Preparation of cerium-doped surface-modified activated carbon and its application in adsorption of perfluorinated compounds

Abstract

The present invention belongs to the field of environmental governance technology, and specifically relates to the preparation of cerium-doped surface-modified activated carbon and its application in the adsorption of perfluorinated compounds. The present invention dissolves cerium salt and citric acid in water to form a transparent solution, then adds NaOH and activated carbon (AC), and then sequentially undergoes hydrothermal reaction and calcination treatment to obtain a cerium-doped surface-modified activated carbon. The modified activated carbon synthesized by the method of the present invention has efficient adsorption performance and a significantly improved specific surface area, thereby increasing the contact area between the AC material and the pollutants, and greatly improving the adsorption performance and adsorption efficiency of the material, so that it can efficiently remove perfluorinated compounds in water. It is particularly suitable for treating multiple types of high-concentration wastewater and can meet the multiple demands of the wastewater treatment field for high efficiency, economy and environmental protection.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental governance, and particularly relates to the preparation of cerium-doped surface-modified activated carbon and its application in adsorbing perfluorinated compounds. Background Art

[0002] With the advancement of industrialization and urbanization, environmental problems are becoming increasingly severe. New, persistent trace pollutants are constantly being detected, placing new pressure on our efforts to control environmental pollution. Perfluorinated compounds (PFOCs) are a typical example. Perfluorinated compounds (PFOCs) are organic compounds in which all hydrogen atoms attached to carbon atoms are replaced by fluorine atoms. Due to their exceptional thermal and chemical stability and surface activity, they are widely used in non-stick products, fire extinguishing foams, and electronics manufacturing. Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are the most produced and widely used. The high stability of their long carbon chain makes these compounds difficult to degrade naturally, resulting in persistent environmental impacts. Perfluorooctanoic acid (PFOA), a prominent example, has attracted significant public attention due to its persistence and high toxicity. It has been designated a new persistent organic pollutant (POP) and is included on the Stockholm Convention's priority list. However, due to its extensive use over the past few decades, PFOA has become widespread in various environmental media, making its control a significant environmental challenge. At the same time, PFOA can enter the human bloodstream through the food chain, adversely affecting human growth and development. This makes the management of PFOA both urgent and unavoidable. Therefore, research on PFOA removal technologies has become a hot topic in the environmental field that cannot be avoided.

[0003] Although a number of treatment technologies are currently being used to remove PFOA, including biological treatment, advanced oxidation, and thermal degradation, biological treatment and advanced oxidation technologies produce a large number of highly toxic intermediates during the PFOA treatment process, causing secondary pollution. Thermal degradation technologies, on the other hand, are energy-intensive, complex, and require demanding reaction conditions. These limitations hinder the large-scale application of these new technologies. Adsorption, however, is expected to become the optimal technology for PFOA removal due to its advantages such as low cost, simple design, high efficacy, no byproducts during adsorption, and the ability to remove pollutants adsorbed on the adsorbent during regeneration. Currently, activated carbon adsorption is the most widely used adsorption method for removing PFOA from water. However, traditional activated carbon relies solely on physical adsorption to eliminate PFOA, resulting in very low removal efficiency. Therefore, the development of new activated carbon adsorbents with high removal efficiency is of great significance. Summary of the Invention

[0004] In order to overcome the above-mentioned shortcomings of the prior art, the present invention modifies the surface of activated carbon by doping it with cerium, thereby increasing the contact area between the AC material and the pollutants, improving the adsorption performance and adsorption efficiency of the material, and enabling it to efficiently remove perfluorinated compounds in water.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A first aspect of the present invention provides a method for preparing cerium-doped surface-modified activated carbon, the method comprising the following steps:

[0007] S1. Dissolving cerium salt and citric acid in water to form a transparent solution, then adding NaOH and activated carbon, and performing a hydrothermal reaction;

[0008] S2. After the reaction, the mixture is cooled to room temperature, and the solids after the reaction are collected. After washing and drying, the solids are transferred to an inert gas atmosphere for calcination to obtain the finished product.

[0009] The material's synthesis process is simple, with few steps and easy operation, resulting in a low production cost, making the production process economical and efficient. The preparation requirements are low, requiring no high-precision equipment or extreme operating conditions, making it suitable for large-scale production.

[0010] Preferably, the mass ratio of the cerium salt, citric acid, NaOH, and activated carbon is 140-160:20-30:13-19:900-1100.

[0011] Preferably, the temperature of the hydrothermal reaction is 150-250° C., and the time is 20-30 h.

[0012] Preferably, the cerium salt includes cerium chloride, cerium nitrate, and cerium sulfate.

[0013] Preferably, the calcination temperature is 500-900° C., the calcination time is 1-3 h, and the heating rate is 8-12° C. / min.

[0014] The second aspect of the present invention provides cerium-doped surface-modified activated carbon prepared by the preparation method described in the first aspect.

[0015] The third aspect of the present invention provides the use of the cerium-doped surface-modified activated carbon described in the second aspect in the adsorption of perfluorinated compounds.

[0016] The modified activated carbon synthesized using the method of the present invention exhibits highly efficient adsorption properties, effectively removing perfluorinated compounds from water and is particularly suitable for treating diverse, high-concentration wastewater. It also effectively prevents secondary contamination. During the treatment process, pollutants are effectively concentrated on the material surface, facilitating subsequent treatment and reducing the risk of secondary contamination. Furthermore, the adsorbent is reusable and easily regenerated, eliminating the need for complex regeneration processes. This reduces maintenance costs and operational complexity, making it suitable for long-term use.

[0017] Preferably, the perfluorinated compound is perfluorooctanoic acid (PFOA).

[0018] Preferably, the specific application method is: putting the cerium-doped surface-modified activated carbon according to claim 6 into a water body containing perfluorinated compounds and adsorbing it for more than 30 minutes.

[0019] More preferably, the input amount of cerium-doped surface-modified activated carbon is 5-10 mg / 100 mL.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention discloses a method for preparing cerium-doped surface-modified activated carbon. The method involves dissolving a cerium salt and citric acid in water to form a transparent solution, then adding NaOH and activated carbon. The solution is then subjected to a hydrothermal reaction and calcination. The modified activated carbon synthesized using the present method exhibits highly efficient adsorption properties and a significantly increased specific surface area, thereby increasing the contact area between the AC material and pollutants. This significantly enhances the material's adsorption performance and efficiency, enabling it to efficiently remove perfluorinated compounds from water. The material is particularly suitable for treating diverse, high-concentration wastewater. Overall, the present invention offers the following advantages:

[0022] (1) Significantly Increased Specific Surface Area: Compared to traditional activated carbon adsorbents, the cerium-doped activated carbon adsorbent of the present invention significantly increases its specific surface area through optimized preparation processes and cerium doping. This feature allows more pollutants to be effectively contacted and adsorbed, improving overall treatment capacity and efficiency.

[0023] (2) Increased adsorption active sites: Cerium doping improves the microstructure of activated carbon and increases the number of adsorption active sites. This structural improvement not only enhances the adsorption capacity of target pollutants, but also enhances the selectivity of the adsorbent, enabling it to more efficiently remove different types of pollutants in wastewater.

[0024] (3) Improved Adsorption Performance and Rate: Thanks to the increased specific surface area and active sites, the adsorbent of the present invention exhibits excellent adsorption performance and a faster treatment rate during wastewater treatment. Compared to existing activated carbon adsorbents, the present invention can achieve higher removal efficiency in a shorter time, significantly improving the rate and effectiveness of wastewater treatment.

[0025] (4) Significantly improved material stability: The cerium-doped activated carbon exhibits excellent chemical and physical stability during use, maintaining efficient adsorption performance over extended periods of operation. Compared to existing activated carbon adsorbents, the adsorbent of the present invention is less susceptible to performance degradation during processing, reducing replacement frequency and maintenance costs.

[0026] (5) Broad Applicability: The cerium-doped activated carbon adsorbent of the present invention can effectively treat a wide range of wastewater types and concentrations, particularly when treating wastewater containing perfluorinated compounds, demonstrating exceptional performance. This broad applicability enables the adsorbent to meet wastewater treatment needs across diverse industrial and environmental sectors, demonstrating its potential for widespread application.

[0027] (6) Low cost and simple preparation process: The cerium-doped activated carbon adsorbent of the present invention has a low preparation cost and a simple preparation process with relatively low requirements for conditions. This advantage makes the adsorbent more economical and feasible to produce, and has significant cost-effectiveness compared to the complex and high-cost preparation processes of existing activated carbon adsorbents.

[0028] In summary, the new cerium-doped activated carbon adsorbent prepared by the method of the present invention shows significant advantages in terms of specific surface area, adsorption active sites, adsorption performance, material stability, wide treatment range, reaction conditions, environmental protection and preparation cost, enabling it to meet the multiple needs of wastewater treatment for high efficiency, economy and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The full spectrum of X-ray photoelectron spectra of different cerium-doped activated carbon adsorbents;

[0030] Figure 2 X-ray photoelectron spectroscopy Ce 3d spectra of different cerium-doped activated carbon adsorbents;

[0031] Figure 3 The BET results of different cerium-doped activated carbon adsorbents were measured by nitrogen adsorption and desorption;

[0032] Figure 4 is the removal rate of PFOA by cerium-doped activated carbon adsorbent at different times;

[0033] Figure 5The removal efficiency of PFOA at different concentrations by cerium-doped activated carbon adsorbent AC-Ce-900 at different times;

[0034] Figure 6 is the removal efficiency of PFOA at different initial pH values ​​by cerium-doped activated carbon adsorbent AC-Ce-900 at different times;

[0035] Figure 7 is the removal efficiency of PFOA by cerium-doped activated carbon adsorbent AC-Ce-900 in the presence of humic acid (HA) or fulvic acid (FA);

[0036] Figure 8 The removal efficiency of PFOA by cerium-doped activated carbon adsorbent AC-Ce-900 under different coexisting ion conditions;

[0037] Figure 9 The removal efficiency of PFOA at different temperatures and at different times by cerium-doped activated carbon adsorbent AC-Ce-900;

[0038] Figure 10 The removal efficiency of PFOA in different actual water bodies by cerium-doped activated carbon adsorbent AC-Ce-900 at different times. DETAILED DESCRIPTION

[0039] The following is a further description of specific embodiments of the present invention. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0040] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0041] Example 1: Preparation of cerium-doped surface-modified activated carbon

[0042] (1) 149.032 mg of CeCl₃·7H₂O and 26.4165 mg of citric acid were dissolved in 80 mL of deionized water to form a transparent solution. 16 mg of NaOH was then added while stirring magnetically. After stirring for 15 min, 1 g of activated carbon was slowly added. The mixture was then transferred to a Teflon-lined autoclave and hydrothermally treated at 200°C for 24 h.

[0043] (2) After the reaction, the mixture was cooled to room temperature, and the solid was collected by filtration. The solid was washed several times with deionized water and dried in an oven at 60° C. overnight to obtain a precursor.

[0044] (3) The precursor was transferred to a tube furnace and calcined at 500°C, 700°C, and 900°C for 2 h under a nitrogen atmosphere at a heating rate of 10°C / min. The calcined AC-Ce material was then ground into powder to obtain the finished product. The AC-Ce materials obtained at 500°C, 700°C, and 900°C were labeled AC-Ce-500, AC-Ce-700, and AC-Ce-900, respectively.

[0045] Figure 1 The full spectrum of X-ray photoelectron spectroscopy shows that compared with the AC before modification, the modified material has a new peak of Ce 3d in the range of 880-910eV, indicating that Ce is successfully doped in the modified material.

[0046] As shown in Table 1 and Figure 2 As shown, the Ce of AC-Ce-900 3+ Content higher than Ce 4+ , Ce 3+ The content is about 50.77%, and Ce 4+ The Ce content of AC-Ce-700 is about 49.23%. 3+ The content is also higher than Ce 4+ , Ce 3+ The content is about 53.48%, and Ce 4+ The Ce content of AC-Ce-500 is about 46.52%. 3+ The content is lower than Ce 4+ , Ce 3+ The content is about 48.64%, and Ce 4+ The content is about 51.36%.

[0047] Table 1 X-ray photoelectron spectroscopy Ce 3d test results of different cerium-doped activated carbon adsorbents

[0048] catalyst <![CDATA[Ce 4+ (%)]]> <![CDATA[Ce 3+ (%)]]> AC-Ce-900 49.23 50.77 AC-Ce-700 46.52 53.48 AC-Ce-500 51.36 48.64 AC 0 0

[0049] As shown in Table 2 and Figure 3 As shown in Figure 2, the introduction of Ce significantly increased the specific surface area of ​​AC. The introduction of Ce and calcination at 900 °C increased the specific surface area of ​​AC from 1131.6 m 2 / g increased to 1431.3m 2 / g, the improvement effect is most obvious.

[0050] Table 2 Nitrogen adsorption and desorption test results of different cerium-doped activated carbon adsorbents

[0051] catalyst AC-Ce-900 AC-Ce-700 AC-Ce-500 AC <![CDATA[BET result (m 2 / g)]]> 1431.3 1400.1 1321.6 1131.6

[0052] Example 2: Investigation of the adsorption performance of cerium-doped surface-modified activated carbon

[0053] In order to evaluate the adsorption performance of the new cerium-doped activated carbon adsorbent, the following experiments were conducted:

[0054] (1) 100 mL of a 10 mg / L perfluorooctanoic acid (PFOA) solution was prepared using 1 g / L perfluorooctanoic acid (PFOA) mother liquor and stirred evenly on a magnetic stirrer at 520 rpm. Then, 6 mg of the adsorbent materials (AC-Ce-500, AC-Ce-700, and AC-Ce-900) prepared in Example 1 were added to the 100 mL PFOA solution and an adsorption reaction was carried out for 30 min.

[0055] (2) Sampling was performed at 0 min, 10 min, 20 min, and 30 min, and 1 mL of the sample was taken using a syringe and filtered through a 0.45 μm filter membrane, and then tested using high performance liquid chromatography.

[0056] From Table 3 and Figure 4 It can be seen that AC-Ce-900 has the highest removal efficiency, which can remove 86% of PFOA in 30 minutes. Compared with the activated carbon before modification, the PFOA removal efficiency is increased by 7.88 times.

[0057] Table 3 Removal efficiency of PFOA by cerium-doped activated carbon adsorbent

[0058] adsorbent AC AC-Ce-500 AC-Ce-700 AC-Ce-900 PFOA removal rate (%) 10.88 26.98 70.04 85.71

[0059] Example 3: Adsorption performance of cerium-doped surface-modified activated carbon at different initial PFOA concentrations

[0060] In order to evaluate the adsorption performance of the new cerium-doped activated carbon adsorbent AC-Ce-900 at different initial PFOA concentrations, the following experiments were conducted:

[0061] (1) 100 mL of PFOA solutions with concentrations of 10, 75, and 150 mg / L were prepared using 1 g / L PFOA stock solution and stirred evenly on a magnetic stirrer at 520 rpm. Then, 6 mg of AC-Ce-900 adsorbent material was added to the 100 mL PFOA solution and the adsorption reaction was carried out for 60 min.

[0062] (2) Sampling was performed at 0 min, 5 min, 10 min, 15 min, 20 min, 30 min, and 60 min, and 1 mL of the sample was taken using a syringe and filtered through a 0.45 μm polyethersulfone needle filter, and then tested using high performance liquid chromatography.

[0063] From Table 4 and Figure 5It can be seen that with the increase of the initial concentration of PFOA, the adsorption rate gradually decreases, indicating that the adsorption sites of the adsorbent are limited, while with the increase of the initial concentration of PFOA, the adsorption amount gradually increases, indicating that high concentration of pollutants is conducive to promoting the adsorption process towards adsorption saturation.

[0064] Table 4 Removal efficiency of PFOA at different concentrations by cerium-doped activated carbon adsorbent AC-Ce-900

[0065] PFOA concentration (mg / L) Adsorption rate (%) 60min adsorption capacity (mg / g) 10 77.27 128.78 75 26.64 328 150 18.37 459.25

[0066] Example 4: Adsorption performance of PFOA on cerium-doped surface-modified activated carbon at different initial pH values

[0067] In order to evaluate the adsorption performance of the novel cerium-doped activated carbon adsorbent AC-Ce-900 for PFOA at different initial pH values, the following experiments were performed:

[0068] (1) 100 mL of 20 mg / L PFOA solution was prepared with 1 g / L PFOA mother liquor, and its initial pH was adjusted to 3, 5, 7, 9, and 11 using 1 mol / L HCl and NaOH solutions, respectively. The mixture was then stirred on a magnetic stirrer at 520 rpm, and 6 mg of AC-Ce-900 adsorbent material was added to the 100 mL PFOA solution for 30 min of adsorption reaction.

[0069] (2) Sampling was performed at 0 min, 5 min, 10 min, 15 min, 20 min, and 30 min, and 1 mL of the sample was taken using a syringe and filtered through a 0.45 μm polyethersulfone needle filter, and then tested using high performance liquid chromatography.

[0070] from Figure 6 It can be seen that as the initial pH of the solution decreases, the adsorption rate of PFOA by AC-Ce-900 adsorbent gradually increases, indicating that acidic conditions are conducive to the adsorption of PFOA by AC-Ce-900 adsorbent.

[0071] Example 5: Adsorption performance of cerium-doped surface-modified activated carbon under the influence of organic matter

[0072] In order to evaluate the adsorption performance of the new cerium-doped activated carbon adsorbent AC-Ce-900 under the influence of organic matter humic acid (HA) and fulvic acid (FA), the following experiments were conducted:

[0073] (1) 100 mL of a mixed solution was prepared with 1 g / L PFOA mother solution and 2 g / L HA and FA mother solutions, wherein the concentration of HA or FA was 5 mg / L or 10 mg / L, and the concentration of PFOA was 10 mg / L. The mixture was then stirred evenly on a magnetic stirrer at a speed of 520 rpm. 6 mg of AC-Ce-900 adsorbent material was then added to the 100 mL mixed solution for 30 min of adsorption reaction.

[0074] (2) Sampling was performed at 0 min and 30 min, and 1 mL of the sample was taken using a syringe and filtered through a 0.45 μm polyethersulfone needle filter, and then tested using high performance liquid chromatography.

[0075] from Figure 7 It can be seen that humic acid (HA) and fulvic acid (FA) have little effect on adsorption, and the presence of 5 mg / L FA will promote the adsorption of PFOA by AC-Ce-900.

[0076] Example 6: Adsorption performance of PFOA by cerium-doped surface-modified activated carbon under the influence of different coexisting ions

[0077] In order to evaluate the adsorption performance of the new cerium-doped activated carbon adsorbent AC-Ce-900 for PFOA under the influence of different coexisting ions, the following experiments were conducted:

[0078] (1) 100 mL of 10 mg / L PFOA solution was prepared with 1 g / L PFOA mother liquor. NaCl, Na2SO4, Na2CO3, and NaH2PO4 were then added to the solution to form a mixed solution with a coexisting ion concentration of 5 mmol / L. The solution was then stirred evenly on a magnetic stirrer at a speed of 520 rpm. 6 mg of AC-Ce-900 adsorbent material was then added to the 100 mL solution for 30 min of adsorption reaction.

[0079] (2) Sampling was performed at 0 min and 30 min, and 1 mL of the sample was taken using a syringe and filtered through a 0.45 μm polyethersulfone needle filter, and then tested using high performance liquid chromatography.

[0080] from Figure 8 It can be seen that only CO3 2- It will inhibit the adsorption of PFOA by AC-Ce-900 adsorbent, probably because CO3 2- Will hydrolyze to produce OH - , making the solution alkaline and inhibiting the adsorption of PFOA by AC-Ce-900 adsorbent. - It will not affect the adsorption performance of the adsorbent, and SO4 2- and H2PO 4- On the contrary, it will promote the adsorption of PFOA by the material.

[0081] Example 7: Adsorption performance of PFOA by cerium-doped surface-modified activated carbon under the influence of different solution temperatures

[0082] In order to evaluate the adsorption performance of the new cerium-doped activated carbon adsorbent AC-Ce-900 for PFOA under the influence of different solution temperatures, the following experiments were conducted:

[0083] (1) 100 mL of 10 mg / L PFOA solution was prepared with 1 g / L PFOA mother solution, and then stirred evenly on a magnetic heating stirrer at a speed of 520 rpm. The heating temperatures were set at 25°C, 35°C, and 50°C, respectively. When the solution temperature stabilized, 6 mg of AC-Ce-900 adsorbent material was added to the solution for 30 min of adsorption reaction.

[0084] (2) Sampling was performed at 0 min, 5 min, 10 min, 20 min and 30 min, and then 1 mL of sample was taken using a syringe and filtered through a 0.45 μm polyethersulfone needle filter, and then tested using high performance liquid chromatography.

[0085] from Figure 9 It can be seen that as the solution temperature increases, the adsorption amount of PFOA by AC-Ce-900 adsorbent gradually decreases, indicating that the adsorption of PFOA by this material is an exothermic process.

[0086] Example 8: Adsorption performance of PFOA by cerium-doped surface-modified activated carbon in different actual water bodies

[0087] In order to evaluate the adsorption performance of the new cerium-doped activated carbon adsorbent AC-Ce-900 for PFOA in different actual water conditions, the following experiments were conducted:

[0088] (1) Prepare 100 mL of 10 mg / L PFOA solution using deionized water, tap water, river water, and seawater, respectively. Stir the mixture on a magnetic stirrer at 520 rpm and then add 6 mg of AC-Ce-900 adsorbent material to the 100 mL PFOA solution for 30 min of adsorption reaction.

[0089] (2) Sampling was performed at 0 min, 5 min, 10 min, 20 min and 30 min, and 1 mL of the sample was taken using a syringe and filtered through a 0.45 μm polyethersulfone needle filter, and then tested using high performance liquid chromatography.

[0090] from Figure 10 It can be seen that different actual water bodies have little effect on the adsorption performance of AC-Ce-900 material, indicating that AC-Ce-900 can be used in actual water bodies to treat PFOA pollutants.

[0091] In summary, the cerium-doped surface-modified activated carbon prepared by the method of the present invention has a significantly improved specific surface area, thereby increasing the contact area between the AC material and the pollutants, improving the adsorption performance and adsorption efficiency of the material, so that it can efficiently remove perfluorinated compounds in water, and is particularly suitable for treating multi-type, high-concentration wastewater.

[0092] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. It is apparent to those skilled in the art that various changes, modifications, substitutions, and variations of these embodiments may be made without departing from the principles and spirit of the present invention, and the changes still fall within the scope of protection of the present invention.

Claims

1. Application of cerium-doped surface-modified activated carbon in the adsorption of perfluorinated compounds, characterized in that: The perfluorinated compound is perfluorooctanoic acid PFOA; The preparation method of the cerium-doped surface-modified activated carbon comprises the following steps: S1. Dissolving a cerium salt and citric acid in water to form a transparent solution, adding NaOH and activated carbon, and performing a hydrothermal reaction; the mass ratio of the cerium salt, citric acid, NaOH, and activated carbon is (140-160):(20-30):(13-19):(900-1100), and the hydrothermal reaction temperature is 150-250° C., and the time is 20-30 h; S2. After the reaction, the mixture is cooled to room temperature, and the solids after the reaction are collected. After washing and drying, the solids are transferred to an inert gas atmosphere for calcination to obtain a finished cerium-doped surface-modified activated carbon; the calcination temperature is 700-900°C, the time is 1-3h, and the heating rate is 8-12°C / min.

2. The use according to claim 1, characterized in that The cerium salt includes cerium chloride, cerium nitrate or cerium sulfate.

3. The use according to claim 1, characterized in that The specific application method is: put the cerium-doped surface-modified activated carbon into water containing perfluorinated compounds and adsorb it for more than 30 minutes.

4. The use according to claim 3, characterized in that The input amount of cerium-doped surface-modified activated carbon is 5-10 mg / 100 mL.

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