Adsorption film for selectively removing phosphate in water body and preparation of adsorption film

Abstract

The invention discloses an adsorption film for selectively removing phosphate in a water body and a preparation method thereof.The preparation method comprises the steps that firstly, palygorskite, lanthanum nitrate hexahydrate, zinc nitrate hexahydrate, sodium carbonate and a sodium hydroxide solution are used for preparing turbid liquid, a sealed high-pressure sterilization container is used for reacting, cooling, centrifuging, washing and vacuum drying are conducted, and ZL2-coated Pal1 is obtained; secondly, ZL2 (at) Pal1 is added into dimethylformamide, and ZL2 (at) Pal1 suspension liquid is prepared; the preparation method comprises the following steps: dissolving polyacrylonitrile and polyethylene glycol in dimethylformamide to obtain a mixed polymer solution; finally, the ZL2-coated Pal1 suspension and the mixed polymer solution are mixed according to the volume ratio of 1: 1, the surface of a base material is coated with the mixture, and the ZL2-coated Pal1-PAN / PEG adsorption film is prepared. According to the preparation method, the raw materials are cheap and easy to obtain, the operation is simple, the prepared adsorption film can be recycled, and the adsorption film still has a very high phosphate rejection rate after being recycled for multiple times.

Description

Technical Field

[0001] The present invention belongs to the technical field of heavy metal ion removal, and relates to an adsorption membrane, specifically an adsorption membrane for selectively removing phosphate in water bodies. Background Art

[0002] Phosphorus in wastewater is an important factor leading to eutrophication. A very small amount of phosphorus in the environment is sufficient to disrupt the ecosystem. Total phosphorus pollution has become an important problem that urgently needs to be solved in the current water treatment process.

[0003] In recent years, many phosphorus removal methods have been used to reduce the adverse effects of phosphate on the environment, such as plant absorption, biological treatment, chemical precipitation, membrane separation technology, and advanced oxidation processes. With the increasingly strict supervision of phosphate emissions around the world, membrane separation technology, as an efficient, controllable, and environmentally friendly water treatment method, has gradually received attention. In addition, membrane separation technology can achieve continuous operation, high treatment efficiency, large treatment capacity, and is suitable for wastewater treatment plants of various scales. However, the pore size of commonly used microfiltration membranes is relatively large, usually between 0.1 micrometer and 10 micrometers, which results in limited interception effect on phosphate, unable to intercept smaller particles or solutes, and affecting the removal effect.

[0004] The surface and internal pores of the adsorption membrane have a large number of adsorption active sites, combining the filtration function of the membrane and the adsorption function of the adsorbent, showing stronger adsorption ability and smaller pore size compared with commonly used microfiltration membranes. It can efficiently remove phosphate in water through the combination of physical interception and chemical adsorption, providing a new solution for solving the problem of water body eutrophication. Summary of the Invention

[0005] The purpose of the present invention is to provide an adsorption membrane for selectively removing phosphate in water bodies to achieve rapid and highly selective removal of phosphate in water bodies.

[0006] I. ZL 2 @Pal 1 - Preparation of PAN / PEG Adsorption Membrane An adsorption membrane for selectively removing phosphate in water bodies is prepared by the following steps: 1) Respectively take zinc nitrate hexahydrate and lanthanum nitrate hexahydrate and add them to deionized water, stir the solution until the solids are completely dissolved, and then add palygorskite powder to the mixed solution under continuous stirring to obtain a suspension solution A; then dissolve NaOH and Na 2 CO 3 together in deionized water to obtain a mixed solution B, dropwise add the mixed solution B to the suspension solution A under stirring, carry out hydrothermal reaction at 150 - 180 °C for 6 - 8 h, centrifuge to collect the product, wash and dry to obtain ZL 2 @Pal 1 ; The molar ratio of zinc nitrate hexahydrate to lanthanum nitrate hexahydrate is 2:1 to 5:1; the addition amount of palygorskite powder is 40% to 60% of the total mass of zinc nitrate hexahydrate and lanthanum nitrate hexahydrate; the molar ratio of NaOH to Na 2 CO 3 is 2:1 to 4:1.

[0007] 2) Disperse ZL 2 @Pal 1 in N,N-dimethylformamide to obtain suspension solution C; then dissolve polyacrylonitrile and polyethylene glycol in N,N-dimethylformamide to obtain mixed solution D; mix suspension solution C and mixed solution D in equal volume and stir and react at 60 - 80 °C for 45 - 60 min to obtain ZL 2 @Pal 1 -PAN / PEG casting solution; The concentration of ZL 2 @Pal 1 in N,N-dimethylformamide is 15% - 25%, the concentration of polyacrylonitrile in N,N-dimethylformamide is 20% - 30%, and the concentration of polyethylene glycol in N,N-dimethylformamide is 5% - 15%.

[0008] 3) Coat the ZL 2 @Pal 1 -PAN / PEG casting solution onto the surface of the substrate, wait for it to dry, soak it in deionized water for 20 - 24 h, then peel it off from the substrate, and naturally dry it to obtain ZL 2 @Pal1-PAN / PEG adsorption film; The substrate is one of glass, plastic, metal or ceramic, and the coating method is one of spraying, spin coating, blade coating or drop coating.

[0009] Clay materials such as palygorskite have good stability. It is a hydrated octahedral layered magnesium silicoaluminum clay mineral with a high concentration of hydroxyl groups on the surface, providing active sites for adsorbing phosphate in water. Layered double hydroxides (LDHs) have the advantages of low cost, good chemical stability, large ion exchange capacity, and easy modification. Intercalating palygorskite between the layers of layered double hydroxides can not only reduce the layer stacking of layered double hydroxides to achieve good dispersion, but also greatly increase the amount of oxygen-containing functional groups on the LDH sheets, thus obtaining a better phosphorus removal effect, being more likely to capture phosphate in water, and realizing phosphate adsorption at low phosphate concentrations while improving the adsorption capacity.

[0010] In the present invention, palygorskite is intercalated into the interlayer of Zn-La layered double hydroxide to obtain ZL 2 @Pal 1 , and then ZL 2@Pal 1 The suspension and the PAN / PEG polymer solution are mixed to obtain a casting solution, and ZL is obtained by coating. 2 @Pal 1 -PAN / PEG adsorption film. Among them, ZL 2 @Pal 1 is obtained from Zn(NO 3 ) 2 ·6(H 2 O), La(NO 3 ) 3 ·6H 2 O and palygorskite through a one-step hydrothermal method, ZL 2 @Pal 1 -PAN / PEG adsorption film is prepared by mixing the ZL 2 @Pal 1 suspension and the PAN / PEG polymer solution and then spraying them onto the surface of the substrate.

[0011] II. Structure Characterization of ZL 2 @Pal 1 -PAN / PEG Adsorption Film Figure 1 This is a physical picture of the adsorption film prepared in the embodiment of the present invention. As can be seen from Figure 1 a, the coating method enables the adsorption film to adjust the size and thickness of the film as needed and can be fabricated in large areas. A large-area film cut with a circular mold with a diameter of 5 cm can be used for subsequent experiments ( Figure 1 b).

[0012] Figure 2 This is the SEM image of the adsorption film prepared in Example 1 of the present invention. Figure 2 Figures 2a and 2b are the scanning electron microscope images of the surface and cross-section of the film, respectively. It can be seen that the surface of the film is flat, and ZL 2 @Pal 1 is closely arranged in the film, and the thickness is about 12.88 μm. Figure 2 Figure 2c is the distribution map of carbon elements on the adsorption film, Figure 2 Figure 2d is the distribution map of oxygen elements on the adsorption film, Figure 2 Figure 2e is the distribution map of lanthanum elements on the adsorption film, Figure 2 Figure 2f is the distribution map of zinc elements on the adsorption film. From Figure 2 Figures 2c~2f, it can be seen that zinc and lanthanum are evenly distributed on the film.

[0013] III. Performance Evaluation of ZL 2 @Pal 1 -PAN / PEG Adsorption Film 1. Determination of Water Flux Under an external pressure of 0.9 MPa and an effective area of 12.57 cm 2 , the water flux of the ZL 2 @Pal 1 -PAN / PEG adsorption membrane was tested through a suction filtration device, and the results Figure 3 are shown as follows. It can be seen from Figure 3 that the maximum water flux of the membrane is 132.4 L / m 2 ·h, and the water flux gradually decreases with the increase of suction filtration time.

[0014] 2. Determination of isothermal adsorption curve Prepare 50 mL of KH 2 PO 4 solutions containing 2.5 mg, 5 mg, 10 mg, 20 mg, 40 mg, 60 mg, 80 mg, 100 mg, 120 mg, and 140 mg of phosphorus (P) per liter of solution respectively. Add 5 mg of the ZL 2 PO 4 -PAN / PEG adsorption membrane material prepared in the embodiment of the present invention to each KH 2 @Pal 1 solution. After continuous stirring for 24 hours, measure the ultraviolet absorption spectra of all mixed solutions by ammonium molybdate spectrophotometry, record the peak value at 700 nm to calculate the reaction equilibrium concentration, and draw the isothermal adsorption curve as shown in Figure 4 . Figure 4 It shows that the adsorption capacity of the ZL 2 @Pal 1 -PAN / PEG adsorption membrane prepared by the preparation method of the present invention increases with the increase of phosphate concentration. The isothermal adsorption curve fits well with the Langmuir model, indicating that monolayer phosphate is evenly adsorbed on the adsorption sites of the ZL 2 @Pal 1 -PAN / PEG adsorption membrane. The maximum adsorption capacity is about 448.78 mg P / g, showing excellent adsorption ability.

[0015] 3. Determination of adsorption kinetics Prepare KH 2 PO 4 solution containing 5 mg of phosphorus (P) per liter of solution. Each KH 2 PO 4Add 10 mg of the adsorption film prepared in the embodiment of the present invention to the solution. Use the ammonium molybdate spectrophotometric method to measure the ultraviolet absorption spectra of the phosphate solution after adding the adsorption film for 0.5, 1, 5, 10, 30, 60, 90, 120, 150, 180, 210, and 240 minutes respectively. Record the peak value at 700 nm to calculate the reaction equilibrium concentration, and make Figure 5 the adsorption kinetic curve shown. Figure 5 It shows that the adsorption film prepared by the present invention can rapidly capture phosphate ions in a short time, and about 83% of the phosphate is removed within 5 minutes. The adsorption equilibrium is gradually reached after 12 hours, and about 99% of the phosphate is adsorbed by ZL 2 @Pal 1 -PAN / PEG adsorption. It fully shows that the adsorption film prepared by the method of the present invention has extremely high adsorption efficiency for phosphate and can rapidly remove phosphate ions in water in a short time.

[0016] 4. Retention experiments of phosphates with different concentrations Prepare initial phosphate solutions with concentrations of 2, 5, 10, 20, and 40 mg P / L respectively. Under the conditions of an external pressure of 0.9 MPa and an effective area of 12.57 cm 2 , the retention rate of ZL 2 @Pal 1 -PAN / PEG adsorption film for phosphate was tested through a suction filtration device. As the initial concentration increases, the maximum retention rate of the film for phosphate gradually decreases ( Figure 6 ). The retention process shows the characteristics of dynamic adsorption, and the retention rate first increases and then gradually decreases with the extension of the retention time. When the initial concentration is 2 mg P / L, the maximum retention rate shown by the adsorption film is about 99.5%, and the residual phosphate concentration in the filtered solution is reduced to 9.7 μg P / L. When the initial concentration is 40 mg P / L, the maximum retention rate decreases to 85.7%, and the residual phosphate concentration in the filtered solution is reduced to 5.7 mg P / L.

[0017] 5. Retention experiments of phosphates in different pH environments Prepare 5 mg P / L inorganic phosphate solutions with pH values of 3, 5, 7, 9, and 11 respectively. Under the conditions of a pressure of 0.9 MPa and an effective area of 12.57 cm 2 , respectively pass through ZL 2 @Pal 1 -PAN / PEG adsorption film, use the ammonium molybdate spectrophotometric method to measure the ultraviolet absorption spectra of the mixed solution, record the peak value at 700 nm to calculate the reaction equilibrium concentration, and draw the Figure 7 dot-line graph shown. From Figure 7It can be seen that the ZL prepared by the preparation method of the present invention 2 @Pal 1 -PAN / PEG membrane shows a decreasing phosphate rejection rate with the increase of pH, and exhibits a very high phosphate rejection rate in a wide pH range of 3-9. The maximum rejection rate remains above 85%, making it an effective phosphate adsorption membrane.

[0018] 6. Selectivity and anti-interference experiments of phosphate in the presence of different metal ions Prepare 50 mL of an inorganic phosphate solution with a mass-volume concentration of 5 mg P / L, and add 0.01 M of Cl - , CO 3 2- , F - , NO 3 - and SO 4 2- to this inorganic phosphate solution respectively; then pass through the ZL 2 @Pal 1 -PAN / PEG adsorption membrane respectively, measure the ultraviolet absorption spectrum of the solution, and draw a bar chart as shown in Figure 8 . It can be seen that the coexisting ions have little effect on the adsorption capacity, indicating that the ZL 2 @Pal 1 -PAN / PEG adsorption membrane prepared by the present invention has high selective phosphate removal ability and strong anti-interference ability.

[0019] 7. Recycling experiment Prepare a KH 2 PO 4 solution containing 10 mg of phosphorus (P) per liter of solution, and pass it through the ZL 2 @Pal 1 -PAN / PEG adsorption membrane in a suction filtration device to measure the ultraviolet absorption spectrum of the solution. Place the used adsorption membrane in a 1.0 M NaOH solution and react for 4 hours for regeneration, and then filter the KH 2 PO 4 solution with 10 mg P / L, and continue to measure the ultraviolet absorption spectrum of the filtered solution. Repeat the above steps five times, and draw a graph according to the rejection rates of the five times as shown in Figure 9 . It can be seen from Figure 9 that the adsorption membrane prepared by the preparation method of the present invention shows excellent regeneration efficiency, and there is no obvious change in its appearance after five regeneration cycles ( Figure 9 a), and the rejection rate is still higher than 90%.

[0020] In summary, the adsorption membrane prepared by the present invention is applicable to the adsorption of phosphate in water bodies containing low-concentration phosphate, with high removal efficiency, low cost, simple operation, high reusability, and being non-toxic and harmless. Description of the Drawings

[0021] Figure 1 It is a physical photo of the adsorption membrane prepared in the embodiment of the present invention.

[0022] Figure 2 It is an SEM image of the adsorption membrane prepared in the embodiment of the present invention.

[0023] Figure 3 It is the water flux of the adsorption membrane prepared in the embodiment of the present invention for the phosphate solution.

[0024] Figure 4 It is the adsorption isotherm diagram of the adsorption membrane prepared in the embodiment of the present invention.

[0025] Figure 5 It is the adsorption kinetic curve diagram of the adsorption membrane prepared in the embodiment of the present invention.

[0026] Figure 6 It is the rejection rate of the adsorption membrane prepared in the embodiment of the present invention for phosphate solutions with different concentrations Figure 7 It is the influence of different pH values on the phosphate rejection rate of the adsorption membrane prepared in the embodiment of the present invention.

[0027] Figure 8 It is the influence of coexisting anions on the phosphate rejection rate of the adsorption membrane prepared in the embodiment of the present invention.

[0028] Figure 9 It is the bar chart of the cyclic regeneration experiment of the adsorption membrane prepared in the embodiment of the present invention. Detailed Embodiments

[0029] The following further explains the present invention in conjunction with specific embodiments Embodiment

[0030] 1. The ZL 2 @Pal 1 composite material was prepared by a one-step hydrothermal method. First, 5.58 g of zinc nitrate hexahydrate and 2.71 g of lanthanum nitrate hexahydrate were added to 25 mL of deionized water, and the solution was stirred until the solids were completely dissolved. Then, 4.41 g of Pal powder was added to the mixed solution under continuous stirring to obtain a suspension solution A. 1.5 g of NaOH and 1.33 g of Na 2 CO 3Dissolve it in 25 mL of deionized water to obtain a mixed solution B. Dropwise add the mixed solution B into the suspension solution A under continuous stirring. After stirring for 1 hour, pour it into a hydrothermal reaction kettle and react continuously at 160 °C for 8 hours. Collect the solid product by high-speed centrifugation, and wash the product with deionized water and ethanol until the pH value of the solution is 7. Finally, freeze-dry the product for subsequent use; 2. First, dissolve 1 g of ZL 2 @Pal 1 in 5 mL of dimethylformamide (DMF), and ultrasonically stir for 3 hours until the ZL 2 @Pal 1 powder is evenly dispersed in DMF to prepare a 20 wt.% ZL 2 @Pal 1 suspension. Secondly, dissolve 1.25 g of PAN and 0.5 g of PEG in 5 mL of DMF solution, and stir for 3 hours to obtain a mixed polymer solution. Mix the ZL 2 @Pal 1 suspension and the polymer solution in a volume ratio of 1:1, and stir at a temperature of 70 °C for 1 hour to obtain ZL 2 @Pal 1 -PAN / PEG casting solution; then scrape the obtained casting solution onto a polyimide plastic sheet. After drying, soak it in deionized water solution for 24 hours to dissolve the excess PEG, and obtain ZL 2 @Pal 1 -PAN / PEG adsorption membrane after air drying.

[0031] For the structural characterization and performance evaluation, see the above text.

Claims

1. An adsorption membrane for selectively removing phosphate from water, characterized in that: The adsorption film was prepared by the following steps: 1) Zinc nitrate hexahydrate and lanthanum nitrate hexahydrate are respectively added to deionized water, and the solution is stirred until the solid is completely dissolved. Then, palygorskite powder is added to the mixed solution under continuous stirring to obtain a suspension solution A; NaOH and Na2CO3 are co-dissolved in deionized water to obtain a mixed solution B, and the mixed solution B is added dropwise to the suspension solution A under stirring, and a hydrothermal reaction is carried out at 150-180°C for 6-8h, and the product is collected by centrifugation, washed and dried to obtain ZL2@Pal1; 2) Disperse ZL2@Pal1 in N,N-dimethylformamide to obtain suspension solution C; then dissolve polyacrylonitrile and polyethylene glycol in N,N-dimethylformamide to obtain mixed solution D; mix equal volumes of suspension solution C and mixed solution D, stir and react at 60-80°C for 45-60 minutes to obtain ZL2@Pal1-PAN / PEG casting solution; 3) The ZL2@Pal1-PAN / PEG casting liquid was coated on the surface of the substrate, and after drying, it was soaked in deionized water for 20 to 24 hours, then peeled off from the substrate, and naturally dried to obtain the ZL2@Pal1-PAN / PEG adsorption film.

2. An adsorption membrane for selectively removing phosphate from water as claimed in claim 1, characterized in that: In step 1), the molar ratio of zinc nitrate hexahydrate to lanthanum nitrate hexahydrate is 2:1-5:

1.

3. An adsorption membrane for selectively removing phosphate from water as claimed in claim 1, characterized in that: In step 1), the amount of palygorskite powder added is 40% to 60% of the total mass of zinc nitrate hexahydrate and lanthanum nitrate hexahydrate.

4. An adsorption membrane for selectively removing phosphate from water as claimed in claim 1, characterized in that: In step 1), the molar ratio of NaOH to Na2CO3 is 2:1 to 4:

1.

5. An adsorption membrane for selectively removing phosphate from water as claimed in claim 1, characterized in that: In step 2), the concentration of ZL2@Pal1 in N,N-dimethylformamide is 15%~25%.

6. An adsorption membrane for selectively removing phosphate from water as claimed in claim 1, characterized in that: In step 2), the concentration of polyacrylonitrile in N,N-dimethylformamide is 20% to 30%, and the concentration of polyethylene glycol in N,N-dimethylformamide is 5% to 15%.

7. An adsorption membrane for selectively removing phosphate from water as claimed in claim 1, characterized in that: In step 3), the substrate is one of glass, plastic, metal or ceramic.

8. An adsorption membrane for selectively removing phosphate from water as claimed in claim 1, characterized in that: In step 3), the coating method is one of spray coating, spin coating, scraping coating or drip coating.

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