CN111389438B - 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: 1. preparing graphene oxide powder; 2. preparing nitrogen-doped three-dimensional graphene aerogel with high elasticity; 3. supporting 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 organics 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 MnO 2 Is 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:
1. 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;
2. preparing a 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, placing 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 0.8-1 cm and the height of 0.3-0.5 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;
3. loading a manganese dioxide catalyst:
(1) firstly, putting nitrogen-doped three-dimensional graphene aerogel with high elasticity into a high-pressure hydrothermal kettle with a polytetrafluoroethylene lining, and then adding KMnO 4 Completely immersing the nitrogen-doped three-dimensional graphene aerogel with high elasticity into KMnO 4 In 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 a reaction product II by using deionized water, then soaking in absolute ethyl alcohol, and finally drying 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:
1. 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, the catalyst can be recycled for many times, and the catalyst is a heterogeneous catalyst, so the recycling operation is simple and easy;
2. according to the invention, a heterogeneous catalyst is adopted, the size of the catalyst is in the centimeter level, and the catalyst can be recovered after the test is finished, so that the possibility of practical engineering application is ensured;
3. 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;
4. 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 higher 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 catalyst is rare in the existing catalyst;
5. the nitrogen-doped three-dimensional graphene-loaded manganese dioxide catalyst prepared by the invention has a 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 be still kept at about 95%, which shows that the catalyst has less loss in the recycling process and a 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 examples, 2 is an FTIR profile of nitrogen-doped three-dimensional graphene aerogel having high elasticity obtained in one step two (4) of the examples, and 3 is an FTIR profile of nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst obtained in one step three (2) of the examples;
fig. 2 is a diagram showing the removal effect of a catalyst on quinoline, in which 1 is a curve of the removal effect of single ozonization on quinoline, 2 is a curve of the removal effect of a three-dimensional graphene aerogel prepared in the first comparative example on quinoline, 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 4 is a curve of the removal effect of a nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst on quinoline obtained in the third step (2) of the example;
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:
1. 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;
2. preparing a 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, placing 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 0.8-1 cm and the height of 0.3-0.5 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;
3. loading a manganese dioxide catalyst:
(1) firstly, putting nitrogen-doped three-dimensional graphene aerogel with high elasticity into a high-pressure hydrothermal kettle with a polytetrafluoroethylene lining, and then adding KMnO 4 Completely immersing the nitrogen-doped three-dimensional graphene aerogel with high elasticity into KMnO 4 In 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 a reaction product II by using deionized water, then soaking in absolute ethyl alcohol, and finally drying in a drying oven to obtain the nitrogen-doped three-dimensional graphene supported manganese dioxide catalyst.
The advantages of this embodiment:
1. 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;
2. the embodiment adopts the heterogeneous catalyst, 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;
3. the embodiment saves materials, the cost of the adopted effective component manganese oxide 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;
4. the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst prepared by the embodiment has an excellent catalytic effect, and through experiments, 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 compared with the single ozonization TOC removal rate, the removal rate is improved by about 47%, and can reach 75.31%, so that the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst is rare in the existing catalyst;
5. the nitrogen-doped three-dimensional graphene-loaded manganese dioxide catalyst prepared by the embodiment has a good effect after being recycled for multiple times, and through 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 concrete implementation mode: the present embodiment differs from the first or second embodiment in that: the concentration of the graphene oxide solution in the step two (1) is 4 mg/mL-8 mg/mL; the ultrasonic dispersion time in the step two (1) is 20min to 40min, and the ultrasonic power is 300W to 500W. The other steps are the same as in the first or second embodiment.
The fourth concrete implementation mode: the difference between this embodiment and one of the first to third embodiments is as follows: the volume ratio of the ethylenediamine to the graphene oxide solution in the step two (2) (60-100 mu L) is 10mL; the volume ratio of the sodium borate solution to the graphene oxide solution is (40-60 muL): 10mL. The other steps are the same as those in the first to third embodiments.
The fifth concrete implementation mode: the difference between this embodiment and one of the first to fourth embodiments is: the ultrasonic dispersion time in the step two (2) is 5-15 min, and the ultrasonic power is 300-500W; the mass fraction of the sodium borate solution is 4-7%. The other steps are the same as those in the first to fourth embodiments.
The sixth specific implementation mode is as follows: the difference between this embodiment and one of the first to fifth embodiments is as follows: the temperature of the heat treatment in the step two (3) is 120-140 ℃, and the time of the heat treatment is 12-14 h; the volume ratio of the deionized water to the absolute ethyl alcohol in the ethyl alcohol aqueous solution is 100; the dialysis time is 5-7 h. The other steps are the same as those in the first to fifth embodiments.
The seventh embodiment: the difference between this embodiment and one of the first to sixth embodiments is: pre-freezing in the step two (4), specifically freezing for 10-14 h at-10 ℃; the natural drying time is 20-24 h. The other steps are the same as those in the first to sixth embodiments.
The specific implementation mode is eight: the difference between this embodiment and one of the first to seventh embodiments is: KMnO described in step three (1) 4 The 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. The other steps are the same as those in the first to seventh embodiments.
The specific implementation method nine: the difference between this embodiment and the first to eighth embodiments is: the cleaning times in the step three (2) are 5-8 times, and the soaking time is 5-10 min; the drying temperature is 60-70 ℃, and the drying time is 4-6 h. The other steps are the same as those in the first to eighth embodiments.
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:
1. 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 100mL of 98% concentrated sulfuric acid by mass for 8 times under the stirring condition, wherein the time interval of adding 98% concentrated sulfuric acid by mass for every two times is 12min, heating the temperature of the system to 35 ℃ after adding 98% concentrated sulfuric acid by mass, keeping the temperature for 4h, adding 200mL of deionized water for 5 times, heating to 95 ℃ for reaction for 0.5h, cooling to room temperature, transferring into a 1000mL beaker, adding hydrogen peroxide while stirring until no bubbles are generated, adding deionized water to 1000mL, cleaning twice with 15% hydrochloric acid, cleaning twice with deionized water, centrifuging at 10000r/min by a centrifuge, and taking a centrifugal liquid to obtain a graphene oxide solution; h in the hydrogen peroxide 2 O 2 The mass fraction of (A) is 30%;
2. preparing a 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 6 mg/mL;
(2) mixing 10mL of graphene oxide solution with the concentration of 6mg/mL, 80 mu L of ethylenediamine and 50 mu L of sodium borate solution with the mass fraction of 5%, and performing ultrasonic dispersion at the ultrasonic power of 500W for 10min 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 13 hours, 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 for 6 hours to obtain a dialyzed reaction product I, wherein the reaction product I is a cylinder with the diameter of 0.8-1 cm and the height of 0.3-0.5 cm;
the volume ratio of the deionized water to the absolute ethyl alcohol in the ethyl alcohol aqueous solution is 100;
(4) pre-freezing the cylindrical reaction product I at-10 ℃ for 12 hours, and naturally drying at room temperature for 24 hours to obtain the nitrogen-doped three-dimensional graphene aerogel with high elasticity;
3. loading a manganese dioxide catalyst:
(1) firstly, putting nitrogen-doped three-dimensional graphene aerogel with high elasticity into a high-pressure hydrothermal kettle with a polytetrafluoroethylene lining, and then adding KMnO with the concentration of 0.05mol/L 4 Completely immersing the nitrogen-doped three-dimensional graphene aerogel with high elasticity into KMnO 4 In 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 a reaction product II for 5 times by using deionized water, then soaking in absolute ethyl alcohol for 10min, and finally drying in a 60 ℃ oven 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 examples, 2 is an FTIR profile of nitrogen-doped three-dimensional graphene aerogel having high elasticity obtained in one step two (4) of the examples, and 3 is an FTIR profile of nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst obtained in one step three (2) of the examples;
as can be seen from FIG. 1, the graphene oxide is 3389.33cm -1 A wider and stronger absorption peak is arranged nearby, and the absorption peak is attributed to an O-H telescopic vibration peak; 1729cm -1 The position is a stretching vibration peak of C = O on the carboxyl of the graphene oxide; at 1620cm -1 The absorption peak at (A) may belong to the bending vibration absorption peak of C-OH; 1225. 1048.2cm -1 The absorption peaks are vibration absorption peaks for C-O-C and C-O, respectively, indicating the presence of-OH, -COOH, C-O-C and-C = O functionalities on the graphene oxide used.
After nitrogen doping, the absorption peaks at all positions are weakened or even disappear, which indicates that GO is reduced, and 1559.01cm -1 The absorption peak at (a) is considered to be an N-H peak indicating that ethylenediamine was successfully introduced as a nitrogen source; 1630.91cm -1 And 1167.59cm -1 The existence of the absorption peak indicates that the C-O bond GO is not completely reduced
Load MnO 2 Then, at 526.84cm -1 The 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 MnO 2 The 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:
1. obtaining graphene oxide powder with the sheet diameter of 30-50 microns according to the scheme of the first step of the embodiment;
2. preparing a 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 6 mg/mL;
(2) mixing 10mL of graphene oxide solution with the concentration of 6mg/mL and 50 mu L of 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 13 hours, 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 for 6 hours to obtain a dialyzed reaction product I;
the volume ratio of the deionized water to the absolute ethyl alcohol in the ethyl alcohol aqueous solution is 100;
(4) and pre-freezing the dialyzed reaction product I at-10 ℃ for 12 hours, and naturally drying at room temperature for 24 hours to obtain the three-dimensional graphene aerogel.
Catalyst effect verification test:
the adopted ozone reaction device consists of three systems: ozone generation 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 refractory organic matters, a static reaction is selected, the 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 500mL, oxygen is generated by an oxygen generator and then enters an ozone generator to generate ozone. During the experiment, the reactor is fixed in a water bath magnetic stirrer, the catalyst and the quinoline are added into the reactor by water, and the temperature is kept at 25 ℃. Ozone tail gas is discharged outdoors after being decomposed by 5 percent KI solution, and the whole experimental 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, before the experiment begins, an ozone generator and an ozone testing machine are preheated, oxygen is firstly turned on, after the stabilization is carried out for 5-10 min, an ozone measuring instrument is connected, and the air inflow (generally controlled at 100 mL/min) and the power of the ozone generator required by the experiment are selected. Adding a water sample into a reactor, adding a catalyst (or not), introducing ozone, recording the reaction time according to the experimental design, and sampling 200uL of thiosulfideSodium salt (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 0, closing the ozone generator, closing the magnetic stirrer, continuously introducing oxygen for 10-15 min, closing 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 the magnetic stirrer, ozone is generated by an aeration head at the bottom of the reactor, and the ozone is uniformly distributed in the ozone reactor through the magnetic stirring, so that the target object is in full contact 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 step (4) of the example, and the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst obtained in the third step (2) of the example as catalysts;
control of the experimental conditions ([ quinoline)] 0 ＝65mg·L -1 ，[TOC] 0 ＝49mg·L -1 ，[O 3 ] Water (W) =60 mg. L, [ catalyst]＝9mg·L -1 ) The experimental results are shown in fig. 2 and 3;
fig. 2 is a diagram showing the removal effect of a catalyst on quinoline, in which 1 is a curve of the removal effect of single ozonization on quinoline, 2 is a curve of the removal effect of a three-dimensional graphene aerogel prepared in the first comparative example on quinoline, 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 4 is a curve of the removal effect of a nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst on quinoline obtained in the third step (2) of the example;
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. The TOC removal efficiency of the three-dimensional graphene aerogel is found to be about 26-28% by combining with figure 3, compared with that of single ozonization method, the TOC removal rate of the nitrogen-doped three-dimensional graphene aerogel with high elasticity is slightly higher, and is about 32%, which shows that the addition of the three-dimensional graphene aerogel mainly plays a role of an adsorbent, a target object is not really removed, and the adsorption performance of the three-dimensional graphene aerogel is improved by loaded nitrogen. 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 (9)
1. The application of the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst is characterized in that the application of the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst in an ozone catalytic oxidation system is used for catalytically degrading quinoline;
the preparation method of the nitrogen-doped three-dimensional graphene-loaded manganese dioxide catalyst is completed according to the following steps:
1. 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;
2. preparing a 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, placing 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 0.8cm to 1cm and the height of 0.3cm to 0.5cm;
(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;
pre-freezing in the step two (4), specifically freezing at-10 ℃ for 10h to 14h;
3. loading a manganese dioxide catalyst:
(1) firstly, putting the nitrogen-doped three-dimensional graphene aerogel with high elasticity into a high-pressure hydrothermal kettle with a polytetrafluoroethylene lining, and then adding KMnO 4 Completely immersing the nitrogen-doped three-dimensional graphene aerogel with high elasticity into KMnO 4 In solution, poly-tetra-ethyl is finally addedCarrying out heat treatment on the high-pressure hydrothermal kettle with the vinyl fluoride lining, and naturally cooling to room temperature to obtain a reaction product II;
(2) firstly, washing a reaction product II by using deionized water, then soaking in absolute ethyl alcohol, and finally drying in a drying oven to obtain the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst.
2. The application of the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst as claimed in claim 1, wherein the sheet diameter of the graphene oxide powder in the first step is 30 μm to 50 μm.
3. The application 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 4 mg/mL-8 mg/mL; the time of ultrasonic dispersion in the step two (1) is from 20min to 40min, and the ultrasonic power is from 300W to 500W.
4. The application of the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst according to claim 1, wherein the volume ratio of the ethylenediamine to the graphene oxide solution in the step two (2) is (60 μ L-100 μ L): 10mL; the volume ratio of the sodium borate solution to the graphene oxide solution is (40-60 muL): 10mL.
5. The application of the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst according to claim 1 is characterized in that the ultrasonic dispersion time in the second step (2) is 5min to 15min, and the ultrasonic power is 300W to 500W; the mass fraction of the sodium borate solution is 4-7%.
6. The application of the nitrogen-doped three-dimensional graphene-loaded manganese dioxide catalyst according to claim 1, wherein the heat treatment temperature in the second step (3) is 120-140 ℃, and the heat treatment time is 12-14h; the volume ratio of the deionized water to the absolute ethyl alcohol in the ethyl alcohol aqueous solution is 100; the dialysis time is 5h to 7h.
7. The application of the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst as claimed in claim 1, wherein the natural drying time is from 20h to 24h.
8. The application of the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst as claimed in claim 1, wherein the KMnO in the step three (1) 4 The concentration of the solution is 0.04-0.06 mol/L; the heat treatment temperature is 120 to 140 ℃, and the heat treatment time is 5 to 7 hours.
9. The application of the nitrogen-doped three-dimensional graphene-supported manganese dioxide catalyst according to claim 1, wherein the number of times of cleaning in the step three (2) is 5 to 8, and the soaking time is 5 to 10min; the drying temperature is 60-70 ℃, and the drying time is 4-6 h.
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