Phosphorus-containing modified magnetic chitosan microsphere, preparation method thereof and application of phosphorus-containing modified magnetic chitosan microsphere in chromium-containing underground water treatment

Abstract

The invention belongs to the technical field of water treatment, and particularly relates to phosphorus-containing modified magnetic chitosan microspheres, a preparation method of the phosphorus-containing modified magnetic chitosan microspheres and application of the phosphorus-containing modified magnetic chitosan microspheres in chromium-containing underground water treatment. Compared with the prior art, the phosphorus-containing modified magnetic chitosan microsphere provided by the invention takes the magnetic nanoparticles as the inner core, and can be quickly separated from a reaction system by virtue of magnetic force outside the system; hydrogen bonds are formed by hydroxyl groups of the magnetic nanoparticles and amino groups and hydroxyl groups of chitosan molecular chains, so that the stability and the dispersity of the magnetic nanoparticles are improved; furthermore, a tetrakis hydroxymethyl phosphonium sulfate solution is used as a cross-linking agent, so that phosphorus-containing cation groups in the tetrakis hydroxymethyl phosphonium sulfate are grafted to chitosan molecules, the adsorption performance of the chitosan on anionic heavy metal pollutants such as Cr (VI) is greatly enhanced, and the long-term stability of repairing the Cr (VI) polluted underground water is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and in particular relates to phosphorus-modified magnetic chitosan microspheres, a preparation method thereof and application thereof in the treatment of chromium-containing groundwater. Background Art

[0002] The global industrialization process is accelerating, and a large amount of heavy metals produced by mining, metallurgy, chemical industry, electroplating, battery and other industries enter the water environment and threaten human health. Heavy metals cannot be degraded by microorganisms and can accumulate in the ecological environment for a long time, and pose a threat to human health through bioaccumulation. Chromium is a representative heavy metal with certain toxicity and bioaccumulation. It usually exists in groundwater in the form of Cr(III) and Cr(VI), and the latter is much more toxic than the former. Cr(VI) is removed by photocatalysis, chemical precipitation, membrane separation, ion exchange, adsorption and other methods.

[0003] Among them, adsorption is one of the main technologies for treating chromium-containing groundwater, which has the characteristics of simple operation, low cost, no secondary pollution, and good treatment effect. However, when some traditional adsorbents are used to remove heavy metals, there are disadvantages such as low adsorption capacity or long time required for adsorption to reach equilibrium.

[0004] Chitosan is widely available and has good biocompatibility, biodegradability and non-toxicity. It is a natural and completely biodegradable polymer material that can be used as an ideal adsorbent for removing chromium-containing groundwater. The surface of chitosan molecules is rich in amino and hydroxyl groups and has a relatively high reactivity. Chitosan can be given various functional properties while improving its solubility through functional modification or modification methods. Chitosan is combined with magnetic substances to obtain magnetic chitosan microspheres, which are easy to separate and widely used in various fields.

[0005] Magnetic chitosan microspheres contain ultrafine powders with magnetic properties, such as Fe3O4, γ-Fe2O3, etc. The microspheres can be chemically introduced with a variety of reactive functional groups on the surface of the microspheres. Commonly used crosslinking agents include formaldehyde, glutaraldehyde, epichlorohydrin and epichlorohydrin. However, the crosslinking process of these crosslinking agents is complicated and requires a large amount 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, a preparation method thereof and application in the treatment of chromium-containing groundwater. The preparation method is simple and environmentally friendly, and the prepared phosphorus-modified magnetic chitosan microspheres not only retain the active groups of chitosan, but also can achieve simple and rapid solid-liquid separation, and can also efficiently remove anionic heavy metal pollutants such as Cr(VI) in groundwater.

[0007] The invention provides a phosphorus-modified magnetic chitosan microsphere, which is a core-shell structure; the core-shell structure comprises an inner core and an outer shell wrapped outside the inner core; the inner core is a magnetic nanoparticle; the outer shell is formed by cross-linking chitosan with a cross-linking agent; the cross-linking agent is tetrakis(hydroxymethyl)phosphonium 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 deacetylation degree of the chitosan is 75% to 95%.

[0011] The present invention also provides a method for preparing the phosphorus-modified magnetic chitosan microspheres.

[0012] A cross-linking agent solution; the cross-linking agent is tetrakis hydroxymethyl phosphonium sulfate;

[0013] S2) mixing the magnetic nanoparticles with an acidic aqueous solution of chitosan, then adding a crosslinking agent solution, heating for reaction, separating the solid, and freeze-drying to obtain phosphorus-modified magnetic chitosan microspheres.

[0014] Preferably, the concentration of chitosan in the acidic aqueous solution of chitosan 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 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;

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

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

[0018] Preferably, the volume ratio of the cross-linking 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; the time of the ultrasonic mixing is 0.5h to 2h;

[0020] The temperature of the heating reaction is 40° C. to 80° C.; the time of the heating reaction is 1 h to 3 h.

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

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

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

[0024] The present invention provides a phosphorus-modified magnetic chitosan microsphere, which is a core-shell structure; the core-shell structure includes an inner core and an outer shell wrapped outside the inner core; the inner core is a magnetic nanoparticle; the outer shell is formed by cross-linking chitosan with a cross-linking agent; the cross-linking agent is tetrakis(hydroxymethyl)phosphonium sulfate. Compared with the prior art, the phosphorus-modified magnetic chitosan microsphere provided by the present invention uses magnetic nanoparticles as the inner core, can be quickly separated from the reaction system by relying on the magnetic force outside the system, is convenient, fast, simple and efficient; and forms hydrogen bonds between the hydroxyl groups of the magnetic nanoparticles and the amino and hydroxyl groups of the chitosan molecular chains, thereby improving the stability and dispersibility of the magnetic nanoparticles; furthermore, using tetrakis(hydroxymethyl)phosphonium sulfate solution as a cross-linking agent, the phosphorus-containing cationic groups in the tetrakis(hydroxymethyl)phosphonium sulfate are grafted onto chitosan molecules, thereby greatly enhancing its adsorption performance for anionic heavy metal pollutants such as Cr(VI), and repairing Cr(VI)-contaminated groundwater has long-term stability.

[0025] Experiments show that the maximum removal rate of Cr(VI) by the phosphorus-modified magnetic chitosan microspheres prepared by the present invention can reach 96%, and the effluent meets the "Groundwater Environmental Quality Standard (GB / T 14848-2017)", which has practical application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0027] Figure 2 This is a magnetic separation diagram of phosphorus-modified magnetic chitosan microspheres prepared in Example 1 of the present invention;

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

[0029] Figure 4 FT-IR spectra of phosphorus-modified magnetic chitosan microspheres prepared in Example 1 of the present invention, phosphorus-modified chitosan microspheres prepared in Comparative Example 1, chitosan and ferrosoferric oxide;

[0030] Figure 5 The 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, chitosan and ferrosoferric oxide;

[0031] Figure 6 The adsorption kinetics of phosphorus-modified magnetic chitosan microspheres prepared in Example 1 of the present invention, phosphorus-modified chitosan microspheres prepared in Comparative Example 1, chitosan and ferrosoferric oxide on a pH 6 Cr(VI) aqueous solution;

[0032] Figure 7 This is the adsorption isotherm diagram of the phosphorus-modified magnetic chitosan microspheres prepared in Example 1 of the present invention for an aqueous solution of Cr(VI). DETAILED DESCRIPTION

[0033] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0034] The invention provides a phosphorus-modified magnetic chitosan microsphere, which is a core-shell structure; the core-shell structure comprises an inner core and an outer shell wrapped outside the inner core; the inner core is a magnetic nanoparticle; the outer shell is formed by cross-linking chitosan with a cross-linking agent; the cross-linking agent is tetrakis(hydroxymethyl)phosphonium sulfate.

[0035] According to the present invention, the inner core of the phosphorus-modified magnetic chitosan microspheres is magnetic nanoparticles; the magnetic nanoparticles can be magnetic nanoparticles well known to those skilled in the art without any special limitation, and nano-Fe3O4 and / or γ-Fe2O3 are preferred in the present invention.

[0036] According to the present invention, the magnetic nanoparticles are wrapped with a shell; the shell is formed by cross-linking chitosan with a cross-linking agent; the deacetylation degree of the chitosan is preferably 75% to 95%; optionally, the deacetylation degree of the chitosan is 75%, 80%, 85%, 90%, 95% or a range between any two of the above values; the molecular weight of the chitosan is preferably 1×10 5 ~3×10 5 , more preferably 1.26×10 5 ~2.65×10 5 , and preferably 1.5×10 5 ~2.65×10 5 , the most preferred value is 2.0×10 5 ~2.5×10 5 ; The cross-linking agent is tetrakis hydroxymethyl phosphine sulfate.

[0037] According to the present invention, the mass ratio of chitosan in the core and the shell is preferably 1:(1-10); 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 a range between any two of the above ratios.

[0038] The phosphorus-containing modified magnetic chitosan microspheres provided by the invention have magnetic nanoparticles as the core, can be quickly separated from the reaction system by relying on the magnetic force outside the system, and are convenient, fast, simple and efficient; and the hydroxyl groups of the magnetic nanoparticles form hydrogen bonds with the amino groups and hydroxyl groups of the chitosan molecular chains, thereby improving the stability and dispersibility of the magnetic nanoparticles; and tetrakis hydroxymethyl phosphonium sulfate solution is used as a crosslinking agent, so that the phosphorus-containing cationic groups in the tetrakis hydroxymethyl phosphonium sulfate are grafted onto the chitosan molecules, thereby greatly enhancing the adsorption performance of the chitosan molecules for anionic heavy metal pollutants such as Cr(VI), and repairing the Cr(VI)-contaminated groundwater has long-term stability.

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

[0040] See also Figure 1 , Figure 1 The present invention provides a schematic diagram of the preparation process of phosphorus-modified magnetic chitosan microspheres.

[0041] The present invention has no particular limitation on the sources of all raw materials, and any raw materials available on the market can be used.

[0042] According to the present invention, the concentration of chitosan in the acidic aqueous solution of chitosan is preferably 5g / L to 15g / L; optionally, the concentration of chitosan in the acidic aqueous solution of chitosan is 5g / L, 8g / L, 10g / L, 12g / L, 15g / L or a range between 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 volume of the solvent; optionally, the volume of the acid is 0.5%, 0.8%, 1%, 1.5%, 2% of the volume of the solvent or a range between any two of the above values; the acid can be an acid well known to those skilled in the art without any special restrictions, and in the present invention, it is preferably one or more of acetic acid, formic acid and hydrochloric acid.

[0043] In a specific embodiment provided by the present invention, the acidic aqueous solution of chitosan is prepared according to 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; and the mixing time is preferably 2h to 3h.

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

[0045] Then, a crosslinking agent solution is added and heated to react; the mass concentration of the crosslinking agent in the crosslinking agent solution is preferably 25% to 75%, more preferably 50% to 75%, and more preferably 70% to 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 a range between 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 a range between any two of the above ratios; the temperature of the heating reaction is preferably 40°C to 80°C, more preferably 60°C to 80°C, and more preferably 60°C to 70°C; the time of the heating reaction is preferably 1 to 3h, more preferably 1 to 2h.

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

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

[0048] The phosphorus-modified magnetic chitosan microspheres provided by the invention have a wide range of raw material sources, low cost, simple operation, mild reaction conditions, are green and environmentally friendly, and have low requirements on equipment.

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

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

[0051] To further illustrate the present invention, the phosphorus-modified magnetic chitosan microspheres provided by the present invention, the preparation method thereof and the application thereof in the treatment of chromium-containing groundwater are described in detail below in conjunction with the examples.

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

[0053] Example 1

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

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

[0056] (2) dissolving 1 g of nano-ferroferric oxide in the clarified chitosan acetic acid aqueous solution A in step (1), and ultrasonicating for 1 h (power 480 W) to mix the mixture evenly to form a mixture B;

[0057] (3) adding 20 mL of tetrakis(hydroxymethyl)phosphonium sulfate solution (concentration 75 wt%) to mixture B, stirring continuously and heating to 70° C., and maintaining the reaction for 2 h. After the reaction is completed, cooling to room temperature, and performing solid-liquid separation using a centrifuge for 10 min at a speed of 4500 rpm, and then washing 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 with 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 picture showing that the phosphorus-modified magnetic chitosan microspheres prepared in this example can be subjected to magnetic separation.

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

[0061] Figure 4 FT-IR spectra of phosphorus-modified magnetic chitosan microspheres (PCC / Fe3O4) prepared in this example, phosphorus-modified chitosan microspheres (PCC) prepared in comparative example 1, chitosan (CS), and ferroferric oxide (Fe3O4). As can be seen from the figure, in the chitosan spectrum, 3370 cm -1 Nearby are the stretching vibration peaks of OH and NH, 1650cm -1 Nearby is the bending vibration peak of NH in -NH2, 1030cm -1 Nearby is the stretching vibration peak of C-OH; in the PCC / Fe3O4 spectrum, 3370cm -1 The broad absorption peak at 1410cm is the stretching vibration peak of hydroxyl -OH and -NH2, which is stronger and sharper than the peak of chitosan at this wave number, indicating that a large number of THPS molecules are cross-linked to chitosan molecules through -OH; there are many basic amino groups distributed on the chitosan molecular chain, which can be electrostatically adsorbed with sulfate ions to form salts, 1410cm -1 It is the S=O stretching vibration absorption peak; 1310cm -1 It is the absorption peak of the stretching vibration of secondary amine CN, indicating that the amino group in chitosan reacts with the hydroxyl group in tetrakis(hydroxymethyl)phosphonium sulfate to achieve cross-linking; 1110cm -1 CO stretching vibration absorption peak; 916cm -1 NH out-of-plane bending vibration absorption peak; 610cm -1 The peak of the PC bond vibration absorption peak indicates that the cross-linking effect of the phosphorus-containing cationic groups destroys the hydrogen bond structure between chitosan molecules, thereby greatly improving the stability and acid and corrosion resistance of the adsorbent. -1 It is the characteristic stretching absorption peak of Fe-O bond. At 560cm -1 At , a new characteristic absorption peak appeared in PCC / Fe3O4, which was related to the stretching vibration of Fe-O bond of nano-ferroferric oxide. In summary, it can be determined that THPS and chitosan were successfully combined with nano-ferroferric oxide to form phosphorus-modified magnetic chitosan microspheres.

[0062] Figure 5The SEM images of phosphorus-modified magnetic chitosan microspheres (PCC / Fe3O4) prepared in this example, phosphorus-modified chitosan microspheres (PCC), chitosan (CS), ferroferric oxide (Fe3O4) and phosphorus-modified magnetic chitosan microspheres after adsorption of Cr(VI) prepared in Comparative Example 1. Chitosan wraps nano-Fe3O4 to form a core-shell structure. After chitosan undergoes a cross-linking reaction with THPS, the composite microspheres are hardened and easily separated from the mixed system. Figure 5 It can be seen that compared with the unmodified chitosan with a smooth surface and a stacked structure, 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 tetrakis(hydroxymethyl)phosphonium sulfate and spherical nano-ferroferric oxide. When the Cr(VI) solution diffuses to the surface of the adsorbent, the contact area between the adsorbent and Cr(VI) can be increased, thereby effectively improving the adsorption rate and adsorption amount.

[0063] Example 2

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

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

[0066] (2) dissolving 1 g of nano-ferroferric oxide in the clarified chitosan acetic acid aqueous solution A in step (1), and ultrasonicating for 1 h (power 480 W) to mix the mixture evenly to form a mixture B;

[0067] (3) adding 20 mL of tetrakis(hydroxymethyl)phosphonium sulfate solution (concentration 75 wt%) to mixture B, stirring continuously and heating to 40° C., and maintaining the reaction for 2 h. After the reaction is completed, cooling to room temperature, and performing solid-liquid separation using a centrifuge for 10 min at a speed of 4500 rpm, and then washing 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 with 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, and the specific steps are as follows:

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

[0072] (2) dissolving 1 g of nano-ferroferric oxide in the clarified chitosan acetic acid aqueous solution A in step (1), and ultrasonicating for 1 h (power 480 W) to mix the mixture evenly to form a mixture B;

[0073] (3) adding 20 mL of tetrakis(hydroxymethyl)phosphonium sulfate solution (concentration 50 wt%) to mixture B, stirring continuously and heating to 70° C., and maintaining the reaction for 2 h. After the reaction is completed, cooling to room temperature, and performing solid-liquid separation using a centrifuge for 10 min at a speed of 4500 rpm, and then washing 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 with 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, and the specific steps are as follows:

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

[0078] (2) dissolving 1 g of nano-ferroferric oxide in the clarified chitosan acetic acid aqueous solution A in step (1), and ultrasonicating for 1 h (power 480 W) to mix the mixture evenly to form a mixture B;

[0079] (3) adding 20 mL of tetrakis(hydroxymethyl)phosphonium sulfate solution (concentration 25 wt%) to mixture B, stirring continuously and heating to 70° C., and maintaining the reaction for 2 h. After the reaction is completed, cooling to room temperature, and performing solid-liquid separation using a centrifuge for 10 min at a speed of 4500 rpm, and then washing 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 with 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, and the specific steps are as follows:

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

[0084] (2) dissolving 1 g of nano-ferroferric oxide in the clarified chitosan acetic acid aqueous solution A in step (1), and ultrasonicating for 1 h (power 480 W) to mix the mixture evenly to form a mixture B;

[0085] (3) adding 20 mL of tetrakis(hydroxymethyl)phosphonium sulfate solution (concentration 75 wt%) to mixture B, stirring continuously and heating to 70° C., and maintaining the reaction for 2 h. After the reaction is completed, cooling to room temperature, and performing solid-liquid separation using a centrifuge for 10 min at a speed of 4000 rpm, and then washing 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 with 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, and the specific steps are as follows:

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

[0090] (2) dissolving 2 g of nano-ferroferric oxide in the clarified chitosan acetic acid aqueous solution A in step (1), and ultrasonically mixing for 1.5 h (power 480 W) to form a mixture B;

[0091] (3) adding 20 mL of tetrakis(hydroxymethyl)phosphonium sulfate solution (concentration 75 wt%) to mixture B, stirring continuously and heating to 70° C., and maintaining the reaction for 2 h. After the reaction is completed, cooling to room temperature, and performing solid-liquid separation using a centrifuge for 10 min at a speed of 4500 rpm, and then washing 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 with 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-containing modified chitosan microspheres (PCC), and the specific steps are as follows:

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

[0096] (2) adding 20 mL of tetrakis(hydroxymethyl)phosphonium sulfate solution (concentration 75 wt%) to solution A, stirring continuously and heating to 70° C., and maintaining the reaction for 2 h. After the reaction is completed, cooling to room temperature to obtain a mixture B;

[0097] (3) using a centrifuge to separate the mixture B into solid and liquid for 10 min at a speed of 4500 rpm, pouring out the supernatant and treating it, and washing the solid with deionized water alternately to remove unreacted THPS;

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

[0099] Comparative Example 2

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

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

[0102] (2) adding 20 mL of tetrakis(hydroxymethyl)phosphonium sulfate solution (concentration 75 wt%) to solution A, stirring continuously and heating to 70° C., and maintaining the reaction for 2 h. After the reaction is completed, cooling to room temperature to obtain a mixture B;

[0103] (3) using a centrifuge to separate the mixture B into solid and liquid for 10 min at a speed of 4500 rpm, pouring out the supernatant and treating it, and washing the solid with deionized water alternately to remove unreacted THPS;

[0104] (4) The product obtained in step (3) was freeze-dried at -45°C for 2 days, ground with 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, and the specific steps are as follows:

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

[0108] (2) dissolving 1 g of nano-ferroferric oxide in the clarified chitosan acetic acid aqueous solution A in step (1), and ultrasonicating for 1 h (power 480 W) to mix the mixture evenly to form a mixture B;

[0109] (3) using a centrifuge to separate the mixture B into solid and liquid for 10 min at a speed of 4500 rpm, and then washing 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 with 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 microbeads, and the specific steps are as follows:

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

[0114] (2) dissolving 1 g of nano-ferroferric oxide in the clarified chitosan acetic acid aqueous solution A in step (1), and ultrasonicating for 1 h (power 480 W) to mix the mixture evenly to form a mixture B;

[0115] (3) slowly adding the mixture B to 100 mL of 5% calcium chloride solution by a 5 mL sterile syringe, standing at room temperature for 8 h, separating and washing with deionized water 2 to 3 times at room temperature and pressure until the pH value is neutral, thereby obtaining magnetic chitosan microbeads;

[0116] (4) adding the magnetic chitosan microbeads prepared in step (3) to 100 mL of 7% tetrakis (hydroxymethyl) phosphine sulfate solution, stirring continuously and heating to 70° C., and maintaining the reaction for 2 h. After the reaction is completed, cooling to room temperature, and performing solid-liquid separation using a centrifuge for 10 min at a speed of 4500 rpm, and then washing the separated solids alternately with anhydrous ethanol and deionized water;

[0117] (5) The product obtained in step (4) was freeze-dried at -45°C for 2 days, ground with 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, and the specific steps are as follows:

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

[0121] (2) dissolving 1 g of nano-ferroferric oxide in the clarified chitosan acetic acid aqueous solution A in step (1), and ultrasonicating for 1 h (power 480 W) to mix the mixture evenly to form a mixture B;

[0122] (3) adding 20 mL of tetrakis(hydroxymethyl)phosphonium sulfate solution (concentration 75 wt%) to mixture B, stirring continuously at room temperature, and maintaining the reaction for 2 h. After the reaction is completed, cooling to room temperature, and performing solid-liquid separation using a centrifuge for 10 min at a speed of 4500 rpm, and then washing 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 with 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 deacetylation degree of 95%.

[0126] Comparative Example 7

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

[0128] Performance Test:

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

[0130] A Cr(VI) aqueous solution with an initial concentration of 1 mg / L and a pH of 3 or 6 was prepared. A reagent bottle with a volume of 300 ml was used as a reactor. 250 ml of the Cr(VI) aqueous solution was added to each reagent bottle. The amount of the prepared adsorbent added was 0.01 g. The reagent bottle was sealed and placed in a constant temperature shaking incubator. The temperature in the incubator was adjusted to 25°C and the rotation speed was 200 rpm. After dynamic adsorption for 2 hours, 5 mL of the suspension was drawn with a syringe. After the suspension was filtered through a 0.45 μm membrane, the equilibrium concentration of the Cr(VI) solution was determined by diphenylcarbazide spectrophotometry. The results are shown in Table 1.

[0131] Table 1 Adsorption results of the adsorbents prepared in Examples 1 to 6 and Comparative Examples 1 to 7 in aqueous solutions containing Cr(VI)

[0132]

[0133]

[0134] It can be seen from Table 1 that when the pH value is 6, the adsorption amount of Cr(VI) by the phosphorus-modified magnetic chitosan microspheres prepared in Example 1 reaches 23.950 mg / g, and the removal rate is as high as 95.8%, showing 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, chitosan and ferrosoferric oxide were used to study the adsorption kinetics of aqueous solutions containing Cr(VI).

[0136] A Cr(VI) aqueous solution with an initial concentration of 1 mg / L and a pH of 6 was prepared. A reagent bottle with a volume of 300 ml was used as a reactor. 250 mL of Cr(VI) aqueous solution was added to each reagent bottle. The amount of adsorbent added was 0.01 g. The reagent bottle was sealed and placed in a constant temperature shaking incubator. The temperature in the incubator was adjusted to 25°C and the rotation speed was 200 rpm. 5 mL of the suspension was drawn with a syringe after 5 min, 10 min, 15 min, 20 min, 30 min, 40 min, 50 min, 60 min, 120 min and 1440 min, respectively. After the suspension was filtered through a 0.45 μm membrane, the equilibrium concentration of the Cr(VI) solution was determined by diphenylcarbazide spectrophotometry. The results are as follows: Figure 6 , Figure 7 shown.

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

[0138] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as 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 are of a core-shell structure; the core-shell structure comprises an inner core and an outer shell wrapped outside the inner core; the inner core is a magnetic nanoparticle; the outer shell is formed by cross-linking chitosan with a cross-linking agent; the cross-linking agent is tetrakis(hydroxymethyl)phosphonium sulfate.

2. The phosphorus-modified magnetic chitosan microspheres according to claim 1, characterized in that: The mass ratio of chitosan in the core to that in the shell is 1:(1-10).

3. The phosphorus-modified magnetic chitosan microspheres according to claim 1, characterized in that: The magnetic nanoparticles are selected from Fe3O4 and / or γ-Fe2O3; And / or, the deacetylation degree of the chitosan is 75% to 95%.

4. A method for preparing phosphorus-modified magnetic chitosan microspheres according to claim 1, characterized in that: The following steps are involved: S1) providing an acidic aqueous solution of chitosan; Providing a cross-linking agent solution; the cross-linking agent is tetrakis hydroxymethyl phosphonium sulfate; S2) mixing the magnetic nanoparticles with an acidic aqueous solution of chitosan, then adding a crosslinking agent solution, heating for reaction, separating the solid, and freeze-drying to obtain phosphorus-modified magnetic chitosan microspheres.

5. The preparation method according to claim 4, characterized in that: The concentration of chitosan in the acidic aqueous solution of chitosan is 5 g / L to 15 g / L; The solvent of the acidic aqueous solution of chitosan includes 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; The mass concentration of the cross-linking agent in the cross-linking agent solution is 25% to 75%.

6. The preparation method according to claim 4, characterized in that: The ratio of the magnetic nanoparticles to the acidic aqueous solution of chitosan is 5g-10g:1L.

7. The preparation method according to claim 4, characterized in that: The volume ratio of the cross-linking agent solution to the acidic aqueous solution of chitosan is 1:(5-20).

8. The preparation method according to claim 4, characterized in that: The mixing in step S2) is ultrasonic mixing; the power of the ultrasonic mixing is 400W to 500W; the time of the ultrasonic mixing is 0.5h to 2h; The temperature of the heating reaction is 40° C. to 80° C.; the time of the heating reaction is 1 h to 3 h.

9. The preparation method according to claim 4, characterized in that: The method for separating solids is centrifugation; the speed of the centrifugation is 4000rpm to 5000rpm; The freeze-drying temperature is -40°C to -60°C; the freeze-drying time is 2 to 3 days.

10. Use of the phosphorus-modified magnetic chitosan microspheres according to any one of claims 1 to 3 or the phosphorus-modified magnetic chitosan microspheres prepared by the preparation method according to any one of claims 4 to 9 in the treatment of chromium-containing groundwater.

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