A porous sodium alginate / cellulose nanofiber gel microsphere and a preparation method and application thereof

Abstract

The application provides a porous sodium alginate / cellulose nanofiber gel microsphere and a preparation method and application thereof, and belongs to the technical field of preparation of heavy metal ion adsorbents. The preparation method comprises the following steps: adding polyethylene glycol and sodium alginate into an aqueous dispersion of cellulose nanofiber, stirring and dissolving to obtain an aqueous solution of sodium alginate / cellulose nanofiber / polyethylene glycol; mixing the aqueous solution of sodium alginate / cellulose nanofiber / polyethylene glycol and an oil phase through a microfluidic chip to obtain a water-in-oil emulsion; outputting the water-in-oil emulsion into a stirring CaCl2 solution, reacting, washing, and freeze-drying to obtain dry porous sodium alginate / cellulose nanofiber gel microspheres. The gel microspheres prepared by the application have high adsorption rate and adsorption capacity for heavy metal ions, and have wide application prospects in the field of treatment of heavy metal ions in wastewater.

Description

Technical Field

[0001] This invention relates to the field of heavy metal ion adsorbent preparation technology, specifically to a porous sodium alginate / cellulose nanofiber gel microsphere, its preparation method, and its application. Background Technology

[0002] With continuous industrial development, the demand for water resources is constantly increasing, leading to the generation of large amounts of industrial wastewater. This wastewater typically contains varying concentrations and types of heavy metal ions. Heavy metals are defined as those with atomic weights between 63.5 and 200.6 and a relative density of 4.5 g / cm³. 3 The aforementioned heavy metals constitute a class of highly hazardous environmental pollutants. These pollutants typically exhibit characteristics such as mobility, persistence, and biomagnification. Most heavy metals are toxic, harmful, and carcinogenic substances, exhibiting toxicity even at low concentrations of approximately 1.0–10.0 mg / L. Direct discharge into natural water bodies without treatment poses a serious threat to human health and the flora and fauna, and will accumulate over time in the food chain, eventually entering the human body and causing various diseases. Furthermore, heavy metal pollution in surface water is gradually shifting from single-metal pollution to mixed pollution of multiple heavy metals. Currently, various heavy metal treatment technologies exist, including membrane separation, chemical precipitation, electrochemical methods, biological methods, coagulation, and ion exchange. However, these methods are generally limited by high costs and low feasibility. Adsorption, due to its simple operation, high efficiency, and low cost, has become the most widely used method for removing heavy metals.

[0003] The key to adsorption methods lies in the adsorbent with good adsorption performance. Common adsorbents include activated carbon, montmorillonite, and graphene oxide; however, these materials typically suffer from low adsorption capacity, poor reusability, and susceptibility to contamination. In recent years, hydrogel adsorbents based on biomass polymers have gradually gained attention. They possess advantages such as wide material availability, good biocompatibility, no environmental pollution, and excellent anti-fouling ability, showing great application potential in adsorbing heavy metal ions in water. Among them, sodium alginate hydrogel adsorbents contain abundant hydroxyl and carboxyl functional groups, giving them a high affinity for heavy metal ions. Furthermore, their rapid gelation rate makes them one of the most studied heavy metal ion adsorbents. However, traditional sodium alginate-based hydrogels suffer from weak mechanical strength and are prone to disintegration in complex environments. Therefore, researchers often improve sodium alginate through physicochemical modification. Among various methods, blending sodium alginate (SA) with polyvinyl alcohol, chitosan, and polyacrylamide provides an important approach for developing SA adsorbents with ideal application performance. Cellulose, as the most widely distributed and abundant natural polysaccharide, is an ideal blending modifier. However, existing methods report that such materials often exhibit slow adsorption rates and low adsorption capacities for heavy metal ions in water due to their high internal density and low porosity, making them unsuitable for practical applications. Therefore, there is an urgent need to develop a simple method to prepare sodium alginate composite gel microspheres with high adsorption performance for heavy metal ions. Summary of the Invention

[0004] The purpose of this invention is to propose a porous sodium alginate / cellulose nanofiber gel microsphere, its preparation method and application. The prepared gel microsphere has excellent heavy metal ion adsorption performance.

[0005] The technical solution of this invention is implemented as follows:

[0006] This invention provides a method for preparing porous sodium alginate / cellulose nanofiber gel microspheres, comprising the following steps:

[0007] S1. Add cellulose nanofibers to deionized water and disperse them by stirring at 20,000 r / min for 5-10 min using a high-speed homogenizer to obtain an aqueous dispersion of cellulose nanofibers.

[0008] S2. Add polyethylene glycol and sodium alginate to the aqueous dispersion of cellulose nanofibers, stir to dissolve, and obtain an aqueous solution of sodium alginate / cellulose nanofibers / polyethylene glycol;

[0009] S3. The aqueous solution of sodium alginate / cellulose nanofibers / polyethylene glycol and the oil phase are mixed through a standard glass microfluidic chip to obtain a water-in-oil emulsion;

[0010] S4. The water-in-oil emulsion is fed into a stirred CaCl2 solution through a conduit and reacted for 6-12 h to form microspheres. The oil phase is removed by washing with isopropanol for 4-12 h, and the microspheres are then washed with deionized water for 24-48 h to remove polyethylene glycol. The microspheres are then freeze-dried to obtain dry porous sodium alginate / cellulose nanofiber gel microspheres.

[0011] As a further improvement of the present invention, the cellulose nanofibers in step S1 have a diameter of 10-20 nm, a length of 10-100 μm, and contain carboxyl groups on their surface, with a carboxyl group content of 1-5 mmol / g.

[0012] As a further improvement of the present invention, the weight percentage of the cellulose nanofibers in the aqueous dispersion in step S1 is 0.2-0.3 wt%.

[0013] As a further improvement of the present invention, in step S2, the polyethylene glycol is selected from one of PEG-400, PEG-600, and PEG-800, the concentration of the polyethylene glycol in the aqueous solution is 2-4 wt%, and the concentration of the sodium alginate in the aqueous solution is 2-3 wt%.

[0014] As a further improvement of the present invention, in step S3, the oil phase is one of liquid paraffin, n-decane, and n-hexane.

[0015] As a further improvement of the present invention, in step S3, the standard glass microfluidic chip has two inlets and one outlet. The aqueous solution of sodium alginate / cellulose nanofiber / polyethylene glycol and the oil phase are respectively input through the two inlets at a flow rate of 1:3-5. After the oil and water are mixed, they are output through the outlet.

[0016] As a further improvement of the present invention, in step S3, the diameter of the water-in-oil emulsion droplets is 60-200 μm.

[0017] As a further improvement of the present invention, in step S4, the concentration of the CaCl2 solution is 2-5 wt%.

[0018] This invention further protects a porous sodium alginate / cellulose nanofiber gel microsphere prepared by the above preparation method.

[0019] This invention further protects the application of porous sodium alginate / cellulose nanofiber gel microspheres prepared by the above preparation method in the adsorption and removal of heavy metal ions in the aquatic environment.

[0020] The present invention has the following beneficial effects:

[0021] 1. This invention uses carboxyl-containing cellulose nanofibers (CNF) and polyethylene glycol (PEG) as modifying materials to prepare porous sodium alginate / cellulose nanofiber gel microspheres using microfluidic technology. The addition of CNF not only improves the mechanical strength of SA, but also increases the number of adsorption sites. Microfluidic technology can greatly reduce the particle size of microspheres and increase the specific surface area.

[0022] 2. PEG acts as a porogen, and its addition greatly increases the porosity of the gel microspheres, allowing more adsorption sites inside the microspheres to come into contact with heavy metal ions, thereby improving adsorption efficiency and adsorption capacity.

[0023] 3. The porous sodium alginate / cellulose nanofiber gel microspheres prepared by this invention have excellent adsorption properties and stable properties. They are also green and environmentally friendly and can be recycled multiple times. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is an optical microscope image of the gel microspheres prepared in Example 1 of the present invention.

[0026] Figure 2 This is a surface SEM image of the gel microspheres prepared in Example 1 of the present invention.

[0027] Figure 3 This is a surface SEM image of the gel microspheres prepared in Comparative Example 1 of the present invention.

[0028] Figure 4 This is a surface SEM image of the gel microspheres prepared in Comparative Example 2 of the present invention.

[0029] Figure 5 This is an optical microscope image of the gel microspheres prepared in Comparative Example 3 of the present invention.

[0030] Figure 6 This is the dynamic adsorption curve from test example 3 of the present invention. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0032] This embodiment provides a method for preparing porous sodium alginate / cellulose nanofiber gel microspheres, including the following steps:

[0033] S1. Cellulose nanofibers (diameter 10-20 nm, length 10-100 μm, surface carboxyl group content 1.24 mmol / g) were added to deionized water and dispersed by stirring at 20000 r / min for 10 min using a high-speed homogenizer to obtain an aqueous dispersion of cellulose nanofibers with a concentration of 0.3wt%.

[0034] S2. Add 4 wt% PEG-400 and 2 wt% sodium alginate to the aqueous dispersion of cellulose nanofibers, stir to dissolve, and obtain an aqueous solution of sodium alginate / cellulose nanofibers / polyethylene glycol.

[0035] S3. An aqueous solution of sodium alginate / cellulose nanofibers / polyethylene glycol and liquid paraffin were mixed using a standard glass microfluidic chip at an input flow rate of 1:3 to obtain a water-in-oil emulsion with an average droplet diameter of 200 μm.

[0036] S4. The water-in-oil emulsion was fed into a stirred 2wt% CaCl2 solution through a conduit and reacted for 12 h to form microspheres. The microspheres were washed with isopropanol for 12 h to remove the oil phase and with deionized water for 48 h to remove polyethylene glycol. The microspheres were then freeze-dried to obtain dry porous sodium alginate / cellulose nanofiber gel microspheres.

[0037] Observation under an optical microscope revealed that the particle size of the prepared microspheres was approximately 300 μm. Figure 1 ). Scanning electron microscopy revealed a distinct macroporous structure on the surface of the microspheres. Figure 2 ).

[0038] Comparative Example 1: The only difference between this comparative example and Example 1 is that PEG-400 is not added in step S2. Its surface scanning electron microscope image is shown below. Figure 3 As shown, compared with Example 1, there is no obvious macroporous structure on the surface.

[0039] Comparative Example 2: The only difference between this comparative example and Example 1 is that cellulose nanofibers and PEG-400 were not added during the preparation process. The specific preparation process is as follows: 2 wt% sodium alginate aqueous solution and liquid paraffin were mixed at an input flow ratio of 1:3 using a standard glass microfluidic chip to obtain a water-in-oil emulsion with an average droplet diameter of 200 μm. The water-in-oil emulsion was then fed into a stirred 2 wt% CaCl2 solution through a conduit and reacted for 12 h to form microspheres. The microspheres were washed with isopropanol for 12 h to remove the oil phase, and then washed with deionized water for 48 h to remove polyethylene glycol. The microspheres were then freeze-dried to obtain dried sodium alginate gel microspheres. The surface scanning electron microscope image is shown below. Figure 4 As shown, compared to Comparative Example 1, the surface roughness of the microspheres decreased significantly due to the absence of added cellulose nanofibers. Furthermore, because the addition of cellulose nanofibers did not improve mechanical properties, the microspheres were prone to collapse after drying.

[0040] Comparative Example 3: The difference between this comparative example and Example 1 is that the microspheres are not prepared using microfluidics, but rather by direct drop-addition. The specific steps are as follows:

[0041] S1. Cellulose nanofibers (diameter 10-20 nm, length 10-100 μm, surface carboxyl group content 1.24 mmol / g) were added to deionized water and dispersed by stirring at 20000 r / min for 10 min using a high-speed homogenizer to obtain an aqueous dispersion of cellulose nanofibers with a concentration of 0.3wt%.

[0042] S2. Add 4 wt% PEG-400 and 2 wt% sodium alginate to the aqueous dispersion of cellulose nanofibers, stir to dissolve, and obtain an aqueous solution of sodium alginate / cellulose nanofibers / polyethylene glycol.

[0043] S3. An aqueous solution of sodium alginate / cellulose nanofibers / polyethylene glycol was directly added dropwise to a stirred 2wt% CaCl2 solution using a 10ml syringe. The reaction was allowed to proceed for 12 h to form microspheres. The microspheres were then washed with isopropanol for 12 h to remove the oil phase, followed by washing with deionized water for 48 h to remove the polyethylene glycol. Finally, the microspheres were freeze-dried to obtain dry porous sodium alginate / cellulose nanofiber gel microspheres.

[0044] Its optical microscope images are as follows Figure 5 As shown, the particle size is approximately 2 mm.

[0045] Example 2

[0046] This embodiment provides a method for preparing porous sodium alginate / cellulose nanofiber gel microspheres, including the following steps:

[0047] S1. Cellulose nanofibers (diameter 10-20 nm, length 10-100 μm, surface carboxyl group content 1.24 mmol / g) were added to deionized water and dispersed by stirring at 20000 r / min for 10 min using a high-speed homogenizer to obtain an aqueous dispersion of cellulose nanofibers with a concentration of 0.3wt%.

[0048] S2. Add 2wt% PEG-600 and 2wt% sodium alginate to the aqueous dispersion of cellulose nanofibers, stir to dissolve, and obtain an aqueous solution of sodium alginate / cellulose nanofibers / polyethylene glycol.

[0049] S3. An aqueous solution of sodium alginate / cellulose nanofibers / polyethylene glycol and liquid paraffin were mixed using a standard glass microfluidic chip at an input flow rate of 1:3 to obtain a water-in-oil emulsion with an average droplet diameter of 200 μm.

[0050] S4. The water-in-oil emulsion was fed into a stirred 2wt% CaCl2 solution through a conduit and reacted for 12 h to form microspheres. The microspheres were washed with isopropanol for 12 h to remove the oil phase and with deionized water for 48 h to remove polyethylene glycol. The microspheres were then freeze-dried to obtain dry porous sodium alginate / cellulose nanofiber gel microspheres.

[0051] Example 3

[0052] This embodiment provides a method for preparing porous sodium alginate / cellulose nanofiber gel microspheres, including the following steps:

[0053] S1. Cellulose nanofibers (diameter 10-20 nm, length 10-100 μm, surface carboxyl group content 1.24 mmol / g) were added to deionized water and dispersed by stirring at 20000 r / min for 10 min using a high-speed homogenizer to obtain an aqueous dispersion of cellulose nanofibers with a concentration of 0.3wt%.

[0054] S2. Add 4 wt% PEG-400 and 2 wt% sodium alginate to the aqueous dispersion of cellulose nanofibers, stir to dissolve, and obtain an aqueous solution of sodium alginate / cellulose nanofibers / polyethylene glycol.

[0055] S3. An aqueous solution of sodium alginate / cellulose nanofibers / polyethylene glycol and n-decane were mixed through a standard glass microfluidic chip at an input flow rate of 1:3 to obtain a water-in-oil emulsion with an average droplet diameter of 180 μm.

[0056] S4. The water-in-oil emulsion was fed into a stirred 2wt% CaCl2 solution through a conduit and reacted for 12 h to form microspheres. The microspheres were washed with isopropanol for 12 h to remove the oil phase and with deionized water for 48 h to remove polyethylene glycol. The microspheres were then freeze-dried to obtain dry porous sodium alginate / cellulose nanofiber gel microspheres.

[0057] Example 4

[0058] This embodiment provides a method for preparing porous sodium alginate / cellulose nanofiber gel microspheres, including the following steps:

[0059] S1. Cellulose nanofibers (diameter 10-20 nm, length 10-100 μm, surface carboxyl group content 1.24 mmol / g) were added to deionized water and dispersed by stirring at 20000 r / min for 10 min using a high-speed homogenizer to obtain an aqueous dispersion of cellulose nanofibers with a concentration of 0.3wt%.

[0060] S2. Add 3wt% PEG-400 and 2wt% sodium alginate to the aqueous dispersion of cellulose nanofibers, stir to dissolve, and obtain an aqueous solution of sodium alginate / cellulose nanofibers / polyethylene glycol.

[0061] S3. An aqueous solution of sodium alginate / cellulose nanofibers / polyethylene glycol and liquid paraffin were mixed using a standard glass microfluidic chip at an input flow rate of 1:3 to obtain a water-in-oil emulsion with an emulsion droplet diameter of 200 μm.

[0062] S4. The water-in-oil emulsion was fed into a stirred 2wt% CaCl2 solution through a conduit and reacted for 12 h to form microspheres. The microspheres were washed with isopropanol for 12 h to remove the oil phase and with deionized water for 48 h to remove polyethylene glycol. The microspheres were then freeze-dried to obtain dry porous sodium alginate / cellulose nanofiber gel microspheres.

[0063] Test Example 1: Heavy Metal Ion Adsorption Effect Test

[0064] The adsorption effect of microspheres on metal ions was investigated through static adsorption experiments. The specific steps were as follows: Pb was prepared at pH 5 and a concentration of 300 mg / L. 2+ Cu 2+ and Cd 2+100 mL of each solution was mixed with 100 mg of the gel microspheres prepared in this invention, and the mixture was shaken at 200 rpm at 25 °C until adsorption reached equilibrium. The supernatant was filtered through a 0.45 μm microporous membrane, and the concentration of heavy metal ions in the filtrate was determined by flame spectroscopy using an atomic absorption spectrophotometer (AAS, CFA-6880, Shimadzu Corporation, Japan), and the equilibrium adsorption capacity was calculated. The results are shown in Table 1 below.

[0065] Table 1. Equilibrium adsorption capacity of the microspheres prepared in Examples 1-4 and Comparative Examples 1-3 for the three metal ions.

[0066] Equilibrium adsorption capacity (mg / g) <![CDATA[Pb 2+ ]]> <![CDATA[Cu 2+ ]]> <![CDATA[Cd 2+ ]]> Example 1 298.9 190.6 162.2 Example 2 296.1 188.7 160.5 Example 3 293.3 187.5 158.1 Example 4 292.8 185.6 157.8 Comparative Example 1 255.4 167.4 138.5 Comparative Example 2 216.6 145.7 117.7 Comparative Example 3 150.6 112.7 82.8

[0067] As shown in Table 1, the microspheres prepared in Examples 1-4 have significantly better adsorption capacities for the three metal ions than the microspheres prepared in Comparative Examples 1-3.

[0068] In Comparative Example 1, since no porogen PEG-400 was added, the prepared microspheres did not have a significant macroporous structure, resulting in many adsorption sites inside the microspheres not being able to function fully, thus the adsorption capacity was significantly reduced compared to the example.

[0069] In Comparative Example 2, since no cellulose nanofibers and PEG-400 were added during the preparation process, compared with Comparative Example 1, the adsorption capacity of Comparative Example 2 was further reduced than that of Comparative Example 1 because cellulose nanofibers can increase the roughness of the sphere surface and improve the mechanical strength of sodium alginate composite microspheres, making the spheres less prone to collapse after drying.

[0070] In Comparative Example 3, since microfluidic methods were not used to prepare microspheres, but rather direct drop-addition was employed, the resulting microspheres had a larger particle size, approximately 2 mm. According to the formula for calculating the specific surface area of ​​a sphere, the specific surface area of ​​a microsphere is inversely proportional to its particle size. Therefore, the specific surface area of ​​the microspheres prepared in Comparative Example 3 was significantly reduced compared to that in Example 1, resulting in many active sites not being able to fully function, and thus the adsorption capacity was also greatly reduced.

[0071] Test Example 2: Reusability Test

[0072] The reusability of the gel microspheres prepared in Example 1 was verified using desorption-adsorption experiments. The specific steps are as follows: After adsorption of Pb... 2+ After being dissolved, the gel microspheres were placed in a 0.1 mol / L HCl solution and stirred for 2 h using a constant-temperature magnetic stirrer to displace the heavy metal ions adsorbed by the gel microspheres. The microspheres were then filtered, rinsed several times with deionized water, and used again to treat Pb according to the static adsorption method in Test Example 1. 2+Solution. Results showed that the gel microspheres prepared in Example 1, after 10 desorption-adsorption cycles, exhibited good adhesion to Pb. 2+ The removal rate can still reach more than 85% of the initial removal rate, and the spherical shape is well maintained without significant damage. This indicates that the porous sodium alginate / cellulose nanofiber gel microspheres prepared by this invention have good stability and reusability.

[0073] Test Example 3: Dynamic Adsorption Effect Test

[0074] Dynamic adsorption experiments were conducted in a self-made miniature adsorption column with an inner diameter of 5 mm and a height of 10 cm (filled with 8 cm of dried gel microspheres prepared in Example 1 of this invention, with a mass of 0.5 g). Pb at a concentration of 300 mg / L was introduced using a peristaltic pump at a flow rate of 7 mL / min. 2+ The solution passed through porous sodium alginate / cellulose nanofiber gel microspheres in a small adsorption column from bottom to top. Every 3 minutes, 0.3 mL of water sample was collected at the outlet and stored in a 10 mL test tube. Pb in the water sample was determined using an atomic absorption spectrophotometer (AAS, CFA-6880, Shimadzu Corporation, Japan) via flame spectroscopy. 2+ The concentration. The obtained dynamic adsorption curve is as follows. Figure 6 As shown. From Figure 6 It can be seen that in the first 36 minutes of adsorption, the adsorption column effectively adsorbs Pb passing through it. 2+ The adsorption efficiency of the simulated wastewater was 100%. The adsorption reached the breakthrough point of the adsorption column after 45 minutes, the breakthrough point after 120 minutes, and the adsorption reached saturation after 138 minutes.

[0075] Total adsorption capacity q of the adsorption column e (mg / g) and treated Pb 2+ The total volume of wastewater (V) can be calculated using the following formula: V = Q0t e In the formula: Q0 is the initial influent flow rate (mL / min), t e The time (in minutes) required to reach adsorption saturation was calculated. The volume of water sample treated in this test example was 966 ml. This demonstrates that the porous sodium alginate / cellulose nanofiber gel microspheres prepared in this invention also exhibit excellent treatment effects in the dynamic adsorption of heavy metal ions.

[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing porous sodium alginate / cellulose nanofiber gel microspheres, characterized in that, Includes the following steps: S1. Cellulose nanofibers are added to deionized water and dispersed using a high-speed homogenizer at 20,000 r / min for 5-10 min to obtain an aqueous dispersion of cellulose nanofibers; the weight percentage of the cellulose nanofibers in the aqueous dispersion is 0.2-0.3 wt%. S2. Polyethylene glycol and sodium alginate are added to an aqueous dispersion of cellulose nanofibers and stirred to dissolve, yielding an aqueous solution of sodium alginate / cellulose nanofibers / polyethylene glycol; the concentration of polyethylene glycol in the aqueous solution is 2-4 wt%, and the concentration of sodium alginate in the aqueous solution is 2-3 wt%. S3. An aqueous solution of sodium alginate / cellulose nanofibers / polyethylene glycol and an oil phase are mixed through a standard glass microfluidic chip to obtain a water-in-oil emulsion. The standard glass microfluidic chip has two inlets and one outlet. The aqueous solution of sodium alginate / cellulose nanofibers / polyethylene glycol and the oil phase are respectively input through the two inlets at a flow rate of 1:3-5. After the oil and water are mixed, the mixture is output through the outlet. S4. The water-in-oil emulsion is fed into a stirred CaCl2 solution through a conduit and reacted for 6-12 h to form microspheres. The oil phase is removed by washing with isopropanol for 4-12 h, and the microspheres are then washed with deionized water for 24-48 h to remove polyethylene glycol. The microspheres are then freeze-dried to obtain dry porous sodium alginate / cellulose nanofiber gel microspheres.

2. The method for preparing porous sodium alginate / cellulose nanofiber gel microspheres according to claim 1, characterized in that, The cellulose nanofibers described in step S1 have a diameter of 10-20 nm, a length of 10-100 μm, and contain carboxyl groups on their surface, with a carboxyl group content of 1-5 mmol / g.

3. The method for preparing porous sodium alginate / cellulose nanofiber gel microspheres according to claim 1, characterized in that, In step S2, the polyethylene glycol is selected from one of PEG-400, PEG-600, and PEG-800.

4. The method for preparing porous sodium alginate / cellulose nanofiber gel microspheres according to claim 1, characterized in that, In step S3, the oil phase is one of liquid paraffin, n-decane, and n-hexane.

5. The method for preparing porous sodium alginate / cellulose nanofiber gel microspheres according to claim 1, characterized in that, In step S3, the diameter of the water-in-oil emulsion droplets is 60-200 μm.

6. The method for preparing porous sodium alginate / cellulose nanofiber gel microspheres according to claim 1, characterized in that, In step S4, the concentration of the CaCl2 solution is 2-5 wt%.

7. A porous sodium alginate / cellulose nanofiber gel microsphere prepared by the preparation method according to any one of claims 1-6.

8. The application of porous sodium alginate / cellulose nanofiber gel microspheres prepared by the preparation method according to any one of claims 1-6 in the adsorption and removal of heavy metal ions in the aquatic environment.

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