CN111825197B

CN111825197B - nZVI composite material, preparation method thereof and method for degrading halogenated organic matters

Info

Publication number: CN111825197B
Application number: CN202010791667.3A
Authority: CN
Inventors: 管运涛; 蒋超金
Original assignee: Shenzhen International Graduate School of Tsinghua University
Current assignee: Shenzhen International Graduate School of Tsinghua University
Priority date: 2020-08-07
Filing date: 2020-08-07
Publication date: 2022-02-22
Anticipated expiration: 2040-08-07
Also published as: CN111825197A

Abstract

The invention provides an nZVI composite material for degrading halogenated organic matters, a preparation method thereof and a method for degrading the halogenated organic matters, wherein the nZVI composite material comprises the following components in parts by weight: Ca-Al-LDH layered compounds, AA anions, nZVI and PEG as substrate materials; wherein the AA anion is inserted into the interlayer of the Ca-Al-LDH layered compound, the PEG is used as a stabilizer of the nZVI and coated on the surface of the nZVI, the PEG-coated nZVI is loaded on the surface of the Ca-Al-LDH layered compound, and the nZVI composite material is AA intercalated Ca-Al-LDH-based PEG-stabilized nZVI, which is written as PEG-nZVI @ Ca-Al-AA-LDH. The invention can degrade halogenated organic matters efficiently, quickly and thoroughly.

Description

nZVI composite material, preparation method thereof and method for degrading halogenated organic matters

Technical Field

The invention relates to the technical field of treatment of organic pollutants in the environment, in particular to an nZVI composite material for degrading halogenated organic matters, a preparation method thereof and a method for degrading the halogenated organic matters.

Background

The use and discharge of a large amount of halogenated organic matters cause the pollution of the halogenated matters in the water body/environment to be increasingly serious, and threaten the ecological safety and the human health. The halogenated organic matters have the characteristics of environmental persistence, difficult biodegradation, biological accumulation, high toxicity, long-distance migration capability and the like, are distributed in field environments such as soil, atmosphere and the like, and how to effectively solve the problem of halogenated pollutants becomes the focus of attention in the environmental field.

Taking Hexabromocyclododecane (HBCD) in halogenated organic matters as an example, HBCD is a typical Brominated Flame Retardant (BFRs) and is widely applied to products such as building materials, furniture decorations, electronic and electric appliances, packaging materials, textiles, coating coatings and the like, HBCD is mainly an additive type flame retardant and is easy to release to the surrounding environment in the processes of manufacturing, transporting, using, treating and disposing of the products, and HBCD is frequently detected in the environment, human serum and wild animals and plants in recent years along with the wide use of HBCD flame retardants. HBCD has the characteristics of persistence, bioaccumulation and biological amplification, and in addition, many studies show that HBCD has endocrine toxicity, immunotoxicity, hepatotoxicity and neurotoxicity. Therefore, the harm of the halogenated organic materials including HBCD to the ecological environment and human health is gradually recognized, and the halogenated organic materials become hot spots for the research of environmental organic pollutants in recent years.

Currently, the repair of halogenated organic compounds mainly includes non-biological degradation such as biodegradation, photocatalytic degradation, ultrasonic degradation, thermal degradation, and chemical reductive degradation. At present, the commonly used chemical reduction degradation is a zero-valent metal type chemical reduction technology, but the technology has the defects of low degradation efficiency, incomplete degradation and the like, so that a method and a material for efficiently, quickly and thoroughly developing halogenated organic matters are urgently needed.

The above background disclosure is only for the purpose of assisting understanding of the inventive concept and technical solutions of the present invention, and does not necessarily belong to the prior art of the present patent application, and should not be used for evaluating the novelty and inventive step of the present application in the case that there is no clear evidence that the above content is disclosed at the filing date of the present patent application.

Disclosure of Invention

In view of the limitations of the existing organic matter reduction and degradation technologies, the invention aims to provide an nZVI composite material for degrading halogenated organic matters, a preparation method thereof and a method for degrading halogenated organic matters, so as to degrade the halogenated organic matters efficiently, quickly and thoroughly.

In order to achieve the purpose, the invention adopts the following technical scheme:

an nZVI composite for degrading halogenated organics, comprising: Ca-Al-LDH layered compounds, AA anions, nZVI and PEG as substrate materials; wherein the AA anion is inserted into the interlayer of the Ca-Al-LDH layered compound, the PEG is used as a stabilizer of the nZVI and coated on the surface of the nZVI, the PEG-coated nZVI is loaded on the surface of the Ca-Al-LDH layered compound, and the nZVI composite material is AA intercalated Ca-Al-LDH-based PEG-stabilized nZVI, which is written as PEG-nZVI @ Ca-Al-AA-LDH.

The preparation method of the nZVI composite material for degrading halogenated organic matters comprises the following steps: (1) preparation of Ca-Al-AA-LDH: dissolving calcium nitrate and aluminum nitrate in water, dropwise adding a mixed alkali solution of ascorbate and alkali under continuous stirring, controlling the pH value in a reaction system to be 10.5-11.5 all the time, and synthesizing a Ca-Al-AA-LDH composite material by adopting a coprecipitation method under an anoxic condition; (2) preparation of PEG-nZVI @ Ca-Al-AA-LDH: reacting Ca-Al-AA-LDH prepared in the step (1), salt of Fe (II), AA and PEG under the anoxic condition, and adopting NaBH₄PEG is coated on the surface of nZVI by a reduction method and then loaded on Ca-Al-AA-LDH.

Preferably, the step (1) of preparing the Ca-Al-AA-LDH specifically comprises the following steps: 1.1, mixing Ca (NO)₃)₂·4H₂O、Al(NO₃)₃·9H₂Adding O and ultrapure water into a reaction container, wherein the molar ratio of Ca to Al is 2-2.3/1, stirring and mixing uniformly, and continuously introducing inert gas; 1.2, dropwise adding a mixed alkali liquor of NaOH and sodium ascorbate or a mixed alkali liquor of KOH and potassium ascorbate into the reaction container, wherein the concentration of NaOH or KOH in the mixed alkali liquor is 0.176mol/L, the concentration of sodium ascorbate or potassium ascorbate is 0.1mol/L, stirring vigorously at the rotating speed of 800-1000 rpm/min in the dropwise adding process, continuously introducing inert gas, the reaction temperature is 15-30 ℃, and controlling the pH value in the reaction container to be 10.5-11.5 in the dropwise adding process of the mixed alkali liquor; and 1.3, after the reaction is finished, aging the reaction container in a vacuum drying oven at the temperature of 15-30 ℃ for 3-5 days, and then carrying out centrifugal separation, washing, drying, grinding and sieving to obtain Ca-Al-AA-LDH.

Preferably, the step (2) of preparing PEG-nZVI @ Ca-Al-AA-LDH specifically comprises the following steps: 2.1, introducing inert gas into the mixed solution of ethanol and water to drive off the air in the reaction vessel, and adding FeSO₄·7H₂O and AA, wherein, FeSO₄·7H₂The molar ratio of O to AA is 0.09-0.11: 0.09-0.11, and Ca-Al-AA-LDH and PEG8000 prepared in the step (1) are added, wherein the mass ratio of the Ca-Al-AA-LDH to the PEG8000 is 0.5-E0.6: 4.4-4.6, continuously introducing inert gas and stirring at the rotating speed of 800-1000 rpm/min to fully and uniformly mix a reaction system; 2.2, dropwise adding 0.35-0.45 mol/L NaBH in an inert gas atmosphere under vigorous stirring₄Solution of Fe²⁺Fully reducing to nZVI, and continuously stirring until no H exists in the reaction system₂After generation, the PEG-nZVI @ Ca-Al-AA-LDH is obtained by centrifugal separation, washing, drying, grinding and sieving.

The method for degrading halogenated organic matters by using the nZVI composite material comprises the following steps: subjecting the nZVI composite material of claim 1 to a reductive degradation reaction with a halogenated organic-containing system under anoxic and oscillatory conditions to degrade the halogenated organic.

Preferably, the addition amount of the nZVI composite material is 0.015-0.03 g of the nZVI composite material added into a system containing halogenated organic matters per 1 g; in the halogenated organic matter-containing system, the initial concentration of the halogenated organic matter is 1-100 mg/kg.

Preferably, the method further comprises the step of carrying out oxidative degradation on a reduction product generated after the halogenated organic matter is subjected to reductive degradation under the anoxic and oscillatory conditions, and the method comprises the following steps: mixing the nZVI composite of claim 1 with a system comprising the reduction product, and then adding H at predetermined time intervals₂O₂So as to subject the reduction products to oxidative degradation.

Preferably, when the reduction product is subjected to oxidative degradation, the addition amount of the nZVI composite material is 0.015-0.03 g of the nZVI composite material added into each 1g of the system containing the reduction product; in the system containing the reduction product, the initial concentration of the reduction product is 1 mg/kg-100 mg/kg; each time H is added at intervals₂O₂When H is present₂O₂The amount of (B) is 0.05-0.07 mL/g.

Preferably, the oscillation speed during the reduction degradation reaction is 200-250 rpm/min, and the temperature is 25-45 ℃; the oscillation speed during the oxidative degradation reaction is 200-250 rpm/min, and the temperature is 25-45 ℃.

Preferably, the anoxic condition is that inert gas is introduced into the reaction container to blow air in the reaction container, and the reaction container is sealed to realize the anoxic condition in the reaction system.

Preferably, the halogenated organic matter-containing system refers to soil, sediment or liquid phase containing halogenated organic matter.

The beneficial effects of the invention include:

the present invention uses hydrotalcite-like layered double hydroxide (Ca-Al-LDH layered compound, hereinafter also referred to as LDH) as a substrate material, and Ascorbic Acid (AA) anions (AA) are intercalated between the layers of the Ca-Al-LDH layered compound^-) PEG is coated on the surface of nZVI (nano zero-valent iron) as a stabilizer, the PEG coated nZVI is loaded on the surface of a Ca-Al-LDH layered compound, an nZVI composite material is Ca-Al-LDH-based PEG stabilized nZVI intercalated by AA, which is written as PEG-nZVI @ Ca-Al-AA-LDH (which can be abbreviated as PEG-nZVI @ AA-LDH), in the reduction reaction process of degrading halogenated organic matters by using the nZVI composite material, the AA anions between layers are replaced by the reduction dehalogenation products of the halogenated organic matters, so that the AA anions are slowly released in the reaction process and continuously react with the nZVI or the iron ions on the surface of the composite material, the iron ions are coupled, the dissolution of the nZVI is promoted, the generation of a passivation layer on the surface of the nZVI is inhibited, and the slowly released AA anions are combined with hydrogen ions in a system to generate AA, Fe (III) can be reduced into Fe (II), the redox cycle between Fe (III)/Fe (II) is realized. Meanwhile, the PEG and Ca-Al-LDH layered compound in the composite material can adsorb halogenated organic matters to the surface of the composite material through lipophilicity and hydrogen bond action, so that the adsorption action of the PEG-nZVI @ AA-LDH material on the halogenated organic matters is increased, the contact of the halogenated organic matters and nZVI on the surface of the PEG-nZVI @ AA-LDH material is further enhanced, and the reductive degradation of the halogenated organic matters is accelerated. The invention can degrade halogenated organic matters efficiently, quickly and thoroughly.

Drawings

FIGS. 1a, 1b and 1c are SEM images of nZVI, LDH and PEG-nZVI @ AA-LDH materials, respectively;

FIG. 2 is an EDS diagram of the PEG-nZVI @ AA-LDH material;

FIG. 3 is a comparison XRD plot of nZVI, LDH and PEG-nZVI @ AA-LDH;

FIG. 4 is a graph comparing FT-IR spectra of PEG-nZVI @ AA-LDH composite material with NaAA;

FIG. 5 is a schematic diagram of a structural model of a PEG-nZVI @ AA-LDH composite material;

FIG. 6 is the ability of AA-LDH and PEG-nZVI @ AA-LDH composite materials to release interlayer AA anions slowly

FIG. 7 shows the degradation rate of PEG-nZVI @ AA-LDH of example 1 of the present invention and its comparative example for reductive degradation of HBCD in soil;

FIG. 8 shows a mechanism diagram of reductive degradation of HBCD in soil by the nZVI composite material of example 1 of the present invention;

FIG. 9 shows PEG-nZVI @ AA-LDH/H in example 2 of the present invention₂O₂The system and its comparative examples oxidatively degrade the rate of degradation of CDT in the soil.

Detailed Description

The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary in nature and is not intended to limit the scope of the invention or its application.

Through the research of the inventor, the problems of the current zero-valent metal type chemical reduction technology are mainly as follows: (1) easy agglomeration among zero-valent metal particles: because small size effect and interface effect exist among the zero-valent metal particles, the particles are easy to agglomerate; (2) the performance of the material is reduced after long-term operation: in the process of reducing and degrading the pollutants by the zero-valent metal, the metal is gradually corroded, and oxide and hydroxide passivation layers which are generated on the surfaces of the zero-valent metal particles are coated on the surfaces of the zero-valent metal particles, so that the zero-valent metal is difficult to continuously corrode and dissolve, the electron transfer between a reducing material and the pollutants is hindered, the reducing and degrading performance of the zero-valent metal is greatly reduced, and the phenomenon is more obvious in a high-pH environment; (3) the chemical reduction technology can only break carbon-halogen bonds, and is difficult to continue degrading and completely dehalogenating products. Therefore, the present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a haloorganic degradation material system and method.

The specific embodiment of the invention provides an nZVI composite material for degrading halogenated organic matters, which comprises the following components in percentage by weight: Ca-Al-LDH layered compounds, AA anions, nZVI and PEG as substrate materials; wherein the AA anion is inserted into the interlayer of the Ca-Al-LDH layered compound, the PEG is used as a stabilizer of the nZVI and coated on the surface of the nZVI, the PEG-coated nZVI is loaded on the surface of the Ca-Al-LDH layered compound, and the nZVI composite material is AA intercalated Ca-Al-LDH-based PEG-stabilized nZVI, which is written as PEG-nZVI @ Ca-Al-AA-LDH.

Preferably, PEG is PEG-8000.

The specific embodiment of the invention also provides a preparation method of the nZVI composite material for degrading halogenated organic matters, which comprises the following steps:

(1) preparation of Ca-Al-AA-LDH: dissolving calcium nitrate and aluminum nitrate in water, dropwise adding a mixed alkali solution of ascorbate and alkali under continuous stirring, controlling the pH value in a reaction system to be 10.5-11.5 all the time, and synthesizing the Ca-Al-AA-LDH composite material (which can be abbreviated as AA-LDH) by adopting a coprecipitation method under an anoxic condition. The anoxic condition is that inert gas (such as nitrogen) is introduced into the reaction vessel to blow air in the reaction vessel and is sealed to realize the anoxic condition in the reaction system, and preferably, the inert gas is continuously introduced into the reaction system.

Preferably, the method specifically comprises the following steps: 1.1, mixing Ca (NO)₃)₂·4H₂O、Al(NO₃)₃·9H₂Adding O and ultrapure water into a reaction container, wherein the molar ratio of Ca to Al is 2-2.3/1, stirring and mixing uniformly, and continuously introducing inert gas; 1.2, dropwise adding a mixed alkali liquor of NaOH and sodium ascorbate or a mixed alkali liquor of KOH and potassium ascorbate into the reaction container, wherein the concentration of NaOH or KOH in the mixed alkali liquor is 0.176mol/L, the concentration of sodium ascorbate or potassium ascorbate is 0.1mol/L, stirring vigorously at the rotating speed of 800-1000 rpm/min in the dropwise adding process, continuously introducing inert gas, the reaction temperature is 15-30 ℃, and controlling the pH value in the reaction container to be 10.5-11.5 in the dropwise adding process of the mixed alkali liquor; and 1.3, after the reaction is finished, aging the reaction container in a vacuum drying oven at the temperature of 15-30 ℃ for 3-5 days, and then carrying out centrifugal separation, washing, drying, grinding and sieving to obtain Ca-Al-AA-LDH.

In a more specific example, the preparation of the Ca-Al-AA-LDH comprises the steps of: weighing 2.72gCa(NO₃)₂·4H₂O and 1.88g of Al (NO)₃)₃·9H₂Adding O (Ca/Al is 2.3/1, n/n) into a flat-bottom three-neck flask filled with 50mL of ultrapure water, starting stirring and continuously introducing inert gas, dropwise adding 150mL of NaOH (1.06g, 0.176mol/L) and sodium ascorbate (NaAA, 2.97g, 0.1mol/L) mixed alkali liquor into the flat-bottom three-neck flask after 20-40 min (30 min in the example), violently stirring at the rotating speed of 800rpm/min in the dropwise adding process, continuously introducing inert gas, controlling the dropwise adding speed in the dropwise adding process to control the pH in the flat-bottom three-neck flask to be about 11.00 at the reaction temperature of 25 ℃; after the mixed solution is added, continuously stirring for 60min, aging the mixed solution in the flat-bottom three-neck flask for 3 days in a vacuum drying oven at 25 ℃ to fully improve the crystallinity of the composite material, finally, centrifugally separating, washing the synthesized composite material with deionized water, repeatedly washing for many times to remove redundant salt, fully drying the composite material in a freeze dryer, grinding the composite material through a 100-mesh sieve, and storing the composite material in the dryer for later use, wherein the prepared composite material is named Ca-Al-AA-LDH and can be abbreviated as AA-LDH.

(2) Preparation of PEG-nZVI @ Ca-Al-AA-LDH: under the anoxic condition, adopting NaBH to the Ca-Al-AA-LDH prepared in the step (1), the salt of Fe (II), AA and PEG₄PEG is coated on the surface of nZVI by a reduction method and then loaded on Ca-Al-AA-LDH.

Preferably, the preparation of PEG-nZVI @ Ca-Al-AA-LDH specifically comprises the following steps: 2.1, introducing inert gas into the mixed solution of ethanol and water to drive off the air in the reaction vessel, and adding FeSO₄·7H₂O and AA, wherein, FeSO₄·7H₂The molar ratio of O to AA is 0.09-0.11: 0.09-0.11 (preferably, FeSO)₄·7H₂The concentration of O and AA is 0.09-0.11 mol/L), and then adding the Ca-Al-AA-LDH and PEG8000 prepared in the step (1), wherein the mass ratio of the Ca-Al-AA-LDH to the PEG8000 is 0.5-0.6: 4.4-4.6 (preferably, the addition amount of Ca-Al-AA-LDH is 0.5-0.6 g, the addition amount of PEG8000 is 4.4-4.6 g), continuously introducing inert gas and stirring at the rotating speed of 800-1000 rpm/min to ensure that the reaction system is fully and uniformly mixed; 2.2 under inert gas atmosphere and vigorous stirringDropwise adding 0.35-0.45 mol/L NaBH₄Solution of Fe²⁺Fully reducing to nZVI, and continuously stirring until no H exists in the reaction system₂After generation, the PEG-nZVI @ Ca-Al-AA-LDH is obtained by centrifugal separation, washing, drying, grinding and sieving.

In a more specific example, the preparation of PEG-nZVI @ Ca-Al-AA-LDH comprises the following steps: introducing inert gas into 100mL of ethanol/water (3/7, v/v) mixed solution for 20-40 min (30 min in the example), and adding FeSO₄·7H₂O and AA are added to the reaction system to ensure that the concentration of the O and the AA is 0.1mol/L, then 0.56g of Ca-Al-AA-LDH and 4.48g of PEG-8000 stabilizer are added, inert gas is continuously introduced, and the mixture is stirred for 30min at the rotating speed of 800rpm/min to ensure that the reaction system is fully and uniformly mixed; under the atmosphere of inert gas and with vigorous stirring, 100mL of 0.4mol/L NaBH is dropwise added₄Solution of Fe²⁺Fully reducing to nZVI, and continuously stirring until no H exists in the reaction system₂Generating; and then, centrifugally separating a solid phase and a liquid phase, cleaning the solid phase for 3 times by using ultrapure water, cleaning the solid phase for 3 times by using ethanol to remove redundant impurities, finally, putting the prepared material into a freeze dryer for full drying, grinding the material through a 100-mesh sieve, and storing the ground material in the dryer for later use, wherein the prepared composite material is named as AA intercalated Ca-Al-LDH-based PEG stabilized nZVI, which is written as PEG-nZVI @ Ca-Al-AA-LDH and can be abbreviated as PEG-nZVI @ AA-LDH.

The PEG-nZVI @ AA-LDH prepared above is characterized as follows:

1. surface topography map of materials

As shown in the SEM images of nZVI, Ca-Al-LDH and PEG-nZVI @ AA-LDH materials in FIGS. 1a, 1b and 1c, respectively, the conventional nZVI particles exhibit surface morphologies that are rough, irregular and mutually agglomerated to be amorphous in the absence of the addition of Ca-Al-AA-LDH as a substrate, from the surface morphology. The Ca-Al-LDH material alone (fig. 1b) exhibits a typical hexagonal sheet structure and has a crystalline morphology. As shown in FIG. 1c, when Ca-Al-AA-LDH is introduced as a substrate and a PEG stabilizer in the process of preparing nZVI, the particles on the surface of the prepared PEG-nZVI @ AA-LDH composite material become large, obvious spherical particles are presented, and the particles are uniformly distributed on the surface of a sheet structure. The characterization results show that after the Ca-Al-AA-LDH is introduced to be used as a substrate and a PEG stabilizer, the dispersion effect of the nano zero-valent iron particles is obviously improved, and the agglomeration phenomenon among the nano particles is effectively inhibited.

2. Composition analysis of materials

The compositions of the prepared PEG-nZVI @ AA-LDH composite material were analyzed by EDS, and the results are shown in FIG. 2. the results of EDS analysis showed that C, O, Al, Ca and Fe were present in the PEG-nZVI @ AA-LDH composite material, and the relative contents of C, O, Al, Ca and Fe in the material were 40.76%, 38.71%, 1.15%, 3.48% and 15.90%, respectively. The EDS analysis results indicated the presence of iron, and possibly LDH, in the composite material, which was confirmed by XRD analysis below to be indeed present.

3. Surface crystal form structure analysis of material

XRD analysis is carried out on the PEG-nZVI @ AA-LDH composite material so as to further study the structural property of the PEG-nZVI @ AA-LDH composite material. A comparison of the XRD patterns for nZVI, LDH and PEG-nZVI @ AA-LDH is shown in FIG. 3. As can be seen, the XRD diffraction peak intensity and position of the nZVI sample are basically consistent with that of a standard card of zero-valent iron (JCPDS No. 06-0696). As can be seen from the XRD pattern of the LDH material, characteristic diffraction peaks of (003), (006) and (009) planes with larger diffraction intensity appear, and the characteristic diffraction peaks have the characteristics of narrow peak pattern, sharpness and high symmetry, which indicates that the synthesized LDH sample has a highly ordered typical layered structure. The XRD pattern of the composite PEG-nZVI @ AA-LDH showed distinct diffraction peaks for nZVI and LDH of (003), (006) and (009), indicating that nZVI was successfully synthesized on the AA-LDH substrate. The crystal structure of LDH is not changed obviously in the synthesis process; the characteristic diffraction peaks (003) and (006) of the PEG-nZVI @ AA-LDH composite material are broadened, the interlayer spacing is slightly larger than that of the LDH material, and the positions of the characteristic diffraction peaks are shifted to low angles, which indicates that AA anions are successfully inserted into the LDH interlayer, so that the crystallinity of the LDH is reduced.

4. Functional group type characterization of materials

FT-IR spectroscopy was performed on the PEG-nZVI @ AA-LDH composite to confirm that AA had been successfully inserted into the LDH. The FT-IR spectra of the PEG-nZVI @ AA-LDH composite material and NaAA were compared, and the results are shown in FIG. 4 (curve (a) represents NaAA, and curve (b) is shown in the tablePEG-nZVI @ AA-LDH). 3000-3680 cm^-1The wide absorption peak belongs to the characteristic peaks in LDH and AA, and is the stretching vibration peak of AA molecules, LDH plate layers, crystal water or O-H bonds in physical adsorption water; below 1000cm^-1Is caused by the vibration of the M-O or O-M-O (M ═ Ca, Al, and Fe) bond. In the FT-IR spectrum of NaAA (curve (a) in FIG. 4), a stretching vibration peak of O-H bond of 1612 to 1620cm was observed^-1And 1357-1362 cm^-1The two characteristic absorption peaks in the range are the symmetric and antisymmetric stretching vibration peaks of O-C ═ O in the lactone ring of AA molecule. The characteristic absorption peaks of the PEG-nZVI @ AA-LDH composite material are slightly shifted towards the direction of large wave number, which is probably because the introduction of AA leads to the weakening of hydrogen bonds acting in molecules; 1627-1630 cm^-1And 1362-1364 cm^-1Antisymmetric and symmetric extensional vibrational peaks typical of C-O-C and C ═ O in AA also appear. Therefore, the results of the FT-IR analysis also confirmed the successful synthesis of AA in the composite.

In conclusion, XRD test results show that nZVI and highly ordered LDH exist in the PEG-nZVI @ AA-LDH material, and the introduction of AA causes the layer spacing of LDH to be large and the position of a characteristic diffraction peak to be shifted to the left, thereby confirming that AA is successfully inserted into the LDH layers; according to the analysis result of SEM, the prepared nZVI particles are dispersed on the surface of the AA-LDH substrate material; EDS and IR characterization detected the presence of iron, calcium, aluminum and AA, respectively. Thus, the PEG-nZVI @ AA-LDH composite material has a typical LDH layered structure, PEG-nZVI is dispersed in LDH surface, and AA is inserted into LDH interlayer, the structure model of the PEG-nZVI @ AA-LDH material is shown in FIG. 5, wherein the largest gray spheres represent Ca or Al, and the dark gray spheres represent OH^-Black pellets represent PEG-coated nZVI.

In order to investigate the capability of AA-LDH and PEG-nZVI @ AA-LDH composite materials for slowly releasing the AA anions among the layers, 0.1mol/L NaBr is adopted as a slow release agent to investigate the AA anions among the layers of the replacement composite material LDH. As can be seen from FIG. 6, NaBr shows better capability of displacing and slowly releasing AA anions in the AA-LDH composite material, within the first 3h of displacement, the AA-LDH composite material quickly releases the AA anions, and a large amount of Br exists in the reaction system at the beginning stage of the reaction^-Can beRapidly displacing AA anions between LDH layers. However, in the PEG-nZVI @ AA-LDH composite material, the concentration of AA in a replacement system is not high all the time, mainly because AA anions replaced by the NaBr sustained-release agent can quickly react with iron ions generated by dissolution of nZVI on the surface of the composite material, and the AA anions are difficult to stably exist in the reaction system in the form of AA molecules. The experimental result also proves that AA can participate in the subsequent reaction of the PEG-nZVI @ AA-LDH composite material.

The specific embodiment of the invention also provides a method for degrading halogenated organic matters by using the nZVI composite material, which comprises the following steps: and under the conditions of oxygen deficiency and oscillation, carrying out reduction degradation reaction on the nZVI composite material and a system containing halogenated organic matters so as to degrade the halogenated organic matters.

In some preferred embodiments, the nZVI composite is added in an amount of 0.015 to 0.03gnZVI composite per 1g halogenated organic-containing system; in the halogenated organic matter-containing system, the initial concentration of the halogenated organic matter is 1-100 mg/kg.

In some preferred embodiments, the method further comprises subjecting the reduction product generated after the halogenated organic compound is subjected to reductive degradation to oxidative degradation under anoxic and oscillatory conditions, and comprises the following steps: mixing said nZVI composite with a system comprising said reduction product and then adding H at predetermined time intervals₂O₂So as to subject the reduction products to oxidative degradation.

In some preferred embodiments, the amount of the nZVI composite added to the system is 0.015 to 0.03g of nZVI composite per 1g of the system containing the reduction product when the reduction product is oxidatively degraded; in the system containing the reduction product, the initial concentration of the reduction product is 1 mg/kg-100 mg/kg; each time H is added at intervals₂O₂When H is present₂O₂The amount of (B) is 0.05-0.07 mL/g.

In some preferred embodiments, the oscillation speed during the reductive degradation reaction is 200-250 rpm/min, and the temperature is 25-45 ℃; the oscillation speed during the oxidative degradation reaction is 200-250 rpm/min, and the temperature is 25-45 ℃.

In some preferred embodiments, the anoxic condition is to introduce an inert gas into the reaction vessel to blow air in the reaction vessel and seal the reaction vessel to realize the anoxic condition in the reaction system.

In some preferred embodiments, the halogenated organic-containing system refers to a soil, sediment, or liquid phase containing halogenated organic.

In a further preferred embodiment, the haloorganic is HBCD or BDE-47.

Aiming at the problem that the existing halogenated organic matters are difficult to degrade efficiently, quickly and thoroughly, the invention mainly provides a composite material system which is a polyethylene glycol stabilized nano zero-valent iron composite material (which can be written as PEG-nZVI @ AA-LDH) based on ascorbic acid intercalated layered double hydroxide load and is used for reducing and degrading the halogenated organic matters, and further provides PEG-nZVI @ AA-LDH/H₂O₂The system is used for further oxidizing the product after the reduction of the halogenated organic matter.

The invention is suitable for treating systems containing halogenated organic substances, which are mainly present in the soil and sediments or in the liquid phase formed after the primary treatment of the soil or sediments.

The following examples further describe embodiments of the present invention by degrading HBCD in soil as examples, in conjunction with comparative examples.

Example 1

In the sacrifice experiment under the anoxic environment, 2g HBCD contaminated soil and 1.5-2.5 mL (2 mL in the example) of ultrapure water are added into a 20mL brown glass reaction vial, the pH value of the initial soil is measured to be 5.01 (in the system to be treated, the pH value is preferably 5-11, if the pH value is not in the range, NaOH or HCl can be used for adjusting the pH value of the reaction solution to be 5-11), a certain amount of PEG-nZVI @ AA-LDH is added, and a polytetrafluoroethylene cover is quickly covered. The reaction vial was placed in a constant temperature shaker and shaken to react at a speed of 200 to 250rpm/min (200 rpm/min in this example) at a temperature of 25. + -. 2 ℃. At the experimentally set time points (0, 1, 3, 6, 9 and 12h) a reaction vial was taken, 40-60. mu.L (in this case 40. mu.L) of 12mol/L HCl was added rapidly to stop the reduction reaction and dissolve the metal particles to release the adsorbed species.

Wherein the anoxic condition in the reaction system is realized by introducing nitrogen into the reaction device to blow air in the reaction device and covering and sealing the reaction device. During the reaction, nitrogen gas may be continuously introduced. The initial concentration of HBCD in the soil system is 10mg/kg, and the water content of the soil is 50 wt%. The addition amount of the PEG-nZVI @ AA-LDH composite material is 0.015g/g based on the mass of the HBCD-polluted soil.

Comparative examples of example 1:

comparative example 1: the difference from example 1 is that PEG-nZVI @ AA-LDH is replaced by nZVI, and the amount of added nZVI is 0.012 g/g.

Comparative example 2: the difference from example 1 is that PEG-nZVI @ AA-LDH was replaced with Ca-Al-AA-LDH, and the amount of Ca-Al-AA-LDH added was 0.0075 g/g.

Comparative example 3: the difference from example 1 is that PEG-nZVI @ AA-LDH was replaced with both PEG-nZVI and Ca-Al-AA-LDH (i.e., PEG-nZVI + AA-LDH), and the amounts of PEG-nZVI and Ca-Al-AA-LDH added were each 0.0075 g/g.

All the above experiments were performed in 3 replicates.

As shown in FIG. 7, in order to show the degradation rate of HBCD in the soil reduced and degraded by the examples 1 and the comparative examples, wherein the curve C1 corresponds to the blank, the curve C2 corresponds to AA-LDH, and the materials corresponding to other curves are shown in the upper left corner of the figure, the results of the reduced degradation of HBCD of 10mg/kg in the soil are as follows:

(1) in comparative example 1 in which 0.012g/g of nZVI was added, the degradation rate of HBCD at 10mg/kg in soil was 73.2% after 12 hours of reaction.

(2) In comparative example 2 in which 0.0075g/g of Ca-Al-AA-LDH was added, the degradation rate of HBCD in soil at 10mg/kg after 12 hours of reaction was 10.5%.

(3) In comparative example 3 in which 0.0075g/g of PEG-nZVI and 0.0075g/g of AA-LDH were added, the degradation rate of HBCD in soil at 10mg/kg after 12 hours of reaction was 82.4%.

(4) Example 1 with 0.015g/g of PEG-nZVI @ AA-LDH composite material added can efficiently reduce and degrade HBCD, and under the conditions of normal temperature and normal pressure, 10mg/kg of HBCD in soil can be degraded by 98.9% after 12h of reaction, and the complete debromination is CDT.

As shown in fig. 8, it is a mechanism diagram of reducing and degrading HBCD in soil by nZVI composite material of example 1 of the present invention, and the specific description is as follows: the invention adopts a functional material Ca-Al-LDH layered compound as a substrate material to load PEG-coated nZVI, which can improve the dispersibility of nZVI, and the Ca-Al-LDH layered compound is a hydrotalcite-like layered double hydroxide with low cost, excellent performance and environmental friendliness, has adsorption performance on heavy metal ions and organic matters, can adsorb iron ions generated in the reaction process and organic degradation products of HBCD, and reduces the possible secondary pollution. Meanwhile, Ascorbic Acid (AA) anions are inserted into LDH interlayers, the stability of the AA anions can be improved, and debromination product Br is reduced by HBCD in the reduction reaction process^-And replacing interlayer AA anions to slowly release in the reaction process, continuously reacting with zero-valent iron or iron ions on the surface of the material, coupling the iron ions, promoting the dissolution of nZVI, inhibiting the generation of a passivation layer on the surface of the nZVI, combining the slowly released AA anions with hydrogen ions in a system to generate AA, wherein the AA can reduce Fe (III) into Fe (II), and realizing the redox cycle among Fe (III)/Fe (II). In addition, in order to further improve the stability of nZVI, the dispersed and stabilized PEG-nZVI @ AA-LDH composite material is prepared by adding PEG through an in-situ reduction method. PEG and Ca-Al-LDH in the composite material can adsorb HBCD in soil to the surface of the composite material through lipophilicity and hydrogen bond action, the adsorption effect of the PEG-nZVI @ AA-LDH material on the HBCD in the soil is increased, the contact of the HBCD and nZVI on the surface of the PEG-nZVI @ AA-LDH material is further enhanced, and the reductive degradation of the HBCD in the polluted soil is accelerated.

Example 2

HBCD in the soil of example 1 is reduced in PEG-nZVI @ AA-LDH for 12h, and then is reduced to be a complete debromination product, CDT (cyclododecatriene), so that CDT-polluted soil is obtained. In this example, PEG-nZVI @ AA-LDH was used with the addition of H₂O₂(PEG-nZVI@AA-LDH/H₂O₂System of) Carrying out oxidative degradation on CDT, and comprising the following steps:

PEG-nZVI@AA-LDH/H₂O₂the Fenton-like oxidative degradation reaction of the system on CDT in soil is carried out in a 20mL brown glass reaction vial, and the original pH value in the reaction vial is 2.5-3.5. In order to ensure the concentration parallelism among the samples, the standard substance is added to make the CDT initial concentration of the CDT polluted soil be 5mg/kg, and the initial pH of the reaction system be 3.00. A20 mL glass reaction vial was charged with 2g of CDT contaminated soil and 2mL of ultrapure water. PEG-nZVI @ AA-LDH (0.015 g/g based on CDT contaminated soil) was then added to the reaction vial, followed by H addition at intervals (which may be at sampling intervals, e.g., 0, 1, 3, 6, 9 and 12H)₂O₂(0.06 mL/g is added in each time based on CDT contaminated soil); and placing the batch of reaction vials in a constant-temperature shaking table to shake for reaction at the speed of 200rpm/min and at the temperature of 25 +/-2 ℃. After the reaction is started, taking out a reaction vial at a set time point, rapidly adding 20 mu L of 1mol/L tert-butyl alcohol serving as an oxidation inhibitor, stopping the reaction, performing extraction analysis, and detecting the concentration of CDT before and after the reaction to calculate the degradation rate of CDT.

The nZVI is used as a long-acting activator, provides Fe (II) and electrons in a reaction system, and can gradually activate H₂O₂The single nZVI particles are easy to agglomerate, passivate and inactivate, so that the reaction activity is greatly reduced.

Comparative examples of example 2:

comparative example 1: the difference from example 2 is that the PEG-nZVI @ AA-LDH/H in example 2₂O₂The system is replaced by adding only 0.015g/g PEG-nZVI @ AA-LDH and no H₂O₂。

Comparative example 2: the difference from example 2 is that the PEG-nZVI @ AA-LDH/H in example 2₂O₂System replacement by addition of H only intermittently₂O₂(0.06 mL/g added initially and at the point of sampling) without the PEG-nZVI @ AA-LDH composite.

As shown in FIG. 9, in order to evaluate the degradation rate of CDT in the oxidative degradation soil of example 2 and its comparative example, the results of oxidative degradation of CDT (5mg/kg) which is a product of complete debromination of HBCD in soil were as follows:

(1) comparative example 1, in which 0.015g/g PEG-nZVI @ AA-LDH was added alone, had no significant effect on the degradation of CDT in soil after 9 hours of reaction.

(2) With intermittent addition of H₂O₂(0.06 mL/g added initially and at the point of sampling) in comparative example 2, the CDT degradation rate in the soil after 9h of reaction was 34.7%.

(3) 0.015g/g PEG-nZVI @ AA-LDH was added and H was added at a distance₂O₂(initial and sample point addition 0.06mL/g) of example 2, the CDT degradation rate in soil after 9h of reaction was as high as 92.1%.

As can be seen from the above examples and comparative examples, the present invention has the following advantageous effects:

(1) prepare a stable, dispersed and activated H₂O₂The acting AA intercalated LDH-based PEG stabilizes the nZVI composite (PEG-nZVI @ AA-LDH).

(2) The PEG-nZVI @ AA-LDH can efficiently reduce and degrade HBCD of 10mg/kg in soil. After reaction for 12h, the degradation effect of the composite material on HBCD in soil is obviously higher than that of nZVI, AA-LDH and PEG-nZVI + AA-LDH.

(3) The HBCD polluted soil which is difficult to be directly oxidized can be repaired by adopting a reduction and then oxidation method, and the HBCD polluted soil is treated by PEG-nZVI @ AA-LDH/H₂O₂After the composite reaction system is repaired, the environmental hazard of HBCD polluted soil is basically removed.

(4) The composite material has the advantages of less reaction system condition limitation, convenience and quickness in operation and low cost, and can be generated at normal temperature and normal pressure.

The following further describes embodiments of the present invention by way of example of degrading BDE-47 in soil.

Example 3

The experimental conditions of this example were substantially the same as those of example 1 except that soil contaminated with tetrabromobisphenol (BDE-47), which is a brominated flame retardant of diphenyl ether, was treated and the initial concentration of BDE-47 was 10 mg/kg.

And the concentration analysis of the BDE-47 in the soil sample at different times in the degradation process is completed by adopting ultra-high liquid chromatography, and the soil sample analysis result in the reduction degradation process shows that the degradation rate of the BDE-47 is over 90 percent after the reduction is carried out for 12-24 hours.

The reduction-oxidation degradation method based on the PEG-nZVI @ AA-LDH composite material has the advantages of short reaction time, high degradation efficiency, strong operability, and stable and dispersed composite material, and mainly comprises the following reasons: (1) after Ca-Al-AA-LDH is introduced as a carrier and PEG is introduced as a stabilizer, the stability and the dispersibility of the nZVI particles are obviously improved, so that the composite material can provide more reaction sites for the degradation of halogenated organic matters (such as HBCD), thereby improving the reaction activity of the composite material; (2) in the HBCD degradation process, AA anions serving as reducing agents are slowly released from intercalation of the PEG-nZVI @ AA-LDH composite material, the slowly released AA anions are combined with hydrogen ions in a system to generate AA, Fe (III) can be reduced into Fe (II), and the redox cycle of Fe (III)/Fe (II) is realized. The redox cycle of Fe (III)/Fe (II) can increase the rate of electron transfer to target pollutants, and the regenerated Fe (II) with reducing property can participate in the reduction degradation of the target pollutants, thereby promoting the debromination degradation of the HBCD by PEG-nZVI @ AA-LDH; (3) AA and Ca-Al-AA-LDH in the composite material have a large number of hydroxyl groups, and can serve as ligands to form coordination compounds with iron ions, promote the dissolution of nZVI and inhibit the formation of a surface passivation layer of nZVI; (4) the PEG and Ca-Al-AA-LDH in the composite material can adsorb HBCD in soil to the surface of the composite material through lipophilicity and hydrogen bond action, so that the adsorption effect of the PEG-nZVI @ AA-LDH on the HBCD is increased, the contact of the HBCD and the nZVI on the surface of the PEG-nZVI @ AA-LDH is further enhanced, and the complete reduction and degradation of the HBCD in the polluted soil are accelerated; (5) nZVI in PEG-nZVI @ AA-LDH composite material and Fe (II) generated by dissolving nZVI₂O₂Generating a large amount of OH radicals; (6) PEG-nZVI @ AA-LDH has the ability to adsorb degradation intermediates (heavy metal ions, bromide ions and organic intermediates), thereby increasing the reaction rate and reducing the toxicity of the debrominated product.

The foregoing is a more detailed description of the invention in connection with specific/preferred embodiments and is not intended to limit the practice of the invention to those descriptions. It will be apparent to those skilled in the art that various substitutions and modifications can be made to the described embodiments without departing from the spirit of the invention, and these substitutions and modifications should be considered to fall within the scope of the invention. In the description herein, references to the description of the term "one embodiment," "some embodiments," "preferred embodiments," "an example," "a specific example," or "some examples" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Various embodiments or examples and features of various embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction. Although embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope of the claims.

Claims

1. A preparation method of an nZVI composite material for degrading halogenated organic matters is characterized by comprising the following steps:

(1) preparation of Ca-Al-AA-LDH: dissolving calcium nitrate and aluminum nitrate in water, dropwise adding a mixed alkali solution of ascorbate and alkali under continuous stirring, controlling the pH value in a reaction system to be 10.5-11.5 all the time, and synthesizing a Ca-Al-AA-LDH composite material by adopting a coprecipitation method under an anoxic condition; the preparation of the Ca-Al-AA-LDH specifically comprises the following steps:

1.1, mixing Ca (NO)₃)₂·4H₂O、Al(NO₃)₃·9H₂Adding O and ultrapure water into a reaction container, wherein the molar ratio of Ca to Al is Ca/Al = 2-2.3/1, stirring and mixing uniformly, and continuously introducing inert gas;

1.2, dropwise adding a mixed alkali liquor of NaOH and sodium ascorbate or a mixed alkali liquor of KOH and potassium ascorbate into the reaction container, wherein the concentration of NaOH or KOH in the mixed alkali liquor is 0.176mol/L, the concentration of sodium ascorbate or potassium ascorbate is 0.1mol/L, stirring vigorously at the rotating speed of 800-1000 rpm/min in the dropwise adding process, continuously introducing inert gas, the reaction temperature is 15-30 ℃, and controlling the pH value in the reaction container to be 10.5-11.5 in the dropwise adding process of the mixed alkali liquor;

1.3, after the reaction is finished, aging the reaction container in a vacuum drying oven at 15-30 ℃ for 3-5 days, and then carrying out centrifugal separation, washing, drying, grinding and sieving to obtain Ca-Al-AA-LDH;

(2) preparation of PEG-nZVI @ Ca-Al-AA-LDH: reacting Ca-Al-AA-LDH prepared in the step (1), salt of Fe (II), AA and PEG under the anoxic condition, and adopting NaBH₄PEG is coated on the surface of nZVI and then loaded on Ca-Al-AA-LDH by a reduction method;

wherein AA is ascorbic acid.

2. The method of claim 1, wherein:

the preparation of PEG-nZVI @ Ca-Al-AA-LDH in the step (2) specifically comprises the following steps:

2.1, introducing inert gas into the mixed solution of ethanol and water to drive off the air in the reaction vessel, and adding FeSO₄·7H₂O and AA, wherein, FeSO₄·7H₂The molar ratio of O to AA is 0.09-0.11: 0.09-0.11, and Ca-Al-AA-LDH and PEG8000 prepared in the step (1) are added, wherein the mass ratio of the Ca-Al-AA-LDH to the PEG8000 is 0.5-0.6: 4.4-4.6, continuously introducing inert gas and stirring at the rotating speed of 800-1000 rpm/min to fully and uniformly mix a reaction system;

2.2, dropwise adding 0.35-0.45 mol/L NaBH in an inert gas atmosphere under vigorous stirring₄Solution of Fe²⁺Fully reducing to nZVI, and continuously stirring until no H exists in the reaction system₂After generation, the PEG-nZVI @ Ca-Al-AA-LDH is obtained by centrifugal separation, washing, drying, grinding and sieving.

3. An nZVI composite material for degrading halogenated organic compounds obtained by the preparation method of any one of claims 1 to 2, comprising: Ca-Al-LDH layered compounds, AA anions, nZVI and PEG as substrate materials; the AA anion is inserted into the interlayer of the Ca-Al-LDH layered compound to obtain Ca-Al-AA-LDH, the PEG is used as a stabilizer of the nZVI and coated on the surface of the nZVI, the PEG-coated nZVI is loaded on the surface of the Ca-Al-AA-LDH, and the nZVI composite material is AA intercalated Ca-Al-LDH-based PEG-stabilized nZVI, which is written as PEG-nZVI @ Ca-Al-AA-LDH.

4. A method of degrading halogenated organics in nZVI composite material according to claim 3 comprising the steps of: and under the conditions of oxygen deficiency and oscillation, carrying out reduction degradation reaction on the nZVI composite material and a system containing halogenated organic matters so as to degrade the halogenated organic matters.

5. The method of claim 4, wherein the nZVI composite is added in an amount of 0.015 to 0.03g nZVI composite per 1g halogenated organic containing system; in the halogenated organic matter-containing system, the initial concentration of the halogenated organic matter is 1-100 mg/kg.

6. The method of claim 4, further comprising oxidatively degrading the reduction product formed after reductive degradation of said halogenated organic material in the absence of oxygen and under shaking conditions, comprising the steps of: mixing the nZVI composite of claim 3 with a system comprising the reduction product, and then adding H at predetermined time intervals₂O₂So as to subject the reduction products to oxidative degradation.

7. The method of claim 6, wherein the nZVI composite is added in an amount of 0.015 to 0.03g nZVI composite per 1g system containing the reduction product when the reduction product is oxidatively degraded; the body containing the reduction productIn the system, the initial concentration of the reduction product is 1 mg/kg-100 mg/kg; each time H is added at intervals₂O₂When H is present₂O₂The amount of (B) is 0.05-0.07 mL/g.

8. The method according to claim 6, wherein the oscillation speed during the reductive degradation reaction is 200-250 rpm/min, and the temperature is 25-45 ℃; the oscillation speed during the oxidative degradation reaction is 200-250 rpm/min, and the temperature is 25-45 ℃.

9. The method of claim 4 or 6, wherein the anoxic condition is a condition in which an inert gas is introduced into the reaction vessel to blow air from the reaction vessel and sealed to achieve anoxic conditions in the reaction system.

10. The method of claim 4, wherein the halogenated organic-containing system is a soil, sediment, or liquid phase containing halogenated organic matter.