A kind of iron-zinc co-doped carbon-nitrogen polymer porous catalyst and preparation method

Abstract

The invention relates to the field of sewage treatment and discloses an iron-zinc co-doped carbon-nitrogen polymer porous catalyst, comprising an iron source, 0.01-0.06 mol of 2-methylimidazole, 0.0016-0.0047 mol of zinc salt, 0.5-8 g of urea, water and 1-7 g of precursor silkworm feces. The iron-zinc co-doped carbon-nitrogen polymer porous catalyst can achieve efficient removal of pollutants in water through a self-purification process under neutral conditions at room temperature during the reaction process.

Description

Technical Field

[0001] The invention relates to the field of sewage treatment, and in particular to an iron-zinc co-doped carbon-nitrogen polymer porous catalyst and a preparation method thereof. Background Art

[0002] In the past few decades, water pollution caused by the release of emerging refractory organic compounds into the aquatic environment has become a highly concerned environmental issue. Most organic pollutants, such as synthetic dyes, environmental hormones, pharmaceuticals and pesticides, are toxic to aquatic organisms and humans even at trace concentrations due to their cumulative biological effects. In order to remove these refractory pollutants, excessive consumption of resources and energy in the water treatment process is inevitable, which has become a bottleneck restricting the development of existing water treatment technologies. Complex micro-pollution of water bodies is a scientific challenge facing current water quality safety. Therefore, it is urgent to break through traditional concepts and develop new water treatment technologies with high efficiency and low energy consumption.

[0003] In recent years, scholars have found that by constructing a micro-electric field on the catalyst surface through the cation-π interaction to form a polarization center, the electrons of the pollutants can be effectively used to supply the oxidant for directional reduction to produce hydroxyl radicals with strong oxidizing properties, which not only greatly improves the sewage treatment efficiency, but also reduces the excessive consumption of oxidants. These studies show that there is great prospect for solving the problem of excessive energy consumption in the application stage through catalyst structure regulation. In addition, the current preparation of multiphase catalysts is often a resource- and energy-consuming process, which does not meet the goal of sustainable development. Studies have shown that feces contains a large amount of organic matter, which can serve as a nitrogen source and polymer precursor in the catalyst preparation process. Therefore, using feces as a raw material to prepare catalysts may be an innovative strategy that can not only solve the actual feces treatment problem but also reduce the energy consumption of water treatment. For this reason, we propose an iron-zinc co-doped carbon-nitrogen polymer porous catalyst and preparation method. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the deficiencies in the prior art, the present invention provides an iron-zinc co-doped carbon-nitrogen polymer porous catalyst and a preparation method thereof, which solve the above-mentioned problems.

[0006] (II) Technical solution

[0007] To achieve the above-mentioned purpose, the present invention provides the following technical solution: an iron-zinc co-doped carbon-nitrogen polymer porous catalyst, comprising an iron source, 0.01-0.06 mol of 2-methylimidazole, 0.0016-0.0047 mol of zinc salt, 0.5-8 g of urea, water and 1-7 g of precursor silkworm feces;

[0008] The amount of iron ions added in the iron source is 0.0020-0.0060 mol, and the iron source is at least one of ferric chloride hexahydrate, ferric nitrate, and ferric sulfate;

[0009] The zinc salt includes at least one of anhydrous zinc chloride, zinc acetate, zinc sulfate, and zinc nitrate hexahydrate.

[0010] Preferably, the zinc salt is added in an amount of 0.0021 mol, and the zinc salt is zinc nitrate hexahydrate;

[0011] The amount of 2-methylimidazole added was 0.04 mol;

[0012] The amount of urea added was 4 g;

[0013] The added amount of precursor silkworm feces is 4.5g.

[0014] When the amount of silkworm feces added is less than 4.5g, the precursor content is too low, the surface of the dried solid particles A is brown, the synthesized target catalyst (Fe-Zn-NC@NG) has too many surface oxides, and the catalytic activity is poor; when the amount of silkworm feces added is 4.5g, the surface of the dried solid particles A is black, the active iron species can be evenly doped into the substrate and chemically bonded with it to form a micro-electric field with strong surface potential energy, and the synthesized target catalyst (Fe-Zn-NC@NG) has the best catalytic performance against pollutants; when the amount of silkworm feces added is greater than 4.5g, the precursor content is too high, the synthesized target catalyst (Fe-Zn-NC@NG) has a relatively underdeveloped pore structure, fewer active sites, and poor catalyst activity.

[0015] A method for preparing an iron-zinc co-doped carbon-nitrogen polymer porous catalyst comprises the following steps:

[0016] S1: Add the iron source to 20 ml of water and stir evenly to form solution A;

[0017] S2: Add 2-methylimidazole, zinc salt, 2-20 ml of solution A and urea to 10-80 ml of water and stir evenly to form solution B;

[0018] S3: adding the precursor silkworm excrement to solution B and magnetically stirring for 0.5 to 4 hours to form dispersion A;

[0019] S4: placing the dispersion A in an oven for drying at a temperature of 30 to 100° C. for a drying time of 12 to 72 hours to obtain solid particles A;

[0020] S5: Place solid particles A in a tube furnace under N 2 Calcinate under atmosphere and obtain solid product A after natural cooling;

[0021] S6: Wash the solid product A three times with water, and place it in an oven for drying at a temperature of 60 to 120° C. for a drying time of 6 to 36 hours to obtain the iron-zinc co-doped carbon-nitrogen polymer porous catalyst Fe-Zn-NC@NG.

[0022] Preferably, the amount of solution A added in S2 is 10 ml, and the amount of water added is 20 ml.

[0023] When the amount of solution A added is less than 10 ml, the doping amount of iron species is too low, and the catalytic activity of the synthesized target catalyst (Fe-Zn-NC@NG) is poor; when the volume of solution A added is greater than 10 ml, the doping amount of iron species is too high, the synthesized target catalyst (Fe-Zn-NC@NG) is hard in texture and slightly gray in appearance, the catalyst activity is relatively low, and the iron species is easy to fall off and dissolve more during the reaction process; when the volume of solution A added is 10 ml, the active iron species can be uniformly doped into the porous carbon-nitrogen polymer grown with ZIF-8 metal organic framework as a template and bonded with it, and the synthesized target catalyst (Fe-Zn-NC@NG) has the best catalytic degradation activity and adaptability to pollutants.

[0024] Preferably, the magnetic stirring time in S3 is 1 h.

[0025] Preferably, the drying temperature in S4 is 60° C. and the drying time is 24 hours.

[0026] Preferably, the calcination temperature in S5 is 550-1000°C, the calcination time is 1-4h, and the heating rate is 2-15°C / min. A too fast heating rate will cause the Fe species on the catalyst surface to agglomerate rapidly to form iron oxides, and the template and precursor will be rapidly carbonized, which is not conducive to the transformation of the precursor to form a nitrogen-doped graphene structure; while slow heating is conducive to gradually removing the trace adsorbed water in the Fe-Zn-NC@NG solid product, so that its active species can be dispersed and denatured, and uniformly doped into the nitrogen-doped graphene structure through chemical bonding, and the target catalyst particles are uniform and black-gray.

[0027] Preferably, the drying temperature in S6 is 60° C. and the drying time is 24 hours.

[0028] The present invention also provides a porous catalyst of iron-zinc co-doped carbon-nitrogen polymer prepared according to the above method, in which the carbonized ZIF-8 template and the carbon-nitrogen polymer are connected by N-Zn-O-C bond bridges, and the composite organic polymer forms C-O-Fe and CN-Fe chemical coordination bonds with the active iron species. Based on this special structural characteristic, the π electrons on NC@NG are activated and migrate through these chemical bond bridges to concentrate on the periphery of the iron species, forming an electron high density region, while an electron low density region is formed near NC@NG, thereby forming a strong and stable micro-electric field on the surface of Fe-Zn-NC@NG, and its surface potential energy can reach 6440.51 to 6477.58 kJ / mol. Under the action of this strong surface potential energy, the surface micro-electric field is easy to have a strong orbital interaction with water molecules or organic pollutants adsorbed on the surface, and the chemical bond energy of these molecules is reduced through the electron delocalization effect. With the assistance of weak electron acceptors such as oxygen, the interfacial cleavage-hydrolysis-hydroxylation-cleavage process of organic pollutants is triggered, and water molecules are continuously converted to produce a large number of hydroxyl free radicals, which cause the organic pollutants to be degraded, thereby achieving low-energy and high-efficiency purification of sewage, especially complex sewage.

[0029] (III) Beneficial effects

[0030] Compared with the prior art, the present invention provides an iron-zinc co-doped carbon-nitrogen polymer porous catalyst and a preparation method thereof, which has the following beneficial effects:

[0031] 1. The iron-zinc co-doped carbon-nitrogen polymer porous catalyst of the present invention can achieve efficient removal of pollutants in water through a self-purification process under neutral conditions at room temperature during the reaction process.

[0032] Second, compared with conventional sewage oxidation treatment methods, the catalyst of the present invention can effectively overcome the adverse effects of natural organic matter (NOM) in water on the pollutant removal process.

[0033] Third, the catalyst of the present invention utilizes the micro-electric field with strong surface potential energy on the surface to effectively reduce the chemical bond energy of pollutants with strong orbital interactions, and only on weak electron acceptors (such as O 2 , Fe 3+ With the assistance of the electrons of pollutants, etc., the mineralization removal of pollutants is achieved without the assistance of external energy, which effectively overcomes the problem of excessive energy consumption in current sewage treatment.

[0034] Fourth, the catalyst of the present invention has good adaptability and stability in the process of removing organic pollutants.

[0035] 5. The catalyst of the present invention is a solid catalyst and has magnetism, so it is easy to separate from water and to recycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the SEM image of Fe-Zn-NC@NG prepared in Example;

[0037] Figure 2 The Mössbauer spectrum of Fe-Zn-NC@NG prepared in Example;

[0038] Figure 3 Degradation curves of Fe-Zn-NC@NG prepared in Example for BPA, DP and ATZ;

[0039] Figure 4 TOC removal diagram of Fe-Zn-NC@NG prepared in Example for BPA, DP and ATZ;

[0040] Figure 5 Activity evaluation diagram of Fe-Zn-NC@NG obtained in Example after repeated experiments;

[0041] Figure 6 This is the degradation curve of BPA, DP and ATZ in urban sewage by Fe-Zn-NC@NG prepared in the example. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] See also Figure 1-6 , Example

[0044] A method for synthesizing Fe-Zn-NC@NG comprises the following steps:

[0045] (1) Add ferric chloride hexahydrate to 20 ml of water and stir evenly to form solution A for later use;

[0046] (2) 0.04 mol 2-methylimidazole, 0.0021 mol zinc nitrate hexahydrate, 10 ml solution A and 4 g urea were added to 20 ml deionized water and stirred to form solution B;

[0047] (3) 4.5 g of precursor silkworm feces was added to solution B and magnetically stirred for 1 h to form dispersion A;

[0048] (4) The dispersion A was placed in an oven at 60° C. and dried for 24 h to obtain solid particles A;

[0049] (5) Place solid particles A in a tube furnace at N 2Calcinate under atmosphere at a heating rate of 5°C / min, heat to 700°C and hold for 2h, then cool naturally to obtain solid product A;

[0050] (6) The solid product A was washed three times with water, and baked in an oven at 60° C. for 24 h to obtain the iron-zinc co-doped carbon-nitrogen polymer porous catalyst Fe-Zn-NC@NG of the present invention.

[0051] Structural characterization of Fe-Zn-NC@NG prepared in the embodiment:

[0052] Figure 1 and Figure 2 The SEM image and Mössbauer spectrum of Fe-Zn-NC@NG prepared in the example. It can be seen from the figure that Fe-Zn-NC@NG has a honeycomb porous structure with a pore size of 0.2 to 300 nm. Through Mössbauer spectrum analysis, the iron species in Fe-Zn-NC@NG are α-Fe, Fe 3 C and Fe 3 O 4 Existing in form.

[0053]

[0054] Table 1 shows the numerical fitting results of the Fe-order EXAFS oscillation of Fe-Zn-NC@NG. In the first shell, in addition to the Fe-Fe shell, a bond length of The Fe-O shell with a coordination number of 0.6 and a bond length of Fe-N shell with a coordination number of 1.3. In addition, in the second shell, Fe-Zn-NC@NG shows a bond length of Fe-C shell with a coordination number of 4.8. These results confirm that Fe is successfully doped into the carbon-nitrogen polymer graphene-like structure grown using ZIF-8 as a template, forming CO-Fe and CN-Fe chemical bond bridges.

[0055] Application experiment:

[0056] 0.03 g of the Fe-Zn-NC@NG sample prepared in the example was put into 50 mL of a pollutant solution with a concentration of 10 mg / L. Under neutral reaction conditions, the temperature was kept at 35°C and magnetic stirring was continued to start the degradation reaction. Samples were taken at different time points and the concentration of pollutants therein was detected.

[0057] Figure 3 , Figure 4 and Figure 5 They are the degradation curve of Fe-Zn-NC@NG under neutral conditions for different pollutants, TOC degradation diagram, repeated experimental activity evaluation diagram, and catalytic degradation effect diagram for different pollutants in urban sewage. Figure 3 and Figure 4 It can be seen that without external energy assistance, the Fe-Zn-NC@NG air saturated suspension can remove 97.4% of BPA, 77.6% of DP and 63.3% of ATZ through the self-purification process within 120 minutes, and the TOC removal rates corresponding to the pollutant degradation process are as high as 62.6%, 41.7% and 31.6%, respectively, indicating that Fe-Zn-NC@NG has good catalytic performance in treating organic pollutants in water. Figure 5 It can be seen that after 6 consecutive runs, the removal rate of bisphenol A by Fe-Zn-NC@NG remained above 95.9%, and the amount of iron released during the entire reaction process was only 0.06 mg / L. These results fully demonstrate that Fe-Zn-NC@NG has good stability. Figure 6 It can be seen that in urban sewage, Fe-Zn-NC@NG showed a higher removal rate for the degradation of BPA, DP and ATZ, indicating that NOM in urban sewage can effectively promote the catalytic degradation process of Fe-Zn-NC@NG, which is completely different from the usual oxidation process. This shows that Fe-Zn-NC@NG is a promising low-energy catalyst for the treatment of composite polluted sewage.

[0058] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An iron-zinc co-doped carbon-nitrogen polymer porous catalyst, characterized in that: The preparation method comprises the following steps: S1: Add the iron source to 20 ml of water and stir evenly to form solution A; S2: Add 2-methylimidazole, zinc salt, 2-20 ml of solution A and urea to 10-80 ml of water and stir evenly to form solution B; S3: adding the precursor silkworm excrement to solution B and magnetically stirring for 0.5 to 4 hours to form dispersion A; S4: placing the dispersion A in an oven for drying at a temperature of 30 to 100° C. for a drying time of 12 to 72 hours to obtain solid particles A; S5: placing solid particles A in a tube furnace and calcining them under a N2 atmosphere, and obtaining a solid product A after natural cooling; S6: Wash the solid product A three times with water, and place it in an oven for drying at a temperature of 60 to 120° C. for a drying time of 6 to 36 hours to obtain an iron-zinc co-doped carbon-nitrogen polymer porous catalyst Fe-Zn-NC@NG.

2. The iron-zinc co-doped carbon-nitrogen polymer porous catalyst according to claim 1, characterized in that: The zinc salt addition amount is 0.0021 mol, and the zinc salt is zinc nitrate hexahydrate; The amount of 2-methylimidazole added was 0.04 mol; The amount of urea added was 4 g; The added amount of precursor silkworm feces is 4.5g.

3. The iron-zinc co-doped carbon-nitrogen polymer porous catalyst according to claim 1, characterized in that: The amount of solution A added to S2 is 10 ml, and the amount of water added is 20 ml.

4. The iron-zinc co-doped carbon-nitrogen polymer porous catalyst according to claim 1, characterized in that: The magnetic stirring time in S3 is 1 h.

5. The iron-zinc co-doped carbon-nitrogen polymer porous catalyst according to claim 1, characterized in that: The drying temperature in S4 is 60° C. and the drying time is 24 h.

6. The iron-zinc co-doped carbon-nitrogen polymer porous catalyst according to claim 1, characterized in that: The calcination temperature in S5 is 550-1000° C., the calcination time is 1-4 hours, and the heating rate is 2-15° C. / min.

7. The iron-zinc co-doped carbon-nitrogen polymer porous catalyst according to claim 1, characterized in that: The drying temperature in S6 is 60° C. and the drying time is 24 hours.

8. The iron-zinc co-doped carbon-nitrogen polymer porous catalyst according to claim 1, characterized in that: The Fe-Zn-co-doped carbon-nitrogen polymer porous catalyst Fe-Zn-NC@NG was applied to the catalytic degradation of organic pollutants such as bisphenol A, diphenhydramine and atrazine through a self-purification process without the need for external energy assistance.

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