A material for efficiently removing heavy metal pollutants based on fluorinated zero-valent iron and a preparation method thereof

Abstract

The application discloses a material for efficiently removing heavy metal pollutants based on fluorinated zero-valent iron and a preparation method thereof, and belongs to the field of environmental functional materials. 0 The material comprises a core layer of zero-valent iron (Fe 0 ) with a particle size of 50-100 nm, and a shell layer of a composite layer of fluorinated iron (FeF3) and fluorine-doped hydroxyl iron oxide (FeOOH-F) with a thickness of 5-20 nm. The heterojunction shell layer formed by the fluorinated iron (FeF2 / FeF3) and the fluorine-doped hydroxyl iron oxide (FeOOH-F) significantly improves the surface active sites and promotes electron transfer, thereby realizing efficient reduction / adsorption of heavy metals (such as Cr(VI), Pb(II), As(III), etc.); the wide pH adaptability (pH 3-9, optimal pH 5-7) overcomes the defects that traditional zero-valent iron is prone to passivation under acidic or alkaline conditions.

Description

Technical Field

[0001] This invention relates to the field of environmental functional materials technology, and in particular to a material based on zero-valent iron fluoride for the efficient removal of heavy metal pollutants and its preparation method. Background Technology

[0002] Zero-valent iron (Fe) 0 Due to its strong reducing power and low cost, it is widely used for the remediation of heavy metal pollution, but it has the following drawbacks:

[0003] 1. Surface passivation: Fe 0 It is easily oxidized to form a dense oxide layer (Fe3O4 / Fe2O3), which hinders electron transfer and reduces reactivity;

[0004] 2. Poor selectivity: Not effective against specific heavy metals (such as Cr). 6+ The adsorption capacity of ) is limited;

[0005] 3. Easy to aggregate: Nano-sized Fe 0 It tends to aggregate and settle, reducing the effective reaction sites.

[0006] Existing modification techniques (such as sulfidation and carbon coating) partially improve performance, but cannot simultaneously solve the passivation and selectivity problems. Fluorination modification (introducing F-) can regulate Fe... 0 The surface electronic structure forms electron-rich active sites, enhancing the coordination and reduction capabilities for heavy metals, but related research has not yet been reported. Summary of the Invention

[0007] The purpose of this invention is to provide a material based on zero-valent iron fluoride for the efficient removal of heavy metal pollutants and its preparation method, for the efficient removal of heavy metal pollutants (such as Pb) from water bodies. 2+ Cd 2+ Hg 2+ Cr 6+ (etc.), and provides its preparation method and application process.

[0008] To address the aforementioned technical problems, this invention provides a material based on zero-valent iron fluoride for the efficient removal of heavy metal pollutants, comprising:

[0009] Core layer: Zero-valent iron (Fe) 0 Particle size 50-100 nm;

[0010] Shell: A composite layer of iron fluoride (FeF3) and fluorine-doped iron hydroxyl oxide (FeOOH-F), with a thickness of 5-20 nm.

[0011] Preferably, in the shell layer, the fluorine doping amount F / Fe molar ratio is 0.1-0.5.

[0012] A method for preparing a material based on zero-valent iron fluoride for efficient removal of heavy metal pollutants, comprising:

[0013] a. Precursor preparation: FeSO4·7H2O was reacted with NaBH4 under nitrogen protection to generate nano-Fe. 0 Suspension;

[0014] b. Surface fluorination: Applying Fe... 0 The suspension was mixed with NH4F solution and stirred to induce a displacement reaction.

[0015] c. Shell growth: Adding a trace amount of H2O2 to oxidize part of the Fe. 0 This forms a FeF3-FeOOH-F heterostructure shell layer;

[0016] d. Post-processing: After magnetic separation, freeze-drying was performed to obtain F-Fe. 0 powder.

[0017] Preferably, in step a, the molar ratio of FeSO4·7H2O to NaBH4 is 1:3.

[0018] Preferably, in step b, the concentration of the NH4F solution is 0.1-1.0M, and the stirring displacement is carried out at 60°C for 2 hours.

[0019] Preferably, in step c, the weight of the trace amount of H2O2 added is 0.1 wt% of the weight of the mixed solution in step b.

[0020] Preferably, in step d, F-Fe 0 Powder specific surface area ≥80m² 2 / g, saturation magnetization ≥120emu / g.

[0021] The application of a material based on zero-valent iron fluoride for the efficient removal of heavy metal pollutants in the treatment of heavy metal wastewater, with a dosage of 0.1-1.0 g / L (adjusted according to the concentration of heavy metals); reaction conditions of pH 3-9 (optimal pH = 5-7), temperature 15-45℃, and reaction time 10-60 min.

[0022] Beneficial effects:

[0023] 1. The heterojunction shell formed by iron fluoride (FeF3) and fluorine-doped iron hydroxyl oxide (FeOOH-F) significantly enhances the surface active sites, promotes electron transfer, and achieves efficient reduction / adsorption of heavy metals (such as Cr(VI), Pb(II), As(III)). It has a wide pH adaptability (pH 3–9, optimal pH 5–7), overcoming the defect of traditional zero-valent iron being easily passivated under acidic or alkaline conditions.

[0024] 2. Core-shell structure (Fe 0The core + FeF3 / FeOOH-F shell effectively isolates zero-valent iron from direct contact with water, reducing Fe... 0 It reduces ineffective oxidation losses, extends the service life of materials, and fluorine doping (F / Fe = 0.1–0.5) strengthens the shell lattice structure, inhibits corrosion dissolution, and improves acid and alkali resistance.

[0025] 3. An ultrathin shell (5–20 nm) ensures rapid diffusion of heavy metal ions to the active interface, combined with a high specific surface area (≥80 nm). 2 / g), achieving short-time and efficient processing (reaction completed in 10–60 min).

[0026] 4. Low dosage (0.1–1.0 g / L), saving costs; high saturation magnetization (≥120 emu / g), supporting rapid magnetic separation and recovery, avoiding secondary pollution. Attached Figure Description

[0027] Figure 1 The images show SEM comparisons before and after the preparation of fluorinated zero-valent iron for treating wastewater containing 50 mg / L of Cr(VI) according to the present invention; Figure a is the SEM image before the preparation of fluorinated zero-valent iron for treating wastewater according to the present invention, and Figure b is the SEM image after the preparation of fluorinated zero-valent iron for treating wastewater according to the present invention.

[0028] Figure 2 The particle size distribution diagram of fluorinated zero-valent iron prepared for this invention.

[0029] Figure 3 The diagram shows a comparison of the reaction kinetics of different dosages of fluorinated zero-valent iron prepared in this invention on the removal of Cr(VI) from wastewater containing 50 mg / L.

[0030] Figure 4 A comparative graph showing the reaction kinetics of different dosages of ordinary zero-valent iron in the treatment of wastewater containing 50 mg / L of Cr(VI).

[0031] Figure 5 A schematic diagram showing the effect of pH on the removal efficiency of fluorinated zero-valent iron prepared by this invention and ordinary zero-valent iron at a dosage of 1.0 g / L when treating wastewater containing 50 mg / L of Cr(VI). Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] Preparation parameters:

[0035] Precursor: FeSO4·7H2O 2.78g (0.01mol) + NaBH4 1.14g (0.03mol), react under nitrogen protection for 30min;

[0036] Fluorination: 200 mL of 0.1 M NH4F solution, stirred at 60 °C for 2 h (F / Fe ≈ 0.1);

[0037] Oxidation: 0.1 wt% H2O2 added (total solution 300 g, add 0.3 g H2O2);

[0038] Post-processing: magnetic separation, freeze-drying at -50℃ for 24 hours;

[0039] Material properties:

[0040] Shell thickness: 5nm;

[0041] F / Fe molar ratio: 0.1;

[0042] Specific surface area: 85m² 2 / g;

[0043] Saturation magnetization: 125 emu / g, with... Figure 1 Image a is a SEM image of the wastewater before the preparation of fluorinated zero-valent iron according to this invention. (Attached) Figure 2 The particle size distribution diagram of fluorinated zero-valent iron prepared for this invention.

[0044] Application effect (treatment of wastewater containing Cr(VI) 50mg / L):

[0045] Dosage: 0.5 g / L, pH = 5, 25℃, with additional... Figure 3 This invention provides a comparative kinetic diagram of the effects of different dosages of fluorinated zero-valent iron on the removal reaction of wastewater containing 50 mg / L of Cr(VI).

[0046] Removal rate after 30 minutes: 98.2%;

[0047] Magnetic recovery rate: 96%, with attachment Figure 1 b is a SEM image of the wastewater treated with fluorinated zero-valent iron prepared according to the present invention.

[0048] Example 2:

[0049] Preparation parameters:

[0050] Precursor: FeSO4·7H2O 2.78g (0.01mol) + NaBH4 1.14g (0.03mol), react under nitrogen protection for 30min;

[0051] Fluorination: 200 mL of 1.0 M NH4F solution, stirred at 60 °C for 2 h (F / Fe≈0.5);

[0052] Oxidation: H2O2 addition amount 0.1wt%;

[0053] Post-processing: magnetic separation, freeze-drying at -50℃ for 24 hours.

[0054] Material properties:

[0055] Shell thickness: 20nm;

[0056] F / Fe molar ratio: 0.5;

[0057] Specific surface area: 80m² 2 / g, saturation magnetization: 130 emu / g.

[0058] Application effect (treatment of wastewater containing 100 mg / L of Pb(II):

[0059] Dosage: 1.0 g / L, pH = 7, 25℃;

[0060] Removal rate at 60 min: 99.5%;

[0061] Magnetic recovery rate: 97%.

[0062] Example 3

[0063] Preparation parameters:

[0064] Precursor: FeSO4·7H2O 2.78g (0.01mol) + NaBH4 1.14g (0.03mol), react under nitrogen protection for 30min;

[0065] Fluorination: 200 mL of 0.5 M NH4F solution, stirred at 60 °C for 2 h (F / Fe≈0.3);

[0066] Oxidation: H2O2 addition amount 0.1wt%;

[0067] Post-processing: magnetic separation, freeze-drying at -50℃ for 24 hours.

[0068] Material properties:

[0069] Shell thickness: 12nm;

[0070] F / Fe molar ratio: 0.3;

[0071] Specific surface area: 95m² 2 / g, saturation magnetization: 128 emu / g.

[0072] Application effect (treatment of mixed wastewater containing Cd(II) + Hg(II), 50 mg / L each):

[0073] Dosage: 0.8 g / L, pH = 6, 30℃;

[0074] Removal rates at 45 min: Cd(II) 99.1%, Hg(II) 99.8%;

[0075] Magnetic recovery rate: 96.5%.

[0076] Comparative Example 1

[0077] Preparation parameters: Skip step b (surface fluorination) and proceed directly to step c (H2O2 oxidation), with other conditions the same as in Example 3.

[0078] Material properties:

[0079] Shell composition: Pure FeOOH (without FeF) x );

[0080] Specific surface area: 90m² 2 / g, saturation magnetization: 110 emu / g.

[0081] Application effect:

[0082] Under the same conditions, the removal rate of Cr(VI) wastewater was only 82.4% after 60 minutes.

[0083] The material corrodes significantly at pH 5, and its activity decreases by 40% after three repeated uses.

[0084] Comparative Example 2

[0085] Preparation parameters: Only step a (preparation of Fe) is performed. 0 (Suspension), skip steps b / c, and directly perform magnetic separation and drying.

[0086] Material properties:

[0087] It has no core-shell structure and its surface is covered with an iron oxide layer.

[0088] Specific surface area: 45m² 2 / g, saturation magnetization: 95 emu / g.

[0089] Application effect (treatment of wastewater containing Cr(VI) 50mg / L):

[0090] Dosage: 1.0 g / L, pH = 5, Cr(VI) removal rate: 68.5% after 60 min, with added... Figure 4 A comparative graph showing the reaction kinetics of different dosages of ordinary zero-valent iron on the removal of Cr(VI) from wastewater containing 50 mg / L;

[0091] At pH=9, the removal rate drops sharply to 31.2% (strong passivation), with... Figure 5A schematic diagram comparing the effect of pH on the removal efficiency of fluorinated zero-valent iron prepared by this invention and ordinary zero-valent iron at a dosage of 1.0 g / L when treating wastewater containing 50 mg / L of Cr(VI).

[0092] Magnetic recovery rate: 89% (easily lost).

[0093] The statistical results of the experiment are shown in the table below:

[0094]

[0095]

[0096] Experimental Results: This invention, through the design of a fluorinated heterojunction shell (Examples 1-3), significantly improves the removal efficiency, pH adaptability, and material stability of heavy metals. The fluorinated zero-valent iron prepared by this invention (Examples 1-3) achieved a removal rate of >98% (maximum 99.6%) of 50 mg / L Cr(VI) within 60 min, while traditional zero-valent iron (Comparative Example 2) only achieved 68.5%, and the fluorine-free FeOOH shell material (Comparative Example 1) achieved 82.4%. The fluorinated zero-valent iron prepared by this invention exhibited a Cr(VI) removal rate fluctuation of <5% at pH = 3–9 (Example 2 only 2%), while the removal rate of traditional zero-valent iron plummeted to 31.2% at pH > 8 (see attached figure).

[0097] 5) The fluorinated zero-valent iron prepared by this invention maintains an activity of ≥92% after 5 cycles (95% in Example 2), while the activity of Comparative Example 1 decreases by 40% after 3 cycles at pH=5. The saturation magnetization of the fluorinated zero-valent iron prepared by this invention is ≥125 emu / g (Example 1), with a magnetic recovery rate of 96%–97%. Traditional materials have a recovery rate of only 95 emu / g and 89% (Comparative Example 2). The fluorinated zero-valent iron prepared by this invention has outstanding advantages, especially in high-concentration and mixed pollution scenarios. The performance of traditional zero-valent iron (Comparative Example 2) and fluorine-free doped materials (Comparative Example 1) is greatly reduced due to passivation / corrosion problems.

[0098] The above description is not intended to limit the present invention, nor is the present invention limited to the examples given above. Any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the present invention are also within the protection scope of the present invention.

Claims

1. A material for efficient removal of heavy metal pollutants based on fluorinated zero-valent iron, characterized in that, Comprising: Core layer: Zero-valent iron Particle size 50-100 nm; Shell: Iron fluoride with fluorine-doped iron oxyhydroxide FeOOH-F complex layer, thickness 5-20 nm.

2. The material for efficient removal of heavy metal pollutants based on fluorinated zero-valent iron according to claim 1, characterized in that, The shell layer has a fluorine doping amount F / Fe molar ratio of 0.1-0.

5.

3. A method for the preparation of a material based on fluorinated zero-valent iron for the efficient removal of heavy metal pollutants according to any one of claims 1-2, characterized in that, Comprise: a. Precursor preparation: ... and The reaction was carried out under nitrogen protection to generate nanoparticles. Suspension; b. Surface fluorination: The suspension is mixed with the solution and stirred for the displacement reaction. the solution and stirred for the displacement reaction. c. shell growth: addition of trace amounts of oxidizing moieties , forming heterojunction shell; d. Work-up: After magnetic separation, lyophilization gave powder.

4. The method of claim 3, wherein the method is characterized by, The molar ratio of the step a, With 1:

3.

5. The method of claim 3, wherein the method is characterized by, The step b in the method, The solution concentration is 0.1-1.0 M, and the stirring replacement is stirred at 60°C for 2h.

6. The method of claim 3, wherein the method is characterized by, In step c, a trace amount of 0.1 wt% of the weight of the mixed solution in step b.

7. The method of claim 3, wherein the method is characterized by, The step d, The powder specific surface area is > 80 m2 / g and the saturation magnetization is > 120 emu / g.

8. Use of the material based on fluorinated zero-valent iron for efficient removal of heavy metal pollutants according to any one of claims 1 to 2 or the material based on fluorinated zero-valent iron for efficient removal of heavy metal pollutants prepared according to any one of claims 3 to 7 for the treatment of heavy metal wastewater, characterized in that, The dosage is 0.1-1.0 g / L; the reaction conditions are pH 3-9, temperature 15-45 DEG C, and reaction time 10-60 min.

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