CN115055679A - Zero-valent iron reducing agent and preparation method and application thereof - Google Patents
Zero-valent iron reducing agent and preparation method and application thereof Download PDFInfo
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- CN115055679A CN115055679A CN202210638383.XA CN202210638383A CN115055679A CN 115055679 A CN115055679 A CN 115055679A CN 202210638383 A CN202210638383 A CN 202210638383A CN 115055679 A CN115055679 A CN 115055679A
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 title claims abstract description 243
- 239000003638 chemical reducing agent Substances 0.000 title claims abstract description 198
- 238000002360 preparation method Methods 0.000 title abstract description 17
- 238000000034 method Methods 0.000 claims abstract description 59
- PAYRUJLWNCNPSJ-UHFFFAOYSA-N Aniline Chemical compound NC1=CC=CC=C1 PAYRUJLWNCNPSJ-UHFFFAOYSA-N 0.000 claims abstract description 44
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 33
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 31
- 238000000197 pyrolysis Methods 0.000 claims abstract description 27
- 239000000178 monomer Substances 0.000 claims abstract description 20
- 239000011248 coating agent Substances 0.000 claims abstract description 19
- 238000000576 coating method Methods 0.000 claims abstract description 19
- 238000000151 deposition Methods 0.000 claims abstract description 19
- 238000001035 drying Methods 0.000 claims abstract description 15
- 239000011247 coating layer Substances 0.000 claims abstract description 13
- 230000001681 protective effect Effects 0.000 claims abstract description 13
- LCPVQAHEFVXVKT-UHFFFAOYSA-N 2-(2,4-difluorophenoxy)pyridin-3-amine Chemical compound NC1=CC=CN=C1OC1=CC=C(F)C=C1F LCPVQAHEFVXVKT-UHFFFAOYSA-N 0.000 claims abstract description 12
- CHQMHPLRPQMAMX-UHFFFAOYSA-L sodium persulfate Substances [Na+].[Na+].[O-]S(=O)(=O)OOS([O-])(=O)=O CHQMHPLRPQMAMX-UHFFFAOYSA-L 0.000 claims abstract description 12
- 238000005229 chemical vapour deposition Methods 0.000 claims abstract description 7
- 238000002791 soaking Methods 0.000 claims abstract description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 45
- 238000006722 reduction reaction Methods 0.000 claims description 26
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 claims description 18
- JOPOVCBBYLSVDA-UHFFFAOYSA-N chromium(6+) Chemical compound [Cr+6] JOPOVCBBYLSVDA-UHFFFAOYSA-N 0.000 claims description 18
- 239000000203 mixture Substances 0.000 claims description 17
- GPNNOCMCNFXRAO-UHFFFAOYSA-N 2-aminoterephthalic acid Chemical compound NC1=CC(C(O)=O)=CC=C1C(O)=O GPNNOCMCNFXRAO-UHFFFAOYSA-N 0.000 claims description 14
- 239000007789 gas Substances 0.000 claims description 13
- NQXWGWZJXJUMQB-UHFFFAOYSA-K iron trichloride hexahydrate Chemical compound O.O.O.O.O.O.[Cl-].Cl[Fe+]Cl NQXWGWZJXJUMQB-UHFFFAOYSA-K 0.000 claims description 13
- 238000001027 hydrothermal synthesis Methods 0.000 claims description 12
- 238000010000 carbonizing Methods 0.000 claims description 11
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 10
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- 229910052757 nitrogen Inorganic materials 0.000 claims description 5
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- 229910052742 iron Inorganic materials 0.000 abstract description 13
- 239000002105 nanoparticle Substances 0.000 abstract description 5
- 230000010757 Reduction Activity Effects 0.000 abstract description 4
- 238000011065 in-situ storage Methods 0.000 abstract description 2
- 239000010842 industrial wastewater Substances 0.000 abstract description 2
- 238000004065 wastewater treatment Methods 0.000 abstract description 2
- 239000011651 chromium Substances 0.000 description 46
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- 239000002245 particle Substances 0.000 description 6
- 239000000126 substance Substances 0.000 description 6
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 4
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- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
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- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 2
- BUGBHKTXTAQXES-UHFFFAOYSA-N Selenium Chemical compound [Se] BUGBHKTXTAQXES-UHFFFAOYSA-N 0.000 description 2
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- QMKYBPDZANOJGF-UHFFFAOYSA-N benzene-1,3,5-tricarboxylic acid Chemical compound OC(=O)C1=CC(C(O)=O)=CC(C(O)=O)=C1 QMKYBPDZANOJGF-UHFFFAOYSA-N 0.000 description 2
- SXDBWCPKPHAZSM-UHFFFAOYSA-M bromate Inorganic materials [O-]Br(=O)=O SXDBWCPKPHAZSM-UHFFFAOYSA-M 0.000 description 2
- SXDBWCPKPHAZSM-UHFFFAOYSA-N bromic acid Chemical group OBr(=O)=O SXDBWCPKPHAZSM-UHFFFAOYSA-N 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 238000005253 cladding Methods 0.000 description 2
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- NWUYHJFMYQTDRP-UHFFFAOYSA-N 1,2-bis(ethenyl)benzene;1-ethenyl-2-ethylbenzene;styrene Chemical compound C=CC1=CC=CC=C1.CCC1=CC=CC=C1C=C.C=CC1=CC=CC=C1C=C NWUYHJFMYQTDRP-UHFFFAOYSA-N 0.000 description 1
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 1
- 239000012692 Fe precursor Substances 0.000 description 1
- 239000013144 Fe-MIL-100 Substances 0.000 description 1
- 229910002588 FeOOH Inorganic materials 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
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- BRPQOXSCLDDYGP-UHFFFAOYSA-N calcium oxide Chemical compound [O-2].[Ca+2] BRPQOXSCLDDYGP-UHFFFAOYSA-N 0.000 description 1
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- ZCDOYSPFYFSLEW-UHFFFAOYSA-N chromate(2-) Chemical compound [O-][Cr]([O-])(=O)=O ZCDOYSPFYFSLEW-UHFFFAOYSA-N 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
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- SOCTUWSJJQCPFX-UHFFFAOYSA-N dichromate(2-) Chemical compound [O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O SOCTUWSJJQCPFX-UHFFFAOYSA-N 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
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- HVENHVMWDAPFTH-UHFFFAOYSA-N iron(3+) trinitrate hexahydrate Chemical compound O.O.O.O.O.O.[Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O HVENHVMWDAPFTH-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/16—Metallic particles coated with a non-metal
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/05—Metallic powder characterised by the size or surface area of the particles
- B22F1/054—Nanosized particles
-
- 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
- C02F1/705—Reduction by metals
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C26/00—Coating not provided for in groups C23C2/00 - C23C24/00
-
- 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
- C02F2101/22—Chromium or chromium compounds, e.g. chromates
Abstract
The invention relates to the field of industrial wastewater treatment, and discloses a zero-valent iron reducing agent, and a preparation method and application thereof, wherein the preparation method comprises the following steps: a1, soaking and drying a source reducing agent by using a sodium persulfate solution, and then depositing an aniline monomer on the dried source reducing agent by using a chemical vapor deposition method to obtain an intermediate; a2, carrying out high-temperature pyrolysis on the intermediate in a protective gas atmosphere to form a nitrogen-doped carbon Coating (CN) on the surface of zero-valent iron, and thus obtaining the zero-valent iron reducing agent with a coating structure; wherein the source reducing agent is nano zero-valent iron or load type zero-valent iron. In the invention, the reduction activity of the obtained zero-valent iron reducing agent is high by adopting a method of in-situ forming a CN coating layer to activate the zero-valent iron by adopting a vapor deposition-pyrolysis strategy; the CN coating layer coated on the surface of the zero-valent iron nano-particles can prevent the loss of iron species, and improve the utilization rate and stability of the zero-valent iron, thereby realizing the continuous utilization of the reducing agent.
Description
Technical Field
The invention relates to the field of industrial wastewater treatment, and particularly relates to a zero-valent iron reducing agent, and a preparation method and application thereof.
Background
Chromium is widely found in nature, and mainly exists in the forms of hexavalent chromium (Cr (VI)) and trivalent chromium (Cr (III)) in an aqueous environment. Among them, Cr (VI) is often produced in industrial production processes, such as electroplating, smelting, leather tanning and the like, and has the characteristics of large discharge amount and high discharge concentration. Cr (vi), a typical heavy metal, has toxicity 100 times higher than cr (iii), and is more easily absorbed by human body, causing serious damage to human body. Cr (VI) has high accumulation, and if being absorbed by human body for a long time, the Cr (VI) can be accumulated in the human body and poison various organs of the human body, such as kidney, liver, stomach and the like; high concentrations of cr (vi) are also carcinogenic and mutagenic.
For the reasons, discharge standards of Cr (VI) applied to water bodies are formulated in all countries in the world. The maximum allowable concentration of Cr (VI) in drinking water is regulated to be 0.05mg/L by the United states Environmental Protection Agency (EPA); the sanitary standard of domestic drinking water in China also stipulates that the content of Cr (VI) in the drinking water cannot exceed 0.05 mg/L. Since cr (iii) is the main industrial raw material, the reduction of cr (vi) to cr (iii), an important treatment strategy, has been considered by various techniques.
At present, the commonly used cr (vi) treatment methods mainly include adsorption-reduction, chemical reduction, ion exchange, and photocatalytic reduction. The technology inevitably has negative effects of high energy consumption, low efficiency, secondary pollution and the like in application. If the activated carbon is used for adsorbing and treating Cr (VI), the adsorbent needs to be regenerated and replaced after reaching saturation, and the cost is higher. The chemical precipitation method is that Cr (VI) is reduced into Cr (III) by using a reducing agent, then lime or sodium hydroxide is added to generate a precipitate, and the precipitate is removed. The ion exchange method for treating Cr (VI) in water mainly utilizes ion exchange resin to exchange with Cr (VI) ions, and has the defects that the resin used in the method is easy to pollute and lose effectiveness, and impurity ions such as sodium, iron and the like in the regenerated waste liquid cannot be directly recycled and can cause secondary pollution when discharged into the environment. The photo/electro-catalytic reduction method is based on that the catalyst efficiently reduces Cr (VI) under the condition of energy input, but consumes a large amount of energy, and has low economic benefit.
Nanometer zero-valent iron (Fe) 0 ) Has the advantages of low cost, environmental protection and low Fe II /Fe 0 The electrode potential (-0.44Vvs. SHE) is widely used in Cr (VI) reduction due to the strong oxidizing Cr (VI) by Fe 0 Direct reduction, Fe is oxidized. However, the existing nano zero-valent iron reducing agent has low reduction efficiency, and the recycling of the reducing agent is difficult to realize.
Disclosure of Invention
The invention aims to solve the problems that the reduction efficiency of a zero-valent iron reducing agent is low and the recycling of the reducing agent is difficult to realize in the prior art, and provides the zero-valent iron reducing agent and a preparation method and application thereof.
The inventor finds that the existing nano zero-valent iron reducing agent has low reduction efficiency, and the recovery and the reuse of the reducing agent are difficult to realize mainly because: fe 0 Inert iron oxide film (e.g. FeO) formed by contact with air x And FeOOH) inhibits the reaction from proceeding, inhibiting the activity; (2) the large-size blocky structure makes Fe in the bulk phase difficult to be utilized, so that the utilization rate of Fe is reduced; (3) the dissolution and loss of Fe species cause the waste of Fe resources and secondary pollution.
The inventor further researches and discovers that zero-valent iron nanoparticles with carbon-doped nitrogen (CN) coating, namely a zero-valent iron reducing agent, can be prepared by activating a source reducing agent (zero-valent iron) by adopting a vapor deposition-pyrolysis technology, and the zero-valent iron reducing agent has excellent reduction efficiency and stability, and high stability, so that the zero-valent iron reducing agent can be recycled, regenerated and reused.
In order to achieve the above object, an aspect of the present invention provides a method for preparing a zero-valent iron reducing agent, the method comprising the steps of:
a1, soaking and drying a source reducing agent by using a sodium persulfate solution, and then polymerizing and depositing an aniline monomer on the dried source reducing agent by using a chemical vapor deposition method to obtain an intermediate;
a2, carrying out high-temperature pyrolysis on the intermediate in a protective gas atmosphere to form a nitrogen-doped carbon coating layer on the surface of zero-valent iron, and thus obtaining the zero-valent iron reducing agent with a coating structure;
wherein the source reducing agent is nano zero-valent iron or load type zero-valent iron.
Preferably, in step a1, the depositing includes: and respectively placing the dried source reducing agent and the aniline monomer on two sides of the tubular furnace, and sealing for deposition.
Preferably, the mass ratio of the source reducing agent to the aniline monomer is 1: 2-1: 10.
preferably, the concentration of the sodium persulfate solution is 0.15-0.25 g/mL.
Preferably, the chemical vapor deposition conditions include: the deposition temperature is 40-80 ℃, and the deposition time is 8-12 h.
Preferably, in step a2, the shielding gas is nitrogen or argon.
Preferably, the operating conditions of the high-temperature pyrolysis include: the flow speed of the protective gas is 100-200 mL/min, the temperature is 700-1000 ℃, and the time is 5-8 h.
Preferably, the supported zero-valent iron is porous carbon supported zero-valent iron or nitrogen-doped porous carbon supported zero-valent iron, and preferably the nitrogen-doped porous carbon supported zero-valent iron.
Preferably, the method further comprises preparing the nitrogen-doped porous carbon loaded zero-valent iron according to the following procedure:
b1, uniformly mixing ferric trichloride hexahydrate, 2-amino terephthalic acid and N, N-dimethylformamide, carrying out hydrothermal reaction, and then washing, centrifuging and drying to obtain a mixture;
and B2, carbonizing the mixture at high temperature in a protective atmosphere to obtain the nitrogen-doped porous carbon loaded zero-valent iron.
Preferably, in the step B1, the mass ratio of ferric trichloride hexahydrate to 2-amino terephthalic acid is 1: 3-3: 1.
preferably, the temperature of the hydrothermal reaction is 100-200 ℃, and the reaction time is 18-24 h.
Preferably, the operating conditions for carbonizing at high temperature include: the flow speed of the protective gas is 100-200 mL/min, the temperature is 700-1000 ℃, and the time is 5-8 h.
The invention provides a zero-valent iron reducing agent, which is prepared by the preparation method of the zero-valent iron reducing agent.
In a third aspect, the invention provides the use of a zero-valent iron reducing agent prepared by a method as described above for the treatment of oxidic contaminants in a body of water.
Preferably, the oxidic contaminant is a bromate, dichromate or selenate.
In a fourth aspect, the present invention provides a method for treating hexavalent chromium in a body of water, the method being for treating a body of water containing hexavalent chromium contaminants using a zero-valent iron reducing agent, the zero-valent iron reducing agent being prepared by the method as described above.
Preferably, the method comprises the steps of: and adding a zero-valent iron reducing agent into the water body containing the hexavalent chromium pollutants, adjusting the pH of the water body to 1.5-3, and carrying out reduction reaction to remove the hexavalent chromium in the water body.
The invention has the advantages and beneficial effects that:
(1) in the invention, the reduction activity of the zero-valent iron is improved by adopting a method of in-situ forming a CN coating layer to activate the zero-valent iron by adopting a vapor deposition-pyrolysis strategy, so that the reduction activity of the obtained zero-valent iron reducing agent is high, and the defect that the stability is replaced by the activity sacrifice in the traditional coating technology is overcome;
(2) the CN coating layer coated on the surface of the zero-valent iron nano particle can prevent the loss of iron species, and improve the utilization rate and stability of the zero-valent iron, so that the continuous utilization of the reducing agent can be realized by utilizing the carbothermic reaction and the carbon addition regeneration;
(3) the zero-valent iron reducing agent synthesized by the invention is used for reducing Cr (VI) in water and can efficiently remove the toxicity of Cr (VI); in the using process, no other special equipment condition is needed, the operation can be carried out at normal temperature and normal pressure, the operation is simple, and the application range is wide;
(4) each step in the preparation method of the zero-valent iron reducing agent provided by the invention is a basic chemical process, and the operation is easy; the used source reducing agent only needs to contain iron element, the material is easy to obtain, and the technical feasibility is realized;
(5) the invention relies on a chemical vapor deposition-pyrolysis strategy, and the reduction performance of the catalyst can be effectively improved by applying the catalyst to commercial reducing agents such as nano zero-valent iron, load-type zero-valent iron and the like, and the catalyst has universality.
Drawings
FIG. 1 is a transmission electron micrograph of a product obtained in each step of example 1;
FIG. 2 is an atomic force microscope image of the CN coating, zero-valent iron reducing agent in example 1;
FIG. 3 is an XRD pattern of the source reductant, zero valent iron reductant, and product after acid treatment of the zero valent iron reductant of example 1;
FIG. 4 is a Raman spectrum of the source reducing agent, zero valent iron reducing agent, the product of the acid treatment of the zero valent iron reducing agent obtained in example 1, and the zero valent iron reducing agent obtained in example 2 of example 1;
FIG. 5 is a UPS plot of the source reductant and zero-valent iron reductant of example 1, along with the calculated work function;
FIG. 6 is a Nyquist plot of the source reductant and the zero-valent iron reductant of example 1;
FIG. 7 is a graph of the magnetic saturation and magnetic separation of the source reductant and zero-valent iron reductant prepared in example 1 and the zero-valent iron reductant used in application example 1;
FIG. 8 shows the results of the Cr (VI) treatment effect of example 1, comparative examples 1 to 3, and the reduction performance test of each reducing agent;
FIG. 9 shows the results of the cycle performance and regeneration effect tests and the reducing performance test of the reducing agent of application example 1;
FIG. 10 is a graph showing the effect of applying examples 1-4 to Cr (VI) in a water body;
FIG. 11 is a graph showing the effect of application example 1 and application examples 5 to 6 on Cr (VI) in a water body;
FIG. 12 is a graph showing the effect of application example 7 and application comparative example 4 on Cr (VI) in a water body;
FIG. 13 is a graph showing the effect of application example 8 and application comparative example 5 on the treatment of Cr (VI) in a water body;
FIG. 14 is a graph showing the effect of comparative example 6 on Cr (VI) in a water body.
Detailed Description
The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation. The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The invention provides a preparation method of a zero-valent iron reducing agent, which comprises the following steps:
step A1, soaking and drying a source reducing agent by using a sodium persulfate solution, and then polymerizing and depositing aniline monomers on the dried source reducing agent by adopting a chemical vapor deposition method to obtain an intermediate;
step A2, performing high-temperature pyrolysis on the intermediate in a protective gas atmosphere to form a nitrogen-doped carbon coating layer on the surface of zero-valent iron, and thus obtaining a zero-valent iron reducing agent with a coating structure;
wherein the source reducing agent is nano zero-valent iron or supported zero-valent iron.
When the source reducing agent is the supported zero-valent iron, before step a1, the method further includes: the source reducing agent is milled to form a uniform powder for uniform deposition.
In the invention, the nitrogen-doped carbon coating layer (CN coating layer) is obtained by chemical vapor deposition-pyrolysis of a precursor aniline monomer, and the zero-valent iron precursor is obtained by carbonizing an Fe-based metal organic framework. In addition, the content of iron in the zero-valent iron reducing agent is 20-80%.
In a specific embodiment, in step a1, the depositing includes: and respectively placing the dried source reducing agent and the aniline monomer on two sides of a tubular furnace, sealing, and depositing to obtain an intermediate.
In a specific embodiment, the mass ratio of the source reducing agent to the aniline monomer is 1: 2-1: 10, in particular, may be 1: 2. 1: 4. 1: 5. 1: 7 or 1: 10, preferably 1: 4.
in one embodiment, the concentration of the sodium persulfate solution may be 0.15g/mL, 0.18g/mL, 0.20g/mL, or 0.25 g/mL.
In a preferred embodiment, the temperature of the chemical vapor deposition may be 40 ℃, 45 ℃, 50 ℃, 54 ℃ or 60 ℃ and the time may be 8h, 10h, 11h or 12 h.
In a preferred embodiment, in step a2, the shielding gas is nitrogen or argon.
In a preferred embodiment, in step a2, the operating conditions of the high-temperature pyrolysis include: the flow speed of the protective gas is 100-200 mL/min, the temperature is 700-1000 ℃, and the time is 5-8 h. In the high-temperature pyrolysis process, the inert oxide film on the surface of the zero-valent iron particles can be removed, and the activity of the zero-valent iron is improved.
Wherein the supported zero-valent iron is porous carbon supported zero-valent iron (Fe) 0 C) or nitrogen-doped porous carbon loaded zero-valent iron (Fe) 0 /CN), preferably nitrogen-doped porous carbon loaded with zero-valent iron.
The specific preparation method of the nitrogen-doped porous carbon loaded zero-valent iron is not limited in the invention, and can be a commercially available preparation method or a conventional preparation method in the field. Preferably, the nitrogen-doped porous carbon loaded zero-valent iron is prepared according to the following procedure:
step B1, uniformly mixing ferric trichloride hexahydrate, 2-amino terephthalic acid and N, N-dimethylformamide, carrying out hydrothermal reaction, washing, centrifuging and drying to obtain a mixture,
and step B2, carbonizing the mixture at high temperature in a protective atmosphere to obtain the nitrogen-doped porous carbon loaded zero-valent iron.
In one embodiment, in step B1, the mass ratio of ferric trichloride hexahydrate to 2-aminoterephthalic acid is 1: 3-3: 1, that is, may be 1: 3. 1.5: 3. 3: 3. 3: 2 or 3: 1, preferably 3: 1.
in a specific embodiment, in step B1, 2-amino terephthalic acid and N, N-Dimethylformamide (DMF) are mixed uniformly to obtain a 2-amino terephthalic acid solution, and then ferric chloride hexahydrate is added to perform hydrothermal reaction. Preferably, the temperature of the hydrothermal reaction is 100-200 ℃, and the reaction time is 18-24 h.
In a preferred embodiment, the operating conditions for carbonizing at high temperature include: the flow speed of the protective gas is 100-200 mL/min, the temperature is 700-1000 ℃, and the time is 5-8 h.
According to the invention, aniline is used as a precursor, a source reducing agent is soaked and dried by a sodium persulfate solution, the aniline monomer and the source reducing agent are placed in a tubular furnace together, volatile aniline molecules are captured by vapor deposition, and then oxidative polymerization is carried out, namely a layer of Polyaniline (PANI) is coated on the surface of the source reducing agent, and a uniform CN coating layer is formed after high-temperature pyrolysis and coated on the surface of a zero-valent iron nanoparticle, namely the zero-valent iron reducing agent.
The invention also provides a zero-valent iron reducing agent prepared by the preparation method of the zero-valent iron reducing agent.
The invention also provides an application of the zero-valent iron reducing agent in treating oxidized pollutants in water, wherein the zero-valent iron reducing agent is prepared by the method.
In a specific embodiment, the oxidizing contaminant is a bromate, chromate, or selenate.
In addition, the invention also provides a method for treating hexavalent chromium in the water body, which comprises the following steps: a water body containing hexavalent chromium contaminants is treated with a zero-valent iron reducing agent, which is prepared by the method described above.
In a preferred embodiment, the method comprises the steps of: and adding a zero-valent iron reducing agent into the water body containing the hexavalent chromium pollutants, adjusting the pH of the water body to 1.5-3, and carrying out a reduction reaction. More preferably, the pH of the body of water is adjusted to 2.
The use amount of the zero-valent iron reducing agent is not limited, and can be determined according to the concentration of specific pollutants, and in the method, when the initial concentration of the hexavalent chromium pollutants is 5-15 mg/L, and the use amount of the zero-valent iron reducing agent is 30-50 mg/L, the removal rate of the hexavalent chromium pollutants in the water body can be more than 80% within 50-120 min.
The present invention will be described in detail below by way of examples, but the scope of the present invention is not limited thereto.
Example 1
This example illustrates the preparation of the zero-valent iron reducing agent of the present invention.
(1) Uniformly mixing 2-amino terephthalic acid and DMF (dimethyl formamide), adding ferric chloride hexahydrate, uniformly stirring, carrying out hydrothermal reaction at 110 ℃ for 24 hours, washing, centrifuging and drying to obtain a mixture, wherein the mass ratio of the ferric chloride hexahydrate to the 2-amino terephthalic acid is 3: 1;
(2) mixing the above mixture with N 2 Carbonizing at 900 deg.C for 5h at flow rate of 150mL/min to obtain source reducing agent denoted as Fe 0 /CN；
(3) Grinding the source reducing agent, soaking and drying the ground source reducing agent by using a sodium persulfate solution with the concentration of 0.15g/mL, placing the ground source reducing agent and an aniline monomer in a tubular furnace together, sealing two sides of the tubular furnace, and depositing for 12 hours at the temperature of 50 ℃ to obtain an intermediate, wherein the mass ratio of the source reducing agent to the aniline monomer is 1: 4;
(4) reacting the intermediate in N 2 Pyrolyzing at a flow rate of 150mL/min and a temperature of 800 ℃ for 5h to obtain a CN-coated iron zero-valent iron reducing agent, namely a zero-valent iron reducing agent, which is marked as Fe 0 @CN。
Example 2
This example illustrates the preparation of the zero-valent iron reducing agent of the present invention.
The process was carried out as described in example 1, except that the source reducing agent in step (3) was porous carbon-supported zero-valent iron (Fe) 0 /C), the zero-valent iron reducing agent obtained is denoted as Fe 0 The preparation method comprises the following steps of dissolving ferric nitrate hexahydrate and trimesic acid in deionized water, stirring for 30min, transferring to a hydrothermal reaction kettle, and carrying out hydrothermal reaction at 180 ℃ for 12 h. Cooling to room temperature, filtering the mixture, washing with deionized water and methanol, and drying to obtain mixture MIL-100 (Fe); carbonizing MIL-100(Fe) under nitrogen to obtain Fe 0 /C。
Example 3
This example illustrates the preparation of the zero-valent iron reducing agent of the present invention.
The process was carried out as described in example 1, except that the source reducing agent in step (3) was commercially available zero-valent iron nZVI (available from the national chemical agency, ltd (china)), and it was understood that steps (1) and (2) were adaptively deleted.
Example 4
(1) Uniformly mixing 2-amino terephthalic acid and DMF (dimethyl formamide), adding ferric chloride hexahydrate, uniformly stirring, carrying out hydrothermal reaction at 100 ℃ for 20 hours, washing, centrifuging and drying to obtain a mixture, wherein the mass ratio of the ferric chloride hexahydrate to the 2-amino terephthalic acid is 3: 3:
(2) mixing the above mixture with N 2 Carbonizing at flow rate of 100mL/min and temperature of 700 deg.C for 8h to obtain source reducing agent denoted as Fe 0 /CN；
(3) Grinding the source reducing agent, soaking and drying the ground source reducing agent by using a sodium persulfate solution with the concentration of 0.2g/mL, placing the ground source reducing agent and an aniline monomer in a tubular furnace together, sealing two sides of the tubular furnace, and depositing for 10 hours at the temperature of 40 ℃ to obtain an intermediate, wherein the mass ratio of the source reducing agent to the aniline monomer is 1: 10;
(4) reacting the intermediate with N 2 Flow velocity of 200mL/min, and the temperature is 1000 ℃ for 6h, thus obtaining the CN-coated iron zero-valent iron reducing agent, namely the zero-valent iron reducing agent.
Example 5
(1) Uniformly mixing 2-amino terephthalic acid and DMF (dimethyl formamide), adding ferric chloride hexahydrate, uniformly stirring, carrying out hydrothermal reaction at 200 ℃ for 18h, washing, centrifuging and drying to obtain a mixture, wherein the mass ratio of the ferric chloride hexahydrate to the 2-amino terephthalic acid is 1: 3;
(2) mixing the above mixture with N 2 Carbonizing at 1000 deg.C and flow rate of 200mL/min for 6h to obtain source reducing agent denoted as Fe 0 /CN；
(3) Grinding the source reducing agent, soaking and drying the ground source reducing agent by using a sodium persulfate solution with the concentration of 0.25g/mL, placing the ground source reducing agent and an aniline monomer in a tubular furnace together, sealing two sides of the tubular furnace, and depositing for 8 hours at the temperature of 80 ℃ to obtain an intermediate, wherein the mass ratio of the source reducing agent to the aniline monomer is 1: 2;
(4) reacting the intermediate in N 2 Pyrolyzing for 8h under the conditions that the flow rate is 100mL/min and the temperature is 700 ℃, and obtaining the CN-coated iron zero-valent iron reducing agent, namely the zero-valent iron reducing agent.
Comparative example 1
The procedure was followed as described in example 1, except that the aniline monomer was an oxypolymerization coating-pyrolysis synthetic zero-valent iron reducing agent in the liquid phase. Specifically, the method comprises the following steps:
(1) the source reductant Fe was prepared as described in example 1 0 /CN；
(2) Dissolving sodium persulfate in 1M hydrochloric acid solution, and adding Fe 0 The solution was dispersed in CN, and after stirring for 0.5h, the purified aniline monomer was added dropwise to the mixture. Continuously stirring for 5h, and finally making the material appear dark green;
(3) magnetically separating the above materials from the solution, filtering and cleaning for several times, and placing in a tube furnace N 2 Pyrolyzing for 5 hours under the conditions of atmosphere (flow rate of 150mL/min) and temperature of 800 ℃. The final product is Fe synthesized by liquid phase deposition-pyrolysis method 0 @ CN reducing agent.
Application example 1
The application example is used for illustrating the method for treating hexavalent chromium in the water body (namely, the application of the zero-valent iron reducing agent) provided by the invention.
Adding the zero-valent iron reducing agent prepared in the example 1 into a water body containing hexavalent chromium pollutants (wherein the initial concentration of Cr (VI) in the water body is 10.4mg/L), so that the concentration of the reducing agent is 40mg/L, adjusting the pH value of the water body to 2, and carrying out reduction reaction for 2h at normal temperature and normal pressure.
Application examples 2 to 4
The method is implemented according to the application example 1, except that in the application example 2, the initial concentration of Cr (VI) in the water body is 6.2 mg/L; in application example 3, the initial concentration of Cr (VI) in the water body is 8.2 mg/L; the initial concentration of Cr (VI) in the water body in application example 4 is 12.4 mg/L.
Application examples 5 to 6
The method is implemented according to the application example 1, except that in the application example 5, the concentration of the reducing agent in the water body is 32 mg/L; in application example 6, the concentration of the reducing agent was 51 mg/L.
Application example 7
The procedure was as in application example 1, except that the reducing agent used was the zero-valent iron reducing agent obtained in example 2 (i.e., the source reducing agent was Fe) 0 /C)。
Application example 8
The procedure was followed as in application example 1 except that the reducing agent used was the zero valent reducing agent prepared in example 3 (i.e., the source reducing agent was commercial zero valent iron).
Application comparative examples 1 to 3
The procedure of application example 1 was followed, except that the reducing agent used in application example 1 was a pure CN material; use of reducing agent used in comparative example 2 was Fe obtained in step (2) of example 1 0 a/CN; use of the reducing agent used in comparative example 3 as the zero-valent iron reducing agent obtained in example 1 after acid treatment (i.e. the zero-valent iron reducing agent is stirred in 2M hydrochloric acid solution for 3h, washed until the washing liquid is neutral, and the obtained solid is dried), and recorded as Fe 0 @ CN-acid treatment.
Application comparative example 4
Was carried out in accordance with the procedure of application example 1, except that the reducing agent used was the source reducing agent (Fe) of example 2 0 /C)。
Comparative application example 5
The procedure of application example 1 was followed, except that the reducing agent used was commercial zero-valent iron (nZVI) as the source reducing agent in example 3.
Comparative application example 6
The procedure of application example 1 was followed except that the reducing agent used in application comparative example 6 was the zero-valent reducing agent prepared in comparative example 1 (i.e., prepared using an aqueous polymerization-pyrolysis strategy).
Test example 1
The mixture obtained in step (1), the source reducing agent obtained in step (2), the intermediate obtained in step (3), and the zero-valent iron reducing agent obtained in step (4) in example 1 were characterized by using a transmission electron microscope, and the results are shown in fig. 1.
In which FIG. 1(a) is an electron micrograph of the mixture. As can be seen from FIG. 1(a), the obtained product is an iron-based MOFs with a regular octahedral structure.
Fig. 1(b) is an electron micrograph of the source reducing agent, and it can be seen from fig. 1(b) that Fe particles are supported on the surface of the porous carbon.
Fig. 1(c) is an electron micrograph of the intermediate, and as can be seen from fig. 1(c), the Fe particle contours after deposition are blurred, indicating effective coating.
FIG. 1(d) is an electron microscope image of a zero-valent iron reducing agent, and it can be seen from FIG. 1(d) that the states of the coating layer and the particles are not obviously changed after pyrolysis, which indicates that the coating structure is not damaged by high-temperature pyrolysis.
In addition, the iron content in the zero valent iron reducing agent shown was tested to be 28.9 wt%.
Test example 2
The CN coating layer obtained in example 1 and the zero-valent iron reducing agent were characterized by an atomic force microscope, and the results are shown in fig. 2.
Wherein FIG. 2(a) is a representation of the CN cladding layer, consisting ofAs can be seen in FIG. 2(a), the CN cladding thickness is about 5 nm. FIG. 2(b) is a diagram showing the results of the characterization of the zero-valent iron reducing agent, and it can be seen from FIG. 2 that the zero-valent iron reducing agent (i.e., Fe after coating) 0 Nanoparticles and CN coating) were about 28.6nm, so the Fe particle size was about 24 nm.
The source reducing agent (Fe) obtained in example 1 was added 0 /CN), zero-valent iron reducing agent (Fe) 0 @ CN), and acid treatment (Fe) of the zero-valent iron reducing agent 0 @ CN-acid treatment) was subjected to X-ray diffraction, and the results are shown in FIG. 3. In addition, the acid treatment step is Fe 0 @ CN reducer in 2M hydrochloric acid solution stirring for 3h, washing until the washing liquid is neutral, the solid drying.
Fe in FIG. 3 0 @ CN and Fe 0 The spectra corresponding to/CN all showed characteristic peaks of Fe with similar intensity, because the thickness of the carbon coating layer was not enough to affect the intensity of Fe, and the Fe particles were removed after the acid treatment, so the characteristic peaks disappeared.
Test example 3
The source reducing agent (Fe) obtained in example 1 was added 0 /CN), zero-valent iron reducing agent (Fe) 0 @ CN), acid treatment (Fe) of the zero-valent iron reducing agent obtained in example 1 0 @ CN — acid treatment) and the zero-valent iron reducing agent obtained in example 2, and the results thereof are shown in fig. 4.
As can be seen from a comparison of fig. 4, the zero-valent iron reducing agent obtained after coating CN is more graphitized than the source reducing agent before coating, which is advantageous for improving the activity. In contrast, the supported type Fe in example 2 0 The low graphitization degree of the coated/C is because the pure carbon carrier is not easy to graphitize.
The source reducing agent (Fe) obtained in example 1 was added 0 /CN) and zero-valent iron reducing agent (Fe) 0 @ CN) was tested using an Ultraviolet Photoelectron Spectrometer (UPS), and the corresponding work function was calculated, with the results shown in fig. 5.
As can be seen from FIG. 5, Fe 0 Work function of @ CN less than Fe 0 and/CN represents a reduced energy barrier and is beneficial to the reaction. Similar conclusions are also drawn by the Nyquist plotWas verified to be Fe 0 @ CN has an impedance of 10.03. omega. lower than that of Fe 0 @ CN (15.41 Ω) (as shown in FIG. 6).
FIG. 7 shows the source reductant (Fe) obtained in example 1 0 /CN) and zero-valent iron reducing agent (Fe) 0 @ CN), and zero-valent iron reducing agent (Fe) used in application example 1 0 @ CN-after use) magnetic saturation (a) and magnetic separation (b) effect plots.
Fe shown in FIG. 7(a) 0 @CN，Fe 0 [ solution ] CN and Fe 0 @ CN-the magnetic saturations after use were 12emu/g, 47emu/g and 49emu/g, respectively, indicating that the reducing agent after activation and use had higher magnetic saturations, which were favorable for magnetic separation, and were sufficient to allow the material to be effectively separated within 3min (as shown in FIG. 7 (b)).
Test example 4
The treatment effects of the application example 1 and the application comparative examples 1 to 3 on Cr (VI) in the water body are tested, the activity and the removal amount of each reducing agent are tested, and the test results are shown in fig. 8. In FIGS. 8 to 14, C t /C 0 The ratio of the contaminant concentration to the initial contaminant concentration at time t is referred to, initial activity is referred to as initial activity, and removal capacity is referred to as removal capacity.
As can be seen from fig. 8, the pure CN material cannot effectively remove cr (vi), and the reduction of cr (vi) all occurs on the reducing agent containing iron. Therefore, the reaction of the system is Cr (VI) reduction in which Fe participates. Fe 0 @ CN at 70min, the set Cr (VI) can be completely reduced, and Fe 0 The amount of Cr (VI) removed by the/CN is less than 10 percent, and the ultra-high reduction performance is shown. Specific activity and removal amount comparative data As shown in FIG. 8(b), activity after coating (2037 mg/g) reductant h.L) and the amount of Cr (VI) removed (0.26 gCr/g) reductant ) Are each Fe 0 75.4 times and 10 times of/CN, illustrating the use of a chemical vapor deposition-pyrolysis strategy on the source reductant Fe 0 The reduction performance of the catalyst can be greatly improved by activating the/CN.
After repeating the procedure of example 14 times, the separated Fe 0 @ CN is subjected to carbothermic regeneration and carbon addition treatment, wherein the carbon addition treatment is carried out in a gas phaseDeposition-pyrolysis steps (3) and (4) in example 1). The procedure of example 1 was repeated 1 more times and the effect of cr (vi) treatment and the activity and removal amount of the reducing agent were measured.
As can be seen from FIG. 9, under the same reaction conditions, Fe 0 @ CN is capable of maintaining high stability by carbon thermal regeneration (same conditions as those for synthesizing CN coating) and carbon addition. As shown in fig. 9(a), the reducing performance of the reducing agent regenerated in the first three cycles is basically kept unchanged, and the activity of the reducing agent regenerated in the fourth cycle is reduced, mainly because the carbon layer in the material is not enough to reduce zero-valent iron, so that the performance of the reducing agent after carbon addition treatment is restored to the original level, as shown in fig. 9(b) in particular.
Test example 5
The results of testing the effect of the application examples 1-4 on Cr (VI) in water are shown in FIG. 10, i.e., Cr (VI) in Fe at different initial concentrations (6.2mg/L, 8.2mg/L, 10.4mg/L and 12.4mg/L) 0 The reduction curve of @ CN reducer, and the corresponding initial activity and removal amount.
It can be seen from fig. 10 that when the amount of the reducing agent is 40mg/L, the reducing agent can completely remove cr (vi) within 50min at the concentration of cr (vi) in the water body lower than 10.4mg/L (inclusive), and above this concentration, the cr (vi) can not be completely removed even if the time is prolonged to 120min (as shown in fig. 10(a)), which is mainly because Fe in the reducing agent is enough to reduce all cr (vi) at the concentration lower than 10.4mg/L, and the content of Fe above this concentration becomes a limiting factor. With respect to kinetic analysis, this reaction is adsorption-controlled (see fig. 10(b)), so as the initial cr (vi) concentration increases, the activity increases, and the amount removed increases, until the reducing agent is completely reacted (see fig. 10 (c)).
The results of the tests of application example 1 and application examples 5-6 on the treatment effect of Cr (VI) in the water body are shown in FIG. 11, namely the reduction curves of different reducing agent addition amounts (32mg/L, 40mg/L and 51mg/L) on Cr (VI), and the corresponding initial activity and removal amount.
As can be seen from FIG. 11, the results are similar to those of FIG. 10, in the case of excess reducing agent, Cr (VI) can be completely reduced within 70min, and in the case of insufficient reducing agent, the amount of Cr (VI) reduced is correspondingly reduced. The removal amount and initial activity were also consistent with the results shown in FIG. 10, as shown in FIG. 11 (b).
Test example 6
Test application example 7 (Fe) 0 /C @ CN) and comparative application example 4 (Fe) 0 The results of the treatment of Cr (VI) in water with Fe are shown in FIG. 12 0 Reducing agent and corresponding vapour deposition-pyrolysis treated Fe 0 the/C @ CN reducer has a Cr (VI) reduction curve and corresponding initial activity and removal amount.
As can be seen from FIG. 12(a), Fe was found to be present within 120min 0 Cr (VI) reduced by/C less than 10%, and Fe 0 the/C @ CN can reach more than 80 percent. As can be seen from FIG. 12(b), Fe 0 Corresponding activity to removal ratio Fe of/C @ CN 0 the/C is 17 times and 8.5 times higher. Illustrating the use of a chemical vapor deposition-pyrolysis strategy on the source reductant Fe 0 The reduction performance of the catalyst can be greatly improved by activating the catalyst/C.
The effect of application example 8 and application comparative example 5 on the treatment of cr (vi) in a water body was tested, and the results are shown in fig. 13, i.e., the commercial zero-valent iron (nZVI) and the corresponding vapour deposition-pyrolysis treated zero-valent iron reductant (nZVI @ CN) on the cr (vi) reduction curve, and the corresponding initial activity and removal amount.
As can be seen from FIG. 13, the activity and the removal amount of commercial zero-valent iron are greatly improved after the commercial zero-valent iron is activated by the chemical vapor deposition-pyrolysis strategy.
The results of testing the effect of comparative example 6 on the treatment of Cr (VI) in a water body are shown in FIG. 14.
As can be seen from fig. 14, the reduction activity and the removal amount of the zero-valent iron reducing agent obtained by the aqueous phase polymerization-pyrolysis strategy were low.
The hexavalent chromium in the water body is treated according to the same method as that in example 1 in examples 4 and 5, and the treatment effect is tested, and the results show that the reduction performance of examples 4 and 5 is equivalent to that in example 1, and the details are not repeated.
In conclusion, after the vapor deposition-pyrolysis strategy provided by the invention is adopted to activate the source reducing agent, the activity of the source reducing agent and the removal amount of pollutants can be greatly improved.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (10)
1. A method for preparing a zero-valent iron reducing agent, the method comprising the steps of:
a1, soaking and drying a source reducing agent by using a sodium persulfate solution, and then polymerizing and depositing an aniline monomer on the dried source reducing agent by using a chemical vapor deposition method to obtain an intermediate;
a2, carrying out high-temperature pyrolysis on the intermediate in a protective gas atmosphere to form a nitrogen-doped carbon coating layer on the surface of zero-valent iron, and thus obtaining the zero-valent iron reducing agent with a coating structure;
wherein the source reducing agent is nano zero-valent iron or load type zero-valent iron.
2. The method of claim 1, wherein in step a1, the depositing comprises: and respectively placing the dried source reducing agent and the aniline monomer on two sides of the tubular furnace, and sealing for deposition.
3. The method for producing a zero-valent iron reducing agent according to claim 1 or 2, wherein the mass ratio of the source reducing agent to the aniline monomer is 1: 2-1: 10;
preferably, the concentration of the sodium persulfate solution is 0.15-0.25 g/mL;
preferably, the chemical vapor deposition conditions include: the deposition temperature is 40-80 ℃, and the deposition time is 8-12 h.
4. The method for preparing a zero-valent iron reducing agent according to any one of claims 1 to 3, wherein in the step A2, the shielding gas is nitrogen or argon;
preferably, the operating conditions of the high-temperature pyrolysis include: the flow speed of the protective gas is 100-200 mL/min, the temperature is 700-1000 ℃, and the time is 5-8 h.
5. The method for preparing the zero-valent iron reducing agent according to claim 1, wherein the supported zero-valent iron is porous carbon supported zero-valent iron or nitrogen-doped porous carbon supported zero-valent iron, preferably nitrogen-doped porous carbon supported zero-valent iron.
6. The method of preparing a zero-valent iron reducing agent according to claim 5, further comprising preparing the nitrogen-doped porous carbon-loaded zero-valent iron according to the following procedure:
b1, uniformly mixing ferric trichloride hexahydrate, 2-amino terephthalic acid and N, N-dimethylformamide, carrying out hydrothermal reaction, and then washing, centrifuging and drying to obtain a mixture;
and B2, carbonizing the mixture at high temperature in a protective atmosphere to obtain the nitrogen-doped porous carbon loaded zero-valent iron.
7. The method for preparing a zero-valent iron reducing agent according to claim 6, wherein in step B1, the mass ratio of ferric trichloride hexahydrate to 2-amino terephthalic acid is 1: 3-3: 1;
preferably, the temperature of the hydrothermal reaction is 100-200 ℃, and the reaction time is 18-24 h;
preferably, the operating conditions for carbonizing at high temperature include: the flow speed of the protective gas is 100-200 mL/min, the temperature is 700-1000 ℃, and the time is 5-8 h.
8. A zero-valent iron reducing agent, characterized by being produced by the method for producing a zero-valent iron reducing agent according to any one of claims 1 to 7.
9. A process for treating hexavalent chromium in a body of water, wherein a body of water containing hexavalent chromium contaminants is treated with a zero-valent iron reducing agent, said zero-valent iron reducing agent being produced by the process of any of claims 1 to 7.
10. The process for treating hexavalent chromium in bodies of water according to claim 9, wherein said process comprises the steps of: and adding a zero-valent iron reducing agent into the water body containing the hexavalent chromium pollutants, adjusting the pH of the water body to 1.5-3, and carrying out reduction reaction to remove the hexavalent chromium in the water body.
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