A method for breaking the pH limit of nanoscale enzyme to degrade phenol pollutants in water

Abstract

The application discloses a method for breaking the pH limitation of nanometer enzyme to degrade phenol pollutants in water, in particular a method for breaking the pH limitation on catalytic activity of a heterometallic MOF nanometer enzyme double biological enzyme simulation activity, which comprises the following steps: preparing the heterometallic MOF by using a room temperature reflux method, and utilizing the characteristics that the heterometallic MOF has peroxidase activity under low pH conditions and has laccase activity under high pH conditions to realize degradation of the phenol pollutants in water, and establishing a method for breaking the pH limitation on catalytic activity of the heterometallic MOF, so that the heterometallic MOF can be applied to degradation of pollutants in different pH environments. The application has the advantages that the preparation of the heterometallic MOF can be synthesized at room temperature, energy consumption is low, and the method is simple and easy to implement; in addition, the method ingeniously breaks the pH limitation of the nanometer enzyme in practical application by utilizing the double biological enzyme simulation activity of the heterometallic MOF, and has important significance for solving the technical bottleneck of organic pollutant degradation.

Description

Technical Field

[0001] This invention relates to a method for degrading phenol pollutants in water by breaking the pH limitation on the catalytic activity of nanoenzymes, and in particular, a method for degrading phenol pollutants in water by utilizing the dual bioenzyme mimicry activity of heterometallic MOFs, which exhibit peroxidase activity under low pH conditions and laccase activity under neutral and alkaline pH conditions, thereby breaking the pH limitation. Technical Background

[0002] Phenolic substances are one of the most typical organic pollutants in surface water sources. Most phenolic substances have estrogenic effects, bioaccumulation, toxic effects, and are difficult to degrade. Even at very low concentrations, they can harm the liver, lungs, kidneys, reproductive, immune, and nervous systems of humans and animals, and even induce malignant tumors. Therefore, the degradation and removal of phenolic pollutants in water bodies has become particularly important.

[0003] Nanoenzymes, based on nanomaterials, are biomimetic catalytic systems that combine the characteristics of both biocatalysis and chemical catalysis. They not only possess the unique advantages of natural enzymes, such as high efficiency, high selectivity, mild reaction conditions, and environmental friendliness, but also largely overcome the disadvantages of natural enzymes, exhibiting excellent properties such as low cost, stable performance, tunable catalytic activity, easy functional modification, and scalable preparation.

[0004] Most reported nanozymes currently available mimic peroxidase activity. In comparison, very few nanozymes exhibit oxidase-mimicking activity, and nano-oxidases with laccase activity are extremely rare. Furthermore, most nanozymes exhibiting both peroxidase and oxidase activity show optimal catalytic activity at lower pH conditions, with significantly reduced or even inactive activity under neutral or alkaline conditions. This severely limits their practical application in organic matter degradation, and overcoming pH limitations remains an unsolved problem for nanozymes.

[0005] We found that nanozymes with laccase-mimicking activity exhibit high and stable catalytic activity at pH 5–11, while nanozymes mimicking peroxidase generally show optimal activity at pH < 5. Therefore, designing and constructing an ideal nanozyme possessing both peroxidase and laccase-mimicking activities, exhibiting peroxidase activity at low pH and laccase activity at neutral and alkaline conditions, and capable of switching between peroxidase and laccase functions under specific pH conditions, would not only overcome the pH limitations of nanozymes in practical applications but also be key to solving the bottleneck in organic pollutant degradation technology.

[0006] MOFs constructed from metal ions such as Fe, V, Cu, and Zr with organic ligands such as terephthalic acid, trimesic acid, and iron porphyrin often exhibit peroxidase activity. However, MOFs with laccase activity are rarely reported. Existing MOFs with laccase activity typically use complex biomolecules as organic ligands, such as Cu... 2+ MOFs and Cu formed by binding with nucleotides + / Cu 2+ CH-Cu nanozymes are formed by coordination with dipeptides. To date, there are few reports of nanozymes with dual bio-enzyme mimicry activities of peroxidase and laccase. This shows that designing and constructing nanozymes with dual bio-enzyme mimicry activities is a challenge. In the degradation of organic matter, it is even more challenging to use its dual bio-enzyme mimicry activities to overcome the limitation of pH value on its catalytic activity. Summary of the Invention

[0007] This invention provides a method for degrading phenol pollutants by utilizing dual-bioenzyme mimicry to overcome the pH limitation of nanoenzymes. The method includes the preparation of heterometallic MOFs with dual-bioenzyme activity, and the utilization of their peroxidase activity under low pH conditions and laccase activity under high pH conditions to achieve the degradation of phenol pollutants in water. This establishes a method that breaks the pH limitation on the catalytic activity of heterometallic nanoenzymes, making it applicable to the degradation of pollutants in different pH environments.

[0008] The technical solution of the present invention:

[0009] A method for overcoming the pH limitation of nanozymes to degrade phenol pollutants in water, wherein the nanozymes are heterometallic MOFs, and the preparation steps are as follows:

[0010] 1) Preparation of heterometallic MOFs with dual bioenzyme mimicry activity

[0011] 4-Chloroisophthalic acid was dissolved in acetone to prepare solution A; copper acetate and other doped metal salts were dissolved in deionized water to prepare metal solution B; a regulator was dissolved in deionized water to prepare solution C; under magnetic stirring, solutions B and C were slowly added dropwise to solution A, and the reaction was continued at room temperature for 6-12 hours. The reaction products were thoroughly washed with water and acetone, and then dried under vacuum at 60°C for 12 hours.

[0012] The other doped metal salts may be manganese acetate, cobalt acetate, nickel acetate, iron oxalate, or zinc acetate.

[0013] The heterometallic MOFs have a ratio of divalent copper salt to other metal salts of 1:0 to 1:9.

[0014] The regulator is an amino polysilsesquioxane, polyvinylpyrrolidone, polyethyleneimine, imidazole, or dimethylimidazole.

[0015] The ratio of the mixed metal salt, 4-chloroisophthalic acid, and regulator is 1:0.6:0.0025;

[0016] 2) Determination of the activity of heterometallic MOF dual-biomimic enzymes

[0017] Determination of peroxidase-mimicking enzyme activity: A buffer solution with pH 2–10, a 3,3′,5,5′-tetramethylbenzidine (TMB) solution, an H2O2 solution, and a heterometallic MOF suspension were added sequentially to a centrifuge tube. The concentration of the buffer solution was 80 mM, the concentration of TMB was 1 mM, the concentration of H2O2 was 20 mM, and the amount of catalyst was 0.2 mg / mL. After the added substances were mixed evenly, the mixture was shaken in a water bath at room temperature for 20 min. Then, the change in absorbance of the supernatant at 652 nm was measured using a UV-Vis spectrophotometer.

[0018] Determination of laccase mimic enzyme activity: A buffer solution with pH 3–10, a 2,4-dichlorophenol (2,4-DCP) solution, a 4-aminoantipyrine (4-AP) aqueous solution, and a heterometallic MOF suspension were added sequentially to a centrifuge tube. The concentration of the buffer solution was 20 mM, the concentration of 2,4-DCP was 100 mg / L, the concentration of the chromogenic reagent 4-AP was 100 mg / L, and the amount of catalyst was 0.1 mg / mL. After the added substances were mixed evenly, the mixture was shaken in a water bath at room temperature for 60 min, and the change in absorbance of the supernatant at 510 nm was measured.

[0019] 3) The application of heterometallic MOFs to the degradation of phenol pollutants in water bodies involves the following steps:

[0020] When the pH of the ambient water is 2-5, phenol pollutants are degraded using peroxidase. The volume of the reaction system is 100 mL, the concentration of phenol is 20-200 mg / L, the concentration of H2O2 solution is 5-80 mM, and the amount of catalyst is 0.1-0.8 mg / mL. The reaction is carried out at room temperature. 2 mL of the reaction solution is taken every 30 min, and the amount of remaining phenol is determined by colorimetric reaction using potassium ferricyanide. The change of the absorption peak of the supernatant at 510 nm is measured by ultraviolet-visible spectrophotometer.

[0021] When the pH of the ambient water is 5-10, laccase activity is used to degrade phenol pollutants. The volume of the reaction system is 100 mL, the concentration of phenol is 20-200 mg / L, the concentration of the colorimetric reagent 4-AP is 20-200 mg / L, and the amount of catalyst is 0.1-0.8 mg / mL. The mixture is magnetically stirred at room temperature. Every 30 min, 3 mL of the reaction solution is taken, and the change of the absorption peak of the supernatant at 510 nm is measured using a UV-Vis spectrophotometer.

[0022] The present invention has the following advantages and beneficial effects:

[0023] The method involves the preparation of heterometallic MOFs, which is simple, energy-efficient, and easy to implement. Utilizing the pH characteristics of dual biomimetic enzyme catalytic activity, the novel and ingeniously designed method breaks the pH limitation on nanozyme catalytic activity, and is of great significance for the widespread application of nanozymes in environmental remediation. [Attached Image Description]

[0024] Figure 1 Cu-MOF and Cu 0.5 Mn 0.5 - SEM image of MOF Figure 1 In the middle: (A) Cu-MOF; (B) Cu 0.5 Mn 0.5 -MOF.

[0025] Figure 2 Cu-MOF and Cu 0.5 Mn 0.5 XRD patterns of MOF.

[0026] Figure 3 Cu at pH 4 0.5 Mn 0.5 -MOF simulates the degradation of phenol contaminants in aqueous solution by peroxidase. The inset figure shows the change in solution color from dark to light over time after potassium ferricyanide color development.

[0027] Figure 4 Cu at pH 7 0.5 Mn 0.5 -MOF simulation simulates the degradation of phenol contaminants in aqueous solution by laccase. After 4-AP color development, the solution color changes from light to dark over time.

Detailed Implementation Methods

[0028] The technical solution of the present invention will be further described below through specific embodiments.

[0029] Example:

[0030] 1) Preparation of Cu with dual bioenzyme mimicry activity 0.5 Mn 0.5 -MOF

[0031] 0.46 mmol of 4-chloroisophthalic acid was dissolved in 10 mL of acetone to prepare solution A. 0.383 mmol each of copper acetate and manganese acetate were weighed and dissolved in 6.0 mL of deionized water to prepare metal solution B. 20 mg of aminopolysilsesquioxane was dissolved in deionized water to prepare 4.0 mL of solution C. Under magnetic stirring, solutions B and C were slowly added dropwise to solution A, and the reaction was continued at room temperature for 6-12 h. The reaction product was thoroughly washed with water and acetone, and then dried under vacuum at 60 °C for 12 h.

[0032] 2) Cu 0.5 Mn 0.5 Assay of MOF dual-biological mimic enzyme activity

[0033] Determination of peroxidase-mimicking enzyme activity: Buffer solutions of different pH values, 3,3′,5,5′-tetramethylbenzidine (TMB) solution, H2O2 solution, and heterometallic MOF suspension were added to centrifuge tubes. The concentrations of the buffer solutions were 80 mM, TMB was 1 mM, H2O2 was 20 mM, and the catalyst concentration was 0.2 mg / mL. After thorough mixing, the mixture was shaken in a water bath at room temperature for 20 min. The absorbance of the supernatant at 652 nm was then measured using a UV-Vis spectrophotometer.

[0034] Determination of laccase mimic enzyme activity: Buffer solutions of different pH values, 2,4-dichlorophenol (2,4-DCP) solution, 4-aminoantipyrine (4-AP) aqueous solution, and heterometallic MOF suspension were added sequentially to centrifuge tubes. The concentrations of the buffer solutions were 21 mM, 2,4-DCP was 100 mg / L, 4-AP was 100 mg / L, and the catalyst was 0.1 mg / mL. After thorough mixing, the mixture was shaken in a water bath at room temperature for 60 min, and the absorbance of the supernatant at 510 nm was measured.

[0035] 3) Cu 0.5 Mn 0.5 - MOF is applied to the degradation of phenol pollutants in water bodies, and the steps are as follows:

[0036] When the pH of the ambient water is 4, phenol pollutants are degraded using peroxidase. The reaction system has a volume of 100 mL, a phenol concentration of 100 mg / L, an H2O2 solution concentration of 20 mM, and a catalyst dosage of 0.2 mg / mL. The reaction is carried out at room temperature. 2 mL of the reaction solution is taken every 30 min, and the amount of remaining phenol is determined by a colorimetric reaction using potassium ferricyanide. The change in the absorption peak of the supernatant at 510 nm is measured using a UV-Vis spectrophotometer. Figure 3 dissimilar metal MOFs Cu 0.5 Mn 0.5-MOF simulation of the ultraviolet spectrum of peroxidase degradation of phenol in acidic water. The inset shows the color of the solution changing from dark to light after potassium ferricyanide color development at different sampling times.

[0037] When the pH of the ambient water is 7, laccase activity is used to degrade phenol pollutants. The volume of the reaction system is 100 mL, the concentration of phenol is 100 mg / L, the concentration of the colorimetric reagent 4-AP is 100 mg / L, and the amount of catalyst is 0.2 mg / mL. The reaction is magnetically stirred at room temperature. Every 30 min, 3 mL of the reaction solution is taken, and the change of the absorption peak of the supernatant at 510 nm is measured using a UV-Vis spectrophotometer.

[0038] Figure 1 Cu-MOF(A) and Cu 0.5 Mn 0.5 SEM images of -MOF(B) show that, compared with Cu-MOF morphology, Mn-doped heterometallic MOFs Cu are visible. 0.5 Mn 0.5 - MOF rods become thinner, almost like threads.

[0039] Figure 2 Cu-MOF and Cu 0.5 Mn 0.5 XRD patterns of MOFs, specifically Mn-doped heterometallic MOFs (Cu). 0.5 Mn 0.5 The XRD peaks of -MOF and Cu-MOF are in perfect agreement.

[0040] Figure 3 Cu at pH 4 0.5 Mn 0.5 -MOF simulates the degradation of phenol contaminants in aqueous solution by peroxidase. The inset figure shows the change in solution color from dark to light over time after potassium ferricyanide color development.

[0041] Figure 4 Cu at pH 7 0.5 Mn 0.5 -MOF simulation simulates the degradation of phenol contaminants in aqueous solution by laccase. After 4-AP color development, the solution color changes from light to dark over time.

Claims

1. A method for overcoming the pH limitation of nanozymes in degrading phenol in water, wherein the nanozyme is a heterometallic MOF with dual biomimetic enzyme activity, characterized in that: Solution A was prepared by dissolving 4-chloroisophthalic acid in acetone. Solution B was prepared by dissolving copper acetate and manganese acetate in deionized water. Solution C was prepared by dissolving aminopolysilsesquioxane as a regulator in deionized water. Solution B and solution C were slowly added dropwise to solution A under magnetic stirring. The reaction was continued at room temperature for 6-12 hours. The reaction product was thoroughly washed with water and acetone and then vacuum dried at 60°C for 12 hours to obtain heterometallic MOFs. The molar ratio of copper acetate to manganese acetate is 1:1; The ratio of the metal salt composed of copper acetate and manganese acetate, 4-chloroisophthalic acid, and aminopolysilsesquioxane is 0.766 mmol: 0.46 mmol: 20 mg.

2. The method for overcoming the pH limitation of nanoenzymes to degrade phenol in water according to claim 1, characterized in that... The aforementioned heterometallic MOFs are used for the degradation of phenol pollutants in water. Their dual-bioenzyme mimicry activity overcomes the pH limitation on the catalytic activity of their nanoenzymes. The method is as follows: 1) When the pH of the water body is 2-5, the peroxidase activity is used to degrade phenol pollutants. The volume of the reaction system is 100 mL, the concentration of phenol is 20-200 mg / L, the concentration of H2O2 solution is 5-80 mM, and the amount of nanozyme is 0.1-0.8 mg / mL. The reaction is carried out at room temperature. 2 mL of reaction solution is taken every 30 min. Potassium ferricyanide is used for colorimetric reaction to determine the amount of remaining phenol. The change of the absorption peak of the supernatant at 510 nm is measured by ultraviolet-visible spectrophotometer. 2) When the pH of the water body is 5-11, the laccase activity is used to degrade phenol pollutants. The volume of the reaction system is 100 mL, the concentration of phenol is 20-200 mg / L, the concentration of the colorimetric reagent 4-AP is 20-200 mg / L, and the amount of nanozyme is 0.1-0.8 mg / mL. The mixture is magnetically stirred at room temperature. 3 mL of the reaction solution is taken every 30 min, and the change of the absorption peak of the supernatant at 510 nm is measured using a UV-Vis spectrophotometer.

Images