Butanediamine-modified biochar composite gel spheres, their preparation method and applications

Abstract

This invention discloses a butanediamine-modified biochar composite gel sphere, its preparation method, and its application. The preparation method includes: uniformly mixing a solution of sodium alginate, carboxymethyl chitosan, and Sedum aizoon biochar; then adding calcium chloride solution to react and form gel spheres; epichlorohydrin as an intermediate intermolecular branching agent to open the ring and connect butanediamine; placing the modified gel spheres in a glutaraldehyde solution of a certain concentration for surface cross-linking to improve the surface strength of the material; washing with ultrapure water and then vacuum freeze-drying to obtain the butanediamine-modified biochar composite gel spheres. The butanediamine-modified biochar composite gel spheres prepared by this invention have good removal effects on Cr(VI) and Cu(II) in solution, with adsorption capacities of 300-500 mg / g and 60-90 mg / g, respectively. They possess advantages such as strong stability, easy separation from solution, good adsorption and regeneration performance, simple preparation process, and low cost, making them an environmentally friendly green adsorbent.

Description

Technical Field

[0001] This invention relates to the field of water pollution removal technology, and in particular to a butanediamine-modified biochar composite gel ball, its preparation method, and its application. Background Technology

[0002] Copper- and chromium-containing wastewater mainly originates from industries such as mining, metal electroplating, non-ferrous metal processing, and textiles, with the electroplating industry being a particularly significant source of emissions. Heavy metal pollution in water not only threatens aquatic ecosystems but also poses potential risks to human health. While chromium and copper are essential trace elements for the human body, excessive intake can cause irreversible damage. Chromium primarily exists as Cr(VI) and Cr(III), and studies have shown that Cr(VI) is 100 times more toxic than Cr(III). The World Health Organization sets the upper limit for Cr(VI) concentration in surface water at 0.1 ppm. When the Cr(VI) concentration in drinking water exceeds this limit, it can lead to heavy metal poisoning, carcinogenicity, and mutagenicity, among other health problems. Copper exists in water as free Cu(II) and in complexes. Although hydroxides and sulfides can be used for solid-liquid separation, the highly stable copper complexes formed by ligands are more harmful than the free form. As persistent heavy metal pollutants, copper complexes are difficult to degrade, readily soluble, and widely migrate, posing serious threats to cells, aquatic plants, and microorganisms. my country stipulates that the maximum discharge concentration of Cu(II) in industrial wastewater is 1.0 ppm, and the concentration of copper ions in drinking water must be below 1.0 ppm. Traditional wastewater treatment technologies often fall short of meeting the requirements for efficient removal of these two metal ions; therefore, research into novel adsorption materials and methods is particularly important.

[0003] Adsorption is a widely used and effective method in wastewater treatment. It separates and removes harmful substances from wastewater through physical or chemical reactions between the adsorbent and the wastewater. Against this backdrop, this patent relates to a composite adsorbent based on carboxymethyl chitosan, sodium alginate, and biochar. This adsorbent exhibits excellent adsorption performance, particularly high efficiency in removing hexavalent chromium and divalent copper. Carboxymethyl chitosan, as a natural polyhydroxy biopolymer, possesses good hydrophilicity and adsorption properties. Sodium alginate is a natural high-molecular-weight polysaccharide extracted from seaweed; its carboxyl and hydroxyl groups have the ability to bind to metal ions. Biochar, due to its porous structure and abundant functional groups, is widely used to adsorb organic and inorganic substances from wastewater.

[0004] Taking the above factors into consideration, the research results of this invention show that the composite adsorbent of these three materials exhibits superior adsorption performance in removing hexavalent chromium and divalent copper. Through the technology of this patented invention, not only can hexavalent chromium and divalent copper be efficiently removed, but the adsorbent material, existing in the form of gel spheres, also possesses the characteristics of high feasibility, low cost, easy separation, and recyclability, providing a new solution for the wastewater treatment field. Through a detailed description and explanation of this technology, this patent aims to provide practitioners in the fields of environmental protection and wastewater treatment with an effective and economical method for removing harmful metal ions. Summary of the Invention

[0005] The purpose of this invention is to provide a butanediamine-modified biochar composite gel sphere, its preparation method, and its application. This method uses two natural polymer materials, carboxymethyl chitosan and sodium alginate, as matrices, and adds Sedum aizoon biochar as a carbon skeleton to prepare biochar composite gel beads with abundant active sites. Further chemical modification yields butanediamine-modified biochar composite gel spheres, which possess excellent properties such as simple preparation method, low cost, easy separation and recycling, large specific surface area, and stable structure, enabling efficient removal of Cr(VI) and Cu(II).

[0006] The technical solution adopted in this invention is as follows:

[0007] The method for preparing butanediamine-modified biochar composite gel spheres involves using sodium alginate, carboxymethyl chitosan, and biochar as substrates, dispersing them in water and mixing them evenly to obtain a composite solution. The composite solution is then dropped into a calcium chloride solution to form biochar composite gel beads. Epichlorohydrin is used as an intermediate insemination to modify the biochar composite gel beads, followed by grafting with butanediamine. The modified gel beads are then placed in a glutaraldehyde solution for surface cross-linking to obtain gel spheres. Finally, the gel spheres are freeze-dried to obtain the butanediamine-modified biochar composite gel spheres. The mass ratio of sodium alginate to carboxymethyl chitosan is 1–4:1, preferably 1.5–2:1, and the total mass ratio of sodium alginate and carboxymethyl chitosan to biochar is 2.5–6:1, preferably 5–6:1.

[0008] The preparation method of the butanediamine-modified biochar composite gel spheres specifically includes the following steps:

[0009] 1) Place the Sedum australis powder in a quartz boat, cover it, place it in a muffle furnace, continuously introduce nitrogen to purge the air, and pyrolyze it under nitrogen protection. After the muffle furnace cools naturally, you will get Sedum australis biochar, grind it, sieve it, and then seal it for storage.

[0010] 2) Add sodium alginate, carboxymethyl chitosan and biochar powder to ultrapure water and stir thoroughly to obtain a composite solution;

[0011] 3) Using calcium chloride solution as the continuous phase and composite solution as the dispersed phase, the dispersed phase was dropped into the continuous phase, soaked and solidified, and allowed to stand overnight. After solid-liquid separation, the mixture was washed multiple times with ultrapure water to obtain biochar composite gel beads.

[0012] 4) Disperse the biochar composite gel beads from step 3) in ultrapure water, then add epichlorohydrin and ethanol to react and obtain epichlorohydrin-grafted biochar composite gel balls.

[0013] 5) The epichlorohydrin-grafted biochar composite gel balls obtained in step 4) were dispersed in ethanol and butanediamine solution, and after the grafting reaction was carried out, they were taken out, washed multiple times with ethanol and ultrapure water, and then placed in a glutaraldehyde solution of a certain concentration for cross-linking reaction to obtain butanediamine-modified biochar composite gel balls.

[0014] 6) After washing the butanediamine-modified biochar composite gel balls from step 5) several times with ultrapure water, freeze-dry them to obtain dried butanediamine-modified biochar composite gel balls.

[0015] The method for preparing butanediamine-modified biochar composite gel spheres is characterized in that, in step 1), the pyrolysis temperature is 700-900℃, the pyrolysis time is 2-4h, and the sieve mesh size is 80-200 mesh.

[0016] The method for preparing butanediamine-modified biochar composite gel spheres is characterized in that, in step 2), the mass ratio of sodium alginate to carboxymethyl chitosan is 1-4:1, preferably 1.5-2:1; the mass ratio of the total mass of sodium alginate and carboxymethyl chitosan to biochar is 2.5-6:1, preferably 5-6:1; and the mass ratio of the total mass of sodium alginate, carboxymethyl chitosan, and biochar to ultrapure water is 2-3:100, preferably 2.4-2.5:100.

[0017] The method for preparing butanediamine-modified biochar composite gel spheres is characterized in that, in step 3), the mass concentration of the calcium chloride solution is 1-5%; the volume ratio of the dispersed phase to the continuous phase is 1:10-30; and the soaking, curing, and overnight standing time is 12-24 hours.

[0018] The method for preparing butanediamine-modified biochar composite gel spheres is characterized in that, in step 4), the mass concentration of the biochar composite gel spheres in the mixed solution is 5-15%, the volume concentration of epichlorohydrin is 3-10%, preferably 5-6%, and the volume concentration of ethanol is 5-10%; the reaction temperature is 25-70℃, preferably 40-60℃; the reaction time is 2-8h, preferably 3-5h; and after the reaction, the mixture is washed multiple times with ethanol and ultrapure water.

[0019] The method for preparing butanediamine-modified biochar composite gel spheres is characterized in that, in step 5), the epichlorohydrin-grafted biochar composite gel spheres are dispersed in a mixture of ethanol and butanediamine solution for grafting reaction, wherein the mass concentration of the epichlorohydrin-grafted biochar composite gel spheres is 15-25%, the volume concentration of butanediamine is 2-5%, preferably 3-3.5%, the reaction temperature is 25-70℃, preferably 40-60℃, and the reaction time is 2-8h, preferably 3-5h.

[0020] The method for preparing butanediamine-modified biochar composite gel spheres is characterized in that, in step 5), the volume concentration of glutaraldehyde is 0.5-2%, the reaction is carried out in glutaraldehyde solution with shaking at room temperature for 2-5 hours, and then left to stand for 10-15 hours; the reaction time in glutaraldehyde solution depends on the reaction of the gel beads in the solution, and the reaction ends when the beads change color completely.

[0021] The method for preparing butanediamine-modified biochar composite gel spheres is characterized in that step 6) involves freeze-drying at a temperature of -80 to -60°C for 60 to 90 hours using a vacuum freeze dryer.

[0022] This invention proposes the application of butanediamine-modified biochar composite gel spheres described in the above technical solution and the butanediamine-modified biochar composite gel spheres prepared by the above technical solution in the adsorption of hexavalent chromium or divalent copper ions.

[0023] Furthermore, after the gel spheres adsorb hexavalent chromium, the regeneration process includes placing the adsorbed material in a 3-8% sodium hydroxide solution for desorption for 20-30 hours, then separating the material from the solution and washing it with ultrapure water, or directly placing the material in a 3-8% hydrochloric acid solution for desorption for 20-30 hours and washing it with ultrapure water to achieve material regeneration.

[0024] Furthermore, after the gel spheres adsorb divalent copper ions, the regeneration process involves placing the adsorbed material in a 3-8% hydrochloric acid solution for desorption for 10-15 hours, then separating the material from the solution and washing it with ultrapure water, thus achieving material regeneration.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The present invention provides a method for preparing the butanediamine-modified biochar composite gel ball. The biochar composite gel ball is prepared by mixing Sedum sarmentosum biochar into sodium alginate and carboxymethyl chitosan matrix to serve as a carbon skeleton, which effectively improves the mechanical strength and pore structure of the gel ball; improves the problems of cleaning, separation and clogging of biochar; the biochar composite gel ball contains abundant active sites and can be used as a modification precursor.

[0027] (2) The butanediamine-modified biochar composite gel spheres prepared in this invention contain a large number of amino, hydroxyl, and carboxyl functional groups, synthesized from sodium alginate, carboxymethyl chitosan, and biochar. The subsequently grafted butanediamine also contains a large number of amino functional groups. The presence of these reducing polar functional groups effectively enhances the electrostatic adsorption and redox of Cr(VI) to Cr(III) by the butanediamine-modified biochar composite gel spheres. Furthermore, the oxygen atoms in the hydroxyl and carboxyl functional groups on the material can form coordination bonds with Cr(III), achieving chelation. The addition of butanediamine increases the specific surface area and porosity of the biochar composite gel spheres; they can recover to a gel state after contact with water and have good stability and strong acid resistance; they can be used for adsorption in chromium- and copper-containing wastewater and can be efficiently separated, recycled, and reused.

[0028] Ethylenediamine, due to its compact molecular structure with two closely adjacent amino groups, typically exhibits high reactivity. However, this compactness can lead to decreased stability under high temperatures or extreme pH conditions. In contrast, 1,4-butanediamine has a more loose molecular structure, with the two amino groups separated by a longer carbon chain, which provides it with better thermal and chemical stability. The use of butanediamine as the adsorbent material in this application achieves better technical results. Attached Figure Description

[0029] Figure 1 This is a scanning electron microscope (SEM) image of the BDA@GA-BSC prepared in Example 1.

[0030] Figure 2 The Zeta potential diagram of the BDA@GA-BSC prepared in Example 1;

[0031] Figure 3 Fourier transform infrared spectra of BSC and BDA@GA-BSC prepared in Example 1.

[0032] Figure 4 The adsorption results of BDA@GA-BSC, ECH-BSC and BSC prepared in Example 1 on Cr(VI) are shown.

[0033] Figure 5 The results of the adsorption experiments of BDA@GA-BSC prepared in Example 1 on Cr(VI) in solutions of different pH values ​​are shown.

[0034] Figure 6 The adsorption results of BDA@GA-BSC prepared in Example 1 on Cr(VI) at different initial concentrations are shown.

[0035] Figure 7The adsorption results of BDA@GA-BSC prepared in Example 1 for Cr(VI) at different contact times;

[0036] Figure 8 The results of the adsorption experiments of Cu(II) on BDA@GA-BSC prepared in Example 1 in solutions of different pH values ​​are shown.

[0037] Figure 9 The adsorption results of Cu(II) by BDA@GA-BSC prepared in Example 1 at different initial concentrations are shown.

[0038] Figure 10 The adsorption results of Cu(II) by BDA@GA-BSC prepared in Example 1 at different contact times;

[0039] Figure 11 The adsorption results of BDA@GA-BSC prepared in Example 1 on Cr(VI) in five consecutive adsorption-desorption cycles;

[0040] Figure 12 The adsorption results of Cu(II) by BDA@GA-BSC prepared in Example 1 in five consecutive adsorption-desorption cycles are shown. Detailed Implementation

[0041] The present invention will now be described in detail with reference to specific examples, but the present invention is not limited to these specific embodiments.

[0042] In this embodiment of the invention, the carboxymethyl chitosan was sourced from Hangzhou Bangyi Chemical Co., Ltd., CAS No. 83512-85-0. Butanediamine refers to 1,4-butanediamine.

[0043] Example 1:

[0044] This invention provides a method for preparing butanediamine-modified biochar composite gel spheres, the specific steps of which are as follows:

[0045] 1) Wash the stems and leaves of Sedum aizoon in the field with tap water to remove soil and other impurities, as well as the roots. Then rinse several times with ultrapure water and let the surface moisture dry. Place the plant material in a 105℃ oven for 30 minutes to blanch, and then dry it at 60℃ to constant weight. Use a plant pulverizer to pulverize it to obtain Sedum aizoon natural substances.

[0046] 2) Take 5.0g of Sedum aizoon biochar from step 1) and place it in a quartz boat wrapped in tin foil. Pyrolyze the biochar in a muffle furnace at 700℃ (heating from room temperature to 700℃ at a rate of 10℃ / min) under a nitrogen atmosphere (200mL / min) for 2 hours. After natural cooling, wash the pyrolysis product 3-4 times with ethanol and ultrapure water respectively. After drying and grinding through a 100-mesh sieve, obtain Sedum aizoon biochar.

[0047] 3) Take 50 mL of ultrapure water into a round-bottom flask, add 0.6 g of sodium alginate, 0.4 g of carboxymethyl chitosan and 0.2 g of Sedum aizoon biochar from step 2), stir thoroughly with magnetic force to obtain a uniform biochar composite material gel solution.

[0048] 4) Take 10 mL of the biochar composite gel solution from step 3) into a syringe, with the needle 1-3 cm away from the calcium chloride solution. Use a syringe pump to drip the solution into 200 mL of 2% calcium chloride solution at a rate of 1 drop / s. Let it stand and solidify for 18 h. Separate the solid and liquid, and use ultrapure water to sonicate and wash the gel balls multiple times to obtain the biochar composite gel balls.

[0049] 5) Take 10g of the biochar composite gel ball from step 4) into a round-bottom flask, add 5mL of ethanol, 5mL of epichlorohydrin and 90mL of ultrapure water, place the round-bottom flask in a magnetically stirred oil bath, and magnetically stir at 50℃ for 4h. Use ultrapure water and ethanol to sonicate and wash the gel ball multiple times to obtain epichlorohydrin-grafted biochar composite gel ball.

[0050] 6) Take 10g of the epichlorohydrin-grafted biochar composite gel spheres from step 5) into a round-bottom flask, add 1.73mL of butanediamine (i.e., 1.5g of butanediamine) and 48.27mL of ethanol, place the round-bottom flask in a magnetically stirred oil bath, and magnetically stir for 4h at 50℃. Use ultrapure water and ethanol to sonicate and wash the gel spheres multiple times, then put the gel spheres into a glutaraldehyde solution (98mL of ultrapure water, 1mL of ethanol, and 1mL of glutaraldehyde), shake and react at room temperature for 3h, let stand for 12h, take out the gel spheres and wash them multiple times with ultrapure water and ethanol to obtain butanediamine-modified biochar composite gel spheres.

[0051] The biochar composite gel spheres synthesized in step 4), the epichlorohydrin-grafted biochar composite gel spheres synthesized in step 5), and the butanediamine-modified biochar composite gel spheres synthesized in step 6) were placed in a vacuum freeze dryer and dried at -60°C for 72 hours. The products obtained after drying were named BSC, ECH-BSC, and BDA@GA-BSC, respectively.

[0052] The SEM image of BDA@GA-BSC in Example 1 is shown below. Figure 1 Zeta potential diagrams in aqueous solutions at different pH values ​​are shown below. Figure 2 .

[0053] To confirm the successful synthesis of the BDA@GA-BS composite material and the key reaction sites generated during its preparation, Fourier transform infrared (FT-IR) spectroscopy analysis was performed on the materials before and after modification. Figure 3Fourier transform infrared spectra of BSC and BDA@GA-BSC from Example 1 are shown. Comprehensive analysis shows that the two materials exhibit similar characteristics at 3430 cm⁻¹. -1 Significant absorption peaks were observed in the vicinity, mainly due to the resonant stretching vibrations of the OH and NH groups. Furthermore, at 1045 cm⁻¹... -1 and 1047cm -1 The absorption peak at 602 cm⁻¹ indicates the presence of CO bonds in the carboxyl groups of sodium alginate and carboxymethyl chitosan, while the peak at 602 cm⁻¹ indicates the presence of CO bonds in the carboxyl groups of sodium alginate and carboxymethyl chitosan. -1 and 598cm -1 The absorption peak at 1613 cm⁻¹ reflects the stretching vibration of the CH bond. In local analysis, the FT-IR spectrum of BSC shows a peak at 1613 cm⁻¹. -1 An absorption peak is observed at 877 cm⁻¹, which corresponds to the stretching vibration of C=C in unsaturated hydrocarbons, indicating that the material contains a large number of aromatic structures. -1 The weak absorption peak at 1419 cm⁻¹ reveals the presence of aromatic compounds, while the weak absorption peak at 1419 cm⁻¹... -1 The absorption peak at 2933 cm⁻¹ may be related to the bending vibrations of the alkyl groups -CH₃ and -CH₂. For the FT-IR spectrum of BDA@GA-BS, the peak at 2933 cm⁻¹ is... -1 The new absorption peak at [value] indicates that butanediamine underwent a substitution reaction with the intermediate epichlorohydrin, leading to an increase in the number of CH groups. After modification, the original peak at 1613 cm⁻¹ [value]... -1 The absorption peak shifted to 1647 cm⁻¹ -1 This may be due to the cross-linking reaction between butanediamine and glutaraldehyde, which generates a new imine group (-N=CH-), resulting in a height of 1647 cm⁻¹. -1 The peak intensity at 1419 cm⁻¹ increases. Meanwhile, the peak intensity at 1419 cm⁻¹... -1 The absorption peak at 1410 cm⁻¹ shifted to 1410 cm⁻¹ -1 The intensity of the newly generated CN stretching vibration peak decreased, indicating that it partially overlapped with the existing -CH3 and -CH2 bending vibration peaks. These changes confirm the successful synthesis of BDA@GA-BS microspheres. In summary, the FT-IR spectrum of the BDA@GA-BS composite material reveals its abundant organic active functional groups, which facilitate its adsorption of Cr(VI) and Cu(II) in solution.

[0054] Example 2

[0055] 0.0125 g of each of the BSC, ECH-BSC, and BDA@GA-BSC prepared in Example 1 were placed in 25 mL of a Cr(VI) concentration of 40 mg / L. The pH of the solution was adjusted to 2 with 0.1 M HCl. The horizontal constant-temperature shaker was set to 150 rpm and the temperature to 25 °C. The adsorption time was 24 h. The Cr(VI) concentration in the solution after adsorption was measured using a UV spectrophotometer. The removal efficiency of the materials prepared at different stages for Cr(VI) was compared. The results are shown in [Figure 1]. Figure 4 .

[0056] from Figure 4 The results show that BDA@GA-BSC achieved a Cr(VI) removal rate of 92.45%, while ECH-BSC and BSC achieved 9.61% and 15.08% removal rates, respectively. The removal rate of Cr(VI) by BDA@GA-BSC is more than six times that of BSC, indicating that the modified gel spheres BDA@GA-BSC prepared according to the steps of Example 1 of this invention were successfully modified and significantly improved the adsorption capacity of the prepared adsorbent for Cr(VI). Since the adsorption effects of BSC and ECH-BSC gel spheres on Cr(VI) are relatively poor, subsequent performance tests and investigations into the adsorption performance on Cu(II) will only be conducted on BDA@GA-BSC gel spheres.

[0057] Example 3

[0058] 0.02 g of BDA@GA-BSC prepared in Example 1 was placed in 50 mL of a Cr(VI) solution with a concentration of 60 mg / L. The pH of the solution was adjusted to 2, 3, 4, 5, 6, 7, and 8 using 0.1 M NaOH or 0.1 M HCl. The horizontal constant-temperature shaker was set to 150 rpm and the temperature to 25 °C. The adsorption time was 48 h. The Cr(VI) concentration in the solution after adsorption at different pH values ​​was measured using a UV spectrophotometer. The adsorption experimental results are as follows: Figure 5 .

[0059] Under the above pH conditions, the adsorption capacity of BDA@GA-BSC for Cr(VI) gradually decreased with increasing pH, reaching a maximum adsorption capacity of 140.44 mg / L at pH=2 and a minimum adsorption capacity of 1.58 mg / L at pH=8. This indicates that BDA@GA-BSC gel beads have good adsorption performance for Cr(VI) in acidic environments, with the best removal effect at pH=2. At pH>7, they almost completely lose their adsorption capacity for Cr(VI). In subsequent performance tests for Cr(VI), the pH was set to 2.

[0060] Example 4

[0061] 0.02 g of BDA@GA-BSC prepared in Example 1 was placed in 50 mL of a Cu(II) solution with a concentration of 40 mg / L. The pH of the solution was adjusted to 2, 3, 4, 5, 6, and 7 using 0.1 M NaOH or 0.1 M HCl. The horizontal constant-temperature shaker was set to 150 rpm and the temperature was adjusted to 25 °C. The adsorption time was 48 h. The Cu(II) concentration in the solution after adsorption at different pH values ​​was measured using a flame atomic absorption spectrophotometer. The adsorption experimental results are as follows: Figure 8 .

[0062] Under the above pH conditions, the adsorption capacity of BDA@GA-BSC for Cu(II) increased with increasing pH, reaching a maximum adsorption capacity of 96.56 mg / L at pH=7 and a minimum adsorption capacity of 4.75 mg / L at pH=2. Figure 8 The data shows an adsorption abrupt change between pH 6 and pH 7. At pH 7, the adsorption capacity increases significantly, which may be due to the presence of OH- in the solution. - At higher concentrations, Cu(II) mainly reacts with OH- in the solution. - Complexation precipitation, rather than adsorption, occurred. Therefore, the pH was set to 6 in subsequent performance tests of Cu(II).

[0063] Example 5

[0064] 0.02 g of BDA@GA-BSC prepared in Example 1 was placed in 50 mL of solutions with Cr(VI) concentrations of 40, 80, 120, 160, 200, 240, 280, and 320 mg / L. The pH of the solution was adjusted to 2 with 0.1 M NaOH or 0.1 M HCl. The horizontal constant-temperature shaker was set to 150 rpm and the temperature was adjusted to 25 °C. The adsorption time was 48 h. The Cr(VI) concentration in the solution after adsorption at different concentrations was measured using a UV spectrophotometer. The adsorption experimental results are as follows: Figure 6 .

[0065] from Figure 6 The results show that under the above conditions, the adsorption capacity of BDA@GA-BSC for Cr(VI) increases with increasing solution concentration, while the removal rate shows the opposite trend, with the saturated adsorption capacity of the adsorbent approaching 365 mg / g. To achieve both high efficiency in adsorbing Cr(VI) and a high removal rate, the initial concentration of Cr(VI) in the solution was chosen to be 120 mg / L. At this concentration, the adsorption capacity of BDA@GA-BSC for Cr(VI) was 257.49 mg / g, and the removal rate was 83.68%.

[0066] Example 6

[0067] 0.02 g of BDA@GA-BSC prepared in Example 1 was placed into 50 mL of Cu(II) solutions with concentrations of 10, 20, 40, 80, 160, and 320 mg / L. The pH of the solution was adjusted to 6 with 0.1 M NaOH or 0.1 M HCl. The horizontal constant-temperature shaker was set to 150 rpm and the temperature was adjusted to 25 °C. The adsorption time was 48 h. The Cu(II) concentration in the solutions after adsorption at different concentrations was measured using a flame atomic absorption spectrophotometer. The adsorption experimental results are as follows: Figure 9 .

[0068] from Figure 9 The results show that under the above conditions, the adsorption capacity of BDA@GA-BSC for Cu(II) increases with increasing solution concentration, while the removal rate shows the opposite trend, with the saturated adsorption capacity of the adsorbent approaching 77 mg / g. To achieve both high efficiency in adsorbing Cu(II) and a high removal rate, the initial concentration of Cu(II) in the solution was chosen to be 40 mg / L. At this concentration, the adsorption capacity of BDA@GA-BSC for Cu(II) was 62.92 mg / g, and the removal rate was 62.92%.

[0069] Example 7

[0070] 0.04 g of the BDA@GA-BSC prepared in Example 1 was placed in 100 mL of a Cr(VI) solution with a concentration of 120 mg / L. The pH of the solution was adjusted to 2 with 0.1 M NaOH or 0.1 M HCl. The horizontal constant temperature shaker was set to 150 rpm and the temperature was adjusted to 25 °C for adsorption. Samples were taken at 1, 2, 3, 4, 6, 8, 12, 18, 24, 36, 48, and 72 h. The adsorption amount of Cr(VI) in the solution at different shaking times was measured using a UV spectrophotometer. The adsorption experimental results are as follows: Figure 7 .

[0071] from Figure 7 The results show that, with the change of adsorption time, the adsorption of Cr(VI) by BDA@GA-BSC is in a rapid adsorption phase before 2 hours, at which time the adsorption capacity is 191.74 mg / g. After 12 hours, it is in a slow adsorption phase for a long period of time, and the adsorption capacity is 267.77 mg / g at 72 hours.

[0072] Example 8

[0073] 0.04 g of the BDA@GA-BSC prepared in Example 1 was placed in 100 mL of a Cu(II) solution with a concentration of 40 mg / L. The pH of the solution was adjusted to 6 with 0.1 M NaOH and 0.1 M HCl. The horizontal constant-temperature shaker was set to 150 rpm and the temperature was adjusted to 25 °C for adsorption. Samples were taken at 1, 2, 3, 4, 6, 8, 12, 18, 24, 36, 48, and 72 h. The adsorption amount of Cu(II) in the solution at different shaking times was determined using a flame atomic absorption spectrophotometer. The adsorption experimental results are as follows: Figure 10 .

[0074] from Figure 10 The results show that, with the change of adsorption time, the adsorption of Cu(II) by BDA@GA-BSC is in a rapid adsorption stage before 6 h, at which time the adsorption capacity is 65.02 mg / g. It approaches equilibrium at around 24 h, at which time the adsorption capacity is 76.52 mg / g, and then enters a slow adsorption stage, with an adsorption capacity of 267.77 mg / g at 72 h.

[0075] Example 9

[0076] 0.02 g of the BDA@GA-BSC prepared in Example 1 was placed in 50 mL of a Cr(VI) solution with a concentration of 120 mg / L. The pH of the solution was adjusted to 2 with 0.1 M NaOH and 0.1 M HCl. The horizontal isothermal shaker was set to 150 rpm and the temperature was adjusted to 25 °C. The adsorption time was 48 h. After adsorption, the material was separated from the solution, and the Cr(VI) concentration in the post-adsorption solution was measured using a UV spectrophotometer to calculate the removal rate. A 5% sodium hydroxide solution and a 5% hydrochloric acid solution were prepared. Subsequently, the adsorbed material was placed in 100 mL of a 5% sodium hydroxide solution and desorbed at 30 °C with a horizontal isothermal shaker at 150 rpm for 24 h. The material was then separated from the solution and washed multiple times with ultrapure water. Next, the material was placed in 100 mL of a 5% hydrochloric acid solution and desorbed for 24 hours at 30°C using a horizontal constant-temperature shaker at 150 rpm. After washing several times with ultrapure water, the material was immersed in 50 mL of a 60 mg / L Cr(VI) solution for secondary adsorption. The adsorption-desorption experiment was repeated 5 times. The adsorption results are as follows: Figure 11 .

[0077] from Figure 11 As can be seen, after 5 cycles of use, BDA@GA-BSC maintains a good adsorption capacity for Cr(VI), has a good adsorption effect, and the material shape is relatively intact.

[0078] Example 10

[0079] 0.02 g of the BDA@GA-BSC prepared in Example 1 was placed in 50 mL of a Cu(II) solution with a concentration of 40 mg / L. The pH of the solution was adjusted to 6 with 0.1 M NaOH or 0.1 M HCl. The horizontal isothermal shaker was set to 150 rpm and the temperature was adjusted to 25 °C. The adsorption time was 48 h. After adsorption, the material was separated from the solution, and the Cu(II) concentration in the post-adsorption solution was measured using a flame atomic emission spectrophotometer to calculate the removal rate. A 5% hydrochloric acid solution was prepared. Subsequently, the adsorbed material was placed in 100 mL of a 5% hydrochloric acid solution and desorbed at 25 °C with a horizontal isothermal shaker at 150 rpm for 12 h. The material was then separated from the solution and washed multiple times with ultrapure water. The material was then placed in 50 mL of a Cu(II) solution with a concentration of 40 mg / L for secondary adsorption. The above adsorption-desorption experiment was repeated 5 times. The adsorption experimental results are as follows. Figure 12 .

[0080] from Figure 12 As can be seen, BDA@GA-BSC maintains a good adsorption capacity for Cu(II) after 5 cycles, demonstrating good adsorption performance and material integrity.

[0081] Example 11: Orthogonal Experiment for the Preparation of Butanediamine-Modified Biochar Composite Gel Spheres

[0082] To investigate the optimal preparation conditions for BDA@GA-BSC, the material preparation process of Example 1 was repeated, with the following differences: the mass ratio of sodium alginate to carboxymethyl chitosan (SA:CCS), the mass of biochar (Cm), the concentration of epichlorohydrin (ECH), and the mass of butanediamine (BDA) were set as influencing factors.

[0083] 1) In the orthogonal experiment, the total mass of sodium alginate and carboxymethyl chitosan is 1g. For example, if the mass ratio of SA:CCS is 3:2, then the mass of sodium alginate and carboxymethyl chitosan are 0.6g and 0.4g respectively.

[0084] 2) The mass of biochar (Cm) refers to the amount of Sedum sarmentosum biochar fed in step 3);

[0085] 3) The concentration of epichlorohydrin (ECH) refers to the volume concentration of epichlorohydrin in the ethanol-epoxychlorohydrin-ultrapure water mixed solution calculated by changing the volume of epichlorohydrin in step 5).

[0086] 4) The mass of butanediamine (BDA) refers to the amount of butanediamine fed in step 6).

[0087] L9(3) 4Orthogonal experiments were conducted to analyze the effects of various factors on the adsorption of Cr(VI) by the adsorbent BDA@GA-BSC, and the preparation conditions were optimized to obtain the best adsorbent. The levels of orthogonal factors are shown in Table 1 below.

[0088] The adsorption conditions for Cr(VI) by different adsorbents were as follows: 0.02 g of adsorbent was placed in 40 mL of a Cr(VI) concentration of 100 mg / L. The pH of the solution was adjusted to 2 with 0.1 M HCl. The horizontal constant temperature shaker was set to 150 rpm and the temperature was adjusted to 25 °C. The adsorption time was 48 h. The concentration of Cr(VI) in the solution after adsorption was measured using a UV spectrophotometer to test the removal effect of the material on Cr(VI). The adsorption results of the orthogonal experiment are shown in Table 2 below.

[0089] Table 1. Orthogonal Factor Level Table

[0090]

[0091] Table 2 Results of the orthogonal experiment

[0092]

[0093]

[0094] From direct observation in Table 2, it can be inferred that the range R represents the difference between the maximum and minimum values ​​of K1, K2, and K3. This range reveals the relative magnitude of the influence of each factor on adsorption efficiency; that is, the larger the value of the range R, the more significant the effect of that factor on adsorption efficiency.

[0095] The order of influence of the four factors on the adsorption performance of BDA@GA-BSC is: mass of butanediamine (BDA) > mass of biochar (C). m The optimal adsorbent ratio is determined by the mass ratio of sodium alginate to carboxymethyl chitosan (SA:CCS) and the concentration of epichlorohydrin (ECH). The optimal ratio is A1B1C1D3, i.e., an SA:CCS ratio of 3:2 (0.6g:0.4g). m With a mass of 0.2 g, an ECH concentration of 5.0%, and a BDA mass of 1.5 g, the synthesized adsorbent BDA@GA-BSC achieved a Cr(VI) removal rate of 91.27% and an adsorption capacity of 182.54 mg / g. This demonstrates the correctness of the orthogonal experimental optimization conditions.

[0096] The explanation for the ranking of the four influencing factors is as follows: First, the higher the concentration of butanediamine, the more amino functional groups it carries. The amino groups can react with the aldehyde groups on the molecular structure of glutaraldehyde, which subsequently acts as a cross-linking agent, to form C=N double bonds, directly affecting the adsorption performance of the adsorbent for Cr(VI). Second, during the adsorbent synthesis process, biochar acts as the carbon framework of the gel microspheres, providing support. While it possesses a good porous structure and abundant oxygen-containing functional groups, offering more adsorption active sites, its alkalinity means that excessive biochar during sphere formation can negatively impact the structural stability of the microspheres. Therefore, the influence of biochar on the adsorption performance of BDA@GA-BSC ranks second. Finally, the mass ratio of sodium alginate to carboxymethyl chitosan and the concentration of epichlorohydrin had relatively low and essentially the same impact on the adsorption performance of BDA@GA-BSC. Sodium alginate and carboxymethyl chitosan mainly served as the matrix of the adsorbent and provided active sites, while epichlorohydrin served as an intermediate branching agent, utilizing its active epoxy groups to achieve intramolecular crosslinking. Butylenediamine could also be introduced through functionalization reactions.

[0097] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A method for preparing butanediamine-modified biochar composite gel spheres, characterized in that: Sodium alginate, carboxymethyl chitosan and biochar were dispersed in water and mixed evenly to obtain a composite solution. The composite solution was then dropped into a calcium chloride solution to form biochar composite gel beads. Epichlorohydrin was used as an intermediate indirect graft to modify biochar composite gel beads, which were then grafted with butanediamine. The modified gel beads were placed in a glutaraldehyde solution for surface cross-linking to obtain gel beads. Finally, the gel beads were freeze-dried to obtain the butanediamine-modified biochar composite gel beads. The mass ratio of sodium alginate to carboxymethyl chitosan was 1~4:1, and the mass ratio of the total mass of sodium alginate and carboxymethyl chitosan to the mass of biochar was 2.5-6:

1.

2. The method for preparing butanediamine-modified biochar composite gel spheres as described in claim 1, characterized in that: The mass ratio of sodium alginate to carboxymethyl chitosan is 1.5-2:1, and the total mass ratio of sodium alginate and carboxymethyl chitosan to biochar is 5-6:

1.

3. The method for preparing butanediamine-modified biochar composite gel spheres as described in claim 1, characterized in that... The biochar is Sedum sarmentosum biochar, and its preparation method is as follows: Sedum sarmentosum powder is placed in a quartz boat, the lid is closed, and it is placed in a muffle furnace. Nitrogen gas is continuously introduced to purge the air. Under nitrogen protection, it is pyrolyzed at a temperature of 700~900℃ for 2~4 hours. Then it is naturally cooled to obtain Sedum sarmentosum biochar. After grinding and sieving, it is sealed and stored. The sieve mesh size is 80-200 mesh.

4. The method for preparing butanediamine-modified biochar composite gel spheres as described in claim 1, characterized in that... Specifically, the steps include the following: 1) Add sodium alginate, carboxymethyl chitosan and biochar powder to ultrapure water and stir thoroughly to obtain a composite solution; 2) Using calcium chloride solution as the continuous phase and composite solution as the dispersed phase, the dispersed phase was dropped into the continuous phase, soaked and solidified, and allowed to stand overnight. After solid-liquid separation, the mixture was washed multiple times with ultrapure water to obtain biochar composite gel beads. 3) Disperse biochar composite gel beads in ultrapure water, then add epichlorohydrin and ethanol to react and obtain epichlorohydrin-grafted biochar composite gel spheres. 4) The epichlorohydrin-grafted biochar composite gel balls obtained in step 3) are dispersed in ethanol and butanediamine solution, and after the grafting reaction is carried out, they are taken out, washed, and placed in glutaraldehyde solution for cross-linking reaction to obtain butanediamine-modified biochar composite gel balls. After washing with ultrapure water several times, they are finally freeze-dried to obtain the butanediamine-modified biochar composite gel balls.

5. The method for preparing butanediamine-modified biochar composite gel spheres as described in claim 4, characterized in that... In step 1), the total mass ratio of sodium alginate, carboxymethyl chitosan, and biochar to ultrapure water is 2-3:

100. In step 2), the mass concentration of the calcium chloride solution is 1-5%; the volume ratio of the dispersed phase to the continuous phase is 1:10-30; and the soaking and solidification overnight standing time is 12-24 hours.

6. The method for preparing butanediamine-modified biochar composite gel spheres as described in claim 5, characterized in that... In step 1), the total mass ratio of sodium alginate, carboxymethyl chitosan, and biochar to ultrapure water is 2.4-2.5:

100.

7. The method for preparing butanediamine-modified biochar composite gel spheres as described in claim 4, characterized in that... Step 3) In the mixed solution, the mass concentration of the biochar composite gel spheres is 5-15%, the volume concentration of epichlorohydrin is 3-10%, the volume concentration of ethanol is 5-10%, the reaction temperature is 25-70℃, the reaction time is 2-8h, and after the reaction is completed, the mixture is washed with ultrapure water and ethanol.

8. The method for preparing butanediamine-modified biochar composite gel spheres as described in claim 7, characterized in that... Step 3) In the mixed solution, the volume concentration of epichlorohydrin is 5-6%, the reaction temperature is 40-60℃, and the reaction time is 3-5h.

9. The method for preparing butanediamine-modified biochar composite gel spheres as described in claim 4, characterized in that... Step 4) The epichlorohydrin-grafted biochar composite gel spheres are dispersed in a mixture of ethanol and butanediamine solution for grafting reaction. The mass concentration of the epichlorohydrin-grafted biochar composite gel spheres is 15-25%, the volume concentration of butanediamine is 2-5%, the reaction temperature is 25-70℃, and the reaction time is 2-8h. In step 4), the volume concentration of glutaraldehyde is 0.5-2%, and the reaction is carried out in glutaraldehyde solution at room temperature with shaking for 2-5h, followed by standing for 10-15h.

10. The method for preparing butanediamine-modified biochar composite gel spheres as described in claim 9, characterized in that... Step 4) The epichlorohydrin-grafted biochar composite gel spheres are dispersed in a mixture of ethanol and butanediamine solution for grafting reaction. The volume concentration of butanediamine is 3-3.5%, the reaction temperature is 40-60℃, and the reaction time is 3-5h.

11. The method for preparing butanediamine-modified biochar composite gel spheres as described in claim 4, characterized in that... Step 4) The freeze-drying process involves using a vacuum freeze dryer to dry the product at a temperature of -80 to -60°C for 60 to 90 hours.

12. A butanediamine-modified biochar composite gel ball prepared by any one of claims 1-11.

13. The application of the butanediamine-modified biochar composite gel spheres as described in claim 12 in the adsorption of hexavalent chromium or divalent copper ions.

14. The application as described in claim 13, characterized in that... After the gel spheres adsorb hexavalent chromium, the regeneration process includes placing the adsorbed material in a 3-8% sodium hydroxide solution for 20-30 hours to desorb, then separating the material from the solution and washing it with ultrapure water, or directly placing the material in a 3-8% hydrochloric acid solution for 20-30 hours to desorb, and then washing it with ultrapure water to regenerate the material. After the gel spheres adsorb divalent copper ions, the regeneration process involves placing the adsorbed material in a 3-8% hydrochloric acid solution for desorption for 10-15 hours, then separating the material from the solution and washing it with ultrapure water, thus achieving material regeneration.

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