An LLDPE / PDA / TCS composite plastic film capable of adsorbing Cu 2+ and Cd 2+ and its preparation method

Abstract

The present invention relates to an LLDPE / PDA / TCS composite plastic film capable of adsorbing Cu<supgt;2+< / supgt> and Cd<supgt;2+< / supgt> and a preparation method thereof. The steps adopted are as follows: 1) Preparation of the LLDPE film; 2) Preparation of the dopamine solution; 3) Preparation of the LLDPE / PDA film; 4) Preparation of sulfonated chitosan TCS; 5) Preparation of the LLDPE / PDA / TCS composite film. The LLDPE plastic film capable of adsorbing Cu<supgt;2+< / supgt> and Cd<supgt;2+< / supgt> prepared by the present invention can achieve adsorption amounts of 110 and 70 mg / g for Cu<supgt;2+< / supgt> and Cd<supgt;2+< / supgt> respectively in solution or soil, and can reach adsorption saturation in 90 min in solution. After three cycles of desorption, the adsorption capacities for Cu<supgt;2+< / supgt> and Cd<supgt;2+< / supgt> can still reach 43 and 20 mg / g. The present invention can obtain an LLDPE plastic film capable of adsorbing Cu<supgt;2+< / supgt> and Cd<supgt;2+< / supgt>. By functionalizing and improving the surface of the common plastic film, the present invention can adsorb Cu<supgt;2+< / supgt> and Cd<supgt;2+< / supgt> heavy metals in aqueous solution and soil, and can truly achieve the purpose of removing heavy metals from the soil at low cost and conveniently. The adsorption and removal of Cu<supgt;2+< / supgt> and Cd<supgt;2+< / supgt> by this plastic film has the characteristic of recyclability.

Description

Technical Field

[0001] The present invention relates to the technical field of plastic films, and particularly relates to an LLDPE / PDA / TCS composite plastic film capable of adsorbing Cu 2+ and Cd 2+ and a preparation method thereof. Background Art

[0002] A good green ecological environment is crucial for human health and survival. However, with the rapid development of modern technology and economy, environmental pollution problems such as air pollution, water pollution, and soil pollution have emerged. In particular, heavy metal pollution in the soil poses a great threat to human health and the ecological environment.

[0003] Heavy metals mainly exist in the environment in the form of ions. They cannot be biodegraded. On the contrary, in the presence of environmental and biological factors, they are likely to be amplified and enriched. For example, the heavy metals in the soil migrate with the soil leachate, which will cause heavy metal ions to deposit on the surface of plant leaves. These heavy metal ions will enter the interior of plant leaves through the stomata, surface pores, through pores, outer connecting pores, and water pores on the plant leaves, and then be transported to the roots and other organs. The accumulation of heavy metals in plant organs not only inhibits the growth and productivity of plants, but also enters the human body through the food chain, affecting human health. Therefore, the removal of heavy metals is crucial for maintaining human health and protecting the ecological environment.

[0004] At present, there are mainly the following three ways to treat heavy metal pollution in the soil:

[0005] 1. Using dilution means to reduce the concentration of heavy metal ions in the soil;

[0006] 2. Changing the forms of heavy metals existing in the soil, such as using chemical or microbial methods to fix the ions;

[0007] 3. Removing heavy metals from the soil.

[0008] Although both methods 1 and 2 have effects, they do not directly remove heavy metal elements from the ecological cycle, and the change of form is not necessarily permanent. Therefore, adopting method 3 is the optimal choice. However, some technologies involved in method 3 have problems such as difficult application and high cost. Therefore, it is necessary to develop a new green, economic, and practical removal method. Summary of the Invention

[0009] In order to solve the problems of difficult application and high cost of removing heavy metal ions Cu 2+ and Cd 2+ from the soil, the present invention provides an LLDPE / PDA / TCS composite plastic film capable of adsorbing Cu 2+ and Cd 2+ and a preparation method thereof.

[0010] To achieve the above-mentioned invention purpose, the present invention adopts the following technical solution: A preparation method of an LLDPE / PDA / TCS composite plastic film capable of adsorbing Cu 2+ and Cd 2+ , characterized in that the steps are as follows:

[0011] 1) Cleaning of the LLPDE film:

[0012] Immerse the polyethylene (LLDPE) film in absolute ethanol and ultrasonically clean it for 24 h, then rinse it with deionized water. After rinsing, place it at room temperature to dry;

[0013] 2) Preparation of the dopamine solution:

[0014] Dissolve tris(hydroxymethyl)aminomethane (Tris) in deionized water, adjust the pH using an HCl solution to obtain a Tris-HCl buffer solution, and take the buffer solution and dopamine and shake them well to obtain a dopamine (PDA) solution;

[0015] 3) Preparation of the LLDPE / PDA film:

[0016] Place the LLDPE film cleaned in step 1) into the dopamine (PDA) solution obtained in step 2), soak it at room temperature for 24 - 48 h, then rinse it with deionized water and absolute ethanol to obtain a modified LLDPE / PDA film;

[0017] 4) Preparation of sulfonated chitosan TCS:

[0018] In a 250 mL round-bottom flask, add chitosan (CS) to glacial acetic acid diluted with deionized water, stir at room temperature until it dissolves, then add thiosemicarbazide (TC), and continue to stir until the solution is clear and transparent; after 0.8 - 1.5 h, add formaldehyde to the solution, continue to stir at room temperature for 6 - 12 h. After the reaction ends, neutralize the reaction system with dilute sodium hydroxide solution to obtain a white flocculent precipitate. After filtering the precipitate, wash it thoroughly with deionized water and absolute ethanol, and vacuum dry it to obtain light yellow sulfonated chitosan TCS;

[0019] 5) Preparation of the LLDPE / PDA / TCS composite film

[0020] Weigh sulfonated chitosan TCS, add it to deionized water, then add glacial acetic acid solution, and ultrasonically dissolve it completely to obtain a mixed solution with a TCS concentration of 15 - 25 mg / mL; immerse the modified LLDPE / PDA film obtained in step 3) in the mixed solution, take it out and dry it in the air after 0.8 - 1.5 h to obtain the LLDPE / PDA / TCS composite plastic film.

[0021] Further, the drying temperature of the LLDPE film obtained after cleaning in step 1) is 0 - 40°C.

[0022] Further, the drying time of the LLDPE film obtained after cleaning in step 1) is 3 - 12 h.

[0023] Further, the pH of the Tris-HCl buffer solution obtained in step 2) is 8.5; the mass ratio of the buffer solution to dopamine is 0.8 - 1.3:2.

[0024] Further, the soaking duration in step 3) is 12 - 48 h.

[0025] Further, in step 4)

[0026] The mass ratio of chitosan to the volume of deionized water is 0.6 - 0.8 g:40 mL;

[0027] The volume ratio of glacial acetic acid to the volume of deionized water is 0.7 - 1.3:4.

[0028] The mass ratio of thiosemicarbazide to the volume of deionized water is 0.35 - 0.55 g:40 mL.

[0029] The volume ratio of formaldehyde to the volume of deionized water is 0.8 - 1.2:20.

[0030] Further, the white flocculent precipitate after washing in step 4) is vacuum dried at 0 - 40°C for 6 - 18 h.

[0031] Further, the volume ratio of the glacial acetic acid solution to the volume of deionized water in step 5) is 0.7 - 3:50.

[0032] The LLDPE / PDA / TCS composite ground film prepared by the above preparation method and capable of adsorbing Cu 2+ and Cd 2+ .

[0033] Compared with the prior art, the advantages of the present invention are as follows:

[0034] 1. The present invention utilizes the mussel biomimetic adhesiveness and high reactivity based on PDA, and uses the immersion surface coating modification technology to deposit PDA on the surface of the LLDPE film, and uses the PDA layer as a secondary modification platform, so that the prepared LLDPE / PDA / TCS film has heavy metal ion adsorption, high hydrophilicity and wettability;

[0035] 2. The present invention adopts a simple and green polymer film surface modification method, that is, uses the oxidative self-polymerization of natural dopamine to modify the surface of the LLDPE film, so that it has the function of further connecting heavy metal adsorption materials and improves the hydrophilicity of the LLDPE film.

[0036] 3. The present invention obtains an LLDPE / PDA / TCS composite plastic film, which has good adsorption capacity for Cu 2+ and Cd 2+ . When the pH of the solution is 5 - 9 respectively, the adsorption amounts of Cu 2+ and Cd 2+ can reach 110 and 70 mg / g, and the adsorption reaches saturation in 90 min, achieving efficient absorption of Cu 2+ and Cd 2+ in the soil.

[0037] 4. The LLDPE / PDA / TCS composite plastic film of the present invention can be desorbed cyclically. After three - cycle desorption, the adsorption capacities for Cu 2+ and Cd 2 + can still reach 43 and 20 mg / g, and it is a green and efficient material for adsorbing Cu 2+ and Cd 2+ .

[0038] 5. The sulfonated chitosan modified on the film surface of the present invention can selectively complex and adsorb Cu 2+ and Cd 2+ , and improves the hydrophilicity of the LLDPE film modified by PDA. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is the preparation flow chart of the present invention;

[0040] Figure 2 is the appearance morphology diagram of the LLDPE / PDA film before and after modification; among them,

[0041] (a) is the appearance morphology diagram of the LLDPE / PDA film before and after modification obtained by direct observation;

[0042] (b) is the appearance morphology diagram of the LLDPE / PDA film before and after modification obtained by scanning electron microscope observation;

[0043] Figure 3 is the change diagram of the water contact angle on the surface of the LLDPE / PDA / TCS film;

[0044] Figure 4 is the curve diagram of the LLDPE / PDA / TCS film; among them,

[0045] (a) is the thermogravimetric curve diagram; (b) is the differential thermal analysis curve diagram;

[0046] Figure 5 is the influence diagram of pH on the adsorption of Cu 2+ and Cd 2+ by the LLDPE / PDA / TCS film;

[0047] Figure 6 Effect of adsorption time on the adsorption of Cu 2+ and Cd 2+ by the LLDPE / PDA / TCS membrane;

[0048] Figure 7 Effect of Cu 2+ and Cd 2+ concentration on the adsorption by the LLDPE / PDA / TCS membrane;

[0049] Figure 8 Cyclic adsorption results of the LLDPE / PDA / TCS membrane; Specific implementation mode

[0050] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the invention.

[0051] Agricultural mulch films can maintain soil moisture, regulate soil temperature, limit weed growth, and thus promote crop yield increase, and are widely used in modern agricultural production. The agricultural mulch film has a large contact area with plant leaves and soil, and is cheap and inexpensive. Therefore, the present invention modifies the modified LLDPE film and applies it to adsorb Cu 2+ and Cd 2+ .

[0052] Example 1:

[0053] An LLDPE / PDA / TCS composite agricultural mulch film capable of adsorbing Cu 2+ and Cd 2+ has the following preparation method steps (as shown in Figure 1 ):

[0054] 1. Cleaning of the LLPDE film:

[0055] Immerse the linear low-density polyethylene (LLDPE) film in absolute ethanol and ultrasonically clean it for 24 h, then rinse it with deionized water. After rinsing, dry it at room temperature for 8 h;

[0056] 2. Preparation of the dopamine solution:

[0057] Dissolve 605.7 mg of tris(hydroxymethyl)aminomethane (Tris) in 500 mL of deionized water, adjust the pH to 8.5 with 0.1 M HCl solution to obtain a 10 mM Tris-HCl buffer solution. Take 200 mL of the buffer solution and 400 mg of dopamine, and shake well to obtain a 2 mg / mL dopamine solution;

[0058] 3. Preparation of the LLDPE / PDA film:

[0059] The cleaned LLDPE film was placed in a dopamine (PDA) solution and soaked at room temperature for 24 h. After that, it was rinsed with deionized water and absolute ethanol to obtain the modified LLDPE / PDA film.

[0060] 4. Preparation of sulfonated chitosan TCS:

[0061] In a 250 mL round-bottom flask, chitosan (CS, 0.8 g) was added to 10 mL of glacial acetic acid diluted with 40 mL of deionized water and stirred at room temperature until dissolved. Then, thiosemicarbazide (TC, 0.45 g, equivalent to 1 mol of chitosan pyranose ring) was added and stirring continued until the solution was clear and transparent. After 1 h, 2 mL of formaldehyde was added to the solution and stirring continued at room temperature for 8 h. After the reaction ended, the reaction system was neutralized with dilute sodium hydroxide solution to obtain a white flocculent precipitate. After the precipitate was filtered by suction, it was thoroughly washed with deionized water and absolute ethanol and vacuum dried for 12 h to obtain pale yellow sulfonated chitosan TCS.

[0062] 5. Preparation of LLDPE / PDA / TCS composite film

[0063] Weigh 400 mg of TCS, add it to 19.6 mL of deionized water, and then add 0.4 mL of glacial acetic acid solution. Ultrasonic it until it is completely dissolved to obtain a mixed solution with a concentration of 20 mg / mL.

[0064] The LLDPE / PDA film was soaked in the above TCS solution and taken out to dry after 1 h to obtain the LLDPE / PDA / TCS composite film.

[0065] Example 2:

[0066] An LLDPE / PDA / TCS composite plastic film that can adsorb Cu 2+ and Cd 2+ The preparation method steps of are as follows:

[0067] 1. Cleaning of LLPDE film:

[0068] The linear low-density polyethylene (LLDPE) film was soaked in absolute ethanol and ultrasonically cleaned for 24 h, then rinsed with deionized water. After rinsing, it was placed at room temperature to dry for 3 h;

[0069] 2. Preparation of dopamine solution:

[0070] Dissolve 605.7 mg of tris(hydroxymethyl)aminomethane (Tris) in 500 mL of deionized water, and adjust the pH to 8.5 using 0.1 M HCl solution to obtain a 10 mM Tris-HCl buffer solution. Take 160 mL of the buffer solution and 430 mg of dopamine, and shake well to obtain a 2 mg / mL dopamine solution;

[0071] 3. Preparation of LLDPE / PDA film:

[0072] Place the cleaned LLDPE film in the dopamine (PDA) solution, soak it at room temperature for 12 hours, then rinse it with deionized water and absolute ethanol to obtain the modified LLDPE / PDA film.

[0073] 4. Preparation of sulfonated chitosan TCS:

[0074] In a 250 mL round-bottom flask, add chitosan (CS, 0.7 g) to 10 mL of glacial acetic acid diluted with 36 mL of deionized water, and stir at room temperature until dissolved. Then, add thiosemicarbazide (TC, 0.36 g, equivalent to 1 mol of chitosan pyranose ring), and continue stirring until the solution is clear and transparent; after 1 hour, add 2 mL of formaldehyde to the solution, and continue stirring at room temperature for 8 hours; after the reaction is completed, neutralize the reaction system with dilute sodium hydroxide solution to obtain a white flocculent precipitate. After filtering the precipitate, wash it thoroughly with deionized water and absolute ethanol, and vacuum dry it for 6 hours to obtain light yellow sulfonated chitosan TCS;

[0075] 5. Preparation of LLDPE / PDA / TCS composite film

[0076] Weigh 500 mg of TCS, add it to 21 mL of deionized water, and then add 0.3 mL of glacial acetic acid solution, and ultrasonically dissolve it completely to obtain a mixed solution with a concentration of 20 mg / mL.

[0077] Immerse the LLDPE / PDA film in the above TCS solution, take it out and dry it after 1 hour to obtain the LLDPE / PDA / TCS composite film.

[0078] Example 3:

[0079] An LLDPE / PDA / TCS composite plastic film that can adsorb Cu 2+ and Cd 2+ The preparation method steps are as follows:

[0080] 1. Cleaning of LLPDE film:

[0081] Immerse the linear low density polyethylene (LLDPE) film in absolute ethanol and ultrasonically clean it for 24 hours, then rinse it with deionized water. After rinsing, dry it at room temperature for 12 hours;

[0082] 2. Preparation of dopamine solution:

[0083] Dissolve 605.7 mg of tris(hydroxymethyl)aminomethane (Tris) in 500 mL of deionized water, and adjust the pH to 8.5 with 0.1 M HCl solution to obtain 10 mM Tris-HCl buffer solution. Take 230 mL of the buffer solution and 500 mg of dopamine, and shake well to obtain 2 mg / mL dopamine solution;

[0084] 3. Preparation of LLDPE / PDA membrane:

[0085] Place the cleaned LLDPE membrane in dopamine (PDA) solution, soak it at room temperature for 48 h, and then rinse it with deionized water and absolute ethanol to obtain the modified LLDPE / PDA membrane.

[0086] 4. Preparation of sulfonated chitosan TCS:

[0087] In a 250 mL round-bottom flask, add chitosan (CS, 0.9 g) to 10 mL of glacial acetic acid diluted with 44 mL of deionized water, and stir at room temperature until dissolved. Then, add thiosemicarbazide (TC, 0.5 g, equivalent to 1 mol of chitosan pyranose ring), and continue to stir until the solution is clear and transparent; after 1 h, add 2 mL of formaldehyde to the solution, and continue to stir at room temperature for 8 h; after the reaction is completed, neutralize the reaction system with dilute sodium hydroxide solution to obtain a white flocculent precipitate. After filtering the precipitate, wash it thoroughly with deionized water and absolute ethanol, and vacuum dry it to obtain light yellow sulfonated chitosan TCS;

[0088] 5. Preparation of LLDPE / PDA / TCS composite membrane

[0089] Weigh 300 mg of TCS, add it to 17.6 mL of deionized water, and then add 0.35 mL of glacial acetic acid solution. Ultrasonic it until it is completely dissolved to obtain a mixed solution with a concentration of 20 mg / mL.

[0090] Immerse the LLDPE / PDA membrane in the above TCS solution, take it out and dry it after 1 h to obtain the LLDPE / PDA / TCS composite membrane.

[0091] Verify the adsorption effect of the LLDPE / PDA / TCS composite membrane obtained in Example 1:

[0092] Figure 2 Figure showing the appearance morphology of the LLDPE / PDA membrane before and after modification (LLDPE / PDA / TCS);

[0093] Figure 2 (a) Figure showing the appearance morphology of the LLDPE / PDA membrane before and after modification observed directly,Figure 2 (b) Scanning electron microscope observation of the appearance of the obtained LLDPE / PDA film before and after modification;

[0094] from Figure 2 (a) It can be seen that after coating with a layer of TCS, the brown color of the membrane surface becomes lighter and its surface becomes relatively smooth; from the SEM image ( Figure 2 (b) It can be seen that a large number of PDA aggregates are deposited on the surface of the LLDPE film, making its surface relatively rough. After TCS coating modification, the PDA particles on the film surface disappear, which is due to the fact that TCS evenly covers the PDA layer and forms a relatively smooth TCS layer on the film surface.

[0095] The water contact angle of the LLDPE / PDA / TCS film was measured by an optical contact angle analyzer. Figure 3 As shown, from Figure 3 It can be seen that the initial water contact angle of the TCS-modified LLDPE / PDA / TCS membrane is 40.5°, which is close to hydrophobic compared to the LLDPE membrane surface. After 90s, it drops to 0° and becomes a superwetting state, indicating that the LLDPE / PDA / TCS membrane has a high hydrophilicity.

[0096] The LLDPE / PDA / TCS film was analyzed using a thermal differential thermogravimetric analyzer, and the results are as follows: Figure 4 Shown: From Figure 4 It can be seen that the decomposition of LLDPE / PDA / TCS film can be divided into three stages at 70, 280 and 450°C. The weight losses at 70°C and 280°C come from the evaporation of water in the TCS structure and the decomposition of TC, respectively, and they are endothermic processes. The decomposition at 450°C comes from the decomposition of the branched chains of LLDPE, so the weight loss below this temperature comes from the decomposition of the TCS and PDA layers. Therefore, it is proved that the introduction of the TCS layer has no effect on the thermal decomposition behavior of the LLDEP / PDA film.

[0097] Using 1000mg / L Cu 2+ The standard solution was prepared with a concentration of 160 mg / L Cu 2+ solution, and then the concentration of 160mg / L Cu 2+ The pH value of the solution was adjusted to 3-9, and the LLDPE / PDA / TCS films prepared in Example 1 were immersed in Cu2O3 / PE / PDA / TCS solution at 25°C. 2+ In the solution, the effective area of ​​the membrane is 10 cm2. When the adsorption time is 90 min, the composite membrane is taken out and the pH value of Cu is 3 to 9. 2+ The concentration of metal ions in the adsorbed solution was determined using a flame atomic absorption spectrometer.

[0098] Using 1000mg / L Cd2+ Prepare a Cd solution with a standard solution concentration of 100 mg / L 2+ solution, and then adjust the pH value of the Cd solution with a concentration of 100 mg / L to 3 - 9. At 25 °C, immerse the LLDPE / PDA / TCS membrane prepared in Example 1 into the Cd2+ solution with a pH value of 3 - 9. The effective area of the membrane is 10 cm2. When the adsorption time is 90 min, take out the composite membrane and use a flame atomic absorption spectrometer to measure the metal ion concentration in the solution after adsorption for the Cd 2+ solution 2+ The adsorption data obtained are as follows

[0099] shown. It can be seen from Figure 5 that the adsorption of the two metal ions generally increases with the increase of pH value. The adsorption capacities of the membrane for Cu Figure 5 and Cd 2+ are 110 mg / g (pH = 6) and 70 mg / g (pH = 5) respectively 2+ .

[0100] Prepare a Cu solution with a concentration of 160 mg / L using a 1000 mg / L Cu 2+ standard solution, and then adjust the pH value of the Cu solution with a concentration of 160 mg / L to 6. At 25 °C, immerse the LLDPE / PDA / TCS membrane prepared in the example into the Cu solution with a pH value of 6 and a concentration of 160 mg / L 2+ . The effective area of the membrane is 10 cm 2+ , and conduct kinetic studies within 0 min - 480 min; when adsorbing for different times, take out the composite membrane and use a flame atomic absorption spectrometer to measure the metal ion concentration in the solution after adsorption 2+ . 2

[0101] Prepare a Cd solution with a concentration of 100 mg / L using a 1000 mg / L Cd 2+ standard solution, and then adjust the pH value of the Cd solution with a concentration of 100 mg / L to 5. At 25 °C, immerse the LLDPE / PDA / TCS membrane prepared in Example 1 into the Cd solution with a pH value of 5 and a concentration of 100 mg / L 2+ . The effective area of the membrane is 10 cm2, and conduct kinetic studies within 0 min - 480 min; when adsorbing for different times, take out the composite membrane and use a flame atomic absorption spectrometer to measure the metal ion concentration in the solution after adsorption 2+ . 2+

[0102] The adsorption data obtained are as follows Figure 6 shown. It can be seen from Figure 6 that Cu 2+ and Cd​​2+ The removal rate of ions increases with time. 2+ and Cd 2+ The adsorption amount reached equilibrium after 90 min.

[0103] Using 1000mg / L Cu 2+ The standard solutions were prepared with concentrations of 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, 40 mg / L, 80 mg / L, 100 mg / L and 160 mg / L of Cu2+ solutions; 2+ The pH value of the solution was adjusted to 6; the LLDPE / PDA / TCS membrane prepared in Example was added to the above Cu 2+ In the solution, when the adsorption time is 90 min, the composite membrane is taken out from the above solution, and the metal ion concentration in the solution after adsorption is measured by flame atomic absorption spectrometer.

[0104] Using 1000mg / L Cd 2+ Standard solutions were prepared with concentrations of 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, 40 mg / L, 80 mg / L, 100 mg / L and 160 mg / L of Cd 2+ solution; Cd at concentrations of 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, 40 mg / L, 80 mg / L, 100 mg / L and 160 mg / L 2+ The pH value of the solution was adjusted to 5; the LLDPE / PDA / TCS film prepared in Example was added to the above Cd 2+ In the solution, when the adsorption time is 90 min, the composite membrane is taken out from the above solution, and the metal ion concentration in the solution after adsorption is measured by flame atomic absorption spectrometer.

[0105] The adsorption data obtained are as follows Figure 7 shown; from Figure 7 It can be seen that with Cu 2+ and Cd 2+ With the increase of Cu 2+ and Cd 2+ The adsorption capacity on the membrane increased significantly, and stopped increasing after the concentrations reached 160 and 100 mg / L. 2+ The capacity is greater than Cd 2+ .

[0106] The LLDPE / PDA / TCS films prepared in Example 1 were added with 2+ and Cd2+ In a plastic centrifuge tube containing a solution (10 mL, 50 mg / L), its repeatability was tested and the required pH was maintained at room temperature. After 12 h of adsorption, the metal-loaded polymer membrane was taken out and gently washed with deionized water to remove unadsorbed metal ions on the surface. Then, the polymer membrane was soaked in 10 mL (10 mM) EDTA solution for 4 h, taken out, washed with deionized water, and dried at room temperature. To test the reusability of the polymer membrane, the same polymer membrane was used to repeat the adsorption-desorption cycle 3 times. Then, AAS was used to determine the concentration of Cu 2+ and Cd 2+ in the solution after adsorption.

[0107] The adsorption data obtained are as Figure 8 shown. It can be seen from Figure 8 that after 3 cycles, the recovery efficiency of Cu 2+ and Cd 2+ ions decreased slowly with the increase in the number of cycles. At the third cycle, the adsorption capacities of the LLDPE / PDA / TCS membrane for Cu 2+ and Cd 2+ could still reach 43 mg / g and 20 mg / g.

[0108] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several improvements and transformations can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A method for preparing an LLDPE / PDA / TCS composite plastic film capable of adsorbing Cu 2+ and Cd 2+ , characterized in that, The steps are as follows: 1) Cleaning of the LLDPE membrane: Immerse the linear low density polyethylene (LLDPE) membrane in absolute ethanol and ultrasonically clean it for 24 h, then rinse it with deionized water. After rinsing, dry it at room temperature. 2) Preparation of the dopamine solution: Dissolve tris(hydroxymethyl)aminomethane (Tris) in deionized water, adjust the pH using HCl solution to obtain a Tris-HCl buffer solution. Take the buffer solution and dopamine and shake well to obtain a dopamine (PDA) solution. 3) Preparation of the LLDPE / PDA membrane: Place the LLDPE membrane cleaned in step 1) into the dopamine PDA solution obtained in step 2), soak it at room temperature for 24 - 48 h, then rinse it with deionized water and absolute ethanol to obtain a modified LLDPE / PDA membrane. 4) Preparation of sulfonated chitosan (TCS): In a 250 mL round-bottom flask, add chitosan (CS) to glacial acetic acid diluted with deionized water, stir at room temperature until dissolved, then add thiosemicarbazide (TC) and continue stirring until the solution is clear and transparent. After 0.8 - 1.5 h, add formaldehyde to the solution and continue stirring at room temperature for 6 - 12 h. After the reaction ends, neutralize the reaction system with dilute sodium hydroxide solution to obtain a white flocculent precipitate. Filter the precipitate by suction, wash it thoroughly with deionized water and absolute ethanol, and vacuum dry it to obtain light yellow sulfonated chitosan (TCS). 5) Preparation of the LLDPE / PDA / TCS composite membrane Weigh sulfonated chitosan (TCS), add it to deionized water, then add glacial acetic acid solution, and ultrasonically dissolve it completely to obtain a mixed solution with a TCS concentration of 15 - 25 mg / mL. Immerse the modified LLDPE / PDA membrane obtained in step 3) in the mixed solution, take it out and air-dry it after 0.8 - 1.5 h to obtain an LLDPE / PDA / TCS composite mulch film.

2. A method for preparing an LLDPE / PDA / TCS composite plastic film capable of adsorbing Cu 2+ and Cd 2+ , characterized in that In step 1), the drying temperature of the cleaned LLDPE membrane is 0 - 40 °C.

3. A preparation method of an LLDPE / PDA / TCS composite plastic film capable of adsorbing Cu 2+ and Cd 2+ , characterized in that In step 1), the drying time of the cleaned LLDPE membrane is 3 - 12 h.

4. A method for preparing an LLDPE / PDA / TCS composite plastic film capable of adsorbing Cu 2+ and Cd 2+ , characterized in that The pH of the Tris-HCl buffer solution obtained in step 2) is 8.5; the mass ratio of the buffer solution to dopamine is 0.8 - 1.3:

2.

5. The LLDPE / PDA / TCS composite plastic film capable of adsorbing Cu 2+ and Cd 2+ prepared by the preparation method according to claim 4, characterized in that In step 3), the soaking duration is 12 - 48 h.

6. The LLDPE / PDA / TCS composite plastic film capable of adsorbing Cu 2+ and Cd 2+ prepared by the preparation method according to claim 5, characterized in that In step 4) The mass ratio of chitosan to the volume of deionized water is 0.6 - 0.8 g:40 mL; The volume ratio of glacial acetic acid to the volume of deionized water is 0.7 - 1.3:4; The mass ratio of thiosemicarbazide to the volume of deionized water is 0.35 - 0.55 g:40 mL; The volume ratio of formaldehyde to the volume of deionized water is 0.8 - 1.2:

20.

7. The LLDPE / PDA / TCS composite plastic film capable of adsorbing Cu 2+ and Cd 2+ prepared by the preparation method according to claim 6, characterized in that In step 4), the washed white flocculent precipitate is vacuum dried at 0 - 40 °C for 6 - 18 h.

8. The adsorbable Cu prepared by the preparation method according to claim 7 2+ and Cd 2+ of the LLDPE / PDA / TCS composite plastic film, characterized in that In step 5), the volume ratio of the glacial acetic acid solution to the volume of deionized water is 0.7 - 3:

50.

9. The LLDPE / PDA / TCS composite plastic film capable of adsorbing Cu 2+ and Cd 2+ prepared by the preparation method according to claim 1.

Images