Preparation method and application of sulfur-doped nitrogen-containing carbon material

Abstract

The invention aims to provide a preparation method and application of a sulfur-doped nitrogen-containing carbon material, and belongs to the technical field of materials and wastewater treatment. According to the preparation method of the sulfur-doped carbon material provided by the invention, the original synchronous raw material carbonization and heteroatom doping process at the same temperature is converted into step-by-step raw material carbonization and heteroatom doping at different temperatures; the defects of insufficient precursor activity excitation, low-efficiency heteroatom doping and low catalyst activity caused by different precursor carbonization temperature and heteroatom doping temperature are overcome. Sulfur vacancies, defects and thiophene sulfur active sites are formed through sulfur doping to promote the electron transfer capacity of the nitrogen-containing carbon material, the persulfate activation performance of the catalyst can be improved, rapid degradation and mineralization of phenol in waste water can be achieved, and the nitrogen-containing carbon material has good application prospects in organic waste water treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of materials and wastewater treatment, and particularly relates to a preparation method and application of a sulfur-doped nitrogen-containing carbon material. Background Art

[0002] Phenol is an important chemical raw material, mainly used in industries such as petrochemical, medicine, pesticide, dye, and paper making. A large amount of wastewater is generated during the production of phenol. Such wastewater is characterized by high yield, difficult degradation, and high toxicity, and has potential toxicity of carcinogenesis, teratogenesis, and mutagenesis. Therefore, how to efficiently and rapidly remove phenol from wastewater has become an issue of concern to many researchers.

[0003] The advanced oxidation technology of persulfate (PS-AOPs) has been widely used to remove refractory organic pollutants in water due to its advantages such as high catalytic activity, selectivity, and simple operation. However, there are very few industrial application cases of the advanced oxidation technology of persulfate. The reason is that there are still many key problems to be solved in its activation process. For example, the activation of persulfate by means such as heat, ultrasonic wave, ultraviolet light, and radiation has the defect of energy consumption; the activation of persulfate by homogeneous transition metal ions (Fe 2+ , Cu 2+ , Mn 2+ , Co 2+ etc.) has the problem of secondary pollution; the activation of persulfate by heterogeneous metal-based materials has the risk of metal leaching. Therefore, in order to realize the industrial application of the advanced oxidation technology of persulfate, it is imperative to design and develop a persulfate activator with low cost, high efficiency, and strong stability.

[0004] However, due to the advantages of no secondary pollution and low cost, non-metallic carbon-based materials have received extensive attention as an alternative to transition metal-based catalysts for activating persulfate. Research shows that heteroatom doping is an effective method to endow carbon materials with higher activity. However, studies have shown that the conductive polymer polypyrrole (PPY) can be used as a good nitrogen-containing carbon material precursor. Without adding a nitrogen source, it can effectively activate persulfate after direct carbonization. Similarly, the conductive polymer polyaniline (PANI), which can be used as both a carbon source and a nitrogen source, has the characteristics of cheap raw materials and mature preparation processes, and can also be an excellent candidate for the preparation of nitrogen-doped carbon materials. However, single heteroatom doping has limited improvement on the catalytic activity of carbon materials. Research shows that heteroatom-combined doped carbon materials not only have excellent catalytic performance but also exist more stably in an oxidative environment. This advantage stems from the synergistic effect between heteroatoms. Among the possible co-doping options, N and S seem to be the natural choices for heteroatoms and are widely used to enhance the activation of persulfate by carbon catalysts because when N and S are combined in a carbonaceous platform, a higher synergistic effect will be generated. Currently, the preparation of heteroatom-doped carbon materials is achieved by simultaneously carbonizing raw materials and sulfur doping at the same temperature. Due to the different carbonization temperatures of the precursors and the heteroatom doping temperatures, such doping methods have the disadvantages of insufficient activation of precursor activity, inefficient heteroatom doping, and poor catalyst stability.

[0005] Therefore, it is of great significance to develop an efficient preparation method for heteroatom-doped nitrogen-containing carbon materials and combine the prepared catalyst with the advanced oxidation technology of persulfate to provide a theoretical basis and technical support for the treatment of phenol-containing wastewater in coal chemical industry. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method and application of sulfur-doped nitrogen-containing carbon materials, which can achieve efficient doping of sulfur, improve the catalytic activity of carbon materials, and provide a win-win strategy for the treatment of phenol-containing wastewater.

[0007] The present invention adopts the following technical solutions: A preparation method of sulfur-doped nitrogen-containing carbon materials includes the following steps: S1. Dry the conductive polymer in an oven at 75 °C for 24 h. Then place the dried conductive polymer in a tubular furnace. Under nitrogen protection, raise the temperature to 300 - 900 °C at a heating rate of 5 °C / min, and directly calcine the conductive polymer at this temperature for 240 min to obtain the nitrogen-containing carbon material; S2. Mix the nitrogen-containing carbon material with a sulfur source in a certain proportion and grind it in an agate mortar for 10 - 20 min; S3. Place the grinding mixture in a tube furnace, and under nitrogen protection, raise the temperature to 550 °C at a heating rate of 5 °C / min, and calcine at this temperature for 240 min to obtain a sulfur-doped nitrogen-containing carbon material catalyst.

[0008] Further, the conductive polymer in S1 includes polyaniline or polypyrrole.

[0009] Further, the sulfur source in S2 is thiourea.

[0010] Further, the mass ratio of the nitrogen-containing carbon material to the sulfur source in S2 is 1-2:1-5.

[0011] A sulfur-doped nitrogen-containing carbon material is used to remove phenol in water.

[0012] A sulfur-doped nitrogen-containing carbon material is used to remove phenol in water, including the following steps: S1. Add the sulfur-doped nitrogen-containing carbon material catalyst to the prepared phenol solution, and place it in a magnetic stirrer to stir evenly; S2. After stirring evenly, add persulfate to initiate the reaction.

[0013] Further, the volume of the phenol solution in S1 is 100-1000 mL, the concentration is 25-100 mg / L, the pH is 3-11, and the amount of the sulfur-doped nitrogen-containing carbon material catalyst is 10-60 mg.

[0014] Further, the concentration of the persulfate in S2 is 0.5-3 mM, and the reaction time is 0-60 min.

[0015] The beneficial effects of the present invention are as follows: 1. The present invention adopts a step-by-step method for precursor carbonization and heteroatom doping. Compared with the existing one-step method, it can fully stimulate the activity of the precursor, improve the heteroatom doping efficiency, and enhance the catalyst stability.

[0016] 2. The sulfur-doped nitrogen-containing carbon material prepared by the present invention has abundant defects, sulfur vacancies and thiophene sulfur (-C-S-C) active sites, which lays a foundation for improving the efficiency of activating persulfate.

[0017] 3. Experimental results show that the sulfur-doped nitrogen-containing carbon material-activated persulfate exhibits high removal performance and mineralization performance for phenol, with a removal rate of up to 98.3% and a mineralization rate of up to 75.3%.

[0018] 4. Based on the advantages of the simple preparation method, low cost, strong stability, and high efficiency of this material, the sulfur-doped nitrogen-containing carbon material of the present invention provides a theoretical basis in the activated persulfate advanced oxidation technology, and at the same time provides a win-win strategy for the treatment of phenol-containing wastewater. Description of the Drawings

[0019] Figure 1 Degradation efficiency of phenol by persulfate activated by the catalysts prepared in Examples 1-6; Figure 2 Degradation efficiency of phenol by persulfate activated by the catalysts prepared in Examples 7-9; Figure 3 Mineralization behavior of phenol degradation by persulfate activated by the catalyst prepared in Example 7; Figure 4 SEM images of the catalysts prepared in Examples 7-9; Figure 5 EPR spectra of the catalysts prepared in Example 1 and Example 7; Figure 6 XRD patterns of the catalysts prepared in Examples 7-9; Figure 7 Raman spectra of the catalysts prepared in Examples 7-9; Figure 8 XPS spectra of the catalysts prepared in Example 1 and Example 7. Detailed Description of the Invention

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0021] Example 1 Put 2 g of polyaniline in a tubular furnace. Under nitrogen protection, raise the temperature to 900 °C at a heating rate of 5 °C / min, and directly calcine the polyaniline at this temperature for 240 min to obtain the precursor CPANI.

[0022] Example 2 Fully grind 0.15 g of CPANI obtained in Example 1 and 0.075 g of thiourea for 15 min, then place them in a tubular furnace. Under nitrogen protection, raise the temperature to 550 °C at a heating rate of 5 °C / min, and directly calcine the polyaniline at this temperature for 240 min to obtain CPANI-S-2:1.

[0023] Example 3 0.15 g of CPANI obtained in Example 1 and 0.15 g of thiourea were thoroughly ground for 15 min and then placed in a tube furnace. Under nitrogen protection, the temperature was raised to 550 °C at a heating rate of 5 °C / min, and the polyaniline was directly calcined at this temperature for 240 min to obtain CPANI-S-1:1.

[0024] Example 4 0.15 g of CPANI obtained in Example 1 and 0.225 g of thiourea were thoroughly ground for 15 min and then placed in a tube furnace. Under nitrogen protection, the temperature was raised to 550 °C at a heating rate of 5 °C / min, and the polyaniline was directly calcined at this temperature for 240 min to obtain CPANI-S-2:3.

[0025] Example 5 0.15 g of CPANI obtained in Example 1 and 0.30 g of thiourea were thoroughly ground for 15 min and then placed in a tube furnace. Under nitrogen protection, the temperature was raised to 550 °C at a heating rate of 5 °C / min, and the polyaniline was directly calcined at this temperature for 240 min to obtain CPANI-S-1:2.

[0026] Example 6 0.15 g of CPANI obtained in Example 1 and 0.375 g of thiourea were thoroughly ground for 15 min and then placed in a tube furnace. Under nitrogen protection, the temperature was raised to 550 °C at a heating rate of 5 °C / min, and the polyaniline was directly calcined at this temperature for 240 min to obtain CPANI-S-2:5.

[0027] Example 7 0.45 g of CPANI obtained in Example 1 and 0.675 g of thiourea were thoroughly ground for 15 min and then placed in a tube furnace. Under nitrogen protection, the temperature was raised to 550 °C at a heating rate of 5 °C / min, and the polyaniline was directly calcined at this temperature for 240 min to obtain CPANI-S.

[0028] Example 8 0.45 g of PANI and 0.675 g of thiourea were thoroughly ground for 15 min and then placed in a tube furnace. Under nitrogen protection, the temperature was raised to 550 °C at a heating rate of 5 °C / min, and the polyaniline was directly calcined at this temperature for 240 min to obtain CPANI-S-5.

[0029] Example 9 0.45 g of PANI and 0.675 g of thiourea were thoroughly ground for 15 min and then placed in a tube furnace. Under nitrogen protection, the temperature was raised to 900 °C at a heating rate of 5 °C / min, and the polyaniline was directly calcined at this temperature for 240 min to obtain CPANI-S-9.

[0030] For the application case of activating persulfate to degrade phenol, all degradation experiments were carried out in a 250 mL glass beaker and continuously stirred by a magnetic stirrer at a speed of 450 r / min.

[0031] Experimental Example 1 First, 50 mg of the catalyst prepared in Examples 1-6 was added to 100 mL of a phenol (50 mg / L) solution. Second, the reaction was triggered by adding the oxidant persulfate (3 mM). During the reaction, 2 mL of the sample was taken at specific time intervals and filtered through a 0.22 μm aqueous disposable filter head. Finally, the filtered sample was detected by high performance liquid chromatography, and the experimental results are as Figure 1 shown.

[0032] Experimental Example 2 First, 60 mg of the catalyst prepared in Examples 7-9 was added to 100 mL of a phenol (50 mg / L) solution. Second, the reaction was triggered by adding the oxidant persulfate (2 mM). During the reaction, 2 mL of the sample was taken at specific time intervals and filtered through a 0.22 μm aqueous disposable filter head. Finally, the filtered sample was detected by a high performance liquid chromatograph, and the experimental results are as Figure 2 shown.

[0033] Experimental Example 3 First, 60 mg of the catalyst prepared in Example 6 was added to 100 mL of a phenol (50 mg / L) solution. Second, the reaction was triggered by adding the oxidant persulfate (2 mM). During the reaction, 2 mL of the sample was taken at specific time intervals and filtered through a 0.22 μm aqueous disposable filter head. Finally, the filtered sample was detected by a total organic carbon analyzer, and the experimental results are as Figure 3 shown.

[0034] Figure 1For the efficiency of catalysts with different sulfur doping ratios in activating persulfate to degrade phenol, the results show that: the material without sulfur doping has a poor activation effect on persulfate (69.4%, 20 min). With the increase of sulfur doping, the effect of activating persulfate gradually improves within the same reaction time, reaching 91.8% when CPANI:S = 2:3. When the sulfur doping ratio continues to increase, the effect of activating persulfate no longer improves, because excessive sulfur doping is not conducive to the charge distribution of the carbon catalyst.

[0035] Figure 2 For the efficiency of catalysts prepared by different methods in activating persulfate to degrade phenol, the results show that: the catalyst (CPANI-S) prepared by the two-step method proposed in the present invention has a phenol removal rate as high as 98.3% after 20 min of activating persulfate. While the catalysts (CPANI-S-5) and (CPANI-S-9) prepared by synchronous carbonization and doping have phenol removal rates of only 10.2% and 36.2% after 20 min of activating persulfate, which fully proves the superiority of the present invention.

[0036] Figure 3 For the mineralization efficiency of the best catalyst in activating persulfate to degrade phenol, the results show that: the mineralization rate of phenol by CPANI-S activating persulfate is as high as 75.3% after 20 min.

[0037] Figure 4 For the scanning electron microscope (SEM) images of CPANI-S, CPANI-S-5 and CPANI-S-9, the results show that: CPANI-S exhibits small spherical sizes, rough surfaces and abundant interstitial spaces, while CPANI-S-5 and CPANI-S-9 completely change the original spherical and rough porous morphologies, presenting agglomerated, less porous and smooth morphologies.

[0038] Figure 5 For the electron paramagnetic resonance (EPR) spectra of CPANI and CPANI-S, the results show that: an obvious signal appears near g = 2.004 for CPANI-S, which proves that sulfur doping also leads to the generation of sulfur vacancies, and they are also important active sites.

[0039] Figure 6 For the X-ray diffraction (XRD) patterns of CPANI-S, CPANI-S-5 and CPANI-S-9, the results show that: two broad diffraction peaks represent the (002) and (100) crystal planes of graphite carbon, which indicates that the structure of PANI is destroyed during the high-temperature calcination process and transformed into low-crystallinity disordered carbon between graphite and amorphous carbon.

[0040] Figure 7Raman spectra of CPANI-S, CPANI-S-5 and CPANI-S-9. The results show that the catalyst obtained by the preparation method proposed in the present invention has more abundant defects, which also provides better active sites for activating persulfate.

[0041] Figure 8 X-ray photoelectron spectroscopy (XPS) diagrams of CPANI and CPANI-S. The results show that after sulfur doping, the main existing forms are thiophene sulfur (-C-S-C) at 164.05 eV and 165.15 eV and sulfur oxide (-C-SO x -C) at 167.85 eV and 169.31 eV. In addition, thiophene sulfur (-C-S-C) is an important active site for activating persulfate, while sulfur oxide (-C-SO x -C) is chemically inert to persulfate activation. However, the content of thiophene sulfur (-C-S-C) in the catalyst prepared in the present invention can reach 80%, laying a foundation for improving its efficiency in activating persulfate.

[0042] Matters not covered in the present invention are well-known technologies. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a sulfur-doped nitrogen-containing carbon material, characterized in that: The steps include: S1. Dry the conductive polymer in an oven at 75 °C for 24 h, then place the dried conductive polymer in a tube furnace, raise the temperature to 300-900 °C at a heating rate of 5 °C / min under nitrogen protection, and directly calcine the conductive polymer at this temperature for 240 min to obtain a nitrogen-containing carbon material; S2, mixing the nitrogen-containing carbon material and the sulfur source in proportion, and grinding them in an agate mortar for 10-20 min; S3. Place the ground mixture in a tubular furnace, raise the temperature to 550°C at a heating rate of 5°C / min under nitrogen protection, and calcine at this temperature for 240 min to obtain a sulfur-doped nitrogen-containing carbon material catalyst.

2. The method for preparing a sulfur-doped nitrogen-containing carbon material according to claim 1, characterized in that: The conductive polymer in S1 includes polyaniline or polypyrrole.

3. The method for preparing a sulfur-doped nitrogen-containing carbon material according to claim 1, characterized in that: The sulfur source in S2 is thiourea.

4. The method for preparing a sulfur-doped nitrogen-containing carbon material according to claim 1, characterized in that: The mass ratio of the nitrogen-containing carbon material to the sulfur source in S2 is 1-2:1-5.

5. A sulfur-doped nitrogen-containing carbon material prepared by the preparation method as claimed in claim 1 is used to remove phenol in water.

6. The sulfur-doped nitrogen-containing material catalyst according to claim 5 is used to remove phenol from water, characterized in that: The steps include: S1. Add the sulfur-doped nitrogen-containing carbon material catalyst to the prepared phenol solution, and place it in a magnetic stirrer to stir evenly; S2. After stirring evenly, add persulfate to initiate the reaction.

7. The sulfur-doped nitrogen-containing carbon material according to claim 6 is used to remove phenol in water, characterized in that: The volume of the phenol solution in S1 is 100-1000 mL, the concentration is 25-100 mg / L, the pH is 3-11, and the amount of the sulfur-doped nitrogen-containing carbon material catalyst is 10-60 mg.

8. The sulfur-doped nitrogen-containing carbon material according to claim 6 is used to remove phenol in water, characterized in that: The concentration of the persulfate in S2 is 0.5-3 mM, and the reaction time is 0-60 min.

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