Millimeter-scale PEI / AFL / PVA aerogel and its preparation method and application

Abstract

The present invention discloses a millimeter-scale PEI / AFL / PVA aerogel and its preparation method and application. The preparation method comprises adjusting the pH value of a whey protein powder aqueous solution, incubating it in a water bath with shaking at 60°C to 65°C, collecting the supernatant and repeatedly centrifuging it, filtering it, and freeze-drying it to obtain βLG powder; dissolving the βLG powder in water, adjusting the pH value to 2-3, heating it in a water bath with stirring at 85°C to 90°C, and then cooling it with an ice-water mixture to obtain an AFL dispersion; mixing a PVA solution, a PEI solution, and an AFL dispersion, dripping the resulting mixture into a mold and subjecting it to 3-5 cycles of freeze-thawing to form a hydrogel, demoulding it, placing it in a glutaraldehyde solution with stirring, washing it, and freeze-drying it to obtain the aerogel. The aerogel of the present invention is easy to separate and recycle, has strong adsorption capacity, good mechanical properties and stability, and the preparation method is simple, convenient, and environmentally friendly. It can be applied to the treatment of Cr(VI)-contaminated wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment and relates to a millimeter-scale PEI / AFL / PVA aerogel and a preparation method and application thereof, and specifically relates to a large-scale millimeter-scale polyethyleneimine / protein amyloid fibril / polyvinyl alcohol aerogel bead and a preparation method thereof and application thereof in remediating hexavalent chromium-contaminated wastewater. Background Art

[0002] Chromium (Cr), a typical heavy metal, exists in the environment in two main forms: trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI). Cr(III), the most stable chromium species, is considered an essential element found only in trace amounts. In contrast, Cr(VI) compounds are highly mobile and soluble, and are teratogenic, carcinogenic, and mutagenic. Long-term exposure can cause significant damage to the liver, kidneys, lungs, and respiratory tract. Given the harmful effects of Cr(VI), numerous methods have been developed to remove Cr(VI) from natural water and wastewater, including membrane filtration, ion exchange, adsorption, and chemical precipitation.

[0003] Adsorption is a popular method due to its low cost, minimal environmental impact, and ease of operation. However, currently developed adsorbents are mostly nano- and micro-sized, making them difficult to recycle and reuse. Large (millimeter-sized) adsorbents often have insufficient adsorption capacity compared to smaller adsorbents. Therefore, developing a large-scale adsorbent with a high adsorption capacity is a worthy technical challenge in practical production. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology, especially to address the technical problems that small-sized adsorbents in existing Cr(VI)-contaminated wastewater remediation methods are easy to aggregate and difficult to recycle and reuse, and large-sized (millimeter-sized) adsorbents have insufficient adsorption capacity. The present invention provides a millimeter-sized PEI / AFL / PVA aerogel that can effectively remove Cr(VI) from actual water bodies, has high adsorption efficiency and good effect, is easy to recycle, is simple and efficient to prepare, and is economical and environmentally friendly, as well as a preparation method and application thereof.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions.

[0006] A method for preparing millimeter-scale PEI / AFL / PVA aerogel comprises the following steps:

[0007] (1) Purification of βLG: The pH value of the aqueous solution of whey protein powder was first adjusted to 4.2-4.5, and then incubated in a water bath at 60°C-65°C under shaking conditions until the solution became turbid. The supernatant was collected after centrifugation, and the centrifugation was repeated twice or more. The obtained supernatant was filtered and freeze-dried to obtain βLG powder;

[0008] (2) Preparation of AFL: βLG powder was dissolved in water and the pH was adjusted to 2-3 to obtain an aqueous solution of βLG. The aqueous solution of βLG was then heated in a water bath at 85-90°C with stirring for 5-6 hours. After heating, the resulting solution was cooled with an ice-water mixture to obtain an AFL dispersion.

[0009] (3) Preparation of aerogel: PVA solution, PEI solution and AFL dispersion were mixed to obtain a mixed solution, which was then dripped into a mold. After 3 to 5 cycles of freeze-thaw, a hydrogel was formed. After demolding, the mixture was placed in a glutaraldehyde solution and stirred to achieve complete cross-linking. The mixture was then washed with water and freeze-dried to obtain a millimeter-scale PEI / AFL / PVA aerogel.

[0010] The above-mentioned method for preparing millimeter-scale PEI / AFL / PVA aerogel, preferably, in step (1), the mass fraction of whey protein powder in the aqueous solution of whey protein powder is 10wt% to 12wt%, the pH value is adjusted using concentrated HCl, the water bath oscillation speed is 150rpm to 155rpm, and the incubation time is 2h to 4h.

[0011] In the above-mentioned method for preparing millimeter-scale PEI / AFL / PVA aerogel, preferably, in step (1), the centrifugal speed is 8000 rpm to 10000 rpm, the centrifugal time is 15 min to 30 min, the filtration uses a 0.45 μm cellulose acetate membrane filter, and the obtained βLG powder is stored at 4°C to 6°C.

[0012] In the above-mentioned method for preparing millimeter-scale PEI / AFL / PVA aerogel, preferably, in step (2), the mass fraction of βLG in the aqueous solution of βLG is 2wt% to 3wt%, and the water is Milli-Q water.

[0013] In the above-mentioned method for preparing millimeter-scale PEI / AFL / PVA aerogel, preferably, in step (2), the obtained AFL dispersion is stored at 4°C to 6°C.

[0014] In the above-mentioned method for preparing millimeter-scale PEI / AFL / PVA aerogel, preferably, in step (3), the ratio of the PVA solution, PEI solution, and AFL dispersion is 3g~4g:0.3g~0.4g:16mL~18mL, the mass fraction of the PVA solution is 10wt%~12wt%, and the mass fraction of the PEI solution is 50wt%~52wt%.

[0015] In the above-mentioned method for preparing millimeter-scale PEI / AFL / PVA aerogel, preferably, in step (3), the mold is a spherical mold, the diameter of the spherical mold is 0.5 cm, the concentration of the glutaraldehyde solution is 2% w / v to 3% w / v, the stirring time is 4h to 5h, and the freeze-drying time is 1 day to 2 days.

[0016] As a general technical concept, the present invention also provides a millimeter-scale PEI / AFL / PVA aerogel prepared by the above-mentioned method for preparing the millimeter-scale PEI / AFL / PVA aerogel.

[0017] As a general technical concept, the present invention also provides an application of the above-mentioned millimeter-scale PEI / AFL / PVA aerogel in treating hexavalent chromium-contaminated wastewater.

[0018] The above application preferably includes the following process:

[0019] The pH of Cr(VI)-containing wastewater is adjusted to 2-3, and millimeter-sized PEI / AFL / PVA aerogel is added at a dosage of 1g / L-2g / L. The aerogel is then shaken to perform an adsorption reaction to remove Cr(VI) from the wastewater. The wastewater includes hexavalent chromium-contaminated wastewater with varying Cr(VI) concentrations, hexavalent chromium-contaminated wastewater containing multiple competitive cations, or soil leachate containing Cr(VI). Preferably, the oscillation temperature is room temperature, the oscillation time is 24-25 hours, and the Cr(VI) concentration in the hexavalent chromium-contaminated wastewater is 50mg / L-500mg / L.

[0020] Compared with the prior art, the advantages of the present invention are:

[0021] (1) The millimeter-sized PEI / AFL / PVA aerogel (or aerogel beads) of the present invention, as a large-sized adsorbent, is easier to separate from the solution than existing small-sized adsorbents, which is conducive to recycling, and its adsorption capacity is even better than some nano-sized and micro-sized adsorbents. The present invention uses polyethyleneimine (PEI), protein amyloid fibrils (AFL) and polyvinyl alcohol (PVA) for synergistic effect. Polyethyleneimine (PEI) is a cationic polymer with a large number of primary and secondary amine groups. When reacting with Cr(VI), it can remove Cr(VI) ions through electrostatic interaction and reduction mechanisms. Due to the water solubility of PEI, it cannot be directly used as an adsorbent. In the present invention, PEI is fixed in a matrix and AFL is used as a matrix for loading PEI. Protein amyloid fibrils (AFL) can be formed from β-lactoglobulin (βLG, a by-product of the cheese industry) through the combined hydrolysis and aggregation process of the original protein folding sequence at low pH and high temperature. The surface of the AFL prepared by the present invention contains a large number of amino acid residues, which have a strong affinity for Cr(VI). The aerogel formed by the AFL has an ultra-high porosity and is suitable for use as a substrate. However, due to the poor mechanical properties of AFL and the oily liquid nature of PEI, the mechanical properties of the material formed by the combination of the two are relatively weak. The addition of polyvinyl alcohol (PVA) in the present invention can not only improve the mechanical properties of the material, but also provide active reaction sites. The large number of hydroxyl groups on its surface assist in the reduction of Cr(VI) and chelate Cr(III) to enhance the adsorbent's stability to Cr. As a result, the millimeter-scale PEI / AFL / PVA aerogel of the present invention has excellent adsorption effect, separation and recovery effect, mechanical strength and stability.

[0022] (2) In the preparation method of the present invention, the raw materials are widely available, the method is simple and efficient, the cost is low, and it is environmentally friendly, providing a new type of efficient, economical and environmentally friendly ideal green material for repairing Cr(VI) contaminated water bodies.

[0023] (3) The millimeter-scale PEI / AFL / PVA aerogel of the present invention can be used to repair Cr(VI)-contaminated wastewater. On the one hand, the PAP aerogel has good adsorption effect and high efficiency. On the other hand, the PAP aerogel is easy to recycle and separate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the isothermal adsorption curve of Cr(VI) in solution at different concentrations by the millimeter-scale PEI / AFL / PVA aerogel in Example 2 of the present invention.

[0025] Figure 2 This is a graph showing the removal rate of Cr(VI) by the millimeter-scale PEI / AFL / PVA aerogel in Example 3 of the present invention in Cr(VI)-contaminated wastewater containing multiple competitive cations.

[0026] Figure 3 This is a graph showing changes in ion concentration in soil leachate after treatment with millimeter-sized PEI / AFL / PVA aerogel in Example 4 of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but the scope of protection of the present invention is not limited thereby. The materials and instruments used in the following examples are all commercially available.

[0028] Example 1

[0029] A method for preparing millimeter-scale PEI / AFL / PVA aerogel of the present invention comprises the following steps:

[0030] (1) Purification of βLG: Whey protein powder was added to water to prepare a 10 wt% whey protein powder aqueous solution, and the pH value of the solution was adjusted to 4.2 with concentrated HCl. The conical flask containing the whey protein powder aqueous solution was then placed in a water bath shaker at 60°C and an oscillation speed of 150 rpm for 4 hours until the solution became turbid. It was centrifuged at 8000 rpm for 15 minutes to obtain a nearly transparent solution and a white precipitate. The supernatant was collected and the centrifugation procedure was repeated 3 times in succession. In order to further remove any residual insoluble proteins, the supernatant was passed through a 0.45 μm cellulose acetate membrane filter. Finally, the obtained transparent solution was freeze-dried and stored at 4°C to obtain βLG powder.

[0031] (2) Preparation of AFL: βLG powder was dissolved in Milli-Q water at pH 2 to prepare a 2 wt% βLG solution (a Milli-Q aqueous solution of βLG). The βLG solution was then heated in a water bath with a magnetic stirrer at 90°C for 5 h. Finally, the prepared solution was immediately cooled with an ice-water mixture to obtain an AFL dispersion, which was stored at 4°C.

[0032] (3) Preparation of PAP aerogel: 3 g of a 10 wt% PVA solution, 0.3 g of a 50 wt% PEI solution, and 18 mL of AFL dispersion were thoroughly mixed and the resulting mixture was dropped into a spherical mold with a diameter of 0.5 cm. After three cycles of freeze-thaw, a hydrogel was formed. After demolding, the hydrogel was immediately placed in a 2% w / v glutaraldehyde solution and stirred for 4 h to achieve complete crosslinking. After washing with Milli-Q water and freeze-drying for two days, millimeter-sized PEI / AFL / PVA aerogels, i.e., millimeter-sized PAP aerogels, were obtained.

[0033] Example 2

[0034] An application of the millimeter-scale PEI / AFL / PVA aerogel of the present invention in treating a solution containing Cr(VI) comprises the following steps:

[0035] 1g / L K2Cr2O7 stock solution was diluted with water to prepare Cr(VI) solutions with different initial concentrations (50mg / L to 500mg / L). The pH of the Cr(VI) solution was adjusted to 3 with 1mol / L HCl. Then, millimeter-sized PEI / AFL / PVA aerogel was added. The amount of aerogel was 1g / L. That is, 20mg PAP aerogel and 20mL reaction solution (containing Cr(VI) solution) were fully mixed in a 50mL conical flask. At room temperature, the mixture was shaken at 150rpm on a constant temperature water bath oscillator for 24h. After the reaction, the solution was filtered through a 0.45μm filter membrane and the Cr(VI) concentration in the solution was determined on a UV spectrophotometer. Figure 1 It can be found that with the increase of the initial concentration of Cr(VI), the removal ability of PAP aerogel for Cr(VI) is enhanced, and the PAP adsorption data is more consistent with the Sips isotherm model (R 2 =0.9840). Based on the Sips isotherm model, the maximum adsorption capacity of PAP for Cr(VI) was 307 mg / g, and the maximum Cr(VI) removal efficiency of PAP was 85.2% (Cr 50 mg / L). As a large-scale bulk adsorption material, PAP aerogel has a higher Cr(VI) adsorption capacity than other microspheres and even some nanomaterials.

[0036] Example 3

[0037] An application of the millimeter-scale PEI / AFL / PVA aerogel of the present invention in treating Cr(VI)-containing wastewater containing multiple heavy metal ions comprises the following steps:

[0038] The effects of PAP on heavy metals (Cd 2+ 、Cu 2+ 、Ni 2+ and Pb 2+ ) concentration of 50 mg / L, and the adsorption selectivity of Cr (VI) at each concentration of 50 mg / L. Figure 2As shown, the removal rates of PAP for each metal in the single heavy metal solution were Cr (86.97%) > Pb (8.52%) > Cd (1.76%) > Cu (0.61%) > Ni (0.52%). In the mixed solution, the removal rates of PAP for each metal were Cr (89.63%) > Pb (40.90%) > Ni (22.94%) > Cu (15.17%) > Cd (1.68%). The results indicate that the removal rate of Cr(VI) by PAP was significantly higher than that of other heavy metal cations, both in the single solution and the mixed solution. The removal rate of Cr(VI) in the mixed solution was also slightly higher than that in the single Cr(VI) solution, likely due to the metal cations adsorbed on the PAP surface promoting the electrostatic adsorption of Cr(VI) anions, resulting in synergistic removal. Conversely, the removal of these cationic heavy metals (except Cd) was significantly better in the mixed solution than in the single solution. In summary, the high selectivity of PAP for Cr(VI) and its synergistic removal of Pb in heavy metal co-contaminated water bodies 2+ 、Ni 2+ 、Cu 2+ The ability to treat cations is of great significance in actual polluted water bodies (for example, electroplating wastewater generally contains metals such as Cr, Cu, and Ni).

[0039] Example 4

[0040] An application of the millimeter-scale PEI / AFL / PVA aerogel of the present invention in treating soil leachate containing Cr(VI) comprises the following steps:

[0041] Dry soil and Milli-Q water were mixed at a m / v ratio of 1g:10mL and vibrated at 150rpm for 12 hours to prepare soil leachate. Before the adsorption reaction, the Cr(VI) concentration in the leachate was measured to be 180.3mg / L. The dosage of PAP aerogel was 1g / L, that is, 20mg PAP aerogel and 20mL reaction solution were fully mixed in a 50mL conical flask, and the reaction was carried out at room temperature by maintaining a vibration reaction at 150rpm on a constant temperature water bath oscillator for 24 hours. After the reaction was completed, the solution was filtered through a 0.45μm filter membrane and the Cr(VI) concentration in the solution was determined on a UV spectrophotometer. Figure 3 As shown in the figure, PAP aerogel removed 84.43% of Cr(VI) in the soil leachate containing 180.3 mg / L Cr(VI), while the concentration changes of other metal elements in the soil leachate, such as K, Na, Mg, and Ca, were not obvious.

[0042] Table 1 Concentrations of typical anions (mg / L), DOC (mg / L), pH, and EC (μs / cm) in Example 4

[0043]

[0044] The above results show that the millimeter-scale PEI / AFL / PVA aerogel prepared in the present invention, as a large-sized and easily recyclable adsorbent, exhibits excellent Cr(VI) removal ability in both simulated water samples and actual water bodies, and is an ideal choice for treating Cr(VI)-contaminated wastewater.

[0045] The above description is only a preferred embodiment of the present invention and does not constitute any formal limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the spirit and technical solution of the present invention, use the methods and technical contents disclosed above to make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention, still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing millimeter-scale PEI / AFL / PVA aerogel, characterized in that: The following steps are involved: (1) Purification of βLG: The pH value of the aqueous solution of whey protein powder is first adjusted to 4.2-4.5, and then incubated in a water bath at 60°C-65°C under shaking conditions until the solution becomes turbid. The supernatant is collected after centrifugation, and the centrifugation is repeated twice or more. The obtained supernatant is filtered and freeze-dried to obtain βLG powder; the mass fraction of whey protein powder in the aqueous solution of whey protein powder is 10 wt%-12 wt%, and the incubation time is 2 h-4 h; (2) Preparation of AFL: βLG powder was dissolved in water and the pH value was adjusted to 2-3 to obtain an aqueous solution of βLG. The aqueous solution of βLG was then heated in a water bath at 85-90°C with stirring for 5-6 h. After heating, the resulting solution was cooled with an ice-water mixture to obtain an AFL dispersion. (3) Preparation of aerogel: PVA solution, PEI solution and AFL dispersion are mixed to obtain a mixed solution, which is then dripped into a mold. After 3 to 5 cycles of freeze-thaw, a hydrogel is formed. After demolding, the mixture is placed in a glutaraldehyde solution and stirred to achieve complete cross-linking. The mixture is then washed with water and freeze-dried to obtain a millimeter-scale PEI / AFL / PVA aerogel. The ratio of the PVA solution, PEI solution and AFL dispersion is 3 g to 4 g: 0.3 g to 0.4 g: 16 mL to 18 mL. The mass fraction of the PVA solution is 10 wt% to 12 wt%, and the mass fraction of the PEI solution is 50 wt% to 52 wt%.

2. The method for preparing millimeter-scale PEI / AFL / PVA aerogel according to claim 1, characterized in that: In step (1), the pH value is adjusted using concentrated HCl, and the speed of the water bath oscillation is 150 rpm to 155 rpm.

3. The method for preparing millimeter-scale PEI / AFL / PVA aerogel according to claim 1, characterized in that: In step (1), the centrifugal speed is 8000 rpm to 10000 rpm, the centrifugal time is 15 min to 30 min, the filtration adopts a 0.45 μm cellulose acetate membrane filter, and the obtained βLG powder is stored at 4°C to 6°C.

4. The method for preparing millimeter-scale PEI / AFL / PVA aerogel according to claim 1, characterized in that: In step (2), the mass fraction of βLG in the aqueous solution of βLG is 2 wt% to 3 wt%, and the water is Milli-Q water.

5. The method for preparing millimeter-scale PEI / AFL / PVA aerogel according to claim 1, characterized in that: In step (2), the obtained AFL dispersion is stored at 4°C to 6°C.

6. The method for preparing millimeter-scale PEI / AFL / PVA aerogel according to claim 1, characterized in that: In step (3), the mold is a spherical mold with a diameter of 0.5 cm, the concentration of the glutaraldehyde solution is 2% w / v to 3% w / v, the stirring time is 4 h to 5 h, and the freeze-drying time is 1 day to 2 days.

7. A millimeter-sized PEI / AFL / PVA aerogel prepared by the method for preparing a millimeter-sized PEI / AFL / PVA aerogel according to any one of claims 1 to 6.

8. Use of the millimeter-scale PEI / AFL / PVA aerogel according to claim 7 in treating hexavalent chromium-contaminated wastewater.

9. The use according to claim 8, characterized in that The following processes are included: The pH value of wastewater containing Cr(VI) is adjusted to 2-3, and millimeter-sized PEI / AFL / PVA aerogel is added in an amount of 1g / L-2g / L. Then, oscillation is performed to perform an adsorption reaction to remove Cr(VI) from the wastewater. The wastewater includes hexavalent chromium-contaminated wastewater with different Cr(VI) concentrations, hexavalent chromium-contaminated wastewater containing multiple competitive cations, or soil leachate containing Cr(VI).

Images