Carboxymethyl chitosan adsorbent for adsorbing hexavalent chromium and preparation method thereof

Abstract

This invention discloses a carboxymethyl chitosan adsorbent for adsorbing hexavalent chromium and its preparation method, wherein an aqueous solution of carboxymethyl chitosan is added dropwise to Fe... 3+ and La 3+ A mixed solution was subjected to an ionic crosslinking reaction to obtain carboxymethyl chitosan hydrogel microspheres, which were then allowed to stand, washed, and freeze-dried. The resulting material was then added to a polyethyleneimine aqueous solution, thoroughly mixed, and allowed to stand. Glutaraldehyde aqueous solution was added under stirring to initiate a crosslinking reaction. The resulting product was washed and freeze-dried to obtain the final product, which is used for the efficient removal of hexavalent chromium. This invention is non-toxic and environmentally friendly, prepared through a two-step crosslinking reaction. The adsorbent possesses a high density of adsorption sites for hexavalent chromium, achieving rapid and efficient removal of hexavalent chromium. Its maximum adsorption capacity for hexavalent chromium is 649.62 mg / g. ‑1 Its performance is higher than that of most adsorbents reported in the literature, indicating a promising future for its application.

Description

Technical Field

[0001] This invention belongs to the field of electroplating wastewater treatment technology, specifically relating to a carboxymethyl chitosan adsorbent for adsorbing hexavalent chromium and its preparation method. Background Technology

[0002] Currently, electroplating wastewater contains various heavy metal pollutants with diverse chemical properties, and there is no targeted and effective treatment method yet. Chemical precipitation, chemical reduction, and electrolysis methods for treating electroplating wastewater are costly, complex, and prone to secondary pollution. Using traditional methods also increases the amount of wastewater treatment agents used, further increasing wastewater treatment costs. Adsorption, through ion exchange, electrostatic interaction, and surface complexation, removes heavy metal ions from electroplating wastewater. Its advantages include high removal efficiency, good economic performance, and flexible design and operation, making it one of the most widely used heavy metal ion treatment technologies. Since Cr(VI) exists in wastewater as an anionic complex, it is a representative metal with carcinogenic, mutagenic, and teratogenic effects, posing a significant threat to ecological environment safety and human health. Therefore, how to rapidly and efficiently treat Cr(VI) in electroplating wastewater is an extremely important research topic.

[0003] Chitosan is a homopolymer of 2-amino-2-deoxy-D-glucose monomers linked by β-(1-4) glycosides, and is the only basic polysaccharide found in nature. The numerous hydroxyl (-OH) and amino (-NH2) groups in the chitosan molecule are typical Lewis basic groups, possessing chelating and coordination abilities for most metals. Therefore, chitosan derivatives can effectively remove heavy metal ions, chemical oxygen demand (COD), and color from water without secondary pollution. Carboxymethyl chitosan is one type of chitosan derivative and a natural adsorbent. Its molecules contain active groups such as hydroxyl, amino, and carboxyl groups, which can exert extremely strong adsorption and coordination effects on heavy metal ions through hydrogen bonding, ion exchange, and van der Waals forces. It has been widely used in wastewater and industrial wastewater treatment as an adsorbent, flocculant, bactericide, ion exchanger, and membrane preparation. Although carboxymethyl chitosan itself has adsorption properties, it also has some drawbacks in application, such as a narrow applicable pH range, high water solubility making separation difficult, and long adsorption equilibrium time.

[0004] Polyethyleneimine (PEI), also known as polyazidepropane, is a water-soluble polymer. It contains a large number of amino groups (-NH2) with strong chelating ability for heavy metal ions. It can be protonated over a wide pH range to exhibit positive charge, making it highly effective at removing negatively charged pollutants from water, such as Cr(VI) in anionic complex form, through electrostatic attraction. However, due to its excellent water solubility, solid-liquid separation is difficult, preventing it from being directly used as an adsorbent to adsorb pollutants from water. Therefore, it is mostly used in modified or encapsulated carriers to enhance the adsorption efficiency of the carrier.

[0005] Therefore, how to combine the advantages of carboxymethyl chitosan and PEI to prepare a novel adsorbent for the efficient removal of Cr(VI) from electroplating wastewater is a technical problem that researchers in this field need to solve.

[0006] Therefore, in order to solve the above problems, this paper proposes a carboxymethyl chitosan adsorbent for adsorbing hexavalent chromium and its preparation method. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention designs a carboxymethyl chitosan adsorbent for adsorbing hexavalent chromium and its preparation method. This invention is non-toxic and environmentally friendly, and (CMC@Fe) is prepared through a two-step crosslinking reaction (ionic crosslinking and chemical crosslinking). 3+ / La 3+ -PEI) functional materials. The resulting adsorbent has a high density of adsorption sites (amino, hydroxyl, etc.) for Cr(VI), and achieves the purpose of rapid and efficient removal of Cr(VI).

[0008] To achieve the above-mentioned technical effects, the present invention is implemented through the following technical solution: 1. A carboxymethyl chitosan adsorbent for adsorbing hexavalent chromium, characterized in that the chemical formula of the adsorbent is: (CMC@Fe 3+ / La 3+ -PEI).

[0009] Another object of the present invention is to provide a method for preparing a carboxymethyl chitosan adsorbent for adsorbing hexavalent chromium, characterized by comprising the following steps:

[0010] Step 1: Add the carboxymethyl chitosan (CMC) aqueous solution dropwise to Fe 3+ and La 3+ Carboxymethyl chitosan hydrogel microspheres were obtained by ion crosslinking reaction in a mixed solution and allowed to stand at room temperature for reaction.

[0011] Step 2: Wash the product obtained in Step 1 and freeze-dry it;

[0012] Step 3: Put the freeze-dried material into an aqueous solution of polyethyleneimine (PEI), mix thoroughly and let stand, then add an aqueous solution of glutaraldehyde under stirring to carry out a chemical cross-linking reaction;

[0013] Step 4: Wash the product obtained in Step 3, and freeze-dry it to obtain PEI-modified carboxymethyl chitosan microspheres (CMC@Fe). 3+ / La 3+ -PEI) adsorbent.

[0014] Furthermore, in Step 1, the carboxymethyl chitosan aqueous solution is prepared at a ratio of 25-35 mL of ultrapure water per gram of carboxymethyl chitosan; the Fe... 3+ and La 3+ The concentrations were 0.1–0.3 wt% and 0.2–0.4 wt%, respectively.

[0015] Furthermore, in Step 1, the carboxymethyl chitosan aqueous solution is prepared at a ratio of 30 mL of ultrapure water per gram of carboxymethyl chitosan; the Fe... 3+ and La 3+ The concentrations were 0.2 wt% and 0.3 wt%, respectively.

[0016] Furthermore, in Step 2 and Step 4, the freeze-drying temperature is -50℃ and the time is 48h; in Step 2, the standing time is 24h.

[0017] Furthermore, in Step 3, the PEI solution has a mass concentration of 1.0–3.0 wt%, and the glutaraldehyde solution has a mass concentration of 1.5–2.5 wt%; the standing time is 6 h, and the stirring time is 2 h.

[0018] Furthermore, the PEI solution has a mass concentration of 1.5 wt%, and the glutaraldehyde solution has a mass concentration of 2 wt%.

[0019] The beneficial effects of this invention are:

[0020] This invention is non-toxic and environmentally friendly, and is prepared by a two-step cross-linking reaction (ionic cross-linking and chemical cross-linking) to obtain (CMC@Fe). 3+ / La 3+ -PEI) functional materials; the resulting adsorbent has a high density of adsorption sites (amino, hydroxyl, etc.) for Cr(VI), and achieves the purpose of rapid and efficient removal of Cr(VI), with a maximum adsorption capacity of 649.62 mg·g⁻¹ for Cr(VI). -1 The concentration of Cr(VI) is higher than that of most adsorbents reported in the literature; this adsorbent can be used to remove high concentrations of Cr(VI) from actual electroplating wastewater and has great application prospects. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The (CMC@Fe) obtained in this invention 3+ / La 3+ SEM image of the PEI adsorbent;

[0023] Figure 2 A comparison chart of the adsorption capacity of materials with different ratios for adsorbing Cr(VI);

[0024] Figure 3 For different pH conditions (CMC@Fe) 3+ / La 3+ Adsorption capacity comparison chart of -PEI);

[0025] Figure 4 For different contact times (CMC@Fe) 3+ / La 3+ The effect of PEI on the adsorption capacity of Cr(VI) and the fitting of pseudo-first-order and pseudo-second-order kinetic models;

[0026] Figure 5 For (CMC@Fe 3+ / La 3+ -PEI) to study the changes in adsorption capacity of TC at different initial concentrations and the fitting of Langmuir isotherm model, Freundlich isotherm model and Temkin isotherm model. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] See Figures 1 to 5 As shown, a method for preparing a carboxymethyl chitosan adsorbent for adsorbing hexavalent chromium includes the following steps:

[0030] Step 1: Weigh 1g of carboxymethyl chitosan (CMC) and dissolve it in 30mL of ultrapure water, stirring until dissolved; weigh 0.9655g of FeCl3·6H2O powder and 0.9352g of La(NO3)3·6H2O powder and dissolve them in 100mL of ultrapure water to obtain 0.3wt% La 3+ and 0.2wt% Fe 3+ The mixed solution; the dissolved carboxymethyl chitosan solution was added dropwise to Fe using a syringe. 3+ and La 3+ Cross-linking was carried out in a mixed solution, and the resulting carboxymethyl chitosan hydrogel was allowed to stand at room temperature for 24 hours.

[0031] Step 2: Wash away excess metal ions with deionized water and dry in a -50℃ freeze dryer for 48 hours;

[0032] Step 3: Weigh 1.5g of polyethyleneimine and dissolve it in 100mL of ultrapure water to obtain a 1.5wt% polyethyleneimine solution; weigh 4mL of glutaraldehyde (50wt%) and dissolve it in 100mL of ultrapure water to obtain a 2wt% glutaraldehyde solution; remove the obtained carboxymethyl chitosan composite material from the refrigerated dryer, place it in the 1.5wt% polyethyleneimine solution and let it stand for 6 hours, then add 2wt% glutaraldehyde dropwise and stir gently for 2 hours.

[0033] Step 4: Clean the material surface with deionized water to remove excess PEI and then dry it in a -50℃ freeze dryer for 48 hours to obtain (CMC@Fe). 3+ / La 3+ -PEI) composite materials.

[0034] Example 2

[0035] Instructions for use: Add (CMC@Fe) to the Cr(VI)-containing solution to be treated. 3+ / La 3+ -PEI) material forms a suspension, which is then shaken and adsorbed in a shaker for 24 hours, so that the material surface reaches an adsorption equilibrium for pollutants in the water, thereby removing Cr(VI).

[0036] Example 3

[0037] The study investigated the effect of different metal ratios on Cr(VI) adsorption, including the following steps:

[0038] (1) Material preparation: Weigh 1g of carboxymethyl chitosan (CMC) and dissolve it in 30mL of ultrapure water, stirring until fully dissolved. Weigh 2.4138g FeCl3·6H2O, 1.9310g FeCl3·6H2O, 0.3117g La(NO3)3·6H2O, 1.4483g FeCl3·6H2O, 0.6235g La(NO3)3·6H2O, 0.9655g FeCl3·6H2O, 0.9352g La(NO3)3·6H2O, 0.4828g FeCl3·6H2O, and 0.3117g La(NO3)3·6H2O respectively and dissolve them in 100mL of ultrapure water to prepare a FeCl3 solution with a mass concentration of 0.5wt%. 3+ 0.4wt% Fe 3+ / 0.1% La 3+ 0.3wt% Fe 3+ / 0.2wt%La 3+ 0.2wt% Fe 3+ / 0.3wt% La 3+ and 0.1wt% Fe 3+ / 0.4wt%La 3+ A mixed metal solution was prepared. 1.5 g of polyethyleneimine colloid was dissolved in 100 mL of ultrapure water to obtain a 1.5 wt% polyethyleneimine solution. 4 mL of glutaraldehyde (50 wt%) was dissolved in 100 mL of ultrapure water to obtain a 2 wt% glutaraldehyde solution. A well-stirred carboxymethyl chitosan (CMC) solution was added dropwise to the metal solutions of different concentrations using a syringe. The mixture was allowed to stand at room temperature for 24 hours for crosslinking. Excess metal ions were washed away with deionized water, and the mixture was freeze-dried for 48 hours. Afterward, the mixture was placed in the polyethyleneimine solution and allowed to stand for 6 hours. Glutaraldehyde was then added dropwise with a dropper and stirred gently for 2 hours. Excess solution was washed away with deionized water, and the mixture was freeze-dried for 48 hours to obtain the material.

[0039] (2) Experimental procedure: Prepare a K2Cr2O7 solution with a concentration of 50mg / L and adjust the pH value to 2; weigh 0.01g of each material and put them into a 100mL ground glass conical flask.

[0040] Step 1: Pour in 30 mL of K2Cr2O7 solution; shake at 25℃ and 180 r / min for 24 h;

[0041] Step 2: After removal, desorb with a mixture of 30 mL of 0.2 mol / L NaOH and 0.2 mol / L NaCl solution (v / v = 1:1) for 24 h, then wash with deionized water;

[0042] Step 3: Repeat the above steps three times.

[0043] (3) Experimental results: When the mixed metal solution ratio is 0.2wt% Fe 3+ / 0.3wt% La 3+ When the adsorption effects are similar, the stability is the best.

[0044] (4) Method for determining the residual concentration: After filtering the obtained solution, the residual Cr(VI) concentration was determined by ultraviolet-visible spectrophotometry at a wavelength of 540 nm using diphenylcarbazide.

[0045] Example 4

[0046] The effect of different polyethyleneimine concentrations on Cr(VI) adsorption was investigated, including the following steps:

[0047] (1) Material preparation: Weigh 1g of carboxymethyl chitosan (CMC) and dissolve it in 30mL of ultrapure water, stirring until fully dissolved. Weigh 0.9655g of FeCl3·6H2O and 0.9352g of La(NO3)3·6H2O and dissolve them in 100mL of ultrapure water to prepare a 0.2wt% FeCl3·6H2O solution. 3+ / 0.3wt% La 3+ Metal mixed solutions were prepared. 1g, 1.5g, 2g, and 3g of polyethyleneimine were dissolved in 100mL of ultrapure water to obtain polyethyleneimine solutions with mass concentrations of 1wt%, 1.5wt%, 2wt%, and 3wt%, respectively. 4mL of glutaraldehyde (50wt%) was dissolved in 100mL of ultrapure water to obtain a 2wt% glutaraldehyde solution. A well-stirred carboxymethyl chitosan (CMC) solution was added dropwise to the metal solutions of different mass concentrations using a syringe. The mixtures were allowed to stand at room temperature for 24 hours for crosslinking. Excess metal ions were washed away with deionized water, and the mixture was freeze-dried for 48 hours. Afterward, the mixture was placed in polyethyleneimine solutions of different concentrations and allowed to stand for 6 hours. Glutaraldehyde was then added dropwise with a dropper and the mixture was gently stirred for 2 hours. Excess solution was washed away with deionized water, and the mixture was freeze-dried for 48 hours to obtain the material.

[0048] (2) Experimental procedure: Prepare a K2Cr2O7 solution with a concentration of 50mg / L and adjust the pH value to 2; weigh 0.01g of each material and put them into a 100mL ground glass conical flask, and pour in 30mL of K2Cr2O7 solution; shake at 25℃ and 180r / min for 24h.

[0049] (3) Experimental results: When the concentration of polyethyleneimine is 1.5wt%, the adsorption effect is better.

[0050] (4) Method for determining the residual concentration: After filtering the obtained solution, the residual Cr(VI) concentration was determined by ultraviolet-visible spectrophotometry at a wavelength of 540 nm using diphenylcarbazide.

[0051] Example 5

[0052] The effect of different pH values ​​on adsorption experiments of a single system was investigated, including the following steps:

[0053] (1) Prepare a K2Cr2O7 solution with a concentration of 100 mg / L, and adjust the pH with 1M NaOH and 1M HCl, with a pH range of 1-7;

[0054] (2) Weigh the (CMC@Fe) prepared in Example 1. 3+ / La 3+ 0.01 g of PEI material was placed in a 100 mL ground glass conical flask, and two parallel samples were prepared under different pH conditions.

[0055] (3) Pour 30 mL of the solution in (1) into (2), place it in a shaker, shake for 24 h, and rotate at 180 r / min;

[0056] (4) Experimental results show that the adsorption effect first increases and then decreases with increasing pH value, reaching a maximum of 289.26 mg·g at pH 2. -1 .

[0057] (5) After filtering the obtained solution, the concentration of the remaining Cr(VI) was determined by ultraviolet-visible spectrophotometry at a wavelength of 540 nm using diphenylcarbazide.

[0058] Example 6

[0059] A method for preparing a carboxymethyl chitosan adsorbent for adsorbing hexavalent chromium includes the following steps:

[0060] (1) Prepare a K2Cr2O7 concentration of 100 mg / L and adjust the pH to 2 with 1 M NaOH and 1 M HCl;

[0061] (2) Weigh the (CMC@Fe) prepared in Example 1. 3+ / La 3+ 0.01 g of PEI material was placed in a ground glass conical flask, and two parallel samples were set up for different adsorption times.

[0062] (3) Pour 30 mL of solution from (1) into (2), place it in a shaker, and shake for 0.25, 0.5, 1, 2, 4, 6, 8, 12, 16, 20, 24, 28, 30, 32, 40, and 44 hours respectively, with a rotation speed of 180 r / min;

[0063] (4) Experimental results show that: (CMC@Fe 3+ / La 3+ The adsorption of Cr(VI) by PEI reaches adsorption equilibrium approximately 24 hours after contact.

[0064] (5) Method for determining the remaining concentration: The determination of Cr(VI) is as follows: After filtering the obtained solution, the remaining Cr(VI) concentration is determined by ultraviolet-visible spectrophotometry at a wavelength of 540 nm using diphenylcarbazide.

[0065] To further understand the adsorption process and mechanism, the kinetic data were fitted using pseudo-first-order kinetic equations, pseudo-second-order kinetic equations, and an intraparticle diffusion model (Weber-Morris model):

[0066] The pseudo-first-order dynamic equation:

[0067]

[0068] Pseudo-second-order dynamic equations:

[0069]

[0070] Intraparticle diffusion model (Weber-Morris model):

[0071]

[0072] Where, q t (mg·g -1 ) and q e (mg·g -1 ) represent the adsorption amounts of the target pollutant at time t and at equilibrium, respectively. k1(min) -1 ) and k2(g·mg -1 min -1 ) are the pseudo-first-order and pseudo-second-order kinetic adsorption rate constants, respectively. k i (mg·g -1 min -1 / 2 ) represents the diffusion rate constant within the particle.

[0073] Example 7

[0074] A method for preparing a carboxymethyl chitosan adsorbent for adsorbing hexavalent chromium includes the following steps:

[0075] (1) Prepare K2Cr2O7 concentrations of 100, 200, 300, 400, 500, 600 and 700 mg / L respectively, and adjust the pH to 2 with 1M NaOH and 1M HCl;

[0076] (2) Weigh the (CMC@Fe) prepared in Example 1. 3+ / La 3+ 0.01 g of each of the PEI material was placed in a ground glass conical flask, and two parallel samples were set up for the same adsorption time.

[0077] (3) Pour 30 mL of solution from (1) into (2), place it in a shaker, shake for 48 h, and rotate at 180 r / min;

[0078] (4) Experimental results show that the maximum adsorption capacity of Cr(VI) at 298 K calculated by the Langmuir model is 649.62 mg·g. -1 .

[0079] (5) Method for determining the remaining concentration: The determination of Cr(VI) is as follows: After filtering the obtained solution, the remaining Cr(VI) concentration is determined by ultraviolet-visible spectrophotometry at a wavelength of 540 nm using diphenylcarbazide.

[0080] To further describe (CMC@Fe) 3+ / La 3+ The adsorption behavior of Cr(VI) by PEI was nonlinearly fitted to the isotherm data using the Langmuir, Freundlich, and Temkin isotherm models. The equations for each model are as follows:

[0081] Langmuir isotherm model:

[0082]

[0083] Freundlich isotherm model:

[0084]

[0085] Temkin isotherm model:

[0086] q e =B1ln K T +B1ln C e

[0087] Where C e (mg·L -1 ) and q e (mg·g -1 ) represent the equilibrium concentration and adsorption capacity of Cr(VI), respectively. q max (mg·g -1 K represents the maximum adsorption capacity of the adsorbent. L (L·mg -1 ), K F (L 1 / n ·g -1 ) and represent the Langmuir constant and the Freundlich constant, respectively. nF is the dimensionless constant in the Freundlich model.

[0088] Example 8

[0089] Depend on Figure 1 It can be known that: Figure 1 (a)(b)(c) demonstrates (CMC@Fe 3+ / La 3+ The surface morphology diagram of PEI shows that its surface is not smooth, with dendritic structures attached to the surface and fine cracks, which provide channels for pollutants to enter the interior of the composite material and make it easier for them to come into contact with the adsorption sites. Figure 1 (d)(e)(f) demonstrates CMC@Fe 3+ / La 3+ Surface morphology diagram, and (CMC@Fe 3+ / La 3+ Compared to the surface of -PEI), CMC-Fe 3+ / La 3+ Its surface is relatively smooth and dense, making it difficult for adsorption sites to form. Figure 1 (g)(h)(i) demonstrates (CMC@Fe 3+ / La 3+ The cross-sectional diagram of -PEI shows that the carboxymethyl chitosan cross-linked by the metal solution has a loose porous network structure with large pore size. Figure 1 (j)(k)(l) is CMC-Fe 3+ / La 3+ The cross-sectional view shows CMC-Fe 3+ / La 3+ The cross-section has a layered porous structure without a network structure.

[0090] Depend on Figure 2 It can be known that: Figure 2 (a)(b)(c) demonstrates (CMC@Fe 3+ / La 3+ The material ratio of -PEI) is 0.2 wt% Fe in the metal mixed solution. 3+ / 0.3wt% La 3+ When the mass concentration of the polyethyleneimine solution is 1.5 wt%, the optimal material (CMC@Fe) can be prepared. 3+ / La 3+ -PEI).

[0091] Depend on Figure 3 It can be seen that: (CMC@Fe 3+ / La 3+ The adsorption capacity of PEI varies at different pH values, reaching a maximum of 289.26 mg / g at pH 2, indicating that it can be used as a highly efficient adsorbent for removing Cr(VI).

[0092] Depend on Figure 4 We can obtain the linear fitting curves for the quasi-first-order and quasi-second-order equations as follows: Figure 4 As shown in (a) and (b), the correlation coefficient R of the pseudo-second-order dynamics can be calculated. 2 =0.988) is much higher than the correlation coefficient (R) of the pseudo-first-order dynamic equation. 2 =0.637). Therefore, the pseudo-second-order dynamic model can better describe (CMC@Fe). 3+ / La 3+ The adsorption process of Cr(VI) by PEI. For example Figure 4 As shown in (c), the fitted graph is divided into three straight lines, which means that the adsorption of Cr(VI) involves multiple steps, and intraparticle diffusion is not the only rate-limiting step. The intraparticle diffusion rate constants of the three straight lines, in descending order, are k i,1 >k i,2 >k i,3 The largest value of k i,1 =96.726 corresponds to the first stage of adsorption, in which Cr(VI) diffuses to the adsorbent surface, and the adsorption rate is the fastest; the second stage k i,2 =27.833 represents internal diffusion, where Cr(VI) gradually occupies the internal adsorption sites of the adsorbent; and in the final stage, k i,3 =11.843, indicating that the adsorption rate gradually decreases and slowly reaches adsorption equilibrium. The above conclusions demonstrate that (CMC@Fe 3+ / La 3+ The adsorption of Cr(VI) by PEI is a relatively complex process, which is completed in multiple steps.

[0093] Depend on Figure 5 It can be seen that at different temperatures (298, 308, and 318 K), q e With C e The adsorption capacity increases with increasing temperature, but this increase is not linear, indicating that intraparticle diffusion is not the controlling factor for adsorption. Furthermore, increasing temperature contributes to the increase in adsorption capacity, suggesting that the adsorption process is endothermic. Relevant fitting parameters were obtained through fitting, where the correlation coefficient R corresponding to the Langmuir isotherm model is... 2 The maximum value indicates that it is best suited to describe Cr(VI) in (CMC@Fe). 3+ / La 3+ The adsorption process on Cr(VI) was also observed. Furthermore, based on the Langmuir model, the maximum adsorption capacity of Cr(VI) at 298 K was calculated to be 649.62 mg·g⁻¹. -1 This demonstrates its highly efficient adsorption capacity for TC.

[0094] The above phenomena indicate that this invention is non-toxic and environmentally friendly, and (CMC@Fe) is prepared through simple mixing and cross-linking.3+ / La 3+ -PEI) functional materials. Novel adsorbent (CMC@Fe 3+ / La 3+ -PEI targets multiple adsorption sites for Cr(VI) pollutants and achieves rapid and efficient adsorption, resulting in a maximum adsorption capacity of 649.62 mg·g⁻¹ for Cr(VI). -1 .

Claims

1. A method for preparing a carboxymethyl chitosan adsorbent for adsorbing hexavalent chromium, characterized in that, Includes the following steps: Step 1: Add carboxymethyl chitosan (CMC) aqueous solution dropwise to Fe 3+ and La 3+ Carboxymethyl chitosan hydrogel microspheres were obtained by ion crosslinking reaction in a mixed solution and allowed to stand at room temperature for reaction. Step 2: Wash the product obtained in Step 1 and freeze-dry it; Step 3: Put the freeze-dried material into an aqueous solution of polyethyleneimine (PEI), mix thoroughly and let stand, then add an aqueous solution of glutaraldehyde under stirring to carry out a chemical cross-linking reaction; Step 4: Wash the product obtained in Step 3, freeze-dry it to obtain PEI-modified carboxymethyl chitosan microsphere adsorbent. The chemical formula of this adsorbent is: (CMC@Fe 3+ / La 3+ -PEI); In Step 1, the carboxymethyl chitosan aqueous solution is prepared at a ratio of 25-35 mL of ultrapure water per gram of carboxymethyl chitosan; the Fe... 3+ and La 3+ The concentrations were 0.1–0.3 wt% and 0.2–0.4 wt%, respectively.

2. The method for preparing a carboxymethyl chitosan adsorbent for adsorbing hexavalent chromium according to claim 1, characterized in that: In Step 1, the carboxymethyl chitosan aqueous solution is prepared at a ratio of 30 mL of ultrapure water per gram of carboxymethyl chitosan; the Fe... 3+ and La 3+ The concentrations were 0.2 wt% and 0.3 wt%, respectively.

3. The method for preparing a carboxymethyl chitosan adsorbent for adsorbing hexavalent chromium according to claim 1, characterized in that: In Step 2 and Step 4, the freeze-drying temperature is -50℃ and the time is 48h; in Step 1, the standing time is 24h.

4. The method for preparing a carboxymethyl chitosan adsorbent for adsorbing hexavalent chromium according to claim 1, characterized in that: In Step 3, the PEI solution has a mass concentration of 1.0–3.0 wt%, and the glutaraldehyde solution has a mass concentration of 1.5–2.5 wt%; the standing time is 6 hours, and the stirring time is 2 hours.

5. The method for preparing a carboxymethyl chitosan adsorbent for adsorbing hexavalent chromium according to claim 4, characterized in that: The PEI solution has a mass concentration of 1.5 wt%, and the glutaraldehyde solution has a mass concentration of 2 wt%.

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