CN111389438A - Preparation method and application of nitrogen-doped three-dimensional graphene-loaded manganese dioxide catalyst - Google Patents
Preparation method and application of nitrogen-doped three-dimensional graphene-loaded manganese dioxide catalyst Download PDFInfo
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Abstract
A preparation method and application of a nitrogen-doped three-dimensional graphene-loaded manganese dioxide catalyst relate to a preparation method and application of a catalyst. The invention aims to solve the problems that the existing catalyst is loose in structure and poor in effect of improving the effect of treating difficultly-degraded organic matters by ozone catalytic oxidation frequently after being soaked for a long time. The method comprises the following steps: firstly, preparing graphene oxide powder; secondly, preparing nitrogen-doped three-dimensional graphene aerogel with high elasticity; thirdly, loading a manganese dioxide catalyst. The application of the nitrogen-doped three-dimensional graphene-loaded manganese dioxide catalyst in an ozone catalytic oxidation system has high elasticity and mechanical strength and excellent catalytic effect, and experiments show that the treatment efficiency of target pollutants can reach 88% in 15min, is close to 100% in 25min, is high in treatment efficiency and good in mineralization degree, and the removal rate of TOC (total organic carbon) is increased by about 47% compared with that of a single ozonization system. The invention is suitable for removing the pollutants which are difficult to degrade.
Description
Technical Field
The invention relates to a preparation method and application of a catalyst.
Background
The heterogeneous ozone catalytic oxidation system is a system formed by adding a catalyst in the ozone oxidation process to cooperate with the ozone oxidation effect, so that the activation energy in the reaction process is reduced or the oxidation reaction process is changed, the purpose of deep oxidation is achieved, and organic pollutants are removed. Compared with a homogeneous ozone catalytic oxidation system, the system has solid phase, liquid phase and gas phase, so the reaction is more complicated. Generally, the oxidation efficiency and engineering utility value of this technology are affected by catalyst activity, stability and service life.
Carbon-based materials such as activated carbon, graphene, multi-walled carbon nanotubes, mesoporous carbon and the like have a good adsorption effect, and have been proved to be a very effective method for treating refractory organic matters in the aspect of ozone catalytic oxidation in recent years. The graphene has a two-dimensional layered structure and an sp2 carbon hybridization orbit, so that the graphene can act with pi bonds in an organic molecular structure to generate strong adsorption force. However, graphene nanolayers in a liquid phase can be laminated together due to the hydrophobicity of the graphene nanolayers and the action force of pi-pi bonds between the layers, so that a large number of active sites are concealed, a 3-dimensional integral porous macro structure generated by the self-combination of the nano-layered graphene can avoid the lamination phenomenon and promote mass transfer, and the graphene nanolayers are more convenient to collect and operate in water due to larger volume. In addition, researches show that the adsorption and degradation performance of the catalyst is obviously improved after the three-dimensional graphene is doped with nitrogen.
Due to MnO2Is often prepared in powder and nano-size to obtain high surface area and more reaction sites, but the small size is not suitable for its separation treatment in solution, causing secondary pollution, and since 3-dimensional graphene is in the order of cm, it is easily separated from water, and has good conductivity, which can accelerate the reaction rate. Therefore, the catalyst can be considered to be combined as the catalyst for catalytic oxidation of ozone, but the existing supported catalyst also has some problems, such as the problem that the catalyst soaked for a long time is often loose in structure, and the effect of improving the catalytic oxidation treatment of the difficultly-degraded organic matters by ozone is poor.
Disclosure of Invention
The invention aims to solve the problems that the existing catalyst is loose in structure and poor in effect of improving the degradation-resistant organic matter of ozone catalytic oxidation treatment frequently caused by long-time soaking, and provides a preparation method and application of a nitrogen-doped three-dimensional graphene-loaded manganese dioxide catalyst.
A preparation method of a nitrogen-doped three-dimensional graphene-loaded manganese dioxide catalyst is completed according to the following steps:
firstly, preparing graphene oxide powder:
firstly, preparing a graphene oxide solution by adopting an improved Hummer method, then drying and shearing the graphene oxide solution, and finally grinding and sieving to obtain graphene oxide powder;
secondly, preparing the nitrogen-doped three-dimensional graphene aerogel with high elasticity:
①, adding graphene oxide powder into deionized water, and performing ultrasonic dispersion to obtain a graphene oxide solution;
②, mixing the graphene oxide solution, the ethylenediamine and the sodium borate solution, and performing ultrasonic dispersion to obtain a mixture;
③, firstly putting the mixture into a high-pressure hydrothermal kettle with a polytetrafluoroethylene lining, then carrying out heat treatment on the high-pressure hydrothermal kettle with the polytetrafluoroethylene lining, and finally naturally cooling to room temperature to obtain a reaction product I, pouring the reaction product I into an ethanol water solution for dialysis to obtain a dialyzed reaction product I, wherein the reaction product I is a cylinder with the diameter of 0.8 cm-1 cm and the height of 0.3 cm-0.5 cm;
④, pre-freezing the reaction product I, and naturally drying at room temperature to obtain the nitrogen-doped three-dimensional graphene aerogel with high elasticity;
thirdly, loading a manganese dioxide catalyst:
①, firstly putting the nitrogen-doped three-dimensional graphene aerogel with high elasticity into a polytetrafluoroethylene-lined high-pressure hydrothermal kettle, and then adding KMnO4Completely immersing the nitrogen-doped three-dimensional graphene aerogel with high elasticity into KMnO4In the solution, finally, the high-pressure hydrothermal kettle with the polytetrafluoroethylene lining is subjected to heat treatment and then naturally cooled to room temperature to obtain a reaction product II；
②, firstly, washing the reaction product II by using deionized water, then, soaking the reaction product II in absolute ethyl alcohol, and finally, drying the reaction product II in a drying oven to obtain the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst.
The application of the nitrogen-doped three-dimensional graphene-loaded manganese dioxide catalyst in an ozone catalytic oxidation system.
The invention has the advantages that:
the method provided by the invention uses Graphene Oxide (GO) with the price which is reduced continuously in recent years, and has great advantages in the aspect of the manufacturing cost of the catalyst, meanwhile, the catalyst prepared by the method provided by the invention has high elasticity and mechanical strength, can recover to the original micro and macro morphology under the pressure strength of 1MPa, the Young modulus is almost unchanged after 50 times of extrusion, the ultimate stress is reduced by only 6% after 100 times of circulation, the repeated use efficiency is stable, and the catalyst can be recycled for multiple times, and the recycling operation is simple and easy because the catalyst is a heterogeneous catalyst;
the heterogeneous catalyst is adopted, the size of the catalyst is in the centimeter level, and the catalyst can be recycled after the test is finished, so that the possibility of practical engineering application is ensured;
the material is saved, the cost of the manganese oxide which is the effective component is low, and the cost of the graphene is gradually reduced in recent years although the graphene has a certain value, so that the method is economically feasible;
the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst prepared by the invention has excellent catalytic effect, and through experiments, the treatment efficiency of target pollutants can reach 88% in 15min, is close to 100% in 25min, has high treatment efficiency and good mineralization degree, and compared with the single ozonization TOC removal rate, the removal rate is improved by about 47% and can reach 75.31%, and the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst is rare in the existing catalyst;
the nitrogen-doped three-dimensional graphene-loaded manganese dioxide catalyst prepared by the invention has good effect after being recycled for multiple times, and after more than 10 times of recycling experiments, the removal effect of the catalyst on a target object can still be kept at about 95%, which shows that the catalyst has less loss in the recycling process and certain service life.
The invention is suitable for removing the pollutants which are difficult to degrade.
Drawings
Fig. 1 is an FTIR characterization, in which 1 is an FTIR profile of graphene oxide powder obtained in one step one of the example, 2 is an FTIR profile of nitrogen-doped three-dimensional graphene aerogel having high elasticity obtained in one step two ④ of the example, and 3 is an FTIR profile of nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst obtained in one step three ② of the example;
fig. 2 is a diagram of the removal effect of a catalyst on quinoline, in which fig. 1 is a curve of the removal effect of single ozonation on quinoline, fig. 2 is a curve of the removal effect of a three-dimensional graphene aerogel prepared in the first comparative example on quinoline, fig. 3 is a curve of the removal effect of a nitrogen-doped three-dimensional graphene aerogel with high elasticity obtained in the second step ④ of the example, and fig. 4 is a curve of the removal effect of a nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst obtained in the third step ② of the example on quinoline;
fig. 3 is a graph showing the removal effect of a catalyst on TOC, in which fig. 1 is a graph showing the removal effect of a single ozonation on TOC, fig. 2 is a graph showing the removal effect of a three-dimensional graphene aerogel prepared in the first comparative example on TOC, fig. 3 is a graph showing the removal effect of a nitrogen-doped three-dimensional graphene aerogel with high elasticity obtained in the second step ④ of the example, and fig. 4 is a graph showing the removal effect of a nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst obtained in the third step ② of the example on TOC.
Detailed Description
The first embodiment is as follows: a preparation method of a nitrogen-doped three-dimensional graphene-loaded manganese dioxide catalyst is completed according to the following steps:
firstly, preparing graphene oxide powder:
firstly, preparing a graphene oxide solution by adopting an improved Hummer method, then drying and shearing the graphene oxide solution, and finally grinding and sieving to obtain graphene oxide powder;
secondly, preparing the nitrogen-doped three-dimensional graphene aerogel with high elasticity:
①, adding graphene oxide powder into deionized water, and performing ultrasonic dispersion to obtain a graphene oxide solution;
②, mixing the graphene oxide solution, the ethylenediamine and the sodium borate solution, and performing ultrasonic dispersion to obtain a mixture;
③, firstly putting the mixture into a high-pressure hydrothermal kettle with a polytetrafluoroethylene lining, then carrying out heat treatment on the high-pressure hydrothermal kettle with the polytetrafluoroethylene lining, and finally naturally cooling to room temperature to obtain a reaction product I, pouring the reaction product I into an ethanol water solution for dialysis to obtain a dialyzed reaction product I, wherein the reaction product I is a cylinder with the diameter of 0.8 cm-1 cm and the height of 0.3 cm-0.5 cm;
④, pre-freezing the reaction product I, and naturally drying at room temperature to obtain the nitrogen-doped three-dimensional graphene aerogel with high elasticity;
thirdly, loading a manganese dioxide catalyst:
①, firstly putting the nitrogen-doped three-dimensional graphene aerogel with high elasticity into a polytetrafluoroethylene-lined high-pressure hydrothermal kettle, and then adding KMnO4Completely immersing the nitrogen-doped three-dimensional graphene aerogel with high elasticity into KMnO4In the solution, finally, carrying out heat treatment on the high-pressure hydrothermal kettle with the polytetrafluoroethylene lining, and naturally cooling to room temperature to obtain a reaction product II;
②, firstly, washing the reaction product II by using deionized water, then, soaking the reaction product II in absolute ethyl alcohol, and finally, drying the reaction product II in a drying oven to obtain the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst.
The advantages of this embodiment:
the method provided by the embodiment uses Graphene Oxide (GO) with the price which is reduced continuously in recent years, and has great advantages in the aspect of the manufacturing cost of the catalyst, meanwhile, the catalyst prepared by the method provided by the embodiment has high elasticity and mechanical strength, can recover to the original micro and macro morphology under the pressure strength of 1MPa, the Young modulus is almost unchanged after 50 times of extrusion, the ultimate stress is reduced by only 6% after 100 times of circulation, the repeated use efficiency is stable, the catalyst can be recycled for multiple times, and the catalyst is a heterogeneous catalyst, so the recycling operation is simple and easy;
the heterogeneous catalyst is adopted in the embodiment, the size of the catalyst is in the centimeter level, and the catalyst can be recycled after the test is finished, so that the possibility of practical engineering application is ensured;
the material is saved, the cost of the manganese oxide which is the effective component is low, and the cost of the graphene is gradually reduced in recent years although the graphene has a certain value, so that the method is economically feasible;
the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst prepared by the embodiment has excellent catalytic effect, and through experiments, the treatment efficiency of target pollutants can reach 88% in 15min, is close to 100% in 25min, has high treatment efficiency and good mineralization degree, and compared with the single ozonization TOC removal rate, the removal rate is improved by about 47% and can reach 75.31%, and the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst is rare in the existing catalyst;
fifth, the nitrogen-doped three-dimensional graphene-loaded manganese dioxide catalyst prepared by the embodiment is still good in effect after being recycled for multiple times, and after more than 10 times of recycling experiments, the removal effect of the catalyst on a target object can still be kept at about 95%, which indicates that the catalyst is less in loss in the recycling process and has a certain service life.
The embodiment is suitable for removing the pollutants which are difficult to degrade.
The second embodiment is as follows: the present embodiment differs from the present embodiment in that: the sheet diameter of the graphene oxide powder in the first step is 30-50 microns. Other steps are the same as in the first embodiment.
The third specific embodiment is different from the first specific embodiment or the second specific embodiment in that the concentration of the graphene oxide solution in the second step ① is 4mg/m L-8 mg/m L, the ultrasonic dispersion time in the second step ① is 20-40 min, and the ultrasonic power is 300-500W.
Fourth embodiment the present embodiment is different from the first to third embodiments in that the volume ratio of ethylenediamine to graphene oxide solution in the second ② is (60 μ L-100 μ L) to 10m L, the volume ratio of sodium borate solution to graphene oxide solution is (40 μ L-60 μ L) to 10m L, and other steps are the same as those in the first to third embodiments.
Fifth embodiment the difference between this embodiment and one of the first to fourth embodiments is that the ultrasonic dispersion time in step two ② is 5min to 15min, the ultrasonic power is 300W to 500W, the mass fraction of the sodium borate solution is 4% to 7%, and the other steps are the same as those in the first to fourth embodiments.
Sixth embodiment a sixth difference from the first to fifth embodiments is that the temperature of the heat treatment in the second step ③ is 120 to 140 ℃, the time of the heat treatment is 12 to 14 hours, the volume ratio of the deionized water to the absolute ethyl alcohol in the ethanol aqueous solution is 100:1, the dialysis time is 5 to 7 hours, and other steps are the same as the first to fifth embodiments.
The seventh embodiment is different from the first to sixth embodiments in that the pre-freezing in the second step ④ is performed specifically at-10 ℃ for 10h to 14h, the natural drying time is 20h to 24h, and other steps are the same as the first to sixth embodiments.
Eighth embodiment the difference between this embodiment and one of the first to seventh embodiments is that the KMnO in step three ①4The concentration of the solution is 0.04 mol/L-0.06 mol/L, the heat treatment temperature is 120-140 ℃, the heat treatment time is 5-7 h, and other steps are the same as those in the first to seventh specific embodiments.
Ninth embodiment, the difference between this embodiment and one of the first to eighth embodiments is that the number of times of cleaning in step three ② is 5 to 8, the soaking time is 5 to 10min, the drying temperature is 60 to 70 ℃, and the drying time is 4 to 6 h.
The detailed implementation mode is ten: the embodiment is an application of a nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst in an ozone catalytic oxidation system.
The following examples were used to demonstrate the beneficial effects of the present invention:
the first embodiment is as follows: a preparation method of a nitrogen-doped three-dimensional graphene-loaded manganese dioxide catalyst is completed according to the following steps:
firstly, preparing graphene oxide powder:
firstly, preparing a graphene oxide solution by adopting an improved Hummer method, then drying and shearing the graphene oxide solution, and finally grinding and sieving to obtain graphene oxide powder with the sheet diameter of 30-50 microns;
the preparation of the graphene oxide solution by adopting the improved Hummer method in the step one is completed according to the following steps:
putting 3g of 325-mesh flake graphite and 3g of sodium nitrate into an ice-bath three-neck flask, adding 98% concentrated sulfuric acid 100m L by mass for 8 times under the condition of stirring, wherein the time interval of adding 98% concentrated sulfuric acid every two times is 12min, heating the system to 35 ℃ after adding 98% concentrated sulfuric acid by mass, keeping the temperature for 4H, adding deionized water for 5 times to obtain 200m L, heating to 95 ℃ for reaction for 0.5H, cooling to room temperature, transferring to a 1000m L beaker, adding hydrogen peroxide while stirring until no bubbles are generated, adding deionized water to 1000m L, cleaning twice by using 15% hydrochloric acid by mass, cleaning twice by using deionized water, centrifuging by using a centrifuge at the speed of 10000r/min, taking centrifugal liquid to obtain a graphene oxide solution, and adding H in hydrogen peroxide to obtain the graphene oxide solution2O2The mass fraction of (A) is 30%;
secondly, preparing the nitrogen-doped three-dimensional graphene aerogel with high elasticity:
①, adding graphene oxide powder into deionized water, and performing ultrasonic dispersion for 30min under the ultrasonic power of 500W to obtain a graphene oxide solution with the concentration of 6mg/m L;
②, mixing a graphene oxide solution with the concentration of 10m L of 6mg/m L, 80 mu L of ethylenediamine and 50 mu L of a sodium borate solution with the mass fraction of 5%, and performing ultrasonic dispersion for 10min under the ultrasonic power of 500W to obtain a mixture;
③, firstly putting the mixture into a high-pressure hydrothermal kettle with a polytetrafluoroethylene lining, then carrying out heat treatment on the high-pressure hydrothermal kettle with the polytetrafluoroethylene lining at 120 ℃ for 13h, and finally naturally cooling to room temperature to obtain a reaction product I, pouring the reaction product I into an ethanol aqueous solution for dialysis for 6h to obtain a dialyzed reaction product I, wherein the reaction product I is a cylinder with the diameter of 0.8 cm-1 cm and the height of 0.3 cm-0.5 cm;
the volume ratio of the deionized water to the absolute ethyl alcohol in the ethyl alcohol aqueous solution is 100: 1;
④, pre-freezing the cylindrical reaction product I at-10 ℃ for 12h, and naturally drying at room temperature for 24h to obtain the nitrogen-doped three-dimensional graphene aerogel with high elasticity;
thirdly, loading a manganese dioxide catalyst:
①, firstly putting the nitrogen-doped three-dimensional graphene aerogel with high elasticity into a polytetrafluoroethylene-lined high-pressure hydrothermal kettle, and then adding KMnO with the concentration of 0.05 mol/L4Completely immersing the nitrogen-doped three-dimensional graphene aerogel with high elasticity into KMnO4In the solution, finally, carrying out heat treatment on the polytetrafluoroethylene-lined high-pressure hydrothermal kettle at 120 ℃ for 6 hours, and naturally cooling to room temperature to obtain a reaction product II;
②, firstly, washing the reaction product II with deionized water for 5 times, then soaking in absolute ethyl alcohol for 10min, and finally drying in an oven at 60 ℃ for 6h to obtain the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst.
Fig. 1 is an FTIR characterization, in which 1 is an FTIR profile of graphene oxide powder obtained in one step one of the example, 2 is an FTIR profile of nitrogen-doped three-dimensional graphene aerogel having high elasticity obtained in one step two ④ of the example, and 3 is an FTIR profile of nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst obtained in one step three ② of the example;
as can be seen from FIG. 1, the graphene oxide is 3389.33cm-1A wider and stronger absorption peak is arranged nearby, and the absorption peak is attributed to an O-H telescopic vibration peak; 1729cm-1The position is a stretching vibration peak of C ═ O on the carboxyl of the graphene oxide; in that1620cm-1The absorption peak at (A) may belong to the bending vibration absorption peak of C-OH; 1225. 1048.2cm-1The absorption peaks are vibration absorption peaks of C-O-C and C-O, respectively, indicating that the graphene oxide used has-OH, -COOH, -C-O-C and-C-O functional groups.
After doping with nitrogen, the absorption peaks at all positions are weakened or even disappear, which indicates that GO is reduced, and 1559.01cm-1The absorption peak at (a) is considered to be an N-H peak indicating that ethylenediamine was successfully introduced as a nitrogen source; 1630.91cm-1And 1167.59cm-1The existence of the absorption peak indicates that the C-O bond GO is not completely reduced
Load MnO2After that, at 526.84cm-1The strong absorption peak exists nearby and is considered as the vibration absorption peak of Mn-O-C from infrared analysis, the graphene oxide surface contains a large number of oxygen-containing groups which can be combined with manganese through chemical bonds to ensure MnO2The loading on GO is more facilitated, and the dispersion of the active component is improved, which is also proved from the angle that: the graphene is combined with the surface of the manganese oxide compound through chemical bonds.
Comparative example one: the three-dimensional graphene aerogel is prepared by the following steps:
firstly, obtaining graphene oxide powder with the sheet diameter of 30-50 microns according to the scheme of the first step of the embodiment;
secondly, preparing the three-dimensional graphene aerogel with high elasticity:
①, adding graphene oxide powder into deionized water, and performing ultrasonic dispersion for 30min under the ultrasonic power of 500W to obtain a graphene oxide solution with the concentration of 6mg/m L;
②, mixing a graphene oxide solution with the concentration of 10m L of 6mg/m L with a sodium borate solution with the mass fraction of 50 mu L of 5%, and performing ultrasonic dispersion for 10min under the ultrasonic power of 500W to obtain a mixture;
③, firstly putting the mixture into a polytetrafluoroethylene-lined high-pressure hydrothermal kettle, then carrying out heat treatment on the polytetrafluoroethylene-lined high-pressure hydrothermal kettle at 120 ℃ for 13h, and finally naturally cooling to room temperature to obtain a reaction product I;
the volume ratio of the deionized water to the absolute ethyl alcohol in the ethyl alcohol aqueous solution is 100: 1;
④, pre-freezing the reaction product I after dialysis at-10 ℃ for 12h, and naturally drying at room temperature for 24h to obtain the three-dimensional graphene aerogel.
Catalyst effect verification test:
the adopted ozone reaction device consists of three systems: ozone generating system, reaction system, tail gas processing system. The ozone generating system comprises an oxygen generator, an ozone generator, a gas flowmeter and an ozone concentration detector, wherein the oxygen generated by the oxygen generator is a generating gas source, and the ozone output is calculated by measuring the flow and the ozone concentration.
In order to verify the removal effect of the catalyst on the organic matters difficult to degrade, a static reaction is selected, a reactor is a three-neck flask, the reactor is provided with an air inlet, an air outlet and a sampling port, the effective volume is 500m L, oxygen is generated by an oxygen generator and then enters an ozone generator to generate ozone, during an experiment, the reactor is fixed in a water bath magnetic stirrer, the catalyst and quinoline are added with water and the water is added into the reactor, the temperature is kept at 25 ℃, the ozone tail gas is decomposed by 5% KI solution and then is discharged outdoors, and the whole experiment process is carried out under the condition of a fume hood.
Can change the waste gas flow direction among the tail gas system according to the experiment needs, utilize the ozone detector to calculate the utilization ratio of ozone, contain a small amount of ozone in the tail gas, discharge through the solution that contains 5% potassium iodide at last, titrate surplus KI solution with sodium thiosulfate after the experiment, calculate the ozone surplus.
The intermittent experiment adopts a one-time water inlet mode, an ozone generator and an ozone testing machine are preheated before the experiment begins, oxygen is firstly turned on, after the experiment is stabilized for 5-10 min, an ozone tester is connected, the air input (generally controlled at 100m L/min) and the ozone generator power required by the experiment are selected, a water sample is added into a reactor, a catalyst is added (or no catalyst is added), ozone is introduced, the reaction time is recorded according to the experimental design, 200u L sulfur is added after samplingSodium thiosulfate (0.01 mol. L)-1) Added to terminate the ozone oxidation reaction. And finally introducing the tail gas into a 5% potassium iodide solution for absorption. And (3) ending the experiment: adjusting the power of the ozone generator to be 0, turning off the ozone generator, turning off the magnetic stirrer, continuously introducing oxygen for 10-15 min, turning off the oxygen generator to achieve the purpose of removing residual ozone in the device and the reactor, taking out the reactor, cleaning the reactor with deionized water, and drying the reactor for later use.
Heterogeneous catalyst is added from the top, water is absorbed and immersed into the solution through the stirring of a magnetic stirrer, ozone is generated by an aeration head at the bottom of the reactor, the ozone is uniformly distributed in the ozone reactor through the magnetic stirring, and the target object is enabled to be fully contacted with the catalyst.
The device and the steps are adopted to verify the effect of the catalyst:
the three catalysts and the single ozonization method are used for verifying the quinoline removal effect by respectively using the three-dimensional graphene aerogel prepared in the first comparative example, the nitrogen-doped three-dimensional graphene aerogel with high elasticity obtained in the second ④ of the first step of the example, and the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst obtained in the third ② of the first step of the example as catalysts;
control of the experimental conditions ([ quinoline)]0＝65mg·L-1，[TOC]0＝49mg·L-1，[O3]Water (W)60 mg-L, [ catalyst]＝9mg·L-1) The experimental results are shown in fig. 2 and 3;
fig. 2 is a diagram of the removal effect of a catalyst on quinoline, in which fig. 1 is a curve of the removal effect of single ozonation on quinoline, fig. 2 is a curve of the removal effect of a three-dimensional graphene aerogel prepared in the first comparative example on quinoline, fig. 3 is a curve of the removal effect of a nitrogen-doped three-dimensional graphene aerogel with high elasticity obtained in the second step ④ of the example, and fig. 4 is a curve of the removal effect of a nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst obtained in the third step ② of the example on quinoline;
fig. 3 is a graph showing the removal effect of a catalyst on TOC, in which fig. 1 is a graph showing the removal effect of a single ozonation on TOC, fig. 2 is a graph showing the removal effect of a three-dimensional graphene aerogel prepared in the first comparative example on TOC, fig. 3 is a graph showing the removal effect of a nitrogen-doped three-dimensional graphene aerogel with high elasticity obtained in the second step ④ of the example, and fig. 4 is a graph showing the removal effect of a nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst obtained in the third step ② of the example on TOC.
As can be seen from fig. 2, in the ozone system, the removal effect of quinoline is substantially stable for about 30 minutes, the removal rate of the target object by single ozonization is 39.7%, the removal rate is increased to 47.6% after the three-dimensional graphene aerogel is added, the removal rate is 68.9% when the nitrogen-doped three-dimensional graphene aerogel with high elasticity is used, and the target object is completely removed by the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst prepared in example one. It is found that the efficiency of TOC is all around 26 ~ 28% with single ozonization to three-dimensional graphene aerogel in combination with 3 discovery, and the TOC clearance that has the nitrogen doping three-dimensional graphene aerogel of high elasticity is slightly higher than under the comparison, about 32%, shows that the effect of adsorbent has mainly been played in the addition of three-dimensional graphene aerogel, does not really get rid of the target, and load nitrogen has promoted the adsorption performance of three-dimensional graphene aerogel. Meanwhile, the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst prepared in the first embodiment in fig. 3 shows a good TOC removal effect, which can finally reach about 75%, which illustrates that manganese dioxide is used as a main active substance of the catalyst, has a good synergistic effect with a carrier, and effectively degrades a target in an ozone catalytic oxidation process.
In addition, the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst prepared in the first embodiment has high elasticity and mechanical strength, can recover to the original micro and macro morphology under the pressure strength of 1MPa, and the Young modulus is almost unchanged after 50 times of extrusion, and the ultimate stress is only reduced by 6% after 100 times of circulation. The recycling efficiency is stable, the catalyst can be recycled for multiple times, and the recycling operation is simple and easy because the catalyst is a heterogeneous catalyst; experiments show that the removal effect of the catalyst on a target object can still be kept at about 95% after more than 10 times of cyclic experiments, which shows that the catalyst has less loss and certain service life in the cyclic use process.
Claims (10)
1. A preparation method of a nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst is characterized in that the preparation method of the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst is completed according to the following steps:
firstly, preparing graphene oxide powder:
firstly, preparing a graphene oxide solution by adopting an improved Hummer method, then drying and shearing the graphene oxide solution, and finally grinding and sieving to obtain graphene oxide powder;
secondly, preparing the nitrogen-doped three-dimensional graphene aerogel with high elasticity:
①, adding graphene oxide powder into deionized water, and performing ultrasonic dispersion to obtain a graphene oxide solution;
②, mixing the graphene oxide solution, the ethylenediamine and the sodium borate solution, and performing ultrasonic dispersion to obtain a mixture;
③, firstly putting the mixture into a high-pressure hydrothermal kettle with a polytetrafluoroethylene lining, then carrying out heat treatment on the high-pressure hydrothermal kettle with the polytetrafluoroethylene lining, and finally naturally cooling to room temperature to obtain a reaction product I, pouring the reaction product I into an ethanol water solution for dialysis to obtain a dialyzed reaction product I, wherein the reaction product I is a cylinder with the diameter of 0.8 cm-1 cm and the height of 0.3 cm-0.5 cm;
④, pre-freezing the reaction product I, and naturally drying at room temperature to obtain the nitrogen-doped three-dimensional graphene aerogel with high elasticity;
thirdly, loading a manganese dioxide catalyst:
①, firstly putting the nitrogen-doped three-dimensional graphene aerogel with high elasticity into a polytetrafluoroethylene-lined high-pressure hydrothermal kettle, and then adding KMnO4Completely immersing the nitrogen-doped three-dimensional graphene aerogel with high elasticity into KMnO4In the solution, finally, carrying out heat treatment on the high-pressure hydrothermal kettle with the polytetrafluoroethylene lining, and naturally cooling to room temperature to obtain a reaction product II;
②, firstly, washing the reaction product II by using deionized water, then, soaking the reaction product II in absolute ethyl alcohol, and finally, drying the reaction product II in a drying oven to obtain the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst.
2. The method for preparing nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst according to claim 1, wherein the sheet diameter of the graphene oxide powder in the first step is 30 μm to 50 μm.
3. The preparation method of the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst according to claim 1, wherein the concentration of the graphene oxide solution in the second step ① is 4mg/m L-8 mg/m L, the ultrasonic dispersion time in the second step ① is 20-40 min, and the ultrasonic power is 300-500W.
4. The method for preparing nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst according to claim 1, wherein the volume ratio of ethylenediamine to graphene oxide solution in step two ② is (60 μ L-100 μ L) to 10m L, and the volume ratio of sodium borate solution to graphene oxide solution is (40 μ L-60 μ L) to 10m L.
5. The preparation method of the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst according to claim 1, wherein the ultrasonic dispersion time in the second step ② is 5-15 min, the ultrasonic power is 300-500W, and the mass fraction of the sodium borate solution is 4-7%.
6. The preparation method of the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst according to claim 1, wherein the heat treatment temperature in the second step ③ is 120-140 ℃, the heat treatment time is 12-14 hours, the volume ratio of deionized water to absolute ethyl alcohol in the ethanol aqueous solution is 100:1, and the dialysis time is 5-7 hours.
7. The preparation method of the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst according to claim 1, wherein the pre-freezing in the second step ④ is performed specifically by freezing at-10 ℃ for 10h to 14h, and the natural drying time is 20h to 24 h.
8. The method for preparing nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst according to claim 1, wherein the KMnO in step III ①4The concentration of the solution is 0.04 mol/L-0.06 mol/L, the heat treatment temperature is 120-140 ℃, and the heat treatment time is 5-7 h.
9. The preparation method of the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst according to claim 1, wherein the cleaning time in the step three ② is 5 to 8 times, the soaking time is 5 to 10min, the drying temperature is 60 to 70 ℃, and the drying time is 4 to 6 hours.
10. Application of the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst prepared by the preparation method according to claims 1 to 9, wherein the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst is applied to an ozone catalytic oxidation system.
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