Cellulose-based composite for simultaneously removing copper and tetracycline from water body and preparation method thereof

Abstract

The application discloses a cellulose-based composite material for simultaneously removing copper and tetracycline from water bodies and a preparation method thereof, and belongs to the technical field of environmental functional composite materials. The cellulose-based composite material is Zr-MOF / CNF, and the specific preparation steps include the following steps: first, a zirconium (Zr)-based MOF is prepared by using an ultrasonic method; then, nanocellulose is prepared by using a TEMPO oxidation method; and finally, the obtained white suspension liquid is mixed under ultrasonic assistance, centrifuged, washed with water and washed with alcohol, so as to obtain a Zr-MOF / CNF composite material. The material is synthesized by using the ultrasonic method, the preparation process is simple, the raw material cost is low, and the problems of the cellulose, such as the lack of a porous structure, the MOF particle agglomeration and the poor water stability, are improved, and the practical application capability of the Zr-MOF / CNF is improved. The cellulose-based composite material can effectively adsorb copper and tetracycline, when the initial concentrations of the copper and the tetracycline are 32 mg / L and 444 mg / L respectively, and the initial solution pH is 7.0, the adsorption capacities of the Zr-MOF / CNF for the copper and the tetracycline are 157.08 mg / g and 1532 mg / g respectively.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional composite materials technology, specifically relating to a Zr-MOF / CNF composite material that can simultaneously remove copper and tetracycline from water and its preparation method, which is mainly used in the treatment of copper and tetracycline wastewater. Background Technology

[0002] Copper and tetracycline are widely added to animal feed to promote growth and treat diseases. However, most of both copper and tetracycline cannot be absorbed by animals and are excreted into the natural environment. Furthermore, when these two pollutants coexist, they form more toxic complexes, resulting in combined copper and tetracycline pollution. Treatment methods for combined copper and tetracycline pollution in water bodies mainly include physical methods (adsorption, membrane separation), biological methods (immobilized microorganism treatment, anaerobic-aerobic combined treatment), and chemical methods (electrochemical methods, chlorination, advanced oxidation technologies). Among these, adsorption methods are increasingly attracting attention due to their advantages of high efficiency, low cost, simple operation, and low secondary pollution.

[0003] Cellulose is the most abundant polysaccharide in nature, prized for its high aspect ratio, rich functional groups, excellent mechanical properties, good water stability, and environmental friendliness. Metal-organic frameworks (MOFs) are three-dimensional porous organic-inorganic hybrid materials. They possess abundant porosity and extremely high specific surface area. By changing the introduced organic ligands and different reaction conditions, the structure and size of MOFs can be tuned. Due to these advantages, MOFs have been widely used in water pollution control. Zr-based MOFs have been shown to possess excellent water stability, chemical stability, and wide pH adaptability, making them ideal for underwater operation. Our method deviates from the traditional solvothermal method, instead using an ultrasonic method, which has received little attention in the field. MOFs are synthesized in situ on CNFs under ultrasonication. Simultaneously, the introduction of CNFs provides a dispersion carrier for small MOFs, significantly reducing their aggregation and achieving a synergistic effect.

[0004] Against this backdrop, we developed a general and effective strategy to load functionalized Zr-based MOFs onto cellulose nanofibers (CNFs) and synthesize porous materials with good adsorption properties, namely Zr-MOF / CNF composites, using an in-situ growth method under ultrasonic assistance. The Zr-MOF / CNF composites effectively removed copper and tetracycline while maintaining their structural stability in aqueous solution. We also investigated the reusability of the composites for copper and tetracycline and their adsorption mechanism.

[0005] In the prior art, there have been some achievements in the preparation methods of MOF / cellulose composite materials. For example, Chinese Patent No. 202310622290.2, published on May 30, 2023, published a patent document entitled "A MOF / cellulose hydrogel and its preparation method and application". This patent combines MOF into the matrix of the hydrogel, and the self-assembly produces a network nanofiber structure, which greatly improves the mechanical strength, fatigue resistance, self-healing properties and biocompatibility of the hydrogel. The preparation method is relatively complex, and it is still unknown whether improving the mechanical strength of the hydrogel is feasible for use as an adsorbent for adsorbing pollutants. Chinese patent application number: 202311400310.8, published on February 27, 2024, published a patent document entitled "A carboxylated cellulose-based magnetic MOF material and its preparation method and application". This patent firstly prepares carboxylated cellulose-coated magnetic Fe3O4 in one step at room temperature and pressure using a co-precipitation method, and then grows MOF on the surface of carboxylated cellulose-coated magnetic Fe3O4 to obtain carboxylated cellulose-based magnetic MOF for immobilizing pullulanase. This material exhibits good environmental stability and recyclability, and if developed into an adsorbent for adsorbing pollutants, it will have wide applicability. Chinese patent application number: 202110812440.7, published on October 8, 2021, discloses a patent document entitled "A method for preparing MOF-supported aerogel for adsorbing VOCs". This patent involves first grafting modified nanocellulose, and then using hydrothermal reduction, one-step crosslinking, freeze drying and in-situ synthesis to construct a three-dimensional graphene oxide composite aerogel supported on UIO-66-COOH, which is applied to adsorb VOCs. The synergistic adsorption of the composite aerogel carrier and the loaded crystals improves the adsorption capacity and allows the aerogel to rapidly and reversibly adsorb a large amount of VOCs waste gas, which helps to deal with VOCs waste gas with complex composition. However, the adsorption performance of pollutants in water is still unknown. Chinese patent application No. 202210520373.6, published on August 23, 2022, published a patent document entitled "Preparation of HP-UIO-66-NH2 / cellulose composite aerogel material and its application in CO2 adsorption". This patent first prepares microcrystalline cellulose hydrogel, and then grows MOF on the surface of hydrogel to obtain HP-UIO-66-NH2 / cellulose composite aerogel, which is applied to CO2 adsorption.This method attempts to address the issues of MOF particle aggregation and poor mechanical stability. However, it remains uncertain whether the CO2 adsorption mechanism can be applied to the adsorption of pollutants in water. Chinese patent application number 201810467766.9, published on October 12, 2018, discloses a patent document entitled "A MOF-100(Fe) / bacterial cellulose composite material and its preparation method and application." This patent first activates a bacterial cellulose membrane in an alkaline mixed solution to obtain an activated bacterial cellulose membrane. Then, a MOF-100(Fe) / bacterial cellulose composite membrane material is prepared by a cyclic oscillation method for adsorbing organic pollutants such as diclofenac sodium. It shows good removal effects on PPCPs such as diclofenac sodium in natural water environments, but its adsorption and removal capabilities for copper and tetracycline are unknown.

[0006] Several patent documents already exist for the adsorption and removal of copper and tetracycline from water. For example, Chinese Patent Application No. 202410323544.5, published on May 28, 2024, discloses a patent entitled "Preparation of Peanut Shell Biochar and its Adsorption Method for Copper and Nickel Ions in Electroplating Wastewater"; and Chinese Patent Application No. 202410501489.4, published on August 6, 2024, discloses a patent entitled "A Steel Slag-Based Molecular Sieve Adsorption Material in..." The patent documents mentioned above mainly focus on the adsorption and removal of copper ions from wastewater; Chinese patent application number 202111230288.8, published on May 24, 2024, entitled "Preparation method of a composite adsorbent for removing tetracycline from wastewater"; and Chinese patent application number 202111427480.6, published on January 28, 2022, entitled "Application of nylon 6 / chitosan-Fe nanofiber composite material in the adsorption of tetracycline". These patents primarily address the adsorption and removal of single pollutants such as copper and tetracycline in water, but do not cover binary composite pollutants. Summary of the Invention

[0007] To address the shortcomings and deficiencies of existing technologies in removing copper and tetracycline from water, the problems of MOF particle agglomeration and poor water stability, and the lack of porous structure in cellulose, this invention provides a porous MOF-nanocellulose CNF composite material and its preparation method, aiming to overcome the above-mentioned deficiencies of existing technologies.

[0008] To solve the above problems, the present invention adopts the following technical solution.

[0009] This invention provides a cellulose-based composite material for simultaneously removing copper and tetracycline from water. This composite material is Zr-MOF / CNF, and MOF is synthesized in situ on the CNF surface under ultrasonic assistance. The specific steps include:

[0010] (1) Mix Ulva cellulose and water to form a suspension and stir magnetically until evenly dispersed; add TEMPO and NaBr and stir until completely dissolved, then add NaClO solution; control the pH at 10 by adding NaOH solution, and immediately add anhydrous ethanol to terminate the reaction when the pH no longer changes within 15 min. Then filter the oxidized cellulose and wash it with distilled water until the pH is neutral; sonicate the obtained nanocellulose suspension for 15 min, freeze dry to obtain CNF; the mass ratio of TEMPO to NaBr is 4:25.

[0011] (2) Add ZrCl4·8H2O and H3BTC to a mixed solution of DMF and formic acid, stir to ensure uniform mixing, and then sonicate. After centrifugation, pour off the supernatant and wash with deionized water and anhydrous ethanol to remove residual ZrCl4·8H2O and H3BTC. Then put the centrifuged precipitate into a drying oven to dry. After complete drying, grind and sieve to obtain Zr-MOF. The molar ratio of ZrCl4·8H2O and H3BTC is 1:1.

[0012] (3) Add Zr-MOF and CNF to deionized water, and after ultrasonic treatment, put the precipitate after centrifugation into a drying oven and dry it completely to obtain a Zr-MOF / CNF composite material; the mass ratio of Zr-MOF to CNF is 10-0.1:1.

[0013] Furthermore, in step (2), the conditions for ultrasonic treatment are: ultrasonic waves at 70°C for 90 minutes with a power of 600W.

[0014] Furthermore, in step (3), the mass ratio of Zr-MOF to CNF is 1:5.

[0015] Furthermore, in step (3), the conditions for the ultrasonic treatment are: ultrasonic treatment at room temperature for 60 minutes.

[0016] The cellulose-based composite material obtained by the above preparation method can simultaneously remove copper and tetracycline from water.

[0017] The specific principles of this invention are speculated as follows:

[0018] The adsorption mechanism of copper and tetracycline in water by Zr-MOF / CNF involves the electrostatic attraction of copper and tetracycline to the Zr-MOF / CNF surface. These substances then diffuse into the pores through the macroporous structure of Zr-MOF / CNF, and finally, copper and tetracycline are adsorbed by the -COOH groups on the Zr-MOF / CNF surface. Furthermore, it is hypothesized that the adsorption and removal process is related to interactions with copper complexes, protonated functional groups, and chelating bonds.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) The Zr-MOF / CNF composite material of the present invention provides more adsorption sites for the composite material by in-situ growth of MOF on CNF surface. Anchoring MOF and nanocellulose both increase the porous structure and promote the adsorption of copper and tetracycline in water.

[0021] (2) The preparation process of this invention is simple. The composite material is synthesized by a simple ultrasonic method, which has low production cost, high adsorption efficiency, and wide applicability. At the same time, it improves the problems of MOF particle agglomeration and poor water stability, thereby improving the practical application capability of Zr-MOF / CNF.

[0022] (3) The Zr-MOF / CNF composite material of the present invention can effectively adsorb copper and tetracycline. When the initial concentrations of copper and tetracycline are 32 mg / L and 444 mg / L respectively and the initial solution pH is 7.0, the adsorption capacity of Zr-MOF / CNF for copper and tetracycline reaches 157.08 mg / g and 1532 mg / g respectively. Attached Figure Description

[0023] Figure 1 This is a comparison chart of the adsorption capacity of Zr-MOF / CNF composite materials with different mass ratios (mass ratios of 10:1, 5:1, 1:1, 1:5, 1:10) prepared according to the preparation methods shown in Examples 1-5, and the adsorption capacity of Zr-MOF and CNF prepared in the comparative example for copper and tetracycline in water.

[0024] As shown in the figure, the Zr-MOF / CNF composite material (mass ratio 1:5) prepared in Example 4 of this invention has the best adsorption capacity for 0.1 mmol / L TC-Cu solution.

[0025] Figure 2 The graph shows the effect of solution pH on the adsorption and removal of copper and tetracycline by the Zr-MOF / CNF composite material in Example 4 of this invention (experimental conditions: tetracycline-copper concentration of 0.1 mmol / L (2:1); adsorption temperature of 25℃; and adsorption material dosage of 0.1 g / L).

[0026] As shown in the figure, the adsorption effect of the composite material in Example 4 of the present invention on copper and tetracycline gradually increases as the pH increases from 2 to 7, and the adsorption amount reaches the highest at pH 7. After the pH is greater than 7, the adsorption amount gradually decreases.

[0027] Figure 3 This is an adsorption-desorption experimental diagram of the Zr-MOF / CNF composite material obtained according to Example 4 of the present invention;

[0028] As shown in the figure, the composite material in Example 4 of the present invention still retains a good adsorption capacity after four cycles, which verifies that the composite material has a good cyclic adsorption capacity. Detailed Implementation

[0029] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but this is not intended to limit the present invention.

[0030] Example 1

[0031] This embodiment provides a method for preparing Zr-MOF / CNF (the mass ratio of zirconium-based MOF to nanocellulose is 10:1), the method comprising the following steps:

[0032] (1) Preparation of nanocellulose: 1.000 g of *Ulva prolifera* cellulose was mixed with water to prepare a suspension (1:100, w / v), and magnetically stirred until uniformly dispersed. 0.016 g of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxo) and 0.1 g of NaBr were added and stirred for 30 min until completely dissolved. Then, 20 mmol of 13% (w / w) NaClO solution was added. The pH was then controlled at 10 by adding 0.5 M NaOH solution. When the pH no longer changed within 15 min, anhydrous ethanol was immediately added to terminate the reaction. The oxidized cellulose was then filtered and washed with distilled water until the pH was neutral. The resulting nanocellulose suspension was then sonicated for 15 min and lyophilized to obtain nanocellulose (CNF).

[0033] (2) Preparation of zirconium-based MOF: 3 mmol of ZrCl4·8H2O and 3 mmol of H3BTC were added to 30 mL of DMF and formic acid, and the mixture was stirred at 200 r·min. -1 Stir at a constant speed for 20 minutes to ensure uniform mixing, then react ultrasonically at 70°C and 600W for 90 minutes. Finally, reduce the suspension to 6000 rpm. -1 Centrifuge for 10 min, pour off the supernatant, and wash five times with deionized water and anhydrous ethanol to remove residual ZrCl4·8H2O and H3BTC. Then, place the centrifuged precipitate in a drying oven and dry at 60°C for 12 hours. After complete drying, grind with slurry and sieve through a 100-mesh sieve to obtain Zr-MOF.

[0034] (3) Preparation of Zr-MOF / CNF: Under the assistance of ultrasound, Zr-MOF and CNF were weighed at 10 mg and 1 mg respectively and added to deionized water. The mixture was sonicated at room temperature for 60 min. The precipitate after centrifugation was placed in a drying oven and dried completely to obtain the Zr-MOF / CNF composite material.

[0035] Example 2

[0036] This embodiment provides a method for preparing a Zr-MOF / CNF composite material (the mass ratio of zirconium-based MOF to nanocellulose is 5:1), the method comprising the following steps:

[0037] (1) The preparation of nanocellulose is the same as in step (1) of Example 1.

[0038] (2) The preparation of zirconium-based MOF is the same as that in step (2) of Example 1.

[0039] (3) The preparation of Zr-MOF / CNF composite material is the same as in step (3) of Example 1. The difference is the addition of 2 mg of nanocellulose.

[0040] Example 3

[0041] This embodiment provides a method for preparing a Zr-MOF / CNF composite material (the mass ratio of zirconium-based MOF to nanocellulose is 1:1), the method comprising the following steps:

[0042] (1) The preparation of nanocellulose is the same as in step (1) of Example 1.

[0043] (2) The preparation of zirconium-based MOF is the same as that in step (2) of Example 1.

[0044] (3) The preparation of Zr-MOF / CNF composite material is the same as in step (3) of Example 1. The difference is the addition of 10 mg of nanocellulose.

[0045] Example 4

[0046] This embodiment provides a method for preparing a Zr-MOF / CNF composite material (the mass ratio of zirconium-based MOF to nanocellulose is 1:5), the method comprising the following steps:

[0047] (1) The preparation of nanocellulose is the same as in step (1) of Example 1.

[0048] (2) The preparation of zirconium-based MOF is the same as that in step (2) of Example 1.

[0049] (3) The preparation of the Zr-MOF / CNF composite material is the same as in step (3) of Example 1. The difference is the addition of 50 mg of nanocellulose.

[0050] Example 5

[0051] This embodiment provides a method for preparing a Zr-MOF / CNF composite material (the mass ratio of zirconium-based MOF to nanocellulose is 1:10), the method comprising the following steps:

[0052] (1) The preparation of nanocellulose is the same as in step (1) of Example 1.

[0053] (2) The preparation of zirconium-based MOF is the same as that in step (2) of Example 1.

[0054] (3) The preparation of Zr-MOF / CNF composite material is the same as in step (3) of Example 1. The difference is that 100 mg of nanocellulose is added.

[0055] Comparative Example 1:

[0056] This comparative example provides a method for preparing nanocellulose (CNF), the method comprising the following steps:

[0057] The preparation of nanocellulose is the same as in step (1) of Example 1.

[0058] Comparative Example 2:

[0059] This comparative example provides a method for preparing Zr-MOF, the method comprising the following steps:

[0060] The preparation of zirconium-based MOFs is the same as described in step (2) of Example 2.

[0061] Zr-MOF / CNF composite materials with different mass ratios (mass ratios of 10:1, 5:1, 1:1, 1:5, and 1:10) prepared by the methods shown in Examples 1-5 above, as well as CNF and Zr-MOF prepared in the comparative examples, were subjected to copper and tetracycline adsorption experiments. The adsorbent dosage was 0.1 g / L. CuCl2 and tetracycline hydrochloride were used to prepare copper and tetracycline wastewater, respectively, with a tetracycline to copper molar ratio of 2:1 and concentrations of 444 mg / L and 32 mg / L, respectively. The reaction pH was 7, the temperature was 25℃, and the reaction time was 4 h and 24 h. The remaining concentrations of copper and tetracycline were then measured, and the adsorption capacity was calculated. The experimental results are as follows: Figure 1 As shown, after 4 hours of adsorption, the adsorption of each material tended to be saturated. Among them, the Zr-MOF / CNF composite material with a mass ratio of 1:5 showed the best adsorption effect, with adsorption capacities of 1532 mg / L for copper and 157.08 mg / L for tetracycline.

[0062] Test data show that the Zr-MOF / CNF obtained in Examples 1-5 of this invention has a very significant adsorption efficiency for copper and tetracycline in water (as shown in Table 1).

[0063] Table 1. Experimental results of copper and tetracycline adsorption in different embodiments.

[0064]

Claims

1. A cellulose-based composite material for simultaneous removal of copper and tetracycline from water bodies, characterized in that, The composite material is Zr-MOF / CNF, and its preparation comprises the following steps: (1) mixing Enteromorpha cellulose and water to prepare a suspension, and stirring by magnetic force until evenly dispersed; adding TEMPO and NaBr and stirring until completely dissolved, and then adding NaClO solution; controlling the pH at 10 by adding NaOH solution, and immediately adding anhydrous ethanol to terminate the reaction when the pH does not change within 15 min; then filtering the oxidized cellulose, and washing with distilled water until the pH value is neutral; ultrasonically oscillating the obtained nanocellulose suspension for 15 min, and obtaining CNF after freeze-drying; the mass ratio of TEMPO to NaBr is 4:25; (2) adding ZrCl4·8H2O and H3BTC into a mixed solution of DMF and formic acid, stirring to ensure uniform mixing, and then ultrasonically treating, and then centrifuging the suspension, pouring out the supernatant, and washing to remove residual ZrCl4·8H2O and H3BTC; then drying the precipitate after centrifugation; grinding and sieving after complete drying to obtain Zr-MOF; the molar ratio of ZrCl4·8H2O to H3BTC is 1:1; (3) adding the CNF obtained in step (1) and the Zr-MOF obtained in step (2) into deionized water, ultrasonically treating, and then drying the precipitate after centrifugation to obtain the Zr-MOF / CNF composite material; the mass ratio of Zr-MOF to CNF is 10-0.1:

1.

2. The cellulose-based composite material for simultaneously removing copper and tetracycline from water bodies according to claim 1, characterized in that, In step (2), the ultrasonic treatment is performed at 600 W power and 70℃ for 90 min.

3. The cellulose-based composite material for simultaneously removing copper and tetracycline from water according to claim 1, wherein In step (3), the mass ratio of Zr-MOF to CNF is 1:

5.

4. The cellulose-based composite material for simultaneously removing copper and tetracycline from water according to claim 1, wherein In step (3), the ultrasonic treatment is performed at room temperature for 60 min.

5. Use of the cellulose-based composite material according to any one of claims 1-4 in simultaneously removing copper and tetracycline from water bodies.

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