Chitosan activated activated carbon loaded iron / silver composite ball and its preparation method and application

Abstract

The invention discloses a preparation method of a chitosan-activated activated carbon-loaded iron / silver composite ball, a preparation method thereof, and an application thereof. The method comprises the following steps: (1) dissolving activated carbon and chitosan in an acetic acid solution to obtain a chitosan-activated carbon mixed solution; (2) adding an iron compound and a silver compound, and stirring and mixing them uniformly; the iron compound is selected from ferric sulfate and ferric nitrate; the silver compound is silver nitrate; the mass ratio of the iron element to the activated carbon is 0.07-0.20:1, and the molar ratio of the silver element in the silver compound to the iron in the iron compound is 1:10-50; (3) dropping the mixed solution obtained in step (2) into an ammonia solution for alkalization, and rinsing the formed gel particles with deionized water; (4) adding the gel particles into a crosslinking agent solution for crosslinking, washing, and freeze-drying; and (5) calcining the gel particles at 350-650° C. for 0.8-1.5 h to obtain the chitosan-coated iron / silver-loaded activated carbon composite balls.

Description

Technical Field

[0001] The invention relates to the technical field of environmental pollution control materials, and in particular to a chitosan-activated activated carbon-loaded iron / silver composite ball, a preparation method and an application thereof. Background Art

[0002] Against the backdrop of rapid global economic growth, alternative energy sources are rapidly developing. Nuclear energy, as a green and clean energy source, has seen significant growth. However, this process also results in the release of large amounts of nuclear wastewater and waste residue into ecosystems, causing varying degrees of damage to the environment and human health. In recent years, many researchers have used activated carbon to purify radionuclide-laden wastewater. This approach leverages the carbon's large surface area and rich pore structure to adsorb radioactive elements onto its surface. However, after a period of use, activated carbon loses its adsorption capacity due to saturation. Radionuclides adsorbed on the carbon surface may fall off, causing secondary contamination. Therefore, modified activated carbon is necessary.

[0003] A common method for modifying activated carbon is metal loading. Iron, in particular, can significantly enhance the removal performance of activated carbon by leveraging its high reactivity. Recently, reports have emerged of bimetallic activated carbon loading, based on activated carbon as a carrier. This leverages the strong electron transfer capabilities of the micro-electrochemical cells formed by the two metals, combined with the strong adsorption capacity of activated carbon, making it a highly efficient and safe adsorbent.

[0004] The liquid phase reduction method is used to prepare activated carbon loaded with iron and silver, which is currently a more common method. Chinese invention patent application CN106955667A discloses a method for preparing activated carbon nano-zero-valent iron and silver metal clusters by liquid phase reduction. This method has complex preparation steps, requires the consumption of a large amount of chemical reagents, and has poor practicality. At the same time, the loaded iron and silver often grow unevenly. Chinese patent application CN116393095A discloses a method for preparing biochar loaded with nickel ferrite, which comprises mixing biochar with a salt solution of nickel and iron and an oxalic acid solution, placing the mixture in a tubular furnace and calcining it to obtain a magnetic nickel ferrite loaded biochar material. However, compared with activated carbon, biochar has a smaller specific surface area and lower strength. Moreover, long-term heating consumes a lot of energy and has low economic benefits. Both methods have a common problem, that is, the materials are in powder form, which is difficult to control in practical applications. Summary of the Invention

[0005] The purpose of the present invention is to solve the above problems and provide a chitosan activated carbon loaded iron / silver composite ball and its preparation method and application.

[0006] In order to achieve its purpose, the present invention adopts the following technical solutions:

[0007] A method for preparing chitosan-activated activated carbon-loaded iron / silver composite balls comprises the following steps:

[0008] (1) dissolving activated carbon and chitosan in an acetic acid solution to obtain a chitosan-activated carbon mixed solution;

[0009] (2) adding an iron compound and a silver compound to the chitosan-activated carbon mixed solution, stirring and mixing at 30-60° C.; the iron compound is selected from ferric sulfate and ferric nitrate; the silver compound is silver nitrate; the mass ratio of the iron element in the iron compound to the activated carbon is 0.07-0.20:1, and the molar ratio of the silver element in the silver compound to the iron element in the iron compound is 1:10-50;

[0010] (3) dropping the mixed solution obtained in step (2) into an ammonia solution at 30-60° C. for alkalization, and washing the gel particles formed after the alkalization with deionized water until the pH of the effluent remains unchanged;

[0011] (4) adding the gel particles obtained in step (3) to a crosslinking agent solution for crosslinking, washing, and freeze-drying; the crosslinking agent is selected from formaldehyde, pentanediol, and jingpinniol;

[0012] (5) calcining the freeze-dried gel particles obtained in step (4) at 350-650° C. for 0.8-1.5 h to obtain chitosan-coated iron / silver-loaded activated carbon composite spheres.

[0013] In the step (1), the mass ratio of activated carbon to chitosan is 1:1.5-2.5, the mass volume ratio of activated carbon to acetic acid solution is 1g:80-120ml, the concentration of acetic acid solution is 1.5-2.5wt%, and the activated carbon and chitosan are added to the acetic acid solution and stirred at 30-60°C for 40-120min.

[0014] In the step (1), the mass ratio of activated carbon to chitosan is 1:1.8-2.2, the mass volume ratio of activated carbon to acetic acid solution is 1g:90-110ml, the concentration of acetic acid solution is 1.8-2.2wt%, and the activated carbon and chitosan are added to the acetic acid solution and stirred at 30-60°C for 40-80min.

[0015] In the step (2), the mixture is stirred at 30-60° C. for 40-100 minutes; the mass ratio of the iron element in the iron compound to the activated carbon is 0.08-0.15:1 or 0.08-0.12:1 or 0.09-0.11:1; and the molar ratio of the silver element in the silver compound to the iron in the iron compound is 1:10-35 or 1:10-20 or 1:10-13.

[0016] In the step (3), the concentration of the ammonia solution is 0.07-0.15M, the volume ratio of the mixed solution in step (2) to the ammonia solution is 1:1-2, and the alkalization is carried out at 30-60°C for 2-4h.

[0017] In the step (4), the concentration of the crosslinker solution is 0.08-1.5 wt %, and the amount of the crosslinker solution used is the mass volume ratio of the activated carbon used in step (1) to the crosslinker solution of 1 g:30-80 ml, preferably 1 g:40-60 ml; crosslinking is performed for 0.8-1.5 h, and then cleaned with ethanol and ultrapure water, and freeze-dried at -50°C to -30°C for 14-22 h.

[0018] In the step (5), the freeze-dried gel particles obtained in the step (4) are placed in a tubular furnace and calcined at 350-650° C. at a rate of 8-12° C. / min under the protection of an inert gas flow.

[0019] A chitosan-activated activated carbon-loaded iron / silver composite ball is prepared by any of the methods described above.

[0020] The chitosan activated activated carbon loaded iron / silver composite balls are used to remove Sr, Pb or tetracycline hydrochloride pollution in the environment.

[0021] The application is preferably: application of the chitosan activated carbon loaded iron / silver composite balls in removing Sr, Pb or tetracycline hydrochloride pollution in water environment;

[0022] The concentration of Sr(II) in the wastewater to be treated is preferably 0.1-15 mg / L, the dosage of the composite ball is 0.4-1.0 g / L, and the adsorption is carried out for more than 22 hours after the composite material is added;

[0023] The preferred concentration of Pb(II) in the wastewater to be treated is 0.1-120 mg / L, the dosage of the composite ball is 0.4-1.0 g / L, and the composite material is adsorbed for more than 22 hours.

[0024] The principles of the present invention are as follows:

[0025] First, chitosan reacts with acetic acid to form chitosan ester. The chitosan gel immobilizes the silver- and iron-loaded activated carbon. The chitosan encapsulates the iron- and silver-loaded activated carbon powder particles, forming a spherical shape. This results in a granular activated carbon adsorbent that is more suitable for practical water treatment.

[0026] In step (3), the mixed solution is dropped into an ammonia solution for alkalization, so that the chitosan-activated activated carbon-loaded silver-iron solution is gelled. Then, in step (4), the chitosan molecules and the cross-linking agent are cross-linked to give the material higher strength, stiffness, thermal stability and chemical resistance. Water is removed by drying, and freeze drying is more effective than high-temperature drying.

[0027] Finally, through high-temperature calcination, the composite material's specific surface area and total pore volume were significantly increased, while the average pore diameter was reduced, developing a microporous structure. Microporous adsorbents are more suitable for removing pollutants such as heavy metals. Furthermore, XPS elemental analysis revealed that some of the iron was reduced to zero-valent iron, significantly improving its pollutant removal capacity.

[0028] The beneficial effects of the present invention are:

[0029] The preparation method of the silver-loaded and iron-loaded activated carbon composite ball of the present invention is simple and easy to carry out, has low consumption of chemical reagents and good repeatability. The iron-silver loading of the composite ball obtained is stable, and the amount of iron and silver leached into the water is lower than the national drinking water standard, and no secondary pollution is caused. The prepared iron-loaded and silver-loaded activated carbon composite ball can efficiently remove heavy metal ions, radioactive nuclides (such as Sr) and organic pollution, is widely applicable to various pollutants in drinking water, and has the effects of adsorption, catalysis and degradation of pollutants. At the same time, due to the presence of silver, it has a certain bactericidal effect and inhibits the growth of bacteria to a certain extent. At the same time, the spherical adsorbent is easy to separate in actual water treatment, is suitable for industrial wastewater treatment, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a SEM image of the composite material of Example 1.

[0031] Figure 2 is the EDX image of the composite material of Example 1.

[0032] Figure 3 is a SEM image of the composite material of Example 2.

[0033] Figure 4 This is the EDX image of the composite material of Example 2.

[0034] Figure 5 is a SEM image of the composite material of Example 3.

[0035] Figure 6 This is the EDX image of the composite material of Example 3.

[0036] Figure 7 is a SEM image of the composite material of Example 4.

[0037] Figure 8 This is the EDX image of the composite material of Example 4.

[0038] Figure 9 This is the time adsorption curve of the radioactive element Sr by the composite material of Examples 1-4.

[0039] Figure 10 This is the XPS fine spectrum of iron.

[0040] Figure 11 Graph showing the effect of pH on the adsorption of Sr for the composite materials of Examples 1-4.

[0041] Figure 12 This is the time adsorption curve of Pb by the composite materials of Examples 1-4. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the embodiments.

[0043] The experimental methods in the following examples are conventional methods unless otherwise specified; the chemical reagents used are conventional reagents in the art and can be purchased unless otherwise specified.

[0044] Sources of main materials and reagents:

[0045] Activated carbon: Coconut shell activated carbon, purchased from Fujian Xinsen Carbon Industry Co., Ltd. (particle size about 200 mesh). Product parameters: BET specific surface area 903.512m 2 / g, ash content ≤7%, pH 6-10.

[0046] Chitosan: chitosan, CAS: 9012-76-4.

[0047] Fe2(SO4)3·9H20: ferric sulfate nonahydrate.

[0048] Example 1: Preparation of Iron- and Silver-Loaded Activated Carbon Composite Balls

[0049] 1. Preparation of Iron- and Silver-Loaded Activated Carbon Composite Ball Samples of Examples 1-4

[0050] Preparation of iron- and silver-loaded activated carbon composite balls: The composite ball sample of Example 1 was prepared according to the following steps:

[0051] (1) Filter 200-mesh coconut shell activated carbon, wash with deionized water and dry.

[0052] (2) Pour 2 g of activated carbon into 200 mL of 2 wt% acetic acid solution and stir for 20 min. Then add 4 g of chitosan and continue stirring for 40 min. The water bath temperature is 60°C.

[0053] (3) 2.007 g of Fe2(SO4)3·9H20 and 3.572 mL of 0.1 M AgNO3 were added to the activated carbon and chitosan solutions as iron and silver sources, respectively, and stirred in a 60°C water bath at a speed of 150 r / min for 60 min.

[0054] (4) Using a 10 mL syringe, slowly drip the solution obtained in step (3) into 150 mL of 0.1 M NH3·H2O. Alkalinize the solution in a water bath at 60°C for 3 h to form gel particles. Rinse the gel particles with ultrapure water until the pH of the effluent remains constant.

[0055] (5) The gel particles washed in step (4) were placed in 100 mL of 1 wt% glutaraldehyde solution for cross-linking for 1 h, then washed several times with anhydrous ethanol and ultrapure water, and freeze-dried at -50°C for 18 h.

[0056] (6) The dried gel particles were placed in a tubular furnace and heated to 350°C at a rate of 10°C / min and calcined for 1 h under N2 flow protection to obtain iron- and silver-loaded activated carbon composite balls.

[0057] The composite ball samples of Examples 2-4 were prepared using the above method, with the raw material ratios in step 3) and the calcination process parameters in step 6) being different. The remaining operating steps and process parameters were the same as those in Example 1. The differences are shown in Table 1.

[0058] Table 1 Proportions and process parameters of Examples 1-4

[0059]

[0060] The specific surface area of ​​the composite material of Example 1 was measured by BET and was 5.374 m 2 / g, and a total pore volume of 0.032 cm 3 / g. Figure 1 This is an SEM image of the composite material prepared in Example 1. It can be seen from the figure that the addition of chitosan successfully encapsulates the silver / iron loaded activated carbon into a spherical adsorbent, and the iron and silver are attached to the surface of the adsorbent in the form of white particles. Figure 2 This is an EDX image of the composite material prepared in Example 1. The composite material is mainly composed of carbon, iron, silver, and oxygen, with the atomic percentages of each element being 66.0%, 21.36%, 8.62%, and 1.60%, respectively.

[0061] The specific surface area of ​​the composite material of Example 2 was measured by BET and was 9.437 m 2 / g, and a total pore volume of 0.078 cm 3 / g. Figure 3 This is an SEM image of the composite material prepared in Example 2. It can be seen from the figure that the addition of chitosan successfully encapsulates the silver / iron loaded activated carbon into a spherical adsorbent, and the iron and silver are attached to the surface of the adsorbent in the form of white particles. Figure 4This is an EDX image of the composite material prepared in Example 2. The composite material is mainly composed of carbon, iron, silver, and oxygen, with the atomic percentages of each element being 75.47%, 4.78%, 18.94%, and 0.50%, respectively.

[0062] The specific surface area of ​​the composite material of Example 3 was measured by BET and was 8.941 m 2 / g, and a total pore volume of 0.074 cm 3 / g. Figure 5 This is an SEM image of the composite material prepared in Example 3. It can be seen from the figure that the addition of chitosan successfully encapsulates the silver / iron loaded activated carbon into a spherical adsorbent, and the iron and silver are attached to the surface of the adsorbent in the form of white particles. Figure 6 This is an EDX image of the composite material prepared in Example 3. The composite material is mainly composed of carbon, iron, silver, and oxygen, with the atomic percentages of each element being 72.53%, 4.24%, 21.72%, and 1.16%, respectively.

[0063] The specific surface area of ​​the composite material of Example 4 was measured by BET and was 79.543 m 2 / g, and a total pore volume of 0.127 cm 3 / g. Figure 7 This is an SEM image of the composite material prepared in Example 4. It can be seen from the figure that the addition of chitosan successfully encapsulates the silver / iron loaded activated carbon into a spherical adsorbent, and the iron and silver are attached to the surface of the adsorbent in the form of white particles. Figure 8 This is an EDX image of the composite material prepared in Example 4. The composite material is mainly composed of carbon, iron, silver, and oxygen, with the atomic percentages of each element being 77.24%, 7.97%, 12.30%, and 1.33%, respectively.

[0064] 2. Experimental study on single factor influence

[0065] Different samples (Samples 1-12 in Tables 2-4) were prepared according to the sample preparation method described in Example 1. The effects of ferric sulfate dosage, silver nitrate dosage, and calcination temperature on the specific surface area, total pore volume, and zeta potential of the composite spheres were investigated. The properties of the composite spheres obtained using the different formulation ratios and process parameters are shown in Tables 2-4.

[0066] Table 2 Effect of ferric sulfate dosage on materials

[0067]

[0068] Table 3 Effect of silver nitrate dosage on materials

[0069]

[0070] Table 4 Effect of calcination temperature on materials

[0071]

[0072] It can be seen that the effect of iron loading on material performance lies in the Zeta potential of the composite material. Too high iron loading will lead to an increase in the Zeta potential of the material, which is not conducive to the adsorption of cations. The effect of silver loading on material performance is not significant. The addition of silver is to form a bimetallic system with iron, which improves the iron removal capacity under the catalytic effect of silver. The calcination temperature has a great influence on the specific surface area and pore volume of the material. When the temperature is increased from 350℃ to 600℃, the specific surface area and pore volume increase by 70.602m 2 / g and 0.053cm 3 / g.

[0073] Example 5: Sr(II) treatment experiment one,

[0075] This experimental example treated Sr(II)-containing wastewater and investigated the adsorption properties of the composite material of the present invention through static adsorption tests. A 10 mg / L Sr(II) solution was prepared at a pH of 7. 0.02 g of untreated coconut shell activated carbon and the composite material prepared in Examples 1-4 were placed in 100 mL polyvinyl chloride centrifuge tubes. 50 mL of the 10 mg / L Sr(II) solution was added and the mixture was shaken at 180 rpm for 24 hours in a 25°C air bath constant temperature shaker. After the reaction, the total Sr content was determined using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0076] The results are as follows Figure 9 As shown. It can be seen that the adsorption amount of Sr(Ⅱ) by untreated coconut shell activated carbon (AC) is very small, while the removal efficiency of Sr(Ⅱ) by the composite material prepared by the present invention can reach 86.91%. Among them, the calcination temperature has the greatest influence on the adsorption effect. On the one hand, the calcination temperature has a significant effect on the specific surface area and pore size of the material. Increasing the calcination temperature can promote the growth of the specific surface area and pore volume of the material. On the other hand, when the calcination temperature is increased to 600℃, part of the iron element is reduced to zero-valent iron, Figure 10 XPS analysis of the composite spheres prepared in Example 4 reveals that the strong oxidizing properties of zero-valent iron at 706.5 eV significantly enhance pollutant removal efficiency. However, as the calcination temperature continues to increase, the adsorption performance of the material decreases. This may be due to the collapse of the pore structure caused by the high temperature. Excessive iron loading will result in a decrease in the adsorption of Sr(II) by the composite spheres. Figure 1-2It shows that the iron loading of the composite ball of Example 1 is higher than that of Examples 2-4, resulting in the Zeta potential being increased to about 7, resulting in the adsorption amount of Sr(II) by the composite material being lower than that of Examples 2-4.

[0077] 2. Study on the anti-iron and silver loss performance of composite materials during water purification

[0078] The concentrations of iron and silver in the solution after the adsorption treatment in Example 2 were measured using an inductively coupled plasma optical emission spectrometer (ICP-OES). The iron and silver concentrations were 0.162 mg / L and 0.0097 mg / L, respectively, both lower than the 0.3 mg / L and 0.05 mg / L in the national drinking water standard (GB 5749-2006), indicating that the composite material of the present invention is safe in the water treatment process.

[0079] 3. Investigating the effect of pH on chitosan-coated iron / silver activated carbon composite spheres

[0080] The composite material prepared in Example 1-4 was placed in a 100 mL polyvinyl chloride centrifuge tube, 50 mL of a 10 mg / L Sr(II) solution was added, and the pH was adjusted to 3-8. The tube was placed in an air bath constant temperature shaker and shaken at 180 rpm for 24 h.

[0081] The results are as follows Figure 11 As shown in the figure, all materials show a trend that when the solution pH is neutral to alkaline, the composite material has a good Sr removal effect, with a removal rate of 87.32%. The pH of actual domestic sewage is also around 6.5, indicating that this material can achieve a good removal effect on Sr(II) pollution in actual conditions.

[0082] 4. Experiment on removing Pb from composite materials

[0083] This experimental example treated wastewater containing Pb(II) and investigated the adsorption properties of the composite material of the present invention through static adsorption tests. A 100 mg / L Pb(II) solution was prepared at a pH of 7. 0.02 g of untreated coconut shell activated carbon and the composite material prepared in Examples 1-4 were each placed in a 100 mL polyvinyl chloride centrifuge tube, and 50 mL of the 100 mg / L Pb(II) solution was added. The mixture was shaken in a 25°C air bath incubator at 180 rpm for 24 hours. After the reaction, the total Pb content was directly determined using an inductively coupled plasma optical emission spectrometer (ICP-OES).

[0084] The results are as follows Figure 12As shown in the figure, untreated coconut shell activated carbon (AC) has a very low adsorption capacity for Pb(II), while the composite material prepared by the present invention can achieve a Pb(II) removal efficiency of over 95%. The iron loading has a significant impact on Pb(II) adsorption. When the iron loading is too high, the removal of Pb(II) drops to only 44.61%. This is mainly because the high iron loading increases the Zeta potential of the adsorbent, which is not conducive to the adsorption of cations.

Claims

1. Application of chitosan activated carbon loaded iron / silver composite balls in removing Sr or Pb pollution in water environment, characterized by: The preparation method of the chitosan activated activated carbon loaded iron / silver composite balls comprises the following steps: (1) Dissolving activated carbon and chitosan in acetic acid solution, wherein the mass ratio of activated carbon to chitosan is 1:1.5-2.5, the mass volume ratio of activated carbon to acetic acid solution is 1 g:80-120 ml, and the concentration of acetic acid solution is 1.5-2.5 wt%. After adding activated carbon and chitosan to the acetic acid solution, stirring at 30-60°C for 40-120 min to obtain a chitosan-activated carbon mixed solution; (2) adding an iron compound and a silver compound to the chitosan-activated carbon mixed solution, stirring and mixing at 30-60° C.; the iron compound is selected from ferric sulfate or ferric nitrate; the silver compound is silver nitrate; the mass ratio of the iron element in the iron compound to the activated carbon is 0.09-0.11:1, and the molar ratio of the silver element in the silver compound to the iron element in the iron compound is 1:10-20; (3) dropping the mixed solution obtained in step (2) into an ammonia solution at 30-60° C. for alkalization, and washing the gel particles formed after the alkalization with deionized water until the pH of the effluent remains unchanged; (4) adding the gel particles obtained in step (3) to a crosslinking agent solution for crosslinking, washing, and then freeze-drying; the crosslinking agent is selected from formaldehyde, pentanediol, or jingpinniol; the concentration of the crosslinking agent solution is 0.08-1.5 wt%, and the mass volume ratio of the activated carbon used in step (1) to the crosslinking agent solution is 1 g: 30-80 ml; (5) The freeze-dried gel particles obtained in step (4) are calcined at 600-650° C. for 0.8-1.5 h, so that part of the iron element is reduced to zero-valent iron, thereby obtaining chitosan-activated activated carbon-loaded iron / silver composite spheres.

2. The use according to claim 1, characterized in that: In step (1), the mass ratio of activated carbon to chitosan is 1:1.8-2.2, the mass volume ratio of activated carbon to acetic acid solution is 1g:90-110ml, the concentration of acetic acid solution is 1.8-2.2 wt%, and the activated carbon and chitosan are added to the acetic acid solution and stirred at 30-60°C for 40-80 min.

3. The use according to claim 1, characterized in that: In the step (2), the mixture is stirred at 30-60° C. for 40-100 min.

4. The use according to claim 1, characterized in that: In the step (3), the concentration of the ammonia solution is 0.07-0.15 M, the volume ratio of the mixed solution in step (2) to the ammonia solution is 1:1-2, and the alkalization is carried out at 30-60°C for 2-4 hours.

5. The use according to claim 1, characterized in that: In the step (4), cross-linking is performed for 0.8-1.5 h, and then the cross-linked product is cleaned with ethanol and ultrapure water, and freeze-dried at -50°C to -30°C for 14-22 h.

6. The use according to claim 1, characterized in that: In the step (5), the freeze-dried gel particles obtained in the step (4) are placed in a tubular furnace and heated to 600-650° C. at a rate of 8-12° C. / min under the protection of an inert gas flow, and calcined.

7. The use according to claim 1, characterized in that: The concentration of Sr(II) in the wastewater to be treated is 0.1-15 mg / L, the dosage of the composite ball is 0.4-1.0 g / L, and the adsorption is carried out for more than 22 hours after the composite ball is added; The concentration of Pb(II) in the sewage to be treated is 0.1-120 mg / L, the dosage of the composite balls is 0.4-1.0 g / L, and the adsorption is carried out for more than 22 hours after the composite balls are added.

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