Preparation method and application of chitosan-coated coce-lDH catalyst
By encapsulating CoCe-LDH material with chitosan, the problems of poor adsorption of Co-based materials and leaching of iron-based materials were solved, achieving efficient activation of PMS and removal of inorganic arsenic, and improving the stability and arsenic removal rate of the material.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- EAST CHINA UNIV OF SCI & TECH
- Filing Date
- 2024-01-19
- Publication Date
- 2026-05-05
AI Technical Summary
Existing Co-based materials have poor adsorption capacity for inorganic arsenic during the activation of PMS, while iron-based materials are prone to leaching during the activation of PMS, causing secondary pollution of water bodies and catalyst deactivation.
A method using chitosan to encapsulate CoCe layered double hydroxide CoCe-LDH was adopted. By dispersing active sites with chitosan and adsorbing PMS, combined with the anion exchange mechanism of LDH, the efficient activation of PMS and removal of inorganic arsenic were achieved.
The rapid and efficient degradation of roxarsone and in-situ removal of inorganic arsenic by PMS were achieved. The introduction of chitosan improved the stability of the material and the removal rate of inorganic arsenic, reaching 98.5%, which is better than the 95.6% of the uncoated material.
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Figure CN118142581B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for preparing chitosan-encapsulated CoCe layered double hydroxide CoCe-LDH (CCHG) and its application in the activation and degradation of roxarsone by peroxymonosulfate PMS and in-situ removal of inorganic arsenic, belonging to the field of functional technical materials. Background Technology
[0002] In recent years, advanced oxidation processes (AOPs) have been widely applied in the field of pollutant remediation, degrading organic pollutants by generating reactive species. Persulfate-activated AOPs are considered promising due to their rapid reaction rate and high mineralization rate. During the activation of PMS, reactive oxygen species (ROS), such as ·OH, SO4·-, and... 1 O2, with its high oxidation potential, can not only degrade ROX but also oxidize the generated As(III) to As(V). Currently, widely studied Co-based materials exhibit good performance in activating PMS, but their adsorption of inorganic arsenic is poor, hindering complete ROX removal. Iron-based materials are commonly used to adsorb inorganic arsenic, but they are prone to leaching during PMS activation, causing secondary water pollution and rapid catalyst deactivation. Therefore, a bimetallic composite strategy has attracted our attention. Abundant metal ions and their valence state changes lead to faster PMS activation, and a suitable choice of bimetal can simultaneously satisfy both PMS activation and inorganic arsenic adsorption. Chitosan is a common biodegradable cationic biopolymer. The -NH2 in chitosan can adsorb metal ions in water, thereby reducing ion leaching, promoting PMS adsorption, and enhancing PMS activation, making it an excellent substrate for metal-based catalysts. Therefore, chitosan-encapsulated CoCe-LDH appears to be a catalyst that can efficiently activate PMS with high stability. Summary of the Invention
[0003] This invention provides a method for preparing chitosan-encapsulated CoCe layered double hydroxide CoCe-LDH (CCHG) and its application in the activation and degradation of roxarsone by PMS and in-situ removal of inorganic arsenic. This material can achieve rapid and efficient degradation of roxarsone and removal of the generated inorganic arsenic. The LDH in this material is encapsulated by chitosan, resulting in a sheet-like material. Chitosan can disperse active sites and adsorb and enrich PMS, while LDH can transfer PMS ions into the anion layer through anion exchange, thereby increasing the active sites. After coupling with the material, PMS is specifically converted to... 1 O2 accelerates the degradation rate.
[0004] A method for preparing chitosan-encapsulated CoCe layered double hydroxide CoCe-LDH, characterized by the following specific preparation steps:
[0005] Step 1): Dissolve cobalt nitrate and cerium nitrate in deionized water at a molar ratio of 2:1, add sodium hydroxide and sodium carbonate solution dropwise until pH = 10, stir under oil bath heating, after the reaction is complete, a precipitate is obtained, washed and dried to obtain CoCe layered double hydroxide CoCe-LDH;
[0006] Step 2): Weigh a certain amount of the product obtained in Step 1), add it to a chitosan solution containing acetic acid, stir evenly, then drop it into a sodium hydroxide solution, filter to obtain the product, wash until neutral, add it to a glutaraldehyde solution for crosslinking, let stand, filter, wash, dry, and grind to obtain chitosan-encapsulated CoCe layered double hydroxide CoCe-LDH (CCHG).
[0007] Furthermore, in step 2), the mass ratio of the product from step 1 to chitosan is 0.2-0.8:1, preferably 0.6-0.8:1.
[0008] Furthermore, in step 1), the concentration of sodium hydroxide is 0.3 mol / L.
[0009] Furthermore, in step 1), the concentration of sodium carbonate is 0.15 mol / L.
[0010] Furthermore, in step 1), the heating temperature is 65°C and the time is 24 hours.
[0011] Furthermore, in step 2), the volume concentration of acetic acid is 5% (v / v), and the concentration of chitosan is 33.3 mg / mL.
[0012] Furthermore, in step 2), the concentration of the sodium hydroxide solution is 0.5 mol / L.
[0013] Furthermore, in step 2), the concentration of glutaraldehyde is 0.025 mol / L.
[0014] A chitosan-encapsulated CoCe layered double hydroxide material, the material being prepared by the aforementioned preparation method.
[0015] The application of the chitosan-encapsulated CoCe layered double hydroxide material in the simultaneous removal of inorganic arsenic during the degradation of roxarsone by activated PMS (peroxymonosulfate).
[0016] Beneficial technical effects of the present invention
[0017] 1. In the CoCe-LDH structure, the anion layer exchanges with PMS ions, increasing the number of active sites. In the combination of cobalt and cerium, cerium provides coupling sites with PMS. Compared to other metals, cerium has an extremely strong ability to remove inorganic arsenic, while cobalt, compared to other transition elements, can effectively reduce cerium, greatly promoting its recycling effect. Therefore, the combination of cobalt and cerium ensures both efficient activation of PMS for roxarsone degradation and thorough removal of the generated inorganic arsenic. The introduction of chitosan disperses the active sites, enriches PMS to accelerate the reaction rate, reduces leaching, and enhances stability. The synergistic effect of the CoCe bimetallic LDH structure and chitosan coating improves the removal efficiency of inorganic arsenic. Compared to CCH material (1 gram), when the CCH loading in CCHG is 0.6 grams, the removal capacity of inorganic arsenic reaches its maximum, with a removal rate of 98.5%, higher than the 95.6% removal rate of CCH. Chitosan coating can improve the arsenic removal rate of CCH and reduce the amount of CCH used.
[0018] 2. Acetic acid can adequately spread chitosan, and as a weak acid, it will not excessively damage the LDH structure at lower concentrations (5% v / v), thus ensuring uniform loading of chitosan on the CoCe layered bimetallic hydroxide surface. Furthermore, acetic acid and the sodium acetate produced by its reaction with sodium hydroxide have excellent water solubility and are easily removed during water washing.
[0019] 3. Compared with CoCe layered bimetallic hydroxide, CoCe layered bimetallic hydroxide can activate PMS rapidly and efficiently, and has a better adsorption capacity for inorganic arsenic. Furthermore, due to the unique anionic structure of LDH, a PMS-rich microenvironment can be obtained through anion exchange, thereby promoting the degradation process.
[0020] 4. In the synthesis of layered double hydroxides, sodium carbonate is used as the anion-occupying ion in the anion layer, which further facilitates the exchange of anion layers in the LDH structure with PMS ions, increasing the number of active sites. At the same time, the introduction of glutaraldehyde enhances the structural stability of chitosan.
[0021] 5. The raw materials involved in this invention are all economical and readily available, and the experimental steps are simple and convenient. Attached Figure Description
[0022] Figure 1 SEM images of CCH(a) and CCHG(b), and TEM images of CCH(c) and CCHG(d).
[0023] Figure 2 XRD pattern of the prepared catalyst
[0024] Figure 3TEM mapping of CCHG(C,N,O,CoandCe)
[0025] Figure 4 The effect of the prepared catalyst on ROX degradation
[0026] Figure 5 The speciation of arsenic after 90 min of reaction Detailed Implementation
[0027] The invention will be described in more detail by way of examples and comparative examples, but the invention is not limited to these examples without departing from its spirit.
[0028] Example 1
[0029] Preparation of chitosan-encapsulated CoCe-LDH 0.2 (CCHG 0.2 )
[0030] Dissolve 2 mmol cobalt nitrate and 1 mmol cerium nitrate in 100 mL of deionized water, and add dropwise 14 g / L sodium hydroxide and 16 g / L anhydrous sodium carbonate solution until the pH reaches 10. Then stir in an oil bath at 65 °C for 24 hours. After the reaction is complete, centrifuge, wash, and dry. Weigh 0.2 g of the product and add it to 30 mL of a 33.3 mg / mL chitosan solution containing 5% (v / v) acetic acid. Stir, add it dropwise to a sodium hydroxide solution, filter and wash until neutral, add it to a 0.025 mol / L glutaraldehyde solution for crosslinking, let stand, wash, air dry, and grind in a ball mill to obtain chitosan-encapsulated CoCe-LDH. 0.2 (CCHG 0.2 ).
[0031] Example 2
[0032] Preparation of chitosan-encapsulated CoCe-LDH 0.4 (CCHG 0.4 )
[0033] Dissolve 2 mmol cobalt nitrate and 1 mmol cerium nitrate in 100 mL of deionized water, and add dropwise 14 g / L sodium hydroxide and 16 g / L anhydrous sodium carbonate solution until the pH reaches 10. Then stir in an oil bath at 65 °C for 24 hours. After the reaction is complete, centrifuge, wash, and dry. Weigh 0.4 g of the product and add it to 30 mL of a 33.3 mg / mL chitosan solution containing 5% (v / v) acetic acid. Stir, add it dropwise to a sodium hydroxide solution, filter and wash until neutral, add it to a 0.025 mol / L glutaraldehyde solution for crosslinking, let stand, wash, air dry, and grind in a ball mill to obtain chitosan-encapsulated CoCe-LDH. 0.4 (CCHG 0.4 ).
[0034] Example 3
[0035] Preparation of chitosan-encapsulated CoCe-LDH (CCHG)
[0036] 2 mmol of cobalt nitrate and 1 mmol of cerium nitrate were dissolved in 100 mL of deionized water. A solution of 14 g / L sodium hydroxide and 16 g / L anhydrous sodium carbonate was added dropwise until the pH reached 10. The mixture was then stirred in an oil bath at 65 °C for 24 hours. After the reaction was complete, the mixture was centrifuged, washed, and dried. 0.6 g of the product was weighed and added to 30 mL of a 33.3 mg / mL chitosan solution containing 5% (v / v) acetic acid. The mixture was stirred and then added dropwise to a sodium hydroxide solution. After filtration and washing until neutral, the mixture was added to a 0.025 mol / L glutaraldehyde solution for crosslinking. The mixture was allowed to stand, washed, air-dried, and then milled using a ball mill to obtain chitosan-encapsulated CoCe-LDH (CCHG).
[0037] Example 4
[0038] Preparation of chitosan-encapsulated CoCe-LDH 0.8 (CoHG 0.8 )
[0039] Dissolve 2 mmol cobalt nitrate and 1 mmol cerium nitrate in 100 mL of deionized water, and add dropwise 14 g / L sodium hydroxide and 16 g / L anhydrous sodium carbonate solution until the pH reaches 10. Then stir in an oil bath at 65 °C for 24 hours. After the reaction is complete, centrifuge, wash, and dry. Weigh 0.8 g of the product and add it to 30 mL of a 33.3 mg / mL chitosan solution containing 5% (v / v) acetic acid. Stir, add it dropwise to a sodium hydroxide solution, filter and wash until neutral, add it to a 0.025 mol / L glutaraldehyde solution for crosslinking, let stand, filter and wash, air dry, and grind in a ball mill to obtain chitosan-encapsulated CoCe-LDH. 0.8 (CCHG 0.8 ).
[0040] Comparative Example 1
[0041] Preparation of Co 2+ solution
[0042] 11.77 mg of cobalt nitrate was added to 50 mL of deionized water to obtain the sample Co. 2+ Solution.
[0043] Comparative Example 2
[0044] Preparation of CoCe layered bimetallic oxide CoCe-LDO(CCO)
[0045] 2 mmol of cobalt nitrate and 1 mmol of cerium nitrate were dissolved in 100 mL of deionized water, and 14 g / L sodium hydroxide and 16 g / L anhydrous sodium carbonate solutions were added dropwise until the pH reached 10. The mixture was then stirred in an oil bath at 65 °C for 24 hours. After the reaction was complete, the mixture was centrifuged, washed, dried, and then heated in a muffle furnace at 500 °C for 2 hours to obtain CoCe-LDO(CCO).
[0046] Comparative Example 3
[0047] Preparation of chitosan-encapsulated CoCe layered bimetallic oxide CoCe-LDO (CCOG)
[0048] 2 mmol of cobalt nitrate and 1 mmol of cerium nitrate were dissolved in 100 mL of deionized water. A solution of 14 g / L sodium hydroxide and 16 g / L anhydrous sodium carbonate was added dropwise until the pH reached 10. The mixture was then stirred in an oil bath at 65 °C for 24 hours. After the reaction was complete, the mixture was centrifuged, washed, dried, and then heated in a muffle furnace at 500 °C for 2 hours. 0.6 g of the product was weighed and added to 30 mL of a 33.3 mg / mL chitosan solution containing 5% (v / v) acetic acid. The mixture was stirred, and then added dropwise to a sodium hydroxide solution. After washing until neutral, glutaraldehyde solution was added for crosslinking. The mixture was allowed to stand, washed, air-dried, and then milled using a ball mill to obtain chitosan-encapsulated CoCe-LDO (CCOG).
[0049] Comparative Example 4
[0050] Preparation of chitosan-encapsulated Co-LDH (CoHG)
[0051] Dissolve 3 mmol of cobalt nitrate in 100 mL of deionized water, and add dropwise 14 g / L sodium hydroxide and 16 g / L anhydrous sodium carbonate solution until the pH reaches 10. Then stir in an oil bath at 65 °C for 24 hours. After the reaction is complete, centrifuge, wash, and dry. Weigh 0.6 g of the product and add it to 30 mL of a 33.3 mg / mL chitosan solution containing 5% (v / v) acetic acid. Stir, add dropwise to sodium hydroxide solution, wash until neutral, add glutaraldehyde solution for crosslinking, let stand, wash, air dry, and grind in a ball mill to obtain chitosan-encapsulated Co-LDH (CoHG).
[0052] Comparative Example 4
[0053] Preparation of chitosan-encapsulated Ce-LDH (CeHG)
[0054] Dissolve 3 mmol of cerium nitrate in 100 mL of deionized water, and add dropwise 14 g / L sodium hydroxide and 16 g / L anhydrous sodium carbonate solution until the pH reaches 10. Then stir in an oil bath at 65 °C for 24 hours. After the reaction is complete, centrifuge, wash, and dry. Weigh 0.6 g of the product and add it to 30 mL of a 33.3 mg / mL chitosan solution containing 5% (v / v) acetic acid. Stir, add dropwise to sodium hydroxide solution, wash until neutral, add glutaraldehyde solution for crosslinking, let stand, wash, air dry, and grind in a ball mill to obtain chitosan-encapsulated Ce-LDH (CeHG).
[0055] Comparative Example 5
[0056] Preparation of chitosan-encapsulated CoCe-LDH(CCH)
[0057] 2 mmol of cobalt nitrate and 1 mmol of cerium nitrate were dissolved in 100 mL of deionized water. 14 g / L sodium hydroxide and 16 g / L anhydrous sodium carbonate solutions were added dropwise until the pH reached 10. The mixture was then stirred in an oil bath at 65 °C for 24 hours. After the reaction was complete, the mixture was centrifuged, washed, and dried to obtain CoCe-LDH (CCH).
[0058] Experiments and Data
[0059] The method for evaluating the degradation performance of roxarsone and the removal performance of inorganic arsenic provided by this invention is as follows:
[0060] In a typical experiment, 20 mg of catalyst was mixed with 50 mL of a 15 mg / L roxarsone (ROX) solution in a beaker, and the suspension was stirred with a magnetic stirrer. After adsorption equilibrium was reached, PMS was added. To obtain degradation kinetic data, 1 mL of solution was taken out at specified times, of which 0.5 mL was used to determine the ROX concentration by high performance liquid chromatography (HPLC), and the other 0.5 mL was used for inorganic arsenic detection.
[0061] Figure 1 SEM and TEM images of CoCe-LDH (CCH) from Comparative Example 5 and the chitosan-encapsulated CoCe-LDH (CCHG) from Example 3 are shown. CCH is layered with protrusions on its surface, while CCHG has a smooth surface. The final composite material CCHG is a chitosan-encapsulated structure.
[0062] Figure 2The XRD patterns are for Comparative Examples 1, 2, 3, 4, and 5, and Examples 1, 2, 3, and 4. The peak intensity of CCH decreased after loading onto GCS, likely due to a reduction in the loading amount. A Co(OH)₂ peak was detected in the CCHG sample. This is because acetic acid was present in the chitosan solution during preparation, causing some cobalt to leach out. Subsequently, Co(OH)₂ was formed during the preparation of chitosan beads under highly alkaline conditions, resulting in sharp peaks at 18.86°, 37.82°, and 51.3°. Figure 2 b indicates that CCO is composed of Co3O4 and CeO2, which retain their original peak shape after being loaded onto GCS.
[0063] Figure 3 The mapping spectrum of CCHG from Example 3 is shown, revealing uniform dispersion of C, N, O, Co, and Ce without significant agglomeration. In summary, we successfully prepared CoCe-LDH and encapsulated it with GCS. During the synthesis, some cobalt formed Co(OH)2, but this did not disrupt the overall structure of CCH. Therefore, we successfully synthesized CCHG.
[0064] Figure 4 The images show the samples prepared in Comparative Examples 1-5 and Examples 1-4, along with their degradation patterns. It can be seen that both CCH and the chitosan-encapsulated catalyst exhibit excellent degradation capabilities, with CCHG achieving a k-value of 2.55 min. -1 .
[0065] Figure 5 The figures show the arsenic removal of samples prepared in Examples 1-5 and 1-4. After a 90-minute degradation and adsorption process, the removal of inorganic arsenic was measured. Comparison of CCHGx and CoHG clearly shows that Ce is the main adsorption site for arsenic, while GCS only adsorbs a small amount of arsenic. After CCH is loaded onto GCS, the catalyst's adsorption and removal capacity for inorganic arsenic significantly increases with increasing CCH loading. When the loading is 0.6 g, the removal capacity for inorganic arsenic reaches its maximum, with a removal rate of 98.5%, even higher than the 95.6% removal rate of CCH. This indicates that cross-linked chitosan also acts as a dispersant for CCH, providing more active sites for the adsorption of inorganic arsenic. The combination of cross-linked chitosan and PMS can effectively degrade ROX and adsorb inorganic arsenic in situ.
[0066] Although the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be considered as a limitation of the present invention.
Claims
1. A method for preparing chitosan-encapsulated CoCe layered double hydroxide CoCe-LDH, characterized in that, The specific preparation steps are as follows: Step 1): Dissolve cobalt nitrate and cerium nitrate in deionized water at a molar ratio of 2:1, and add sodium hydroxide and sodium carbonate solutions dropwise until pH=10. Stir under oil bath heating. After the reaction is complete, a precipitate is obtained, washed and dried to obtain CoCe layered double hydroxide CoCe-LDH; Step 2): Weigh a certain amount of the product obtained in Step 1), add it to a chitosan solution containing acetic acid, stir evenly, then drop it into a sodium hydroxide solution, filter to obtain the product, wash until neutral, add it to a glutaraldehyde solution for crosslinking, let stand, filter, wash, dry, and grind to obtain chitosan-encapsulated CoCe layered double hydroxide CoCe-LDH.
2. The preparation method according to claim 1, characterized in that: In step 2), the mass ratio of the product from step 1) to chitosan is 0.2-0.8:
1.
3. The preparation method according to claim 1, characterized in that: In step 2), the mass ratio of the product from step 1) to chitosan is 0.6-0.8:
1.
4. The preparation method according to claim 1, characterized in that: In step 1), the concentration of sodium hydroxide in the solution is 0.3 mol / L and the concentration of sodium carbonate is 0.15 mol / L.
5. The preparation method according to claim 1, characterized in that: In step 1), the heating temperature is 65℃ and the time is 24h.
6. The preparation method according to claim 1, characterized in that: In step 2), the volume concentration of acetic acid in the solution is 5%; the concentration of chitosan in the solution is 33.3 mg / mL.
7. The preparation method according to claim 1, characterized in that: In step 2), the concentration of the sodium hydroxide solution is 0.5 mol / L.
8. The preparation method according to claim 1, characterized in that: In step 2), the concentration of glutaraldehyde is 0.025 mol / L.
9. A chitosan-encapsulated CoCe layered double hydroxide material, said material being prepared by the preparation method according to any one of claims 1-8.
10. The application of the chitosan-encapsulated CoCe layered double hydroxide material as described in claim 9 in the simultaneous removal of inorganic arsenic during the degradation of roxarsone by activated peroxymonosulfate PMS.