An iron and nitrogen co-doped carbon material, its preparation method and application

Abstract

The present invention relates to the field of water treatment, and particularly to an iron and nitrogen co-doped carbon material, a preparation method thereof and an application, which include the following steps: S1: Pyrolyze an iron salt, wash and dry it to obtain a solid powder; S2: In-situ pyrolyze the solid powder obtained in step S1 with a triazole precursor to obtain the iron and nitrogen co-doped carbon material. Compared with the prior art, the present invention uses an iron and nitrogen-doped carbon material as a catalyst, and has a high degradation performance for organic dyes in combination with hydrogen peroxide. In particular, even in high-salt wastewater and high-concentration pollutants, a high pollutant removal efficiency can still be maintained. And compared with the traditional Fenton reaction, this catalytic system not only has excellent performance, but also has advantages such as wide pH tolerance, high efficiency, low cost, and large-scale preparation, and has potential commercial value.

Description

Technical Field

[0001] The present invention relates to the field of water treatment, and particularly to an iron and nitrogen co-doped carbon material, a preparation method thereof and an application thereof. Background Art

[0002] With the development of society and economy and the improvement of people's living standards, more and more chemicals (such as organic dyes) have entered our daily life. Although it brings convenience to our life, it also brings great challenges to our living environment.

[0003] Typical organic dyes include rhodamine B, methylene blue, methyl orange, methyl red and crystal violet. It is difficult for them to be metabolized or degraded after entering the environment. Instead, they accumulate along the food chain and can remain in the human body or other animals for a long time. Even if partially decomposed, some of the formed intermediate products often have greater toxicity. Therefore, there is an urgent need to develop a method that can quickly remove organic pollutants in water. For the above problems, physical methods are simple and easy to implement, such as adsorption, membrane filtration, extraction, etc. However, physical methods only achieve the transfer of pollutants rather than their removal. The microbial decomposition method is an effective means to remove pollutants, but limited by the activity and cost of microorganisms, it is difficult to apply it to rapid water purification.

[0004] Carbon materials are a promising advanced oxidation catalyst. Carbon materials have many attractive properties, such as environmental friendliness, high stability, high conductivity, high mechanical strength, high adsorption performance, etc. However, the perfect sp 2 hybridized carbon network has a zero bandgap and a relatively high chemical potential, showing chemical inertness in many catalytic reaction processes. Therefore, there is an urgent need to develop an efficient advanced oxidation technology based on carbon-based catalysts to remove organic pollutants in water. Summary of the Invention

[0005] The purpose of the present invention is to provide an iron and nitrogen co-doped carbon material, a preparation method thereof and an application thereof to solve at least one of the above problems. Using the iron and nitrogen co-doped carbon material as a catalyst and combining it with hydrogen peroxide realizes the removal of organic pollutants, and can be used for water treatment in actual situations, having good application prospects.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The first aspect of the present invention discloses a preparation method of an iron and nitrogen co-doped carbon material, including the following steps:

[0008] S1: Hydrothermally treat an iron salt, wash and dry it to obtain a solid powder;

[0009] S2: In-situ pyrolyze the solid powder obtained in step S1 with a triazole precursor to obtain the iron and nitrogen co-doped carbon material.

[0010] Preferably, the iron metal salt described in step S1 includes one or more of iron acetylacetonate, iron acetate, ferric chloride, and ferric sulfate.

[0011] Preferably, the temperature of the hydrothermal treatment in step S1 is 140 - 200 °C, and the time is 1 - 4 h.

[0012] Preferably, the washing liquid used for washing in step S1 includes one or more of water, dilute hydrochloric acid, ethanol, DMF, methanol, and dimethyl sulfoxide, and the time is 0 - 48 h; the drying temperature is 40 - 180 °C, and the time is not less than 12 h.

[0013] Preferably, the triazole precursor described in step S2 is one or more of 3 - amino - 1,2,4 - triazole, 3 - amino - 1,2,4 - triazole - 5 - carboxylic acid, and 3,5 - diamino - 1,2,4 - triazole.

[0014] Preferably, the mass ratio of the solid powder to the triazole precursor is 0.2 - 0.5:0.1.

[0015] Preferably, the in - situ pyrolysis is carried out in an inert gas atmosphere, the heating rate is 1 - 15 °C / min, the pyrolysis temperature is 300 - 800 °C, and the holding time is 2 - 8 h.

[0016] Preferably, the inert gas is nitrogen, helium, or argon.

[0017] The second aspect of the present invention discloses an iron, nitrogen - co - doped carbon material prepared by any of the above - mentioned methods.

[0018] The third aspect of the present invention discloses the application of the iron, nitrogen - co - doped carbon material as described above in water treatment.

[0019] Preferably, the application of the iron, nitrogen - co - doped carbon material in water treatment is for the treatment of wastewater containing organic dyes.

[0020] Preferably, the organic dyes include organic dyes such as rhodamine B, methylene blue, methyl orange, methyl red, and crystal violet.

[0021] Preferably, the iron, nitrogen - co - doped carbon material can be regenerated after use, specifically: wash the used catalyst, and after drying, anneal it at 300 - 1000 °C for 0 - 10 h in an inert atmosphere at a heating rate of 1 - 15 °C / min.

[0022] The constructed carbon - based catalyst system can rapidly remove organic dyes and can be used for water treatment in actual situations, having good application prospects.

[0023] The high removal rate of the carbon-based catalyst / hydrogen peroxide system of the present invention is attributed to two points: (1) Co-doping of iron and nitrogen forms a heterojunction in the carbon-based material, which is beneficial to electron transport; (2) Fenton-like properties, the material can be recycled and has undemanding requirements for pH.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention synthesizes iron and nitrogen co-doped materials by means of hydrothermal and pyrolysis distribution treatments. The active sites are regulated by changing the iron salt, carbon source (triazole-based precursor) and their dosages, so as to regulate the catalytic performance and change the catalytic mechanism, thereby achieving efficient catalysis.

[0026] (2) The iron and nitrogen co-doped carbon material obtained in the present invention can achieve efficient removal of high-concentration dyes in combination with hydrogen peroxide. Among them, the dosage of hydrogen peroxide is 5-15 mL added per liter of wastewater.

[0027] (3) The catalyst of the present invention can be reused. It can be separated by centrifugation without causing secondary pollution. In addition, the catalyst can almost reach the initial degradation efficiency after being recycled four times and then regenerated.

[0028] (4) Compared with the traditional Fe 2+ / H2O2 Fenton system (the reaction pH is strictly limited between 3 and 4), this catalyst has high catalytic activity in the range of pH = 4-11.

[0029] (5) In the present invention, the combination of the catalyst and hydrogen peroxide has achieved high removal efficiency for the degradation of rhodamine B, methylene blue, crystal violet, methyl red and methyl orange. In particular, even in high-salt wastewater (anion content up to 100 mM) and high-concentration pollutants (200 ppm), a high pollutant removal efficiency can still be maintained. And compared with the traditional Fenton reaction, this catalytic system not only has excellent performance, but also has advantages such as wide pH tolerance, high efficiency, low cost, and large-scale preparation, and has potential commercial value. Description of the Drawings

[0030] Figure 1 It is the degradation curve diagram of methylene blue by different catalysts in Example 1;

[0031] Figure 2 It is the degradation curve diagram of different pollutants by catalyst 3 in Example 2;

[0032] Figure 3 It is the degradation curve diagram of methyl red under different operating parameters in Example 3; among them, a is the optimization diagram of the catalyst content, b is the optimization diagram of the H2O2 content, c is the pH optimization diagram, and d is the temperature optimization diagram;

[0033] Figure 4 It is a degradation test and cycle test diagram of the H2O2 / catalyst 3 system under high-salt or high-concentration pollutant conditions in Example 4; among them, a is the degradation curve diagram under different actual water qualities, b is the degradation curve diagram under high-concentration pollutants, c is the degradation curve diagram under high-concentration anionic conditions, and d is the cycle performance curve diagram. Detailed implementation manners

[0034] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Ultraviolet-visible spectrophotometry: It can measure the absorbance of substances with absorption wavelengths between 200-850 nm. Since according to Lambert-Beer's law: A = lg(1 / T) = Kcb, the concentration of the solution is proportional to the absorbance. By measuring the absorbance before and after dye degradation, the degradation situation of the dye can be obtained. The detection wavelengths of rhodamine B, methylene blue, crystal violet, methyl red, and methyl orange are 554 nm, 664 nm, 590 nm, 410 nm, and 463 nm respectively. Among them, A: absorbance; T: transmittance; K: absorption coefficient, which is numerically equal to the absorbance of the solution at a certain wavelength when the concentration is 1 g / L and the liquid layer thickness is 1 cm; b: liquid layer thickness; c: mass concentration.

[0036] In the following examples, if not otherwise specified, commercially available products that can be routinely obtained by those skilled in the art can be used.

[0037] Example 1

[0038] Preparation of catalyst and performance test:

[0039] (1) Preparation of catalyst

[0040] Catalyst 1: 3 g of iron acetylacetonate was heated to 200 °C at a heating rate of 5 °C / min in a hydrothermal reactor and held for 1 h. The powder was collected and washed with 1 M HCl and then with ultrapure water until neutral. After drying overnight at 60 °C, the final product catalyst 1 was obtained.

[0041] Catalyst 2: Weigh 0.1667 g of catalyst 1 and 0.8333 g of 3-amino-1,2,4-triazole and place them in a mortar and grind evenly. Then put them into a 50 ml porcelain boat and place it in a tubular furnace. Heat it to 800 °C at a heating rate of 5 °C / min in an Ar atmosphere and hold for 3 h. The final product catalyst 2 was obtained.

[0042] Catalyst 3: Weigh 0.2000 g of Catalyst 1 and 0.8000 g of 3 - aminotriazole - 5 - carboxylic acid and place them in a mortar for grinding evenly. Then put them into a 50 - ml porcelain boat and place it in a tubular furnace. Heat it up to 800 °C at a heating rate of 5 °C / min in an Ar atmosphere and keep it for 3 h. The final product Catalyst 3 is obtained.

[0043] Catalyst 4: Weigh 0.2500 g of Catalyst 1 and 0.7500 g of 3,5 - diamino - 1,2,4 - triazole and place them in a mortar for grinding evenly. Then put them into a 50 - ml porcelain boat and place it in a tubular furnace. Heat it up to 800 °C at a heating rate of 5 °C / min in an Ar atmosphere and keep it for 3 h. The final product Catalyst 4 is obtained.

[0044] Catalyst 5: Weigh 0.3333 g of Catalyst 1 and 0.6667 g of 3 - aminotriazole - 5 - carboxylic acid and place them in a mortar for grinding evenly. Then put them into a 50 - ml porcelain boat and place it in a tubular furnace. Heat it up to 800 °C at a heating rate of 5 °C / min in an Ar atmosphere and keep it for 3 h. The final product Catalyst 5 is obtained.

[0045] (2) Performance testing

[0046] All degradation experiments were carried out in a 250 - ml reactor and maintained in a 25 °C water bath. To adjust the pH, H2SO4 or NaOH aqueous solution was used. Generally, 10 mg of the catalyst was added to 100 ml of methyl red solution (20 mg / L), and pre - mixed for 30 minutes to achieve adsorption / desorption equilibrium. Then, 10 ml / L H2O2 was added into the suspension to start the degradation reaction. At several predetermined time intervals, 0.3 ml of the reaction mixture was taken out and mixed with 0.3 ml of MeOH, and then immediately analyzed by a 0.22 - μm PTFE filter. When rhodamine B, methylene blue, crystal violet, methyl red, and methyl orange were selected as pollutants, the initial concentration was 20 mg / L, and other conditions remained unchanged. The residual pollutants were analyzed using a UV - Vis spectrometer.

[0047] The RhB degradation effects of Catalysts 1 - 5 are as Figure 1 shown. Catalyst 3 can achieve complete removal of pollutants within 90 min.

[0048] Example 2

[0049] Taking Catalyst 3 as the optimal catalyst, removal experiments of various dyes were carried out:

[0050] The catalytic activity was evaluated in a 250 ml reactor containing a certain concentration of catalyst, H2O2 and dye, and stirred in a water bath at 25 °C. 10 mg of the catalyst was added to 100 ml of different pollutant solutions for 20 minutes until the adsorption-desorption equilibrium was reached. H2O2 was added to the above solution to initiate the reaction. The specific method is described in the performance test section of Example 1, and all experiments were carried out under the condition of pH = 7. The results are as Figure 2 shown that the H2O2 / catalyst 3 system has a high removal efficiency for different dyes. Specifically, when the initial pollutant concentration reaches a relatively high 20 ppm, the complete removal of crystal violet and methylene blue can be achieved within 90 min.

[0051] Example 3

[0052] Optimizing the operating parameters of the H2O2 / catalyst 3 oxidation system:

[0053] In this Example 2, compared with other dyes, the degradation effect of methyl red was relatively low. Therefore, taking methyl red as the object, the addition amount of the catalyst, the addition amount of H2O2, different pH values and temperatures were optimized in turn. The results are as Figure 3 shown. The catalytic performance gradually improved with the increase of the addition amount of the catalyst. However, when the amount of the catalyst increased from 100 mg / L to 200 mg / L, the catalytic performance of the system did not increase significantly, only increased from 78.6% to 90.3%, indicating that when the amount of the catalyst was 200 mg / L, the factor limiting the degradation of methyl red might be the insufficient amount of H2O2. When the amount of the catalyst was fixed at 100 mg / L, the dosage of H2O2 was adjusted (the results are shown in Figure 3 b). We found that when the dosage of H2O2 was 15 ml / L, the catalytic efficiency was the highest, but the increase was relatively small compared with that at 10 ml / L. This should be attributed to the radical self-quenching effect caused by excessive H2O2, which led to the self-consumption of a large number of active species. By investigating the removal efficiency of methyl red in a wide pH range (4 - 11), it was proved that this catalytic system could adapt to a wide pH window (the results are shown in Figure 3 c). Moreover, the removal of methyl red was accelerated under alkaline conditions, which should be attributed to the easier generation of singlet oxygen under alkaline conditions and the easier conversion of methyl red under alkaline conditions. Since the decomposition reaction of methyl red is a typical endothermic reaction, increasing the reaction temperature is beneficial to the improvement of the catalytic efficiency (the results are shown in Figure 3 d).

[0054] Example 4

[0055] Taking the H2O2 / catalyst 3 system as an example, the degradation and recycling performance of methyl red under special conditions:

[0056] In this embodiment, the experiment was carried out with H2O2 / catalyst 3 as an example. First, the effects of different water qualities on the removal of methyl red were studied ( Figure 4 a). When tap water and Lihu Lake water were used as media, the removal trend of methyl red was basically the same as that when ultrapure water was used as the media, and the removal rate could reach 80% after 90 min. This also shows that the constructed catalytic oxidation system has a relatively wide applicability. Since printing and dyeing wastewater and the like often have a high pollutant concentration and complex components. Therefore, it is necessary to investigate the removal of pollutants at high concentrations. As Figure 4 b, when the concentration of methyl red was increased to 200 ppm, only by increasing the concentration of H2O2 and appropriately extending the reaction time could the removal efficiency of more than 80% be achieved. This shows that this oxidation system is not only suitable for the removal of low-concentration pollutants but also suitable for the removal of high-concentration pollutants. Since there are often a large number of common anions in actual wastewater samples, such as chloride ions, nitrate ions, bicarbonate ions, sulfate ions, phosphate ions, and so on. Therefore, it is necessary to investigate the effects of a series of high-concentration anions on the constructed oxidation system. As Figure 4 c, nitrate ions, chloride ions, dihydrogen phosphate ions, and sulfate ions showed negligible effects on the degradation of methyl red, and the removal rate could reach 80% after 80 min. In addition, bicarbonate ions accelerated the removal of methyl red, and almost complete removal of methyl red could be achieved within 30 min. The acceleration of degradation by bicarbonate ions can be attributed to the fact that this anion provides a slightly alkaline pH environment, which is beneficial to 1 the generation of O2, so the reaction was accelerated. Figure 4 d shows the recycling performance of the catalyst. After four cycles, the catalytic performance can be maintained at 87.3% of the initial performance. And after regeneration, the catalyst can completely return to the initial performance level. The high-temperature regeneration process regenerated the used catalyst 3 in Example 1 at high temperature as follows: The used catalyst 3 was collected by centrifugation, washed three times with deionized water, and then dried in an oven at 80 °C for 6 h. The dried material was collected and placed in a porcelain boat, and heated to 700 °C at a heating rate of 5 °C / min in a nitrogen atmosphere and held for 1 h. After natural cooling, the product was collected. The collected catalyst is the regenerated catalyst.

[0057] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. Those who are familiar with the technology in this field can obviously make various modifications to these embodiments easily and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art according to the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A preparation method of an iron and nitrogen co-doped carbon material, characterized in that It includes the following steps: S1: Hydrothermally treat the iron salt, wash and dry it to obtain a solid powder; S2: In-situ pyrolyze the solid powder obtained in step S1 with a triazole precursor to obtain the iron and nitrogen co-doped carbon material; The iron salt described in step S1 includes one or more of iron acetylacetonate, iron acetate, ferric chloride, and ferrous sulfate; the temperature of the hydrothermal treatment is 140 - 200 °C; The triazole precursor described in step S2 is one or more of 3-amino-1,2,4-triazole, 3-aminotriazole-5-carboxylic acid, and 3,5-diamino-1,2,4-triazole. The mass ratio of the solid powder to the triazole precursor is 0.2 - 0.5:0.1; the pyrolysis temperature of the in-situ pyrolysis is 300 - 800 °C, and the heat preservation time is 2 - 8 h.

2. The preparation method of an iron and nitrogen co-doped carbon material according to claim 1, characterized in that, The time of the hydrothermal treatment described in step S1 is 1 - 4 h.

3. The preparation method of an iron and nitrogen co-doped carbon material according to claim 1, wherein, The washing liquid used for washing in step S1 includes one or more of water, dilute hydrochloric acid, ethanol, N,N-dimethylformamide, methanol, and dimethyl sulfoxide, and the time is 0 - 48 h; the drying temperature is 40 - 180 °C, and the time is not less than 12 h.

4. The preparation method of an iron and nitrogen co-doped carbon material according to claim 1, wherein The in-situ pyrolysis is carried out in an inert gas atmosphere, and the heating rate is 1 - 15 °C / min.

5. The preparation method of an iron and nitrogen co-doped carbon material according to claim 4, characterized in that, The inert gas is nitrogen, helium, or argon.

6. Application of the iron and nitrogen co-doped carbon material prepared by the preparation method as described in claim 1 in the treatment of wastewater containing organic dyes.

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