Preparation method and application of monatomic iron-doped carbon quantum dot nano-enzyme

Abstract

The invention discloses a preparation method and application of monatomic iron-doped carbon quantum dot nano enzyme, and the preparation method comprises the following steps: fully dispersing citric acid, urea and iron salt, and fully reacting in a closed container; the ferric salt is any one of ferric citrate, iron methionine or ferrous lactate. The monatomic iron-doped carbon quantum dot nano-enzyme provided by the invention is good in dispersity, excellent in water solubility and uniform and stable in structure, has efficient antioxidant enzyme activity, can be easily absorbed by plants, can remarkably improve the antioxidant capacity and stress resistance of the plants after being applied, can remove excessively accumulated active oxygen of the plants, and also can effectively inhibit the growth of the plants. The soil heavy metal pollution control agent can control soil heavy metal pollution, also can improve the removal efficiency of antioxidant enzymes in plants, reduce heavy metal absorption and increase the plant yield, has the characteristics of small dosage, low cost, high efficiency, high environmental safety and easy use, and provides a new technology and product choice with practical application value for treatment of soil heavy metal pollution.

Description

Technical Field

[0001] The present invention relates to the field of agricultural environmental technology, and in particular to a preparation method and application of a single-atom iron-doped carbon quantum dot nanozyme. Background Art

[0002] The control of soil heavy metal pollution is one of the major environmental issues facing my country. Due to soil heavy metal pollution, crops produce excessive reactive oxygen, which causes serious damage to their oxidative defense system, ultimately leading to reduced crop yields and excessive heavy metal content. Therefore, effectively removing the excessive accumulation of reactive oxygen in crops under heavy metal stress is a key way to achieve standard crop cultivation.

[0003] Nanozymes are mimetic enzymes that remove the function of active oxygen. They themselves have the ability to catalyze oxygen to produce active substances. In addition, they have the unique properties of nanomaterials, with the advantages of high catalytic efficiency, stability, economy and large-scale preparation. Without changing the existing planting pattern, a very small amount of nanozymes is applied, and the function of antioxidant enzymes is directly exerted, and the excessive active oxygen produced in the plant body due to heavy metal stress is converted into oxygen and water, thereby effectively alleviating plant heavy metal stress, and then achieving stable yield, high yield and quality improvement of crops. Some nanozymes containing metal elements have been developed in the prior art (such as CN114887644A, CN117019155A), but the preparation method requires complex processes such as calcination and pickling, and whether the anti-metal stress ability of plants can be improved is still unknown. Therefore, it has become a huge challenge to explore the structure of novel nanozymes and enzyme-like activity to give them the function of repairing the growth ability of farmland crops under heavy metal pollution. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a preparation method and application of single-atom iron-doped carbon quantum dot nanozyme.

[0005] The first object of the present invention is to provide a method for preparing single-atom iron-doped carbon quantum dot nanozyme.

[0006] The second object of the present invention is to provide single-atom iron-doped carbon quantum dot nanozyme prepared by the preparation method.

[0007] The third object of the present invention is to provide the use of the single-atom iron-doped carbon quantum dot nanozyme in the preparation of antioxidant products.

[0008] The fourth object of the present invention is to provide the application of the single-atom iron-doped carbon quantum dot nanozyme in improving the antioxidant capacity of plants.

[0009] The fifth object of the present invention is to provide the application of the single-atom iron-doped carbon quantum dot nanozyme in improving the stress resistance of plants.

[0010] The sixth object of the present invention is to provide a plant growth regulator.

[0011] In order to achieve the above object, the present invention is implemented by the following scheme:

[0012] Iron plays an important role in the growth process of plants. Iron deficiency in plants will directly lead to a decrease in chlorophyll content, which will subsequently reduce the efficiency of photosynthesis. Single-atom iron nanozymes have the characteristics of small particle size, large specific surface area, and many reaction sites, but single-atom iron is easy to aggregate, resulting in poor dispersibility and a significant decrease in catalytic ability. The present invention modifies single-atom iron nanozymes, improves the preparation method, and improves the dispersibility and biocompatibility of single-atom iron through simple emulsification and heating reactions, thereby obtaining a new type of single-atom iron-doped carbon quantum dot nanozyme.

[0013] A method for preparing a single-atom iron-doped carbon quantum dot nanozyme comprises the following steps: fully dispersing citric acid, urea and iron salt in a mass ratio of 1: (0.1-1): (0.5-3), and then fully reacting them in a closed container; the iron salt is any one of ferric citrate, ferric methionine or ferrous lactate; the method for fully dispersing comprises emulsification; the conditions for fully reacting comprise: a temperature of 200°C to 300°C and a pressure of 1MPa to 5MPa.

[0014] Preferably, the method comprises the following steps: firstly emulsifying the citric acid, the urea, the iron salt and the emulsifier to obtain an emulsion, and then fully reacting the emulsion in a closed container; the emulsifier is any one of Span 20, Tween 20 or Triton X-100.

[0015] More preferably, the emulsification comprises the following steps: fully reacting the mother liquor with the emulsifier to obtain an emulsion; the mother liquor is an aqueous solution containing the citric acid, the urea and the iron salt.

[0016] Further preferably, the method for fully reacting the mother liquor with the emulsifier comprises: fully stirring the mother liquor and the emulsifier.

[0017] More preferably, the method for fully reacting the mother liquor with the emulsifier comprises: stirring the mother liquor and the emulsifier to react for 1 hour to 3 hours.

[0018] More preferably, the mass ratio of the mother liquid to the emulsifier is 100:(0.1-1).

[0019] More preferably, the iron salt is ferric citrate, and the emulsifier is Span 20.

[0020] Further preferably, the method for fully reacting the mother liquor with the Span 20 comprises: stirring the mother liquor and the Span 20 at a mass ratio of 100:(0.1-1) for 1 hour to 3 hours.

[0021] More preferably, the method for fully reacting the mother liquor with the Span 20 comprises: stirring the mother liquor and the Span 20 at a mass ratio of 100:0.1 for 1 to 3 hours.

[0022] Still further preferably, the method for fully reacting the mother liquor with the Span 20 comprises: stirring the mother liquor and the Span 20 at a mass ratio of 100:0.1 for 3 hours.

[0023] More preferably, the iron salt is iron methionine, and the emulsifier is Tween 20.

[0024] Further preferably, the method for fully reacting the mother liquor with the Tween 20 comprises: stirring the mother liquor and the Span 20 at a mass ratio of 100:(0.1-1) for 1 hour to 3 hours.

[0025] More preferably, the method for fully reacting the mother liquor with the Tween 20 comprises: stirring the mother liquor and the Span 20 at a mass ratio of 100:0.5 for 1 to 3 hours.

[0026] Still more preferably, the method for fully reacting the mother liquor with the Tween 20 comprises: stirring the mother liquor and the Span 20 at a mass ratio of 100:0.5 for reaction for 1 hour.

[0027] More preferably, the iron salt is ferrous lactate, and the emulsifier is Triton X-100.

[0028] Further preferably, the method for fully reacting the mother liquor with the Triton X-100 comprises: stirring the mother liquor and the Triton X-100 at a mass ratio of 100:1 for reaction for 1 hour to 3 hours.

[0029] More preferably, the method for fully reacting the mother liquor with the Triton X-100 comprises: stirring the mother liquor and the Triton X-100 at a mass ratio of 100:1 for 3 hours.

[0030] Further preferably, the fully dispersing method further comprises ultrasound, and the mother liquor is obtained by dispersing the citric acid, the urea and the iron salt in water through ultrasound.

[0031] Specifically, the ultrasonic conditions include 50KHz ultrasonic treatment for 1 hour to 3 hours.

[0032] Preferably, the conditions for sufficient reaction also include: the reaction time is 4 hours to 5 hours.

[0033] More preferably, the method for fully reacting comprises: reacting the emulsion in a sealed container at a pressure of 1 MPa to 5 MPa and a temperature of 200° C. to 300° C. for 4 to 5 hours.

[0034] More preferably, the iron salt is ferric citrate, and the emulsifier is Span 20, and the obtained emulsion is reacted in a closed container at a pressure of 5 MPa and a temperature of 300° C. for 4 to 5 hours.

[0035] More preferably, the iron salt is ferric citrate, and the emulsifier is Span 20, and the obtained emulsion is reacted in a closed container at a pressure of 5 MPa and a temperature of 300° C. for 5 hours.

[0036] More preferably, the iron salt is iron methionine, and the emulsifier is Tween 20, and the obtained emulsion is reacted in a closed container at a pressure of 1 MPa and a temperature of 200° C. for 4 to 5 hours.

[0037] More preferably, the iron salt is iron methionine, and the emulsifier is Tween 20, and the obtained emulsion is reacted in a closed container at a pressure of 1 MPa and a temperature of 200° C. for 4 hours.

[0038] Further preferably, the iron salt is ferrous lactate, and the emulsifier is Triton X-100, and the obtained emulsion is reacted in a closed container at a pressure of 2 MPa and a temperature of 250° C. for 4 to 5 hours.

[0039] More preferably, the iron salt is ferrous lactate, and the emulsifier is Triton X-100, and the obtained emulsion is reacted in a closed container at a pressure of 2 MPa and a temperature of 250° C. for 4 hours.

[0040] Preferably, the closed container includes a reaction kettle.

[0041] More preferably, the reactor comprises a high-pressure reactor.

[0042] Further preferably, the inner lining of the high-pressure reactor comprises polytetrafluoroethylene.

[0043] Preferably, the preparation method further comprises the following steps: after the reaction is fully completed, purifying the obtained reactant.

[0044] More preferably, the purification method comprises: centrifugation, filtration and dialysis.

[0045] Further preferably, the centrifugal conditions include: centrifugation at 5000 rpm to 10000 rpm for 5 to 10 minutes.

[0046] Further preferably, the filtering method comprises vacuum filtration.

[0047] Further preferably, the dialysis method comprises dialysis using a dialysis membrane with a molecular weight of 100KD for 5 to 10 hours.

[0048] More preferably, the dialysate used for the dialysis is water.

[0049] More preferably, after purification, the obtained purified product is dried.

[0050] More preferably, the drying method is freeze-drying.

[0051] The single-atom iron-doped carbon quantum dot nanozyme prepared by any of the preparation methods described should also be within the protection scope of the present invention.

[0052] The single-atom iron-doped carbon quantum dot nanozyme provided by the present invention has a size of 2 to 3.5 nm, a uniform and stable structure, obvious lattice fringes, good dispersibility, is completely water-soluble, has efficient antioxidant enzyme activity, and can effectively remove superoxide anions and hydroxyl radicals.

[0053] Therefore, the present invention also requests protection for the following contents:

[0054] The application of the single-atom iron-doped carbon quantum dot nanozyme in the preparation of antioxidant products should also be within the protection scope of the present invention.

[0055] The application of the single-atom iron-doped carbon quantum dot nanozyme in improving the antioxidant capacity of plants should also be within the protection scope of the present invention.

[0056] Preferably, the plants are crop plants.

[0057] More preferably, the crops are food crops or vegetable crops.

[0058] More preferably, the food crop is rice.

[0059] More preferably, the vegetable crop is lettuce.

[0060] The application of the single-atom iron-doped carbon quantum dot nanozyme in improving the stress resistance of plants should also be within the protection scope of the present invention.

[0061] Preferably, the plants are crop plants.

[0062] More preferably, the crops are food crops or vegetable crops.

[0063] More preferably, the food crop is rice.

[0064] More preferably, the vegetable crop is lettuce.

[0065] Preferably, the stress resistance includes heavy metal stress resistance.

[0066] More preferably, the ability to resist heavy metal stress includes the ability to resist arsenic stress or cadmium stress.

[0067] A plant growth regulator comprises the single-atom iron-doped carbon quantum dot nanozyme.

[0068] Preferably, the plant growth regulator is a liquid agent.

[0069] More preferably, the solvent of the liquid agent is water.

[0070] Further preferably, the working concentration of the single-atom iron-doped carbon quantum dot nanozyme is 50 mg / mL to 300 mg / mL.

[0071] More preferably, the working concentration of the single-atom iron-doped carbon quantum dot nanozyme is 300 mg / mL.

[0072] Preferably, the plant growth regulator is a foliar agent.

[0073] Compared with the prior art, the present invention has the following beneficial effects:

[0074] The single-atom iron-doped carbon quantum dot nanozyme provided by the present invention has good dispersibility, good water solubility, uniform and stable structure, high-efficiency antioxidant enzyme activity, and is easily absorbed by plants. After application, it can significantly improve the antioxidant capacity and anti-stress ability of plants. It can not only remove the excessive accumulated active oxygen in plants, but also improve the removal efficiency of antioxidant enzymes in plants, reduce heavy metal absorption, and increase plant yield. It has the characteristics of small dosage, low cost, high efficiency, high environmental safety and easy use, providing a new choice of technology and products with practical application value for large-scale treatment of heavy metal pollution in farmland. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 This is a transmission electron microscope image of Fe-CDs-2 of Example 2.

[0076] Figure 2 This is the particle size distribution diagram of Fe-CDs-2 in Example 2.

[0077] Figure 3 The phenotype of lettuce sprayed with water containing different concentrations of Fe-CDs-1 under or without arsenic stress.

[0078] Figure 4These are the results of determination of relevant physiological indicators of lettuce leaves sprayed with clean water containing different concentrations of Fe-CDs under arsenic stress; A is the determination result of arsenic content; B is the determination result of total phenol content; C is the determination result of malondialdehyde (MDA) content; D is the determination result of peroxidase (POD) activity; E is the determination result of superoxide dismutase (SOD) activity; F is the determination result of catalase (CAT) activity.

[0079] Figure 5 These are the results of measurement of relevant physiological indices of rice stems and leaves sprayed with clean water containing different concentrations of Fe-CDs-3 or CDs-2 under cadmium stress; A is the result of measurement of peroxidase (POD) activity; B is the result of measurement of superoxide dismutase (SOD) activity; C is the result of measurement of malondialdehyde (MDA) content; D is the result of measurement of cadmium content. DETAILED DESCRIPTION

[0080] The present invention is further described in detail below in conjunction with the accompanying drawings and specific examples of the specification. The examples are only used to explain the present invention and are not used to limit the scope of the present invention. The test methods used in the following examples are conventional methods unless otherwise specified; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0081] Example 1 A method for preparing single-atom iron-doped carbon quantum dot nanozyme

[0082] 1. Preparation of mother liquor

[0083] Weigh 1g of citric acid powder (CAS No.: 77-92-9), 1g of urea powder (CAS No.: 57-13-6) and 0.5g of ferric citrate (CAS No.: 3522-50-7), and then measure 50mL of water, add them into a 200mL beaker, and treat them with 50KHz ultrasound for 3 hours. After sufficient dispersion, a mixed solution is obtained, which is the mother liquor.

[0084] 2. Emulsification of mother liquor

[0085] The nanozyme mother solution obtained in step 1 was added with an emulsifier (Span 20, CAS No.: 1338-39-2) with a final concentration of 0.1 wt %, and the final mass percentage of Span 20 was 0.1%. The mixture was stirred for 3 hours to obtain an emulsion of the nanozyme mother solution.

[0086] 3. Preparation of precursor solution

[0087] The emulsion obtained in step 2 was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene, placed in an oven, heated at a pressure of 5 MPa and 300° C. for 5 h, and naturally cooled to room temperature (25° C.) to obtain a precursor solution.

[0088] 4. Preparation of single-atom iron-doped carbon quantum dots filtrate

[0089] The precursor solution obtained in step 3 was centrifuged at high speed for 5 minutes at a speed of 10,000 rpm, and then the supernatant was vacuum filtered through a 0.22 μm water filter membrane to remove impurities and obtain a single-atom iron-doped carbon quantum dot filtrate.

[0090] 5. Dialysis

[0091] The single-atom iron-doped carbon quantum dot filtrate obtained in step 4 was dialyzed using a dialysis membrane with a molecular weight of 100KD. The dialysate was distilled water and the dialysis time was 5 hours. The dialysate obtained was a uniform and stable single-atom iron-doped carbon quantum dot nanozyme, named Fe-CDs-1, and was freeze-dried for storage.

[0092] Example 2 A method for preparing single-atom iron-doped carbon quantum dot nanozyme

[0093] 1. Preparation of mother liquor

[0094] Weigh 1 g of citric acid powder, 0.5 g of urea powder and 1 g of methionine iron (CAS No.: 63-68-3), and then measure 50 mL of water, add them into a 200 mL beaker, and treat them with ultrasound at 50 KHz for 1 hour. After sufficient dispersion, a mixed solution is obtained, which is the mother liquor.

[0095] 2. Emulsification of mother liquor

[0096] The nanozyme mother solution obtained in step 1 was added with Tween 20 (CAS No.: 9005-64-5) with a final concentration of 0.5 wt %, and the mixture was stirred for reaction for 1 hour to obtain an emulsion of the nanozyme mother solution.

[0097] 3. Preparation of precursor solution

[0098] The emulsion obtained in step 2 was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene, placed in an oven, heated at a pressure of 1 MPa and 200° C. for 4 h, and naturally cooled to room temperature (25° C.) to obtain a precursor solution.

[0099] 4. Preparation of single-atom iron-doped carbon quantum dots filtrate

[0100] The precursor solution obtained in step 3 was centrifuged at high speed for 5 minutes at a speed of 10,000 rpm, and then the supernatant was vacuum filtered through a 0.22 μm water filter membrane to remove impurities and obtain a single-atom iron-doped carbon quantum dot filtrate.

[0101] 5. Dialysis

[0102] The single-atom iron-doped carbon quantum dot filtrate obtained in step 4 was dialyzed using a dialysis membrane with a molecular weight of 100KD. The dialysate was distilled water and the dialysis time was 8 hours. The dialysate obtained was a uniform and stable single-atom iron-doped carbon quantum dot nanozyme, named Fe-CDs-2, and was freeze-dried for storage.

[0103] Example 3 A method for preparing single-atom iron-doped carbon quantum dot nanozyme

[0104] 1. Preparation of mother liquor

[0105] Weigh 1 g of citric acid powder, 0.1 g of urea powder and 3 g of ferrous lactate (CAS No.: 5905-52-2), and then measure 50 mL of water, add them into a 200 mL beaker, and treat them with ultrasound at 50 KHz for 2 hours. After sufficient dispersion, a mixed solution is obtained, which is the mother liquor.

[0106] 2. Emulsification of mother liquor

[0107] The nanozyme mother solution obtained in step 1 was added with Triton X-100 (CAS No.: 9002-93-1) at a final concentration of 1 wt %, and the mixture was stirred for reaction for 3 hours to obtain an emulsion of the nanozyme mother solution.

[0108] 3. Preparation of precursor solution

[0109] The emulsion obtained in step 2 was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene, placed in an oven, heated at a pressure of 2 MPa and 250° C. for 4 h, and naturally cooled to room temperature (25° C.) to obtain a precursor solution.

[0110] 4. Preparation of single-atom iron-doped carbon quantum dots filtrate

[0111] The precursor solution obtained in step 3 was centrifuged at high speed for 5 minutes at a speed of 5000 rpm, and then the supernatant was vacuum filtered through a 0.22 μm water filter membrane to remove impurities and obtain a single-atom iron-doped carbon quantum dot filtrate.

[0112] 5. Dialysis of filtrate

[0113] The single-atom iron-doped carbon quantum dot filtrate obtained in step 4 was dialyzed using a dialysis membrane with a molecular weight of 100KD. The dialysate was distilled water and the dialysis time was 10 hours. The dialysate obtained was a uniform and stable single-atom iron-doped carbon quantum dot nanozyme, named Fe-CDs-3, and was freeze-dried for storage.

[0114] Comparative Example 1: A method for preparing a nanozyme

[0115] 1. Preparation of mixed solution

[0116] Weigh 0.5 g of urea powder and 2 g of ferric sulfate, and then measure 50 mL of water, add them into a 100 mL beaker, treat with 50 KHz ultrasound, and obtain a mixed solution after sufficient dispersion.

[0117] 2. Preparation of precursor fluid

[0118] The mixed solution obtained in step 1 was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene, placed in an oven, reacted at a pressure of 1.5 MPa and 230° C. for 4 h, and naturally cooled to room temperature (25° C.) to obtain a precursor solution.

[0119] 3. Preparation of filtrate

[0120] The precursor liquid obtained in step 2 was centrifuged at high speed for 5 minutes at a speed of 5000 rpm, and then the supernatant was vacuum filtered through a 0.22 μm water filter membrane to remove impurities and obtain a filtrate.

[0121] 4. Dialysis of filtrate

[0122] The filtrate obtained in step 3 was dialyzed through a dialysis membrane with a molecular weight of 100KD. The dialysate was distilled water. The dialysis time was 10 hours, and the filtrate was freeze-dried and stored to obtain a nanozyme named CDs-1.

[0123] Comparative Example 2: Preparation method of a nanozyme

[0124] 1. Preparation of mixed solution

[0125] Weigh 2 g of citric acid powder, 2 g of urea powder and 6 g of sodium ferric ethylenediaminetetraacetate (CAS No.: 15708-41-5), and then measure 50 mL of water, add them into a 100 mL beaker, and ultrasonically treat them at 50 KHz to obtain a mixed solution after sufficient dispersion.

[0126] 2. Preparation of precursor fluid

[0127] The mixed solution obtained in step 1 was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene, placed in an oven, heated at a pressure of 5 MPa and 300° C. for 6 h, and naturally cooled to room temperature (25° C.) to obtain a precursor solution.

[0128] 3. Preparation of filtrate

[0129] The precursor liquid obtained in step 2 was centrifuged at high speed for 10 minutes at a speed of 5000 rpm, and then the supernatant was vacuum filtered through a 0.22 μm water filter membrane to remove impurities and obtain a filtrate.

[0130] 4. Dialysis of filtrate

[0131] The filtrate obtained in step 3 was dialyzed through a dialysis membrane with a molecular weight of 100KD. The dialysate was distilled water. The dialysis time was 10 hours, and the filtrate was freeze-dried and stored to obtain a nanozyme named CDs-2.

[0132] Application Example 1 Structural Characterization and Evaluation of Nanozymes

[0133] 1. Structural characterization

[0134] The particle size distribution and size structure of the nanozymes of Examples 1 to 3 (Fe-CDs-1 to Fe-CDs-3) and the nanozymes of Comparative Examples 1 to 2 (CDs-1 and CDs-2) were analyzed by laser particle size analyzer and transmission electron microscope. The electron microscope image of Fe-CDs-2 of Example 2 is as follows: Figure 1 The particle size distribution is shown in Figure 2 As shown in the figure, Fe-CDs-1 and Fe-CDs-3 showed similar structural shapes to Fe-CDs-2 under transmission electron microscopy. Data analysis results showed that the average particle size of Fe-CDs-1 was 3.1±0.3nm, the average particle size of Fe-CDs-2 was 2.5±0.4nm, and the average particle size of Fe-CDs-3 was 2.8±0.6nm, all of which had obvious lattice fringes and a lattice spacing of 0.23nm; while the average particle size of CDs-1 was 2.3±0.4nm, and the average particle size of CDs-2 was 2.6±0.5nm, with a circular structure and no obvious lattice fringes.

[0135] 2. Component Analysis

[0136] The elemental composition of the nanozymes of Examples 1 to 3 (Fe-CDs-1 to Fe-CDs-3) and the nanozymes of Comparative Examples 1 to 2 (CDs-1 and CDs-2) was analyzed by electron energy spectroscopy. The results showed that Fe-CDs-1 to Fe-CDs-3 all contained elements such as iron, oxygen and carbon. The contents of iron, oxygen and carbon in Fe-CDs-1 were 0.84%, 2.18% and 89.15%, respectively. The contents of iron, oxygen and carbon in Ds-2 are 0.51%, 2.26% and 87.69% respectively, and the contents of iron, oxygen and carbon in Fe-CDs-3 are 0.82%, 2.33% and 87.55% respectively; CDs-1 to CDs-2 all contain elements such as carbon and oxygen, and the contents of carbon and oxygen in CDs-1 are 90.11% and 3.38% respectively, and the contents of carbon and oxygen in CDs-2 are 91.43% and 3.47% respectively.

[0137] 3. Enzyme activity evaluation

[0138] The nanozymes of Examples 1 to 3 (Fe-CDs-1 to Fe-CDs-3) and the nanozymes of Comparative Examples 1 to 2 (CDs-1 and CDs-2) were prepared into test samples with a concentration of 8 mg / mL, and the scavenging effect of each test sample on superoxide anions in vitro was detected by NBT method; the scavenging effect of each test sample on hydroxyl radicals in vitro was also detected by colorimetry. The specific steps are as follows: 1.8 mM salicylic acid, 1.8 mM FeSO 4 , 5 mM H 2 O 2 The buffer solution has a pH of 7.4, the sample to be tested is added into the buffer solution and mixed, the buffer solution is used as a control, the mixture is adjusted to zero, and the absorbance of the mixture is measured at 510 nm.

[0139] Table 1 Scavenging effect of superoxide anions and hydroxyl radicals

[0140]

[0141] The results are shown in Table 1. At a concentration of 8 mg / mL, the nanozymes (Fe-CDs-1 to Fe-CDs-3) of Examples 1 to 3 can effectively remove superoxide anions and hydroxyl radicals, and the removal rates are significantly higher than those of the nanozymes CDs-1 and CDs-2 of Comparative Examples 1 to 2. This shows that the single-atom iron-doped carbon quantum dot nanozymes provided by the present invention can more efficiently remove superoxide anions and hydroxyl radicals, have excellent antioxidant enzyme activity, and have superoxide dismutase (SOD)-like activity. Among them, the Fe-CDs-3 prepared in Example 3 has the strongest antioxidant capacity.

[0142] Application Example 2: Performance evaluation of nanozymes in plant resistance to heavy metal stress

[0143] 1. Arsenic stress experiment

[0144] (1) Lettuce cultivation and stress treatment

[0145] Italian lettuce (Lactuca sativa L. var. ramosa Hort.) was cultured with Hoagland nutrient solution. After 10 days of conventional culture, conventional culture was performed with plant nutrient solution as a non-arsenic stress group, and stress treatment was performed with plant nutrient solution containing 20 μM sodium arsenite as an arsenic stress group.

[0146] (2) Spraying treatment

[0147] After 12 days of treatment with or without arsenic stress, at 5 pm on a sunny day, the arsenic-free stress group and the arsenic stress group were evenly sprayed with equal amounts of clean water containing different concentrations (0 mg / mL, 50 mg / mL, 100 mg / mL or 300 mg / mL) of single-atom iron-doped carbon quantum dot nanozyme (Fe-CDs-1), respectively. The spraying lasted for 30 days, with 6 seedlings in each treatment and each treatment repeated three times.

[0148] (3) Biomass and physiological index determination

[0149] like Figure 3 As shown, after 30 days of spraying, the biomass of the lettuce in the non-arsenic stress group was significantly increased after being treated with Fe-CDs-1. The higher the concentration of Fe-CDs-1, the more significant the increase in the biomass of the lettuce; the arsenic stress group also showed the same growth trend. Compared with spraying with clean water, the biomass of the lettuce sprayed with different concentrations of Fe-CDs-1 increased significantly, and the increase in fresh weight was 25.46% to 48.51%. The nanozymes of Examples 2 to 3 (Fe-CDs-2 to Fe-CDs-3) sprayed with or without arsenic stress treatment also had similar growth conditions. It shows that the single-atom iron-doped carbon quantum dot nanozyme provided by the present invention can promote plant growth under normal culture and arsenic stress, and significantly increase the biomass of plants.

[0150] This example also measured physiological indicators of the arsenic stress group, including the activity of related scavenging enzymes that reflect the homeostasis of active oxygen in plants and the MDA content that reflects the integrity of the cell membrane structure. The total phenol content, malondialdehyde (MDA) content, peroxidase (POD) activity, superoxide dismutase (SOD) activity and catalase (CAT) activity were measured using a detection kit (Nanjing Jiancheng Biotechnology Co., Ltd.).

[0151] like Figure 4 As shown in A to E in, after 30 days of spraying, compared with the treatment of 0 mg / mL Fe-CDs-1 spraying, the inorganic arsenic content in the lettuce leaves under the treatment of 50 mg / mL, 100 mg / mL or 300 mg / mL Fe-CDs-1 spraying was significantly reduced by 35.47% to 47.52%, the total phenol content was significantly increased by 21.44% to 496.67%, the MDA content was significantly reduced by 44.34% to 49.44%, and the activities of the antioxidant enzymes POD, SOD and CAT were significantly improved. The lettuce treated with arsenic stress sprayed with the nanozymes (Fe-CDs-2 to Fe-CDs-3) of Examples 2 to 3 also had similar test results. It shows that under arsenic stress, the single-atom iron-doped carbon quantum dot nanozyme provided by the present invention exerts the activity of antioxidant enzymes, effectively removes excessive reactive oxygen in the plant body, improves the plant's ability to resist arsenic stress, enhances the defense mechanism, effectively inhibits the plant's absorption of arsenic, reduces the degree of membrane lipid peroxidation, and better maintains the integrity of the cell membrane.

[0152] 2. Cadmium stress experiment

[0153] (1) Rice seedling cultivation

[0154] Select full rice seeds and place them in a beaker. After disinfecting them with 75% alcohol for 1 minute, wash them with ultrapure water, soak them in 2.5% sodium hypochlorite solution for 10 minutes, and rinse them with ultrapure water for 5 to 6 times. Spread the disinfected seeds on a seedling tray, add water until it just touches the bottom of the seeds to keep them moist, cover the seedling tray with tin foil to avoid light for germination, and remove the tin foil after two days;

[0155] (2) Rice transplanting and cadmium stress treatment

[0156] After 14 days of seedling raising, rice seedlings with the same growth potential were selected and transplanted into plastic barrels, with at least 10 seedlings in each barrel. After transplanting, they continued to grow for 7 days, and then a nutrient solution containing cadmium chloride solution (the final cadmium concentration was 10 μM) was added; one week after the stress treatment, at 2 o'clock in the afternoon on a sunny day, clean water containing different concentrations (0 mg / mL, 50 mg / mL, 100 mg / mL or 300 mg / mL) of Fe-CDs-3 in Example 3 or CDs-2 in Comparative Example 2 was evenly sprayed, and the total amount of spraying was 5 mL. One barrel was used as one treatment unit, and each treatment was repeated three times.

[0157] (3) Detection of rice antioxidant capacity and cadmium content

[0158] The malondialdehyde (MDA) content, peroxidase (POD) activity, superoxide dismutase (SOD) activity, and cadmium content of rice stems and leaves were determined using detection kits (Nanjing Jiancheng Biotechnology Co., Ltd.).

[0159] like Figure 5 As shown in A to D, compared with spraying CDs-2, the peroxidase activity in the rice stems and leaves sprayed with Fe-CDs-3 was significantly increased by 78.83% to 125.88%, the superoxide dismutase activity was significantly increased by 76.51% to 281.72%, the MDA content was significantly reduced by 29.13% to 57.63%, and the cadmium content was significantly reduced by 36.73% to 51.06%. It shows that although both Comparative Example 2 and Example 3 are nanozymes prepared with organic iron as raw materials, the former uses sodium ferric ethylenediaminetetraacetate and the latter uses ferrous lactate, under cadmium stress, the single-atom iron-doped carbon quantum dot nanozyme prepared with ferrous lactate in Example 3 is more conducive to the activity of antioxidant enzymes, more effectively improves the antioxidant capacity of plants, enhances the defense mechanism, effectively removes excessive reactive oxygen, and improves the stress capacity of plants, thereby inhibiting the absorption of cadmium by plants.

[0160] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. For ordinary technicians in this field, other different forms of changes or modifications can be made based on the above descriptions and ideas. It is not necessary and impossible to list all the implementation methods here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing single-atom iron-doped carbon quantum dot nanozyme, characterized in that: The method comprises the following steps: fully dispersing citric acid, urea and iron salt in a mass ratio of 1:(0.1-1):(0.5-3), and then fully reacting them in a closed container; The iron salt is any one of ferric citrate, ferric methionine or ferrous lactate; The method of sufficient dispersion includes emulsification; The conditions for sufficient reaction include: temperature of 200° C. to 300° C. and pressure of 1 MPa to 5 MPa.

2. The preparation method according to claim 1, characterized in that: The following steps are involved: Firstly, the citric acid, the urea, the iron salt and the emulsifier are emulsified to obtain an emulsion, and then the emulsion is fully reacted in a closed container; The emulsifier is any one of Span 20, Tween 20 or Triton X-100.

3. The preparation method according to claim 2, characterized in that: The emulsification comprises the following steps: fully reacting the mother liquid with the emulsifier to obtain an emulsion; The mother liquor is an aqueous solution containing the citric acid, the urea and the iron salt.

4. The preparation method according to claim 3, characterized in that: The mass ratio of the mother liquid to the emulsifier is 100:(0.1-1).

5. The preparation method according to claim 1, characterized in that: The conditions for sufficient reaction also include: the reaction time is 4 hours to 5 hours.

6. The single-atom iron-doped carbon quantum dot nanozyme prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the single-atom iron-doped carbon quantum dot nanozyme according to claim 6 in the preparation of antioxidant products.

8. Use of the single-atom iron-doped carbon quantum dot nanozyme according to claim 6 in improving the antioxidant capacity of plants.

9. Use of the single-atom iron-doped carbon quantum dot nanozyme according to claim 6 in improving the stress resistance of plants.

10. A plant growth regulator, characterized in that: It comprises the single-atom iron-doped carbon quantum dot nanozyme as described in claim 6.

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