Composite hydrogel adsorbent as well as preparation method and application thereof

Abstract

The invention discloses a composite hydrogel adsorbent and a preparation method and application thereof, and belongs to the technical field of wastewater treatment.The preparation method comprises the specific steps that S1, neutralized acrylic acid, acrylamide and a cross-linking agent are added into deionized water and stirred to be uniform, and a precursor solution is obtained; s2, adding alkali-activated fly ash into the precursor solution, uniformly mixing, sequentially adding alkali liquor and an initiator, and fully stirring for reaction to obtain a mixed solution; and S3, curing the obtained mixed solution in a mold, washing with water, and drying to obtain the composite hydrogel adsorbent. According to the invention, the reaction system is optimized, so that the super-fast polymerization curing of the hydrogel is realized; the prepared composite hydrogel has excellent mechanical property and metal ion adsorption property; the whole preparation process is simple to operate, high in gel forming speed, free of light / heat initiation, mild in condition and low in cost, and can be applied to adsorption of heavy metal ions in wastewater.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and in particular to a composite hydrogel adsorbent, its preparation method, and its application. Background Technology

[0002] With the rapid development of the mining, metallurgy, and chemical industries, large quantities of industrial wastewater containing heavy metal ions such as copper, cadmium, and lead are being discharged, posing a serious threat to the ecological environment and human health. Heavy metal pollutants in water are persistent, difficult to detect, non-degradable, and easily accumulate in organisms. Once the concentration reaches a certain threshold, these metals catalyze the metabolism of other substances, accumulating in the human body through the food chain and ultimately harming human health. The removal of heavy metal ions from wastewater has become a bottleneck in wastewater purification and recycling.

[0003] Currently, common methods for treating heavy metal wastewater include chemical precipitation, ion exchange, membrane separation, and adsorption. Among these, adsorption has attracted much attention due to its simplicity, low cost, and high efficiency. Among various adsorption materials, hydrogels exhibit excellent adsorption performance due to their three-dimensional network structure rich in active groups, such as carboxyl and amide groups, which can coordinate with heavy metal ions and perform electrostatic adsorption ion exchange. However, current heavy metal adsorption hydrogels face challenges such as complex preparation processes, the need for external energy input, poor mechanical strength, and limited adsorption performance.

[0004] Therefore, there is an urgent need to develop a high-performance adsorption hydrogel that can be prepared ultrafast. Summary of the Invention

[0005] The purpose of this invention is to provide a composite hydrogel adsorbent, its preparation method, and its application, in order to solve the problems in the prior art.

[0006] To achieve the above objectives, the present invention provides a method for preparing a composite hydrogel adsorbent, comprising the following steps: S1. Add the neutralized acrylic acid, acrylamide and crosslinking agent to deionized water and stir until homogeneous to obtain the precursor solution; S2. Add alkali-activated fly ash to the precursor solution, mix well, then add alkali solution and initiator in sequence, stir thoroughly to react and obtain a mixed solution. S3. Place the obtained mixed solution in a mold and allow it to solidify rapidly for 85~95s. After washing and drying with water, a composite hydrogel adsorbent is obtained.

[0007] Preferably, in S1, the molar ratio of acrylic acid to acrylamide is 1:1.

[0008] Preferably, in step S1, the acrylic acid is neutralized with sodium hydroxide, and the degree of neutralization is 100%.

[0009] Preferably, in S1, the molar ratio of the crosslinking agent to the total amount of acrylic acid and acrylamide is 1:1231; the crosslinking agent is N,N'-methylenebisacrylamide.

[0010] Preferably, in step S2, the alkaline activation process of fly ash is as follows: fly ash is placed in a 4-8 mol / L sodium hydroxide solution, magnetically stirred, washed and filtered, dried, and then ground to obtain alkaline activated fly ash.

[0011] Preferably, in step S2, the alkaline solution is sodium hydroxide, and the initiator is potassium persulfate or ammonium persulfate.

[0012] Preferably, the molar ratio of the initiator in S2 to the crosslinking agent in S1 is 4~8:1.

[0013] Preferably, the molar ratio of the initiator in S2 to the crosslinking agent in S1 is 8:1.

[0014] Preferably, in step S3, the water washing process is as follows: the composite hydrogel is immersed in deionized water, and the deionized water is replaced every 1 hour for a total of 3 times.

[0015] The present invention also provides a composite hydrogel adsorbent, which is prepared by the above preparation method.

[0016] Preferably, in the composite hydrogel adsorbent, acrylic acid and acrylamide serve as monomers, with their important functional groups being carboxyl and amide groups, respectively, and are stable in aqueous solution. N,N'-methylenebisacrylamide, acting as a crosslinking agent, possesses two carbon-carbon double bonds. Under the action of potassium persulfate, the carbon-carbon double bonds of acrylic acid, acrylamide, and N,N'-methylenebisacrylamide undergo homolytic cleavage, generating free radicals. Ultimately, the two carbon-carbon double bonds of the crosslinking agent break and connect to two main chains, forming a three-dimensional network. The main chains are formed by the polymerization of acrylic acid and acrylamide, and alkali-activated fly ash is used as a filler to fill the hydrogel.

[0017] The rapid polymerization of hydrogels in approximately 90 seconds can be attributed to the following factors: fly ash generates heat when coexisting with sodium hydroxide solution, promoting the decomposition of potassium persulfate; potassium persulfate produces SO4 under the action of sodium hydroxide. ·- It is further converted into OH ·- Transition metals in fly ash can undergo a Fenton-like reaction with potassium persulfate to produce OH-. ·- This promotes the rapid polymerization of hydrogels.

[0018] This invention also provides an application of the composite hydrogel adsorbent, which is used as a heavy metal ion adsorbent in wastewater treatment to remove heavy metal ions from wastewater.

[0019] In this invention, the mechanism by which the polyacrylic acid / acrylamide and alkali-activated fly ash composite hydrogel adsorbs heavy metal ions is as follows: 1) Due to Si-O - Al-O - With -COO - Electrostatic attraction between metals and heavy metals; positive and negative charges attract each other and adsorb metal ions.

[0020] 2) Alkali activation of Na in fly ash + K + Metal ions exchange ions with heavy metals in the solution that have larger radii and higher charges.

[0021] 3) The Si-OH, Al-OH and -CONH2 / -COOH groups in the hydrogel provide lone pairs of electrons, which interact with the empty orbitals of heavy metal ions through coordination complexation.

[0022] Therefore, the composite hydrogel adsorbent, its preparation method, and its application disclosed in this invention have the following beneficial effects: (1) By optimizing the reaction system, the present invention achieves ultra-fast polymerization and solidification of hydrogels, which can complete the transformation from solution to solid in only about 90 seconds. Compared with the polymerization process of traditional hydrogels which takes several hours or even tens of hours, the efficiency is increased by more than 10 times. It greatly shortens the production cycle, reduces energy consumption, and lays a solid foundation for large-scale, continuous industrial production.

[0023] (2) The composite hydrogel not only retains the strong complexing ability of a large number of carboxyl and amide groups of the polyacrylic acid / acrylamide network for heavy metal ions, but also introduces fly ash activated by alkali. After alkali activation, the surface area and adsorption performance of fly ash increase, and the negatively charged active sites on the surface can form stable surface complexes with heavy metal ions through complexation, thereby realizing the synergistic adsorption effect of organic polymer network and inorganic active components, and has higher adsorption capacity and faster adsorption rate for a variety of heavy metal ions.

[0024] (3) Using industrial solid waste fly ash as a functional filler partially replaces the more expensive organic monomers, significantly reducing the cost of raw materials; it not only realizes the high added value of waste resource utilization, which is in line with the concept of green circular economy, but also makes the final product highly cost competitive in wastewater treatment applications; and its preparation method is simple, the gelation speed is fast, it does not require light / heat initiation, the conditions are mild, the cost is low, and it is suitable for large-scale production.

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0026] Figure 1This is a schematic diagram of the preparation process in Example 1 of the present invention; Figure 2 The infrared spectra of the products of Examples 1-3 and Comparative Example 1 of this invention are shown below. Figure 3 This is a SEM image of application example 1 of the present invention, where a represents unadsorbed metal ions and b represents adsorbed Cu. 2+ c represents adsorbed Cd 2+ d represents the adsorption of Pb 2+ ; Figure 4 This is a schematic diagram showing the metal ion adsorption capacity and removal efficiency of Application Examples 1-3 and Application Comparative Example 1 of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0029] Example 1 like Figure 1 As shown in the figure, this embodiment provides a method for preparing a composite hydrogel adsorbent, as detailed below: S1. Weigh 4g of acrylamide monomer and add it to a beaker; in another beaker, weigh 4g of acrylic acid, neutralize it to neutral (100% neutralization) with 6mol / L sodium hydroxide solution, pour it into the acrylamide beaker, and stir with a glass rod until completely dissolved. Then add 0.014g of N-N'-methylenebisacrylamide and stir with a glass rod until completely dissolved to obtain a polyacrylic acid / acrylamide hydrogel precursor solution.

[0030] S2. First, prepare alkali-activated fly ash. Modify the fly ash according to a liquid / ash ratio of 8:1. Weigh 32g of sodium hydroxide flakes and add them to a beaker. Add 50mL of deionized water and stir to dissolve. After the solution cools to room temperature, transfer it to a 200mL volumetric flask. Wash the beaker three times with deionized water, pouring all the washing liquid into the volumetric flask. Add deionized water to the mark in the volumetric flask and shake well to obtain a 4mol / L sodium hydroxide solution. Add 25g of fly ash to 200mL of sodium hydroxide solution and stir magnetically for 16h. Wash and filter three times to obtain blocky, moist fly ash. Dry it in an oven at 80℃ for 10h and grind it into a fine powder using a mortar and pestle to obtain alkali-activated fly ash.

[0031] Weigh 15g of alkali-activated fly ash and pour it into the polyacrylic acid / acrylamide hydrogel precursor solution. Stir with a glass rod until completely dissolved to obtain a mixed solution.

[0032] S3. Weigh 2.4g of sodium hydroxide and measure 10mL of deionized water. Dissolve the sodium hydroxide in the deionized water and stir thoroughly until completely dissolved to obtain a sodium hydroxide solution. Add the sodium hydroxide solution to the mixed solution and stir to mix them evenly. Then add 0.195g of potassium persulfate and stir with a glass rod until completely dissolved. Inject the dissolved solution into a 2.5mm radius silicone mold using a syringe. After 90s, composite hydrogel microspheres are obtained. Immerse the composite hydrogel in deionized water and change the deionized water every 1h for a total of 3 times. Dry at 80℃ to obtain the composite hydrogel adsorbent PAA-AM / FA4.

[0033] Example 2 This embodiment provides a method for preparing a composite hydrogel adsorbent, as detailed below: S1. Weigh 4g of acrylamide monomer and add it to a beaker; in another beaker, weigh 4g of acrylic acid, neutralize it to neutral (100% neutralization) with 6mol / L sodium hydroxide solution, pour it into the acrylamide beaker, and stir with a glass rod until completely dissolved. Then add 0.014g of N-N'-methylenebisacrylamide and stir with a glass rod until completely dissolved to obtain a polyacrylic acid / acrylamide hydrogel precursor solution.

[0034] S2. First, prepare alkali-activated fly ash by adding 25g of fly ash to 200mL of 6mol / L sodium hydroxide solution, stirring magnetically for 16h, washing and filtering three times to obtain blocky moist fly ash, drying it in an oven at 80℃ for 10h, and grinding it into fine powder with a mortar to obtain alkali-activated fly ash.

[0035] Weigh 15g of alkali-activated fly ash and pour it into the polyacrylic acid / acrylamide hydrogel precursor solution. Stir with a glass rod until completely dissolved to obtain a mixed solution.

[0036] S3. Add 6 mol / L sodium hydroxide solution to the mixed solution and stir to mix them evenly; then add 0.195 g potassium persulfate and stir with a glass rod until completely dissolved. Use a syringe to inject the dissolved solution into a silicone mold with a radius of 2.5 mm. After about 90 seconds, composite hydrogel microspheres are obtained. Immerse the composite hydrogel in deionized water and change the deionized water every 1 hour for a total of 3 times. Dry it at 80℃ to obtain the composite hydrogel adsorbent PAA-AM / FA6.

[0037] Example 3 This embodiment provides a method for preparing a composite hydrogel adsorbent, as detailed below: S1. Weigh 4g of acrylamide monomer and add it to a beaker; in another beaker, weigh 4g of acrylic acid, neutralize it to neutral (100% neutralization) with 6mol / L sodium hydroxide solution, pour it into the acrylamide beaker, and stir with a glass rod until completely dissolved. Then add 0.014g of N-N'-methylenebisacrylamide and stir with a glass rod until completely dissolved to obtain a polyacrylic acid / acrylamide hydrogel precursor solution.

[0038] S2. First, prepare alkali-activated fly ash by adding 25g of fly ash to 200mL of 8mol / L sodium hydroxide solution, stirring magnetically for 16h, washing and filtering three times to obtain blocky moist fly ash, drying it in an oven at 80℃ for 10h, and grinding it into fine powder with a mortar to obtain alkali-activated fly ash.

[0039] Weigh 15g of alkali-activated fly ash and pour it into the polyacrylic acid / acrylamide hydrogel precursor solution. Stir with a glass rod until completely dissolved to obtain a mixed solution.

[0040] S3. Add 6 mol / L sodium hydroxide solution to the mixed solution and stir to mix them evenly; then add 0.195 g ammonium persulfate and stir with a glass rod until completely dissolved. Use a syringe to inject the dissolved solution into a silicone mold with a radius of 2.5 mm. After about 90 seconds, composite hydrogel microspheres are obtained. Immerse the composite hydrogel in deionized water and change the deionized water every 1 hour for a total of 3 times. Dry it at 80℃ to obtain the composite hydrogel adsorbent PAA-AM / FA8.

[0041] Comparative Example 1 The steps in this comparative example are the same as those in Example 3, except that unmodified fly ash is used in step S2 to prepare the composite hydrogel adsorbent PAA-AM / FA0.

[0042] The products obtained in Examples 1-3 and Comparative Example 1 were tested respectively, and their infrared spectra are shown below. Figure 2 As shown, fly ash is rich in Fe2O3 and SiO2-based active glass microspheres. These irregularly shaped glassy particles contain varying numbers of tiny active channels, giving the fly ash surface a porous structure and a large specific surface area, which can be used for the adsorption of toxic metal ions. However, if not activated, the surface of fly ash is mostly smooth and scaly, and its adsorption capacity is quite limited. In Examples 1-3, the fly ash underwent physicochemical modification, resulting in a rougher, more porous surface and enhanced adsorption capacity.

[0043] Application Example 1 The composite hydrogel adsorbent prepared in Example 2 was used as a heavy metal ion adsorbent in wastewater treatment, and heavy metal ion removal tests were conducted.

[0044] The specific testing steps are as follows: 0.1g of the composite hydrogel adsorbent was added to 200mL of solution containing Cu. 2+ Cd 2+ Pb 2 + In simulated wastewater, the samples were treated with horizontal shaking at 25°C for 24 hours.

[0045] The composite hydrogel adsorbent without adsorption and the composite hydrogel adsorbent with adsorbed metal ions were tested separately, and the results are as follows: Figure 3 As shown in the figure, the composite hydrogel adsorbent prepared in Example 2 exhibits significant adsorption of metal ions, with a large amount of flocculent material appearing on its surface after adsorbing heavy metals. This is because alkali activation alters the surface morphology and structure of fly ash, making the fly ash surface rougher and the porous structure more pronounced, thus significantly enhancing its surface area and adsorption performance. Secondly, the negatively charged active sites (SiO₂) on the fly ash surface... - FeO - AlO - (etc.) can react with heavy metal ions (M 2+ Stable surface complexes are formed through complexation reactions, thereby fixing metal ions on the surface of fly ash.

[0046] Application Example 2 The composite hydrogel adsorbent prepared in Example 1 was used as a heavy metal ion adsorbent in wastewater treatment, and heavy metal ion removal tests were conducted; the specific method was the same as in Example 1.

[0047] Application Example 3 The composite hydrogel adsorbent prepared in Example 3 was used as a heavy metal ion adsorbent in wastewater treatment, and heavy metal ion removal tests were conducted; the specific method was the same as in Application Example 1.

[0048] Application Comparative Example 1 The composite hydrogel adsorbent prepared in Comparative Example 1 was used as a heavy metal ion adsorbent in wastewater treatment, and heavy metal ion removal tests were conducted; the specific method was the same as in Application Example 1.

[0049] During the testing of Application Examples 1-3 and Application Comparative Example 1, heavy metal ions (Cu) in the simulated wastewater before and after adsorption were measured using inductively coupled plasma optical emission spectrometry (ICP-OES). 2+ Cd 2+ Pb 2+ The concentration change was analyzed. Based on the change in the concentration of heavy metal ions before and after adsorption, the adsorption capacity and removal efficiency were calculated.

[0050] Adsorption capacity is expressed as: ; Removal efficiency is expressed as: .

[0051] The results are as follows Figure 4 As shown in the figures, the polyacrylic acid / acrylamide and alkali-activated fly ash composite hydrogels prepared by the present invention in Application Examples 1-3 have excellent adsorption effects on heavy metal ions in simulated wastewater and can effectively purify industrial wastewater.

[0052] Therefore, this invention provides a composite hydrogel adsorbent, its preparation method, and its application. By optimizing the reaction system (especially by using the synergistic effect of high-concentration alkali and initiator), ultra-fast polymerization and solidification of the hydrogel are achieved, completing the transformation from solution to solid microspheres in just around 90°C. The composite hydrogel not only retains the strong complexing ability of a large number of carboxyl and amide groups in the polyacrylic acid / acrylamide network for heavy metal ions, but also introduces alkali-activated fly ash, thereby achieving a synergistic adsorption effect between the organic polymer network and the inorganic active components, exhibiting excellent mechanical properties and metal ion adsorption performance. The entire preparation process is simple to operate, has a fast gelation speed, does not require light / heat initiation, operates under mild conditions, and is low in cost, making it applicable to the adsorption of heavy metal ions in wastewater.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a composite hydrogel adsorbent, characterized in that, Includes the following steps: S1. Add the neutralized acrylic acid, acrylamide and crosslinking agent to deionized water and stir until homogeneous to obtain the precursor solution; S2. Add alkali-activated fly ash to the precursor solution, mix well, then add alkali solution and initiator in sequence, stir thoroughly to react and obtain a mixed solution. S3. Place the obtained mixed solution in a mold and allow it to solidify rapidly for 85~95s. After washing and drying with water, a composite hydrogel adsorbent is obtained.

2. The method for preparing a composite hydrogel adsorbent according to claim 1, characterized in that: In S1, the molar ratio of acrylic acid to acrylamide is 1:

1.

3. The method for preparing a composite hydrogel adsorbent according to claim 1, characterized in that: In S1, acrylic acid is neutralized with sodium hydroxide, and the degree of neutralization is 100%.

4. The method for preparing a composite hydrogel adsorbent according to claim 1, characterized in that: In S1, the molar ratio of the crosslinking agent to the total amount of acrylic acid and acrylamide is 1:1231; the crosslinking agent is N,N'-methylenebisacrylamide.

5. The method for preparing a composite hydrogel adsorbent according to claim 1, characterized in that: In S2, the alkaline activation process of fly ash is as follows: fly ash is placed in a 4-8 mol / L sodium hydroxide solution, magnetically stirred, washed and filtered, dried and ground to obtain alkaline activated fly ash.

6. The method for preparing a composite hydrogel adsorbent according to claim 1, characterized in that: In S2, the alkaline solution is sodium hydroxide, and the initiator is potassium persulfate or ammonium persulfate.

7. The method for preparing a composite hydrogel adsorbent according to claim 1, characterized in that: The molar ratio of the initiator in S2 to the crosslinking agent in S1 is 4~8:

1.

8. The method for preparing a composite hydrogel adsorbent according to claim 1, characterized in that: In step S3, the water washing process involves immersing the composite hydrogel in deionized water.

9. A composite hydrogel adsorbent, characterized in that: The composite hydrogel adsorbent is prepared by the preparation method according to any one of claims 1-8.

10. An application of a composite hydrogel adsorbent, characterized in that: The composite hydrogel adsorbent prepared by the preparation method according to any one of claims 1-8 is used as a heavy metal ion adsorbent in wastewater treatment.

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