Iron composite nitrogen-doped graphene-like catalyst as well as preparation method and application thereof

Abstract

The invention provides an iron composite nitrogen-doped graphene-like catalyst as well as a preparation method and application thereof, and belongs to the technical field of water treatment catalyst preparation. The catalyst provided by the invention comprises an outer coating layer and an inner core to form a coated structure, the outer layer is a nitrogen-doped graphene-like material; the inner core is metal iron nanoparticles, and the size of the metal iron nanoparticles is smaller than 200 nm. The preparation method is simple and low in equipment requirement. The prepared NG-coated Fe catalyst can effectively and rapidly remove organic pollutants such as bisphenol, ciprofloxacin and atrazine in water under the condition that an oxidizing agent is not added, and the removal rate within 15 minutes is larger than 80%; the catalyst has a good removal effect on organic pollutants which are difficult to biodegrade under the neutral room temperature condition, and is good in stability and very low in dissolution rate of metal ions in the catalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of water treatment catalyst preparation, and specifically relates to an iron-composite nitrogen-doped graphene-like catalyst and a preparation method and application thereof. Background Art

[0002] Water pollution is becoming increasingly serious. In addition to traditional pollutants, some emerging pollutants are attracting widespread attention due to their unique properties and potential hazards. Among these emerging pollutants, endocrine disruptors and antibiotics are typical emerging water pollutants. Their widespread presence and potential harm in the environment have become a focus of research and control.

[0003] To address this challenge, advanced oxidation processes (AOPs) have emerged as a highly effective wastewater treatment method. AOPs can effectively degrade a variety of organic pollutants by producing hydroxyl radicals (·OH) with strong oxidizing properties. Common AOPs include ozone oxidation (O3), photocatalytic oxidation using hydrogen peroxide (H2O2) and ultraviolet light (UV), Fenton reaction, electrochemical oxidation, etc. These technologies have performed well in treating refractory organic matter, but they also have significant limitations, especially high energy consumption and the need to add chemical agents, which increase operating costs and the risk of secondary pollution.

[0004] Therefore, reducing operating costs and avoiding secondary pollution are issues that need to be urgently addressed by those skilled in the art. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the prior art by providing an iron-complex nitrogen-doped graphene catalyst, its preparation method, and its application. The catalyst of the present invention can degrade organic pollutants including bisphenol compounds, ciprofloxacin, and atrazine.

[0006] In order to achieve the purpose of the present invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing an iron-complex nitrogen-doped graphene-like catalyst, the method comprising the following steps:

[0008] (1) dissolving an iron metal salt and anhydrous citric acid to obtain solution A;

[0009] (2) adding urea and melamine to solution A and mixing to obtain dispersion B;

[0010] (3) drying the dispersion B to obtain a solid product C;

[0011] (4) Grinding the solid product C, ammonium chloride, and polyvinylpyrrolidone together to obtain a solid product D;

[0012] (5) calcining the solid product D, grinding it after cooling, and obtaining the iron-complex nitrogen-doped graphene-like catalyst.

[0013] The present invention uses a two-step synthesis method, first through a simple heating and stirring precipitation method, and then through a calcination method to prepare an iron-complexed nitrogen-doped graphene-like catalyst. The catalyst prepared by the present invention is a black solid powder. Its microstructure is a blocky porous material with a typical encapsulated structure, that is, an iron-complexed graphene-like structure encapsulating a metallic iron nanoparticle structure. The graphene-like structure forms Fe-O-C and / or Fe-N-C bond bridges. The formation of these two bond bridges creates electron-rich centers around the metallic Fe sites and electron-deficient centers around the graphene-like C sites.

[0014] In the invention, iron metal salt is an iron source, anhydrous citric acid is a functional group modifier, urea is a nitrogen source, melamine is a carbon source, ammonium chloride is a layered template, and polyvinyl pyrrolidone is a binder.

[0015] As a preferred embodiment of the second aspect of the present invention, the mass ratio of the iron metal salt to the anhydrous citric acid in step (1) is (1-2):1. For example, the mass ratio can be any value or range of values ​​selected from 1:1, 1.2:1, 1.5:1, 1.8:1, or 2:1. The present invention has found that when the mass ratio of the iron metal salt to the anhydrous citric acid is (1-2):1, the catalyst performance is better, and in particular, when the mass ratio of the iron metal salt to the anhydrous citric acid is 1.41:1, the catalyst performance is optimal.

[0016] As a preferred embodiment of the second aspect of the present invention, the iron metal salt in step (1) is ferric chloride hexahydrate, ferric chloride, ferric nitrate nonahydrate, ferric acetate, ferric sulfate or ferric acetylacetonate, preferably ferric chloride hexahydrate.

[0017] As a preferred embodiment of the second aspect of the present invention, the mass ratio of urea to melamine in step (2) is (1-2):1. For example, it can be any value or range of values ​​selected from 1:1, 1.2:1, 1.5:1, 1.8:1, or 2:1. The present invention has found that the catalyst performance is better when the mass ratio of urea to melamine is (1-2):1, and particularly when the mass ratio of urea to melamine is 1.71:1, the catalyst performance is optimal.

[0018] As a preferred embodiment of the second aspect of the present invention, in step (4), the mass ratio of the solid product C to ammonium chloride and polyvinyl pyrrolidone is (2-3):1:1, for example, it can be any value or range of values ​​selected from 2:1:1, 2.2:1:1, 2.4:1:1, 2.5:1:1, 2.8:1:1 or 3:1:1. The present invention has found that when the mass ratio of the solid product C to ammonium chloride and polyvinyl pyrrolidone is (2-3):1:1, the performance of the catalyst is better, and in particular, when the mass ratio of the solid product C to ammonium chloride and polyvinyl pyrrolidone is 2.86:1:1, the catalyst performance is optimal.

[0019] As a preferred embodiment of the second aspect of the present invention, the calcination step in step (6) includes: a calcination temperature of 700-900° C. and a calcination time of 2-5 hours.

[0020] In a second aspect, the present invention provides an iron-complexed nitrogen-doped graphene-like catalyst prepared by the preparation method of the first aspect. The catalyst comprises an outer coating layer and an inner core, forming an encapsulated structure; the outer layer comprises nitrogen-doped graphene-like; and the inner core comprises metallic iron nanoparticles, wherein the metallic iron nanoparticles are less than 200 nm in size.

[0021] The structural composition of the catalyst of the present invention is mainly nitrogen-doped graphene-coated iron metal. The metal in the catalyst of the present invention is tightly coated by the nitrogen-doped graphene-coated framework, and metallic iron (various valence states of iron, including zero-valent iron) mainly plays the role of regulating the internal electron distribution of the material, and zero-valent iron does not directly react with pollutants as an active center, so iron is non-consumable and has low dissolution. The metal content that can be detected on the catalyst surface is very low, which makes the catalytic performance of the iron metal more stable and not easy to dissolve in the water body. The catalyst has a large specific surface area and numerous voids. The aqueous solution enters the interior of the material through the voids and contacts with the iron metal to produce an interfacial reaction. Due to the particularity of the structure, the catalyst of the present invention can degrade organic pollutants without adding any oxidant.

[0022] In a third aspect, the present invention provides the use of the iron-complex nitrogen-doped graphene-like catalyst in the degradation of organic pollutants in water.

[0023] As a preferred embodiment of the third aspect of the present invention, the organic pollutants include bisphenol organic compounds, ciprofloxacin and atrazine.

[0024] Experiments have shown that the iron-complex nitrogen-doped graphene catalyst prepared by the present invention can catalytically degrade organic pollutants in sewage, especially pharmaceutical substances such as bisphenol organic compounds, ciprofloxacin and atrazine.

[0025] In a fourth aspect, the present invention provides a method for degrading organic pollutants in wastewater, comprising the following steps: adding the catalyst into wastewater containing organic pollutants, stirring at a temperature of 30-35°C to start degradation, wherein the mass ratio of the catalyst to the wastewater containing organic pollutants is (2-4):5000.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention has developed a new iron-complex nitrogen-doped graphene-like catalyst that can effectively and rapidly remove organic pollutants such as bisphenols (including bisphenol A, bisphenol F, and bisphenol S), ciprofloxacin (CIP), and atrazine (ATZ) from water without the addition of an oxidant, achieving a removal rate exceeding 80% in 15 minutes. The catalyst also exhibits excellent removal efficiency for difficult-to-biodegrade organic pollutants at neutral room temperature, exhibits excellent stability, and exhibits a very low metal ion dissolution rate. The preparation method is simple and requires minimal equipment.

[0028] The present invention activates dissolved oxygen in water by constructing a sufficiently strong electric field on the catalyst surface to drive the self-degradation of pollutants on the catalyst surface without adding other chemical agents. It can treat organic pollutants in wastewater with low energy consumption and reduce wastewater treatment costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the XRD spectrum of the NG@Fe catalyst prepared in Example 1;

[0030] Figure 2 This is a scanning electron microscope (SEM) image of the NG@Fe catalyst prepared in Example 1;

[0031] Figure 3 This is a transmission electron microscopy (TEM) image of the NG@Fe catalyst prepared in Example 1;

[0032] Figure 4 This is a graph showing the recycling activity evaluation of the NG@Fe catalyst prepared in Example 1 for the degradation of bisphenol A;

[0033] Figure 5 This is the degradation curve of the NG@Fe catalyst prepared in Example 1 for bisphenol A, bisphenol F, bisphenol S, CIP, and ATZ (bisphenol A: BPA; bisphenol F: BPF; bisphenol S: BPS; ciprofloxacin: CIP; atrazine: ATZ). DETAILED DESCRIPTION

[0034] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0035] Example 1

[0036] This embodiment provides a method for preparing an iron-complex nitrogen-doped graphene-like catalyst, comprising the following steps:

[0037] (1) Weigh 85.7 mg of ferric chloride hexahydrate and 60.9 mg of anhydrous citric acid and dissolve them in 200 ml of deionized water. Let it stand for 30 min to form solution A. The mass ratio of ferric chloride hexahydrate to anhydrous citric acid is 1.41:1.

[0038] (2) 1714 mg of urea and 1 g of melamine were added to solution A and stirred for 2 h to form dispersion B; the mass ratio of urea to melamine was 1.71:1;

[0039] (3) Dispersion B was stirred in a water bath at 80°C until dry and then dried in a forced air drying oven for 12 h to obtain solid product C;

[0040] (4) The solid product C obtained in (3), 1 g of ammonium chloride, and 1 g of polyvinyl pyrrolidone were mixed and ground uniformly in an agate mortar to obtain a solid product D; the mass ratio of the solid product C to the ammonium chloride and the polyvinyl pyrrolidone was 2.86:1:1;

[0041] (5) The solid product D obtained in (4) was placed in a square porcelain boat, and the temperature was raised to 900°C in a tubular furnace under nitrogen flow at a heating rate of 5°C / min, and the temperature was kept for 4 hours. After calcination, the iron-complex nitrogen-doped graphene-like catalyst (denoted as: NG@Fe catalyst) was obtained by grinding.

[0042] Example 2

[0043] This embodiment provides a method for preparing an iron-complex nitrogen-doped graphene-like catalyst, comprising the following steps:

[0044] (1) Weigh 30 mg of ferric chloride hexahydrate and 20 mg of anhydrous citric acid and dissolve them in 200 ml of deionized water. Let it stand for 30 min to form solution A. The mass ratio of ferric chloride hexahydrate to anhydrous citric acid is 1.5:1.

[0045] (2) 3400 mg of urea and 3 g of melamine were added to solution A and stirred for 2 h to form dispersion B; the mass ratio of urea to melamine was 1.13:1;

[0046] (3) Dispersion B was stirred in a water bath at 80°C until dry and then dried in a forced air drying oven for 12 h to obtain solid product C;

[0047] (4) The solid product C obtained in (3) was mixed with 0.2 g of ammonium chloride and 0.2 g of polyvinyl pyrrolidone in an agate mortar and ground uniformly to obtain a solid product D; the mass ratio of the solid product C to the ammonium chloride and the polyvinyl pyrrolidone was 2:1:1;

[0048] (5) The solid product D obtained in (4) was placed in a square porcelain boat, and the temperature was raised to 700°C at a heating rate of 5°C / min in a tubular furnace under nitrogen flow, and the temperature was kept for 5 hours. After calcination, the iron-complex nitrogen-doped graphene-like catalyst was obtained by grinding.

[0049] Example 3

[0050] This embodiment provides a method for preparing an iron-complex nitrogen-doped graphene-like catalyst, comprising the following steps:

[0051] (1) Weigh 100 mg of ferric chloride hexahydrate and 100 mg of anhydrous citric acid and dissolve them in 200 ml of deionized water. Let it stand for 30 minutes to form solution A. The mass ratio of ferric chloride hexahydrate to anhydrous citric acid is 1:1.

[0052] (2) 3400 mg of urea and 2 g of melamine were added to solution A and stirred for 2 h to form dispersion B; the mass ratio of urea to melamine was 1.7:1;

[0053] (3) Dispersion B was stirred in a water bath at 80°C until dry and then dried in a forced air drying oven for 12 h to obtain solid product C;

[0054] (4) The solid product C obtained in (3) was mixed with 1.5 g of ammonium chloride and 1.5 g of polyvinyl pyrrolidone in an agate mortar and ground uniformly to obtain a solid product D; the mass ratio of the solid product C to the ammonium chloride and the polyvinyl pyrrolidone was 3:1:1;

[0055] (5) The solid product D obtained in (4) was placed in a square porcelain boat, and the temperature was raised to 700°C at a heating rate of 5°C / min in a tubular furnace under nitrogen conditions, and the temperature was kept for 2 hours. After calcination, the iron-complex nitrogen-doped graphene-like catalyst was ground to obtain the above-mentioned catalyst.

[0056] Example 4

[0057] The difference between Example 4 and Example 1 is that the mass ratio of ferric chloride hexahydrate to anhydrous citric acid is 4:1, and the rest is the same as Example 1.

[0058] Example 5

[0059] The difference between Example 5 and Example 1 is that the mass ratio of urea to melamine is 4:1, and the rest is the same as Example 1.

[0060] Example 6

[0061] The difference between Example 6 and Example 1 is that the mass ratio of the solid product C to ammonium chloride and polyvinyl pyrrolidone is 1:1:1, and the rest is the same as Example 1.

[0062] Comparative Example 1

[0063] The difference between Comparative Example 1 and Example 1 is that the anhydrous citric acid in Example 1 is replaced with an equal amount of tannic acid, and the rest is the same as Example 1.

[0064] Comparative Example 2

[0065] The difference between Comparative Example 2 and Example 1 is that the urea in Example 1 is replaced by an equal amount of biuret, and the rest is the same as Example 1.

[0066] Comparative Example 3

[0067] The difference between Comparative Example 3 and Example 1 is that the melamine in Example 1 is replaced by an equal amount of dicyandiamide, and the rest is the same as Example 1.

[0068] Comparative Example 4

[0069] The difference between Comparative Example 4 and Example 1 is that the ammonium chloride in Example 1 is replaced with an equal amount of ammonium sulfate, and the rest is the same as Example 1.

[0070] Comparative Example 5

[0071] The difference between Comparative Example 5 and Example 1 is that the polyvinylpyrrolidone in Example 1 is replaced by an equal amount of 2-methylimidazole, and the rest is the same as Example 1.

[0072] Comparative Example 6

[0073] The difference between Comparative Example 6 and Example 1 is that anhydrous citric acid is missing and the missing mass is made up with water. The rest is the same as Example 1.

[0074] Comparative Example 7

[0075] The difference between Comparative Example 7 and Example 1 is that urea is missing and the missing mass is made up with water. The rest is the same as Example 1.

[0076] Comparative Example 8

[0077] The difference between Comparative Example 8 and Example 1 is that melamine is missing and the missing mass is made up with water. The rest is the same as Example 1.

[0078] Comparative Example 9

[0079] The difference between Comparative Example 9 and Example 1 is that ammonium chloride is lacking, and the lacking mass portion is made up with water, and the rest is the same as Example 1.

[0080] Comparative Example 10

[0081] The difference between Comparative Example 10 and Example 1 is that polyvinyl pyrrolidone is missing and the missing mass is made up with water. The rest is the same as Example 1.

[0082] Test Example 1: Verification of the catalytic degradation performance of the catalysts of Examples 1-6 and Comparative Examples 1-10

[0083] The NG@Fe catalysts prepared in Example 1 and the comparative example were used to degrade organic pollutants in water, respectively, in the following steps:

[0084] 0.03g of the prepared NG@Fe catalyst was added to 50mL of a 5mg / L bisphenol A solution and stirred continuously at 35°C to initiate the degradation reaction. After reaching adsorption-desorption equilibrium, the bisphenol A concentration in the solution was measured. The results are shown in the following table:

[0085] Table 1

[0086]

[0087]

[0088] As can be seen from the table above, compared with Examples 2-3, Example 1 has a bisphenol A degradation rate of 100%, which is superior to Examples 2-3. This indicates that the parameters and process of the preparation method in Example 1 can produce a catalyst with the best degradation performance. Using the parameters and process of Examples 2-3, a catalyst with a degradation rate of 90% can also be produced.

[0089] Comparison of Example 1 with Examples 4-6 shows that the mass ratio of ferric chloride hexahydrate to anhydrous citric acid, the mass ratio of urea to melamine, and the mass ratio of solid product C to ammonium chloride and polyvinyl pyrrolidone are factors that affect catalyst performance. The mass ratio of ferric chloride hexahydrate to anhydrous citric acid should not exceed 2:1, the mass ratio of urea to melamine should not exceed 2:1, and the mass ratio of solid product C to ammonium chloride and polyvinyl pyrrolidone should not be less than 2:1:1, otherwise it will affect the performance of the catalyst. Therefore, when these three mass ratios are as in Example 1, the catalyst performance is optimal.

[0090] Comparison of Example 1 with Comparative Examples 1-10 shows that Comparative Examples 1-5 have reduced catalytic performance due to the replacement of the components of the catalyst of the present invention with other components, and Comparative Examples 6-10 have reduced catalytic performance due to the lack of the components of the catalyst of the present invention. In Comparative Example 10, the catalyst will not be able to form at high temperatures due to the absence of polyvinyl pyrrolidone, and therefore there is no corresponding degradation rate. It can be seen that the components used to prepare the NG@Fe catalyst of the present invention have a synergistic effect. If one of them is replaced or missing, the structure of the catalyst will be destroyed, thereby affecting the catalytic activity.

[0091] Test Example 2: Characterization of NG@Fe Catalyst

[0092] The NG@Fe catalyst prepared in Example 1 was characterized as follows:

[0093] Depend on Figure 1 The XRD spectrum of NG@Fe catalyst shows that it is consistent with the characteristic diffraction peaks of ferrosoferric oxide (220), (311), (400), (422), (511), and (440) when compared with the standard card. Figure 2 The scanning electron microscope (SEM) image of NG@Fe catalyst shows that it can be observed as a bulk porous material. Figure 3 The transmission electron microscopy (TEM) image of the NG@Fe catalyst shows that elemental analysis reveals that the white nanoparticles in the image are mainly composed of ferroferric oxide structures.

[0094] Test Example 3: Testing the stability of NG@Fe catalyst

[0095] The NG@Fe catalyst prepared in Example 1 was used to degrade organic pollutants in water, and its stability was tested. The specific method included the following steps:

[0096] (1) 0.03 g of the NG@Fe catalyst prepared in Example 1 was added to 50 mL of a 5 mg / L bisphenol A solution and the mixture was stirred continuously in a water bath at 35° C. to initiate the degradation reaction.

[0097] (2) After 2 h of reaction, the concentration of bisphenol A was measured;

[0098] (3) After the NG@Fe catalyst in step (2) is separated and dried, the catalyst is taken and steps (1 to 3) are repeated 6 times.

[0099] The results are as follows Figure 4 As shown in the figure, it can be observed that the effect of the prepared catalyst in degrading bisphenol A does not decrease significantly after continuous cycle reaction. In 6 repeated experiments, the removal effect can reach more than 98%.

[0100] Test Example 4: Testing the degradation performance of NG@Fe catalyst on other organic pollutants

[0101] 0.03 g of the prepared NG@Fe catalyst was added into 50 mL of 5 mg / L bisphenol A solution (BPA), bisphenol F solution (BPF), bisphenol S solution (BPS), ciprofloxacin solution (CIP), and atrazine solution (ATZ), respectively. The degradation reaction was started by continuous stirring at 35°C, and the concentration of organic pollutants in the solution was measured after reaching adsorption-desorption equilibrium.

[0102] The results are as follows Figure 5As shown in the figure, within 120 minutes of reaction, the degradation rates of NG@Fe for bisphenol A, bisphenol F, bisphenol S, ciprofloxacin and atrazine were 99.6%, 99.9%, 94.0%, 99.4% and 92.2%, respectively.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an iron-complex nitrogen-doped graphene-like catalyst, characterized in that: The method comprises the following steps: (1) dissolving an iron metal salt and anhydrous citric acid to obtain solution A; (2) adding urea and melamine to solution A and mixing to obtain dispersion B; (3) drying the dispersion B to obtain a solid product C; (4) Grinding the solid product C, ammonium chloride, and polyvinylpyrrolidone together to obtain a solid product D; (5) calcining the solid product D, grinding it after cooling, and obtaining the iron-complex nitrogen-doped graphene-like catalyst.

2. The preparation method according to claim 1, wherein The mass ratio of the iron metal salt to the anhydrous citric acid in the step (1) is (1-2):

1.

3. The preparation method according to claim 1, wherein The iron metal salt in step (1) is any one of ferric chloride hexahydrate, ferric chloride, ferric nitrate nonahydrate, ferric acetate, ferric sulfate, and ferric acetylacetonate.

4. The preparation method according to claim 1, wherein The mass ratio of urea to melamine in step (2) is (1-2):

1.

5. The preparation method according to claim 1, wherein The mass ratio of the solid product C to ammonium chloride and polyvinyl pyrrolidone in the step (4) is (2-3):1:

1.

6. The preparation method according to claim 1, wherein The calcination step in step (5) includes: a calcination temperature of 700-900° C. and a calcination time of 2-5 hours.

7. An iron-complex nitrogen-doped graphene-like catalyst prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The catalyst comprises an outer coating layer and an inner core, forming a coating structure; The outer layer is nitrogen-doped graphene-like; The core is a metallic iron nanoparticle, and the size of the metallic iron nanoparticle is less than 200 nm.

8. Use of the iron-complex nitrogen-doped graphene-like catalyst as claimed in claim 7 in degrading organic pollutants in water.

9. The use according to claim 8, characterized in that The organic pollutants include bisphenol organic compounds, ciprofloxacin and atrazine.

10. A method for degrading organic pollutants in wastewater, characterized in that: The method comprises the following steps: adding the catalyst according to claim 7 into wastewater containing organic pollutants, stirring at a temperature of 30-35° C., and starting degradation, wherein the mass ratio of the catalyst to the wastewater containing organic pollutants is (2-4):5000.

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