Bi-C-CoOx peroxide nano-enzyme as well as preparation method and application thereof

Abstract

The invention relates to the technical field of nano materials, in particular to a Bi-C-CoOx peroxide nano enzyme, a preparation method and application thereof, and the preparation method comprises the following steps: preparing a BiCoMOFs precursor by a solvothermal method; and carrying out thermal activation treatment on the BiCoMOFs precursor, so as to obtain the Bi-C-CoOx peroxide nano enzyme. The Bi-C-CoOx nano-enzyme catalyst is successfully prepared, and high-precision and high-sensitivity detection of PMS and glyphosate is successfully realized by taking Bi-C-CoOx as a catalyst, PMS as an oxidizing agent and TMB as a chromogenic substrate.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials technology, and more specifically, to a Bi-C-CoOx type peroxide nanozyme, its preparation method, and its application. Background Technology

[0002] Nanozymes are nanomaterials with catalytic activity similar to natural enzymes. Due to their unique advantages such as low cost, simple preparation methods, high stability, tunable catalytic activity, and flexible composition and structural design, they have become an effective alternative to natural enzymes. In recent years, nanozymes have been widely used in the development of novel biosensors, serving as a key sensing signal amplification technology in colorimetric, fluorescence, and electrochemical analyses. Especially in colorimetric detection, they have attracted widespread attention due to their ease of operation, low cost, visualization capabilities, and compatibility with portable platforms. During the catalytic colorimetric process, nanozymes catalyze the reaction of peroxides such as H₂O₂ and ROOH, or O₂, to generate reactive oxygen species such as hydroxyl radicals (·OH) with strong oxidizing capabilities. These reactive oxygen species then further oxidize the chromogenic substrate (such as TMB and OPD), thereby achieving the detection of visual signals.

[0003] However, these colorimetric reactions are condition-dependent and have certain limitations. For example, considering the stability of H₂O₂ and the solubility and protonation of TMB, the reaction is usually carried out in acidic solutions. Furthermore, nanozymes are temperature-sensitive and typically require heating to reach the appropriate optimal temperature. Due to the short half-life of ·OH and the insufficient activity of nanozymes, the colorimetric reaction often takes tens of minutes or even hours to generate a detectable visual signal.

[0004] Therefore, in the existing colorimetric detection methods, peroxidases often rely on H2O2 as a substrate oxidant. Their availability, stability, and potential cytotoxicity in biological systems, as well as the sensitivity of nanozymes to reaction conditions and insufficient activity, all seriously affect the practicality and safety of the relevant analytical methods. Summary of the Invention

[0005] The purpose of this invention is to provide a Bi-C-CoOx type peroxide nanozyme, its preparation method, and its application in the detection of PMS and glyphosate. The invention successfully prepared a Bi-C-CoOx nanozyme catalyst, and used Bi-C-CoOx as the catalyst, PMS as the oxidant, and TMB as the chromogenic substrate as the core, thus successfully achieving high-precision and high-sensitivity detection of PMS and glyphosate.

[0006] The embodiments of the present invention are achieved through the following technical solutions:

[0007] Firstly, this invention provides a method for preparing Bi-C-CoOx type peroxide nanozymes, comprising the following steps:

[0008] (1) Preparation of BiCoMOF precursors by solvothermal method;

[0009] (2) The BiCoMOF precursor is thermally activated to obtain Bi-C-CoOx peroxide nanozymes; wherein CoOx is CoO or Co2O3 or Co3O4.

[0010] More specifically, the preparation method of BiCoMOFs precursor includes the following steps: dissolving Co salt and Bi salt in an organic solvent, first adding H3BTC to fully dissolve, then adding PVP to fully dissolve, and then transferring the resulting mixed solution to a high-pressure reactor for heat treatment; subsequently, after washing, solid-liquid separation and drying, the BiCoMOFs precursor is obtained.

[0011] The preparation method of Bi-C-CoOx peroxide nanozymes specifically includes the following steps: placing a ceramic boat containing BiCoMOF precursors in the heat preservation zone of a tube furnace, gradually increasing the temperature and holding it at that temperature for a period of time in an air atmosphere, and then naturally cooling it to room temperature to obtain Bi-C-CoOx peroxide nanozymes.

[0012] Furthermore, the Co salt includes, but is not limited to, cobalt nitrate, cobalt chloride, or cobalt sulfate, with Co(NO3)2·6H2O being a preferred choice.

[0013] Furthermore, the Bi salt includes, but is not limited to, bismuth nitrate, bismuth chloride, or bismuth citrate, with Bi(NO3)2·5H2O being a preferred choice.

[0014] Furthermore, the molar amount of the Co salt is 50% to 90% of the total molar amount of the Co salt and the Bi salt; the molar amount of H3BTC is 3 to 5 times the total molar amount of the Co salt and the Bi salt; the organic solvent is a mixed solvent of DMF and ethanol with a volume ratio of 2 to 5:1; and the ratio of H3BTC to PVP is 3 to 5 mmol: 1g.

[0015] Furthermore, during heat treatment: the heat treatment temperature is 110–130℃, and the heat treatment time is 5–15 hours.

[0016] Furthermore, during gradient heating, the temperature is increased to 300–400°C at a rate of 5°C / min and held for 1–3 hours.

[0017] Secondly, the present invention provides a nanozyme, which is prepared by the above-mentioned preparation method.

[0018] Thirdly, this invention provides an application of the above-mentioned nanozyme in water pollution detection; mainly in the detection of PMS and glyphosate.

[0019] Specifically, the detection method of PMS is as follows: add the nanozyme, PMS oxidant, chromogenic substrate and buffer solution prepared by the above preparation method to the test solution, incubate the above reaction solution at room temperature for a period of time, and measure the absorbance of the reaction solution; substitute the measured absorbance data into the linear equation of absorbance and PMS concentration to obtain the PMS concentration in the test solution.

[0020] In addition, the detection method for glyphosate is as follows: add the nanozyme, PMS oxidant, chromogenic substrate and buffer solution prepared by the above preparation method to the test solution, incubate the above reaction solution at room temperature for a period of time, and measure the absorbance of the reaction solution; substitute the measured absorbance data into the linear equation of absorbance and glyphosate concentration to obtain the glyphosate concentration in the test solution.

[0021] Furthermore, the chromogenic substrate can be selected from 3,3',5,5'-tetramethylbenzidine (TMB), o-phenylenediamine (OPD), or 2,2'-azido-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS), with TMB being the preferred chromogenic substrate.

[0022] Furthermore, the buffer solution can be selected from HAc (acetic acid)-NaAc (sodium acetate) buffer solution or Tris-HCl buffer solution.

[0023] The technical solution of the present invention has at least the following advantages and beneficial effects:

[0024] 1. This invention successfully replaces the traditional peroxidase-based oxidant H2O2 with PMS to construct a colorimetric detection strategy based on Bi-C-CoOx. This colorimetric strategy, with Bi-C-CoOx, PMS and TMB as its core, successfully achieves rapid, wide pH range, and high-precision and high-sensitivity detection of PMS and glyphosate under room temperature conditions. Compared with the traditional H2O2 oxidant, the colorimetric detection strategy based on PMS as the oxidant has the following advantages: (1) It significantly reduces the amount of nanozymes and oxidants used, thereby effectively reducing environmental costs; (2) It expands the pH range (3 < pH < 11) and can be applied at room temperature or even low temperature conditions; (3) It exhibits rapid kinetic characteristics and has a shorter response time, making it suitable for different environmental conditions. The colorimetric detection strategy proposed in this invention has shown good application performance in actual water samples. Attached Figure Description

[0025] Figure 1 The characterization spectrum of Bi-C-CoOx obtained in Example 1 of this invention is shown below. Figure 1 (a) shows the XRD pattern of Bi-C-CoOx. Figure 1 (b) is the Raman spectrum of Bi-C-CoOx. Figure 1 (c)-(f) are XPS spectra of Co2p, Bi4f, C1s and O1s of Bi-C-CoOx, respectively;

[0026] Figure 2 The characterization spectrum of Bi-C-CoOx obtained in Example 1 of this invention is shown below. Figure 2 (a) Figure 2 (b) SEM images under low and high magnification, respectively. Figure 2 (c) is a TEM image of Bi-C-CoOx. Figure 2 (d) is the elemental mapping diagram of Bi-C-CoOx;

[0027] Figure 3 (a) is the adsorption-desorption isotherm of the BiCoMOFs precursor and Bi-C-CoOx peroxide nanozyme prepared in Example 1 of the present invention. Figure 3 (b) is a pore size distribution curve of the BiCoMOF precursor and Bi-C-CoOx peroxide nanozyme prepared in Example 1 of the present invention.

[0028] Figure 4 The figure shows the catalytic activity results of Bi-C-CoOx prepared in Example 1 of this invention, where 4(a) represents different Co values. 2+ / (Co 2+ +Bi 3+ 4(b) shows the catalytic activity results of Bi-C-CoOx at different molar percentages, 4(c) shows the catalytic activity results of Bi-C-CoOx at different PVP amounts, and 4(d) shows the storage stability results of Bi-C-CoOx in Example 1.

[0029] Figure 5 (a) shows the UV-Vis spectra of the reaction systems of different experimental groups in this invention. Figure 5 (b)-(f) are the results of the effects of different Bi-C-CoOx concentrations, pH, temperature and reaction time on the catalytic activity of Bi-C-CoOx when H2O2 and PMS are used as oxidants, respectively.

[0030] Figure 6 (a) shows the response curves of PMS at different concentrations; Figure 6 (b) Linear fitting curve of PMS detection in Bi-C-CoOx-PMS-TMB system (built-in image: top left is the corresponding photo, bottom right is a local magnification (CPMS: 0.10~2.00μM); Figure 6 (c)-(e) are the experimental results of the anti-interference of common cations, anions, small organic molecules and H2O2 on the detection of PMS in the Bi-C-CoOx-PMS-TMB system;

[0031] Figure 7 (a) Graph showing the experimental results for detecting the selectivity of glyphosate; Figure 7 (b) is a linear fitting curve of glyphosate detection in the Bi-C-CoOx-PMS-TMB system. Detailed Implementation

[0032] 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 clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0033] The following is a detailed description of a Bi-C-CoOx type peroxide nanozyme, its preparation method, and its application provided by embodiments of the present invention.

[0034] A method for preparing Bi-C-CoOx type peroxide nanozymes includes the following steps:

[0035] (1) Preparation of BiCoMOF precursor by solvothermal method: Co salt and Bi salt were dissolved in an organic solvent. H3BTC was added first to dissolve them completely, and then PVP was added to dissolve them completely. The resulting mixed solution was then transferred to a high-pressure reactor and reacted at 110-130℃ for 5-15 h, and then naturally cooled to room temperature. Subsequently, the obtained purple precipitate was washed 3-5 times with DMF and ethanol respectively, and then vacuum dried at 50-80℃ to obtain the BiCoMOF precursor.

[0036] The Co salt includes, but is not limited to, cobalt nitrate, cobalt chloride, or cobalt sulfate, with Co(NO3)2·6H2O being preferred; the Bi salt includes, but is not limited to, bismuth nitrate, bismuth chloride, or bismuth citrate, with Bi(NO3)2·5H2O being preferred; the molar amount of the Co salt is 50% to 90% of the total molar amount of the Co salt and the Bi salt; the molar amount of H3BTC is 3 to 5 times the total molar amount of the Co salt and the Bi salt; the organic solvent is a mixture of DMF and EtOH in a volume ratio of 2 to 5:1; the ratio of H3BTC to PVP is 3 to 5 mmol: 1 g;

[0037] (2) Thermal activation of BiCoMOF precursor: Place the ceramic boat containing BiCoMOF precursor in the heat preservation zone of the tube furnace, heat it to 300-400℃ at a rate of 5℃ / min in the air atmosphere, and keep it at the temperature for 1-3h. After naturally cooling to room temperature, Bi-C-CoOx peroxide nanozymes are obtained.

[0038] The specific applications of the Bi-C-CoOx peroxide nanozymes obtained above are as follows:

[0039] The method for detecting PMS using colorimetry is as follows: Bi-C-CoOx, the chromogenic substrate, and different concentrations of PMS (0–100 μM) are sequentially added to HAc-NaAc buffer solution (50 mM, pH = 3.5–5.0). After incubating the reaction solution at room temperature for 8 min, the absorbance A of the reaction solution at 652 nm is measured. 652 Substituting the measured absorbance data into the linear equation relating absorbance and PMS concentration, the PMS concentration in the test solution is obtained. A good linear relationship is observed between the PMS concentration and ΔA, where ΔA represents the concentration of PMS in the reaction system with and without PMS. 652 The difference is expressed by the linear equation: y = 0.01254x + 0.0002(R). 2 =0.9985), with a detection limit (LOD) as low as 0.1 μM; where x represents the PMS concentration and y represents ΔA.

[0040] The colorimetric method for detecting glyphosate is as follows: Different concentrations of glyphosate, Bi-C-CoOx, a chromogenic substrate, and PMS are added to an HAc-NaAc buffer solution (50 mM, pH = 3.5-5.0). The mixture is reacted at room temperature for 7 min, and the absorbance (A) of the reaction solution at 652 nm is measured. 652 Substituting the measured absorbance data into the linear equation relating absorbance and glyphosate concentration, the glyphosate concentration in the test solution is obtained; where ΔA value (i.e., A before and after adding glyphosate) represents the glyphosate concentration. 652 The difference between the glyphosate concentration and the concentration increases with increasing glyphosate concentration, showing a good linear relationship. The linear equation is: y = 0.07069x + 0.1104(R) 2 =0.9984); where x represents the glyphosate concentration and y represents ΔA.

[0041] This invention utilizes PMS (peroxymonosulfate) as an oxidant to replace H2O2, the oxidant used in traditional peroxidases, to construct a colorimetric detection strategy based on Bi-C-CoOx. This colorimetric strategy, with Bi-C-CoOx, PMS, and TMB as its core, successfully achieves high-precision and high-sensitivity detection of PMS and glyphosate. Compared with traditional H2O2, the colorimetric detection strategy based on PMS as an oxidant has the following advantages: (1) It significantly reduces the amount of nanozyme and oxidant used, thereby effectively reducing environmental costs; (2) It expands the pH range (3 < pH < 11) and can be applied at room temperature or even low temperatures; (3) It exhibits rapid kinetic characteristics and has a shorter response time, making it suitable for different environmental conditions.

[0042] This is mainly because PMS has a high oxidation potential, allowing it to be used in both acidic and alkaline media. Furthermore, by utilizing Bi-C-CoOx as a heterojunction transition metal to activate PMS, it generates sulfate radicals (SO42-). ·- ), superoxide anion (O2) ·- ) and singlet oxygen free radicals ( 1 Reactive oxygen species such as O2, compared to hydroxyl radicals (·OH), SO42- ·- Its higher redox potential and longer half-life enable it to effectively contact and oxidize target pollutants and function over a wider pH range. Furthermore, SO42- ·- It exhibits higher selectivity than ·OH, enabling it to directly attack specific electron-rich functional groups, such as amino (-NH2), hydroxyl (-OH), and other organic compounds containing unsaturated bonds, through electron transfer reactions. Similarly, 1 O2 has a longer lifetime and wider pH tolerance, and due to its unoccupied π* orbitals, it exhibits high electrophilicity and selectivity towards electron-rich substances. Therefore, SO4 ·- and 1 O2 can rapidly and effectively oxidize high-priority pollutants, such as endocrine disruptors and pharmaceuticals, with minimal interference from the actual wastewater matrix. This lays the foundation for the selective detection of organophosphorus pesticides in the environment. Therefore, using PMS instead of H2O2 can effectively overcome the limitations of traditional nanozyme-based colorimetric sensing platforms in terms of operating conditions.

[0043] When PMS is activated using Bi-C-CoOx, due to its Co... 3+ / Co 2+ High standard reduction potential can promote Co 2+ It achieves efficient self-circulation in the catalytic reaction, enabling the catalytic reaction to proceed continuously, and exhibits excellent catalytic performance even under neutral pH and low reagent dosage conditions;

[0044] The inventors discovered during their research and practice that Co 2+ Leaching may occur, affecting the activation of PMS. Therefore, to make the cobalt-based catalyst more stable and inhibit Co... 2+ To address the leaching and loss of cobalt, this invention introduces Bi metal doping to form bimetallic oxides, which can immobilize cobalt in carbon-based materials. This not only effectively solves the aforementioned problems but also enhances electron transfer between organic matter and persulfate. Metal-organic frameworks (MOFs), with their abundant and regularly arranged metal nodes and organic ligands, ordered pore structure, and high specific surface area, are excellent precursors for preparing metal oxides. Therefore, this invention uses BiCoMOFs as precursors and synthesizes a Bi-C-CoOx composite material via low-temperature air calcination. This composite material is used to activate PMS to replace H2O2 oxidation of TMB, and a colorimetric detection method is constructed for water sample detection. Compared with traditional H2O2 oxidants, the PMS-based colorimetric detection method exhibits faster response time, wider pH range, lower energy consumption, and lower nanozyme requirements. In summary, this invention not only synthesizes a highly efficient PMS-activated composite material but also proposes a rapid, wide-pH-range, and room-temperature-suitable method for the detection of PMS and glyphosate.

[0045] Example 1

[0046] This embodiment provides a method for preparing Bi-C-CoOx type peroxide nanozymes, including the following steps:

[0047] (1) Dissolve 0.54 mmol Co(NO3)3·6H2O and 0.06 mmol Bi(NO3)3·5H2O in a DMF / EtOH mixed solvent with a volume ratio of 3:1. Add 2 mmol H3BTC and stir for 5 min until dissolved. Then add 0.5 g PVP and stir for 5 min. Transfer the above mixed solution to a high-pressure reactor and react at 120 °C for 10 hours. Then cool naturally to room temperature. Subsequently, wash the obtained purple precipitate three times with DMF and ethanol respectively, and dry it under vacuum at 60 °C to obtain the BiCoMOFs precursor.

[0048] (2) A ceramic boat containing 200 mg of BiCoMOF precursor was placed in the heat preservation area of ​​a tube furnace. Under air atmosphere, the temperature was increased to 350°C at 5°C / min and kept at that temperature for 2 hours. After naturally cooling to room temperature, Bi-C-CoOx was obtained.

[0049] The prepared Bi-C-CoOx was used for the detection of PMS in water samples. The detection method was as follows: 200 μL of 100 mg / L Bi-C-CoOx, 100 μL of 5 mM PMS, and 100 μL of 5 mM TMB were added sequentially to 4.6 mL of HAc-NaAc buffer solution (50 mM, pH = 5). The reaction solution was incubated at room temperature (T = 20 °C) for 7 min, and A was recorded. 652 The reading at that location.

[0050] To examine the feasibility and accuracy of this method, the concentration of PMS in actual water samples (tap water, Fuhe River water, and Xihu Lake water) was determined using the spiked recovery method. Tap water was obtained from laboratory water samples, while Fuhe River and Xihu Lake water were obtained from the Fuhe River and Xihu Lake near Southwest Jiaotong University. The lake and river water samples were filtered through a 0.22 μm aqueous filter membrane before use. Different concentrations of PMS were added to the actual water samples. 2 mL of the actual water sample was then added to a reaction solution containing 4 mg / L Bi-C-CoOx, 0.1 mM TMB, and 50 mM pH 5.0 HAc-NaAc buffer solution, for a total reaction volume of 5 mL. After reacting for 7 min at room temperature, the UV-Vis spectrum of the reaction solution was measured. All experiments were repeated three times. Detailed experimental results are provided in the experimental examples.

[0051] The prepared Bi-C-CoOx was used to detect glyphosate in water samples. The detection method was as follows: 100 μL of glyphosate of different concentrations (final concentration of 0.08-12 mg / L), 200 μL of 100 mg / L Bi-C-CoOx, 100 μL of 5 mM TMB and 100 μL of 5 mM PMS were added to 4.5 mL of HAc-NaAc buffer solution (50 mM, pH=5). The mixture was reacted at room temperature for 7 min, and the UV-Vis spectrum of the reaction solution was measured.

[0052] To examine the practicality of this method, the concentration of glyphosate in actual water samples (tap water, Fuhe River water, and Xihu Lake water) was tested using the spiked recovery method. Different concentrations of glyphosate were added to the filtered water samples. 0.5 mL of the actual water sample was added to a reaction solution containing 4 mg / L Bi-C-CoOx, 0.1 mM TMB, 0.1 mM PMS, and 50 mM pH 5.0 HAc-NaAc buffer solution. The reaction was carried out at room temperature for 7 min, and the UV-Vis spectrum of the reaction solution was measured. All experiments were repeated three times. For detailed experimental results, please refer to the experimental examples.

[0053] Example 2

[0054] The difference between this embodiment and Example 1 is that the molar ratio of Co(NO3)2·6H2O to Bi(NO3)2·5H2O is 0.3mmol:0.3mmol.

[0055] Example 3

[0056] The difference between this embodiment and Example 1 is that the molar ratio of Co(NO3)2·6H2O to Bi(NO3)2·5H2O is 0.48mmol:0.12mmol.

[0057] Example 4

[0058] The difference between this embodiment and Example 1 is that the molar ratio of Co(NO3)2·6H2O to Bi(NO3)2·5H2O is 0.36mmol:0.24mmol.

[0059] Example 5

[0060] The difference between this embodiment and Example 1 is that the molar ratio of Co(NO3)2·6H2O to Bi(NO3)2·5H2O is 0.42mmol:0.18mmol.

[0061] Example 6

[0062] The difference between this embodiment and Example 1 is that the molar ratio of Co(NO3)2·6H2O to Bi(NO3)2·5H2O is 0.51mmol:0.09mmol.

[0063] Comparative Example 1

[0064] In this comparative example, H2O2 was used as the oxidant. The detection method for PMS was as follows: 150 μL of 1000 mg / L Bi-C-CoOx, 100 μL of 0.1 M H2O2, and 100 μL of 5 mM TMB were added sequentially to 4.65 mL of HAc-NaAc buffer solution (50 mM, pH = 3.5). After incubating the reaction solution at 45 °C for 25 min, A was recorded. 652 The reading at that location.

[0065] Comparative Example 2

[0066] The difference between this comparative example and Example 1 is that step (1) does not contain Co(NO3)3·6H2O.

[0067] Comparative Example 3

[0068] The difference between this comparative example and Example 1 is that step (1) does not contain Bi(NO3)3·5H2O.

[0069] It should be noted that, unless otherwise specified, the Bi-C-CoOx used in the following experimental examples were all prepared by the method described in Example 1.

[0070] Experimental Example 1 - Verification of successful synthesis of Bi-C-CoOx

[0071] 1. The structure and surface properties of Bi-C-CoOx were systematically characterized using XRD, Raman spectroscopy, XPS, SEM, and TEM. XRD results (see...) Figure 1 (a) shows that weak BiCoMOF precursor characteristic peaks (2θ = 19.9°, 25.3°, 28.4°, and 32.4°, etc.) were observed in Bi-C-CoOx, along with some new sharp diffraction peaks, indicating that most of the BiCoMOF composition had been pyrolyzed. Some of the newly appearing diffraction peaks overlapped with those of C2CoO4 (PDF#48-1069), while others overlapped with those of carbonaceous materials, indicating that the material obtained at 350 °C was a mixture of C2CoO4, carbonaceous materials, and residual BiCoMOFs. Raman spectroscopy (see...) Figure 1 (b) shows that in the Bi-C-CoOx sample, the D band (1338 cm⁻¹) -1 ) and G-band (1561cm) -1 The characteristic peaks of are clearly visible, representing the presence of disordered and ordered carbon structures, respectively. The formation of disordered carbon structures is related to the presence of a large number of N and O heteroatoms in the carbon matrix, which lead to significant defects; while ordered graphitic carbon is achieved through cobalt-catalyzed graphitization reactions of the surrounding carbonaceous material. (Located at 2720 cm⁻¹) -1 The broad and weak peak is a characteristic peak of thin-layer graphene. It is located at 1450 cm⁻¹. -1 The characteristic peak at 192 cm⁻¹ indicates that the pyrolysis of the BiCoMOF precursor at this temperature is incomplete. Furthermore, Bi-C-CoOx shows a peak at 192 cm⁻¹. -1 473cm -1 514cm -1 613cm -1 and 680cm -1 The characteristic peaks at these locations correspond to the F of Co3O4, respectively. 2g E g F 2g 1 F 2g 2 and A 2g 1 The peak position has shifted somewhat compared to the theoretical peak position. This may be due to the bonding between the Co3O4 surface and the carbon layer.

[0072] The chemical elements and coordination environment of Bi-C-CoOx were characterized using XPS technology. Figure 1 As shown in (c), two distinct signals can be observed in the XPS spectrum of Co2p, located at 780.48 eV and 796.58 eV, respectively, corresponding to 2p.3 / 2 and 2p 1 / 2 These two signals can be further decomposed into Co. 3+ and Co 2+ This indicates that the prepared material contains Co. 3+ and Co 2+ Coexistence. Furthermore, two satellite peaks were also found at 785.69 eV and 801.48 eV, further supporting the above conclusion. In the Bi 4f spectrum ( Figure 1 In (d)), 158.92 eV (Bi 4f) was observed. 7 / 2 ) and 164.27eV (Bi 4f 5 / 2 The two main peaks at () correspond to Bi 3+ Characteristic peaks. Figure 1 The C1s signal in (e) can be decomposed into two peaks, corresponding to CC / C=C (284.8eV) and carbon atoms bonded to oxygen atoms (288.53eV), respectively. Figure 1 The O1s signal in (f) can be decomposed into three peaks, namely lattice oxygen (O) lat 530.55 eV), chemically adsorbed species at surface oxygen vacancies (such as strongly bound O2 and H2O) (O ads ,531.16eV) and carbon-oxygen bonds (O O-C＝O (532.61 eV). In summary, XPS results indicate that Bi-C-CoOx composite materials containing -COOH and oxygen vacancies were successfully prepared.

[0073] 2. The Bi-C-CoOx peroxide nanozyme prepared in Example 1 was characterized, and the results are shown in the figure. Figure 2 ;in: Figure 2 (a) Figure 2 (b) SEM images at low and high magnification, respectively. Figure 2 (c) is a TEM image; Figure 2 (d) is the elemental mapping diagram; meanwhile, the adsorption-desorption isotherms and pore size distribution curves of the BiCoMOFs precursor and Bi-C-CoOx peroxide nanozyme prepared in Example 1 are shown in the figure. Figure 3 (a) Figure 3 (b)

[0074] Depend on Figure 2 (a) Figure 2 (b) SEM results show that Bi-C-CoOx retained the microsphere shape of the precursor, but the nanorod structure on its surface collapsed, exhibiting a certain degree of sintering. This change led to a significant reduction in specific surface area and pore structure. Figure 3 (a) Figure 3(b) It can be seen that after low-temperature calcination, the specific surface area of ​​Bi-C-CoOx decreased significantly, the pore structure was significantly reduced, and the pore volume was significantly decreased.

[0075] Figure 2 The TEM image in (c) shows that Bi-C-CoOx contains various lattice spacings, including 0.46 nm, 0.28 nm, 0.24 nm, 0.205 nm, and 0.158 nm. These spacings correspond to the (111), (220), (311), and (440) crystal planes of Co3O4, and the (420) crystal plane of carbonaceous materials, respectively. Furthermore, Figure 2 The elemental mapping diagram in (d) shows that C, O, Co, and Bi elements are uniformly distributed in Bi-C-CoOx. These results demonstrate that Example 1 of this invention successfully synthesized the Bi-C-CoOx composite material.

[0076] Experiment Example 2

[0077] This experimental example is to explore different Co... 2+ / (Co 2+ +Bi 3+ The effects of factors such as molar percentage and PVP dosage on the catalytic activity of nanozymes;

[0078] 2.1Co 2+ / (Co 2+ +Bi 3+ ) mole percentage

[0079] Co 2+ / (Co 2+ +Bi 3+ The molar percentages were set to 0%, 50%, 80%, 90%, and 100% (i.e., Comparative Example 2, Examples 1-3, and Comparative Example 1), and the nanozyme catalytic activity results are shown in [the table below]. Figure 4 (a), by Figure 4 (a) It can be seen that when Co is not added to the MOF precursor 2+ When Bi-C-CoOx was present, it showed almost no peroxidase-like activity; while in the absence of Bi... 3+ At that time, the enzyme-like activity of Bi-C-CoOx decreased significantly. With the increase of Co... 2+ and Bi 3+ Coexisting, the enzyme-like activity of Bi-C-CoOx increases with Co 2+ The effect increases with increasing dosage, and in Co 2+ / (Co 2+ +Bi 3+The highest enzyme-like activity was observed when the molar percentage of Bi-C-CoOx reached 90%. These results indicate that the high peroxidase-like activity of Bi-C-CoOx mainly stems from the synergistic effect between the two metals, with Co being the key catalytic active site, significantly enhancing catalytic performance.

[0080] 2.2 PVP Dosage

[0081] The dosage of PVP was set at 0, 0.2, 0.5, 1, and 2 mg / L, respectively, and the results were as follows: Figure 4 As shown in (b), it can be seen that with the increase of PVP dosage, the catalytic activity of the nanozyme first gradually increases and reaches its maximum value at 0.5 mg / L. After that, with further increases in PVP dosage, the catalytic activity of the nanozyme begins to show a downward trend. In conclusion, a PVP dosage of 0.5 mg / L is selected as the optimal PVP dosage for the preparation of nanozymes.

[0082] 2.3 Reproducibility between different batches

[0083] Using Examples 1-6 as experimental subjects, the catalytic activity of the six groups of nanozymes was investigated, and the results are shown in [Figure 1]. Figure 4 (c), by Figure 4 (c) The results showed that the peroxidase-like activities of different batches were comparable, and the RSD value of different batches was 4.18%, indicating that the nanozyme has good reproducibility.

[0084] 2.4 Stability of nanozymes

[0085] Using Example 1 as the experimental subject, the storage stability of Bi-C-CoOx prepared in Example 1 was investigated after being stored at room temperature for 0, 10, 20, 30, 40, and 50 days. The results are shown in [Figure 1]. Figure 4 (d), by Figure 4 (d) The results showed that Bi-C-CoOx still maintained a high level of catalytic activity after 50 days, which further indicated that Bi-C-CoOx has good storage stability.

[0086] Experimental Example 3

[0087] This experiment aims to demonstrate the potential of PMS as an oxidant in the colorimetric detection of Bi-C-CoOx-based peroxidases. Three control groups were set up: Bi-C-CoOx + TMB as control group 1, H2O2 + TMB as control group 2, and PMS + TMB as control group 3. Additionally, Examples 1 and Comparative Example 1 were used as experimental subjects. The UV-Vis spectra were measured, and the results are shown in [Figure 1]. Figure 5 (a).

[0088] like Figure 5As shown in (a), when Bi-C-CoOx, H2O2, and TMB are present simultaneously (i.e., Example 1), a distinct characteristic absorption peak of oxTMB appears at 652 nm; however, in the reaction system lacking H2O2 or Bi-C-CoOx, no absorption peak at 652 nm is observed. This indicates that Bi-C-CoOx possesses peroxidase-like activity. Similarly, when PMS is present with Bi-C-CoOx and TMB, a significant absorption peak is also observed at 652 nm. This indicates that PMS can be catalyzed by Bi-C-CoOx to oxidize TMB, exhibiting similar characteristics to H2O2.

[0089] The activity of nanozymes is typically affected by factors such as material concentration, pH, and reaction temperature. This experimental example investigated the effects of reaction conditions on the activity of Bi-C-CoOx enzymes when H2O2 and PMS were used as oxidants. Figure 5 (b) shows that as the concentration of Bi / C / Co3O4 increases, the absorbance of the reaction solution at 652 nm (AL) decreases. 652 The value gradually increased, reaching its maximum at PMS concentrations of 4 mg / L and H2O2 concentrations of 30 mg / L, respectively. Afterward, A... 652 The value did not change significantly. Figure 5 (c) indicates that when using H₂O₂ as the oxidant, Bi-C-CoOx exhibits catalytic activity at pH < 6.0, reaching its optimum at pH 3–3.5, which may be related to the low solubility of TMB under weakly alkaline conditions. However, when using PMS as the oxidant, Bi-C-CoOx shows good catalytic activity over a wide pH range of 3–11, reaching its optimum at pH 5.0. Figure 5 (d) It can be seen that Bi-C-CoOx maintains high peroxidase-like activity over a wide temperature range. Specifically, when using H₂O₂ as the oxidant, its enzyme-like activity increases with increasing temperature, reaching its optimal catalytic activity at T≥45℃; while when using PMS as the oxidant, Bi-C-CoOx exhibits enzyme-like activity in the 0–70℃ range, with the best performance at 20℃, indicating that the reaction can proceed at room temperature and achieve optimal catalytic activity when using PMS as the oxidant. Furthermore, from Figure 5 (e) shows that in the Bi-C-CoOx+H2O2+TMB reaction system, the time required to reach equilibrium is 25 min. However, in the Bi-C-CoOx+PMS+TMB system, equilibrium is reached in only 8 min. 5(f) shows that as the oxidant concentration increases, the corresponding A... 652The concentration gradually increased, reaching its maximum at 0.1 mM (PMS) and 2 mM (H2O2), respectively. This indicates that using PMS as the oxidant results in milder reaction conditions (the reaction can proceed at room temperature and achieve optimal catalytic activity). The optimal reaction conditions are: 4 mg / L Bi-C-CoOx, 0.1 mM PMS, and 0.1 mM TMB, in a buffer solution at pH 5.0, reacting for 8 min at room temperature.

[0090] Experimental Example 4 - Colorimetric Detection of PMS and Its Application

[0091] Given that Bi-C-CoOx can efficiently catalyze the oxidation of TMB by PMS under mild conditions, this material has the potential to construct a rapid and simple colorimetric sensor for high-sensitivity detection of PMS. Figure 6 As shown in (a), under optimal experimental conditions, A 652 The effect was significantly enhanced with increasing PMS concentration. Figure 6 (b) This demonstrates a good linear relationship between PMS concentration and ΔA in the range of 0.10–100.00 μM, with the linear equation being ΔA = 0.01254[PMS] + 0.0002(R). 2 =0.9985), with a detection limit (LOD) as low as 0.1 μM. Here, ΔA represents A in the reaction system with and without PMS. 652 The difference.

[0092] Meanwhile, the colorimetric detection method of this invention, which uses Bi-C-CoOx as a catalyst and PMS as an oxidant, was compared with other colorimetric or fluorescence methods (specific conditions and parameters are detailed in Table 1). The results are shown in Table 1. As can be seen from the results in Table 1, compared with other colorimetric or fluorescence methods, the concentration of the material used in this method is low, and the risk of secondary pollution is avoided. At the same time, the detection conditions are mild, the linear response range is wide, and the detection limit is low, showing excellent detection performance.

[0093] Table 1 - Performance Comparison of Different PMS Sensors

[0094]

[0095]

[0096] In addition, to evaluate the anti-interference capability of the Bi-C-CoOx-PMS-TMB system in PMS detection, this experimental example investigated the influence of common substances in environmental samples on the contrast color signal. These substances included cations (1 mM Na+). + K + Zn 2+ Ca 2 + Mg 2+Pb 2+ 0.3mM Cu 2+ Mn 2+ Ba 2+ ; 40μM Al 3+ Fe 3+ 5 μM Fe 2+ ), anion (1mM SO42-) 2- Cl - F - NO3 - PO4 3- HCO3 - 60 μM Br - ), small organic molecules (1 mM methanol (MeOH), formaldehyde (FORMALD), ethyl acetate (EAC), toluene (Benzene); 0.8 mM formic acid (FA); 1 mg / L humic acid (HA); 50 mg / L bovine serum albumin (BSA)) and H2O2. Figure 6 The results (c)-(e) indicate that the coexistence of these common anions and cations, humic substances, and small organic molecules with 60 μM PMS did not significantly affect the detection by PMS. Furthermore, from Figure 6 (f) It is evident that the oxidant H2O2 did not interfere with the PMS determination. This is attributed to the fact that the conditions for PMS detection (4 mg / L Bi-C-CoOx, pH = 5.0, reaction at room temperature for 8 min) could not effectively catalyze H2O2. These results demonstrate that the method of the present invention exhibits high selectivity and excellent anti-interference capability in PMS detection.

[0097] To evaluate the practicality of this method, water samples from different sources (tap water, Xihu Lake water, and Fuhe River water) were also analyzed, and the results are shown in Table 2. As shown in Table 2, although PMS was not detected in these water samples, the recovery rate was 96.87%–105.66% through spiked recovery experiments of different concentrations of PMS. These results indicate that the detection method has good detection performance in actual water samples and can effectively monitor the concentration of PMS in actual water bodies.

[0098] Table 2 - Comparison of PMS detection in different actual water samples

[0099]

[0100] Experimental Example 5 - Colorimetric Detection of Glyphosate and Its Application

[0101] To further explore the application performance of the Bi-C-CoOx-PMS-TMB system, this experimental example evaluates its potential in glyphosate detection. Figure 7As shown in (a), when different organophosphorus pesticides were added to the Bi-C-CoOx-PMS-TMB system, only glyphosate showed a significant inhibitory effect. Based on this phenomenon, a colorimetric sensing method for glyphosate was established. Figure 7 (b) shows that, under optimal experimental conditions, the ΔA value (i.e., A before and after the addition of glyphosate) is... 652 The difference ( ) increases with increasing glyphosate concentration and shows a good linear relationship in the range of 0.08–12 mg / L, with the linear equation being y = 0.07069x + 0.1104(R) 2 =0.9984); where x represents the glyphosate concentration and y represents ΔA, with a detection limit as low as 80 μg / L.

[0102] Meanwhile, the colorimetric detection method of this invention, which uses Bi-C-CoOx as a catalyst, PMS as an oxidant, and TMB as a chromogenic substrate, was compared with other colorimetric or fluorescence methods (see Table 3 for specific conditions and parameters). The results are shown in Table 3.

[0103] Table 3 - Comparison of PMS detection in different actual water samples

[0104]

[0105] As shown in Table 3, this method enables rapid detection of glyphosate under mild conditions, exhibiting a wider linear response range and a lower detection limit. These data demonstrate that the proposed method possesses excellent glyphosate detection performance. Furthermore, Figure 6 (c)-(f) show that the Bi-C-CoOx-PMS-TMB system is not affected by common anions, cations, small organic molecules and H2O2, further demonstrating its application potential in practical sample analysis.

[0106] To further verify the practicality of this method, the Bi-C-CoOx-PMS-TMB system was applied to the determination of glyphosate in different environmental water samples (tap water, Xihu Lake water and Fuhe River water). The results are shown in Table 4.

[0107] Table 4 - Comparison of glyphosate detection in different actual water samples

[0108]

[0109] Table 4 lists the recovery rates of glyphosate in different environmental water samples. Although PMS was not detected in these water samples, the average recovery rate of glyphosate was 95.24%–101.81% with an RSD of <6.3% through spiked recovery experiments with different concentrations of glyphosate and three replicate experiments. These results indicate that the colorimetric sensor based on Bi-C-CoOx nanozymes has good potential for analyzing glyphosate content in environmental water samples.

[0110] In summary, this invention successfully replaces the traditional peroxidase-based oxidant H2O2 with PMS, constructing a colorimetric detection strategy based on Bi-C-CoOx. This colorimetric strategy, with Bi-C-CoOx, PMS, and TMB as its core, successfully achieves high-precision and high-sensitivity detection of PMS and glyphosate. Compared with the traditional H2O2 oxidant, the colorimetric detection strategy based on PMS as the oxidant has the following advantages: (1) it significantly reduces the amount of nanozyme and oxidant used, thereby effectively reducing environmental costs; (2) it expands the pH range (3 < pH < 11) and can be applied at room temperature or even low temperatures; (3) it exhibits rapid kinetic characteristics and a shorter response time, making it suitable for different environmental conditions. The proposed colorimetric detection strategy has shown good application performance in actual water samples.

Claims

1. A method for preparing a Bi-C-CoOx peroxidase nanozyme, characterized in that: The following steps are involved: (1) Preparation of BiCoMOFs precursors by solvothermal method; (2) The BiCoMOFs precursor is thermally activated to obtain Bi-C-CoOx peroxidase nanozymes.

2. The method for preparing the Bi-C-CoOx peroxidase nanozyme according to claim 1, characterized in that: The preparation method of the BiCoMOFs precursor comprises the following steps: dissolving Co salt and Bi salt in an organic solvent, first adding H3BTC to fully dissolve, then adding PVP to fully dissolve, obtaining a mixed solution, and then heat treating the obtained mixed solution; subsequently, washing, solid-liquid separation and drying are performed to obtain a BiCoMOFs precursor.

3. The method for preparing the Bi-C-CoOx peroxidase nanozyme according to claim 2, characterized in that: The preparation method of the Bi-C-CoOx peroxidase nanozyme comprises the following steps: the prepared BiCoMOFs precursor is gradually heated and kept warm for a period of time under an air atmosphere, and then naturally cooled to room temperature to obtain the Bi-C-CoOx peroxidase nanozyme.

4. The method for preparing the Bi-C-CoOx peroxidase nanozyme according to claim 2, characterized in that: The Co salt is any one or more of cobalt nitrate, cobalt chloride or cobalt sulfate; the Bi salt is any one or more of bismuth nitrate, bismuth chloride or bismuth citrate.

5. The method for preparing the Bi-C-CoOx peroxidase nanozyme according to claim 3, characterized in that: During heat treatment: the heat treatment temperature is 110-130°C, and the heat treatment time is 5-15h; during gradient heating, the temperature is increased to 300-400°C at a rate of 5°C / min, and kept warm for 1-3h.

6. A Bi-C-CoOx peroxidase nanozyme, characterized in that: The method is prepared according to any one of claims 1 to 5.

7. An application of Bi-C-CoOx peroxidase nanozyme, characterized in that: The Bi-C-CoOx peroxidase nanozyme prepared by the preparation method according to any one of claims 1 to 5 is used in the detection of PMS and glyphosate.

8. The use of the Bi-C-CoOx peroxidase nanozyme according to claim 7, characterized in that: The detection method of PMS is as follows: adding the nanozyme, PMS oxidant, chromogenic substrate and buffer solution prepared by the above preparation method to the test liquid, incubating the obtained reaction solution at room temperature for a period of time, and then testing the absorbance of the reaction solution; substituting the measured absorbance data into the linear equation of absorbance and PMS concentration to obtain the PMS concentration in the test liquid.

9. The use of the Bi-C-CoOx peroxidase nanozyme according to claim 7, characterized in that: The glyphosate detection method is as follows: adding the nanozyme, PMS oxidant, chromogenic substrate and buffer solution prepared by the above preparation method to the test solution, incubating the obtained reaction solution at room temperature for a period of time, and then testing the absorbance of the reaction solution; substituting the measured absorbance data into the linear equation of absorbance and glyphosate concentration to obtain the glyphosate concentration in the test solution.

10. The use of the Bi-C-CoOx peroxidase nanozyme according to claim 8 or 9, characterized in that: The color developing substrate is any one of 3,3',5,5'-tetramethylbenzidine, o-phenylenediamine or 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid.

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