Carboxylated chitosan adsorbent, its preparation method and use

Abstract

The application discloses a preparation method of a carboxylated chitosan adsorbent and application of the carboxylated chitosan adsorbent in removal of metal ions in an organic solvent. In view of the harm of residual metal ions in organic synthesis and the low efficiency of traditional adsorbents in DMF and other organic solvents, the carboxylated chitosan adsorbent is prepared by alkali activation, allylation and free radical addition reaction on chitosan to introduce a carboxyl functional group, and the adsorbent is efficient and environmentally friendly. The method has mild reaction conditions, does not introduce metal ions, and has low raw material cost and environmental friendliness. The prepared carboxylated chitosan adsorbent has excellent adsorption efficiency on aluminum ions, nickel ions and the like in DMF, and has wide application prospects in the fields of medicine, fine chemical industry and other high-purity requirement fields. The application provides a new solution for deep removal of metal ions in an organic solvent, and has important industrial application value.

Description

Technical Field

[0001] This invention relates to the field of adsorbent technology, specifically to a carboxylated chitosan adsorbent, its preparation method, and its uses. Background Technology

[0002] In the field of organic synthesis, various metal-containing catalysts and metal salts are often used to promote reactions, such as aluminum chloride and nickel chloride. Simultaneously, organic reactions require large amounts of organic solvents as reaction media. This often results in metal ions remaining in the organic solvents after the reaction and even in the final products. If these chemicals containing metal residues (such as pharmaceutical intermediates and fine chemicals) are used without adequate purification, they can harm human health.

[0003] To ensure chemical safety, it is essential to thoroughly remove metal ions from synthetic products and waste solvents. Existing treatment methods include adsorption, ion exchange, and chemical precipitation. Compared to other methods, adsorption has attracted considerable attention due to its advantages such as simple operation, mild conditions, high cost-effectiveness, environmental friendliness, and ease of integration with existing processes. However, traditional adsorbents are mostly suitable for water treatment systems. Organic solvents such as DMF, with their amide functional groups, greatly enhance the electron cloud density and electron-donating ability of the carbonyl oxygen atom through resonance and induction effects, making it an excellent coordinating atom with a strong complexing effect on metal ions. This makes it difficult for traditional adsorbents to remove metal ions in DMF environments, and traditional adsorbents also suffer from low efficiency in DMF environments, making them unsuitable for the removal of metal ions from DMF.

[0004] Chitosan, a natural and biodegradable amino polysaccharide, is considered a promising green adsorbent material due to the effective coordination sites of its amino and hydroxyl groups on its molecular chain. However, the adsorption sites of natural chitosan are mainly amino groups, and its adsorption capacity is insufficient for efficient purification of metal ions with different electronic properties present in organic media. By introducing carboxyl groups with strong coordination ability into the chitosan molecular chain, its binding capacity for metal ions can be significantly increased, and its backbone stability in complex chemical environments can be enhanced through cross-linking.

[0005] However, existing carboxylation modification methods (such as those using chloroacetic acid) often involve insufficiently mild reaction conditions, expensive raw materials, and may lead to chitosan chain degradation or the introduction of other harmful metal ions. This not only increases production costs but may also introduce new biosafety concerns, limiting its application in high-purity fields such as pharmaceuticals and fine chemicals. Therefore, developing a method with mild reaction conditions, simple process, low cost, and good adsorption properties for metal ions is of great significance. Summary of the Invention

[0006] (a) Technical problems to be solved In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a carboxylated chitosan adsorbent and its preparation method to improve the adsorption efficiency of the adsorbent for metal ions in organic solvents. The preparation process is mild, the materials are readily available, no metal ions are introduced, the production cost is low, and the safety is good. It can be better applied to high-purity applications such as pharmaceuticals and fine chemicals.

[0007] (II) Technical Solution In a first aspect, the present invention provides a method for preparing a carboxylated chitosan adsorbent, comprising: S1. Chitosan and isopropanol are mixed evenly and stirred to obtain a mixture of chitosan and isopropanol. Sodium hydroxide or potassium hydroxide solution is added to the mixture and stirred to obtain a first precursor solution. S2. Mix the first precursor solution with allyl bromide and react to obtain the second precursor solution. After evaporating at least a small amount of isopropanol from the second precursor solution, mix it with water evenly and stir. Separate the solid and liquid to obtain crude allyl chitosan. S3. The crude allyl chitosan is washed with water, dried and ground to obtain allyl chitosan. S4. Disperse the allyl chitosan in tetrahydrofuran, add thiomalic acid and a photoinitiator to the tetrahydrofuran, mix thoroughly to obtain a third precursor solution; the photoinitiator is at least one of 2,2-dimethoxy-2-phenylacetophenone DMPA, 2-hydroxy-2-methyl-1-phenyl-1-propanone Irgacure 1173, and benzophenone BP. S5. Irradiate the third precursor liquid with an ultraviolet lamp to react and obtain crude carboxylated chitosan adsorbent. S6. The crude carboxylated chitosan adsorbent is washed, dried and ground with an organic solvent to obtain the carboxylated chitosan adsorbent.

[0008] Optionally, in step S1, the stirring temperature is 25-30℃; the mass fraction of the sodium hydroxide solution is 30%-35%, and the dropping rate is one drop every 5 seconds, preferably one drop every 7 seconds; and 3-4 mL of the sodium hydroxide solution is added for every 1g of chitosan.

[0009] Optionally, in step S1, the chitosan molecular weight is 50,000 to 500,000 Da. This range of chitosan can ensure sufficient reactivity and form a carboxylated chitosan adsorbent with good mechanical strength and adsorption properties.

[0010] Optionally, in step S1, the mass-to-volume ratio of chitosan to isopropanol is 1g:15-20mL.

[0011] Optionally, in step S2, the mass-to-volume ratio of chitosan to allyl bromide is 1 g: 4-6 mL.

[0012] Optionally, in step S2, the reaction temperature is 50-55℃ and the time is 5-7h.

[0013] Optionally, in step S2, when the isopropanol in the second precursor solution is evaporated to 1 / 4 to 1 / 2 of its remaining volume (preferably 1 / 3 of its volume), it is mixed evenly with 3-8 times the volume of water remaining isopropanol and stirred. After filtration, crude allyl chitosan is obtained; the water is deionized water.

[0014] Optionally, in step S3, the drying temperature is 50-55℃; in step S6, the drying temperature is 30-40℃.

[0015] Optionally, in step S4, the mass-to-volume ratio of allyl chitosan to tetrahydrofuran is 1g:40-60mL, preferably 1g:50mL; the initiator is thiomalic acid and 2,2-dimethoxy-2-phenylacetophenone, and the mass ratio of allyl chitosan to thiomalic acid and 2,2-dimethoxy-2-phenylacetophenone is 100:(150-250):(2-4), preferably 100:200:3.

[0016] Optionally, in S5, the UV lamp has a wavelength of 365nm, a power of 50-100W, a reaction temperature of ambient temperature, and a reaction time of 28-35 minutes. The UV lamp wavelength is not strictly limited to 365nm. Other wavelengths (such as UV light in the 300-400nm range) can also be used, as long as the UV light wavelength can be effectively absorbed by the photoinitiator and generate enough free radicals to initiate the reaction. In practical applications, adjustments can be made according to specific reaction conditions and equipment. 365nm UV light has moderate energy, effectively initiating the reaction while reducing excessive damage to the chitosan molecular chains or the occurrence of side reactions. 365nm is a commonly used UV wavelength in laboratories and industrial production; related UV lamp equipment is readily available, low in cost, and convenient for practical application.

[0017] Secondly, the present invention provides a carboxylated chitosan adsorbent, which is prepared by any of the above-mentioned methods.

[0018] Thirdly, the present invention provides the use of the carboxylated chitosan adsorbent in DMF to adsorb metal ions, wherein the metal ions include one or more of aluminum ions and nickel ions.

[0019] (III) Beneficial Effects The present invention has the following technical effects: 1. Highly efficient and selective adsorption: By introducing carboxyl functional groups with strong coordination ability into the chitosan molecular chain, the binding ability to metal ions is significantly increased, which can efficiently remove metal ions such as aluminum ions and nickel ions from DMF.

[0020] 2. Mild reaction conditions: The entire preparation process adopts mild reaction conditions, avoiding the harsh conditions used in traditional carboxylation methods and reducing the risk of chitosan chain degradation.

[0021] 3. No metal ion introduction: No additional metal ions are introduced during the preparation process, ensuring the purity and biosafety of the adsorbent, making it suitable for high-purity applications such as pharmaceuticals and fine chemicals.

[0022] 4. Simple process and low cost: The raw materials are inexpensive and relatively less toxic, the process is simple to operate, the reaction efficiency is high, and it is suitable for industrial production.

[0023] 5. Environmentally friendly: Chitosan itself is a natural and biodegradable material. The preparation process and the adsorbent after use are environmentally friendly, which is in line with the development trend of green chemistry and is suitable for the application needs of high-purity fields such as pharmaceuticals and fine chemicals.

[0024] In summary, the carboxylated chitosan adsorbent of the present invention has great application potential in the field of selective adsorption in organic systems. It can effectively solve the technical problems in the prior art, such as low removal efficiency and poor selectivity of metal ions in organic solvents such as DMF, and the introduction of new biological safety concerns. Attached Figure Description

[0025] Figure 1 SEM image of the carboxylated chitosan adsorbent prepared in Example 1.

[0026] Figure 2 This is a comparison chart of the adsorption capacity of the carboxylated chitosan adsorbent prepared in Example 2 and the original chitosan.

[0027] Figure 3 The curves showing the change in adsorption capacity of the carboxylated chitosan adsorbent prepared in Example 3 for trivalent aluminum ions and divalent nickel ions over time.

[0028] Figure 4 a) is a linear fit plot of the Langmuir isotherm model for the adsorption of trivalent aluminum ions by the carboxylated chitosan adsorbent prepared in Example 4 at different temperatures; b) is a linear fit plot of the Langmuir isotherm model for the adsorption of divalent nickel ions by the adsorbent at different temperatures; c) is a linear fit plot of the Freundlich isotherm model for the adsorption of trivalent aluminum ions by the adsorbent at different temperatures; d) is a linear fit plot of the Freundlich isotherm model for the adsorption of divalent nickel ions by the adsorbent at different temperatures.

[0029] Figure 5 a) is a pseudo-first-order kinetic model fitting diagram of the adsorption of trivalent aluminum ions and divalent nickel ions by the carboxylated chitosan adsorbent prepared in Example 5; b) is a pseudo-second-order kinetic model fitting diagram of the adsorbent for the adsorption of trivalent aluminum ions and divalent nickel ions.

[0030] Figure 6 The infrared spectrum of the carboxylated chitosan adsorbent prepared in Example 6. Detailed Implementation

[0031] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] This invention provides a method for preparing a carboxylated chitosan adsorbent, comprising: S1. Mix chitosan and isopropanol at a ratio of 1g:15-20mL until homogeneous, and stir at 25-30℃ to obtain a mixture of chitosan and isopropanol. Add a 30-35wt% sodium hydroxide or potassium hydroxide solution to the mixture and stir to obtain the first precursor solution. The sodium hydroxide or potassium hydroxide solution is added at a dropping rate of one drop every 5 or 7 seconds, and 3-4mL of the sodium hydroxide solution is added for every 1g of chitosan.

[0033] S2. Mix the first precursor solution with allyl bromide and react at 50-55°C for 5-7 hours to obtain the second precursor solution. Evaporate the isopropanol in the second precursor solution to 1 / 2-1 / 4 (preferably 1 / 3) of its initial volume, then mix it with 3-8 times the volume of deionized water of the remaining isopropanol and stir. Separate the solid and liquid (preferably by vacuum filtration) to obtain crude allyl chitosan. For every 1g of chitosan in the first precursor solution, add 4-6mL of allyl bromide.

[0034] Retaining 1 / 2 to 1 / 4 of the volume of isopropanol ensures that allyl chitosan can be fully dispersed and precipitated when mixed with water later, while avoiding insufficient or even no product precipitation due to excessive solvent residue.

[0035] S3. The crude allyl chitosan is washed with water, dried at 50-55°C and ground to obtain allyl chitosan.

[0036] S4. The allyl chitosan is dispersed in tetrahydrofuran at a mass-to-volume ratio of 1g:40-60mL. Thiomalic acid and a photoinitiator are added to the tetrahydrofuran and mixed evenly to obtain the third precursor solution.

[0037] The photoinitiator is at least one selected from 2,2-dimethoxy-2-phenylacetophenone (DMPA), 2-hydroxy-2-methyl-1-phenyl-1-propanone (Irgacure 1173), and benzophenone (BP). The mass ratio of allyl chitosan to thiomalic acid and DMPA is 100:(150-250):(2-4), preferably 100:200:3.

[0038] A mass-to-volume ratio of allyl chitosan to tetrahydrofuran of 1 g: 40-60 mL ensures sufficient dispersion of allyl chitosan in the reaction system, providing a favorable reaction environment for subsequent free radical addition reactions. Appropriate adjustment of the thiomalic acid ratio (150-250) ensures a sufficient source of carboxyl groups, while the photoinitiator ratio (2-4) guarantees effective initiation and progression of the reaction.

[0039] S5. Irradiate the third precursor solution with a 365nm ultraviolet lamp at a power of 50-100W, and react at ambient temperature for 28-35 minutes to obtain crude carboxylated chitosan adsorbent. A power range of 50-100W is suitable for reaction systems of different scales, providing sufficient energy to initiate the photochemical reaction while avoiding side reactions or product decomposition due to excessive power.

[0040] 365nm is long-wave ultraviolet light (UVA), which can effectively excite DMPA to generate free radicals, initiating subsequent addition reactions. It also reduces excessive damage to the chitosan molecular chains or the occurrence of side reactions. If the wavelength is too short or the energy too high, it may lead to chitosan degradation or the generation of unnecessary free radical side reactions.

[0041] S6. The crude carboxylated chitosan adsorbent is washed with an organic solvent, dried at 30-40°C, and ground to obtain the carboxylated chitosan adsorbent.

[0042] The reaction mechanisms of each step in the above preparation method are as follows: S1: Alkali activation of chitosan Reaction Mechanism: Chitosan is dispersed in isopropanol, and a sodium hydroxide solution is added. Sodium hydroxide, acting as a base catalyst, abstracts protons from the hydroxyl (-OH) and amino (-NH2) groups on the chitosan molecular chain, converting these groups into more nucleophilic oxonions (-O). - ) and nitrogen anions (-NH - This step, through alkali activation, enhances the reactivity of chitosan, making it more readily react with subsequent allyl bromide.

[0043] S2: Allylation reaction (etherification reaction) Reaction mechanism: Activated chitosan oxygen anions (-O -As a nucleophile, the chitosan attacks the bromine atom in the allyl bromide (CH2=CH-CH2Br) molecule, undergoing a nucleophilic substitution reaction (SN2). The bromine atom is removed as a leaving group, and the chitosan molecule is linked to the allyl group via an ether bond (-O-CH2-CH=CH2), generating allyl chitosan. This step introduces an allyl functional group into the chitosan molecular chain, providing a reaction site (double bond) for the subsequent carboxylation reaction.

[0044] S3: Purification of allyl chitosan This step involves washing with water to remove unreacted sodium hydroxide, allyl bromide, and reaction byproducts (such as sodium bromide), followed by drying and grinding to obtain pure allyl chitosan. This step is a physical purification process without any chemical reaction.

[0045] S4: Preparation for free radical addition reactions Reaction Mechanism: Allyl chitosan is dispersed in tetrahydrofuran (THF), and thiomalic acid (HS-CH2-CH(COOH)-COOH) and the photoinitiator 2,2-dimethoxy-2-phenylacetophenone (DMPA) are added. Thiomalic acid provides thiol (-SH) and carboxyl (-COOH) groups, while the photoinitiator generates free radicals under ultraviolet light irradiation. This step provides reactants and initiation conditions for the subsequent photochemical reaction.

[0046] S5: Photo-initiated free radical addition reaction Reaction Mechanism: Under UV irradiation, the photoinitiator DMPA decomposes to generate free radicals. These free radicals abstract hydrogen atoms from the thiomalic acid molecule's thiosulfate group (-SH), generating thiosulfate free radicals (·S-CH2-CH(COOH)-COOH). These thiosulfate free radicals attack the carbon-carbon double bond (C=C) in the allyl chitosan molecule, undergoing a radical addition reaction to attach the thiomalic acid molecule to the chitosan molecular chain, thereby introducing carboxyl functional groups. This step, through radical addition, introduces a large number of carboxyl functional groups onto the chitosan molecular chain, significantly enhancing its adsorption capacity and selectivity for metal ions.

[0047] S6: Purification of carboxylated chitosan adsorbent This step involves washing with an organic solvent (such as ethanol or acetone) to remove unreacted thiomalic acid, photoinitiators, and other impurities, followed by drying and grinding to obtain the final carboxylated chitosan adsorbent. This step is also a physical purification process without any chemical reaction.

[0048] The above-described synthesis method introduces allyl and carboxyl functional groups into the chitosan molecular chain through a three-step chemical reaction involving alkali activation, etherification, and free radical addition. This successfully prepares a carboxylated chitosan adsorbent with high selectivity and high adsorption efficiency for metal ions in organic solvents. The entire process is carried out under mild conditions, at a low temperature (not exceeding 55°C), without introducing metal ions, and is environmentally friendly.

[0049] The following description, in conjunction with preferred embodiments of the present invention, provides further details. Chitosan with a molecular weight of 50,000 to 500,000 Da can be used in this application. The following examples use chitosan with a molecular weight of 100 kDa to 200 kDa as examples. Except for the test temperatures described in Examples 4 and 5, the adsorption test temperature in the other examples is 30°C. The test pressure in all examples is atmospheric pressure. For other conditions not specifically specified, conventional conditions or the conditions recommended by the manufacturer of the equipment used can be followed. For reagents or instruments whose manufacturers are not specified, commercially available conventional products can be used. For technical means or processes involved, if specific conditions are not specified, they should be carried out according to existing methods in the relevant art.

[0050] Example 1 This embodiment provides a method for preparing a carboxylated chitosan adsorbent, the steps of which are as follows: S1. Mix 1g of chitosan with 15ml of isopropanol and stir at 30℃ for 1h to obtain a mixture of chitosan and isopropanol. Add 3ml of 35% sodium hydroxide solution dropwise to the mixture of chitosan and isopropanol at a rate of 1 drop every 7 seconds to obtain the first precursor solution.

[0051] S2. Add 4 ml of allyl bromide to the first precursor solution and react at 50°C for 5 h to obtain the second precursor solution. When the isopropanol in the second precursor solution is reduced to one-third by rotary evaporation, add 3 times the volume of deionized water and stir. Filter to obtain crude allyl chitosan.

[0052] S3. Wash the crude allyl chitosan with deionized water, dry it at 50°C and grind it to obtain allyl chitosan.

[0053] S4. Disperse 1.5g of allyl chitosan in 75ml of tetrahydrofuran, then add 3g of thiomalic acid and 0.045g of 2,2-dimethoxy-2-phenylacetophenone to the tetrahydrofuran, stir and mix evenly to obtain the third precursor solution.

[0054] S5. Irradiate the third precursor solution with an 80W, 365nm ultraviolet lamp and react for 30 minutes. Filter the solution to obtain crude carboxylated chitosan adsorbent.

[0055] S6. Wash the crude carboxylated chitosan adsorbent with tetrahydrofuran, dry it at 30°C and grind it to obtain the carboxylated chitosan adsorbent.

[0056] The carboxylated chitosan adsorbent prepared in this embodiment was scanned by electron microscopy, and the results are as follows: Figure 1 As shown in the image, the carboxylated chitosan adsorbent exhibits a distinct distribution of pores and voids through scanning electron microscopy. This structure provides a large specific surface area, which is beneficial for the diffusion of metal ions and the exposure of adsorption sites, thereby improving the adsorption effect on metal ions.

[0057] Example 2 The difference between this embodiment and Embodiment 1 lies in the different operating conditions for steps S1-S3. Steps S1-S3 of this embodiment are as follows: S1. Mix 1g of chitosan with 15ml of isopropanol and stir at 25℃ for 1h to obtain a mixture of chitosan and isopropanol. Add 4ml of 30% sodium hydroxide solution to the mixture of chitosan and isopropanol dropwise at 1 drop every 5 seconds to obtain the first precursor solution.

[0058] S2. Add 5 ml of allyl bromide to the first precursor solution and react at 50°C for 5 h to obtain the second precursor solution. When the isopropanol in the second precursor solution is reduced to one-third by rotary evaporation, add 4 times the volume of deionized water and stir. Filter to obtain crude allyl chitosan.

[0059] S3. Wash the crude allyl chitosan with deionized water, dry it at 50°C and grind it to obtain allyl chitosan.

[0060] Steps S4-S6 are the same as in Example 1.

[0061] The adsorption capacity of carboxylated chitosan adsorbent and original chitosan in DMF was tested and compared. The test results are as follows: Figure 2 .Depend on Figure 2It can be seen that, under the same conditions, after reaching adsorption equilibrium, the adsorption capacity Qe of the carboxylated chitosan adsorbent for trivalent aluminum ions is >0.07 mmol / g (approximately 0.075 mmol / g), and the adsorption capacity Qe of divalent nickel ions is >0.02 mmol / g (approximately 0.021 mmol / g), while the adsorption capacity Qe of the original chitosan for trivalent aluminum ions is <0.02 mmol / g (approximately 0.012 mmol / g), and it has almost no adsorption capacity for divalent nickel ions (zero). Therefore, the carboxylated chitosan adsorbent prepared in this invention exhibits significantly higher adsorption performance for trivalent aluminum ions and divalent nickel ions in DMF than the original chitosan, and its selectivity for trivalent aluminum ions is greater than that for divalent nickel ions. This is mainly because DMF is a polar aprotic solvent with a certain solvation effect on metal ions. The original chitosan mainly interacts with metal ions through amino and hydroxyl groups, but the complexing ability of amino and hydroxyl groups is limited, and the dispersibility of the original chitosan in DMF is also poor. The carboxylated chitosan adsorbent prepared in this invention incorporates a large number of carboxyl functional groups through modification. Carboxyl groups are strong metal complexing sites, and the introduction of carboxyl groups increases polarity, resulting in better compatibility with DMF. This allows the carboxylated chitosan adsorbent to disperse better in DMF, facilitating the full exposure of carboxyl groups. Therefore, the adsorption performance of the carboxylated chitosan adsorbent for trivalent aluminum ions and divalent nickel ions in DMF is far superior to that of the original chitosan.

[0062] Example 3 The difference between this embodiment and Embodiment 1 lies in the different operating conditions for steps S1-S3. Steps S1-S3 of this embodiment are as follows: S1. Mix 1g of chitosan with 15ml of isopropanol and stir at 25℃ for 1h to obtain a mixture of chitosan and isopropanol. Add 3ml of 30% sodium hydroxide solution dropwise to the mixture of chitosan and isopropanol at a rate of 1 drop every 7 seconds to obtain the first precursor solution.

[0063] S2. Add 6 ml of allyl bromide to the first precursor solution and react at 50°C for 5 h to obtain the second precursor solution. When the isopropanol in the second precursor solution is reduced to one-third by rotary evaporation, add 5 times the volume of deionized water and stir. Filter to obtain crude allyl chitosan.

[0064] S3. Wash the crude allyl chitosan with deionized water, dry it at 50°C and grind it to obtain allyl chitosan.

[0065] Steps S4-S6 are the same as in Example 1.

[0066] The adsorption capacity of the carboxylated chitosan adsorbent in this embodiment changes over time, as shown in the curve. Figure 3 As shown. By Figure 3It can be observed that the adsorption capacity of the carboxylated chitosan adsorbent prepared in Example 3 for trivalent aluminum ions and divalent nickel ions in DMF exhibits a trend of "increasing rapidly at first, then increasing slowly, and finally tending towards equilibrium." The adsorption capacity increases rapidly in the first few minutes of adsorption. As time progresses, the adsorption capacity approaches the equilibrium adsorption capacity because the metal ion concentration is initially high, allowing the functional groups of the adsorbent to bind with a large number of trivalent aluminum ions and divalent nickel ions. Subsequently, as the metal ion concentration decreases, the adsorption capacity increases slowly until it no longer increases, reaching an equilibrium state.

[0067] Example 4 The difference between this embodiment and Embodiment 1 lies in the different operating conditions for steps S1-S3. Steps S1-S3 of this embodiment are as follows: S1. Mix 1g of chitosan with 20ml of isopropanol evenly and stir at 25℃ for 1h to obtain a mixture of chitosan and isopropanol. Add 3ml of 30% sodium hydroxide solution dropwise to the mixture of chitosan and isopropanol at a rate of 1 drop every 7 seconds to obtain the first precursor solution.

[0068] S2. Add 4 ml of allyl bromide to the first precursor solution and react at 50°C for 5 h to obtain the second precursor solution. When the isopropanol in the second precursor solution is reduced to one-third by rotary evaporation, add 6 times the volume of deionized water and stir. Filter to obtain crude allyl chitosan.

[0069] S3. Wash the crude allyl chitosan with deionized water, dry it at 50°C and grind it to obtain allyl chitosan.

[0070] Steps S4-S6 are the same as in Example 1.

[0071] The adsorption process of the carboxylated chitosan adsorbent in this embodiment on metal ions at different times was observed, and the linear fitting plots of the Langmuir isotherm model and the Freundlich isotherm model for the adsorbent on metal ions were recorded.

[0072] The linear fitting plots of the Langmuir isotherm model and the Freundlich isotherm model for the adsorption of trivalent aluminum ions and divalent nickel ions in DMF by the carboxylated chitosan adsorbent prepared in Example 4 above are shown below. Figure 4 As shown in a~d.

[0073] like Figure 4 As shown in a and c: For the adsorption of trivalent aluminum ions, the correlation coefficient R of the Langmuir model (a) at 20℃, 30℃, 40℃, and 50℃. 2 Both are less than the correlation coefficient R of the Freundlich model (c). 2This indicates that the Freundlich model is more suitable for predicting the adsorption of trivalent aluminum ions by carboxylated chitosan adsorbents, further illustrating that the adsorption process of trivalent aluminum ions by the carboxylated chitosan adsorbents of this invention is a multilayer adsorption process. Figure 4 Figures b and d show the correlation coefficients Ri of the Langmuir model for the adsorption of divalent nickel ions at 20℃, 30℃, 40℃, and 50℃. 2 Both are less than the correlation coefficient R of the Freundlich model. 2 This indicates that the Freundlich model is more suitable for predicting the adsorption of divalent nickel ions by carboxylated chitosan adsorbents, further illustrating that the adsorption process of divalent nickel ions by the carboxylated chitosan adsorbents of the present invention is a multilayer adsorption.

[0074] Example 5 The difference between this embodiment and Embodiment 1 lies in the different operating conditions for steps S1-S3. Steps S1-S3 of this embodiment are as follows: S1. Mix 1g of chitosan with 20ml of isopropanol evenly and stir at 25℃ for 1h to obtain a mixture of chitosan and isopropanol. Add 3ml of 30% sodium hydroxide solution dropwise to the mixture of chitosan and isopropanol at a rate of 1 drop every 7 seconds to obtain the first precursor solution.

[0075] S2. Add 6 ml of allyl bromide to the first precursor solution and react at 55°C for 7 h to obtain the second precursor solution. When the isopropanol in the second precursor solution is reduced to half by rotary evaporation, add 7 times the volume of deionized water and stir. Filter to obtain crude allyl chitosan.

[0076] S3. Wash the crude allyl chitosan with deionized water, dry it at 50°C and grind it to obtain allyl chitosan.

[0077] Steps S4-S6 are the same as in Example 1.

[0078] Observe and record the pseudo-first-order kinetic model linear fitting graphs and pseudo-second-order kinetic model linear fitting graphs of the carboxylated chitosan adsorbent prepared in this embodiment for metal ions. The test temperature is 30℃. Figure 5 As shown in Figures a and b, the pseudo-first-order kinetic model fitting diagrams and pseudo-second-order kinetic model fitting diagrams for the adsorption of trivalent aluminum ions and divalent nickel ions by carboxylated chitosan adsorbents are respectively shown. The correlation coefficient R of the pseudo-first-order kinetic model for the adsorption of trivalent aluminum ions and divalent nickel ions is [not specified]. 2 Both are less than the correlation coefficient R of the quasi-second-order dynamic model. 2 Furthermore, the adsorption capacity calculated by the pseudo-second-order kinetic model is closer to that measured in the experiment. This indicates that the adsorption mechanism of the carboxylated chitosan adsorbent prepared in this invention for trivalent aluminum ions and divalent nickel ions is mainly chemical adsorption.

[0079] Example 6 The difference between this embodiment and Embodiment 1 lies in the different operating conditions for steps S1-S3. Steps S1-S3 of this embodiment are as follows: S1. Mix 1g of chitosan with 20ml of isopropanol evenly and stir at 25℃ for 1h to obtain a mixture of chitosan and isopropanol. Add 3ml of 30% sodium hydroxide solution dropwise to the mixture of chitosan and isopropanol at a rate of 1 drop every 7 seconds to obtain the first precursor solution.

[0080] S2. Add 5 ml of allyl bromide to the first precursor solution and react at 50°C for 7 h to obtain the second precursor solution. When the isopropanol in the second precursor solution is reduced to half by rotary evaporation, add 8 times the volume of deionized water and stir. Filter to obtain crude allyl chitosan.

[0081] S3. Wash the crude allyl chitosan with deionized water, dry it at 50°C and grind it to obtain allyl chitosan.

[0082] Steps S4-S6 are the same as in Example 1.

[0083] Observe and record the infrared spectrum of the carboxylated chitosan adsorbent prepared in this embodiment, such as... Figure 6 As shown. Infrared spectrum shows 1720 cm⁻¹ -1 The absorption peak at 3433 cm⁻¹ corresponds to the stretching vibration of C=O, and... -1 The stretching vibration peaks of NH and OH were significantly weakened, indicating that thiomalic acid was successfully grafted onto chitosan.

[0084] Example 7 The difference between this embodiment and embodiment 1 is that step S4 is different. In this embodiment, step S4 is as follows: 1.5g of allyl chitosan was dispersed in 90ml of tetrahydrofuran, and then 3g of thiomalic acid and 0.06g of DMPA were added to the tetrahydrofuran. The mixture was stirred and stirred until homogeneous to obtain the third precursor solution. The remaining steps of this embodiment, including S1-S3 and S5-S6, are the same as those in Example 1.

[0085] Example 8 The difference between this embodiment and embodiment 1 is that step S4 is different. In this embodiment, step S4 is as follows: 1.5g of allyl chitosan was dispersed in 60ml of tetrahydrofuran, and then 3g of thiomalic acid and 0.03g of DMPA were added to the tetrahydrofuran. The mixture was stirred and stirred until homogeneous to obtain the third precursor solution. The remaining steps of this embodiment, including S1-S3 and S5-S6, are the same as those in Example 1.

[0086] Example 9 The difference between this embodiment and embodiment 1 is that step S4 is different. In this embodiment, step S4 is as follows: 1.5g of allyl chitosan was dispersed in 90ml of tetrahydrofuran, and then 3g of thiomalic acid and 0.045g of Irgacure 1173 were added to the tetrahydrofuran. The mixture was stirred until homogeneous to obtain the third precursor solution. The remaining steps of this embodiment, including S1-S3 and S5-S6, are the same as those in Example 1.

[0087] Example 10 The difference between this embodiment and embodiment 1 is that step S4 is different. In this embodiment, step S4 is as follows: 1.5g of allyl chitosan was dispersed in 90ml of tetrahydrofuran, and then 3g of thiomalic acid and 0.045g of BP were added to the tetrahydrofuran. The mixture was stirred and stirred until homogeneous to obtain the third precursor solution. The remaining steps of this embodiment, including S1-S3 and S5-S6, are the same as those in Example 1.

[0088] Example 11 The difference between this embodiment and embodiment 1 is that step S5 is different. In this embodiment, step S5 is as follows: The third precursor solution was irradiated with a 60W, 365nm UV lamp and reacted for 35 minutes. The solution was then filtered to obtain crude carboxylated chitosan adsorbent. The remaining steps of this embodiment, including S1-S4 and S6, are the same as in Example 1.

[0089] Example 12 The difference between this embodiment and embodiment 1 is that step S5 is different. In this embodiment, step S5 is as follows: The third precursor solution was irradiated with a 100W, 365nm UV lamp and reacted for 28 minutes. The solution was then filtered to obtain crude carboxylated chitosan adsorbent. The remaining steps of this embodiment, including S1-S4 and S6, are the same as in Example 1.

[0090] The test results of the carboxylated chitosan adsorbents prepared in Examples 7-12 were similar to those of the aforementioned examples. Their SEM images can be found in Example 1, and their infrared spectra can be found in Example 2. Figure 6 It is expected that the adsorbent samples prepared in Examples 7-12 will have similar adsorption performance for metal ions in DMF as the samples in Examples 1-6.

[0091] In summary, the carboxylated chitosan adsorbent provided by this invention possesses numerous pores and voids, resulting in a larger specific surface area and improved adsorption efficiency for trivalent aluminum ions and divalent nickel ions. The preparation method of the carboxylated chitosan adsorbent of this invention operates under mild conditions and low temperatures, without introducing other metal ions. The adsorption process for trivalent aluminum ions and divalent nickel ions involves multilayer adsorption. The entire preparation process is simple to operate, requires minimal equipment, and has a short flow, making it suitable for large-scale preparation and industrial production. Furthermore, the materials used are environmentally friendly and have low hazard to the environment and organisms.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. These modifications or substitutions, or combinations of technical features in the above embodiments that do not conflict with each other, can be made in accordance with the manner described in the embodiments. These modifications, substitutions or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a carboxylated chitosan adsorbent, characterized in that, include: S1. Chitosan and isopropanol are mixed evenly and stirred to obtain a mixture of chitosan and isopropanol. Sodium hydroxide or potassium hydroxide solution is added to the mixture and stirred to obtain a first precursor solution. S2. Mix the first precursor solution with allyl bromide and react to obtain the second precursor solution. After evaporating at least a small amount of isopropanol from the second precursor solution, mix it with water evenly and stir. Separate the solid and liquid to obtain crude allyl chitosan. S3. Wash the crude allyl chitosan with water, dry it and grind it to obtain allyl chitosan; S4. Disperse the allyl chitosan in tetrahydrofuran, add thiomalic acid and a photoinitiator to the tetrahydrofuran, mix thoroughly to obtain a third precursor solution; the photoinitiator is at least one of 2,2-dimethoxy-2-phenylacetophenone DMPA, 2-hydroxy-2-methyl-1-phenyl-1-propanone Irgacure 1173, and benzophenone BP. S5. Irradiate the third precursor liquid with an ultraviolet lamp to react and obtain crude carboxylated chitosan adsorbent. S6. The crude carboxylated chitosan adsorbent is washed, dried and ground with an organic solvent to obtain the carboxylated chitosan adsorbent.

2. The preparation method according to claim 1, characterized in that, In step S1, the stirring temperature is 25-30℃; the sodium hydroxide solution has a mass fraction of 30%-35% and a dropping rate of one drop every 5 seconds; and 3-4 mL of the sodium hydroxide solution is added for every 1g of chitosan.

3. The preparation method according to claim 1, characterized in that, In step S1, the mass-to-volume ratio of chitosan to isopropanol is 1g:15-20mL.

4. The preparation method according to claim 1, characterized in that, In step S2, the mass-to-volume ratio of chitosan to allyl bromide is 1 g: 4-6 mL.

5. The preparation method according to claim 1, characterized in that, In step S2, the reaction temperature is 50-55℃ and the time is 5-7h.

6. The preparation method according to claim 1, characterized in that, In step S2, when the isopropanol in the second precursor solution is evaporated to 1 / 4 to 1 / 2 of its remaining volume, it is mixed evenly with 3-8 times the volume of water remaining isopropanol and stirred. After filtration, crude allyl chitosan is obtained; the water is deionized water.

7. The preparation method according to claim 1, characterized in that, In step S3, the drying temperature is 50-55℃; in step S6, the drying temperature is 30-40℃.

8. The preparation method according to claim 1, characterized in that, In step S4, the mass-to-volume ratio of allyl chitosan to tetrahydrofuran is 1g:40-60mL; the initiator is thiomalic acid and 2,2-dimethoxy-2-phenylacetophenone, and the mass ratio of allyl chitosan to thiomalic acid and 2,2-dimethoxy-2-phenylacetophenone is 100:(150-250):(2-4).

9. The preparation method according to claim 1, characterized in that, In step S5, the wavelength of the ultraviolet lamp is 365nm, the power is 50-100W, the reaction temperature is ambient temperature, and the reaction time is 28-35min.

10. The carboxylated chitosan adsorbent according to any one of claims 1-9 and its use in adsorbing metal ions in DMF, wherein the metal ions include one or more of aluminum ions and nickel ions.

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