Perovskite tantalum-nitrogen co-doped strontium titanate, and preparation method therefor and use thereof

Abstract

The invention belongs to the technical field of photocatalytic materials. Provided are perovskite tantalum-nitrogen co-doped strontium titanate, and a preparation method therefor and the use thereof. Titanium isopropoxide and tantalum pentachloride are dissolved in methyl alcohol, ethylene glycol, citric acid and strontium carbonate are then added thereto, and after polymerization, organic carbon is removed by means of roasting with air, thereby obtaining tantalum-doped strontium titanate; same is then mixed with a magnesium powder, and the resulting mixture is nitrided in an ammonia gas flow atmosphere; and the resulting reaction product is subjected to acid pickling, water washing and drying, thereby obtaining perovskite tantalum-nitrogen co-doped strontium titanate. Titanium-oxygen bonds are weakened by means of pre-doping with tantalum, and the spatial distribution of a high-content nitrogen dopant in strontium titanate is then achieved by means of a magnesium-powder-assisted nitriding method; therefore, the synthesized catalyst has a wider light absorption range, and has significant photocatalytic activity in both hydrogen production by means of photocatalytic water splitting and oxygen production by means of water splitting.

Description

Tantalum-nitrogen co-doped perovskite strontium titanate and its preparation method and application Technical Field

[0001] The present invention relates to a perovskite tantalum-nitrogen co-doped strontium titanate and a preparation method and application thereof, belonging to the technical field of photocatalytic materials. Background Art

[0002] Photocatalytic water splitting is a sustainable, environmentally friendly method for directly converting solar energy into chemical energy. Over the past few decades, a wide range of photocatalysts have been developed, including metal oxides, metal oxysalts, (oxy)sulfides, (oxy)nitrides, oxyhalides, and metal-organic frameworks. Among them, strontium titanate (SrTiO3) has attracted considerable attention due to its suitable energy band position, excellent photocatalytic performance, and photochemical stability. Currently, the highest external quantum efficiency (EQE) for SrTiO3 photocatalytic water splitting can reach 96% (at 360 nm). However, due to its limited light absorption capacity (absorption edge at 390 nm), its solar hydrogen production efficiency is only 0.65%. Therefore, enhancing its ability to absorb strong visible light is a prerequisite for achieving efficient photocatalysis. Metal ion doping, such as with Mn, Ru, Rh, and Cr / Sb, is a common approach to narrow the SrTiO3 band gap. However, the extension of the band gap caused by localized states is limited. In addition to metal doping, anion doping, particularly nitrogen doping, has also been widely used to modify the electronic structure to extend the light absorption range. However, to date, whether it is single-element nitrogen-doped strontium titanate or La / N, Cr / N co-doped strontium titanate, the light absorption only shows shoulder-shaped absorption at 400-550nm, and band-to-band absorption with a wide spectral response has not yet been achieved. The main reason is that it is difficult to introduce substitutional nitrogen into the bulk strontium titanate. The dopant is difficult to diffuse from the surface to the bulk, resulting in low solubility of the substitutional nitrogen. The first prerequisite for achieving efficient photocatalytic water splitting is that the semiconductor material has the ability to strongly absorb visible light. Therefore, the development of new doping methods to improve the spatial distribution of nitrogen dopants in strontium titanate remains challenging and urgently needed.

[0003] Summary of the Invention

[0004] To address the problem that existing nitridation methods cannot achieve high-content nitrogen doping in strontium titanate, the present invention provides a perovskite tantalum-nitrogen co-doped strontium titanate and its preparation method. By pre-doping tantalum to weaken the titanium-oxygen bond, and then using a magnesium powder-assisted nitridation method, a high-content nitrogen dopant is spatially distributed in the strontium titanate, thereby synthesizing strontium titanate with a 600nm wide spectral response, which has potential application value in photocatalytic reactions. To achieve the above objectives, the technical means adopted by the present invention are as follows:

[0005] A first aspect of the present invention provides a method for preparing tantalum-nitrogen co-doped strontium titanate perovskite, the method comprising the following steps:

[0006] (1) dissolving titanium isopropoxide and tantalum pentachloride in methanol, and adding ethylene glycol and citric acid to fully dissolve them to obtain a first solution;

[0007] (2) adding strontium carbonate to the first solution obtained in step (1) to fully dissolve it, thereby obtaining a second solution;

[0008] (3) heating the second solution obtained in step (2) to 150-200° C. and maintaining the temperature for 0.1-5 hours to carry out a polymerization reaction to obtain a polymer;

[0009] (4) heating the polymer obtained in step (3), wherein the first stage is heated to 300-400° C. and maintained for 0.5-2 h for carbonization, the second stage is heated to 500-600° C. and maintained for 0.1-20 h for decarbonization, and the third stage is heated to 800-1100° C. and maintained for 0.1-20 h to obtain an oxide precursor powder;

[0010] (5) grinding and mixing the oxide precursor powder obtained in step (4) with magnesium powder to obtain a mixed powder;

[0011] (6) placing the mixed powder obtained in step (5) in a tube furnace and introducing ammonia gas for nitridation;

[0012] (7) The powder after nitriding treatment in step (6) is acid-washed, then filtered, washed with water, and dried to obtain perovskite tantalum-nitrogen co-doped strontium titanate.

[0013] In the above technical solution, further, in step (1), the ratio of the total amount of tantalum pentachloride and titanium isopropoxide, the amount of ethylene glycol, and the amount of citric acid is 1:15:60, and the molar ratio of tantalum in tantalum pentachloride and titanium in titanium isopropoxide is 0.001:0.999 to 0.1:0.9.

[0014] In the above technical solution, further, in step (2), the ratio of the amount of strontium carbonate to the total amount of tantalum pentachloride and titanium isopropoxide is 1.03:1.

[0015] In the above technical solution, further, in step (5), the mass ratio of magnesium powder to oxide precursor powder is 0.5 to 10:1.

[0016] In the above technical solution, further, in step (6), the ammonia flow rate is 50-500 mL / min, the nitriding temperature is 650-800° C., the nitriding time is 3-20 h, and the heating rate is 5° C. / min.

[0017] The second aspect of the present invention provides a perovskite tantalum-nitrogen co-doped strontium titanate prepared by the above-mentioned preparation method, characterized in that the tantalum doping amount in the tantalum-nitrogen co-doped strontium titanate is 1-10wt%, and the nitrogen doping amount is 0.1-5wt%.

[0018] The third aspect of the present invention provides a perovskite tantalum-nitrogen co-doped strontium titanate photocatalyst, which is obtained by loading the above-mentioned perovskite tantalum-nitrogen co-doped strontium titanate with a precious metal or metal oxide to obtain a perovskite tantalum-nitrogen co-doped strontium titanate photocatalyst.

[0019] In the above technical solution, further, the noble metal includes at least one of Ru, Rh, Pd, Ag, Ir, Pt, and Au, and the loading amount of the noble metal is 0.01 to 5 wt%; the metal oxide includes CoO x 、RuO x 、IrO x At least one of the above, the loading amount of the metal oxide is 0.01 to 5 wt%.

[0020] In the above technical solution, further, the noble metal loading method is: dispersing the tantalum nitrogen doped strontium titanate powder in a solution containing a noble metal precursor, evaporating it in a water bath after ultrasonic dispersion, and reducing it at 100-400°C for 0.5-3h under a hydrogen flow.

[0021] The metal oxide loading method is as follows: dispersing tantalum nitrogen doped strontium titanate powder in a solution containing a metal precursor, evaporating it in a water bath after ultrasonic dispersion, and calcining it at 100-500° C. for 0.5-4 hours in air, nitrogen or argon atmosphere.

[0022] The fourth aspect of the present invention provides an application of the above-mentioned perovskite tantalum-nitrogen co-doped strontium titanate photocatalyst in a photocatalytic hydrogen production reaction, wherein one or more of lactic acid, sodium sulfide, ascorbic acid, formic acid, sodium formate, methanol, and triethanolamine are used as hole sacrificial reagents, and are dispersed in water with the powder of the photocatalyst, and water is decomposed under light to produce hydrogen.

[0023] The fifth aspect of the present invention provides an application of the above-mentioned perovskite tantalum-nitrogen co-doped strontium titanate photocatalyst in a photocatalytic oxygen production reaction, wherein one or more of silver nitrate, potassium iodate, and ferric chloride are used as hole sacrificial reagents and dispersed in water with the powder of the photocatalyst, and water is decomposed under light to produce oxygen.

[0024] The beneficial effects of the present invention are:

[0025] 1. The synthesis process of the present invention is simple, the steps are simple, the preparation cycle is short, and it is easy to be produced on a large scale industrially;

[0026] 2. The present invention weakens the titanium-oxygen bond by pre-doping tantalum, and then accelerates the nitridation kinetics by assisting nitridation with magnesium powder, which can effectively reduce the nitridation temperature, shorten the nitridation time, and avoid the increase in defects caused by long-term high-temperature nitridation;

[0027] 3. The present invention achieves the spatial distribution of high-content nitrogen dopants in strontium titanate, so that the synthesized catalyst has a wider light absorption range and has significant photocatalytic activity in both photocatalytic water decomposition to produce hydrogen and water decomposition to produce oxygen. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG1 is a scanning electron microscope image of SrTiO3:Ta(3%) / N synthesized in Example 1;

[0029] FIG2 is an XRD spectrum of SrTiO3:Ta(3%) / N synthesized in Example 1;

[0030] FIG3 is a UV-Vis absorption spectrum of SrTiO3:Ta(3%) / N synthesized in Example 1;

[0031] FIG4 is a scanning electron micrograph of SrTiO3:Ta(6%) / N synthesized in Example 2;

[0032] FIG5 is an XRD spectrum of SrTiO3:Ta(6%) / N synthesized in Example 2;

[0033] FIG6 is a UV-Vis absorption spectrum of SrTiO3:Ta(6%) / N synthesized in Example 2;

[0034] FIG7 is a graph showing the photocatalytic water splitting hydrogen production activity of SrTiO3:Ta(6%) / N in Example 3;

[0035] FIG8 is a graph showing the photocatalytic water splitting and oxygen production activity of SrTiO3:Ta(6%) / N in Example 4;

[0036] FIG9 is a graph showing the photocatalytic water decomposition and hydrogen production activity of SrTiO3:N in Comparative Example 1. DETAILED DESCRIPTION

[0037] The following non-limiting examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0038] Example 1

[0039] (1) dissolving titanium isopropoxide and tantalum pentachloride in methanol, adding ethylene glycol and citric acid (the molar ratio of titanium isopropoxide, tantalum pentachloride, ethylene glycol, and citric acid is 0.97:0.03:15:60) to completely dissolve them, thereby obtaining a first solution;

[0040] (2) After the solution is completely dissolved, strontium carbonate (the molar ratio of Sr, Ti, and Ta is 1.03:0.97:0.03) is added to the first solution to completely dissolve the solution, thereby obtaining a second solution;

[0041] (3) After the solution becomes transparent, the second solution is heated to 160° C. and refluxed for 5 h to form a polymer gel;

[0042] (4) The polymer gel is further heated to 350°C to evaporate the organic solvent, and the temperature is maintained for 2 hours for pyrolysis. After pyrolysis, the resulting powder is transferred to a corundum crucible and placed in a muffle furnace for decarbonization. The crucible is calcined at 550°C in an air atmosphere for 10 hours, and then the temperature is raised to 1000°C and calcined in an air atmosphere for 10 hours to obtain an oxide precursor.

[0043] (5) Mixing magnesium powder and oxide precursor (the mass ratio of magnesium powder to oxide precursor is 2:1) and manually grinding in an agate mortar for 30 min to obtain a mixed powder;

[0044] (6) The mixed powder obtained in step (5) was placed in a corundum porcelain boat, and the porcelain boat was placed in the central temperature control zone of the tube furnace. Ammonia flow was introduced at a flow rate of 200 mL / min, and the temperature was increased to 700°C at a rate of 5°C / min. The nitriding time was 10 h, and the temperature was naturally cooled to room temperature;

[0045] (7) The nitrided powder was taken out, washed with 0.5 M hydrochloric acid by stirring, washed with water by centrifugation until neutral, and dried to obtain SrTiO3:Ta(3%) / N powder.

[0046] Figure 1 is a scanning electron microscope image of the perovskite SrTiO3:Ta(3%) / N synthesized in Example 1, which is composed of stacked nanoparticles; Figure 2 is an XRD spectrum of the perovskite SrTiO3:Ta(3%) / N synthesized in Example 1, which corresponds to the diffraction peak of the SrTiO3 standard card PDF#89-4934, proving that pure phase strontium titanate was synthesized; Figure 3 is the UV-Vis absorption spectrum of the perovskite SrTiO3:Ta(3%) / N synthesized in Example 1, and its absorption edge extends to 600nm.

[0047] Example 2

[0048] (1) dissolving titanium isopropoxide and tantalum pentachloride in methanol, adding ethylene glycol and citric acid (the molar ratio of titanium isopropoxide, tantalum pentachloride, ethylene glycol, and citric acid is 0.94:0.06:15:60) to completely dissolve them, thereby obtaining a first solution;

[0049] (2) After the solution is completely dissolved, a certain amount of strontium carbonate (the molar ratio of Sr, Ti, and Ta is 1.03:0.94:0.06) is added to the first solution to completely dissolve it, thereby obtaining a second solution;

[0050] (3) After the solution becomes transparent, the second solution is heated to 160° C. and refluxed for 5 h to form a polymer gel;

[0051] (4) The polymer gel is further heated to 350°C to evaporate the organic solvent, and the temperature is maintained for 2 hours for pyrolysis. After pyrolysis, the resulting powder is transferred to a corundum crucible and placed in a muffle furnace for decarbonization. The crucible is calcined at 550°C in an air atmosphere for 10 hours, and then the temperature is raised to 1000°C and calcined in an air atmosphere for 10 hours to obtain an oxide precursor.

[0052] (5) Mix the magnesium powder and the oxide precursor (the mass ratio of magnesium powder to oxide precursor is 2:1), grind manually in an agate mortar for 30 min, and mix the powders;

[0053] (6) The mixed powder obtained in step (5) was placed in a corundum porcelain boat, and the porcelain boat was placed in the central temperature control zone of the tube furnace. Ammonia flow was introduced at a flow rate of 200 ml / min, and the temperature was increased to 700°C at a rate of 5°C / min. The nitriding time was 10 h, and the temperature was naturally cooled to room temperature;

[0054] (7) The nitrided powder was taken out, washed with 0.5 M hydrochloric acid by stirring, washed with water by centrifugation until neutral, and dried to obtain SrTiO3:Ta(6%) / N powder.

[0055] Figure 4 is a scanning electron microscope image of the perovskite SrTiO3:Ta(6%) / N synthesized in Example 2, which is composed of stacked nanoparticles; Figure 5 is an XRD spectrum of the perovskite SrTiO3:Ta(6%) / N synthesized in Example 2, which corresponds to the diffraction peak of the SrTiO3 standard card PDF#89-4934, proving that pure phase strontium titanate was synthesized; Figure 6 is the UV-Vis absorption spectrum of the perovskite SrTiO3:Ta(6%) / N synthesized in Example 2, and its absorption edge extends to 600nm.

[0056] Example 3

[0057] The SrTiO3:Ta(3%) / N obtained in Example 2 was used for photocatalytic hydrogen production testing:

[0058] 0.2g of tantalum-nitrogen-doped strontium titanate powder was ultrasonically dispersed in a 1wt% Pd solution of sodium chloropalladate, heated in a waterbath and evaporated to dryness. The mixture was then reduced at 200°C for 1h under a mixed flow of hydrogen and argon. The photocatalytic water splitting reaction to produce hydrogen was carried out in a photocatalytic reaction apparatus equipped with an online detection system. The reaction temperature was maintained at 15°C. Using a xenon lamp as a top-light source, 150mg of the Pd-loaded catalyst powder was ultrasonically dispersed in 150mL of a 10mM sodium formate solution. Prior to illumination, the system was evacuated to remove air, and ultraviolet light was filtered through a filter (λ ≥ 420nm). The photocatalyst's hydrogen production activity was tested under visible light.

[0059] FIG7 is a graph showing the photocatalytic water splitting hydrogen production activity of SrTiO 3 :Ta (6%) / N in Example 3, indicating that this catalyst can be used in the photocatalytic water splitting hydrogen production reaction.

[0060] Example 4

[0061] The SrTiO3:Ta(3%) / N obtained in Example 2 was used for photocatalytic oxygen production test:

[0062] 50 mg of tantalum nitrogen-doped strontium titanate powder was ultrasonically dispersed in a 1 wt% iridium oxide colloidal solution and stirred continuously in the dark for 1 hour. The photocatalytic water splitting reaction to produce oxygen was carried out in a photocatalytic reaction apparatus equipped with an online detection system. The reaction temperature was maintained at 15°C, and top irradiation was performed using a xenon lamp. 50 mg of yttrium oxide-loaded catalyst powder was ultrasonically dispersed in 150 mL of a 10 mM silver nitrate solution. Prior to irradiation, the system was evacuated to remove air, and ultraviolet light was filtered through a filter (λ ≥ 420 nm). The photocatalyst's oxygen production activity was tested under visible light.

[0063] FIG8 is a graph showing the photocatalytic water splitting and oxygen production activity of SrTiO3:Ta(6%) / N in Example 4, indicating that this catalyst can be used in the photocatalytic water splitting and oxygen production reaction.

[0064] Comparative Example 1

[0065] (1) dissolving titanium isopropoxide in methanol, adding ethylene glycol and citric acid (the molar ratio of titanium isopropoxide, ethylene glycol, and citric acid is 1:15:60) to completely dissolve the titanium isopropoxide to obtain a first solution;

[0066] (2) After the solution is completely dissolved, strontium carbonate (the molar ratio of Sr to Ti is 1.03:1) is added to the first solution to completely dissolve it, thereby obtaining a second solution;

[0067] (3) After the solution becomes transparent, the second solution is heated to 160° C. and refluxed for 5 h to form a polymer gel;

[0068] (4) The polymer gel is further heated to 350°C to evaporate the organic solvent, and the temperature is maintained for 2 hours for pyrolysis. After pyrolysis, the resulting powder is transferred to a corundum crucible and placed in a muffle furnace for decarbonization. The crucible is calcined at 550°C in an air atmosphere for 10 hours, and then the temperature is raised to 1000°C and calcined in an air atmosphere for 10 hours to obtain an oxide precursor.

[0069] (5) The oxide precursor was placed in a corundum porcelain boat, and the porcelain boat was placed in the central temperature control zone of the tube furnace. Ammonia flow was introduced at a flow rate of 200 mL / min, and the temperature was raised to 700 °C at a rate of 5 °C / min. The nitridation time was 10 h, and the temperature was naturally cooled to room temperature to obtain the catalyst SrTiO3:N powder.

[0070] The SrTiO3:N obtained in Comparative Example 1 was used for photocatalytic hydrogen production testing:

[0071] 0.2g of nitrogen-doped strontium titanate powder was ultrasonically dispersed in a 1wt% Pd-containing sodium chloropalladate solution, heated in a water bath and evaporated to dryness. The solution was then reduced at 200°C for 1h under a mixed flow of hydrogen and argon. The photocatalytic water splitting reaction to produce hydrogen was carried out in a photocatalytic reaction apparatus equipped with an online monitoring system. The reaction temperature was maintained at 15°C. Using a xenon lamp as a top-light source, 150mg of the Pd-loaded catalyst powder was ultrasonically dispersed in 150mL of a 10mM sodium formate solution. Prior to illumination, the system was evacuated to remove air, and ultraviolet light was filtered through a filter (λ ≥ 420nm). The photocatalyst's hydrogen production activity was tested under visible light.

[0072] FIG9 is a graph showing the photocatalytic water decomposition and hydrogen production activity of SrTiO 3 :N in Comparative Example 1, which illustrates that the catalyst powder obtained by the conventional nitridation method has relatively poor activity.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing tantalum-nitrogen co-doped strontium titanate perovskite, characterized in that: The method comprises the following steps: (1) dissolving titanium isopropoxide and tantalum pentachloride in methanol, and adding ethylene glycol and citric acid to fully dissolve them to obtain a first solution; (2) adding strontium carbonate to the first solution obtained in step (1) to fully dissolve it, thereby obtaining a second solution; (3) heating the second solution obtained in step (2) to 150-200° C. and maintaining the temperature for 0.1-5 hours to carry out a polymerization reaction to obtain a polymer; (4) heating the polymer obtained in step (3), wherein the first stage is heated to 300-400° C. and maintained for 0.5-2 h, the second stage is heated to 500-600° C. and maintained for 0.1-20 h, and the third stage is heated to 800-1100° C. and maintained for 0.1-20 h, to obtain an oxide precursor powder; (5) grinding and mixing the oxide precursor powder obtained in step (4) with magnesium powder to obtain a mixed powder; (6) placing the mixed powder obtained in step (5) in a tube furnace and introducing ammonia gas for nitridation; (7) The powder after nitridation treatment in step (6) is acid-washed, then filtered, washed with water, and dried to obtain perovskite tantalum-nitrogen co-doped strontium titanate.

2. The preparation method according to claim 1, characterized in that: In step (1), the ratio of the total amount of tantalum pentachloride and titanium isopropoxide, the amount of ethylene glycol, and the amount of citric acid is 1:15:60; The molar ratio of tantalum in the tantalum pentachloride to titanium in titanium isopropoxide is 0.001:0.999 to 0.1:0.

9.

3. The preparation method according to claim 1, characterized in that: In step (2), the ratio of the amount of strontium carbonate to the total amount of tantalum pentachloride and titanium isopropoxide is 1.03:

1.

4. The preparation method according to claim 1, characterized in that: In step (5), the mass ratio of magnesium powder to oxide precursor powder is 0.5 to 10:

1.

5. The preparation method according to claim 1, characterized in that: In step (6), the ammonia flow rate is 50-500 mL / min, the nitriding temperature is 650-800° C., the nitriding time is 3-20 h, and the heating rate is 5° C. / min.

6. A perovskite tantalum-nitrogen co-doped strontium titanate prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The tantalum-nitrogen co-doped strontium titanate has a doping amount of tantalum of 1-10 wt % and a doping amount of nitrogen of 0.1-5 wt %.

7. A perovskite tantalum nitrogen co-doped strontium titanate photocatalyst, characterized in that: The perovskite tantalum-nitrogen co-doped strontium titanate described in claim 7 is loaded with a precious metal or a metal oxide to obtain a perovskite tantalum-nitrogen co-doped strontium titanate photocatalyst.

8. The perovskite tantalum-nitrogen co-doped strontium titanate photocatalyst according to claim 7, characterized in that: The noble metal loading method is as follows: dispersing tantalum nitrogen doped strontium titanate powder in a solution containing a noble metal precursor, evaporating in a water bath after ultrasonic dispersion, and reducing at 100-400° C. for 0.5-3 h under a hydrogen flow; The metal oxide loading method is as follows: dispersing tantalum nitrogen doped strontium titanate powder in a solution containing a metal precursor, evaporating it in a water bath after ultrasonic dispersion, and calcining it at 100-500° C. for 0.5-4 hours in air or nitrogen or argon atmosphere.

9. Use of the perovskite tantalum-nitrogen co-doped strontium titanate photocatalyst according to any one of claims 7 to 8 in a photocatalytic hydrogen production reaction, characterized in that: One or more of lactic acid, sodium sulfide, ascorbic acid, formic acid, sodium formate, methanol and triethanolamine are used as hole sacrificial reagents and dispersed in water with the photocatalyst powder, and water is decomposed under light to generate hydrogen.

10. An application of the perovskite tantalum-nitrogen co-doped strontium titanate photocatalyst according to any one of claims 7-8 in a photocatalytic oxygen production reaction, wherein one or more of silver nitrate, potassium iodate, and ferric chloride are used as hole sacrificial reagents and are dispersed in water with the powder of the photocatalyst, and water is decomposed under light to produce oxygen.

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