Green and environment-friendly heavy metal adsorbent based on sodium alginate and preparation method and application thereof

Abstract

The application discloses a green and environment-friendly heavy metal adsorbent based on sodium alginate and a preparation method and application thereof, and comprises the following steps: adding calcium chloride solution dropwise into a mixed aqueous solution of sodium alginate, carboxymethyl chitosan, sodium bentonite and polyethylene glycol to obtain hydrogel balls; placing the hydrogel balls in a 2-morpholinoethanesulfonic acid solution; adding N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl) carbodiimide; stirring and mixing to obtain modified hydrogel balls; and freezing and drying the modified hydrogel balls to obtain the green and environment-friendly heavy metal adsorbent based on sodium alginate; the adsorbent has the advantages of simple preparation process, simple and non-toxic raw materials and easy availability; the adsorbent has strong adsorption selectivity for Cu(II) and Pb(II) in a complex heavy metal water environment, and can be used for treating complex wastewater with large amounts of Cu(II) and Pb(II) emissions.

Description

Technical Field

[0001] This invention belongs to the field of adsorbent preparation, specifically a green and environmentally friendly heavy metal adsorbent based on sodium alginate, its preparation method, and its application. Background Technology

[0002] With the continuous development of large-scale industries such as batteries, mining, and electroplating, large amounts of heavy metals such as Cu(II), Pb(II), and Cd(II) are discharged into water bodies through industrial wastewater. Once in the water, these heavy metals are absorbed by plankton and aquatic plants, accumulate through the food chain, and enter aquatic animals and humans, causing irreversible harm. Therefore, the impact of heavy metal pollution on the aquatic environment and public health is extremely serious and cannot be ignored.

[0003] Current adsorbents are not ideal, mainly due to the high cost caused by the use and production of highly toxic substances in their preparation process and products. In view of this, this invention develops a heavy metal adsorbent based on sodium alginate. This adsorbent has advantages such as an environmentally friendly preparation process, high heavy metal adsorption capacity, suitability for treating wastewater containing Pb and Cu, and low cost, making it valuable for treating wastewater containing Pb(II) and Cu(II). Summary of the Invention

[0004] The purpose of this invention is to provide a green and environmentally friendly heavy metal adsorbent based on sodium alginate, its preparation method and application, in order to solve the problems mentioned in the background art.

[0005] To solve the above problems, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing a heavy metal adsorbent based on sodium alginate, comprising the following steps:

[0007] (1) Add 1-2 parts by weight of sodium alginate, 0.5-0.7 parts by weight of carboxymethyl chitosan, 0.2-0.4 parts by weight of sodium bentonite and 0.2-0.4 parts by weight of polyethylene glycol to 96-99 parts by weight of water to prepare a solution;

[0008] (2) Add calcium chloride solution to the solution obtained in step (1) to obtain hydrogel spheres;

[0009] (3) Place 8-13 parts by weight of the hydrogel balls obtained in step (2) into 85-92 parts by weight of 2-morpholinoethanesulfonic acid solution, add 0.02-0.06 parts by weight of L-glutamine, 0.1-0.5 parts by weight of N-hydroxysuccinimide and 0.01-0.04 parts by weight of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, stir and mix to obtain the modified hydrogel balls;

[0010] (4) The modified hydrogel balls obtained in step (3) are freeze-dried to obtain the sodium alginate-based heavy metal adsorbent.

[0011] Furthermore, the sodium-based bentonite described in step (1) needs to pass through a 60-120 mesh sieve.

[0012] Further, in step (2), the mass ratio of calcium chloride to water in the calcium chloride solution is 1:85-92. Stir and let stand for 8-16 hours (preferably 12 hours).

[0013] Further, in step (3), the mass ratio of 2-morpholine ethanesulfonic acid to water in the 2-morpholine ethanesulfonic acid solution is 1:45-60, and the pH of the solution is between 5.5 and 6.5. Stir and mix for 20-28 hours (preferably 24 hours).

[0014] In a second aspect, the present invention provides a sodium alginate-based heavy metal adsorbent prepared by the above-described preparation method.

[0015] A third aspect of the present invention provides the application of sodium alginate-based heavy metal adsorbents in adsorbing heavy metal ions in water.

[0016] The beneficial effects of this invention are:

[0017] Based on raw materials such as sodium alginate, carboxymethyl chitosan, sodium bentonite, and polyethylene glycol, this invention has the advantages of low cost, non-toxicity to organisms, and ease of operation, while also achieving controllability of product performance.

[0018] Optimizing the modification of gel spheres can significantly improve their adsorption effect on heavy metals and enhance their selective adsorption of Cu(II) and Pb(II) in complex metal environments, which is of great significance for the treatment of wastewater mainly containing Cu(II) or Pb(II).

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] This invention uses sodium alginate, carboxymethyl chitosan, sodium bentonite, and polyethylene glycol as reactants to synthesize a heavy metal stabilizer based on sodium alginate gel. Sodium alginate, carboxymethyl chitosan, and sodium bentonite are naturally sourced, while polyethylene glycol can be obtained through bio-fermentation; all are green and environmentally friendly industrial raw materials with advantages such as low price, low toxicity, biodegradability, abundant sources, and renewability. This heavy metal adsorbent material has a simple synthesis process, mild reaction conditions, and exhibits advantages such as high efficiency, rapid and selective adsorption of Cu(II) and Pb(II). Attached Figure Description

[0021] Figure 1The adsorption effect of the adsorbent obtained in Example 1 of this invention on each heavy metal at different concentrations of mixed heavy metal ions is shown.

[0022] Figure 2 The adsorption selectivity coefficients of the adsorbent obtained in Example 2 of this invention for each heavy metal at different heavy metal ion concentrations.

[0023] Figure 3 The adsorption effect of the adsorbent obtained in Example 3 of this invention on Cu(II) at different pH values ​​is shown.

[0024] Figure 4 The adsorption effect of the adsorbent obtained in Example 4 of this invention on Pb(II) at different pH values ​​is shown.

[0025] Figure 5 This shows the relationship between the amount of Cu(II) adsorbed by the adsorbent obtained in Example 5 of the present invention and the change over time.

[0026] Figure 6 This shows the relationship between the amount of Pb(II) adsorbed by the adsorbent obtained in Example 6 of the present invention and the change over time.

[0027] Figure 7 The images show the SEM and EDS spectra of the adsorbent obtained in Example 1 of this invention before and after modification.

[0028] Figure 8 The images show the infrared spectra of the raw materials and the resulting adsorbent before and after modification in Example 1 of this invention. Detailed Implementation

[0029] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0030] Example 1

[0031] Add 1 part sodium alginate, 0.5 parts carboxymethyl chitosan, 0.2 parts sodium bentonite (passed through a 60-mesh sieve), and 0.2 parts polyethylene glycol (molecular weight 1000) to 98.1 parts distilled water, stir and mix well. Then, use a syringe to drop the mixture drop by drop into a calcium chloride solution with a calcium chloride:water mass ratio of 1:85. Stir and let stand for 12 hours to obtain hydrogel balls.

[0032] Eight parts of hydrogel spheres were added to a 2-morpholine ethanesulfonic acid solution (pH = 5.5) with a mass ratio of 1:45 of 2-morpholine ethanesulfonic acid to water. Then, 0.02 parts by mass of L-glutamine, 0.1 parts by mass of N-hydroxysuccinimide, and 0.01 parts by mass of 1-ethyl-(3-dimethylaminopropyl)carbodiimide were added and stirred for 24 hours. The modified hydrogel spheres were washed with sufficient distilled water and then freeze-dried to obtain the adsorbent.

[0033] Example 2

[0034] Two parts sodium alginate, 0.7 parts carboxymethyl chitosan, 0.4 parts sodium bentonite (passed through a 120-mesh sieve), and 0.4 parts polyethylene glycol (molecular weight 1000) were added to 96.5 parts distilled water and stirred until well mixed. Then, the mixture was added drop by drop into a calcium chloride solution with a mass ratio of 1:92 (calcium chloride:water) using a syringe. The mixture was stirred and allowed to stand for 12 hours to obtain hydrogel spheres.

[0035] Thirteen parts of hydrogel spheres were added to a 2-morpholine ethanesulfonic acid solution (pH = 6.5) with a mass ratio of 1:60 of 2-morpholine ethanesulfonic acid to water. Then, 0.06 parts by mass of L-glutamine, 0.5 parts by mass of N-hydroxysuccinimide, and 0.04 parts by mass of 1-ethyl-(3-dimethylaminopropyl)carbodiimide were added and stirred for 24 hours. The modified hydrogel spheres were washed with sufficient distilled water and then freeze-dried to obtain the adsorbent.

[0036] Example 3

[0037] 1.2 parts sodium alginate, 0.5 parts carboxymethyl chitosan, 0.2 parts sodium bentonite that has passed through an 80-mesh sieve, and 0.4 parts polyethylene glycol (molecular weight 1000) were added to 97.7 parts distilled water and stirred until well mixed. Then, the mixture was added drop by drop into a calcium chloride solution with a mass ratio of 1:90 to water using a syringe. The mixture was stirred and allowed to stand for 12 hours to obtain hydrogel spheres.

[0038] Eight parts of hydrogel spheres were added to a 2-morpholine ethanesulfonic acid solution (pH=6) with a mass ratio of 1:50 of 2-morpholine ethanesulfonic acid to water. Then, 0.04 parts by mass of L-glutamine, 0.3 parts by mass of N-hydroxysuccinimide, and 0.02 parts by mass of 1-ethyl-(3-dimethylaminopropyl)carbodiimide were added and stirred for 24 hours. The modified hydrogel spheres were washed with sufficient distilled water and then freeze-dried to obtain the adsorbent.

[0039] Example 4

[0040] 1.5 parts sodium alginate, 0.5 parts carboxymethyl chitosan, 0.3 parts sodium bentonite that has passed through a 100-mesh sieve, and 0.3 parts polyethylene glycol (molecular weight 1000) were added to 97.4 parts distilled water and stirred until well mixed. Then, the mixture was added drop by drop into a calcium chloride solution with a mass ratio of 1:90 to calcium chloride and water using a syringe. The mixture was stirred and allowed to stand for 12 hours to obtain hydrogel spheres.

[0041] 8.5 parts of hydrogel spheres were added to a 2-morpholine ethanesulfonic acid solution (pH=6.5) with a mass ratio of 1:50 of 2-morpholine ethanesulfonic acid to water. 0.05 parts of L-glutamine, 0.4 parts of N-hydroxysuccinimide, and 0.02 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide were added and stirred for 24 hours. The modified hydrogel spheres were then washed with sufficient distilled water and freeze-dried to obtain the adsorbent.

[0042] Example 5

[0043] 1.5 parts sodium alginate, 0.5 parts carboxymethyl chitosan, 0.4 parts sodium bentonite that has passed through a 120-mesh sieve, and 0.2 parts polyethylene glycol (molecular weight 1000) were added to 97.4 parts distilled water and stirred until well mixed. Then, the mixture was added drop by drop into a calcium chloride solution with a mass ratio of 1:90 to calcium chloride and water using a syringe. The mixture was stirred and allowed to stand for 12 hours to obtain hydrogel spheres.

[0044] Nine parts of hydrogel spheres were added to a 2-morpholine ethanesulfonic acid solution (pH = 6.5) with a mass ratio of 1:60 of 2-morpholine ethanesulfonic acid to water. Then, 0.05 parts by mass of L-glutamine, 0.5 parts by mass of N-hydroxysuccinimide, and 0.02 parts by mass of 1-ethyl-(3-dimethylaminopropyl)carbodiimide were added and stirred for 24 hours. The modified hydrogel spheres were washed with sufficient distilled water and then freeze-dried to obtain the adsorbent.

[0045] Example 6

[0046] 0.10 g of the product prepared in Example 5 was added to 250 ml of a heavy metal solution with a Cu(II) concentration of 1.0 mmol / L. Samples were taken at 25 °C at shaking times for 1, 2, 5, 15, 30, 50, 70, 90, 120, and 150 min, and the Cu(II) concentration was measured. The adsorption amount of Cu(II) at different shaking times was calculated. A curve showing the change in adsorption amount over time was plotted based on the shaking time and the corresponding Cu(II) adsorption amount.

[0047] Example 7

[0048] 0.10 g of the product prepared in Example 5 was added to 250 ml of a heavy metal solution with a Pb(II) concentration of 1.0 mmol / L. Samples were taken at 25 °C at shaking times for 1, 2, 5, 15, 30, 50, 70, 90, 120, and 150 min, and the Pb(II) concentration was measured. The adsorption amount of Pb(II) at different shaking times was calculated. A curve showing the change in adsorption amount over time was plotted based on the shaking time and the corresponding Pb(II) adsorption amount.

[0049] Example 8

[0050] 0.95 parts sodium alginate, 0.95 parts carboxymethyl chitosan, 0.77 parts sodium bentonite that has passed through a 120-mesh sieve, and 0.24 parts polyethylene glycol were added to 97.09 parts distilled water and stirred until well mixed. Then, the mixture was added drop by drop into a calcium chloride solution with a mass ratio of 1:90 to calcium chloride and water using a syringe. The mixture was stirred and allowed to stand for 12 hours to obtain hydrogel spheres.

[0051] Nine parts of hydrogel spheres were added to a 2-morpholine ethanesulfonic acid solution (pH = 6.5) with a mass ratio of 1:48 of 2-morpholine ethanesulfonic acid to water. Then, 0.04 parts by mass of L-glutamine, 0.5 parts by mass of N-hydroxysuccinimide, and 0.02 parts by mass of 1-ethyl-(3-dimethylaminopropyl)carbodiimide were added and stirred for 24 hours. The modified hydrogel spheres were washed with sufficient distilled water and then freeze-dried to obtain the adsorbent.

[0052] Equal masses of the adsorbents obtained in Examples 5 and 8 were placed into equal volumes of a mixed heavy metal solution containing 0.5 mmol / L of Cu(II), Zn(II), Pb(II), Cd(II), and Ni(II) at pH=5. After shaking at 25°C for 2 hours, samples were taken to determine the concentration of each heavy metal remaining in the solution. The Cu(II) removal rate of the adsorbent prepared in Example 8 was 30.7%, and the Pb(II) removal rate was 39.0%. The Cu(II) removal rate of the adsorbent prepared in Example 5 was 42.6%, and the Pb(II) removal rate was 54.6%. This indicates that failure to add raw materials according to the claims of this invention will significantly reduce the adsorption capacity of the prepared adsorbent.

[0053] Example 9

[0054] Add 1.5 parts sodium alginate, 0.5 parts carboxymethyl chitosan, 0.4 parts sodium bentonite that has passed through a 120-mesh sieve, and 0.2 parts polyethylene glycol to 97.4 parts distilled water, stir and mix well. Then, use a syringe to drop the mixture drop by drop into a calcium chloride solution with a calcium chloride:water mass ratio of 1:90. Stir and let stand for 12 hours to obtain hydrogel spheres.

[0055] Nine parts of hydrogel spheres were added to a 2-morpholine ethanesulfonic acid solution (pH=5) with a mass ratio of 1:50 of 2-morpholine ethanesulfonic acid to water. Then, 0.05 parts by mass of L-glutamine, 0.05 parts by mass of N-hydroxysuccinimide, and 0.05 parts by mass of 1-ethyl-(3-dimethylaminopropyl)carbodiimide were added and stirred for 24 hours. The modified hydrogel spheres were washed with sufficient distilled water and then freeze-dried to obtain the adsorbent.

[0056] The adsorbents obtained in Examples 5 and 9 were respectively added to solutions containing 1 mmol / L Cu(II) and 1 mmol / L Pb(II), and the pH was adjusted to 6. After shaking at 25°C for 2 hours, samples were taken to determine the remaining concentration of Cu or Pb in the solution, and the adsorption capacity on the adsorbent was calculated. The adsorbent prepared in Example 9 had an adsorption capacity of 54.1 mg / g for Cu(II) and 156.1 mg / g for Pb(II), while the adsorbent prepared in Example 5 had an adsorption capacity of 88.5 mg / g for Cu(II) and 309.3 mg / g for Pb(II). This indicates that the modification step of the gel spheres according to the claims of this invention will significantly improve the adsorption capacity of the prepared adsorbent.

[0057] like Figure 1 and 2 The figures show the adsorption capacity and adsorption selectivity coefficients of each heavy metal ion in wastewater containing Cu(II), Zn(II), Pb(II), Cd(II), and Ni(II) at different molar concentrations, as obtained by the adsorbent in Example 1. The maximum adsorption capacities for Cu and Pb are 0.772 mmol / L and 1.687 mmol / L, respectively. The adsorbent of this invention exhibits significantly higher adsorption capacities for Cu and Pb than those reported by Qiu et al. in the *Journal of Analytical and Applied Pyrolysis* in 2021. Specifically, the adsorption capacity of the adsorbent of this invention for Cu ranges from 8.9 to 75.99 mg / g (0.14-1.20 mmol / L), while the adsorption capacity for Pb exceeds 53.72 mg / g (0.26 mmol / L). According to the partition coefficient K... dThe calculation results using the formula (Pb adsorption capacity at equilibrium / Pb concentration in equilibrium solution) show that the partition coefficients of the adsorbent prepared in this invention for Cu and Pb reach 202-5269 L / g and 390-18123 L / g, respectively, which are much higher than the partition coefficients for Zn, Cd, and Ni, and significantly higher than the partition coefficients for Pb (0.06-475.23 L / g) of various modified activated carbons reported by Lee et al. in the Journal of Environmental Management in 2021. This indicates that the adsorbent of this invention has good adsorption performance for Cu and Pb, and still exhibits good selective adsorption capacity for Pb(II) and Cu(II) in a multi-element heavy metal system.

[0058] like Figure 3 and Figure 4 The figures show the adsorption effects of the adsorbents obtained in Examples 3 and 4 of this invention on Cu(II) and Pb(II) at different pH values. The adsorption capacity of the adsorbent gradually increases as the pH of the solution increases, and reaches the maximum adsorption capacity at pH 6.5 and 6.0, respectively, which are 94.2 mg / g Cu (1.48 mmol / g) and 309.3 mg / g Pb (1.49 mmol / g).

[0059] like Figure 5 and Figure 6 As shown, the adsorption capacity of the adsorbents obtained in Examples 5 and 6 of this invention for Cu(II) and Pb(II) changes over time. In the initial period of adsorption, the adsorbent adsorbs rapidly, and the adsorption kinetic curve shows a steep upward trend. It reaches a plateau at around 120 min, and the adsorption capacity of the adsorbent is relatively stable. At this time, the adsorption capacity of the adsorbent for Cu(II) and Pb(II) is 81.0 mg / g (1.28 mmol / g) and 265.2 mg / g (1.28 mmol / g), respectively.

[0060] like Figure 7 As shown, (a), (b), and (c) are SEM images and EDS spectra of the adsorbent obtained in Example 1 of this invention before modification, and (d), (e), and (f) are SEM images and EDS spectra of the adsorbent obtained in Example 1 after modification. It can be seen from the figures that their surface microstructures are basically the same before and after modification, both consisting of stacked nanolayers, each layer containing numerous mesopores with a diameter of approximately 20 nm. These dense mesopores provide the adsorbent material with a larger specific surface area and more adsorption sites, resulting in higher Cu and Pb adsorption capacities. The EDS spectra show that the mass ratio of C to N in the modified adsorbent is significantly increased, indicating that L-glutamine was successfully introduced into the gel spheres during the modification process.

[0061] like Figure 8 The image shows the infrared spectra of the raw materials and the resulting adsorbent before and after modification in Example 1. Sodium alginate and carboxymethyl chitosan, the raw materials, were measured at 3224 cm⁻¹. -1 and 3218cm -1 The synthesized adsorbent exhibited broad peaks, with values ​​of 3229 and 3259 cm⁻¹ before and after modification, respectively. -1 A broad peak appears, which is the combined peak of the stretching vibrations of associated OH and NH. The four substances show peaks at 1777-1786 cm⁻¹. -1 The absorption peak of COO- is the asymmetric stretching vibration peak, 1295-1308 cm⁻¹. -1 The absorption peak at 2520-2538 cm⁻¹ is the CO stretching vibration peak. -1 The weak absorption at 1599 cm⁻¹ corresponds to a carboxyl hydroxyl peak, confirming the presence of a carboxyl group. The four substances showed absorption peaks at 1599 cm⁻¹. -1 1580cm -1 1590cm -1 and 1600cm -1 Stretching vibrations of associated NH groups were observed at all locations, and occurred in the range of 1411-1414 cm⁻¹. -1 The CN stretching vibration peak at 2895-2927 cm⁻¹ was confirmed, indicating the presence of amino groups; -1 The absorption peak for CH is 1026-1036 cm⁻¹. -1 The presence of a C2C absorption peak indicates that the adsorbent of this invention is a straight-chain alkane and does not contain aromatic structures. The adsorbent obtained in this invention exhibits a peak at 1413 cm⁻¹ after synthesis. -1 The absorption peak at 1600 cm⁻¹ is significantly enhanced, showing superior performance after modification compared to the introduction of amide groups. -1 The enhanced peak intensity and shift towards higher wavelengths indicate that L-glutamine was successfully introduced into the gel spheres via stable amide bonds, demonstrating successful modification.

[0062] The primary objective of this invention, as described above, is to develop an adsorbent with potential environmental application value. Results show that this adsorbent exhibits a unique layered, loose structure and abundant mesoporous properties, which facilitate the adsorption of metal ions. Furthermore, the adsorbent surface is covered with a large number of amide and carboxyl groups, providing more adsorption sites and significantly improving its adsorption performance. It is worth emphasizing that the distribution of surface functional groups (N and O atoms) makes it easier to form stable coordination structures with metal ions Cu and Pb, thereby achieving selective adsorption of these two ions. In conclusion, this invention is expected to provide a new solution for applications such as the removal and recovery of metal ions in the environmental field.

Claims

1. A method for preparing a green and eco-friendly heavy metal adsorbent based on sodium alginate, characterized by, The preparation method comprises the following steps: Step (1): 1-2 parts by mass of sodium alginate, 0.5-0.7 parts by mass of carboxymethyl chitosan, 0.2-0.4 parts by mass of sodium bentonite and 0.2-0.4 parts by mass of polyethylene glycol are added into 96-99 parts by mass of water to prepare a solution; Step (2): the solution of step (1) is added dropwise into an aqueous solution of calcium chloride, and stirring and standing are performed to obtain hydrogel balls; Step (3): 8-13 parts by mass of the hydrogel balls obtained in step (2) are placed into 85-92 parts by mass of a 2-morpholinoethanesulfonic acid solution, 0.02-0.06 parts by mass of L-glutamine, 0.1-0.5 parts by mass of N-hydroxysuccinimide and 0.01-0.04 parts by mass of 1-ethyl-(3-dimethylaminopropyl) carbonyldiimide are added, and stirring and mixing are performed to obtain modified hydrogel balls; Step (4): the modified hydrogel balls are freeze-dried to obtain a green and environmentally friendly heavy metal adsorbent based on sodium alginate.

2. The method for preparing a green and eco-friendly heavy metal adsorbent based on sodium alginate according to claim 1, characterized in that, In step (1), the sodium bentonite needs to pass through a 60-120 mesh screen.

3. The method for preparing a green and eco-friendly heavy metal adsorbent based on sodium alginate according to claim 1, characterized in that, In step (2), the mass ratio of calcium chloride to water in the aqueous solution of calcium chloride is 1:85-92.

4. The method for preparing a green and eco-friendly sodium alginate-based heavy metal adsorbent according to claim 1, characterized in that, In step (2), stirring and standing are performed for 8-16 hours.

5. The method for preparing a green and eco-friendly heavy metal adsorbent based on sodium alginate according to claim 1, characterized in that, In step (3), the mass ratio of 2-morpholinoethanesulfonic acid to water in the 2-morpholinoethanesulfonic acid solution is 1:45-60, and the pH of the solution is 5.5-6.

5.

6. The process for the preparation of sodium alginate based eco-friendly green heavy metal adsorbent as claimed in claim 1, wherein, In step (3), stirring and mixing are performed for 20-28 hours.

7. Application of the green and environmentally friendly heavy metal adsorbent based on sodium alginate prepared by the preparation method of any one of claims 1-6 to treatment of wastewater containing heavy metals.

8. Use according to claim 7, characterized in that, The heavy metals are Cu(II) and Pb(II).

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