CN110127746B - Method for regulating and controlling concentration of oxygen vacancy of monocrystalline cerium dioxide - Google Patents
Method for regulating and controlling concentration of oxygen vacancy of monocrystalline cerium dioxide Download PDFInfo
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- CN110127746B CN110127746B CN201910503220.9A CN201910503220A CN110127746B CN 110127746 B CN110127746 B CN 110127746B CN 201910503220 A CN201910503220 A CN 201910503220A CN 110127746 B CN110127746 B CN 110127746B
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Abstract
The invention provides a method for regulating and controlling the concentration of oxygen vacancies of monocrystalline cerium dioxide, belonging to the technical field of regulating and controlling nano-micro structures of cerium dioxide nano-materials. The method comprises the steps of respectively injecting cerium salt and a precipitator into a hydrothermal reaction kettle at a certain pressure and temperature, and adjusting reaction parameters under the hydrothermal condition to prepare the nano cerium dioxide with different oxygen vacancy concentrations. The invention prepares single crystal state nano cerium dioxide with different oxygen vacancy concentrations by starting forced hydrothermal reaction at specific temperature and pressure and adjusting reaction parameters without the assistance of a surfactant.
Description
Technical Field
The invention relates to the technical field of regulation and control of a nano-micro structure of a cerium dioxide material, in particular to a method for regulating and controlling the oxygen vacancy concentration of monocrystalline cerium dioxide.
Background
In many application fields of cerium dioxide, the application of catalysis is important, in particular, VOCs (volatile organic compounds) are catalyzed, oxidized and degraded, and the micro-morphology and the nano-microstructure of the cerium dioxide are closely related to the catalytic performance of the cerium dioxide. At present, many documents report that the catalytic capability of the cerium dioxide as an active component of the catalyst is influenced by the properties of the coated crystal plane besides the specific surface area, and the crystal plane characteristics are closely related to the micro-morphology of the cerium dioxide. The research of Zhou et al reports that in the catalytic oxidation of CO, the catalytic activity of the (110) and (100) characteristic crystal faces of the cerium dioxide is better than that of the (111) characteristic crystal face, so that the catalytic capability of the nano cerium dioxide coated by the (110) and (100) crystal faces is better than that of the nano cerium dioxide coated by the (111) crystal face. Meanwhile, the existence of oxygen vacancy in the microstructure also determines the catalytic capability of the cerium dioxide, so that for the catalyst taking the cerium dioxide as a matrix, the catalytic capability is closely related to the existence of the coated crystal face and the oxygen vacancy in the structure. Different crystal faces have different surface energies, and oxygen molecules are activated at the crystal faces and then transported and transferred in vivo through oxygen vacancies in the structure, so that the oxygen storage capacity is improved, and the catalytic effect is enhanced, therefore, the existence and concentration of the oxygen vacancies play an important role in the whole catalytic process.
At present, organic additives such as a template agent, a surfactant and the like are inevitably used in a plurality of liquid-phase synthesis methods of nano cerium dioxide, the process flow is complex, the cost is invisibly increased for production, and meanwhile, the environmental hazard is brought, so that the research work of finding a simple, economic, high-efficiency and one-step synthesis method meeting the green chemical requirements to realize the controllable preparation of different oxygen vacancy concentrations of cerium dioxide nano materials is still a great challenge.
The invention provides a process flow for synthesizing nano cerium dioxide particles by one step without the assistance of organic solvents such as surfactants, and the like, the preparation process is simple and easy to implement, can be used for large-scale production, has low production cost, is nontoxic and pollution-free, has high yield, and can meet the requirements of production and life. Meanwhile, the prepared sample has high crystallinity, good uniformity and strong stability, and is suitable for long-time application and storage. The preparation technology provided by the invention realizes the regulation and control of the oxygen vacancy concentration through the change of special processes and reaction parameters (concentration, temperature, time and the like).
Disclosure of Invention
The invention aims to provide a method for regulating and controlling the oxygen vacancy concentration of monocrystalline cerium dioxide.
The upper end of a hydrothermal reaction kettle used in the method is provided with a storage tank capable of being pressurized, and the storage tank is connected with the reaction kettle through a sealing switch valve. The process for regulating and controlling the concentration of the oxygen vacancies of the crystal lattice is not assisted by a surfactant, cerium salt and a precipitator are respectively injected under certain pressure and temperature according to the characteristics of the crystallization process of the cerium dioxide, the disordered growth of crystal grains in the long-time heating process and the low-pressure state is avoided, and the reaction parameters (reaction temperature, time, concentration of the precipitator and the like) under the hydrothermal condition are regulated to prepare the nano cerium dioxide with different oxygen vacancy concentrations. The whole preparation process comprises the following steps:
(1) selecting one of sodium hydroxide or potassium hydroxide as a precipitator, taking water-soluble cerium salt as a cerium source, adding no surfactant, taking pure water as a solvent, pouring the prepared precipitator with the concentration of 6-10 mol/L and the cerium salt with the concentration of 0.4-0.6 mol/L into two pressurizable storage tanks respectively;
(2) pouring pure water with the volume of 1/4 into a reaction kettle, sealing, heating to 125-170 ℃, pressurizing a material storage tank after the pressure is 0.2-0.6 MPa, opening a sealing switch valve between the reaction kettle and the material storage tank when the pressure of the material storage tank is higher than the pressure of the reaction kettle at the moment to inject reaction material liquid in the material storage tank into the reaction kettle, sealing, heating to 130-180 ℃, continuing to react for a period of time, and stopping heating;
(3) cooling to room temperature, releasing the pressure, carrying out solid-liquid separation on the reaction product mixed solution, washing the obtained solid particles with deionized water for three times, and then washing with ethanol for three times;
(4) and (3) drying the washed particles in a vacuum oven at a certain temperature to obtain the nano cerium dioxide with different oxygen vacancy concentrations.
Wherein the initial concentration of the precipitant in the step (1) is 6-10 mol/L.
In the step (1), the cerium salt is cerium nitrate or cerium chloride, and the initial concentration of the cerium salt is 0.4-0.6 mol/L.
In the step (2), the initial temperature of the reaction in the reaction kettle is 125-170 ℃, and the pressure is 0.2-0.6 MPa.
The filling degree of the reaction kettle after the reactants are injected under pressure in the step (2) is 75 percent.
And (3) after the reactants are injected under pressure in the step (2), the reaction set temperature in the reaction kettle is 130-180 ℃, and the hydrothermal reaction time is 24-48 hours.
In the step (4), the drying temperature of the particles is 80 ℃, and the vacuum degree is 50 Pa.
The technical scheme of the invention has the following beneficial effects:
the invention prepares single crystal state nano cerium dioxide with different oxygen vacancy concentrations by starting forced hydrothermal reaction at specific temperature and pressure and adjusting reaction parameters without the assistance of a surfactant. The preparation method is simple and easy to implement, and disordered growth of crystal grains in a long-time heating process and a low-pressure state is avoided.
Drawings
FIG. 1 is an XRD diffraction pattern of cerium oxide nanofibers and nanocubes fabricated in examples of the present invention;
FIG. 2 is a TEM photograph of cerium oxide nanofibers and nanocubes prepared in examples of the present invention, wherein (a) is cerium oxide nanofibers and (b) is cerium oxide nanocubes;
FIG. 3 is an SEM photograph of the cerium oxide nano-fiber and the nano-cube prepared in the example of the present invention, wherein (a) is the cerium oxide nano-fiber and (b) is the cerium oxide nano-cube;
FIG. 4 shows the effect of the cerium oxide nanofibers and nanocubes prepared in the examples of the present invention in catalytic oxidation of CO.
Detailed Description
In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.
The invention provides a method for regulating and controlling the concentration of oxygen vacancies of monocrystalline cerium dioxide.
The upper end of a hydrothermal reaction kettle used in the method is provided with a storage tank capable of being pressurized, and the storage tank is connected with the reaction kettle through a sealing switch valve. The method comprises the following steps:
(1) selecting one of sodium hydroxide or potassium hydroxide as a precipitator, taking water-soluble cerium salt as a cerium source, adding no surfactant, taking pure water as a solvent, pouring the prepared precipitator with the concentration of 6-10 mol/L and the cerium salt with the concentration of 0.4-0.6 mol/L into two pressurizable storage tanks respectively;
(2) pouring pure water with the volume of 1/4 into a reaction kettle, sealing, heating to 125-170 ℃, pressurizing a material storage tank after the pressure is 0.2-0.6 MPa, opening a sealing switch valve between the reaction kettle and the material storage tank when the pressure of the material storage tank is higher than the pressure of the reaction kettle at the moment to inject reaction material liquid in the material storage tank into the reaction kettle, sealing, heating to 130-180 ℃, continuing to react for a period of time, and stopping heating;
(3) cooling to room temperature, releasing the pressure, carrying out solid-liquid separation on the reaction product mixed solution, washing the obtained solid particles with deionized water for three times, and then washing with ethanol for three times;
(4) and (3) drying the washed particles in a vacuum oven at a certain temperature to obtain the nano cerium dioxide with different oxygen vacancy concentrations.
Example 1
1.736 kg of cerium nitrate is added into 10L of deionized water, 2.4 kg of sodium hydroxide is added into 10L of deionized water, and the cerium nitrate and the sodium hydroxide are respectively added into two storage tanks for standby after being completely dissolved. To 40L volumetric reation kettleAdding 10L of pure water, heating to 125 ℃ in a sealing way, when the pressure in the kettle is about 0.2MPa, pressurizing the two material storage tanks to the pressure of more than 0.2MPa, opening a switch valve between the material storage tanks and the reaction kettle, injecting a reaction material liquid of cerium salt and alkali into the reaction tank, sealing the reaction tank, stirring at the speed of 100 r/min, setting the hydrothermal reaction temperature of the reaction tank to 130 ℃, carrying out hydrothermal reaction, stopping the reaction after 48h, cooling to room temperature, discharging the pressure, carrying out solid-liquid separation on the reaction product mixed liquid, washing with deionized water for three times, washing with ethanol for three times, putting the obtained particles into a vacuum oven with the temperature of 80 ℃ and the vacuum degree of 50Pa for drying to finally obtain the single-crystal cerium dioxide particles, wherein the micro-morphology is nano-fiber, and the concentration of oxygen vacancy is 5.2 × 10 according to the following formula20/cm3。
[VO]＝[O2-]c/4 (2)
Remarking: a' is the expanded lattice parameter (the lattice parameter of the prepared sample),
and
represents Ce3+,Ce4 +Oxygen vacancies and O2-Constant c is Ce in the sample3+/Ce4+A proportionality coefficient of [ V ]O]Represents the concentration of oxygen vacancies, wherein,
a0＝0.5411nm(CeO2lattice parameter of standard sample card); CeO (CeO)2Has a density of 7.28g/cm3.
Example 2
2.604 kg of cerium nitrate is added into 10L of deionized water, and 4 is takenAdding 10L of pure water into a 40L reaction kettle, sealing and heating to 170 ℃, pressurizing the two storage tanks to the pressure of more than 0.6MPa when the pressure in the kettle is about 0.6MPa, opening a switch valve between the storage tanks and the reaction kettle, injecting a reaction feed liquid of cerium salt and alkali into the reaction kettle, sealing the reaction kettle, stirring at the speed of 100 revolutions per minute, setting the hydrothermal reaction temperature of the reaction kettle to be 180 ℃, carrying out hydrothermal reaction, stopping the reaction after 24 hours, cooling to room temperature, discharging the pressure, carrying out solid-liquid separation on a mixed liquid of the reaction products, washing with deionized water for three times, washing with ethanol for three times, placing the obtained particulate matters into a vacuum oven with the temperature of 80 ℃ and the vacuum degree of 50Pa for drying, finally obtaining single-crystal cerium dioxide particles, wherein the micro-morphology is a nano cube, and the oxygen vacancy concentration is 3.895 to 10. 3.5 × 1020/cm3。
Example 3
Adding 1.232 kg of cerium chloride into 10L of deionized water, adding 4.48 kg of potassium hydroxide into 10L of deionized water, respectively adding the cerium chloride and the potassium hydroxide into two storage tanks for standby after the cerium chloride and the potassium hydroxide are completely dissolved, adding 10L of pure water into a 40L-volume reaction kettle, sealing and heating the kettle to 150 ℃ and keeping the pressure in the kettle at about 0.4MPa, pressurizing the two storage tanks to a pressure higher than 0.4MPa, opening a switch valve between the storage tanks and the reaction kettle, injecting a reaction feed liquid of cerium salt and alkali into the reaction kettle, sealing the reaction kettle, stirring at a speed of 100 revolutions per minute, setting the hydrothermal reaction temperature of the reaction kettle at 160 ℃, carrying out hydrothermal reaction, stopping the reaction after 36 hours, cooling to room temperature, discharging the pressure, carrying out solid-liquid separation on the mixed liquid of the reaction product, washing with the deionized water for three times, washing with ethanol for three times, placing the obtained particles into a vacuum oven with the temperature of 80 ℃ and the vacuum degree of 50Pa, drying, finally obtaining single-crystal-state cerium dioxide particles, wherein the morphology is nano fibers, and the micro-state oxygen20/cm3。
The prepared cerium dioxide particles are fluorite crystal structures as shown in figure 1, and the micro-morphologies are respectively nano fibers and nano cubes as shown in figures 2 and 3.
Catalytic detection
The prepared cerium dioxide is subjected to a catalytic test, and the influence of samples with different oxygen vacancy concentrations on the catalytic capability is examined. And respectively taking the prepared monocrystalline cerium dioxide nano-fiber and the nanocubes, pressing the monocrystalline cerium dioxide nano-fiber and the nanocubes into sheets under the pressure of 10MPa, and sieving the sheets by using a sieve with 40-60 meshes. A quartz reaction tube with a sand plate device in the middle is taken, a layer of superfine and extremely pure quartz cotton is laid above the sand plate, then 50mg of samples are weighed from the screened particles and poured into the quartz reaction tube, and a layer of quartz cotton is laid above the samples, so that the samples do not need to be extruded too densely. Placing the reaction tube in a tube furnace, connecting the outlet end of the reaction tube with a gas chromatograph, connecting the inlet end of the reaction tube with a reaction gas, and controlling the flow rate of the reaction gas to be 50mL/min (WHSV: 60,000mL g) by a mass flow meter-1h-1) The temperature in the catalytic reaction process is adjusted by a digital thermocouple, the temperature rise rate is 5 ℃/min, the tail gas components are measured by gas chromatography, and the conversion rate of CO is finally obtained by integral calculation and normalization treatment with a standard curve, so that the catalytic performance of the sample is evaluated.
The results show that the catalytic effect of the ceria nanofibers with high concentration of oxygen vacancies is better than that of the ceria nanocubes with low concentration of oxygen vacancies as shown in fig. 4, where the ceria nanofibers and nanocubes are samples prepared at the same concentration, the same reaction time and different temperatures in fig. 4.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (4)
1. A method for regulating and controlling the oxygen vacancy concentration of monocrystalline cerium dioxide is characterized in that: the method comprises the following steps:
(1) selecting one of sodium hydroxide or potassium hydroxide as a precipitator, taking water-soluble cerium salt as a cerium source, adding no surfactant, taking pure water as a solvent, pouring the prepared precipitator with the concentration of 6-10 mol/L and the cerium salt with the concentration of 0.4-0.6 mol/L into two pressurizable storage tanks respectively;
(2) pouring pure water with the volume of 1/4 into a reaction kettle, sealing, heating to 125-170 ℃, pressurizing a material storage tank after the pressure is 0.2-0.6 MPa, opening a sealing switch valve between the reaction kettle and the material storage tank when the pressure of the material storage tank is higher than the pressure of the reaction kettle at the moment to inject reaction material liquid in the material storage tank into the reaction kettle, sealing, heating to 130-180 ℃, continuing to react for a period of time, and stopping heating;
(3) cooling to room temperature, releasing the pressure, carrying out solid-liquid separation on the reaction product mixed solution, washing the obtained solid particles with deionized water for three times, and then washing with ethanol for three times;
(4) drying the washed particles in a vacuum oven at a certain temperature to obtain nano cerium dioxide with different oxygen vacancy concentrations;
in the step (1), cerium salt is cerium nitrate or cerium chloride, and the initial concentration of the cerium salt is 0.4-0.6 mol/L;
the filling degree of the reaction kettle after the reactants are injected in the step (2) under pressure is 75 percent;
in the step (4), the drying temperature of the particles is 80 ℃, and the vacuum degree is 50 Pa.
2. The method of controlling oxygen vacancy concentration of monocrystalline cerium oxide according to claim 1, wherein: in the step (1), the initial concentration of the precipitant is 6-10 mol/L.
3. The method of controlling oxygen vacancy concentration of monocrystalline cerium oxide according to claim 1, wherein: the initial temperature of the reaction in the reaction kettle in the step (2) is 125-170 ℃, and the pressure is 0.2-0.6 MPa.
4. The method of controlling oxygen vacancy concentration of monocrystalline cerium oxide according to claim 1, wherein: and (3) after the reactants are injected under pressure in the step (2), the reaction set temperature in the reaction kettle is 130-180 ℃, and the hydrothermal reaction time is 24-48 hours.
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