Method for removing nitrate from water using modified zero-valent iron aerogel electrocatalyst

Abstract

The present invention provides a method for removing nitrate from water using a modified zero-valent iron aerogel electrocatalyst. The method comprises the following steps: preparing a mixed solution of ferrous sulfate and sodium sulfide, preparing a sodium borohydride solution, mixing the two and magnetically stirring them to obtain a black colloid, and finally obtaining a sulfide zero-valent iron aerogel; dispersing the obtained sulfide zero-valent iron aerogel and a Nafion solution in anhydrous ethanol to prepare a catalyst mixture; dissolving potassium nitrate and potassium hydroxide in a pure water solution as an electrolyte; performing an electrocatalytic reduction reaction using a three-electrode system, using a sulfide zero-valent iron aerogel electrode as a cathode, a platinum sheet as an anode, and a mercury oxide electrode as a reference electrode. This technology not only improves the efficiency of nitrate pollution control in water bodies, but also conforms to the concept of green and low-carbon development and has broad environmental application prospects.

Description

Technical Field

[0001] The present invention mainly relates to the technical field related to water treatment, and specifically to a method for removing nitrate from water using a modified zero-valent iron aerogel electrocatalyst. Background Art

[0002] The rapid development of modern industry has greatly promoted socioeconomic progress, but it has also led to the discharge of large amounts of pollutants, particularly the increasingly serious problem of nitrate-containing wastewater. Nitrate (NO⁻), a major pollutant in industrial, agricultural, and municipal wastewater, originates from a wide range of sources, including fertilizer application, mining, metal smelting, electroplating wastewater, and food processing. Due to its high water solubility and chemical stability, nitrate's accumulation in aquatic environments has long been a global environmental concern.

[0003] Currently, treatment methods for nitrate-containing wastewater primarily include physical methods (ion exchange, reverse osmosis), chemical methods (chemical reduction, catalytic reduction), and biological methods (heterotrophic and autotrophic denitrification). However, these methods still face numerous limitations in practical application. For example, while ion exchange and reverse osmosis can effectively remove nitrates, they are energy-intensive, prone to resin saturation, and require frequent replacement. Biological denitrification is sensitive to environmental conditions, susceptible to factors such as temperature and pH, and requires prolonged treatment times. Traditional chemical catalytic reduction methods (such as Cu-Zn reduction) typically require the use of external reducing agents such as hydrogen or formic acid, which not only increases operating costs but also may lead to secondary pollution. Therefore, the development of efficient, low-cost, and environmentally friendly nitrate removal technologies has become a research hotspot in water pollution control.

[0004] In recent years, electrocatalytic nitrate reduction technology has garnered widespread attention due to its environmental sustainability, ease of operation, and strong selectivity. This technology utilizes catalytic reactions on the electrode surface to regulate the electron transfer process, gradually reducing nitrate to nitrogen (N2) under the action of an applied electric field. Compared to traditional methods, electrocatalytic nitrate reduction not only avoids the addition of chemical reagents but also enables efficient nitrogen generation at room temperature and pressure. However, existing electrocatalytic materials still suffer from low catalytic activity, insufficient selectivity, and excessive byproducts (such as ammonia and nitrite), which limit the large-scale application of this technology.

[0005] Zero valent iron (Fe 0 ) show great potential in electrocatalytic nitrate reduction due to their excellent electron transfer ability and low cost. However, traditional zero-valent iron materials have low catalytic efficiency and stability and are prone to surface oxidation and passivation, resulting in decreased catalytic activity. Summary of the Invention

[0006] To address the shortcomings of current technologies, this paper combines existing technologies with practical applications to provide a method for removing nitrate from water using a modified zero-valent iron aerogel electrocatalyst. By introducing an appropriate amount of sulfur doping into the zero-valent iron aerogel, an effective sulfur site network is constructed, significantly improving the selectivity and efficiency of the electrocatalytic reaction and achieving efficient conversion of nitrate to nitrogen. This technology not only improves the efficiency of nitrate pollution control in water bodies but also aligns with the concept of green and low-carbon development, promising broad environmental applications.

[0007] The technical solutions of the present invention are as follows:

[0008] A method for removing nitrate from water using a modified zero-valent iron aerogel electrocatalyst comprises the following steps:

[0009] Step 1: dissolving ferrous sulfate and sodium sulfide simultaneously in a pure water solution treated with nitrogen aeration, stirring them evenly with a magnetic stirrer for later use;

[0010] Step 2: dissolving sodium borohydride in a pure water solution aerated with nitrogen, stirring the solution evenly with magnetic stirring for later use;

[0011] Step 3: The solution obtained in step 1 is quickly mixed with the solution obtained in step 2, and magnetic stirring is performed to obtain a black colloid, which is then subjected to aging treatment;

[0012] Step 4: Filter and collect the black colloidal product obtained in step 3, and wash it with deionized water and tert-butanol multiple times, and freeze-dry the washed colloid to obtain sulfide zero-valent iron aerogel;

[0013] Step 5: Dispersing the sulfide zero-valent iron aerogel obtained in Step 4 and a 5 wt.% Nafion solution in anhydrous ethanol, ultrasonically treating to ensure uniform mixing, and preparing a catalyst mixture; then, coating the prepared catalyst mixture on both sides of carbon paper to form a working electrode, and then drying the coated carbon paper in an oxygen-free glove box at room temperature;

[0014] Step 6: dissolving potassium nitrate and potassium hydroxide in a pure water solution as an electrolyte;

[0015] Step 7: injecting the electrolyte prepared in step 6 into the anode chamber and cathode chamber of the H-type electrolytic cell; using the sulfide zero-valent iron aerogel electrode prepared in step 5 as the cathode, a platinum sheet as the anode, and a mercury oxide electrode as the reference electrode, and performing an electrocatalytic reduction reaction using a three-electrode system;

[0016] Step 8: Continuously introduce argon gas into the cathode chamber, apply a constant voltage, and start the nitrate electrocatalytic reduction reaction. After a period of reaction, the nitrate dye can be selectively converted into nitrogen for harmless treatment.

[0017] Furthermore, in step 1, the molar concentration ratio of ferrous sulfate and sodium sulfide after being dissolved in pure aqueous solution is 10:1;

[0018] In step 2, the molar ratio of the concentration of sodium borohydride dissolved in pure aqueous solution to the molar ratio of ferrous sulfate dissolved in pure aqueous solution in step 1 is 5:1;

[0019] In step 3, the solution obtained in step 1 and the solution obtained in step 2 are mixed in a volume ratio of 9:1.

[0020] Furthermore, in step 1, the concentration of ferrous sulfate is 10 mmol / L, and the concentration of sodium sulfide is 1 mmol / L;

[0021] In step 2, the concentration of sodium borohydride is 50 mmol / L.

[0022] Furthermore, in step 3, the aging time of the black colloid is not less than 2 hours; and in step 4, the alternating freeze-drying time after washing is not less than 20 hours.

[0023] Furthermore, in step 5, the sulfide zero-valent iron aerogel, Nafion solution and anhydrous ethanol are mixed in the following ratio: 5 mg of sulfide zero-valent iron aerogel corresponds to 20 μl of 5 wt.% Nafion solution and 980 μl of anhydrous ethanol.

[0024] Furthermore, in step 6, the molar concentration ratio of potassium nitrate and potassium hydroxide after being dissolved in pure aqueous solution is 1:(25-30).

[0025] Furthermore, in step 6, the concentration of potassium nitrate after being dissolved in pure aqueous solution is 360 mg / L, and the concentration of potassium hydroxide after being dissolved in pure aqueous solution is 0.1 mol / L.

[0026] Beneficial effects of the present invention:

[0027] (1) The sulfide zero-valent iron aerogel catalyst used in the present invention has a simple preparation process, high stability, and high selectivity for the reduction of nitrate pollutants.

[0028] (2) When using the new electrocatalytic reduction method constructed by the present invention to treat nitrate pollutants in water, it can effectively avoid the limitations of traditional electrocatalytic reduction methods such as high energy consumption, high material consumption and high carbon emissions. There is no need to add a large amount of chemical reagents, and the reaction is carried out at room temperature and pressure, which has good environmental adaptability.

[0029] (3) The sulfide zero-valent iron aerogel catalyst prepared by the present invention can achieve a higher nitrate conversion rate and nitrogen selectivity yield, and has a longer service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1This is a high-magnification transmission electron microscopy image of the sulfide zero-valent iron aerogel in Example 1;

[0031] Figure 2 This is a comparison chart of nitrate removal efficiency and nitrogen selectivity performance of Example 1 and Comparative Examples 1-2 under different electrode conditions;

[0032] Figure 3 This is the product distribution diagram of the electrocatalytic reduction of nitrate by sulfide zero-valent iron aerogel at different times in Example 1;

[0033] Figure 4 This is a performance diagram of the continuous flow cycle use of the sulfide zero-valent iron aerogel electrode in Example 1;

[0034] Figure 5 The figure is a comparison chart of nitrogen selectivity performance of Example 1 and Comparative Examples 3-6 under different initial potassium nitrate concentration conditions. DETAILED DESCRIPTION

[0035] The present invention will be further described with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the contents of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the present application.

[0036] Example 1:

[0037] This embodiment provides a method for removing nitrate from water using a modified zero-valent iron aerogel electrocatalyst, and the steps are as follows:

[0038] (1) Dissolve ferrous sulfate and sodium sulfide simultaneously in a pure water solution treated with nitrogen aeration, stir magnetically and set aside; wherein the concentration of ferrous sulfate is 10 mmol / L; the concentration of sodium sulfide is 1 mmol / L;

[0039] (2) Dissolve sodium borohydride in a nitrogen-aerated pure water solution, stir magnetically and set aside; wherein the concentration of sodium borohydride is 50 mmol / L;

[0040] (3) The solution obtained in step 1 and the solution obtained in step 2 were quickly mixed, magnetically stirred to obtain a black colloid, and then aged for 2 hours;

[0041] (4) The black colloidal product obtained in step 3 was collected by filtration and washed three times with deionized water and tert-butanol respectively. The washed colloid was freeze-dried for 20 hours to obtain sulfide zero-valent iron aerogel;

[0042] (5) Weigh 5 mg of the sulfide zero-valent iron aerogel obtained in step 4 and disperse it with 20 μL of 5 wt.% Nafion solution in 980 μL of anhydrous ethanol, and ultrasonicate for 30 minutes to ensure uniform mixing to prepare a catalyst mixture; then, apply 80 μL of catalyst ink on a 1×1 cm 2 On both sides of the carbon paper, the working electrode area is controlled to 2 cm 2 ; The coated carbon paper was then placed in an oxygen-free glove box and dried at room temperature for 6 hours;

[0043] (6) Potassium nitrate and potassium hydroxide were dissolved in pure water as electrolyte, with the concentrations of potassium nitrate and potassium hydroxide being 360 mg / L and 0.1 mol / L, respectively;

[0044] (7) The electrolyte prepared in step 6 was injected into the anode chamber and cathode chamber of the H-type electrolytic cell; the zero-valent iron aerogel electrode prepared in step 5 was used as the cathode, and the platinum sheet (1 × 1 cm 2 ) as the anode, a mercury oxide electrode as the reference electrode, and a three-electrode system for electrocatalytic reduction reaction;

[0045] (8) Argon gas is continuously introduced into the cathode chamber, and a constant voltage is applied to initiate the nitrate electrocatalytic reduction reaction. After a period of reaction, the nitrate dye can be selectively converted into nitrogen for harmless treatment. The constant voltage applied is −0.6 V vs. RHE, and the reaction time is 8 hours.

[0046] The high magnification transmission electron microscope image of the sulfide zero-valent iron aerogel prepared in Example 1 is as follows: Figure 1 The image in the upper left corner of the frame is an enlarged view of the crystal area. The image shows that the aerogel has a unique core-shell structure. Its crystalline Fe core is wrapped by a thin layer of amorphous S-rich shell. The fast Fourier transform and inverse fast Fourier transform results show that it conforms to the lattice parameters. Figure 2 It can be seen that using the sulfide zero-valent iron aerogel electrode, nitrate can be removed by 100% within 8 hours, and the selectivity for nitrogen can reach 85.6%. This result shows that the electrocatalytic reduction system with sulfide zero-valent iron aerogel as the cathode can simultaneously achieve the removal of nitrate and directional conversion to nitrogen for harmless treatment under ambient conditions. In addition, after 20 consecutive cycles of use, the catalytic activity of the sulfide zero-valent iron aerogel electrode was not significantly inhibited, indicating that it has high stability ( Figure 4 ).

[0047] Comparative Example 1:

[0048] Comparative Example 1 uses the method of Example 1 to remove nitrate from water, with the difference that in step (1), only ferrous sulfate with a concentration of 10 mmol / L is used, and sodium sulfide is not used, and zero-valent iron aerogel is obtained in step (4).

[0049] Comparative Example 2:

[0050] Comparative Example 2 uses the method of Comparative Example 1 to remove nitrate from water, with the difference being that the solution obtained in step 1 and the solution obtained in step 2 are slowly mixed and magnetically stirred to obtain black particles, and zero-valent iron nanoparticles are obtained in step (4).

[0051] Depend on Figure 2 A comparison of the nitrate removal rate and nitrogen selectivity performance of Example 1, Comparative Example 1, and Comparative Example 2 under different electrode conditions is provided. It can be seen that when using zero-valent iron aerogel and zero-valent iron nanoparticle electrodes as cathodes, although 100% nitrate removal from water is achieved within 8 hours, the selectivity for nitrogen is only 7.3% and 15.2%, respectively, indicating that the zero-valent iron aerogel catalyst has no selectivity for the catalytic reduction of nitrate to nitrogen.

[0052] Depend on Figure 2 、 Figure 3 It can be seen that when sulfide zero-valent iron aerogel is used as the cathode, nitrate in water can be removed by 100% within 8 hours, while ammonia nitrogen and nitrite nitrogen by-products are significantly suppressed, and its selectivity for nitrogen can reach 85.6%. Compared with the catalytic performance of zero-valent iron aerogel, it can be found that the introduction of sulfur element can promote the electrocatalytic reduction of nitrate by sulfide zero-valent iron aerogel to the harmless and directional conversion of nitrogen.

[0053] Comparative Example 3:

[0054] The difference between this comparative example 3 and example 1 is that the initial potassium nitrate concentration in the electrolyte in step (6) is adjusted to 180 mg / L.

[0055] Comparative Example 4:

[0056] The difference between this comparative example 4 and example 1 is that the initial potassium nitrate concentration in the electrolyte in step (6) is adjusted to 720 mg / L.

[0057] Comparative Example 5

[0058] The difference between this comparative example and Example 1 is that the initial potassium nitrate concentration in the electrolyte in step (6) is adjusted to 1080 mg / L.

[0059] Comparative Example 6

[0060] The difference between this comparative example and Example 1 is that the initial potassium nitrate concentration in the electrolyte in step (6) is adjusted to 1440 mg / L.

[0061] The selectivity of the electrocatalytic reduction system for converting nitrate to nitrogen under different initial potassium nitrate concentrations in Example 1 and Comparative Examples 3 to 6 is as follows: Figure 5 The results show that sulfide zero-valent iron aerogel can achieve harmless directional conversion of nitrate to nitrogen in a wide range of nitrate concentrations, but the best effect is achieved when the potassium nitrate concentration is 360 mg / L.

[0062] It can be seen from the above embodiments and comparative examples that the method provided by the present invention for selectively converting nitrate in water into nitrogen by using electrocatalytic reduction can not only achieve the effect of purifying wastewater, but also simultaneously realize the harmless and directional conversion of nitrate.

Claims

1. A method for removing nitrate from water using a modified zero-valent iron aerogel electrocatalyst, characterized in that: The steps include: Step 1: dissolving ferrous sulfate and sodium sulfide simultaneously in a pure water solution treated with nitrogen aeration, stirring them evenly with a magnetic stirrer for later use; Step 2: dissolving sodium borohydride in a pure water solution aerated with nitrogen, stirring the solution evenly with magnetic stirring for later use; Step 3: The solution obtained in step 1 is quickly mixed with the solution obtained in step 2, and magnetic stirring is performed to obtain a black colloid, which is then subjected to aging treatment; Step 4: Filter and collect the black colloidal product obtained in step 3, and wash it with deionized water and tert-butanol multiple times, and freeze-dry the washed colloid to obtain sulfide zero-valent iron aerogel; Step 5: Dispersing the sulfide zero-valent iron aerogel obtained in Step 4 and a 5 wt.% Nafion solution in anhydrous ethanol, ultrasonically treating to ensure uniform mixing, and preparing a catalyst mixture; then, coating the prepared catalyst mixture on both sides of carbon paper to form a working electrode, and then drying the coated carbon paper in an oxygen-free glove box at room temperature; Step 6: dissolving potassium nitrate and potassium hydroxide in a pure water solution as an electrolyte; Step 7: injecting the electrolyte prepared in step 6 into the anode chamber and cathode chamber of the H-type electrolytic cell; using the sulfide zero-valent iron aerogel electrode prepared in step 5 as the cathode, a platinum sheet as the anode, and a mercury oxide electrode as the reference electrode, and performing an electrocatalytic reduction reaction using a three-electrode system; Step 8: Continuously introduce argon gas into the cathode chamber, apply a constant voltage, and start the nitrate electrocatalytic reduction reaction. After a period of reaction, the nitrate dye can be selectively converted into nitrogen for harmless treatment.

2. The method for removing nitrate from water using a modified zero-valent iron aerogel electrocatalyst according to claim 1, characterized in that: In step 1, the molar concentration ratio of ferrous sulfate and sodium sulfide after being dissolved in pure aqueous solution is 10:1; In step 2, the molar ratio of the concentration of sodium borohydride dissolved in pure aqueous solution to the molar ratio of ferrous sulfate dissolved in pure aqueous solution in step 1 is 5:1; In step 3, the solution obtained in step 1 and the solution obtained in step 2 are mixed in a volume ratio of 9:

1.

3. The method for removing nitrate from water using a modified zero-valent iron aerogel electrocatalyst according to claim 2, wherein: In step 1, the concentration of ferrous sulfate is 10 mmol / L and the concentration of sodium sulfide is 1 mmol / L; In step 2, the concentration of sodium borohydride is 50 mmol / L.

4. The method for removing nitrate from water using a modified zero-valent iron aerogel electrocatalyst according to claim 1, wherein: In step 3, the black colloid is aged for no less than 2 hours; and in step 4, the alternating freeze-drying time after washing is no less than 20 hours.

5. The method for removing nitrate from water using a modified zero-valent iron aerogel electrocatalyst according to claim 1, wherein: In step 5, the sulfide zero-valent iron aerogel, Nafion solution, and anhydrous ethanol are mixed in the following ratio: 5 mg of sulfide zero-valent iron aerogel corresponds to 20 μL of 5 wt.% Nafion solution and 980 μL of anhydrous ethanol.

6. The method for removing nitrate from water using a modified zero-valent iron aerogel electrocatalyst according to claim 1, wherein: In step 6, the molar concentration ratio of potassium nitrate and potassium hydroxide after being dissolved in pure aqueous solution is 1:(25-30).

7. The method for removing nitrate from water using a modified zero-valent iron aerogel electrocatalyst according to claim 6, characterized in that: In step 6, the concentration of potassium nitrate after being dissolved in pure water solution is 360 mg / L, and the concentration of potassium hydroxide after being dissolved in pure water solution is 0.1 mol / L.

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