Polyvinyl alcohol-based heteropolyacid composite foam material and preparation method thereof

Abstract

The invention discloses a polyvinyl alcohol-based heteropolyacid composite foam material and a preparation method thereof, the polyvinyl alcohol-based foam material with a three-dimensional network structure is prepared by a physical foaming-chemical crosslinking method, and heteropolyacid anions are compounded on the polyvinyl alcohol-based foam material in situ. When dye wastewater containing micron-sized emulsified oil passes through the composite foam material disclosed by the invention, emulsified oil drops (hydrophobic) can be quickly intercepted by the polyvinyl alcohol with the super-hydrophilic network structure in a large scale, and dye can be adsorbed by the heteropolyacid material, so that relatively pure water is obtained. After the material adsorbs dye, hydroxyl in the super-hydrophilic substrate environment and heteropolyacid anions generate an intermediate-state coordination compound, transfer of charges is promoted, dye molecules are effectively degraded under irradiation of visible light or ultraviolet light, the degradation rate is 30 times that of pure heteropolyacid anions with the same mass, and then the initial state is rapidly recovered. The method effectively improves wastewater treatment efficiency and is suitable for large-scale dye wastewater treatment.

Description

Technical Field

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

[0002] Dye wastewater has always been a very important research topic in the chemical and environmental protection fields because it contains a large amount of organic pollutants, has high chromaticity, complex composition, difficult biodegradation, high toxicity, and is carcinogenic. Traditional treatment methods mainly include physical treatment, biological treatment, and chemical treatment. Physical treatment methods include flotation, ion exchange, membrane separation, ultrafiltration, nanofiltration, and adsorption. Biological treatment methods mainly include aerobic, anaerobic, and two combined methods. They use some oxidation, reduction, and hydrolysis activities of microorganisms to destroy the unsaturated chemical bonds and chromophores in the structure of organic pollutants, and ultimately degrade the organic pollutants in the wastewater into non-polluting inorganic substances. Chemical treatment methods use the oxidation of oxidants to destroy the internal structure of organic molecules and thus degrade 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 at home and abroad.

[0003] Polyoxometalates (POMs) are a type of metal-oxygen clusters composed of transition metals. They are formed by the condensation of different oxygen-containing acids into heteropoly anions. Under the conditions of visible light or ultraviolet light, they undergo oxidation or reduction reactions and have been used as photocatalytic degradation catalysts. Polyvinyl alcohol (PVA) is a foam material with a three-dimensional network structure. It has super-hydrophilic porosity and can physically separate and filter out lipophilic organic phase droplets in wastewater. So far, there have been no reports on polyvinyl alcohol-based heteropoly acid composite foam materials. Summary of the invention

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

[0005] The technical solution of the present invention is: a polyvinyl alcohol-based heteropoly acid composite foam material, on which a polyvinyl alcohol-based foam material having a three-dimensional network structure is in-situ composited with heteropoly acid anions through chitosan. Preferably, the heteropoly acid is phosphotungstic acid or silicotungstic acid.

[0006] A method for preparing the above-mentioned polyvinyl alcohol-based heteropolyacid composite foam material is carried out according to the following steps:

[0007] Step 1. preparing a 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, then add a heteropoly acid, continue heating and stirring in the oil bath, and then put it into an oven for curing and cross-linking, then wash with deionized water, put it into an oven and dry it 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] Preferably, the curing and cross-linking temperature is 50-80° C., and the curing and cross-linking time is 3-5 hours.

[0010] Preferably, the 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 to a mass concentration of 5-20% of the polyvinyl alcohol, heat and stir in an oil bath, then add aldehyde and a surfactant and stir to form liquid foam, pour H2SO4 into the liquid foam and continue to stir 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 the aldehyde to polyvinyl alcohol is 2-1:1-2.

[0012] Preferably, the surfactant is Triton X-100, sodium hexadecylbenzenesulfonate or dodecylammonium chloride, and the mass ratio of the surfactant to polyvinyl alcohol is 1:5-15.

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

[0014] The present invention prepares a polyvinyl alcohol-based foam material with a three-dimensional network structure by a physical foaming-chemical crosslinking method, and in-situ composites heteropolyacid anions thereon. When dye wastewater containing micron-sized emulsified oil passes through the composite foam material of the present invention, the emulsified oil droplets (being hydrophobic) will be quickly and in large quantities intercepted by the super-hydrophilic network structure polyvinyl alcohol, and the dye will be adsorbed by the heteropolyacid material, thereby obtaining relatively pure water. After the material adsorbs the dye, the hydroxyl groups of the super-hydrophilic substrate environment and the heteropolyacid anions generate intermediate state coordination compounds, promote the transfer of charges, effectively degrade the dye molecules under visible light or ultraviolet light irradiation, and the degradation rate is 30 times that of pure heteropolyacid anions under the same mass, thereby quickly recovering to the initial state, effectively improving the wastewater treatment efficiency, and being suitable for large-scale dye wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[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 microscopic 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.

[0019] Figure 5 This is a comparative diagram of the degradation of methyl orange (MO) of the polyvinyl alcohol-based heteropolyacid composite foam material of Example 1 of the present invention and a comparative sample under sunlight irradiation. DETAILED DESCRIPTION

[0020] Embodiment 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. preparing a polyvinyl alcohol foam solution;

[0023] First, 10 g of polyvinyl alcohol (PVA) was weighed and poured into a round-bottom flask, 50 g of deionized water was added thereto, and the mixture was heated in an oil bath at 90° C. and stirred for 1 h; then 10.9 g of formaldehyde and 1 g of Triton X-100 were added to form liquid foam; 13.2 g of 50 wt% H2SO4 was poured into the liquid foam and stirred until the maximum volume was reached to form a polyvinyl alcohol foam solution;

[0024] Step 2. Weigh 0.5g chitosan (CS) and add 20g deionized water to prepare a chitosan aqueous solution, pour the chitosan aqueous solution into the polyvinyl alcohol foam solution, and continue to heat it in a 90°C oil bath for 0.5h to the maximum volume; then, weigh 0.1g phosphotungstic acid (PW12) and add 10g deionized water, pour it into the mixed solution and continue to heat it in a 90°C oil bath for 0.5h; after stopping heating, put it in a 60°C oven for curing and crosslinking for 5h; finally, wash the prepared foam material with deionized water 5-6 times to wash away the unreacted substances, and continue to put it in a 60°C oven to dry to constant weight to obtain a polyvinyl alcohol-chitosan-phosphotungstic acid composite foam material (PVA-CS-PW12).

[0025] Embodiment 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. preparing a polyvinyl alcohol foam solution;

[0028] First, 10 g of polyvinyl alcohol (PVA) was weighed and poured into a round-bottom flask, 50 g of deionized water was added thereto, and the mixture was heated in an oil bath at 90° C. and stirred for 1 h; then 10.9 g of formaldehyde and 1 g of Triton X-100 were added to form liquid foam; 13.2 g of 50 wt% H2SO4 was poured into the liquid foam and stirred until the maximum volume was reached to form a polyvinyl alcohol foam solution;

[0029] Step 2. Weigh 0.5g chitosan (CS) and add 20g deionized water to prepare a chitosan aqueous solution, pour the chitosan aqueous solution into the polyvinyl alcohol foam solution, and continue to heat it in a 90°C oil bath for 0.5h to the maximum volume; then, weigh 0.1g silicophosphate (SiW12) and add 10g deionized water, pour it into the mixed solution and continue to heat it in a 90°C oil bath for 0.5h; after stopping the heating, put it in a 60°C oven for curing and crosslinking for 5h; finally, wash the prepared foam material with deionized water 5-6 times to wash away the unreacted substances, and continue to put it in a 60°C oven to dry to constant weight to obtain a polyvinyl alcohol-chitosan-silicotungstic acid composite foam material (PVA-CS-SiW12).

[0030] The macroscopic photograph of the polyvinyl alcohol-based heteropolyacid composite foam material of Example 1 of the present invention is as follows: Figure 1 As shown in the scanning electron microscope image Figure 2 As shown. 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] The macroscopic schematic diagram of the polyvinyl alcohol-based heteropolyacid composite foam material of Example 1 of the present invention filtering an aqueous solution containing micron-sized toluene droplets is shown in FIG. Figure 3 As shown. Figure 3 It can be seen that after the aqueous solution containing toluene droplets was filtered 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) turned into a clear and transparent aqueous solution (lower part).

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

[0033] The degradation comparison of methyl orange (MO) after adsorption of methyl orange (MO) by polyvinyl alcohol-based heteropolyacid composite foam material (PVA-CS-PW12) and comparative samples (PVA-CS and PW12) under sunlight is shown in the figure below: Figure 5 As shown. Figure 5It can be seen that under the irradiation of sunlight, PVA-CS-PW12 is compared with PVA-CS and PW12. PVA-CS has almost no dye degradation, the degradation rate of PW12 is slower, and the degradation rate of PVA-CS-PW12 is faster, which is 30 times the degradation rate of PW12. The reason for the improvement of the catalytic degradation rate of PVA-CS-PW12 of the present invention may be attributed to the super-hydrophilic hydroxyl group in the foam material and the catalytic heteropolyacid anion generating an intermediate state coordination compound, which promotes the transfer of charge. Therefore, the synergistic effect greatly promotes the degradation rate of the material, far exceeding other current modification methods of the same type.

Claims

1. A polyvinyl alcohol-based heteropolyacid composite foam material, characterized in that: The heteropolyacid anions are in-situ composited with chitosan on the polyvinyl alcohol-based foam material with a three-dimensional network structure.

2. The polyvinyl alcohol-based heteropolyacid composite foam material according to claim 1, characterized in that: The heteropoly acid is phosphotungstic acid or silicotungstic acid.

3. A method for preparing a polyvinyl alcohol-based heteropolyacid composite foam material as claimed in claim 1 or 2, characterized in that Follow these steps: Step 1. preparing a 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, then add a heteropoly acid, continue heating and stirring in the oil bath, and then put it into an oven for curing and cross-linking, then wash with deionized water, put it into an oven and dry it 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.

4. The method for preparing the polyvinyl alcohol-based heteropolyacid composite foam material according to claim 3, characterized in that: The curing and cross-linking temperature is 50-80° C., and the curing and cross-linking time is 3-5 hours.

5. The method for preparing the polyvinyl alcohol-based heteropolyacid composite foam material according to claim 4, characterized in that The 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 to a mass concentration of 5-20% of the polyvinyl alcohol, heat and stir in an oil bath, then add aldehyde and a surfactant and stir to form liquid foam, pour H2SO4 into the liquid foam and continue to stir until the maximum volume, to form a polyvinyl alcohol foam solution.

6. The method for preparing the polyvinyl alcohol-based heteropolyacid composite foam material according to claim 5, characterized in that The aldehyde is formaldehyde or glutaraldehyde, and the mass ratio of the aldehyde to polyvinyl alcohol is 2-1:1-2.

7. The method for preparing the polyvinyl alcohol-based heteropolyacid composite foam material according to claim 6, characterized in that The surfactant is Triton X-100, sodium hexadecylbenzenesulfonate or dodecylammonium chloride, and the mass ratio of the surfactant to polyvinyl alcohol is 1:5-15.

8. The method for preparing the polyvinyl alcohol-based heteropolyacid composite foam material according to claim 7, characterized in that The sulfuric acid is a solution with a mass concentration of 50%, and the mass ratio of sulfuric acid to polyvinyl alcohol is 2-1:1-2.

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