Polyvinyl alcohol-based heteropoly acid composite foam material and preparation method thereof

Abstract

This invention discloses a polyvinyl alcohol-based heteropolyacid composite foam material and its preparation method. The polyvinyl alcohol-based foam material with a three-dimensional network structure is prepared through a physical foaming-chemical crosslinking method, and heteropolyacid anions are in situ composited onto it. When dye wastewater containing micron-sized emulsified oil passes through the composite foam material of this invention, the emulsified oil droplets (which are hydrophobic) are rapidly and massively retained by the superhydrophilic network structure of polyvinyl alcohol, while the dye is adsorbed by the heteropolyacid material, resulting in relatively pure water. After the material adsorbs the dye, the hydroxyl groups in its superhydrophilic substrate environment generate intermediate-state coordination compounds with the heteropolyacid anions, promoting charge transfer. Under visible or ultraviolet light irradiation, this effectively degrades dye molecules at a rate 30 times faster than that of pure heteropolyacid anions of the same mass, thus rapidly restoring the initial state and effectively improving wastewater treatment efficiency. This method is suitable for large-scale dye wastewater treatment.

Description

Technical Field

[0001] This invention belongs to the field of water treatment materials, and in particular to a polyvinyl alcohol-based heteropolyacid composite foam material and its preparation method. Background Technology

[0002] Dye wastewater, containing large amounts of organic pollutants, is characterized by high color intensity, complex composition, difficulty in biodegradation, high toxicity, and carcinogenicity, making it a crucial research topic in the chemical and environmental fields. Traditional treatment methods mainly include physical, biological, and chemical methods. Physical treatment methods include flotation, ion exchange, membrane separation, ultrafiltration / nanofiltration, and adsorption. Biological treatment methods mainly include aerobic, anaerobic, and combined methods, utilizing the oxidation, reduction, and hydrolysis activities of microorganisms to break down unsaturated chemical bonds and chromophores in the structure of organic pollutants, ultimately degrading the organic pollutants in the wastewater into harmless inorganic substances. Chemical treatment methods utilize the oxidation of organic molecules by oxidants to destroy their internal structure, thus degrading them. Photocatalytic degradation is the most promising method among chemical treatment methods. Photocatalytic degradation can degrade organic pollutants under mild conditions with less secondary pollution, and has become one of the key research areas both domestically and internationally.

[0003] Polyoxometalates (POMs) are a class of metal-oxygen clusters composed of transition metals. They are heteropolyanions formed by the condensation of different oxyacids. Under visible or ultraviolet light irradiation, they undergo oxidation or reduction reactions and have been applied to photocatalytic degradation catalysts. Polyvinyl alcohol (PVA) is a three-dimensional network foam material with superhydrophilic porosity, capable of physically separating and filtering lipophilic organic droplets from wastewater. To date, there are no reports on polyvinyl alcohol-based heteropolyacid composite foam materials. Summary of the Invention

[0004] The present invention aims to solve the above-mentioned technical problems existing in the prior art by providing a polyvinyl alcohol-based heteropolyacid composite foam material and its preparation method.

[0005] The technical solution of this invention is: a polyvinyl alcohol-based heteropolyacid composite foam material, wherein heteropolyacid anions are in situ composited onto a polyvinyl alcohol-based foam material with a three-dimensional network structure via chitosan. Preferably, the heteropolyacid is phosphotungstic acid or silicotungstic acid.

[0006] A method for preparing the above-mentioned polyvinyl alcohol-based heteropolyacid composite foam material comprises the following steps:

[0007] Step 1. Prepare polyvinyl alcohol foam solution;

[0008] Step 2. Prepare a chitosan aqueous solution. Pour the chitosan aqueous solution into a polyvinyl alcohol foam solution, heat and stir in an oil bath until the maximum volume is reached, then add the heteropolyacid. Continue heating and stirring in an oil bath, then place in an oven for curing and crosslinking. Afterward, wash with deionized water and dry in an oven to constant weight to obtain a polyvinyl alcohol-chitosan-heteropolyacid composite foam material. The mass ratio of chitosan to polyvinyl alcohol is 1:15-25; the mass ratio of heteropolyacid to polyvinyl alcohol is 1:80-120.

[0009] The preferred curing and crosslinking temperature is 50-80℃, and the curing and crosslinking time is 3-5h.

[0010] The preferred step 1 is to prepare a polyvinyl alcohol foam solution according to the following steps: weigh polyvinyl alcohol and pour it into a flask, add deionized water until the mass concentration of polyvinyl alcohol is 5-20%, heat and stir in an oil bath, then add aldehyde and surfactant and stir to form liquid foam, pour H2SO4 into the liquid foam and continue stirring until the maximum volume is reached to form a polyvinyl alcohol foam solution.

[0011] Preferably, the aldehyde is formaldehyde or glutaraldehyde, and the mass ratio of formaldehyde to polyvinyl alcohol is 2-1:1-2.

[0012] The preferred surfactant is Triton X-100, sodium hexadecylbenzenesulfonate, or dodecyl ammonium chloride, with a mass ratio of 1:5-15 to polyvinyl alcohol.

[0013] Preferably, the sulfuric acid is a 50% (w / w) solution with a (w / w) mass ratio of 2-1:1-2 to polyvinyl alcohol.

[0014] This invention prepares a polyvinyl alcohol-based foam material with a three-dimensional network structure through a physical foaming-chemical crosslinking method, and then in-situ composites heteropolyacid anions onto it. When dye wastewater containing micron-sized emulsified oil passes through the composite foam material of this invention, the emulsified oil droplets (which are hydrophobic) are rapidly and massively trapped by the superhydrophilic network structure of polyvinyl alcohol, while the dye is adsorbed by the heteropolyacid material, resulting in relatively pure water. After the material adsorbs the dye, the hydroxyl groups in its superhydrophilic substrate environment generate intermediate-state coordination compounds with the heteropolyacid anions, promoting charge transfer. Under visible or ultraviolet light irradiation, this effectively degrades dye molecules at a rate 30 times faster than that of pure heteropolyacid anions of the same mass, thus rapidly restoring the initial state and effectively improving wastewater treatment efficiency, making it suitable for large-scale dye wastewater treatment. Attached Figure Description

[0015] Figure 1 This is a macroscopic photograph of the polyvinyl alcohol-based heteropolyacid composite foam material of Example 1 of the present invention.

[0016] Figure 2This is a scanning electron microscope image of the polyvinyl alcohol-based heteropolyacid composite foam material of Example 1 of the present invention.

[0017] Figure 3 This is a macroscopic schematic diagram of the filtration of an aqueous solution containing micron-sized toluene droplets by the polyvinyl alcohol-based heteropolyacid composite foam material of Example 1 of the present invention.

[0018] Figure 4 This is a macroscopic schematic diagram of the degradation of methyl orange (MO) in the polyvinyl alcohol-based heteropolyacid composite foam material of Example 1 of the present invention under sunlight irradiation.

[0019] Figure 5 This is a comparison chart showing the degradation of methyl orange (MO) in the polyvinyl alcohol-based heteropolyacid composite foam material of Example 1 of the present invention and the control sample under sunlight irradiation. Detailed Implementation

[0020] Example 1:

[0021] The preparation method of the polyvinyl alcohol-based heteropolyacid composite foam material of the present invention is carried out according to the following steps:

[0022] Step 1. Prepare polyvinyl alcohol foam solution;

[0023] First, weigh 10g of polyvinyl alcohol (PVA) and pour it into a round-bottom flask. Add 50g of deionized water and heat in an oil bath at 90°C for 1 hour. Then add 10.9g of formaldehyde and 1g of Triton X-100 to form liquid foam. Add 13.2g of 50wt% H2SO4 to the liquid foam and continue stirring until the maximum volume is reached to form a polyvinyl alcohol foam solution.

[0024] Step 2. Weigh 0.5g of chitosan (CS) and add 20g of deionized water to prepare a chitosan aqueous solution. Pour the chitosan aqueous solution into the polyvinyl alcohol foam solution and continue heating in an oil bath at 90℃ for 0.5h until the maximum volume is reached. Then, weigh 0.1g of phosphotungstic acid (PW12) and add 10g of deionized water to the mixed solution and continue heating in an oil bath at 90℃ for 0.5h. After stopping heating, place it in a 60℃ oven for curing and crosslinking for 5h. Finally, wash the prepared foam material with deionized water 5-6 times to remove unreacted substances, and continue drying it in a 60℃ oven until constant weight to obtain polyvinyl alcohol-chitosan-phosphotungstic acid composite foam material (PVA-CS-PW12).

[0025] Example 2:

[0026] The preparation method of the polyvinyl alcohol-based heteropolyacid composite foam material of the present invention is carried out according to the following steps:

[0027] Step 1. Prepare polyvinyl alcohol foam solution;

[0028] First, weigh 10g of polyvinyl alcohol (PVA) and pour it into a round-bottom flask. Add 50g of deionized water and heat in an oil bath at 90°C for 1 hour. Then add 10.9g of formaldehyde and 1g of Triton X-100 to form liquid foam. Add 13.2g of 50wt% H2SO4 to the liquid foam and continue stirring until the maximum volume is reached to form a polyvinyl alcohol foam solution.

[0029] Step 2. Weigh 0.5g of chitosan (CS) and add 20g of deionized water to prepare a chitosan aqueous solution. Pour the chitosan aqueous solution into the polyvinyl alcohol foam solution and continue heating in an oil bath at 90℃ for 0.5h until the maximum volume is reached. Then, weigh 0.1g of silicic acid (SiW12) and add 10g of deionized water to the mixed solution and continue heating in an oil bath at 90℃ for 0.5h. After stopping heating, place it in a 60℃ oven for curing and crosslinking for 5h. Finally, wash the prepared foam material with deionized water 5-6 times to remove unreacted substances, and continue drying it in a 60℃ oven until constant weight to obtain polyvinyl alcohol-chitosan-silicotungstic acid composite foam material (PVA-CS-SiW12).

[0030] Macroscopic photographs of the polyvinyl alcohol-based heteropolyacid composite foam material of Example 1 of this invention are shown below. Figure 1 As shown, the microscopic scanning electron microscope image is as follows: Figure 2 As shown. By Figure 1 and Figure 2 It can be seen that the polyvinyl alcohol-based heteropolyacid composite foam material obtained in Example 1 of the present invention is a three-dimensional porous material.

[0031] A macroscopic schematic diagram of the filtration of an aqueous solution containing micron-sized toluene droplets by the polyvinyl alcohol-based heteropolyacid composite foam material of Example 1 of this invention is shown below. Figure 3 As shown. By Figure 3 As can be seen, after filtering an aqueous solution containing toluene droplets using the polyvinyl alcohol-based heteropolyacid composite foam material of Example 1 of the present invention, the originally turbid toluene solution (upper part of the photo) becomes a clear and transparent aqueous solution (lower part).

[0032] A macroscopic schematic diagram of the degradation of methyl orange (MO) under sunlight after adsorption by the polyvinyl alcohol-based heteropolyacid composite foam material of Example 1 of this invention. Figure 4 It can be seen that after the material adsorbs methyl orange, the methyl orange degrades under sunlight, and the material becomes colorless again.

[0033] Example 1 of this invention: A comparative graph showing the degradation of methyl orange (MO) after adsorption of methyl orange (MO) in polyvinyl alcohol-based heteropolyacid composite foam material (PVA-CS-PW12) and control samples (PVA-CS and PW12) under sunlight is shown. Figure 5 As shown. By Figure 5It can be seen that under sunlight irradiation, compared with PVA-CS and PW12, PVA-CS shows almost no dye degradation, PW12 degrades slowly, and PVA-CS-PW12 degrades rapidly, 30 times faster than PW12. The improved catalytic degradation rate of PVA-CS-PW12 in this invention may be attributed to the formation of intermediate coordination compounds between the superhydrophilic hydroxyl groups in the foam material and the catalytically active heteropolyacid anions, promoting charge transfer. Therefore, the synergistic effect greatly promotes the degradation rate of the material, far exceeding other similar modification methods currently available.

Claims

1. A polyvinyl alcohol-based heteropolyacid composite foam material, characterized in that: Heteropolyacid anions are in situ composited with chitosan onto a polyvinyl alcohol-based foam material with a three-dimensional network structure. The heteropolyacid is phosphotungstic acid or silicotungstic acid. The preparation is carried out according to the following steps: Step 1. Preparation of polyvinyl alcohol foam solution: Weigh polyvinyl alcohol and pour it into a flask, add deionized water until the mass concentration of polyvinyl alcohol is 5-20%, heat and stir in an oil bath, then add aldehyde and surfactant and stir to form liquid foam, pour sulfuric acid into the liquid foam and continue stirring until the maximum volume is reached to form polyvinyl alcohol foam solution; Step 2. Prepare a chitosan aqueous solution. Pour the chitosan aqueous solution into a polyvinyl alcohol foam solution, heat and stir in an oil bath until the maximum volume is reached, then add heteropolyacid. Continue heating and stirring in an oil bath, then place in an oven for curing and crosslinking. Afterward, wash with deionized water and dry in an oven to constant weight to obtain a polyvinyl alcohol-chitosan-heteropolyacid composite foam material. The mass ratio of chitosan to polyvinyl alcohol is 1:15~25; the mass ratio of heteropolyacid to polyvinyl alcohol is 1:80~120; the curing and crosslinking temperature is 50~80℃; and the curing and crosslinking time is 3~5 h.

2. The method for preparing polyvinyl alcohol-based heteropolyacid composite foam material according to claim 1, characterized in that... The aldehyde is formaldehyde or glutaraldehyde, and the mass ratio of formaldehyde to polyvinyl alcohol is 2-1:1-2.

3. The method for preparing polyvinyl alcohol-based heteropolyacid composite foam material according to claim 2, characterized in that... The surfactant is Triton X-100, sodium hexadecylbenzenesulfonate, or dodecyl ammonium chloride, and the mass ratio of the surfactant to polyvinyl alcohol is 1:5-15.

4. The method for preparing polyvinyl alcohol-based heteropolyacid composite foam material according to claim 3, characterized in that... The sulfuric acid is a 50% (w / w) solution, and its mass ratio with polyvinyl alcohol is 2-1:1-2.

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