Preparation method and application of carbon-supported nanometer Fe-Cu bimetallic composite for treating nitrate nitrogen

Abstract

The application relates to the development and application fields of water treatment functional materials, and discloses a preparation method and application of a carbon-loaded nanometer Fe-Cu bimetallic composite material for treating nitrate nitrogen, which comprises the following steps: preparing biochar by high-temperature pyrolysis treatment of wheat straw after treatment; under the condition of nitrogen, the biochar is subjected to ultrasonic homogenization treatment with a ferrous sulfate solution; a sodium borohydride solution and a copper sulfate solution are added; and the carbon-loaded nanometer Fe-Cu bimetallic composite material is prepared through ultrasonic homogenization and freeze drying; when the dosing amount of the nitrate nitrogen to be removed is 3-6 g / L, the pH is 4-10, and the reaction time is 90 min, the removal rate of the nitrate nitrogen can reach more than 98 %.

Description

Technical Field

[0001] This invention relates to the field of water treatment functional materials development and application technology, and in particular to a method for preparing and applying a carbon-supported nano-Fe-Cu bimetallic composite material for treating nitrate nitrogen. Background Technology

[0002] Nitrate nitrogen (NO3-N) pollution is a pressing water environment problem worldwide. In recent years, industrial and domestic wastewater discharge, as well as the use of nitrogen fertilizers and pesticides in rural areas, have led to abnormally high levels of nitrate nitrogen in water. When the nitrate nitrogen content in environmental water bodies is too high, it can cause eutrophication and reduce the biodiversity of aquatic ecosystems. Irrigating farmland with water bodies containing excessive nitrate nitrogen can damage the root tissues of crops. Excessive nitrate nitrogen accumulated during the growth and development of crops can be converted into nitrite nitrogen, which is harmful to the human body. After entering the human body, nitrite nitrogen can cause cell carcinogenesis and liver damage. Excessive nitrate nitrogen can also cause vision and intellectual impairment, and even death. The maximum safe content of nitrate nitrogen in drinking water is limited to below 10 mg / L.

[0003] Nano-zero-valent iron is a functional material for aquatic environments, possessing advantages such as strong reducing properties and high removal capacity. However, nano-zero-valent iron is prone to oxidation and aggregation, with its surface structure mainly consisting of aggregates in chains or clusters. This reduces the contact area with nitrate nitrogen, thereby decreasing the reactivity of nano-zero-valent iron and resulting in a slow nitrate nitrogen removal rate. Simultaneously, nano-zero-valent iron reduces nitrate nitrogen in water to ammonia nitrogen or nitrogen gas. During the reduction process, the selectivity for nitrogen gas is poor, and the reduction product is mainly ammonia nitrogen. High concentrations of ammonia nitrogen in water can easily lead to eutrophication, posing a threat to humans, fish, and aquatic organisms.

[0004] To address the issues of low nitrate nitrogen removal rate, slow reaction, and poor nitrogen selectivity in single nano-zero-valent iron materials, Chinese invention patent CN113019431B was published, which utilizes sheet graphene as a carbon carrier to load iron and palladium composite metals to prepare composite metal materials. However, my country has relatively scarce platinum metal resources, and palladium metal is scarce on Earth, making mining and smelting difficult. As a rare and precious metal, it is very expensive. Modifying nano-zero-valent iron materials with palladium metal would significantly increase costs. Furthermore, graphene has poor chemical stability and high preparation costs, all of which are unfavorable for large-scale applications. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing carbon-supported nano-Fe-Cu bimetallic composite materials for treating nitrate nitrogen, which has the advantages of high nitrate nitrogen removal rate, fast reaction, good nitrogen selectivity, and low preparation cost.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a method for preparing carbon-supported nano-Fe-Cu bimetallic composite material for treating nitrate nitrogen, comprising the following steps: S1, raw material pretreatment: wheat straw is cut into straw strips, soaked in acidic water to soften, and then the straw strips are soaked in clean water and rinsed 2-3 times to remove impurities, and then dried, ground and sieved to obtain straw powder.

[0007] S2. Biochar preparation: Straw powder is pyrolyzed at high temperature under nitrogen protection. After the pyrolysis product is cooled to room temperature, it is heated in a water bath and stirred to remove ash. After washing and drying, clean biochar is obtained.

[0008] S3. Under the protection of nitrogen, clean biochar is mixed with ferrous sulfate solution and ultrasonically homogenized. NaBH4 solution is added to obtain biochar-supported nano-zero ferrous iron solid. The biochar-supported nano-zero ferrous iron solid is added to copper sulfate solution, ultrasonically homogenized, and the liquid is filtered out to obtain solid particles.

[0009] S4. Freeze-dry the solid particles for 5-10 hours to obtain carbon-supported nano-Fe-Cu bimetallic composite material.

[0010] The invention is further configured such that: in step S1, the length of the straw strip is 3-8 cm, the soaking and softening time is 2 h, the drying temperature is 80 °C, the drying time is 8 h, and a 100 mesh sieve is used with a residue of no more than 15%.

[0011] A further provision of the present invention is that, in step S1, the acidic water is prepared by mixing sulfuric acid and pure water at a mass ratio of 1 to 2.4:300.

[0012] A further feature of this invention is that, in step S2, the heating rate during high-temperature pyrolysis is controlled at 10℃ / min to 20℃ / min, and when the temperature reaches 500℃ to 600℃, the biochar is held at that temperature for 2 to 3 hours, resulting in a biochar with a specific surface area greater than 25 m². 2 / g, drying temperature is 100~105℃, drying time is 2~2.5h.

[0013] A further setting of the present invention is that in step S3, the mass ratio of ferrous sulfate solution to biochar is 4 to 20:1.

[0014] A further feature of the present invention is that, in step S3, the NaBH4 solution is added at a rate of 1 to 2 drops / s, and the mixture is continuously stirred during the addition process. The molar ratio of the added NaBH4 solution to the ferrous sulfate solution is 2 to 3:1.

[0015] A further setting of the present invention is as follows: in step S3, the ultrasonic homogenization time is 30 min to 50 min, the ultrasonic power is 100 to 500 W, and the ultrasonic frequency is 10 to 50 kHz.

[0016] A further setting of the present invention is that in step S3, the mass ratio of copper sulfate solution to ferrous sulfate solution is 1 to 3:16.

[0017] Application of a method for preparing a carbon-supported nano-Fe-Cu bimetallic composite material for treating nitrate nitrogen: The carbon-supported nano-Fe-Cu bimetallic composite material for treating nitrate nitrogen is added to wastewater containing nitrate nitrogen. The concentration of nitrate nitrogen in the wastewater is 40–50 mg / L. The amount of the carbon-supported nano-Fe-Cu bimetallic composite material for treating nitrate nitrogen is 3–6 g / L. The reaction pH is 4–10, and the reaction time is 90–100 min.

[0018] The beneficial effects of this invention are:

[0019] 1. This invention prepares nano-zero valent iron using a liquid-phase reduction method and loads it onto biochar via co-precipitation. Based on the loaded biochar, a second loading metal, Cu, is selected to prepare a nano-Fe-Cu bimetallic composite material. The addition of Cu can further enhance the dispersion ability and antioxidant properties of the nano-zero valent iron, making its surface exhibit a loose granular structure, thereby increasing the contact area between the nano-zero valent iron and nitrate nitrogen, achieving the effect of improving the nitrate nitrogen removal rate. At the same time, the addition of Cu enhances the rate of electron transfer in the solution, stimulating the nano-zero valent iron to corrode at a faster rate, thus providing more electrons. The electrons adsorbed by the active sites on the Cu surface will promote the further conversion of nitrite nitrogen into ammonia nitrogen and nitrogen gas, which has the advantage of improving nitrogen gas selectivity.

[0020] 2. This invention utilizes biochar made from solid waste wheat straw as a carrier for nano-Fe-Cu bimetallic materials. The biochar has a smooth surface and abundant internal pores. The composite material loaded with biochar has a good nanoporous structure, and the surface has more active sites. The contact area between the composite material and nitrate nitrogen is increased, which further improves the removal efficiency of nitrate nitrogen. It also realizes the reuse of solid waste. Iron, copper metal and wheat straw are inexpensive, the production cost is low, and it is convenient for large-scale promotion and application.

[0021] 3. In the process of preparing biochar from straw, the present invention acidifies wheat straw. The acidic water not only increases the solubility of metals such as lead, zinc, chromium, and magnesium in the straw, rapidly reducing metal impurities on the straw surface and preventing heavy metal ions from entering the water and causing secondary pollution, but also modifies the wheat straw, removing lignin and hemicellulose from the fibers, increasing the proportion of cellulose in the straw, increasing the thermal stability and surface functional groups of the straw, thereby increasing the surface adsorption performance and sites of the straw biochar, further improving the loading of nano-zero valent iron and copper on the straw biochar, and enhancing the ability to remove nitrate nitrogen. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0023] Figure 1 This is the SEM spectrum of the carbon-supported nano-Fe-Cu bimetallic composite material prepared in Example 1 of this invention.

[0024] Figure 2 This is the XRD pattern of the carbon-supported nano-Fe-Cu bimetallic composite material prepared in Example 1 of this invention. Detailed Implementation

[0025] The technical solution of the present invention will now be clearly and completely described with reference to specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] Example 1:

[0027] S1. Raw material pretreatment: Prepare acidic water by mixing sulfuric acid and pure water at a mass ratio of 1:300. Cut wheat straw into 3cm lengths and soak them in the acidic water for 2 hours to soften. After softening, rinse the straw with clean water 2-3 times, dry it at 80℃, and grind it through a 100-mesh sieve to obtain straw powder with a sieve residue of no more than 15%.

[0028] S2. Biochar Preparation: Straw powder is heated at a rate of 10℃ / min under nitrogen protection and carbonized at 500℃ for 3 hours for high-temperature pyrolysis. After cooling to room temperature, the pyrolysis product is heated in a water bath and stirred to remove ash. After washing, it is dried at 100℃ for 2 hours to obtain clean biochar. The drying temperature is 100-105℃, and the drying time is 2-2.5 hours. The specific surface area of ​​the biochar exceeds 25m². 2 / g.

[0029] S3. Under nitrogen protection, ferrous sulfate (FeSO4·7H2O) powder was dissolved in a 30% (v / v) alcohol solution to prepare a ferrous sulfate solution. The mass ratio of ferrous sulfate powder to alcohol solution was 5:1. Biochar was added at a mass ratio of ferrous sulfate solution to biochar of 4:1. The mixture was ultrasonically homogenized for 30 min at an ultrasonic power of 100–500 W and an ultrasonic frequency of 10–50 kHz. Then, NaBH4 solution was added at a molar ratio of 2:1 to ferrous sulfate solution, with the NaBH4 solution added dropwise at 1–2 drops / s and continuously stirred during the addition process to obtain biochar-supported nano-zero valent iron solids. Finally, copper sulfate solution was added at a mass ratio of 1:16 to ferrous sulfate solution. The mixture was ultrasonically homogenized for 30 min at an ultrasonic power of 100–500 W and an ultrasonic frequency of 10–50 kHz. The liquid was then filtered to obtain solid particles.

[0030] S4. Freeze-dry the solid particles for 5 hours to obtain carbon-supported nano-Fe-Cu bimetallic composite material.

[0031] When the prepared carbon-supported Fe-Cu bimetallic composite material was used to remove nitrate nitrogen, the dosage was 3 g / L, the pH of the nitrate nitrogen solution was 4, the reaction time was 90 min, and the removal rate of nitrate nitrogen reached 98.5%.

[0032] Example 2:

[0033] S1. Raw material pretreatment: Prepare acidic water by mixing sulfuric acid and pure water at a mass percentage of 2.4:300. Cut wheat straw into 8cm pieces and soak them in the acidic water to soften for 2 hours. After softening, rinse the straw with clean water 2-3 times, dry it at 80℃, grind it and pass it through a 100-mesh sieve, with a residue of no more than 15%.

[0034] S2. Biochar Preparation: Straw powder was heated at a rate of 20℃ / min under nitrogen protection and carbonized at 600℃ for 3 hours for high-temperature pyrolysis. After cooling to room temperature, the pyrolysis product was heated in a water bath and stirred to remove ash. After washing, it was dried at 105℃ for 2.5 hours to obtain clean biochar with a specific surface area exceeding 25m². 2 / g.

[0035] S3. Under nitrogen protection, ferrous sulfate (FeSO4·7H2O) powder was dissolved in a 30% (v / v) alcohol solution to prepare a ferrous sulfate solution. The mass ratio of ferrous sulfate powder to alcohol solution was 5:1. Biochar was added at a mass ratio of ferrous sulfate solution to biochar of 20:1. The mixture was ultrasonically homogenized for 50 min at an ultrasonic power of 100–500 W and an ultrasonic frequency of 10–50 kHz. Then, NaBH4 solution was added at a molar ratio of 3:1 to ferrous sulfate solution. The NaBH4 solution was added dropwise at 2 drops / s with continuous stirring during the addition to obtain biochar-supported nano-zero valent iron solids. Finally, copper sulfate solution was added at a mass ratio of 3:16 to ferrous sulfate solution. The mixture was ultrasonically homogenized for 50 min at an ultrasonic power of 100–500 W and an ultrasonic frequency of 10–50 kHz. The liquid was then filtered to obtain solid particles.

[0036] S4. Freeze-dry the solid particles for 10 hours to obtain carbon-supported nano-Fe-Cu bimetallic composite material.

[0037] When the prepared carbon-supported nano-Fe-Cu bimetallic composite material was used to remove nitrate nitrogen, the dosage was 6 g / L, the pH of the nitrate nitrogen solution was 10, the reaction time was 90 min, and the nitrate nitrogen removal rate reached 99.2%.

[0038] Example 3:

[0039] S1. Raw material pretreatment: Prepare acidic water by mixing sulfuric acid and pure water at a mass percentage of 2:300. Cut wheat straw into 5cm pieces and soak them in the acidic water to soften for 2 hours. After softening, rinse the straw three times with clean water to remove impurities. Dry the straw at 80℃ and grind it through a 100-mesh sieve, with a residue of no more than 15%.

[0040] S2. Biochar Preparation: Straw powder was heated at a rate of 15℃ / min under nitrogen protection and carbonized at 550℃ for 2.5h for high-temperature pyrolysis. After cooling to room temperature, the pyrolysis product was heated in a water bath and stirred to remove ash. After washing, it was dried at 105℃ for 2.5h to obtain clean biochar with a specific surface area exceeding 25m². 2 / g.

[0041] S3. Under nitrogen protection, ferrous sulfate (FeSO4·7H2O) powder was dissolved in a 30% (v / v) alcohol solution to prepare a ferrous sulfate solution. The mass ratio of ferrous sulfate powder to alcohol solution was 5:1. Biochar was added at a mass ratio of ferrous sulfate solution to biochar of 12:1. The mixture was ultrasonically homogenized for 40 min at an ultrasonic power of 100–500 W and an ultrasonic frequency of 10–50 kHz. Then, NaBH4 solution was added at a molar ratio of 2.5:1 to ferrous sulfate solution, with continuous stirring during the addition of NaBH4 solution at a rate of 1.5 drops / s. This yielded biochar-supported nano-zero ferrous iron solids. Finally, copper sulfate solution was added at a mass ratio of 2:16 to ferrous sulfate solution. The mixture was ultrasonically homogenized for 40 min at an ultrasonic power of 100–500 W and an ultrasonic frequency of 10–50 kHz. The liquid was then filtered to obtain solid particles.

[0042] S4. Freeze-dry the solid particles for 8 hours to obtain carbon-supported nano-Fe-Cu bimetallic composite material.

[0043] When the prepared carbon-supported Fe-Cu bimetallic composite material was used to remove nitrate nitrogen, the dosage was 4 g / L, the pH of the nitrate nitrogen solution was 6, and the reaction time was 90 min, and the nitrate nitrogen removal rate reached 100%.

[0044] Comparative Example 1: Under the same conditions as Comparative Example 1, except that copper sulfate solution was not added, the prepared composite material achieved a nitrate removal rate of 56.5%.

[0045] Comparative Example 2: Under the same conditions as Comparative Example 1, except that no biochar was added, the prepared composite material achieved a nitrate removal rate of 58.2%.

[0046] Comparative Example 3: The conditions were the same as those in Comparative Example 1, except that the wheat straw was soaked in pure water for 2 hours to soften it. The prepared composite material achieved a removal rate of 81.2% when applying it to remove nitrate nitrogen.

Claims

1. A method for preparing carbon-supported nano-Fe-Cu bimetallic composite materials for treating nitrate nitrogen, characterized in that: Includes the following steps: S1. Raw material pretreatment: Wheat straw is cut into straw strips, soaked in acidic water to soften, and then soaked and rinsed in clean water 2-3 times to remove impurities. After drying, grinding, and sieving, straw powder is obtained. The straw strips are 3-8cm in length, the soaking and softening time is 2 hours, the drying temperature is 80℃, the drying time is 8 hours, and a 100-mesh sieve is used with a residue of no more than 15%. S2. Biochar preparation: Straw powder is pyrolyzed at high temperature under nitrogen protection. After the pyrolysis product is cooled to room temperature, it is heated in a water bath and stirred to remove ash. After washing and drying, clean biochar is obtained. S3. Under the protection of nitrogen, clean biochar is mixed with ferrous sulfate solution and ultrasonically homogenized. NaBH4 solution is added to obtain biochar-supported nano-zero ferrous iron solid. The biochar-supported nano-zero ferrous iron solid is added to copper sulfate solution, ultrasonically homogenized, and the liquid is filtered out to obtain solid particles. S4. Freeze-dry the solid particles for 5-10 hours to obtain carbon-supported nano-Fe-Cu bimetallic composite material.

2. The method for preparing carbon-supported nano-Fe-Cu bimetallic composite material for treating nitrate nitrogen according to claim 1, characterized in that: In step S1, the acidic water is prepared by mixing sulfuric acid and pure water at a mass ratio of 1~2.4:

300.

3. The method for preparing carbon-supported nano-Fe-Cu bimetallic composite material for treating nitrate nitrogen according to claim 1, characterized in that: In step S2, the heating rate during high-temperature pyrolysis is controlled at 10 ℃ / min to 20 ℃ / min. When the temperature reaches 500 ℃ to 600 ℃, carbonization is carried out for 2 to 3 hours. The prepared biochar has a specific surface area greater than 25 m². 2 / g, drying temperature is 100~105℃, drying time is 2~2.5h.

4. The method for preparing a carbon-supported nano-Fe-Cu bimetallic composite material for treating nitrate nitrogen according to claim 1, characterized in that: In step S3, the mass ratio of ferrous sulfate solution to biochar is 4~20:

1.

5. The method for preparing a carbon-supported nano-Fe-Cu bimetallic composite material for treating nitrate nitrogen according to claim 1, characterized in that: In step S3, the NaBH4 solution is added at a rate of 1-2 drops / s, and the mixture is stirred continuously during the addition process. The molar ratio of the added NaBH4 solution to the ferrous sulfate solution is 2-3:

1.

6. The method for preparing a carbon-supported nano-Fe-Cu bimetallic composite material for treating nitrate nitrogen according to claim 3, characterized in that: In step S3, the ultrasonic homogenization time is 30 min to 50 min, the ultrasonic power is 100 to 500 W, and the ultrasonic frequency is 10 to 50 kHz.

7. The method for preparing a carbon-supported nano-Fe-Cu bimetallic composite material for treating nitrate nitrogen according to claim 1, characterized in that: In step S3, the mass ratio of copper sulfate solution to ferrous sulfate solution is 1~3:

16.

8. An application of a method for preparing carbon-supported nano-Fe-Cu bimetallic composite materials for treating nitrate nitrogen, characterized in that: The carbon-supported nano-Fe-Cu bimetallic composite material for treating nitrate nitrogen is added to nitrate nitrogen-containing wastewater for reaction. The concentration of nitrate nitrogen-containing wastewater is 40~50 mg / L, the amount of carbon-supported nano-Fe-Cu bimetallic composite material for treating nitrate nitrogen added is 3~6 g / L, the reaction pH is 4~10, and the reaction time is 90~100 min.

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