Application of graphene oxide / zinc oxide composite nanomaterials in improving soil pollution caused by cadmium heavy metal and methods for soil improvement

Abstract

This invention discloses the application of a graphene oxide / zinc oxide composite nanomaterial in improving soil pollution caused by cadmium. The graphene oxide / zinc oxide composite nanomaterial is a composite nanomaterial formed by the covalent bonding of nano-graphene oxide and nano-zinc oxide. During soil improvement, the composite nanomaterial is directly added to the soil as a solution to exert its effect. In this invention, the graphene oxide / zinc oxide composite nanomaterial can significantly reduce the bioavailability of cadmium in soil and improve soil physicochemical properties such as pH, organic matter content, available cadmium content, and cation exchange capacity. Compared to other nanomaterials, the application of the graphene oxide / zinc oxide composite nanomaterial exhibits high specificity, high antagonistic efficiency, rapid action, and ease of operation, and it can effectively improve some of the physicochemical properties of soil, showing promising application prospects in environmental remediation for reducing cadmium pollution in the soil environment.

Description

Technical Field

[0001] This invention relates to the field of environmental protection and remediation technology, specifically to the application of graphene oxide / zinc oxide composite nanomaterials in improving soil pollution caused by heavy metal cadmium and a method for soil improvement. Background Technology

[0002] Currently, the main methods for remediating cadmium in soil include planting hyperaccumulating plants and applying nano-sized soil heavy metal amendments. Planting hyperaccumulating plants involves considerations of plant adaptability to the growing environment, remediation time, remediation efficiency, and subsequent plant treatment. Conversely, applying nano-sized soil amendments can reduce the bioavailability of cadmium in soil to some extent, but it can also cause other environmental pollution problems. For example, the commonly used method of applying nZVI (nano-zero valent iron) to soil can adsorb and bind various heavy metals and organic pollutants in the soil. When these pollutants aggregate, they can cause new environmental problems, and the slowly released iron ions can also affect soil properties and soil protozoa. Furthermore, it has been reported that nano-sized soil amendments have low passivation efficiency for cadmium in soil and a weak effect in reducing bioavailability. Existing research results show that graphene oxide nanomaterials can passivate cadmium in soil and reduce its bioavailability; however, single nano-sized soil amendments have problems such as low remediation efficiency and slow effect. Composite nano-sized soil amendments have good application prospects.

[0003] Chinese patent application document CN108938666A discloses a method for antagonizing the toxicity of heavy metal Cd based on ZnO / GO composite nanomaterials. It can specifically and effectively prevent and detoxify Cd poisoning in organisms, but it does not disclose its application in soil environments. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an application of graphene oxide / zinc oxide composite nanomaterials in improving soil pollution caused by heavy metal cadmium and a method for soil improvement.

[0005] The present invention solves the above-mentioned technical problems through the following technical means:

[0006] The application of a graphene oxide / zinc oxide composite nanomaterial in improving soil pollution caused by heavy metal cadmium, wherein the graphene oxide / zinc oxide composite nanomaterial is a composite nanomaterial formed by the covalent bonding of nano-graphene oxide and nano-zinc oxide.

[0007] Preferably, the nano zinc oxide is spherical nanoparticles with a particle size of 5-10 nm.

[0008] Preferably, the preparation method of the graphene oxide / zinc oxide composite nanomaterial includes the following steps:

[0009] S1. Dissolve zinc acetate in anhydrous ethanol, heat and stir to obtain zinc acetate solution; add lithium hydroxide ethanol solution to graphene oxide dispersion to obtain mixed solution;

[0010] S2. After cooling the zinc acetate solution, add it to the mixture and stir to react. After the reaction is complete, a reaction solution is obtained. Add n-hexane to the reaction solution, let it stand, and separate the solid and liquid to obtain the graphene oxide / zinc oxide composite nanomaterial.

[0011] Preferably, in S1, the mass-to-volume ratio of zinc acetate to anhydrous ethanol is 0.25-0.75 g: 45-55 mL; the stirring after heating includes heating to 75-85°C and stirring for 15-25 min; the concentration of the lithium hydroxide ethanol solution is 0.006-0.017 g / mL; the mass concentration of graphene oxide in the graphene oxide dispersion is 2 mg / mL; and the mass ratio of lithium hydroxide in the lithium hydroxide ethanol solution to graphene oxide in the graphene oxide dispersion is 0.15-0.25 g: 50-70 mg.

[0012] Preferably, in step S2, the zinc acetate solution is cooled to 45-55°C and then added to the mixture; the stirring reaction time is 35-45 min; the mass ratio of zinc acetate in the zinc acetate solution to graphene oxide in the mixture is 0.25-0.75 g: 50-70 mg.

[0013] Preferably, in S2, the volume ratio of the reaction solution to n-hexane is 1:2; the standing temperature is 3-5°C, and the time is 8-12 hours.

[0014] This invention also proposes a method for improving soil contaminated with the heavy metal cadmium, comprising the following steps:

[0015] S1. Prepare a solution from the graphene oxide / zinc oxide composite nanomaterials.

[0016] S2. Apply the solution from S1 to soil contaminated with the heavy metal cadmium to improve the soil.

[0017] Preferably, in S1, the concentration of the solution is 30-50 μg / mL.

[0018] Preferably, the mass of the solvent in the applied solution is 20-25% of the mass of the soil contaminated with the heavy metal cadmium.

[0019] Preferably, in S2, the soil improvement time is ≥14 days.

[0020] The advantages of this invention are:

[0021] 1. The treatment method is simple and quick. A solution of graphene oxide / zinc oxide composite nanomaterials can be directly added to the soil to exert its effect, showing broad application prospects in the development of novel soil heavy metal amendments.

[0022] 2. Significant effect in reducing the ecotoxicity of cadmium in soil. The graphene oxide / zinc oxide composite nanomaterial solution began to take effect after one day of exposure to cadmium-contaminated soil (beginning to reduce the toxicity of heavily cadmium-contaminated cadmium to nematodes), and after 14 days, it could basically return to normal levels (the toxicity of nematodes caused by heavily cadmium-contaminated cadmium was basically restored).

[0023] 3. Excellent soil amendment properties. Compared with other reported nanomaterials applied to cadmium-contaminated soils, graphene oxide / zinc oxide composite nanomaterials have the advantages of rapid effectiveness and high efficiency, and have good application prospects in the environmental remediation of cadmium pollution in soil environments.

[0024] In summary, the graphene oxide / zinc oxide composite nanomaterials of this invention can significantly reduce the ecotoxicity of cadmium-induced soil invertebrate *Caenorhabditis elegans* (reducing the bioavailability of cadmium in the soil), and can also improve soil physicochemical properties such as pH, soil organic matter content, soil available cadmium content, and soil cation exchange capacity. Compared with some nanomaterials already used for the remediation of heavy metal cadmium in soil, the graphene oxide / zinc oxide composite nanomaterials of this invention exhibit strong specificity, high antagonistic efficiency, rapid action, and ease of operation, and can effectively improve some of the physicochemical properties of soil, showing promising application prospects in the environmental remediation of heavy metal cadmium pollution in the soil environment. Attached Figure Description

[0025] Figure 1 This is a flowchart of the soil treatment process in Embodiment 1 of the present invention;

[0026] Figure 2 The Fourier transform infrared (FT-IR) spectrum characterization of the graphene oxide / zinc oxide composite nanomaterial prepared in Example 1 of this invention is shown below.

[0027] Figure 3 This is a diagram illustrating the antagonistic effect of applying graphene oxide / zinc oxide composite nanomaterials under different exposure time gradients on the growth (body length) of Caenorhabditis elegans in cadmium-contaminated soil in Example 1 of the present invention.

[0028] Figure 4 This is a diagram illustrating the antagonistic effect of applying graphene oxide / zinc oxide composite nanomaterials under different exposure time gradients on the reproduction (offspring number) of Caenorhabditis elegans in cadmium-contaminated soil in Example 1 of the present invention.

[0029] Figure 5This is a graph showing the change in soil pH after applying graphene oxide / zinc oxide composite nanomaterials in Example 1 of the present invention.

[0030] Figure 6 This is a graph showing the change in soil organic matter content after applying graphene oxide / zinc oxide composite nanomaterials in Example 1 of the present invention.

[0031] Figure 7 This is a graph showing the change in available cadmium content in the soil after applying graphene oxide / zinc oxide composite nanomaterials in Example 1 of the present invention.

[0032] Figure 8 This is a graph showing the change in soil cation exchange capacity after applying graphene oxide / zinc oxide composite nanomaterials in Example 1 of the present invention.

[0033] Figure 9 This is a comparison of the antagonistic effects of graphene oxide / zinc oxide composite nanomaterials and other nanomaterials on the growth (body length) of Caenorhabditis elegans in cadmium-contaminated soil in Example 1 of the present invention (the comparison is based on an application time of 14 days, i.e., the time gradient of the basic recovery of Caenorhabditis elegans toxicity caused by severe cadmium pollution after the application of graphene oxide / zinc oxide composite nanomaterials).

[0034] Figure 10 This is a comparison chart of the antagonistic effects of the application of graphene oxide / zinc oxide composite nanomaterials and other nanomaterials on the reproduction (offspring number) of Caenorhabditis elegans in cadmium-contaminated soil in Example 1 of the present invention (the comparison is based on an application time of 14 days, i.e. the time gradient of the basic recovery of Caenorhabditis elegans toxicity caused by severe cadmium pollution after the application of graphene oxide / zinc oxide composite nanomaterials).

[0035] Figure 11 This is a comparison chart of the effects of graphene oxide / zinc oxide composite nanomaterials and other nanomaterials on soil pH in cadmium-contaminated soil in Example 1 of the present invention (the comparison is based on a 14-day application period, i.e., the time gradient of the basic recovery of cadmium-induced nematode toxicity caused by the application of graphene oxide / zinc oxide composite nanomaterials).

[0036] Figure 12 This is a comparison chart of the effects of applying graphene oxide / zinc oxide composite nanomaterials and other nanomaterials on the soil organic matter content in cadmium-contaminated soil in Example 1 of the present invention (the comparison is based on a 14-day application period, i.e., the time gradient of the basic recovery of cadmium-induced nematode toxicity caused by the application of graphene oxide / zinc oxide composite nanomaterials).

[0037] Figure 13This is a comparison chart of the effective cadmium content in cadmium-contaminated soil after the application of graphene oxide / zinc oxide composite nanomaterials and other nanomaterials in Example 1 of the present invention (the comparison is based on an application time of 14 days, i.e., the time gradient of the basic recovery of cadmium toxicity caused by severe cadmium pollution after the application of graphene oxide / zinc oxide composite nanomaterials).

[0038] Figure 14 This is a comparison chart of the effects of applying graphene oxide / zinc oxide composite nanomaterials and other nanomaterials on the cation exchange capacity of cadmium-contaminated soil in Example 1 of the present invention (the comparison is based on a 14-day application period, i.e., the time gradient of the basic recovery of cadmium-induced toxicity in *C. elegans* caused by the application of graphene oxide / zinc oxide composite nanomaterials). Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0041] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0042] Example 1

[0043] (1) Synthesis of graphene oxide / zinc oxide composite nanomaterials (GO / ZnO): Zinc acetate, lithium hydroxide, anhydrous ethanol, and n-hexane required for the synthesis were all purchased from Sinopharm Chemical Reagent Co., Ltd. The anhydrous ethanol-dispersed nano-graphene oxide dispersion was purchased from Nanjing Xianfeng Nanomaterials Technology Co., Ltd. The specific synthesis steps are as follows: ① Weigh 0.55g of zinc acetate and dissolve it in 50mL of anhydrous ethanol, stirring at 80℃ for 20 minutes. ② Weigh 0.2g of lithium hydroxide and dissolve it in 20mL of anhydrous ethanol. ③ Add the dissolved lithium hydroxide solution to 30mL of the 2mg / mL nano-graphene oxide dispersion. ④ After the zinc acetate solution is stirred, when the temperature drops to 50℃, add the mixture of lithium hydroxide and graphene oxide to the zinc acetate solution, stirring for 40 minutes to obtain a mixed solution. ⑤ After the reaction is complete, add n-hexane equivalent to twice the volume of the mixed solution, and let it stand at 4℃ for 12 hours. ⑥ Centrifuge and discard the supernatant. Wash the material with anhydrous ethanol and ultrapure water respectively. Centrifuge to collect the product, and you will get graphene oxide / zinc oxide composite nanomaterials.

[0044] To understand the structure of the graphene oxide / zinc oxide composite nanomaterial, Fourier transform infrared spectroscopy was used for its characterization. Figure 2 As shown in the Fourier transform infrared spectrum of the graphene oxide / zinc oxide composite nanomaterial, different absorption peaks indicate that the surface of the graphene oxide / zinc oxide composite nanomaterial contains abundant functional groups such as hydroxyl and carbonyl groups.

[0045] (2) The specific soil treatment flowchart is as follows: Figure 1 As shown, soil culture: In this example, CdCl2 was purchased from Sinopharm Chemical Reagent Co., Ltd. and prepared into a 20 μmol / L CdCl2 aqueous solution. The prepared CdCl2 aqueous solution was added to the test soil, wherein the mass of water in the CdCl2 aqueous solution was 22% of the mass of the soil. During the process, the total mass of the system was kept constant, and cadmium-contaminated soil was obtained after 30 days of culture.

[0046] (3) Application of graphene oxide / zinc oxide composite nanomaterials to cadmium-contaminated soil: A 40 μg / mL aqueous solution of graphene oxide / zinc oxide composite nanomaterials was added to cadmium-contaminated soil. The water content in the aqueous solution was 22% of the soil content. The soil was exposed at time gradients of 1, 7, 14 and 30 days. Each time gradient was divided into a blank soil control group, a cadmium-contaminated soil treatment group, and a cadmium-contaminated soil treatment group exposed to graphene oxide / zinc oxide composite nanomaterials. The total system mass was kept constant during the incubation period.

[0047] (4) Detection of the antagonistic effect of graphene oxide / zinc oxide composite nanomaterials on the toxicity of soil cadmium to soil nematodes (C. elegans): The antagonistic efficiency of graphene oxide / zinc oxide composite nanomaterials on the bioavailability of soil cadmium was evaluated using ecotoxicological indicators of cultured nematodes in soil. The specific steps are as follows: ① The blank soil control group, the cadmium-contaminated soil treatment group, and the soil treated with graphene oxide / zinc oxide composite nanomaterials exposed to cadmium-contaminated soil were sieved through a 2 mm sieve. The experiment was conducted according to the detection of ecotoxicology of nematodes in soil in ISO 10872 standard. The experiment was carried out in a 12-well plate. Each well was filled with: 0.3 g of test soil, 0.2 mL of K-medium solution, 0.5 mL of Escherichia coli OP50 concentrated bacteria, and 10 L1 stage nematodes. ② After the experimental treatment, *C. elegans* needs to be extracted from the soil. The specific extraction steps are as follows: First, add 0.5 mL of Bengal rose red dye to each experimental well to stain the *C. elegans*. Heat the 12-well plate used in the experiment in an 80℃ oven for 10 minutes to terminate the measurement. Wash the soil and *C. elegans* from each treatment well into a centrifuge tube with 5 mL of ultrapure water. After thorough mixing, centrifuge at 800 x g for 5 minutes. After discarding the supernatant, resuspend the particles in 2 mL of an extraction solution containing colloidal SiO2 (Ludox TM50, Sigma) and deionized water at a volume ratio of 1:2. After thorough mixing, centrifuge at 800 x g for 5 minutes to extract the nematodes. ③ After culturing *C. elegans* in soil for 48 hours, extract the nematodes and measure their body length under a fluorescence microscope. After culturing for 96 hours, extract the nematodes and measure the number of progeny under a stereomicroscope.

[0048] The ecotoxicological effects of treated soils were determined according to the standard method described in ISO 10872 (2020), using the developmental (body length) and reproductive (progeny number) indicators of *C. elegans* in the treated soil. The developmental indicators (body length) and reproductive (progeny number) of *C. elegans* are as follows: Figure 3 and Figure 4 As shown, the graphene oxide / zinc oxide composite nanomaterials, when added to cadmium-contaminated soil, can mitigate the toxic effects of available cadmium in the soil on *C. elegans*, effectively reducing the impact of available cadmium on the development and reproduction of *C. elegans*. This mitigating effect essentially eliminated the developmental toxicity of available cadmium in the soil on nematodes by day 14. These results demonstrate that the addition of graphene oxide / zinc oxide composite nanomaterials can effectively reduce the bioavailability of the heavy metal cadmium in soil, and the effect is short-lived.

[0049] (5) Improvement of some soil physicochemical properties after application of graphene oxide / zinc oxide composite nanomaterial aqueous solution. After application of the graphene oxide / zinc oxide composite nanomaterial aqueous solution, the soil pH ( Figure 5The levels of organic matter in the soil have increased to some extent, which has a certain effect on alleviating soil acidification; it can increase the content of organic matter in the soil. Figure 6 It also has a certain effect on increasing soil fertility; it significantly reduces the content of available cadmium in the soil. Figure 7 This reduces the bioavailability of cadmium in the soil; it also affects the soil cation exchange capacity (COC). Figure 8 It has a certain improvement and is effective in enhancing the soil's fertilizer retention capacity; among them, Figure 5-8 In the text, Ctrl represents uncontaminated soil, Cd-spiked represents cadmium-contaminated soil, and GO / ZnO+Cd represents cadmium-contaminated soil after application of an aqueous solution of graphene oxide / zinc oxide composite nanomaterials.

[0050] (6) Ecotoxicity of *C. elegans* after application of graphene oxide / zinc oxide composite nanomaterials and other nanomaterials ( Figure 9-10 Comparison of related soil physicochemical properties () Figure 11-14 It can also be found that, compared with some reported nanomaterials that have antagonistic effects on cadmium toxicity, graphene oxide / zinc oxide composite nanomaterials have the advantages of rapid effect and high efficiency.

[0051] In the figure, Control represents the blank control group (the blank control group is soil without cadmium solution addition), Cd-contaminated represents the cadmium-contaminated soil treatment group (the cadmium-contaminated soil treatment group is soil contaminated with cadmium solution addition), GO / ZnO+Cd represents the cadmium-contaminated soil treatment group exposed to graphene oxide / zinc oxide composite nanomaterials (representing the treatment group where GO / ZnO is added to the cadmium-contaminated soil in (2) according to the method described in (3) above), GO+Cd represents the cadmium-contaminated soil in (2) exposed to 40 μg / mL graphene oxide aqueous solution, where the mass of water in the graphene oxide aqueous solution is 22% of the soil mass, ZnO+Cd represents the cadmium-contaminated soil in (2) exposed to 40 μg / mL zinc oxide aqueous solution, where the mass of water in the zinc oxide aqueous solution is 22% of the soil mass, and ... ions+Cd indicates that 40 μg / mL zinc chloride aqueous solution was added to the cadmium-contaminated soil in (2) for exposure, wherein the mass of water in the zinc chloride aqueous solution was 22% of the mass of the soil, and T=1, T=7, T=14 and T=30 represent the number of exposure days.

[0052] The above specific embodiments illustrate the technical approach of the present invention in detail. However, the invention is not limited to the heavy metal cadmium and the selected test soil—Hubei paddy soil according to the national standard soil GBW07415a (ASA-4a). The implementation of this technical solution may also include other pollutants containing the heavy metal cadmium, as well as other model organisms and test soils. Therefore, this should not be used to limit the scope of protection of the present invention. Any changes or modifications made without departing from the principles of the present invention should fall within the scope of protection of the present invention.

[0053] Example 2

[0054] We used the GO / ZnO composite nanomaterial from Example 1 in soil samples taken from a mining area near Tongling, where cadmium pollution was the main heavy metal contamination (available cadmium content in the soil was approximately 7.0-8.0 mg / kg). The addition of GO / ZnO also promoted the remediation of soil pH, soil organic matter content, soil cation exchange capacity, available cadmium in the soil, and soil ecotoxicity.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. The application of a graphene oxide / zinc oxide composite nanomaterial in improving soil pollution caused by heavy metal cadmium, wherein the graphene oxide / zinc oxide composite nanomaterial is a composite nanomaterial formed by the covalent bonding of nano-graphene oxide and nano-zinc oxide; the application process includes the following steps: S1. Prepare a solution from the graphene oxide / zinc oxide composite nanomaterials. S2. Apply the solution from S1 to soil contaminated with the heavy metal cadmium to improve the soil.

2. The application of the graphene oxide / zinc oxide composite nanomaterial according to claim 1 in improving soil pollution caused by heavy metal cadmium, characterized in that: The zinc oxide nanoparticles are spherical nanoparticles with a particle size of 5-10 nm.

3. The application of the graphene oxide / zinc oxide composite nanomaterial according to claim 1 in improving soil pollution caused by heavy metal cadmium, characterized in that: The preparation method of the graphene oxide / zinc oxide composite nanomaterial includes the following steps: S1. Dissolve zinc acetate in anhydrous ethanol, heat and stir to obtain zinc acetate solution; add lithium hydroxide ethanol solution to graphene oxide dispersion to obtain mixed solution; S2. After cooling the zinc acetate solution, add it to the mixture and stir to react. After the reaction is complete, a reaction solution is obtained. Add n-hexane to the reaction solution, let it stand, and separate the solid and liquid to obtain the graphene oxide / zinc oxide composite nanomaterial.

4. The application of the graphene oxide / zinc oxide composite nanomaterial according to claim 3 in improving soil pollution caused by heavy metal cadmium, characterized in that: In S1, the mass-to-volume ratio of zinc acetate to anhydrous ethanol is 0.25-0.75 g: 45-55 mL; the stirring after heating includes heating to 75-85°C and stirring for 15-25 min; the concentration of the lithium hydroxide ethanol solution is 0.006-0.017 g / mL; the mass concentration of graphene oxide in the graphene oxide dispersion is 2 mg / mL; and the mass ratio of lithium hydroxide in the lithium hydroxide ethanol solution to graphene oxide in the graphene oxide dispersion is 0.15-0.25 g: 50-70 mg.

5. The application of the graphene oxide / zinc oxide composite nanomaterial according to claim 3 in improving soil pollution caused by heavy metal cadmium, characterized in that: In step S2, the zinc acetate solution is cooled to 45-55°C and then added to the mixture; the stirring reaction time is 35-45 min; the mass ratio of zinc acetate in the zinc acetate solution to graphene oxide in the mixture is 0.25-0.75 g: 50-70 mg.

6. The application of the graphene oxide / zinc oxide composite nanomaterial according to claim 3 in improving soil pollution caused by heavy metal cadmium, characterized in that: In S2, the volume ratio of the reaction solution to n-hexane is 1:2; the settling temperature is 3-5℃ and the time is 8-12h.

7. A method for improving soil contaminated with the heavy metal cadmium, characterized in that: Includes the following steps: S1. Prepare a solution from the graphene oxide / zinc oxide composite nanomaterial according to any one of claims 1-6; S2. Apply the solution from S1 to soil contaminated with the heavy metal cadmium to improve the soil.

8. The method for improving soil contaminated with heavy metal cadmium according to claim 7, characterized in that: In S1, the concentration of the solution is 30-50 μg / mL.

9. The method for improving soil contaminated with heavy metal cadmium according to claim 7, characterized in that: The mass of the solvent in the applied solution is 20-25% of the mass of the soil contaminated with the heavy metal cadmium.

10. The method for improving soil contaminated with the heavy metal cadmium according to any one of claims 7-9, characterized in that: In S2, the soil improvement time is ≥14 days.

Images