CN114558558A

CN114558558A - Attapulgite-doped double-crosslinked hydrogel and preparation method and application thereof

Info

Publication number: CN114558558A
Application number: CN202210410014.5A
Authority: CN
Inventors: 朱霞萍; 贺广喜; 黄超; 魏霄; 王晶晶; 何铁
Original assignee: Chengdu Univeristy of Technology
Current assignee: Chengdu Univeristy of Technology
Priority date: 2022-04-19
Filing date: 2022-04-19
Publication date: 2022-05-31
Anticipated expiration: 2042-04-19
Also published as: CN114558558B

Abstract

The invention relates to attapulgite-doped double-crosslinked hydrogel and a preparation method and application thereof, belonging to the technical field of heavy metal adsorption in wastewater treatment. The invention solves the technical problem of providing a preparation method of attapulgite-doped double-crosslinked hydrogel. The method adds attapulgite and NaHCO into double-crosslinking hydrogel of sodium alginate and polyvinyl alcohol₃And CaCl is utilized in the solidification and molding stage₂-acetic acid and NaHCO in acetic acid solution₃The pore-making technology for producing bubbles by reaction prepares the sodium alginate and the polyvinyl alcohol which are doped with attapulgite and have porous structuresThe double-crosslinking spherical hydrogel (SA/PVA/ATP) not only overcomes the defects of difficult separation, low permeability and the like of the attapulgite, but also overcomes the defect of insufficient mechanical strength of the hydrogel, and promotes the practical application of the attapulgite and the hydrogel in industrial wastewater. The obtained material can be used as an adsorbent for adsorbing heavy metal ions in a water body, the adsorption effect is good, and the time required for reaching adsorption balance is short. The method is simple, low in cost and suitable for industrial production.

Description

Attapulgite-doped double-crosslinked hydrogel and preparation method and application thereof

Technical Field

The invention relates to attapulgite-doped double-crosslinked hydrogel and a preparation method and application thereof, belonging to the technical field of heavy metal adsorption in wastewater treatment.

Background

With the development of society, the problem of environmental pollution is increasingly prominent. Among them, heavy metals in water environment can directly or indirectly enter human body through agricultural irrigation, skin contact and drinking water and form potential harm to human health. The sources of heavy metal contamination are human activities and natural evolution, respectively. Human activities include petrochemical, fertilizer, battery manufacturing, printing, leather waste water, metallurgical and other industrial activities. Natural sources include rock efflorescence, erosion, sedimentation, volcanic activity, and the like. At present, heavy metal pollution of water is a global problem which exists for a long time.

The adsorption method has the advantages of convenient design, low cost and the like, is one of the most promising methods for treating heavy metal wastewater, and is especially important for the design and development of adsorbents because the adsorbent is the most critical in the adsorption method. Attapulgite is commonly used as an adsorbent for various metal ions due to its large ion exchange capacity and electrostatic adsorption capacity. In addition, it can be easily modified by chemical treatment to increase its adsorption capacity. Attapulgite and its modified products can adsorb many pollutants, but in practice there are drawbacks: (I) attapulgite swells when contacted with water and forms a highly stable colloidal suspension which is difficult to separate from water; (II) in practical treatment processes, the use of attapulgite as an adsorbent material in columns is limited due to the low permeability of the compacted attapulgite bed. The hydrogel is green and economical, has abundant functional groups on the surface, and is often used as an adsorbent, but the single hydrogel has poor mechanical strength, and the adsorption effect is poor due to high crosslinking density, so the hydrogel is limited in practical application.

Ren et al (2016) crosslinked SA-CMC hydrogel beads by blending with Sodium Alginate (SA) and sodium carboxymethylcellulose (CMC) for 5mg/L Pb²⁺The removal rate of the catalyst can reach 99 percent. The clay mineral is coated in the hydrogel, so that the clay hydrogel with good adsorbability, stability and reusability can be prepared, and the utilization rate of the clay mineral is improved. The bentonite is added into the chitosan-polyvinyl alcohol precursor solution, and the prepared nano composite material can improve the adsorption selectivity to Hg (II) ions due to the addition of the bentonite (Wang, et al 2013). Liu et al (2012) use alginate to fix halloysite nanotubes, prepare a novel porous microsphere for adsorbing methylene blue dye, and through 10 continuous adsorption-desorption cycles, the removal rate of methylene blue can be maintained above 90%. Belhouuchat et al (2017) prepare organic activated AObent/SA microspheres by using bentonite (Bent) and Sodium Alginate (SA), and can be applied to adsorption removal of Methylene Blue (MB) and Methyl Orange (MO). Huanglianxian et al (2021) combines polyvinyl alcohol (PVA), boric acid, Sodium Alginate (SA) and calcium chloride to construct a double-cross-linked gel network, and loads potassium humate (KHA) and calcium montmorillonite (MMT) nanoparticles, and the prepared double-cross-linked gel spheres (PVA/SA/KHA/MMT) have high removal rate for methylene blue and Pb (II).

The Chinese patent with the application number of 202011077914 discloses a modified attapulgite/sodium alginate/polyvinyl alcohol composite adsorbent and a preparation method and application thereof, wherein attapulgite is subjected to acid modification, is doped with magnesium oxide to prepare modified attapulgite, is mixed with water, polyvinyl alcohol and sodium alginate, is molded and solidified to obtain the adsorbent, and the adsorbent basically achieves adsorption balance in 6 hours and is used for adsorbing Cd²⁺The adsorption amount of (A) was 54.6mg/g, and the adsorption effect was further improved.

Disclosure of Invention

The invention aims to provide a preparation method of attapulgite-doped double-crosslinked hydrogel with a good adsorption effect.

The preparation method of the attapulgite-doped double-crosslinked hydrogel comprises the following steps:

a. mixing attapulgite with water to obtain attapulgite suspension; sodium alginate, polyvinyl alcohol and NaHCO₃Mixing with water to obtain a mixed solution A;

b. adding the attapulgite turbid liquid into the mixed liquid A, and stirring for reaction to obtain a mixed liquid B;

c. adding the mixed solution B into CaCl₂And (3) solidifying and forming in an acetic acid aqueous solution, and then washing and drying to obtain the attapulgite-doped double-crosslinked hydrogel.

In some embodiments of the invention, the weight ratio of the attapulgite, the sodium alginate and the polyvinyl alcohol is 0.5-2.0: 0.8-1.2: 2-2.4. In a preferred embodiment, the weight ratio of attapulgite, sodium alginate and polyvinyl alcohol is 1.0:1.0: 2.4.

In some embodiments of the invention, NaHCO₃The weight ratio of the polyvinyl alcohol to the polyvinyl alcohol is 0.3-1.0: 2.4. In a preferred embodiment, NaHCO₃The weight ratio to polyvinyl alcohol was 0.8: 2.4.

In one embodiment of the invention, in the step b, the stirring reaction is carried out at a temperature of 25-80 ℃ for 2-6 h. In a preferred embodiment, the reaction is preferably stirred at a temperature of 40 ℃ for a period of 4 hours.

In a preferred embodiment, CaCl₂In aqueous acetic acid, CaCl₂The concentration of (A) is 0.25-5 wt%. More preferred CaCl₂Is 0.5 wt%.

In one embodiment of the invention, CaCl₂The molar weight of acetic acid in the acetic acid aqueous solution is NaHCO in the mixed solution B ₃100 to 150% of the molar amount of (A). In a specific embodiment, CaCl₂The molar weight of acetic acid in the acetic acid aqueous solution is NaHCO in the mixed solution B₃110% of the molar weight。

The invention also provides the attapulgite-doped double-crosslinked hydrogel prepared by the preparation method of the attapulgite hydrogel.

The attapulgite-doped double-crosslinked hydrogel has a porous structure, has a good effect of adsorbing heavy metal ions in a water body, and can adsorb Cd²⁺The saturated adsorption capacity can reach 68.50mg/g, the adsorption is basically balanced after adsorption is carried out for 150min, the time is short, and the efficiency is high.

The invention also provides application of the attapulgite-doped double-crosslinked hydrogel in adsorbing heavy metal ions in a water body.

The attapulgite-doped double-crosslinked hydrogel can be used for adsorbing heavy metal ions in water. In some embodiments of the present invention, the heavy metal ions are at least one of Cd, Pb, and Cu ions.

In a specific embodiment of the invention, before adsorption, the pH value of the water body is adjusted to 3.5-6.

Compared with the prior art, the invention has the following beneficial effects:

the invention adds Attapulgite (ATP) and NaHCO into the double-crosslinking hydrogel of Sodium Alginate (SA) and polyvinyl alcohol (PVA)₃And CaCl is utilized in the curing and forming stage₂-acetic acid and NaHCO in acetic acid solution₃The hole making technology for generating bubbles through reaction prepares the attapulgite-doped sodium alginate and polyvinyl alcohol double-crosslinked spherical hydrogel (SA/PVA/ATP) with a porous structure, overcomes the defects of difficult separation, low permeability and the like of the attapulgite, overcomes the defect of insufficient mechanical strength of the hydrogel, and promotes the practical application of the attapulgite and the hydrogel in industrial wastewater.

The attapulgite-doped double-crosslinked hydrogel is prepared by a bubble pore-forming method, has a porous structure, can be used as an adsorbent for adsorbing heavy metal ions in a water body, and has a good adsorption effect and short time for achieving adsorption balance.

The preparation method of the attapulgite-doped double-crosslinked hydrogel does not need to acidify and dope the attapulgite, is simple, has lower cost and is suitable for industrial production.

Drawings

FIG. 1 is a schematic diagram of the preparation of attapulgite-doped double-crosslinked hydrogel.

FIG. 2 is an FTIR spectrum of attapulgite-doped double-crosslinked hydrogel (SA/PVA/ATP) obtained in example 1 of the present invention.

FIG. 3 is an FTIR spectrum of Attapulgite (ATP) used in the present invention.

FIG. 4 shows the amount of the attapulgite-doped double-crosslinked hydrogel (SA/PVA/ATP) obtained in example 7 of the present invention added to Cd²⁺The effect of the removal.

FIG. 5 shows the initial concentration vs. Cd in example 7 of the present invention²⁺The effect of the removal.

FIG. 6 shows the pH value of the solution to Cd in example 7 of the present invention²⁺The effect of the removal.

FIG. 7 shows the adsorption time vs. Cd in example 7 of the present invention²⁺The effect of the removal.

FIG. 8 shows the adsorption temperature vs. Cd in example 7 of the present invention²⁺The effect of the removal.

FIG. 9 shows the ion intensity vs. Cd in example 7 of the present invention²⁺Influence of removal

FIG. 10 is a diagram showing the saturated adsorption capacity of attapulgite-doped double-crosslinked hydrogel (SA/PVA/ATP) for Cd in example 7 of the present invention.

Detailed Description

a. mixing Attapulgite (ATP) with water to obtain attapulgite suspension; sodium Alginate (SA), polyvinyl alcohol (PVA), NaHCO₃Mixing with water to obtain a mixed solution A;

c. adding the mixed solution B into CaCl₂And (4) solidifying and forming in an acetic acid aqueous solution, and then washing and drying to obtain the attapulgite-doped double-crosslinked hydrogel.

According to the method, the attapulgite-doped double-crosslinked hydrogel is prepared by a specific method, the attapulgite is not required to be acidified and doped, and the method is simple and low in cost. The obtained attapulgite-doped double-crosslinked hydrogel material can be used as an adsorbent for adsorbing heavy metals in a water body, and has good adsorption effect and short adsorption balance time.

Adding NaHCO₃The hydrogel can react with acetic acid to generate bubbles in the subsequent curing stage, so that the generation of pores in the hydrogel is promoted, and the adsorption effect of the hydrogel is improved. Without the addition of NaHCO₃In the case of hydrogels prepared directly from aqueous calcium chloride solution, NaHCO₃The occupied position can not be consumed by reaction with acid, bubbles can not be generated, the hole expanding effect is avoided, and the pore passages are fewer, so that the adsorption of heavy metal ions is not facilitated.

The temperature and time of the stirring reaction have certain influence on the adsorption effect of the product, and in one embodiment of the invention, in the step b, the temperature of the stirring reaction is 25-80 ℃ and the time is 2-6 h. In a preferred embodiment, the reaction is preferably stirred at a temperature of 40 ℃ for a period of 4 hours.

CaCl₂As curing agent, the crosslinking degree of hydrogel is directly determined, CaCl in solution₂Too low solubility to be enough for hydrogel balling, CaCl₂At too high a concentration, the hydrogel crosslinks more tightly, which can lose too many adsorptive active sites and is not conducive to ion transport to the interior, reducing the adsorptive effect. In a preferred embodiment, CaCl₂In aqueous acetic acid, CaCl₂The concentration of (A) is 0.25-5 wt%. More preferably, CaCl₂Is 0.5 wt%.

The invention adopts a bubble hole making technology, CaCl₂-aqueous acetic acid, acetic acid and NaHCO₃The reaction generates bubbles and the bubbles are coated in the hydrogel in the curing and forming stage, and in addition, the acetic acid consumes NaHCO₃The occupied positions all play a role of reaming.

Typically, the acetic acid is used in an equal or excess amount, and in one embodiment of the invention, CaCl is used₂The molar weight of acetic acid in the acetic acid aqueous solution is NaHCO in the mixed solution B ₃100 to 150% of the molar amount of (A). In a specific embodiment, CaCl₂The molar quantity of acetic acid in the aqueous solution of acetic acid is NaHCO in the mixed solution B₃110% of the molar amount of (c).

The attapulgite-doped double-crosslinked hydrogel has a porous structure, has a good effect of adsorbing heavy metal ions in a water body, and can adsorb Cd²⁺The saturated adsorption capacity can reach 68.50mg/g, and after adsorption is carried out for 150min, the adsorption basically reaches balance, the time is short, and the efficiency is high.

In a specific embodiment of the invention, before adsorption, the pH value of the water body is adjusted to 3.5-6. The following examples are provided to further illustrate the embodiments of the present invention and are not intended to limit the scope of the present invention.

The adsorption process in the examples was:

weighing a certain amount of SA/PVA/ATP hydrogel into a 50mL conical flask, adding 25mL of Cd solution with a certain concentration, adding 0.1mol/L NaOH and 0.1mol/L HAnd adjusting the pH value of the solution by Cl, placing the solution into a constant-temperature oscillator for oscillation, controlling the oscillation temperature and time, and measuring the concentration of Cd by moving supernate by flame atomic absorption spectrophotometer. Removal rate (R) and saturated adsorption capacity (Q)_e) The calculation is made by the following formula:

wherein C is₀And C_eThe initial and equilibrium mass concentrations of heavy metal in the solution, mg/L, respectively; v is the volume of the aqueous solution, L; m is the mass of the adsorbent, g.

Example 1

1.0g of SA, 2.4g of PVA and 0.8g of NaHCO are weighed out₃Then, 60mL of distilled water was added to a small 100mL beaker, and the mixture was stirred in a 60 ℃ constant temperature water bath. Meanwhile, 1.0g of attapulgite is weighed into a small beaker of 50mL, 20mL of distilled water is added, and then ultrasonic treatment is carried out for 1 h. Then slowly pouring the ultrasonic attapulgite suspension into the SA and PVA solution under stirring, and continuously stirring at constant temperature of 60 ℃ for 3 h. After the reaction is fully carried out, the reaction solution is pumped and dripped into 200mL of CaCl by a constant flow pump₂CaCl with a concentration of 0.5 wt%₂And (3) curing and molding an acetic acid aqueous solution (the concentration of acetic acid is 0.052mol/L) overnight, washing the solution with a large amount of distilled water after full curing, then putting the solution into a culture dish, freezing the culture dish in a refrigerator for 24 hours, and finally air-drying the culture dish to obtain the attapulgite-doped double-crosslinked hydrogel (SA/PVA/ATP).

FIG. 1 is a schematic diagram of the preparation of the material. The Fourier transform infrared spectroscopy (FTIR) spectrum of the attapulgite-doped double-crosslinked hydrogel is shown in figure 2, and the FTIR spectrum of the Attapulgite (ATP) as a raw material is shown in figure 3.

As can be seen from the figure, 3436cm^-1The wide scattered peak is telescopic vibration of SA/PVA/ATP and O-H on the ATP surface, 1630cm^-1The left and right peaks are bending vibration of O-H, 1362cm in SA/PVA/ATP spectrum^-1The peak intensity at (A) is higher, this is-COO^-Is caused by symmetrical vibration of 1032cm^-1The absorption peak is caused by Si-O-Si, and the peak intensity of SA/PVA/ATP is obviously reduced compared with that of ATP, which is caused by surface coating of sodium alginate and polyvinyl alcohol. 513cm^-1And 473cm^-1The absorption peaks are the stretching vibration of Mg-O and Al-O.

Comparative example 1

1.0g of SA and 2.4g of PVA were weighed into a 100mL beaker, and 60mL of distilled water was added and stirred in a 60 ℃ constant temperature water bath. Meanwhile, 1.0g of attapulgite is weighed in a small beaker of 50mL, 20mL of distilled water is added, and then ultrasonic treatment is carried out for 1 h. Then slowly pouring the ultrasonic attapulgite suspension into the SA and PVA solution under stirring, and continuously stirring at constant temperature of 60 ℃ for 3 h. After fully and evenly stirred, the mixture is pumped and dripped to 0.5 wt% of CaCl by a constant flow pump₂And (4) solidifying and forming the aqueous solution at night, after full solidification, washing the aqueous solution with a large amount of distilled water, then putting the aqueous solution into a culture dish, putting the culture dish into a refrigerator for freezing for 24 hours, and finally drying the culture dish in the air to obtain the SA/PVA/ATP without holes, wherein the SA/PVA/ATP has fewer holes and is not beneficial to the adsorption of heavy metal ions.

Example 2 study of Attapulgite addition amount on adsorption Performance

1.0g of SA, 2.4g of PVA and 0.8g of NaHCO are weighed out₃60mL of distilled water was added to a small 100mL beaker, and the mixture was stirred in a 60 ℃ constant temperature water bath. Simultaneously weighing attapulgite with different masses (0, 0.5, 1.0, 1.5 and 2.0g respectively) in a small beaker of 50mL, adding 20mL of distilled water, and performing ultrasonic treatment for 1 h. Then slowly pouring the ultrasonic attapulgite suspension into the SA and PVA solution under stirring, and continuously stirring at constant temperature of 60 ℃ for 3 h. After the reaction is fully carried out, the reaction solution is pumped and dripped into 200mL of CaCl by a constant flow pump₂CaCl with a concentration of 0.5 wt%₂And (3) solidifying and molding an acetic acid aqueous solution (the concentration of acetic acid is 0.052mol/L) overnight, washing the solution with a large amount of distilled water after full solidification, then putting the solution into a culture dish, putting the culture dish into a refrigerator, freezing the culture dish for 24 hours, and finally air-drying the culture dish to obtain the attapulgite-doped double-crosslinked hydrogel (SA/PVA/ATP).

The SA/PVA/ATP hydrogel is adopted to react 50mg/L Cd²⁺The solution was adsorbed and the results are shown in table 1. AdsorptionConditions are as follows: SA/PVA/ATP: 0.1g, volume of adsorption solution: 25mL of Cd in the adsorption solution²⁺Initial concentration 50mg/L, temperature: 25 ℃, adsorption time: and 2 h.

TABLE 1

Example numbering	Attapulgite addition amount (g)	Cd²⁺Removal Rate (%)
			2-1	0	71.31
2-2	0.5	78.38
			2-3	1.0	82.80
2-4	1.5	81.01
			2-5	2.0	75.10

Therefore, the adsorption effect of the hydrogel is improved after ATP is added, the adsorption effect is the best when the addition amount is 1.0g, and Cd is²⁺The removal rate of (D) was 82.8%, which was increased by 11% compared to that obtained without addition. ATP is in a lamellar layer chain structure, has strong ion exchange capacity and permanent negative charge, and has a plurality of hydroxyl functional groups on the surface. The ATP sheet layer chain structure can be used as a physical cross-linking agent in a composite system to play an additional cross-linking role, so that the pores in the gel sphere network are increased, the porosity is improved, and the exposed adsorption sites are increased. When the amount of ATP added exceeds 1.0g, the amount of Cd added is adjusted²⁺The removal rate of (2) is decreased because too much attapulgite consumes adsorption sites. In addition, experiments show that the viscosity of the precursor solution can be greatly increased when the dosage of the attapulgite is 2.0g, and the preparation of hydrogel spheres can become very difficult when the dosage exceeds 2.0 g.

Example 3NaHCO₃Study on adsorption Properties by addition amount

1.0g of SA, 2.4g of PVA and different masses (0, 0.3, 0.5, 0.8, 1.0g, respectively) of NaHCO were weighed out₃60mL of distilled water was added to a 100mL beaker, and the mixture was stirred in a 60 ℃ thermostat water bath. Simultaneously, 1.0g of attapulgite is added into a small beaker with the volume of 50mL, and 20mL of distilled water is added for 1 hour of ultrasonic treatment. Then slowly pouring the ultrasonic attapulgite suspension into the SA and PVA solution under stirring, and continuously stirring at constant temperature of 60 ℃ for 3 h. After the reaction is fully carried out, the reaction solution is pumped and dripped into 200mL of CaCl by a constant flow pump₂CaCl with a concentration of 0.5 wt%₂And (3) solidifying and forming an acetic acid aqueous solution (with the acetic acid concentration of 0, 0.020, 0.033, 0.052 and 0.065mol/L) at the middle and night, after full solidification, washing with a large amount of distilled water, then putting into a culture dish, putting into a refrigerator, freezing for 24 hours, and finally air-drying to obtain the attapulgite-doped double-crosslinked hydrogel (SA/PVA/ATP).

The SA/PVA/ATP hydrogel is adopted to react 50mg/L Cd²⁺The solution was adsorbed and the results are shown in table 2. The adsorption conditions are as follows: SA/PVA/ATP: 0.05g, volume of adsorption solution: 25mL, temperature: 25 ℃, adsorption time: and 2 h.

TABLE 2

Example numbering	NaHCO₃Addition amount (g)	Cd²⁺Removal Rate (%)
			3-1	0	40.57
3-2	0.3	50.59
			3-3	0.5	71.58
3-4	0.8	83.11
			3-5	1.0	82.58

As can be seen, with NaHCO₃Increasing the amount of the hydrogel to Cd²⁺The better the removal effect, when the dosage is 0.8g, the Cd content is good²⁺The removal effect of (2) is best, and the removal rate reaches 83.11%. It was found that, when the amount of sodium bicarbonate was increased, a large amount of bubbles were generated to seriously affect the formation and mechanical strength of the hydrogel. Thus, NaHCO₃The addition amount is 0.8g as the optimum amount.

EXAMPLE 4 investigation of reaction time on adsorption Performance

1.0g of SA, 2.4g of PV were weighed outA and 0.8g NaHCO₃60mL of distilled water was added to a small 100mL beaker, and the mixture was stirred in a 60 ℃ constant temperature water bath. Simultaneously, 1.0g of attapulgite is added into a small beaker with the volume of 50mL, and 20mL of distilled water is added for 1 hour of ultrasonic treatment. Slowly pouring the ultrasonic attapulgite suspension into the stirring SA and PVA solution, and continuously stirring at constant temperature of 60 deg.C for a certain time (2, 3, 4, 5, 6h respectively). After the reaction is fully carried out, the reaction solution is pumped and dripped into 200mL of CaCl by a constant flow pump₂CaCl with a concentration of 0.5 wt%₂And (3) curing and forming in an acetic acid aqueous solution (the concentration of acetic acid is 0.052mol/L) overnight, washing with a large amount of distilled water after full curing, then putting into a culture dish, putting into a refrigerator, freezing for 24 hours, and finally air-drying to obtain the attapulgite-doped double-crosslinked hydrogel (SA/PVA/ATP).

The SA/PVA/ATP hydrogel is adopted to react 50mg/L Cd²⁺The solution was adsorbed and the results are shown in table 3. Adsorption conditions: SA/PVA/ATP: 0.1g, volume of adsorption solution: 25mL, temperature: 25 ℃, adsorption time: and 2 h.

TABLE 3

Example numbering	Reaction time (h)	Cd²⁺Removal Rate (%)
			4-1	2	75.10
4-2	3	78.35
			4-3	4	82.50
4-4	5	77.03
			4-5	6	75.10

Visible, hydrogel pair Cd²⁺The removal rate of (a) tends to increase first and then decrease as the stirring time is prolonged. Hydrogel pair Cd prepared in 4h of stirring time²⁺The removal rate of (2) is up to 82.5%. When the stirring time is too short, ATP is not uniformly mixed in the SA and PVA precursor solutions, and the adsorption effect of the material is influenced. When the stirring time is too long, the viscosity of the precursor solution is increased, so that the material is more tightly crosslinked, and the adsorption effect of the material is influenced.

EXAMPLE 5 investigation of reaction temperature vs. adsorption Performance

1.0g of SA, 2.4g of PVA and 0.8g of NaHCO are weighed out₃60mL of distilled water was added to a small 100mL beaker, and the mixture was stirred in a 60 ℃ constant temperature water bath. Simultaneously adding 1.0g of attapulgite into a 50mL small beaker, adding 20mL of distilled water, and carrying out ultrasonic treatment for 1 h. Slowly pouring the ultrasonic attapulgite suspension into the SA and PVA solution under stirring, and continuously stirring at constant temperature for 4h at different temperatures (25 deg.C, 40 deg.C, 60 deg.C and 80 deg.C respectively). After the reaction is fully carried out, the reaction solution is pumped and dripped into 200mL of CaCl by a constant flow pump₂CaCl with a concentration of 0.5 wt%₂And (3) curing and forming in an acetic acid aqueous solution (the concentration of acetic acid is 0.052mol/L) overnight, washing with a large amount of distilled water after full curing, then putting into a culture dish, putting into a refrigerator, freezing for 24 hours, and finally air-drying to obtain the attapulgite-doped double-crosslinked hydrogel (SA/PVA/ATP).

The SA/PVA/ATP hydrogel is adopted to react 50mg/L Cd²⁺The solution was adsorbed and the results are shown in table 4. AdsorptionConditions are as follows: SA/PVA/ATP: 0.1g, volume of adsorption solution: 25mL, temperature: 25 ℃, adsorption time: and 2 h.

TABLE 4

Example numbering	Reaction temperature (. degree.C.)	Cd²⁺Removal Rate (%)
			5-1	25	82.35
5-2	40	85.10
			5-3	60	81.69
5-4	80	78.90

Visible, hydrogel pair Cd²⁺The removal rate of (a) increases and then decreases with increasing stirring temperature. Hydrogel para-Cd prepared at 40 ℃²⁺The highest removal rate of (2) is 85.1%.

Example 6CaCl₂Study of Mass concentration on adsorption Performance

1.0g of SA, 2.4g of PVA and 0.8g of NaHCO are weighed out₃Adding 60mL of steam into a small 100mL beakerDistilling water, and stirring in a 60 deg.C constant temperature water bath. Simultaneously adding 1.0g of attapulgite into a 50mL small beaker, adding 20mL of distilled water, and carrying out ultrasonic treatment for 1 h. Slowly pouring the ultrasonic attapulgite suspension into the stirring SA and PVA solution, and continuously stirring at constant temperature of 60 ℃ for 4 h. After full reaction, the reaction solution is respectively pumped and dripped into 200mL of CaCl by a constant flow pump₂Is CaCl with certain concentration (0.25, 0.5, 1, 3, 5 wt% respectively)₂-H₃BO₃Aqueous solution (H)₃BO₃Concentration of 0.323mol/L) or certain concentration (0.25, 0.5, 1, 3, 5 wt% respectively) of CaCl₂And (3) solidifying and molding an acetic acid aqueous solution (the concentration of acetic acid is 0.052mol/L) overnight, washing the solution with a large amount of distilled water after full solidification, then putting the solution into a culture dish, putting the culture dish into a refrigerator, freezing the culture dish for 24 hours, and finally air-drying the culture dish to obtain the attapulgite-doped double-crosslinked hydrogel (SA/PVA/ATP).

The SA/PVA/ATP hydrogel is adopted to react with 50mg/L Cd²⁺The solution was adsorbed and the results are shown in table 5. Adsorption conditions: SA/PVA/ATP: 0.1g, volume of adsorption solution: 25mL, temperature: 25 ℃, adsorption time: and 2 h.

TABLE 5

Example numbering	Solidifying solution	CaCl₂Concentration (wt%)	Cd²⁺Removal Rate (%)
				6-1	CaCl₂-H₃BO₃Aqueous solution	0.25	76.51
6-2	CaCl₂-H₃BO₃Aqueous solution	0.5	82.76
				6-3	CaCl₂-H₃BO₃Aqueous solution	1	81.10
6-4	CaCl₂-H₃BO₃Aqueous solution	3	79.82
				6-5	CaCl₂-H₃BO₃Aqueous solution	5	80.12
6-6	CaCl₂-aqueous acetic acid solution	0.25	90.54
				6-7	CaCl₂-aqueous acetic acid solution	0.5	93.43
6-8	CaCl₂-aqueous acetic acid solution	1	90.68
				6-9	CaCl₂-aqueous acetic acid solution	3	88.53
6-10	CaCl₂-aqueous acetic acid solution	5	89.59

Visible, and conventional CaCl₂-H₃BO₃Compared with the solidified solution, CaCl is adopted₂The hydrogel prepared by the acetic acid curing solution greatly improves the adsorption performance of the material. Addition of H₃BO₃Later, the hydrogel cross-links more tightly, blocking Cd in a short time²⁺Internal adsorption transport. When CaCl₂At too low a concentration, the resulting hydrogel is mechanically too weak, which severely influences the structural shape of the hydrogel. When 0.5 wt% CaCl is used₂Hydrogel pair Cd²⁺The removal rate of the catalyst reaches 93.43 percent. When CaCl is continuously added₂When the amount is added, the hydrogel is added to Cd²⁺The removal rate of (A) is reduced, and finally, a balance trend is presented.

Example 7

1.0g of SA, 2.4g of PVA and 0.8g of NaHCO are weighed out₃60mL of distilled water was added to a small 100mL beaker, and the mixture was stirred in a 60 ℃ constant temperature water bath. Simultaneously adding 1.0g of attapulgite into a 50mL small beaker, adding 20mL of distilled water, and carrying out ultrasonic treatment for 1 h. Slowly pouring the well-sonicated attapulgite suspension into the SA and PVA solution under stirring, and continuously stirring at constant temperature of 40 ℃ for 4 hours. After the reaction is fully carried out, the solution is pumped and dripped into 200mL of 0.5 wt% CaCl by a constant flow pump₂Aqueous solution of acetic acid (acetic acid concentration 0.052mol/L) was solidified overnightAnd (3) after the attapulgite is fully solidified, washing with a large amount of distilled water, then putting into a culture dish, putting into a refrigerator, freezing for 24h, and finally air-drying to obtain the attapulgite-doped double-crosslinked hydrogel (SA/PVA/ATP) for later use.

1. For Cd²⁺Adsorption condition study of removal Rate of

(1) Selection of the amount of adsorbent (i.e. SA/PVA/ATP material)

Respectively weighing 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 and 0.10g SA/PVA/ATP material, performing adsorption experiment, as shown in FIG. 4, with the increase of the addition amount of adsorbent, the adsorption capacity gradually decreases, and Cd is adsorbed²⁺The removal rate of (b) is gradually increased. At lower dosages, the adsorption activity sites on the material are limited and the saturated adsorption state is easily achieved. With the increase of the dosage of the gel spheres, the number of adsorption active sites is increased, and a large number of active sites are in a non-saturated adsorption state, so that the gel spheres can adsorb Cd²⁺The removal rate of (2) is increased and the equilibrium adsorption amount is decreased.

(2) Selection of initial concentration

Respectively weighing 20, 30, 40, 50, 60, 70, 80, 90 and 100mg/L Cd²⁺Solution, adsorption experiment was performed. As shown in FIG. 5, with Cd²⁺Increase of concentration, gradual increase of adsorption capacity, and increase of Cd content²⁺The removal rate of (a) gradually decreases. Higher Cd when the mass of the adsorbent is the same²⁺The concentration of the solution can increase Cd²⁺Driving force from water phase to solid phase to overcome mass transfer resistance and make more Cd²⁺Entering the interior of the gel sphere to be combined with the adsorption sites on the gel network; at the same time, higher Cd²⁺Cd provided in concentration² ⁺The ion number is large, so that Cd²⁺Can be fully combined with the adsorption sites on the gel spheres, and the adsorption quantity is obviously improved.

(3) Selection of the pH of the solution

The solutions were adjusted to pH 3.5, 4.0, 4.5, 5.5, 6.0, respectively, for adsorption experiments. As shown in FIG. 6, the material pair Cd as the pH increased²⁺The removal rate and adsorption capacity of (a) gradually increase. H in solution at lower pH⁺Large number of gel spheres with a part of-COO^-Will be protonated to-COOH resulting in a reduced number of adsorption sites on the hydrogel network; at the same time, too much H⁺Will increase H⁺With Cd²⁺Electrostatic repulsion between molecules, competitive adsorption and reduction of hydrogel and Cd²⁺Electrostatic interactions between molecules.

(4) Influence of adsorption time

0.05g of each material was weighed out and added to 100mL of 50mg/L Cd²⁺In the solution, the adsorption experiment was performed by adjusting the pH of the solution to 6. The measurement was carried out by taking the supernatant at 5, 10, 20, 30, 40, 50, 60, 80, 100, 120, 150, 180, 210, and 240min after adsorption, respectively. As shown in FIG. 7, after adsorption was carried out for 150min, adsorption was substantially in equilibrium with Cd²⁺The removal rate was 74.47%.

(5) Influence of adsorption temperature

0.05g of each material was weighed out and added to 100mL of 50mg/L Cd²⁺In the solution, adsorption experiments were performed while adjusting the pH to 6. Adsorbing at 20, 30, and 40 deg.C, respectively, and collecting supernatant at 5, 10, 20, 30, 40, 50, 60, 80, 100, 120, 150, 180, 210, and 240min for determination. The results are shown in FIG. 8, with increasing temperature, for Cd at equilibrium²⁺The removal rate is gradually increased, and Cd is treated at 40 DEG C²⁺The removal rate of (D) is improved by 18.16 percent compared with that at the temperature of 20 ℃. And with the rise of temperature, the Cd is greatly accelerated²⁺The mass transfer rates in the solution were 12.59%, 42.30%, 51.44% removal at 20, 30, 40 ℃ within the first 5min, respectively.

(6) Influence of the Ionic Strength

0.05g of each material was weighed out and added to 25mL of 50mg/L Cd²⁺Adding KNO into the solution₃The concentrations were set to 0, 0.02, 0.04, 0.08, 0.10, 0.16, 0.20, and 0.40mol/L, respectively, and the influence of the ionic strength on the adsorption was examined. The experimental results are shown in FIG. 9, in which the removal of cadmium from the material is slightly reduced with the increase of the ionic strength, and in KNO₃When the concentration reaches 0.20mol/L, the influence of the ionic strength on the material is basically kept unchanged.

2. Saturated adsorption capacity

Respectively taking 50mL of 50, 80 and 110. 150, 200, 250, 300mg/L Cd²⁺0.05g of the hydrogel material prepared above is added into the solution, and the solution is vibrated and adsorbed for 180min at 25 ℃. The saturated adsorption capacity was measured and the results are shown in FIG. 10. Therefore, with the increase of the concentration of Cd, the adsorption capacity of the SA/PVA/ATP to Cd is continuously increased and finally reaches the balance, the saturated adsorption capacity of the material is 68.50mg/g, compared with the saturated adsorption capacity of the PVA/SA which is not added with attapulgite, the saturated adsorption capacity of the PVA/SA is 45.3mg/g, and the adsorption performance of the PVA/SA to the material is improved by 51.21% after the attapulgite is added.

3. Study of adsorption selectivity

In order to simulate the adsorption selectivity of SA/PVA/ATP in practical application, the experiment adopts 0.05g of material addition amount, 200mg/L of Cd, Pb and Cu as research objects, four combinations of Cd-Cu, Cd-Pb, Pb-Cu and Cd-Pb-Cu are adopted, and the distribution coefficient K is selected_dAs an index, the selectivity of SA/PVA/ATP to Cd, Pb and Cu is examined. K_dDenotes the adsorption affinity of the metal cation in solution to the adsorbent, K_dThe higher the indication that the metal is retained by the solid phase by adsorption reaction, and conversely the greater the retention of the metal in solution.

Wherein Q_tMg/g, C as adsorption capacity at the end of adsorption_fThe mass concentration of the metal in the solution at the end of adsorption, mg/L.

The results of the adsorption selectivity study are shown in table 6.

TABLE 6 selectivity of SA/PVA/ATP to Cd, Pb, Cu

Thus, in a Cd-Cu system with the initial concentration of 200mg/L, the material pair CdAnd Cu adsorption capacities of 10.33 and 32.43mg/g, respectively, K_dIs Cu>Cd in Cd-Pb system, the adsorption capacity of the material to Cd and Pb is 23.07, 84.52mg/g, K_dIs Pb>Cd in Pb-Cu system has Cu and Pb adsorbing capacity of 18.20-75.83 mg/g and K_dIs Pb>Cu, the effect of the comprehensive material on removing Cd, Pb and Cu is Pb>Cd>Cu。

Claims

1. The preparation method of the attapulgite-doped double-crosslinked hydrogel is characterized by comprising the following steps of:

2. The method for preparing attapulgite-doped double-crosslinked hydrogel according to claim 1, wherein the method comprises the following steps: the weight ratio of the attapulgite to the sodium alginate to the polyvinyl alcohol is 0.5-2.0: 0.8-1.2: 2-2.4; preferably, the weight ratio of the attapulgite to the sodium alginate to the polyvinyl alcohol is 1.0:1.0: 2.4.

3. The method for preparing attapulgite-doped double-crosslinked hydrogel according to claim 1, wherein the method comprises the following steps: NaHCO 2₃The weight ratio of the polyvinyl alcohol to the polyvinyl alcohol is 0.3-1.0: 2.4; preferred is NaHCO₃The weight ratio to polyvinyl alcohol was 0.8: 2.4.

4. The method for preparing attapulgite-doped double-crosslinked hydrogel according to claim 1, wherein the method comprises the following steps: in the step b, the stirring reaction is carried out at the temperature of 25-80 ℃ for 2-6 h; the reaction is preferably stirred at 40 ℃ for 4 h.

5. The method for preparing attapulgite-doped double-crosslinked hydrogel according to claim 1, wherein the method comprises the following steps: CaCl₂In aqueous acetic acid, CaCl₂The concentration of (A) is 0.25-5 wt%; preferably CaCl₂Is 0.5 wt%.

6. The method for preparing attapulgite-doped double-crosslinked hydrogel according to claim 1, wherein the method comprises the following steps: CaCl₂The molar quantity of acetic acid in the aqueous solution of acetic acid is NaHCO in the mixed solution B₃100-150% of the molar weight of (A); preferably CaCl₂The molar quantity of acetic acid in the aqueous solution of acetic acid is NaHCO in the mixed solution B₃110% of the molar amount of (c).

7. The attapulgite-doped double-crosslinked hydrogel prepared by the method for preparing the attapulgite-doped double-crosslinked hydrogel according to any one of claims 1 to 6.

8. The use of the attapulgite-doped double-crosslinked hydrogel of claim 7 for adsorbing heavy metal ions in a water body.

9. The application of the attapulgite-doped double-crosslinked hydrogel in adsorbing heavy metal ions in a water body according to claim 8 is characterized in that: the heavy metal ions comprise at least one of Cd, Pb and Cu ions.

10. The application of the attapulgite-doped double-crosslinked hydrogel in adsorbing heavy metal ions in a water body according to claim 8, wherein the attapulgite-doped double-crosslinked hydrogel comprises the following components in percentage by weight: and before adsorption, adjusting the pH value of the water body to 3.5-6.