A nitrogen-doped carbon nanofiber ozone catalyst, preparation method and application

Abstract

The present invention provides a nitrogen-doped carbon nanofiber catalyst for ozone catalytic oxidation, which comprises selecting one or more of water-soluble polymers such as polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and polyethylene oxide (PEO) as carbon sources, urea as a nitrogen source, and water as a solvent to prepare an electrospinning precursor solution. Through electrospinning, stabilization, and carbonization processes at high temperatures, the preparation of the nitrogen-doped carbon nanofiber ozone catalyst is achieved. By adjusting the ratio of the carbon source and the nitrogen source in the precursor solution, a nitrogen-doped carbon nanofiber ozone catalyst with a nitrogen element doping mass fraction of 0.1-25% can be prepared. Due to the high efficiency of the nitrogen-doped carbon nanofiber catalyst in activating ozone, the catalyst can be used in various chemical wastewater treatment fields to degrade refractory organic substances in sewage, etc. It is especially suitable for refractory biodegradable sewage with BOD5 < 0.3, and can reduce the COD of the wastewater Cr from 800 mg / L to below 30 mg / L, achieving the up-to-standard discharge of the wastewater or meeting the standard for recycling of circulating water.

Description

Technical Field

[0001] The present invention relates to the field of environmental protection technology, and in particular to a nitrogen-doped carbon nanofiber ozone catalyst, a preparation method and an application thereof. Background Art

[0002] In recent years, with the severe environmental situation and the direction of national policies, the standards for sewage discharge and recycling have become increasingly stringent, and sewage treatment has become particularly important. Chemical industry production often produces difficult-to-degrade industrial wastewater, mainly including phenols, polycyclic aromatic compounds, thiocyanates and other difficult-to-degrade organic pollutants. Using traditional general deep treatment methods such as physical and chemical treatment, biochemical treatment and coagulation and sedimentation, it is difficult to meet the standards for discharge or recycling, which usually manifests as excessive COD, high chroma, high toxicity and other problems, requiring further deep treatment of the effluent.

[0003] At present, the commonly used deep treatment methods are adsorption, ozone oxidation and catalytic ozone oxidation. The principle of ozone degradation of organic matter is: under the induction of hydroxide ions in water, ozone is decomposed into hydroxyl radicals. Hydroxyl radicals have a high oxidation potential, strong oxidation ability, and no selectivity. They can indiscriminately degrade almost all organic matter in wastewater into carbon dioxide and water, which is especially suitable for difficult-to-degrade organic matter. The purpose of catalytic ozonation is mainly to trigger a chain reaction of ozone under the action of a catalyst to produce more hydroxyl radicals, while reducing intermediate products that may become free radical inhibitors, thereby improving the effective decomposition rate of ozone and the removal rate of organic matter.

[0004] Conventional catalytic ozone technology uses homogeneous or heterogeneous metal ion catalysts. The addition or leaching of metal ions causes secondary pollution of wastewater. After the degradation of organic matter, other treatment processes must be added to remove metal ions, thereby increasing the cost of wastewater treatment. At the same time, the metal ions of organic catalysts leach out, and the ion concentration in the wastewater will gradually decrease, resulting in a decrease in catalytic efficiency, low ozone utilization rate, and high cost. In addition, the metal ions used for catalysis are often toxic, which has a negative impact on the compliance of wastewater discharge or recycling. It is very necessary to develop an efficient non-metallic ozone catalytic oxidation catalyst. Therefore, the present invention provides a nitrogen-doped carbon nanofiber ozone catalyst, a preparation method and an application. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a nitrogen-doped carbon nanofiber ozone catalyst, a preparation method and an application thereof.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] On the one hand, the present invention provides a nitrogen-doped carbon nanofiber ozone catalyst, which is prepared by using one or more of polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP) or polyethylene oxide (PEO) as a carbon source and urea (Urea) as a nitrogen source through a process of preparing a precursor solution, electrospinning, fiber stabilization and high-temperature carbonization, and the mass fraction of nitrogen in the ozone catalyst is 0.1 to 25%.

[0008] In another aspect, the present invention provides a method for preparing a nitrogen-doped carbon nanofiber ozone catalyst, comprising the following steps:

[0009] Step 1: Prepare the precursor solution:

[0010] Dispersing a water-soluble polymer and urea in water as a precursor solution for electrospinning, wherein the water-soluble polymer is one or more of polyvinyl alcohol, polyvinyl pyrrolidone or polyethylene oxide;

[0011] Step 2: Electrospinning:

[0012] The precursor solution obtained in step 1 is subjected to electrospinning at 80-120° C., and an aluminum foil is used as a receiving plate to receive the polymer nanofibers;

[0013] Step 3: Fiber stabilization:

[0014] placing the polymer nanofibers obtained in step 2 in a tubular furnace for carbonization to promote the stability of the polymer nanofibers to obtain stable fibers;

[0015] Step 4: High temperature carbonization:

[0016] Under the protection of an argon atmosphere, the stable fibers obtained in step three are carbonized at high temperature using a tubular furnace to obtain nitrogen-doped carbon nanofibers.

[0017] Furthermore, in step 1, the dispersion process of the water-soluble polymer and urea in water is carried out by stirring at 60° C. for 4 hours.

[0018] Furthermore, in step 2, the parameters of the electrospinning are: spinning voltage 50-70 kV, preferably 55-65 kV; spinning distance 10-20 cm, preferably 13-18 cm.

[0019] Furthermore, in step three, the carbonization conditions are: heating rate 5°C / min, carbonization temperature 250°C, and insulation time 2 to 3h.

[0020] Furthermore, in step 4, the carbonization conditions are: heating rate 5°C / min, carbonization temperature 450°C, and insulation time 1 to 3 hours.

[0021] In one aspect, the present invention provides an application of a nitrogen-doped carbon nanofiber ozone catalyst in treating industrial wastewater, wherein the COD Cr The concentration of ozone is 60-800 mg / L, the dosage of ozone is 15-80 mg / L, and the residence time in the catalyst layer is 20-80 min.

[0022] The beneficial effects of the present invention are:

[0023] 1. The nitrogen-doped carbon nanofiber ozone catalyst provided by the present invention is a non-metallic heterogeneous catalyst. Due to nitrogen doping, the carbon atoms connected to nitrogen on the carbon nanotubes have catalytic activity similar to that of metals. By changing the ratio of the carbon source and the nitrogen source and adjusting the CN sites with catalytic oxidation activity, a nitrogen-doped carbon nanofiber ozone catalyst with a mass fraction of 0.1 to 25% of the doped nitrogen element can be prepared. Because it has an adjustable nitrogen doping amount, its catalytic activity can also be adjusted. The catalyst is easy to prepare and has good initiation ability for the chain reaction of ozone;

[0024] 2. Currently, metal catalysts commonly used for ozone oxidation often have the problem of rapid activity decline due to the loss of active center metal. The nitrogen-doped carbon nanofiber ozone catalyst provided by the present invention has a CN active site connected to the surrounding atoms by a covalent bond with highly delocalized electrons, so the active site is not easily lost and the catalyst has good stability;

[0025] 3. The nitrogen-doped carbon nanofiber ozone catalyst provided by the present invention can be conveniently recovered and reused by filtering after the reaction is completed;

[0026] 4. The present invention provides a method for treating industrial wastewater by ozone catalytic oxidation, which has a simple process flow, can significantly improve the ability of ozone to degrade CODCr, greatly improve the utilization rate of ozone, and reduce treatment costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the X-ray photoelectron spectrum of nitrogen-doped carbon nanofiber ozone catalyst;

[0028] Figure 2 The dispersion energy spectrum of C and N elements of nitrogen-doped carbon nanofiber ozone catalyst;

[0029] Figure 3 This is a 1μm scale electron microscope photo of nitrogen-doped carbon nanofiber ozone catalyst;

[0030] Figure 4 This is a 10μm scale electron microscope photo of nitrogen-doped carbon nanofiber ozone catalyst;

[0031] Figure 5 This is a 100μm scale electron microscope photo of nitrogen-doped carbon nanofiber ozone catalyst. DETAILED DESCRIPTION

[0032] In order to solve the problems of secondary pollution of metal ion catalysts, low ozone utilization rate, easy loss of catalyst active components, etc. when the existing catalytic ozone method is used for deep treatment of wastewater, the present invention provides a wastewater deep treatment process with nitrogen-doped carbon nanofiber ozone catalyst as the core, which has the advantages of non-metallic catalyst, stable catalyst, difficult loss of active components, simple process flow, and can significantly improve the ozone degradation of COD Cr The ability to greatly improve the utilization rate of ozone and reduce treatment costs.

[0033] Example 1

[0034] 183g polyvinyl alcohol (PVA) and 0.214g urea (Urea) were dissolved in water to prepare a 10wt% aqueous solution as an electrospinning precursor solution. The precursor solution was stirred at 60°C for 4h to obtain a PVA / Urea spinning precursor solution. Electrospinning was performed at 110°C, the spinning voltage was 60kV, the spinning distance was 15cm, and a layer of aluminum foil was laid on the receiving device as a receiving plate. The obtained polymer nanofibers were placed in a tubular furnace and subjected to the following fiber stabilization and carbonization process: the temperature was increased from room temperature to 250°C at a heating rate of 5°C / min and kept warm for 2h; then, under the protection of an argon atmosphere, the temperature was increased to 450°C at the same heating rate and kept warm for 2h, and finally, the nitrogen-doped carbon nanofiber ozone catalyst was obtained under the protection of an argon atmosphere. The N doping amount was about 0.1%.

[0035] Example 2

[0036] 100g polyvinyl alcohol (PVA) and 10g urea (Urea) were dissolved in water to prepare a 10wt% aqueous solution as an electrospinning precursor solution. The precursor solution was stirred at 60°C for 4h to obtain a PVA / Urea spinning precursor solution. Electrospinning was performed at 110°C, the spinning voltage was 60kV, the spinning distance was 15cm, and a layer of aluminum foil was laid on the receiving device as a receiving plate. The obtained polymer nanofibers were placed in a tubular furnace and subjected to the following fiber stabilization and carbonization process: the temperature was increased from room temperature to 250°C at a heating rate of 5°C / min and kept warm for 2h; then, under the protection of an argon atmosphere, the temperature was increased to 450°C at the same heating rate and kept warm for 2h, and finally, the nitrogen-doped carbon nanofiber ozone catalyst was obtained under the protection of an argon atmosphere, and the N doping amount was about 7.6%.

[0037] Example 3

[0038] 100g polyvinyl alcohol (PVA) and 40g urea (Urea) were dissolved in water to prepare a 10wt% aqueous solution as an electrospinning precursor solution. The precursor solution was stirred at 60°C for 4h to obtain a PVA / Urea spinning precursor solution. Electrospinning was performed at 110°C, the spinning voltage was 70kV, the spinning distance was 18cm, and a layer of aluminum foil was laid on the receiving device as a receiving plate. The obtained polymer nanofibers were placed in a tubular furnace and subjected to the following fiber stabilization and carbonization process: the temperature was increased from room temperature to 250°C at a heating rate of 5°C / min and kept warm for 3h; then, under the protection of an argon atmosphere, the temperature was increased to 450°C at the same heating rate and kept warm for 3h, and finally, the nitrogen-doped carbon nanofiber ozone catalyst was obtained under the protection of an argon atmosphere, and the N doping amount was about 23.0%.

[0039] Example 4

[0040] 100g polyvinyl pyrrolidone (PVP) and 10g urea (Urea) were dissolved in water to prepare a 10wt% aqueous solution as an electrospinning precursor solution. The precursor solution was stirred at 60°C for 4h to obtain a PVP / Urea spinning precursor solution. Electrospinning was performed at 90°C, the spinning voltage was 60kV, the spinning distance was 15cm, and a layer of aluminum foil was laid on the receiving device as a receiving plate. The obtained polymer nanofibers were placed in a tubular furnace and subjected to the following fiber stabilization and carbonization process: the temperature was increased from room temperature to 250°C at a heating rate of 5°C / min and kept warm for 2h; then, under the protection of an argon atmosphere, the temperature was increased to 450°C at the same heating rate and kept warm for 2h, and finally, the nitrogen-doped carbon nanofiber ozone catalyst was obtained under the protection of an argon atmosphere, and the N doping amount was about 20.5%.

[0041] Example 5

[0042] 100g polyvinyl pyrrolidone (PVP) and 1g urea (Urea) were dissolved in water to prepare a 10wt% aqueous solution as an electrospinning precursor solution. The precursor solution was stirred at 60°C for 3h to obtain a PVP / Urea spinning precursor solution. Electrospinning was performed at 90°C, the spinning voltage was 60kV, the spinning distance was 15cm, and a layer of aluminum foil was laid on the receiving device as a receiving plate. The obtained polymer nanofibers were placed in a tubular furnace and subjected to the following fiber stabilization and carbonization process: the temperature was increased from room temperature to 250°C at a heating rate of 5°C / min and kept warm for 2h; then, under the protection of an argon atmosphere, the temperature was increased to 450°C at the same heating rate and kept warm for 2h, and finally, the nitrogen-doped carbon nanofiber ozone catalyst was obtained under the protection of an argon atmosphere, and the N doping amount was about 16.7%.

[0043] Example 6

[0044] 100g polyethylene oxide (PEO) and 2g urea (Urea) were dissolved in water to prepare a 10wt% aqueous solution as an electrospinning precursor solution. The precursor solution was stirred at 60°C for 4h to obtain a PEO / Urea spinning precursor solution. Electrospinning was performed at 90°C, the spinning voltage was 65kV, the spinning distance was 14cm, and a layer of aluminum foil was laid on the receiving device as a receiving plate. The obtained polymer nanofibers were placed in a tubular furnace and subjected to the following fiber stabilization and carbonization process: the temperature was increased from room temperature to 250°C at a heating rate of 5°C / min and kept warm for 3h; then, under the protection of an argon atmosphere, the temperature was increased to 450°C at the same heating rate and kept warm for 2h, and finally, the nitrogen-doped carbon nanofiber ozone catalyst was obtained under the protection of an argon atmosphere, and the N doping amount was about 1.7%.

[0045] The XPS spectra of the nitrogen-doped carbon nanofiber ozone catalysts prepared in Examples 1 to 6 are ( Figure 1 )、C and N element EDS spectra ( Figure 2 ) and morphology ( Figures 3 to 5 ) are similar, the main difference lies in the different amounts of nitrogen doping, which also leads to different catalytic activities.

[0046] Comparative Example 1

[0047] 100g of polyvinyl alcohol (PVA) was dissolved in water to prepare a 10wt% aqueous solution as an electrospinning precursor solution. The precursor solution was stirred at 60°C for 4h to obtain a PVA spinning precursor solution. Electrospinning was performed at 110°C, the spinning voltage was 60kV, the spinning distance was 15cm, and a layer of aluminum foil was laid on the receiving device as a receiving plate. The obtained polymer nanofibers were placed in a tubular furnace and subjected to the following fiber stabilization and carbonization process: the temperature was increased from room temperature to 250°C at a heating rate of 5°C / min and kept warm for 2h; then, under the protection of an argon atmosphere, the temperature was increased to 450°C at the same heating rate and kept warm for 2h, and finally, the carbon nanofiber ozone catalyst was obtained under the protection of an argon atmosphere and cooled to room temperature.

[0048] Industrial wastewater degradation test:

[0049] An ozone oxidation reactor with the same specifications and an effective volume of 50 ml was used, and the nitrogen-doped carbon nanofiber ozone catalyst prepared in Examples 1 to 6, the nitrogen-free carbon nanofiber ozone catalyst prepared in Comparative Example 1, and the purchased commercial alumina-supported copper ozone catalyst (supporting 0.5% of metal copper ions) were filled with the same mass. Cr The ozone dosage was 40 mg / L and the hydraulic retention time was 30 min. The comparison of the ozone catalytic oxidation effect evaluation results is shown in Table 1.

[0050] Table 1 Ozone catalyst treatment effect evaluation table

[0051]

[0052]

[0053] It can be seen from Table 1 that non-nitrogen-doped carbon nanofibers also have a certain catalytic activity. The activation effect of nitrogen-doped carbon nanofiber catalyst on ozone is significantly enhanced, which can significantly improve the removal of COD in sewage by ozone. Cr At the same time, the ozone catalytic effect of the nitrogen-doped carbon nanofiber catalysts prepared in Examples 1 to 6 is significantly better than that of commercial ozone catalysts. The nitrogen-doped carbon nanofiber ozone catalyst can make COD Cr Drop to below 30mg / L, COD Cr The relative removal rate can reach over 85%.

[0054] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. Application of nitrogen-doped carbon nanofiber ozone catalyst in treating industrial wastewater, It is characterized in that The ozone catalyst uses one or more of polyvinyl alcohol, polyvinyl pyrrolidone or polyethylene oxide as a carbon source and urea as a nitrogen source, and is prepared by preparing a precursor solution, electrospinning, fiber stabilization and high-temperature carbonization. The mass fraction of nitrogen in the ozone catalyst is 0.1 to 25%. The COD of the industrial wastewater Cr The concentration is 60-800 mg / L and the residence time in the catalyst layer is 20-80 min.

2. Application of the nitrogen-doped carbon nanofiber ozone catalyst according to claim 1 in treating industrial wastewater, It is characterized in that The preparation method of the nitrogen-doped carbon nanofiber ozone catalyst comprises the following steps: Step 1: Prepare the precursor solution: Dispersing a water-soluble polymer and urea in water as a precursor solution for electrospinning, wherein the water-soluble polymer is one or more of polyvinyl alcohol, polyvinyl pyrrolidone or polyethylene oxide; Step 2: Electrospinning: The precursor solution obtained in step 1 is subjected to electrospinning at 80-120° C., and an aluminum foil is used as a receiving plate to receive the polymer nanofibers; Step 3: Fiber stabilization: placing the polymer nanofibers obtained in step 2 in a tubular furnace for carbonization to promote the stability of the polymer nanofibers to obtain stable fibers; Step 4: High temperature carbonization: Under the protection of an argon atmosphere, the stable fibers obtained in step three are carbonized at high temperature using a tubular furnace to obtain nitrogen-doped carbon nanofibers.

3. Application of the nitrogen-doped carbon nanofiber ozone catalyst according to claim 2 in treating industrial wastewater, It is characterized in that In step 1, the dispersion process of the water-soluble polymer and urea in water is stirred at 60° C. for 4 hours.

4. Application of a nitrogen-doped carbon nanofiber ozone catalyst according to claim 2 in treating industrial wastewater, It is characterized in that In step 2, the electrospinning parameters are: spinning voltage 50-70 kV, spinning distance 10-20 cm.

5. Application of a nitrogen-doped carbon nanofiber ozone catalyst in treating industrial wastewater according to claim 2, It is characterized in that In step 3, the carbonization conditions are: heating rate 5°C / min, carbonization temperature 250°C, and insulation time 2 to 3h.

6. Application of a nitrogen-doped carbon nanofiber ozone catalyst in treating industrial wastewater according to claim 2, It is characterized in that In step 4, the carbonization conditions are: heating rate 5°C / min, carbonization temperature 450°C, and insulation time 1 to 3 hours.

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