CN115044379A - Heavy metal contaminated soil remediation agent based on graphene oxide and application thereof - Google Patents
Heavy metal contaminated soil remediation agent based on graphene oxide and application thereof Download PDFInfo
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Abstract
The invention discloses a heavy metal contaminated soil remediation agent based on graphene oxide and application thereof. The heavy metal contaminated soil remediation agent comprises the following raw materials in parts by weight: 35-65 parts of graphene oxide/cellulose composite material, 8-18 parts of hydrotalcite-like compound loaded with elemental sulfur, 5-12 parts of peanut bran, 2-6 parts of pH regulator and 20-30 parts of chitosan grafted polyvinyl alcohol emulsion. According to the invention, the heavy metal contaminated soil remediation agent is obtained by mixing the raw materials, the prepared heavy metal contaminated soil remediation agent is applied to soil, and the raw materials act synergistically, so that variable negative charges on the surface of the soil can be increased, the adsorption of soil colloid on effective cadmium is promoted, and the effectiveness of heavy metal cadmium in the soil is reduced, thereby shortening the remediation period, improving the remediation efficiency, and simultaneously improving the fertility of the soil, so that the soil remediation comprehensive effect is good, and the production process is simple, the cost is low, and the soil remediation agent has a good environmental effect in the soil.
Description
Technical Field
The invention relates to the field of soil remediation, in particular to a heavy metal contaminated soil remediation agent based on graphene oxide and application thereof.
Background
With the rapid development of industry, a large amount of heavy metal cadmium enters soil, so that the heavy metal cadmium in the soil exceeds the standard, the cadmium pollution phenomenon is more and more serious, cadmium is absorbed in the growth and development process of plants and is accumulated in a food chain, and the health of human beings is further influenced. Therefore, the treatment and restoration of the heavy metal cadmium polluted soil become an important environmental protection task at present. The current remediation technology for cadmium-contaminated soil mainly comprises three modes: firstly, a physical mode comprises soil dressing, deep ploughing and soil turning, leaching, soil washing, electric repairing and the like, the repairing effect is obvious, but the cost is high, and large-area popularization is difficult; secondly, a biological mode is adopted, wherein some animals, plants and soil microorganisms are generally used for absorbing cadmium contained in soil, and then the cadmium is recycled; and thirdly, a chemical mode is adopted, including a chemical preparation, a passivating agent, soil clay and organic matters addition, complexing extraction and the like, and the method has the advantages of simplicity in operation, better treatment effect, moderate cost and the like.
Heavy metal ions exist in various forms in soil, wherein the form of heavy metal having mobility has special significance for plant growth and is generally called an available state. When the concentration of the heavy metal in the effective state in the soil solution is too high, certain measures are necessary to reduce the absorption and accumulation of the heavy metal by plants. The in-situ fixation remediation technology is characterized in that a remediation agent is added into soil to adjust and change the physical and chemical properties of heavy metal in the soil, so that the heavy metal is subjected to a series of reactions such as precipitation, adsorption, ion exchange, humification, oxidation-reduction and the like, thereby converting the heavy metal into a form with relatively stable chemical properties, reducing the content of an effective state of the heavy metal in a soil environment, and further reducing the toxicity of the heavy metal elements to animals and plants. Currently, commonly used repair agents include inorganic passivators, organic passivators, and organic-inorganic composite passivators.
Because the existing passivator has the defects of low passivation stability, low passivation strength, difficult recovery and easy secondary pollution, when the external environment is changed, heavy metal ions are easy to release again, and the passivation (fixing) effect is greatly influenced.
The carbon nano material has a large specific surface area and a fine porous structure, so that the carbon nano material has strong adsorption capacity, simultaneously has huge negative charges on the surface of the carbon nano material, has high density of the charges, has groups similar to hydroxyl and the like, and can adsorb heavy metals. Therefore, the mobility and the biological effectiveness of the heavy metal are weakened, so that the aim of repairing the soil polluted by the heavy metal is fulfilled, and the method is widely applied to the field of heavy metal treatment of water and soil in recent years. Graphene is a typical carbon nanomaterial, Graphene Oxide (GO) is surface functionalized graphene with a 2D crystal form independent lamellar structure, contains multiple functional groups such as hydroxyl, epoxy, carbonyl, carboxyl and the like, has unique huge specific surface area and abundant functional groups, can perform physical and chemical reaction with pollutants, adsorbs passivated pollutants, and further has good removing capability on the pollutants.
In view of the above, the invention provides a heavy metal contaminated soil remediation agent based on graphene oxide and an application thereof.
Disclosure of Invention
The invention provides a heavy metal polluted soil repairing agent based on graphene oxide and application thereof to solve the problems.
In order to achieve the purpose, the invention adopts the following technical scheme:
the heavy metal contaminated soil remediation agent based on the graphene oxide comprises the following raw materials in parts by weight: 35-65 parts of graphene oxide/cellulose composite material, 8-18 parts of hydrotalcite-like compound loaded with elemental sulfur, 5-12 parts of peanut bran, 2-6 parts of pH regulator and 20-30 parts of chitosan grafted polyvinyl alcohol emulsion.
Preferably, the graphene oxide/cellulose composite material is prepared by compounding carboxylated cellulose microspheres and amino-functionalized graphene oxide.
Preferably, the preparation of the graphene oxide/cellulose composite material comprises the following steps: (1) preparing graphene oxide by using a Hummers method, dispersing the graphene oxide in deionized water, adding a polyamino polymer and a potassium hydroxide solution into a dispersion liquid, and stirring for reaction to obtain amino functionalized graphene oxide; wherein the mass ratio of the graphene oxide to the polyamino polymer is 100: 2-12; (2) dispersing a mercaptosilane coupling agent into a carboxylated cellulose microsphere suspension, and freeze-drying to obtain the modified cellulose microsphere, wherein the mass ratio of the carboxylated cellulose microsphere to the mercaptosilane coupling agent is 10: 0.5 to 1; (3) adding modified cellulose microspheres into amino functionalized graphene oxide, stirring and mixing, then adding a cross-linking agent into a system, carrying out heat preservation reaction, carrying out centrifugal separation, washing, freeze drying and grinding to obtain a graphene oxide/cellulose composite material, wherein the mass ratio of the modified cellulose microspheres to the amino functionalized graphene oxide to the cross-linking agent is 3: 8-12: 0.1 to 0.5.
Preferably, the polyamino polymer is a polyamide-amine Polymer (PAMAM).
Preferably, the crosslinking agent is any one of epichlorohydrin, glutaraldehyde, diazobenzidine-2, 2' -disulfonic acid or phenol-2, 4-disulfonyl chloride.
Preferably, the graphene oxide is loaded with zero-valent iron graphene oxide.
Preferably, the preparation of the hydrotalcite-like compound loaded with elemental sulfur comprises the following steps: dispersing hydrotalcite-like compound into deionized water to obtain a suspension, adding sulfite and sulfide into the suspension under stirring, adding dilute sulfuric acid to adjust the pH to 3.0-5.0, reacting at room temperature, dehydrating, drying and crushing to obtain hydrotalcite-like compound loaded with elemental sulfur, wherein the mass ratio of hydrotalcite-like compound to sulfite to sulfide is 100: 1-10: 2 to 5.
Preferably, the pH regulator is one or a combination of two or more of calcium oxide, calcium sulfate, and ferrous sulfate.
The invention also aims to provide a preparation method of the heavy metal polluted soil repairing agent based on the graphene oxide, which comprises the following steps:
s1, weighing the raw materials in parts by weight;
s2, sequentially adding the graphene oxide/cellulose composite material, the hydrotalcite-like compound loaded with the elemental sulfur, the peanut bran and the pH regulator into the chitosan grafted polyvinyl alcohol emulsion, carrying out ball milling mixing, and carrying out vacuum drying to obtain the heavy metal contaminated soil remediation agent.
The invention also aims to provide the application of the heavy metal polluted soil repairing agent based on the graphene oxide in repairing heavy metal Cd polluted soil. The method specifically comprises the following steps: the heavy metal contaminated soil remediation agent with the soil weight of 5.0 wt% is applied to the position 20cm away from the plants in the soil planted with pakchoi.
Compared with the prior art, the invention has the following beneficial effects:
1. in the invention, the used Graphene Oxide (GO) has a large number of oxygen-containing functional groups on the surface, so that the interlayer spacing of graphene sheets is increased, a larger loading space is provided for nano metal and metal oxide particles, and a composite material with excellent structural properties is easy to form. In view of this, according to the invention, firstly, metal oxide (zero-valent iron) particles are anchored on the graphene oxide nanosheet layer, and the morphology, such as a fold structure, a pore structure and a size structure, of the graphene oxide nanosheet layer is regulated, so that the defects that graphene oxide is easy to agglomerate and difficult to separate can be overcome, the performance of the graphene oxide material can be fully exerted, and meanwhile, the loaded zero-valent iron has high reaction activity and can perform a reduction reaction with heavy metals in soil, and the removal capacity of the heavy metals in the soil is further improved.
2. In the invention, in order to improve the chelating capacity of the graphene oxide material to heavy metals, the high-density polyamino polymer is introduced to the surface of the graphene oxide, so that on one hand, the number and density of functional groups with the heavy metal chelating capacity on the surface of the graphene oxide can be improved; on the other hand, amino grafted on the surface of graphene oxide can perform an amide (amination) reaction with a carboxylated cellulose microsphere partially modified by a mercaptosilane coupling agent, the carboxylated cellulose microsphere is grafted on the surface of the graphene oxide, the cellulose microsphere is renewable cellulose and has unique structures such as porosity and a network structure, the adsorption capacity of the composite material on heavy metals in soil can be further improved by combining introduced mercapto and carboxyl, meanwhile, the grafted polyamino polymer can also improve the biocompatibility of the material surface, in addition, the carboxylated cellulose microsphere can also coat zero-valence nano iron loaded on the surface of the graphene oxide, the dispersibility and the stability of the zero-valence nano iron are improved, and the problem that the carboxylated cellulose microsphere is easy to oxidize in the process of repairing the heavy metal contaminated soil is solved.
3. According to the invention, the talcum powder loaded with elemental sulfur is used, namely, elemental sulfur with a chemical fixing effect is loaded on hydrotalcite-like compound, so that heavy metal adsorbed by the talcum powder-like and graphene oxide/cellulose composite material can be fixed, the passivation (fixing) effect is enhanced, and the content of effective heavy metal in soil is reduced; the peanut bran is used, so that heavy metals in the soil can be effectively fixed, and the contents of organic matters and nutrient elements in the soil can be improved; a pH regulator is used as a soil regulator, and the acidity of the soil can be regulated; the chitosan grafted polyvinyl alcohol emulsion is used as a dispersing agent, so that the dispersing performance of each raw material can be improved, and the stability of the repairing agent is improved. According to the invention, the heavy metal contaminated soil remediation agent is obtained by mixing the raw materials with specific dosage, the prepared remediation agent is applied to the heavy metal contaminated soil, and the raw materials act synergistically, so that variable negative charges on the soil surface can be increased, the adsorption of soil colloid on effective cadmium is promoted, the effectiveness of heavy metal cadmium in the soil is reduced, the remediation period is shortened, the remediation efficiency is improved, the fertility of the soil can be improved, and the comprehensive soil remediation effect is good.
4. The heavy metal contaminated soil remediation agent prepared by the invention has strong adsorption capacity on heavy metal cadmium in soil, has high passivation stability, is easy to recover, and has good environmental effect in soil.
Drawings
FIG. 1 shows that the initial concentration of the equilibrium liquid in the example of the present invention is 0-1 mg.L -1 Hour Cd 2+ An adsorption isotherm graph of the rice soil under different remediation agent treatments;
FIG. 2 shows that the initial concentration of the equilibrium liquid in the embodiment of the present invention is 10-100 mg.L -1 Hour Cd 2+ In No. atThe adsorption isotherm curve of the rice soil treated by the repairing agent;
FIG. 3 is a field diagram of a modern intelligent greenhouse employed in embodiments of the present invention;
FIG. 4 is a graph of soil content change for different remediation agent treatments;
FIG. 5 is a graph showing the variation of the total cadmium content in the plantlets of Chinese cabbage treated with different repairing agents;
FIG. 6 is a structural formula of a polyamide-amine polymer in an example of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.
Example 1
The heavy metal contaminated soil remediation agent based on the graphene oxide comprises the following raw materials in parts by weight: 52 parts of graphene oxide/cellulose composite material, 12 parts of hydrotalcite-like compound loaded with elemental sulfur, 10 parts of peanut bran, 6 parts of calcium sulfate and 20 parts of chitosan grafted polyvinyl alcohol emulsion;
the preparation method comprises the following steps: sequentially adding the weighed graphene oxide/cellulose composite material, the hydrotalcite-like compound loaded with the elemental sulfur, the peanut bran and the pH regulator into the chitosan grafted polyvinyl alcohol emulsion, performing ball milling and mixing at the rotating speed of 1000rpm for 20min, and performing vacuum drying (the vacuum degree is 10) at 60 DEG C -1 MPa) for 1h, obtaining the heavy metal contaminated soil remediation agent;
the preparation method of the graphene oxide/cellulose composite material comprises the following steps:
(1) preparing graphene oxide by using a Hummers method, adding 100mg of graphene oxide into 1200mg of deionized water, performing ultrasonic dispersion for 30min to obtain a graphene oxide dispersion solution, adding 8g of polyamide-amine polymer and 0.15g of KOH into the graphene oxide, and continuously stirring and reacting at 80 ℃ for 12h to obtain amino-functionalized graphene oxide; (2) dispersing 0.8g of gamma-mercaptopropyltriethoxysilane KH-580 into 10g of carboxylated cellulose microsphere suspension, adjusting the pH to 4-9, stirring at room temperature for 6h, then placing in liquid nitrogen for freezing for 15min, then freeze-drying for 2h, and baking and curing at 90 ℃ for 20min to obtain modified cellulose microspheres; (3) adding modified cellulose microspheres into amino functionalized graphene oxide, stirring and mixing, then adding 0.5g of epoxy chloropropane into the system, reacting for 12 hours at 80 ℃, after the reaction is finished, carrying out centrifugal separation, repeatedly washing the obtained solid with ethanol and deionized water in sequence to remove incompletely reacted polyamino polymer and glutaraldehyde, freeze-drying, and grinding to obtain a graphene oxide/cellulose composite material;
the preparation method of the hydrotalcite-like compound loaded with the elemental sulfur comprises the following steps: dispersing 12g of hydrotalcite-like compound into 100g of deionized water to obtain a suspension, slowly adding 1.8g of sulfite and 3.6g of sulfide into the suspension slurry obtained in the step 1) under stirring, adding dilute sulfuric acid, adjusting the pH to 3.0-5.0, reacting at room temperature, dehydrating, drying and crushing to obtain the hydrotalcite-like compound loaded with elemental sulfur.
The polyamino polymer is a polyamide-amine polymer, and the structural formula of the polyamino polymer is shown in figure 6.
Example 2
The heavy metal contaminated soil remediation agent based on the graphene oxide comprises the following raw materials in parts by weight: 35 parts of graphene oxide/cellulose composite material, 18 parts of hydrotalcite-like compound loaded with elemental sulfur, 11 parts of peanut bran, 6 parts of pH regulator (formed by mixing calcium oxide and calcium sulfate in a mass ratio of 1: 3) and 30 parts of chitosan grafted polyvinyl alcohol emulsion;
the rest is the same as example 1.
Example 3
The heavy metal contaminated soil remediation agent based on the graphene oxide comprises the following raw materials in parts by weight: 65 parts of graphene oxide/cellulose composite material, 8 parts of hydrotalcite-like compound loaded with elemental sulfur, 5 parts of peanut bran, 2 parts of pH regulator (formed by mixing calcium oxide, calcium sulfate and ferrous sulfate in a mass ratio of 1: 1: 1), and 20 parts of chitosan grafted polyvinyl alcohol emulsion;
the preparation method is the same as example 1 except that the crosslinking agent epichlorohydrin in the raw material for preparing the graphene oxide/cellulose composite material is replaced by phenol-2, 4-disulfonyl chloride.
Example 4
The heavy metal contaminated soil remediation agent based on the graphene oxide comprises the following raw materials in parts by weight: 48 parts of graphene oxide/cellulose composite material, 15 parts of hydrotalcite-like compound loaded with elemental sulfur, 12 parts of peanut bran, 3 parts of ferrous sulfate and 22 parts of chitosan grafted polyvinyl alcohol emulsion;
the same as in example 1 is repeated except that the crosslinking agent epichlorohydrin in the raw material for preparing the graphene oxide/cellulose composite material is replaced by diazobenzidine-2, 2' -disulfonic acid.
Example 5
Except that the graphene oxide in the raw material for preparing the graphene oxide/cellulose composite material is changed into the loaded zero-valent iron graphene oxide, wherein the loaded zero-valent iron graphene oxide is obtained by adopting a preparation method disclosed in the field, and details are not repeated here.
The rest is the same as example 1.
Example 6
The heavy metal contaminated soil remediation agent based on the graphene oxide comprises the following raw materials in parts by weight: 52 parts of graphene oxide/cellulose composite material, 15 parts of hydrotalcite-like compound loaded with elemental sulfur, 8 parts of peanut bran, 3 parts of calcium sulfate and 22 parts of chitosan grafted polyvinyl alcohol emulsion; the rest is the same as example 5.
Comparative example 1
Example 1 was repeated except that the graphene oxide/cellulose composite was replaced with a mixture of graphene oxide and carboxylated cellulose microspheres.
Comparative example 2
The same procedure as in example 1 was repeated, except that the added graphene oxide/cellulose composite material was changed to carboxylated cellulose microspheres.
And (3) performance detection:
(A) The graphene oxide/cellulose composite material prepared in example 1 was subjected to elemental detection by ICP-OES (inductively coupled plasma-emission spectroscopy), and the detection results are shown in table 1;
TABLE 1 test results
| Serial number | Test element | Test results | Detection limit | Unit of |
| 1 | Manganese oxide | Not detected out | 1 | mg/kg |
| 2 | Iron | 17 | - | mg/kg |
| 3 | Arsenic (As) | Not detected out | 1 | mg/kg |
| 4 | Antimony (Sb) | Not detected out | 1 | mg/kg |
| 5 | Copper (Cu) | Not detected out | 1 | mg/kg |
| 6 | Bismuth (Bi) | Not detected out | 1 | mg/kg |
| 7 | Zinc | Not detected out | 1 | mg/ |
| 8 | Silver | Not detected out | 1 | mg/kg |
| 9 | Nickel (II) | Not detected out | 1 | mg/kg |
| 10 | Cadmium (Cd) | Undetected | 1 | mg/kg |
| 11 | Particle size (D50) | 47.70 | - | μm |
As can be seen from the results in table 1, the graphene oxide/cellulose composite material prepared in embodiment 1 of the present invention does not contain toxic and harmful substances, and is environment-friendly.
And (II) researching the adsorption behavior of the exogenous cadmium in the soil after different repairing agents are applied through an adsorption isotherm curve.
(1) Test soil
The soil type is rice soil in Hangzhou Zhejiang, the sampling depth is 0-20cm, the soil is dried by air and then is sieved by a 20-mesh sieve, and the physicochemical properties are shown in Table 2.
TABLE 2 basic physicochemical Properties and heavy Metal background values of the soil tested
The repairing agents prepared in examples 1 to 6 and comparative examples 1 to 2 were diluted at a concentration of 1: 100, and then adding the mixture into soil to be tested for test treatment, and taking the repairing agent prepared in comparative example 2 without adding graphene oxide, namely blank treatment and the repairing agent prepared in comparative example 1 as a control. Each experimental treatment was repeated 3 times. Wherein the amount of the repairing agent is 5 wt% of the amount of the soil to be tested. The test design is shown in Table 3;
table 3 Experimental design (5% of repairing agent in soil)
(3) And (3) soil adsorption determination: weighing 1.00g of sieved air-dried soil into a 100ml plastic centrifuge tube, adding 20ml of air-dried soil containing 0.1 mol.L -1 Ca 2+ (supporting electrolyte CaCl) 2 ) CdCl of (2) 2 Solution (CdCl) 2 The initial concentration is respectively pure Cd 2+ Concentrations of 0.5, 1.0, 2.0, 5.0, 10.0, 25.0, 50.0 and 100.0 mg.L -1 ) Shaking at constant temperature (25 deg.C) for 2 hr, standing in constant temperature incubator (25 + -1 deg.C) for 24 hr, taking out, and culturing at 5000 r.min -1 Centrifugation and atomic absorption spectrophotometry for measuring Cd in adsorption equilibrium liquid 2+ Ca in concentration experiments 2+ The method has the function that the initial concentration of the non-specific adsorption sites which can occur after the saturated cadmium enters the soil is selected to be 1.0 mg.L -1 CdCl of (2) 2 Shaking the solution for 1, 2, 5, 10, 15, 30, 60, 120, 240 and 360min, centrifuging, and measuring Cd in the supernatant by atomic absorption spectrophotometry 2+ Concentration and calculating Cd 2+ The above test treatments were repeated 3 times for the adsorption amount on the soil to be tested.
The calculation method comprises the following steps:
Cd 2+ adsorption amount (Y, mg. kg) -1 )：
Y＝V 1 (C 0 -C 1 )/m
In the formula, V 1 Volume of liquid in centrifuge tube (20ml), C 0 Is CdCl 2 Initial concentration (mg.L) -1 )，C 1 Cd in the centrifuged supernatant 2+ Concentration (mg. L) -1 ) And m is the soil weight (g), the adsorption thermodynamic model is fitted by EXCEL2017, the correlation coefficient (R2) is used for judging the quality of the model, and the larger the R2 is, the optimal model is.
(4)Cd 2+ Thermodynamic behavior of adsorption
Respectively treating the soil sample to be tested with different repairing agents in different CdCl 2 Initial concentration (mg.L) -1 ) Cd in equilibrium liquid 2+ The adsorption quantity of the sample is measured, and then Cd of the test soil sample is drawn 2+ The isotherms were adsorbed and the results are shown in fig. 1 and 2.
As can be seen from the results of FIGS. 1 and 2, the curve rises faster when the concentration in the equilibrium solution is lower, with the Cd in the equilibrium solution 2+ The concentration is increased continuously, and the curve is gradually gentle. Rice soil in E7 (example 6) for Cd 2+ Has an adsorption capacity of up to 199.09 mg/kg -1 Followed by E6 (example 5) and E2 (example 1), with maximum adsorption capacities of 198.26 and 197.79mg kg -1 The three are respectively comparedBlank E0 (comparative example 2) was 17.14%, 16.67% and 16.38% higher, E5, E3 and E4 were centered, and E1 (comparative example 1) was the worst, only 3.10% higher than blank E0.
(III) potting test
The absorption effect in the soil for planting pakchoi treated by different repairing agents was studied.
(1) Soil(s)
Foundation soil: the foundation soil used for the experiment is collected in the test field of Beijing college of agriculture, and the previous crop is the planting field of spring corn. Before collecting soil to be tested, the surface is firstly refitted and cleaned, the most superficial layer of floating soil, plants and the like are removed, 0-20cm of plough layer soil is collected, multi-point sampling is carried out, a polyethylene plastic bag is used for containing collected mixed soil samples, the mixed soil samples are taken back and placed in a cool and ventilated place, the mixed soil samples are evenly spread out and crushed, and impurities in the mixed soil samples are removed. Air-drying under natural conditions, grinding and crushing the air-dried soil by using a soil crusher, sieving by using a standard test sieve of 10 meshes (the aperture of a square hole is 2mm), and subpackaging and storing the sieved soil by using self-sealing bags for later use. And weighing a certain amount of soil samples to be tested, and measuring the physical and chemical properties of the soil samples. The basic physicochemical properties of the foundation soil are specified in Table 4.
TABLE 4 background values of the basic soil
Test soil: and (3) treating the sieved soil by using 30mg/L cadmium chloride solution to ensure that the final total cadmium content in the soil reaches 1.75mg/kg and the final total cadmium content in the soil reaches 0.20mg/kg, and storing for later use.
(3) Design of experiments
The test was carried out in a modern intelligent greenhouse of the institute for biological and resource environments, Beijing college of agriculture, as shown in FIG. 3. The pH values of the repairing agents prepared in examples 1 to 6 and comparative examples 1 to 2 were adjusted to 6.8. Diluting the repairing agent by using commercially available Yibao mineral water respectively, wherein the dilution concentration is 1: and 100, adding the diluted different repairing agents into the soil to be tested for test treatment. And the repairing agent prepared in comparative example 2 without adding graphene oxide, namely the blank treatment and the repairing agent prepared in comparative example 1, are used as controls. Each experimental treatment was repeated 3 times. Wherein the dosage of the repairing agent is 5 wt% of the amount of the potting soil. The test design is shown in Table 5;
TABLE 5 potted plant experimental design of cadmium contaminated soil
(4) Pot experiment
Adding seedling substrate into seedling tray, selecting Chinese cabbage seed with uniform seed size, full grain, and sterilizing (30% H) 2 O 2 Disinfecting seeds for 10min by using the solution, washing the seeds with deionized water for 3-5 times), sowing the seeds in a seedling tray, sowing 3-5 seeds in each hole during sowing, irrigating the seeds with a full nutrient solution at regular intervals, transplanting the seeds into a flowerpot with the diameter of 5cm and the height of 8cm after the seeds grow to three leaves, and hardening the seedlings for 7-10 days (selecting robust and uniform-growing Chinese cabbage seedlings).
To each of the pots (upper part diameter 18cm, bottom diameter 11cm, height 13cm) used in the test, 1.0kg of soil to be tested was added. Firstly, weighing the air-dried soil to be tested and a repairing agent with a certain dilution concentration, uniformly mixing the soil and the repairing agent by stirring, and filling the mixed soil into a flowerpot. Nitrogen, phosphorus and potassium fertilizers (0.2 g of converted pure N and P) are applied to soil of each flowerpot at one time before sowing 2 O 5 0.3g、K 2 O0.2 g) is used as a base fertilizer for plant growth. The fertilizer is mainly added in the form of a solution. And (3) adding deionized water to carry out dry-wet alternation, and transplanting the trained seedlings into a treated flowerpot for planting after the soil is balanced for two weeks. 15 plantlets are planted in each treatment according to the size and the growth condition of the plantlets of the pakchoi. Watering with deionized water regularly, performing pest control management, randomly placing each potted plant in a greenhouse, disordering every 3 days, and placing again to keep growth conditions (air flow, illumination conditions, etc.) of pakchoi basically consistent, recording changes of experiment conditions such as greenhouse temperature and humidity every day during experiment, transplanting for 80 days, and harvesting
(5) Measurement items and methods
(a) Determination of content in potting soil: the potted soil after harvesting the pakchoi is uniformly mixed, about 50g of the mixed soil is taken out, air-dried and crushed, sieved by a standard test sieve of 100 meshes (the square hole diameter is 0.15mm), and stored under certain conditions for soil analysis. Leaching by using a diethylenetriamine pentaacetic acid solution, wherein the ratio of the sample soil to the solution is 1: 2, measuring by inductively coupled plasma mass spectrometry. The specific method comprises the following steps: in a 100ml conical flask, 10g of a soil sample is weighed using an analytical balance (accuracy in parts per million). Then 20ml of the extract (DTPA) was added and the stopper was closed. On a water bath constant temperature oscillator at the temperature of 20 +/-2 ℃ and at the temperature of 200 r.min -1 The oscillation frequency of (2) oscillates for 2 hours. Then slowly pouring the leaching solution into a centrifuge tube, placing the centrifuge tube on a centrifuge, and performing centrifugation at 4000 r.min -1 Was centrifuged at the speed of (1) for 10min, and the supernatant was filtered through a microfiltration membrane having a pore size of 0.45 μm and measured by ICP-MS over a period of 48 hours. And blank experiments are carried out, each experiment treatment is repeated for 3 times, and finally, the average value is taken, and the recovery rate is calculated. In order to ensure the quality of the experiment, loess (GBW07408), which is a national standard substance soil standard reference sample, is used for carrying out the experiment. The results are shown in FIG. 4.
As can be seen from the results in FIG. 4, the content of the soil of 0-20cm treated by 8 plants decreases slightly when the planting time is prolonged, and the soil is planted for 40 days; the content of the soil with the depth of 0-20cm in the treatments 3-8 all decreased greatly when the soil was planted for 80 days, wherein the treatment 3 (example 1), the treatment 7 (example 5) and the treatment 8 (example 6) decreased maximally, and decreased by 27.5%, 31% and 29% respectively compared with the soil when the soil was planted for 0 days. For treatment 2 (comparative example 2), the decrease in the content in the soil of 0 to 20cm was the smallest regardless of whether the growth was for 40 days or 80 days, and the content in the soil of 0 to 20cm at 80 days was 9.5% lower than that at 0 day of planting. Therefore, the addition of the heavy metal contaminated soil remediation agent prepared in the embodiments 1 to 6 of the invention to the test soil can effectively passivate the available cadmium in the soil.
(b) Determining the content of all cadmium (Cd) in the plantlets of the Chinese cabbages: HNO 3 －H 2 O 2 (V 1 ：V 2 3: 1) microwave digestion, ICAnd (4) P-MS measurement. Adding 0.1g of plant sample weighed by using an analytical balance (with accuracy of ten-thousandth), 3ml of concentrated nitric acid (super grade pure, preferably MOS grade), and 2ml of H into a digestion tank 2 O 2 . Covering a cover tightly, shaking forcibly to mix the mixture evenly, then putting the mixture into a microwave digestion instrument for digestion, putting the mixture into an acid dispelling instrument at 160 ℃, adding a nitric acid solution with the mass fraction of 1% for rinsing for 3 times after all the acid is removed, pouring the rinsing solution into a 25ml volumetric flask for constant volume, filtering the solution through a microporous filter membrane with the aperture of 0.45 mu m, storing the solution in a 10ml centrifugal tube, and storing the solution to be tested at 4 ℃. And blank experiments are carried out, each experiment treatment is repeated for 3 times, and finally, the average value is taken, and the recovery rate is calculated. The results are shown in FIG. 5.
From the results in fig. 5, it can be seen that the total cadmium content of 8 treated pakchoi plants all increased slightly at 40 days of planting, and among the 8 treatments, the total cadmium content of the pakchoi plants treated 7 (example 5) and 8 (example 6) increased slightly, followed by treatment 3 (example 1); when the plantlets are planted for 80 days, the total cadmium content in the plantlets of the 8 treated plantlets is greatly increased, wherein the increase amplitude of the treatment 2 (comparative example 2) is the highest and is 187.19% higher than that of the plantlets of the 40 days, and the total cadmium content in the plantlets of the treatments 3, 7 and 8 is respectively 0.453mg/kg, 0.421mg/kg and 0.434mg/kg and is respectively 154.49%, 209.56% and 199.31% higher than that of the plantlets of the 40 days. Therefore, the accumulation of the total cadmium content in the plantlets of the pakchoi is mainly in the later growth stage.
From the above test results, it can be derived: when the heavy metal polluted soil restoration agent based on graphene oxide is applied to the soil for planting the pakchoi, the concentration of effective cadmium in the soil and the content of all cadmium in the pakchoi plants can be effectively reduced, so that the toxicity of cadmium in the soil can be reduced, and the absorption of the pakchoi plants to the effective cadmium can be reduced.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered as the technical solutions and the inventive concepts of the present invention within the technical scope of the present invention.
Claims (8)
1. The heavy metal contaminated soil remediation agent based on graphene oxide is characterized by comprising the following raw materials in parts by weight: 35-65 parts of graphene oxide/cellulose composite material, 8-18 parts of hydrotalcite-like compound loaded with elemental sulfur, 5-12 parts of peanut bran, 2-6 parts of pH regulator and 20-30 parts of chitosan grafted polyvinyl alcohol emulsion.
2. The heavy metal contaminated soil remediation agent of claim 1, wherein said graphene oxide/cellulose composite is prepared by compounding carboxylated cellulose microspheres and amino functionalized graphene oxide.
3. The heavy metal contaminated soil remediation agent of claim 2, wherein said graphene oxide/cellulose composite is prepared by the steps of:
(1) preparing graphene oxide by using a Hummers method, dispersing the graphene oxide in deionized water, adding a polyamino polymer and a potassium hydroxide solution into a dispersion liquid, and stirring for reaction to obtain amino functionalized graphene oxide; wherein the mass ratio of the graphene oxide to the polyamino polymer is 100: 2-12;
(2) dispersing a mercaptosilane coupling agent into a carboxylated cellulose microsphere suspension, and freeze-drying to obtain the modified cellulose microsphere, wherein the mass ratio of the carboxylated cellulose microsphere to the mercaptosilane coupling agent is 10: 0.5 to 1;
(3) adding modified cellulose microspheres into amino functionalized graphene oxide, stirring and mixing, then adding a cross-linking agent into a system, carrying out heat preservation reaction, carrying out centrifugal separation, washing, freeze drying and grinding to obtain a graphene oxide/cellulose composite material, wherein the mass ratio of the modified cellulose microspheres to the amino functionalized graphene oxide to the cross-linking agent is 3: 8-12: 0.1 to 0.5.
4. The heavy metal contaminated soil remediation agent of claim 3, wherein said polyamino polymer is a polyamidoamine polymer; the cross-linking agent is any one of epichlorohydrin, glutaraldehyde, diazobenzidine-2, 2' -disulfonic acid or phenol-2, 4-disulfonyl chloride.
5. The heavy metal contaminated soil remediation agent of claim 3, wherein said graphene oxide is loaded with zero valent iron graphene oxide.
6. The heavy metal contaminated soil remediation agent of claim 1, wherein said preparation of hydrotalcite-like compound loaded with elemental sulfur comprises the steps of: dispersing hydrotalcite-like compound into deionized water to obtain a suspension, adding sulfite and sulfide into the suspension under stirring, adding dilute sulfuric acid to adjust the pH to 3.0-5.0, reacting at room temperature, dehydrating, drying and crushing to obtain hydrotalcite-like compound loaded with elemental sulfur, wherein the mass ratio of hydrotalcite-like compound to sulfite to sulfide is 100: 1-10: 2 to 5.
7. A method for preparing graphene oxide-based heavy metal contaminated soil remediation agent according to any one of claims 1-6, comprising the steps of:
s1, weighing the raw materials in parts by weight;
and S2, sequentially adding the graphene oxide/cellulose composite material, the hydrotalcite-like compound loaded with the elemental sulfur, the peanut bran and the pH regulator into the chitosan grafted polyvinyl alcohol emulsion, performing ball milling mixing, and performing vacuum drying to obtain the heavy metal contaminated soil remediation agent.
8. The application of the graphene oxide-based heavy metal polluted soil remediation agent in remediation of heavy metal Cd-polluted soil according to any one of claims 1 to 6.
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