CN119281284A

CN119281284A - Biochar-loaded sulfur-modified zero-valent iron material and its application in groundwater remediation

Info

Publication number: CN119281284A
Application number: CN202411423446.5A
Authority: CN
Inventors: 郭亚丹; 刘向媛; 宣铿; 郭耀萍; 蒋浩; 马文洁; 王学刚; 周仲魁
Original assignee: East China Institute of Technology
Current assignee: East China Institute of Technology
Priority date: 2024-10-12
Filing date: 2024-10-12
Publication date: 2025-01-10

Abstract

The present invention provides a biochar-loaded sulfur-modified zero-valent iron material and its application in groundwater remediation, and specifically relates to the field of inorganic material technology. The biochar-loaded sulfur-modified zero-valent iron material is a material in which sulfur-modified zero-valent iron is loaded in the porous structure of biochar; the sulfur-modified zero-valent iron has a core-shell structure; wherein the core in the core-shell structure is zero-valent iron and the shell is iron sulfide. The biochar-loaded sulfur-modified zero-valent iron material provided by the present invention forms a sulfide layer on the surface of the zero-valent iron, which not only protects the zero-valent iron core from direct contact with water or dissolved oxygen, but also improves its durability. The delocalized electrons in the sulfide layer promote the electron transfer process and enhance the catalytic performance of the material. The biochar-loaded sulfur-modified zero-valent iron material provided by the present invention is not only highly stable, but also has a wide range of applications. The versatility of this material makes it have potential application value in multiple fields such as environmental remediation and pollutant degradation.

Description

Biochar-loaded sulfur-modified zero-valent iron material and application thereof in groundwater remediation

Technical Field

The invention relates to the technical field of inorganic materials, in particular to a biochar-loaded sulfur-modified zero-valent iron material and application thereof in groundwater remediation.

Background

Zero-valent iron (Zero Valent Iron, ZVI) is a long-history water treatment material with an application history of over 130 years. The method is mainly used for effectively removing metal and organic pollutants in underground water and wastewater through oxidation-reduction reaction and adsorption of iron corrosion products. The cost of using zero-valent iron is relatively low due to the abundant content of iron elements in the crust. In addition, zero-valent iron has strong reducing power, the reducing potential is-0.44V, which enables it to reduce various pollutants, and at the same time, as an environment-friendly repairing medium, it is not easy to cause secondary pollution.

The operation process is simple, the field application is convenient, and the method is another great advantage of zero-valent iron. Its strong magnetism is also favorable to separation and recovery of materials, and increases its practicality in water treatment process. However, despite these advantages, zero-valent iron also presents challenges in practical applications. Due to van der waals forces, high surface energy and magnetic effects, zero-valent iron is susceptible to agglomeration in aqueous solutions, which affects its dispersibility and may reduce the treatment efficiency. In addition, the stability of zero-valent iron is relatively poor, and is easily affected by the surrounding environment, forming a passivation layer, which further reduces its reducing ability. During migration, zero-valent iron may age rapidly, which limits its long-term effectiveness.

In view of this, the present invention has been made.

Disclosure of Invention

The invention aims to provide a biochar-loaded sulfur-modified zero-valent iron material, which aims to solve at least one of the technical problems in the prior art.

The second purpose of the invention is to provide a preparation method of the biochar-supported sulfur-modified zero-valent iron material.

The invention further aims to provide an application of the biochar-loaded sulfur-modified zero-valent iron material.

In order to solve the technical problems, the invention adopts the following technical scheme:

The first aspect of the invention provides a biochar-loaded sulfur-modified zero-valent iron material, wherein sulfur-modified zero-valent iron is loaded in a porous structure of the biochar;

The sulfur-modified zero-valent iron has a core-shell structure;

wherein the inner core in the core-shell structure is zero-valent iron, and the outer shell is ferric sulfide.

Further, the particle size of the biochar-supported sulfur-modified zero-valent iron material is 100-250 nm.

Further, in the biochar-loaded sulfur-modified zero-valent iron material, the element ratio of C to Fe to S is 1-2:1:1-4.

The second aspect of the invention provides a preparation method of the biochar-supported sulfur-modified zero-valent iron material, which comprises the steps of pyrolyzing a biomass raw material to obtain biochar, uniformly mixing iron powder, sulfur powder and the biochar, and performing mechanochemical synthesis to obtain the biochar-supported sulfur-modified zero-valent iron material.

Further, the heating program of pyrolysis is:

And (3) raising the temperature to 500-800 ℃ according to the temperature raising speed of 5-10 ℃ per minute, and carrying out a cooling procedure after heat preservation for 1-3 hours.

Further, the pyrolysis is performed under the protection of argon.

Further, the mass ratio of the iron powder to the sulfur powder to the biochar is 1-2:1:1-4, preferably 1-2:1:1-2.

Further, the mechanochemical synthesis means includes ball milling.

Further, the rotation speed of the ball milling is 300-500 rpm, and the time is 3-5 hours.

The third aspect of the invention provides application of the biochar-loaded sulfur-modified zero-valent iron material in groundwater remediation.

Compared with the prior art, the invention has at least the following beneficial effects:

the biochar-loaded sulfur-modified zero-valent iron material provided by the invention uses sulfur to modify zero-valent iron, and aims to improve the stability and the reactivity of the biochar-loaded sulfur-modified zero-valent iron material. The modification process not only protects the zero-valent iron core from direct contact with water or dissolved oxygen, but also improves its durability by forming a sulfide layer on the zero-valent iron surface. Delocalized electrons in the sulfide layer play a role in promoting the electron transfer process and enhance the catalytic performance of the material. The biochar serving as the base material of the invention not only has excellent adsorption capacity due to the porous structure, but also provides additional adsorption performance and catalytic activity for the material due to the abundant active catalytic sites and defect structures. The biochar can also be used as an electron donor, so that the catalytic efficiency of the material is further enhanced. The biochar sulfur-loaded modified zero-valent iron material provided by the invention is strong in stability and wide in application range. The versatility of the material makes the material have potential application value in a plurality of fields such as environmental remediation, pollutant degradation and the like.

The preparation method provided by the invention has the advantages of simple process, low cost and environmental friendliness, and chemical reagents do not need to be added dropwise. The prepared material has uniform particle size, the size is between 100nm and 250nm, the appearance is regular, the good structural characteristics are shown, and the material is suitable for industrial mass production.

The application provided by the invention provides a material with higher efficiency and more stable performance for groundwater remediation, and particularly has large adsorption capacity and high removal rate in the treatment process of uranium and metronidazole in water, the removal rate of uranium can reach 97%, and the removal rate of activated peroxymonosulfate for degrading the metronidazole can reach 98%.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.

FIG. 1 is an SEM image of the BC/S-ZVI material obtained in example 1 under a1 μm scale;

FIG. 2 is an SEM image of the BC/S-ZVI material obtained in example 1 under a 200nm scale;

FIG. 3 is an X-ray diffraction chart obtained in characterization example 2.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. The components of the embodiments of the invention generally described and illustrated herein may be arranged and designed in a wide variety of different configurations.

The sulfur-modified zero-valent iron has a core-shell structure;

Compared with single zero-valent iron, the biochar-loaded sulfur-modified zero-valent iron (BC/S-ZVI) material provided by the invention has higher stability, and meanwhile, the adsorption effect is obviously improved due to the loading of the biochar. The introduction of the biochar not only increases the specific surface area of the material, but also provides more active sites, thereby enhancing the adsorption performance of the material on radioactive heavy metal uranium and the degradation capability of the material on metronidazole. The combination of sulfur modification and biochar loading ensures that the BC/S-ZVI material has stable structure and good cycle performance, and effectively improves the defects of the independent zero-valent iron material in adsorption performance and cycle effect.

The particle size of the BC/S-ZVI material is within the range of 100-250 nm, which is beneficial to increasing the specific surface area of the material, thereby providing more active sites, and being beneficial to improving the adsorption capacity to pollutants and the efficiency of catalytic reaction. Secondly, the BC/S-ZVI material with the particle size has better dispersity, can effectively avoid the agglomeration phenomenon like zero-valent iron in use, and keeps the high activity of the material in the reaction process. In addition, the material with smaller particle size has higher mobility and permeability in the reaction medium, so that the contact between the pollutant and the active site is more sufficient, and the dynamic performance of the reaction is improved.

At the same time, the nanoscale particle size also helps to increase the reaction kinetics of the material, since smaller particle size means a shorter diffusion distance between the reactant molecules and the active sites, thereby increasing the reaction rate. In addition, the sedimentation speed of the material in the particle size range in the water treatment process is low, which is beneficial to realizing longer contact and treatment and enhancing the efficiency of the material in practical application.

The particle size of the biochar-supported sulfur-modified zero-valent iron material may be, for example, 100nm, 125nm, 150nm, 175nm, 200nm or 250nm, or any value within the range of 100nm to 250 nm.

Compared with a liquid phase synthesis method, the preparation method provides a more direct and economic synthesis way. Such methods typically utilize mechanical forces acting on the iron powder, sulfur powder, and biochar to promote contact and mixing between the aforementioned powdered reactants, thereby stimulating chemical reactions. The mechanical synthesis has the advantages that a large amount of solvents can be avoided, the generation of chemical wastes is reduced, and the principle of green chemistry is met. In addition, the mechanical synthesis method has relatively mild operation condition and low energy consumption, is suitable for large-scale production, can reduce the reaction time and improve the production efficiency. The method is also beneficial to realizing the accurate control of the reaction conditions and improving the purity and uniformity of the product.

In a specific implementation, the biomass material is typically, but not limited to, rice straw, corn straw, coconut husk, reed straw, or walnut husk.

Further, the heating program of pyrolysis is:

Before pyrolysis, biomass raw materials are crushed, so that the pyrolysis efficiency is improved. In the pyrolysis process, the biomass feedstock first undergoes dehydration and thermal decomposition, where moisture and volatile components are released, and then high molecular organic substances such as cellulose, hemicellulose, and lignin begin to decompose into smaller hydrocarbons and char. The biochar produced by the pyrolysis process has a high specific surface area and porosity.

The biomass charcoal is selected because the biomass charcoal is derived from renewable biomass resources, has better environmental sustainability, and is beneficial to reducing dependence on fossil fuels. Secondly, the biomass charcoal generally has high porosity and larger specific surface area, which provides more active sites for loading sulfur modified zero-valent iron and enhances the adsorption capacity and catalytic performance of the material. In addition, the pore structure of the biomass charcoal is beneficial to improving the dispersibility and stability of the material and reducing the agglomeration phenomenon of sulfur modified zero-valent iron, so that the long-term reactivity of the material is maintained. The surface of the biomass charcoal is rich in oxygen-containing functional groups, and the functional groups can form stronger chemical bonds with sulfur modified zero-valent iron, so that the structural stability and the reaction selectivity of the material are further improved.

Typically, but not limited to, the temperature may be raised at a temperature of 5 ℃,6 ℃,7 ℃,8 ℃,9 ℃ or 10 ℃ or at any value within the range of 5 ℃ to 10 ℃, the target temperature may be raised at a temperature of 500 ℃, 550 ℃, 600 ℃, 650 ℃, 700 ℃, 750 ℃ or 800 ℃ or at any value within the range of 500 ℃ to 800 ℃, and the heat-preserving time may be 1h, 1.5h, 2h or 3h or at any value within the range of 1h to 3 h.

Further, the pyrolysis is performed under the protection of argon.

The mass ratio of the iron powder to the sulfur powder to the biochar is in the above proportion range, so that the synergistic effect among the components is ensured, and the dispersibility of the sulfur modified zero-valent iron on the biochar is better, thereby improving the reactivity and stability of the overall material.

The addition amount of the sulfur powder in the proportion range is favorable for forming a sulfide layer on the surface of the zero-valent iron, so that the corrosion resistance of the material is enhanced, the promotion effect of the material on electron transfer is also improved, and the catalytic performance of the material is further improved.

The ratio of the biochar in the range not only provides a porous substrate with high specific surface area and increases adsorption sites, but also enhances the interaction with sulfur modified zero-valent iron through oxygen-containing functional groups of the biochar, thereby improving the loading capacity and structural stability of the material.

Typically, but not limited to, the mass ratio of the iron powder, the sulfur powder and the biochar may be 1:1:1, 1:1:2, 1:1:3, 2:1:1:2, 2:1:4 or 2:1:3, or may be any ratio value within a range of 1 to 2:1:1 to 4, and the preferred mass ratio may be 1:1:1, 1.5:1:1.5, 2:1:1.5 or 2:1:2, or may be any ratio value within a range of 1 to 2:1:1 to 2.

Further, the mechanochemical synthesis means includes ball milling.

Typically, but not limited to, the rotation speed of the ball milling can be 300rpm, 350rpm, 400rpm, 450rpm or 500rpm, or any value within the range of 300 rpm-500 rpm, and the time of the ball milling treatment can be 3h, 3.5h, 4h, 4.5h or 5h, or any value within the range of 3 h-5 h.

The application provided by the invention provides a material with higher efficiency and more stable performance for groundwater remediation, particularly in the treatment process of uranium and metronidazole in a water body, the adsorption capacity is large, the removal rate is high, the removal rate of uranium can reach 97%, the removal rate of activated peroxymonosulfate for degrading the metronidazole can reach 98%, target pollutants can be removed in a complex water environment in a targeted manner, the removal of beneficial components in the water body is reduced, and the water ecological balance is protected.

In the specific use process, when uranium in a water body is adsorbed, the uranium concentration is controlled to be 5-40 mg/L, a better adsorption effect is achieved, the adding amount of the BC/S-ZVI material is 0.1-0.6 g/L, and the adsorption capacity of the BC/S-ZVI material is 21.24mg/g.

When the metronidazole in the water body is specifically removed, the BC/S-ZVI material degrades the metronidazole by activating the peroxymonosulfate, and specifically, the BC/S-ZVI material can promote the peroxymonosulfate to decompose to generate high-activity sulfate radicals (SO ₄·^-) and hydroxyl radicals (OH), and the high-activity sulfate radicals have extremely strong oxidizing capacity and can attack active groups in the metronidazole molecules in a non-selective manner, SO that the active groups are mineralized or converted into low-toxicity small-molecule compounds. The adsorption effect of the biochar in the BC/S-ZVI material can primarily enrich the metronidazole, so that the metronidazole is closer to a catalytic active site, and the degradation efficiency is improved.

In the specific use process, when the metronidazole in the water body is degraded, the concentration of the metronidazole is controlled to be 5-30 mg/L, the adding amount of the peroxymonosulfate is 0.1-1 mmol/L, and the adding amount of the BC/S-ZVI material is 0.05-0.5 g/L.

Some embodiments of the present invention will be described in detail below with reference to examples. The following embodiments and features of the embodiments may be combined with each other without conflict. The raw materials used in the present invention are commercially available unless otherwise specified.

Example 1

The embodiment provides a BC/S-ZVI material, which is prepared by the following steps:

1. 10g of rice straw powder is placed in a corundum crucible, the temperature is increased to 800 ℃ in a tube furnace according to 10 ℃ per min, and the heat preservation pyrolysis is carried out for 2 hours, so that black biochar powder is obtained.

2. Uniformly mixing iron powder, sulfur powder and the biochar obtained in the step 1 in a ball milling tank according to a mass ratio of 1:1:2, adding stainless steel balls, setting the rotating speed of the ball milling machine to 400r/min, and performing ball milling for 4 hours to obtain the BC/S-ZVI material.

Example 2

The present embodiment provides a BC/S-ZVI material, which is different from embodiment 1 in that the mass ratio of iron powder, sulfur powder and biochar is 1:1:1, and other steps are the same as embodiment 1, and are not described herein.

Example 3

The present embodiment provides a BC/S-ZVI material, which is different from embodiment 1 in that the mass ratio of iron powder, sulfur powder and biochar is 1:1:4, and the other steps are the same as embodiment 1, and are not described herein.

Example 4

The present embodiment provides a BC/S-ZVI material, which is different from embodiment 1 in that the mass ratio of iron powder, sulfur powder and biochar is 2:1:4, and the other steps are the same as embodiment 1, and are not described herein.

Example 5

1. 10g of corn stalk powder is placed in a corundum crucible, the temperature is increased to 800 ℃ in a tube furnace according to 10 ℃ per min, and the heat preservation pyrolysis is carried out for 2 hours, so that black biochar powder is obtained.

2. This step is the same as in example 2.

Example 6

1. 10g of rice straw powder is placed in a corundum crucible, the temperature is increased to 700 ℃ in a tube furnace according to 10 ℃ per min, and the heat preservation pyrolysis is carried out for 2 hours, so that black biochar powder is obtained.

2. This step is the same as in example 2.

Example 7

Example 8

The present embodiment provides a BC/S-ZVI material, which is different from embodiment 1 in that the mass ratio of iron powder, sulfur powder and biochar is 1:2:1, and other steps are the same as embodiment 1, and are not described herein.

Example 9

The present embodiment provides a BC/S-ZVI material, which is different from embodiment 1 in that the mass ratio of iron powder, sulfur powder and biochar is 4:1:1, and the other steps are the same as embodiment 1, and are not described herein.

Example 10

Comparative example 1

The comparative example provides a zero-valent iron material, which is iron powder, and the iron powder used in the example is the same specification and batch of products.

Comparative example 2

The comparative example provides a sulfur-modified zero-valent iron (abbreviated as S-ZVI) material, and the preparation method adopts a sodium sulfide loading method. Placing iron powder into acetic acid-sodium acetate buffer solution, performing anaerobic oscillation for 10 minutes to fully release Fe ²⁺, adding Na ₂ S into the system, continuously performing constant-temperature oscillation for 12 hours, filtering, freeze-drying for 2 hours, and sealing and storing for standby.

Characterization example 1

SEM pictures obtained under a1 μm scale and under a 200nm scale of the BC/S-ZVI material obtained in example 1 are shown in FIGS. 1 and 2, respectively.

From FIG. 1, it can be observed that the surface of the biochar has smooth zero-valent iron spherical particles, the particle sizes are not uniform, and the particles are connected together in a chain shape, which is probably caused by ball milling. In the ball milling process, chain iron particles are distributed on biochar to form BC, S and ZVI ternary complex, heterogeneous filler is formed, and the surface is coated by a carbon plate to prevent the new ZVI from generating a passivation layer.

As can be seen from fig. 2, sulfur forms a thin film on the surface of the zero-valent iron particles due to the formation of the outer layer containing a large amount of iron sulfide and a small amount of iron oxide, and is supported on biochar.

Characterization example 2

The BC/S-ZVI material in example 2, iron powder (abbreviated as ZVI), biomass carbon (abbreviated as BC) and the S-ZVI material obtained in comparative example 2 were subjected to X-ray diffraction patterns, and the obtained diffraction patterns are shown in FIG. 3.

As can be seen from FIG. 3, the characteristic peaks of BC and ZVI are embodied in BC/S-ZVI, and the peak intensities of the (200) and (110) crystal faces of the prepared BC/S-ZVI are higher, which indicates that the preparation of the biochar-loaded sulfur-modified zero-valent iron BC/S-ZVI material is successful.

Test example 1

The materials obtained in examples and comparative examples were used as adsorbents for the adsorption test of the solution U (VI).

The U (VI) aqueous solution used in the adsorption experiment is prepared by diluting 1g/L uranium standard solution. The initial mass concentration of U (VI) is 10mg/L, the pH=6 is regulated by 0.1mol/L HCl and NaOH solution, the adding amount of the adsorbent is 0.1g/L, the reaction temperature is 30 ℃, and the reaction time is 3 hours. The pH was adjusted with 0.1mol/L HCl and NaOH solutions.

The adsorbent was placed in a triangular conical flask containing 100mL of U (VI) aqueous solution and reacted on a shaker at 220 r/min. After the completion of the shaking, the mixture was filtered through a 0.45 μm filter, and the uranium U (VI) concentration in the filtrate was measured by an ultraviolet-visible spectrophotometer.

The data obtained are shown in table 1 below.

TABLE 1

From Table 1, it can be seen that when the compounding ratio is 1:1:1, the adsorption effect of the material on uranium U (VI) is best, rice straw has certain superiority in preparing the composite material in many biomass raw materials, in addition, the influence of the roasting temperature of biochar on the performance of the material is larger, the higher the temperature is, the better the adsorption performance of the material is, and finally, the composite material is found to have remarkable advantages in removing uranium U (VI) in groundwater by comparing the composite material with zero-valent iron ZVI and sulfur modified zero-valent iron S-ZVI.

Test example 2

The materials obtained in the examples and comparative examples were subjected to a metronidazole degradation test.

Two sets of tests were performed for each set of materials:

In the first test, 10mg of the material and 0.5mmol/L of potassium hydrogen persulfate (PMS for short in English) were weighed and added to 100mL of a 10mg/L solution of metronidazole.

A second set of tests weighed 10mg of material was added to 100mL of 10mg/L Metronidazole solution.

The solution was placed in a shaker and oscillated at 220r/min for 2 hours to perform an activation degradation experiment, and after completion, the content of metronidazole in the solution was measured, and the obtained data are shown in table 2 below.

TABLE 2

As can be seen from Table 2, the composite material BC/S-ZVI can better remove the metronidazole from the water body compared with zero-valent iron ZVI and sulfur modified zero-valent iron S-ZVI, and meanwhile, two groups of test results show that the adsorption effect of the material on the metronidazole is very little, negligible and is mainly removed by adding a persulfate activating material for advanced oxidation.

It should be noted that the above embodiments are merely for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the technical solution described in the above embodiments may be modified or some or all of the technical features may be equivalently replaced, and these modifications or substitutions do not make the essence of the corresponding technical solution deviate from the scope of the technical solution of the embodiments of the present invention.

Claims

1. A biochar-loaded sulfur-modified zero-valent iron material, characterized in that sulfur-modified zero-valent iron is loaded in the porous structure of the biochar;

The sulfur-modified zero-valent iron has a core-shell structure;

The core of the core-shell structure is zero-valent iron, and the shell is iron sulfide.

2. The biochar-loaded sulfur-modified zero-valent iron material according to claim 1 is characterized in that the particle size is 100 to 250 nm.

3. The biochar-loaded sulfur-modified zero-valent iron material according to claim 1, characterized in that the element ratio of C:Fe:S is 1-2:1:1-4.

4. A method for preparing the biochar-loaded sulfur-modified zero-valent iron material according to any one of claims 1 to 3, characterized in that the biomass raw material is pyrolyzed to obtain biochar, and iron powder, sulfur powder and the biochar are evenly mixed and subjected to mechanochemical synthesis to obtain the biochar-loaded sulfur-modified zero-valent iron material.

5. The preparation method according to claim 4, characterized in that the temperature rise program of the pyrolysis is:

The temperature is raised to 500-800°C at a rate of 5-10°C/min, kept at that temperature for 1-3 hours, and then a cooling procedure is performed.

The preparation method according to claim 4 , characterized in that the pyrolysis is carried out under argon protection.

7. The preparation method according to claim 4, characterized in that the mass ratio of the iron powder, the sulfur powder and the biochar is 1-2:1:1-4, preferably 1-2:1:1-2.

8. The preparation method according to claim 4 is characterized in that the mechanochemical synthesis method comprises ball milling.

9 . The preparation method according to claim 8 , characterized in that the rotation speed of the ball mill is 300 to 500 rpm and the time is 3 to 5 hours.

10. Use of the biochar-loaded sulfur-modified zero-valent iron material according to any one of claims 1 to 3 in groundwater remediation.