Preparation method of efficient perovskite type lanthanum-titanium-nitrogen oxide photocatalyst material

Abstract

The invention belongs to the technical field of photocatalyst synthesis, and particularly discloses a preparation method of an efficient perovskite type lanthanum titanium nitrogen oxide photocatalyst material. The preparation method comprises the following steps: taking TiS2 and La2 (CO3) 3 hydrates as metal precursors, taking NaCl and KCl as molten salt components, uniformly mixing the metal precursors and the NaCl and the KCl in a grinding manner, and drying for later use; calcining the precursor molten salt mixture to obtain La2Ti2O7 crystals, cleaning the obtained product, removing impurities, and drying for later use; and then taking the dried La2Ti2O7 crystal as a precursor, carrying out high-temperature nitridation in NH3 by adopting a tubular furnace, and cleaning and removing impurities to obtain the La2Ti2O7 crystal. The preparation method disclosed by the invention is simple in process and convenient to operate, and the prepared LaTiO2N photocatalyst shows higher visible light catalytic activity than the LaTiO2N photocatalyst prepared by taking TiO2 and La2O3 as metal precursors traditionally, and has a large-scale industrial application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalyst synthesis, and particularly relates to a preparation method of a highly efficient perovskite-type lanthanum titanium oxynitride photocatalyst material. Background Art

[0002] Due to global warming and the depletion of fossil energy, the efficient utilization of renewable energy to replace fossil energy as primary energy has become a research topic widely concerned by the academic and industrial circles. However, the currently widely used renewable energy sources such as solar energy have the characteristics of intermittency and volatility, resulting in an urgent need to develop technologies for efficient solar energy storage. Solar-driven water splitting technology is considered to be a highly potential technology for converting solar energy into hydrogen energy. The obtained hydrogen can be used as a highly efficient and green energy source to supply fuel cells or raw materials for chemical synthesis such as ammonia synthesis reaction.

[0003] There are three technical solutions for the mainstream solar water splitting technology: (1) photovoltaic module coupling electrolyzer technology; (2) photoelectrochemical water splitting technology; (3) powder photocatalyst water splitting technology. Among them, the powder photocatalyst water splitting technology is a method that can be operated on a large scale and is scalable. Currently, the 100m 2 flat plate photocatalytic hydrogen production reactor uses Al-doped SrTiO 3 (Al-SrTiO 3 ) as a photocatalyst. Although the quantum efficiency of this catalyst is close to 100%, the relatively wide bandgap of Al-SrTiO3 makes it only absorb ultraviolet light, and the efficiency of converting solar energy into hydrogen energy (STH) is limited to less than 1.5%.

[0004] In fact, the proportion of visible light in solar energy exceeds 40%. How to utilize this part of light to achieve photocatalytic water splitting is a key issue for the further development of photocatalytic hydrogen production technology. Currently, methods such as valence band engineering, doping, solid solution preparation, and dye sensitization are widely used to improve the visible light response ability of photocatalysts. However, theoretically, metal oxide photocatalysts have a relatively wide bandgap due to their valence bands containing relatively deep O 2p orbitals. The valence band position can be adjusted by doping with elements having relatively shallow 2p orbitals, such as N and S. Metal oxide photocatalysts doped with nitrogen elements have been proven to significantly change the valence band position, thereby reducing the bandgap of the photocatalyst.

[0005] Perovskite-type LaTiO 2 N is considered to be a highly potential visible light-driven water splitting catalyst due to its unique physical and chemical properties, such as a band structure suitable for water splitting, a relatively low bandgap (~2.1 eV), and visible light absorption properties. The mainstream LaTiO 2 N photocatalyst is prepared by using TiO 2 and La 2 O 3As a precursor, La is first prepared by the molten salt method 2 Ti2O 7 , and then nitrided in an NH 3 atmosphere to form LaTiO 2 N. However, the LaTiO 2 N prepared from this precursor has a relatively large size, and excessive surface defects lead to more photogenerated electron-hole recombination centers, reducing the light energy utilization rate. Summary of the Invention

[0006] Aiming at the technical problems existing in the prior art, the present application proposes a preparation method for an efficient perovskite-type lanthanum titanium nitride oxide photocatalyst material. The present application uses TiS 2 and La 2 (CO 3 ) 3 as precursors. Due to the lower bond energy of the Ti-S bond compared to the Ti-O bond, and the special local environment micro-airflow disturbance kinetic process during the decomposition of La 2 (CO 3 ) 3 , LaTiO 2 N has a smaller size and fewer surface defects. Tests show that it has a higher photogenerated hole-electron transfer efficiency, and this photocatalyst exhibits higher photocatalytic oxygen evolution half-reaction activity under visible light irradiation.

[0007] The primary object of the present application is to provide a preparation method for an efficient perovskite-type lanthanum titanium nitride oxide photocatalyst material. The present application is prepared by the molten salt method using TiS 2 and La 2 (CO 3 ) 3 as precursors.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A preparation method for an efficient perovskite-type lanthanum titanium nitride oxide photocatalyst material, specifically including the following steps:

[0010] S1. Grinding of the precursor molten salt mixture: The metal precursor and the molten salt are mixed evenly by grinding and dried for use; the metal precursor is composed of TiS 2 and La 2 (CO 3 ) 3 hydrate, and the molten salt is composed of NaCl and KCl;

[0011] S2. La 2 Ti 2 O 7Crystal preparation: Calcine the precursor molten salt mixture in step S1 to obtain La 2 Ti 2 O 7 Crystals, washing and removing impurities from the obtained product, and drying for later use;

[0012] S3, La 2 Ti 2 O 7 Preparation of LaTiO by crystal nitridation 2 N: Use a tube furnace to dry La in step S2 2 Ti 2 O 7 The crystals were used as precursors in NH 3 The high-efficiency perovskite-type lanthanum titanium oxynitride photocatalyst material (LaTiO 2 N crystal);

[0013] Preferably, the component contents and proportions of the metal precursors in the mixture in step S1 are: TiS 2 10-25 mol% based on Ti element 2 (CO 3 ) 3 The hydrate contains 10-25 mol% La element, and the molar ratio of Ti to La is 1:1; the component contents and proportions of the molten salt are respectively: NaCl 25-40 mol%, KCl 25-40 mol%, and the molar ratio of NaCl to KCl is 1:1.

[0014] In a preferred embodiment of the present invention, the metal precursor and molten salt component contents are respectively: TiS 2 The Ti element is 16.7 mol%, La 2 (CO 3 ) 3 The La element in the hydrate is 16.7 mol%, the NaCl is 33.3 mol%, and the KCl is 33.3 mol%.

[0015] Preferably, the grinding process in step S1 is carried out on a heating table, the heating temperature is 80-160° C., and the grinding time is 20-45 min; more preferably, the heating temperature is 120° C. and the time is 30 min to ensure that the metal precursor and the molten salt are fully mixed and dried.

[0016] Preferably, the calcination temperature in step S2 is 850-1250° C., the heating rate is 10° C. / min, and the calcination time is 2-6 h; more preferably, the calcination temperature is 1150° C., and the calcination time is 5 h.

[0017] Preferably, the step of cleaning and removing impurities from the obtained product in step S2 is specifically as follows: First, ultrasonically clean with deionized water for 10 - 30 min, then transfer it to a heating table and heat and stir at 80 - 120 °C for 30 - 60 min, then filter with deionized water three times by suction, and finally perform vacuum drying for 3 - 6 h for standby.

[0018] Preferably, in step S3, the specific process of high-temperature nitridation in the tubular furnace with NH 3 atmosphere is as follows: First, introduce NH 3 and N 2 mixed gas into the tubular furnace at room temperature for a period of time. The flow rate of NH 3 is set to 10 - 50 mL / min, and the flow rate of N 2 is set to 50 - 300 mL / min. Then, heat up to the required nitridation temperature of 850 - 1250 °C, the nitridation time is 2 - 24 h, the heating rate is set to 10 °C / min. After nitridation, cool down to 300 °C, stop introducing NH 3 , and keep introducing N 2 until the temperature drops to room temperature. More preferably, the above-mentioned flow rate of NH 3 is set to 20 mL / min, the flow rate of N 2 is set to 200 mL / min, the nitridation temperature is 950 °C, and the nitridation time is 15 h.

[0019] Preferably, the step of cleaning and removing impurities from the obtained product in step S3 is specifically as follows: First, ultrasonically clean with deionized water for 10 - 30 min, then transfer it to a heating table and heat and stir at 80 - 120 °C for 30 - 60 min, then filter with deionized water three times by suction, and finally perform vacuum drying for 3 - 6 h for standby.

[0020] The second object of the present application is to provide a perovskite-type lanthanum titanium nitride oxide photocatalyst material prepared by the above method. The LaTiO 2 N particles prepared in the present application exhibit a regular cubic morphology, small grain size, high crystallinity, and an average particle size of 50 - 500 nm.

[0021] The third object of the present application is to provide the application of the above perovskite-type lanthanum titanium nitride oxide photocatalyst material in photocatalytic water splitting. The research results show that compared with the photocatalyst prepared from traditional metal oxides, the photocatalyst material prepared in the present application exhibits higher photocatalytic oxygen evolution half-reaction activity, significantly improving the photocatalytic water splitting oxygen evolution yield.

[0022] Compared with the prior art, the beneficial effects of the present application are as follows:

[0023] The present invention selects TiS 2 and La 2 (CO 3 ) 3As a precursor for preparing LaTiO 2 N, compared with traditional metal oxide precursors, the prepared LaTiO 2 N nanocrystalline particles are smaller, have higher crystallinity, and the nanoparticles exhibit a more regular cubic morphology, which is beneficial to improving the separation efficiency of photo-generated electron-hole pairs. In addition, the photocatalytic oxygen evolution half-reaction test shows that the LaTiO 2 N photocatalyst material prepared by the method of the present invention has a higher O 2 yield compared with the photocatalyst prepared using traditional metal oxides as precursors. Description of the Drawings

[0024] Figure 1 Scanning electron microscope photos of the LaTiO 2 N photocatalysts prepared in Example 1 and Comparative Example 1 of the present invention, (a) is Example 1, and (b) is Comparative Example 1.

[0025] Figure 2 X-ray diffraction spectra (XRD) of the LaTiO 2 N photocatalysts prepared in Example 1 and Comparative Example 1 of the present invention.

[0026] Figure 3 Ultraviolet-visible diffuse reflectance spectra of the products prepared in Example 1 and Comparative Example 1.

[0027] Figure 4 Comparison chart of the oxygen evolution half-reaction yields of the LaTiO 2 N photocatalysts prepared in Examples 1-5 and the LaTiO 2 N photocatalyst prepared in Comparative Example 1. Detailed Description of the Invention

[0028] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0029] The test methods used in the embodiments of the present invention are all conventional methods unless otherwise specified; the materials, reagents, etc. used are reagents and materials that can be obtained from commercial sources unless otherwise specified.

[0030] TiS 2 , La 2 (CO 3 ) 3 4H 2 O, NaCl, and KCl used in the embodiments of the present invention are all of analytical grade. The NH3 and N 2 The purity is 99.99% for both.

[0031] Example 1

[0032] A preparation method of a perovskite-type lanthanum titanium oxynitride photocatalyst specifically includes the following steps:

[0033] a) Grinding of the precursor molten salt mixture: Weigh a certain molar ratio of TiS 2 , La 2 (CO 3 ) 3 4H 2 O, NaCl, KCl, with masses of 0.2000 g, 0.4088 g, 0.2087 g, 0.2663 g respectively (in TiS 2 the Ti element is 16.7 mol%, in La 2 (CO 3 ) 3 the hydrate the La element is 16.7 mol%, NaCl is 33.3 mol%, and KCl is 33.3 mol%). Add the above precursors and molten salts into a mortar, place the mortar on a heating table, set the temperature of the heating table to 120 °C, and the grinding time to 30 min to ensure that the grinding mixture is fully mixed and dried.

[0034] b) Preparation of La 2 Ti 2 O 7 crystals: Place the mixture obtained by grinding in step a) in a crucible and calcine it. Set the calcination temperature to 1150 °C, the heating rate to 10 °C / min, and the calcination time to 5 h. After the calcination is completed, place the obtained product in a 250 mL beaker, add 150 mL of deionized water, sonicate for 10 min, then transfer it to a heating table and heat and stir for cleaning at 80 °C for 30 min, then filter it three times with deionized water, and finally transfer it to a vacuum drying oven to dry for 3 h for use.

[0035] c) Nitridation of La 2 Ti 2 O 7 crystals to prepare LaTiO 2 N: Place the La 2 Ti 2 O 7 crystals obtained by calcining in a muffle furnace in step b) in a tube furnace, and carry out high-temperature nitridation in an NH 3 atmosphere. First, introduce an NH 3 and N 2 mixed gas into the tube furnace at room temperature for a period of time. Set the NH 3 flow rate to 20 mL / min, and N 2The flow rate was set to 200 mL / min, then the temperature was raised to the required nitriding temperature of 950 °C, the nitriding time was 15 h, the heating rate was set to 10 °C / min, and after nitriding, the temperature was cooled to 300 °C, and the NH 3 was stopped while keeping N 2 flowing until the temperature dropped to room temperature. Then the product obtained by high-temperature nitriding in the tubular furnace was ultrasonically cleaned with deionized water, then transferred to a heating table and heated and stirred at 80 °C, then filtered three times with deionized water, and finally vacuum dried to obtain LaTiO 2 N photocatalyst.

[0036] Example 2

[0037] A preparation method of a perovskite-type lanthanum titanate nitride photocatalyst specifically includes the following steps:

[0038] a) Grinding of precursor molten salt mixture: Weigh a certain molar ratio of TiS 2 , La 2 (CO 3 ) 3 4H 2 O, NaCl, and KCl with masses of 0.1198 g, 0.2448 g, 0.2530 g, and 0.3278 g respectively (the Ti element in TiS 2 is 10 mol%, the La element in La 2 (CO 3 ) 3 hydrate is 10 mol%, NaCl is 40 mol%, and KCl is 40 mol%). Add the above precursors and molten salts to a mortar, place the mortar on a heating table, set the heating table temperature to 120 °C, and grind for 30 min to ensure that the grinding mixture is fully mixed and dried.

[0039] b) Preparation of La 2 Ti 2 O 7 crystals: Place the mixture obtained by grinding in step a) in a crucible and calcine it. Set the calcination temperature to 1150 °C, the heating rate to 10 °C / min, and the calcination time to 5 h. After calcination, place the obtained product in a 250 mL beaker, add 150 mL of deionized water, ultrasonicate for 10 min, then transfer it to a heating table and heat and stir for cleaning at 80 °C for 30 min, then filter three times with deionized water, and finally transfer it to a vacuum drying oven and dry for 3 h for use.

[0040] c) Nitridation of La 2 Ti 2 O 7 crystals to prepare LaTiO 2 N: The La 2 Ti2 O 7 The crystal was placed in a tube furnace and subjected to a high-temperature nitridation process under an NH 3 atmosphere. First, NH 3 and N 2 mixed gas was introduced into the tube furnace at room temperature for a period of time. The flow rate of NH 3 was set to 20 mL / min, and the flow rate of N 2 was set to 200 mL / min. Then, the temperature was raised to the required nitridation temperature of 950 °C, the nitridation time was 15 h, the heating rate was set to 10 °C / min. After nitridation, the temperature was lowered to 300 °C, and the supply of NH 3 was stopped, while N 2 was continuously supplied until the temperature dropped to room temperature. Then, the product obtained from the high-temperature nitridation of the tube furnace was ultrasonically cleaned with deionized water, transferred to a heating platform, heated and stirred at 80 °C, filtered three times with deionized water, and finally dried under vacuum to obtain the LaTiO 2 N photocatalyst.

[0041] Example 3

[0042] A preparation method of a perovskite-type lanthanum titanium nitride oxide photocatalyst specifically includes the following steps:

[0043] a) Grinding of the precursor molten salt mixture: Weigh a certain molar ratio of TiS 2 , La 2 (CO 3 ) 3 4H 2 O, NaCl, and KCl with masses of 0.2994 g, 0.6120 g, 0.1581 g, and 0.2017 g respectively (the Ti element in TiS 2 is 25 mol%, the La element in La 2 (CO 3 ) 3 hydrate is 25 mol%, NaCl is 25 mol%, and KCl is 25 mol%). Add the above precursors and molten salts into a mortar, place the mortar on a heating platform, set the heating platform temperature to 120 °C, and grind for 30 min to ensure that the grinding mixture is fully mixed and dried.

[0044] b) La 2 Ti 2 O 7Crystal preparation: Place the mixture obtained by grinding in step a) in a crucible and calcine it. Set the calcination temperature to 1150 °C, the heating rate to 10 °C / min, and the calcination time to 5 h. After calcination, place the obtained product in a 250 mL beaker, add 150 mL of deionized water, sonicate for 10 min, then transfer it to a heating plate and heat and stir for cleaning at 80 °C for 30 min. Then filter it three times with deionized water, and finally transfer it to a vacuum drying oven to dry for 3 h for use.

[0045] c) La 2 Ti 2 O 7 Preparation of crystal nitride LaTiO 2 N: Place the La 2 Ti 2 O 7 crystal obtained by calcining in a muffle furnace in step b) in a tube furnace, and carry out the high-temperature nitridation process under NH 3 atmosphere. First, introduce NH 3 and N 2 mixed gas into the tube furnace at room temperature for a period of time. Set the flow rate of NH 3 to 20 mL / min and the flow rate of N 2 to 200 mL / min. Then heat up to the required nitridation temperature of 950 °C, and the nitridation time is 15 h. Set the heating rate to 10 °C / min. After nitridation, cool down to 300 °C and stop introducing NH 3 , and keep introducing N 2 until the temperature drops to room temperature. Then ultrasonically clean the product obtained by high-temperature nitridation of the tube furnace with deionized water, then transfer it to a heating plate and heat and stir at 80 °C, then filter it three times with deionized water, and finally perform vacuum drying treatment to obtain LaTiO 2 N photocatalyst.

[0046] Example 4

[0047] A preparation method of a perovskite-type lanthanum titanium oxynitride photocatalyst specifically includes the following steps:

[0048] a) Grinding of precursor molten salt mixture: Weigh a certain molar ratio of TiS 2 , La 2 (CO 3 ) 3 4H 2 O, NaCl, KCl, with masses of 0.2000 g, 0.4088 g, 0.2087 g, and 0.2663 g respectively (the Ti element in TiS 2 is 16.7 mol%, La 2 (CO 3 ) 3The hydrate contains 16.7 mol% of La element, 33.3 mol% of NaCl, and 33.3 mol% of KCl.); The above-mentioned precursor and molten salt are added to a mortar, and the mortar is placed on a heating table. The temperature of the heating table is set at 120 °C, and the grinding time is 30 min to ensure that the grinding mixture is fully mixed and dried.

[0049] b) La 2 Ti 2 O 7 Crystal preparation: The mixture obtained by grinding in step a) is placed in a crucible and calcined. The calcination temperature is set at 850 °C, the heating rate is set at 10 °C / min, and the calcination time is set at 5 h. After the calcination is completed, the obtained product is first placed in a 250 mL beaker, 150 mL of deionized water is added, and it is ultrasonically treated for 10 min. Then it is transferred to a heating table and heated and stirred for cleaning at 80 °C for 30 min. Then it is filtered three times with deionized water, and finally transferred to a vacuum drying oven and dried for 3 h for use.

[0050] c) La 2 Ti 2 O 7 Crystal nitridation to prepare LaTiO 2 N: The La 2 Ti 2 O 7 crystal obtained by calcining in a muffle furnace in step b) is placed in a tube furnace, and during the high-temperature nitridation process in an NH 3 atmosphere, first, NH 3 and N 2 mixed gas is introduced into the tube furnace at room temperature for a period of time. The flow rate of NH 3 is set at 20 mL / min, and the flow rate of N 2 is set at 200 mL / min. Then it is heated to the required nitridation temperature of 950 °C, and the nitridation time is 15 h. The heating rate is set at 10 °C / min. After the nitridation is completed, the temperature is cooled to 300 °C, and the supply of NH 3 is stopped, and the supply of N 2 is maintained until the temperature drops to room temperature. Then the product obtained by high-temperature nitridation in the tube furnace is ultrasonically cleaned with deionized water, then transferred to a heating table and heated and stirred at 80 °C, and then filtered three times with deionized water, and finally vacuum dried to obtain the LaTiO 2 N photocatalyst.

[0051] Example 5

[0052] A preparation method of a perovskite-type lanthanum titanium oxynitride photocatalyst specifically includes the following steps:

[0053] a) Grinding of precursor molten salt mixture: Weigh a certain molar ratio of TiS 2 , La 2 (CO 3) 3 4H 2 O, NaCl, KCl, with masses of 0.2000 g, 0.4088 g, 0.2087 g, 0.2663 g (in TiS 2 the Ti element is 16.7 mol%, La 2 (CO 3 ) 3 hydrate, the La element is 16.7 mol%, NaCl is 33.3 mol%, and KCl is 33.3 mol%).; Add the above-mentioned precursor and molten salt into a mortar, place the mortar on a heating table, set the temperature of the heating table to 120 °C, and the grinding time to 30 min to ensure that the grinding mixture is fully mixed and dried.

[0054] b) La 2 Ti 2 O 7 Crystal preparation: Place the mixture obtained by grinding in step a) in a crucible and calcine it. Set the calcination temperature to 1250 °C, the heating rate to 10 °C / min, and the calcination time to 5 h. After the calcination is completed, place the obtained product in a 250 mL beaker, add 150 mL of deionized water, sonicate for 10 min, then transfer it to a heating table and heat and stir for cleaning at 80 °C for 30 min. Then filter it three times with deionized water, and finally transfer it to a vacuum drying oven and dry it for 3 h for use.

[0055] c) La 2 Ti 2 O 7 Crystal nitridation to prepare LaTiO 2 N: Place the La 2 Ti 2 O 7 crystals obtained by calcining in a muffle furnace in step b) in a tube furnace. During the high-temperature nitridation process in an NH 3 atmosphere, first introduce a mixture of NH 3 and N 2 into the tube furnace at room temperature for a period of time. Set the flow rate of NH 3 to 20 mL / min and the flow rate of N 2 to 200 mL / min. Then heat up to the required nitridation temperature of 950 °C, the nitridation time is 15 h, the heating rate is 10 °C / min. After the nitridation is completed, cool down to 300 °C and stop passing NH 3 , and keep passing N 2 , until the temperature drops to room temperature. Then ultrasonically clean the product obtained by high-temperature nitridation in the tube furnace with deionized water, then transfer it to a heating table and heat and stir at 80 °C, then filter it three times with deionized water, and finally perform vacuum drying treatment to obtain the LaTiO 2 N photocatalyst.

[0056] Example 6

[0057] A preparation method of a perovskite-type lanthanum titanium oxynitride photocatalyst specifically includes the following steps:

[0058] a) Grinding of the precursor molten salt mixture: Weigh a certain molar ratio of TiS 2 , La 2 (CO 3 ) 3 4H 2 O, NaCl, KCl, with masses of 0.2000 g, 0.4088 g, 0.2087 g, and 0.2663 g respectively (the Ti element in TiS 2 is 16.7 mol%, the La element in La 2 (CO 3 ) 3 hydrate is 16.7 mol%, NaCl is 33.3 mol%, and KCl is 33.3 mol%). Add the above precursors and molten salts into a mortar, place the mortar on a heating table, set the temperature of the heating table to 120 °C, and grind for 30 min to ensure that the grinding mixture is fully mixed and dried.

[0059] b) Preparation of La 2 Ti 2 O 7 crystals: Place the mixture obtained by grinding in step a) in a crucible and calcine it. Set the calcination temperature to 1150 °C, the heating rate to 10 °C / min, and the calcination time to 5 h. After the calcination is completed, place the obtained product in a 250 mL beaker, add 150 mL of deionized water, sonicate for 10 min, then transfer it to a heating table and heat and stir for cleaning at 80 °C for 30 min. Then filter it three times with deionized water, and finally transfer it to a vacuum drying oven to dry for 3 h for use.

[0060] c) Nitridation of La 2 Ti 2 O 7 crystals to prepare LaTiO 2 N: Place the La 2 Ti 2 O 7 crystals obtained by calcining in a muffle furnace in step b) in a tube furnace, and carry out the high-temperature nitridation process in an NH 3 atmosphere. First, introduce a mixture of NH 3 and N 2 into the tube furnace at room temperature for a period of time. Set the flow rate of NH 3 to 20 mL / min and the flow rate of N 2 to 200 mL / min. Then heat up to the required nitridation temperature of 850 °C, with a nitridation time of 15 h and a heating rate of 10 °C / min. After the nitridation is completed, cool down to 300 °C and stop passing NH3 , keep it open to N 2 , until the temperature drops to room temperature. Then, the product obtained by high-temperature nitridation in the tubular furnace is ultrasonically cleaned with deionized water, transferred to a heating table, heated and stirred at 80 °C, filtered three times with deionized water, and finally dried under vacuum to obtain LaTiO 2 N photocatalyst.

[0061] Example 7

[0062] A preparation method of a perovskite-type lanthanum titanate nitride photocatalyst specifically includes the following steps:

[0063] a) Grinding of the precursor molten salt mixture: Weigh a certain molar ratio of TiS 2 , La 2 (CO 3 ) 3 xH 2 O, NaCl, KCl, with masses of 0.2000 g, 0.4088 g, 0.2087 g, and 0.2663 g respectively (the Ti element in TiS 2 is 16.7 mol%, the La element in La 2 (CO 3 ) 3 hydrate is 16.7 mol%, NaCl is 33.3 mol%, and KCl is 33.3 mol%). Add the above precursors and molten salts to a mortar, place the mortar on a heating table, set the heating table temperature to 120 °C, and grind for 30 min to ensure that the grinding mixture is fully mixed and dried.

[0064] b) Preparation of La 2 Ti 2 O 7 crystals: Place the mixture obtained by grinding in step a) in a crucible and calcine it. Set the calcination temperature to 1150 °C, the heating rate to 10 °C / min, and the calcination time to 5 h. After the calcination is completed, place the obtained product in a 250 mL beaker, add 150 mL of deionized water, ultrasonicate for 10 min, then transfer it to a heating table, heat and stir for cleaning at 80 °C for 30 min, filter three times with deionized water, and finally transfer it to a vacuum drying oven and dry for 3 h for later use.

[0065] c) Nitridation of La 2 Ti 2 O 7 crystals to prepare LaTiO 2 N: Place the La 2 Ti 2 O 7 crystals obtained by calcining in a muffle furnace in step b) in a tubular furnace, and in NH 3Under high-temperature nitridation, first, NH is introduced into the tubular furnace at room temperature. 3 and N 2 mixed gas for a period of time. The flow rate of NH 3 is set to 20 mL / min, and the flow rate of N 2 is set to 200 mL / min. Then, it is heated to the required nitridation temperature of 1050 °C, the nitridation time is 15 h, the heating rate is set to 10 °C / min. After nitridation, it is cooled to 300 °C, and the supply of NH 3 is stopped, and N 2 is continuously supplied until the temperature drops to room temperature. Then, the product obtained by high-temperature nitridation in the tubular furnace is ultrasonically cleaned with deionized water, transferred to a heating table, heated and stirred at 80 °C, filtered three times with deionized water, and finally vacuum dried to obtain LaTiO 2 N photocatalyst.

[0066] Comparative Example 1

[0067] A preparation method of a perovskite-type lanthanum titanium oxynitride photocatalyst specifically includes the following steps:

[0068] a) Grinding of the precursor molten salt mixture: Weigh a certain molar ratio of TiO 2 , La 2 O 3 , NaCl, and KCl with masses of 0.1426 g, 0.2910 g, 0.2087 g, and 0.2663 g respectively (the Ti element in TiO 2 is 16.7 mol%, the La element in La 2 O 3 hydrate is 16.7 mol%, NaCl is 33.3 mol%, and KCl is 33.3 mol%). Add the above precursors and molten salts into a mortar, place the mortar on a heating table, set the heating table temperature to 120 °C, and grind for 30 min to ensure that the grinding mixture is fully mixed and dried.

[0069] b) Preparation of La 2 Ti 2 O 7 crystals: Place the mixture obtained by grinding in step a) in a crucible and calcine it. Set the calcination temperature to 1150 °C, the heating rate to 10 °C / min, and the calcination time to 5 h. After calcination, the obtained product is first placed in a 250 mL beaker, add 150 mL of deionized water, ultrasonicate for 10 min, then transfer it to a heating table, heat and stir at 80 °C for 30 min, filter three times with deionized water, and finally transfer it to a vacuum drying oven and dry for 3 h for use.

[0070] c) La 2 Ti 2 O 7Preparation of LaTiO by Crystal Nitridation 2 N: The La obtained by calcining in a muffle furnace in step b) 2 Ti 2 O 7 crystals were placed in a tube furnace, and during the high-temperature nitridation process under NH 3 atmosphere, first, NH was introduced into the tube furnace at room temperature 3 and N 2 mixed gas for a period of time. The flow rate of NH 3 was set to 20 mL / min, and the flow rate of N 2 was set to 200 mL / min. Then, it was heated to the required nitridation temperature of 1050 °C, the nitridation time was 15 h, the heating rate was set to 10 °C / min. After nitridation, it was cooled to 300 °C, and the supply of NH 3 was stopped, and the supply of N 2 was maintained until the temperature dropped to room temperature. Then, the product obtained by high-temperature nitridation in the tube furnace was ultrasonically cleaned with deionized water, then transferred to a heating table and heated and stirred at 80 °C, then filtered three times with deionized water, and finally dried under vacuum to obtain the LaTiO 2 N photocatalyst.

[0071] Phase Characterization and Performance Test Analysis

[0072] Figure 1 a is the scanning electron microscope photograph of the LaTiO 2 N photocatalyst prepared in Example 1. It can be observed that the LaTiO 2 N photocatalyst is in the shape of cubic single crystal particles, the crystal planes are clearly visible, the edges between the crystal planes are sharp, the crystal planes are smooth, showing a high single crystal morphology. The size of the cube is between 50 - 500 nm. The good single crystal property, regular crystal plane profile and small particle size are conducive to the separation of photo-generated carriers, which is the main reason for the photocatalytic performance. Figure 2 shows the XRD of the LaTiO 2 N photocatalysts prepared in Example 1 and Comparative Example 1. It can be seen that the LaTiO 2 N prepared in this example and the comparative example shows significant LaTiO 2 N (PDF: 48 - 1230) diffraction peak positions and intensities, and the diffraction peaks of the example are stronger and sharper, indicating that the LaTiO 2 N prepared in Example 1 has higher crystallinity. Figure 3 For the LaTiO prepared in Example 1 and Comparative Example 1 2For the UV-Vis diffuse reflectance spectra of the N photocatalyst, it can be observed that both samples exhibit light absorption ability in the visible light range. The light absorption peak of the sample in this example is around 500 nm, and the light absorption peak of the comparative example sample is around 498 nm. At the same time, it can be observed that the light absorption cut-off wavelengths of the samples are all above 600 nm, and in the light wave range greater than 600 nm, there is still a certain light absorption ability, which may be due to the light trapping effect caused by the gaps between nanoparticles.

[0073] In order to investigate the effect of the catalyst prepared in the examples of the present invention on the photocatalytic oxygen evolution half-reaction at room temperature, the LaTiO prepared in the examples and Comparative Example 1 2 The N photocatalyst was loaded with 1 wt% of Ir as an oxygen evolution cocatalyst by a conventional microwave method and then subjected to photocatalytic oxygen evolution half-reaction tests respectively. The test process is as follows: Weigh 100 mg of the LaTiO 2 N photocatalyst loaded with Ir and place it in 100 mL of a solution containing 20 mM AgNO 3 , 200 mg of La 2 O 3 as a buffer. The reaction solution and the photocatalyst were stirred for 30 min to be fully mixed, and then transferred to a photocatalytic reactor. The photocatalytic reaction was carried out in an Ar gas environment of 5 kPa and under illumination with a wavelength greater than 420 nm for 3 h. Each example and comparative example was tested 5 times and the data average was taken.

[0074] Figure 4 For the yield of the LaTiO 2 N photocatalyst O 2 prepared in Examples 1-7 and Comparative Example 1, as can be seen from the figure, the yields of the photocatalysts O 2 prepared in Examples 1-7 are all higher than the yield of Comparative Example 1 (up to 4 times). This shows that the LaTiO 2 N photocatalyst prepared by the present invention has stronger photogenerated electron-hole transfer efficiency and photocatalytic performance.

[0075] Obviously, the above-mentioned examples of the present invention are only examples for clearly explaining the technical solutions of the present invention, rather than limitations on the specific implementation manners of the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the claims of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a perovskite-type lanthanum titanium oxynitride photocatalyst material, characterized in that: The steps include: S1, grinding and mixing the metal precursor and the molten salt to obtain a mixture; S2, calcining the mixture obtained in step S1 to obtain La2Ti2O7 crystals, washing the obtained product to remove impurities and then drying; S3, using the La2Ti2O7 crystal dried in step S2 as a precursor, heating and nitriding in the presence of NH3 in a tube furnace, and cleaning and removing impurities from the obtained product to obtain the material; In step S1, the metal precursor consists of TiS2 and La2(CO3)3 hydrate, and the molten salt consists of NaCl and KCl.

2. The preparation method according to claim 1, characterized in that: The component contents and proportions of the metal precursors in the mixture of step S1 are: 10-25 mol% of Ti element in TiS2, 10-25 mol% of La element in La2(CO3)3 hydrate, and the molar ratio of Ti to La is 1:1; the component contents and proportions of the molten salt are: 25-40 mol% of NaCl, 25-40 mol% of KCl, and the molar ratio of NaCl to KCl is 1:

1.

3. The preparation method according to claim 1, characterized in that: The grinding process in step S1 is carried out on a heating table, the heating temperature is 80-160° C., and the grinding time is 20-45 minutes.

4. The preparation method according to claim 1, characterized in that: The calcination temperature in step S2 is 850-1250° C., the heating rate is 5-10° C. / min, and the calcination time is 2-6 hours.

5. The preparation method according to claim 1, characterized in that: The steps of cleaning and removing impurities from the obtained product in step S2 are specifically as follows: first, ultrasonically clean the product with deionized water for 10 to 30 minutes, then transfer it to a heating table and heat and stir it at 80-120° C. for 30 to 60 minutes, then filter it with deionized water for 3 times, and finally vacuum dry it for 3 to 6 hours for use.

6. The preparation method according to claim 1, characterized in that: The specific process of nitriding under NH3 in the tubular furnace in step S3 is: first, pass NH3 and N2 mixed gas into the tubular furnace at room temperature for a period of time, the NH3 flow rate is set to 10-50mL / min, the N2 flow rate is set to 50-300mL / min, and then heat to the required nitriding temperature of 850-1250°C, the nitriding time is 2-24h, the heating rate is set to 10°C / min, and after the nitriding is completed, the temperature is lowered to 300°C, and NH3 is stopped, and N2 is kept flowing until the temperature drops to room temperature.

7. The preparation method according to claim 1, characterized in that: The steps of cleaning and removing impurities from the obtained product in step S3 are specifically as follows: first, ultrasonically clean the product with deionized water for 10 to 30 minutes, then transfer it to a heating table and heat and stir it at 80 to 120° C. for 30 to 60 minutes, then filter it with deionized water for 3 times, and finally vacuum dry it for 3 to 6 hours for use.

8. The perovskite-type lanthanum titanium oxynitride photocatalyst material prepared by the method according to any one of claims 1 to 7.

9. An application of the perovskite-type lanthanum titanium oxynitride photocatalyst material as claimed in claim 8, characterized in that: The application includes photocatalytic decomposition of water to produce oxygen.

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