CN110589890B - A method and application for simultaneously preparing spinel-type and perovskite-type manganese titanate nanoparticles - Google Patents

Abstract

The invention provides a method for simultaneously preparing spinel-type and perovskite-type manganese titanate nanoparticles and application thereof, and relates to the field of catalyst synthesis ₂ Nanosheets as a Mn precursor, titanic acidSelective hydrolysis of tetrabutyl ester as Ti source in MnO ₂ The surface of the nano sheet forms a continuous coating layer, thereby generating MnO ₂ /TiO ₂ Calcining the obtained composite nanosheet in flowing argon at different temperatures to respectively obtain spinel-type and perovskite-type manganese titanate nanoparticles; the invention utilizes tetrabutyl titanate in a sol-gel system of pure ethanol in MnO ₂ Selectively hydrolyzing the surface of the nano sheet to generate amorphous titanium oxide, and calcining the amorphous titanium oxide in an argon atmosphere to promote titanium oxide and MnO ₂ Solid-phase reaction to obtain MnTi ₂ O ₄ And MnTiO ₃ The nano-particles do not need to be prepared into manganese titanate nano-particles of each crystal form by two different methods, the method has less steps, and no intermediate product harmful to the environment is generated.

Description

A method for simultaneously preparing spinel-type and perovskite-type manganese titanate nanoparticles and application

technical field

The invention relates to the field of catalyst synthesis, in particular to a method and application for simultaneously preparing spinel-type and perovskite-type manganese titanate nanoparticles.

Background technique

Perovskite and spinel titanates have broad application prospects in photocatalytic degradation of organic pollutants, dye-sensitive solar cells, nanosensors, and lithium-ion batteries. In recent years, a series of technologies for preparing manganese titanate have been developed, such as solid-phase reaction method, hydrothermal preparation method, sol-gel method, complexing agent-assisted precipitation and co-precipitation method, etc. However, among the currently disclosed preparation methods of manganese titanate, spinel-type and perovskite-type manganese titanate can only be prepared separately through different ways, and there is no method that can simultaneously prepare manganese titanate with these two structures.

For example, patent CN108423713A discloses a method for preparing pure perovskite-type manganese titanate nanosheet materials, and the application of the manganese titanate nanosheets as catalysts in the degradation of pollutants in heterogeneous Fenton-like materials, which solves the problem of existing The manganese titanate prepared by the method has the problem of large particle size and few surface active sites. The method includes the following steps: first, dissolving both manganese salt and titanium salt in deionized water to obtain manganese salt and titanium salt solution; second, dissolving the organic base Dissolve in manganese salt and titanium salt solution; 3. Dissolve caustic alkali in deionized water to form caustic alkali solution, and then add caustic alkali solution into manganese salt and titanium salt solution to react to generate manganese and titanium hydroxide precursor; 4. The manganese hydroxide titanium precursor is transferred into a hydrothermal kettle, and heated to obtain manganese titanate nanosheet materials with different shapes; 5. After washing and drying the manganese titanate nanosheet materials, the finished product is obtained; the method improves the The pure perovskite-type manganese titanate nanosheets have uniform particle size and particle size, large specific surface area, and abundant surface active centers. Another example is the method of hydrothermal synthesis disclosed in patent CN102989446A, using titanate nanowires as Ti source, MnCl ₂ as Mn source, and NaF as F source, under the condition of adding NaOH, prepared uniform morphology and diameter. The method of sheet-like structure _MnTiO3 and F- _MnTiO3 , and the application of these two materials for catalytic degradation of organic dye Rhodamine B under visible light irradiation conditions.

The preparation methods disclosed in the above two patents are to directly prepare a single crystal form of perovskite-type manganese titanate by hydrothermal method, and both methods cannot be applied to the preparation of spinel-type manganese titanate. Manganese titanate requires other methods, such as solid-phase reaction method, sol-gel method, etc. When two crystalline forms of manganese titanate are required for comparative tests, different methods need to be used to prepare the two crystalline forms. manganese titanate, the process steps are complicated.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method and application for simultaneously preparing spinel-type and perovskite-type manganese titanate nanoparticles, using tetrabutyl titanate in the sol-gel system of pure ethanol on the surface of MnO ₂ nanosheets Selectively hydrolyzed to generate amorphous titanium oxide, and then heated in an argon atmosphere to promote solid-phase reaction of titanium oxide and manganese dioxide to obtain spinel-type manganese titanate and perovskite-type manganese titanate, without using two Methods Manganese titanate nanoparticles with different crystal forms were prepared respectively.

In order to achieve the above purpose, the present invention proposes the following technical scheme: a method for simultaneously preparing spinel-type and perovskite-type manganese titanate nanoparticles, comprising the following steps:

S1. Disperse the MnO ₂ nanosheets in ethanol to obtain a MnO ₂ nanosheet suspension;

S2, under stirring conditions, adjust the pH of the _MnO nanosheet suspension of S1 to be alkaline;

S3, adding the ethanol solution of tetrabutyl titanate dropwise to the alkaline _MnO nanosheet suspension of S2, and stirring continuously until tetrabutyl titanate fully reacts on the surface of the _MnO nanosheet;

S4, take the solid product after filtering the reaction solution of S3, and use ethanol and deionized water alternately to centrifugally wash and then dry to obtain titanium-manganese composite nanosheets;

S5, calcining the titanium-manganese composite nanosheets obtained from S4 at different temperatures in an argon atmosphere to obtain spinel-type manganese titanate nanoparticles and perovskite-type manganese titanate nanoparticles, respectively.

Further, in the S2, ammonia water is added to the MnO ₂ nanosheet suspension to adjust the MnO ₂ nanosheet suspension to be alkaline; the purpose of using ammonia water to adjust the MnO ₂ nanosheet suspension to be alkaline is to be the tetrabutyl titanate of S3. The ethanolic solution of the ester presets an alkaline environment to slow down the hydrolysis of tetrabutyl titanate in the _MnO nanosheet suspension.

Further, the calcination temperature of the spinel-type manganese titanate nanoparticles prepared in the S5 is 450°C, and the calcination temperature of the perovskite-type manganese titanate nanoparticles is 650°C.

Further, the calcination process for preparing the manganese titanate nanoparticles is as follows: setting the calcination temperature, the heating rate of 10°C/min, and constant temperature calcination for 2 hours at the set calcination temperature.

Further, the ultrasonic pulverization method is used in the S1 to uniformly disperse the MnO ₂ nanosheets in ethanol, to ensure that the ethanol solution of tetrabutyl titanate is uniformly adsorbed and hydrolyzed on the surface of the MnO ₂ nanosheets.

Further, the ethanol is pure ethanol solvent.

Further, in the S3, the concentration of the ethanolic solution of tetrabutyl titanate is 10mL/L～100mL/L, and the ethanolic solution of tetrabutyl titanate is to avoid hydrolysis of tetrabutyl titanate directly. If the solubility is too large, it is easy to directly hydrolyze in contact with air, and if the solubility is too small, the reaction efficiency is low.

The invention also discloses the application of manganese titanate nanoparticles prepared by the above-mentioned method for simultaneously preparing spinel type and perovskite type manganese titanate nanoparticles as catalysts in the direction of selective catalytic reduction of NH ₃ .

As can be seen from the above technical solutions, the method and application for simultaneously preparing spinel-type and perovskite-type manganese titanate nanoparticles provided by the technical solution of the present invention have obtained the following beneficial effects:

The method and application of preparing spinel type and perovskite type manganese titanate nanoparticles at the same time disclosed by the invention, in the sol-gel system of pure ethanol, use _MnO2 ultra-thin nanosheets as Mn precursor, titanic acid Tetrabutyl ester (TBOT) was selectively hydrolyzed as a Ti source to form a continuous coating on the surface of MnO ₂ nanosheets, thereby generating MnO ₂ /TiO ₂ composite nanosheets, which were obtained by calcining the obtained composite nanosheets in flowing argon gas. Manganese titanate nanoparticles. By changing the calcination temperature, spinel-type _MnTi2O4 nanoparticles and _perovskite -type _MnTiO3 nanoparticles were sequentially prepared. The invention utilizes tetrabutyl titanate in the sol-gel system of pure ethanol to selectively hydrolyze the surface of _MnO2 nanosheets to generate amorphous titanium oxide, and then promotes the solid phase of titanium oxide and _MnO2 by heating in an argon atmosphere Reaction to obtain MnTi ₂ O ₄ and MnTiO ₃ nanoparticles, there is no need to use two different methods to prepare manganese titanate nanoparticles of different crystal forms, and the method has few steps, the solvent is ethanol, and no intermediate products harmful to the environment are produced. .

The present invention adopts the _{MnTi 2} O ₄ and MnTiO ₃ nanoparticles prepared by the above method to carry out the application experiment of selective catalytic reduction of NH _{3 .} It has excellent performance for the selective catalytic reduction of _NH3 , and the NO conversion efficiency reaches 96%; compared with the spinel _- type _MnTi2O4 nanoparticles, the perovskite-type _MnTiO3 nanoparticles have a lower temperature than 160 °C. The conversion efficiency to NO is relatively low.

It is to be understood that all combinations of the foregoing concepts, as well as additional concepts described in greater detail below, are considered to be part of the inventive subject matter of the present disclosure to the extent that such concepts are not contradictory.

The foregoing and other aspects, embodiments and features of the present teachings can be more fully understood from the following description when taken in conjunction with the accompanying drawings. Other additional aspects of the invention, such as the features and/or benefits of the exemplary embodiments, will be apparent from the description below, or learned by practice of specific embodiments in accordance with the teachings of this invention.

Description of drawings

The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by the same reference numeral. For clarity, not every component is labeled in every figure. Embodiments of various aspects of the present invention will now be described by way of example and with reference to the accompanying drawings, wherein:

1 is a TEM image of spinel-type manganese titanate nanoparticles prepared at a calcination temperature of 450° C. in accordance with the present invention;

Figure 2 is a TEM image of perovskite-type manganese titanate nanoparticles prepared at a calcination temperature of 650°C in the present invention;

Figure 3 is a TEM image of the manganese titanate nanoparticles prepared at a calcination temperature of 350°C in the present invention;

Figure 4 is a TEM image of the manganese titanate nanoparticles prepared at a calcination temperature of 550°C in the present invention;

Fig. 5 is the XRD spectrum of the manganese titanate nanoparticles prepared under each calcination temperature of the present invention;

Fig. 6 is a graph showing the selective catalytic NH ₃ efficiency of the manganese titanate nanoparticles prepared at each calcination temperature of the present invention.

Detailed ways

In order to better understand the technical content of the present invention, specific embodiments are given and described below in conjunction with the accompanying drawings.

Aspects of the invention are described in this disclosure with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. The embodiments of the present disclosure are not defined to include all aspects of the present invention. It should be understood that the various concepts and embodiments described above, as well as those described in greater detail below, can be implemented in any of a variety of ways, as the concepts and embodiments disclosed herein do not limited to any implementation. Additionally, some aspects of the present disclosure may be used alone or in any suitable combination with other aspects of the present disclosure.

Based on the prior art, when preparing manganese titanate nanoparticles of different crystal forms, different methods need to be used to prepare them respectively, and there are many reaction steps, and it is impossible to obtain spinel-type MnTi ₂ O ₄ nanoparticles and perovskite simultaneously by a single method. Ore-type _MnTiO3 nanoparticles; the invention aims to provide a method and application for simultaneously preparing spinel-type and perovskite-type manganese titanate nanoparticles, with few reaction steps and being environmentally friendly.

The method for simultaneously preparing spinel-type and perovskite-type manganese titanate nanoparticles disclosed in the present invention includes the following steps: S1, dispersing _MnO2 nanosheets in ethanol to obtain a _MnO2 nanosheet suspension; S2, stirring Under the conditions, adjust the pH of the MnO ₂ nanosheet suspension of S1 to be alkaline; S3, add the ethanol solution of tetrabutyl titanate dropwise to the alkaline MnO ₂ nanosheet suspension of S2, and continue to stir until the tetrabutyl titanate The butyl ester is fully reacted on the surface of the MnO ₂ nanosheets; S4, filter the reaction solution of S3 to take the solid product, and use ethanol and deionized water to alternately centrifuge and wash, respectively, and then dry to obtain the titanium-manganese composite nanosheets; S5, the S4 The obtained titanium-manganese composite nanosheets are calcined at different temperatures in an argon atmosphere to obtain spinel-type manganese titanate nanoparticles and perovskite-type manganese titanate nanoparticles, respectively.

The design principle of the above reaction steps is to use tetrabutyl titanate in the sol-gel system of pure ethanol to selectively hydrolyze the surface of _MnO nanosheets to generate amorphous titanium oxide, and then adjust the calcination temperature and heat it in an argon atmosphere. Promote the solid-phase reaction of titanium oxide and manganese dioxide to obtain spinel-type manganese titanate and perovskite-type manganese titanate, that is, directly obtain titanic acid of different crystal forms through the combination of sol-gel method and solid-phase reaction method Manganese nanoparticles.

The method and application of the present invention for simultaneously preparing spinel-type and perovskite-type manganese titanate nanoparticles will be further described in detail below with reference to the embodiments shown in the accompanying drawings.

Example 1

Preparation of spinel _- type _MnTi2O4 nanoparticles

The _MnO2 nanosheets were uniformly dispersed in pure ethanol solvent by ultrasonic pulverization method to form a stable _MnO2 nanosheet suspension, the concentration was ₂ mg/mL, the ultrasonic power was 700w, and the ultrasonic wave was 30min; Under the stirring condition of the magnetic stirrer, add 0.1 mL of ammonia water to the MnO ₂ nanosheet suspension to adjust the pH of the MnO ₂ nanosheet suspension to be alkaline; take another dry beaker and add 10 mL of ethanol, and add 0.5 mL of titanium to it under stirring conditions. Tetrabutyl titanate (TBOT) was made into an ethanol solution of tetrabutyl titanate with a concentration of 50mL/L, and the TBOT ethanol solution with a concentration of 50mL/L was added dropwise to the alkaline _MnO nanosheet suspension, and stirred overnight Until TBOT fully reacted on the surface of MnO ₂ nanosheets; filter the reacted reaction solution and take the solid product, and then centrifuge and wash three times with deethanol and ionized water, respectively, and then dry. The drying conditions are drying at 80 °C for 12 hours to obtain titanium Manganese composite nanosheets; put the aforementioned dried titanium-manganese composite nanosheets in a flowing argon tube furnace, set a calcination temperature of 450°C, a programmed heating rate of 10°C/min, and calcined for 2 hours to obtain a calcination with low crystallinity. Spinel-type MnTi ₂ O ₄ nanoparticles, the transmission electron microscope image of the product is shown in Figure 1, and the crystal structure of the product is shown in Figure 5.

In the present invention, ammonia water is used to adjust the pH of the _MnO nanosheet suspension to make it alkaline, and the purpose is that the alkaline environment is conducive to slowing down the hydrolysis rate of the subsequently added tetrabutyl titanate on the surface of the _MnO nanosheets. The hydrolysis of tetrabutyl ester is too fast, and the formed amorphous titanium oxide cannot be uniformly attached to the _MnO2 nanosheets, and the titanium oxides are stacked with each other, which affects the purity of the manganese titanate nanoparticles in the final product. In the same way, dissolving tetrabutyl titanate in ethanol first is also to prevent hydrolysis of tetrabutyl titanate from being directly hydrolyzed in the air when taking it.

Example 2

Preparation of perovskite-type _MnTiO3 nanoparticles

The difference between Example 2 and Example 1 is that the dried titanium-manganese composite nanosheets were placed in a flowing argon tube furnace, the calcination temperature was set to 650 °C, the temperature programmed rate was 10 °C/min, and the calcination was performed for 2 h. The crystallinity of the perovskite-type _MnTiO3 nanoparticles, the TEM image of the product is shown in Figure 2.

Example 3

The difference between Example 3 and Example 1 is that the dried titanium-manganese composite nanosheets were placed in a flowing argon tube furnace, the calcination temperature was set to 350°C, the temperature-programmed rate was 10°C/min, and the calcination was performed for 2 hours. The spinel-type manganese titanate nanoparticles with poor degree of degree, the transmission electron microscope image of the product is shown in Figure 3.

Example 4

The difference between Example 4 and Example 1 is that the dried titanium-manganese composite nanosheets were placed in a flowing argon tube furnace, the calcination temperature was set to 350°C, the temperature-programmed heating rate was 10°C/min, and the calcination was performed for 2 hours. The spar-type and perovskite-type manganese titanate nanoparticles are mixed, and the transmission electron microscope image of the product is shown in Figure 4.

As shown in Figure 5, at a calcination temperature of 350 °C, the titanium-manganese composite nanosheets start to produce spinel-type MnTi ₂ O ₄ with very poor crystallinity; at a calcination temperature of 450 °C, a spinel-type MnTi ₂ O ₄ nanoparticles; as the calcination temperature increased to 550 °C, a small part of the final product began to transform into perovskite-structured MnTiO ₃ with higher crystallinity; when the calcination temperature increased to At 650 °C, the final product is highly crystalline perovskite-type _MnTiO3 nanoparticles.

The invention also discloses the application of the manganese titanate nanoparticles prepared by the above preparation method in the direction of selective catalytic (SCR) reduction of NH ₃ , and the final product manganese titanate nanoparticles is used as a catalyst for selective catalytic reduction of NH ₃ , and the specific process is as follows Examples are shown. The data about NO at each reaction temperature in Example 5 are the NO concentration data measured by sampling at the current temperature, and the unit is ppm.

Example 5

Take 50 mg of each of the manganese titanate nanoparticles obtained in Example 1 to Example 4 as a catalyst, respectively pass through a 50-60 mesh sieve and grind any part of the catalyst through a tablet press at 20 MPa to obtain solid small particles, Load the obtained particles into the fixed-bed quartz reactor for the SCR test; before the test, purging for 40 minutes is performed to make the fixed-bed quartz reactor reach a stable state, and then the temperature rises. When the temperature of the reactor reaches 80°C, 120°C , 160 ℃, 200 ℃, 240 ℃ and stable for 10min, take samples respectively, and analyze and detect the samples. In this example, the efficiency of catalytic reduction of NH ₃ by the catalyst is characterized by the change of NO concentration after catalysis in the simulated flue gas, that is, the gas concentration of NO in the sample is measured online by a flue gas analyzer. The specific results are shown in Table 1 and Figure 6. .

The manganese titanate nanoparticles obtained at different temperatures were used as catalysts for selective catalytic reduction of NH3. The results showed that the spinel _- type _MnTi2O4 nanoparticles with low crystallinity were at low temperature, that is, the reaction temperature was lower than 240℃. The SCR of _NH3 has excellent performance under low temperature, while the NO conversion efficiency reaches 96% when the reaction temperature rises to 240 °C. Compared with spinel-type _MnTi2O4 nanoparticles, the NO conversion rate of _perovskite -type _MnTiO3 nanoparticles is relatively low when the reaction temperature is lower than 160 °C, and the NO conversion rate gradually increases when the reaction temperature exceeds 160 °C. .

Table 1 Efficiency of selective catalytic reduction of _NH3 by manganese titanate nanoparticles prepared at different calcination temperatures

In the application documents of the present invention, the effect of selective catalytic (SCR) reduction of NH ₃ by spinel-type MnTi ₂ O ₄ nanoparticles prepared from TBOT ethanol solutions with different concentrations was further studied. The specific results are shown in Table 2.

Table ₂ Efficiency of selective catalytic reduction of NH with manganese titanate nanoparticles prepared with different reactant concentrations

Combined with Table 2, different concentrations of TBOT ethanol solution have little effect on the catalytic reduction of NH ₃ by spinel-type MnTi ₂ O ₄ nanoparticles, among which, when the concentration of TBOT ethanol solution is 50 mL/L, the NO conversion efficiency is the highest. When the concentration of TBOT ethanol solution was lower than 50 mL/L, the amount of TBOT substance was small, and the surface of MnO ₂ nanosheets could not be completely covered. When the concentration of TBOT ethanol solution is higher than 50mL/L, due to the excessive amount of TBOT substances, which affects the purity of the phase, there is excess TiO ₂ that fails to react with MnO ₂ nanosheets, thus affecting the catalysis of manganese titanate nanoparticles. Effect.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Those skilled in the art to which the present invention pertains can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be determined according to the claims.

Claims (3)

1. a method for simultaneously preparing spinel type and perovskite type manganese titanate nanoparticles, is characterized in that, comprises the steps: S1, disperse _MnO nanosheets in ethanol to obtain _MnO nanosheet suspension; wherein, the ethanol is a pure ethanol solvent; S2, under stirring conditions, adjust the pH of the _MnO nanosheet suspension of S1 to be alkaline; S3. Add the ethanol solution of tetrabutyl titanate with a concentration of 10mL/L～100mL/L dropwise to the alkaline _MnO nanosheet suspension of S2, and continue stirring until the tetrabutyl titanate is on the surface of the _MnO nanosheets adequate response; S4, filter the reaction solution of S3 to get the solid product, and then use ethanol and deionized water to alternately centrifuge and wash and then dry to obtain titanium-manganese composite nanosheets; wherein, the titanium-manganese composite nanosheets have amorphous titanium oxide on the surface. _MnO2 nanosheets; S5, calcining the titanium-manganese composite nanosheets obtained from S4 at different temperatures in an argon atmosphere to obtain spinel-type manganese titanate nanoparticles and perovskite-type manganese titanate nanoparticles respectively; Wherein, the reaction process of S5 is that the MnO ₂ nanosheets and the amorphous titanium oxide on the surface undergo solid-phase reaction to obtain MnTi ₂ O ₄ or MnTiO ₃ nanoparticles; and the calcination process in S5 is to set the calcination temperature and the heating rate to 10 ℃/min, constant temperature calcination for 2 h at the set calcination temperature, the calcination temperature for preparing spinel-type manganese titanate nanoparticles is 450℃, and the calcining temperature for perovskite-type manganese titanate nanoparticles is 650℃. 2. the method for simultaneously preparing spinel type and perovskite type manganese titanate nanoparticles according to claim 1, is characterized in that, in the described S2, to MnO ₂ in nano-sheet suspension, add ammoniacal liquor to regulate MnO ₂ nanometers The tablet suspension is alkaline. 3. the method for simultaneously preparing spinel type and perovskite type manganese titanate nanoparticles according to claim 1, is characterized in that, in described S1, adopt ultrasonic pulverizing method to _MnO Nano sheet is uniformly dispersed in ethanol .

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