WO2024077929A1

WO2024077929A1 - Oxynitride heterojunction, and preparation method therefor and use thereof

Info

Publication number: WO2024077929A1
Application number: PCT/CN2023/090661
Authority: WO
Inventors: 罗彦佩; 王乐乐; 方朝君; 鲍强; 陈宝康; 姚燕; 马云龙; 孔凡海; 杨晓宁; 雷嗣远; 王凯
Original assignee: 苏州西热节能环保技术有限公司
Priority date: 2022-10-14
Filing date: 2023-04-25
Publication date: 2024-04-18
Also published as: CN115518668A

Abstract

The present disclosure discloses an oxynitride heterojunction, and a preparation method therefor and the use thereof. The preparation method comprises the following steps: (1) preparing a first precursor, which is AM2Ta3O10 or ARTa2O7, wherein in AM2Ta3O10, A is Cs or Rb, and M is Ca, Sr or Ba; and in ARTa2O7, A is Cs or Rb, and R is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or Y; (2) preparing a second precursor from the first precursor by means of a liquid phase exfoliation method; (3) subjecting the second precursor to a molten salt treatment or a hydrothermal treatment to prepare a third precursor; and (4) nitriding the third precursor to generate an oxynitride heterojunction in situ.

Description

An oxygen-nitrogen compound heterojunction and its preparation method and application

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on the Chinese patent application with application number 202211258567.X and application date October 14, 2022, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby introduced into this application as a reference.

Technical Field

The present disclosure belongs to the field of material synthesis and renewable clean energy utilization. Specifically, the present disclosure relates to an oxygen-nitrogen compound heterojunction, a preparation method thereof, and use thereof as a water decomposition photocatalyst.

Background technique

As the use of large amounts of fossil fuels has caused increasing energy consumption and environmental problems, decomposing water into hydrogen and oxygen is one of the most important ways to solve the future shortage of fossil fuels and reduce environmental pollution associated with fossil fuel consumption. Water decomposition consists of two half reactions, namely the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER).

(Oxygen) nitrogen compounds have suitable band gaps and conduction/valence band positions for water splitting and are considered to be an attractive class of visible light responsive photocatalysts. However, these (oxygen) nitrogen compound photocatalysts are generally synthesized by high-temperature solid-phase methods, which inevitably produce anion vacancies or low-valent metal species, which are usually considered to be recombination centers and reduce the photocatalytic activity. Ta ₃ N ₅ is a star material among (oxygen) nitrogen compound photocatalysts with a band gap of 2.10 eV and a theoretical solar-to-hydrogen conversion efficiency of up to 15.9%. However, it is still plagued by rapid carrier recombination, which seriously affects its photocatalytic activity. Therefore, it is very necessary to develop effective strategies (such as constructing heterojunctions) to accelerate the spatial charge separation of (oxygen) nitrogen compounds and improve their photocatalytic water splitting activity.

Constructing heterojunctions is one of the basic strategies to promote charge separation in the field of solar cells or solar fuels. The built-in electric field generated at the heterojunction interface is the driving force for the directional movement of photogenerated electrons and holes. Its successful construction depends not only on the relative energy level positions of the two materials, but also on the close contact interface of the two substances. As for oxynitride heterojunctions, most of the reported examples are mixed by mechanical mixing, and the contact interface between the two substances is relatively small. The ideas to solve this problem mainly include two aspects: 1) Use a soluble salt solution to impregnate an oxide precursor to form a new substance on the oxide surface, and then nitride to obtain an oxynitride heterojunction, such as impregnating tantalum oxide with a salt solution of barium, and then nitriding to obtain _a _BaTaO2N / _Ta3N5 heterojunction. 2) Using the different ratios of tantalum and alkaline earth elements in the precursor oxide, in-situ generation of oxynitride heterojunctions is performed. For example, using KBa ₂ Ta ₅ O ₁₀ as a precursor template, high-temperature nitridation is used to in-situ generate 0D/1D BaTaO ₂ N/Ta ₃ N ₅ heterojunctions; using layered oxide KCa ₂ Ta ₃ O ₁₀ as a precursor template, high-temperature nitridation is used to in-situ generate 2D/1D CaTaO ₂ N/Ta ₃ N ₅ heterojunctions. Compared with mechanical mixing and core-shell structure heterojunctions, the in-situ synthesized oxynitride heterojunctions have richer contact interfaces, and the constructed heterojunctions can significantly promote charge separation.

However, the oxygen-nitrogen compound heterojunction in the related technology still has the following problems:

(1) The particle size of the perovskite oxide precursor synthesized by the high-temperature solid-phase method is at the micron level, and the particle size of the generated oxygen-nitrogen compound heterojunction is mostly at the micron level, which is not conducive to the diffusion of photogenerated electrons and holes to the catalyst surface, affecting the charge separation efficiency.

(2) Due to the large size of the precursor particles, the nitridation process is limited by the diffusion kinetics of ammonia and requires a long time for nitridation, which often produces a large number of low-valent metal defects. Low-valent metal defects are often considered to be the recombination centers of electron holes, affecting the charge separation efficiency of the catalyst.

Summary of the invention

The present disclosure provides a method for preparing an oxygen-nitrogen compound heterojunction, comprising:

( ₁ ) preparing _a first precursor, wherein the first precursor is _AM2Ta3O10 or _ARTa2O7 _; in _{the AM2Ta3O10} _, A is Cs or Rb, and M is Ca, Sr or Ba; in _the _ARTa2O7 , A is Cs or _Rb , and R is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or Y;

(2) preparing a second precursor by liquid phase exfoliation of the first precursor;

(3) treating the second precursor with molten salt or hydrothermally to prepare a third precursor;

(4) Nitriding the third precursor in situ to generate an oxygen-nitrogen compound heterojunction.

In some embodiments, _{the AM2Ta3O10} _is prepared by a sol-gel method or _a high-temperature solid phase method using an A precursor, an M precursor and a Ta precursor as raw materials; wherein the A precursor, the M precursor and the Ta precursor are stoichiometrically proportioned according to a molar ratio of A, M and Ta of (1-1.8):2:3.

In some embodiments, _the _ARTa2O7 is prepared using an A precursor, an R precursor, and a Ta precursor as raw materials by a sol-gel method or a high-temperature solid phase method; wherein the A precursor, the R precursor, and the Ta precursor are stoichiometrically proportioned according to a molar ratio of A, R, and Ta of (1-1.8): 1:2.

In some embodiments, the A precursor is selected from at least one of A carbonate, A oxide, A oxalate, and A nitrate.

In some embodiments, the M precursor is selected from at least one of M carbonate, M oxide, M oxalate, and M nitrate.

In some embodiments, the R precursor is selected from at least one of a carbonate of R, an oxide of R, an oxalate of R, and a nitrate of R.

In some embodiments, when the sol-gel method is used, the Ta precursor is selected from TaCl ₅ and tantalum ethoxide.

In some embodiments, when a high temperature solid phase method is used, the Ta precursor is selected from Ta oxides.

In some embodiments, the sol-gel method is to add the raw materials to methanol or ethanol, then add citric acid, and then add ethylene glycol as a binder, heat at 200-300°C to form a sol-gel solution, and then calcine at 500-800°C for 1-4 hours.

In some embodiments, the high temperature solid phase method is to grind and evenly mix the raw materials, and then calcine at 800-1100° C. for 2-10 hours.

In some embodiments, the step of preparing the second precursor by liquid phase exfoliation of the first precursor is:

The first precursor is first subjected to acid treatment, then subjected to ultrasonic treatment in a tetrabutylammonium hydroxide aqueous solution, and then subjected to centrifugal separation to obtain the second precursor;

Optionally, the acid is 0.5-3 mol/L hydrochloric acid or nitric acid; the acid treatment time is 4-10 days, the acid solution is replaced every 2 days, and stirring is carried out at room temperature.

Optionally, the temperature of the ultrasonic treatment is 40 to 80° C., and the time is 7 to 14 days.

In some embodiments, the ultrasound is intermittent ultrasound, and the ultrasound power is 350W.

In some embodiments, the temperature of the molten salt treatment is 300-400° C., and the treatment time is 24-48 hours; the molten salt is selected from at least one of KNO ₃ , LiNO ₃ , and NaNO ₃ .

In some embodiments, the temperature of the hydrothermal treatment is 100-200° C., and the treatment time is 24-48 hours; the aqueous solution is at least one of a KOH aqueous solution, a LiOH aqueous solution, and a NaOH aqueous solution.

In some embodiments, in step (4), the third precursor and the molten salt are mixed in a molar ratio of 1:(0.5-5) and then nitrided.

In some embodiments, the nitridation temperature in step (4) is 900-1000° C., and the nitridation time is 0.05-3 h in a 200-300 mL/min ammonia gas flow. Compared with the related art, the shortening of the nitridation time effectively reduces the generation of low-valent metal defects and further improves the charge separation efficiency.

The present disclosure also provides an oxygen-nitrogen compound heterojunction, which is prepared by the above-mentioned preparation method.

In some embodiments, the size of the oxynitride heterojunction is nanometer scale.

The present disclosure also provides the use of the above-mentioned oxygen-nitrogen compound heterojunction as a water decomposition photocatalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or additional aspects and advantages of the present disclosure will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

FIG1 is a diagram showing the formation mechanism of the oxygen-nitrogen compound heterojunction disclosed in the present invention. In FIG1 , 0＜x＜1.

FIG2 is a transmission electron microscope image and element mapping image of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction prepared in Example 1 of the present disclosure;

FIG3 is a high-magnification transmission electron microscopy image of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction prepared in Example 1 of the present disclosure;

FIG4 is an XRD graph of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction, single-phase Ta ₃ N ₅ , and single-phase CaTaO ₂ N prepared in Example 1 of the present disclosure.

FIG5 is a scanning electron microscope image of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction prepared in Comparative Example 1 of the present disclosure;

FIG6 is a transmission electron microscope image of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction prepared in Comparative Example 1 of the present disclosure;

FIG. 7 is an element mapping diagram of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction prepared in Comparative Example 1 of the present disclosure;

FIG8 is an XRD graph of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction, single-phase Ta ₃ N ₅ , and single-phase CaTaO ₂ N prepared in Comparative Example 1 of the present disclosure;

FIG9 is a graph showing the full water splitting activity of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction prepared in Example 1 of the present disclosure;

FIG. 10 is a graph showing the full water splitting activity of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction prepared in Comparative Example 1 of the present disclosure.

Detailed ways

Embodiments of the present disclosure are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present disclosure, but should not be understood as limiting the present disclosure.

The present disclosure aims to solve at least one of the technical problems existing in the above-mentioned related technologies to a certain extent. To this end, one purpose of the embodiments of the present disclosure is to provide a method for preparing an oxygen-nitrogen compound heterojunction.

Another object of the embodiments of the present disclosure is to provide an oxygen-nitrogen compound heterojunction prepared by the method of the embodiments of the present disclosure.

Another object of the embodiments of the present disclosure is to provide the use of the above-mentioned oxygen-nitrogen compound heterojunction as a water decomposition photocatalyst.

The liquid phase exfoliation method used in the method of the embodiment of the present disclosure can prepare precursors with uniform particle sizes and sizes at the nanometer level, which is very helpful in reducing the carrier migration distance and can significantly promote charge separation.

Non-limiting examples include: A precursor, M precursor, and Ta precursor are metered and mixed according to the molar ratio of A, M, and Ta of 1:2:3, 1.2:2:3, 1.4:2:3, 1.6:2:3, or 1.8:2:3.

In some embodiments, ARTa ₂ O ₇ is prepared using A precursor, R precursor and Ta precursor as raw materials by a sol-gel method or a high-temperature solid phase method; wherein the A precursor, R precursor and Ta precursor are stoichiometrically proportioned according to the molar ratio of A, R and Ta: (1-1.8): 1:2.

Non-limiting examples include: A precursor, R precursor, and Ta precursor are metered and mixed according to the molar ratio of A, R, and Ta of 1:1:2, 1.2:1:2, 1.3:1:2, 1.4:1:2, 1.6:1:2, or 1.8:1:2.

Non-limiting examples include:

The heating temperature may be 200°C, 220°C, 235°C, 260°C, 270°C, 285°C, 300°C, etc.

The calcination temperature may be 500° C., 550° C., 580° C., 600° C., 660° C., 700° C., 750° C., 800° C., etc. The calcination time may be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 4 h, etc.

In some embodiments, the high temperature solid phase method is to grind and mix the raw materials uniformly, and then calcine at 800-1100° C. for 2-10 hours.

Non-limiting examples include:

The calcination temperature may be 800° C., 850° C., 880° C., 900° C., 950° C., 1000° C., 1100° C., etc. The calcination time may be 2 h, 4 h, 6 h, 7 h, 8 h, 9 h, 10 h, etc.

The first precursor is firstly treated with acid, then ultrasonically treated in a tetrabutylammonium hydroxide aqueous solution, and then centrifugally separated to obtain the second precursor.

In some embodiments, the acid is 0.5-3 mol/L hydrochloric acid or nitric acid; the acid treatment time is 4-10 days, the acid solution is replaced every 2 days, and stirring is performed at room temperature.

Non-limiting examples include: the acid can be 0.5 mol/L, 1 mol/L, 2 mol/L or 3 mol/L hydrochloric acid or nitric acid; the acid treatment time can be 4 days, 6 days, 8 days, 10 days, etc.

In some embodiments, the concentration of the tetrabutylammonium hydroxide aqueous solution is 30-40 wt %.

In some embodiments, the temperature of the ultrasonic treatment is 40-80° C., and the time is 7-14 days.

For example, the ultrasonic treatment may be carried out at a temperature of 40°C, 50°C, 60°C or 80°C, and for a period of 7 days, 8 days, 10 days, 12 days, 14 days, etc.

Non-limiting examples include intermittent ultrasound treatment for 12 hours every 12 hours, or ultrasound treatment for 8 hours every 8 hours, etc.

Non-limiting examples include: the temperature of the molten salt treatment can be 300°C, 320°C, 350°C, 380°C, 400°C, etc., and the treatment time can be 24h, 28h, 30h, 36h, 40h, 45h, 48h, etc.

In some embodiments, the temperature of the hydrothermal treatment is 100-200° C., and the treatment time is 24-48 hours; the aqueous solution is at least one of a KOH aqueous solution (1-3 mol/L), a LiOH aqueous solution (1-3 mol/L), and a NaOH aqueous solution (1-3 mol/L).

Non-limiting examples include: the temperature of the hydrothermal treatment can be 100°C, 120°C, 150°C, 180°C, 200°C, etc., and the treatment time can be 24h, 28h, 30h, 36h, 40h, 45h, 48h, etc.

For non-limiting example, the third precursor and the molten salt can be mixed in a molar ratio of 1:0.5, 1:1, 1:2, 1:4, or 1:5.

For example, the nitriding temperature in step (4) can be 900°C, 920°C, 950°C, 1000°C. etc.; the ammonia flow rate can be 200mL/min, 220mL/min, 250mL/min, 300mL/min, etc.; the nitridation time can be 0.05h, 0.5h, 1h, 1.2h, 1.5h, 2h, 2.3h, 2.5h, 3h, etc.

The present disclosure also provides the use of the above oxygen-nitrogen compound heterojunction as a water decomposition photocatalyst. In this use, the catalyst has higher activity and significantly improves the photocatalytic reaction rate.

FIG1 shows the formation mechanism diagram of the oxygen-nitrogen compound heterojunction disclosed in the present invention. First, the first precursor RbCa ₂ Ta ₃ O ₁₀ is synthesized by a sol-gel method or a high-temperature solid-phase synthesis method, and then TBA _x H _1-x Ca ₂ Ta ₃ O 10 (0＜x＜1) is generated by a liquid phase exfoliation method (acid treatment + ultrasonic treatment of tetrabutylammonium hydroxide aqueous solution); then, TBA _x K _1-x Ca ₂ Ta ₃ O ₁₀ (0＜x＜1) _is synthesized by KOH low-temperature hydrothermal treatment or KNO ₃ molten salt treatment, and then mixed with K ₂ CO ₃ , and nitrided with ammonia at high temperature to finally obtain the corresponding oxygen-nitrogen compound heterojunction Ta ₃ N ₅ /CaTaO ₂ N.

The method of the embodiment of the present disclosure first prepares the first precursor (AM ₂ Ta ₃ O ₁₀ or ARTa ₂ O ₇ ) by a sol-gel method or a high-temperature solid-phase synthesis method, and then prepares the second precursor (nano-sized HM ₂ Ta ₃ O ₁₀ or HRTa ₂ O ₇ ) by a liquid phase exfoliation method, and then prepares the third precursor by molten salt treatment or hydrothermal treatment (taking KOH low-temperature hydrothermal or KNO ₃ molten salt as an example, the synthesized third precursor is KM ₂ Ta ₃ O ₁₀ or KRTa ₂ O ₇ ), and finally nitriding with ammonia at high temperature to finally obtain the corresponding oxygen-nitrogen compound heterojunction Ta ₃ N ₅ /MTaO ₂ N or Ta ₃ N ₅ /RTaON _2. The embodiment of the present disclosure combines the sol-gel method (or high-temperature solid-phase synthesis method) with the liquid phase exfoliation method, etc., and the size of the prepared oxygen-nitrogen compound heterojunction is relatively small, and it shows higher catalyst activity in the photocatalytic water decomposition reaction.

The disclosed embodiment adopts the liquid phase exfoliation method to prepare a precursor with uniform particle size and nanometer size, which is very helpful in reducing the carrier migration distance and can significantly promote charge separation.

Compared with the related art, the embodiments of the present disclosure use short-time nitridation to effectively reduce the generation of low-valent metal defects and further improve the charge separation efficiency.

The method of the embodiment of the present disclosure finally produces the corresponding oxygen-nitrogen compound heterojunction Ta ₃ N ₅ /MTaO ₂ N or Ta ₃ N ₅ /RTaON ₂ , and the range of choices for M and R is wide. The method of the embodiment of the present disclosure has certain universality.

The oxygen-nitrogen compound heterojunction prepared in the embodiment of the present disclosure is applied to the catalytic reaction of decomposing water, has higher catalyst activity, and significantly improves the photocatalytic reaction rate.

The following are non-limiting examples of the present disclosure.

Example 1 (Preparation of Ta ₃ N ₅ /CaTaO ₂ N Heterojunction)

A method for preparing a Ta ₃ N ₅ /CaTaO ₂ N heterojunction comprises the following steps:

(1) RbCa ₂ Ta ₃ O ₁₀ was synthesized by sol-gel method.

According to the stoichiometric ratio of n(Rb ₂ CO ₃ ):n(CaCO ₃ ):n(TaCl ₅ )=0.75:2:3, 0.0075 mol Rb ₂ CO ₃ , 0.02 mol CaCO ₃ , and 0.03 mol TaCl ₅ were weighed and added into 75 mL methanol, and then 40 g citric acid and 40 mL ethylene glycol were added. The mixture was heated and stirred at 250°C to turn into a brown viscous sol-gel liquid. The mixture was calcined at 600°C for 2 h to obtain a first precursor RbCa ₂ Ta ₃ O ₁₀ with a smaller particle size.

(2) Liquid phase stripping

The first precursor RbCa ₂ Ta ₃ O ₁₀ was treated in a 1 mol/L nitric acid solution for 8 days, and the nitric acid solution was replaced every 2 days. Stir at room temperature;

Then, the mixture was subjected to intermittent ultrasonic treatment in a 40 wt% tetrabutylammonium hydroxide aqueous solution for 10 days, the water temperature was maintained at 60°C, and the ultrasonic treatment was performed every 12 hours for 12 hours, with an ultrasonic power of 350W; then, the mixture was centrifuged at a speed of 10000 r/min for 10 minutes, and the supernatant was taken to obtain a second precursor;

(3) Molten salt treatment

Select KNO ₃ molten salt, at 400 ° C, the treatment time is 48h to prepare the third precursor;

(4) Ammonia nitriding treatment

The third precursor was mixed with K ₂ CO ₃ according to n(K ₂ CO ₃ ):n(third precursor)=1:1, and then nitrided at 950° C. in a 250 mL/min ammonia flow for 1 h to in-situ generate a Ta ₃ N ₅ /CaTaO ₂ N heterojunction.

FIG2 is a transmission electron microscope image and element mapping diagram of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction prepared in Example 1 of the present disclosure. It can be seen from FIG2 that the synthesized oxynitride compound has a nanosheet morphology with a size of about 200 nm. Due to the small size, the element mapping diagram cannot distinguish between tantalum nitride and calcium tantalum oxynitride, proving that the interface contact between the two substances is relatively close. FIG3 is a high-resolution transmission electron microscope image of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction prepared in Example 1 of the present disclosure. It can be seen from FIG3 that the lattice fringes with spacings of 0.279 nm and 0.363 nm correspond to the (121) and (110) crystal planes of calcium tantalum oxynitride and tantalum nitride, respectively, and it can be judged that tantalum nitride and calcium tantalum oxynitride exist at the same time. FIG4 is an XRD diagram of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction prepared in Example 1 of the present disclosure. The main peak positions of the XRD diagram correspond to CaTaO ₂ N and Ta ₃ N ₅ , proving that Ta ₃ N ₅ /CaTaO 2 N heterojunction is synthesized. _2N heterojunction.

Example 2 (Preparation of Ta ₃ N ₅ /CaTaO ₂ N Heterojunction)

(1) Synthesis of RbCa ₂ Ta ₃ O ₁₀ by high temperature solid phase method

The precursor was ground according to the stoichiometric ratio of n(Rb ₂ CO ₃ ):n(CaCO ₃ ):n(Ta ₂ O ₅ )=0.75:2:1.5 to be uniformly mixed, and calcined at 900° C. for 6 h to obtain the precursor RbCa ₂ Ta ₃ O ₁₀ .

(2) Liquid phase stripping

Treat the first precursor RbCa ₂ Ta ₃ O ₁₀ in a 3 mol/L nitric acid solution for 8 days, replace the nitric acid solution every 2 days, and stir at room temperature;

Then, the mixture was subjected to intermittent ultrasonic treatment in a 40 wt % tetrabutylammonium hydroxide aqueous solution for 12 days, the water temperature was maintained at 50° C., the ultrasonic treatment was performed every 12 hours for 12 hours, and the ultrasonic power was 350 W; then, the mixture was centrifuged at a speed of 10,000 r/min for 10 minutes, and the supernatant was taken to obtain a second precursor;

(3) Hydrothermal treatment

The aqueous solution for the hydrothermal treatment is a KOH aqueous solution (1 mol/L), the temperature for the hydrothermal treatment is 140° C., and the time is 48 h, to obtain a third precursor;

(4) Ammonia nitriding treatment

The third precursor was mixed with K ₂ CO ₃ according to n(K ₂ CO ₃ ):n(third precursor)=2:1, and then nitrided at 950° C. in a 250 mL/min ammonia flow for 1 h to in-situ generate a Ta ₃ N ₅ /CaTaO ₂ N heterojunction.

Example 3 (Preparation of Ta ₃ N ₅ /LaTaON ₂ Heterojunction)

The preparation method of Ta ₃ N ₅ /LaTaO ₂ N heterojunction comprises the following steps:

(1) Synthesis of RbLaTa ₂ O ₇ by sol-gel method

According to the stoichiometric ratio of n(Rb ₂ CO ₃ ):n(La ₂ O ₃ ):n(TaCl ₅ )=0.75:0.5:2, 0.0075 mol Rb ₂ CO ₃ , 0.005 mol La ₂ O ₃ and 0.02 mol TaCl ₅ were weighed and added to 40 g citric acid, and then 40 mL ethylene glycol and 75 mL methanol were added. The mixture was heated and stirred at 280°C to turn into a brown viscous sol-gel liquid. The mixture was calcined at 550°C for 3 h to obtain a first precursor RbLaTa ₂ O ₇ with smaller particle size.

(2) Liquid phase stripping

Treat the first precursor RbLaTa ₂ O ₇ in a 1 mol/L nitric acid solution for 10 days, replace the nitric acid solution every 2 days, and stir at room temperature;

Then, the product was subjected to intermittent ultrasonic treatment in a 40 wt % tetrabutylammonium hydroxide aqueous solution for 8 days, the water temperature was maintained at 50° C., the ultrasonic treatment was performed every 12 hours for 12 hours, and the ultrasonic power was 350 W; and then, the product was centrifuged at a speed of 10000 r/min for 10 minutes to obtain a second precursor;

(3) Hydrothermal treatment

The aqueous solution for the hydrothermal treatment is a KOH aqueous solution (1 mol/L), the temperature for the hydrothermal treatment is 120° C., and the time is 30 h, to obtain a third precursor;

(4) Ammonia nitriding treatment

The third precursor was mixed with K ₂ CO ₃ according to n(K ₂ CO ₃ ):n(third precursor)=3:1, and then nitrided at 950° C. in a 250 mL/min ammonia flow for 2 h to in-situ generate a Ta ₃ N ₅ /LaTaON ₂ heterojunction.

The embodiments of the present disclosure provide methods for preparing Ta ₃ N ₅ /CaTaO ₂ N heterojunction, Ta ₃ N ₅ /LaTaON ₂ heterojunction, etc. It can be understood that by replacing the corresponding raw materials according to the methods of the embodiments of the present disclosure, the corresponding other oxygen and nitrogen compound heterojunctions Ta ₃ N ₅ /MTaO ₂ N (M is Sr or Ba) or Ta ₃ N ₅ /RTaON ₂ (R is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or Y can be prepared.

Comparative Example 1

(1) Synthesis of RbCa ₂ Ta ₃ O ₁₀ by sol-gel method

According to the stoichiometric ratio of n(Rb ₂ CO ₃ ):n(CaCO ₃ ):n(TaCl ₅ )=0.75:2:3, 0.0075 mol Rb ₂ CO ₃ , 0.02 mol CaCO ₃ , and 0.03 mol TaCl ₅ were weighed and added to 40 g citric acid, and then 40 mL ethylene glycol and 75 mL methanol were added. The mixture was heated and stirred at 250°C to turn into a brown viscous sol-gel liquid. The mixture was calcined at 600°C for 2 h to obtain a first precursor RbCa ₂ Ta ₃ O ₁₀ with a smaller particle size.

(2) Ion exchange reaction of molten salt

Select KNO ₃ molten salt, at 400℃, for 48h to synthesize KCa ₂ Ta ₃ O ₁₀ precursor;

(3) Ammonia nitriding treatment

According to n(K ₂ CO ₃ ):n(KCa ₂ Ta ₃ O ₁₀ )=1:1, KCa ₂ Ta ₃ O ₁₀ precursor was mixed with K ₂ CO ₃ , and then nitrided at 950° C. and 250 mL/min ammonia flow for 15 h to in-situ generate Ta ₃ N ₅ /CaTaO ₂ N heterojunction.

FIG5 is a scanning electron microscope image of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction prepared in comparative example 1 of the present disclosure; FIG5 shows that the size of the synthesized oxynitride compound is at the micrometer level; a small amount of Ta ₃ N ₅ rods has a diameter of about 100 nm and a length of about 200 nm to 1 μm, and the interface contact is relatively close; FIG6 is a high-resolution through-hole image of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction prepared in comparative example 1 of the present disclosure ... From the radio electron microscope image, it can be seen from Figure 6 that the lattice fringes with spacings of 0.279nm and 0.364nm correspond to the (121) and (110) crystal planes of calcium tantalum oxynitride and tantalum nitride, respectively, and it can be judged that tantalum nitride and calcium tantalum oxynitride exist at the same time; Figure 7 is an element mapping diagram of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction prepared in Comparative Example 1 of the present disclosure; it can be seen from Figure 7 that a structure of stacking rod-shaped Ta ₃ N ₅ and layered CaTaO ₂ N is synthesized; Figure 8 is an XRD diagram of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction prepared in Comparative Example 1 of the present disclosure, and its main peak positions correspond to CaTaO ₂ N and Ta ₃ N ₅ , proving that a Ta ₃ N ₅ /CaTaO ₂ N heterojunction is synthesized.

Experimental example

Activity evaluation of photocatalytic water splitting of the Ta ₃ N ₅ /CaTaO ₂ N heterojunction prepared in Example 1 and Comparative Example 1 of the present disclosure as a photocatalyst:

Reaction conditions:

Example 1: 50 mg of 0.1 wt% Pt-loaded Ta ₃ N ₅ /CaTaO ₂ N sample, 100 mg of 0.45 wt% PtO _x /WO ₃ sample, 150 mL of 2 mM NaI solution, 300 W xenon lamp light source;

Comparative Example 1: 50 mg of 0.3 wt % Pt-loaded Ta ₃ N ₅ /CaTaO ₂ N sample, 100 mg of 0.45 wt % PtO _x /WO ₃ sample, 150 mL of 1 mM NaI solution, and 300 W xenon lamp light source.

in,

Preparation of Pt-loaded Ta ₃ N ₅ /CaTaO ₂ N samples: The reduction promoter Pt was loaded on the hydrogen evolution photocatalyst Ta ₃ N ₅ /CaTaO ₂ N by impregnation and hydrogen reduction. A certain amount of H ₂ PtCl ₆ ·6H ₂ O (99.9%, Sinopharm) was added to 2 mL of deionized water containing 0.2 g of Ta ₃ N ₅ /CaTaO ₂ N sample. The resulting aqueous solution was ultrasonically treated for 5 minutes and then stirred and evaporated to dryness in a water bath (80°C). After the water was evaporated to dryness, the catalyst was collected and reduced in a hydrogen-argon mixed gas with a hydrogen volume fraction of 5% at 200°C (total 200 mL min ^-1 ) for one hour.

PtO _x /WO ₃ sample: PtO _x (0.45 wt% in terms of metal Pt) was loaded on the oxygen evolution photocatalyst WO ₃ by impregnation. A certain amount of H ₂ PtCl ₆ ·6H ₂ O was added to 2 mL of deionized water containing 0.2 g of WO ₃ sample. After ultrasonic treatment, the mixture was stirred and evaporated to dryness in a water bath (80°C), and the collected powder was calcined in air at 525°C for 30 minutes.

The results are shown in Figures 9 and 10. Compared with Comparative Example 1, the Ta ₃ N ₅ /CaTaO ₂ N sample prepared in Example 1 has a higher overall water splitting activity, which is about 5 times that of the sample in Comparative Example 1. The higher overall water splitting activity should be attributed to the smaller catalyst size, which effectively reduces the diffusion distance of photogenerated carriers and prolongs the carrier lifetime.

In the present disclosure, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" and the like mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

Although the embodiments of the present disclosure have been shown and described above, it is to be understood that the above embodiments are illustrative and are not to be construed as limitations of the present disclosure. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present disclosure.

Claims

A method for preparing an oxygen-nitrogen compound heterojunction, comprising:

( 1 ) preparing a first precursor, wherein the first precursor is AM2Ta3O10 or ARTa2O7 ; in the AM2Ta3O10 , A is Cs or Rb, and M is Ca, Sr or Ba; in the ARTa2O7 , A is Cs or Rb , and R is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or Y;

(2) preparing a second precursor by liquid phase exfoliation of the first precursor;

(3) treating the second precursor with molten salt or hydrothermally to prepare a third precursor;

(4) Nitriding the third precursor in situ to generate an oxygen-nitrogen compound heterojunction.
The method for preparing an oxygen-nitrogen compound heterojunction according to claim 1, wherein:

The AM 2 Ta 3 O 10 is prepared by a sol-gel method or a high-temperature solid phase method using an A precursor, an M precursor and a Ta precursor as raw materials; wherein the A precursor, the M precursor and the Ta precursor are stoichiometrically proportioned according to a molar ratio of A, M and Ta of (1-1.8):2:3;

The ARTa 2 O 7 is prepared by a sol-gel method or a high-temperature solid phase method using A precursor, R precursor and Ta precursor as raw materials; wherein the A precursor, R precursor and Ta precursor are stoichiometrically proportioned according to the molar ratio of A, R and Ta: (1-1.8):1:2.
The method for preparing an oxygen-nitrogen compound heterojunction according to claim 1, wherein:

The A precursor is selected from at least one of a carbonate of A, an oxide of A, an oxalate of A, and a nitrate of A;

The M precursor is selected from at least one of a carbonate of M, an oxide of M, an oxalate of M, and a nitrate of M;

The R precursor is selected from at least one of a carbonate of R, an oxide of R, an oxalate of R, and a nitrate of R;

When the sol-gel method is used for preparation, the Ta precursor is selected from TaCl 5 and tantalum ethoxide; when the high-temperature solid phase method is used for preparation, the Ta precursor is selected from Ta oxide.
The method for preparing an oxygen-nitrogen compound heterojunction according to claim 2 or 3, wherein:

The sol-gel method is to add the raw materials to methanol or ethanol, then add citric acid, then add ethylene glycol, heat at 200-300°C to form a sol-gel solution, and then calcine at 500-800°C for 1-4h;

The high temperature solid phase method comprises grinding and uniformly mixing the raw materials and then calcining at 800 to 1100° C. for 2 to 10 hours.
According to the method for preparing an oxygen-nitrogen compound heterojunction according to claim 1, the step of preparing the second precursor by liquid phase exfoliation of the first precursor is:

The first precursor is first subjected to acid treatment, then subjected to ultrasonic treatment in a tetrabutylammonium hydroxide aqueous solution, and then subjected to centrifugal separation to obtain the second precursor;

Optionally, the acid is 0.5-3 mol/L hydrochloric acid or nitric acid; the acid treatment time is 4-10 days, the acid solution is replaced every 2 days, and stirred at room temperature;

Optionally, the temperature of the ultrasonic treatment is 40 to 80° C., and the time is 7 to 14 days.
The method for preparing an oxygen-nitrogen compound heterojunction according to claim 1, wherein:

The temperature of the molten salt treatment is 300-400°C, and the treatment time is 24-48h; the molten salt is selected from at least one of KNO 3, LiNO 3, and NaNO 3 ;

The temperature of the hydrothermal treatment is 100-200° C., the treatment time is 24-48 hours, and the aqueous solution is at least one of a KOH aqueous solution, a LiOH aqueous solution, and a NaOH aqueous solution.
The method for preparing an oxygen-nitrogen compound heterojunction according to claim 1, wherein in step (4), the third precursor and the molten salt are mixed in a molar ratio of 1:(0.5-5) and then nitrided.
The method for preparing an oxygen-nitrogen compound heterojunction according to claim 1 or 7, wherein the temperature of nitridation in step (4) is 900 to 1000° C., and the nitridation is performed in a 200 to 300 mL/min ammonia gas flow for 0.05 to 3 h.
An oxygen-nitrogen compound heterojunction is prepared by the preparation method according to any one of claims 1 to 8, wherein the oxygen-nitrogen compound heterojunction is nano-sized.
Use of the oxygen-nitrogen compound heterojunction described in claim 9 as a water decomposition photocatalyst.