Multifunctional nano-enzyme as well as preparation method and application thereof

Abstract

The invention discloses a multifunctional nano-enzyme as well as a preparation method and application thereof, and relates to the technical field of environmental protection, the multifunctional nano-enzyme comprises a zeolite imidazate framework material-8 and ferroferric oxide quantum dots loaded on the zeolite imidazate framework material-8. The multifunctional nano-enzyme provided by the invention has more stable peroxidase-like activity, stronger photocatalytic ability and larger adsorption capacity at the same time, the adsorption capacity of the multifunctional nano-enzyme on tetracycline antibiotics in a water body is higher, the photocatalytic effect is stronger, the removal rate is higher, and the multifunctional nano-enzyme has a good application prospect. Meanwhile, the method has specificity and anti-interference performance for adsorbing and treating tetracycline antibiotics, and is suitable for large-scale industrial treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental protection, and particularly relates to a multifunctional nanozyme, a preparation method thereof, and an application thereof. Background Art

[0002] Tetracycline antibiotics (TCs), including oxytetracycline, chlortetracycline, and tetracycline, etc., are one of the most widely used antibiotics globally. They are widely used in the prevention and treatment of bacterial infections in humans and animals, and are often used as feed additives in animal husbandry and aquaculture.

[0003] However, the chemical structure of TCs is stable and difficult to be naturally degraded. Therefore, their residues in environments such as water bodies, soils, and foods are relatively high. These residual antibiotics can not only induce bacteria to produce resistance genes, but also gradually accumulate through the ecosystem cycle and food chain, posing a serious threat to the ecological environment and human health.

[0004] Currently, the methods for TCs monitoring include high performance liquid chromatography - mass spectrometry (HPLC - MS), electrochemical analysis, capillary electrophoresis, etc., and the methods for TCs removal include electrochemical degradation, photocatalysis degradation, etc. However, the above - mentioned monitoring methods require the use of expensive instruments, with complex experimental operations and high costs, and cannot be used in environments with limited resources. Summary of the Invention

[0005] The main object of the present invention is to propose a multifunctional nanozyme, a preparation method thereof, and an application thereof, aiming to provide a new multifunctional nanozyme for monitoring and disposing of TCs.

[0006] To achieve the above object, the present invention proposes a multifunctional nanozyme, which includes zeolitic imidazolate framework - 8 and iron oxide quantum dots loaded on the zeolitic imidazolate framework - 8.

[0007] In one embodiment, the mass ratio of the zeolitic imidazolate framework - 8 to the iron oxide quantum dots in the multifunctional nanozyme is 30.0 - 65.0; and / or,

[0008] The average particle size of the multifunctional nanozyme is 150.0 - 300.0 nm; and / or,

[0009] The average pore size of the multifunctional nanozyme is 2.0 - 10.0 nm; and / or,

[0010] The effective pH range of the multifunctional nanozyme is 2.5 - 4.5; and / or,

[0011] The effective temperature range of the multifunctional nanozyme is 20.0 - 45.0 °C; and / or,

[0012] The peroxidase activity of the multifunctional nanozyme is 30.0 - 150.0 U / mg.

[0013] The present invention also provides a preparation method of a multifunctional nanozyme, comprising the following steps:

[0014] Obtain iron oxide quantum dots, mix the iron oxide quantum dots with a zinc source solution and a 2-methylimidazole solution, and carry out a coordination polymerization reaction to obtain the multifunctional nanozyme.

[0015] In one embodiment, the mass ratio of the iron oxide quantum dots to zinc ions in the zinc source solution and 2-methylimidazole in the 2-methylimidazole solution is (5.0 - 50.0):(150.0 - 350.0):(2500.0 - 4000.0).

[0016] In one embodiment, the step of obtaining iron oxide quantum dots includes: obtaining iron oxide nanoparticles, mixing ascorbic acid with the iron oxide nanoparticles, carrying out a hydrothermal reaction, performing solid-liquid separation, and taking the solid to obtain the iron oxide quantum dots;

[0017] Among them, the mass ratio of ascorbic acid to the iron oxide nanoparticles is (26.0 - 44.0):1, the time of the hydrothermal reaction is 8.0 - 20.0 h, and the temperature of the hydrothermal reaction is 160.0 - 240.0 °C.

[0018] The present invention also provides an application of the aforementioned multifunctional nanozyme or a multifunctional nanozyme prepared by the aforementioned preparation method of a multifunctional nanozyme in adsorbing, detecting, and degrading tetracycline antibiotics.

[0019] In one embodiment, it includes the following steps:

[0020] S10. Mix a solution containing tetracycline antibiotics with the multifunctional nanozyme, carry out an adsorption reaction under dark conditions until the adsorption and desorption reach equilibrium to obtain a first mixture;

[0021] S20. Carry out a photocatalytic degradation reaction on the first mixture under light conditions to degrade the tetracycline antibiotics, perform solid-liquid separation to obtain a treated solution.

[0022] In one embodiment, in step S10, the tetracycline antibiotics include at least one of oxytetracycline, chlortetracycline, and tetracycline; and / or,

[0023] In step S10, the mass ratio of the tetracycline antibiotics in the solution to the multifunctional nanozyme is 0.05 - 1.5; and / or,

[0024] In step S10, the pH of the adsorption reaction is 4.0 to 10.0; and / or,

[0025] In step S10, the temperature of the adsorption reaction is 20.0 to 25.0 °C; and / or,

[0026] In step S10, the time of the adsorption reaction is 0.5 to 3.0 h; and / or,

[0027] In step S20, the power of the light irradiation is 20.0 to 200.0 W; and / or,

[0028] In step S20, the time of the photocatalytic degradation reaction is 0.5 to 12.0 h.

[0029] In one embodiment, the method for judging that the adsorption reaction reaches adsorption and desorption equilibrium includes colorimetric detection method and / or photographic visualization detection method.

[0030] In one embodiment, the detection limit of the colorimetric detection method is 0.015 mg / L; and / or,

[0031] The detection limit of the photographic visualization detection method is 0.12 mg / L; and / or,

[0032] When the mass ratio of tetracycline antibiotics in the solution to the multifunctional nanozyme is 1.0, the relative standard deviation of the recovery rate of adding tetracycline antibiotic standard is ≤8.06%.

[0033] In the technical solution of the present invention, the zeolitic imidazolate framework material-8 (ZIF-8) in the multifunctional nanozyme has a porous structure, and the iron oxide quantum dots (Fe3O4QDs) are dispersed in the porous structure channels of ZIF-8, which improves the dispersibility, stability of Fe3O4QDs and the contact area with the substrate, so that the peroxidase-like (POD) activity of Fe3O4QDs is relatively high and stable, enabling the multifunctional nanozyme to monitor the treatment of TCs in real time based on this POD activity through colorimetric methods and other means; ZIF-8 can achieve the removal of tetracycline through surface adsorption and interaction with tetracycline molecules, but ZIF-8 itself has a large band gap (about 5.1 eV), resulting in weak light response and low catalytic efficiency, and usually cannot decompose TCs under normal light conditions. On this basis, the loading of Fe3O4QDs improves the affinity of the nanozyme for TCs on the one hand, making the adsorption rate and adsorption capacity of the multifunctional nanozyme increase, and on the other hand, the loading of Fe3O4QDs improves the carrier mobility rate of ZIF-8 under light conditions, making ·O2 -The rapid and large - scale generation of ·O₂⁻ and ·OH free radicals makes the oxidation and degradation effect of free radicals on TCs stronger under light, so that the multifunctional nanozyme can simultaneously achieve the integrated treatment effect of adsorption, detection and photocatalytic degradation of TCs. Brief Description of the Drawings

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0035] Figure 1 In (A), it is the POD enzyme activity result diagram of Fe₃O₄ QDs prepared in Examples 6 - 9; Figure 1 In (B), it is the POD enzyme activity result diagram of Fe₃O₄ QDs prepared in Examples 1 and 10 - 12; Figure 1 In (C), it is the POD enzyme activity result diagram of Fe₃O₄ QDs prepared in Examples 1 and 13 - 15;

[0036] Figure 2 In (A), it is the transmission electron microscope image of Fe₃O₄ QDs in Example 1; Figure 2 In (B), it is the HRTEM image of Fe₃O₄ QDs in Example 1; Figure 2 In (C), it is the particle size distribution diagram of Fe₃O₄ QDs in Example 1;

[0037] Figure 3 In (A), it is the scanning electron microscope image of ZIF - 8; Figure 3 In (B), it is the scanning electron microscope image of MOF - F5 in Example 1; Figure 3 In (C), it is the scanning electron microscope image of MOF - F10 in Example 2; Figure 3 In (D), it is the scanning electron microscope image of MOF - F20 in Example 3; Figure 3 In (E), it is the scanning electron microscope image of MOF - F30 in Example 4; Figure 3 In (F), it is the scanning electron microscope image of MOF - F40 in Example 5; Figure 3 In (G), it is the N₂ adsorption / desorption isotherm test diagram of the multifunctional nanozyme in Examples 1 - 5; Figure 3 In (H), it is the particle size test diagram of the multifunctional nanozyme in Examples 1 - 5;

[0038] Figure 4 In (A), it is the pseudo - POD activity result diagram of the multifunctional nanozyme in Examples 1 - 4; Figure 4 In (B), it is the adsorption capacity result diagram of the multifunctional nanozyme for TCs in Examples 1 - 4;Figure 4 Photodegradation percentage results of multifunctional nanozymes on TCs in Examples 1-4 of (C);

[0039] Figure 5 (A) in is the electron image of MOF-F20 in Example 3; Figure 5 The Fe element distribution map of MOF-F20 in Example 3 is shown in (B); Figure 5 The Zn element distribution map of MOF-F20 in Example 3 is shown in (C); Figure 5 The O element distribution map of MOF-F20 in Example 3 is shown in (D); Figure 5 The N element distribution map of MOF-F20 in Example 3 is shown in (E); Figure 5 The C element distribution map of MOF-F20 in Example 3 is shown in (F);

[0040] Figure 6 The HRTEM image of MOF-F20 in Example 3 is shown in (A); Figure 6 Shown in (B) is Figure 5 The enlarged view of (A); Figure 6 The XRD pattern of MOF-F20 in Example 3 is shown in (C); Figure 6 The FT-IR spectrum of MOF-F20 in Example 3 is shown in (D);

[0041] Figure 7 The full XPS scan of MOF-F20 in Example 3 is shown in (A); Figure 7 The high-resolution spectrum of Fe2p of MOF-F20 in Example 3 is shown in (B); Figure 7 The high-resolution spectrum of Zn2p of MOF-F20 in Example 3 is shown in (C); Figure 7 The high-resolution spectrum of O1s of MOF-F20 in Example 3 is shown in (D); Figure 7 The high-resolution spectrum of N1s of MOF-F20 in Example 3 is shown in (E); Figure 7 The high-resolution spectrum of C1s of MOF-F20 in Example 3 is shown in (F);

[0042] Figure 8 The POD activity results of multifunctional nanozymes in Examples 1-5 are shown in (A); Figure 8 The standard curve of TCs concentration under UV-vis method is shown in (B); Figure 8 The adsorption of TCs by ZIF-8 and MOF-F20 in Example 3 at different pH values is shown in (C); Figure 8 The adsorption of TCs by different dosages of MOF-F20 in Example 3 is shown in (D);

[0043] Figure 9Figure (A) shows the effect of pH on the enzyme activity of MOF-F20 in Example 3; Figure 9 Figure (B) shows the effect of temperature on the enzyme activity of MOF-F20 in Example 3; Figure 9 Figures (C) and (E) show the results of the TMB steady-state kinetics measurement of MOF-F20 in Example 3; Figure 9 Figures (D) and (F) show the results of the steady-state kinetics measurement of H2O2 of MOF-F20 in Example 3;

[0044] Figure 10 Figure (A) shows the UV-visible spectra of different concentrations of TCs and MOF-F20 in Example 3; Figure 10 Figure (B) shows the linear fitting graph of the concentration of MOF-F20 and TCs in Example 3; Figure 10 Figure (C) shows the selectivity (inset) and anti-interference results of MOF-F20 on TCs in Example 3; Figure 10 Figure (D) shows the visual linear fitting of different concentrations of TCs and MOF-F20 in Example 3 (the inset is a photographed picture);

[0045] Figure 11 Figure (A) shows the pseudo-first-order model and pseudo-second-order model of MOF-F20 in Example 3 when the initial TCs concentration is 50.0 mg / L; Figure 11 Figure (B) shows the Langmuir and Freundlich isothermal models of MOF-F20 and ZIF-8 adsorbing TCs under the condition of 298K in Example 3;

[0046] Figure 12 Figure (A) shows the degradation of TCs by ZIF-8 and MOF-Fx in Examples 1-4 (first-order kinetic fitting graph); Figure 12 Figure (B) shows the effect of different scavengers on the degradation efficiency of TCs by MOF-F20 in Example 3; Figure 12 Figure (C) shows the EPR spectra of DMPO--OH adduct and DMPO--O2 adduct; Figure 12 Figure (D) shows the evaluation of the adsorption and photocatalytic performance of ZIF-8 and MOF-Fx in Examples 1-4 on TCs;

[0047] Figure 13 Figure (A) shows the treatment effect of MOF-F20 in Example 3 on TCs in actual samples (pure water, tap water and river water); Figure 13 Figure (B) shows the standard curve of TCs concentration under HPLC method.

[0048] The realization, functional characteristics and advantages of the object of the present invention will be further described in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Embodiments

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. For those not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments without indicating the manufacturer can be obtained as conventional products through commercial purchase. In addition, the meaning of "and / or" appearing throughout the text includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0050] Tetracycline antibiotics (TCs), including oxytetracycline, chlortetracycline, and tetracycline, etc., are one of the most widely used antibiotics globally, widely used in the prevention and treatment of bacterial infections in humans and animals, and often used as feed additives in animal husbandry and aquaculture.

[0051] However, the chemical structure of TCs is stable and difficult to be naturally degraded. Therefore, its residue levels in environments such as water bodies, soil, and food are relatively high. These residual antibiotics can not only induce bacteria to produce resistance genes but also gradually accumulate through the ecosystem cycle and food chain, posing a serious threat to the ecological environment and human health.

[0052] Currently, methods for TCs monitoring include high-performance liquid chromatography-mass spectrometry (HPLC-MS), electrochemical analysis, capillary electrophoresis, etc., and methods for TCs removal include electrochemical degradation, photocatalysis, etc. However, the above monitoring methods require the use of expensive instruments, with complex experimental operations and high costs, and cannot be used in environments with limited resource conditions.

[0053] In view of this, the present invention provides a multifunctional nanozyme, including zeolitic imidazolate framework material-8 and iron oxide quantum dots loaded on the zeolitic imidazolate framework material-8.

[0054] In the technical solution of the present invention, the zeolitic imidazolate framework material-8 (ZIF-8) in the multifunctional nanozyme has a porous structure, and the iron oxide quantum dots (Fe3O4QDs) are dispersed in the porous structure channels of ZIF-8, which improves the dispersibility, stability of Fe3O4QDs and the contact area with the substrate. As a result, the peroxidase-like (POD) activity of Fe3O4QDs is relatively high and stable, enabling the multifunctional nanozyme to monitor the treatment of TCs in real time by colorimetric methods and other means based on this POD activity; ZIF-8 can achieve the removal of tetracycline through surface adsorption and interaction with tetracycline molecules. However, due to its large band gap (about 5.1 eV), ZIF-8 itself has problems of weak light response and low catalytic efficiency and usually cannot decompose TCs under normal light conditions. On this basis, the loading of Fe3O4QDs, on the one hand, improves the affinity of the nanozyme for TCs, increasing the adsorption rate and adsorption capacity of the multifunctional nanozyme. On the other hand, the loading of Fe3O4QDs increases the carrier migration rate of ZIF-8 under light conditions, resulting in a large amount of rapid generation of two kinds of free radicals, ·O2 - and ·OH, making the oxidative degradation effect of free radicals on TCs stronger under light, so that the multifunctional nanozyme can simultaneously achieve the effects of adsorbing, detecting and photocatalytically degrading TCs in an integrated manner.

[0055] It can be understood that the POD-like activity of the multifunctional nanozyme (Fe3O4QDs@ZIF-8) in the present invention means that Fe3O4QDs@ZIF-8 can oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue TMB oxidation product (Ox-TMB). It should be noted that other methods that can be used to detect the activity of POD are also applicable to the multifunctional nanozyme of the present invention.

[0056] It can be understood that the multifunctional nanozyme of the present application does not require the addition of additional reagents (H2O2, HCl, etc.) to assist in the degradation of TCs when disposing of TCs, avoiding secondary pollution to the environment and being suitable for large-scale application.

[0057] In some embodiments of the present invention, the mass ratio of the zeolitic imidazolate framework material-8 to the iron oxide quantum dots in the multifunctional nanozyme is 30.0 to 65.0. The mass ratio of ZIF-8 and Fe3O4QDs in Fe3O4QDs@ZIF-8 can be 30.0, 40.0, 50.0 or 65.0. The mass ratio within the above range can ensure better adsorption effect, detection effect and photocatalytic degradation effect on TCs. Excessive loading of Fe3O4QDs will cause the complete disintegration of the ZIF-8 framework, unable to maintain the porous structure and accommodate TCs.

[0058] In some embodiments of the present invention, the average particle size of the multifunctional nanozyme is 150.0 - 300.0 nm. The average particle size of the multifunctional nanozyme Fe3O4QDs@ZIF-8 can be 150.0 nm, 200.0 nm or 300.0 nm. Its average particle size within the above range can ensure relatively high catalytic activity and stability.

[0059] In some embodiments of the present invention, the average pore size of the multifunctional nanozyme is 2.0 - 10.0 nm. The average pore size of the multifunctional nanozyme Fe3O4QDs@ZIF-8 can be 2.0 nm, 5.0 nm or 10.0 nm. Its average pore size within the above range can ensure that the Fe3O4QDs in the pores do not affect the adsorption of TCs, and there is sufficient attachment space, facilitating the rapid achievement of adsorption and desorption equilibrium of TCs. At the same time, it can also ensure that the Fe3O4QDs in the pores can better contact the colorimetric detection substrate and play the detection function.

[0060] In some embodiments of the present invention, the effective pH range of the multifunctional nanozyme is 2.5 - 4.5. The multifunctional nanozyme Fe3O4QDs@ZIF-8 can better exert its POD-like activity within the above pH range, facilitating the detection during the TCs disposal process.

[0061] In some embodiments of the present invention, the effective temperature range of the multifunctional nanozyme is 20.0 - 45.0 °C. The multifunctional nanozyme Fe3O4QDs@ZIF-8 can better exert its POD-like activity within the above temperature range, facilitating the detection during the TCs disposal process.

[0062] In some embodiments of the present invention, the peroxidase activity of the multifunctional nanozyme is 30.0 - 150.0 U / mg. With its peroxidase activity within the above range, the test of TCs can be carried out relatively quickly, facilitating the establishment of a colorimetric detection mode based on ultraviolet-visible spectrophotometer and a visualization detection mode based on smartphone-assisted photography, realizing the instant monitoring and observation of the process of the multifunctional nanozyme disposing of TCs.

[0063] The present invention also provides a preparation method of the multifunctional nanozyme, including the following steps: obtaining iron oxide quantum dots, mixing the iron oxide quantum dots with a zinc source solution and a 2-methylimidazole solution, and carrying out a coordination polymerization reaction to obtain the multifunctional nanozyme.

[0064] In the technical solution of the present invention, the zinc source solution is used to provide divalent zinc ions. When the zinc source solution is mixed with the 2-methylimidazole solution, the divalent zinc ions start to undergo a coordination reaction with 2-methylimidazole. Each zinc ion can coordinate with the nitrogen atoms in four 2-methylimidazole molecules to form [Zn(MeIM)4] 2+units; subsequently, [Zn(MeIM)4] 2+ The units polymerize with each other, bridging adjacent Zn ions through the nitrogen atoms on the imidazole ring 2+ to form a three-dimensional framework similar to the zeolite structure, which has a high specific surface area and adjustable pore size; since the iron oxide quantum dots are mixed in the reaction system, they are deposited in the pores of the three-dimensional framework, and finally a multifunctional nanozyme is obtained. The preparation method of the present invention is simple, with low cost, and the obtained multifunctional nanozyme has high catalytic activity and strong stability.

[0065] In some embodiments of the present invention, the mass ratio of the iron oxide quantum dots to the zinc ions in the zinc source solution and 2-methylimidazole in the 2-methylimidazole solution is (5.0 - 40.0):(150.0 - 350.0):(2500.0 - 4000.0). It can be understood that the mass ratio can be 5:160:3657, 16:220:3164 or 31:279:4000. The mass ratio within the above range can ensure that the iron oxide quantum dots deposited in the three-dimensional framework of the multifunctional nanozyme will not cause its structure to collapse.

[0066] In some embodiments of the present invention, the step of obtaining the iron oxide quantum dots includes: obtaining iron oxide nanoparticles, mixing ascorbic acid with the iron oxide nanoparticles, performing a hydrothermal reaction, performing solid-liquid separation, and taking the solid to obtain the iron oxide quantum dots; wherein, the mass ratio of ascorbic acid to the iron oxide nanoparticles is (26.0 - 44.0):1.0, the time of the hydrothermal reaction is 8.0 - 20.0 h, and the temperature of the hydrothermal reaction is 160.0 - 240.0 °C.

[0067] In the technical solution of the present invention, ascorbic acid is used as a reducing agent and a size control agent, so that the iron oxide nanoparticles (Fe3O4 NPs) are transformed into smaller-sized Fe3O4 QDs. At the same time, controlling the mass ratio of ascorbic acid to Fe3O4 NPs and the parameters of the hydrothermal reaction within the above range can ensure that Fe3O4 NPs are transformed into smaller-sized Fe3O4 QDs faster and more fully.

[0068] The present invention also provides an application of the multifunctional nanozyme as described above or the multifunctional nanozyme prepared by the preparation method of the multifunctional nanozyme as described above in the adsorption, detection, and degradation of tetracycline antibiotics. Since the multifunctional nanozyme of the present invention has a large pore size and specific surface area, it can adsorb and accommodate TCs in water, thereby reducing the content of TCs in water; at the same time, the multifunctional nanozyme has the POD-like activity of Fe3O4QDs, and its POD-like activity decreases with the increase in the adsorbed TCs content. Therefore, the adsorption of TCs in water can be monitored by detecting its POD-like activity; in addition, the multifunctional nanozyme of the present invention can generate ·O2 - and ·OH free radicals under ordinary light conditions to degrade the remaining TCs in water, and further degrade the TCs in water and the adsorbed TCs to reduce pollution. In summary, the multifunctional nanozyme of the present invention integrates TCs adsorption-detection-photodegradation, truly realizing the goal of "diagnosis and treatment integration", and providing a new idea for simultaneously monitoring and disposing of residual TCs in the environment.

[0069] In some embodiments of the present invention, it includes the following steps: S10. Mix a solution containing tetracycline antibiotics with the multifunctional nanozyme, and carry out an adsorption reaction under dark conditions until the adsorption and desorption reach equilibrium to obtain a first mixture; S20. Carry out a photodegradation reaction on the first mixture under light conditions to degrade the tetracycline antibiotics, and perform solid-liquid separation to obtain a treated solution.

[0070] In the technical solution of the present invention, the adsorption of TCs under dark conditions can ensure that the TCs in the solution can be rapidly enriched to reach the adsorption and desorption equilibrium, converting the multifunctional nanozyme into a multifunctional nanozyme adsorbed with TCs; subsequently, the above solution is placed under light conditions for a photodegradation reaction, enabling the multifunctional nanozyme to generate ·O2 - and ·OH free radicals under light. The ·O2 - and ·OH free radicals can undergo redox reactions with the TCs in water and the TCs adsorbed on the surface of the multifunctional nanozyme, causing the TCs molecules to decompose into harmless small molecule substances, achieving the effect of treating TCs. The application method of the present invention is simple, without the need to add additional reagents for photodegradation treatment after adsorption, nor the need for special ultraviolet irradiation for photodegradation treatment. Therefore, the multifunctional nanozyme of the present invention can achieve the integrated treatment of TCs diagnosis and treatment, facilitating large-scale application.

[0071] In some embodiments of the present invention, in step S10, the tetracycline antibiotics include at least one of oxytetracycline, chlortetracycline, and tetracycline; and / or, in step S10, the mass ratio of the tetracycline antibiotics in the solution to the multifunctional nanozyme is 0.05 to 1.5. That is to say, the multifunctional nanozyme of the present invention can individually treat oxytetracycline, chlortetracycline, or tetracycline, or can treat their mixed solution, which is within the protection scope of the present invention. During the application process, the mass ratio of TCs to the multifunctional nanozyme within the above range can ensure better effects of adsorption, monitoring, and photocatalysis degradation.

[0072] In some embodiments of the present invention, in step S10, the pH of the adsorption reaction is 4.0 to 10.0; and / or, in step S10, the temperature of the adsorption reaction is 20.0 to 25.0 °C; and / or, in step S10, the time of the adsorption reaction is 0.5 to 3.0 h. It can be understood that the pH of the adsorption reaction can be 4.0, 6.0, 8.0, or 10.0, the temperature of the adsorption reaction can be 20.0 °C, 22.0 °C, or 25.0 °C, and the time of the adsorption reaction can be 0.5 h, 2.0 h, or 3.0 h. The adsorption effect of the multifunctional nanozyme of the present invention is less affected by the change of pH. At the same time, when the adsorption time reaches 0.5 h, the multifunctional nanozyme can reach the adsorption and desorption equilibrium. Therefore, under the above adsorption parameters, the adsorption of TCs by the multifunctional nanozyme reaches the limit. Preferably, the mass ratio of TCs to the multifunctional nanozyme is 1.

[0073] In some embodiments of the present invention, in step S20, the power of the light irradiation is 20 to 200 W; and / or, in step S20, the time of the photocatalysis degradation reaction is 0.5 to 12 h. The power and time of the light irradiation within the above range can ensure that the multifunctional nanozyme adsorbed with TCs in the system can release more free radicals to degrade the TCs not adsorbed in the water body.

[0074] In some embodiments of the present invention, the methods for judging that the adsorption reaction reaches the adsorption and desorption equilibrium include colorimetric detection method and / or photographic visualization detection method. Since the POD-like activity of the multifunctional nanozyme is limited by the adsorption amount of TCs, its POD activity is negatively correlated with the adsorption amount of TCs. Therefore, the adsorption situation of TCs can be judged by colorimetric detection; in addition, corresponding to the colorimetric reaction, the adsorption situation of TCs can be visually judged by taking pictures.

[0075] In some embodiments of the present invention, the detection limit of the colorimetric detection method is 0.015 mg / L; and / or, the detection limit of the photographic visualization detection method is 0.12 mg / L; and / or, when the mass ratio of the tetracycline antibiotics in the solution to the multifunctional nanozyme is 1.0, the relative standard deviation RSD of the recovery rate of the added tetracycline antibiotic standard is ≤8.06%. Compared with the existing adsorbents, the multifunctional nanozyme of the present invention has higher detection sensitivity and larger adsorption capacity in the colorimetric mode and the photographic visualization detection method, which is higher than other similar materials; the spike recovery rate indicates that the multifunctional nanozyme of the present invention has good accuracy and reproducibility in detecting TCs in actual environmental water samples.

[0076] It can be understood that the multifunctional nanozyme of the present invention simultaneously has more stable peroxidase-like activity, stronger photocatalytic ability and larger adsorption capacity. The multifunctional nanozyme has a higher adsorption amount, stronger photocatalytic effect and higher removal rate of tetracycline antibiotics in water, and at the same time has the specificity and anti-interference ability for adsorbing and treating tetracycline antibiotics, and is suitable for large-scale industrial treatment.

[0077] The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0078] Example 1

[0079] A multifunctional nanozyme includes zeolitic imidazolate framework material-8 and iron oxide quantum dots loaded on the zeolitic imidazolate framework material-8; the mass ratio of the zeolitic imidazolate framework material-8 to the iron oxide quantum dots is 55.

[0080] The multifunctional nanozyme is prepared by the following steps:

[0081] (1) Preparation of iron oxide nanoparticles (Fe3O4 NPs): 4.0 mmol of FeCl3 and 0.68 mmol of sodium citrate are mixed in ethylene glycol (20.0 mL), and then 1.20 g of sodium acetate is added under stirring, and the stirring is continued for 30.0 min to obtain a homogeneous mixture. Then the mixture is transferred to a stainless steel autoclave lined with polytetrafluoroethylene, sealed and heated for 10.0 h to obtain a black product. The black product indicates that iron oxide nanoparticles have been formed. It is transferred to a conical flask, rinsed three times with ethanol and deionized water, and finally dried at 60 °C for 12.0 hours to obtain Fe3O4 NPs solid particles for standby;

[0082] (2) Preparation of iron oxide quantum dots (Fe3O4 QDs): 0.2 M ascorbic acid (AA) and 1.25 mg / mL Fe3O4 NPs were mixed in 70.0 mL of pure water and sonicated until homogeneous to obtain a suspension. The suspension was transferred to a 100.0 mL stainless steel autoclave lined with polytetrafluoroethylene and reacted at 200.0 °C for 12.0 h. After the reaction ended and cooled naturally, it was filtered through a 0.22 μm pore size filter. The filtrate was the Fe3O4 QDs solution, which was stored at 4 °C for later use;

[0083] (3) Preparation of multifunctional nanozyme (Fe3O4 QDs@ZIF-8): 0.6 mmol zinc nitrate hexahydrate was mixed with 20.0 mL of ultrapure water and stirred to obtain solution A; 0.04 mol of 2-methylimidazole and 5.0 mL of Fe3O4 QDs solution were dissolved in 15.0 mL of ultrapure water to obtain solution B; under magnetic stirring, solution A was slowly added to solution B, stirred for 30.0 min, and then left to stand overnight. After centrifugation, washing, and drying, the product Fe3O4 QDs@ZIF-8 was obtained, which was denoted as MOF-F5.

[0084] Example 2

[0085] The difference between Example 2 and Example 1 is that:

[0086] In step (3), 0.04 mol of 2-methylimidazole and 10.0 mL of Fe3O4 QDs were dissolved in 10.0 mL of ultrapure water to obtain solution B, and the product was denoted as MOF-F10.

[0087] Example 3

[0088] The difference between Example 3 and Example 1 is that:

[0089] In step (3), 0.04 mol of 2-methylimidazole was dissolved in 20.0 mL of Fe3O4 QDs to obtain solution B, and the product was denoted as MOF-F20.

[0090] Example 4

[0091] The difference between Example 4 and Example 1 is that:

[0092] In step (3), 0.6 mmol of zinc nitrate hexahydrate was mixed with 15.0 mL of Fe3O4 QDs and stirred to obtain solution A; 0.04 mol of 2-methylimidazole was dissolved in 15 mL of Fe3O4 QDs to obtain solution B, and the product was denoted as MOF-F30.

[0093] Example 5

[0094] Example 5 is different from Example 1 in that:

[0095] In step (3), 0.6 mmol of zinc nitrate hexahydrate was mixed with 20.0 mL of Fe3O4 QDs and stirred to obtain solution A; 0.04 mol of 2-methylimidazole was dissolved in 20 mL of Fe3O4 QDs to obtain solution B, and the product was denoted as MOF-F40.

[0096] Example 6

[0097] Example 6 is different from Example 1 in that:

[0098] In step (2), the amount of ascorbic acid used was 0.15 M.

[0099] Example 7

[0100] Example 7 is different from Example 1 in that:

[0101] In step (2), the amount of ascorbic acid used was 0.175 M.

[0102] Example 8

[0103] Example 8 is different from Example 1 in that:

[0104] In step (2), the amount of ascorbic acid used was 0.225 M.

[0105] Example 9

[0106] Example 9 is different from Example 1 in that:

[0107] In step (2), the amount of ascorbic acid used was 0.25 M.

[0108] Example 10

[0109] Example 10 is different from Example 1 in that:

[0110] In step (2), the reaction was carried out at 200 °C for 8.0 h.

[0111] Example 11

[0112] Example 11 is different from Example 1 in that:

[0113] In step (2), the reaction was carried out at 200 °C for 16.0 h.

[0114] Example 12

[0115] Example 12 is different from Example 1 in that:

[0116] In step (2), the reaction was carried out at 200 °C for 20.0 h.

[0117] Example 13

[0118] Example 13 is different from Example 1 in that:

[0119] In step (2), the reaction is carried out at 160 °C for 20.0 h.

[0120] Example 14

[0121] Example 14 is different from Example 1 in that:

[0122] In step (2), the reaction is carried out at 180 °C for 12.0 h.

[0123] Example 15

[0124] Example 15 is different from Example 1 in that:

[0125] In step (2), the reaction is carried out at 220 °C for 12.0 h.

[0126] Example 16

[0127] This example provides an application of the multifunctional nanozyme MOF-F20 in Example 3, including the following steps:

[0128] S10. Mix a solution containing 50.0 mg / L tetracycline with a pH of 7 with 100.0 μL of the multifunctional nanozyme (2.0 mg / L), and carry out an adsorption reaction under dark conditions until the adsorption and desorption reach equilibrium to obtain a first mixture;

[0129] S20. Expose the first mixture to LED (100 W), carry out a photocatalytic degradation reaction under light for 3.0 h to degrade the tetracycline antibiotics, and then filter to obtain a treated solution.

[0130] Comparative Example 1

[0131] Comparative Example 1 is the same as Example 1 except that the multifunctional nanozyme is replaced by ZIF-8.

[0132] Performance test

[0133] 1. Characterize the Fe3O4 QDs prepared in Examples 6-15

[0134] (1) The POD-like activity of the Fe3O4 QDs prepared in Examples 6-15 was detected. The detection method was as follows: 100 μL of TMB (5.0 mM) and 50 μL of H2O2 (10.0 mM) were added to 1800 μL of HAc-NaAc buffer (0.2 M, pH = 3.5). Finally, 50 μL of Fe3O4 QDs was added and incubated at 30 °C for 15 minutes, and the absorbance at 652 nm (A 652nm ) was measured to represent its POD-like activity. The results are as Figure 1 shown.

[0135] It can be Figure 1 seen that the optimal preparation conditions were to dissolve AA and Fe3O4 NPs (mg:mg) with a mass ratio of 31:1 in ultrapure water, and then carry out a hydrothermal reaction at 200 °C for 12.0 h to obtain Fe3O4 QDs with the highest POD-like activity.

[0136] (2) Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to measure the morphology and particle size of the Fe3O4 QDs prepared in Example 1. The results are as Figure 2 shown. Figure 2 (A) in shows that the formed Fe3O4 QDs are well-distributed, without aggregation in the region, with regular morphology, and the particle size distribution is about 3.57 ± 0.07 nm ( Figure 2 inset C in); the HRTEM image shows that there are 0.25 nm lattice fringes of the (311) plane on the surface of Fe3O4 QDs ( Figure 2 B in).

[0137] 2. Characterization of the multifunctional nanozymes prepared in Examples 1-5

[0138] (1) The morphologies of ZIF-8 and the multifunctional nanozymes prepared in Examples 1-5 were observed by scanning electron microscopy (SEM). The results are as Figure 3 shown in (A) to (F) in.

[0139] It can be clearly Figure 3 seen from (A) in that ZIF-8 has a rhombic dodecahedron structure with uniform size, and the particle size is about 200 nm; from Figure 3 (B), (C), (D), (E), (F) in are the SEM images of MOF-F5, MOF-F10, MOF-F20, MOF-30, and MOF-40 respectively. It was observed that as the volume of the incorporated Fe3O4 quantum dot dispersion increased, the morphology of the multifunctional nanozyme gradually changed, and the framework structure of MOF-F40 completely disintegrated ( Figure 3 F in).

[0140] (2) The multifunctional nanozymes prepared in Examples 1 to 4 were analyzed by energy-dispersive X-ray spectroscopy (EDS), and the results are shown in Table 1 and Figure 5 as follows.

[0141] Table 1 Elemental composition of ZIF-8 and MOF-Fx based on EDS

[0142] Sample Fe (Wt%) Zn (Wt%) O (Wt%) N (Wt%) C (Wt%) ZIF-8 / 16.83 3.15 33.01 47.00 MOF-F5 1.56 19.29 6.19 26.33 46.63 MOF-F10 2.84 16.32 10.68 24.19 45.97 MOF-F20 5.22 16.39 16.03 16.52 45.84 MOF-F30 6.47 16.23 16.81 16.93 43.56

[0143] As can be seen from Table 1, as the addition amount of Fe3O4 QDs increases, the percentage of Fe element gradually increases; it can be Figure 5 clearly seen that Fe elements are evenly distributed on ZIF-8 without large-area aggregation.

[0144] (3) The N2 adsorption / desorption isotherm test was carried out on the multifunctional nanozymes prepared in Examples 1 to 4. The test method was as follows: First, the sample to be tested was degassed by heating and vacuum pumping to remove the impurity gases adsorbed on the surface; then it was weighed and placed in liquid nitrogen; at the temperature of liquid nitrogen, the nitrogen adsorption amount of the sample was measured at different preset pressure points to obtain the adsorption isotherm; finally, the data was processed by computer, and the specific surface area, pore volume, average pore diameter and pore size distribution were calculated from the adsorption isotherm. The results are as Figure 3 shown in (G) below.

[0145] As can be Figure 3 seen from (G) below, as the amount of loaded Fe3O4 QDs increases, the isotherm shows a gradual transition from type II to type IV, which is mainly due to the increase in the pore diameter of the nanomaterial. During the adsorption process, after the mesoporous capillary condensation is filled, the pores with large pore diameters can continue to adsorb to form a multi-molecular layer.

[0146] (4) The particle size test was carried out on the multifunctional nanozymes prepared in Examples 1 to 4, and the results are as Figure 3 shown in (H) below.

[0147] As can be Figure 3 clearly seen from (H) below, as the amount of Fe3O4 QDs loaded on ZIF-8 increases, the pore diameter of the nanomaterial gradually increases, which is mainly because the introduced Fe3O4 QDs affect the structure of ZIF-8, indicating that Fe3O4 QDs are distributed on the surface and inside.

[0148] (5) The surface area test was carried out on the multifunctional nanozymes prepared in Examples 1 to 4, and the results are shown in Table 2.

[0149] Table 2 Porosity of ZIF-8 and MOF-Fx based on nitrogen adsorption-desorption experiments

[0150] Sample <![CDATA[Surface area (m 2 / g)]]> BJH Average Pore Diameter (nm) ZIF-8 1638.9 2.2 MOF-F5 1358.5 5.5 MOF-F10 1113.1 5.7 MOF-F20 927.4 5.7 MOF-F30 635.0 8.5

[0151] As can be seen from Table 2, as the addition amount of Fe3O4 QDs increases, the surface area of the multifunctional nanozyme gradually decreases.

[0152] (6) The pseudo-POD activity, adsorption capacity for TCs, and photocatalytic degradation ability of the multifunctional nanozymes prepared in Examples 1-4 were tested respectively. Among them, the pseudo-POD enzyme activity test method was as follows: 100 μL of TMB (5.0 mM) and 50 μL of H2O2 (10.0 mM) were added to 1800 μL of HAc-NaAc buffer solution (0.2 M, pH = 3.5). Finally, 50 μL of the multifunctional nanozyme (2.0 mg / mL) was added, and it was incubated at 30.0 °C for 15.0 minutes, and the absorbance at 652 nm (A 652nm ) was measured to represent its pseudo-POD activity. The test method for the adsorption capacity of TCs was as follows: 4.0 mL of a TC solution with a concentration of 50 mg / L was mixed with 100 μL of the nanozyme dispersion (2.0 mg / mL), and it was placed on a rotary shaker in the dark at room temperature. After a fixed time, the suspension was filtered, and the residual concentration of TCs at this time was calculated by measuring the absorbance (A 357nm ) of the filtrate at 357 nm, and then the adsorption capacity of the multifunctional nanozyme for TC was calculated. The test method for the photocatalytic degradation ability was as follows: The mixture of TCs and MOF-Fx was shaken in the dark to achieve the adsorption-desorption equilibrium of TCs. After the adsorption was completed, it was exposed to an LED (100.0 W), and the mixture was filtered after 3 hours of light irradiation. Then, by measuring A 357nm , the content of the remaining TCs in the solution and the degradation percentage were calculated (Formula 7). The results are shown in Figure 4 Figures (A), (B), and (C).

[0153] As Figure 4 shown in Figure (A), as the addition amount of Fe3O4 QDs increases, the pseudo-POD activity of the multifunctional nanozyme first increases and then decreases, indicating that appropriate doping of Fe3O4 QDs can significantly improve the pseudo-POD activity of the composite nanozyme. However, when the addition amount is too large, the structure of ZIF-8 will be damaged (which can be clearly seen in the SEM image), making it unable to effectively load Fe3O4 QDs and resulting in a decrease in enzyme activity. Similarly, Figure 4 from Figure (B), it can be seen that the adsorption effect of the multifunctional nanozyme on TCs also shows a phenomenon of first increasing and then decreasing. Figure 4Figure (C) shows the change in the degradation ability of the multifunctional nanozyme against TCs with the incorporated volume of Fe3O4 QDs. Generally speaking, the change in the degradation rate is not significant, which may be due to the fact that most of the TCs have been enriched during the adsorption stage, and there is too little remaining TC in the solution. However, in comparison, the degradation ability of the multifunctional nanozyme is still higher than that of ZIF-8. To sum up, the multifunctional nanozyme (MOF-F20) prepared when the volume of added Fe3O4 QDs is 20 mL has the best POD-like activity and the abilities of TC adsorption and photocatalysis degradation.

[0154] (7) Further perform HRTEM analysis, X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis on the multifunctional nanozyme MOF-F20 prepared in Example 3. The results are as Figure 6 and Figure 7 shown.

[0155] As Figure 6 shown by the red circles in (A), in the HRTEM image of MOF-F20, the distribution of Fe3O4 QDs inside and on the surface of ZIF-8 was observed. Magnifying a local area of it gives Figure 6 (B), and the presence of 0.25 nm lattice fringes belonging to the (311) plane of Fe3O4 QDs was observed on the surface of MOF-F20.

[0156] Figure 6 Figure (C) shows the XRD pattern of the multifunctional nanozyme MOF-F20. The diffraction peaks at 7.4, 10.4, 12.8, 14.7, 16.5, 18.0, 22.2, 24.6 and 26.7° correspond to the (011), (002), (112), (022), (013), (222), (114), (233) and (134) crystal planes of ZIF-8 respectively; the diffraction peaks at 18.3, 30.1, 35.4 and 37.1° correspond to the (111), (220), (311) and (222) crystal planes of Fe3O4 NPs (JCPDS No. 72-2303).

[0157] Characterize the chemical composition and functional groups of MOF-F20 by FT-IR and XPS. As Figure 6 shown in (D), the infrared spectra of MOF-F20 and ZIF-8 are similar. Specifically, the absorption peak at 421 cm -1 is caused by the stretching mode of the Zn-N bond, and the absorption peaks in the 500 - 1350 cm -1 and 1350 - 1500 cm -1 bands are caused by the in-plane bending and stretching of the imidazole ring respectively, and the absorption peak at 1584 cm -1The absorption peak at [specific position] is related to the stretching vibration of C=N, and the absorption peak in the range of 2500 - 3500 cm -1 is attributed to the stretching vibrations of -NH- and -CH3. These signals are present in both MOF-F20 and ZIF-8, indicating that after loading Fe3O4QDs, MOF-F20 retains the framework structure of ZIF-8. For Fe3O4QD and MOF-F20, the absorption peak at 3420 cm -1 is related to the -OH groups on the surface of Fe3O4QDs, and the relatively narrow absorption peak at 1716 cm -1 belongs to the stretching vibration of C=O. Figure 7 The full XPS scan spectrum of MOF-F20 in (A) of [reference] confirmed the presence of Fe2p, C1s, N1s, O1s, and Zn2p. Figure 7 In the high-resolution spectrum of Fe2p in (B) of [reference], the two peaks at 710.85 eV and 724.44 eV correspond to Fe 3+ 2p 3 / 2 and Fe 2+ 2p 1 / 2 , representing metal oxides of Fe(II) and Fe(III) respectively, and the ratio of Fe(II) to Fe(III) is approximately 1:2. For Fe 3+ , weak satellite peaks (Sat.I) at 718.5 eV and (Sat.II) at 733 eV were obtained. Figure 7 In (C) of [reference], the two peaks at 1022.06 eV and 1044.98 eV are respectively attributed to Zn 2p 3 / 2 and Zn 2p 1 / 2 , indicating the presence of Zn-N and Zn-O bonds in MOF-F20. In Figure 7 the high-resolution spectrum of O1s in (D) of [reference], 529.74, 531.49, and 533.28 eV belong to Fe-O, C-O, and C=O respectively; Figure 7 in (E) of [reference], 399.06 eV and 400.62 eV in the high-resolution spectrum of N1s are respectively attributed to C-N and C=N on the imidazole ring of ZIF-8; Figure 7 in (F) of [reference] shows the high-resolution spectrum of C1s, and 284.8 eV and 285.46 eV originate from C-C / C=C and C-N respectively.

[0158] 3. Compare the peroxidase-like activities of Fe3O4NPs, Fe3O4QDs prepared in Example 3, ZIF-8, and the multifunctional nanozymes prepared in Examples 1 - 5

[0159] (1) The peroxidase-like activities of Fe3O4 NPs, Fe3O4 QDs prepared in Example 3, ZIF-8, and the multifunctional nanozymes prepared in Examples 1-5 were measured. The measurement method was as follows: 100 μL of 3,3',5,5'-tetramethylbenzidine (TMB, 5 mM) and 50 μL of H2O2 (10 mM) were added to 1800 μL of acetic acid-sodium acetate (HAc-NaAc) buffer solution (pH = 3.5). Finally, 50 μL of the analyte (2 mg / mL) was added, keeping the total reaction volume at 2000 μL, and incubated in an oscillator at 30 °C for 15 minutes. The absorbance at 652 nm was measured to represent its peroxidase-like activity. The analyte was Fe3O4 NPs, Fe3O4 QDs prepared in Example 3, ZIF-8, or the multifunctional nanozymes prepared in Examples 1-5. The results are as Figure 8 shown.

[0160] As Figure 8 and Figure 4 shown in (A) below, ZIF-8 does not have peroxidase-like activity; Fe3O4 QDs have relatively high peroxidase-like activity, but are prone to aggregation and have poor stability; the multifunctional nanozyme Fe3O4 QDs@ZIF-8 shows different enzyme activities with the change of the incorporated volume of Fe3O4 QDs, which may be related to the structural stability and loading saturation of the material; among them, MOF-F20 has the best peroxidase-like activity. It can be seen that Fe3O4 QDs are dispersed after being loaded by ZIF-8, and at the same time, the contact area with the substrate is increased, thus showing high peroxidase-like activity.

[0161] (2) Optimize the conditions for MOF-F20 nanozyme to exhibit the best enzyme-like activity

[0162] Similar to the method for measuring enzyme activity in step (1), single-factor optimization of pH and temperature was carried out. Without changing other conditions, the initial pH of the reaction system was set to 3.0, 3.5, 4.0, 4.5, 5.0, or 5.5 respectively; without changing other conditions, the reaction temperature was set to 20, 25, 30, 35, 40, 45, 50, 55, or 60 °C respectively. The results are as Figure 9 shown.

[0163] As Figure 9 shown in (A) below, with the increase of the pH value of the HAc-NaAc buffer solution, the absorbance of MOF-F20 reaches the maximum value at pH = 3.5 and then decreases rapidly. It should be that when the pH gradually increases, the gradual decomposition of H2O2 reduces the source of reactive oxygen in the reaction system. As Figure 9As shown in (B), with the increase of temperature, mass transfer is accelerated, and the absorbance of the reaction system reaches the maximum at 30 - 35 °C. However, when the temperature is greater than 40 °C, since H2O2 gradually decomposes at high temperature, the absorbance of the reaction system shows a sharp and gradual decline. Therefore, the optimal application conditions for MOF-F20 are selected as pH = 3.5 and temperature 30 °C.

[0164] (3) Explore the POD-like activity mechanism of MOF-F20 nanozyme

[0165] Steady-state kinetic measurement method of TMB: Add different volumes of TMB (5.0 mM, and keep the concentration range after addition at 0.1 - 1.0 mM) and 50 μL of H2O2 (10.0 mM) into the HAc-NaAc buffer solution (pH = 3.5). Finally, add 50 μL of MOF-F20 (the enzyme concentration before addition is 2.0 mg / mL), keep the total reaction volume at 2000 μL, then measure the time spectrum (absorbance vs. time spectrum, the measurement time is 2 min), and fit it to obtain the rate v. Then, according to the Michaelis-Menten equation and the double-reciprocal Linewever-Burk plot, the values of Km m and Vmax max can be obtained (v is the initial rate, Km m is the Michaelis constant, Vmax max is the maximum reaction rate, and [S] is the substrate concentration). The detection results are as shown in Figure 9 (C).

[0166] The steady-state kinetic measurement method of H2O2 only needs to change the addition amount of H2O2 while keeping the addition amount of TMB fixed (5.0 mM, 100 μL) in the above TMB steady-state kinetic measurement method, and keep the concentration range after addition at 0.1 - 1.0 mM. The detection results are as shown in Figure 9 (D).

[0167] From Figure 9 (C) and Figure 9 (D), it can be seen that within a certain concentration range, the reaction rate v gradually increases with the concentrations of TMB and H2O2 and gradually reaches equilibrium. From the linear correlation coefficients of the Lineweaver-Burk double-reciprocal plots in Figure 9 (E) and Figure 9 (F), it can be known that the change of the reaction rate with the substrate concentration follows the Michalis-Menten model. After calculation, the Michaelis constant Km m values of TMB and H2O2 are 0.24 mM and 0.53 mM respectively, and the maximum reaction rate Vmax max values are 1.97×10 -7 -6 M / s and 1.68×10 -7M / s indicates that both the substrate affinity and enzyme activity of MOF-F20 are relatively high.

[0168] 4. Dual-mode detection of TCs adsorption based on MOF-F20

[0169] (1) Colorimetric detection mode based on ultraviolet-visible spectrophotometer

[0170] To achieve colorimetric detection of the TCs adsorption process, 4.0 mL of TCs solutions with different concentrations (0.1 - 20.0 mg / L) were mixed with 100 μL of MOF-F20 dispersion (2.0 mg / mL). After reaching adsorption equilibrium, the supernatant was discarded by centrifugation. Then, the precipitate was mixed with 1850 μL of HAc-NaAc buffer (pH = 3.5), and 100 μL of TMB (5.0 mM) and 50 μL of H2O2 (5.0 mM) were added. Then, the mixture was incubated at 30 °C for 10 minutes, and the absorbance value A at 652 nm was read. The difference in absorbance (ΔA = A0 - A) between this and the blank system (replacing TCs with pure water) was calculated and linearly fitted with the TCs concentration to obtain the colorimetric sensing standard curve of TCs. The LOD value was calculated according to 3δ / k (δ is the standard deviation of the blank value, k is the slope of the standard curve), and the detection limit of the colorimetric detection mode was obtained. The results are as Figure 10 shown.

[0171] Figure 10 In (A), it shows that the absorbance intensity of the colorimetric reaction system decreases with the increase in TCs concentration. It can be seen that the mimetic enzyme activity of MOF-20 is gradually inhibited as the TCs concentration increases. This may be because TCs contain a phenolic ring structure that forms π-π interactions with the π-conjugated ring structure on the MOF-F20 framework. In addition, intermolecular hydrogen bonds are formed between hydroxyl groups, both of which promote their binding and hinder the contact between MOF-F20 and the substrate TMB, thus inhibiting the colorimetric reaction system. As Figure 10 shown in (B), in the concentration range of 0.1 - 20.0 mg / L, the difference in absorbance between each group and the blank group (ΔA 652nm ) has a good correlation with the TCs concentration. The detection limit (LOD) of TCs was calculated by LOD = 3δ / k to be approximately 0.015 mg / L (0.034 μM).

[0172] (2) Visual detection mode based on smartphone-assisted photography

[0173] To achieve visual detection, under the same conditions as colorimetric detection, the UV-vis was replaced with a smartphone to collect its image, and then the R, G, and B values of the image were extracted using a WeChat mini-program. To reduce the influence of factors such as light on the image, three points were randomly sampled from each sample, and then the average values of the R, G, and B values of the three points were taken as the final R, G, and B values of the sample image. Each group of samples was repeated three times. Finally, RGB was calculated and analyzed to construct a linear equation corresponding to the chromaticity value of the image of the MOF-F20 and TCs reaction system and the TCs concentration. The results are as Figure 10 shown in (D)

[0174] As can be seen from Figure 10 (D), in the range of 0.5 - 80.0 mg / L, as the concentration of TCs increases, (R + G) / (0.5 * B) shows a linear correlation with it, and the linear equation is y = 0.0405x + 1.8422 (R 2 = 0.9998), and the LOD = 3δ / k is calculated to be 0.12 mg / L (0.27 μM). Figure 10 The inset in (D) is a photo of MOF-F20 reacting with different concentrations of TCs and then undergoing a color reaction. As the concentration of TCs increases, the color of the solution changes from blue to yellow-green, the color change is obvious, and the visualization degree is high. If a smartphone application program is developed according to the linear equation, the accurate quantification of TCs can be achieved. Therefore, MOF-F20 has good application value in the rapid on-site detection of TCs.

[0175] (3) Selectivity of MOF-F20 for Adsorbing and Detecting TCs

[0176] Test method: To study the anti-interference ability of MOF-F20 for adsorbing and detecting TCs, a single interfering substance was added to the working solution of TCs for testing, so that there were 400.0 mg / L of Na + , K + , Cu 2+ , Cd 2+ , Mn 2+ , SO4 2- , Cl - , NO3 - in the system respectively, 10.0 mg / L of Fe 3+ , 50.0 nM of Cr 6+ , and 80.0 mg / L of Mg 2+ and Ca 2+, and 50.0 mg / L of phenylalanine (Phe), cysteine (Cys), and tryptophan (Trp), as well as 50.0 mg / L of non-tetracycline antibiotics (SM, EM, SMI, PG, MNZ, and CPL). Then, perform the adsorption-detection operation in step (1), and compare the corresponding absorbance intensities with those of the adsorption-detection of individual TCs. The results are as Figure 10 shown in (C)

[0177] Figure 10 (C) shows the influence of potential interfering substances on the detection of TCs by MOF-F20. It can be seen that when most interfering substances coexist with TCs, the A 652nm of the colorimetric detection system does not change significantly, indicating that they do not affect the detection of TCs by MOF-F20. Among them, the influence of Fe 3+ is relatively large, but the actual concentration of Fe 3+ in surface water is generally 0.1 mg / L, which is much lower than the concentration (10.0 mg / L) used in the experiment. Therefore, the interference of Fe 3+ can still be ignored in practical applications. Figure 10 The inset in (C) shows the selectivity of MOF-F20 for different classes of antibiotics (it should be noted that the interference was tested with TC coexisting with a certain interfering substance. The selectivity was tested separately). Compared with TCs, antibiotics such as SM, CPL, PG, EM, MNZ, and SMI did not significantly affect the POD-like activity of MOF-F20, indicating that MOF-F20 has good selectivity and anti-interference ability for the detection of TCs.

[0178] In summary, based on MOF-F20, the dual-modal detection of TCs can be realized, which is sensitive, efficient, highly visual, and easy to implement on-site detection, providing an economical and effective method for environmental supervision departments to monitor the residues of TCs in environmental samples.

[0179] 5. Adsorption and Photodegradation of TCs by MOF-F20

[0180] (1) Optimize the pH and enzyme addition amount for the adsorption of TCs by MOF-F20

[0181] Specifically, the pH value of the TCs solution was adjusted with HCl and NaOH, and the effects of the initial pH value (4.0 - 10.0) on the adsorption performance of ZIF-8 and MOF-F20 were studied. To determine the addition amount of the multifunctional nanozyme, in the adsorption system, while keeping the total volume of the adsorption system unchanged, the equilibrium adsorption amount of TCs was studied by changing the amount of the multifunctional nanozyme added (5.0 mg / L - 300.0 mg / L), and the concentration corresponding to the optimal adsorption amount was selected as the material dosage for the subsequent experiments. The adsorption amount of TCs was calculated based on the change in the absorption intensity of the solution at 357 nm (the characteristic UV-vis absorption of TCs) before and after adsorption, and the standard curve is as Figure 8 shown in (B) of Figure 8 . The results are as

[0182] shown. As Figure 8 shown in (C) of Figure 8 , in the range of pH 4.0 - 10.0, the change in the adsorption capacity of TCs was not significant, indicating that the pH had no significant effect on the interaction between the adsorption sites and TCs, and at the same time, it also demonstrated the application potential of MOF-F20 in the actual environment; meanwhile, the adsorption capacity of MOF-F20 was significantly higher than that of ZIF-8, indicating that the doping of Fe3O4QDs was helpful to improve the adsorption performance, which might be related to the improvement of the affinity of ZIF-8 for TCs by its incorporation. In the subsequent adsorption experiments, pH = 7.0 was selected as the experimental condition. As can be seen from Figure 8 shown in (D) of

[0183] , when the concentration of MOF-F20 was 50.0 mg / L, the adsorption amount was greater than that under other conditions. According to the principle of green conservation, the optimal concentration of the multifunctional nanozyme used in the integrated platform was determined to be 50 mg / L.

[0183] (2) Adsorption study of MOF-F20 on TCs

[0184] First, the adsorption performances of ZIF-8 and MOF-F20 were compared and studied. Test method: 4 mL of a TCs solution with a concentration of 50 mg / L was mixed with 100 μL of a dispersion of MOF-F20 or ZIF-8 (2 mg / mL), and it was placed in the dark on a rotary shaker at 25 °C. The fixed time was 0.017 - 60 h, and the residual concentration of TCs at this time was calculated by measuring the absorbance of the filtrate at 357 nm, and then the adsorption amounts of ZIF-8 and MOF-F20 on TCs were calculated.

[0185] The adsorption capacity of the multifunctional nanozyme for TCs was calculated according to formula (1), and the adsorption percentage for TCs was calculated according to formula (2).

[0186]

[0187] Among them, C0 is the initial concentration of TCs (mg / L), C t$C_t$ is the concentration of TCs in the supernatant at different times (mg / L), $V$ is the total volume of the adsorption system (L), and $m$ is the mass of the nanomaterial (g).

[0188] Secondly, the adsorption mechanisms of ZIF-8 and MOF-F20 were compared and studied. The test methods are as follows:

[0189] 1) Adsorption kinetics: In the adsorption system, while keeping other conditions unchanged, the adsorption time was changed, the adsorption capacity at each moment was measured, a time-adsorption capacity graph was obtained, and the adsorption process was simulated using kinetic models. The models are as follows:

[0190]

[0191]

[0192] where $Q_t$ t and $Q_e$ e are the adsorption capacities at time $t$ and at equilibrium (mg / g); $k_1$ and $k_2$ represent the rate constants of the pseudo-first-order (3) and pseudo-second-order (4) kinetic models. The results are as Figure 11 shown in Table 3.

[0193] Table 3 Kinetic data of MOF-F20 and ZIF-8 for the adsorption of TCs

[0194]

[0195] From Figure 11 it can be seen from (A) that under the predetermined experimental conditions, the adsorption rate of MOF-F20 is significantly higher than that of ZIF-8. The adsorption capacity of MOF-F20 increases sharply within the first 1 h after the addition of the material and then gradually reaches equilibrium within 3 h. While the adsorption capacity of ZIF-8 increases slowly in the first 24 h and then gradually reaches equilibrium within 48 h. Presumably, on the one hand, hydrogen bonds and π-π stacking are easily formed between TCs molecules and MOF-F20, enhancing their interaction; on the other hand, the introduction of Fe3O4 QDs will increase the surface roughness of the material, thus providing more adsorption binding sites for TCs. The pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models were used to fit the adsorption process respectively, and the calculated parameter results are shown in Table 3. It can be found that the adsorption processes of both MOF-F20 and ZIF-8 fit relatively well with the pseudo-second-order model, indicating that chemical adsorption dominates in the adsorption process. The kinetic constant of MOF-F20 is greater than that of ZIF-8, further indicating that the doping of Fe3O4 QDs improves the adsorption rate of TCs.

[0196] 2) Adsorption thermodynamics: Adsorption was carried out in TCs solutions with different initial concentrations (5.0 - 200.0 mg / L) at a temperature of 298.0 K. Then the experimental data were fitted to the Langmuir (5) and Freundlich (6) isotherm models established by non - linear regression. The corresponding equations are as follows:

[0197]

[0198] Q e = k F C e 1 / n (6)

[0199] where Q e and Q max are the adsorption capacity and the theoretical maximum adsorption capacity (mg / g) at equilibrium. Ce is the remaining TCs concentration (mg / L) at equilibrium; k L and k F represent the constants of the Langmuir and Freundlich isotherm models. n is the heterogeneity factor. The results are shown in Figure 11 and Table 4.

[0200] Table 4 Langmuir and Freundlich isotherm data for the adsorption of TCs by MOF - F20 and ZIF - 8

[0201]

[0202] The experimental data were respectively fitted with the Langmuir model and the Freundlich model, and the fitting curves are shown in Figure 11 (B) as shown, and the model parameters are shown in Table 4. The adsorption amounts of both nanomaterials for TCs increase significantly with the increase of C e . The maximum adsorption amounts (Q max ) of MOF - F20 and ZIF - 8 are 1625.35 mg / g and 1535.01 mg / g, showing significant advantages in terms of adsorption capacity. The R 2 values of the different model fitting curves of MOF - F20 and ZIF - 8 are both close, indicating that chemical adsorption and physical adsorption coexist in both materials. The fitting effect of the Langmuir model for MOF - F20 is slightly better than that of the Freundlich model, indicating that monolayer chemical adsorption is dominant, which is consistent with the results of kinetic studies. In addition, under the Freundlich model, 1 / n is less than 1.0, indicating that both materials have a strong affinity for TCs, and MOF - F20 has a lower 1 / n value than ZIF - 8, further proving that the doping of Fe3O4QDs enhances the affinity of the material for TCs.

[0203] (3) Photodegradation of TCs by multifunctional nanozymes

[0204] First, the photodegradation performances of ZIF-8 and multifunctional nanozymes were comparatively studied. The test method was as follows: The mixture of ZIF-8 or multifunctional nanozyme and TC solution was shaken in the dark for 1 h to achieve the adsorption-desorption equilibrium of TCs. After adsorption, it was exposed to an LED (100 W), and the mixture was filtered after 3 h of light irradiation. Then, the obtained solution was measured and analyzed using UV-vis at 357 nm, and the content of remaining TCs in the solution was calculated. According to formula (7), the degradation percentage of TCs by ZIF-8 or multifunctional nanozyme could be known. Meanwhile, within 3.0 h of light irradiation, the content of remaining TCs in the system was measured every 30 min, and then the degradation process was fitted using the first-order kinetic model. The model is shown in (8). The detection results are as Figure 12 and Figure 4 shown.

[0205]

[0206] Total removal percentage of TCs = Adsorption percentage of TCs + Photodegradation percentage of TCs

[0207] Ln(C t ′ / C0) = -kt (8)

[0208] where C0 is the initial concentration of TCs (mg / L), and C t ′ is the concentration of TCs during the photodegradation process (mg / L);

[0209] k is the rate constant, and t is the time.

[0210] From Figure 12 (A) in Figure 4 and (C) in, it can be seen that compared with ZIF-8, the degradation ability of the multifunctional nanozyme slightly increases with the increase in the doping volume of Fe3O4 QDs. This is because the Fe3O4 QDs loaded on ZIF-8 accelerate the carrier migration rate and accelerate the generation of two kinds of free radicals, ·O2 – and ·OH, resulting in enhanced oxidative degradation effect under light irradiation. From the inset of (A) in Figure 12 , the k values of ZIF-8 and the multifunctional nanozyme were calculated by fitting the data using the first-order kinetic model. The results are shown in Table 5. It can be seen that the degradation ability of MOF-F20 (0.0529 / h) is the best.

[0211] Table 5 Fitting curves of different nanomaterials based on the nonlinear pseudo-first-order model

[0212] Sample Equation <![CDATA[R 2 > ZIF-8 <![CDATA[Ln(C t ′ / C0)=-0.04678t]]> 0.9877 MOF-F5 <![CDATA[Ln(C t ′ / C0) = -0.05252t]]> 0.9841 MOF-F10 <![CDATA[Ln(C t ′ / C0)=-0.04655t]]> 0.9867 MOF-F20 <![CDATA[Ln(C t ′ / C0) = -0.05293t]]> 0.9906 MOF-F30 <![CDATA[Ln(C t ′ / C0) = -0.05273t]]> 0.9946

[0213] Secondly, the photocatalytic degradation mechanism of Fe3O4 QDs@ZIF-8 multifunctional nanozyme on TCs. Measurement method: Free radical trapping experiments and electron paramagnetic resonance (EPR) characterization techniques were used. Specifically, 1 mM tert-butanol (TBA), p-benzoquinone (PBQ), and disodium ethylenediaminetetraacetate (EDTA-2Na) were added to the photocatalytic degradation system as scavengers of superoxide anion (·O2 - ), hydroxyl radical (·OH), and holes (h + ), respectively, to conduct trapping experiments. After 3.0 h of illumination, the solution was analyzed using UV-vis at 357 nm, and the generation of free radicals in the system under dark and different illumination times (500 W xenon lamp) was studied by EPR analysis. 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) dissolved in CH3OH and H2O was used as a spin trap to stabilize ·O2 - and ·OH, respectively. The results are shown as Figure 12 follows.

[0214] As shown in Figure 12 (B), when PBQ was added, the degradation rate of TCs decreased significantly. The addition of TBA decreased the degradation rate by about 50%, while the addition of EDTA-2Na had little effect on the degradation rate of the system. It can be speculated that during the photocatalytic degradation of TCs by MOF-F20, ·O2 - and ·OH produced by it played a combined role, with ·O2 - playing a dominant role and h+ hardly participating. The EPR test results also confirmed this conclusion. As shown in Figure 12 (C), no characteristic peaks of DMPO-·O2 - or DMPO-·OH were observed before illumination. After 10 minutes of illumination, the characteristic peak of DMPO-·O2 - gradually appeared, while the characteristic peak of DMPO-·OH was not obvious. After 20 minutes of illumination, a large amount of ·O2 - and a small amount of ·OH were significantly generated. In summary, in the photocatalytic degradation system of TCs by MOF-F20, ·O2 - and ·OH jointly acted as oxidants to catalyze the oxidative degradation of TCs.

[0215] In conclusion, as shown in Figure 12 (D), MOF-F20 exhibited the best performance in treating TCs. Through adsorption treatment, 83.42% of the TCs concentration was removed, and then 14.33% was removed by photocatalytic degradation under illumination. The overall removal percentage reached 97.75%, demonstrating its excellent performance in the field of actual environmental pollution treatment.

[0216] 6. Verification of the analysis and disposal capabilities of MOF-F20 for actual samples through spike recovery tests

[0217] Spike recovery test: TCs were added to tap water samples and river water (Tangbai River in Xiangyang City) samples filtered through a 0.22 μm microporous filter to configure three concentration levels of low, medium, and high (0.5, 2.0, 6.0 mg / L). 4 mL of TCs solutions with different concentrations (0.5, 2.0, 6.0 mg / L) were mixed with 100 μL of MOF-F20 dispersion (2.0 mg / mL). After 1 hour, the supernatant was taken out by centrifugation. Then the precipitate was mixed with 1850 μL of HAc-NaAc buffer (pH = 3.5), and 100 μL of TMB (5.0 mM) and 50 μL of H2O2 (5 mM) were added. Then the mixture was incubated at 30 °C for 10 minutes, and the absorbance A 652nm was read, and the difference in absorbance ΔA (ΔA = A0 - A) from the blank system (replacing TCs with pure water) was calculated. The detected concentration could be calculated according to the linear equation, and finally the recovery rate and relative standard deviation were calculated. RSD ≤ 9.32%.

[0218] At the same time, the disposal capabilities of MOF-F20 for TCs in actual samples were verified. Specifically, a TCs solution with a concentration of 50.0 mg / L was mixed with MOF-F20. After adsorption, the remaining TCs concentration in the solution was measured to study the adsorption effects on tap water samples and river water samples. Then it was placed under a 100 W LED for degradation treatment, and each sample was repeated 3 times. The spike recovery rate and the total removal rate of TCs were calculated to evaluate the applicability of MOF-F20 in actual samples. The total removal rate of TCs = the percentage of TC adsorption + the percentage of TC photocatalysis degradation. The results are shown in Table 6.

[0219] Table 6 Recovery rate study for the determination of TCs in tap water and river water

[0220]

[0221] As shown in Table 6, the spike recovery rates of tap water samples and river water samples at three concentration levels were 97.87% - 113.87% (RSD ≤ 8.06%) and 96.89% - 111.37% (RSD ≤ 9.32%) respectively. The above results demonstrated the good accuracy and reproducibility of MOF-F20 in detecting TCs in actual environmental water samples. Then, taking the actual sample with a TCs spike concentration of 50.0 mg / L as an example, the adsorption and photocatalysis degradation capabilities of MOF-F20 for TCs in actual samples were investigated by the same method as above. The results are as Figure 13As shown in (A), in the actual water samples, the overall removal rate of TCs decreased slightly (86.98% for tap water and 84.4% for river water), but it was still above a relatively high level, indicating the ability of this composite nanozyme to dispose of TCs in the actual environment.

[0222] 7. Compare the adsorption effect and detection accuracy of MOF-F20 with classical methods

[0223] To further study the adsorption effect and accuracy of MOF-F20, powdered activated carbon (PAC) was used to adsorb TCs and high-performance liquid chromatography (HPLC) was used to determine TCs, and the results were compared with it. Specifically: First, a PAC (2.0 mg / mL) dispersion and a TCs solution (50.0 mg / L) with the same concentration as the multifunctional nanozyme were prepared and incubated in the dark at room temperature for 40 hours. Then, the absorbance of the solution at 357 nm was measured by UV-vis, and the adsorption capacity of PAC was calculated through the formula. Subsequently, a standard curve of TCs was established by HPLC in the range of TCs concentration from 5.0 to 50 mg / L. The HPLC spiked recovery experiment was carried out using tap water samples, and TCs solutions at three concentration levels of 5.0, 10.0, and 15.0 mg / L were prepared for the HPLC spiked recovery experiment. The chromatographic conditions were as follows: WondaCract ODS-2 chromatographic column (4.6×150 mm, 5 μm, Shimadzu), acetonitrile: acetic acid (0.01 M): methanol (v / v / v: 2 / 7 / 1) as the mobile phase, flow rate of 1.0 mL / min, detector wavelength of 357 nm, temperature of 30 °C, and injection volume of 20 μL.

[0224] The standard curve for detecting TCs by the classical HPLC method is as Figure 13 shown in (B). Through the HPLC spiked recovery detection, the recovery rate was between 88.85% and 94.47%, and RSD≤9.41% (Table 7). The accuracy and reproducibility were good. After calculation, the LOD was 2.0 mg / L, and the sensitivity was significantly higher than that of the nanozyme dual-mode detection platform we constructed. In addition, PAC is a commonly used adsorbent in industrial production. Under the same conditions, the maximum adsorption capacity of PAC for TCs was 214.8 mg / g, which was much smaller than the maximum adsorption capacity of MOF-F20 (1625.35 mg / g).

[0225] Table 7 Determination of TC content in actual samples by HPLC method

[0226]

[0227] In summary, the integrated detection and disposal platform for TCs based on MOF-20 constructed in this research has good accuracy, high sensitivity, and excellent disposal performance, and has good application value and significant application advantages in actual production.

[0228] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the patent protection scope of the present invention.

Claims

1. A multifunctional nanozyme, characterized in that, It includes zeolitic imidazolate framework material-8 and iron tetroxide quantum dots loaded on the zeolitic imidazolate framework material-8.

2. The multifunctional nanozyme according to claim 1, wherein In the multifunctional nanozyme, the mass ratio of the zeolitic imidazolate framework material-8 to the iron tetroxide quantum dots is 30.0 to 65.0; and / or, The average particle size of the multifunctional nanozyme is 150.0 to 300.0 nm; and / or, The average pore size of the multifunctional nanozyme is 2.0 to 10.0 nm; and / or, The effective pH range of the multifunctional nanozyme is 2.5 to 4.5; and / or, The effective temperature range of the multifunctional nanozyme is 20.0 to 45.0 °C; and / or, The peroxidase activity of the multifunctional nanozyme is 30.0 to 150.0 U / mg.

3. A preparation method of the multifunctional nanozyme as described in claim 1, characterized in that, It includes the following steps: Obtain iron tetroxide quantum dots, mix the iron tetroxide quantum dots with a zinc source solution and a 2-methylimidazole solution, and carry out a coordination polymerization reaction to obtain the multifunctional nanozyme.

4. The preparation method of the multifunctional nanozyme according to claim 3, wherein, The mass ratio of the iron tetroxide quantum dots to zinc ions in the zinc source solution and 2-methylimidazole in the 2-methylimidazole solution is (5.0 to 50.0):(150.0 to 350.0):(2500.0 to 4000.0).

5. The preparation method of the multifunctional nanozyme according to claim 3, wherein, The step of obtaining the iron tetroxide quantum dots includes: obtaining iron tetroxide nanoparticles, mixing ascorbic acid with the iron tetroxide nanoparticles, carrying out a hydrothermal reaction, performing solid-liquid separation, and taking the solid to obtain the iron tetroxide quantum dots; Among them, the mass ratio of the ascorbic acid to the iron tetroxide nanoparticles is (26.0 to 44.0):1, the time of the hydrothermal reaction is 8.0 to 20.0 h, and the temperature of the hydrothermal reaction is 160.0 to 240.0 °C.

6. Application of the multifunctional nanozyme according to any one of claims 1 to 2 or the multifunctional nanozyme prepared by the preparation method of the multifunctional nanozyme according to any one of claims 3 to 5 in the adsorption, detection and degradation of tetracycline antibiotics.

7. The application according to claim 6, wherein It includes the following steps: S10. Mix a solution containing tetracycline antibiotics with the multifunctional nanozyme, carry out an adsorption reaction under dark conditions until the adsorption and desorption reach equilibrium to obtain a first mixture; S20. Carry out a photocatalytic degradation reaction on the first mixture under light conditions to degrade the tetracycline antibiotics, perform solid-liquid separation to obtain a treated solution.

8. The application according to claim 7, wherein In step S10, the tetracycline antibiotics include at least one of oxytetracycline, chlortetracycline and tetracycline; and / or, In step S10, the mass ratio of the tetracycline antibiotics in the solution to the multifunctional nanozyme is 0.05 to 1.5; and / or, In step S10, the pH of the adsorption reaction is 4.0 to 10.0; and / or, In step S10, the temperature of the adsorption reaction is 20.0 to 25.0 °C; and / or, In step S10, the time of the adsorption reaction is 0.5 to 3.0 h; and / or, In step S20, the power of the light is 20.0 to 200.0 W; and / or, In step S20, the time of the photodegradation reaction is 0.5 to 12.0 h.

9. The application according to claim 7, characterized in that, The methods for determining that the adsorption reaction reaches the adsorption and desorption equilibrium include colorimetric detection method and / or photographic visualization detection method.

10. The application according to claim 9, characterized in that, The detection limit of the colorimetric detection method is 0.015 mg / L; and / or, The detection limit of the photographic visualization detection method is 0.12 mg / L; and / or, When the mass ratio of the tetracycline antibiotics in the solution to the multifunctional nanozyme is 1.0, the relative standard deviation of the recovery rate of adding the tetracycline antibiotic standard is ≤8.06%.

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