Enzyme-modified starch adsorbent and preparation method thereof

Abstract

The present invention discloses an enzymatically modified starch adsorbent and a preparation method thereof, and relates to the field of adsorbent technology. The method comprises the following steps: adding corn starch to deionized water and performing gradient temperature-ultrasound synergistic treatment, first subjecting the pretreated starch solution to cold plasma treatment under a nitrogen atmosphere, adjusting the pH, heating, and then adding a complex enzyme for enzymatic hydrolysis, adding modified sulfonic acid sodium alginate for reaction, and then adding epichlorohydrin and stirring the reaction; then subjecting the solution to cold plasma treatment under a nitrogen atmosphere, adding pretreated attapulgite for reaction, adding ammonium sulfate and acrylamide and excluding air, and then filtering, washing, and drying the solution after the reaction to obtain an enzymatically modified starch adsorbent. The pretreatment of corn starch by the present invention effectively improves the reactivity of starch granules; the introduction of ingredients such as pretreated attapulgite further improves its adsorption capacity and adsorption capacity stability. Therefore, the adsorbent of the present invention has a wider application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of adsorbents, and in particular to an enzymatically modified starch adsorbent and a preparation method thereof. Background Art

[0002] Starch is a natural high-molecular-weight polysaccharide formed by the polycondensation of glucose. It is one of the most abundant renewable substances in nature, is biodegradable, and poses no environmental pollution. The presence of a large number of reactive hydroxyl groups in its molecular chain provides a structural basis for starch modification. Modified starch, based on the inherent properties of natural starch, utilizes physical, chemical, or enzymatic treatments to introduce new functional groups or alter the size of starch molecules and the properties of starch granules to improve the performance and expand its application range. This alters the starch's natural properties, making it more suitable for specific applications. As an adsorbent, modified starch is widely used in food, medicine, agriculture, environmental protection, and other fields due to its safety, non-toxicity, and good biodegradability.

[0003] Porous starch is a natural biosorbent. Currently, amylase enzymatic hydrolysis is often used to form many microporous structures on the surface of starch granules, which helps to increase the specific surface area and pore volume of starch, thereby improving the adsorption capacity of starch. However, the inappropriate enzymatic method will cause porous starch to have defects such as small specific surface area, small pore volume, shallow pore depth, poor particle firmness, and easy breakage. These problems seriously affect the adsorption effect and practical application of porous starch. In order to solve this technical problem, the patent technology document CN105642244B proposes a preparation method of a cross-linking-enzymatic hydrolysis composite ultrafine modified starch adsorbent, which includes the following steps: (1) using an ultrafine grinder to ultrafinely grind corn, sweet potato, and potato starch to ultrafine starch with a particle size of 10-50μm; (2) mixing the three ultrafine starches in a mass ratio of 1:4:3 and adding them into water and stirring to obtain a starch emulsion; (3) adjusting the pH of the starch emulsion to 7.5-8.5, adding a A quantitative sodium tripolyphosphate solution is cross-linked at 75-80°C for 1-1.5 hours; (4) the cross-linked starch emulsion is centrifuged and dehydrated, washed with deionized water, and then freeze-dried; (5) the cross-linked starch is added with water to form a starch emulsion again, the pH is adjusted to 6.5-7.5, and then α-amylase and isoamylase are added to react at 50°C for 12-15 hours; (6) the enzymatically hydrolyzed starch emulsion is centrifuged, washed, dried, and passed through a 40-100 mesh sieve to obtain a cross-linked-enzymatically hydrolyzed composite ultrafine modified starch. The modified starch of the invention significantly increases the specific surface area and mechanical strength of the porous starch, and improves the adsorption capacity of the porous starch for harmful components, especially heavy metal elements.

[0004] However, the adsorption performance and adsorption stability of the enzymatically modified starch adsorbents prepared by these existing solutions still need to be improved. Summary of the Invention

[0005] The purpose of the present invention is to provide an enzymatically modified starch adsorbent and a preparation method thereof, to solve the following technical problems:

[0006] Existing enzymatically modified starch adsorbents still have problems with unsatisfactory adsorption performance and adsorption performance stability.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] A method for preparing an enzymatically modified starch adsorbent comprises the following steps:

[0009] Step S1: adding corn starch to deionized water, and then performing gradient temperature increase-ultrasound synergistic treatment to obtain a pretreated starch solution;

[0010] Step S2: Under a nitrogen atmosphere, the pretreated starch solution is subjected to cold plasma treatment, and then the pH is adjusted to 5-6, the temperature is raised to 40-50°C, a complex enzyme is added, and enzymatic hydrolysis is carried out at 40-50°C for 20-25 hours. After high temperature treatment, an enzymatically hydrolyzed starch solution is obtained;

[0011] Step S3: adding modified sodium sulfonate alginate to the enzymatically hydrolyzed starch solution, stirring and reacting at 35-40° C. for 1.5-2 hours, then adding epichlorohydrin and stirring and reacting for 2.5-3 hours to obtain a pre-cross-linked starch solution;

[0012] Step S4: Under a nitrogen atmosphere, the pre-cross-linked starch solution is subjected to cold plasma treatment, and then the pre-treated attapulgite is added and stirred for 0.8-1 hour, and then ammonium sulfate and acrylamide are added and the air is excluded, and the mixture is reacted at 55-60° C. for 3-4 hours, and then filtered, washed, and dried to obtain an enzymatically modified starch adsorbent;

[0013] The ratio of deionized water to corn starch in step S1 is 100-120 mL: 30-35 g;

[0014] The gradient heating-ultrasound synergistic treatment in step S1 is first performed at 20-30°C with a power of 280-300 W, a frequency of 35-40 kHz, and a duration of 10-15 min for a first ultrasonic treatment, followed by a second ultrasonic treatment at 65-66°C with a power of 280-300 W, a frequency of 30-40 kHz, and a duration of 8-10 min;

[0015] The complex enzyme in step S2 is obtained by mixing α-amylase and saccharifying enzyme;

[0016] The preparation method of the modified sulfonic acid sodium alginate in step S3 is as follows:

[0017] Sodium alginate is added to deionized water, and the mixture is stirred at 200-300 r / min at 50-60°C for 1-2 hours. Then, sulfamic acid is added, and the mixture is stirred until the pH value is adjusted to 8-9 with sodium hydroxide solution, and the mixture is stirred for 3-4 hours. After cooling to 20-30°C, ethanol is added, and the mixture is stirred until the mixture is evenly mixed, filtered, washed, and dried to obtain modified sulfonic acid sodium alginate.

[0018] The preparation method of the pretreated attapulgite in step S4 is as follows:

[0019] The attapulgite is added to the hydrochloric acid solution, and then stirred at 300-400 r / min at 60-80° C. for 12-15 hours, and then filtered and dried to obtain the pretreated attapulgite.

[0020] Preferably, the gas flow rate during the cold plasma treatment in step S2 is 8-10 L / min, the power is 200-300 W, the voltage is 50-100 V, and the total treatment time is 6-10 min;

[0021] In step S2, the ratio of the pretreated starch solution to the complex enzyme is 130-155 g: 0.295-0.345 g;

[0022] The temperature of the high temperature treatment in step S2 is 80-90° C., and the treatment time is 10-20 minutes.

[0023] Preferably, the dosage ratio of α-amylase to saccharifying enzyme in the complex enzyme is 0.075-0.085 g: 0.22-0.26 g.

[0024] Preferably, the usage ratio of the enzymatic starch solution, modified sodium sulfonate alginate, and epichlorohydrin in step S3 is 130-155 g: 4-5 g: 1-2 mL.

[0025] Preferably, in the preparation process of the modified sulfonic acid sodium alginate, the usage ratio of deionized water, sodium alginate, aminosulfonic acid, and ethanol is 200 mL: 5-10 g: 2.4-7.3 g: 200-400 mL;

[0026] The concentration of the sodium hydroxide solution is 0.1 mol / L.

[0027] Preferably, the gas flow rate during the cold plasma treatment in step S4 is 8-10 L / min, the power is 200-300 W, the voltage is 50-100 V, and the total treatment time is 8-10 min;

[0028] In step S4, the usage ratio of the pre-cross-linked starch solution, pretreated attapulgite, ammonium sulfate, and acrylamide is 135-162 g: 2.5-3 g: 0.2-0.3 g: 8-10 g.

[0029] Preferably, the usage ratio of the hydrochloric acid solution and the attapulgite is 100-150 mL: 5-8 g;

[0030] The concentration of the hydrochloric acid solution is 1 mol / L.

[0031] As a further embodiment of the present invention.

[0032] Beneficial effects of the present invention:

[0033] The present invention provides an enzymatically modified starch adsorbent and a preparation method thereof. The present invention effectively improves the adsorption capacity and adsorption capacity stability of the starch adsorbent through the following method.

[0034] (1) During the preparation of the pretreated starch solution, the first ultrasonic treatment changes the surface microstructure of the starch granules, reducing the particle size and increasing the specific surface area, providing more contact sites for subsequent reactions with other reagents, which is beneficial for the binding of enzymes and starch molecules during enzymatic hydrolysis. The specific temperature and ultrasonic wave synergistically act during the second ultrasonic treatment, further destroying the hydrogen bonds and other forces within the starch molecules, causing the molecular chains to stretch to a certain extent, further increasing the reactivity of the starch, thereby accelerating the enzymatic hydrolysis reaction rate and making the enzymatic hydrolysis more complete. Ultimately, the adsorbent can form a more complex, uniform, and porous network structure after subsequent graft copolymerization reactions.

[0035] (2) Cold plasma treatment under specific conditions during the preparation of enzymatic starch solution will make the surface of starch granules rough, forming many tiny grooves and pores, and will also increase the number of active sites and functional groups on the surface, thereby significantly increasing the specific surface area of ​​starch and the contact area between starch molecules and enzymes, making some chemical bonds on starch molecules more easily recognized and broken by enzymes; at the same time, it will also introduce some nitrogen-containing active groups on the surface of starch molecules, enhancing the binding force between the adsorbent and pollutants. Combined with the sufficient enzymatic hydrolysis of α-amylase and saccharifying enzyme compounded in a specific ratio under specific conditions, the starch molecules will form a more stable structure. Therefore, this process further improves the adsorption capacity and adsorption stability of the adsorbent.

[0036] (3) The sulfonic acid groups in the modified sulfonic acid sodium alginate of the present invention can interact with groups such as hydroxyl groups in the enzymatically hydrolyzed starch solution. When epichlorohydrin is subsequently added for cross-linking reaction, these interactions can promote the formation of a more complex, more uniform, and more stable cross-linked network structure. This cross-linked network structure not only enhances the stability of the adsorbent, enabling it to maintain good adsorption performance under different environmental conditions, but also improves the mechanical strength of the adsorbent and reduces the breakage and loss of the adsorbent during use. At the same time, since sodium alginate itself has a certain degree of hydrophilicity, its combination with the hydrophilicity of the sulfonic acid groups enables the modified sulfonic acid sodium alginate to contact and interact with pollutant molecules more quickly, thereby accelerating the adsorption rate.

[0037] (4) The convexopolysaccharide has a special crystal structure and a large specific surface area. The present invention fills the pretreated convexopolysaccharide into the network structure of the enzymatically modified starch, which can provide more adsorption sites for the enzymatically modified starch adsorbent, enhance the ion exchangeability of the adsorbent, and support and reinforce the network structure, so that it can be more stably combined with more adsorbed substances; at the same time, the convexopolysaccharide can adsorb a part of the substance through physical adsorption, while the enzymatically modified starch can react chemically with the adsorbed substance or produce a complexation through its own active groups. The combination of the two can further enhance the overall adsorption performance of the adsorbent.

[0038] Therefore, the modified starch adsorbent prepared by the present invention has more excellent adsorption performance, adsorption performance stability, and broad application prospects. DETAILED DESCRIPTION

[0039] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0040] The properties and sources of some raw materials in the present invention are as follows:

[0041] α-Amylase (BAN 480L) was purchased from Novozymes China Biotechnology Co., Ltd.; saccharifying enzyme (AMG 300L) was purchased from Novozymes China Biotechnology Co., Ltd.; attapulgite was purchased from Hubei Yongkuo Technology Co., Ltd., CAS: 12174-11-7.

[0042] Example 1: A method for preparing an enzymatically modified starch adsorbent is as follows:

[0043] S1: 30 g corn starch was added to 100 mL deionized water, and the solution was first sonicated at 20°C with a power of 280 W and a frequency of 35 kHz for 10 min. The solution was then subjected to a secondary sonication at 65°C with a power of 280 W and a frequency of 30 kHz for 8 min to obtain a pretreated starch solution.

[0044] S2: Under a nitrogen atmosphere, 130 g of pretreated starch solution was treated with cold plasma at a gas flow rate of 8 L / min, a power of 200 W, a voltage of 50 V, and a total treatment time of 6 min. The pH was then adjusted to 5 with a 0.1 mol / L citric acid solution. After heating to 40°C, 0.075 g of α-amylase and 0.22 g of saccharifying enzyme were added. The solution was enzymatically hydrolyzed at 40°C for 20 h, and finally subjected to high-temperature treatment at 80°C for 10 min to obtain an enzymatically hydrolyzed starch solution.

[0045] S3: Add 5 g of sodium alginate to 200 mL of deionized water, stir at 200 r / min at 50°C for 1 h, then slowly add 2.4 g of aminosulfonic acid, stir evenly, add 0.1 mol / L sodium hydroxide solution to adjust the pH to 8 and stir for 3 h. After cooling to 20°C, slowly add 200 mL of ethanol, stir evenly, collect the precipitate by suction filtration, wash the precipitate with ethanol three times, and finally dry at 40-50°C to obtain modified sulfonic acid sodium alginate;

[0046] S4: Add 4 g of modified sulfonic acid sodium alginate to 130 g of enzymatically hydrolyzed starch solution, stir and react at 35°C for 1.5 h, then add 1 mL of epichlorohydrin and stir and react at 35°C for 2.5 h to obtain a pre-crosslinked starch solution;

[0047] S5: adding 5 g of attapulgite to 100 mL of 1 mol / L hydrochloric acid solution, stirring at 300 rpm for 12 h at 60° C., filtering, and drying to obtain pretreated attapulgite;

[0048] S6: Under a nitrogen atmosphere, 135 g of pre-cross-linked starch liquid was subjected to cold plasma treatment with a gas flow rate of 8 L / min, a power of 200 W, a voltage of 50 V, and a total treatment time of 8 min. Then, 2.5 g of pretreated attapulgite was added and stirred for 0.8 h. Then, 0.2 g of ammonium sulfate and 8 g of acrylamide were added, nitrogen was introduced to exclude air, and the mixture was reacted at 55 ° C for 3 h. Then, the mixture was filtered and the precipitate was washed with deionized water 3 times. Finally, the mixture was dried at 55 ° C to obtain an enzymatically modified starch adsorbent.

[0049] Example 2: A method for preparing an enzymatically modified starch adsorbent is as follows:

[0050] S1: 33 g corn starch was added to 110 mL deionized water, and the mixture was first sonicated at 25°C with a power of 290 W and a frequency of 38 kHz for 13 min. The mixture was then sonicated again at 65.5°C with a power of 290 W and a frequency of 35 kHz for 9 min to obtain a pretreated starch solution.

[0051] S2: Under a nitrogen atmosphere, 143 g of pretreated starch solution was treated with cold plasma at a gas flow rate of 9 L / min, a power of 250 W, a voltage of 80 V, and a total treatment time of 8 min. The pH was then adjusted to 5.5 with a 0.1 mol / L citric acid solution. The solution was heated to 45°C and then 0.08 g of α-amylase and 0.24 g of saccharifying enzyme were added. The solution was enzymatically hydrolyzed at 45°C for 23 h, and finally subjected to high-temperature treatment at 85°C for 15 min to obtain an enzymatically hydrolyzed starch solution.

[0052] S3: 8 g of sodium alginate was added to 200 mL of deionized water, and the mixture was stirred at 250 r / min at 55°C for 1.5 h. Then, 4.85 g of aminosulfonic acid was slowly added. After stirring, 0.1 mol / L sodium hydroxide solution was added to adjust the pH to 8.5 and the mixture was stirred for 3.5 h. After cooling to 25°C, 300 mL of ethanol was slowly added. After stirring, the precipitate was collected by filtration and washed with ethanol four times. Finally, the modified sulfonic acid alginate was obtained by drying at 45°C.

[0053] S4: Add 4.5 g of modified sulfonic acid sodium alginate to 143 g of enzymatically hydrolyzed starch solution, stir and react at 38°C for 1.8 h, then add 1.5 mL of epichlorohydrin and stir and react at 38°C for 2.8 h to obtain a pre-crosslinked starch solution;

[0054] S5: adding 7 g of attapulgite to 130 mL of 1 mol / L hydrochloric acid solution, stirring at 70°C and 350 r / min for 14 h, filtering, and drying to obtain pretreated attapulgite;

[0055] S6: Under a nitrogen atmosphere, 149 g of pre-cross-linked starch liquid was subjected to cold plasma treatment with a gas flow rate of 9 L / min, a power of 250 W, a voltage of 80 V, and a total treatment time of 9 min. Then, 2.8 g of pretreated attapulgite was added and stirred for 0.9 h. Then, 0.25 g of ammonium sulfate and 9 g of acrylamide were added, nitrogen was introduced to exclude air, and the mixture was reacted at 58 ° C for 3.5 h. The mixture was then filtered and the precipitate was washed with deionized water 4 times. Finally, the mixture was dried at 58 ° C to obtain an enzymatically modified starch adsorbent.

[0056] Example 3: A method for preparing an enzymatically modified starch adsorbent is as follows:

[0057] S1: 35 g corn starch was added to 120 mL deionized water, and the mixture was first sonicated at 30°C with a power of 300 W and a frequency of 40 kHz for 15 min. Then, the mixture was sonicated again at 66°C with a power of 300 W and a frequency of 40 kHz for 10 min to obtain a pretreated starch solution.

[0058] S2: Under a nitrogen atmosphere, 155 g of pretreated starch solution was treated with cold plasma at a gas flow rate of 10 L / min, a power of 300 W, a voltage of 100 V, and a total treatment time of 10 min. The pH was then adjusted to 6 with a 0.1 mol / L citric acid solution. The solution was heated to 50°C and then 0.085 g of α-amylase and 0.26 g of saccharifying enzyme were added. The solution was enzymatically hydrolyzed at 50°C for 25 h, and finally subjected to high-temperature treatment at 90°C for 20 min to obtain an enzymatically hydrolyzed starch solution.

[0059] S3: Add 10 g of sodium alginate to 200 mL of deionized water, stir at 300 rpm for 2 h at 60°C, then slowly add 7.3 g of aminosulfonic acid, stir evenly, add 0.1 mol / L sodium hydroxide solution to adjust the pH to 9 and stir for 4 h. After cooling to 30°C, slowly add 400 mL of ethanol, stir evenly, collect the precipitate by suction filtration, wash the precipitate with ethanol 5 times, and finally dry at 50°C to obtain modified sulfonic acid sodium alginate;

[0060] S4: Add 5 g of modified sulfonic acid sodium alginate to 155 g of enzymatically hydrolyzed starch solution, stir and react at 40°C for 2 h, then add 2 mL of epichlorohydrin and stir and react at 40°C for 3 h to obtain a pre-crosslinked starch solution;

[0061] S5: adding 8 g of attapulgite to 150 mL of 1 mol / L hydrochloric acid solution, stirring at 400 rpm for 15 h at 80° C., filtering, and drying to obtain a pretreated attapulgite;

[0062] S6: Under a nitrogen atmosphere, 162 g of pre-cross-linked starch liquid was treated with cold plasma at a gas flow rate of 10 L / min, a power of 300 W, a voltage of 100 V, and a total treatment time of 10 min. Then, 3 g of pretreated attapulgite was added and stirred for 1 h. Then, 0.3 g of ammonium sulfate and 10 g of acrylamide were added, nitrogen was introduced to exclude air, and the mixture was reacted at 60 ° C for 4 h. The mixture was then filtered and the precipitate was washed with deionized water 5 times. Finally, the mixture was dried at 60 ° C to obtain an enzymatically modified starch adsorbent.

[0063] Comparative Example 1:

[0064] Compared with Example 1, this comparative example only replaces the "first ultrasonic treatment at 20°C with a power of 280W, a frequency of 35kHz, and a duration of 10min at 20°C, and then the second ultrasonic treatment at 65°C with a power of 280W, a frequency of 30kHz, and a duration of 8min" in the preparation process of the pretreated starch solution with "ultrasonic treatment at 65°C with a power of 280W, a frequency of 30kHz, and a duration of 18min". The remaining steps and parameters are the same, and this comparative example will not be repeated, and the enzymatic modified starch adsorbent is finally obtained.

[0065] Comparative Example 2:

[0066] Compared with Example 1, this comparative example only replaces the "first ultrasonic treatment at 20°C with a power of 280W, a frequency of 35kHz, and a duration of 10min at 20°C, and then a secondary ultrasonic treatment at 65°C with a power of 280W, a frequency of 30kHz, and a duration of 8min" in the preparation process of the pretreated starch solution with "stirring treatment at 300r / min for 18min at 65°C". The remaining steps and parameters are the same, and they will not be repeated in this comparative example. Finally, an enzymatically modified starch adsorbent is obtained.

[0067] Comparative Example 3:

[0068] Compared with Example 1, this comparative example only does not perform cold plasma treatment during the preparation of the enzymatically hydrolyzed starch solution. The remaining steps and parameters are the same and will not be repeated in this comparative example. Finally, an enzymatically modified starch adsorbent is obtained.

[0069] Comparative Example 4:

[0070] Compared with Example 1, this comparative example only replaces the "0.075g of α-amylase and 0.22g of saccharifying enzyme" added during the preparation of the enzymatic starch solution with "0.295g of α-amylase", and the remaining steps and parameters are the same. This comparative example will not be repeated, and finally an enzymatic modified starch adsorbent is obtained.

[0071] Comparative Example 5:

[0072] Compared with Example 1, this comparative example only replaces the "0.075g of α-amylase and 0.22g of saccharifying enzyme" added during the preparation of the enzymatic starch solution with "0.295g of saccharifying enzyme". The remaining steps and parameters are the same, and this comparative example will not be repeated. Finally, an enzymatically modified starch adsorbent is obtained.

[0073] Comparative Example 6:

[0074] Compared with Example 1, this comparative example only replaces the "modified sodium sulfonate alginate" added during the preparation of the pre-cross-linked starch solution with "sodium alginate". The remaining steps and parameters are the same and will not be repeated in this comparative example. Finally, an enzymatically modified starch adsorbent is obtained.

[0075] Comparative Example 7:

[0076] Compared with Example 1, this comparative example only replaced the "modified sodium sulfonate alginate" added in the preparation process of the pre-cross-linked starch solution with the "pretreated attapulgite" prepared in S5 of Example 1 of the present invention. The remaining steps and parameters were the same and will not be repeated in this comparative example. Finally, an enzymatically modified starch adsorbent was obtained;

[0077] Comparative Example 8:

[0078] Compared with Example 1, this comparative example only replaces the "pretreated attapulgite" added in the preparation process of the enzymatically modified starch adsorbent in S6 with "attapulgite", and the remaining steps and parameters are the same, which will not be repeated in this comparative example, and finally the enzymatically modified starch adsorbent is obtained.

[0079] Comparative Example 9:

[0080] Compared with Example 1, this comparative example only replaces the "pretreated attapulgite" added in the enzymatic hydrolysis modified starch adsorbent process in S6 with the "modified sodium sulfonate alginate" prepared in S3 of Example 1 of the present invention. The remaining steps and parameters are the same and will not be repeated in this comparative example. Finally, the enzymatic hydrolysis modified starch adsorbent is obtained;

[0081] Comparative Example 10:

[0082] Compared with Example 1, this comparative example only does not perform cold plasma treatment during the preparation process of the enzymatically modified starch adsorbent in S6. The remaining steps and parameters are the same and will not be repeated in this comparative example. Finally, the enzymatically modified starch adsorbent is obtained.

[0083] Performance testing:

[0084] Adsorption capacity test at 25℃:

[0085] Weigh 0.05g of enzymatically modified starch adsorbent sample and soak it in 50mL of organic (cationic yellow) solution with a concentration of 500mg / L and shake it at constant temperature at 25℃ for 2h. Then use a visible spectrophotometer to measure the concentration of cationic yellow in the solution and calculate the corresponding adsorption amount (mg / g). 2+ , Pb 2+ 、Hg 2+ 、Ni 2+）0.05g of each enzymatically modified starch adsorbent sample was added to 50mL of a 500mg / L heavy metal ion solution. The mixture was then shaken in a constant temperature shaker at 25°C for 2 hours. The heavy metal ion concentration in each solution was then measured using an atomic absorption spectrophotometer, and the corresponding adsorption capacity (mg / g) was calculated. The adsorption capacity (mg / g) of the enzymatically modified starch adsorbents prepared in Examples 1-3 and Comparative Examples 1-10 was determined using this method. The test results are shown in Table 1.

[0086] Adsorption capacity test at 50℃:

[0087] Weigh 0.05g of enzymatically modified starch adsorbent sample and soak it in 50mL of organic (cationic yellow) solution with a concentration of 500mg / L and shake it at constant temperature at 50℃ for 2h. Then use visible spectrophotometer to measure the concentration of cationic yellow in the solution and calculate the corresponding adsorption amount (mg / g). 2+ , Pb 2+ 、Hg 2+ 、Ni 2+ For each of the simulated wastewater solutions, 0.05g of the enzymatically modified starch adsorbent sample was added to 50mL of a 500mg / L heavy metal ion solution. The mixture was then shaken in a constant temperature shaker at 50°C for 2 hours. The heavy metal ion concentration in each solution was then measured using an atomic absorption spectrophotometer, and the corresponding adsorption capacity (mg / g) was calculated. The adsorption capacity (mg / g) of the enzymatically modified starch adsorbents prepared in Examples 1-3 and Comparative Examples 1-10 was measured using this method. The test results are shown in Table 1 below.

[0088] Table 1: Performance test results of Examples 1-3 and Comparative Examples 1-10

[0089]

[0090] Data Analysis:

[0091] As can be seen from Table 1, the enzymatically modified starch adsorbent prepared by the present invention has better adsorption capacity for organic pollutants and heavy metal ions, as well as adsorption capacity stability.

[0092] This may be due to:

[0093] (1) During the preparation of pretreated starch solution, the mechanical effect and cavitation effect of the first ultrasonic treatment will cause microstructural changes such as microcracks and grooves on the surface of starch granules, reduce the particle size, and increase the specific surface area; this provides more contact sites for subsequent reactions with other reagents, which is beneficial to the combination of enzymes and starch molecules during enzymatic hydrolysis. The specific temperature and ultrasonic wave synergistic effect during the second ultrasonic treatment can further destroy the hydrogen bonds and other forces within the starch molecules, causing the molecular chains to stretch to a certain extent, further increasing the reaction activity of starch, thereby accelerating the enzymatic hydrolysis reaction rate and making the enzymatic hydrolysis more complete. Ultimately, the adsorbent forms a more complex, uniform, and porous network structure after subsequent graft copolymerization reactions, thereby improving the adsorption capacity and adsorption stability of heavy metal ions, organic pollutants, etc.

[0094] (2) Cold plasma treatment under specific conditions during the preparation of enzymatic starch solution will make the surface of starch granules rough, forming many tiny grooves and pores, and will also increase the number of active sites and functional groups on the surface, thereby significantly increasing the specific surface area of ​​starch and the contact area between starch molecules and enzymes, making some chemical bonds on starch molecules more easily recognized and broken by enzymes; at the same time, some nitrogen-containing active groups will be introduced on the surface of starch molecules, enhancing the binding force between the adsorbent and pollutants. Combined with the sufficient enzymatic hydrolysis of α-amylase and saccharifying enzyme compounded in a specific ratio under specific conditions, the starch molecules will form a more stable structure. Therefore, this process further improves the adsorption capacity and adsorption stability of the adsorbent.

[0095] (3) The sulfonic acid groups in the modified sulfonic acid sodium alginate of the present invention can interact with groups such as hydroxyl groups in the enzymatically hydrolyzed starch solution. When epichlorohydrin is subsequently added for cross-linking reaction, these interactions can promote the formation of a more complex, more uniform, and more stable cross-linked network structure. This cross-linked network structure not only enhances the stability of the adsorbent, enabling it to maintain good adsorption performance under different environmental conditions, but also improves the mechanical strength of the adsorbent and reduces the breakage and loss of the adsorbent during use. At the same time, since sodium alginate itself has a certain degree of hydrophilicity, its combination with the hydrophilicity of the sulfonic acid groups enables the modified sulfonic acid sodium alginate to contact and interact with pollutant molecules more quickly, thereby accelerating the adsorption rate.

[0096] (4) The convexopolysaccharide has a special crystal structure and a large specific surface area. The present invention fills the pretreated convexopolysaccharide into the network structure of the enzymatically modified starch, which can provide more adsorption sites for the enzymatically modified starch adsorbent, enhance the ion exchangeability of the adsorbent, support and reinforce the network structure, so that it can combine with more adsorbed substances more stably; at the same time, the convexopolysaccharide can adsorb a part of the substance through physical adsorption, and the enzymatically modified starch can react chemically with the adsorbed substance or produce a complexation through its own active groups. The combination of the two further enhances the overall adsorption performance of the adsorbent.

[0097] (5) Subjecting the pre-cross-linked starch solution to cold plasma treatment under specific conditions can improve its pore structure and introduce more active groups or defects, thereby increasing the specific surface area and adsorption sites of the enzymatically modified starch adsorbent. It can also promote further cross-linking reactions of unreacted groups in the pre-cross-linked starch solution and promote changes in the cross-linking structure, making the connections between molecular chains tighter and forming a more stable and regular three-dimensional network structure. Therefore, the enzymatically modified starch adsorbent prepared by the present invention has superior adsorption capacity and adsorption capacity stability.

[0098] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for preparing an enzymatically modified starch adsorbent, characterized in that: The following steps are involved: Step S1: adding corn starch to deionized water, and then performing gradient temperature increase-ultrasound synergistic treatment to obtain a pretreated starch solution; Step S2: Under a nitrogen atmosphere, the pretreated starch solution is subjected to cold plasma treatment, and then the pH is adjusted to 5-6, the temperature is raised to 40-50°C, a complex enzyme is added, and enzymatic hydrolysis is carried out at 40-50°C for 20-25 hours. After high temperature treatment, an enzymatically hydrolyzed starch solution is obtained; Step S3: adding modified sodium sulfonate alginate to the enzymatically hydrolyzed starch solution, stirring and reacting at 35-40° C. for 1.5-2 hours, then adding epichlorohydrin and stirring and reacting for 2.5-3 hours to obtain a pre-cross-linked starch solution; Step S4: Under a nitrogen atmosphere, the pre-cross-linked starch solution is subjected to cold plasma treatment, and then the pre-treated attapulgite is added and stirred for 0.8-1 hour, and then ammonium sulfate and acrylamide are added and the air is excluded, and the mixture is reacted at 55-60° C. for 3-4 hours, and then filtered, washed, and dried to obtain an enzymatically modified starch adsorbent; The ratio of deionized water to corn starch in step S1 is 100-120 mL: 30-35 g; The gradient heating-ultrasound synergistic treatment in step S1 is first performed at 20-30°C with a power of 280-300 W, a frequency of 35-40 kHz, and a duration of 10-15 min for a first ultrasonic treatment, followed by a second ultrasonic treatment at 65-66°C with a power of 280-300 W, a frequency of 30-40 kHz, and a duration of 8-10 min; The complex enzyme in step S2 is obtained by mixing α-amylase and saccharifying enzyme; The preparation method of the modified sulfonic acid sodium alginate in step S3 is as follows: Sodium alginate is added to deionized water, and the mixture is stirred at 200-300 r / min at 50-60°C for 1-2 hours. Then, sulfamic acid is added, and the mixture is stirred until the pH value is adjusted to 8-9 with sodium hydroxide solution, and the mixture is stirred for 3-4 hours. After cooling to 20-30°C, ethanol is added, and the mixture is stirred until the mixture is evenly mixed, filtered, washed, and dried to obtain modified sulfonic acid sodium alginate. The preparation method of the pretreated attapulgite in step S4 is as follows: The attapulgite is added to the hydrochloric acid solution, and then stirred at 300-400 r / min at 60-80° C. for 12-15 hours, and then filtered and dried to obtain the pretreated attapulgite.

2. The method for preparing the enzymatically modified starch adsorbent according to claim 1, wherein The gas flow rate during the cold plasma treatment in step S2 is 8-10 L / min, the power is 200-300 W, the voltage is 50-100 V, and the total treatment time is 6-10 min; In step S2, the ratio of the pretreated starch solution to the complex enzyme is 130-155 g: 0.295-0.345 g; The temperature of the high temperature treatment in step S2 is 80-90° C., and the treatment time is 10-20 minutes.

3. The preparation method of the enzymatically modified starch adsorbent according to claim 1, characterized in that: The dosage ratio of α-amylase and saccharifying enzyme in the complex enzyme is 0.075-0.085 g: 0.22-0.26 g.

4. The method for preparing the enzymatically modified starch adsorbent according to claim 1, wherein In step S3, the usage ratio of the enzymatic starch solution, modified sodium sulfonate alginate, and epichlorohydrin is 130-155 g: 4-5 g: 1-2 mL.

5. The method for preparing the enzymatically modified starch adsorbent according to claim 1, wherein In the preparation process of the modified sulfonic acid sodium alginate, the usage ratio of deionized water, sodium alginate, aminosulfonic acid, and ethanol is 200 mL: 5-10 g: 2.4-7.3 g: 200-400 mL; The concentration of the sodium hydroxide solution is 0.1 mol / L.

6. The method for preparing the enzymatically modified starch adsorbent according to claim 1, wherein The gas flow rate during the cold plasma treatment in step S4 is 8-10 L / min, the power is 200-300 W, the voltage is 50-100 V, and the total treatment time is 8-10 min; In step S4, the usage ratio of the pre-cross-linked starch solution, pretreated attapulgite, ammonium sulfate, and acrylamide is 135-162 g: 2.5-3 g: 0.2-0.3 g: 8-10 g.

7. The method for preparing the enzymatically modified starch adsorbent according to claim 1, wherein The usage ratio of the hydrochloric acid solution and the attapulgite is 100-150 mL: 5-8 g; The concentration of the hydrochloric acid solution is 1 mol / L.

Images