A spherical resin-derived carbon-coated nanomaterial of zero-valent iron, its preparation method and application

Abstract

This invention belongs to the field of water treatment technology, and provides a spherical resin-derived carbon-coated nano-zero-valent iron material, its preparation method, and its application. The invention involves mixing formaldehyde solution and melamine to obtain solution A; mixing ferric ammonium citrate and formaldehyde solution to obtain solution B; mixing solutions A and B to obtain a polymer solution; mixing the prepolymer solution with anhydrous acetic acid to obtain solution C; adding solution C dropwise to an organic solution containing a surfactant for thermal polymerization to obtain resin particles; and carbonizing the resin particles under a protective atmosphere to obtain spherical resin-derived carbon-coated nano-zero-valent iron material. This invention prepares a reusable iron-carbon composite material with high reducing activity and stability. Furthermore, this composite material is applied to the reduction and removal of BrO3 from water bodies with a wide pH range. ‑ It features simple operation, clean and pollution-free operation, high stability, high reactivity, and easy recycling.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a spherical resin-derived carbon-coated nano-zero-valent iron material, its preparation method, and its application. Background Technology

[0002] Bromate pollution in water bodies mainly originates from ozone disinfection processes during water treatment, and bromide ions (Br₂) in natural water sources. - After being oxidized by ozone, bromate is converted into bromate. As a common disinfection byproduct, bromate intake from drinking water increases the risk of cancer in humans. Currently, bromate is classified as a "Group 2B" potential carcinogen, and studies have shown that high concentrations of bromate have genotoxic effects. For these reasons, countries and regions around the world have established corresponding standards for bromate concentrations in water bodies. The World Health Organization (WHO), the European Union (EU), and the US Environmental Protection Agency (USEPA) stipulate that the maximum permissible concentration of bromate in drinking water is 10 μg / L. -1 my country's "Standards for Drinking Water Quality" also stipulates that the bromate content in drinking water should not exceed 10 μg / L. -1 .

[0003] Methods for treating bromate pollution in water include adsorption, chemical reduction, photocatalytic reduction, electrocatalytic reduction, liquid-phase catalytic hydrogenation reduction, and biodegradation. Among these, zero-valent iron (ZVFe) reduction is a highly effective method, capable of reducing bromate in water to bromide ions. ZVFe is an easy-to-produce, low-cost, and environmentally friendly chemical reducing agent. It is magnetic and easily recyclable in water treatment applications. Nano-ZVFe refers to ZVFe materials with a size range of 1–100 nm, characterized by high specific surface area, high reduction potential, and high reactivity. However, several issues remain regarding the direct application and storage of nano-ZVFe. Due to its strong magnetism and high specific surface energy, nano-ZVFe exhibits poor stability, easily colliding and agglomerating into large particles during application. Nano-ZVFe particles exposed to air or water readily react with environmental media (O2 and H2O), potentially oxidizing the iron and converting it to Fe. 2+ or Fe 3+ Furthermore, the leaching of iron ions may further passivate, forming an iron oxide or hydroxide shell, thereby reducing the reactivity of nano-zero-valent iron materials with pollutants. Additionally, the leaching of iron ions can cause secondary pollution and loss of reactive components, all of which limit the application of nano-zero-valent iron in water treatment.

[0004] Several methods have been proposed to improve the stability of nano-zero-valent iron. Existing research has found that adding a coating layer to the outer surface of nano-zero-valent iron can effectively prevent corrosion by iron and form a core-shell structure with iron. The coating layer adsorbs pollutants to the material surface, and then electrons are transferred from the iron core to the surface for reduction and removal. This not only improves the material's migration and dispersion in aqueous media but also enhances its reactivity. Carbon-based materials are inexpensive, easy to synthesize, have a large specific surface area, and controllable physicochemical properties, making them an excellent choice for coating materials. However, most carbon-based materials have relatively low isoelectric points and often carry a negative charge in aqueous solutions, leading to electrostatic repulsion with bromate anions and affecting the adsorption of pollutants by the composite material. Doping carbon-based materials with nitrogen can improve their hydrophilicity and increase their isoelectric point, thus enhancing their adsorption capacity. However, in many studies, the modification of nano-zero-valent iron using carbon coating materials often requires complex operations, and the integrity of the coating layer cannot be guaranteed. Moreover, the preparation of these composite materials typically requires numerous and time-consuming steps. In addition, most of the current modified zero-valent iron materials are at the nano or micron level. Although zero-valent iron materials have strong magnetism and can be recycled with magnets, in practical applications, the recycling process is time-consuming, labor-intensive, and the recycling degree is incomplete.

[0005] Therefore, the research and development of a large-size iron-carbon composite material that exhibits high stability and reactivity over a wide pH range, is easy to prepare, and is readily recyclable has broad application prospects. Summary of the Invention

[0006] The purpose of this invention is to provide a spherical resin-derived carbon-coated nano-zero-valent iron material, its preparation method, and its application, so as to make up for the shortcomings of the prior art.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing spherical resin-derived carbon-coated nano-zero-valent iron materials, comprising the following steps:

[0009] (1) Mix formaldehyde solution and melamine to obtain solution A;

[0010] Solution B is obtained by mixing ferric ammonium citrate and formaldehyde solution;

[0011] The solutions A and B are mixed to obtain a melamine-formaldehyde resin prepolymer solution;

[0012] (2) Mix the obtained melamine-formaldehyde resin prepolymer solution with anhydrous acetic acid to obtain solution C;

[0013] (3) The obtained solution C is added dropwise to an organic solution containing a surfactant for thermal polymerization to obtain resin particles;

[0014] (4) The obtained resin particles are carbonized under a protective atmosphere to obtain spherical resin-derived carbon-coated nano-zero-valent iron materials.

[0015] Preferably, in step (1), during the preparation of solution A, the mass ratio of formaldehyde solution to melamine is 8-15:5, the mixing temperature of formaldehyde solution and melamine is 50-80℃, and the mixing time is 10-30 min;

[0016] In the preparation of solution B, the mass ratio of ferric ammonium citrate to formaldehyde solution is 1:1.5 to 5;

[0017] The mass concentrations of the formaldehyde solutions used in preparing solution A and solution B are independently 35-40%;

[0018] The mass ratio of melamine to ferric ammonium citrate is 5:2 to 6;

[0019] The mixing time for solutions A and B is 5–10 minutes.

[0020] Preferably, in step (2), the volume ratio of melamine-formaldehyde resin prepolymer solution to anhydrous acetic acid is 1:0.005 to 0.025, and the mixing time is 1 to 10 min.

[0021] Preferably, the surfactant in step (3) comprises one or more of Span-80, polyethylene glycol, carboxymethyl cellulose, and sorbitol glyceride;

[0022] The organic solution contains one or more of 1,2-dichloroethane, carbon tetrachloride, n-hexane, n-heptane, and liquid paraffin;

[0023] The mass ratio of surfactant, melamine-formaldehyde resin prepolymer solution and organic solvent is 1:2 to 10:50 to 150;

[0024] The thermal polymerization temperature is 40–80°C, and the time is 2–24 hours.

[0025] Preferably, in step (4), the carbonization temperature is 700-900℃, the time is 2-4h, and the heating rate is 1-5℃ / min;

[0026] The protective atmosphere consists of nitrogen or argon gas at a flow rate of 25–100 mL / min. -1 .

[0027] The present invention also provides spherical resin-derived carbon-coated nano-zero-valent iron materials obtained by the aforementioned preparation method. The spherical resin particles in the material have a particle size range of 0.5–0.8 mm, are porous, and have a specific surface area of ​​190.07–356.17 m². 2 g-1 The iron content ranges from 18.9% to 37.1 wt.%.

[0028] This invention also provides the method for reducing BrO3 in an aqueous phase using the aforementioned spherical resin-derived carbon-coated nano-zero-valent iron material. - Applications.

[0029] Preferably, the pH value of the aqueous system is 4 to 8.5, and the amount of spherical resin-derived carbon-coated nano-zero-valent iron material is 0.5 to 1 g / L.

[0030] Preferably, BrO3 - The initial concentration was 0.02–0.08 mmol / L. -1 The restoration time is 1 to 4 hours.

[0031] The beneficial effects of this invention are as follows:

[0032] (1) This invention uses formaldehyde and melamine as carbon and nitrogen sources, and ferric ammonium citrate as an iron source, to prepare millimeter-sized iron-containing melamine-formaldehyde resin by in-situ thermal polymerization; then, through a simple carbonization process, it is prepared into millimeter-sized spherical resin-derived carbon-coated nano-zero-valent iron materials. In the prepared material, the nano-zero-valent iron particles are well dispersed and have uniform size.

[0033] (2) The millimeter-sized spherical resin-derived carbon-coated nano-zero-valent iron material prepared by this invention can efficiently remove BrO3 from water. - Reduced to non-toxic Br - The nitrogen-carbon coating structure can fix zero-valent iron particles, effectively inhibiting iron leaching and improving the stability of the material. Due to the large size of the material, it is easy to collect after the reduction reaction.

[0034] (3) Due to its coating strategy, the active component, zero-valent iron, does not come into direct contact with the external reaction environment and cannot directly encapsulate BrO3. - Reduction. During the reaction, electrons from the zero-valent iron of the active component are transferred to the material surface through the highly conductive coating layer, where they react with BrO3 adsorbed on the material surface. - The reaction proceeds. During the preparation process of this invention, the introduction of the nitrogen source melamine results in the obtained spherical resin-derived carbon-coated nano-zero-valent iron material exhibiting high hydrophilicity and a high isoelectric point, which is beneficial for the material's dispersion in aqueous phase and the reaction with anionic BrO3. - Adsorption on the surface of materials. Attached Figure Description

[0035] Figure 1XRD patterns of Commercial nZVI, Fe(2)@MF-700, Fe(4)@MF-700, Fe(6)@MF-700, Fe(4)@MF-600 and Fe(4)@MF-800;

[0036] Figure 2 The images show a TEM comparison of Fe(4)@MF-700, Commercial nZVI, Fe(2)@MF-700, and Fe(6)@MF-700, where (a) Commercial nZVI, (b) ...

[0037] Fe(2)@MF-700, (c) Fe(4)@MF-700 and (d) Fe(6)@MF-700;

[0038] Figure 3 Comparison of nitrogen adsorption-desorption for Fe(4)@MF-700, Fe(2)@MF-700, Fe(6)@MF-700 and Fe(4)@PMF-700; where (a) Fe(2)@MF-700, (b) Fe(4)@MF-700, (c) Fe(6)@MF-700 and (d) Fe(4)@PMF-700;

[0039] Figure 4 Commercial nZVI, Fe(2)@MF-700, Fe(4)@MF-700, Fe(6)@MF-700 and Fe(4)@PMF-700 are used to treat BrO3. - The reduction and removal curve;

[0040] Figure 5 XPS spectra of the peak fitting results of the N1s spectrum of Fe(4)@MF-600, 700 and 800 materials, where (a)Fe(4)@MF-600, (b)Fe(4)@MF-700 and (c)Fe(4)@MF-800;

[0041] Figure 6 Zeta curves for Fe(4)@MF-600, Fe(4)@MF-700 and Fe(4)@MF-800;

[0042] Figure 7 Water contact angle diagrams for Fe(4)@MF-600, Fe(4)@MF-700 and Fe(4)@MF-800, where (a) Fe(4)@MF-600, (b) Fe(4)@MF-700 and (c) Fe(4)@MF-800;

[0043] Figure 8BrO3 for Fe(4)@MF-600, Fe(4)@MF-700 and Fe(4)@MF-800 - The reduction and removal curve;

[0044] Figure 9 For different dosages of Fe(4)@MF-700, the effect of BrO3 was investigated. - The reduction and removal curve;

[0045] Figure 10 For different BrO3 - At the initial concentration, Fe(4)@MF-700 affects BrO3 - The reduction and removal curves and the fitting curves are shown, where (a) is the reduction and removal curve and (b) is the fitting curve;

[0046] Figure 11 Commercial nZVI and Fe(4)@MF-700 for the effect of BrO3 at different pH values - The reduction and removal curve. Detailed Implementation

[0047] This invention provides a method for preparing spherical resin-derived carbon-coated nano-zero-valent iron materials, comprising the following steps:

[0048] (1) Mix formaldehyde solution and melamine to obtain solution A;

[0049] Solution B is obtained by mixing ferric ammonium citrate and formaldehyde solution;

[0050] The solutions A and B are mixed to obtain a melamine-formaldehyde resin prepolymer solution;

[0051] (2) Mix the obtained melamine-formaldehyde resin prepolymer solution with anhydrous acetic acid to obtain solution C;

[0052] (3) The obtained solution C is added dropwise to an organic solution containing a surfactant for thermal polymerization to obtain resin particles;

[0053] (4) The obtained resin particles are carbonized under a protective atmosphere to obtain spherical resin-derived carbon-coated nano-zero-valent iron materials.

[0054] In this invention, during the preparation of solution A in step (1), the mass ratio of formaldehyde solution to melamine is 8-15:5, preferably 10-12:5; the mixing temperature of formaldehyde solution and melamine is 50-80°C, preferably 60-70°C; and the mixing time is 10-30 min, preferably 15-25 min, more preferably 18-20 min.

[0055] In the preparation of solution B, the mass ratio of ferric ammonium citrate to formaldehyde solution is 1:1.5 to 5, preferably 1:2.5 to 4;

[0056] The mass concentration of the formaldehyde solution used to prepare solution A and solution B is independently 35-40%, preferably 36-37%;

[0057] The mass ratio of melamine to ferric ammonium citrate is 5:2 to 6, preferably 5:3 to 5;

[0058] The mixing time for solutions A and B is 5 to 10 minutes, preferably 6 to 8 minutes.

[0059] In this invention, the volume ratio of melamine-formaldehyde resin prepolymer solution to anhydrous acetic acid in step (2) is 1:0.005 to 0.025, preferably 1:0.01 to 0.02; the mixing time is 1 to 10 min, preferably 4 to 7 min.

[0060] In this invention, the surfactant in step (3) comprises one or more of span-80, polyethylene glycol, carboxymethyl cellulose and sorbitol glyceride;

[0061] The organic solution contains one or more of 1,2-dichloroethane, carbon tetrachloride, n-hexane, n-heptane, and liquid paraffin;

[0062] The mass ratio of surfactant, melamine-formaldehyde resin prepolymer solution and organic solvent is 1:2 to 10:50 to 150, preferably 1:4 to 6:50 to 100;

[0063] The temperature of the thermal polymerization is 40–80°C, preferably 50–70°C, more preferably 55–65°C, and even more preferably 60°C; the time is 2–24 h, preferably 8–15 h.

[0064] In this invention, the carbonization temperature in step (4) is 700-900℃, preferably 750-800℃; the time is 2-4h, preferably 3h; and the heating rate is 1-5℃ / min, preferably 2-4℃ / min, and more preferably 3℃ / min.

[0065] The protective atmosphere consists of nitrogen or argon at a flow rate of 25–100 mL / min. -1 Preferably 50–75 mL min -1 .

[0066] The present invention also provides spherical resin-derived carbon-coated nano-zero-valent iron materials obtained by the aforementioned preparation method. The spherical resin particles in the material have a particle size range of 0.5–0.8 mm, preferably 0.6–0.7 mm; they are porous, with a specific surface area of ​​190.07–356.17 m².2 g -1 Preferably 250-300m 2 g -1 The iron content is 18.9–37.1 wt.%, preferably 25–30 wt.%.

[0067] In this invention, the particle size of the resin particles before carbonization ranges from 0.8 to 1 mm, preferably from 0.85 to 0.95 mm.

[0068] This invention also provides the method for reducing BrO3 in an aqueous phase using the aforementioned spherical resin-derived carbon-coated nano-zero-valent iron material. - Applications.

[0069] In this invention, the pH value of the aqueous system is 4 to 8.5, preferably 5 to 7; the amount of spherical resin-derived carbon-coated nano-zero-valent iron material is 0.5 to 1 g / L, preferably 0.625 to 0.8 g / L.

[0070] In this invention, BrO3 - The initial concentration is 0.02–0.08 mmol / L, preferably 0.04–0.06 mmol / L; the reduction time is 1–4 h, preferably 2–3 h.

[0071] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0072] The formaldehyde solution used in all embodiments of the present invention has a mass concentration of 37%.

[0073] Example 1

[0074] (1) Preparation of prepolymer solution: Mix 5g of melamine with 10g of formaldehyde solution and stir to dissolve in a 60℃ water bath. After the mixed solution becomes a colorless and transparent solution, cool it to room temperature and name it solution A. Dissolve 4g of ferric ammonium citrate in 6g of formaldehyde solution and name it solution B. Add solution B to solution A and stir for 10min to form an iron-containing melamine-formaldehyde resin prepolymer solution.

[0075] (2) Thermal polymerization of the prepolymer solution: 2g of SPAN-80 and 2g of polyethylene glycol were added to 200g of 1,2-dichloroethane and mixed thoroughly to obtain an organic solution containing a surfactant. 0.4mL of anhydrous acetic acid was added to the prepared prepolymer solution to promote polymerization. After stirring for 1 min, the mixture was added dropwise to the organic solution containing the surfactant, and stirred at 800 rpm to form uniform small droplets. The mixed solution was refluxed in a 60℃ water bath to thermally polymerize the prepolymer solution into resin particles for 4 h. After filtering the resin particles, they were washed several times with ethanol and then soaked in acetone for 12 h. The resin particles were then washed several times with hot water and ethanol, filtered, and dried in a vacuum oven at 80℃.

[0076] (3) Carbonization of resin particles: Spherical resin particles were carbonized under programmed temperature rise with nitrogen purging at a gas flow rate of 50 mL / min. -1 The heating rate was 5℃ / min, the carbonization target temperature was 700℃, and the holding time was 2h. Finally, spherical resin-derived carbon-coated nano zero-valent iron material Fe(4)@MF-700 was obtained.

[0077] Fe(4)@MF-700 was used as a reducing agent to reduce BrO3 in an aqueous phase. - The reaction was carried out under the following conditions: ambient temperature and pressure, mechanical stirring speed of 400 rpm, reaction time of 2 h, and BrO3. - The initial concentration of pollution was 0.04 mmol / L. -1 The initial pH of the reaction system was adjusted to 5.6 using H2SO4 or NaOH; the dosage of the material added was 0.5 g / L. -1 .

[0078] Comparative Example 1

[0079] Preparation of unmodified zero-valent iron nanoparticles. 1 g of commercially available iron nanoparticles with a particle size of approximately 100 nm were added to 100 mL of a 0.025 mol / L solution. -1 The surface oxide layer was removed by dilute hydrochloric acid after deoxygenation. After filtration and washing with deoxygenated water and anhydrous ethanol, the powder was dried in a vacuum oven at 60°C for 12 hours. The resulting gray-black powder was named CommercialnZVI.

[0080] Commercial nZVI was used as a reducing agent to reduce BrO3 in an aqueous phase. - The reaction was carried out under the following conditions: ambient temperature and pressure, mechanical stirring speed of 400 rpm, reaction time of 2 h, and BrO3. - The initial concentration of contamination was 0.04 mmol / L. -1The initial pH of the reaction system was adjusted to 5.6 using H2SO4 or NaOH; the dosage of the material added was 0.5 g / L. -1 .

[0081] Comparative Example 2

[0082] The amount of ferric ammonium citrate in step (1) of Example 1 was adjusted to 2g or 6g, and other implementation conditions were the same as in Example 1. Spherical resin-derived carbon-coated nano-zero-valent iron materials Fe(2)@MF-700 and Fe(6)@MF-700 with different iron loading were synthesized.

[0083] Materials Fe(2)@MF-700 and Fe(6)@MF-700 were used as reducing agents to reduce BrO3 in the aqueous phase. - The reaction was carried out under the following conditions: ambient temperature and pressure, mechanical stirring speed of 400 rpm, reaction time of 2 h, and BrO3. - The initial concentration of contamination was 0.04 mmol / L. -1 The initial pH of the reaction system was adjusted to 5.6 using H2SO4 or NaOH; the dosage of the material added was 0.5 g / L. -1 .

[0084] Comparative Example 3

[0085] The target carbonization temperature in step (3) of Example 1 was adjusted to 600℃ or 800℃, and other implementation conditions were the same as in Example 1. Spherical resin-derived carbon-coated nano-zero-valent iron materials Fe(4)@MF-600 and Fe(4)@MF-800 with different carbonization temperatures were synthesized.

[0086] Fe(4)@MF-600 and Fe(4)@MF-800 were used as reducing agents to reduce BrO3 in aqueous phase. - The reaction was carried out under the following conditions: ambient temperature and pressure, mechanical stirring speed of 400 rpm, reaction time of 2 h, and BrO3. - The initial concentration of contamination was 0.04 mmol / L. -1 The initial pH of the reaction system was adjusted to 5.6 using H2SO4 or NaOH; the dosage of the material added was 0.5 g / L. -1 .

[0087] Comparative Example 4

[0088] The spherical resin particles obtained in step (2) of Example 1 were ground into powder with a mesh size of less than 400 mesh, and then the powder was subjected to the carbonization step in step (3) of Example 1 to synthesize powdered resin-derived carbon-coated nano-zero-valent iron material Fe(4)@PMF-700.

[0089] Fe(4)@PMF-700 was used as a reducing agent to reduce BrO3 in an aqueous phase. - The reaction was carried out under the following conditions: ambient temperature and pressure, mechanical stirring speed of 400 rpm, reaction time of 2 h, and BrO3. - The initial concentration of pollution was 0.04 mmol / L. -1 The initial pH of the reaction system was adjusted to 5.6 using H2SO4 or NaOH; the dosage of the material added was 0.5 g / L. -1 .

[0090] The XRD comparison diagrams of Fe(4)@MF-700 prepared in Example 1, Commercial nZVI prepared in Comparative Example 1, and Fe(2)@MF-700 and Fe(6)@MF-700 prepared in Comparative Example 2 are shown below. Figure 1 As shown, all materials exhibit a distinct and sharp diffraction peak at 2θ = 44.67°, which is attributed to Fe. 0 Characteristic diffraction peaks were observed, and diffraction peaks belonging to Fe3C and graphitic carbon also appeared in the carbonized material. This indicates that during the carbonization process, iron species in the iron-containing melamine-formaldehyde resin can be reduced by carbonization to form zero-valent iron. Among them, Fe... 0 The intensity of the diffraction peaks of Fe3C increases with the increase of Fe doping during the preparation process.

[0091] The XRD patterns of Fe(4)@MF-700 prepared in Example 1 and Fe(4)@MF-600 and Fe(4)@MF-800 prepared in Comparative Example 3 are shown in the figure. Figure 1 As shown. Except for Fe(4)@MF-600 obtained by carbonization at 600℃, all other materials showed Fe. 0 The characteristic diffraction peaks of Fe3C and graphitic carbon indicate that, under a carbothermic temperature of 600℃, the degree of resin carbonization is insufficient to generate the active iron component. 0 The diffraction peak intensities of Fe3C and graphitic carbon all increase with increasing temperature.

[0092] TEM comparison images of Fe(4)@MF-700 prepared in Example 1, Commercial nZVI prepared in Comparative Example 1, and Fe(2)@MF-700 and Fe(6)@MF-700 prepared in Comparative Example 2 are shown below. Figure 2As shown in the figure, (a) represents Commercial nZVI, (b) represents Fe(2)@MF-700, (c) represents Fe(4)@MF-700, and (d) represents Fe(6)@MF-700. The figure shows that the average particle size of Commercial nZVI is 117.3 nm. The figure also shows that in the carbonized resin material, the darker areas represent zero-valent iron particles, while the lighter areas represent the carbon matrix. Fe particles are uniformly dispersed on the resin-derived carbon matrix. The average particle sizes of Fe(2)@MF-700, Fe(4)@MF-700, and Fe(6)@MF-700 are 6.9 nm, 7.5 nm, and 10.4 nm, respectively. This indicates that as the iron doping concentration increases during the preparation process, the zero-valent iron particles aggregate during carbonization, leading to an increase in particle size.

[0093] The nitrogen adsorption-desorption comparison diagrams of Fe(4)@MF-700 prepared in Example 1 and Fe(2)@MF-700 and Fe(6)@MF-700 prepared in Comparative Example 2 are shown below. Figure 3 As shown in Table 1, (a) Fe(2)@MF-700, (b) Fe(4)@MF-700, (c) Fe(6)@MF-700, and (d) Fe(4)@PMF-700 have specific surface areas. The nitrogen adsorption isotherms of all materials indicate that the pore structure is mesoporous and microporous; the specific surface area decreases with increasing iron doping concentration during preparation.

[0094] The nitrogen adsorption-desorption comparison diagram of Fe(4)@MF-700 prepared in Example 1 and Fe(4)@PMF-700 prepared in Comparative Example 4 is shown in the figure. Figure 3 As shown in Table 1, the specific surface area results indicate that the millimeter-sized spherical Fe(4)@MF-700 prepared in this study can achieve the specific surface area of ​​nano-sized powdered Fe(4)@PMF-700, thus demonstrating that it is a porous carbon material.

[0095] Table 1 Specific surface area results

[0096]

[0097] Fe(4)@MF-700 prepared in Example 1, Commercial nZVI prepared in Comparative Example 1, and Fe(2)@MF-700 and Fe(6)@MF-700 prepared in Comparative Example 2, on BrO3 - The comparison chart of the reduction and removal curves is as follows: Figure 4As shown in Table 2, when the reaction time was 120 min, the bromate removal rates of Commercial nZVI, Fe(2)@MF-700, Fe(4)@MF-700, and Fe(6)@MF-700 were 9.85%, 90.8%, 98.6%, and 99.8%, respectively. Combined with the iron content determination results in Table 2, the iron contents of the three materials were 18.9, 32.1, and 37.1 wt.%, respectively. Therefore, it can be inferred that the iron content in the material is positively correlated with the bromate removal rate, because the more reducing active components, the better the material's effect.

[0098] Fe(4)@MF-700 prepared in Example 1 and Fe(4)@PMF-700 prepared in Comparative Example 4 on BrO3 - The comparison chart of the reduction and removal curves is as follows: Figure 4 As shown. The prepared millimeter-sized spherical Fe(4)@MF-700 and nano-sized powdered Fe(4)@PMF-700 are compared with BrO3. - The reduction and removal capabilities are similar. Therefore, this invention synthesizes a large-sized iron-carbon composite material with high reactivity.

[0099] Table 2 Results of iron content determination

[0100]

[0101] The X-ray diffraction photoelectron spectroscopy (XPS) results of Fe(4)@MF-700 prepared in Example 1 and Fe(4)@MF-600 and Fe(4)@MF-800 prepared in Comparative Example 3 are shown in Table 3. With increasing carbonization temperature, the proportion of C on the material surface increases, while the proportions of O and N decrease. This may be due to the volatilization of some unstable N- and O-containing groups during carbonization. On the other hand, with increasing carbonization temperature, the carbonization becomes more thorough, the carbon matrix shrinks, and the thickness of the carbon layer increases, thus reducing the proportion of Fe on the surface.

[0102] Table 3. X-ray diffraction photoelectron spectroscopy (XPS) results

[0103]

[0104] The peak fitting results of the N1s spectra of Fe(4)@MF-600, 700, and 800 materials are as follows: Figure 5As shown, (a) Fe(4)@MF-600, (b) Fe(4)@MF-700, and (c) Fe(4)@MF-800. Three forms of nitrogen species are present: pyrrole nitrogen (398.3 eV), pyridine nitrogen (399.9 eV), and graphitic nitrogen (401.1 eV). With increasing carbonization temperature, pyrrole and pyridine nitrogen species on the material surface transform into graphitic nitrogen species. Because pyridine nitrogen has a strong electron-donating ability, it can effectively increase Lewis basic sites and improve the redox activity of the material. Unstable pyrrole nitrogen species can form certain defect sites, increasing the surface activity of the material. The introduction of graphitic nitrogen will increase the electrical conductivity of the material to some extent.

[0105] The Zeta potential versus pH curves of Fe(4)@MF-700 prepared in Example 1 and Fe(4)@MF-600 and Fe(4)@MF-800 prepared in Comparative Example 3 are shown below. Figure 6 As shown. The intersection of the curve and y=0 is the isoelectric point (IEP) of the material. When the pH of the solution is lower than the isoelectric point of the material, the material surface is positively charged and has an electrostatic adsorption effect on anions in the aqueous solution. Studies have shown that introducing nitrogen-containing groups such as pyrrole nitrogen and pyridine nitrogen onto the material surface can improve the material's IEPs. The isoelectric points of Fe(4)@MF-600, Fe(4)@MF-700, and Fe(4)@MF-800 are 6.07, 5.70, and 5.35, respectively. As the carbothermic temperature increases, the isoelectric point of the material surface decreases. This is because when the carbothermic temperature increases from 600℃ to 800℃, the pyrrole nitrogen and pyridine nitrogen on the material surface may be converted into graphitic nitrogen, leading to a decrease in the basic sites on the material surface. This conclusion is consistent with the XPS analysis results.

[0106] The water contact angles of Fe(4)@MF-700 prepared in Example 1 and Fe(4)@MF-600 and Fe(4)@MF-800 prepared in Comparative Example 3 are as follows: Figure 7 As shown, (a) Fe(4)@MF-600, (b) Fe(4)@MF-700, and (c) Fe(4)@MF-800 are examples. The water contact angle is the angle between the solid-liquid interface, through the liquid interior, and at the gas-liquid interface at the solid-liquid-gas three-phase junction. It can be used to characterize the hydrophilicity or hydrophobicity of a material surface. When the water contact angle θ < 90°, the material surface is hydrophilic; when θ > 90°, the material surface is hydrophobic. As shown in the figure, the water contact angle of all materials is less than 90°. With the increase of carbothermic temperature, the water contact angle increases, and the hydrophilicity of the material surface decreases. This is related to the loss of nitrogen elements from the material surface when the temperature increases.

[0107] The Fe(4)@MF-700 prepared in Example 1 and the Fe(4)@MF-600 and Fe(4)@MF-800 prepared in Comparative Example 3 on BrO3 - The comparison chart of the reduction and removal curves is as follows: Figure 8 As shown. The results showed that under the same reaction conditions, Fe(4)@MF-600 only achieved a bromate removal rate of 6.2%. Combined with the XRD results, it can be seen that at low carbonothermic temperatures, iron species in the resin are difficult to be reduced to the iron active component (Fe). 0 The material has low reduction activity (Fe3C). When the temperature is increased to 700℃, Fe(4)@MF-700 can almost completely remove bromate from water within 2 hours. This is because as the temperature increases, the iron species in the resin are reduced to the iron active component (Fe3C). 0 With the increase of zero-valent iron content (Fe3C), the graphite nitrogen content on the material surface increases, improving the conductivity of the material. This increases the content of active components and enhances the electron transfer efficiency during the reaction process, thereby enhancing the reaction activity. When the temperature continues to rise to 800℃, the removal rate of bromate by Fe(4)@MF-800 decreases to 81%. Combined with XPS and Zeta results, it is found that as the carbonization temperature increases, the nitrogen content of the material is lost, the isoelectric point decreases, resulting in a reduction of alkaline sites on the material surface, weakening the adsorption effect on bromate and reducing the reduction activity.

[0108] Example 2

[0109] To investigate the effect of different material dosages on the reduction and removal of BrO3 - Due to the influence of [unclear], the amount of Fe(4)@MF-700 in Example 1 was adjusted to 0.25 g L. -1 0.375g L -1 0.50g L -1 0.625g L -1 and 1g L -1 The remaining conditions are the same as in Example 1.

[0110] Fe(4)@MF-700 with different material dosages affects BrO3 - The comparison chart of the reduction and removal curves is as follows: Figure 9 As shown. When the dosage of Fe(4)@MF-700 is only 0.25 g L -1 At that time, BrO3 in the solution could not be completely removed within 120 minutes. - Only 61% of bromate was converted. The removal efficiency of bromate improved with increasing dosage, reaching a higher efficiency when the dosage was 1 g / L. -1 At that time, the material could completely remove BrO3 within 40 minutes. - This indicates that increasing the amount of material added can improve the material's response to BrO3. - The removal effect is significant. This is because as the dosage increases, the contact sites between the material and bromate in the aqueous solution increase, and the active components also increase, enabling the reduction of more bromate anions.

[0111] Example 3

[0112] To investigate the effect of different initial concentrations of pollutants on the reduction and removal of bromate, BrO3 from Example 1 was used... - The initial concentration of pollution was adjusted to 0.02 mmol / L. -1 0.06 mmol / L -1 and 0.08 mmol L- 1 The remaining conditions are the same as in Example 1.

[0113] Fe(4)@MF-700 for different initial concentrations of BrO3 - The comparison chart of the reduction and removal curves is as follows: Figure 10 As shown, (a) different BrO3 - At the initial concentration, Fe(4)@MF-700 affects BrO3 - (a) Reduction and removal curve; (b) Fitted curve. As shown in the figure, BrO3... - The initial concentration was 0.02 mmol / L. -1 and 0.04 mmol L -1 At that time, Fe 0 (4) The MF-700 material can completely remove BrO3 within 2 hours. - When BrO3 - The initial concentration was increased to 0.06 mmol / L. -1 and 0.08 mmol L -1 At that time, the material reacted with BrO3 - The removal rates were only 75% and 62%, respectively. This is because, with the same amount of material added, increasing BrO3... - The initial concentration will lead to adsorption saturation, and some BrO3 in the solution will be saturated. - It cannot be reduced. To further investigate BrO3... - The relationship between the reduction removal reaction and the adsorption capacity of the material surface was calculated for different BrO3. - The initial activity of the reaction at the initial concentration was determined, and the reciprocal 1 / r0 of the initial activity and the reciprocal 1 / C0 of the initial concentration were fitted using the Langmuir-Hinshelwood kinetic model. The results are shown in the figure. BrO3 - The initial concentration was 0.02 mmol / L. -1 Rising to 0.08 mmol / L -1 At that time, the fitting results showed good correlation (R0). 2 =0.9998), indicating that the reaction rate is affected by the adsorption rate on the material surface. The entire reaction can be described as BrO3 - The electrons adsorbed onto the material surface are reduced to Br- by the electrons transferred from the iron nucleus of the material.

[0114] Example 4

[0115] To investigate the effect of different reaction pH values ​​on the reduction and removal of bromate, the pH values ​​of the reactions in Example 1 and Comparative Example 1 were adjusted to 4.0, 7.0, and 8.5, respectively, while other conditions remained the same as in Example 1 and Comparative Example 1. Analysis of the XPS and Zeta characterization results revealed that the effect of pH value on the reduction and removal efficiency of bromate can be summarized in two aspects: First, bromate is reduced by electrons transferred from the iron active component on the material surface. The main reaction equation is as follows:

[0116]

[0117] As can be seen from the reaction equation, the reduction reaction of bromate requires the consumption of H₂. + Therefore, the lower the pH, the higher the H + Higher concentrations can promote the forward reduction reaction of bromate.

[0118] Secondly, XPS results show that Fe prepared by carbonization at 700℃ 0 (4) The surface of @MF-700 contains pyrrole nitrogen and pyridine nitrogen, which can enhance the surface positive charge of the material, and Fe 0 (4) The isoelectric point of @MF-700 was measured to be 5.70 by Zeta potentiometer. When the pH value of the solution is less than 5.70, the surface of the material is positively charged and has an electrostatic adsorption effect on bromate anions, which promotes the reduction of bromate by the material.

[0119] Depend on Figure 11 It was found that when the bromate solution changed from alkaline (pH=8.5) to acidic (pH=4), the reduction and removal activities of CommercialnZVI and Fe(4)@MF-700 on bromate were enhanced. The removal rate of bromate by CommercialnZVI increased from 3% to 12%, and the removal rate of bromate by Fe(4)@MF-700 increased from 94% to 99.7%. This indicates that acidic conditions can enhance the reduction and removal of bromate. It is worth mentioning that Fe(4)@MF-700 also has a good removal effect under alkaline conditions. This shows that Fe(4)@MF-700 material can maintain stable reduction activity over a wide range of pH values, can adapt to different types of aquatic environments, and has broad application prospects in practical water remediation projects.

[0120] Example 5

[0121] To investigate the dissolution of iron ions during the reduction and removal of bromate, the solution after 2 hours of reaction was filtered and the Fe content in the solution was determined using the o-phenanthroline spectrophotometric method. 3+Due to limitations in the accuracy of ultraviolet spectrophotometry, the concentration range is used to represent the iron dissolution level in the solution. Table 4 shows that the iron dissolution level of the resin-coated nano-zero-valent iron material during the reaction process is lower than the minimum standard solution concentration and far lower than the iron dissolution level of Commercial nZVI. This indicates that the spherical resin-derived carbon-coated nano-zero-valent iron material Fe(4)@MF-700 prepared in this invention has higher reducing power and stability than the traditional commercial nano-zero-valent iron material Commercial nZVI. It fully complies with the regulations in the drinking water hygiene standards.

[0122] Table 4. Iron dissolution levels in solution

[0123]

[0124] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing spherical resin-derived carbon-coated nano-zero-valent iron materials, characterized in that, It includes the following steps: (1) Mix formaldehyde solution and melamine to obtain solution A; Solution B is obtained by mixing ferric ammonium citrate and formaldehyde solution; The solutions A and B are mixed to obtain a melamine-formaldehyde resin prepolymer solution; (2) Mix the obtained melamine-formaldehyde resin prepolymer solution with anhydrous acetic acid to obtain solution C; (3) The obtained solution C is added dropwise to an organic solution containing a surfactant for thermal polymerization to obtain resin particles; (4) The obtained resin particles are carbonized under a protective atmosphere to obtain spherical resin-derived carbon-coated nano-zero-valent iron materials.

2. The preparation method according to claim 1, characterized in that, In step (1), during the preparation of solution A, the mass ratio of formaldehyde solution to melamine is 8-15:5, the mixing temperature of formaldehyde solution and melamine is 50-80℃, and the mixing time is 10-30 min. In the preparation of solution B, the mass ratio of ferric ammonium citrate to formaldehyde solution is 1:1.5 to 5; The mass concentrations of the formaldehyde solutions used in preparing solution A and solution B are independently 35-40%; The mass ratio of melamine to ferric ammonium citrate is 5:2 to 6; The mixing time for solutions A and B is 5–10 minutes.

3. The preparation method according to claim 1 or 2, characterized in that, In step (2), the volume ratio of melamine-formaldehyde resin prepolymer solution to anhydrous acetic acid is 1:0.005 to 0.025, and the mixing time is 1 to 10 min.

4. The preparation method according to claim 3, characterized in that, The surfactant in step (3) comprises one or more of Span-80, polyethylene glycol, carboxymethyl cellulose, and sorbitol glyceride; The organic solution contains one or more of 1,2-dichloroethane, carbon tetrachloride, n-hexane, n-heptane, and liquid paraffin; The mass ratio of surfactant, melamine-formaldehyde resin prepolymer solution and organic solvent is 1:2 to 10:50 to 150; The thermal polymerization temperature is 40–80°C, and the time is 2–24 hours.

5. The preparation method according to claim 1, 2, or 4, characterized in that, In step (4), the carbonization temperature is 700-900℃, the time is 2-4h, and the heating rate is 1-5℃ / min; The protective atmosphere consists of nitrogen or argon gas at a flow rate of 25–100 mL / min. -1 .

6. The spherical resin-derived carbon-coated nano-zero-valent iron material obtained by the preparation method according to any one of claims 1 to 5, characterized in that, The spherical resin particles in the material range in size from 0.5 to 0.8 mm, are porous, and have a specific surface area of ​​190.07 to 356.17 m². 2 g -1 The iron content ranges from 18.9% to 37.1 wt.%.

7. The spherical resin-derived carbon-coated nano-zero-valent iron material of claim 6 for reducing BrO3 in aqueous phase - Applications.

8. The application according to claim 7, characterized in that, The pH value of the aqueous system is 4 to 8.5, and the amount of spherical resin-derived carbon-coated nano-zero-valent iron material used is 0.5 to 1 g / L.

9. The application according to claim 7 or 8, characterized in that, BrO3 - The initial concentration was 0.02–0.08 mmol / L. -1 The restoration time is 1 to 4 hours.

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