CN114751502B - Core-shell structure modified nano zero-valent iron and preparation method and application thereof - Google Patents

Core-shell structure modified nano zero-valent iron and preparation method and application thereof Download PDF

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CN114751502B
CN114751502B CN202210296060.7A CN202210296060A CN114751502B CN 114751502 B CN114751502 B CN 114751502B CN 202210296060 A CN202210296060 A CN 202210296060A CN 114751502 B CN114751502 B CN 114751502B
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valent iron
nano zero
core
shell structure
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CN114751502A (en
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马晓炜
张凯
张俊峰
彭渊哲
谢金艳
郑春莉
林子深
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Shaanxi Zhongkan Environmental Geology Research Center Co ltd
Xian Jiaotong University
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Shaanxi Zhongkan Environmental Geology Research Center Co ltd
Xian Jiaotong University
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    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/70—Treatment of water, waste water, or sewage by reduction
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
    • B09C—RECLAMATION OF CONTAMINATED SOIL
    • B09C1/00—Reclamation of contaminated soil
    • B09C1/08—Reclamation of contaminated soil chemically
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/20—Heavy metals or heavy metal compounds
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
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Abstract

The invention discloses modified nano zero-valent iron with a core-shell structure, and a preparation method and application thereof, belongs to the technical field of heavy metal pollution restoration, and solves the technical problem that the existing nano zero-valent iron cannot completely overcome the defects of the existing nano zero-valent iron and remarkably improves the reduction and removal efficiency of heavy metal ions. The invention discloses a preparation method of modified nano zero-valent iron with a core-shell structure, which adopts aminocarboxylic acid compounds to chelate ferrous ions and KBH (sodium dodecyl benzene sulfonate) 4 Adding the solution into the mixed solution to form amorphous nano zero-valent iron, and reacting for a certain time to finally obtain modified nano zero-valent iron with a core-shell structure; the method adopts one step and one modified material to prepare the modified nano zero-valent iron material with a core-shell structure, and the preparation process is simple. The modified nano zero-valent iron with the core-shell structure obtained by the method is not easy to oxidize, has weak agglomeration effect and long storage time, has faster electron transfer rate and higher removal efficiency of heavy metal ions.

Description

Core-shell structure modified nano zero-valent iron and preparation method and application thereof
Technical Field
The invention belongs to the technical field of heavy metal pollution repair, and particularly relates to a modified nano zero-valent iron with a core-shell structure, and a preparation method and application thereof.
Background
Nano zero-valent iron (nZVI) as active metal with standard electrode potential of E 0 (Fe 2+ And (2) Fe) = -0.44V, has stronger reducing capability, and can reduce heavy metal ions discharged in the metal activity sequence table to form single substances to be deposited on the surface of iron so as to achieve the aim of removing pollution.
The traditional nano zero-valent iron has three defects: (1) Is easy to be oxidized by air to be deactivated, and is difficult to store for a long time; (2) Gibbs free energy tends to agglomerate due to the high specific surface; (3) The nano iron is in a crystal state, and the capability of giving out electrons is not high. The three defects reduce the reduction and removal efficiency of heavy metal ions, and limit the practical application of nano zero-valent iron. In order to solve the three scientific problems, the zero-valent iron needs to be modified, and common methods are classified into a surface modification method and a carrier immobilization method. The surface modification mainly wraps nano zero-valent iron, so that on one hand, the dispersibility of the zero-valent iron is improved, on the other hand, the zero-valent iron is prevented from being oxidized by air, and the prior literature reports show that common surface modifiers comprise sodium alginate, starch, sodium carboxymethyl cellulose, sodium polyacrylate, biological glue and the like. The carrier fixing method is to load nano zero-valent iron on the surface of porous material with higher specific area, which can obviously reduce the agglomeration of nano iron and increase the action area of nano zero-valent iron and pollutant, thereby improving the removal capacity.
Although these modification methods achieve a certain effect, only one or two of the three scientific problems are usually solved, and three scientific problems are rarely solved at the same time, which makes it difficult to significantly improve the reduction and removal efficiency of heavy metal ions of nano zero-valent iron.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide modified nano zero-valent iron with a core-shell structure, and a preparation method and application thereof, which are used for solving the technical problem that the existing nano zero-valent iron cannot completely overcome the defects of the prior art and obviously improves the reduction and removal efficiency of heavy metal ions.
In order to achieve the above purpose, the invention is realized by adopting the following technical scheme:
the invention discloses a preparation method of modified nano zero-valent iron with a core-shell structure, which comprises the following steps:
mixing ferrous sulfate, amino carboxylic acid compounds and water, and stirring to obtain a mixed solution; KBH of 4 And (3) dripping the solution into the mixed solution for reaction, and then carrying out solid-liquid separation, cleaning and drying to obtain the modified nano zero-valent iron with the core-shell structure.
Further, the dosage ratio of the ferrous sulfate, the aminocarboxylic acid compound and the water is (2.27-4.54) g: (1.2-2.4) g: (200-300) mL.
Further, the aminocarboxylic acid compound comprises 2-aminocyclohexylcarboxylic acid or 1-aminocyclohexylcarboxylic acid.
Further, the stirring time is 5-15 min; the reaction time is 10 min-15 min.
Further, the drying mode is vacuum freeze drying, and the vacuum freeze drying is carried out at the temperature of minus 60 ℃ to minus 50 ℃.
Further, the KBH 4 The preparation method of the solution comprises the following steps: KBH of 4 Mixing with water, stirring to obtain KBH 4 A solution; the KBH 4 And the water dosage ratio is (4-5) g (75-100) mL.
The invention also discloses the modified nano zero-valent core-shell structure prepared by the preparation method.
Further, the modified nano zero-valent iron of the core-shell structure consists of an inner structure and an outer structure, wherein the inner structure is coated by the outer structure; the internal structure is an amorphous zero-valent iron shell, and the external structure is an amorphous iron oxide shell.
The invention also discloses application of the modified nano zero-valent iron with the core-shell structure, and the modified nano zero-valent iron with the core-shell structure is used as a heavy metal ion remover.
Further, the heavy metal ions include Cd (II) ions, pb (II) ions, cu (II) ions, hg (II) ions, cr (VI) ions, or Ni (II) ions.
Compared with the prior art, the invention has the following beneficial effects:
the invention discloses a preparation method of modified nano zero-valent iron with a core-shell structure, which adopts amino carboxylic acid compounds to chelate ferrous ions and KBH (sodium silicate) 4 Adding the solution into the mixed solution to form amorphous nano zero-valent iron, and reacting for a certain time to finally obtain modified nano zero-valent iron with a core-shell structure; the method has simple preparation process, adopts one step and one modified material to prepare the modified nano zero-valent iron material with a core-shell structure, has low preparation cost and is beneficial to industrial production; meanwhile, under the protection of an external core-shell structure, the core-shell structure modified nano zero-valent iron material is not easy to oxidize, has weak agglomeration effect and long storage time, has faster electron transfer rate, higher heavy metal ion removal efficiency and very wide application prospect.
The invention also discloses the modified nano zero-valent iron with the core-shell structure, which is prepared by the preparation method, and because the amino carboxylic acid compound is adopted to chelate ferrous iron ions, the modified nano zero-valent iron with KBH 4 The solution reacts to obtain modified nano zero-valent iron with a core-shell structure; because the outside of the modified nano zero-valent iron with the core-shell structure is an iron oxide shell, and the inside of the modified nano zero-valent iron is a zero-valent iron core, the inside zero-valent iron core is protected from being oxidized by air, and the agglomeration effect among zero-valent irons is slowed down; according to experimental results, the internal zero-valent iron shell is amorphous, so that the e-Fe bond is longer than that of crystalline zero-valent iron, and is easier to break, and the amorphous phase is in a metastable state and is easier to provide electrons, so that the internal iron core is easier to provide electrons, and the reduction activity is obviously enhanced; therefore, under the protection of the external iron oxide shell and the action of the internal amorphous zero-valent iron core, the core-shell structure modified nano zero-valent iron material is not easy to oxidize, has weak agglomeration effect and long storage time, has faster electron transfer rate, has higher efficiency for removing heavy metal ions, and has very wide application prospect.
The invention also discloses application of the modified nano zero-valent iron with the core-shell structure, and the modified nano zero-valent iron with the core-shell structure can be used as a heavy metal ion remover for removing and purifying heavy metal ions in water or soil. According to experimental results, the resistance of the core-shell structure modified nano zero-valent iron prepared by the method is only 80.2 omega, which is far lower than that of other zero-valent iron materials, and the Tafil curve and the work function prove that the core-shell structure modified nano zero-valent iron is easier to provide electrons; the reaction is carried out for 80 minutes, the adding amount is 0.5g/L, and the removal rate of Cd (II), pb (II), cu (II), hg (II), cr (VI) and Ni (II) wastewater with the initial concentration of 30mg/L by the core-shell structure modified nano zero-valent iron material is 99.5%, 100%, 94.2%, 91.8%, 100% and 90.7% on average, which is obviously superior to that of the zero-valent iron material. After 180 days of exposed air aging test, the core-shell structure modified nano zero-valent iron material has the removal rates of Cd (II), pb (II), cu (II), hg (II), cr (VI) and Ni (II) wastewater in water maintained at 94.1%, 96.2%, 88.7%, 85.1%, 94.6% and 82.8%, respectively.
Drawings
FIG. 1 is a TEM image of modified nano zero-valent iron with a core-shell structure prepared by the method;
wherein: a-20nm; b. c-10nm;
FIG. 2 is a TEM image of the nano zero-valent iron obtained in comparative example 1;
FIG. 3 is a SAED comparison chart of the modified nano zero-valent iron with the core-shell structure prepared by the invention and the nano zero-valent iron prepared by comparative example 1;
wherein: a-core-shell structure modified nano zero-valent iron; b-nano zero-valent iron;
FIG. 4 is an X-ray powder diffraction contrast chart of modified nano zero-valent iron and nano zero-valent iron of a core-shell structure prepared by the invention;
FIG. 5 is a comparison chart of electrochemical analysis of modified nano zero-valent iron and nano zero-valent iron with core-shell structures prepared by the invention;
FIG. 6 is a graph showing the comparison of the removal rates of Cd (II) ions, pb (II) ions, cu (II) ions, hg (II) ions, cr (VI) ions and Ni (II) ions in the wastewater by using the modified nano zero-valent iron and nano zero-valent iron with the core-shell structure prepared by the invention;
FIG. 7 is a graph showing the comparison of removal rates of Cd (II) ions, pb (II) ions, cu (II) ions, hg (II) ions, cr (VI) ions and Ni (II) ions in a water body after 180 days of aging of the core-shell structure modified nano zero-valent iron and nano zero-valent iron.
Detailed Description
So that those skilled in the art can appreciate the features and effects of the present invention, a general description and definition of the terms and expressions set forth in the specification and claims follows. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and in the event of a conflict, the present specification shall control.
The theory or mechanism described and disclosed herein, whether right or wrong, is not meant to limit the scope of the invention in any way, i.e., the present disclosure may be practiced without limitation to any particular theory or mechanism.
All features such as values, amounts, contents, and concentrations defined in the numerical range or percent range are herein for brevity and convenience only. Accordingly, the description of a numerical range or percentage range should be considered to cover and specifically disclose all possible sub-ranges and individual values (including integers and fractions) within the range.
Herein, unless otherwise indicated, the terms "comprising," including, "" containing, "" having, "or the like are intended to cover the meanings of" consisting of … … "and" consisting essentially of … …, "e.g.," a includes a "and the meanings of" a includes a and the other "and" a includes a only.
In this context, not all possible combinations of the individual technical features in the individual embodiments or examples are described in order to simplify the description. Therefore, as long as there is no contradiction between the combinations of these technical features, any combination of the technical features in the respective embodiments or examples is possible, and all possible combinations should be considered as being within the scope described in the present specification.
The invention will be further illustrated with reference to specific examples. It is to be understood that these examples are illustrative of the present invention and are not intended to limit the scope of the present invention. Further, it is understood that various changes and modifications may be made by those skilled in the art after reading the teachings of the present invention, and such equivalents are intended to fall within the scope of the claims appended hereto.
The following examples use instrumentation conventional in the art. The experimental methods, in which specific conditions are not noted in the following examples, are generally conducted under conventional conditions or under conditions recommended by the manufacturer. The following examples used various starting materials, unless otherwise indicated, were conventional commercial products, the specifications of which are conventional in the art. In the description of the present invention and the following examples, "%" means weight percent, and "parts" means parts by weight, and ratios means weight ratio, unless otherwise specified.
Example 1
The preparation method of the modified nano zero-valent iron with the core-shell structure comprises the following steps:
2.2700g of ferrous sulfate and 1.2g of 2-aminocyclohexylcarboxylic acid are added into a three-neck flask containing 200mL of ultrapure water at normal temperature and pressure, and stirred for 5min to be mixed to obtain a mixed solution; 4.0000g of potassium borohydride and 75mL of ultrapure water are added into a 100mL beaker at normal temperature and pressure, stirred and dissolved, and uniformly mixed to obtain KBH 4 A solution; under the condition of room temperature and normal pressure, the obtained KBH 4 Adding the solution into the obtained mixed solution dropwise, blackening the solution and gradually forming particles, KBH 4 After the solution is added dropwise, stirring and reacting for 10 minutes, carrying out solid-liquid separation and cleaning, and carrying out freeze drying under the vacuum condition of 60 ℃ below zero to obtain the modified nano zero-valent iron with the core-shell structure.
Example 2
The preparation method of the modified nano zero-valent iron with the core-shell structure comprises the following steps:
3.5600g of ferrous sulfate and 1.8g of 2-aminocyclohexylcarboxylic acid are added into a three-neck flask containing 250mL of ultrapure water at normal temperature and pressure, and stirred for 10min to be mixed to obtain a mixed solution; 4 was added to a 100mL beaker at normal temperature and pressure.6000g of potassium borohydride, 80mL of ultrapure water, stirring and dissolving, and uniformly mixing to obtain KBH 4 A solution; under the condition of room temperature and normal pressure, the obtained KBH 4 Adding the solution into the obtained mixed solution dropwise, blackening the solution and gradually forming particles, KBH 4 After the solution is dripped, stirring and reacting for 13 minutes, separating solid from liquid, cleaning, and freeze-drying under the vacuum condition of-55 ℃ to obtain the modified nano zero-valent iron with the core-shell structure.
Example 3
The preparation method of the modified nano zero-valent iron with the core-shell structure comprises the following steps:
4.5400g of ferrous sulfate and 2.4g of 2-aminocyclohexylcarboxylic acid are added into a three-neck flask containing 300mL of ultrapure water at normal temperature and pressure, and stirred for 15min to be mixed to obtain a mixed solution; 5.0000g of potassium borohydride and 100mL of ultrapure water are added into a 100mL beaker at normal temperature and normal pressure, stirred and dissolved, and uniformly mixed to obtain KBH 4 A solution; under the condition of room temperature and normal pressure, the obtained KBH 4 Adding the solution into the obtained mixed solution dropwise, blackening the solution and gradually forming particles, KBH 4 After the solution is dripped, stirring and reacting for 15 minutes, separating solid from liquid, cleaning, and freeze-drying under the vacuum condition of-50 ℃ to obtain the modified nano zero-valent iron with the core-shell structure.
Example 4
The preparation method of the modified nano zero-valent iron with the core-shell structure comprises the following steps:
3.6400g of ferrous sulfate and 1.8g of 2-aminocyclohexylcarboxylic acid are added into a three-neck flask containing 265mL of ultrapure water at normal temperature and pressure, and stirred for 8min to be mixed to obtain a mixed solution; under normal temperature and pressure, 4.5000g of potassium borohydride and 80mL of ultrapure water are added into a 100mL beaker, stirred and dissolved, and uniformly mixed to obtain KBH 4 A solution; under the condition of room temperature and normal pressure, the obtained KBH 4 Adding the solution into the obtained mixed solution dropwise, blackening the solution and gradually forming particles, KBH 4 After the solution is added dropwise, stirring and reacting for 12 minutes, carrying out solid-liquid separation and cleaning, and carrying out freeze drying under the vacuum condition of 58 ℃ below zero to obtain the modified nano zero-valent iron with the core-shell structure.
Example 5
The preparation method of the modified nano zero-valent iron with the core-shell structure comprises the following steps:
4.4300g of ferrous sulfate and 2.3g of 2-aminocyclohexylcarboxylic acid are added into a three-neck flask containing 220mL of ultrapure water at normal temperature and pressure, and stirred for 13min to be mixed to obtain a mixed solution; 4.5000g of potassium borohydride and 90mL of ultrapure water are added into a 100mL beaker at normal temperature and normal pressure, stirred and dissolved, and uniformly mixed to obtain KBH 4 A solution; under the condition of room temperature and normal pressure, the obtained KBH 4 Adding the solution into the obtained mixed solution dropwise, blackening the solution and gradually forming particles, KBH 4 After the solution is added dropwise, stirring and reacting for 12 minutes, carrying out solid-liquid separation and cleaning, and carrying out freeze drying under the vacuum condition of 60 ℃ below zero to obtain the modified nano zero-valent iron with the core-shell structure.
Example 6
The preparation method of the modified nano zero-valent iron with the core-shell structure comprises the following steps:
2.3g of ferrous sulfate and 2.4g of 2-aminocyclohexylcarboxylic acid are added into a three-neck flask containing 250mL of ultrapure water at normal temperature and normal pressure, and stirred for 5min to be mixed to obtain a mixed solution; 5.0000g of potassium borohydride and 100mL of ultrapure water are added into a 100mL beaker at normal temperature and pressure, stirred and dissolved, and uniformly mixed to obtain KBH 4 A solution; under the condition of room temperature and normal pressure, the obtained KBH 4 Adding the solution into the obtained mixed solution dropwise, blackening the solution and gradually forming particles, KBH 4 After the solution is added dropwise, stirring and reacting for 15 minutes, carrying out solid-liquid separation and cleaning, and carrying out freeze drying under the vacuum condition of-50 ℃ to obtain the modified nano zero-valent iron with the core-shell structure.
Example 7
The preparation method of the modified nano zero-valent iron with the core-shell structure comprises the following steps:
3.5600g of ferrous sulfate and 1.8g of 1-aminocyclohexylic acid are added into a three-neck flask containing 250mL of ultrapure water at normal temperature and pressure, and stirred for 10min to be mixed to obtain a mixed solution; 4 was added to a 100mL beaker at normal temperature and pressure.6000g of potassium borohydride, 80mL of ultrapure water, stirring and dissolving, and uniformly mixing to obtain KBH 4 A solution; under the condition of room temperature and normal pressure, the obtained KBH 4 Adding the solution into the obtained mixed solution dropwise, blackening the solution and gradually forming particles, KBH 4 After the solution is added dropwise, stirring and reacting for 13 minutes, carrying out solid-liquid separation and cleaning, and carrying out freeze drying under the vacuum condition of-55 ℃ to obtain the modified nano zero-valent iron with the core-shell structure.
Comparative example 1
The preparation method and process of the nano zero-valent iron are the same as those of the example 1, except that the aminocarboxylic acid compound is not added in the preparation process.
Application example 1
The modified nano zero-valent iron with the core-shell structure prepared in examples 1 to 3 and the nano zero-valent iron prepared in comparative example 1, 0.025g, which are respectively weighed, are added into a 150mL conical flask, then 50mL of heavy metal Cd (II) wastewater with the concentration of 30mg/L, the mixture is oscillated at room temperature, the mixture is sampled after the reaction for 80 minutes, and the concentration of Cd (II) in the treated wastewater is measured by using an inductively coupled plasma emission spectrometry (ICP-OES).
Application example 2
The modified nano zero-valent iron with the core-shell structure prepared in examples 1 to 3 and the nano zero-valent iron prepared in comparative example 1, 0.025g, which are respectively weighed, are added into a 150mL conical flask, 50mL of heavy metal Pb (II) wastewater with the concentration of 30mg/L, and the mixture is vibrated at room temperature, sampled after the reaction for 80 minutes, and the Pb (II) concentration in the treated wastewater is measured by using an inductively coupled plasma emission spectrometry (ICP-OES).
Application example 3
The modified nano zero-valent iron with the core-shell structure prepared in examples 1 to 3 and the nano zero-valent iron prepared in comparative example 1, 0.025g, were weighed respectively, added into a 150mL conical flask, then 50mL of heavy metal Cu (II) wastewater with the concentration of 30mg/L was added, the mixture was shaken at room temperature, the mixture was sampled after the reaction for 80 minutes, and the Cu (II) concentration in the treated wastewater was measured by using an inductively coupled plasma emission spectrometry (ICP-OES).
Application example 4
The modified nano zero-valent iron with the core-shell structure prepared in examples 1 to 3 and the nano zero-valent iron prepared in comparative example 1, 0.025g, which are respectively weighed, are added into a 150mL conical flask, 50mL of heavy metal Hg (II) wastewater with the concentration of 30mg/L, are then added, the mixture is oscillated at room temperature, the mixture is sampled after the reaction for 80 minutes, and the Hg (II) concentration in the treated wastewater is measured by using an inductively coupled plasma emission spectrometry (ICP-OES).
Application example 5
The modified nano zero-valent iron with the core-shell structure prepared in examples 1 to 3 and the nano zero-valent iron prepared in comparative example 1, 0.025g, were weighed and added into a 150mL conical flask, then 50mL of heavy metal Cr (VI) wastewater with the concentration of 30mg/L was added, the mixture was shaken at room temperature, the mixture was sampled after the reaction for 80 minutes, and the Cr (VI) concentration in the wastewater after the treatment was measured by using an inductively coupled plasma emission spectrometry (ICP-OES).
Application example 6
The modified nano zero-valent iron with the core-shell structure prepared in examples 1 to 3 and the nano zero-valent iron prepared in comparative example 1, 0.025g, were weighed respectively, added into a 150mL conical flask, then 50mL of heavy metal Ni (II) wastewater with the concentration of 30mg/L was added, the mixture was shaken at room temperature, the mixture was sampled after the reaction for 80 minutes, and the concentration of Ni (II) in the wastewater after the treatment was measured by using an inductively coupled plasma emission spectrometry (ICP-OES).
Application example 7
The core-shell structured modified nano zero-valent iron prepared in examples 1 to 3 and the nano zero-valent iron prepared in comparative example 1 were weighed 2g respectively, and placed in air at room temperature. After 180 days, 0.025g of each material is taken and added into a 150mL conical flask, 50mL of heavy metals Cd (II), pb (II), cu (II), hg (II), cr (VI) and Ni (II) wastewater with the concentration of 30mg/L are added, the mixture is oscillated at room temperature, the mixture is sampled after 80 minutes of reaction, and the concentration of the heavy metals Cd (II), pb (II), cu (II), hg (II) and Ni (II) remained in the water is measured by using an inductively coupled plasma emission spectrometry (ICP-OES), and the heavy metal Cr (VI) wastewater is measured by using a dibenzoyl dihydrazide spectrophotometry (GB 7467-1987).
Fig. 1 is a TEM image of modified nano zero-valent iron with a core-shell structure prepared by the method of the present invention, and fig. 2 is a TEM image of nano zero-valent iron obtained in comparative example 1; as can be seen from the comparison between the figures 1 and 2, the modified nano zero-valent iron with the core-shell structure prepared by the invention has an obvious core-shell structure, the modified nano zero-valent iron with the core-shell structure consists of an internal structure and an external structure, the shell thickness of the external structure amorphous iron oxide shell is about 3nm, and the core particle size of the internal structure amorphous zero-valent iron shell is about 40 nm; compared with nano zero-valent iron, the core-shell structure modified nano zero-valent iron prepared by the method has better dispersibility, so that the active sites of the modified nano zero-valent iron are increased, and the method is more beneficial to removing pollutants.
Fig. 3 shows a comparative SAED graph of the core-shell modified nano zero-valent iron according to the present invention and the nano zero-valent iron according to comparative example 1, and it can be seen from the graph that the electron diffraction pattern of the core-shell modified nano zero-valent iron according to the present invention has no bright spots of crystals, only dispersed light halos, which are typical characteristics of amorphous phases, which means that the core-shell modified nano zero-valent iron is amorphous phase, which has higher energy than the crystalline phase of the same component from the energy point of view, and the amorphous system is in a metastable state in energy, which is favorable for reacting with contaminants.
FIG. 4 is a graph showing the comparison of X-ray powder diffraction of modified nano zero-valent iron and nano zero-valent iron with core-shell structure, wherein the graph shows that the modified nano zero-valent iron with core-shell structure has no crystallization peak at 44.9 degrees, which shows that the chelation of 2-aminocyclohexylcarboxylic acid to ferrous iron ions in the invention affects the nucleation process of zero-valent iron in the reaction process, the finally formed zero-valent iron is in an amorphous state, the basic characteristics of the amorphous phase are complex atom and electron structure, and the microstructure is long-range disordered; whereas nano zero-valent iron shows a significant Fe (110) characteristic peak at 44.9 °.
FIG. 5 shows the electrochemical processes of the core-shell modified nano zero-valent iron and nano zero-valent ironThe optical analysis contrast diagram is shown in fig. 5 (a), which is a nyquist diagram of the core-shell structure modified nano zero-valent iron and nano zero-valent iron material, and it can be seen from the diagram that the electron transfer resistance (78.6 ohms) of the core-shell structure modified nano zero-valent iron is smaller than that of the nano zero-valent iron (115.2 ohms), which indicates that the amorphous phase zero-valent iron has faster electron transfer capability; FIG. 5 (b) is a graph showing the comparison of Cyclic Voltammograms (CV) of core-shell modified nano zero-valent iron and nano zero-valent iron materials, using a tangent method to find the reduction peak potential, making a straight line with a vertical transverse axis, and determining the reduction peak current density at the intersection point of the straight line and the CV curve, wherein the reduction current density of the nano zero-valent iron is 0.43mA/cm 2 The reduction current density of the core-shell structure modified nano zero-valent iron is 0.84mA/cm 2 The method shows that the reduction capacity of the core-shell structure modified nano zero-valent iron is stronger; fig. 5 (c) is a comparison graph of tafel corrosion curves of the core-shell structure modified nano zero-valent iron and the zero-valent iron material, where the corrosion potential of the core-shell structure modified nano zero-valent iron is far lower than that of the nano zero-valent iron material, which indicates that the core-shell structure modified nano zero-valent iron has higher electron transfer rate in the reduction reaction. All three electrochemical analyses show that the 2-aminocyclohexylcarboxylic acid selected by the invention chelates ferrous ions so that zero-valent iron formed in the reduction process is in an amorphous state, and the core-shell structure modified nano zero-valent iron has stronger reduction capability and quicker electron transfer capability and can show more excellent effect in the pollutant removal process.
Fig. 6 shows a comparison of the removal rates of the modified nano zero-valent iron and nano zero-valent iron with the core-shell structure prepared by the invention in the wastewater for removing Cd (II) ions, pb (II) ions, cu (II) ions, hg (II) ions, cr (VI) ions and Ni (II) ions, and the removal rate of the modified nano zero-valent iron material with the core-shell structure is obviously better than that of the nano zero-valent iron. The reaction is carried out for 80 minutes, the adding amount is 0.5g/L, the removal rate of Cd (II), pb (II), cu (II), hg (II), cr (VI) and Ni (II) wastewater with the initial concentration of 30mg/L is 99.5%, 100%, 94.2%, 91.8%, 100% and 90.7% on average, and compared with the removal rate of the nano zero-valent iron material, the core-shell structure modified nano zero-valent iron material has higher heavy metal ion removal capability.
FIG. 7 shows a comparison of the removal rates of Cd (II) ions, pb (II) ions, cu (II) ions, hg (II) ions, cr (VI) ions and Ni (II) ions in a water body after 180 days of aging, and shows that the removal rates of Cd (II), pb (II), cu (II), hg (II), cr (VI) and Ni (II) wastewater in water are respectively kept at 94.1%, 96.2%, 88.7%, 85.1%, 94.6% and 82.8%, while the removal rates of Cd (II), pb (II), cu (II), hg (II), cr (VI) and Ni (II) wastewater after the same aging period are only 34.9%, 64.8%, 54.6%, 53.8%, 74.1% and 41.3%.
The above is only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited by this, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Claims (4)

1. The preparation method of the modified nano zero-valent iron with the core-shell structure is characterized by comprising the following steps of:
mixing ferrous sulfate, amino carboxylic acid compounds and water, and stirring to obtain a mixed solution; KBH of 4 Dripping the solution into the mixed solution for reaction, and then carrying out solid-liquid separation, cleaning and drying to obtain the modified nano zero-valent iron with the core-shell structure; the stirring time is 5 min-15 min;
the KBH is carried out 4 The method for dripping the solution into the mixed solution comprises the following steps: KBH of 4 Dropwise adding the solution into the mixed solution, blackening the mixed solution and gradually forming particles, KBH 4 After the solution is added dropwise, stirring and reacting for 10min;
the dosage ratio of the ferrous sulfate to the aminocarboxylic acid compound to the water is (2.27-4.54) g: (1.2-2.4) g: (200-300) mL;
the aminocarboxylic acid compound comprises 2-aminocyclohexylcarboxylic acid or 1-aminocyclohexylcarboxylic acid, and the chelation of ferrous ions by the aminocarboxylic acid compound leads zero-valent iron formed in the reduction process to be in an amorphous state;
the KBH 4 The preparation method of the solution comprises the following steps: KBH of 4 Mixing with water, stirring to obtain KBH 4 A solution; the KBH 4 And the water is used in an amount ratio of (4-5) g (75-100) mL;
the modified nano zero-valent iron of the core-shell structure consists of an inner structure and an outer structure, wherein the inner structure is covered by the outer structure; the internal structure is amorphous zero-valent iron, and the external structure is amorphous iron oxide shell;
the drying mode is vacuum freeze drying, and the vacuum freeze drying is carried out at-60 ℃ to-50 ℃.
2. The modified nano zero-valent iron with the core-shell structure prepared by the preparation method of the modified nano zero-valent iron with the core-shell structure.
3. The use of the modified nano zero-valent iron of the core-shell structure as claimed in claim 2, characterized in that the modified nano zero-valent iron of the core-shell structure is used as a heavy metal ion remover.
4. The use of modified nano zero-valent iron of core-shell structure according to claim 3, wherein the heavy metal ions comprise Cd (II) ions, pb (II) ions, cu (II) ions, hg (II) ions, cr (VI) ions or Ni (II) ions.
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