Preparation method of environment-friendly chitosan-based heavy metal adsorption air coagulation beads

Abstract

The application discloses a preparation method of an environment-friendly chitosan-based heavy metal adsorption air-precipitated bead, and comprises the following steps: preparing chitosan water-precipitated beads through acid-base neutralization solidification, loading the ammonia metal organic framework UiO-66-NH2 prepared through hydrothermal reaction on the chitosan water-precipitated beads through Schiff base reaction of a crosslinking agent, and then further loading polyethylene imine on the composite water-precipitated beads through the same loading means. The CS-UiO-GA-PEI-GA air-precipitated bead adsorbent is prepared through freeze-drying of the water-precipitated beads by a freeze dryer. The secondary crosslinking method gives the adsorbent certain mechanical strength, and provides a basis for regeneration and circulation of the adsorbent; the nitrogen-rich polyethylene imine and the high-porosity UiO-66-NH2 greatly enrich the active adsorption sites of the adsorbent, and significantly improve the adsorption capacity of the adsorbent for Cr(VI); and the removal rate of the adsorbent for Cr(VI) is up to 100% in the detection limit range of Cr(VI).

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment and heavy metal recovery, and particularly relates to a method for preparing environmentally friendly chitosan-based heavy metal adsorption aerosol beads and the environmentally friendly chitosan-based heavy metal adsorption aerosol beads prepared by the method. Background Technology

[0002] Heavy metal pollutants in industrial wastewater, such as mercury (Hg), lead (Pb), chromium (Cr), cadmium (Cd), and arsenic (As), pose a high risk to biological and environmental systems, and even to humans. Among these heavy metals, Cr is a highly toxic substance that severely pollutes water and soil. Furthermore, Cr is one of the biggest pollutants causing various diseases, such as respiratory obstruction, irritation, and immune effects. Moreover, Cr has potential carcinogenic and mutagenic properties, potentially inducing nasopharyngeal carcinoma, lung cancer, skin cancer, and other cancers, seriously threatening human health. The common valence states of Cr are Cr(II), Cr(III), and Cr(VI). Among these, Cr(VI) exhibits high mobility in ecosystems due to its high solubility and stability in water, thus posing a significant threat to ecosystems and human health.

[0003] Currently, the main methods for treating Cr(VI) in wastewater include membrane filtration, photocatalysis, electrochemical treatment, and adsorption. Among these, adsorption is considered one of the best technologies for treating heavy metal pollution in wastewater due to its simplicity, cost-effectiveness, and ability to be used on a large scale. However, most adsorbents are prepared using large amounts of harmful chemical reagents, causing secondary pollution. Furthermore, traditional adsorbents still suffer from fatal flaws such as low adsorption capacity, poor selectivity, and weak regeneration ability, which affect their application in industrial production.

[0004] In view of the above shortcomings, this invention uses chitosan, a natural polymer derived from the deacetylation of chitin (second only to cellulose in abundance in nature), as a base. It employs a highly controllable structure of UiO-66-NH2 and a nitrogen-rich cationic polymer PEI, loading them via a Schiff base reaction with glutaraldehyde, and then prepares a low-cost Cr(VI) adsorption aerosol beads using freeze-drying technology. This adsorbent possesses both environmental friendliness and regenerability, while also exhibiting high Cr(VI) adsorption capacity. Summary of the Invention

[0005] Based on the above analysis, this invention provides a low-cost Cr(VI) adsorption aerosol bead that combines environmental friendliness and adsorption capacity. More specifically, it is an environmentally friendly adsorbent material prepared by covalently modifying a high-porosity UiO-66-NH2 with the cationic polymer polyethyleneimine via a Schiff base reaction with glutaraldehyde, using chitosan as a base. The adsorbent prepared by this invention exhibits excellent Cr(VI) removal capacity; for an initial solution with a high Cr(VI) concentration (150 mg / L) of 20 mL, only 15 mg of the adsorbent from this invention is required for complete removal. This adsorbent also possesses excellent regeneration performance; after six cycles of regeneration, the removal rate still reaches 79.1%. Furthermore, the large volume of 3.20 mm simplifies post-adsorption treatment; simple filtration is sufficient to separate the adsorbent, making it applicable to wastewater treatment.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a method for preparing environmentally friendly chitosan-based heavy metal adsorption aerosol beads, comprising the following steps:

[0008] A method for preparing environmentally friendly chitosan-based heavy metal adsorption aerosol beads includes:

[0009] (1) Preparation of CS-UiO-GA hydrogel beads:

[0010] UiO-66-NH2 powder was dissolved in deionized water and ultrasonically dispersed to prepare UiO-66-NH2 solution. Chitosan hydrogel beads with a mass fraction of 75% of UiO-66-NH2 powder were added to the solution and stirred rapidly for 12 hours. Then, a certain amount of glutaraldehyde was added and the cross-linking reaction was carried out for 2 hours. After the reaction was completed, the solution was filtered and washed to obtain CS-UiO-GA hydrogel beads.

[0011] (2) Preparation of CS-UiO-GA-PEI-GA hydrogel beads:

[0012] Polyethyleneimine solution was added to CS-UiO-GA hydrogel beads at a mass ratio of 1:100 (w / v) of UiO-66-NH2 loading, and the mixture was stirred rapidly for 12 h. Glutaraldehyde was added, and the crosslinking reaction was carried out for 2 h. After the reaction was completed, the mixture was filtered and washed to obtain CS-UiO-GA-PEI-GA hydrogel beads.

[0013] (3) Preparation of CS-UiO-GA-PEI-GA aerosol beads:

[0014] The CS-UiO-GA-PEI-GA hydrogel beads were placed in a refrigerator for rapid freezing, and then quickly transferred to a freeze dryer for freeze drying to obtain CS-UiO-GA-PEI-GA aerogel beads.

[0015] Further, the UiO-66-NH2 powder in step (1) is prepared by the following method:

[0016] Weigh ZrCl4 and 2-aminoterephthalic acid into DMF, stir well, add 18% acid by volume of DMF and sonicate for several minutes. Transfer the reaction solution to a reaction vessel and place it in an oven for hydrothermal reaction. After the reaction is complete, remove the reaction vessel and allow it to cool naturally to room temperature. Wash and centrifuge repeatedly with acetone and methanol solution 5 times, and dry thoroughly in a vacuum oven for 24 hours to obtain UiO-66-NH2 powder.

[0017] Further, the mass ratio of ZrCl4 to 2-aminoterephthalic acid is 0.1-3; the acid is any one of acetic acid, hydrochloric acid, formic acid, benzoic acid, and nitric acid; the hydrothermal reaction temperature is 90-150℃, the reaction time is 24h, and the vacuum drying temperature is 50-90℃.

[0018] Further, the chitosan hydrogel beads described in step (1) are prepared by the following method:

[0019] Chitosan powder is dissolved in an acid solution, stirred thoroughly and mixed evenly, and then allowed to stand for 3 hours. The resulting chitosan solution is then dripped into NaOH solution with a syringe to fully solidify it. After washing until neutral, chitosan hydrogel beads are obtained.

[0020] Further, the acid solution is any one of acetic acid, hydrochloric acid, and nitric acid; the chitosan solution concentration is 1-5 wt%; and the NaOH solution concentration is 0.5-3 mol / L.

[0021] Further, in step (1), the concentration of the UiO-66-NH2 solution is 1-50%, the concentration of the glutaraldehyde is 1-5 wt%, and the amount of glutaraldehyde added is 1-5% of the volume of the system solution.

[0022] Further, in step (2), the concentration of the polyethyleneimine solution is 0.1-5 wt%, and the molecular weight of the polyethyleneimine solution is 600, 1800, 3000, 25000, or 75000 Da; the concentration of the glutaraldehyde is 1-5 wt%, and the amount of glutaraldehyde added is 1-5% of the volume of the system solution.

[0023] Furthermore, in step (3), the refrigerator temperature is -80℃ and the rapid freezing time is 1 hour; the freeze dryer freezes for 24 hours.

[0024] The present invention also discloses an environmentally friendly chitosan-based heavy metal adsorption aerosol beads prepared according to any of the above preparation methods.

[0025] The present invention also discloses the application of the above-mentioned environmentally friendly chitosan-based heavy metal adsorption aerosol beads in wastewater treatment and heavy metal recovery.

[0026] The beneficial effects of this invention are as follows:

[0027] This invention utilizes inexpensive and pollution-free natural chitosan as a base, and uses structurally tunable UiO-66-NH2 and the polyamine cationic polymer polyethyleneimine as modifying materials. Through covalent bonding with a crosslinking agent, the adsorption capacity and stability of the adsorbent are improved, while simultaneously overcoming the shortcomings of UiO-66-NH2, such as easy aggregation and difficult recovery. This adsorbent exhibits excellent Cr(VI) removal capability; for an initial solution with a high Cr(VI) concentration (150 mg / L) of 20 mL, only 15 mg of this adsorbent is required for complete removal. After six cycles of regeneration, the adsorbent still achieves a Cr(VI) removal rate of 79.1%, demonstrating high economic efficiency and applicability in wastewater treatment. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the preparation process of the present invention;

[0030] Figure 2 A is an optical photograph of pure chitosan aerosol beads. Figure 2 B is an optical photograph of CS-UiO-GA aerocondensed beads. Figure 2 C is an optical photograph of CS-UiO-GA-PEI-GA aerocondensed beads. Figure 2 D is a schematic diagram of the dimensions of CS-UiO-GA-PEI-GA aerosol beads.

[0031] Figure 3 This is a comparison chart of the adsorption capacity and removal efficiency of adsorbents prepared by different preparation methods in Examples 1-4 and Comparative Examples 1-3 of this invention;

[0032] Figure 4 This is a comparison chart of the adsorption capacity and removal efficiency of the adsorbent prepared in Example 3 of the present invention under different pH conditions;

[0033] Figure 5 This is a test graph showing the cyclic regeneration performance of the adsorbent prepared in Example 3 of this invention. Detailed Implementation

[0034] The present invention will be described in detail below with reference to specific embodiments. However, the present invention is not limited to the following embodiments. Any variations or implementations that do not depart from the content and scope of the present invention should be included within the technical scope of the present invention.

[0035] Example 1

[0036] Weigh 1g ZrCl4 and 1g 2-aminoterephthalic acid into 120mL DMF, stir well, add 22mL acetic acid to a beaker and sonicate for several minutes. Transfer the reaction solution to a reaction vessel and place it in an oven at 120℃ for 24h. After the reaction is complete, remove the reaction vessel and allow it to cool naturally to room temperature. Then wash and centrifuge 5 times, and dry thoroughly in an 80℃ vacuum oven for 24h to obtain UiO-66-NH2. Weigh 1g of the above UiO-66-NH2 and dissolve it in a 5wt% acetic acid solution, sonicate to disperse evenly, add 0.75g chitosan and stir rapidly to dissolve, let stand for 3h to remove air bubbles. Add the bubble-removed mixed solution dropwise into a 2.5mol / L NaOH solution, solidify for 3h, then filter and wash until neutral, transfer to 100mL deionized water, add 1mL glutaraldehyde and react for 2h, filter and wash to obtain CS / UiO-GA hydrogel beads. The CS / UiO-GA hydrogel beads were placed in 100 mL of 0.5 wt% PEI solution and stirred rapidly for 12 h. 1 mL of glutaraldehyde was added and the reaction proceeded for 2 h. After filtration and washing, the CS / UiO-GA-PEI hydrogel beads were obtained. The CS / UiO-GA-PEI hydrogel beads were then frozen at -80°C for 1 h. The sample was then quickly transferred to a freeze dryer and freeze-dried for 24 h to obtain CS / UiO-GA-PEI aerogel beads.

[0037] Example 2

[0038] Weigh 1g ZrCl4 and 1g 2-aminoterephthalic acid into 120mL DMF, stir well, add 22mL acetic acid into a beaker and sonicate for several minutes. Transfer the reaction solution to a reaction vessel and place it in an oven at 120℃ for 24h. After the reaction is complete, remove the reaction vessel and allow it to cool naturally to room temperature. Then wash and centrifuge 5 times, and dry thoroughly in a vacuum oven at 80℃ for 24h to obtain UiO-66-NH2. Weigh 0.75g chitosan powder, dissolve it in 25mL of 5wt% acetic acid solution, stir thoroughly and mix well, and let stand for 3h to remove air bubbles. Use a syringe to drop the chitosan solution into a 2.5mol / L NaOH solution to solidify it completely, then wash until neutral to obtain white chitosan hydrogel beads (these chitosan hydrogel beads are freeze-dried to obtain pure chitosan aerogel beads, and their optical photographs are shown in the figure). Figure 2(As shown in A). Prepare 100 mL of 0.5 wt% polyethyleneimine aqueous solution. Add the above-mentioned chitosan hydrogel beads to the polyethyleneimine solution and stir rapidly for 12 h. Add 1 mL of glutaraldehyde and allow the cross-linking reaction to proceed for 2 h. After the reaction is complete, filter and wash to obtain CS-PEI-GA hydrogel beads. Weigh 1 g of the above-mentioned UiO-66-NH2 and dissolve it in 100 mL of deionized water. Disperse the mixture evenly by ultrasonication. Add the CS-PEI-GA hydrogel beads and stir rapidly for 12 h. Then add 1 mL of glutaraldehyde and allow the cross-linking reaction to proceed for 2 h. After the reaction is complete, filter and wash to obtain CS-PEI-GA-UiO-GA hydrogel beads. Freeze the CS-PEI-GA-UiO-GA hydrogel beads in a -80℃ freezer for 1 h. Quickly transfer the sample to a freeze dryer and freeze-dry for 24 h to obtain CS-PEI-GA-UiO-GA aerogel beads.

[0039] Example 3

[0040] Weigh 1g ZrCl4 and 1g 2-aminoterephthalic acid into 120mL DMF, stir well, add 22mL acetic acid to a beaker and sonicate for several minutes. Transfer the reaction solution to a reaction vessel and place it in an oven at 120℃ for 24h. After the reaction is complete, remove the reaction vessel and allow it to cool naturally to room temperature. Then wash and centrifuge 5 times, and dry thoroughly in a vacuum oven at 80℃ for 24h to obtain UiO-66-NH2. Weigh 0.75g chitosan powder, dissolve it in 25mL of 5wt% acetic acid solution, stir thoroughly to mix evenly, and let stand for 3h to remove air bubbles. Use a syringe to drop the chitosan solution into a 2.5mol / L NaOH solution to fully solidify, then wash until neutral to obtain white chitosan hydrogel beads. Weigh 1g of the prepared UiO-66-NH2 and dissolve it in 100mL of deionized water. Disperse the mixture evenly using ultrasonication. Add CS hydrogel beads and stir rapidly for 12h. Then add 1mL of glutaraldehyde and allow the cross-linking reaction to proceed for 2h. After the reaction is complete, filter and wash to obtain CS-UiO-GA hydrogel beads. Prepare 100mL of a 0.5wt% polyethyleneimine aqueous solution. Place the above-mentioned CS-UiO-GA hydrogel beads in the polyethyleneimine solution and stir rapidly for 12h. Add 1mL of glutaraldehyde and allow the cross-linking reaction to proceed for 2h. After the reaction is complete, filter and wash to obtain CS-UiO-GA-PEI-GA hydrogel beads. Freeze the CS-UiO-GA-PEI-GA hydrogel beads at -80℃ for 1h. Quickly transfer the sample to a freeze dryer and freeze-dry for 24h to obtain CS-UiO-GA-PEI-GA aerogel beads. Optical photographs and dimensional diagrams are shown below. Figure 2 C and Figure 2 As shown in D.

[0041] Example 4

[0042] Weigh 1g ZrCl4 and 1g 2-aminoterephthalic acid into 120mL DMF, stir well, add 22mL acetic acid to a beaker and sonicate for several minutes. Transfer the reaction solution to a reaction vessel and place it in an oven at 120℃ for 24h. After the reaction is complete, remove the reaction vessel and allow it to cool naturally to room temperature. Then wash and centrifuge 5 times, and dry thoroughly in a vacuum oven at 80℃ for 24h to obtain UiO-66-NH2. Weigh 0.75g chitosan powder, dissolve it in 25mL of 5wt% acetic acid solution, stir thoroughly to mix evenly, and let stand for 3h to remove air bubbles. Use a syringe to drop the chitosan solution into a 2.5mol / L NaOH solution to fully solidify, then wash until neutral to obtain white chitosan hydrogel beads. Weigh 1g of UiO-66-NH2 and dissolve it in 100mL of deionized water. Add 0.5g of PEI, stir rapidly, and then ultrasonically disperse until uniform. Add chitosan hydrogel beads and stir for 12h. Add 1mL of glutaraldehyde to the above solution system and react for 2h. Filter and wash to obtain CS-UiO / PEI-GA hydrogel beads. Freeze the CS-UiO / PEI-GA hydrogel beads in a -80℃ freezer for 1h, and quickly transfer the sample to a lyophilizer. Freeze-dry for 24h to obtain CS-UiO / PEI-GA aerogel beads.

[0043] Comparative Example 1

[0044] Weigh 1g ZrCl4 and 1g 2-aminoterephthalic acid into 120mL DMF, stir well, add 22mL acetic acid to a beaker and sonicate for several minutes. Transfer the reaction solution to a reaction vessel and place it in an oven at 120℃ for 24h. After the reaction is complete, remove the reaction vessel and allow it to cool naturally to room temperature. Then wash and centrifuge 5 times, and dry thoroughly in a vacuum oven at 80℃ for 24h to obtain UiO-66-NH2. Dissolve UiO-66-NH2 in 25mL of 5wt% acetic acid solution, sonicate to mix evenly, add 0.75g chitosan to the mixture, stir thoroughly, and let stand for 3h to remove air bubbles. Use a syringe to drop the mixture into 2.5mol / L NaOH solution to solidify completely, then wash until neutral to obtain CS / UiO hydrogel beads. CS / UiO hydrogel beads were placed in a -80℃ freezer for 1 hour, and the sample was quickly transferred to a freeze dryer and freeze-dried for 24 hours to obtain CS / UiO aerogel beads.

[0045] Comparative Example 2

[0046] Weigh 1g ZrCl4 and 1g 2-aminoterephthalic acid into 120mL DMF, stir well, add 22mL acetic acid to a beaker and sonicate for several minutes. Transfer the reaction solution to a reaction vessel and place it in an oven at 120℃ for 24h. After the reaction is complete, remove the reaction vessel and allow it to cool naturally to room temperature. Then wash and centrifuge 5 times, and dry thoroughly in a vacuum oven at 80℃ for 24h to obtain UiO-66-NH2. Dissolve UiO-66-NH2 in 25mL of 5wt% acetic acid solution, sonicate to mix evenly, add 0.75g chitosan to the mixture, stir thoroughly, and let stand for 3h to remove air bubbles. Use a syringe to drop the mixture into 2.5mol / L NaOH solution to solidify completely, then wash until neutral to obtain CS / UiO hydrogel beads. Place CS / UiO hydrogel beads in 100 mL of deionized water, add 1 mL of glutaraldehyde, react for 2 h, filter and wash to obtain CS / UiO-GA hydrogel beads. Freeze CS / UiO-GA hydrogel beads in a -80℃ freezer for 1 h, quickly transfer the sample to a freeze dryer, and freeze-dry for 24 h to obtain CS / UiO-GA aerogel beads.

[0047] Comparative Example 3

[0048] Weigh 1g ZrCl4 and 1g 2-aminoterephthalic acid into 120mL DMF, stir well, add 22mL acetic acid to a beaker and sonicate for several minutes. Transfer the reaction solution to a reaction vessel and place it in an oven at 120℃ for 24h. After the reaction is complete, remove the reaction vessel and allow it to cool naturally to room temperature. Then wash and centrifuge 5 times, and dry thoroughly in a vacuum oven at 80℃ for 24h to obtain UiO-66-NH2. Weigh 0.75g chitosan powder, dissolve it in 25mL of 5wt% acetic acid solution, stir thoroughly to mix evenly, and let stand for 3h to remove air bubbles. Use a syringe to drop the chitosan solution into a 2.5mol / L NaOH solution to fully solidify, then wash until neutral to obtain white chitosan hydrogel beads. Weigh 1g of the prepared UiO-66-NH2 and dissolve it in 100mL of deionized water. Disperse the mixture evenly using ultrasonication. Add CS hydrogel beads and stir rapidly for 12h. Then add 1mL of glutaraldehyde and allow the cross-linking reaction to proceed for 2h. After the reaction is complete, filter and wash to obtain CS-UiO-GA hydrogel beads. Freeze the CS-UiO-GA hydrogel beads at -80℃ for 1h. Quickly transfer the sample to a freeze dryer and freeze-dry for 24h to obtain CS-UiO-GA aerogel beads. The optical photograph is shown below. Figure 2 As shown in B.

[0049] Test Example 1

[0050] A certain amount of K₂CrO₄ was weighed to prepare a Cr(VI) solution with a concentration of 300 mg / L, and the pH was adjusted to 2.5 using a 0.1 mol / L hydrochloric acid solution. 30 mL of the prepared Cr(VI) solution was measured and placed into several beakers. 20 mg of the adsorbent prepared in Examples 1, 2, 3, 4, Comparative Examples 1, 2, and 3 was weighed and placed into a beaker, and then transferred to an air bath constant temperature shaking oven. The temperature was adjusted to 30 °C, and the shaking rate to 210 rpm. Adsorption was allowed to proceed for 6 hours, and the adsorption data were calculated using the following formula:

[0051] Saturated adsorption capacity:

[0052] Q e =(C0-C e )×V÷m

[0053] Removal rate:

[0054] R = (C0 - C) e ) / C0×100%

[0055] Among them, Q e (mg / g) represents the adsorbent adsorption capacity at adsorption equilibrium, R (%) represents the removal rate, and C0 (mg / L) and C e (mg / L) represents the initial concentration of Cr(VI) solution and the remaining concentration after adsorption equilibrium, respectively; V(L) is the solution volume; and m(g) is the adsorbent mass.

[0056] The results are shown in Table 1. Figure 3 Adsorption data:

[0057] Table 1

[0058] Adsorbent <![CDATA[C e (mg / L)]]> <![CDATA[Q e (mg / g)]]> R(％) Example 1 43.4 384.9 85.5 Example 2 33 400.5 89 Example 3 19.6 420.6 93.5 Example 4 50.8 373.8 83.1 Comparative Example 1 150.9 223.7 49.7 Comparative Example 2 74.4 338.4 75.2 Comparative Example 3 78.8 331.8 73.7

[0059] Depend on Figure 3 As shown in Table 1, the adsorbent prepared in this invention exhibits excellent Cr(VI) removal capabilities. The preparation method in Example 3 demonstrates the best Cr(VI) removal effect, with a saturated adsorption capacity as high as 420.6 mg / g and a removal rate as high as 93.5%. Experimental results indicate that the optimal preparation strategy is to first prepare chitosan hydrogel beads, then load UiO-66-NH2, and finally load polyethyleneimine. Comparison with the comparative examples and the examples reveals that the adsorbent loaded only with UiO-66-NH2 has a worse adsorption effect than the adsorbent loaded with both UiO-66-NH2 and polyethyleneimine, indicating that polyethyleneimine can further enhance the adsorbent's adsorption capacity.

[0060] Test Example 2

[0061] A certain amount of K₂CrO₄ was weighed to prepare a Cr(VI) solution with a concentration of 150 mg / L. 20 mL of the prepared Cr(VI) solution was then placed into several beakers, and the pH was adjusted to 2, 2.5, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 respectively using 0.1 mol / L hydrochloric acid solution. 15 mg of the adsorbent prepared in Example 3 was weighed into the solution and placed in an air bath constant temperature shaking oven at 30°C and a shaking rate of 210 rpm for 6 hours of adsorption. The adsorption results are shown in Table 2. Figure 4 data

[0062] Table 2

[0063] pH <![CDATA[C e (mg / L)]]> <![CDATA[Q e (mg / g)]]> R(％) 2 3.3 195.6 97.8 2.5 0 200.0 100 3 3.3 195.6 97.8 4 69.0 108.0 54.0 5 78.1 95.9 47.9 6 86.4 84.8 42.4 7 109.1 54.5 27.3 8 131.0 25.3 12.7 9 135.0 20.0 10 10 131.9 24.1 12.1 11 132.9 22.8 11.4 12 127.4 30.1 15.1

[0064] Depend on Figure 4 As shown in Table 2, the adsorbent has the best adsorption capacity when pH = 2.5, with an adsorption capacity of 200 mg / g and a removal rate of up to 100%.

[0065] Test Example 3

[0066] A certain amount of K₂CrO₄ was weighed to prepare a Cr(VI) solution with a concentration of 50 mg / L. 20 mL of the prepared Cr(VI) solution was placed in separate beakers, and the pH was adjusted to 2.5 using a 0.1 mol / L hydrochloric acid solution. 20 mg of the adsorbent prepared in Example 3 was weighed into the solution and placed in an air bath constant temperature shaking oven. The temperature was set to 30 °C, the shaking rate to 210 rpm, and adsorption was carried out for 6 hours. The experiment was conducted in duplicate. The results are shown in Table 3 and... Figure 5 data:

[0067] Table 3

[0068]

[0069] Depend on Figure 5 As shown in Table 3, the adsorbent prepared by this invention has excellent recycling performance. The Cr(VI) removal rate is still as high as 97% or more after the first 3 cycles, and the Cr(VI) removal rate is still 79% after 6 cycles, indicating that the adsorbent has excellent recycling performance and can be reused at least 6 times.

[0070] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for preparing environmentally friendly chitosan-based heavy metal adsorption aerosol beads, comprising: Weigh 1g ZrCl4 and 1g 2-aminoterephthalic acid into 120mL DMF, stir well, add 22mL acetic acid into a beaker and sonicate for several minutes. Transfer the reaction solution to a reaction vessel and place it in an oven at 120℃ for 24h. After the reaction is complete, remove the reaction vessel and allow it to cool naturally to room temperature. Then wash and centrifuge 5 times, and dry thoroughly in a vacuum oven at 80℃ for 24h to obtain UiO-66-NH2. Weigh 0.75g of chitosan powder and dissolve it in 25mL of 5wt% acetic acid solution. Stir and mix thoroughly, then let stand for 3 hours to remove air bubbles. Use a syringe to drop the chitosan solution into 2.5mol / L NaOH solution to solidify it completely. Then wash until neutral to obtain white chitosan hydrogel beads. Weigh 1g of the above-prepared UiO-66-NH2 and dissolve it in 100mL of deionized water. Disperse it evenly by ultrasonication, add CS hydrogel beads, stir rapidly for 12h, then add 1mL of glutaraldehyde and crosslink for 2h. After the reaction is complete, filter and wash to obtain CS-UiO-GA hydrogel beads. Prepare 100 mL of 0.5 wt% polyethyleneimine aqueous solution, place the above CS-UiO-GA hydrogel beads in the polyethyleneimine solution, stir rapidly for 12 h, add 1 mL of glutaraldehyde, and perform cross-linking reaction for 2 h. After the reaction is complete, filter and wash to obtain CS-UiO-GA-PEI-GA hydrogel beads; place CS-UiO-GA-PEI-GA hydrogel beads in a -80℃ freezer for 1 h, and quickly transfer the sample to a freeze dryer for freeze drying for 24 h to obtain CS-UiO-GA-PEI-GA aerogel beads.

2. An environmentally friendly chitosan-based heavy metal adsorption aerosol bead prepared by the preparation method according to claim 1.

3. The application of the environmentally friendly chitosan-based heavy metal adsorption aerosol beads according to claim 2 in wastewater treatment and heavy metal recovery.

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