Cellulose-graphene composite hydrogel, preparation method thereof, immobilized enzyme reactor for PFAS defluorination and preparation method of immobilized enzyme reactor

Abstract

The invention relates to the technical field of bioengineering, in particular to cellulose-graphene composite hydrogel, a preparation method thereof, an immobilized enzyme reactor for PFAS defluorination and a preparation method of the immobilized enzyme reactor. The preparation method of the cellulose-graphene composite hydrogel comprises the following steps: adding an aminated graphene dispersion liquid into a cellulose solution, and uniformly mixing to obtain a cellulose-graphene suspension; adding violuric acid into the cellulose-graphene suspension, uniformly mixing, and standing to obtain primary hydrogel; the primary hydrogel is sequentially subjected to deionized soaking and cleaning, and the cellulose-graphene composite hydrogel is obtained. The immobilized enzyme reactor provided by the invention has the characteristics of environmental protection and low cost, and provides an innovative biological solution for PFAS polluted water treatment.

Description

Technical Field

[0001] The present invention relates to the field of bioengineering technology, and particularly relates to a cellulose-graphene composite hydrogel, a preparation method thereof, a fixed enzyme reactor for PFAS defluorination, and a preparation method thereof. Background Art

[0002] Per- and polyfluoroalkyl substances (PFAS) have become a severe challenge for global water safety governance due to their extremely strong chemical stability, environmental persistence, and biological toxicity. Traditional water treatment technologies, such as activated carbon adsorption, ion exchange, reverse osmosis membrane filtration, etc., can partially separate PFAS, but cannot achieve their chemical detoxification and degradation, only transferring pollutants to waste residues or concentrated solutions, resulting in the risk of secondary pollution and high subsequent disposal costs. Some advanced oxidation / reduction technologies, such as ultraviolet-activated persulfate, electrochemical oxidation, etc., can break the carbon chain structure of PFAS, but have problems such as low defluorination efficiency, high energy consumption, limited large-scale application, and are difficult to adapt to complex wastewater environments.

[0003] Bioremediation technology, especially enzyme-catalyzed degradation, is regarded as a potential alternative in the field of water treatment due to its characteristics of efficiently degrading pollutants under mild conditions and being environmentally friendly. However, the inherent structural fragility and limited reusability of enzymes severely limit their application. Immobilizing enzymes on suitable carriers can significantly improve their stability and recyclability while retaining their catalytic activity. Currently, various enzyme immobilization strategies (such as covalent bonding, embedding, etc.) have been developed to load enzymes on carriers such as carbon-based materials and framework materials to synthesize immobilized enzyme reactors. But there are still the following key challenges when using this method to remove PFAS: On the one hand, the defluorination ability is insufficient: the extreme inertness of PFAS makes it difficult to be directly attacked by conventional enzymes or reactive oxygen species, and the existing immobilized enzyme reactors have low defluorination efficiency for PFAS and are difficult to achieve complete detoxification; On the other hand, the practical application feasibility is poor: complex wastewater matrices (such as coexisting heavy metals, organic substances) will severely inhibit enzyme activity and limit the large-scale application of immobilized enzyme reactors.

[0004] These defects make it difficult for the existing technologies to meet the requirements of efficient degradation / defluorination of PFAS, and there is an urgent need to develop a new enzyme immobilization system to break through the above bottlenecks. Summary of the Invention

[0005] To solve or partially solve the problems existing in the related technologies, the present invention provides a cellulose-graphene composite hydrogel, a preparation method thereof, a fixed enzyme reactor for PFAS defluorination, and a preparation method thereof.

[0006] The present invention provides a preparation method of a cellulose-graphene composite hydrogel, which includes: Step a): Add the aminated graphene dispersion into the cellulose solution and mix evenly to obtain a cellulose-graphene suspension. Step b): Add murexide into the cellulose-graphene suspension, mix evenly and then let it stand to obtain a primary hydrogel. Step c): Soak and wash the primary hydrogel with deionized water in sequence to obtain a cellulose-graphene composite hydrogel.

[0007] Furthermore, the content of cellulose in the cellulose solution is 3-5 wt%.

[0008] Furthermore, in step a), the addition amount of aminated graphene is 0.01-0.018 wt% of the cellulose solution; and / or, in step c), the addition amount of murexide is 0.006-0.012 wt% of the cellulose solution.

[0009] Furthermore, the cellulose solution is prepared as follows: Dissolve cotton linter in ionic liquid under heating conditions to obtain a cellulose solution; the ionic liquid is 1-ethyl-3-methylimidazolium acetate solution; the heating temperature is 70-85 °C and the heating time is 2-4 h.

[0010] Furthermore, the aminated graphene dispersion is prepared as follows: Disperse aminated graphene in deionized water and perform ultrasonic treatment to obtain an aminated graphene dispersion; the mass-volume ratio of aminated graphene to deionized water is 0.6-0.85 g: 1 L.

[0011] The present invention also provides a cellulose-graphene composite hydrogel, which includes: a matrix formed by cellulose cross-linking, and aminated graphene and murexide embedded in the matrix.

[0012] The present invention also provides a preparation method of a fixed enzyme reactor for PFAS defluorination, which includes: Immerse the above-mentioned cellulose-graphene composite hydrogel in a buffer solution containing an enzyme and perform shaking treatment, and then wash with the buffer solution to obtain a fixed enzyme reactor for PFAS defluorination.

[0013] Furthermore, the enzyme is laccase, and the content of the enzyme in the buffer solution containing the enzyme is 1-2.0 mg / mL.

[0014] Furthermore, the shaking treatment is specifically: Under light-shielded conditions, shake at 120-200 rpm for 5-8 h.

[0015] The present invention also provides an immobilized enzyme reactor for PFAS defluorination, which comprises: the above-mentioned cellulose-graphene composite hydrogel, and an enzyme encapsulated in the composite hydrogel.

[0016] The immobilized enzyme reactor for PFAS defluorination provided by the present invention may include the following beneficial effects: By synergistically embedding amino-functionalized graphene and murexide into the cellulose hydrogel network, and further immobilizing laccase in the hydrogel, the reactor constructs an immobilized enzyme reactor for efficiently removing PFAS in water. Specifically, the uniform doping of amino-functionalized graphene significantly improves the electron transfer rate, and in combination with murexide as a low-toxic redox mediator, highly active free radicals are generated under the catalysis of laccase to cleave the carbon-fluorine bonds of 17 PFAS in real wastewater. The immobilized enzyme reactor of the present invention has the characteristics of environmental friendliness and low cost, providing an innovative biological solution for the treatment of PFAS-polluted water bodies.

[0017] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] By describing the exemplary embodiments of the present invention in more detail in conjunction with the accompanying drawings, the above and other objects, features, and advantages of the present invention will become more obvious. Among them, in the exemplary embodiments of the present invention, the same reference numerals generally represent the same components.

[0019] Figure 1 is the Fourier transform infrared spectrum of the cellulose-graphene composite hydrogel in Example 1 of the present invention; Figure 2 is the electrochemical impedance spectrogram of the immobilized enzyme reactors in Example 1 and Comparative Example 1 of the present invention; Figure 3 is the defluorination kinetics diagram of 17 PFAS in real wastewater by the immobilized enzyme reactor in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0021] The terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the invention. The singular forms "a", "the", and "said" used in this invention and the appended claims are also intended to include the plural forms unless the context clearly dictates otherwise. It should also be understood that the term "and / or" used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0022] It should be understood that although the terms "first", "second", "third", etc. may be used in this invention to describe various information, such information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of this invention, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this invention, the meaning of "a plurality of" is two or more unless otherwise specifically defined.

[0023] An embodiment of the present invention provides a method for preparing a cellulose-graphene composite hydrogel, which includes: Step a), adding an amino-functionalized graphene dispersion into a cellulose solution and mixing evenly to obtain a cellulose-graphene suspension; Step b), adding murexide into the cellulose-graphene suspension, mixing evenly and then standing to obtain a primary hydrogel; Step c), successively soaking and washing the primary hydrogel with deionized water to obtain a cellulose-graphene composite hydrogel.

[0024] In the above preparation method, step a) is the step of uniformly doping amino-functionalized graphene into the cellulose solution. The cellulose solution is used to form a three-dimensional porous structure after cross-linking and serves as a substrate carrier for enzyme immobilization, with the characteristics of being environmentally friendly and low cost. The cellulose solution in this embodiment is preferably prepared according to the following method: dissolving cotton linter in an ionic liquid under heating conditions to obtain a cellulose solution; the ionic liquid is a 1-ethyl-3-methylimidazolium acetate solution; the heating temperature is 70-85 °C, and the heating time is 2-4 h. The above ionic liquid can efficiently dissolve cellulose. The mixing weight ratio of 1-ethyl-3-methylimidazolium acetate to deionized water in the ionic liquid is preferably 90:10 to avoid excessive degradation of cellulose. Heating can accelerate the depolymerization and dissolution of cellulose molecular chains to form a homogeneous solution, and the heating conditions are more preferably heating at 80 °C for 3 h.

[0025] Doping graphene oxide with amino groups into cellulose can improve the electron transfer rate of the hydrogel. The inventors of this application have proven through experiments that after canceling the doping of graphene oxide with amino groups, the electron transfer rate of the immobilized enzyme reactor will decrease significantly, thereby affecting the total defluorination efficiency and rate.

[0026] The amino-functionalized graphene oxide dispersion used in this step can be prepared according to the following method: Disperse the amino-functionalized graphene oxide in deionized water and perform ultrasonic treatment to obtain an amino-functionalized graphene oxide dispersion; the mass-volume ratio of amino-functionalized graphene oxide to deionized water is 0.6 - 0.85 g: 1 L. The mass-volume ratio of amino-functionalized graphene oxide to deionized water is preferably 0.7 - 0.8 g: 1 L, more preferably 0.75 g: 1 L. The ultrasonic time is preferably 20 - 40 min, most preferably 25 - 30 min.

[0027] Add the amino-functionalized graphene oxide dispersion to the cellulose solution and mix evenly to obtain a cellulose-graphene suspension. Mixing can be carried out by stirring, and the stirring time is not less than 10 min, preferably 15 - 30 min, specifically 20 min.

[0028] Step b) is the step of introducing murexide into the cellulose-graphene suspension. The role of introducing murexide is as follows: on the one hand, it acts as a low-toxic redox mediator to generate highly active free radicals under the catalysis of enzymes (such as laccase) to cleave carbon-fluorine bonds and achieve the defluorination and degradation of PFAS; on the other hand, murexide can be stably adsorbed on the amino-functionalized graphene oxide through π-π interaction, thereby fixing murexide on the hydrogel matrix, increasing the contact area with the wastewater and facilitating recovery. The inventors of this application have proven through experiments that after canceling the addition of murexide, no mediator free radicals can be generated, seriously affecting the total defluorination efficiency and rate of the immobilized enzyme reactor for PFAS in the wastewater, resulting in the total defluorination efficiency and rate of 17 kinds of PFAS in the wastewater approaching 0.

[0029] In this step, the mixing method can be stirring. To ensure the uniform dispersion of murexide in the cellulose-graphene suspension, the stirring time is preferably not less than 5 min, preferably 8 - 12 min, specifically 10 min. After stirring, it can be transferred to a mold and left to stand. During the standing process, the cellulose molecular chains self-assemble to form a physical cross-linked network structure to form a primary hydrogel. The standing time is preferably 2 - 4 h, more preferably 3 h.

[0030] The content of cellulose in the above-mentioned cellulose solution is preferably 3-5 wt%. Further, the addition amount of amino-functionalized graphene in step a) is 0.01-0.018 wt% of the cellulose solution; and / or, in step c), the addition amount of murexide is 0.006-0.012 wt% of the cellulose solution. More preferably, the content of cellulose in the cellulose solution is 4 wt%, the addition amount of amino-functionalized graphene is 0.014-0.016 wt% of the cellulose solution, and the addition amount of murexide is 0.008-0.01 wt% of the cellulose solution; most preferably, the content of cellulose in the cellulose solution is 4 wt%, the addition amount of amino-functionalized graphene is 0.016 wt% of the cellulose solution, and the addition amount of murexide is 0.009 wt% of the cellulose solution.

[0031] Step c) is a process of further cross-linking the primary hydrogel and cleaning to remove impurities. The primary hydrogel is soaked in deionized water to induce cellulose regeneration and physical cross-linking, which helps to enhance the mechanical strength of the hydrogel. The soaking time is preferably 2-3 h, more preferably 2.5-3 h. After soaking, it is washed with deionized water to thoroughly remove residual ionic liquids, unbound murexide and other impurities to avoid interfering with subsequent enzyme immobilization. The washing time is preferably not less than 2 days, and 3 days is preferably used in this example. After washing, the cellulose-graphene composite hydrogel is obtained.

[0032] The cellulose-graphene composite hydrogel prepared by this method is specifically a cellulose-amino-functionalized graphene-murexide composite hydrogel. In this hydrogel, a cellulose cross-linked network structure forms the matrix, and amino-functionalized graphene and murexide are embedded in the matrix.

[0033] Another embodiment of the present invention also provides a cellulose-graphene composite hydrogel, which includes: a matrix formed by cross-linking cellulose, and amino-functionalized graphene and murexide embedded in the matrix. The cellulose-graphene composite hydrogel is prepared according to the method of the above embodiment.

[0034] After assembling an enzyme with this cellulose-graphene composite hydrogel as a carrier, the defluorination ability and rate of PFAS in wastewater can be improved. The working principle is as follows: Murexide is oxidized by laccase to form a mediator murexide free radical for PFAS defluorination and degradation; amino-functionalized graphene is beneficial to electron transfer in the redox and defluorination processes, improving the defluorination rate; cellulose is used as an environmentally friendly and low-cost polymer material to assemble the above components. The inventors of this application have proven through experiments that the immobilized enzyme reactor after assembling the enzyme also has a high PFAS defluorination ability and rate for real wastewater.

[0035] Another embodiment of this application also provides a preparation method of a fixed enzyme reactor for PFAS defluorination, which includes: The above-mentioned cellulose-graphene composite hydrogel was immersed in a buffer solution containing an enzyme and subjected to shaking treatment. After the shaking treatment, it was washed with the buffer solution to obtain a fixed enzyme reactor for PFAS defluorination.

[0036] The above-mentioned enzyme is preferably laccase, which has the advantages of high catalytic activity, environmental friendliness and strong adaptability; most importantly, laccase can be mass-produced by methods such as microbial fermentation, and the relative cost is low. The buffer solution of the above-mentioned enzyme can specifically be a phosphate buffer solution of laccase. The content of the enzyme in the buffer solution containing the enzyme is 1-2.0 mg / mL, more preferably 1.4-1.6 mg / mL, and most preferably 1.6 mg / mL. The shaking treatment helps to promote the diffusion of enzyme molecules into the interior of the hydrogel and adsorption. The specific shaking treatment can be: Under light-shielded conditions, shake at 120-200 rpm for 5-8 h. More preferably, shake at 180 rpm for 6 h.

[0037] Another embodiment of the present application also provides a fixed enzyme reactor for PFAS defluorination, which includes: the cellulose-graphene composite hydrogel of the foregoing embodiment, and an enzyme encapsulated in the composite hydrogel. The fixed enzyme reactor can be prepared according to the foregoing method.

[0038] The working principle of the fixed enzyme reactor for PFAS defluorination provided in this embodiment is as follows: Murexide is oxidized by laccase to form a mediator murexide free radical for PFAS defluorination and degradation; amino-functionalized graphene is beneficial to electron transfer in the redox and defluorination processes, improving the defluorination rate; cellulose is used as an environmentally friendly and low-cost polymer material to assemble the above-mentioned components.

[0039] The technical solutions of the present invention will be further described below with specific embodiments: The sources of raw materials in the following examples are as follows: Cotton linters: purchased from Hubei Jinhanjiang Refined Cotton Co., Ltd. [EMIM]Ac ionic liquid: purchased from Cool Chemical Technology Co., Ltd. Amino-functionalized graphene: purchased from Anhui Zesheng Technology Co., Ltd. Murexide: purchased from Shanghai Macklin Biochemical Co., Ltd. Example 1 (1) Preparation of cellulose solution: Dissolve 4 g of cotton linters (cellulose content > 99%) in 96 g of [EMIM]Ac / H2O (90 wt% / 10 wt%), and heat and mix at 80 °C for 3 h to obtain a cellulose solution.

[0040] (2) Preparation of cellulose-graphene suspension: 15 mg of amino-functionalized graphene was dispersed in 20 mL of deionized water and sonicated for 30 minutes. The resulting dispersion was then added to the cellulose solution in step 1 and stirred for 20 minutes.

[0041] (3) Preparation of cellulose-graphene composite hydrogel: 8 mg of murexide was added to the cellulose-graphene suspension in step 2 and stirred for 10 minutes. Subsequently, it was transferred to a mold and left to stand at room temperature for 3 h to form a primary hydrogel. Then it was taken out and completely immersed in deionized water for 3 h, and finally washed with deionized water for 3 days to remove excess impurities, obtaining the cellulose-graphene composite hydrogel.

[0042] (4) Preparation of immobilized enzyme reactor: 60 mg of cellulose-graphene composite hydrogel was immersed in a phosphate buffer solution (40 mL, KH2PO4, pH 7.0) containing 1.5 mg / mL of laccase and shaken at 180 rpm for 6 h at 25 °C in the dark. Subsequently, it was thoroughly rinsed with the phosphate buffer solution to obtain the final immobilized enzyme reactor.

[0043] The Fourier transform infrared spectra of the cellulose-graphene in step (2) and the cellulose-graphene composite hydrogel prepared in step (3) are as Figure 1 shown. After adding murexide, in the infrared spectrum of cellulose-graphene, the benzene ring peak at 1560 cm -1 disappeared, which generally indicates the occurrence of π-π interaction; at the same time, new peaks at 1700 cm -1 (Amide Ⅰ) and 1623 cm -1 (C=O) (belonging to murexide) appeared, which proved that murexide was adsorbed on cellulose-graphene through π-π interaction.

[0044] Example 2 (1) Preparation of cellulose solution: The same as in Example 1.

[0045] (2) Preparation of cellulose-graphene suspension: 16 mg of amino-functionalized graphene was dispersed in 20 mL of deionized water and sonicated for 25 minutes. The resulting dispersion was then added to the cellulose solution in step 1 and stirred for 20 minutes.

[0046] (3) Preparation of cellulose-graphene composite hydrogel: 9 mg of murexide was added to the cellulose-graphene suspension in step 2 and stirred for 10 minutes. Subsequently, it was transferred to a mold and left to stand at room temperature for 3 h to form a primary hydrogel. Then it was taken out and completely immersed in deionized water for 2.5 h, and finally washed with deionized water for 3 days to remove excess impurities, obtaining the cellulose-graphene composite hydrogel; (4)Preparation of immobilized enzyme reactor: Immerse 60 mg of cellulose-graphene composite hydrogel into a phosphate buffer solution (40 mL, KH2PO4, pH 7.0) containing 1.6 mg / mL of laccase, and oscillate at 180 rpm for 8 h at 25 °C in the dark. Subsequently, rinse thoroughly with phosphate buffer solution to obtain the final immobilized enzyme reactor.

[0047] Example 3 (1)Preparation of cellulose solution: The same as in Example 1.

[0048] (2)Preparation of cellulose-graphene suspension: Disperse 14 mg of amino-functionalized graphene in 20 mL of deionized water and sonicate for 40 minutes. The resulting dispersion is then added to the cellulose solution in step 1 and stirred for 30 minutes.

[0049] (3)Preparation of cellulose-graphene composite hydrogel: Add 10 mg of murexide to the cellulose-graphene suspension in step 2 and stir for 15 minutes. Subsequently, transfer it to a mold and let it stand at room temperature for 4 h to form a primary hydrogel. Then take it out and immerse it completely in deionized water for 3 h, and finally wash it with deionized water for 3 days to remove excess impurities to obtain the cellulose-graphene composite hydrogel; (4)Preparation of immobilized enzyme reactor: Immerse 60 mg of cellulose-graphene composite hydrogel into a phosphate buffer solution (40 mL, KH2PO4, pH 7.0) containing 1.4 mg / mL of laccase, and oscillate at 180 rpm for 9 h at 25 °C in the dark. Subsequently, rinse thoroughly with phosphate buffer solution to obtain the final immobilized enzyme reactor.

[0050] Comparative Example 1 The difference between this comparative example and Example 1 is that step (2) is cancelled. The specific process is as follows: (1)Preparation of cellulose solution: The same as in Example 1.

[0051] (2)Preparation of cellulose-based composite hydrogel: Add 8 mg of murexide to the cellulose solution in step 1 and stir for 10 minutes. Subsequently, transfer it to a mold and let it stand at room temperature for 3 h to form a primary hydrogel. Then take it out and immerse it completely in deionized water for 3 h, and finally wash it with deionized water for 3 days to remove excess impurities to obtain the cellulose-based composite hydrogel.

[0052] (3) Preparation of the immobilized enzyme reactor: Immerse 60 mg of the cellulose-based composite hydrogel in a phosphate buffer solution (40 mL, KH2PO4, pH 7.0) containing 1.5 mg / mL of laccase, and oscillate at 180 rpm for 6 h at 25 °C in the dark. Subsequently, rinse thoroughly with the phosphate buffer solution to obtain the final immobilized enzyme reactor.

[0053] Comparative Example 2 The difference between this comparative example and Example 1 is that the step of adding murexide in step (3) is cancelled. The specific process is as follows: (1) Preparation of the cellulose solution: The same as in Example 1.

[0054] (2) Preparation of the cellulose-graphene suspension: The same as in Example 1.

[0055] (3) Preparation of the cellulose-graphene composite hydrogel: Transfer the cellulose-graphene suspension in step 2 to a mold, and let it stand at room temperature for 3 h to form a primary hydrogel. Then take it out and immerse it completely in deionized water for 3 h, and finally wash it with deionized water for 3 days to remove excess impurities to obtain the cellulose-graphene composite hydrogel.

[0056] (4) Preparation of the immobilized enzyme reactor: The same as in Example 1.

[0057] Comparative Example 3 The difference between this comparative example and Example 1 is that step (4) is cancelled, and the cellulose-graphene composite hydrogel prepared in step (3) is used as the defluorination reactor.

[0058]

Electrochemical performance test

[0059] Figure 2Among them, the radius of the arc can reflect the charge transfer resistance. The larger the radius, the greater the charge transfer resistance and the lower the electron transfer rate. Therefore, the immobilized enzyme reactor with the addition of amino-functionalized graphene (Example 1) has a higher electron transfer rate than the immobilized enzyme reactor without the addition of amino-functionalized graphene (Comparative Example 1).

[0060]

Real Wastewater Defluorination Experiment

[0061] Measure the defluorination kinetic diagram of 17 PFASs in real wastewater by the immobilized enzyme reactor of Example 1. The measurement method is as follows: Take 15 mL of wastewater sample, then add the immobilized enzyme reactor of Example 1, and shake it at 180 rpm and 25 °C for 0.5, 1, 2, 4, 6, 12, 24 h. Through the formula ( C 0 - C e ) / C 0 × 100% to calculate the total defluorination efficiency of 17 PFASs at the 0.5, 1, 2, 4, 6, 12, 24 h. In the formula, C 0 and C e are the sum of the F ion concentrations of 17 PFASs in the solution before and after removal (nmol / L), respectively. The test results are as Figure 3 shown. It can be seen from Figure 3 that the defluorination reaches equilibrium at the 12th h of this immobilized enzyme reactor.

[0062] Measure the total defluorination efficiency of 17 PFASs in real wastewater by the above 6 reactors. The measurement method is as follows: Take 15 mL of wastewater sample, add the immobilized enzyme reactor, and shake it at 180 rpm and 25 °C for 48 h. Calculate the total defluorination efficiency of 17 PFASs according to the above formula. The measurement results are shown in Table 1.

[0063] The defluorination rates of 17 PFASs in real wastewater by the above six reactors were measured, and the measurement method was as follows: Add the immobilized enzyme reactor to 15 mL of wastewater sample, shake at 180 rpm and 25 °C for 0.5, 1, 2, 4, 6, 12, and 24 h, and then calculate through the formula ( C 0 - C e ) / t × V the total defluorination rate of 17 PFASs at the 6th h (because it can be seen from Figure 3 that the reaction has reached defluorination equilibrium at the 12th h); in the formula, C 0 and C e are the sum of the F ion concentrations of 17 PFASs in the solution before and after removal (nmol / L), respectively, t and V represent the removal time (h) and the solution volume (L), respectively. The test results are shown in Table 1: Table 1 Measurement results of the total defluorination efficiency and total defluorination rate of 17 PFASs

[0064] It can be seen from Table 1 that the total defluorination efficiency of the immobilized enzyme reactors prepared in Examples 1 - 3 for 17 PFASs of public concern in real wastewater is 83.6% - 85.9%, and the total defluorination rate is 4.6 - 5.1 nmol / h. This shows that the immobilized enzyme reactor provided in the examples of the present invention has a high defluorination efficiency and defluorination rate for real wastewater and is suitable for the defluorination treatment of industrial wastewater.

[0065] In Comparative Example 1, since amino-functionalized graphene can improve the electron transfer rate of the immobilized enzyme reactor; after canceling the doping of amino-functionalized graphene, the electron transfer rate of the immobilized enzyme reactor will decrease. Therefore, the total defluorination efficiency and rate of 17 PFASs in wastewater decreased to 41.3% and 2.0 nmol / h, respectively.

[0066] In Comparative Example 2, since murexide is a redox mediator and can be oxidized by laccase into a mediator radical, which is a key factor for degrading PFASs; after canceling the addition of murexide, the mediator radical cannot be generated. Therefore, the total defluorination efficiency (0.2%) and rate (0.1 nmol / h) of the immobilized enzyme reactor for 17 PFASs in wastewater are both close to 0.

[0067] In Comparative Example 3, since laccase serves as a precursor for oxidizing purpuric acid, it can oxidize purpuric acid to a mediator free radical to degrade PFAS. After canceling Step 4, the mediator free radical cannot be generated. Therefore, the immobilized enzyme reactor hardly defluoridates 17 kinds of PFAS in the wastewater.

[0068] From the above, it can be seen that: In the present invention, by synergistically embedding amino-functionalized graphene and purpuric acid into the cellulose hydrogel network and further immobilizing laccase in the hydrogel, an immobilized enzyme reactor for efficiently removing PFAS in water is constructed. Specifically, the uniform doping of amino-functionalized graphene significantly improves the electron transfer rate, and combined with purpuric acid as a low-toxic redox mediator, highly active free radicals are generated under the catalysis of laccase to cleave the carbon-fluorine bonds of 17 kinds of PFAS in real wastewater. The immobilized enzyme reactor of the present invention has the characteristics of environmental friendliness and low cost, providing an innovative biological solution for the treatment of PFAS-polluted water bodies.

[0069] The various embodiments of the present invention have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art in the technical field without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technologies in the market, or to enable other ordinary skilled persons in the technical field to understand the embodiments disclosed herein.

Claims

1. A preparation method of a cellulose-graphene composite hydrogel, characterized in that, It includes: Step a): Add the aminated graphene dispersion into the cellulose solution and mix evenly to obtain a cellulose-graphene suspension; Step b): Add murexide into the cellulose-graphene suspension, mix evenly and then let it stand to obtain a primary hydrogel; Step c): Soak and wash the primary hydrogel successively with deionized water to obtain a cellulose-graphene composite hydrogel.

2. The preparation method according to claim 1, characterized in that, The content of cellulose in the cellulose solution is 3-5 wt%.

3. The preparation method according to claim 2, wherein, In step a), the addition amount of aminated graphene is 0.01-0.018 wt% of the cellulose solution; and / or, in step c), the addition amount of murexide is 0.006-0.012 wt% of the cellulose solution.

4. The preparation method according to claim 1, characterized in that, The cellulose solution is prepared according to the following method: Dissolve cotton linter in an ionic liquid under heating conditions to obtain a cellulose solution; the ionic liquid is 1-ethyl-3-methylimidazolium acetate solution; the heating temperature is 70-85 °C and the heating time is 2-4 h.

5. The preparation method according to claim 1, characterized in that The aminated graphene dispersion is prepared according to the following method: Disperse aminated graphene in deionized water and perform ultrasonic treatment to obtain an aminated graphene dispersion; the mass-volume ratio of aminated graphene to deionized water is 0.6-0.85 g:1 L.

6. A cellulose-graphene composite hydrogel, characterized in that, It includes: A matrix formed by cross-linking cellulose, and aminated graphene and murexide embedded in the matrix.

7. A preparation method of a fixed enzyme reactor for PFAS defluorination, characterized in that, It includes: Immerse the cellulose-graphene composite hydrogel according to claim 6 in a buffer solution containing an enzyme and perform shaking treatment. After the shaking treatment, wash it with the buffer solution to obtain a fixed enzyme reactor for PFAS defluorination.

8. The preparation method according to claim 7, characterized in that, The enzyme is laccase, and the content of the enzyme in the buffer solution containing the enzyme is 1-2.0 mg / mL.

9. The preparation method according to claim 7, characterized in that The shaking treatment is specifically: Under light-shielded conditions, shake at 120-200 rpm for 5-8 h.

10. A fixed enzyme reactor for PFAS defluorination, characterized in that, It includes: The cellulose-graphene composite hydrogel according to claim 6, and an enzyme encapsulated in the composite hydrogel.

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