Preparation method of sulfonated cassava starch capable of efficiently adsorbing methylene blue

Abstract

The invention discloses a preparation method of sulfonated cassava starch capable of efficiently adsorbing methylene blue, which comprises the following steps: S1, placing cassava starch milk in a microwave-ultrasonic reactor, and pretreating to obtain pretreated starch; s2, heating and melting the urea and sulfamic acid mixture to form a eutectic solvent, and stirring for the first time; s3, adding the pre-dried pretreated cassava starch, and stirring for the second time to carry out sulfonation reaction, so as to obtain the sulfonated cassava starch. No additional sulfonating agent is added in the preparation process, the preparation method is simple, reaction conditions are mild, toxic and harmful reagents are not used, aftertreatment is simple and convenient, and the obtained sulfonated cassava starch has the advantages of being high in adsorption rate, high in adsorption capacity and wide in applicable pH value.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of biobased materials, and particularly to a preparation method of sulfonated cassava starch for efficiently adsorbing methylene blue. Background Art

[0002] The problem of water resource pollution is gradually becoming a worldwide environmental threat. Methylene blue, which is widely used in the fields of printing and dyeing, biology, medicine, chemistry, etc., is a representative pollutant in wastewater. Methylene blue has certain toxicity and can have adverse effects on human organs, causing symptoms such as dizziness, headache, sweating, and confusion. Therefore, how to remove toxic and harmful methylene blue from wastewater has increasingly become an urgent technical problem to be solved.

[0003] Nowadays, there are various methods for removing pollutants in aqueous solutions, but the most widely used and relatively effective method is still the adsorption method. Therefore, developing an adsorbent for efficiently adsorbing methylene blue in wastewater has important scientific research significance and practical application value.

[0004] Due to its good biocompatibility and biodegradability, natural polymer adsorbents have become a very promising environmentally friendly material. Common natural polymers that can be modified into adsorbents mainly include starch, cellulose, chitin, etc., and starch is a natural polymer with extremely rich resources among them. At the same time, a large number of hydroxyl groups on the starch molecular chain provide excellent modification sites for the modification of starch. Therefore, in recent years, modifying starch into an adsorbent with excellent adsorption performance, environmental protection and biodegradability has gradually become a research hotspot.

[0005] Sulfonated starch, also known as starch sulfate ester, is a starch derivative prepared by introducing sulfonic acid groups (-SO3H) onto the hydroxyl groups of the starch chain. Sulfonated starch has better hydrophilic properties than the original starch due to the sulfonic acid groups existing on its starch chain. Therefore, it has a wide range of applications in the fields of food, medicine, and concrete modification. And the sulfonic acid groups in sulfonated starch dissociate in aqueous solution to generate -SO3 - ions, and these ions are extremely easy to have electrostatic adsorption with cationic dyes such as methylene blue. Therefore, sulfonated starch is a very promising cationic dye adsorbent.

[0006] However, existing starch sulfonation methods all have different degrees of defects, such as low degree of substitution; using a large amount of toxic and harmful chemical reagents (such as concentrated sulfuric acid, chlorosulfonic acid, pyridine, etc.) during the sulfonation process; generating a large amount of environmentally polluting waste such as sulfuric acid after the reaction and requiring a relatively cumbersome post-treatment process, etc. This runs counter to the original intention of using starch as an adsorbent - environmental friendliness. Therefore, finding a more green and lower-cost synthesis method for sulfonated starch is the key to the technical solution of the present invention.

[0007] The present invention uses a deep eutectic solvent formed by mixing non-toxic and harmless urea and sulfamic acid as a reaction solvent, and can sulfonate and modify starch without providing an additional sulfonating agent. Sulfonated starch with good adsorption performance can be synthesized under relatively mild reaction conditions, thus effectively overcoming the defects of the existing starch sulfonation methods, such as complex processes, use of toxic and harmful reagents, generation of a large amount of environmental pollutants, and cumbersome post-treatment processes. Summary of the Invention

[0008] In view of this, the present invention provides a method for preparing sulfonated cassava starch with high efficiency in adsorbing methylene blue.

[0009] To solve the above technical problems, the present invention adopts the following technical solutions:

[0010] A method for preparing sulfonated cassava starch with high efficiency in adsorbing methylene blue, comprising the following steps:

[0011] Step S1: Place cassava starch milk in a microwave-ultrasonic reactor for pretreatment to obtain pretreated starch;

[0012] Step S2: Heat and melt the mixture of urea and sulfamic acid to form a deep eutectic solvent, and then conduct the first stirring;

[0013] Step S3: Add the pre-dried pretreated cassava starch, and conduct the second stirring for sulfonation reaction to obtain sulfonated cassava starch.

[0014] Preferably, in step S1, the concentration of cassava starch milk is 100 g / L; the pretreatment time is 5 h.

[0015] Preferably, in step S1, the ultrasonic power of the microwave-ultrasonic reactor is 550 W, and the microwave power is 25 - 75 W.

[0016] Preferably, in step S2, the heating temperature of the mixture is 85 - 95 °C.

[0017] Preferably, in step S2, the molar ratio of sulfamic acid to urea in the deep eutectic solvent is 1:2.

[0018] Preferably, in steps S2 and S3, the stirring speed is 150 - 250 rpm, the first stirring time is 15 - 30 min, and the second stirring time is 3 - 5 h.

[0019] Preferably, in step S3, the molar ratio of the sugar units contained in cassava starch to urea in the deep eutectic solvent is preferably (1:10) - (1:20).

[0020] Preferably, in step S3, the pre-drying temperature is 55 - 65 °C, and the pre-drying time is 11 - 13 h.

[0021] Preferably, in the step S3, the sulfonation reaction time is 3 - 5 h, and the temperature is 85 - 95 °C.

[0022] Preferably, after the sulfonation reaction, the following treatments are also required:

[0023] Cool the product, filter and wash it with distilled water, dry it under vacuum, and grind it into powder;

[0024] Among them, the cooling temperature is 15 - 20 °C; the number of washing times is 3 - 5 times; the drying temperature is 43 - 47 °C; the drying time is 22 - 26 h; the median particle size of the powder is 14 - 16 μm.

[0025] The present invention has achieved the following technical effects compared with the prior art:

[0026] (1) The present invention can prepare cassava sulfonated starch through simple methods such as heating and stirring, filtration, and vacuum drying, with low equipment requirements, easy to implement, and low preparation costs;

[0027] (2) The present invention only uses two chemical raw materials, urea and aminosulfonic acid, to modify cassava starch, does not involve toxic and harmful raw materials, and does not produce a large amount of environmental pollutants; at the same time, the reaction conditions are mild, which is a more environmentally friendly synthesis method;

[0028] (3) The present invention has obtained a cationic dye - type modified starch adsorbent with a fast adsorption rate (the adsorption equilibrium can be reached in 7 - 12 min), a high adsorption capacity (the maximum adsorption amount is 133.7 mg / g), and a wide applicable pH range (pH = 5 - 10);

[0029] (4) The preparation method of the present invention is also applicable to other types of starch and has broad application prospects in the field of water treatment and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the scanning electron microscope image of the original starch of the present invention and the material prepared in Example 5;

[0031] Among them, (a) is the scanning electron microscope image of the original cassava starch magnified 1.00K X; (b) is the scanning electron microscope image of the original cassava starch magnified 4.00K X; (c) is the scanning electron microscope image of the sulfonated cassava starch magnified 1.00K X; (d) is the scanning electron microscope image of the sulfonated cassava starch magnified 4.00K X;

[0032] Figure 2 It is the adsorption amount change of the material prepared in Example 5 of the present invention in methylene blue solutions with different pH values and the pseudo - first - order kinetic adsorption fitting curve and pseudo - second - order kinetic adsorption fitting curve in methylene blue solutions with different concentrations;

[0033] Among them, (a) is the adsorption capacity variation diagram of the material prepared in Example 5 in methylene blue solutions with different pH values (concentration is 10 mg / g); (b) is the pseudo-first-order kinetic adsorption fitting curve and pseudo-second-order kinetic adsorption fitting curve of the material prepared in Example 5 in a methylene blue solution with a concentration of 1 mg / L; (c) is the pseudo-first-order kinetic adsorption fitting curve and pseudo-second-order kinetic adsorption fitting curve of the material prepared in Example 5 in a methylene blue solution with a concentration of 3 mg / L; (d) is the pseudo-first-order kinetic adsorption fitting curve and pseudo-second-order kinetic adsorption fitting curve of the material prepared in Example 5 in a methylene blue solution with a concentration of 9 mg / L. Detailed implementation manners

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0035] The present invention discloses a preparation method of sulfonated cassava starch for efficiently adsorbing methylene blue, including the following steps:

[0036] Step S1: Place cassava starch milk with a concentration of 100 g / L in a microwave-ultrasonic reactor. The ultrasonic power of the microwave-ultrasonic reactor is 550 W, the microwave power is 25 - 75 W, and pretreat for 5 h to obtain pretreated starch;

[0037] Step S2: After heating the urea and sulfamic acid mixture to 85 - 95 °C to melt and form a deep eutectic solvent, perform the first stirring. The stirring speed is 150 - 250 rpm, and the stirring time is 15 - 30 min. Among them, the molar ratio of sulfamic acid to urea in the deep eutectic solvent is 1:2;

[0038] Step S3: Then add the pretreated cassava starch pre-dried at 55 - 65 °C for 11 - 13 h, perform the second stirring. The stirring speed is 150 - 250 rpm, and the stirring time is 3 - 5 h, carry out the sulfonation reaction. The reaction time is 3 - 5 h, and the temperature is 85 - 95 °C to obtain sulfonated cassava starch.

[0039] In Step S3, the molar ratio of the sugar units contained in the cassava starch to the urea in the deep eutectic solvent is preferably (1:10) - (1:20).

[0040] After the sulfonation reaction, the following treatment is also required:

[0041] Cool the product, filter and wash it with distilled water, dry it under vacuum, and grind it into powder;

[0042] Among them, the cooling temperature is 15-20°C; the number of washing times is 3-5 times; the drying temperature is 43-47°C; the drying time is 22-26h; the median particle size of the powder is 14-16μm.

[0043] Example 1:

[0044] Add 22.22 g of urea and 17.98 g of sulfamic acid to a three-necked flask, heat it in a water bath at 90°C and stir at a stirring speed of 200 rpm. When the urea and sulfamic acid are completely melted to form a clear liquid, continue stirring for 30 min; weigh 3 g of pre-dried starch, add it to the three-necked flask, control the temperature at 85°C, and continue stirring and reacting for 5 h at a stirring speed of 250 rpm; after the reaction is completed, immerse the three-necked flask in cold water and cool it to 20°C to terminate the reaction. Filter and wash the contents of the three-necked flask 3 times with distilled water, then place it in a vacuum drying oven at 40°C and dry for 24 hours. After grinding it into powder, sulfonated starch is finally obtained.

[0045] In the adsorption performance test, a 100 mg / L methylene blue solution was selected for testing. Weigh 50 mg of sulfonated cassava starch and add it to 50 mL of a 200 mg / L methylene blue solution, shake and stir at an oscillation rate of 150 rpm and a temperature of 15°C. After oscillating for 60 min, the adsorption capacity of the sulfonated cassava starch is 78.3 mg / g.

[0046] Example 2:

[0047] Add 33.33 g of urea and 26.97 g of sulfamic acid to a three-necked flask, heat it in a water bath at 90°C and stir at a stirring speed of 200 rpm. When the urea and sulfamic acid are completely melted to form a clear liquid, continue stirring for 30 min; weigh 3 g of pre-dried starch, add it to the three-necked flask, control the temperature at 90°C, and continue stirring and reacting for 3 h at a stirring speed of 250 rpm; after the reaction is completed, immerse the three-necked flask in cold water and cool it to 20°C to terminate the reaction. Filter and wash the contents of the three-necked flask 3 times with distilled water, then place it in a vacuum drying oven at 40°C and dry for 24 hours. After grinding it into powder, sulfonated starch is finally obtained.

[0048] In the adsorption performance test, a 100 mg / L methylene blue solution was selected for testing. Weigh 50 mg of sulfonated cassava starch and add it to 50 mL of a 200 mg / L methylene blue solution, shake and stir at an oscillation rate of 150 rpm and a temperature of 15°C. After oscillating for 60 min, the adsorption capacity of the sulfonated cassava starch is 86.2 mg / g.

[0049] Example 3:

[0050] Add 22.22 g of urea and 17.98 g of sulfamic acid into a three-necked flask, heat it in a water bath at 90 °C and stir with a stirring speed of 250 rpm. When the urea and sulfamic acid are completely melted to form a clear liquid, continue stirring for 30 min; weigh 3 g of pre-dried starch, add it into the three-necked flask, control the temperature at 85 °C, and continue stirring and reacting for 5 h with a stirring speed of 250 rpm; after the reaction is completed, immerse the three-necked flask in cold water and cool it to 20 °C to terminate the reaction. Filter and wash the content of the three-necked flask with distilled water three times, then place it in a vacuum drying oven at 40 °C and dry for 24 hours. After grinding into powder, sulfonated starch is finally obtained.

[0051] In the adsorption performance test, a 100 mg / L methylene blue solution was selected for testing. Weigh 50 mg of sulfonated cassava starch, add it into 50 mL of 200 mg / L methylene blue solution, oscillate and stir. The oscillation rate is 150 rpm, the temperature is 15 °C. After oscillating for 60 min, the adsorption capacity of sulfonated cassava starch is 95.9 mg / g.

[0052] Example 4:

[0053] Add 44.44 g of urea and 35.96 g of sulfamic acid into a three-necked flask, heat it in a water bath at 85 °C and stir with a stirring speed of 200 rpm. When the urea and sulfamic acid are completely melted to form a clear liquid, continue stirring for 30 min; weigh 3 g of pre-dried starch, add it into the three-necked flask, control the temperature at 90 °C, and continue stirring and reacting for 5 h with a stirring speed of 200 rpm; after the reaction is completed, immerse the three-necked flask in cold water and cool it to 20 °C to terminate the reaction. Filter and wash the content of the three-necked flask with distilled water three times, then place it in a vacuum drying oven at 40 °C and dry for 24 hours. After grinding into powder, sulfonated starch is finally obtained.

[0054] In the adsorption performance test, a 100 mg / L methylene blue solution was selected for testing. Weigh 50 mg of sulfonated cassava starch, add it into 50 mL of 200 mg / L methylene blue solution, oscillate and stir. The oscillation rate is 150 rpm, the temperature is 15 °C. After oscillating for 60 min, the adsorption capacity of sulfonated cassava starch is 109.2 mg / g.

[0055] Example 5:

[0056] Add 44.44 g of urea and 35.96 g of sulfamic acid to a three-necked flask, heat it in a water bath at 90 °C and stir at a stirring speed of 200 rpm. When the urea and sulfamic acid are completely melted to form a clear liquid, continue stirring for 30 min; weigh 3 g of pre-dried starch, add it to the three-necked flask, control the temperature at 90 °C, and continue stirring and reacting for 5 h at a stirring speed of 200 rpm; after the reaction is completed, immerse the three-necked flask in cold water and cool it to 20 °C to terminate the reaction. Filter and wash the contents of the three-necked flask 3 times with distilled water, then place it in a vacuum drying oven at 40 °C and dry for 24 hours. After grinding into powder, sulfonated starch is finally obtained.

[0057] In the adsorption performance test, a 100 mg / L methylene blue solution was selected for testing. Weigh 50 mg of sulfonated cassava starch and add it to 50 mL of a 200 mg / L methylene blue solution, then oscillate and stir at an oscillation rate of 150 rpm and a temperature of 15 °C. After oscillating for 60 min, the adsorption capacity of the sulfonated cassava starch is 118.3 mg / g.

[0058] As Figure 1 shown, it is the scanning electron microscope image of the original starch of the present invention and the material prepared in Example 5;

[0059] Among them, (a) is the scanning electron microscope image of the original cassava starch magnified 1.00KX; (b) is the scanning electron microscope image of the original cassava starch magnified 4.00KX; (c) is the scanning electron microscope image of the sulfonated cassava starch magnified 1.00KX; (d) is the scanning electron microscope image of the sulfonated cassava starch magnified 4.00KX;

[0060] It can be seen from the scanning electron microscope images that the original cassava starch is spherical or hemispherical particles with a dense and smooth surface. After modification, ring-shaped irregular protrusions appear on the surface of the sulfonated cassava starch, and at the same time, part of the surface of the starch particles becomes rougher.

[0061] As Figure 2 shown, it is the adsorption capacity change of the material prepared in Example 5 of the present invention in methylene blue solutions with different pH values and the pseudo-first-order kinetic adsorption fitting curve and pseudo-second-order kinetic adsorption fitting curve diagrams in methylene blue solutions with different concentrations;

[0062] Among them, (a) is the adsorption capacity change diagram of the material prepared in Example 5 in methylene blue solutions with different pH values (concentration is 10 mg / g);

[0063] It can be seen from the figure that the sulfonated cassava starch has good adsorption effects under a wide range of pH values (pH = 5 - 10), and the removal rate can reach 95.3%;

[0064] (b) is the pseudo-first-order kinetic adsorption fitting curve and pseudo-second-order kinetic adsorption fitting curve of the material prepared in Example 5 in a methylene blue solution with a concentration of 1 mg / L;

[0065] Among them, the correlation coefficient R of the pseudo-first-order kinetic adsorption fitting curve 2 = 0.9912, and the correlation coefficient R of the pseudo-second-order kinetic adsorption fitting curve 2 = 0.9834;

[0066] (c) is the pseudo-first-order kinetic adsorption fitting curve and pseudo-second-order kinetic adsorption fitting curve of the material prepared in Example 5 in a methylene blue solution with a concentration of 3 mg / L;

[0067] Among them, the correlation coefficient R of the pseudo-first-order kinetic adsorption fitting curve 2 = 0.9964, and the correlation coefficient R of the pseudo-second-order kinetic adsorption fitting curve 2 = 0.9892;

[0068] (d) is the pseudo-first-order kinetic adsorption fitting curve and pseudo-second-order kinetic adsorption fitting curve of the material prepared in Example 5 in a methylene blue solution with a concentration of 9 mg / L;

[0069] Among them, the correlation coefficient R of the pseudo-first-order kinetic adsorption fitting curve 2 = 0.9988, and the correlation coefficient R of the pseudo-second-order kinetic adsorption fitting curve 2 = 0.9907;

[0070] Example 6:

[0071] Add 10 g of tapioca starch and 100 mL of deionized water to a three-necked flask, place it in a reactor, with a microwave power of 550 W and an ultrasonic power of 25 W, and react for 5 h to obtain pretreated tapioca starch. Add 44.44 g of urea and 35.96 g of sulfamic acid to the three-necked flask, heat it in a water bath at 90 °C and stir, with a stirring speed of 200 rpm. When the urea and sulfamic acid are completely melted to form a clear liquid, continue stirring for 30 min; weigh 3 g of pre-dried pretreated tapioca starch, add it to the three-necked flask, control the temperature at 90 °C, and continue stirring and reacting for 5 h, with a stirring speed of 200 rpm; after the reaction is completed, immerse the three-necked flask in cold water and cool it to 20 °C to terminate the reaction. Filter and wash the contents of the three-necked flask with distilled water 3 times, then place it in a vacuum drying oven at 40 °C and dry for 24 hours. Grind it into powder to finally obtain sulfonated starch.

[0072] In the adsorption performance test, a 100 mg / L methylene blue solution was selected for the test. 50 mg of sulfonated cassava starch was weighed and added to 50 mL of a 200 mg / L methylene blue solution, followed by shaking and stirring. The shaking rate was 150 rpm, and the temperature was 15 °C. After shaking for 60 min, the adsorption capacity of the sulfonated cassava starch was 120.3 mg / g.

[0073] Example 7:

[0074] 10 g of cassava starch and 100 mL of deionized water were added to a three-necked flask, which was placed in a reactor. The microwave power was 550 W, and the ultrasonic power was 75 W. After reacting for 5 h, pretreated cassava starch was obtained. 44.44 g of urea and 35.96 g of aminosulfonic acid were added to the three-necked flask, and the mixture was heated in a water bath at 90 °C with stirring at a speed of 200 rpm. After the urea and aminosulfonic acid were completely melted to form a clear liquid, stirring was continued for 30 min. 3 g of pre-dried pretreated cassava starch was weighed and added to the three-necked flask. The temperature was controlled at 90 °C, and the reaction was continued with stirring for 5 h at a speed of 200 rpm. After the reaction was completed, the three-necked flask was immersed in cold water and cooled to 20 °C to terminate the reaction. The contents of the three-necked flask were filtered and washed 3 times with distilled water and then placed in a vacuum drying oven at 40 °C for 24 h. After grinding into powder, sulfonated starch was finally obtained.

[0075] In the adsorption performance test, a 100 mg / L methylene blue solution was selected for the test. 50 mg of sulfonated cassava starch was weighed and added to 50 mL of a 200 mg / L methylene blue solution, followed by shaking and stirring. The shaking rate was 150 rpm, and the temperature was 15 °C. After shaking for 60 min, the adsorption capacity of the sulfonated cassava starch was 132.6 mg / g.

[0076] Example 8:

[0077] 10 g of cassava starch and 100 mL of deionized water were added to a three-necked flask, which was placed in a reactor. The microwave power was 550 W, and the ultrasonic power was 50 W. After reacting for 5 h, pretreated cassava starch was obtained. 44.44 g of urea and 35.96 g of aminosulfonic acid were added to the three-necked flask, and the mixture was heated in a water bath at 90 °C with stirring at a speed of 200 rpm. After the urea and aminosulfonic acid were completely melted to form a clear liquid, stirring was continued for 30 min. 3 g of pre-dried pretreated cassava starch was weighed and added to the three-necked flask. The temperature was controlled at 90 °C, and the reaction was continued with stirring for 5 h at a speed of 200 rpm. After the reaction was completed, the three-necked flask was immersed in cold water and cooled to 20 °C to terminate the reaction. The contents of the three-necked flask were filtered and washed 3 times with distilled water and then placed in a vacuum drying oven at 40 °C for 24 h. After grinding into powder, sulfonated starch was finally obtained.

[0078] In the adsorption performance test, a 100 mg / L methylene blue solution was selected for the test. 50 mg of sulfonated cassava starch was weighed and added to 50 mL of a 200 mg / L methylene blue solution, followed by shaking and stirring at an oscillation rate of 150 rpm and a temperature of 15 °C. After 60 minutes of oscillation, the adsorption capacity of the sulfonated cassava starch was 133.7 mg / g.

[0079] Among them, Table 1 shows the adsorption kinetic parameters of Example 5 for methylene blue dyes at different concentrations (1 mg / L, 3 mg / L, 9 mg / L). The fitting degree of the pseudo-first-order kinetic equation is higher, so the adsorption of sulfonated cassava starch can be described by the pseudo-first-order kinetics.

[0080] Table 1 Adsorption kinetic parameters of sulfonated cassava starch for methylene blue

[0081]

[0082] The above is only a preferred embodiment of the present invention, and it does not limit the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and decorations made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A preparation method of sulfonated cassava starch for efficiently adsorbing methylene blue, characterized in that, It includes the following steps: Step S1: Place the cassava starch milk in a microwave-ultrasonic reactor for pretreatment to obtain pretreated starch; Step S2: Heat and melt the mixture of urea and sulfamic acid to form a deep eutectic solvent, and then conduct the first stirring; Step S3: Add the pre-dried pretreated cassava starch, and conduct the second stirring for sulfonation reaction to obtain sulfonated cassava starch.

2. The preparation method of a sulfonated cassava starch for efficiently adsorbing methylene blue according to claim 1, wherein In the said Step S1, the concentration of the cassava starch milk is 100 g / L; the pretreatment time is 5 h.

3. The preparation method of a sulfonated cassava starch for efficiently adsorbing methylene blue according to claim 1, wherein In the said Step S1, the ultrasonic power of the microwave-ultrasonic reactor is 550 W, and the microwave power is 25 - 75 W.

4. The preparation method of a sulfonated cassava starch for efficiently adsorbing methylene blue according to claim 1, characterized in that, In the said Step S2, the heating temperature of the mixture is 85 - 95 °C.

5. The preparation method of a sulfonated cassava starch for efficiently adsorbing methylene blue according to claim 1, characterized in that, In the said Step S2, the molar ratio of sulfamic acid to urea in the deep eutectic solvent is 1:

2.

6. The preparation method of a sulfonated cassava starch for efficiently adsorbing methylene blue according to claim 1, characterized in that In the said Step S2 and Step S3, the stirring speed is 150 - 250 rpm, the first stirring time is 15 - 30 min, and the second stirring time is 3 - 5 h.

7. The preparation method of a sulfonated cassava starch for efficiently adsorbing methylene blue according to claim 1, wherein, In the said Step S3, the molar ratio of the sugar units contained in the cassava starch to the urea in the deep eutectic solvent is preferably (1:10) - (1:20).

8. The preparation method of sulfonated cassava starch for efficiently adsorbing methylene blue according to claim 1, characterized in that, In the said Step S3, the pre-drying temperature is 55 - 65 °C, and the pre-drying time is 11 - 13 h.

9. The preparation method of a sulfonated cassava starch for efficiently adsorbing methylene blue according to claim 1, characterized in that, In the said Step S3, the sulfonation reaction time is 3 - 5 h, and the temperature is 85 - 95 °C.

10. The preparation method of a sulfonated cassava starch for efficiently adsorbing methylene blue according to claim 1, wherein, After the said sulfonation reaction ends, the following treatment is also required: Cool the product, filter and wash it with distilled water, dry it under vacuum, and grind it into powder; Among them, the cooling temperature is 15 - 20 °C; the number of times of filtration and washing is 3 - 5 times; the drying temperature is 43 - 47 °C; the drying time is 22 - 26 h; the median particle size of the powder is 14 - 16 μm.

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