UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of water pollutant removal, in particular to a UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material and a preparation method and application thereof.The preparation method comprises the steps that zirconium chloride and terephthalic acid are dissolved in an organic solvent to obtain a mixed solution, the mixed solution is transferred into a reaction kettle, and through solvothermal reaction, the UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material is obtained; the preparation method comprises the following steps: preparing UiO-66 powder; putting UiO-66 powder into the sodium carboxymethyl cellulose solution, and uniformly stirring the UiO-66 powder and the sodium carboxymethyl cellulose solution to obtain a UiO-66 / CMC mixed solution; placing the UiO-66 / CMC mixed solution in a polyvinyl alcohol solution, and uniformly stirring the UiO-66 / CMC / PVA mixed solution to obtain a UiO-66 / CMC / PVA mixed solution; the preparation method comprises the following steps: dipping a melamine sponge in a UiO-66 / CMC / PVA mixed solution to obtain an adsorption saturated melamine sponge; the UiO-66 / CMC / PVA / coated MS composite material is obtained by repeatedly freezing and thawing the adsorption saturated melamine sponge for multiple times and then freeze-drying, the composite material can be used for rapidly, efficiently and selectively removing phosphate or fluorine ions and the like in water and is convenient to separate and recycle, and a new thought is provided for development of efficient water treatment adsorbent materials.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of water body pollutant removal, and in particular to a UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material and a preparation method and application thereof. BACKGROUND

[0002] Phosphorus-containing wastewater has the dual attributes of environmental pollution and resource utilization, and efficient recovery and resourceful treatment of phosphorus have become a research hotspot in the field of water treatment. Among various wastewater treatment technologies, the adsorption method is widely used for removal of various pollutants in water due to its advantages of simple operation, high efficiency, and wide source of adsorbents.

[0003] Metal-organic framework (MOF) is a new type of porous material, which has shown excellent adsorption potential due to its ultra-high specific surface area, controllable pore structure, and rich active sites, and has become an important research direction in the field of adsorbent materials. Among them, zirconium-based MOF material UiO-66 has shown significant advantages in phosphorus adsorption due to its high specific surface area, strong affinity and high selectivity to phosphate, and simple preparation process and low cost. However, the pure UiO-66 material is often in the form of powder in the application of actual water bodies, which is easy to agglomerate and difficult to realize solid-liquid separation, seriously limiting its engineering application.

[0004] In order to overcome the above bottleneck, existing research attempts to load MOF materials on porous carriers such as gel balls, biochar or ion exchange resins to improve their dispersibility and separation performance. However, such carrier materials often have problems such as complex synthesis process, poor mechanical stability, easy loss, high cost, etc. In addition, their small specific surface area and limited pore volume are also not conducive to the rapid contact between phosphate ions and active sites, resulting in reduced adsorption rate and adsorption capacity.

[0005] In contrast, sponge-based matrix materials are considered as ideal macroporous scaffold materials due to their low density, low cost, good flexibility, adjustable surface properties, and excellent chemical stability, etc. For example, melamine sponge (MS) and polyurethane sponge (PUF) have highly interconnected open pore structures, can efficiently accommodate liquid, and the surface is rich in amine groups and other functional groups, which are easy to modify, so they are considered as a good candidate for carrier materials.

[0006] In the prior art, Liu et al. (Chemical Engineering Journal, 2021, 421:127848) used melamine sponge as a carrier, prepared a phosphorus removal adsorbent loaded with hydrated aluminum oxide by impregnating an aluminum chloride solution and reacting at high temperature. The material exhibits good performance under a wide range of pH and coexisting anions. Brockgreitens et al. (Environ. Sci. Technol. 2020, 54, 9034-9043) used polyurethane sponge to load ferrous sulfate, and obtained a nano composite sponge adsorbent after heat treatment. However, such materials still have the problems of limited adsorption capacity and insufficient stability, the main reasons including: the unmodified sponge surface has limited functional groups, it is difficult to stably fix a sufficient number of metal nanoparticles without using adhesives; the loaded metal particles are prone to agglomeration, resulting in uneven distribution of active sites and decreased availability.

[0007] In view of this, the present application is proposed. SUMMARY

[0008] The present application aims to provide a UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material and a preparation method thereof. The UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material prepared by the present application has a surface uniformly distributed with abundant UiO-66 crystals and has the characteristics of high porosity, can quickly, efficiently and selectively remove phosphate or fluoride ions in water, and is convenient to separate and recover, thereby providing a new idea for the development of efficient water treatment adsorbent materials.

[0009] In a first aspect, the present application provides a preparation method of a UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material, comprising the following steps:

[0010] S1, dissolving zirconium chloride and terephthalic acid in an organic solvent to obtain a mixed solution, transferring the mixed solution to a reaction kettle, and preparing UiO-66 powder by solvothermal reaction;

[0011] S2, placing the UiO-66 powder in a sodium carboxymethyl cellulose solution and stirring uniformly to obtain a UiO-66 / sodium carboxymethyl cellulose mixed solution;

[0012] S3, placing the UiO-66 / sodium carboxymethyl cellulose mixed solution in a polyvinyl alcohol solution and stirring uniformly to obtain a UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol mixed solution;

[0013] S4, immersing melamine sponge in the UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol mixed solution to obtain adsorption-saturated melamine sponge;

[0014] S5, after repeated freeze-thawing of the adsorption saturated melamine sponge, the UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / melamine sponge composite material is obtained by freeze-drying.

[0015] In the preparation method of the present application, carboxymethyl cellulose sodium (CMC) is a highly hydrophilic polymer with a molecular chain rich in carboxyl (-COOH) and hydroxyl (-OH) functional groups. These functional groups can be combined with the metal zirconium clusters (Zr 4+ ) on the surface of the UiO-66 nanoparticles through electrostatic interactions and coordination bonds, effectively preventing the agglomeration of UiO-66 particles and allowing them to disperse uniformly in water to form a stable suspension, which is a prerequisite for achieving high dispersion of UiO-66 on the sponge framework. Polyvinyl alcohol (PVA) has a synergistic crosslinking effect with CMC, and the PVA molecular chain also contains a large number of hydroxyl groups. When mixed with the CMC solution, the two can form a dense three-dimensional network structure through intermolecular hydrogen bonds. During the subsequent repeated freeze-thawing process, this hydrogen bond network is further strengthened and solidified, ultimately forming a firm "CMC / PVA composite gel" coating. This gel layer can coat and firmly fix the uniformly dispersed UiO-66 particles on the surface of the sponge framework, thereby preventing the loss of active components during actual use. In addition, melamine sponge (MS) itself has a highly interconnected macroporous structure (tens to hundreds of microns), providing a fast transport channel for water flow, which can significantly reduce the pressure drop during adsorption. UiO-66 itself also has a large microporous and mesoporous specific surface area, which is the main active site for capturing phosphate ions. The CMC / PVA gel layer itself also has a porous structure and does not completely block the macroporous channels of the sponge, but rather serves as a functional coating on the framework. Therefore, the multi-level pore structure of the composite material "sponge macropore + gel layer mesopore / micropore + UiO-66 micropore" ensures that phosphate ions can quickly diffuse through the macropores to the interior of the adsorbent and smoothly pass through the gel layer to fully contact the internal UiO-66 active sites, achieving rapid mass transfer and high efficiency adsorption.

[0016] Therefore, by the synergistic effect of CMC and PVA, the present application ingeniously solves the two technical problems of poor dispersion of UiO-66 and poor loading of sponge, successfully preparing a composite adsorbent material with high adsorption performance, excellent mechanical strength, and excellent operational convenience, providing a highly potential new technical solution for the resource treatment of phosphorus-containing or fluorine-containing wastewater.

[0017] As a preferred embodiment of the present technical solution, in step S1, the molar ratio of the zirconium chloride to the terephthalic acid is 1:1, and the volume of the required organic solvent corresponding to 1-1.5 g of the zirconium chloride is 150-250 mL;

[0018] The organic solvent includes any one of N,N-dimethylformamide, absolute ethanol and dimethyl sulfoxide, and is preferably N,N-dimethylformamide.

[0019] As the preferred technical solution, in step S1, the temperature is controlled to be 110-130℃ and the time is 20-30h during the solvothermal reaction.

[0020] After the solvothermal reaction is completed, the precipitate is separated by centrifugation (9000rpm, 10min), then washed 2-4 times with an organic solvent, then soaked in a methanol solution for 24h, finally the precipitate is separated by centrifugation (9000rpm, 10min), and dried in a vacuum drying box (25-35℃) for 24h to obtain a UiO-66 powder.

[0021] As the preferred technical solution, in step S2, the mass fraction of the sodium carboxymethyl cellulose solution is 3wt%-5wt%, the mass ratio of the sodium carboxymethyl cellulose solution to the UiO-66 powder is (1-2):1, and magnetic stirring is performed for 12-24h to obtain a UiO-66 / sodium carboxymethyl cellulose mixed solution.

[0022] As the preferred technical solution, in step S3, the mass fraction of the polyvinyl alcohol solution is 5wt%-6wt%, and after the UiO-66 / CMC mixed solution is added to the polyvinyl alcohol solution, magnetic stirring is performed for 12-24h to obtain a UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol mixed solution.

[0023] As the preferred technical solution, in step S4, the melamine sponge is cut (such as a cylinder with a thickness of 5mm and a diameter of 20mm), soaked in ethanol, washed with pure water, and dried in sequence before use, and then the pretreated melamine sponge is immersed in the UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol mixed solution to obtain an adsorption-saturated melamine sponge.

[0024] As the preferred technical solution, in step S5, the adsorption-saturated melamine sponge is frozen at -18~-24℃ for 8-12h, then thawed at room temperature for 4-6h, the freezing and thawing is repeated for 4-6 times, and finally freeze-dried for 12-24h to obtain a UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material.

[0025] In the freeze-thaw process of the present application, when the melamine sponge impregnated with the UiO-66 / CMC / PVA mixed solution is placed in a low temperature (-18 to -24 DEG C) environment, the water molecules in the system will gradually form ice crystals, and the growth of the ice crystals will repel and squeeze the high molecular chains (CMC and PVA) dissolved in the water and the dispersed UiO-66 particles. This squeezing effect forces the adjacent CMC and PVA molecular chains to come close to each other. During the subsequent room temperature thawing process, the ice crystals melt, and a large number of strong intermolecular hydrogen bonds (-OH and -OH, -OH and -COO-, etc.) are formed between the CMC and PVA molecular chains that are squeezed and closely adjacent. Thereafter, each freeze-thaw cycle is a reorganization and strengthening process of the hydrogen bond network, and after 4-6 repeated cycles, a dense, uniform and firm three-dimensional microporous network structure is formed between the CMC and PVA, thereby firmly wrapping and anchoring the UiO-66 particles on the three-dimensional skeleton of the melamine sponge. Finally, through the freeze-drying technology, the ice is directly sublimated under high vacuum and low temperature, which can maximize the avoidance of the collapse of the gel network and the destruction of the pore structure caused by surface tension during the drying process, and the open porous structure formed during the freeze-thaw process is perfectly preserved. Therefore, the present application realizes the sufficient crosslinking of CMC and PVA through a pure physical freeze-thaw process without using toxic chemical crosslinking agents, and forms a high-strength microporous gel coating.

[0026] As the preferred technical solution of the present application, in step S2 and / or step S3, the stirring can be in the form of magnetic stirring, ultrasonic stirring or mechanical stirring, and preferably magnetic stirring.

[0027] In a second aspect, the present application also discloses a UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / melamine sponge composite prepared by the above preparation method, which also belongs to the protection scope of the present application.

[0028] In a third aspect, the present application also discloses an application of the above UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / melamine sponge composite in adsorbing and removing anions in water, and specifically, the anions include phosphate ions and fluoride ions.

[0029] The UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / melamine sponge composite (UiO-66 / CMC / PVA@MS) is added into wastewater containing phosphate ions or fluoride ions, and the UiO-66 / SA / CMC can selectively adsorb the phosphate ions or fluoride ions therein. Researches show that the above UiO-66 / CMC / PVA@MS has a high and stable adsorption capacity under neutral and alkaline conditions (pH = 7-10), and has excellent selective adsorption performance for phosphorus.

[0030] The preparation method of the UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material has at least the following beneficial effects:

[0031] 1. The UiO-66 particles in the application can be uniformly distributed on the sponge skeleton in the form of single dispersion or small agglomerates, avoiding the problem of active sites being masked due to self-agglomeration, so that most of the adsorption sites are exposed to the water body, greatly improving the utilization rate of the adsorption capacity of UiO-66. Therefore, the composite material can exhibit high adsorption capacity and rapid adsorption kinetics for phosphate and fluoride ions;

[0032] 2. The composite hydrogel coating formed by freezing and thawing of CMC and PVA has excellent mechanical toughness and adhesion, which can firmly bond the UiO-66 on the sponge skeleton. Therefore, the preparation method of the application significantly enhances the overall mechanical strength of the composite material, so that it can withstand the friction and shear force generated in actual application, effectively preventing the powdering and falling off of the functional material, prolonging the service life of the composite material;

[0033] 3. The composite material of the application uses melamine sponge as the matrix, inherits the macro-block morphology and elasticity of melamine sponge, and can easily realize instantaneous solid-liquid separation through simple methods such as clamping and sedimentation after adsorption is completed, completely solving the core technical problem of difficult recovery and easy secondary pollution of powder nanometer adsorbent; in addition, the melamine sponge has the advantages of small water flow resistance and large flux due to its high porosity and open structure, which provides the possibility for direct application in large-scale water treatment engineering;

[0034] 4. The raw materials used in the application are low in cost and easy to obtain, the preparation process does not require complex equipment, and the overall cost is high, which is beneficial to large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the specific embodiments of the application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the description of the specific embodiments or the prior art. Obviously, the drawings described below are some embodiments of the application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0036] Figure 1 The preparation schematic diagram of the UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material of Example 1 of the application;

[0037] Figure 2SEM images of the UiO-66 powder, MS, and the UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS) of Example 1 of the present application, wherein: (a) is the micro-morphology of the UiO-66 powder; (b) is the micro-morphology of the MS; (c) is the micro-morphology of the UiO-66 / CMC / PVA@MS under low magnification; (d) is the micro-morphology of the UiO-66 / CMC / PVA@MS under high magnification;

[0038] Figure 3 XRD spectra of the UiO-66 powder and the UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS) of Example 1 of the present application;

[0039] Figure 4 Mechanical properties of the UiO-66 powder and the UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS) of Example 1 of the present application;

[0040] Figure 5 Adsorption and removal of phosphorus performance of the UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS) of Example 1 of the present application under different pH conditions;

[0041] Figure 6 Adsorption and removal of phosphorus performance of the UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS) of Example 1 of the present application under the influence of different concentrations of coexisting ions;

[0042] Figure 7 Adsorption kinetics of phosphate by the UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS) of Example 1 of the present application;

[0043] Figure 8 Adsorption isotherm of phosphate by the UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS) of Example 1 of the present application. DETAILED DESCRIPTION

[0044] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0045] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0046] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] Example 1

[0048] like Figure 1 As shown, the preparation method of the UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS) in this embodiment includes the following steps:

[0049] Preparation of S1 and UiO-66

[0050] Weigh 4 mmol of zirconium chloride (ZrCl4) and terephthalic acid, dissolve them in 200 mL of N,N-dimethylformamide (DMF) solution, and stir magnetically until homogeneous. Then transfer the homogeneous mixture to a reaction vessel and place the reaction vessel in a vacuum drying oven. React at 120 °C for 24 hours. After the reaction, separate the precipitate by centrifugation (9000 rpm, 10 min), wash it three times with DMF, soak it in methanol solution for 24 hours, and finally separate the precipitate by centrifugation (9000 rpm, 10 min) and dry it in a vacuum drying oven (30 °C) for 24 hours to obtain UiO-66 powder.

[0051] S2. Prepare UiO-66 / CMC mixture.

[0052] Weigh 2g of sodium carboxymethyl cellulose (CMC) and dissolve it in 50mL of deionized water. Add 1.5g of the UiO-66 powder prepared above to the solution and mix evenly by magnetic stirring for 24 hours to obtain a UiO-66 / CMC mixture.

[0053] S4. Prepare the UiO-66 / CMC / PVA mixture.

[0054] Weigh 3g of polyvinyl alcohol (PVA) and dissolve it in 50mL of deionized water. Stir the mixture magnetically until homogeneous. Add the UiO-66 / CMC mixture to the PVA solution and stir magnetically for 24 hours until homogeneous to obtain the UiO-66 / CMC / PVA mixture.

[0055] Preparation of S5, UiO-66 / CMC / PVA@MS

[0056] Commercial melamine sponge (MS) was appropriately cut (e.g., into cylinders with a thickness of 5 mm and a diameter of 20 mm), then soaked in ethanol and pure water to wash it, and finally dried for later use. Then, a certain amount of sponge (50 sponges) was sequentially immersed in the above-mentioned gel precursor solution containing UiO-66. After adsorption saturation, it was taken out and frozen at -20°C for 8 to 12 hours, then thawed at room temperature for 4 to 6 hours. The freeze-thaw cycle was repeated 5 times. Finally, it was freeze-dried for 12 to 24 hours to obtain the UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS).

[0057] Example 2

[0058] like Figure 1 As shown, the preparation method of the UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS) in this embodiment includes the following steps:

[0059] Preparation of S1 and UiO-66

[0060] Weigh 4 mmol of zirconium chloride (ZrCl4) and terephthalic acid, dissolve them in 200 mL of anhydrous ethanol solution, and stir magnetically until homogeneous. Then transfer the homogeneous mixture to a reaction vessel and place the reaction vessel in a vacuum drying oven. React at 110 °C for 30 hours. After the reaction, separate the precipitate by centrifugation (9000 rpm, 10 min), wash it three times with anhydrous ethanol, soak it in methanol solution for 24 hours, and finally separate the precipitate by centrifugation (9000 rpm, 10 min) and dry it in a vacuum drying oven (30 °C) for 24 hours to obtain UiO-66 powder.

[0061] S2. Prepare UiO-66 / CMC mixture.

[0062] Weigh 2.5g of sodium carboxymethyl cellulose (CMC) and dissolve it in 50mL of deionized water. Add 1.5g of the UiO-66 powder prepared above to the solution and mix evenly by magnetic stirring for 24 hours to obtain a UiO-66 / CMC mixture.

[0063] S4. Prepare the UiO-66 / CMC / PVA mixture.

[0064] Weigh 2.5g of polyvinyl alcohol (PVA) and dissolve it in 50mL of deionized water. Stir the mixture magnetically until homogeneous. Add the UiO-66 / CMC mixture to the PVA solution and stir magnetically for 24 hours until homogeneous to obtain the UiO-66 / CMC / PVA mixture.

[0065] Preparation of S5, UiO-66 / CMC / PVA@MS

[0066] Commercial melamine sponge (MS) was appropriately cut (e.g., into cylinders with a thickness of 5 mm and a diameter of 20 mm), then soaked in ethanol and pure water to wash, and finally dried for later use. Then, a certain amount of sponge (50 sponges) was sequentially immersed in the above-mentioned gel precursor solution containing UiO-66. After adsorption saturation, the sponge was removed and frozen at -20°C for 8 to 12 hours, then thawed at room temperature for 4 to 6 hours. This freeze-thaw cycle was repeated 6 times. Finally, the sponge was freeze-dried for 12 to 24 hours to obtain the UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS).

[0067] Example 3

[0068] like Figure 1 As shown, the preparation method of the UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS) in this embodiment includes the following steps:

[0069] Preparation of S1 and UiO-66

[0070] Weigh 4 mmol of zirconium chloride (ZrCl4) and terephthalic acid, dissolve them in 225 mL of N,N-dimethylformamide (DMF) solution, and stir magnetically until homogeneous. Then transfer the homogeneous mixture to a reaction vessel and place the reaction vessel in a vacuum drying oven. React at 130 °C for 20 hours. After the reaction, separate the precipitate by centrifugation (9000 rpm, 10 min), wash three times with DMF, soak in methanol solution for 24 hours, and finally separate the precipitate by centrifugation (9000 rpm, 10 min) and dry in a vacuum drying oven (30 °C) for 24 hours to obtain UiO-66 powder.

[0071] S2. Prepare UiO-66 / CMC mixture.

[0072] Weigh 1.5g of sodium carboxymethyl cellulose (CMC) and dissolve it in 50mL of deionized water. Add 1.5g of the UiO-66 powder prepared above to the solution and mix evenly by magnetic stirring for 24 hours to obtain a UiO-66 / CMC mixture.

[0073] S4, preparation of UiO-66 / CMC / PVA mixed solution

[0074] 2.5 g of polyvinyl alcohol (PVA) was weighed and dissolved in 50 mL of deionized water, and stirred uniformly by magnetic stirring; the UiO-66 / CMC mixed solution was added to the PVA solution, and stirred uniformly by magnetic stirring for 24 hours to obtain a UiO-66 / CMC / PVA mixed solution;

[0075] S5, preparation of UiO-66 / CMC / PVA@MS

[0076] Commercial melamine sponge (MS) was appropriately cut (for example, a cylinder with a thickness of 5 mm and a diameter of 20 mm), then washed with ethanol and pure water, and finally dried for standby use; then, a certain amount of sponge (50) was sequentially immersed in the above-mentioned gel precursor solution containing UiO-66, adsorbed and saturated, taken out, frozen at-20℃ for 8-12 hours, thawed at room temperature for 4-6 hours, repeated freezing and thawing for 4 times, and finally freeze-dried for 12-24 hours to obtain a UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS).

[0077] Test Example 1

[0078] The micro-morphology of the UiO-66 powder, MS, and UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS) of Example 1 was detected by scanning electron microscopy (SEM), and the results are shown in Figure 2 .

[0079] As can be seen from Figure 2 (a), the UiO-66 presents an octahedral crystal shape;

[0080] As can be seen from Figure 2 (b), the MS sponge has a three-dimensional porous framework structure with a smooth surface;

[0081] As can be seen from Figure 2 (c), under low magnification, the inner surface of the UiO-66 / CMC / PVA@MS framework forms a gel layer but still retains a porous structure, which can effectively increase the specific surface area and thus improve the adsorption affinity of the composite sponge;

[0082] As can be seen from Figure 2 (d), under high magnification, the gel layer in the inner surface of the UiO-66 / CMC / PVA@MS framework is loaded with crystal particles, indicating the presence of UiO-66.

[0083] Test Example 2

[0084] The crystal structures of the UiO-66 powder prepared in Example 1 and the UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / foamed melamine sponge composite material (UiO-66 / CMC / PVA@MS) were analyzed by an X-ray powder diffractometer (XRD), and the results are shown in Figure 3 .

[0085] As can be seen from Figure 3 , the UiO-66 powder has obvious characteristic peaks at 2θ = 7.4°, 8.5°, 12.0°, 25.7° and 33.1°, which are consistent with the diffraction peak positions in the UiO-66 spectrum reported in the literature (Zhang et al, Journal of Environmental Chemical Engineering 9 (2021) 106672), indicating that the UiO-66 is successfully prepared. In addition, the UiO-66 / CMC / PVA@MS also has characteristic peaks at the same positions, but the intensity is weakened, indicating that the sponge surface is successfully loaded with UiO-66 crystal particles.

[0086] Test Example 3

[0087] The mechanical properties of the MS and the UiO-66 / CMC / PVA@MS of Example 1 were detected by a universal testing machine, and the results are shown in Figure 4 .

[0088] As can be seen from Figure 4 , compared with the pure MS, the mechanical properties of the UiO-66 / CMC / PVA@MS are greatly improved, and when the compression strain is 8.8%, the compression stress it can withstand is as high as 44.8 kPa. This high mechanical strength is conducive to the application of the adsorbent material in the actual dynamic adsorption process.

[0089] Test Example 4

[0090] The adsorption and phosphorus removal performance of the UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / foamed melamine sponge composite material (UiO-66 / CMC / PVA@MS) of Example 1 at different pH values was detected, and the details are as follows:

[0091] A phosphate solution with a concentration of 100 mg / L was prepared using potassium dihydrogen phosphate, and then 0.1 mol / L NaOH and 0.1 mol / L HCl were used to adjust the pH to 3-11. The UiO-66 / CMC / PVA@MS (50 mg) of Example 1 was placed in 40 mL of the phosphate solution, and was oscillated at 25°C for 24 h. After the reaction, the supernatant was taken to determine the residual phosphorus concentration of the solution, and the adsorption amount was determined according to formula (1).

[0092]

[0093] In the formula: q t V is the amount of adsorbent adsorbed in time t, mg-P / g; V is the volume of the phosphate solution, mL; C o and C t , respectively, represent the phosphorus concentration in the solution before and after adsorption, in mg / L; m is the mass of the adsorbent, in g.

[0094] Figure 5 The adsorption and phosphorus removal performance of UiO-66 / CMC / PVA@MS at different pH values ​​was evaluated.

[0095] Depend on Figure 5 It is known that UiO-66 / CMC / PVA@MS exhibits high adsorption capacity under both neutral and slightly alkaline conditions (pH = 7-10), and its adsorption performance remains stable. Eutrophic lakes typically exhibit neutral or slightly alkaline water due to the presence of large amounts of nutrients. Therefore, the UiO-66 / CMC / PVA@MS composite material of this invention fully meets the practical application requirements for such water bodies.

[0096] Experimental Example 5

[0097] This invention also investigated the effect of coexisting ions on the phosphorus adsorption and removal performance of the UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS) of Example 1, as detailed below:

[0098] Weigh out a certain amount of sodium chloride (NaCl), sodium nitrate (NaNO3) and sodium sulfate (Na2SO4), and add them to a 100 mg / L phosphate solution respectively. Do not adjust the pH of the solution. Then add UiO-66 / CMC / PVA@MS (50 mg) to the solution and shake at 25 °C for 24 h. After the reaction is complete, take the supernatant to determine the concentration of the remaining phosphorus in the solution, and determine the adsorption amount according to formula (1).

[0099] Figure 6 The effect of coexisting ions on the phosphorus removal performance of UiO-66 / CMC / PVA@MS.

[0100] Depend on Figure 6 It can be known that Cl - and NO3 - It has almost no effect on the phosphorus removal efficiency of UiO-66 / CMC / PVA@MS, SO4 2- It has a certain inhibitory effect, but with SO4 2- The inhibitory effect was not significant with increasing concentration. These results indicate that UiO-66 / CMC / PVA@MS exhibits highly efficient selective adsorption of phosphates in water, almost unaffected by coexisting ions.

[0101] Experimental Example 6

[0102] The adsorption kinetics of the UiO-66 / CMC / PVA@MS prepared in Example 1 was also detected, as follows:

[0103] The UiO-66 / CMC / PVA@MS (50 mg) of Example 1 was placed in 40 mL of phosphate solution with pH = 8.0 and a concentration of 100 mg / L prepared by potassium dihydrogen phosphate, and was oscillated at 25°C. The supernatant was taken at different time intervals to determine the residual phosphorus concentration of the solution, and the adsorption amount was determined according to formula (1).

[0104] The obtained experimental data was fitted by using the pseudo-first-order reaction kinetics model and the pseudo-second-order reaction kinetics model, and the equations are as follows:

[0105]

[0106] In the formula: q t and q e are the adsorption amounts (mg-P / g) at time t and at adsorption equilibrium, respectively; k1 and k2 are the adsorption rate constants of the pseudo-first-order and pseudo-second-order reactions, respectively, min -1 , (g / mg / min).

[0107] Figure 7 The adsorption kinetics results of UiO-66 / CMC / PVA@MS.

[0108] As can be seen from Figure 7 , in the initial stage, the adsorption rate of UiO-66 / CMC / PVA@MS is very fast, and with the extension of time, the adsorption rate gradually decreases.

[0109] The results of the kinetic model fitting are shown in Table 1.

[0110] As can be seen from Table 1, the correlation coefficient of the pseudo-second-order kinetics model is higher than that of the pseudo-first-order kinetics model, indicating that the adsorption process of UiO-66 / CMC / PVA@MS on phosphate is mainly chemical adsorption.

[0111] Table 1 Adsorption kinetics model fitting parameters of UiO-66 / CMC / PVA@MS on phosphate in water

[0112]

[0113] Test Example 7

[0114] The application further detects the adsorption isotherm of the UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS) of Example 1, and the detection is specifically as follows:

[0115] The UiO-66 / CMC / PVA@MS (50 mg) of Example 1 is placed in 40 mL of KH2PO4 solution with different concentrations (the concentration is 25-500 mg / L, and the pH is adjusted to 9.0), and the adsorption experiment is carried out in a constant temperature oscillator at 298 K, 308 K and 318 K respectively until the adsorption equilibrium is reached, the residual phosphorus concentration in the supernatant is accurately determined, and the adsorption amount is determined according to formula (1).

[0116] The Langmuir model and the Freundlich model are used to fit the adsorption isotherm data, and the equations are as follows:

[0117]

[0118] q e =k F C e 1 / n (5)

[0119] In the formula, q e is the adsorption amount at the adsorption equilibrium (mg / g), q max is the maximum adsorption amount (mg / g), C e is the phosphorus concentration in the solution at the adsorption equilibrium (mg / L), k L is the Langmuir model constant (L / mg), k F is the Freundlich model constant ((mg / g)·(L / mg) 1 / n ), and n is the Freundlich isotherm equation constant.

[0120] Figure 8 Table 1 is the adsorption isotherm of the UiO-66 / CMC / PVA@MS for the phosphate in water, and Table 2 is the adsorption isotherm model fitting parameter of the UiO-66 / CMC / PVA@MS for the phosphate in water.

[0121] From Figure 8As can be seen from Table 2, the correlation coefficient of the Langmuir model is obviously higher than that of the Freundlich model, which proves that the adsorption process of UiO-66 / CMC / PVA@MS on phosphates in water is more in line with the Langmuir model, indicating that the adsorption process occurs in the monolayer on the surface of the composite. When the temperature is 298K, 308K and 318K, the theoretical adsorption capacity calculated by the Langmuir model is 36.89mg-P / g, 38.38mg-P / g and 40.35mg-P / g respectively, indicating that increasing the temperature is beneficial to the adsorption of phosphorus but has little effect.

[0122] Table 2 Model fitting parameters of adsorption isotherm of UiO-66 / CMC / PVA@MS on phosphates in water

[0123]

[0124]

[0125] Test Example 8

[0126] The performance of the UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol / melamine sponge composite material (UiO-66 / CMC / PVA@MS) of Example 1 in adsorbing phosphates in water was compared with other sponge-based adsorption materials, and the results are shown in Table 3.

[0127] Table 3 Comparison of the maximum adsorption capacity of UiO-66 / CMC / PVA@MS and other sponge-based adsorbents for phosphates in water based on the Langmuir model

[0128]

[0129] As can be seen from Table 3, compared with other sponge-based adsorbent materials, the UiO-66 / CMC / PVA@MS prepared in the application has relatively high adsorption capacity for phosphates in water. This may be due to the synergistic effect of CMC and PVA, which enables UiO-66 to be uniformly and stably loaded on the surface of melamine sponge and improves the utilization rate of adsorption sites.

[0130] In summary, through the synergistic effect of CMC and PVA, the two technical difficulties of poor dispersibility of UiO-66 and poor loading of sponge are ingeniously solved, and a composite adsorbent with high adsorption performance, excellent mechanical strength and excellent operation convenience is successfully prepared, providing a highly potential new technical solution for the resource treatment of phosphorus-containing wastewater.

[0131] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material, characterized in that, Includes the following steps: S1. Dissolve zirconium chloride and terephthalic acid in an organic solvent to obtain a mixed solution. Transfer the mixed solution to a reaction vessel and prepare UiO-66 powder through a solvothermal reaction. S2. Place UiO-66 powder in sodium carboxymethyl cellulose solution and stir evenly to obtain UiO-66 / sodium carboxymethyl cellulose mixture; S3. Place the UiO-66 / carboxymethyl cellulose sodium mixture into a polyvinyl alcohol solution and stir until homogeneous to obtain the UiO-66 / carboxymethyl cellulose sodium / polyvinyl alcohol mixture. S4. Melamine sponge is impregnated in a mixture of UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol to obtain an adsorbed saturated melamine sponge. S5. After repeated freeze-thaw cycles, the adsorbed saturated melamine sponge is freeze-dried to obtain the UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material.

2. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of zirconium chloride to terephthalic acid is 1:1, and the required volume of the organic solvent is 150-250 mL for every 1-1.5 g of zirconium chloride. The organic solvent includes any one of N,N-dimethylformamide, anhydrous ethanol, and dimethyl sulfoxide.

3. The preparation method according to claim 1, characterized in that, In step S1, the solvothermal reaction is carried out at a temperature of 110–130°C for a time of 20–30 h. After the solvothermal reaction is completed, the reaction product is washed with an organic solvent, then soaked in a methanol solution, and finally centrifuged and vacuum dried to obtain UiO-66 powder.

4. The preparation method according to claim 1, characterized in that, In step S2, the mass fraction of the sodium carboxymethyl cellulose solution is 3wt% to 5wt%, and the mass ratio of the sodium carboxymethyl cellulose solution to the UiO-66 powder is (1 to 2):

1.

5. The preparation method according to claim 1, characterized in that, In step S3, the polyvinyl alcohol solution has a mass fraction of 5 wt% to 6 wt%.

6. The preparation method according to claim 1, characterized in that, In step S4, the melamine sponge is cut, soaked in ethanol, washed with pure water, and dried in sequence before use.

7. The preparation method according to claim 1, characterized in that, In step S5, the adsorbed saturated melamine sponge is frozen at -18 to -24°C for 8 to 12 hours, then thawed at room temperature for 4 to 6 hours. This freeze-thaw cycle is repeated 4 to 6 times, and finally freeze-dried for 12 to 24 hours to obtain the UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material.

8. The preparation method according to claim 1, characterized in that, In step S2 and / or step S3, the stirring is performed using magnetic stirring, mechanical stirring, or ultrasonic stirring.

9. A UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material, characterized in that, It is prepared according to any one of claims 1-8.

10. The application of the UiO-66 / sodium carboxymethyl cellulose / polyvinyl alcohol / melamine sponge composite material according to claim 9 in the adsorption and removal of anionic pollutants in water, characterized in that, The anions include phosphate ions and fluoride ions.

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