Phosphorus-containing modified magnetic chitosan microspheres, a preparation method thereof and application of the microspheres in treatment of groundwater containing chromium

Abstract

The application belongs to the technical field of water treatment, and particularly relates to a phosphorus-containing modified magnetic chitosan microsphere, a preparation method thereof and application of the phosphorus-containing modified magnetic chitosan microsphere in treatment of chromium-containing underground water. Compared with the prior art, the phosphorus-containing modified magnetic chitosan microsphere provided by the application takes magnetic nanoparticles as a core, can be quickly separated from a reaction system by relying on external magnetic force of a system, and forms hydrogen bonds through hydroxyl groups of the magnetic nanoparticles and amino groups and hydroxyl groups of a chitosan molecular chain, so that stability and dispersibility of the magnetic nanoparticles are improved. Furthermore, a tetramethylammonium hydroxide solution is used as a crosslinking agent, so that a phosphorus-containing cationic group in the tetramethylammonium hydroxide is grafted on the chitosan molecule, thereby greatly enhancing adsorption performance of the chitosan on anionic heavy metal pollutants such as Cr(VI), and having long-term stability in remediation of Cr(VI)-contaminated underground water.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, and particularly relates to a phosphorus-modified magnetic chitosan microsphere, its preparation method, and its application in the treatment of chromium-containing groundwater. Background Technology

[0002] With the accelerating pace of global industrialization, large quantities of heavy metals generated by industries such as mining, metallurgy, chemicals, electroplating, and batteries have entered the aquatic environment, threatening human health. Heavy metals cannot be degraded by microorganisms and can accumulate in the ecological environment over a long period, posing a threat to human health through bioaccumulation. Chromium is a representative heavy metal, possessing certain toxicity and bioaccumulation properties. It typically exists in groundwater as Cr(III) and Cr(VI), with the latter being far more toxic than the former. Common methods for Cr(VI) removal include photocatalysis, chemical precipitation, membrane separation, ion exchange, and adsorption.

[0003] Adsorption is one of the main technologies for treating chromium-containing groundwater, characterized by its simple operation, low cost, lack of secondary pollution, and good treatment effect. However, some traditional adsorbents have drawbacks when removing heavy metals, such as low adsorption capacity or long time required to reach adsorption equilibrium.

[0004] Chitosan is widely available and possesses excellent biocompatibility, biodegradability, and non-toxicity. It is a natural and fully biodegradable polymer material, making it an ideal adsorbent for removing chromium-containing groundwater. The surface of chitosan molecules is rich in amino and hydroxyl groups, exhibiting high reactivity. Through functionalization or modification, chitosan can be endowed with various functional properties while improving its solubility. Combining chitosan with magnetic materials yields magnetic chitosan microspheres, which are easily separated and thus widely applicable in various fields.

[0005] Magnetic chitosan microspheres contain magnetic ultrafine powders such as Fe3O4 and γ-Fe2O3. These microspheres can be chemically crosslinked with various reactive functional groups, with commonly used crosslinking agents including formaldehyde, glutaraldehyde, epichlorohydrin, and cyclothiochloropropane. However, the crosslinking process with these agents is complex and requires large amounts of organic solvents. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a phosphorus-modified magnetic chitosan microsphere, its preparation method and its application in the treatment of chromium-containing groundwater. The preparation method is simple and environmentally friendly, and the prepared phosphorus-modified magnetic chitosan microsphere retains the active groups of chitosan, can achieve simple and rapid solid-liquid separation, and can also efficiently remove anionic heavy metal pollutants such as Cr(VI) from groundwater.

[0007] This invention provides phosphorus-modified magnetic chitosan microspheres, wherein the phosphorus-modified magnetic chitosan microspheres have a core-shell structure; the core-shell structure includes a core and a shell surrounding the core; the core is a magnetic nanoparticle; the shell is formed by cross-linking chitosan with a cross-linking agent; the cross-linking agent is tetramethylolphosphine sulfate.

[0008] Preferably, the mass ratio of chitosan in the core to that in the shell is 1:(1-10).

[0009] Preferably, the magnetic nanoparticles are selected from Fe3O4 and / or γ-Fe2O3;

[0010] And / or, the degree of deacetylation of the chitosan is 75% to 95%.

[0011] This invention also provides a method for preparing the above-mentioned phosphorus-modified magnetic chitosan microspheres.

[0012] Crosslinking agent solution; the crosslinking agent is tetramethylolphosphine sulfate;

[0013] S2) Magnetic nanoparticles were mixed with an acidic aqueous solution of chitosan, then a crosslinking agent solution was added, the mixture was heated to react, the solid was separated, and the mixture was freeze-dried to obtain phosphorus-modified magnetic chitosan microspheres.

[0014] Preferably, the concentration of chitosan in the acidic aqueous solution is 5 g / L to 15 g / L;

[0015] The solvent of the acidic aqueous solution of chitosan includes acid and water; the volume of acid is 0.5% to 2% of the solvent volume; the acid is selected from one or more of acetic acid, formic acid and hydrochloric acid.

[0016] The mass concentration of the crosslinking agent in the crosslinking agent solution is 25% to 75%.

[0017] Preferably, the ratio of the magnetic nanoparticles to the acidic aqueous solution of chitosan is 5g to 10g: 1L.

[0018] Preferably, the volume ratio of the crosslinking agent solution to the acidic aqueous solution of chitosan is 1:(5-20).

[0019] Preferably, the mixing in step S2) is ultrasonic mixing; the power of the ultrasonic mixing is 400W to 500W; and the ultrasonic mixing time is 0.5h to 2h.

[0020] The heating reaction temperature is 40℃~80℃; the heating reaction time is 1h~3h.

[0021] Preferably, the method for separating the solid is centrifugation; the centrifugation speed is 4000 rpm to 5000 rpm;

[0022] The freeze-drying temperature is -40℃ to -60℃; the freeze-drying time is 2 to 3 days.

[0023] The present invention also provides an application of the above-mentioned phosphorus-modified magnetic chitosan microspheres in the treatment of chromium-containing groundwater.

[0024] This invention provides phosphorus-modified magnetic chitosan microspheres with a core-shell structure. The core-shell structure includes a core and an outer shell. The core is a magnetic nanoparticle, and the outer shell is formed by cross-linking chitosan with a cross-linking agent, specifically tetramethylolphosphine sulfate. Compared to existing technologies, the phosphorus-modified magnetic chitosan microspheres provided by this invention, with magnetic nanoparticles as the core, can be rapidly separated from the reaction system by external magnetic force, offering convenience, speed, simplicity, and efficiency. Furthermore, the formation of hydrogen bonds between the hydroxyl groups of the magnetic nanoparticles and the amino and hydroxyl groups of the chitosan molecular chain improves the stability and dispersibility of the magnetic nanoparticles. Moreover, using tetramethylolphosphine sulfate solution as the cross-linking agent allows the phosphorus-containing cationic groups of tetramethylolphosphine sulfate to be grafted onto the chitosan molecules, thereby significantly enhancing its adsorption performance for anionic heavy metal pollutants such as Cr(VI), and providing long-term stability for the remediation of Cr(VI) contaminated groundwater.

[0025] Experiments show that the phosphorus-modified magnetic chitosan microspheres prepared by this invention can achieve a maximum removal rate of 96% for Cr(VI), and the effluent meets the "Environmental Quality Standard for Groundwater (GB / T 14848-2017)", demonstrating its potential for practical application. Attached Figure Description

[0026] Figure 1 A schematic diagram of the preparation process of phosphorus-modified magnetic chitosan microspheres provided by the present invention;

[0027] Figure 2 The image shows the magnetic separation of phosphorus-modified magnetic chitosan microspheres prepared in Example 1 of this invention.

[0028] Figure 3 This is a schematic diagram illustrating the reaction principle of the phosphorus-modified magnetic chitosan microspheres prepared in Example 1 of this invention.

[0029] Figure 4 The images show the FT-IR spectra of phosphorus-modified magnetic chitosan microspheres prepared in Example 1 of this invention, phosphorus-modified chitosan microspheres prepared in Comparative Example 1, and chitosan and iron oxide.

[0030] Figure 5 SEM images of phosphorus-modified magnetic chitosan microspheres prepared in Example 1 of the present invention, phosphorus-modified chitosan microspheres prepared in Comparative Example 1, and chitosan and iron oxide.

[0031] Figure 6 The images show the phosphorus-modified magnetic chitosan microspheres prepared in Example 1 of this invention, the phosphorus-modified chitosan microspheres prepared in Comparative Example 1, and the adsorption kinetics of chitosan and iron oxide on Cr(VI) aqueous solution at pH 6.

[0032] Figure 7 The image shows the adsorption isotherm of Cr(VI) aqueous solution on the phosphorus-modified magnetic chitosan microspheres prepared in Example 1 of this invention. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] This invention provides phosphorus-modified magnetic chitosan microspheres, wherein the phosphorus-modified magnetic chitosan microspheres have a core-shell structure; the core-shell structure includes a core and a shell surrounding the core; the core is a magnetic nanoparticle; the shell is formed by cross-linking chitosan with a cross-linking agent; the cross-linking agent is tetramethylolphosphine sulfate.

[0035] According to the present invention, the core of the phosphorus-modified magnetic chitosan microspheres is a magnetic nanoparticle; the magnetic nanoparticle can be any magnetic nanoparticle well known to those skilled in the art, and there are no special restrictions. In the present invention, nano Fe3O4 and / or γ-Fe2O3 are preferred.

[0036] According to the present invention, the magnetic nanoparticles are encapsulated in a shell; the shell is formed by cross-linking chitosan with a cross-linking agent; the degree of deacetylation of the chitosan is preferably 75% to 95%; optionally, the degree of deacetylation of the chitosan is 75%, 80%, 85%, 90%, 95% or any two of the above values; the molecular weight of the chitosan is preferably 1 × 10⁻⁶. 5 ~3×10 5 More preferably, it is 1.26 × 10 5 ~2.65×10 5 The optimal value is 1.5 × 10⁻⁶. 5 ~2.65×10 5 The optimal value is 2.0 × 10⁻⁶. 5 ~2.5×10 5 The crosslinking agent is tetrahydroxymethylphosphoric acid.

[0037] According to the present invention, the mass ratio of chitosan in the core to the shell is preferably 1:(1 to 10); optionally, the mass ratio of the core to the shell is 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10 or any two of the above ratios.

[0038] The phosphorus-modified magnetic chitosan microspheres provided by this invention use magnetic nanoparticles as the core, which can be rapidly separated from the reaction system by external magnetic force, making it convenient, fast, simple, and efficient. Furthermore, the stability and dispersibility of the magnetic nanoparticles are improved by forming hydrogen bonds between the hydroxyl groups of the magnetic nanoparticles and the amino and hydroxyl groups of the chitosan molecular chain. In addition, tetramethylol phosphate solution is used as a crosslinking agent to graft the phosphorus-containing cationic groups of tetramethylol phosphate onto the chitosan molecules, thereby greatly enhancing its adsorption performance for anionic heavy metal pollutants such as Cr(VI) and providing long-term stability for the remediation of Cr(VI) contaminated groundwater.

[0039] The present invention also provides a method for preparing the above-mentioned phosphorus-modified magnetic chitosan microspheres, comprising the following steps: S1) providing an acidic aqueous solution of chitosan; providing a crosslinking agent solution; wherein the crosslinking agent is tetramethylolphosphine sulfate; S2) mixing magnetic nanoparticles with the acidic aqueous solution of chitosan, then adding the crosslinking agent solution, heating to react, then separating the solid, and freeze-drying to obtain phosphorus-modified magnetic chitosan microspheres.

[0040] See Figure 1 , Figure 1 A schematic diagram illustrating the preparation process of phosphorus-modified magnetic chitosan microspheres provided by this invention.

[0041] In this invention, there are no special restrictions on the source of any raw materials; they can be commercially available.

[0042] According to the present invention, the concentration of chitosan in the acidic aqueous solution of chitosan is preferably 5 g / L to 15 g / L; optionally, the concentration of chitosan in the acidic aqueous solution of chitosan is 5 g / L, 8 g / L, 10 g / L, 12 g / L, 15 g / L or any two of the above values; the solvent of the acidic aqueous solution of chitosan preferably includes acid and water; the volume of the acid is preferably 0.5% to 2% of the solvent volume; optionally, the volume of the acid is 0.5%, 0.8%, 1%, 1.5%, 2% of the solvent volume or any two of the above values; the acid can be any acid well known to those skilled in the art and is not particularly limited, but is preferably one or more of acetic acid, formic acid and hydrochloric acid in the present invention.

[0043] In a specific embodiment of the present invention, the acidic aqueous solution of chitosan is prepared by the following method: chitosan is mixed with an acidic aqueous solution to obtain an acidic aqueous solution of chitosan; the mixing method is preferably stirring; the mixing time is preferably 2h to 3h.

[0044] Magnetic nanoparticles are mixed with an acidic aqueous solution of chitosan; the ratio of magnetic nanoparticles to the acidic aqueous solution of chitosan is preferably 5g to 10g:1L; optionally, the ratio of magnetic nanoparticles to the acidic aqueous solution of chitosan is 5g:1L, 6g:1L, 8g:1L, 10g:1L or any two of the above values; the mixing is preferably ultrasonic mixing; the power of ultrasonic mixing is preferably 400W to 500W, more preferably 450W to 500W, and even more preferably 480W; the ultrasonic mixing time is preferably 0.5h to 2h, more preferably 0.5h to 1.5h, and even more preferably 1h to 1.5h.

[0045] Then, a crosslinking agent solution is added, and the reaction is heated. The mass concentration of the crosslinking agent in the crosslinking agent solution is preferably 25%–75%, more preferably 50%–75%, and even more preferably 70%–75%. Optionally, the mass concentration of the crosslinking agent in the crosslinking agent solution is 50%, 55%, 60%, 65%, 70%, 71%, 72%, 73%, 74%, 75%, or any two of the above values. The volume ratio of the crosslinking agent solution to the acidic aqueous solution of chitosan is preferably 1:(5–20). Optionally, the volume ratio of the crosslinking agent solution to the acidic aqueous solution of chitosan is 1:5, 1:8, 1:10, 1:12, 1:15, 1:18, 1:20, or any two of the above ratios. The temperature of the heating reaction is preferably 40℃–80℃, more preferably 60℃–80℃, and even more preferably 60℃–70℃. The heating reaction time is preferably 1–3 hours, more preferably 1–2 hours.

[0046] After the reaction is complete, the solid is separated and freeze-dried to obtain phosphorus-modified magnetic chitosan microspheres. The method for separating the solid is preferably centrifugation. The centrifugation speed is preferably 4000 rpm to 5000 rpm, more preferably 4200 rpm to 4800 rpm, and even more preferably 4500 rpm. The centrifugation time is preferably 5 min to 15 min, more preferably 8 min to 12 min, and even more preferably 10 min. The freeze-drying temperature is preferably -40℃ to -60℃, more preferably -45℃ to -55℃. The freeze-drying time is preferably 2 days to 3 days.

[0047] In one specific embodiment of the present invention, after freeze-drying, the material is preferably ground and sieved to obtain phosphorus-modified magnetic chitosan microspheres; the mesh size of the sieve used for sieving is preferably 50-500 mesh, more preferably 50-300 mesh, even more preferably 50-200 mesh, and most preferably 100 mesh.

[0048] The phosphorus-modified magnetic chitosan microspheres provided by this invention have widely available and low-cost raw materials, are easy to operate, have mild reaction conditions, are environmentally friendly, and have low equipment requirements.

[0049] The present invention also provides an application of the above-mentioned phosphorus-modified magnetic chitosan microspheres in the treatment of chromium-containing groundwater.

[0050] In one specific embodiment of the present invention, the chromium-containing groundwater is Cr(VI)-containing groundwater.

[0051] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a phosphorus-modified magnetic chitosan microsphere provided by the present invention, its preparation method, and its application in the treatment of chromium-containing groundwater.

[0052] All reagents used in the following examples are commercially available; the molecular weight range of chitosan used in the examples is 2.0 × 10⁻⁶. 5 ~2.5×10 5 .

[0053] Example 1

[0054] This embodiment provides a method for preparing phosphorus-modified magnetic chitosan microspheres (PCC / Fe3O4), the specific steps of which are as follows:

[0055] (1) Dissolve 2g of chitosan (degree of deacetylation of 95%) in 200mL of 0.5% acetic acid solution and stir for 2h to prepare a clear chitosan acetic acid aqueous solution A;

[0056] (2) Dissolve 1g of nano-iron oxide in the clear chitosan acetic acid aqueous solution A in step (1), and sonicate for 1h (power 480W) to make it evenly mixed and form mixture B;

[0057] (3) Add 20 mL of tetrahydroxymethylphosphoric acid solution (concentration 75 wt%) to mixture B, stir continuously and heat to 70 °C, maintain the reaction for 2 h, after the reaction is completed, cool to room temperature, use a centrifuge to separate solid and liquid for 10 min at a speed of 4500 rpm, and then wash the separated solid with anhydrous ethanol and deionized water alternately.

[0058] (4) The product obtained in step (3) was freeze-dried at -45°C for 2 days, ground in an agate mortar and passed through a 100-mesh sieve to finally obtain phosphorus-modified magnetic chitosan microspheres.

[0059] Figure 2 This is a physical image of the phosphorus-modified magnetic chitosan microspheres prepared in this embodiment, which can be magnetically separated.

[0060] Figure 3 This is a schematic diagram illustrating the reaction principle of the phosphorus-modified magnetic chitosan microspheres prepared in this embodiment.

[0061] Figure 4 The figures show the FT-IR spectra of the phosphorus-modified magnetic chitosan microspheres (PCC / Fe3O4) prepared in this embodiment, the phosphorus-modified chitosan microspheres (PCC) prepared in Comparative Example 1, chitosan (CS), and iron(III) oxide (Fe3O4). As can be seen from the figures, in the chitosan spectrum, at 3370 cm⁻¹... -1 The nearby peaks are the stretching vibration peaks of OH and NH, at 1650 cm⁻¹. -1 The nearby peak is the bending vibration peak of NH in -NH2, at 1030 cm⁻¹. -1 The peak near the point is the stretching vibration peak of C-OH; in the PCC / Fe3O4 spectrum, the peak is at 3370 cm⁻¹. -1 The broad absorption peak at this wavenumber is due to the stretching vibrations of hydroxyl groups -OH and -NH2, and is stronger and sharper than that of chitosan at the same wavenumber, indicating that a large number of THPS molecules are cross-linked to chitosan molecules through -OH. Many basic amino groups are distributed on the chitosan molecular chain, which can electrostatically adsorb sulfate ions to form salts. (1410 cm⁻¹) -1 It is the absorption peak of the S=O stretching vibration; 1310 cm⁻¹ -1 The absorption peak of the CN stretching vibration of the secondary amine indicates that the amino group in chitosan reacts with the hydroxyl group in tetramethylolphosphine sulfate to achieve cross-linking; 1110 cm⁻¹ -1 The absorption peak is for the CO stretching vibration; 916 cm⁻¹ -1 The absorption peak is for the out-of-plane bending vibration of NH; 610 cm⁻¹ -1 The vibrational absorption peak of the PC bond indicates that the cross-linking effect of the phosphorus-containing cationic groups disrupts the hydrogen bond structure between chitosan molecules, thereby greatly improving the stability and acid and corrosion resistance of the adsorbent; the 560 cm⁻¹ peak in the Fe₃O₄ spectrum... -1 The characteristic stretching absorption peak of the Fe-O bond is observed at 560 cm⁻¹. -1 At this point, a new characteristic absorption peak appeared in PCC / Fe3O4, which is related to the stretching vibration of the Fe-O bond in nano-Fe3O4. In summary, it can be confirmed that THPS and chitosan were successfully combined with nano-Fe3O4 to form phosphorus-modified magnetic chitosan microspheres.

[0062] Figure 5SEM images of the phosphorus-modified magnetic chitosan microspheres (PCC / Fe3O4) prepared in this embodiment, the phosphorus-modified chitosan microspheres (PCC) prepared in Comparative Example 1, chitosan (CS), iron(III) oxide (Fe3O4), and the phosphorus-modified magnetic chitosan microspheres after adsorbing Cr(VI). Chitosan encapsulates nano-Fe3O4, forming a core-shell structure. After the chitosan undergoes a cross-linking reaction with THPS, the composite microspheres harden and are easily separated from the mixture. Figure 5 As can be seen, compared with the original smooth, stacked structure of unmodified chitosan, the phosphorus-modified magnetic chitosan microspheres prepared in this embodiment have obvious wrinkles and uneven surfaces, which increases the specific surface area of ​​the adsorbent. This may be attributed to the introduction of tetramethylolphosphine sulfate and spherical nano-iron oxide. When the Cr(VI) solution diffuses to the surface of the adsorbent, it can increase the contact area between the adsorbent and Cr(VI), thereby effectively improving the adsorption rate and adsorption capacity.

[0063] Example 2

[0064] This embodiment provides a method for preparing phosphorus-modified magnetic chitosan microspheres, the specific steps of which are as follows:

[0065] (1) Dissolve 2g of chitosan (degree of deacetylation of 95%) in 200mL of 0.5% acetic acid solution and stir for 2h to prepare a clear chitosan acetic acid aqueous solution A;

[0066] (2) Dissolve 1g of nano-iron oxide in the clear chitosan acetic acid aqueous solution A in step (1), and sonicate for 1h (power 480W) to make it evenly mixed and form mixture B;

[0067] (3) Add 20 mL of tetrahydroxymethyl phosphine sulfate solution (75 wt%) to mixture B, stir continuously and heat to 40 °C, maintain the reaction for 2 h, cool to room temperature after the reaction is completed, use a centrifuge to separate the solid and liquid for 10 min at 4500 rpm, and then wash the separated solid with anhydrous ethanol and deionized water alternately.

[0068] (4) The product obtained in step (3) was freeze-dried at -45°C for 2 days, ground in an agate mortar and passed through a 100-mesh sieve to finally obtain phosphorus-modified magnetic chitosan microspheres.

[0069] Example 3

[0070] This embodiment provides a method for preparing phosphorus-modified magnetic chitosan microspheres, the specific steps of which are as follows:

[0071] (1) Dissolve 2g of chitosan (degree of deacetylation of 95%) in 200mL of 0.5% acetic acid solution and stir for 2h to prepare a clear chitosan acetic acid aqueous solution A;

[0072] (2) Dissolve 1g of nano-iron oxide in the clear chitosan acetic acid aqueous solution A in step (1), and sonicate for 1h (power 480W) to make it evenly mixed and form mixture B;

[0073] (3) Add 20 mL of tetrahydroxymethyl phosphine solution (concentration 50 wt%) to mixture B, stir continuously and heat to 70 °C, maintain the reaction for 2 h, after the reaction is completed, cool to room temperature, use a centrifuge to separate solid and liquid for 10 min at a speed of 4500 rpm, and then wash the separated solid with anhydrous ethanol and deionized water alternately.

[0074] (4) The product obtained in step (3) was freeze-dried at -45°C for 2 days, ground in an agate mortar and passed through a 100-mesh sieve to finally obtain phosphorus-modified magnetic chitosan microspheres.

[0075] Example 4

[0076] This embodiment provides a method for preparing phosphorus-modified magnetic chitosan microspheres, the specific steps of which are as follows:

[0077] (1) Dissolve 2g of chitosan (degree of deacetylation of 95%) in 200mL of 0.5% acetic acid solution and stir for 2h to prepare a clear chitosan acetic acid aqueous solution A;

[0078] (2) Dissolve 1g of nano-iron oxide in the clear chitosan acetic acid aqueous solution A in step (1), and sonicate for 1h (power 480W) to make it evenly mixed and form mixture B;

[0079] (3) Add 20 mL of tetrahydroxymethylphosphoric acid solution (concentration 25 wt%) to mixture B, stir continuously and heat to 70 °C, maintain the reaction for 2 h, after the reaction is completed, cool to room temperature, use a centrifuge to separate solid and liquid for 10 min at a speed of 4500 rpm, and then wash the separated solid with anhydrous ethanol and deionized water alternately.

[0080] (4) The product obtained in step (3) was freeze-dried at -45°C for 2 days, ground in an agate mortar and passed through a 100-mesh sieve to finally obtain phosphorus-modified magnetic chitosan microspheres.

[0081] Example 5

[0082] This embodiment provides a method for preparing phosphorus-modified magnetic chitosan microspheres, the specific steps of which are as follows:

[0083] (1) Dissolve 2g of chitosan (75% degree of deacetylation) in 200mL of 0.5% acetic acid solution and stir for 2h to prepare a clear chitosan acetic acid aqueous solution A;

[0084] (2) Dissolve 1g of nano-iron oxide in the clear chitosan acetic acid aqueous solution A in step (1), and sonicate for 1h (power 480W) to make it evenly mixed and form mixture B;

[0085] (3) Add 20 mL of tetrahydroxymethylphosphoric acid solution (concentration 75 wt%) to mixture B, stir continuously and heat to 70 °C, maintain the reaction for 2 h, after the reaction is completed, cool to room temperature, use a centrifuge to separate solid and liquid for 10 min at a speed of 4000 rpm, and then wash the separated solid with anhydrous ethanol and deionized water alternately.

[0086] (4) The product obtained in step (3) was freeze-dried at -45°C for 3 days, ground in an agate mortar and passed through a 100-mesh sieve to finally obtain phosphorus-modified magnetic chitosan microspheres.

[0087] Example 6

[0088] This embodiment provides a method for preparing phosphorus-modified magnetic chitosan microspheres, the specific steps of which are as follows:

[0089] (1) Dissolve 2g of chitosan (degree of deacetylation of 95%) in 200mL of 0.5% acetic acid solution and stir for 2h to prepare a clear chitosan acetic acid aqueous solution A;

[0090] (2) Dissolve 2g of nano-iron oxide in the clear chitosan acetic acid aqueous solution A in step (1), and sonicate for 1.5h (power 480W) to make it evenly mixed and form mixture B;

[0091] (3) Add 20 mL of tetrahydroxymethylphosphoric acid solution (concentration 75 wt%) to mixture B, stir continuously and heat to 70 °C, maintain the reaction for 2 h, after the reaction is completed, cool to room temperature, use a centrifuge to separate solid and liquid for 10 min at a speed of 4500 rpm, and then wash the separated solid with anhydrous ethanol and deionized water alternately.

[0092] (4) The product obtained in step (3) was freeze-dried at -45°C for 2 days, ground in an agate mortar and passed through a 100-mesh sieve to finally obtain phosphorus-modified magnetic chitosan microspheres.

[0093] Comparative Example 1

[0094] This comparative example provides a method for preparing phosphorus-modified chitosan microspheres (PCC), the specific steps of which are as follows:

[0095] (1) Dissolve 2g of chitosan (degree of deacetylation of 95%) in 200mL of 0.5% acetic acid solution and stir for 2h to prepare a clear chitosan acetic acid aqueous solution A;

[0096] (2) Add 20 mL of tetrahydroxymethylphosphoric acid solution (75 wt%) to solution A, stir continuously and heat to 70 °C, maintain the reaction for 2 h, and after the reaction is completed, cool to room temperature to obtain mixture B;

[0097] (3) Use a centrifuge to separate the solid and liquid components of mixture B for 10 min at a speed of 4500 rpm. Pour out the supernatant and process it. Wash the solid alternately with deionized water to remove unreacted THPS.

[0098] (4) The product obtained in step (3) is dried in a vacuum dryer for 7 days, and then the powder is sieved by a ball mill and passed through a 100-mesh sieve to finally obtain phosphorus-modified chitosan microspheres.

[0099] Comparative Example 2

[0100] This comparative example provides a method for preparing phosphorus-modified chitosan microspheres (PCC), the specific steps of which are as follows:

[0101] (1) Dissolve 2g of chitosan (degree of deacetylation of 95%) in 200mL of 0.5% acetic acid solution and stir for 2h to prepare a clear chitosan acetic acid aqueous solution A;

[0102] (2) Add 20 mL of tetrahydroxymethylphosphoric acid solution (75 wt%) to solution A, stir continuously and heat to 70 °C, maintain the reaction for 2 h, and after the reaction is completed, cool to room temperature to obtain mixture B;

[0103] (3) Use a centrifuge to separate the solid and liquid components of mixture B for 10 min at a speed of 4500 rpm. Pour out the supernatant and process it. Wash the solid alternately with deionized water to remove unreacted THPS.

[0104] (4) The product obtained in step (3) was freeze-dried at -45°C for 2 days, ground in an agate mortar and passed through a 100-mesh sieve to finally obtain phosphorus-modified chitosan microspheres.

[0105] Comparative Example 3

[0106] This comparative example provides a method for preparing magnetic chitosan microspheres, the specific steps of which are as follows:

[0107] (1) Dissolve 2g of chitosan (degree of deacetylation of 95%) in 200mL of 0.5% acetic acid solution and stir for 2h to prepare a clear chitosan acetic acid aqueous solution A;

[0108] (2) Dissolve 1g of nano-iron oxide in the clear chitosan acetic acid aqueous solution A in step (1), and sonicate for 1h (power 480W) to make it evenly mixed and form mixture B;

[0109] (3) Use a centrifuge to separate the solid and liquid components of mixture B for 10 min at a speed of 4500 rpm, and then wash the separated solid with anhydrous ethanol and deionized water alternately.

[0110] (4) The product obtained in step (3) was freeze-dried at -45°C for 2 days, ground in an agate mortar and passed through a 100-mesh sieve to finally obtain magnetic chitosan microspheres.

[0111] Comparative Example 4

[0112] This comparative example provides a method for preparing phosphorus-modified magnetic chitosan microspheres, the specific steps of which are as follows:

[0113] (1) Dissolve 2g of chitosan (degree of deacetylation of 95%) in 200mL of 0.5% acetic acid aqueous solution and stir for 2h to prepare a clear chitosan acetic acid aqueous solution A;

[0114] (2) Dissolve 1g of nano-iron oxide in the clear chitosan acetic acid aqueous solution A in step (1), and sonicate for 1h (power 480W) to make it evenly mixed and form mixture B;

[0115] (3) Mixture B was slowly added dropwise to 100 mL of 5% calcium chloride solution using a 5 mL sterile syringe. After standing at room temperature for 8 h, it was separated at room temperature and pressure and washed 2-3 times with deionized water until the pH value was neutral to obtain magnetic chitosan microbeads.

[0116] (4) Add the magnetic chitosan microbeads prepared in step (3) to 100 mL of a 7% tetrahydroxymethyl phosphonic acid solution, stir continuously and heat to 70 °C, maintain the reaction for 2 h, cool to room temperature after the reaction is completed, and use a centrifuge to separate the solid and liquid for 10 min at a speed of 4500 rpm. Then wash the separated solid with anhydrous ethanol and deionized water alternately.

[0117] (5) The product obtained in step (4) was freeze-dried at -45°C for 2 days, ground in an agate mortar and passed through a 100-mesh sieve to finally obtain phosphorus-modified magnetic chitosan microbeads.

[0118] Comparative Example 5

[0119] This comparative example provides a method for preparing phosphorus-modified magnetic chitosan microspheres, the specific steps of which are as follows:

[0120] (1) Dissolve 2g of chitosan (degree of deacetylation of 95%) in 200mL of 0.5% acetic acid solution and stir for 2h to prepare a clear chitosan acetic acid aqueous solution A;

[0121] (2) Dissolve 1g of nano-iron oxide in the clear chitosan acetic acid aqueous solution A in step (1), and sonicate for 1h (power 480W) to make it evenly mixed and form mixture B;

[0122] (3) Add 20 mL of tetrahydroxymethyl phosphine sulfate solution (concentration 75 wt%) to mixture B, stir continuously at room temperature, and maintain the reaction for 2 h. After the reaction is completed, cool to room temperature and use a centrifuge to separate the solid and liquid for 10 min at a speed of 4500 rpm. Then wash the separated solid with anhydrous ethanol and deionized water alternately.

[0123] (4) The product obtained in step (3) was freeze-dried at -45°C for 2 days, ground in an agate mortar and passed through a 100-mesh sieve to finally obtain phosphorus-modified magnetic chitosan microspheres.

[0124] Comparative Example 6

[0125] The raw material is pure chitosan with a degree of deacetylation of 95%.

[0126] Comparative Example 7

[0127] The raw material is nano-iron oxide.

[0128] Performance testing:

[0129] The materials from Examples 1-6 and Comparative Examples 1-7 were used in the adsorption and removal of Cr(VI) from aqueous solutions.

[0130] An initial concentration of 1 mg / L and a pH of 3 or 6 of Cr(VI) aqueous solution were prepared. Using 300 ml reagent bottles as reactors, 250 ml of Cr(VI) aqueous solution was added to each bottle, along with 0.01 g of the prepared adsorbent. The bottles were sealed and placed in a constant temperature shaking incubator at 25°C and 200 rpm. After 2 hours of dynamic adsorption, 5 mL of the suspension was drawn up using a syringe. The suspension was filtered through a 0.45 μm membrane, and the equilibrium concentration of the Cr(VI) solution was determined using the diphenylcarbazide spectrophotometric method. The results are shown in Table 1.

[0131] Table 1 shows the adsorption results of the adsorbents prepared in Examples 1-6 and Comparative Examples 1-7 in aqueous solutions containing Cr(VI).

[0132]

[0133]

[0134] As shown in Table 1, at pH 6, the phosphorus-modified magnetic chitosan microspheres prepared in Example 1 adsorbed 23.950 mg / g of Cr(VI), with a removal rate as high as 95.8%, demonstrating good Cr(VI) adsorption capacity.

[0135] The phosphorus-modified magnetic chitosan microspheres prepared in Example 1, the phosphorus-modified chitosan microspheres prepared in Comparative Example 1, and chitosan and iron oxide were used to study the adsorption kinetics of Cr(VI)-containing aqueous solutions.

[0136] An initial concentration of 1 mg / L and a pH of 6 Cr(VI) aqueous solution was prepared. Using 300 mL reagent bottles as reactors, 250 mL of Cr(VI) aqueous solution was added to each bottle, along with 0.01 g of adsorbent. The bottles were sealed and placed in a constant temperature shaking incubator at 25°C and 200 rpm. After 5 min, 10 min, 15 min, 20 min, 30 min, 40 min, 50 min, 60 min, 120 min, and 1440 min, 5 mL of the suspension was aspirated using a syringe. The suspension was filtered through a 0.45 μm membrane, and the equilibrium concentration of the Cr(VI) solution was determined using the diphenylcarbazide spectrophotometric method. The results are as follows: Figure 6 , Figure 7 As shown.

[0137] Depend on Figure 6 It can be seen that 0.01g of phosphorus-modified magnetic chitosan microspheres achieved a removal rate of 82.6% for Cr(VI) solution within 5 minutes of adsorption, and a removal rate of over 90% within 15 minutes of adsorption, demonstrating high removal efficiency and good adsorption effect. Figure 7 It can be seen that 0.01g of phosphorus-modified magnetic chitosan microspheres adsorbs more than 23mg / g of Cr(VI) in this system.

[0138] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A phosphorus-modified magnetic chitosan microsphere, characterized in that, The phosphorus-modified magnetic chitosan microspheres have a core-shell structure; the core-shell structure includes a core and an outer shell surrounding the core; the core is a magnetic nanoparticle; the outer shell is formed by cross-linking chitosan with a cross-linking agent; the cross-linking agent is tetramethylolphosphine sulfate. The mass ratio of chitosan in the core to that in the shell is 1:(1~10). The magnetic nanoparticles are selected from Fe3O4 and / or γ-Fe2O3; The degree of deacetylation of the chitosan is 95%. The molecular weight of the chitosan is 2 × 10⁻⁶. 5 ~2.5×10 5 ; The preparation method of the phosphorus-modified magnetic chitosan microspheres includes the following steps: S1) Provide an acidic aqueous solution of chitosan; the solvent of the acidic aqueous solution of chitosan includes an acid and water; the volume of the acid is 0.5% to 2% of the volume of the solvent; the acid is selected from one or more of acetic acid, formic acid and hydrochloric acid; A crosslinking agent solution is provided; the crosslinking agent is tetramethylolphosphine sulfate; S2) Magnetic nanoparticles are mixed with an acidic aqueous solution of chitosan, then a crosslinking agent solution is added, the mixture is heated to react, the solid is separated, and the mixture is freeze-dried to obtain phosphorus-modified magnetic chitosan microspheres; the temperature of the heating reaction is 40℃~80℃; the heating reaction time is 1 h~3 h. The concentration of chitosan in the acidic aqueous solution is 8 g / L to 12 g / L; The mass concentration of the crosslinking agent in the crosslinking agent solution is 50%~75%; The ratio of the magnetic nanoparticles to the acidic aqueous solution of chitosan is 5 g to 10 g: 1 L; The volume ratio of the crosslinking agent solution to the acidic aqueous solution of chitosan is 1:10; The freeze-drying temperature is -40 ℃ to -60 ℃; the freeze-drying time is 2 to 3 days; The phosphorus-modified magnetic chitosan microspheres are used for the treatment of chromium-containing groundwater.

2. The phosphorus-modified magnetic chitosan microspheres according to claim 1, characterized in that, In step S2), the mixing is ultrasonic mixing; the power of ultrasonic mixing is 400 W to 500 W; and the time of ultrasonic mixing is 0.5 h to 2 h.

3. The phosphorus-modified magnetic chitosan microspheres according to claim 1, characterized in that, The method for separating the solids is centrifugation; the centrifugation speed is 4000 rpm to 5000 rpm.

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