CoMn@NG catalyst, preparation method thereof and application of CoMn@NG catalyst in activated peroxymonosulfate degradation of organic pollutants

Abstract

The application discloses a CoMn@NG catalyst and a preparation method and application of the CoMn@NG catalyst in degrading organic pollutants by activating persulfate, and the preparation method of the catalyst is as follows: graphene oxide, urea and deionized water are added into an inner container, and after being uniformly ultrasonically treated, the mixture is moved into a reaction kettle to perform hydrothermal reaction; the product after the reaction is finished is cleaned with a large amount of ethanol and deionized water, the cleaned nitrogen-doped graphene is dissolved in N, N-dimethylformamide, a cobalt source and a manganese source are added, and oil bath reaction is performed for a period of time; after the reaction is finished, the product is again cleaned with a large amount of ethanol and deionized water; then, the product is placed into a freeze-drying machine to be frozen; finally, the product is placed into a tube furnace to be heat-treated for a period of time under a nitrogen atmosphere, so that the CoMn@NG catalyst is obtained. The catalyst has high catalytic activity and good stability, and can be used for degrading organic pollutants by activating persulfate. The method for degrading organic pollutants disclosed by the application has the advantages of simple operation, high degradation efficiency, stable reaction, high catalyst efficiency and stability, and can be applied to actual wastewater treatment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heterogeneous catalysts, and particularly relates to a CoMn@NG catalyst, a preparation method thereof and application of the CoMn@NG catalyst in activating peroxymonosulfate to degrade organic pollutants. BACKGROUND

[0002] At present, advanced oxidation technology is one of the research hotspots for treating organic pollutants at home and abroad. The purpose of advanced oxidation technology is to use different physical or chemical means and catalysts to activate or catalyze oxidants to generate active substances with strong oxidation, so as to efficiently degrade and even completely mineralize some refractory pollutants.

[0003] Compared with other advanced oxidation technologies for generating hydroxyl radicals, the advanced oxidation technology based on persulfate has been rapidly developed due to its stronger oxidation ability, wider pH application range and better selectivity. In addition, persulfate has low storage requirements, low cost, and its operation process is simple and safe, can exist for a long time and effectively oxidize organic pollutants, and has very good commercial value and application prospect.

[0004] Due to the limited ability of persulfate to directly oxidize pollutants, it cannot achieve rapid and complete removal of many pollutants, so a large number of methods for effectively activating persulfate are developed to improve its efficiency in oxidizing and degrading pollutants. At present, some physical processes (ultraviolet, ultrasonic, heat), alkaline activation, metal ions (Fe 2+ , Co 2+ , Fe 0 ) and metal oxides (Co oxides, Cu-Fe composite oxides, Mn-Fe composite oxides), reducing organic matter (benzoquinone) and carbon materials (graphene oxide, carbon nanotubes) can effectively activate persulfate to generate strong oxidizing free radicals or other oxidizing active substances.

[0005] It is found that in the persulfate activation technology, the carbon material-based activation technology has obvious advantages because it can effectively degrade organic pollutants, is efficient, economical, environmentally friendly and easy to prepare. Therefore, in the research of persulfate activation, the synthesis and modification of new carbon materials will become a new research hotspot. Graphene is used as an excellent carbon material for catalysts in various chemical processes due to its large specific surface area, excellent mechanical properties, high thermal conductivity, high optical transmittance and high electron mobility.

[0006] The excellent performance of graphene makes it a substrate material for single-atom catalysts. Doping graphene with heteroatoms such as N, S, and P can increase defect sites and increase electron transfer, preparing for the next step of incorporating metal atoms. Traditional transition metals such as Co, Fe, and Ni can be anchored on nitrogen-doped graphene, greatly increasing the reactivity. However, different metals in the system of activating persulfate can cause different reaction mechanisms, and different metals have different reactivity. As the reaction proceeds, the dissolution of the metal is the main reason for the decrease in the efficiency of pollutant degradation. Therefore, it is urgent to develop a catalyst with high activity and stability that can effectively activate persulfate to efficiently remove organic pollutants in water. SUMMARY

[0007] In view of the above technical problems existing in the prior art, the purpose of the present application is to provide a preparation method of CoMn@NG catalyst and its application in degrading organic pollutants by activating peroxymonosulfate.

[0008] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0009] The preparation method of the CoMn@NG catalyst comprises the following steps:

[0010] In the first step, graphene oxide, a nitrogen source, and deionized water are added to the inner container, ultrasonically mixed, and then moved into a reaction kettle for hydrothermal reaction. After the reaction is completed, the solid product is collected by centrifugation after natural cooling, and nitrogen-doped graphene is obtained.

[0011] In the second step, the nitrogen-doped graphene is washed with ethanol and deionized water, and then dissolved in an organic solvent. Cobalt and manganese sources are added and reacted under oil bath heating for a period of time. After the reaction is completed, the solid product is collected by centrifugation, washed again with ethanol and deionized water, then frozen in a freeze-drying machine, and finally heat-treated in a tube furnace under a nitrogen atmosphere to obtain the CoMn@NG catalyst.

[0012] Further, in the first step, the nitrogen source is urea, and the mass ratio of urea to graphene oxide is 20-30:1. The concentration of graphene oxide dispersed in deionized water is 0.5-3g / L.

[0013] Further, in the first step, the temperature of the hydrothermal reaction is 145-160℃, and the reaction time is 3-4h.

[0014] Further, in the second step, the cobalt source is cobalt nitrate hexahydrate, and the manganese source is anhydrous manganese chloride. The mass ratio of the cobalt source to the manganese source is 1.2-1.6:1, and the mass ratio of the cobalt source to graphene oxide in step one is 1.5-2:1.

[0015] Further, in the second step, the temperature of the oil bath reaction is 60-80 DEG C, and the reaction time is 12-15 h; the organic solvent is N, N-dimethylformamide.

[0016] Further, in the second step, the heat treatment condition is that the temperature is raised from room temperature to 500-600 DEG C at a temperature raising rate of 2-5 DEG C / min in a nitrogen atmosphere, then the temperature is kept for 180-210 min, and finally the temperature is naturally cooled to room temperature.

[0017] The application further provides application of the CoMn@NG catalyst in degradation of organic pollutants in an activated persulfate system, and the application method comprises the following steps:

[0018] 1) CoMn@NG catalyst is ultrasonically dispersed in an organic solvent, and the obtained mixture is filtered on a microporous filtration membrane to prepare a CoMn@NG membrane;

[0019] 2) The CoMn@NG membrane is installed in a filtration type reactor, an organic pollutant solution containing persulfate is pumped into the filtration type reactor by a perfusion pump, the solution enters from one side of the CoMn@NG membrane to the other side, an activation reaction is carried out, persulfate is activated on the CoMn@NG membrane to generate free radicals and non-free radicals with strong oxidizing property, so that the organic pollutants can be effectively degraded, and the solution flowing out of the filtration type reactor is the solution after the organic pollutants are degraded.

[0020] Further, the loading amount of the CoMn@NG catalyst on the microporous filtration membrane is 0.4-1.0 mg / cm 2 , the pore size of the microporous filtration membrane is 1-10 μm, preferably 3-5 μm;

[0021] The organic solvent in step 1) is N, N-dimethylformamide;

[0022] In the organic pollutant solution containing persulfate in step 2), the persulfate is potassium monopersulfate, the concentration is 0.5-1.5 mM, and the concentration of the organic pollutants is less than 5 mg / mL.

[0023] Further, the organic pollutants are levofloxacin LVF, and the flux of the organic pollutant solution containing persulfate through the CoMn@NG membrane is 1-3 mL / (cm 2 *h).

[0024] Compared with the prior art, the application has the following advantages:

[0025] (1) The nitrogen-doped graphene with a large specific surface area is used as the carrier in the application, which is beneficial to the dispersion and fixation of the single-atom catalyst, the porous structure can realize rapid mass and energy transfer, and the adjustable chemical coordination environment. The rich N atoms as anchoring centers are beneficial to anchoring and dispersing single-atom Co / Mn centers. During the high-temperature treatment process, a large number of N atoms will form coordination with metal Co / Mn, and the metal dissolution of single-atom Co / Mn is reduced compared with single-atom Co, and the structural stability is increased, which is expected to exhibit high and stable catalytic performance in the activation of persulfate to remove levofloxacin.

[0026] (2) The CoMn@NG catalyst of the application can efficiently and stably activate persulfate. The activation effect of the CoMn@NG catalyst of the application on persulfate is obviously higher than that of NG, CoFe@NG and FeMn@NG, because compared with NG, new active sites can be introduced in the material after cobalt-manganese doping, the active sites increase, and the catalytic ability of CoMn@NG is enhanced. Compared with CoFe@NG and FeMn@NG, the metal dissolution of CoMn@NG catalyst is reduced during the reaction, so that the reaction can maintain at a high degradation level for a longer time.

[0027] (3) In the application, the synthesis process of the catalyst is simple, the operation is safe, and the requirements for preparation conditions and preparation equipment are low. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The XRD comparison chart of the CoMn@NG catalyst prepared in Example 1 of the application and the catalysts of Comparative Examples 1-3.

[0029] Figure 2 The SEM chart of the CoMn@NG catalyst prepared in Example 1 of the application.

[0030] Figure 3 The effect chart of activating persulfate to remove organic pollutants under different catalyst conditions in Example 2 and Comparative Example 7 of the application.

[0031] Figure 4 The removal effect chart of pollutants under different pollutant concentrations in Example 2 and Comparative Example 5 of the application.

[0032] Figure 5 The removal effect of pollutants LVF under different potassium hydrogen persulfate PMS concentrations in Example 2 and Comparative Example 6 of the application. DETAILED DESCRIPTION

[0033] Preparation of CoMn@NG catalyst in Example 1

[0034] (1) Take 2 g of urea and put it into 80 ml of 1 g / L graphene oxide water dispersion, pour it into a reaction kettle, and put the reaction kettle into an oven for hydrothermal reaction, the reaction temperature is 150 DEG C, and the reaction time is 3.5 h. After the reaction is completed, centrifugal collection of the solid product is performed after natural cooling, and nitrogen-doped graphene is obtained.

[0035] (2) After the nitrogen-doped graphene is washed with a large amount of ethanol and deionized water, it is dissolved in 120 ml of N,N-dimethylformamide, then 0.1455 g of cobalt nitrate hexahydrate and 0.1 g of anhydrous manganese chloride are added, and the reaction is carried out at 60 DEG C for 12 h, and the stirring is continuously performed during the process.

[0036] (3) After the reaction is completed, the solid product is centrifugally collected, and then washed with a large amount of ethanol and deionized water, and then placed in a -80 DEG C freeze dryer for 1-2 days.

[0037] (4) The freeze-dried sample is placed in a tube furnace, heated from room temperature to 500 DEG C at a temperature rising rate of 2 DEG C / min in a nitrogen atmosphere, and then naturally cooled to room temperature after being heat-treated at 500 DEG C for 180 min, to obtain a CoMn@NG catalyst, and the SEM image thereof is shown in Figure 2 .

[0038] Preparation of NG catalyst in Comparative Example 1

[0039] The preparation steps of the NG catalyst in Comparative Example 1 are the same as those in Example 1, except that the operation in step (2) of Example 1 is not performed.

[0040] Preparation of CoFe@NG catalyst in Comparative Example 2

[0041] The preparation steps of the CoFe@NG catalyst in Comparative Example 2 are the same as those in Example 1, except that “0.1 g of anhydrous manganese chloride in step (2) of Example 1 is replaced by 0.08125 g of anhydrous ferric chloride”.

[0042] Preparation of FeMn@NG catalyst in Comparative Example 3

[0043] The preparation steps of the CoFe@NG catalyst in Comparative Example 3 are the same as those in Example 1, except that “0.1455 g of cobalt nitrate hexahydrate in step (2) of Example 1 is replaced by 0.08125 g of anhydrous ferric chloride”.

[0044] The XRD comparison chart of the CoMn@NG catalyst prepared in Example 1 and the catalysts in Comparative Examples 1-3 is shown in Figure 1 . Figures 1-2 It can be seen from the chart that Co and Mn atoms are doped into the catalyst, and no metal oxide is generated.

[0045] Example 2 Experiment of CoMn@NG catalyst activating persulfate to remove organic pollutants

[0046] 10 mg of CoMn@NG catalyst obtained in Example 1 was weighed and dispersed in 50 ml of N, N-dimethylformamide, and after ultrasonic treatment for 30 min, a mixed solution was vacuum filtered using a PTFE filter membrane with a pore size of 4.5 μm (filtering area of 17.34 cm 2 ) to prepare a CoMn@NG membrane. Then, a wastewater solution containing 1 mM PMS and 25 ppm LVF was pumped into the filter reactor at a delivery flow rate of 0.5 mL / min by a peristaltic pump, and the wastewater solution entered from one side of the CoMn@NG membrane to the other side, and the solution filtered out of the filter reactor was the solution after the degradation of the organic pollutants.

[0047] Comparative Example 4

[0048] The experimental operation steps of Comparative Example 4 are the same as those of Example 2, except that no potassium hydrogen persulfate (PMS) is added to the wastewater solution.

[0049] Comparative Example 5

[0050] The experimental operation steps of Comparative Example 5 are the same as those of Example 2, except that the concentration of the pollutant LVF in the wastewater solution is adjusted to 10 ppm, 50 ppm and 100 ppm respectively, and the concentration of PMS is maintained at 1 mM.

[0051] The removal effect of pollutants at different pollutant concentrations in Example 2 and Comparative Example 5 is shown in Figure 4 , and it can be seen that the degradation efficiency decreases with the increase of the concentration of the pollutant. When the concentration of the pollutant LVF in the wastewater solution is below 50 ppm, especially below 25 ppm, the degradation of the pollutant LVF can achieve good results.

[0052] Comparative Example 6

[0053] The experimental operation steps of Comparative Example 6 are the same as those of Example 2, except that the concentration of PMS in the wastewater solution is adjusted to 0.5 mM, 0.35 mM and 0.2 mM respectively, and the concentration of LVF is maintained at 25 ppm.

[0054] The removal effect of the pollutant LVF at different concentrations of potassium hydrogen persulfate (PMS) in Example 2 and Comparative Example 6 is shown in Figure 5 . It can be seen from Figure 5It can be seen that the degradation efficiency of LVF decreases with decreasing PMS concentration. When the PMS concentration in the wastewater solution is above 0.35 mM, the degradation of the pollutant LVF can achieve very good results.

[0055] Comparative Example 7

[0056] The experimental procedure of Comparative Example 7 differs from that of Example 2 only in that "the CoMn@NG catalyst obtained in Example 1 is replaced with the catalyst obtained in Comparative Examples 1-3 of equal mass". All other steps are the same as those in Example 2.

[0057] The removal efficiency of pollutant LVF under different catalyst conditions in Example 2 and Comparative Example 7 is shown in the figure above. Figure 3 .Depend on Figure 3 It is evident that nitrogen-doped graphene (NG) alone exhibits very low catalytic degradation efficiency. In contrast, the catalytic performance of CoFe@NG, FeMn@NG, and CoMn@NG catalysts is significantly improved. However, with prolonged degradation operation, the LVF concentration of the solution after catalytic degradation of organic pollutants by CoFe@NG and FeMn@NG catalysts gradually and significantly increases. This is due to the dissolution of active metals during prolonged operation. In contrast, the CoMn@NG catalyst exhibits reduced metal dissolution during the reaction, thus allowing the reaction to maintain a high-efficiency degradation level for a longer period.

[0058] in, Figures 3-5 The horizontal axis represents the total volume (mL) of the wastewater solution containing PMS and LVF passing through the CoMn@NG membrane, and the vertical axis represents the concentration (ppm) of LVF in the solution effluent from the filtration reactor.

Claims

1. The application of a CoMn@NG catalyst in the degradation of organic pollutants in an activated persulfate system, characterized in that, Preparation of the CoMn@NG catalyst Includes the following steps: The first step involves adding graphene oxide, a nitrogen source, and deionized water to the inner liner, ultrasonicating to homogenize the mixture, and then transferring it to a reaction vessel for hydrothermal reaction. After the reaction is complete and the mixture is allowed to cool naturally, the solid product is collected by centrifugation to obtain nitrogen-doped graphene. The second step involves washing the nitrogen-doped graphene with ethanol and deionized water. The washed nitrogen-doped graphene is then dissolved in an organic solvent. Cobalt and manganese sources are added and the mixture is reacted in an oil bath for a period of time. After the reaction is complete, the solid product is collected by centrifugation, washed again with ethanol and deionized water, and then placed in a freeze dryer for freezing. Finally, it is heat-treated in a tube furnace under a nitrogen atmosphere to obtain the CoMn@NG catalyst. In the second step, the cobalt source is cobalt nitrate hexahydrate, the manganese source is anhydrous manganese chloride, and the mass ratio of the cobalt source to the manganese source is 1.2~1.6:1; In the second step, the temperature of the oil bath reaction is 60~80 ℃, and the reaction time is 12~15 h.

2. The application according to claim 1, characterized in that, In the first step, the nitrogen source is urea, the mass ratio of urea to graphene oxide is 20-30:1, and the concentration of graphene oxide dispersed in deionized water is 0.5-3 g / L.

3. The application according to claim 1, characterized in that, In the first step, the temperature of the hydrothermal reaction is 145~160 ℃, and the reaction time is 3~4 h.

4. The application according to claim 1, characterized in that, In the second step, the mass ratio of cobalt source to graphene oxide in step one is 1.5 to 2:

1.

5. The application according to claim 1, characterized in that, In the second step, the organic solvent is N,N-dimethylformamide.

6. The application according to claim 1, characterized in that, In the second step, the heat treatment conditions are as follows: heating from room temperature to 500-600 ℃ in a nitrogen atmosphere at a heating rate of 2-5 ℃ / min, then holding the temperature for 180-210 min, and finally cooling naturally to room temperature.

7. The application according to claim 1, characterized in that, The application method includes the following steps: 1) After ultrasonically dispersing the CoMn@NG catalyst in an organic solvent, the resulting mixture is filtered onto a microporous filter membrane to prepare a CoMn@NG membrane; 2) The CoMn@NG membrane is installed in a filter reactor. The organic pollutant solution containing persulfate is pumped into the filter reactor through a pump. The solution enters from one side of the CoMn@NG membrane to the other side to carry out the activation reaction. The persulfate is activated on the CoMn@NG membrane to generate free radicals and non-free radicals with strong oxidizing properties, which can effectively degrade organic pollutants. The solution flowing out of the filter reactor is the solution after degrading organic pollutants.

8. The application according to claim 7, characterized in that, The loading capacity of CoMn@NG catalyst on microporous filtration membranes ranged from 0.4 to 1.0 mg / cm². 2 The pore size of the microporous filtration membrane is 1~10μm; The organic solvent mentioned in step 1) is N,N-dimethylformamide; In step 2), the organic pollutant solution containing persulfate contains potassium persulfate at a concentration of 0.5-1.5 mM, and the organic pollutant concentration is below 5 mg / mL.

9. The application according to claim 8, characterized in that, The pore size of the microporous filter membrane is 3~5μm.

10. The application according to claim 7, characterized in that, The organic pollutant is levofloxacin (LVF), and the flux of the organic pollutant solution containing persulfate through the CoMn@NG membrane is 1~3 mL / (cm). 2 *h).

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