Typha orientalis-based carbon quantum dot as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of ecological sewage treatment, and particularly relates to cattail-based carbon quantum dots as well as a preparation method and application thereof. The method comprises the following steps: by taking wetland waste typha orientalis as a raw material, soaking the typha orientalis in ethanol, boiling, deactivating, decoloring and grinding to obtain a precursor; placing the precursor at the temperature of 160-180 DEG C, carrying out hydrothermal reaction for 2-4 hours, and carrying out ultrasonic extraction, filtration, dialysis and drying on the reaction liquid after the reaction to obtain the cattail-based carbon quantum dots. The cattail-based carbon quantum dots have the advantages of stable chemical properties, rich functional groups, greenness, safety and the like, can be used for improving the stress resistance of wetland plants under salt stress, not only can improve the growth condition of overground parts of the plants, promote downward growth of roots and increase the number of lateral roots, but also can remove active oxygen in the plants, so that the growth of the plants is promoted. The activity levels of MDA and total antioxidant enzymes are reduced, and the stress resistance of wetland plants under the salt stress condition is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage ecological treatment and relates to cattail-based carbon quantum dots and a preparation method and application thereof. Background Art

[0002] Constructed wetlands (CWs) are widely used in the treatment of domestic wastewater, industrial wastewater, agricultural drainage, and landfill leachate. However, CWs have the disadvantages of low treatment efficiency and being greatly affected by the external environment during the treatment process. For example, under environmental conditions such as drought, high salt, and low temperature, the ecological stability of the CWs system will be destroyed, reducing the ability of the constructed wetland to remove pollutants. At the same time, if the change in the external environment exceeds the tolerance of the plant, it will have a stressful effect on the growth of the plant, destroying the metabolic balance of reactive oxygen species (ROS) in plant cells and facilitating the accumulation of reactive oxygen species. Excessive reactive oxygen species will cause lipid peroxidation, damage the cell membrane system, reduce the photosynthesis of the plant, and reduce the absorption and assimilation of minerals. In severe cases, it will lead to the death of the plant. Therefore, improving the stress resistance of the plant is particularly important in maintaining the stability of the constructed wetland ecological treatment system.

[0003] Genetic engineering technology, synthetic biology technology, exogenous microbial enhancement technology and nanotechnology are used to improve the restoration ability of artificial wetland plants under abiotic stress conditions. Although these technologies are promoting the development of plant restoration, there are problems such as difficulty in application, poor stability and environmental risks in the application process. Nanomaterials are widely used in agriculture, materials, food, environment and other fields due to their excellent properties, but most of the materials used at this stage are metal nanomaterials, which have toxic inhibitory effects on plant growth and can also cause environmental risks by accumulating in soil and water.

[0004] Carbon quantum dots (CQDs) are a type of carbon nanomaterial that can promote crop growth and increase crop yields. Currently, the commonly used methods for preparing carbon quantum dots include arc discharge, laser ablation, electrochemical method, hydrothermal method and microwave method, but the materials used in these methods are graphene, carbon fiber, etc., the raw materials are relatively expensive, and the strong acids such as concentrated sulfuric acid and concentrated nitric acid used in the preparation process are easy to pollute the environment. Summary of the invention

[0005] In view of the technical problems existing in the above-mentioned prior art, the present invention provides a method for preparing cattail-based carbon quantum dots. This preparation method makes full use of the abandoned wetland plant - cattail. By soaking the cattail in ethanol, boiling to decolorize, withering to decolorize, and grinding and screening, the purity and extraction efficiency of the prepared cattail-based carbon quantum dots are improved, so that the cattail-based carbon quantum dots have the advantages of stable chemical properties, rich functional groups, and green and safe. The cattail-based carbon quantum dots can enhance the resistance of wetland plants under abiotic stress, significantly reduce the stress damage and membrane damage of plants caused by stress, and play a positive role in maintaining the stable operation of the wetland system.

[0006] The first aspect of the present invention provides a method for preparing cattail-based carbon quantum dots, comprising the following steps: The cattail is soaked in ethanol, boiled to remove color, blanched and decolorized, and ground and sieved to obtain a precursor; The precursor is placed in a hydrothermal reaction at 160°C~180°C for 2h~4h, and the reaction solution is subjected to ultrasonic extraction, filtration and dialysis to obtain cattail-based carbon quantum dots.

[0007] Furthermore, the boiling time is 15 min to 25 min.

[0008] Furthermore, the fixing is dry heat fixing, the fixing temperature is 100° C. to 110° C., and the fixing time is 10 min to 20 min.

[0009] Furthermore, the cattail is any one or more of cattail leaves, cattail stems and cattail inflorescences.

[0010] Furthermore, the mesh number of the sieving is 60 mesh to 80 mesh.

[0011] Furthermore, the cattail is cattail leaves and cattail stems, and the mixed mass ratio of the cattail leaves and the cattail stems is 2-3:1.

[0012] Furthermore, the ultrasonic time is 50 min to 70 min, the ultrasonic input power is 180 W to 220 W, and the power frequency is 30 KHZ to 50 KHZ.

[0013] Furthermore, the dialysis is performed in a 1000Da dialysis bag, the dialysis time is 21h~30h, and the water is changed 2 times~4 times during the dialysis process.

[0014] Furthermore, drying is required after the dialysis, and the drying is freeze-drying or heat-drying.

[0015] Furthermore, the drying is freeze-drying.

[0016] The second aspect of the present invention provides a cattail-based carbon quantum dot, which is prepared according to the preparation method provided by the first aspect of the present invention.

[0017] A third aspect of the present invention provides an application of cattail-based carbon quantum dots in improving the resistance of plants to abiotic stress, wherein the abiotic stress is salt stress, nitrogen stress or water stress.

[0018] Furthermore, the abiotic stress is salt stress.

[0019] A fourth aspect of the present invention provides a method for improving the resistance of wetland plants to abiotic stress, the method comprising: The aqueous solution containing the cattail-based carbon quantum dots described above is sprayed on the surface of wetland plants or the matrix of the wetland system.

[0020] Furthermore, the concentration of cattail-based carbon quantum dots in the cattail-based carbon quantum dot aqueous solution is 25 mg / L to 100 mg / L.

[0021] A fifth aspect of the present invention provides an application of the above-mentioned cattail-based carbon quantum dots in improving the antioxidant capacity of plants.

[0022] A sixth aspect of the present invention provides an application of the above-mentioned cattail-based carbon quantum dots in improving the removal rate of ammonia nitrogen, total phosphorus or chemical oxygen demand in wetland systems.

[0023] In summary, compared with the prior art, the present invention has the following advantages and effects: (1) The present invention first provides a method for preparing cattail-based carbon quantum dots, which has the advantages of cheap and readily available raw materials, simple preparation method and environmental friendliness: ① The raw material for preparing cattail-based carbon quantum dots is wetland waste - cattail. At present, a large amount of plant stem and leaf waste will be produced at the end of the growth of wetland plants all over the world. If these wastes are not properly disposed of, they will not only cause blockage to the wetland system, but also bring new environmental problems. The present invention prepares them into cattail-based carbon quantum dots, which not only has cheap and readily available raw materials, but also realizes waste resource utilization. ② Since cattail contains chlorophyll, carotenoids and other pigments, these pigments will participate in the reaction during the preparation of cattail-based carbon quantum dots, resulting in changes in the surface properties and product characteristics of cattail-based carbon quantum dots, and the polyphenols, flavonoids and other substances contained in cattail may also compete with the carbon source during the preparation process, or be adsorbed on the surface of carbon quantum dots, affecting the growth and crystallization process of cattail-based carbon quantum dots, resulting in uneven particle size distribution and irregular shape of cattail-based carbon quantum dots, thereby affecting its performance and application. Therefore, the present invention first soaks cattail with anhydrous ethanol, and then removes the impurities such as pigments and grease contained in cattail by boiling and decolorizing, killing bacteria, fungi and other microorganisms that may exist on the surface of cattail and inside the tissue, preventing microorganisms from growing and reproducing in the subsequent treatment process, affecting the components of the plant, and at the same time causing a certain degree of expansion and softening of the tissue cells of cattail, removing water and gas in plant cells, and improving the extraction efficiency and product quality of carbon quantum dots; the decolorizing step can expose more oxygen-containing functional groups on the surface of cattail-based carbon quantum dots, such as carboxyl, hydroxyl, etc., which not only significantly enhances its electron transfer ability, but also narrows the half-peak width of the fluorescence emission peak, thereby improving the fluorescence quantum yield of cattail-based carbon quantum dots. Specifically, the increase of oxygen-containing functional groups prompts the cattail-based carbon quantum dots to generate more defect sites on the surface, thereby enhancing its emission ability to visible light (blue fluorescence), combined with the improvement of fluorescence quantum yield, it can be shown that the cattail-based carbon quantum dots prepared after decolorizing can further enhance the photosynthesis of plants. Then, by grinding through a 60-mesh to 80-mesh sieve, the particle size of the carbon quantum dots is made more uniform, and the adsorption performance and dispersibility of the carbon quantum dots are improved. ③ By placing the carbon quantum dot precursor at a temperature of 160℃~180℃ for hydrothermal reaction for 2h~4h, the carbon quantum dot precursor undergoes chemical reactions such as hydrolysis and polycondensation, and the atoms and molecules are rearranged and combined, gradually forming nanoparticles with a carbon quantum dot structure prototype; then, through ultrasonic extraction, the precursor is fully dissolved in water, so that the effective components in the cells can be extracted more effectively, and the local high temperature generated can improve the extraction effect; the insoluble impurities in the reaction solution are removed by filtration, and the solution containing carbon quantum dots is retained; the carbon quantum dots are further purified by dialysis to remove small molecule impurities and unreacted precursors, and finally cattail-based carbon quantum dots are obtained.

[0024] (2) The present invention provides a cattail-based carbon quantum dot, which has a spherical shape, an average particle size of 1.77nm, a lattice spacing of 0.22nm, and emits light blue fluorescence under ultraviolet light. It is a green and safe carbon-based zero-dimensional nanomaterial with the advantages of small size, rich functional groups, and extremely low toxicity. It is easy to enter plant cells and promote the absorption of water by plants. By spraying cattail-based carbon quantum dots on ryegrass leaves or wetland substrates, the growth of stems, leaves and roots of wetland plants can be promoted, and the fresh weight and dry weight of plant leaves can be significantly increased.

[0025] (3) The cattail-based carbon quantum dots disclosed in the present invention are beneficial to improving the stress resistance and antioxidant capacity of plants, can remove excess ROS caused by abiotic stress in plant cells, thereby reducing the MDA level and T-AOC enzyme activity, improving the antioxidant defense ability of plants under abiotic stress, alleviating oxidative stress, and improving the stress resistance of plants. At the same time, by strengthening the stress resistance of wetland plants under abiotic stress, the wetland system can also be improved to resist NH4 + -N, TP and COD removal capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 are the TEM and FTIR characterization images of CQDs, where Figure 1 Figure A shows the TEM characterization results of CQDs. Figure 1 Figure (a) in Figure A is the CQDs lattice diagram. Figure 1 Figure B shows the FTIR characterization results of CQDs.

[0027] Figure 2 This is a graph showing the effects of different concentrations of CQDs on ryegrass growth and biomass.

[0028] Figure 3 This is a graph showing the effect of adding CQDs on ryegrass growth and biomass in a salt stress system.

[0029] Figure 4 The effect of adding CQDs on ROS, MDA and antioxidant system enzyme activity (T-AOC) in ryegrass leaves under salt stress conditions.

[0030] Figure 5 The addition of CQDs to wetland system effluent ammonia nitrogen (NH4 + -N), total phosphorus (TP) and organic matter (COD). DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] Unless otherwise specified, the experimental methods described in the following examples are all conventional methods; the reagents and materials described are all commercially available unless otherwise specified.

[0033] Artificial wetlands are widely used in the treatment of domestic wastewater, industrial wastewater, agricultural drainage, and landfill leachate. However, artificial wetlands have the disadvantages of low treatment efficiency and being greatly affected by the external environment during the treatment process. For example, under environmental conditions such as drought, high salt, and low temperature, the ecological stability of artificial wetland systems will be destroyed, reducing the ability of artificial wetlands to remove pollutants. How to improve the stress resistance of plants in a low-toxic, green and efficient manner is an urgent problem that needs to be solved. Carbon quantum dots are a type of carbon nanomaterial that can promote crop growth and increase crop yields. Carbon quantum dots are a type of carbon nanomaterial that can promote crop growth and increase crop yields. At present, the commonly used preparation methods of carbon quantum dots include arc discharge, laser ablation, electrochemical method, hydrothermal method, and microwave method, but the materials used in these methods are relatively expensive, such as graphene, carbon fiber, etc., and strong acids such as concentrated sulfuric acid and concentrated nitric acid are used in the preparation process, which can easily pollute the environment.

[0034] The present invention first provides a method for preparing cattail-based carbon quantum dots. The method can be used to prepare cattail-based carbon quantum dots, which can enhance the stress resistance of wetland plants under abiotic stress, significantly reduce stress damage and membrane damage caused by stress to plants, and play a positive role in maintaining the stable operation of wetland systems.

[0035] The preparation method of cattail-based carbon quantum dots (CQDs) is described in detail below.

[0036] Example 1: A method for preparing cattail-based carbon quantum dots, the preparation method comprising the following steps: S1. Rinse the stems and leaves of cattail with distillation to remove impurities, then soak them in anhydrous ethanol overnight and boil them for 20 minutes.

[0037] S2. The soaked stems and leaves were decolorized at 105° C. for 15 min, dried at 90° C., cut into small pieces of 1 cm in length, ground, and passed through a 60-mesh sieve to obtain powder of cattail stems and leaves.

[0038] S3. Mix the leaves and stems in a ratio of 3:1 to obtain a precursor of cattail-based carbon quantum dots; weigh 2 g of the precursor and put it into a polytetrafluoroethylene liner, add 50 mL of ultrapure water at 50°C, and put it into a reactor after ultrasonication for 20 minutes.

[0039] S4. Place the reactor in a high temperature oven, heat it to 170°C, react for 3 hours, and then cool it to room temperature.

[0040] S5. The inner liner was placed in ultrasonic extraction for 60 minutes. The ultrasonic input power was 200 W and the power frequency was 40 KHZ. After extraction, a 0.45 μm filter membrane was used for suction filtration, and then a 0.22 μm filter membrane was used for filtration to obtain untreated CQDs.

[0041] S6. The untreated CQDs were dialyzed for 24 hours with a dialysis bag with a molecular weight of 1000Da, and ultrapure water was replaced every 6 hours to obtain a dialysate; specifically, the dialysis bag was cut into small pieces of 10cm, and an appropriate amount of 2% (w / v) sodium bicarbonate and 1mmol / L EDTA-2Na mixed solution with pH=8 was placed in a 500mL beaker, and the beaker was placed on an induction cooker and heated and boiled for 15min. The dialysis bag was washed with ultrapure water, and then placed in a 1mmol / L EDTA-2Na solution with pH=8 and boiled for 5min. After the dialysis bag was cleaned with ultrapure water, the untreated CQDs solution was filled into the bag. The dialysis bag containing the solution was placed in a 2L beaker, ultrapure water was added to the scale line, and the dialysis was rotated on a magnetic stirrer for dialysis, with the speed maintained at 850rpm, the time was 24h, and the water change interval was 6h.

[0042] S7. Filter the dialysate with a 0.22 μm filter membrane to obtain a CQDs solution. Freeze the CQDs solution with liquid nitrogen and then perform vacuum freeze-drying. After drying for 48 hours, obtain CQDs powder.

[0043] Example 2: A method for preparing cattail-based carbon quantum dots, the preparation method comprising the following steps: S1. Rinse the stems and leaves of cattail with distillation to remove impurities, then soak them in anhydrous ethanol overnight and boil them for 15 minutes.

[0044] S2. The soaked stems and leaves were decolorized at 100° C. for 20 min, dried at 90° C., cut into small pieces of 1 cm in length, ground, and passed through a 70-mesh sieve to obtain a powder of cattail stems and leaves.

[0045] S3. Mix the leaves and stems in a ratio of 2:1 to obtain a precursor of cattail-based carbon quantum dots; weigh 2 g of the precursor and put it into a polytetrafluoroethylene liner, add 50 mL of ultrapure water at 50°C, and put it into a reactor after ultrasonication for 20 minutes.

[0046] S4. Place the reactor in a high temperature oven, heat it to 180°C, react for 2 hours, and then cool it to room temperature.

[0047] S5. The inner tank was placed in ultrasonic extraction for 50 minutes. The ultrasonic input power was 180W and the power frequency was 50KHZ. After extraction, a 0.45μm filter membrane was used for suction filtration, and then a 0.22μm filter membrane was used for filtration to obtain untreated CQDs.

[0048] S6. The untreated CQDs were dialyzed for 21 hours with a dialysis bag with a molecular weight of 1000Da, and ultrapure water was replaced every 7 hours to obtain a dialysate; specifically, the dialysis bag was cut into small pieces of 10cm, and an appropriate amount of 2% (w / v) sodium bicarbonate and 1mmol / L EDTA-2Na mixed solution with pH=8 was placed in a 500mL beaker, and the beaker was placed on an induction cooker and heated and boiled for 15min. The dialysis bag was washed with ultrapure water, and then placed in a 1mmol / L EDTA-2Na solution with pH=8 and boiled for 5min. After the dialysis bag was cleaned with ultrapure water, the untreated CQDs solution was loaded into the bag. The dialysis bag containing the solution was placed in a 2L beaker, ultrapure water was added to the scale line, and the dialysis was rotated on a magnetic stirrer for dialysis, with the speed maintained at 850rpm, the time was 24h, and the water change interval was 6h.

[0049] S7. Filter the dialysate with a 0.22 μm filter membrane to obtain a CQDs solution. Freeze the CQDs solution with liquid nitrogen and then perform vacuum freeze-drying. After drying for 48 hours, obtain CQDs powder.

[0050] Example 3: A method for preparing cattail-based carbon quantum dots, the preparation method comprising the following steps: S1. Rinse the stems and leaves of cattail with distillation to remove impurities, then soak them in anhydrous ethanol overnight and boil them for 25 minutes.

[0051] S2. The soaked stems and leaves were decolorized at 110° C. for 10 min, dried at 90° C., cut into small pieces of 1 cm in length, ground, and passed through an 80-mesh sieve to obtain a powder of cattail stems and leaves.

[0052] S3. Mix the leaves and stems in a ratio of 3:1 to obtain a precursor of cattail-based carbon quantum dots; weigh 2 g of the precursor and put it into a polytetrafluoroethylene liner, add 50 mL of ultrapure water at 50°C, and put it into a reactor after ultrasonication for 20 minutes.

[0053] S4. Place the reactor in a high temperature oven, heat it to 160°C, react for 4 hours, and then cool it to room temperature.

[0054] S5. The inner liner was placed in ultrasonic extraction for 70 minutes. The ultrasonic input power was 220W and the power frequency was 30KHZ. After extraction, a 0.45μm filter membrane was used for suction filtration, and then a 0.22μm filter membrane was used for filtration to obtain untreated CQDs.

[0055] S6. The untreated CQDs were dialyzed for 30 hours with a dialysis bag with a molecular weight of 1000Da, and ultrapure water was replaced every 6 hours to obtain a dialysate; specifically: the dialysis bag was cut into small pieces of 10cm, and an appropriate amount of 2% (w / v) sodium bicarbonate and 1mmol / L EDTA-2Na mixed solution with pH=8 was placed in a 500mL beaker, and the beaker was placed on an induction cooker and heated and boiled for 15min. The dialysis bag was washed with ultrapure water, and then placed in a 1mmol / L EDTA-2Na solution with pH=8 and boiled for 5min. After the dialysis bag was cleaned with ultrapure water, the untreated CQDs solution was loaded into the bag. The dialysis bag containing the solution was placed in a 2L beaker, ultrapure water was added to the scale line, and the dialysis was rotated on a magnetic stirrer for dialysis, with the speed maintained at 850rpm, the time was 24h, and the water change interval was 6h.

[0056] S7. Filter the dialysate with a 0.22 μm filter membrane to obtain a CQDs solution. Freeze the CQDs solution with liquid nitrogen and then perform vacuum freeze-drying. After drying for 48 hours, obtain CQDs powder.

[0057] Examples 1 to 3 have similar effects. For the convenience of subsequent discussion and reference, the test results of Example 1 shall prevail. The following are the test results of Example 1.

[0058] Experimental Example 1: Characterization of CQDs The present invention firstly characterized the morphology, particle size and surface functional groups of the CQDs prepared in Example 1 by transmission electron microscopy and Fourier transform infrared spectrometer.

[0059] The results are as follows Figure 1 As shown, the CQDs prepared by the present invention are spherical particles with a lattice spacing of 0.22nm, extremely small size, good dispersion and no obvious agglomeration. At the same time, the CQDs surface has a large number of functional groups.

[0060] Experimental Example 2: Potted experiment on the effect of CQDs on wetland plants Ryegrass (Lolium perenne L.) is often used to purify sewage in artificial wetland ecological projects. In the present invention, ryegrass is used as an experimental plant. First, a pot experiment is performed to explore the biosafety of the CQDs prepared in Example 1 on wetland plants, as well as the effects of the concentration and application method of CQDs on wetland plants.

[0061] The concentrations of CQDs are: 0 mg / L; 25 mg / L; 50 mg / L; 75 mg / L; 100 mg / L.

[0062] The CQDs treatment methods are: spraying on plant leaves (P) or adding CQDs directly to the substrate surface (J).

[0063] The experimental process is as follows: Pre-experimental treatment: Place ryegrass seeds in a 500 mL beaker, add distilled water and soak the seeds for 24 hours, then wash the seeds and soak them in 0.5% hypochlorous acid solution for 10 minutes for disinfection. Use filter paper to wipe off excess moisture on the surface of the seeds, select seeds with consistent appearance and fullness and sow them in small potting devices, use sand as the substrate, and start applying CQDs solution after the seeds germinate.

[0064] Preparation of CQDs solution: CQDs powder was dissolved in distilled water to prepare solutions with CQDs concentrations of 0 mg / L, 25 mg / L, 50 mg / L, 75 mg / L, and 100 mg / L, respectively.

[0065] Four experimental groups were set up, with three parallel experiments in each group.

[0066] The first group of experiments: CQDs concentration was 25 mg / L. CQDs were added to the potted system every morning by spraying and acting on the substrate surface. CQDs concentration of 0 mg / L was used as the control. The plant height, root length and biomass of ryegrass were measured 16 days after adding CQDs.

[0067] The second group of experiments: CQDs concentration was 50 mg / L. CQDs were added to the potted system every morning by spraying and acting on the substrate surface. CQDs concentration of 0 mg / L was used as the control. The plant height, root length and biomass of ryegrass were measured 16 days after adding CQDs.

[0068] The third group of experiments: The CQDs concentration was 75 mg / L. CQDs were added to the potted system every morning by spraying and acting on the substrate surface. The CQDs concentration of 0 mg / L was used as the control. The plant height, root length and biomass of ryegrass were measured 16 days after adding CQDs.

[0069] The fourth group of experiments: CQDs concentration was 100 mg / L. CQDs were added to the potted system every morning by spraying and acting on the substrate surface. CQDs concentration of 0 mg / L was used as the control. The plant height, root length and biomass of ryegrass were measured 16 days after adding CQDs.

[0070] The results are as follows Figure 2As shown in the figure, compared with the control group without CQDs, 25 mg / L, 50 mg / L, 75 mg / L, and 100 mg / L CQDs solutions all promoted the root growth of ryegrass, increased plant height, and increased the dry weight and fresh weight of ryegrass. As the concentration of CQDs solution increased, the promoting effect on ryegrass growth and biomass became more significant, and the CQDs solution had the best effect when the concentration was 75 mg / L. Compared with spraying CQDs on the leaves of ryegrass (P), directly applying CQDs to the substrate surface (J) had a better promoting effect on the plant height, root length, and biomass of ryegrass.

[0071] Experimental Example 3: Effects of CQDs on the Salt Stress Resistance of Wetland Plants The present invention further explores the effect of CQDs on the salt stress resistance of wetland plants through an artificial wetland plant stress resistance device system. The specific experimental steps are as follows: (1) Construction of artificial wetland system device: The artificial wetland device selected a conventional artificial wetland (0.6m-CW), the material selected was DN150 organic glass, the device height was 70cm, and the matrix was gravel (5-15mm) and sand. The matrix layer was 60cm high (gravel 40cm + sand 20cm), with an emptying pipe at the bottom of the device and a water inlet pipe at the top, and the effective volume was 2.8L.

[0072] (2) The simulated domestic sewage configuration includes the following components with final mass concentrations: 114.64 mg / L NH4 + -N, 21.95 mg / L KH2PO4, 140.75 mg / L C6H 12 O6, 59.16 mg / L CH3COONa and 0.75 mL / L trace element concentrate. The trace element concentrate includes the following subcomponents with the following final concentrations: 8630 mg / L Na2EDTA, 640 mg / L ZnSO4·7H2O, 360 mg / L CoCl2·6H2O, 490 mg / L MnCl2·4H2O, 130 mg / L CuSO4·5H2O, 330 mg / L Na2MoO4·2H2O, 280 mg / L NiCl2·6H2O, 310 mg / L NaSeO4·10H2O and 14 mg / L H3BO3.

[0073] (3) Pretreatment before stress: Place ryegrass seeds in a 500 mL beaker, add an appropriate amount of distilled water, soak for 24 h, then clean the seeds and soak them in 0.5% hypochlorous acid solution for 10 min for disinfection. Wipe off excess moisture on the surface of the seeds with filter paper, select seeds with consistent appearance and plumpness and sow them in the artificial wetland system device, water the system every morning, and after ryegrass germinates, culture it with Hogland nutrient solution for 7 days when the growth is consistent, and then use artificial domestic sewage to cultivate the system for 30 days. After the system is stable, apply salt stress, set two salt stress conditions with 0.5% NaCl and 1% NaCl concentration gradients, and use the 75 mg / L CQDs solution as the treatment group, and the wetland system without CQDs as the blank control group.

[0074] (4) A subsurface artificial wetland system was used with an intermittent water inlet method, an effective volume of 3.7 L, artificial water inlet and outlet, a water exchange ratio of 100%, and a hydraulic retention time of 3 days. The time for each operation stage was: 0.5 h for water inlet and 0.5 h for water discharge.

[0075] Three groups of experiments were set up respectively: The first group of experiments (CK): 2.8L of simulated domestic sewage was added to the artificial wetland system, the water was changed every 3 days, and the system was operated for 30 days.

[0076] The second group of experiments (Na-0.5 and Na-1): 14g and 28g NaCl were added to 2.8L of simulated domestic sewage, respectively, to obtain biological domestic sewage with salt concentrations of 0.5% and 1%. The water was changed every 3 days, and the simulated domestic sewage without NaCl was used as a blank control. After running for 30 days, the ryegrass leaves at the end of the system operation were taken to measure the antioxidant system enzyme activities (ROS, MDA, T-AOC).

[0077] The third group of experiments (CDs-0.5 and CDs-1): 14g and 28g NaCl were added to 2.8L of simulated domestic sewage to obtain biological domestic sewage with salt concentrations of 0.5% and 1%. The water was changed every 3 days, and 100 mL of 75mg / L CQDs solution was added to the substrate surface every day; the wetland system with 0.5% and 1% salt concentration without CQDs solution treatment was used as a blank control, and the system was operated for 30 days. The ryegrass leaves at the end of the system operation were taken to measure the antioxidant system enzyme activity (ROS, MDA, T-AOC).

[0078] The experimental results are as follows Figure 3As shown in the figure, compared with the CK group, in the 0.5% NaCl (Na-0.5) and 1% NaCl (Na-1) environments, the stems and leaves of ryegrass quickly turned yellow and dried up with the running time, which significantly inhibited the growth of the upper height of the ryegrass, significantly reduced the plant height and root length, and reduced the biomass. The higher the NaCl concentration, the more significant the inhibitory effect. Compared with the Na-0.5 group and the Na-1 group, the addition of CQDS (CDs-0.5) under 0.5% NaCl conditions and the addition of CQDS (CDs-1) under 1% Nacl conditions significantly delayed the time for ryegrass to turn yellow, promoted the plant height and root growth of ryegrass, and increased the biomass.

[0079] like Figure 4 As shown in the figure, compared with the CK group, in the Na-0.5 and Na-1 groups, the ROS content in the ryegrass leaves increased with the increase of NaCl concentration, and significantly increased in the Na-1 group; the MDA level and T-AOC enzyme activity also increased significantly. Compared with the Na-0.5 and Na-1 groups, the ROS content in the ryegrass leaves in the CDs-0.5 and CDs-1 groups decreased significantly; the MDA level and T-AOC activity also decreased significantly.

[0080] like Figure 5 As shown in the figure, with the increase of operation time, the wetland system has a significant impact on ammonia nitrogen (NH4 + -N), total phosphorus (TP) and chemical oxygen demand (COD) also gradually decreased. Compared with the CK group, the salt stress environment reduced the wetland system's ability to remove NH4 + -N, TP and COD removal rates. After adding CQDs, the removal of NH4 + -N, TP and COD removal rates.

[0081] The above results show that adding CQDs solution to the artificial wetland system under salt stress can significantly remove ROS accumulated in ryegrass leaves, reduce MDA and T-AOC levels, and promote the growth of ryegrass stems, leaves and roots. At the same time, adding CQDs can also improve the wetland system's resistance to NH4 + -N, TP and COD removal rates, reducing the concentration of pollutants in the effluent of the wetland system.

[0082] It should be noted that when the present invention involves a numerical range, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes a preferred embodiment. Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the attached claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0083] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing cattail-based carbon quantum dots, characterized in that: The following steps are involved: The cattail is soaked in ethanol, boiled to remove color, blanched and decolorized, and ground and sieved to obtain a precursor; The precursor is placed in a hydrothermal reaction at 160°C~180°C for 2h~4h, and the reaction solution is subjected to ultrasonic extraction, filtration and dialysis to obtain cattail-based carbon quantum dots.

2. The preparation method according to claim 1, characterized in that: The boiling time is 15min-25min; the conditions for the fixing are: temperature 100°C-110°C, time 10min-20min.

3. The preparation method according to claim 1, characterized in that: The cattail is any one or more of cattail leaf, cattail stem and cattail inflorescence; the mesh number of the sieving is 60-80 mesh.

4. The preparation method according to claim 3, characterized in that: The cattails are cattail leaves and cattail stems, and the mixed mass ratio of the cattail leaves to the cattail stems is 2-3:

1.

5. The preparation method according to claim 1, characterized in that: The ultrasonic time is 50min~70min, the ultrasonic input power is 180W~220W, and the power frequency is 30KHZ~50KHZ; the dialysis is carried out in a 1000Da dialysis bag, the dialysis time is 21h~30h, and the water is changed 2 times~4 times during the dialysis process; and drying is required after the dialysis.

6. A cattail-based carbon quantum dot prepared by the preparation method according to any one of claims 1 to 5.

7. A use of the cattail-based carbon quantum dots according to claim 6 in improving the ability of plants to resist abiotic stress, characterized in that: The abiotic stress is salt stress, nitrogen stress or water stress.

8. A method for improving the resistance of wetland plants to abiotic stress, characterized in that: The method comprises: spraying an aqueous solution containing the cattail-based carbon quantum dots described in claim 6 onto the surface of wetland plants or a wetland system matrix; the concentration of the cattail-based carbon quantum dots in the cattail-based carbon quantum dot aqueous solution is 25 mg / L to 100 mg / L.

9. Use of the cattail-based carbon quantum dots according to claim 6 in improving the antioxidant capacity of plants.

10. Use of the cattail-based carbon quantum dots according to claim 6 in improving the removal rate of ammonia nitrogen, total phosphorus or chemical oxygen demand in a wetland system.

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