CN107000064B - Preparation method and application of nanometer zero valent iron - Google Patents

Abstract

The invention discloses a method for preparing nano zero-valent iron, which comprises the following steps: (1) adding polyethylene glycol and deoxyethanol into a ferrous salt water solution in an inert atmosphere, and uniformly mixing; (2) mixing the mixed solution obtained in the step (1) with an alkaline water solution containing boron hydride for reduction reaction; (3) obtaining a precipitate after the reduction reaction in the step (2) is finished; (4) and (3) drying the precipitate in vacuum to obtain the nano zero-valent iron. The method for preparing the nano zero-valent iron has simple preparation process, and does not need load or high-temperature calcination; the prepared nano zero-valent iron has large specific surface area, high reaction activity and high repair efficiency, and can quickly degrade organic pollutants. The nano zero-valent iron prepared by combining the surfactant can obviously improve the remediation efficiency of the soil polluted by the VOCs. The repairing operation is simple, the condition is easy to control, the repairing speed is high, and the energy consumption is low.

Description

Preparation method and application of nanometer zero valent iron

technical field

The invention belongs to the technical field of application of nanometer zero-valent iron, and in particular relates to a preparation method of nanometer zerovalent iron and a method for repairing VOCs polluted soil.

Background technique

In recent years, with the rapid development of urbanization and industrialization and the huge population base of our country, the extensive application of chemical fertilizers and pesticides, industrial wastewater, urban industrial waste and other synthetic substances have continuously entered the soil, and the problem of soil environmental pollution in our country has become increasingly serious. The problem of soil environmental pollution will directly endanger the physical and mental health of human beings, and the area of soil pollution, the types and quantities of pollutants continue to increase, the polluted area continues to expand, and the harm is further deepened.

Volatile organic compounds (volatile organic compounds, VOCs) are widely used as organic solvents, dry cleaning agents, chemical media, metal cleaning agents, etc. If they are not properly managed during use, storage, and disposal, they can easily cause soil pollution. Among them, volatile chlorinated hydrocarbons are more harmful, carcinogenic and extremely toxic, and have low water solubility. Once they enter the soil, they are difficult to degrade. As a typical volatile chlorinated hydrocarbon, trichlorethylene is extremely toxic, carcinogenic, teratogenic, and mutagenic to humans. Trichlorethylene is widely used and has a large production capacity. At present, the total production capacity of trichlorethylene in my country is about 400,000 tons per year.

Since the 1990s, zero-valent iron, as a highly reducing zero-valent metal, has been widely used in soil remediation. However, the application of zero-valent iron in soil remediation is limited due to the chemical stability of most volatile chlorinated hydrocarbons and difficulty in dissolving in water.

Contents of the invention

The object of the present invention is to provide a preparation method of nanometer zero-valent iron and a method for repairing VOCs polluted soil.

A kind of method for preparing nanometer zero valent iron provided by the invention, it comprises the steps:

(1) In an inert atmosphere, add polyethylene glycol and deoxyethanol to the aqueous solution of ferrous salt, and mix well;

(2) mixing the mixed solution obtained in step (1) with the aqueous alkali solution containing borohydride, and performing a reduction reaction;

(3) After the step (2) reduction reaction is completed, a precipitate is obtained;

(4) vacuum-drying the precipitate obtained in step (3) to obtain nanometer zero-valent iron.

The method as described above, preferably, the inert atmosphere is a nitrogen atmosphere, the ferrous salt in the step (1) is ferrous sulfate or ferrous nitrate, and the borohydride is sodium borohydride or potassium borohydride , the aqueous alkali solution is an aqueous solution of ammonia or sodium hydroxide.

In the above-mentioned method, preferably, the ratio of the amount of the ferrous salt to the borohydride is 1:1.5 to 1:2; the final concentration of the polyethylene glycol in the reaction solution is 0.01 ~0.02mol/L, the final concentration of the deoxyethanol in the reaction solution is 1.0~2.0mol/L, and the OH ^- concentration of the aqueous alkali solution is 0.01~0.05mol/L.

In the above method, preferably, the ratio of the amount of the ferrous salt to the borohydride is 1:2, and the concentration of OH ⁻ in the aqueous alkali solution is 0.025 mol/L.

The above-mentioned method, preferably, in the step (2), the reduction reaction temperature is 20°C-30°C, and the reaction time is 20min-40min; in the step (3), it also includes washing the precipitate with water until the pH value is neutral; in the step (4), the drying temperature is 40°C-80°C, and the drying time is 24h-48h.

In the above method, preferably, in the step (2), the reduction reaction temperature is 25° C.; the reaction time is 30 minutes.

The nanometer zero-valent iron prepared by the above-mentioned method is used for repairing VOCs-contaminated soil, and the nanometer zero-valent iron synergistic surfactant is used for repairing VOCs-contaminated soil.

As mentioned above for the method for remediating VOCs polluted soil, preferably, in the process of remediation, the final concentration of the surfactant is 0.05-35mmol·L ^-1 ; the reaction time is 0.5-4h, and the reaction temperature For room temperature.

As mentioned above, it is used to repair the method in VOCs polluted soil, preferably, the surfactant is cetyltrimethylammonium bromide (CATB) or sodium dodecyl sulfate (SDS), and the VOCs pollution is containing Trichlorethylene pollution.

As mentioned above for the method for remediating VOCs polluted soil, preferably, in the remediation process, the final concentration of the nano zero-valent iron is 0.4～36mmol/L; the final concentration of the CATB is 0.5mmol/L ~35mmol/L; the final concentration of the SDS is 0.05mmol/L~3.5mmol/L.

The present invention overcomes the deficiencies in the prior art, and provides a method for preparing nano-zero-valent iron with simple preparation process, cheap raw materials and high reduction performance, without loading and high-temperature calcination; the prepared nano-zero-valent iron has a particle size of The diameter is 20-80nm, and it has the characteristics of large specific surface area, high reactivity and high repair efficiency, and can quickly degrade organic pollutants. The surfactant combined with the prepared nano-zero valent iron can significantly improve the remediation efficiency of VOCs polluted soil. The repair operation is simple, the conditions are easy to control, the repair speed is fast, and the energy consumption is low.

The beneficial effects of the present invention are:

(1) The preparation method of nanometer zero-valent iron is simple, the raw materials are cheap and easy to obtain, the synthesis process period is short, and the prepared particle size is small, which has certain industrial value.

(2) The surfactant is cheap and easy to obtain, combined with the nano-zero-valent iron prepared by the present invention and used in soil remediation, the removal rate of trichlorethylene in the soil can be improved in a short time, which is beneficial to its practical application.

Utilizing the nanometer zero-valent iron combined with the surfactant prepared by the invention for soil restoration has important practical application value, not only can reduce the cost of soil restoration, but also greatly improve the efficiency of soil restoration.

Description of drawings

Fig. 1 is the TEM figure of the nanometer zero valent iron that embodiment 1 makes.

Fig. 2 is the XRD spectrum of the nanometer zero valent iron prepared in Example 1.

Wherein, A is the figure enlarged 8000 times of ordinary reduced iron powder, B is the figure enlarged 40000 times of ordinary reduced iron powder, C is the figure enlarged 5000 times of the nanometer zero-valent iron prepared in this embodiment, and D is the figure prepared in this embodiment A 80,000-fold magnification of nanoscale zero-valent iron.

Detailed ways

The present invention will be further described below in conjunction with specific examples, but the present invention is not limited to the following examples. The methods are conventional methods unless otherwise specified. The raw materials can be obtained from open commercial channels unless otherwise specified.

The specifications of various raw materials used in the following examples of the present invention and the information of the manufacturer are shown in Table 1.

Table 1 The raw material specifications used in the embodiment and the information of the manufacturer

Example 1

Preparation of nano zero-valent iron:

①Set up the reaction device and continuously feed N ₂ into the three-necked round bottom flask for about 30 minutes to remove oxygen; add 0.04mol ferrous sulfate heptahydrate (FeSO ₄ 7H ₂ O) Add deionized water to the above-mentioned three-necked round-bottomed flask with _N2 atmosphere, stir until dissolved, then add 2.0g polyethylene glycol (PEG-4000) and 20mL deoxyethanol, and continue to stir rapidly until the mixture is uniform;

② Dissolve 0.08mol KBH ₄ in 60mL NaOH solution with a molar concentration of 0.025mol/L and transfer it to a constant pressure funnel;

③ Place the constant pressure funnel with KBH ₄ solution on the mouth of the three-neck bottle and add the KBH ₄ solution to the FeSO ₄ solution drop by drop. After the dropwise addition, the reduction reaction is fully carried out, and the reaction is carried out at 25°C for 30 minutes. back,

④ Centrifuge the reaction system obtained in the above step ③, wash the obtained precipitate with water until the pH value of the washing water is neutral, dry the precipitate in vacuum at 50° C. for 24 hours, and grind to obtain nanometer zero-valent iron.

Added polyethylene glycol (PEG-4000 and deoxyethanol) in the present invention, its effect is as modifying agent, changes the characteristic of nano-iron, is conducive to generating the nano-iron of smaller particle size.

Nano zero-valent iron is easily oxidized in the air, and drying under vacuum can effectively avoid the oxidation of nano-zero-valent iron and avoid affecting its reduction effect and purity.

The nanometer zero-valent iron prepared above was analyzed by a transmission electron microscope (TEM), and its TEM photo is shown in FIG. 1 . Among them, A is a magnified figure of 8000 times for ordinary reduced iron powder, B is a magnified figure of 40000 times for ordinary reduced iron powder, C is a magnified figure of 5000 times for the nanometer zero-valent iron prepared in this example, and D is the nanometer zero-valent iron prepared in this example. 80,000-fold magnification of zero-valent iron.

It can be seen from Figure 1 that under the magnification of 8000 times in A, the ordinary iron powder is scattered spherical, but the size is not uniform; in B, under the magnification of 40000 times, the particle size of ordinary iron powder is about 8 μm.

This example prepares nano-sized zero-valent iron. In C, under magnification of 5000 times, the nano-iron powder is connected together by single particles of uniform size and similar to spherical shape, in the shape of a chain; in D, under magnification of 80000 times, it is a single particle. The particle size is about 20-80nm, and the particle size of a single self-made nano-iron is uniform, similar to a spherical shape. The particle size of nano zero-valent iron prepared in this embodiment is 100-400 times smaller than that of ordinary iron powder.

The specific surface area (BET) of the nanometer zero-valent iron prepared above was measured, and the results are shown in Table 2.

Table 2 Specific surface area and pore diameter of ordinary iron powder and self-made nano-iron powder

It can be seen from Table 2 that the specific surface area of nano-iron can reach 20 times that of ordinary iron powder, which determines its higher reactivity, so the rate of reducing and degrading pollutants by nano-iron is higher than that of ordinary iron powder. It can be seen from the pore size that ordinary iron powder and nano-iron powder are mesoporous materials (2-50nm). performance.

The nanometer zero-valent iron is subjected to X-ray diffraction, and its diffraction pattern is analyzed, and its XRD pattern is shown in FIG. 2 . Wherein, (a): reduced iron powder; (b): nanometer zero-valent iron prepared in this embodiment.

The XRD test results show that: when the scanning diffraction angle (2θ) is 10-80°, the 2θ corresponding to the diffraction peaks are 33-35°, 44-46°, 64-66°, respectively. Among them, ordinary reduced iron powder and The self-made nano-iron powder has the largest diffraction peaks at 44.66° and 44.76° respectively, and the diffraction peaks of the self-made nano-iron powder hardly shift compared with the reduced iron powder. The standard PDF card corresponding to iron is found to correspond to the corresponding 110-plane diffraction (44.76°) and 200-plane diffraction (65.02°). The description shows that the crystal structure of zero-valent iron has a crystal phase of Fe ⁰ , and the particles are zero-valent iron.

When ferrous nitrate is used to replace ferrous sulfate heptahydrate, ammonia water is used to replace sodium hydroxide solution, and sodium borohydride is used to replace potassium borohydride to prepare nanometer zero-valent iron, nanometer zero-valent iron can be prepared. And the prepared nanometer zero-valent iron has a particle size of 20-80nm.

Example 2

The nanometer zero-valent iron prepared in Example 1 is used in combination with an anionic surfactant, such as sodium dodecyl sulfate (SDS), for soil remediation.

The nano-zero-valent iron prepared in Example 1 was combined with cationic surfactants such as cetyltrimethylammonium bromide (CATB) for soil remediation.

The present invention selects trichlorethylene-contaminated soil as the evaluation index of volatile organic compound-contaminated soil. Because trichlorethylene has a low boiling point, it is a volatile organic pollutant, which is easy to volatilize into the atmosphere to cause pollution, and is not easy to decompose in soil and water. Poor sex. Trichlorethylene has a wide range of uses and a large amount of use. It is often used as a metal surface treatment agent, cleaning agent, extraction agent, animal anthelmintic, intestinal anthelmintic, organic synthesis, and pesticide production. Toxicity: Teratogenic, carcinogenic and mutagenic, "three-caused" and can change the potential harm of genetic traits. The content of trichlorethylene in the soil is large, how to effectively degrade the trichlorethylene in the soil is of great significance for soil restoration.

For the evaluation criteria of soil remediation, the reduction activity evaluation test is used, and the following steps are carried out:

Composition of simulated polluted soil: soil: 10g, water: 200ml; the concentration of trichlorethylene is 60μg/kg.

Activity evaluation method: in the above-mentioned mixture of simulated polluted soil and water, add 0.2g of nanometer zero-valent iron prepared in Example 1, add surfactant 1*CMC (critical micelle concentration), after reacting for 3h, use centrifuge to Centrifuge the reacted solution at a speed of 3000r/min for 10min, and after vacuum ultrafiltration through a 0.22μm organic filter membrane, collect the filtrate, extract it with n-hexane and store it. The reacted soil is sealed and preserved.

Use a headspace sampler, gas chromatography-mass spectrometry (GC-MS) to draw the standard concentration of trichlorethylene, and then calculate the removal rate of trichlorethylene.

The standard curve used is y=0.9979x+2.7826, wherein, y is the peak area of trichloroethylene, x is the concentration of trichloroethylene; R ² =0.9979;

The removal rate of trichlorethylene%=(C0-C)/C0×100%; where C0 is the initial concentration of trichlorethylene in the simulated polluted soil-water system; C is the concentration of trichlorethylene after the reaction.

Wherein, when the surfactant is anionic SDS, add 0.05g;

When the surfactant is cationic CTAB, add 0.6 g.

It should be noted that the amount of surfactant added is determined by its critical micelle concentration. Both surfactants take 1*CMC (critical micelle concentration). Solubilization in aqueous solution is beneficial to the removal of target pollutants by iron powder.

Comparative example 1

Ordinary reduced iron powder is used for soil remediation. The specific operation method is carried out according to the above-mentioned reducing activity evaluation test.

Comparative example 2

Nano zero valent iron powder for soil remediation. The specific operation method is carried out according to the above-mentioned reducing activity evaluation test.

Comparative example 3

Cationic surfactants (CATB) are used in soil remediation. The specific operation method is carried out according to the above-mentioned reducing activity evaluation test.

Comparative example 4

Anionic surfactants (SDS) are used in soil remediation. The specific operation method is carried out according to the above-mentioned reducing activity evaluation test.

Comparative example 5

Ordinary reduced iron powder combined with cationic surfactant (CATB) for soil remediation. The specific operation method is carried out according to the above-mentioned reducing activity evaluation test.

Comparative example 6

Ordinary reduced iron powder combined with anionic surfactant (SDS) for soil remediation. The specific operation method is carried out according to the above-mentioned reducing activity evaluation test.

The ordinary reduced iron powder used in the comparative example was the reduced iron powder purchased from Tianjin Jinke Fine Chemical Research Institute. The reduction activity evaluation results are shown in Table 3.

Table 3 shows the evaluation results of the reducing activity of the nanometer zero-valent iron obtained in this example.

Table 3 Evaluation results of reducing activity

After the application of the nanometer zero-valent iron in combination with the negative and positive surfactants, the removal rates of trichlorethylene in the reduced and degraded soil reach 78.51% and 90.73% respectively.

It can be seen from the above table that the nano-zero-valent iron provided by the present invention has higher reduction activity than ordinary reduced iron powder; the combination of nano-zero-valent iron with negative and positive surfactants can significantly improve the removal of soil trichlorethylene efficiency. Moreover, the selected anion and cationic surfactants SDS and CTAB have a small critical micelle concentration, which not only saves costs during use, but also does not interfere with the experiment due to the ions contained in them.

The nanometer zero-valent iron binding surfactant prepared by the present invention is used to repair the soil polluted by trichlorethylene, and by adding the surfactant, the solubility or fluidity of trichlorethylene in the soil in the water phase is increased, and the iron powder in the water phase is promoted. The contact with trichlorethylene in the soil improves the reductive dechlorination efficiency of nano-zero-valent iron to trichlorethylene, thereby achieving the purpose of remediating contaminated soil. Preferably, the final concentration of the surfactant used is 0.05-35mmol· L ^-1 ; that is, the final reaction concentration of the surfactant is 0.05-35 mmol·L ^-1 ; in the reaction step of soil remediation, the reaction time is 0.5-4 hours, and the reaction temperature is normal temperature, and the effect is better.

The dosage of nano zero-valent iron and surfactant prepared by the present invention is more preferably: in the repair process, the final concentration after adding nano zero-valent iron is 0.4～36mmol/L; the final concentration after adding CATB is 0.5mmol/L-35mmol/L; the effect is better when the final concentration after adding the SDS is 0.05mmol/L-3.5mmol/L.

The preparation process of the nano-zero-valent iron of the present invention is simple, the preparation period is short, and the prepared nano-zero-valent iron has a particle size of 20 to 80 nm, has a large specific surface area, high reactivity and high repair efficiency, and can quickly degrade organic pollution characteristics of things. The surfactant used is cheap and easy to obtain. In practical application, it not only greatly saves the cost, but also improves the restoration efficiency of the soil.

Claims (6)

1. A method for preparing nanometer zero-valent iron, is characterized in that, comprises the steps: (1) In an inert atmosphere, add polyethylene glycol and deoxyethanol to the aqueous solution of ferrous salt, and mix well; the final concentration of the polyethylene glycol in the reaction solution is 0.01～0.02mol/L, and the deoxygenated The final concentration of ethanol in the reaction solution is 1.0-2.0mol/L; (2) Mix the mixed solution obtained in step (1) with the aqueous alkali solution containing borohydride to carry out a reduction reaction; the reduction reaction temperature is 20°C to 30°C, and the reaction time is 20min to 40min; the ferrous salt and the The ratio of borohydride substances is 1:1.5 to 1:2; the OH ^- concentration of the alkali aqueous solution is 0.01 to 0.05mol/L; (3) After the reduction reaction in step (2) is completed, a precipitate is obtained, and the precipitate is washed with water until the pH value is neutral; (4) Vacuum-dry the precipitate obtained in step (3), the drying temperature is 40°C-80°C, and the drying time is 24h-48h to obtain nano-zero valent iron; 0.05cc/g, pore diameter 2.21nm, uniform size, spherical single particles connected together in a chain shape. 2. the method for claim 1 is characterized in that, the inert atmosphere in described step (1) is nitrogen atmosphere, and described ferrous salt is ferrous sulfate or ferrous nitrate, and described borohydride is boron sodium hydride or potassium borohydride, and the aqueous alkali solution is aqueous ammonia or sodium hydroxide. 3. The method according to claim 1, characterized in that, the ratio of the amount of the ferrous salt to the borohydride is 1:2, and the concentration of OH ⁱⁿ the aqueous alkali solution is 0.025mol/ L. 4. The method according to claim 1, characterized in that, in the step (2), the reduction reaction temperature is 25°C; the reaction time is 30min. 5. The method that the nanometer zero-valent iron prepared by the method described in claim 1-4 is used to repair the method in VOCs polluted soil, it is characterized in that, the method adopts the synergistic surfactant of described nanometer zerovalent iron prepared For repairing the soil polluted by VOCs; the surfactant is cetyltrimethylammonium bromide, and the VOCs pollution is pollution containing trichlorethylene; in the repair process, the final concentration of the nanometer zero-valent iron is 0.4-36mmol/L; the final concentration of the surfactant is 0.05-35mmol·L ^-1 ; the reaction time is 0.5-4h, and the reaction temperature is normal temperature. 6. The method for remediating VOCs-contaminated soil according to claim 5, wherein the final concentration of cetyltrimethylammonium bromide is 0.5mmol/L˜35mmol/L.