A modified CaFe-LDH composite material and its application in Cd removal 2+ With Cr 6+ Applications in

Abstract

This invention discloses a modified CaFe-LDH composite material and its application in Cd removal. 2+ With Cr 6+ The application of this material involves the fields of environmental functional materials and pollution remediation technology. The preparation method of the modified CaFe-LDH composite material includes the following steps: mixing calcium nitrate or its hydrate, ferric nitrate or its hydrate, and water; stirring and reacting the mixture; allowing it to stand for aging; and then drying it to obtain CaFe-NO3. ‑ -LDH; utilizing Mo3S 13 2‑ The solution for CaFe-NO3 ‑ Ion exchange with -LDH yields CaFe-Mo3S 13 2‑ -LDH refers to the modified CaFe-LDH composite material. The modified CaFe-LDH composite material of this invention possesses adsorption, reduction, and passivation functions simultaneously, enabling multi-stage pollution control in water purification and in-situ soil remediation.

Description

Technical Field

[0001] This invention relates to the field of environmental functional materials and pollution remediation technology, and in particular to a modified CaFe-LDH composite material and its application in the removal of heavy metal Cd. 2+ With Cr 6+ Applications in [the field]. Background Technology

[0002] With the rapid development of the metallurgical, electroplating, leather, and battery manufacturing industries, the discharge of wastewater and solid waste containing Cd2+ and Cr6+ continues to increase. Cd2+ can accumulate in crops and the human body, causing diseases such as Itai-itai disease; Cr6+ has strong oxidizing and carcinogenic properties. Traditional treatment methods for Cd2+ and Cr6+ include chemical precipitation, ion exchange, membrane separation, and electrochemical reduction, but these methods generally suffer from high energy consumption, excessive sludge production, and significant secondary pollution, and are insufficient to address Cd2+ / Cr6+ complex pollution systems.

[0003] In recent years, layered hydrogen hydroxides (LDHs) have been widely studied due to their tunable layers and strong anion exchange capacity. Typical MgAl-LDH and ZnFe-LDH can achieve removal rates of over 90% for anionic pollutants (such as PO43- and CrO42-), but their adsorption capacity for cationic Cd2+ is usually less than 80 mg / g. Fe3+-containing LDHs have electron transfer potential and can reduce Cr6+ to Cr3+, but the electron transfer efficiency is limited by pH and the type of anions in the interlayer, resulting in poor reduction performance. In addition, most existing LDHs are prepared by a single-step co-precipitation method, which suffers from a narrow pH window (9.5±0.5), short aging time (<12 h), poor pore structure, and poor stability, leading to poor adsorption capacity, reduction capacity, and cycle stability. Although ion exchange methods can improve the interlayer environment, they often use CO32- or NO3- anions, which have limited controllability and cannot synergize the adsorption-reduction process, thus failing to achieve effective removal of Cd2+ / Cr6+ complex pollution systems.

[0004] In summary, there is an urgent need to provide a novel LDH material with stable structure that can simultaneously achieve Cd2+ adsorption and Cr6+ reduction, in order to overcome the shortcomings such as insufficient adsorption capacity, selectivity and cycle stability. Summary of the Invention

[0005] The purpose of this invention is to provide a modified CaFe-LDH (layered double hydroxide) composite material and its application in Cd removal. 2+ With Cr 6+ This invention addresses the problems existing in the prior art by applying the modified CaFe-LDH composite material, which simultaneously possesses adsorption, reduction, and passivation functions. It can achieve multiple pollution control (simultaneously controlling Cd) in water purification and in-situ soil remediation. 2+and Cr 6+ ).

[0006] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of the present invention: a method for preparing a modified CaFe-LDH composite material, comprising the following steps: Calcium nitrate or its hydrate, ferric nitrate or its hydrate, and water are mixed, stirred to react, allowed to stand for aging, and then dried to obtain CaFe-NO3. - -LDH; utilizing Mo3S 13 2- The solution for CaFe-NO3 - -LDH ion exchange yields CaFe-Mo3S 13 2- -LDH (abbreviated as CaFe-TMB) 2- -LDH), which is the modified CaFe-LDH composite material.

[0007] The modified CaFe-LDH composite material of this invention possesses both high adsorption capacity and high reduction efficiency, and can simultaneously adsorb Cd. 2+ And reduce Cr 6+ For Cr 3+ Precipitation. The modified CaFe-LDH composite material of the present invention has the following advantages: (1) Bimetallic synergistic effect: Ca 2+ Provides structural stability and cation exchange sites, Fe 3+ It participates in the construction of laminations and provides surface hydroxyl active sites, thereby benefiting Cd. 2+ Adsorption fixation and layered structure stability.

[0008] (2) Interlayer electron mediation enhancement: Mo3S 13 2- (abbreviated as TMB) 2- Anions improve electron mobility, achieving adsorption-reduction synergy.

[0009] (3) Adjustable structure and high stability: It maintains a layered structure in the pH range of 5-9 and has excellent cycling performance.

[0010] (4) Environmentally friendly and economical: the raw materials are cheap, the preparation process is mild, and there is no secondary pollution.

[0011] Furthermore, the calcium nitrate or its hydrate contains Ca 2+ With the Fe contained in the ferric nitrate or its hydrate 3+ The molar ratio is 1:1.

[0012] Furthermore, the calcium nitrate or its hydrate comprises Ca(NO3)2·4H2O.

[0013] Furthermore, the ferric nitrate or its hydrate comprises Fe(NO3)3·9H2O.

[0014] Furthermore, the ratio of the amount of calcium nitrate or its hydrate to the amount of water is 0.01 mol: 80-120 mL.

[0015] Furthermore, the temperature for both the stirring reaction and the static aging is 20-35 ℃, and the time is 12-36 h.

[0016] Furthermore, the utilization of Mo3S 13 2- The solution for CaFe-NO3 - -LDH ion exchange includes: [removing / converting] the CaFe-NO3... - -LDH and Mo3S 13 2- Mix the solutions and stir for 12-36 hours.

[0017] Furthermore, the Mo3S 13 2- The solution preparation steps include: (NH4)6Mo7O 24 A mixture of 4H₂O, HONH₂·HCl, and an aqueous solution of (NH₄)₂S₃ reacts upon heating to yield (NH₄)₂Mo₃S. 13 ·H2O; The (NH4)2Mo3S 13 H2O dissolves in an organic solvent to obtain the Mo3S. 13 2- Solution (abbreviated as TMB) 2- (solution).

[0018] Furthermore, the concentration of the (NH4)2S3 aqueous solution is 10-30 wt%.

[0019] Furthermore, the (NH4)6Mo7O 24 The ratio of the amounts of 4H2O, HONH2·HCl, and (NH4)2S3 aqueous solution is 1-2 g: 1-3 g: 60 mL.

[0020] Furthermore, the heating reaction is carried out at a temperature of 220 °C for a duration of 12-36 h.

[0021] Furthermore, the organic solvent includes N,N-dimethylformamide (DMF).

[0022] Furthermore, the (NH4)2Mo3S 13The ratio of H2O to the organic solvent is 1 mmol: 150-200 mL.

[0023] Furthermore, the CaFe-NO3 - -LDH and the Mo3S 13 2- The volume ratio of the solution used is 0.5-0.7 g: 20 mL.

[0024] Furthermore, the stirring temperature during the 12-36 h stirring period is 20-35 ℃.

[0025] Furthermore, after the stirring is completed, the process also includes steps of filtering, washing, and drying.

[0026] Furthermore, the drying temperature is 60-80 ℃.

[0027] The second technical solution of the present invention: a modified CaFe-LDH composite material prepared according to the above preparation method.

[0028] Furthermore, the modified CaFe-LDH composite material has an interlayer spacing of 0.80-0.90 nm and a specific surface area ≥40 m². 2 / g.

[0029] The third technical solution of the present invention: A modified CaFe-LDH composite material for removing Cd from water. 2+ and / or Cr 6+ Applications in [the field].

[0030] Furthermore, the dosage of the modified CaFe-LDH composite material in water is 0.5-2.0 g / L.

[0031] Fourth technical solution of the present invention: A modified CaFe-LDH composite material as described above in Cd 2+ (i.e., Cd(II)) and / or Cr 6+ Application in the remediation of Cr(VI) contaminated soil.

[0032] Furthermore, the modified CaFe-LDH composite material in Cd 2+ and / or Cr 6+ The application rate in contaminated soil is 0.5-2.0 wt%.

[0033] The present invention discloses the following technical effects: The modified CaFe-LDH composite material of this invention possesses both high adsorption capacity and high reduction efficiency, and can simultaneously adsorb Cd. 2+ and Cr 6+ And reduce Cr 6+ For Cr 3+Precipitation. Experiments show that in Cd... 2+ With Cr 6+ In the 100 mg / L composite system, CaFe-TMB 2- - When LDH is added at 1 g / L, Cd within 4 hours 2+ Removal rate was 98.3%, Cr 6+ The removal rate was 95.4%. (CaFe-TMB) 2- -LDH for Cd 2+ and Cr 6+ The Langmuir model adsorption capacities were 289.6 mg / g and 245.78 mg / g, respectively. And CaFe-TMB 2- -LDH was regenerated in 5 cycles for Cd 2+ and Cr 6+ The removal rate remains above 80%.

[0034] The preparation method of this invention has mild reaction conditions and inexpensive and readily available raw materials; the reaction system can be directly scaled up to 10L with low energy consumption; the resulting modified CaFe-LDH composite material has high stability and can be recycled ≥5 times, making it suitable for engineering applications in in-situ remediation of industrial wastewater and heavy metal contaminated soil. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 CaFe-TMB prepared in Example 1 2- SEM and TEM images of -LDH (i.e., modified CaFe-LDH composite material), where (a) and (b) are SEM images and (c) is a TEM image.

[0037] Figure 2 CaFe-NO3 prepared for Comparative Example 1 - SEM and TEM images of -LDH (i.e. CaFe-LDH composite material), where (a) and (b) are SEM images and (c) is a TEM image.

[0038] Figure 3 CaFe-NO3 prepared for Comparative Example 1 - -LDH, CaFe-TMB prepared in Example 1 2- -LDH and CaFe-TMB prepared in Example 1 2--LDH adsorption of Cd 2+ The XRD pattern after that.

[0039] Figure 4 CaFe-NO3 prepared for Comparative Example 1 - -LDH, CaFe-TMB prepared in Example 1 2- -LDH and CaFe-TMB prepared in Example 1 2- -LDH adsorption of Cd 2+ The FTIR plot after that.

[0040] Figure 5 CaFe-TMB prepared in Example 1 2- -LDH and CaFe-TMB prepared in Example 1 2- -LDH adsorption of Cr 6+ The XRD pattern after that.

[0041] Figure 6 CaFe-TMB prepared in Example 1 2- -LDH and CaFe-TMB prepared in Example 1 2- -LDH adsorption of Cr 6+ The FTIR plot after that.

[0042] Figure 7 CaFe-TMB prepared in Example 1 2- -LDH for Cd 2+ and Cr 6+ The adsorption isotherm fitting results are shown, where (a) represents the adsorption isotherm fitting results for Cd. 2+ The adsorption isotherm fitting results are shown in (b), which shows the adsorption isotherm fitting results for Cr. 6+ The fitting of the adsorption isotherm.

[0043] Figure 8 CaFe-TMB prepared in Example 1 2- XPS spectra of -LDH before and after the adsorption reaction, where (a) is the full XPS spectrum, (b) is the Mo 3d spectrum, (c) is the S 2p spectrum, and (d) is the Cr 2p spectrum. Detailed Implementation

[0044] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0045] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0046] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0047] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0048] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0049] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0050] Unless otherwise specified, the room temperature mentioned in the following embodiments and comparative examples of the present invention refers to 20-30 ℃.

[0051] All raw materials used in the following embodiments and comparative examples of this invention are commercially available products.

[0052] Example 1 A modified CaFe-LDH composite material is prepared by the following steps: (1) Dissolve 0.01 mol Ca(NO3)2·4H2O and 0.01 mol Fe(NO3)3·9H2O in 100 mL of deionized water. First, stir at 25 °C (400 rpm) for 12 h, then let stand at 25 °C for 12 h to age, and then dry at 60 °C to obtain CaFe-NO3. - -LDH.

[0053] (2) Take 2 g of (NH4)6Mo7O 24 ·4H₂O, 1.5 g of HONH₂·HCl and 60 mL of (NH₄)₂S₃ aqueous solution (concentration 25 wt%) were added to a reaction vessel, and the mixture was heated at 220 °C for 24 h. After the reaction was completed, the mixture was allowed to cool naturally, and the solid product was filtered and washed repeatedly with water and acetone to obtain red needle-like crystals of (NH₄)₂Mo₃S. 13 ·H₂O. Take 1 mmol of (NH₄)₂Mo₃S 13 H₂O was dissolved in 180 mL of DMF to remove insoluble impurities, yielding Mo₃S. 13 2- Solution (abbreviated as TMB) 2- (solution).

[0054] (3) Take 0.57 g CaFe-NO3 - -LDH was added to 20 mL of the above TMB. 2- Ion exchange was completed in the solution by stirring at a constant temperature (25 °C) and 400 rpm for 24 h. The precipitate was then separated by filtration, washed with DMF and deionized water, and dried at 60 °C to obtain CaFe-Mo3S. 13 2- -LDH (abbreviated as CaFe-TMB) 2- -LDH), which is a modified CaFe-LDH composite material.

[0055] Comparative Example 1 A CaFe-LDH composite material is prepared by the following steps: 0.01 mol Ca(NO3)2·4H2O and 0.01 mol Fe(NO3)3·9H2O were dissolved in 100 mL of deionized water. The mixture was first stirred at 25 °C (400 rpm) for 12 h, then allowed to stand at 25 °C for 12 h to age, and finally dried at 60 °C to obtain CaFe-NO3. - -LDH, which is a CaFe-LDH composite material.

[0056] Comparative Example 2 A MgFe-LDH composite material is prepared by the following steps: 0.01 mol Mg(NO3)2·6H2O and 0.01 mol Fe(NO3)3·9H2O were dissolved in 100 mL of deionized water. The mixture was first stirred at 25 °C (400 rpm) for 12 h, then allowed to stand at 25 °C for 12 h to age, and finally dried at 60 °C to obtain MgFe-NO3. - -LDH, which is the MgFe-LDH composite material.

[0057] Comparative Example 3 (1) Dissolve 0.01 mol Ca(NO3)2·4H2O and 0.01 mol Fe(NO3)3·9H2O in 100 mL of deionized water. First, continue stirring at 25 °C (400 rpm) for 12 h, then let stand at 25 °C for 12 h to age, and then dry at 60 °C to obtain CaFe-NO3. - -LDH.

[0058] (2) Take 1 mmol of (NH4)2Mo3S 13 The sulfur content of H2O is equivalent to that of (NH4)2S3 (i.e., the molar amount of S in (NH4)2S3 is equal to that in 1 mmol (NH4)2Mo3S). 13 (The H₂O contains an equal molar amount of sulfur) was dissolved in 180 mL of DMF, and insoluble impurities were removed to obtain S₃. 2- Solution.

[0059] (3) Take 0.57 g CaFe-NO3 - -LDH was added to 20 mL of the above S3. 2- Ion exchange was completed in the solution by stirring at a constant temperature (25 °C) (400 rpm) for 24 h. The precipitate was then separated by filtration, washed with DMF and deionized water, and dried at 60 °C to obtain the CaFe-S-LDH composite material.

[0060] Comparative Example 4 (1) Dissolve 0.01 mol Ca(NO3)2·4H2O and 0.01 mol Fe(NO3)3·9H2O in 100 mL of deionized water. First, continue stirring at 25 °C (400 rpm) for 12 h, then let stand at 25 °C for 12 h to age, and then dry at 60 °C to obtain CaFe-NO3. - -LDH.

[0061] (2) Take 1 mmol of (NH4)2Mo3S 13 The amount of metal element contained in H2O is equivalent to that in (NH4)2WS4 (i.e., the molar amount of W in (NH4)2WS4 is equal to that in 1 mmol (NH4)2Mo3S). 13 (The molar amount of Mo in H2O is equal) is dissolved in 180 mL of DMF, and insoluble impurities are removed to obtain WS4. 2- Solution.

[0062] (3) Take 0.57 g CaFe-NO3 --LDH was added to 20 mL of the above WS4. 2- In the solution, ion exchange was completed by stirring at a constant temperature (25 °C) and 400 rpm for 24 h. The precipitate was then separated by filtration, washed with DMF and deionized water, and dried at 60 °C to obtain CaFe-WS4. 2- -LDH composite material.

[0063] Test Example 1 Structural characterization Figure 1 CaFe-TMB prepared in Example 1 2- SEM and TEM images of CaFe-TMB are shown, with (a) and (b) being SEM images and (c) being a TEM image. The SEM images show that at a scale of 5 µm, CaFe-TMB... 2- The main morphological characteristics of -LDH are rough surface, bulky and porous. At the 500 nm scale, CaFe-TMB 2- -LDH possesses a loose spatial structure, exhibiting more adsorption surfaces and stacked layered LDH. TEM images reveal the nanosheet layered structure, confirming the presence of CaFe-TMB. 2- -LDH is a stacked layered LDH, consistent with the SEM characterization results.

[0064] Figure 2 CaFe-NO3 prepared for Comparative Example 1 - SEM and TEM images of -LDH are shown, where (a) and (b) are SEM images, and (c) is a TEM image. It can be seen that CaFe-NO3... - -LDH and CaFe-TMB 2- -LDH has a similar morphological structure, but is similar to CaFe-NO3. - Compared to -LDH, CaFe-TMB 2- -LDH has increased interlamellar spacing and good dispersion.

[0065] Figure 3 CaFe-NO3 prepared for Comparative Example 1 - -LDH, CaFe-TMB prepared in Example 1 2- -LDH and CaFe-TMB prepared in Example 1 2- -LDH adsorption of Cd 2+ After (adsorption of Cd) 2+ The subsequent sample was derived from the adsorption model analysis process in Test Example 3, Cd 2+ The XRD pattern of the solution (concentration 100 mg / L, sampled after adsorption equilibrium) shows that CaFe-NO3 -The (003) characteristic peak of -LDH is located at 2θ = 10.1°, and the interlayer spacing is 0.827 nm; CaFe-TMB prepared in Example 1 2- The (003) peak of -LDH shifted to 11.1°, and the interlayer spacing was 0.899 nm; CaFe-TMB prepared in Example 1 2- -LDH adsorption of Cd 2+ The characteristic peak of (003) shifts to a higher angle, with an interlayer spacing of 0.885 nm, and characteristic diffraction peaks appear at 2θ≈19.9° and 29.1°.

[0066] Figure 4 CaFe-NO3 prepared for Comparative Example 1 - -LDH, CaFe-TMB prepared in Example 1 2- -LDH and CaFe-TMB prepared in Example 1 2- -LDH adsorption of Cd 2+ The subsequent FTIR plot. For CaFe-NO3 - -LDH, observed at 1384 cm -1 The characteristic peak at this location belongs to NO3. - For CaFe-TMB 2- -LDH, observed at 480 cm -1 The characteristic peak at 568 cm⁻¹ belongs to the Mo-S stretching vibration. -1 The characteristic peak at this location, attributed to the SS bridge, is 1350 cm⁻¹. -1 The characteristic peak at this location belongs to NO3. − Tensile vibration peak, 1381 cm -1 The characteristic peak belongs to NO3 − NO antisymmetric tensile vibration, 3446 and 1614 cm -1 The characteristic peaks correspond to the stretching and bending vibrations of OH molecules in the hydroxide layer and interlayer water molecules; however, at 1381 and 1350 cm⁻¹... -1 NO3 showed signs of weakening or even disappearing. − The peak confirms CaFe-NO3 - -LDH interlayer NO3 − The polysulfide anions were replaced by ion exchange reactions, and the polysulfide anions were successfully introduced to modify LDH. In CaFe-TMB 2- -LDH adsorption of heavy metal Cd 2+ The subsequent infrared spectrum shows that at 480 cm⁻¹ -1 The characteristic peak at 568 cm⁻¹ belongs to the Mo-S stretching vibration. -1 The characteristic peaks at 3446 and 1614 cm⁻¹ belong to the SS bridge. -1The characteristic peaks correspond to the stretching and bending vibrations of OH molecules in the hydroxide layer and interlayer water molecules, however, at 480 and 568 cm⁻¹. -1 The characteristic peak weakens at 2813 cm⁻¹. -1 The appearance of a new characteristic peak indicates that the polysulfide anion has undergone a certain chemical reaction, possibly with Cd. 2+ Coordination occurs to form Cd-S coordinate bonds.

[0067] Figure 5 CaFe-TMB prepared in Example 1 2- -LDH and CaFe-TMB prepared in Example 1 2- -LDH adsorption of Cr 6+ After (Cr adsorption) 6+ The subsequent sample was derived from the adsorption model analysis process in Test Example 3, Cr 6+ The XRD pattern of the solution (concentration 100 mg / L, sampled after adsorption equilibrium) shows that, in Cr... 6+ After adsorption, CaFe-TMB 2- The characteristic peaks of the 003 crystal plane in the XRD pattern of -LDH shift to higher angles and show a weakening trend, indicating the formation of a reduced interlayer spacing. This may be caused by interlayer products formed by redox reactions between hexavalent chromium and polysulfide anions.

[0068] Figure 6 CaFe-TMB prepared in Example 1 2- -LDH and CaFe-TMB prepared in Example 1 2- -LDH adsorption of Cr 6+ The subsequent FTIR image shows that at 480 cm⁻¹ -1 The characteristic peak at 568 cm⁻¹ belongs to the Mo-S stretching vibration. -1 The characteristic peaks at 3446 and 1614 cm⁻¹ belong to the SS bridge. -1 The characteristic peaks correspond to the stretching and bending vibrations of OH molecules in the hydroxide layer and interlayer water molecules, however, at 480 and 568 cm⁻¹. -1 The weakening of the characteristic peak at this point indicates that the polysulfide anion underwent a certain degree of chemical reduction. CrO4 2− The characteristic peaks are located at 1049 and 886 cm⁻¹. -1 However, CaFe-TMB 2- -LDH adsorption of heavy metal Cr 6+ 1049 and 886 cm⁻¹ in the subsequent infrared spectrum -1 The characteristic peaks almost disappeared, indicating that hexavalent chromium does not exist in the form of CrO4. 2− CrO4 2−First, chromium enters the interlayer via electrostatic adsorption and ion exchange through surface positive charge, then hexavalent chromium is reduced to trivalent chromium. (1725-1925 cm⁻¹) -1 A faint band at the location, which may be due to Cr 6+ The structural changes and reductions are caused by this. Overall, after the adsorption of hexavalent chromium, CaFe-TMB... 2- The characteristic peaks of the functional groups of -LDH did not change significantly, at 480 and 568 cm⁻¹. -1 Proof of CaFe-TMB's invariant characteristic peak mode 2- -LDH has high stability.

[0069] Test Example 2 Specific surface area test CaFe-NO3 prepared in Comparative Example 1 was analyzed by the BET method. - -LDH and CaFe-TMB prepared in Example 1 2- The specific surface area of ​​-LDH was tested, and the results showed that CaFe-NO3 - The specific surface area of ​​-LDH is 42 m². 2 / g, CaFe-TMB prepared in Example 1 2- The specific surface area of ​​-LDH is 51 m². 2 / g.

[0070] Test Example 3 (1) Adsorption performance test At 100 mg / L Cd 2+ With 100 mg / L Cr 6+ In a mixed solution (using Cd(NO3)2 and K2Cr2O7 as solutes and water as solvent), 1 g / L of the sample prepared in each example or comparative example was added. After adjusting the pH to 7, the solution was shaken at 200 rpm for 4 h at room temperature (25 °C). After the process, the remaining Cd in the solution was determined by ICP-MS. 2+ and Cr 6+ The concentration was determined, and the removal rate was calculated. The results are shown in Table 1.

[0071] Table 1

[0072] As shown in Table 1, the MgFe-NO3 prepared in Comparative Example 2... - Compared to -LDH, CaFe-NO3 prepared in Comparative Example 1 - -LDH for Cd 2+ and Cr 6+ The removal rate is higher, demonstrating the synergistic effect of the Ca and Fe bimetallic layers. This is in contrast to the CaFe-NO3 prepared in Comparative Example 1. -Compared to -LDH, the CaFe-TMB prepared in Example 1 2- -LDH for Cd 2+ and Cr 6+ The removal rate was further improved because ion exchange introduced TMB. 2- It significantly enhanced electron transfer and adsorption sites. The CaFe-S-LDH prepared in Comparative Example 3 significantly enhanced the adsorption of Cd. 2+ and Cr 6+ The removal rate of Cd was significantly lower than that of Example 1, indicating that although the introduction of sulfur-containing sites can improve the material properties to some extent, the lack of synergistic active centers involving Mo limits its ability to remove Cd. 2+ / Cr 6+ The comprehensive removal capacity of complex pollutants remains limited. Comparative Example 4 prepared CaFe-WS4 2- -LDH for Cd 2+ and Cr 6+ Although the removal rate was higher than that of CaFe-S-LDH, it was still lower than that of Example 1, indicating that after replacing Mo with W, the material still has a certain adsorption and reduction capacity, but its electron transfer efficiency and synergistic effect with the laminate are weaker than that of TMB. 2- The system further demonstrates that the Mo-S synergistic structure is a key factor in improving the material removal performance, and that Mo has a more prominent role compared to other metallic elements.

[0073] (2) Adsorption model analysis A series of Cr solutions with different initial concentrations (10-1000 mg / L) were prepared under constant temperature (25 ℃) conditions. 6+ Solution or Cd 2 + The solutions were prepared by adding quantitative amounts of the material (0.05 g of the analyte to 50 mL of solution), adjusting the pH to 7, and then allowing the mixture to fully contact at room temperature (25℃) and shaken at 200 rpm until adsorption equilibrium was reached. The equilibrium concentration C was then measured. e And according to q e =(C0−C e Calculate the equilibrium adsorption capacity q using C0 / m (where C0 represents the initial concentration, V represents the solution volume, and m represents the amount of material added). e The Langmuir model q is used. e The maximum adsorption capacity q is obtained by performing a nonlinear fitting on the experimental data using the formula: =qmax·KL·Ce / (1+KL·Ce). max And the Langmuir constant KL, and combined with the goodness-of-fit evaluation of the material on Cr 6+ or Cd 2+ Monolayer adsorption characteristics.

[0074] Tests showed that the CaFe-NO3 prepared in Comparative Example 1...- -LDH adsorption conforms to the Langmuir model for Cd. 2+ The monolayer adsorption capacity is 90.36 mg / g, and it has a high adsorption capacity for Cr. 6+ The monolayer adsorption capacity is 97.1 mg / g.

[0075] CaFe-TMB prepared in Example 1 2- -LDH adsorption conforms to the Langmuir model for Cd. 2+ The monolayer adsorption capacity is 289.6 mg / g, for Cr 6+ The monolayer adsorption capacity is 245.78 mg / g. The corresponding adsorption isotherm fitting is as follows: Figure 7 As shown, (a) is CaFe-TMB 2- -LDH for Cd 2+ The adsorption isotherm fitting results are shown in (b) for CaFe-TMB. 2- -LDH on Cr 6+ The fitting of the adsorption isotherm.

[0076] CaFe-TMB prepared in Example 1 before and after the adsorption reaction 2- -LDH was used for XPS testing, and the results were as follows: Figure 8 As shown, (a) is the XPS full spectrum, (b) is the Mo 3d energy spectrum, (c) is the S 2p energy spectrum, and (d) is the Cr 2p energy spectrum. It can be seen that before the adsorption reaction, CaFe-TMB... 2- -LDH has an S / Mo ratio of 4.14, compared to Mo3S. 13 2− The similar ratios indicate that CaFe-TMB 2- -LDH material was successfully synthesized. In Mo 3d, the peaks with binding energies at 228.7 and 232.2 eV were attributed to Mo 3d5 / 2 and Mo 3d3 / 2, respectively, indicating the presence of Mo. 4+ The S 2p spectrum was deconvolved into two bimodal peaks, with one at 165.0 eV and the other at 163.5 eV belonging to S 2p1 / 2 and S 2p3 / 2, respectively, originating from the top S 2p1 / 2 and S 2p3 / 2. 2− and bridging S2 2− The other bimodality, S 2p1 / 2 (159.1 eV) and S 2p3 / 2 (157.6 eV), is attributed to the terminal S2. 2− Adsorption of Cd 2+ Subsequently, the Mo element in the Mo 3d spectrum did not interact with Cd. 2+A valence state change reaction occurs; the peaks at 412.9 and 406.1 eV in the Cd 3d spectrum correspond to Cd 3d3 / 2 and Cd 3d5 / 2, respectively. The characteristic peak of S 2s (226.3 eV) appears after the reaction, indicating the formation of Cd-S precipitate. The double shift peaks of S 2p at 158.1 and 156.7 eV emphasize the formation of S. 2− It exists in the form of CdS. The S 2p binding energy is lower than that of CaFe-TMB. 2- The corresponding value of -LDH is due to Cd 2+ With Mo3S 13 2− Coordination between them. Adsorption of Cr 6+ Subsequently, weakened doublets at 232.0 and 229.3 eV were observed for Mo(IV)3d3 / 2 and Mo(IV)3d5 / 2, while strong doublets at 235.2 and 232.4 eV, attributable to Mo3d, were observed for Mo(VI)3d3 / 2 and Mo(VI)3d5 / 2. Partial conversion of Mo(IV) to Mo(VI) reflects the CaFe-TMB... 2- A significant oxidation process of Mo(IV) is observed during the adsorption of Cr(VI) by -LDH. Signal peaks of 573.6 eV and 583.9 eV are observed in the Cr 2p spectrum, corresponding to Cr 2p2 / 3 and Cr 2p1 / 2, which typically originate from Cr(III). These indicate a redox reaction between Mo(IV) and Cr(VI). In the S 2p spectrum, the binding energy peak at 168.0 eV indicates that the sulfide functional groups are oxidized to SO42-. 2− The decrease in the binding energy of S 2p (163.5 eV) indicates that Cr(III) forms a coordinate bond with S, and S 2− The weakening of the characteristic peak indicates that S 2− Oxidized to SO4 2− With Mo(IV) and S 2− Reduce Cr(VI) to Cr(III), S 2− Partially oxidized to SO4 2− Mo(IV) is oxidized to Mo(VI), and Cr-S coordination further captures the generated Cr(III).

[0077] (3) Effect of different dosages on adsorption performance At 100 mg / L Cd 2+ With 100 mg / L Cr 6+ Different amounts of CaFe-TMB prepared in Example 1 were added to the mixed solution. 2- After adjusting the pH to 7 with -LDH, the solution was shaken at 200 rpm for 4 h at room temperature (25 ℃). Afterward, the remaining Cd in the solution was determined by ICP-MS.2+ and Cr 6+ The concentration was determined, and the removal rate was calculated. The test results are shown in Table 2.

[0078] Table 2

[0079] As shown in Table 2, Cd 2+ and Cr 6+ The removal rates all increased with increasing dosage, indicating that the dosage is a crucial factor affecting the removal efficiency. This is because a higher dosage provides more surface-active sites and interlayer exchange sites, enhancing the removal of Cd. 2+ Complexation / fixation and Cr 6+ The system exhibits exchange, reduction, and stabilization effects. However, when the dosage is further increased from 1.0 g / L, the increase in removal rate decreases, indicating that the system gradually approaches adsorption-reaction equilibrium.

[0080] (4) Effect of pH on removal performance At 100 mg / L Cd 2+ With 100 mg / L Cr 6+ The CaFe-TMB prepared in Example 1 was added to the mixed solution. 2- -LDH 1 g / L was added, and the pH of the solution was adjusted to 5, 7, or 9 respectively. The solution was then shaken at 200 rpm for 4 h at room temperature (25 ℃). After the reaction, the remaining Cd in the solution was determined by ICP-MS. 2+ and Cr 6+ The concentration was determined, and the removal rate was calculated. The results are shown in Table 3.

[0081] Table 3

[0082] As shown in Table 3, Cd 2+ The fixation of Cr generally prefers a neutral to slightly alkaline environment because this is conducive to surface deprotonation, hydroxyl complexation, and Cd(OH)₂ formation. 6+ The reduction of HCrO4 is often easier to carry out in slightly acidic to neutral conditions because HCrO4 - / Cr2O7 2- It is easier to reduce, and the reduction process is often accompanied by H + Participation. Under the same bulk pH conditions, CaFe-TMB 2- -LDH for Cd 2+ Fixation and Cr 6+ Reduction and fixation can occur simultaneously, but their optimal pH ranges may not be entirely the same. This may be attributed to the presence of different functional sites on the material surface: Cd 2+ It is mainly fixed through lamellar substitution, surface complexation, and precipitation, while Cr6+ The two types of pollutants can be synergistically removed in the same system mainly through anion exchange and Mo-S site-mediated reduction and fixation.

[0083] (5) Cyclic performance test At 100 mg / L Cd 2+ With 100 mg / L Cr 6+ The CaFe-TMB prepared in Example 1 was added to the mixed solution. 2- -LDH 2 g / L, after adjusting pH=7, the material was shaken at 200 rpm at room temperature (25 ℃) until adsorption equilibrium was reached, and then centrifuged to recover the material. Desorption was performed using a mixed regeneration solution of 0.05 mol / L EDTA-2Na and 0.1 mol / L NaNO3 for 6 h (50 mL of the mixed regeneration solution was added for every 0.10 g of adsorbed material for desorption). The material was then washed with deionized water until neutral and dried at 60 ℃ before entering the next cycle. Results showed that CaFe-TMB... 2- -LDH on Cd in cycles 1 through 5 2+ The removal rate can be gradually reduced from 99.2% to 90.2%, and the removal rate of Cr can be reduced from 99.2% to 90.2%. 6+ The removal rate can be reduced from 98.0% to 84.6%, while still maintaining a high overall removal efficiency, indicating that the material has good recycling potential. Among them, Cr... 6+ The removal rate decreased slightly more significantly, mainly because some of the Mo-S active sites were consumed during the reduction process, while Cd... 2+ A high removal level can still be maintained through interlayer exchange, surface complexation, and precipitation fixation.

[0084] Test Example 4 Remediation performance and long-term stability of contaminated soil Experimental conditions: Soil samples (total Cd content 3.26 mg / kg, total Cr content 63.97 mg / kg) were collected from a contaminated electroplating area. After adjusting the moisture content to 60%, 1 wt% of the dry weight of the soil samples prepared in each example or comparative example were applied. After incubation at 25 ℃ for 30 days, Cd content was determined by ICP-MS. 2+ and Cr 6+ The residual content.

[0085] The results showed that the CaFe-TMB prepared in Example 1 was applied 2- Cr in the soil of the LDH experimental group 6+ The concentration of Cr in the soil decreased by 83.5%; the concentration of bioavailable Cd (the form that can be directly absorbed and utilized by organisms) decreased by 64.4%. In contrast, after applying CaFe-S-LDH, the concentration of Cr in the soil decreased by 83.5%. 6+The concentration of Cd decreased by 62.0%, and the effective Cd decreased by 39.6%; the CaFe-NO3 prepared in Comparative Example 1 was applied. - After -LDH, Cr in the soil 6+ The concentration of bioavailable Cd decreased by 47.8%; bioavailable Cd decreased by 28.6%. BCR speciation analysis indicated that CaFe-TMB... 2- After CaFe-S-LDH treatment, the extractable form of highly active acids in Cd and Cr was significantly reduced and transformed into a more stable residual form, with the proportions of residual Cd and Cr increasing by approximately 28% and 18%, respectively; while after CaFe-S-LDH treatment, the proportions of residual Cd and Cr increased by approximately 25% and 9%, respectively.

[0086] Mechanism Explanation: CaFe-TMB 2- The Mo-S active component introduced into the LDH interlayer can reduce Cr 6+ Reduced to Cr 3+ Furthermore, Cr-S coordination and interlayer immobilization further inhibit its re-release; simultaneously, hydroxyl and Ca sites on the surface of the LDH laminations can immobilize Cd through complexation, isomorphic substitution, and precipitation. 2+ In contrast, although CaFe-S-LDH possesses certain sulfur-containing coordination sites, it does not significantly affect Cd. 2+ and Cr 6+ It also has a certain fixing effect, but due to the lack of Mo-S synergistic active centers, its effect on Cr is limited. 6+ Its deep reduction ability and synergistic remediation ability for Cd / Cr dual pollution are both weaker than CaFe-TMB. 2- -LDH. Therefore, CaFe-TMB 2- -LDH can more effectively achieve long-term in-situ remediation of actual Cd / Cr contaminated soils.

[0087] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a modified CaFe-LDH composite material, characterized in that, Includes the following steps: Calcium nitrate or its hydrate, ferric nitrate or its hydrate, and water are mixed, stirred to react, allowed to stand for aging, and then dried to obtain CaFe-NO3. - -LDH; utilizing Mo3S 13 2- The solution for CaFe-NO3 - -LDH ion exchange yields CaFe-Mo3S 13 2- -LDH refers to the modified CaFe-LDH composite material.

2. The preparation method of the modified CaFe-LDH composite material as described in claim 1, characterized in that, The calcium nitrate or its hydrate contains Ca. 2+ With the Fe contained in the ferric nitrate or its hydrate 3+ The molar ratio is 1:

1.

3. The preparation method of the modified CaFe-LDH composite material as described in claim 1, characterized in that, The calcium nitrate or its hydrate includes Ca(NO3)2·4H2O; And / or, the ferric nitrate or its hydrate comprises Fe(NO3)3·9H2O.

4. The preparation method of the modified CaFe-LDH composite material as described in claim 1, characterized in that, The stirring reaction and the static aging were both carried out at temperatures of 20-35 °C for 12-36 h.

5. The method for preparing the modified CaFe-LDH composite material as described in claim 1, characterized in that, The use of Mo3S 13 2- The solution for CaFe-NO3 - -LDH ion exchange includes: [removing / converting] the CaFe-NO3... - -LDH and Mo3S 13 2- Mix the solutions and stir for 12-36 hours.

6. The method for preparing the modified CaFe-LDH composite material as described in claim 5, characterized in that, The Mo3S 13 2- The solution preparation steps include: (NH4)6Mo7O 24 A mixture of 4H₂O, HONH₂·HCl, and an aqueous solution of (NH₄)₂S₃ reacts upon heating to yield (NH₄)₂Mo₃S. 13 ·H2O; The (NH4)2Mo3S 13 H2O dissolves in an organic solvent to obtain the Mo3S. 13 2- Solution.

7. The method for preparing the modified CaFe-LDH composite material as described in claim 6, characterized in that, The concentration of the (NH4)2S3 aqueous solution is 10-30 wt%; And / or, the (NH4)6Mo7O 24 The ratio of the amount of 4H2O, the amount of HONH2·HCl and the amount of (NH4)2S3 aqueous solution is 1-2 g: 1-3 g: 60 mL; And / or, the heating reaction is carried out at a temperature of 220 °C for a time of 12-36 h; And / or, the organic solvent includes N,N-dimethylformamide; And / or, the (NH4)2Mo3S 13 The ratio of H2O to the organic solvent is 1 mmol: 150-200 mL; And / or, the CaFe-NO3 - -LDH and the Mo3S 13 2- The volume ratio of the solution used is 0.5-0.7 g: 20 mL.

8. A modified CaFe-LDH composite material prepared by the preparation method according to any one of claims 1-7.

9. A modified CaFe-LDH composite material as described in claim 8 for the removal of Cd from water. 2+ and / or Cr 6+ Applications in [the field].

10. A modified CaFe-LDH composite material as described in claim 8 in Cd 2+ and / or Cr 6+ Applications in contaminated soil remediation.

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