A method for preparing the oxygen-nitrogen compound LaTiO2N and its product

Abstract

The application discloses a preparation method of an oxynitride LaTiO2N and a product thereof, and the preparation method comprises the following steps: step one, preparing a precursor I; the precursor I is A2La2Ti3O 10 wherein A is any one of Cs, Rb, K and Na; step two, performing liquid phase stripping on the precursor I to obtain a precursor II; step three, mixing the precursor II, LaCl3 and a fused salt, and then performing nitridation to obtain the required oxynitride LaTiO2N. The preparation method of the oxynitride LaTiO2N and the product thereof provided by the application can prepare a precursor II with a smaller size by performing liquid phase stripping on the precursor I, and then the precursor II is mixed with LaCl3 and a fused salt which are not easy to volatilize, and the oxynitride LaTiO2N can be prepared after short-time nitridation, so that the preparation method has a better charge separation efficiency and exhibits water decomposition activity in a photocatalytic water decomposition reaction.

Description

Technical Field

[0001] This invention belongs to the field of materials synthesis and renewable clean energy utilization technology, specifically relating to a method for preparing the oxygen-nitrogen compound LaTiO2N and its product. Background Technology

[0002] (Oxygen)nitrogen compounds have suitable band gaps and conduction / valence band positions, making them suitable for water splitting and considered a highly attractive class of visible light-responsive photocatalysts. However, these (Oxygen)nitrogen compound photocatalysts are generally synthesized using high-temperature solid-state methods, which inevitably generate anion vacancies or low-valence metal species. These anion vacancies or low-valence metal species are often considered recombination centers, which reduce the activity of the photocatalyst.

[0003] The traditional method for synthesizing the oxygen-nitrogen compound LaTiO2N is to first synthesize the La2Ti2O7 precursor and then directly nitrid it. However, due to the large particle size of the precursor and the long high-temperature nitriding process, the density of low-valence defects increases and the charge separation ability decreases.

[0004] Researchers have made many attempts to suppress oxygen and nitrogen compound defects, mainly in the following three aspects:

[0005] (1) Doping with low-valence metals, that is, suppressing the generation of low-valence metal defects by doping with low-valence metal species that are not easily reduced (such as Mg, Sc, Zr, etc.).

[0006] (2) Molten salt assisted nitriding, that is, molten salt assisted nitriding is beneficial to suppressing defects in low-valence metals and improving the crystallinity of materials. For example, using RbCl molten salt assisted nitriding of BaCO3 and Ta2O5 precursors to generate BaTaO2N.

[0007] (3) Reduce the nitriding time, that is, nitrid the KTaO3 precursor for a short time at high temperature to obtain high quality and low defect Ta3N5 nanorods at the edge of KTaO3. Unfortunately, short-time nitriding cannot completely convert the precursor oxide into (oxy)nitrogen compounds. The Ta3N5 nanorods are mainly located on the surface of the material.

[0008] All three methods have their merits, but for suppressing defects in low-valence metals, the strategy of reducing nitriding time has the highest priority, because the number of low-valence metal defects can be controlled by changing the precursor or molten salt type.

[0009] Traditional methods for reducing nitriding time primarily involve shrinking the precursor geometry. Specific methods include sol-gel methods for preparing oxide precursors and liquid-phase exfoliation of layered oxide precursors. Theoretically, liquid-phase exfoliation produces oxide precursors with smaller radii and easier microstructure control. However, current work on preparing (oxy)nitrogen compounds via liquid-phase exfoliation of oxide precursors is scarce, and primarily focuses on preparing nitrogen-doped oxides. There are two main reasons for this:

[0010] 1) After stripping, the cations on the surface of the layered oxide are replaced by hydrogen ions, which are more easily lost under high temperature conditions. Due to the charge imbalance, it is more difficult for nitrogen atoms to replace oxygen atoms thermodynamically and kinetically.

[0011] 2) Prolonged high-temperature nitriding leads to more defects in low-valence metals, and smaller precursors may agglomerate during nitriding, affecting catalyst activity. Summary of the Invention

[0012] To address the technical problems existing in the prior art, the present invention aims to provide a method for preparing the oxygen-nitrogen compound LaTiO2N and its product.

[0013] To achieve the above objectives and technical effects, the technical solution adopted by this invention is as follows:

[0014] A method for preparing the oxygen-nitrogen compound LaTiO2N includes the following steps:

[0015] Step 1: Preparation of Precursor I

[0016] The precursor I is A2La2Ti3O 10 Where A is any one of Cs, Rb, K, and Na;

[0017] Step 2: Perform liquid phase stripping on precursor I to obtain precursor II;

[0018] Step 3: After mixing precursor II, LaCl3 and molten salt, nitriding is performed to obtain the desired oxygen-nitrogen compound LaTiO2N.

[0019] Furthermore, in step one, the precursor I is prepared using a sol-gel method or a high-temperature solid-state method, and the A2La2Ti3O 10 It is prepared using A precursor, La precursor and Ti precursor as raw materials, with the molar ratio of A, La and Ti being (2~3):2:3.

[0020] Furthermore, in step one, the A precursor contains at least one of the following: oxide of A, carbonate, oxalate, and nitrate; the La precursor contains at least one of the following: oxide of La, carbonate, oxalate, and nitrate; and the Ti precursor contains at least one of the following: oxide of Ti, carbonate, oxalate, and chloride.

[0021] Furthermore, in step two, the step of liquid-phase stripping precursor I to obtain precursor II includes:

[0022] Precursor I was first acid-treated, then ultrasonically treated in a tetrabutylammonium hydroxide aqueous solution, and then centrifuged to obtain precursor II.

[0023] The acid comprises 0.5–6 mol / L hydrochloric acid or nitric acid, and the acid treatment time is 4–10 days;

[0024] The concentration of the tetrabutylammonium hydroxide aqueous solution is 20-40 wt%, the ultrasonic treatment temperature is 40-80℃, and the ultrasonic treatment time is 7-14 days.

[0025] Furthermore, in step three, the molar ratio of precursor II, LaCl3, and molten salt is 1:1:(5-10), and the molten salt is at least one of NaOH and KOH;

[0026] Nitriding was carried out in an ammonia gas flow of 200–300 mL / min, at a nitriding temperature of 800–1000 °C, for a nitriding time of 0.5–5 h.

[0027] The present invention also discloses an oxygen-nitrogen compound LaTiO2N prepared by the method described above.

[0028] The present invention also discloses the application of the oxygen-nitrogen compound LaTiO2N as described above in water decomposition.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1) This invention prepares a smaller precursor II by liquid-phase exfoliation of precursor I, which is then mixed with non-volatile LaCl3 and molten salt, and nitrided for a short time to prepare the oxygen-nitrogen compound LaTiO2N, which has better charge separation efficiency and exhibits water-splitting activity in photocatalytic water splitting reaction.

[0031] 2) This invention can reduce the size of the precursor through liquid phase stripping. The smaller precursor size can shorten the nitriding time, effectively reduce the generation of low-valence metal defects, improve charge separation efficiency, and is simple to operate. It has a certain degree of universality and is suitable for promotion and application in industrial production. Attached Figure Description

[0032] Figure 1 This is a diagram illustrating the formation mechanism of the oxygen-nitrogen compound LaTiO2N in Example 1 of the present invention, where 0 < x < 1;

[0033] Figure 2 The scanning electron microscope image and elemental mapping diagram of the oxygen-nitrogen compound LaTiO2N in Example 1 of the present invention are shown.

[0034] Figure 3 The XRD pattern of the oxygen-nitrogen compound LaTiO2N in Example 1 of the present invention;

[0035] Figure 4 This is a diagram showing the oxygen-nitrogen compound LaTiO2N's activity in water decomposition to produce oxygen in Example 1 of the present invention. Detailed Implementation

[0036] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0037] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0038] On the one hand, such as Figure 1-4 As shown, this invention discloses a method for preparing the oxygen-nitrogen compound LaTiO2N, which first synthesizes a layered perovskite oxide precursor A2La2Ti3O. 10 Then, by liquid-phase exfoliation, small and uniformly sized perovskite nanosheets can be obtained. These nanosheets are then nitrided with LaCl3 and molten salt to prepare the perovskite-type oxynitrogen compound LaTiO2N. This method mainly includes the following steps:

[0039] Step 1: Preparation of Precursor I

[0040] Precursor I is A2La2Ti3O 10 Where A is any one of Cs, Rb, K, and Na;

[0041] Step 2: Precursor I is subjected to liquid-phase exfoliation to obtain precursor II. The specific steps are as follows: First, precursor I is acid-treated with 0.5-6 mol / L hydrochloric acid or nitric acid for 4-10 days; then, it is ultrasonically treated in a 20-40 wt% tetrabutylammonium hydroxide aqueous solution at a temperature of 40-80℃ for 7-14 days. After centrifugation, precursor II can be obtained.

[0042] Step 3: Mix precursor II, LaCl3 and molten salt in a molar ratio of 1:1:(5-10), and nitrify them in an ammonia gas flow of 200-300 mL / min. The nitrification temperature is 800-1000℃ and the nitrification time is 0.5-5 h to obtain the desired oxygen-nitrogen compound LaTiO2N.

[0043] In step one, precursor I is prepared by sol-gel method or high-temperature solid-state method, A2La2Ti3O 10 It is prepared using A precursor, La precursor and Ti precursor as raw materials, with the molar ratio of A, La and Ti being (2~3):2:3.

[0044] A precursors include at least one of the following: oxides, carbonates, oxalates, and nitrates of A.

[0045] La precursors include at least one of La oxides, carbonates, oxalates, and nitrates.

[0046] Ti precursors include at least one of the following: Ti oxides, carbonates, oxalates, and chlorides.

[0047] The molten salt is at least one of NaOH and KOH.

[0048] On the other hand, the present invention also discloses an oxygen-nitrogen compound LaTiO2N prepared by the method described above.

[0049] The present invention also discloses the application of the oxygen-nitrogen compound LaTiO2N as described above in water decomposition.

[0050] The high-temperature nitriding process causes the volatilization of low-valence, volatile alkali metals. This invention balances the charge by adding high-valence, non-volatile lanthanide metals, which facilitates the substitution of oxygen atoms by nitrogen atoms, resulting in A₂La₂Ti₃O₃. 10 Since there are fewer La atoms than Ti atoms, adding a small amount of La atoms can generate the corresponding oxygen-nitrogen compound LaTiO2N.

[0051] Example 1

[0052] like Figure 1-4As shown, this invention discloses a method for preparing the oxygen-nitrogen compound LaTiO2N, which first synthesizes a layered perovskite oxide precursor A2La2Ti3O. 10 Then, by liquid-phase exfoliation, small and uniformly sized perovskite nanosheets can be obtained. These nanosheets are then nitrided with LaCl3 and molten salt to prepare the perovskite-type oxynitrogen compound LaTiO2N. This method mainly includes the following steps:

[0053] Step 1: Preparation of precursor I K2La2Ti3O using a high-temperature solid-state method 10

[0054] K₂CO₃, La₂(CO₃)₃, and TiO₂ were mixed and ground in a molar ratio of A:La:Ti of 3:2:3 until homogeneous. The mixture was then calcined at 1000℃ for 6 hours to obtain precursor I, K₂La₂Ti₃O₂. 10 ,spare;

[0055] Step 2: Perform liquid phase stripping on precursor I to obtain precursor II.

[0056] First, the precursor I K2La2Ti3O 10 The precursor was treated in a 6 mol / L nitric acid solution for 4 days, with the nitric acid solution being replaced every 2 days and stirred at room temperature. Then, it was intermittently sonicated in a 40 wt% tetrabutylammonium hydroxide aqueous solution for 12 days, with sonication every 12 hours at a temperature of 40–80 °C. Finally, it was centrifuged at 5000 r / min for 10 min, and the supernatant was collected to obtain precursor II.

[0057] Step 3: According to the stoichiometric ratio of n(precursor II):n(LaCl3):n(NaOH):n(KOH)=1:1:5:5, precursor II is mixed with LaCl3, NaOH and KOH, and then nitrided in an ammonia gas flow of 200mL / min at 850℃ for 2h to obtain the desired oxygen-nitrogen compound LaTiO2N.

[0058] The oxygen and nitrogen compound LaTiO2N prepared in Example 1 was used as a photocatalyst to evaluate the photocatalytic water splitting activity. The reaction conditions are as follows:

[0059] 200mg loaded with 2wt% CoO x The LaTiO2N sample contained 200 mg La2O3, 1.6988 g AgNO3, 200 mL H2O, and a 300 W xenon lamp light source.

[0060] Figure 1 This is a diagram illustrating the formation mechanism of the oxygen-nitrogen compound LaTiO2N in Example 1.

[0061] Figure 2The image shows a scanning electron microscope (SEM) image and elemental mapping diagram of the oxygen-nitrogen compound LaTiO2N from Example 1.

[0062] Figure 3 The image shows the XRD pattern of the oxygen-nitrogen compound LaTiO2N from Example 1.

[0063] Figure 4 The diagram shows the oxygen-nitrogen compound LaTiO2N's activity in water decomposition to produce oxygen in Example 1.

[0064] like Figure 2-4 As shown, LaTiO2N was synthesized. Its XRD pattern and scanning electron microscopy elemental mapping confirmed that the synthesized LaTiO2N, after being loaded with a suitable oxygen-generating co-catalyst, can achieve the photocatalytic oxygen-generating half-reaction. With prolonged reaction time, the oxygen-generating rate decreases because the sacrificial agent AgNO3 is reduced to elemental Ag and deposited on LaTiO2N, leading to blocked light absorption and decreased reaction activity—a common phenomenon. This experiment demonstrates that the generated LaTiO2N possesses photocatalytic oxygen-generating properties.

[0065] Any parts or structures not specifically described in this invention can be made using existing technologies or products, and will not be elaborated upon here.

[0066] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing the oxygen-nitrogen compound LaTiO2N, characterized in that, Includes the following steps: Step 1: Preparation of Precursor I The precursor I is A2La2Ti3O 10 Where A is any one of Cs, Rb, K, and Na; Step 2: Perform liquid phase stripping on precursor I to obtain precursor II; Step 3: After mixing precursor II, LaCl3 and molten salt, nitriding is performed to obtain the desired oxygen-nitrogen compound LaTiO2N; Step two, which involves liquid-phase stripping of precursor I to obtain precursor II, includes the following steps: Precursor I was first acid-treated, then ultrasonically treated in a tetrabutylammonium hydroxide aqueous solution, and then centrifuged to obtain precursor II. The acid comprises 0.5-6 mol / L hydrochloric acid or nitric acid, and the acid treatment time is 4-10 days; The concentration of the tetrabutylammonium hydroxide aqueous solution is 20~40wt%, the ultrasonic treatment temperature is 40~80℃, and the ultrasonic treatment time is 7~14 days; In step three, nitriding is carried out in an ammonia gas flow of 200~300 mL / min, at a nitriding temperature of 800~1000℃, and for a nitriding time of 0.5~5 h.

2. The method for preparing the oxygen-nitrogen compound LaTiO2N according to claim 1, characterized in that, In step one, the precursor I is prepared by sol-gel method or high-temperature solid-state method, and the A2La2Ti3O 10 It is prepared using A precursor, La precursor and Ti precursor as raw materials, with the molar ratio of A, La and Ti being (2~3):2:

3.

3. The method for preparing the oxygen-nitrogen compound LaTiO2N according to claim 2, characterized in that, In step one, the A precursor contains at least one of the following: oxide, carbonate, oxalate, and nitrate of A; the La precursor contains at least one of the following: oxide, carbonate, oxalate, and nitrate of La; and the Ti precursor contains at least one of the following: oxide, carbonate, oxalate, and chloride of Ti.

4. The method for preparing the oxygen-nitrogen compound LaTiO2N according to claim 1, characterized in that, In step three, the molar ratio of precursor II, LaCl3, and molten salt is 1:1:(5~10), and the molten salt is NaOH or KOH.

5. An oxygen-nitrogen compound LaTiO2N prepared by a method according to any one of claims 1-4.

6. The application of the oxygen-nitrogen compound LaTiO2N according to claim 5 in water decomposition.

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