Modified magnetic biochar adsorption material, and preparation method and application thereof

Abstract

The application belongs to the technical field of adsorbing materials, and particularly relates to a modified magnetic biochar adsorbing material and a preparation method and application thereof, and the preparation thereof comprises the following steps: (1) oxygen-limited activation of litchi shell, grinding, and obtaining litchi shell biochar; (2) placing the litchi shell biochar in a cobalt chloride solution, stirring and mixing, ultrasonic treatment, aging, drying and grinding, reacting in the oxygen-limited condition, and grinding after cooling, so as to obtain magnetic litchi shell biochar; (3) mixing the magnetic litchi shell biochar with chitosan, adding acetic acid, stirring, adding sodium hydroxide solution, then washing away soluble salt substances, drying and grinding, so as to obtain the modified magnetic biochar adsorbing material. The application uses litchi shell as a biochar raw material, introduces magnetic materials and chitosan to modify the function of the biochar, so that the prepared material has many surface active sites, realizes good Cr(Ⅵ) adsorption performance, and can be recycled and reused.

Description

Technical Field

[0001] This invention belongs to the field of adsorption materials technology, specifically relating to a modified magnetic biochar adsorption material, its preparation method, and its application. Background Technology

[0002] Chromium is a well-known heavy metal pollutant, mainly originating from industrial production such as electroplating, metallurgy, mining, and leather making. Waste chromium is discharged into the environment in the form of waste gas, wastewater, and waste residue. The water pollution caused by chromium in surface water, wastewater, and groundwater is widespread throughout the world. Cr has a very high redox potential and can exist in various oxidation states from (II) to (IV). Trivalent chromium Cr(III) and hexavalent chromium Cr(VI) are its most stable forms. However, hexavalent chromium Cr(VI) and trivalent chromium Cr(III) pose a great threat to the natural environment and human health. Among them, the toxicity of Cr(VI) is much higher than that of Cr(III), more than 100 times stronger.

[0003] The main methods for removing hexavalent chromium from polluted water bodies include adsorption, membrane treatment, chemical precipitation, bioremediation, ion exchange, and mixed technologies. These are currently the main approaches for treating chromium-polluted water bodies and can be used to reduce the concentration of Cr(VI) in chromium-polluted water bodies. However, all of these methods have problems such as complicated processes, complex equipment operation, and high treatment costs. Moreover, the removal effect of Cr(VI) is not ideal, and the treated products are not easy to handle. Even if they can be handled, the residues may damage the environment.

[0004] Therefore, there is an urgent need to develop more efficient, low-cost, and environmentally friendly treatment methods to address the current limitations of Cr(VI) removal technology from polluted water bodies, as well as the problems of high-cost treatment technologies and equipment. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a modified magnetic biochar adsorbent material, its preparation method and application, so as to achieve good Cr(VI) adsorption performance and be recyclable.

[0006] To achieve the above objectives, the technical solution adopted by the present invention includes:

[0007] In a first aspect, the present invention provides a method for preparing a modified magnetic biochar adsorbent material, comprising the following steps:

[0008] (1) The litchi shell was activated under oxygen-limited conditions and ground to obtain litchi shell biochar.

[0009] (2) The litchi shell biochar was placed in a cobalt chloride solution, stirred and mixed, ultrasonically treated, aged, dried and ground, reacted under limited oxygen conditions, cooled and ground to obtain magnetic litchi shell biochar.

[0010] (3) Mix magnetic litchi shell biochar with chitosan, add acetic acid solution, stir, then add sodium hydroxide solution, then wash away soluble salts, dry and grind to obtain the modified magnetic biochar adsorbent material.

[0011] Biochar, as an adsorbent with low raw material price, easy availability, low operating cost, and environmental friendliness, has attracted increasing attention from researchers in recent years. Using waste agricultural crops as raw materials can greatly reduce the cost of biochar raw materials. Furthermore, the introduction of magnetic materials can achieve solid-liquid separation. On this basis, the introduction of chitosan can modify the function of biochar, and the subsequent treatment process will not cause harm to the environment or cause secondary pollution. Therefore, it is an adsorbent with good development prospects.

[0012] This invention uses litchi shells as biochar raw materials and introduces magnetic materials and chitosan to modify the biochar's function. This results in a modified magnetic biochar adsorbent material with numerous surface active sites, a rich variety of functional groups, and easy binding with Cr(VI), exhibiting high adsorption efficiency and the ability to treat wastewater with high concentrations of Cr(VI). Furthermore, the adsorbent material is magnetic, making it easy to separate from the treated water, and can be reused multiple times, resulting in high reusability, a more environmentally friendly material, and reduced treatment costs. This provides a new theoretical basis for the removal of Cr(VI) from wastewater.

[0013] Preferably, in step (3), the mass percentage of chitosan in the total mass of magnetic litchi shell biochar and chitosan is 5-40%.

[0014] Preferably, in step (3), the mass percentage of chitosan in the total mass of magnetic litchi shell biochar and chitosan is 10%.

[0015] Chitosan (CS) is a product obtained by deacetylation of chitin, which is abundant in nature. Due to the large number of hydroxyl (-OH) and amino (-NH2) groups in its molecular structure, when combined with magnetic biochar, it can increase the number of active sites on the magnetic biochar, enhancing its reactivity and physicochemical properties, and effectively strengthening the material's adsorption performance for Cr(VI). Experimental studies have shown that when the ratio of chitosan to magnetic biochar is within the aforementioned preferred range (chitosan accounting for 5-40% of the total mass), the adsorbent material exhibits the best Cr(VI) adsorption effect. The best Cr(VI) adsorption effect is achieved when the mass percentage of chitosan is the optimal value of 10%. However, when the chitosan content exceeds the specified range, many micropores in the biochar material are filled with chitosan, which reduces its adsorption performance.

[0016] Preferably, in step (1), the specific process of oxygen-limited activation is: activation at 450-550℃ for 180-220 min under argon atmosphere.

[0017] This invention involves oxygen-limited activation of litchi shell raw materials to increase the pore structure and specific surface area of ​​biochar materials, and effectively improves the content of surface functional groups, thereby enhancing their chemical reactivity and selectivity. Experimental studies have shown that when litchi shell raw materials undergo oxygen-limited activation treatment under the aforementioned optimized conditions, the resulting modified magnetic biochar material exhibits a significant increase in surface active sites and a markedly enhanced adsorption performance for Cr(VI).

[0018] More preferably, in step (1), the specific process of oxygen-limited activation is: activation at 500°C for 200 min in an argon atmosphere.

[0019] Preferably, in step (2), the concentration of the cobalt chloride solution is 0.08-0.12 mol / L, and the mass-to-volume ratio of litchi shell biochar to cobalt chloride solution is 4-6 g: 45-55 ml.

[0020] More preferably, in step (2), the concentration of cobalt chloride solution is 1 mol / L, and the mass-to-volume ratio of litchi shell biochar to cobalt chloride solution is 5 g: 50 ml.

[0021] Preferably, in step (2), the stirring time is 100-140 min, the ultrasonic treatment time is 50-70 min, and the aging time is 1420-1460 min; in step (2), the specific process of the reaction under oxygen-limited conditions is: reacting at 500-600℃ for 180-220 min in an argon atmosphere.

[0022] Experimental research revealed that when litchi shell biochar is mixed with cobalt chloride solution and the mixture is treated using the aforementioned defined parameter ranges, the contact area between cobalt ions and biochar can be maximized. This ensures that cobalt ions are uniformly distributed on the surface or in the micropores of the biochar. Furthermore, by controlling the oxygen-limited reaction conditions, cobalt ions can be effectively reduced and fixed in the biochar structure, thereby significantly enhancing the magnetic properties of the biochar and maintaining the structural stability of the final adsorbent material.

[0023] More preferably, in step (2), the stirring time is 120 min, the ultrasonic treatment time is 60 min, and the aging time is 1440 min; in step (2), the specific process of the reaction under oxygen-limited conditions is: reacting at 550°C for 200 min in an argon atmosphere.

[0024] Preferably, in step (3), the ratio of the total mass of the magnetic litchi shell biochar and chitosan, the acetic acid solution, and the sodium hydroxide solution is 1.8-2.2g: 80-120ml: 550-650ml, the mass concentration of the acetic acid solution is 1-3%, and the mass concentration of the sodium hydroxide solution is 8-12%.

[0025] More preferably, in step (3), the ratio of the total mass of the magnetic litchi shell biochar and chitosan, the acetic acid solution, and the sodium hydroxide solution is 2g:100ml:600ml, the mass concentration of the acetic acid solution is 2%, and the mass concentration of the sodium hydroxide solution is 10%.

[0026] Secondly, the present invention provides a modified magnetic biochar adsorbent material prepared by the preparation method described above.

[0027] Thirdly, the present invention provides the application of the modified magnetic biochar adsorbent material in the adsorption of pollutant Cr(VI).

[0028] Preferably, the application method includes the following steps: adding the modified magnetic biochar adsorbent material to wastewater containing Cr(VI) at a concentration of 50 mg / L, shaking at 40°C for 180 min, with the shaking speed controlled at 160 r / min, filtering and sampling after the reaction is completed, thus completing the adsorption and removal of Cr(VI); the mass ratio of the modified magnetic biochar adsorbent material to Cr(VI) is 0.1 g: 1.5-5.5 mg.

[0029] More preferably, the application method includes the following steps: adding the modified magnetic biochar adsorbent material to wastewater containing Cr(VI) at a concentration of 30-110 mg / L, shaking for 180 min at 30-50℃, with the shaking speed controlled at 90 r / min, filtering and sampling after the reaction is completed, thus completing the adsorption and removal of Cr(VI); the mass ratio of the modified magnetic biochar adsorbent material to Cr(VI) is 0.1 g: 4.5 mg.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) This invention uses litchi shell as biochar raw material and introduces magnetic materials and chitosan to modify the function of biochar, so that the prepared modified magnetic biochar adsorbent material has many surface active sites, rich functional groups and is easy to combine with Cr(VI), with high adsorption efficiency, and can treat high concentrations of Cr(VI) wastewater; in addition, the adsorbent material is magnetic, which makes it easy to separate from the treated water, and can be reused many times, with high reuse rate, more environmentally friendly material, and reduced treatment cost, providing a new theory for the removal of Cr(VI) from wastewater;

[0032] (2) The raw material, litchi shell, is abundant and low in cost. Furthermore, the preparation method and process of chitosan / magnetic litchi shell biochar adsorbent material are simple, enabling large-scale production and application in actual Cr(VI)-containing wastewater treatment. Attached Figure Description

[0033] Figure 1 The infrared spectra of LSB (Figure A), MLSB (Figure B), and CS / MLSB (Figure C) are shown.

[0034] Figure 2 Here are the LSB scanning electron microscope images and elemental distribution maps;

[0035] Figure 3 Electron micrograph and elemental distribution map of MLSB;

[0036] Figure 4 CS / MLSB electron micrographs, elemental distribution maps, and content maps;

[0037] Figure 5 X-ray diffraction patterns of three different materials: LSB, MLSB, and CS / MLSB;

[0038] Figure 6 The graph shows the adsorption performance of CS / MLSB prepared in Example 1 on Cr(VI) at different times.

[0039] Figure 7 The graph shows the adsorption performance of CS / MLSB prepared in Example 1 on Cr(VI) at different initial Cr(VI) concentrations.

[0040] Figure 8 The image shows the elemental analysis of EDS after Cr(VI) adsorption by CS / MLSB prepared in Example 1.

[0041] Figure 9 The images show the adsorption effect of CS / MLSB on Cr(VI) prepared in Examples 1 and 4-6. Detailed Implementation

[0042] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0043] Unless otherwise specified, all raw materials used in the following examples are commercially available general-purpose materials.

[0044] Example 1

[0045] This embodiment provides a method for preparing modified magnetic biochar adsorbent material, including the following steps:

[0046] (1) Cut the dried lychee shells into fine particles, activate them in a tube furnace at 500°C under limited oxygen for 200 min in an argon atmosphere, and grind them into powder using an agate mortar to obtain lychee shell biochar (LSB).

[0047] (2) Prepare 50 ml of 0.1 mol / L cobalt chloride solution, weigh 5 g of LSB and add it, stir with a magnetic stirrer for 120 min, sonicate for 60 min, age for 1440 min, dry at 80℃, grind into powder, react in a tube furnace in an argon atmosphere at 550℃ for 200 min, cool and grind into uniform powder with an agate mortar to obtain magnetic litchi shell biochar (MLSB);

[0048] (3) Mix magnetic litchi shell biochar with chitosan, with a total amount of 2g, of which the mass fraction of chitosan is 10%. Add the mixture to 100ml of 2% acetic acid and stir with a magnetic stirrer for 3.5h. Pour the mixture into 600ml of 10% sodium hydroxide solution and wash away the soluble salts with ultrapure water multiple times. Dry the mixture at 90℃ and grind it into powder to obtain the modified magnetic biochar adsorbent material.

[0049] Example 2

[0050] This embodiment provides a method for preparing modified magnetic biochar adsorbent material, including the following steps:

[0051] (1) The dried lychee shells were cut into fine particles and activated in a tube furnace at 450°C for 220 min under limited oxygen in an argon atmosphere. After cooling, they were ground into powder using an agate mortar to obtain lychee shell biochar (LSB).

[0052] (2) Prepare 45 ml of 0.12 mol / L cobalt chloride solution, weigh 4 g of LSB and add it, stir with a magnetic stirrer for 100 min, sonicate for 70 min, age for 1440 min, dry at 80℃, grind into powder, react in a tube furnace in an argon atmosphere at 500℃ for 220 min, cool and grind into uniform powder with an agate mortar to obtain magnetic litchi shell biochar (MLSB);

[0053] (3) Mix magnetic litchi shell biochar with chitosan, with a total amount of 2g, of which the mass fraction of chitosan is 10%. Add the mixture to 80ml of 1% acetic acid and stir with a magnetic stirrer for 3.5h. Pour the mixture into 550ml of 12% sodium hydroxide solution and wash away the soluble salts with ultrapure water multiple times. Dry the mixture at 90℃ and grind it into powder to obtain the modified magnetic biochar adsorbent material.

[0054] Example 3

[0055] This embodiment provides a method for preparing modified magnetic biochar adsorbent material, including the following steps:

[0056] (1) The dried lychee shells were cut into fine particles and activated in a tube furnace at 550°C for 180 min under limited oxygen in an argon atmosphere. After cooling, they were ground into powder using an agate mortar to obtain lychee shell biochar (LSB).

[0057] (2) Prepare 55 ml of 0.08 mol / L cobalt chloride solution, weigh 6 g of LSB and add it, stir with a magnetic stirrer for 140 min, sonicate for 50 min, age for 1440 min, dry at 80℃, grind into powder, react in a tube furnace in an argon atmosphere at 600℃ for 180 min, cool and grind into uniform powder with an agate mortar to obtain magnetic litchi shell biochar (MLSB).

[0058] (3) Mix magnetic litchi shell biochar with chitosan, with a total amount of 2g, of which the mass fraction of chitosan is 10%. Add the mixture to 120ml of 3% acetic acid and stir with a magnetic stirrer for 3.5h. Pour the mixture into 650ml of 8% sodium hydroxide solution and wash away soluble salts with ultrapure water multiple times. Dry the mixture at 90℃ and grind it into powder to obtain the modified magnetic biochar adsorbent material (CS / MLSB).

[0059] Example 4

[0060] This embodiment provides a method for preparing a modified magnetic biochar adsorbent material. The difference between this method and Example 1 is that in step (3), chitosan accounts for 5% of the total mass of the magnetic litchi shell biochar and chitosan, while the rest are the same.

[0061] Example 5

[0062] This embodiment provides a method for preparing a modified magnetic biochar adsorbent material. The difference between this method and Example 1 is that in step (3), chitosan accounts for 20% of the total mass of the magnetic litchi shell biochar and chitosan, while the rest are the same.

[0063] Example 6

[0064] This embodiment provides a method for preparing a modified magnetic biochar adsorbent material. The difference between this method and Example 1 is that in step (3), chitosan accounts for 40% of the total mass of the magnetic litchi shell biochar and chitosan, while the rest are the same.

[0065] Comparative Example 1

[0066] This comparative example provides a method for preparing magnetic biochar adsorbent material. The difference from Example 1 is that in step (2), the cobalt chloride solution is replaced with ferric chloride solution, and the rest are the same.

[0067] Comparative Example 2

[0068] This comparative example provides a method for preparing magnetic biochar adsorbent material. The difference from Example 1 is that in step (3), chitosan accounts for 50% of the total mass of magnetic litchi shell biochar and chitosan.

[0069] Comparative Example 3

[0070] This comparative example provides a method for preparing magnetic biochar adsorbent material. The difference from Example 1 is that in step (3), chitosan accounts for 2% of the total mass of magnetic litchi shell biochar and chitosan.

[0071] Comparative Example 4

[0072] This comparative example provides a method for preparing magnetic biochar adsorbent material. The difference from Example 1 is that in step (1), the material is activated with limited oxygen at 400°C for 160 min in a tube furnace under argon atmosphere.

[0073] Comparative Example 5

[0074] This comparative example provides a method for preparing magnetic biochar adsorbent material. The difference from Example 1 is that in step (1), the material is activated with limited oxygen at 600°C for 240 min in a tube furnace under argon atmosphere.

[0075] Comparative Example 6

[0076] This comparative example provides a method for preparing magnetic biochar adsorbent material. The difference from Example 1 is that in step (2), the reaction is carried out in a tube furnace under argon atmosphere at 450°C for 240 min.

[0077] Comparative Example 7

[0078] This comparative example provides a method for preparing magnetic biochar adsorbent material. The difference from Example 1 is that in step (2), the reaction is carried out in a tube furnace under argon atmosphere at 650°C for 160 min.

[0079] Example 1: Characterization Analysis

[0080] 1. Fourier Transform Infrared Spectroscopy (FT-IR) Analysis

[0081] LSB, MLSB, and CS / MLSB were characterized using a Fourier transform infrared spectrometer and the KBr solid pellet method for sample preparation, with scanning wavenumbers ranging from 4000 to 400 cm⁻¹.-1 Wavenumber analysis is used to perform qualitative analysis on samples by plotting FT-IR spectra, analyzing the functional groups present, and determining whether the target substance has been introduced.

[0082] The infrared spectrum of LSB is as follows: Figure 1 As shown in (A), at 3410.09cm -1 and 1378.85cm -1 The characteristic peak of -OH (hydroxyl group) appears at 1578.41 cm⁻¹, originating from cellulose in litchi shell biochar. -1 A characteristic peak for ketone groups appears at 2917.63 cm⁻¹. -1 1578.41cm -1 872.98cm -1 780.95cm -1 Characteristic peaks for carboxyl, CH, ketone, and aldehyde groups were observed in all samples. The infrared spectrum of MLSB is shown below. Figure 1 As shown in (B), at 3551.16cm -1 The broad peak at 1560.51 cm⁻¹ is a characteristic peak of -OH and Co, and its stretching vibration becomes sharper, indicating a greater increase in the content of -OH and successful Co loading on biochar; -1 Stretching vibration of the ketone group, 1095.19 cm⁻¹ -1 The CH characteristic peak at 842.39 cm⁻¹ -1 The characteristic peaks of the aldehyde group at each position were all enhanced; the infrared spectrum of CS / MLSB is as follows. Figure 1 (C), 3451cm -1 The broad peak at 1671 cm⁻¹ is attributed to the stretching vibrations of -OH and -NH₂, and the characteristic peak of Co. The peak at 865 cm⁻¹ is assigned to the bending vibration of NH₃. -1 The out-of-plane deformation vibration attributed to NH indicates that the chitosan loading was successful.

[0083] 2. Field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS) analysis

[0084] Microscopic morphology analysis of LSB, MLSB, and CS / MLSB was performed using field emission scanning electron microscopy (FESEM), and the changes in their microscopic morphology were compared. Simultaneously, energy dispersive spectroscopy (EDS) coupled with FESEM was used to analyze the elemental content and distribution of LSB, MLSB, and CS / MLSB, to preliminarily determine the presence of target elements and their uniformity in the material. The specific procedure was as follows: a suitable piece of conductive adhesive was cut and attached to the SEM stage, the powder sample was adhered to the adhesive, and any loose particles were blown off with a syringe before observation in the SEM sample chamber.

[0085] like Figure 2The images show the LSB scanning electron microscope (SEM) image and elemental distribution map. The images reveal that while some areas of the litchi peel surface are smooth, the majority of the structure is convex and concave, with a considerable number of pores of varying sizes. This structure facilitates the introduction of other substances onto the litchi peel surface, thereby modifying the litchi peel. The MLSB SEM image and elemental distribution map are shown below. Figure 3 As shown, the microstructure of litchi shell biochar shows that the surface and pores are loaded with a large number of small particles without obvious aggregation. The distribution maps of C and Co elements show that Co or Co compounds were successfully introduced into MLSB. Furthermore, the map shows that most of the higher-content Co is aggregated in the MLSB pores, indicating that Co was successfully loaded onto the litchi shell biochar surface. This increases the magnetism of the litchi shell biochar and adds many uneven structures to the surface, forming more and finer pores, increasing its specific surface area and providing more active sites for Cr(VI) adsorption. CS / MLSB electron micrographs and elemental distribution and content maps are shown below. Figure 4 As shown, the microscopic structure of the litchi peel reveals significantly more wrinkles than the branches. Figure 2-3 The increased quantity and coarser texture indicate a significant increase in lumps and fine particles, resulting in richer pores. In addition to the main element C, the outlines of N, O, and Co are clearly visible. Combined with the elemental content diagram, this indicates that N and O elements were successfully introduced into the sample. Since the main elements of chitosan are N and O, it shows that chitosan was successfully loaded onto the MLSB surface. Furthermore, the surface of chitosan, a natural polymer, has a large number of hydroxyl (-OH) and amino (-NH2) groups, which can provide more adsorption sites. The combination of chitosan and magnetic biochar can effectively enhance the adsorption performance of Cr(VI), increase the number of active sites in the magnetic biochar, and improve the reactivity and physicochemical properties of chitosan magnetic biochar.

[0086] 3. X-ray diffraction (XRD) analysis

[0087] X-ray diffractometer was used to test LSB, MLSB, and CS / MLSB to obtain XRD patterns of LSB, MLSB, and CS / MLSB. The obtained patterns were compared with standard patterns on PDF cards to determine whether the required crystal structure exists.

[0088] X-ray diffraction patterns of LSB, MLSB, and CS / MLSB are as follows: Figure 5As shown in the figure, a broad diffraction peak of sp3 hybrid carbon appears at 2θ = 16° to 30°, indicating that the biochar is an amorphous structure. MLSB and CS / MLSB have similar characteristic peaks, with sharp peaks at 2θ of 42.3°, 47.5°, and 77.1°, consistent with the characteristic diffraction peaks of Co crystals, corresponding to the (002), (101), and (110) crystal planes of Co crystals, respectively, indicating that Co was successfully loaded onto litchi shell biochar. CS / MLSB also shows a Co diffraction peak at 2θ of 47.5°, indicating that Co was successfully introduced during the preparation of CS / MLSB. Its diffraction peak is significantly weakened because the introduction of chitosan into CS / MLSB reduces the mass proportion of Co in the biochar, and loading chitosan and Co does not change the LSB structure. All the above results indicate that biochar was successfully loaded with Co and chitosan.

[0089] 4. Specific surface area (BET) analysis

[0090] The adsorption performance of biochar is related to its specific surface area, pore volume, and average pore size. The more developed the specific surface area and pore structure, the better the adsorption performance of the biochar. The specific surface area, pore volume, and average pore size of LSB, MLSB, and CS / MLSB were measured using a fully automated rapid specific surface area and pore size analyzer.

[0091] Table 1 shows the data measured by BET, which indicates that LSB has the smallest specific surface area, at 1.7235 m². 2 / g, after being magnetically loaded with cobalt, the specific surface area of ​​MLSB increased significantly, reaching 111.9558m². 2 / g; After loading chitosan onto MLSB, the specific surface area of ​​CS / MLSB reached a maximum of 231.8243 m². 2 The reason for the increase in CS / MLSB is that the high specific surface area provides more active sites, resulting in better adsorption. During the preparation process, the cobalt loading not only increases the specific surface area of ​​LSB, but also forms certain pores in MLSB, increasing the pore volume. Additionally, the decrease in average pore size may be due to cobalt entering the LSB during preparation and filling its pores, thus forming larger pores. Compared to MLSB, CS / MLSB shows an increase in both pore volume and average pore size, indicating that chitosan has entered the pores of MLSB and filled the internal space. Although the increased specific surface area increases the contact area between the adsorbent and Cr(VI) in the solution, thus facilitating adsorption, the chitosan loading not only increases the contact area between the adsorbent and Cr(VI) but also increases the effective active sites on its surface, thereby improving the adsorbent's adsorption performance.

[0092] Table 1

[0093]

[0094] Example 2: Investigation of Cr(VI) Adsorption Performance

[0095] 1. Investigation of adsorption conditions:

[0096] Using the magnetic biochar adsorbent material (CS / MLSB) prepared in Example 1 as a sample, we investigated its adsorption performance for Cr(VI) at different adsorption times and different initial concentrations, so as to achieve better application effect of adsorbing Cr(VI) in wastewater.

[0097] (1) Study on the adsorption performance of CS / MLSB at different times

[0098] To compare the adsorption performance of the CS / MLSB prepared in this invention on Cr(VI) at different times, five 0.1g portions of the CS / MLSB prepared in Example 1 were weighed and placed in 50mL of Cr(VI) solution with a concentration of 70mg / L. The solutions were then placed in a constant temperature shaker and shaken at 40℃ and 160r / min for 30min, 80min, 130min, 180min, and 230min, respectively. After the reaction was completed, the samples were filtered and taken for adsorption performance determination.

[0099] Adsorption performance results are as follows Figure 6 As shown, within the range of 30-180 min, the removal rate and adsorption capacity of Cr(VI) by CS / MLSB showed an increasing trend. This is because in the initial stage of adsorption, the number of surface functional groups is sufficient, and the surface pores of CS / MLSB are numerous, providing enough active sites. Cr(VI) is easily adsorbed on the surface and enters through the pores. As the adsorption time increases, Cr(VI) occupies most of the surface adsorption active sites, and the particles diffuse internally, eventually filling the pore channels. Therefore, the removal rate and adsorption capacity of Cr(VI) reach their maximum values ​​and then show a decreasing trend. Therefore, considering both adsorption time and performance, the adsorption performance of the sample on CS / MLSB is better when the adsorption time is 130-230 min, and 180 min is the optimal time for CS / MLSB to adsorb Cr(VI).

[0100] (2) Adsorption performance of CS / MLSB at different initial concentrations

[0101] To compare the adsorption performance of the CS / MLSB prepared in this invention on Cr(VI) at different initial concentrations of Cr(VI) solutions, five 0.1g portions of CS / MLSB prepared in Example 1 were weighed and placed in 50mL of Cr(VI) solutions with concentrations of 30mg / L, 50mg / L, 70mg / L, 90mg / L, and 110mg / L, respectively. The solutions were then placed in a constant temperature shaker and shaken at 40℃ and 160r / min for 180min. After the reaction was completed, the samples were filtered and taken for adsorption performance determination.

[0102] Adsorption performance results are as follows Figure 7 As shown, with increasing Cr(VI) concentration, the adsorption capacity of CS / MLSB reaches a maximum of 19.2 mg / L and then decreases, while the removal rate continues to decline. This is because the increasing concentration of Cr(VI) in the solution leads to a larger concentration difference between the solution and CS / MLSB, resulting in increased mass transfer driving force. Consequently, more hexavalent chromium from the solution enters CS / MLSB. With the increase in adsorption capacity, Cr(VI) gradually occupies all adsorption sites, while the increase in Cr(VI) adsorption by CS / MLSB becomes smaller, leading to a decrease in the removal rate. Therefore, the adsorption performance of the modified magnetic biochar adsorbent material (CS / MLSB) to Cr(VI) is optimal when the mass ratio is 0.1 g: 4.5 mg.

[0103] (3) EDS analysis of Cr(VI) adsorbent

[0104] To test whether LSB, MLSB, and CS / MLSB successfully adsorbed Cr(VI), the adsorption performance of the three materials was compared. After the reaction, the samples were filtered and dried in an oven at 90℃ for 3 hours. Subsequently, the samples were taken for EDS analysis to obtain the elemental distribution map and elemental content map.

[0105] Figure 8 This study investigates the adsorption of Cr(VI) by CS / MLSB using elemental mapping of EDS. The figures show that the surface of the CS / MLSB after adsorption has larger pores, a rougher and more expanded morphology compared to before adsorption, and a few fine particles distributed on the surface. The Co elemental distribution map shows that the Co element is relatively uniformly and densely distributed, indicating that Co and chitosan are still loaded on the adsorbent material and there is no significant detachment. The presence of Cr indicates that CS / MLSB successfully adsorbed Cr(VI) with good adsorption efficiency.

[0106] (4) Comparison of adsorption performance of different adsorption materials

[0107] Using different adsorbent materials prepared in Examples 1-6 and Comparative Examples 1-7, as well as LSB and MLSB, as samples, their adsorption effects on Cr(VI) were investigated. The above samples were weighed and placed in 50 mL of a 90 mg / L Cr(VI) solution, and then placed in a constant temperature shaker at 40 °C and 160 r / min for 180 min. After the reaction was completed, the samples were filtered and their adsorption performance was measured. The results are shown in Table 2.

[0108] Table 2

[0109]

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. The application of a modified magnetic biochar adsorbent material in the adsorption of pollutant Cr(VI), characterized in that, The preparation method of the modified magnetic biochar adsorbent material includes the following steps: (1) The litchi shell was activated under limited oxygen and ground to obtain litchi shell biochar; (2) The litchi shell biochar was placed in a cobalt chloride solution, stirred and mixed, ultrasonically treated, aged, dried and ground, reacted under limited oxygen conditions, cooled and ground to obtain magnetic litchi shell biochar. (3) Mix magnetic litchi shell biochar with chitosan, add acetic acid solution, stir, then add sodium hydroxide solution, then wash away soluble salts, dry and grind to obtain the modified magnetic biochar adsorbent material. In step (2), the specific process of the reaction under oxygen-limited conditions is as follows: the reaction is carried out at 500-600℃ for 180-220 min in an argon atmosphere; In step (3), chitosan accounts for 10% of the total mass of magnetic litchi shell biochar and chitosan.

2. The application as described in claim 1, characterized in that, In step (1), the specific process of oxygen-limited activation is as follows: activation at 450-550℃ for 180-220 min under argon atmosphere.

3. The application as described in claim 1, characterized in that, In step (2), the concentration of cobalt chloride solution is 0.08-0.12 mol / L, and the mass-volume ratio of litchi shell biochar to cobalt chloride solution is 4-6 g: 45-55 ml.

4. The application as described in claim 1, characterized in that, In step (2), the stirring time is 100-140 min, the ultrasonic treatment time is 50-70 min, and the aging time is 1420-1460 min.

5. The application as described in claim 1, characterized in that, In step (3), the ratio of the total mass of the magnetic litchi shell biochar and chitosan, the acetic acid solution, and the sodium hydroxide solution is 1.8-2.2g: 80-120ml: 550-650ml, the mass concentration of the acetic acid solution is 1-3%, and the mass concentration of the sodium hydroxide solution is 8-12%.

6. The application as described in claim 1, characterized in that, The application includes the following steps: adding the modified magnetic biochar adsorbent material to wastewater containing Cr(VI) at a concentration of 30-110 mg / L, shaking for 130-230 min at 30-50℃, with the shaking speed controlled at 140-180 r / min, filtering and sampling after the reaction is completed, thus completing the adsorption and removal of Cr(VI); The mass ratio of the modified magnetic biochar adsorbent material to Cr(VI) is 0.1g:1.5-5.5mg.

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