1A-50 type freeze dryer to -50 °C, place the sample obtained in S5 in the cold trap and quickly freeze it to below -40 °C, turn on the vacuum pump, maintain the pressure ≤ 10 Pa, continuously freeze-dry until completely dried, to obtain a polyvinyl alcohol - flaxseed gum composite sponge, take out the sample, seal it and store it in a desiccator for standby.

[0069] Example 2

[0070] S1. Use a 20 mL glass syringe to accurately measure 15 mL of flaxseed gum solution, transfer it to a 50 mL beaker, add 5 mL of pre-prepared 10 wt.% polyvinyl alcohol aqueous solution, turn on the timing stirrer, set the rotation speed to 300 rpm, and stir for 5 min to obtain a mixed system of polyvinyl alcohol and flaxseed gum, and the volume of this mixed system is 20 mL;

[0071] S2. Use a micropipette to accurately add 0.5 mL of n-pentane to the mixed system obtained in S1, immediately seal the bottle mouth with a sealing film, set the rotation speed to 400 rpm, and continuously stir until the volume of the mixed system expands to 40 mL to form a stable foam system;

[0072] S3. Slowly add 1 mL of dilute sulfuric acid (5 wt.%) with a pipette, maintain the stirring speed at 400 rpm, and continuously stir until the volume of the system stabilizes at 30 mL. During this period, monitor the pH value with pH test paper and it should drop to 5;

[0073] S4. Use a pipette to add 1.5 mL of 25 wt.% glutaraldehyde aqueous solution to the system obtained in S3, adjust the pH to 3 again, maintain stirring at 400 rpm at room temperature, and immediately stop stirring when the viscosity of the system significantly increases (the rotation speed of the magnetic stirrer decreases by ≥ 30%), re-seal the bottle mouth and let it stand for curing for 30 min;

[0074] S5. Transfer the sample obtained by curing in S4 to a petri dish, spread it into a thickness of 1 cm, place it in a DHG-9070A type electrothermal blast drying oven, dry it at 70 °C for 10 min, take it out and cool it to constant weight at room temperature, then transfer it to a 4 °C refrigerator and let it stand overnight.

[0075] S6. Pre-cool the FD-1A-50 type freeze dryer to -50°C, place the sample obtained in S5 in the cold trap and quickly freeze it to below -40°C. Turn on the vacuum pump, maintain the pressure ≤ 10 Pa, and continue freeze-drying until completely dried to obtain a polyvinyl alcohol-flaxseed gum composite sponge. Take out the sample, seal it and store it in a desiccator for later use.

[0076] Example 3

[0077] S1. Use a 20 mL glass syringe to accurately measure 15 mL of flaxseed gum solution, transfer it to a 50 mL beaker, add 5 mL of the pre-prepared 10 wt.% polyvinyl alcohol aqueous solution, turn on the timing stirrer, set the rotation speed to 300 rpm, and stir for 5 min to obtain a mixed system of polyvinyl alcohol and flaxseed gum. The volume of this mixed system is 20 mL.

[0078] S2. Use a micropipette to accurately add 0.5 mL of n-pentane to the mixed system obtained in S1, immediately seal the bottle mouth with a sealing film, set the rotation speed to increase to 400 rpm and continue stirring until the volume of the mixed system expands to 40 mL to form a stable foam system.

[0079] S3. Slowly add 1 mL of dilute sulfuric acid (5 wt.%) with a pipette, keep the stirring speed at 400 rpm, and continue stirring until the system volume stabilizes at 30 mL. During this period, monitor the pH value with a pH test paper and it should drop to 5.

[0080] S4. Use a pipette gun to add 1.0 mL of 25 wt.% glutaraldehyde aqueous solution to the system obtained in S3, adjust the pH to 3 again, keep stirring at 400 rpm at room temperature, and immediately stop stirring when the system viscosity increases significantly (the rotation speed of the stirrer decreases by ≥ 30%). Re-seal the bottle mouth and let it stand for curing for 30 min.

[0081] S5. Transfer the sample obtained by curing in S4 to a petri dish, spread it into a thickness of 1 cm, place it in a DHG-9070A type electrothermal blast drying oven, dry it at 70°C for 10 min, take it out and cool it to constant weight at room temperature, and then transfer it to a 4°C refrigerator and let it stand overnight.

[0082] S6. Pre-cool the FD-1A-50 type freeze dryer to -50°C, place the sample obtained in S5 in the cold trap and quickly freeze it to below -40°C. Turn on the vacuum pump, maintain the pressure ≤ 10 Pa, and continue freeze-drying until completely dried to obtain a polyvinyl alcohol-flaxseed gum composite sponge. Take out the sample, seal it and store it in a desiccator for later use.

[0083] Figure 1 is a cross-sectional view of the polyvinyl alcohol-flaxseed gum composite sponge prepared in Example 3. As can be seen from Figure 1 it, the composite sponge prepared by the present invention has a uniform texture and dense pores.

[0084] Figure 2 The infrared spectrum of the polyvinyl alcohol - flaxseed gum composite sponge prepared in Example 3; It can be seen from Figure 2 that this composite sponge has many groups and has a significant adsorption effect on lead ions.

[0085] Example 4

[0086] S1. Use a 20 mL glass syringe to accurately measure 18 mL of flaxseed gum solution, transfer it to a 50 mL beaker, add 2 mL of the pre - prepared 10 wt.% polyvinyl alcohol aqueous solution, turn on the timing stirrer, set the rotation speed to 300 rpm, and stir for 5 min to obtain a mixed system of polyvinyl alcohol and flaxseed gum. The volume of this mixed system is 20 mL;

[0087] S2. Use a micropipette to accurately add 0.5 mL of n - pentane to the mixed system obtained in S1, immediately seal the bottle mouth with a sealing film, set the rotation speed to be increased to 400 rpm, continuously stir until the volume of the mixed system expands to 40 mL, and quickly cool to room temperature to form a stable foam system;

[0088] S3. Slowly add 1 mL of dilute sulfuric acid (5 wt.%) with a pipette, keep the stirring speed at 400 rpm, continuously stir until the system volume stabilizes at 30 mL, and monitor the pH value with pH test paper during this period, which should drop to 5;

[0089] S4. Use a pipette gun to add 1.0 mL of 25 wt.% glutaraldehyde aqueous solution to the system obtained in S3, adjust the pH to 3 again, keep stirring at 400 rpm at room temperature, turn off the magnetic stirrer when the system viscosity increases significantly, take out the rotor, reseal the bottle mouth and let it stand for curing for 30 min;

[0090] S5. Transfer the sample obtained by curing in S4 to a petri dish, spread it into a 1 cm thickness, place it in a DHG - 9070A type electro - thermal blast drying oven, dry it at 70 °C for 10 min, take it out and cool it to constant weight at room temperature, then transfer it to a 4 °C refrigerator and let it stand overnight.

[0091] S6. Pre - cool the FD - 1A - 50 type freeze - dryer to - 50 °C, place the sample obtained in S5 in the cold trap and quickly freeze it to below - 40 °C, turn on the vacuum pump, maintain the pressure ≤ 10 Pa, continuously freeze - dry until it is completely freeze - dried, then obtain the polyvinyl alcohol - flaxseed gum composite sponge, take out the sample, seal it and store it in a desiccator for standby.

[0092] Comparative Example 1

[0093] Same as Example 3, the difference is that 15 mL of flaxseed gum solution is replaced with the pre - prepared 10 wt.% polyvinyl alcohol aqueous solution in equal volume. The specific operation is as follows:

[0094] S1. Use a 20 mL glass syringe to accurately measure 20 mL of the pre-prepared 10 wt.% polyvinyl alcohol aqueous solution. Turn on the timing stirrer, set the rotation speed to 300 rpm, and stir for 5 min to obtain a polyvinyl alcohol system with a volume of 20 mL.

[0095] S2 - S6 are the same as in Example 1.

[0096] Comparative Example 2

[0097] Same as Example 1, except that the volumes of the flaxseed colloid solution and the pre-prepared 10 wt.% polyvinyl alcohol aqueous solution added in S1 are different. The specific operation is as follows:

[0098] Use a 20 mL glass syringe to accurately measure 5 mL of the flaxseed colloid solution, transfer it to a 50 mL beaker, add 15 mL of the pre-prepared 10 wt.% polyvinyl alcohol aqueous solution, turn on the timing stirrer, set the rotation speed to 300 rpm, and stir for 5 min to obtain a mixed system of polyvinyl alcohol and flaxseed gum. The volume of this mixed system is 20 mL.

[0099] S2 - S6 are the same as in Example 1.

[0100] Comparative Example 3

[0101] Same as Example 2, except that the volumes of the flaxseed colloid solution and the pre-prepared 10 wt.% polyvinyl alcohol aqueous solution added in S1 are different. The specific operation is as follows:

[0102] Use a 20 mL glass syringe to accurately measure 5 mL of the flaxseed colloid solution, transfer it to a 50 mL beaker, add 15 mL of the pre-prepared 10 wt.% polyvinyl alcohol aqueous solution, turn on the timing stirrer, set the rotation speed to 300 rpm, and stir for 5 min to obtain a mixed system of polyvinyl alcohol and flaxseed gum. The volume of this mixed system is 20 mL.

[0103] S2 - S6 are the same as in Example 2.

[0104] Performance Test

[0105] 1. Removal rate test of lead ions by the composite sponges prepared in Examples 1 - 4 and Comparative Examples 1 - 3

[0106] Weigh different masses of lead chloride. Based on lead ions, prepare lead ion solutions with initial concentrations of 10 mg / L, 50 mg / L, and 100 mg / L (pH = 5) respectively. Add the composite sponges prepared in Examples 1 - 4 and Comparative Examples 1 - 3 to the above lead ion solutions at a ratio of 0.3 g composite sponge / 30 mL. At room temperature, test the adsorption performance of the above composite sponges for lead ions after soaking and adsorbing for 10 min. The test results are shown in Table 1.

[0107] Table 1

[0108]

[0109]

[0110] As can be seen from Table 1, within 10 minutes, the composite sponges prepared in Examples 1-4 have high adsorption performance for lead ion solutions with concentrations of 10 mg / L and 50 mg / L. When the lead ion concentration reaches 100 mg / L, the adsorption performance decreases due to reaching the saturation state. In Comparative Example 1, no colloidal solution was added, resulting in a significant decrease in the adsorption performance of the obtained composite sponge, indicating that the hierarchical porous structure constructed by the amphiphilic molecules of polyvinyl alcohol and linseed gum is particularly important for the adsorption performance. Compared with Example 1 in Comparative Example 2 and with Example 2 in Comparative Example 3, too little colloidal solution and too much polyvinyl alcohol were added, leading to a decrease in the adsorption performance, indicating that linseed gum is crucial for the construction of the porous structure during sponge preparation. Its surface activity can reduce the surface tension of the gas-liquid interface, promote the formation of bubbles and retain them as porous structures after curing; at the same time, it can form a stable protective film on the surface of the bubbles, increase the viscosity of the system, inhibit the rupture and coalescence of bubbles, and ensure the uniformity and stability of the porous structure; by adjusting its dosage and process parameters, the pore size and porosity can be effectively regulated; in addition, it can also adsorb and deposit on the pore wall, improving the surface properties of the pore wall (such as smoothness or roughness), thereby affecting the physical properties and adsorption loading capacity of the sponge, and playing multiple key roles in the formation, stability, pore size regulation and pore wall optimization of the porous structure.

[0111] 2. Removal rate of lead ions at different pH values

[0112] At different pH values (adsorption time is 10 minutes, 0.3 g of composite sponge / 30 mL), the removal rate of lead ions in the lead ion solution with an initial concentration of 10 mg / L by the polyvinyl alcohol-linseed gum composite sponge prepared in Example 3 was investigated, and the test results are shown in Table 2.

[0113] Table 2

[0114]

[0115]

[0116] As can be seen from Table 2, the pH of the solution will affect the adsorption performance of the composite sponge. When the pH is too large (≥8) or too small (≤4), the adsorption performance of the composite sponge prepared in the present invention for lead ions will decrease. Therefore, when adsorbing lead ions, the pH of the solution needs to be adjusted to 5-7.

[0117] 3. Removal rate of lead ions at different times

[0118] The removal rate of lead ions by the polyvinyl alcohol - flaxseed gum composite sponge prepared in Example 3 was investigated at different adsorption times (lead ion solution with an initial concentration of 10 mg / L, pH = 5, 0.3 g composite sponge / 30 mL). The test results are shown in Table 3.

[0119] Table 3

[0120]

[0121] As can be seen from Table 3, the polyvinyl alcohol - flaxseed gum composite sponge prepared in the present invention can effectively adsorb lead ions within a short time (5 - 10 min), and basically achieve complete adsorption within 2 h.

[0122] 4. Experiment on repeated use

[0123] An experiment on the repeated use of lead ion adsorption was carried out using the polyvinyl alcohol - flaxseed gum composite sponge prepared in Example 3. The specific operation is as follows: Prepare a lead chloride solution with an initial concentration of 10 mg / L in terms of the mass concentration of lead ions (pH = 5), the adsorption dosage is 0.1 g sponge / 50 mL lead ion solution, shake at room temperature for 6 h, measure the removal rate after complete adsorption, soak the composite sponge in 0.1 M HNO3 for 2 h for desorption after taking it out, wash it with deionized water until neutral and then dry it, and repeat the above process five times. The measurement results are shown in Table 4.

[0124] Table 4

[0125]

[0126]

[0127] As can be seen from Table 4, the polyvinyl alcohol - flaxseed gum composite sponge prepared in the present invention still has a certain adsorption performance after being reused several times and can be reused 1 - 3 times.

[0128] 5. Hydrophilicity test experiment

[0129] The hydrophilicity of the composite sponges prepared in Examples 1 - 4 and Comparative Examples 1 - 3 was tested. The specific test method was the contact angle measurement method. By measuring the static contact angle formed by water droplets on the material surface, the hydrophilicity was judged. The contact angle test results of each composite sponge after 1 s are shown in Table 5.

[0130] Table 5

[0131]

[0132] As can be seen from Table 5, the composite sponge has good hydrophilicity.

[0133] 6. Adsorption performance test for different metal ions

[0134] Weigh lead chloride, copper chloride, cadmium chloride and chromium chloride. Based on the mass concentrations of lead ions, copper ions, cadmium ions and chromium ions, prepare the above metal ion solutions with a concentration of 10 mg / L respectively (pH is 5.5 at 25 °C). Place the polyvinyl alcohol - flaxseed gum composite sponge prepared in Example 3 into the above solutions (adsorption dosage: 0.3 g composite sponge / 30 mL metal ion solution), and the adsorption time is 24 h to ensure adsorption equilibrium. The measurement results are shown in Table 6.

[0135] Table 6

[0136] <![CDATA[Pb 2 +]]> Cu2+ <![CDATA[Cd 2 +]]> <![CDATA[Cr 3 +]]> Removal rate (%) 91.8 41.5 28.3 15.6

[0137] It can be seen from Table 6 that the polyvinyl alcohol - flaxseed gum composite sponge prepared by the present invention has a high selectivity for lead ions.

[0138] The above is only the preferred specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any change or replacement that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A preparation method of a polyvinyl alcohol - flaxseed gum composite sponge, characterized in that, It includes the following steps: Mix and stir the linseed gum solution and the polyvinyl alcohol solution to obtain a mixed system; add n-pentane to the mixed system, add a rotor and seal it with plastic wrap, adjust the magnetic stirrer to 400 rpm and then start stirring until the expanded volume of the mixed system reaches 2 times the initial volume to obtain a stable foam system; add an acid solution to the stable foam system for acid-catalyzed crosslinking and adjust the pH for the first time; then add an aqueous glutaraldehyde solution, adjust the pH again, and carry out chemical crosslinking and curing; dry to prepare the polyvinyl alcohol-linseed gum composite sponge.

2. The preparation method according to claim 1, wherein The volume ratio of the linseed gum solution to the polyvinyl alcohol solution is (15-18):(2-5); and / or, the mass concentration of the polyvinyl alcohol solution is 10%; and / or, the mass concentration of the linseed gum solution is 5%.

3. The preparation method according to claim 1, wherein, The volume ratio of the n-pentane to the mixed system is 1:

40.

4. The preparation method according to claim 1, characterized in that, The first pH adjustment is 3.5-5.

0.

5. The preparation method according to claim 1, wherein The volume ratio of the aqueous glutaraldehyde solution to the mixed system is (0.1-0.3):4; and / or, the mass concentration of the aqueous glutaraldehyde solution is 25%.

6. The preparation method according to claim 1, wherein The time for the chemical crosslinking and curing is 30 min; and / or, the second pH adjustment is 3.

7. A polyvinyl alcohol-linseed gum composite sponge prepared by the preparation method according to any one of claims 1-6.

8. Use of the polyvinyl alcohol - flaxseed gum composite sponge according to claim 7 in the treatment of heavy metal ion - contaminated wastewater, characterized in that, The pH of the heavy metal ion-polluted wastewater is adjusted to 5-7.

9. The application according to claim 9, wherein The heavy metal ion is lead ion.

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