Preparation and application of single-layered layered double hydroxide adsorbent with modified oxygen vacancy density

Abstract

The application discloses a preparation and application of an oxygen vacancy modified monolayer layered double hydroxide adsorbent, and belongs to the field of adsorption material preparation processes.The oxygen vacancy modified monolayer layered double hydroxide adsorbent provided by the application uses a polar solvent as an inhibitor for the growth of layered double hydroxide along a Z axis to obtain monolayer layered double hydroxide; and by controlling the pH value of a solution in a synthesis process, the purpose of constructing oxygen vacancies on the surface of the monolayer layered double hydroxide is achieved, so that a high-performance adsorbent material is synthesized.The application introduces oxygen vacancies on the surface of the monolayer layered double hydroxide, thereby regulating the surface electric field structure, improving the adsorption performance, the bonding capacity and the anti-interference capacity, and the adsorbent still maintains good adsorption capacity in a relatively wide pH value range (pH approximately 5-10), and can be used for adsorbing phosphate in environmental water samples.

Description

Technical Field

[0001] This invention belongs to the field of adsorption material preparation technology, specifically relating to the preparation and application of a single-layer layered double hydroxide adsorbent with modified oxygen vacancy density. Background Technology

[0002] Eutrophication of natural water bodies is a serious ecological problem, threatening the survival of various plants, animals, and even humans. Reducing nitrogen (N) and phosphorus (P) concentrations is the simplest, most effective, and most direct method for restoring the ecology of natural water systems. Over the past few decades, researchers have explored various methods to mitigate the harm of eutrophication, among which adsorption has gradually become the mainstream method due to its simplicity, efficiency, and cost-effectiveness. However, the application of many adsorbents in phosphorus removal is limited due to the lack of active adsorption sites. Therefore, developing novel and highly efficient adsorption materials is crucial for mitigating the harm of eutrophication.

[0003] Layered double hydroxides (LDHs) are a class of layered compounds consisting of two metal cations forming the main layers, with exchangeable anions between the layers to balance their charges. Their general chemical formula can be represented as follows: LDHs can not only regulate the divalent (such as Mg) in the layers 2 +、Cu 2 +、Ni 2+ and Zn 2+ (etc.) and trivalent metal ions (such as Al) 3 +, Fe 3 + and Ga 3+ The molar ratio (1:1-4:1) of the components (e.g., CO32-) allows for precise control of the composition, and the interlayer anions (e.g., CO32-) are controlled. 2 The dynamic exchange properties of NO3- can directionally expand the interlayer spacing to 1.5-3.0 nm, combined with 50-300 nm... 2 The high specific surface area of ​​LDHs (dihydrogen hydroxyl groups) has made them widely studied as anion adsorption materials. However, existing natural or synthetic LDHs materials still have significant limitations: natural minerals have an adsorption capacity of less than 50 mg / g due to their dense stacking of layers and scarce surface active sites; while conventionally synthesized LDHs can increase the adsorption capacity to 200 mg / g through intercalation modification, their multilayer stacking structure still causes more than 60% of the internal active sites to be masked, and the binding energy between the surface hydroxyl sites and the target anion is weak (≤2.5 eV), which restricts further improvement in adsorption efficiency.

[0004] Single-layered LDH nanosheets (SLDH-NS) possess large specific surface area and good hydrophilicity; however, a uniform surface electric field distribution is detrimental to the activation of surface active sites. Oxygen vacancies (Ov) successfully disrupt the uniformity of the surface electric field of SLDH-NS, facilitating the activation of active sites. This strategy is frequently used in catalysis and energy storage. Ov modulation of the surface electric field structure of SLDH-NS (Ov-SLDH-NS) provides the possibility for adsorbing anions from solution. In this regard, the adsorption performance of SLDH-NS for anionic pollutants in solution has been reported to be greater than that of original LDH adsorbents. To improve adsorption capacity, we believe it is interesting to explore the role of surface Ov and density on the adsorption performance of SLDH-NS. Currently, there are no reports on improving the adsorption performance of SLDH-NS for anionic pollutants by constructing surface Ov and density gradients. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing and applying an SLDH-NS adsorbent with modified surface Ov density. The Ov-density modified SLDH-NS adsorbent provided by this invention introduces Ov onto the surface of SLDH-NS, disrupting the uniformity of the original surface electric field, thereby increasing its affinity for phosphate anion pollutants, improving adsorption performance, exhibiting strong bonding and stable properties, and can be used in a wide pH range (pH≈5~10). It demonstrates excellent adsorption and enrichment capacity for phosphate anions in water.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides an Ov density-modified SLDH-NS adsorbent. By using a polar solvent as a growth inhibitor to limit the growth of LDHs along the Z-axis, SLDH-NS was successfully constructed. By controlling the reaction temperature and adjusting the pH value of the solution during the synthesis process with an alkaline solution, the Ov density on the surface of SLDH-NS can be regulated, thus obtaining a single SLDH-NS adsorbent with Ov density modification.

[0008] Further, the SLDH-NS adsorbent is prepared by the following method: appropriate amounts of divalent and trivalent metal salt hydrate powders are weighed at a molar ratio of 4 to 1:1 and dissolved in a polar solvent solution with a concentration of 10 to 100 vol.%; the mixed solution of metal salt and polar solvent is vigorously stirred in a water bath at room temperature to 80°C; the reaction is carried out for at least 30 minutes, followed by centrifugation, washing, and vacuum drying at 60°C to obtain the SLDH-NS adsorbent.

[0009] Furthermore, the preparation method of the Ov density SLDH-NS adsorbent is as follows: The pH value of a mixed solution of divalent and trivalent metal salts and a polar solvent is adjusted to the range of 8 to 13 using 0.4M NaOH solution, and then vigorously stirred in a water bath at room temperature to 80°C to obtain the Ov density SLDH-NS adsorbent, which is named Ov-SLDH-NS-x (x represents the pH value of the solution). The Ov density SLDH-NS adsorbent prepared by the above method exhibits advantages such as large adsorption capacity, strong anti-interference ability, and good reproducibility when used for the adsorption of phosphate pollutants in water samples.

[0010] On the other hand, the present invention provides a method for preparing an Ov density-modified SLDH-NS adsorbent by dissolving a divalent / trivalent metal salt in a polar solvent solution of a certain concentration and controlling the temperature during the reaction process to prepare SLDH-NS; by controlling the pH value of the reaction solution in the range of 8 to 13, the Ov density-modified SLDH-NS adsorbent is successfully prepared.

[0011] The aforementioned polar solvents include formamide, N,N-dimethylformamide, N-methylformamide, N-methylacetamide (polar amides), and dimethyl sulfoxide and N-methylpyrrolidone (polar non-amide solvents); hydrate powders of divalent and trivalent metal salts include common divalent metals such as Ca. 2+ Mn 2+ Mg 2+ Cu 2+ Co 2+ Ni 2+ and Zn 2+ and trivalent metal Al 3+ Fe 3+ Cr 3+ and Ga 3+ Nitrates, sulfates, and halide salts.

[0012] The beneficial technical effects of this invention are as follows:

[0013] (1) Compared with existing LDHs modification technologies, this invention proposes to prepare an adsorbent for removing phosphate anions in solution by modifying SLDH-NS with Ov density. SLDH-NS is prepared by using a polar solvent as an inhibitor for the growth of LDHs layer along the Z-axis. Secondly, the pH value of the solution during the reaction is controlled by NaOH solution and the reaction temperature is controlled to obtain SLDH-NS with Ov density, which effectively improves its surface electric field structure.

[0014] (2) The Ov density-modified SLDH-NS adsorbent synthesized in this invention has the advantages of large adsorption capacity, strong anti-interference ability and good reproducibility for negatively charged phosphate anion pollutants in solution. Attached Figure Description

[0015] Figure 1 This is a TEM image of SLDH-NS.

[0016] Figure 2 This is a curve showing the specific surface area of ​​Ov-SLDH-NS-x prepared under different pH conditions.

[0017] Figure 3 This is a graph showing the adsorption performance of Ov-SLDH-NS-x prepared under different pH conditions.

[0018] Figure 4 This is a graph showing the adsorption performance of Ov-SLDH-NS-11 adsorbent as a function of adsorbent concentration (solid line represents adsorption performance, dashed line represents removal rate). Detailed Implementation

[0019] To further disclose without limiting the invention, the following examples further illustrate the content of the invention.

[0020] This invention provides a method for preparing Ov-modified SLDH-NS adsorbent. Appropriate amounts of copper nitrate and ferric nitrate hydrate are weighed at a molar ratio of 4 to 1:1 and dissolved in a formamide solution with a concentration of 10 to 100 vol.%. The mixed solution of metal salt and formamide is vigorously stirred in a water bath at room temperature to 80°C, and the pH value of the solution is adjusted to a range of 8 to 13 using 0.4 M NaOH solution. The reaction is carried out for at least 30 minutes, followed by centrifugation, washing, and vacuum drying at 60°C to obtain the Ov-density-modified SLDH-NS adsorbent.

[0021] Example 1

[0022] Effect of formamide concentration on the preparation of SLDH-NS

[0023] (1) Synthesis of SLDH-NS adsorbent: Appropriate amounts of copper nitrate and ferric nitrate hydrate powders were weighed at a molar ratio of 2:1 and dissolved in a 50 vol.% formamide solution; the mixture of nitrate and formamide was vigorously stirred in a water bath at 60°C; after the addition was complete, the reaction was allowed to proceed for 120 minutes, followed by centrifugation, washing, and vacuum drying at 60°C to obtain the SLDH-NS adsorbent. Figure 1 As shown in the TEM image, SLDH-NS was successfully prepared.

[0024] (2) SLDH-NS adsorbent with Ov density: Weigh appropriate amounts of copper nitrate and ferric nitrate hydrate powders at a molar ratio of 2:1 and dissolve them in a 50 vol.% formamide solution; vigorously stir the mixed solution of nitrate and formamide in a water bath at 60°C, and adjust the pH of the reaction solution with 0.4 M NaOH; after the addition is complete, react for 120 minutes, and obtain the SLDH-NS adsorbent by centrifugation, washing and vacuum drying at 60°C.

[0025] Example 2

[0026] Effect of different pH values ​​on Ov density on SLDH-NS surface

[0027] (1) Synthesis of SLDH-NS adsorbent: Weigh appropriate amounts of copper nitrate and ferric nitrate hydrate powders at a molar ratio of 2:1 and dissolve them in a 50 vol.% formamide solution; stir the mixed solution of nitrate and formamide vigorously in a water bath at 60°C; after the addition is complete, react for 120 minutes, centrifuge, wash and vacuum dry at 60°C to obtain SLDH-NS adsorbent.

[0028] (2) Ov-SLDH-NS-x adsorbent with Ov density: Appropriate amounts of copper nitrate and ferric nitrate hydrate powder were weighed at a molar ratio of 2:1 and added to a 50 vol.% formamide solution. The mixture of nitrate and formamide was vigorously stirred in a 60°C water bath, and the pH of the reaction solution was adjusted to 10, 11, and 12 using 0.4 M NaOH. After the addition was complete, the reaction was allowed to proceed for 120 minutes. The solution was then centrifuged, washed, and vacuum dried at 60°C to obtain the Ov-density SLDH-NS adsorbent, which was named Ov-SLDH-NS-x (x = 10, 11, 12). Figure 2 As shown, the surface area distribution curves of Ov-SLDH-NS-x prepared under different pH conditions are presented.

[0029] Example 3

[0030] Adsorption performance of Ov-SLDH-NS-x prepared under different pH conditions

[0031] Static experiments were conducted on solutions of different adsorbents. The adsorption performance was calculated by measuring the absorption efficiency using ultraviolet spectrophotometry. Figure 3 The adsorption performance of Ov-SLDH-NS-x adsorbent for phosphate was studied under different pH conditions. The initial phosphate concentration was 200 ppm, the adsorbent dosage was 20 mg, the shaking time was 120 min, the test volume was 50 mL, and the temperature was 20 °C.

[0032] Example 4

[0033] Effect of different amounts of adsorbent on the adsorption performance of Ov-SLDH-NS-x adsorbent

[0034] Static experiments were conducted on solutions of different adsorbents. The adsorption performance was calculated by measuring the absorption efficiency using ultraviolet spectrophotometry. Figure 4 The adsorption performance of Ov-SLDH-NS-x adsorbent varies with the amount of adsorbent. Initial phosphate concentration: 100 ppm; adsorbent dosage: 10, 20, 30, 40, 50 mg; shaking time: 120 minutes; test volume: 50 mL; temperature: 20℃.

[0035] Those skilled in the art should understand that the following description is illustrative and not restrictive, and should not be construed as limiting the scope of protection of this invention.

Claims

1. A single-layer layered double hydroxide adsorbent with oxygen vacancy density modification, characterized in that: By using a polar solvent as a growth inhibitor to restrict the growth of layered double hydroxides along the Z-axis, a monolayer layered double hydroxide was successfully constructed. By controlling the reaction temperature and adjusting the pH value of the solution during the synthesis process with an alkaline solution, the oxygen vacancy density on the surface of the monolayer layered double hydroxide was regulated, thus obtaining a monolayer layered double hydroxide adsorbent with oxygen vacancy density modification.

2. The oxygen vacancy density-modified monolayer layered double hydroxide adsorbent according to claim 1, characterized in that: The monolayer layered double hydroxide adsorbent is prepared by the following method: Appropriate amounts of divalent and trivalent metal salt hydrate powders are weighed at a molar ratio of 4 to 1:1 and dissolved in a polar solvent solution with a concentration of 10 to 100 vol.%; the mixed solution of metal salt and polar solvent is vigorously stirred in a water bath at room temperature to 80°C; the reaction is carried out for at least 30 minutes, followed by centrifugation, washing, and vacuum drying at 60°C to obtain the monolayer layered double hydroxide adsorbent.

3. The oxygen vacancy density-modified monolayer layered double hydroxide adsorbent according to claim 2, characterized in that: The oxygen vacancy density monolayer layered double hydroxide adsorbent is prepared by the following method: the pH value of a mixed solution of divalent and trivalent metal salts and polar solvent is adjusted to the range of 8 to 13 using 0.4M NaOH solution, and the solution is vigorously stirred in a water bath at room temperature to 80°C to obtain the oxygen vacancy density monolayer layered double hydroxide adsorbent.

4. The oxygen vacancy density-modified monolayer layered double hydroxide adsorbent according to claim 2, characterized in that: The polar solvents include formamide, N,N-dimethylformamide, N-methylformamide, N-methylacetamide, and dimethyl sulfoxide and N-methylpyrrolidone, which are polar non-amide solvents.

5. The oxygen vacancy density-modified monolayer layered double hydroxide adsorbent according to claim 2, characterized in that: The hydrate powders of divalent and trivalent metal salts include common divalent metals such as Ca. 2+ Mn 2+ Mg 2+ Cu 2+ Co 2+ Ni 2+ and Zn 2+ and trivalent metal Al 3+ Fe 3+ Cr 3+ and Ga 3+ Nitrates, sulfates, and halide salts.

6. A method for preparing a monolayer layered double hydroxide adsorbent with oxygen vacancy density modification as described in claims 1-5, characterized in that: The preparation method involves dissolving divalent / trivalent metal salts in a polar solvent solution of a certain concentration and controlling the temperature during the reaction process to prepare a monolayer layered double hydroxide. By controlling the pH value of the reaction solution in the range of 8 to 13, a monolayer layered double hydroxide adsorbent with modified oxygen vacancy density was successfully prepared.

7. The application of a monolayer layered double hydroxide adsorbent with oxygen vacancy density as described in claims 1-5, characterized in that: Used for the adsorption of phosphate pollutants in water samples.

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