Method for synthesizing cerium-based metal organic framework nano-enzyme at freezing temperature

Abstract

The invention discloses a method for synthesizing cerium-based metal organic framework nano-enzyme at low temperature, and relates to the technical field of metal organic framework materials and nano-enzyme synthesis. Preparing a Ce (NO3) 3 solution and an H3BTC solution; the Ce (NO3) 3 solution and the H3BTC solution are fully mixed and then placed in an environment with the temperature ranging from-80 DEG C to-10 DEG C for coordination polymerization-nucleation-growth; after coordination polymerization, nucleation and growth are completed, room-temperature unfreezing is conducted, precipitates are separated from a reaction solution through centrifugal operation after unfreezing, and the cerium-based metal organic framework nano-enzyme is obtained through washing and drying. The synthesis of the metal organic framework material can be completed through low-temperature standing, zero heating and zero high pressure are realized in the whole process, the energy consumption and the safety risk are synchronously reduced to the minimum, and the realization is simple; and an ultrasonic probe, a microwave cavity or vacuum / electrolysis equipment is not needed, so that the investment and operation cost is remarkably reduced.

Description

Technical Field

[0001] This invention relates to the field of metal-organic framework materials and nanozymes, specifically a method for synthesizing cerium-based metal-organic framework nanozymes at low temperatures. Background Technology

[0002] The synthesis of cerium-based metal-organic framework nanozymes generally relies on "heat-based" routes, mainly including solvothermal methods, ultrasonic and microwave methods, liquid-phase methods, vapor deposition, and electrochemical methods. Among these, the most mainstream is the solvothermal method, which involves sealing metal salts and organic ligands in a high-pressure metal reactor and conducting a solvothermal / hydrothermal reaction in an oil bath or oven at 100–220 °C. This process is energy-intensive and requires high-pressure explosion protection. At the laboratory level, ultrasonic and microwave methods are commonly used, utilizing high-frequency vibration or electromagnetic fields to rapidly supply energy through ultrasonic baths or microwave reactors. However, this method has significant limitations; during scale-up, uneven energy distribution and localized overheating are prone to occur, making it difficult to obtain uniform products. Traditional liquid-phase methods rely on mechanical stirring combined with oil bath heating, but heat and mass transfer efficiency drops sharply when dealing with large volumes or high-viscosity solutions. For thin film or electrode integration, chemical vapor deposition, atomic layer deposition, or electrochemical deposition are used. While these methods allow for precise orientation control, they require expensive equipment such as vacuum chambers or electrolytic cells, limiting yield. In summary, most existing methods for synthesizing cerium-based metal-organic framework nanozymes rely on "heating + dedicated reactors," which either have significant limitations in the production process or require expensive equipment, making them unsuitable for large-scale production.

[0003] Based on this, the present invention aims to provide a simple method for synthesizing cerium-based metal-organic framework nanozymes, eliminating the dependence on expensive equipment and equipment with high heat and high safety requirements. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a method for synthesizing cerium-based metal-organic framework nanozymes at low temperatures. The method involves thoroughly mixing a cerium nitrate (Ce(NO3)3) solution with a 1,3,5-benzenetricarboxylicacid (H3BTC) solution, then transferring the mixture to a low-temperature environment for static setting. This low-temperature environment can be achieved using cold storage or refrigerators, resulting in low cost and ease of implementation. Furthermore, the uniform low-temperature environment eliminates differences in product morphology and particle size caused by uneven energy distribution, leading to good batch-to-batch reproducibility.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for synthesizing cerium-based metal-organic framework nanozymes at low temperature includes the following steps: (1) Dissolve cerium nitrate hexahydrate (Ce(NO3)3·6H2O) in ultrapure water to prepare a Ce(NO3)3 solution; (2) Dissolve H3BTC in a mixed solvent prepared from ultrapure water and anhydrous ethanol to prepare an H3BTC solution; (3) After thoroughly mixing Ce(NO3)3 solution and H3BTC solution, place them in an environment of -86 to -3 °C to allow coordination polymerization-nucleation-growth of cerium-based metal-organic framework (Ce-MOF) nanozymes to be carried out. (4) After complete coordination polymerization-nucleation-growth, the precipitate was thawed at room temperature. After thawing, the precipitate was separated from the reaction solution by centrifugation. After washing and drying, cerium-based metal-organic framework nanozymes were obtained.

[0006] In this invention, the concentration of Ce(NO3)3·6H2O in step (1) is 0.01-0.1 g / mL (e.g., 0.08 g / mL).

[0007] In this invention, the concentration of the H3BTC solution in step (2) is 0.01-0.1 g / mL (e.g., 0.04 g / mL).

[0008] In this invention, the volume ratio of ultrapure water to anhydrous ethanol is 1:1.

[0009] In this invention, the volume ratio of Ce(NO3)3 solution in step (2) to H3BTC solution in step (3) is 9:2.

[0010] In this invention, step (3) is preferably carried out in an environment of -80 to -20°C for coordination polymerization-nucleation-growth.

[0011] In this invention, the precipitate is separated from the reaction solution by centrifugation at 7500 to 8500 rpm.

[0012] In this invention, the washing operation in step (4) is to first wash with ultrapure water three times, and then wash with anhydrous ethanol three times.

[0013] In this invention, step (4) drying operation: drying in an oven at 45 to 75 °C for 11 to 12 hours or freeze drying.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention achieves coordination polymerization, nucleation, and MOF growth through "low-temperature static incubation," where low temperature refers to sub-zero degrees Celsius, i.e., below the freezing point of aqueous solutions. The entire process involves zero heating and zero high pressure, minimizing energy consumption and safety risks simultaneously, and is simple to implement; moreover, it eliminates the need for ultrasonic probes, microwave cavities, or vacuum / electrolysis equipment, significantly reducing investment and operating costs.

[0015] 2. This invention only requires a uniform temperature environment (cold storage or refrigerator can meet this condition), eliminating the differences in product morphology and particle size caused by uneven energy distribution. It has good batch repeatability, and the Ce-MOFs synthesized at low temperature exhibit a strong characteristic absorption peak of oxTMB at 652 nm. The peak intensity decreases in the order of Ce-MOF(-80), Ce-MOF(-20) and Ce-MOF(-10).

[0016] 3. The present invention adopts a "low-temperature static" treatment method, which significantly reduces the rate of crystal nucleus formation and crystal growth, thereby providing sufficient time for molecules to align in the correct positions, ultimately promoting the formation of an ordered structure. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the synthesis of cerium metal-organic framework nanozymes according to the present invention.

[0018] Figure 2 This is a comparative analysis diagram of the Ce-MOF(X) activity in this invention.

[0019] Figure 3 X-ray diffraction pattern of (A) Ce-MOF(X) and analysis diagrams of specific surface area and pore size.

[0020] Figure 4 These are scanning electron microscope images and transmission electron microscope images of Ce-MOFs (X) at different times in this invention.

[0021] Figure 5 This is a schematic diagram of the synthesis of Ce-MOF(X) in this invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] I. Synthesis Methods of Cerium-based Metal-Organic Framework Nanozymes A method for synthesizing cerium-based metal-organic framework nanozymes at low temperatures employs a cryogenic strategy to synthesize novel cerium-based metal-organic framework materials (Ce-MOFs). 4.34 g of Ce(NO3)3·6H2O was dissolved in 45 mL of ultrapure water; separately, 2.1 g of H3BTC was dissolved in 10 mL of a mixed solvent consisting of ultrapure water and anhydrous ethanol (volume ratio 1:1). Subsequently, the two solutions were thoroughly mixed in centrifuge tubes and placed in low-temperature environments (-10, -20, and -80 °C) for a period of time under vigorous magnetic stirring. After the cryogenic synthesis was completed, the centrifuge tubes were slowly thawed at room temperature. The precipitate was then separated from the reaction solution by centrifugation at 8000 rpm, washed three times with ultrapure water and anhydrous ethanol, and finally dried in an oven at 70 °C for 12 hours. The collected Ce-MOFs were labeled Ce-MOF(X) according to the synthesis temperature, where X represents the synthesis temperature (X = +60, -10, -20, and -80). °C).

[0024] II. Activity Analysis of Cerium-based Metal-Organic Framework Nanozymes Synthesized at Different Temperatures Ce-MOFs synthesized at different temperatures are denoted as Ce-MOF(X), where X represents the synthesis temperature. The original hydrothermal synthesis of Ce-MOF is denoted as Ce-MOF(+60). Ce-MOFs synthesized at -10, -20, and -80 °C are denoted as Ce-MOF(-10), Ce-MOF(-20), and Ce-MOF(-80), respectively.

[0025] The mixture contained H2O2 (1 mM), TMB (3 mM), and Ce-MOF(X) (0.5 mg / mL) −1 The Ce-MOF(X) solution was incubated in Tris-HCl buffer (0.1 M, pH 7.0) at room temperature for 25 minutes. Subsequently, the absorption peak of oxidized TMB (oxTMB) at 652 nm was measured using a spectrophotometer. Each activity assay was repeated at least three times. Different Ce-MOF(X) catalytic reaction solutions exhibited different reaction rates. Figure 2 (A) shows that it exhibits a strong characteristic absorption peak of oxTMB at 652 nm, with the peak intensity decreasing in the order of Ce-MOF(-80), Ce-MOF(-20), and Ce-MOF(-10), while Ce-MOF(+60) shows almost no absorption. Figure 2 (As shown in (B)). To further verify the activity level, the absorption intensity of the four Ce-MOF(X)-catalyzed TMB colorimetric reactions was measured, with TMB concentrations ranging from 0.2 to 2.5 mg / mL. The absorption intensity of the blue product oxTMB increased with increasing Ce-MOF(X) concentration, as shown in (B). Figure 2(C) is shown. Furthermore, the nanozyme activity of Ce-MOFs was quantitatively calculated. One nanozyme activity unit is defined as the amount of nanozyme capable of catalyzing the production of 1 µmol of product per minute. Specific activity values ​​were calculated by plotting nanozyme activity against mass and measuring the slope of the resulting linear regression line. The specific enzyme activity of Ce-MOF(+60) was determined to be 0.065 U / mg, while the specific enzyme activity of Ce-MOF(-80) was significantly increased (3.775 U / mg), approximately 60 times that of Ce-MOF(+60). The specific enzyme activities of Ce-MOF(-10) and Ce-MOF(-20) were 1.88 and 2.347 U / mg, respectively. Figure 2 As shown in (D), it is clear that the characteristic activities of Ce-MOFs gradually increase as the low-temperature synthesis temperature decreases.

[0026] Structure of cerium-based metal-organic framework nanozymes Ce-MOF(-10), Ce-MOF(-20), Ce-MOF(-80), Ce-MOF(+60), and [La(BTC)(H2O)6] were obtained respectively. n The X-ray diffraction pattern is shown in the figure. Figure 3 As shown in (A), comparing the above spectra, it is found that the X-ray diffraction patterns of Ce-MOF(-10), Ce-MOF(-20), Ce-MOF(-80), and Ce-MOF(+60) are similar to those of [La(BTC)(H2O)6]. n The X-ray diffraction patterns were consistent, confirming the successful synthesis of Ce-MOF(-10), Ce-MOF(-20), Ce-MOF(-80), and Ce-MOF(+60). Furthermore, the more numerous and sharper the root peaks in the spectra, the better the crystallinity. It can be observed that the crystallinity gradually decreases with decreasing synthesis temperature, which reasonably suggests that the superior activity of Ce-MOF(-80) may be attributed to its reduced crystallinity. In addition, detailed specific surface area and pore size analyses of the four Ce-MOFs were performed using Bruner-Emmett-Taylor analysis. Figure 3 As shown in (B), the results indicate that Ce-MOF(-80) has a significantly larger specific surface area and a significantly smaller pore size, consistent with the excellent catalytic activity of Ce-MOF(-80).

[0027] Scanning electron microscopy (SEM) was used to observe and analyze Ce-MOF(-80) and Ce-MOF(+60), revealing significant morphological differences between the two. SEM images showed that Ce-MOF synthesized for 1 day and 3 days at -80 °C exhibited mutual adhesion. Figure 4 (A) and Figure 4(B). In contrast, the Ce-MOF(-80) synthesized in 7 days showed a significantly reduced width, approximately 58-62 nm, exhibiting a dispersed rod-like structure and a unique morphology, see [link to article]. Figure 4 (C). Furthermore, Ce-MOF(+60) nanorods exhibit numerous elongated structures with widths of approximately 155-171 nm, arranged in a relatively ordered manner; however, Ce-MOF(+60) nanorods show significant aggregation and cannot be effectively separated, see [link to article]. Figure 4 (D) This is attributed to the lack of a low-temperature environment. Therefore, it can be concluded that lower synthesis temperatures and longer synthesis times promote the formation or more complete decomposition of Ce-MOF nanorods. This is because, at lower temperatures, the rates of nucleation and crystal growth are significantly reduced, thus providing sufficient time for molecules to align in the correct positions, ultimately leading to the formation of an ordered structure.

[0028] In addition, the synthesis process of Ce-MOF(-80) was investigated. The morphological changes of Ce-MOF(-80) on days 1, 3, 5, and 7 were observed using transmission electron microscopy (TEM). TEM images of Ce-MOF(-80) on days 1, 3, 5, and 7 are shown below. Figure 4 (E)-4(H). Thus, a judgment is formed regarding the formation process of Ce-MOF morphology (e.g., Figure 5 (As shown): In the initial stage of synthesis, the ligand H3BTC tends to form coordination bonds with cerium ions. On day 1, Ce-MOF(-80) exhibits an opaque and thick blocky structure. By day 3, the blocky structure begins to split, gradually forming rod-shaped ends, and the color gradually becomes clearer. On day 5, the blocky structure splits further, and the rod-shaped features become more pronounced. Finally, on day 7, Ce-MOF(-80) completely splits into slender rod-shaped structures. Further research shows that under low-temperature conditions, the formation rate of nanorods is relatively slow, requiring a specific time to form uniform size and an ordered structure. This is because water molecules permeate into the pores of the porous material. Under low-temperature conditions, water condenses into ice crystals, leading to an increase in the concentration of ligands and ions, and a significant volume expansion. As ice crystals grow from the outer region of the pores towards the inner region, the resulting volume expansion introduces mechanical stress into the material, causing the material to gradually crack and eventually form slender rod-shaped structures. Furthermore, as the temperature decreases further and the exposure time increases, the depth of ice crystal penetration into the pores gradually increases, thereby exacerbating the material's splitting phenomenon.

[0029] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for synthesizing cerium-based metal-organic framework nanozymes at low temperature, characterized in that, Includes the following steps: (1) Dissolve Ce(NO3)3·6H2O in ultrapure water to prepare Ce(NO3)3 solution; (2) Prepare an H3BTC solution by dissolving pyromellitic acid (H3BTC) in a mixed solvent prepared from ultrapure water and anhydrous ethanol; (3) After thoroughly mixing the cerium nitrate Ce(NO3)3 solution and the H3BTC solution, place them in an environment of -86 to -3 °C for coordination polymerization-nucleation-growth; (4) After coordination polymerization-nucleation-growth, the mixture is thawed at room temperature. After thawing, the precipitate is separated from the reaction solution by centrifugation. After washing and drying, cerium-based metal-organic framework nanozymes are obtained.

2. The method for synthesizing cerium-based metal-organic framework nanozymes at low temperature according to claim 1, characterized in that, The concentration of Ce(NO3)3·6H2O in step (1) is 0.01-0.1 g / mL.

3. The method for synthesizing cerium-based metal-organic framework nanozymes at low temperature according to claim 1, characterized in that, In step (2), the concentration of H3BTC solution is 0.01-0.1 g / mL.

4. The method for synthesizing cerium-based metal-organic framework nanozymes at low temperature according to claim 1, characterized in that, The volume ratio of ultrapure water to anhydrous ethanol is 1:

1.

5. The method for synthesizing cerium-based metal-organic framework nanozymes at low temperature according to claim 1, characterized in that, The volume ratio of Ce(NO3)3 solution in step (2) to H3BTC solution in step (3) is 9:

2.

6. The method for synthesizing cerium-based metal-organic framework nanozymes at low temperature according to claim 1, characterized in that, In step (3), coordination polymerization-nucleation-growth is preferably carried out in an environment of -80 to -20°C.

7. The method for synthesizing cerium-based metal-organic framework nanozymes at low temperature according to claim 1, characterized in that, In step (4), the centrifugation operation is to separate the precipitate from the reaction solution by centrifuging at 2500 to 10000 rpm.

8. The method for synthesizing cerium-based metal-organic framework nanozymes at low temperature according to claim 1, characterized in that, In step (4), the washing operation is to first wash with ultrapure water three times, and then wash with anhydrous ethanol three times.

9. The method for synthesizing cerium-based metal-organic framework nanozymes at low temperature according to claim 1, characterized in that, In step (4), the drying operation is to dry in an oven at 30 to 75 °C for 5 to 12 hours or to freeze dry.

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