Preparation method and application of PDA / CS composite adsorbent loaded with bimetallic system

Abstract

The invention belongs to the technical field of water treatment, and particularly relates to a preparation method and application of a PDA / CS composite adsorbent loaded with a bimetallic system, and the preparation method comprises the following steps: 1) dissolving dopamine in a Tris buffer solution to prepare a dopamine prepolymer solution; then adding FeCl3, and carrying out constant-temperature water bath; centrifuging the obtained black suspension, performing suction filtration, washing, collecting a filter cake, and performing freeze drying to obtain PDA microspheres; 2) dispersing PDA microspheres in deionized water, and carrying out ultrasonic treatment until the PDA microspheres are uniformly dispersed; 3) dissolving chitosan in an acetic acid solution, and adding CuCl2 to prepare a mixed solution; the suspension obtained in the step 2 is dropwise added into a mixed solution for constant-temperature water bath, the pH of the mixed solution is adjusted through a NaOH solution, glutaraldehyde is added for constant-temperature water bath after constant-temperature water bath, and 4, the obtained suspension is subjected to centrifugation, suction filtration, washing, filter cake collection and freeze drying.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, and particularly relates to a method for preparing and applying a PDA / CS composite adsorbent supported on a bimetallic system. Background Technology

[0002] In recent years, with rapid economic development, marine pollution has become increasingly serious. Organic pollution in the ocean is one of the most common types of pollution. Furthermore, due to the diverse types and complex structures of organic matter, and its ability to combine with heavy metals to produce various derivatives, water pollution control is extremely difficult. Humic acid, as a natural organic compound, is widely distributed in the soil, water bodies, and plant tissues of the Earth's ecosystem, accounting for 60-80% of water-soluble organic matter. It possesses abundant functional groups such as carboxyl, phenolic hydroxyl, and carbonyl groups, and also has a loose, sponge-like structure, which can combine with organic pollutants and metal ions to form toxic metal compounds, thereby reducing its biodegradability and disrupting the stability of the ecological environment. Humic acid is a major precursor to halogenation byproducts of chlorination disinfection in drinking water treatment and is also one of the main causes of Kashin-Beck disease, seriously endangering human health. Humic acid can combine with Fe... 3+ The reaction occurs when the substance is adsorbed onto the pipe surface. Microorganisms in the water use it as a nutrient to multiply and accumulate it, forming a biofilm on the pipe surface, which in turn accelerates the corrosion of the pipe network.

[0003] Common methods for removing humic acid include enhanced coagulation, pre-oxidation, membrane filtration, biodegradation, and adsorption. Enhanced coagulation refers to methods that enhance the removal of pollutants such as fine particulate matter and organic matter from water by adding large amounts of coagulants, coagulant aids, or oxidants, or adjusting the pH of the raw water, based on conventional treatment technologies. Al(III) salts and Fe(II) salts are most widely used in water treatment. The removal mechanism of humic acid includes adsorption charge neutralization and complexation precipitation, and the removal rate can reach more than 90%. Pre-oxidation increases the polarity and hydrophilicity of humic acid by oxidizing the carbon-carbon double bonds, hydroxyl groups, and carbonyl groups in the humic acid molecule, thereby losing the double bonds and aromaticity. However, oxidation generates carcinogenic, mutagenic, and teratogenic byproducts, increases the mutagenicity of effluent, and has high operating costs. Membrane filtration mainly uses ultrafiltration (UF) and nanofiltration (NF) technologies to remove natural organic matter such as humic acid from water, but investment costs and issues related to reversible and irreversible membrane fouling limit its application in actual water treatment. Biodegradation utilizes various fungi and bacteria to selectively degrade the aromatic structures in humic substances, but biodegradation is less efficient, and biological processes are easily affected by external hydraulic load, pH, temperature, and aeration rates. Adsorption is often used to remove organic matter and heavy metals from wastewater due to its economic efficiency, high efficiency, and simple operation. Ideal adsorbent materials should be widely available, safe and environmentally friendly, readily available, and inexpensive. Chitosan (CS) and dopamine (DA) are two widely derived natural biomass materials with abundant functional groups, such as hydroxyl, carboxyl, and amino groups, which chelate with various polyvalent metal ions such as iron, zinc, and copper ions. Humic acid contains carboxyl, phenolic, and hydroxyl aromatic compounds in its core, exhibiting excellent adsorption, complexation, and stabilization effects on metal ions. Therefore, using chitosan and dopamine as metal ion carriers to prepare adsorbent materials can achieve the removal of humic acid. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a method for preparing and applying a PDA / CS composite adsorbent with a loaded bimetallic system. By using dopamine and chitosan, which have complexation effects with metals, to coat metal ions, the stability of the metal is increased while the rich functional groups of dopamine and chitosan are utilized to achieve efficient and rapid removal of humic acid, thus avoiding secondary pollution to water bodies.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a PDA / CS composite adsorbent supported on a bimetallic system includes the following steps:

[0007] 1) Weigh dopamine and dissolve it in tris(hydroxymethyl)aminomethane to form a dopamine prepolymer solution. Add ferric chloride and heat in a constant temperature water bath at 25-40℃ for 1-12 hours to obtain a black suspension. Centrifuge, filter, collect the filter cake, freeze dry to obtain PDA microspheres. Disperse the PDA microspheres in water and sonicate to obtain a uniform suspension.

[0008] 2) Chitosan was dissolved in acetic acid solution, and copper chloride was added to form a CS / CuCl2 mixed solution. The solution was defoamed by sonication, and then the uniform suspension described in step 1 was added. The solution was heated in a constant temperature water bath at 25~40℃ for 1~2 hours. Alkali solution was added to adjust the pH to 6.5~8.0, and the solution was heated in a constant temperature water bath at 25~40℃ for 1~12 hours. Then glutaraldehyde with a volume fraction of 1%~50% was added, and the solution was heated in a constant temperature water bath at 25~40℃ for 4~12 hours. The suspension after the reaction was centrifuged, filtered, washed with water, and the filter cake was collected and freeze-dried to obtain CuCl2 / PDA / CS composite microspheres with a core-shell structure.

[0009] In step 1), the concentration of ferric chloride is 1~10 mmol / L, and the concentration of dopamine in the dopamine prepolymer solution is 1~5 g / L.

[0010] The freeze-drying conditions in step 1) are as follows:

[0011] The freeze-drying temperature is -60~-40℃;

[0012] The freeze-drying time is 12-24 hours;

[0013] The ultrasonic dispersion time in step 1) is 15-30 minutes;

[0014] The concentration of the uniform suspension is 0.1~0.5 mg / mL.

[0015] The concentration of the acetic acid solution mentioned in step 2) is 1% to 3%; the volume of the acetic acid solution is the same as that of tris(hydroxymethyl)aminomethane.

[0016] In step 2), the mass ratio of chitosan to copper chloride in the CS / CuCl2 mixed solution is (0.5~1):1.

[0017] Step 2) The alkaline solution is a NaOH solution with a concentration of 1~5 mol / L;

[0018] The molar ratio of glutaraldehyde to chitosan in step 2) is 1:1 to 3:1;

[0019] The freeze-drying conditions described in step 2) are as follows:

[0020] The freeze-drying temperature is -60~-40℃;

[0021] The freeze-drying time is 12-24 hours.

[0022] An application of a PDA / CS composite adsorbent supported on a bimetallic system involves adding FeCl3 / PDA / CS composite microspheres with a core-shell structure into a solution containing humic acid to form an adsorbent-humic acid suspension, which is then placed in a constant temperature shaking chamber for adsorption. After adsorption, the suspension is centrifuged, and the supernatant is taken to determine the concentration of humic acid after adsorption.

[0023] The concentration of the FeCl3 / PDA / CS composite microspheres with a core-shell structure in the humic acid suspension is 0.1~1.0 g / L, the concentration of the humic acid solution is 1~5 mg / L, and the pH is 4~10.

[0024] The solution containing humic acid includes competing ions, namely Cl- and CO32-. 2- SO4 2- At least one of the following, wherein humic acid, Cl - CO3 2- SO4 2- The concentration ratio is 1:(5~1):(5~1):(5~1).

[0025] The adsorption process involves washing and filtering the composite microspheres after reaching adsorption equilibrium, freeze-drying them, placing them in an eluent, magnetically stirring, filtering, washing, freeze-drying, and then adding a humic acid solution containing competing ions for regeneration adsorption.

[0026] The adsorption temperature is 25~40℃;

[0027] The eluent is a mixed solution of acetic acid and anhydrous ethanol with a volume ratio of (0.05~0.1):1.

[0028] The regeneration adsorption is performed 1 to 10 times. Compared with the prior art, the beneficial effects of the present invention are:

[0029] This composite adsorbent has excellent adsorption performance and is a safe and environmentally friendly adsorbent material.

[0030] 1. The method of this invention employs FeCl3-modified polydopamine as the core and CuCl2-modified chitosan as the shell to obtain a PDA / CS composite adsorbent with abundant adsorption sites supporting a bimetallic system. This composite adsorbent increases metal stability while utilizing the abundant functional groups of dopamine and chitosan to achieve efficient and rapid removal of humic acid.

[0031] 2. This invention employs a method for treating humic acid in water by adsorbing bimetallic modified polydopamine / chitosan composite microspheres. Compared with traditional adsorbents, the materials selected in this invention are widely available, safe, non-toxic, and environmentally friendly.

[0032] 3. This invention utilizes the abundant functional groups of dopamine and chitosan, as well as the loaded bimetallic compounds, to achieve good adsorption of humic acid. Even after ten cycles of regeneration, it still exhibits good removal performance, and the adsorbent regeneration process is easy to operate. Attached Figure Description

[0033] Figure 1 This is a graph showing the effect of the number of cycles on the humic acid removal rate of the adsorbent in this invention. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0035] Example 1:

[0036] A method for preparing a PDA / CS composite adsorbent supported on a bimetallic system includes the following steps:

[0037] 1) Weigh 0.2g of dopamine and dissolve it in 100mL of Tris buffer solution to prepare a 2g / L dopamine prepolymer solution;

[0038] 2) Add 10 mmol of FeCl3 to the dopamine prepolymer solution in step 1), place it in a constant temperature water bath at 25°C, and react for 4 hours;

[0039] 3) The black suspension obtained in step 2) was centrifuged, filtered, and washed. The filter cake was collected, and the resulting product was freeze-dried for 12 hours to obtain PDA microspheres.

[0040] 4) Disperse the PDA microspheres obtained in step 3) in deionized water to prepare a 0.25 mg / mL suspension, and sonicate for 15 min until uniformly dispersed;

[0041] 5) Weigh 0.1g of chitosan and dissolve it in 100mL of acetic acid solution. After complete dissolution, add 0.1g of CuCl2 to prepare a CS / CuCl2 mixed solution with a mass ratio of 1:1. After complete dissolution, defoam by sonication. Add the suspension obtained in step 4) dropwise to the mixed solution and place it in a constant temperature water bath at 25℃ for 1 hour.

[0042] 6) Adjust the pH of the mixed solution obtained in step 5) to 6.5-8.0 with 2 mol / L NaOH solution, react in a constant temperature water bath at 25℃ for 1 h, then add 50% glutaraldehyde by volume to the mixed solution, wherein the molar ratio of chitosan to glutaraldehyde is 1:1, react in a constant temperature water bath at 30℃ for 4 h.

[0043] 7) Centrifuge the suspension obtained in step 6), filter, wash, collect the filter cake, and freeze-dry for 12 hours to obtain a PDA / CS composite adsorbent with a core-shell structure and a supported bimetallic system. This adsorbent exhibits good regenerability. (See attached image.) Figure 1 .

[0044] Example 2:

[0045] 0.1g of the PDA / CS composite adsorbent with a bimetallic system was added to 100mL of humic acid solution with an initial concentration of 5mg / L and placed in a constant temperature shaking chamber at 25℃ for adsorption experiments. After 2 hours of adsorption reaction, the composite adsorbent achieved a humic acid removal rate of over 95%.

[0046] Example 3:

[0047] 0.1–1.0 g of the PDA / CS composite adsorbent loaded with a bimetallic system was added to 100 mL of humic acid solution with an initial concentration of 5 mg / L and placed in a constant temperature shaking chamber at 25 °C for adsorption experiments. After 2 h of adsorption reaction, adsorption reached equilibrium. The composite microspheres that reached adsorption equilibrium were washed 3–4 times with deionized water and anhydrous ethanol, filtered, and the filter cake was collected. After freeze-drying for 12 h, the microspheres were placed in an eluent with an acetic acid / anhydrous ethanol volume ratio of 0.1 and magnetically stirred at 25 °C for 1 h. After filtration, washing, freeze-drying, and adding 100 mL of humic acid solution with an initial concentration of 5 mg / L, the adsorption experiment was carried out again. After ten cycles of regeneration experiments, the humic acid removal rate of the composite adsorbent could still reach more than 78%.

[0048] Example 4:

[0049] 0.1 g of the PDA / CS composite adsorbent with a supported bimetallic system was added to 100 mL of competing ion (Cl) - CO3 2- SO4 2- The composite adsorbent was placed in a 25°C constant temperature shaking chamber and subjected to competitive adsorption experiments in a mixed solution with an initial concentration ratio of 1:1, 3:1, and 5:1 to humic acid. After 2 hours of adsorption reaction, the solution was centrifuged and the supernatant was taken to determine the concentration of humic acid after adsorption. The composite adsorbent can still achieve a humic acid removal rate of more than 52%, and has a certain adsorption selectivity.

[0050] Example 5:

[0051] Add 0.01 g of the PDA / CS composite adsorbent with a supported bimetallic system to 100 mL of humic acid / Cl - An adsorption experiment was conducted in a 25°C constant temperature shaking chamber with an initial concentration ratio of 1:1 in a mixed solution. After 2 hours of adsorption reaction, the composite adsorbent achieved a humic acid removal rate of over 95.2%.

[0052] Example 6:

[0053] 0.1 g of the PDA / CS composite adsorbent with a loaded bimetallic system was added to 100 mL of humic acid at an initial concentration and a competing ion concentration (Cl). -CO3 2- SO4 2- A competitive adsorption experiment was conducted in a mixed solution with a concentration ratio of 1:5:5:5 in a constant temperature shaking chamber at 25℃. After 2 hours of adsorption reaction, the solution was centrifuged, and the supernatant was taken to determine the concentration of humic acid after adsorption. The composite adsorbent can still achieve a humic acid removal rate of over 72%, demonstrating a certain degree of adsorption selectivity.

[0054] Example 7:

[0055] A method for preparing a PDA / CS composite adsorbent supported on a bimetallic system includes the following steps:

[0056] 1) Weigh 0.1g of dopamine and dissolve it in 100mL of Tris buffer solution to prepare a 1g / L dopamine prepolymer solution;

[0057] 2) Add 1 mmol of FeCl3 to the dopamine prepolymer solution in step 1), place it in a constant temperature water bath at 40℃, and react for 12 h;

[0058] 3) The black suspension obtained in step 2) was centrifuged, filtered, and washed. The filter cake was collected, and the resulting product was freeze-dried for 24 hours to obtain PDA microspheres.

[0059] 4) Disperse the PDA microspheres obtained in step 3) in deionized water to prepare a 0.5 mg / mL suspension, and sonicate for 30 min until uniformly dispersed;

[0060] 5) Weigh 0.1g of chitosan and dissolve it in 100mL of acetic acid solution. After complete dissolution, add 0.1g of CuCl2 to prepare a CS / CuCl2 mixed solution with a mass ratio of 1:1. After complete dissolution, defoam by sonication. Add the suspension obtained in step 4) dropwise to the mixed solution and place it in a constant temperature water bath at 40℃ for 2 hours.

[0061] 6) Adjust the pH of the mixed solution obtained in step 5) to 6.5-8.0 with 1 mol / L NaOH solution, react in a constant temperature water bath at 40℃ for 12 h, then add 5% glutaraldehyde by volume to the mixed solution, wherein the molar ratio of chitosan to glutaraldehyde is 1:1, and react in a constant temperature water bath at 40℃ for 12 h.

[0062] 7) Centrifuge the suspension obtained in step 6), filter, wash, collect the filter cake, freeze-dry for 24 hours to obtain a PDA / CS composite adsorbent with a core-shell structure and a loaded bimetallic system.

[0063] Example 8:

[0064] A method for preparing a PDA / CS composite adsorbent supported on a bimetallic system includes the following steps:

[0065] 1) Weigh 0.5g of dopamine and dissolve it in 100mL of Tris buffer solution to prepare a 5g / L dopamine prepolymer solution;

[0066] 2) Add 10 mmol of FeCl3 to the dopamine prepolymer solution in step 1), place it in a constant temperature water bath at 35°C, and react for 6 h;

[0067] 3) The black suspension obtained in step 2) was centrifuged, filtered, and washed. The filter cake was collected, and the resulting product was freeze-dried for 12 hours to obtain PDA microspheres.

[0068] 4) Disperse the PDA microspheres obtained in step 3) in deionized water to prepare a 0.1 mg / mL suspension, and sonicate for 30 min until uniformly dispersed;

[0069] 5) Weigh 0.1g of chitosan and dissolve it in 100mL of acetic acid solution. After complete dissolution, add 0.2g of CuCl2 to prepare a mixed solution with a CS / CuCl2 mass ratio of 0.5:1. After complete dissolution, defoam by sonication. Add the suspension obtained in step 4) dropwise to the mixed solution and place it in a constant temperature water bath at 35℃ for 2 hours.

[0070] 6) Adjust the pH of the mixed solution obtained in step 5) to 6.5-8.0 with 1 mol / L NaOH solution, react in a constant temperature water bath at 35℃ for 6 hours, then add 2% glutaraldehyde by volume to the mixed solution, wherein the molar ratio of chitosan to glutaraldehyde is 1:1, and react in a constant temperature water bath at 35℃ for 6 hours.

[0071] 7) Centrifuge the suspension obtained in step 6), filter, wash, collect the filter cake, freeze-dry for 12 hours to obtain a PDA / CS composite adsorbent with a core-shell structure and a loaded bimetallic system.

[0072] The experimental parameters and results of the embodiments of the present invention are shown in Table 1.

[0073] Table 1: Experimental parameters and results of the examples.

[0074]

[0075] As can be seen, after ten cycles of regeneration, the adsorbent still achieved a humic acid removal rate of over 52% in the competitive test, demonstrating good regenerability and selectivity.

[0076] This invention employs a FeCl3-modified polydopamine core and a CuCl2-modified chitosan shell to obtain a PDA / CS composite adsorbent with abundant adsorption sites, forming a bimetallic supported system. This composite adsorbent enhances metal stability while utilizing the abundant functional groups of dopamine and chitosan to achieve highly efficient and rapid removal of humic acid. Compared to traditional adsorbents, the materials used in this invention are widely available, safe, non-toxic, and environmentally friendly. This invention utilizes the abundant functional groups of dopamine and chitosan, along with the supported bimetallic structure, to achieve good adsorption of humic acid. Even after ten cycles of regeneration, it still exhibits good removal performance, and the adsorbent regeneration process is easy to operate.

Claims

1. A method for preparing a PDA / CS composite adsorbent supported on a bimetallic system, characterized in that, Includes the following steps: 1) Weigh dopamine and dissolve it in tris(hydroxymethyl)aminomethane to form a dopamine prepolymer solution. Add ferric chloride and heat in a constant temperature water bath at 25-40℃ for 1-12 hours to obtain a black suspension. Centrifuge, filter, collect the filter cake, freeze dry to obtain PDA microspheres. Disperse the PDA microspheres in water and sonicate to obtain a uniform suspension. 2) Chitosan was dissolved in acetic acid solution, and copper chloride was added to form a CS / CuCl2 mixed solution. The solution was defoamed by sonication, and then the uniform suspension described in step 1 was added. The solution was heated in a constant temperature water bath at 25~40℃ for 1~2 hours. Alkali solution was added to adjust the pH to 6.5~8.0, and the solution was heated in a constant temperature water bath at 25~40℃ for 1~12 hours. Then glutaraldehyde with a volume fraction of 1%~50% was added, and the solution was heated in a constant temperature water bath at 25~40℃ for 4~12 hours. The suspension after the reaction was centrifuged, filtered, washed with water, and the filter cake was collected and freeze-dried to obtain CuCl2 / PDA / CS composite microspheres with a core-shell structure.

2. The method for preparing a PDA / CS composite adsorbent supported on a bimetallic system according to claim 1, characterized in that, In step 1), the concentration of ferric chloride is 1~10 mmol / L, and the concentration of dopamine in the dopamine prepolymer solution is 1~5 g / L.

3. The method for preparing a PDA / CS composite adsorbent supported on a bimetallic system according to claim 1, characterized in that, The freeze-drying conditions in step 1) are as follows: The freeze-drying temperature is -60~-40℃; The freeze-drying time is 12-24 hours; The ultrasonic dispersion time in step 1) is 15-30 minutes; The concentration of the uniform suspension is 0.1~0.5 mg / mL.

4. The method for preparing a PDA / CS composite adsorbent supported on a bimetallic system according to claim 1, characterized in that, The concentration of the acetic acid solution mentioned in step 2) is 1% to 3%; the volume of the acetic acid solution is the same as that of tris(hydroxymethyl)aminomethane. In step 2), the mass ratio of chitosan to copper chloride in the CS / CuCl2 mixed solution is (0.5~1):

1. Step 2) The alkaline solution is a NaOH solution with a concentration of 1~5 mol / L; The molar ratio of glutaraldehyde to chitosan in step 2) is 1:1 to 3:1; The freeze-drying conditions described in step 2) are as follows: The freeze-drying temperature is -60~-40℃; The freeze-drying time is 12-24 hours.

5. The application of a PDA / CS composite adsorbent with a supported bimetallic system as described in any one of claims 1-4, characterized in that, FeCl3 / PDA / CS composite microspheres with a core-shell structure were added to a solution containing humic acid to form an adsorbent humic acid suspension. The suspension was then placed in a constant temperature shaking incubator for adsorption. After adsorption, the suspension was centrifuged, and the supernatant was taken to determine the concentration of humic acid after adsorption.

6. The application of the PDA / CS composite adsorbent supported on a bimetallic system according to claim 5, characterized in that, The concentration of the FeCl3 / PDA / CS composite microspheres with a core-shell structure in the humic acid suspension is 0.1~1.0 g / L, the concentration of the humic acid solution is 1~5 mg / L, and the pH is 4~10.

7. The application of the PDA / CS composite adsorbent supported on a bimetallic system according to claim 5, characterized in that, The solution containing humic acid includes competing ions, namely Cl- and CO32-. 2- SO4 2- At least one of the following, wherein humic acid, Cl - CO3 2- SO4 2- The concentration ratio is 1:(5~1):(5~1):(5~1).

8. The application of the PDA / CS composite adsorbent supported on a bimetallic system according to claim 5, characterized in that, The adsorption process involves washing and filtering the composite microspheres after reaching adsorption equilibrium, freeze-drying them, placing them in an eluent, magnetically stirring, filtering, washing, freeze-drying, and then adding a humic acid solution containing competing ions for regeneration adsorption.

9. The application of the PDA / CS composite adsorbent supported on a bimetallic system according to claim 8, characterized in that, The adsorption temperature is 25~40℃; The eluent is a mixed solution of acetic acid and anhydrous ethanol with a volume ratio of (0.05~0.1):

1. The number of times the regeneration adsorption is performed is 1 to 10.

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