Metal-doped niobium oxide nanocrystal, preparation method and application thereof

Abstract

The application belongs to the technical field of niobium oxide material preparation, and particularly relates to metal-doped niobium oxide nanocrystals, a preparation method and application thereof. The specific steps are as follows: niobium oxide is dissolved in hydrofluoric acid, the pH of the solution is adjusted to 7-9 to obtain a precipitate; the cleaned precipitate is added into a citric acid solution, and then a metal ion solution is added to perform a hydrothermal reaction; the reaction product is washed, dried, ground, calcined and cooled to obtain the metal-doped niobium oxide nanocrystals. The metal-doped niobium oxide nanocrystals based on cheap commercial niobium oxide and hydrofluoric acid have a small size, which is conducive to the separation of photo-generated carriers; mesoporous channels are formed between the crystal particles, and the specific surface area is large, which is conducive to the flow of reactants and products and the adsorption of reactants; the doped metal ions can regulate the energy band structure of niobium oxide, and the doped metal ions and the niobium oxide matrix constitute a single-atom catalyst, providing more active sites, so that the metal-doped niobium oxide nanocrystals have high photocatalytic activity.

Description

Technical Field

[0001] This invention belongs to the field of niobium oxide material preparation technology, specifically relating to a metal-doped niobium oxide nanocrystal, its preparation method, and its application. Background Technology

[0002] Photocatalysis is a technology that uses solar energy to convert water or carbon dioxide into clean energy. Its principle involves a semiconductor catalyst generating electrons and holes under light. Utilizing the reducing power of electrons, water or carbon dioxide can be reduced to hydrogen, hydrocarbon fuels, and other energy sources. The requirements for the catalyst are: smaller size to facilitate the separation of electrons and holes, larger surface area to facilitate the adsorption of reactant gases, and more active sites to promote the reaction. Based on these requirements, small-sized, mesoporous nanocatalysts with large specific surface areas are currently the focus of photocatalyst development.

[0003] Niobium oxide is a common photocatalyst, and its modification can yield more efficient catalysts. Existing niobium oxide single-atom catalysts often require subsequent loading onto synthesized niobium oxide catalysts, and current preparation methods often require niobium precursors such as niobium pentachloride, niobium ethoxide, and niobium oxalate, which are difficult to store or expensive, making the preparation methods cumbersome and costly.

[0004] Therefore, developing a new type of metal-doped niobium oxide nanocrystal is of great significance. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the shortcomings of existing technologies by providing a metal-doped niobium oxide nanocrystal based on inexpensive commercial niobium oxide and hydrofluoric acid. The synthesized niobium oxide crystals are small in size, which is beneficial for the separation of photogenerated carriers. Mesoporous channels are formed between the crystal particles, which have a large specific surface area and are conducive to the flow of reactants and products. The doped metal ions can regulate the band structure of niobium oxide, and the doped metal ions appearing on the surface and the niobium oxide matrix constitute a single-atom catalyst, providing more active sites.

[0006] To address the aforementioned technical problems, this invention discloses a method for preparing metal-doped niobium oxide nanocrystals, comprising the following steps: dissolving niobium oxide in hydrofluoric acid, adjusting the pH of the solution to 7-9 to obtain a precipitate; adding the washed precipitate to a citric acid solution, followed by adding a metal ion solution for a hydrothermal reaction; washing, drying, and grinding the reaction product; and calcining and cooling to obtain the metal-doped niobium oxide nanocrystals.

[0007] The concentration of niobium oxide in hydrofluoric acid is 0.25~1.25 mmol / mL.

[0008] In some embodiments of the present invention, the concentration of niobium oxide in hydrofluoric acid is 0.5 mmol / mL.

[0009] The pH of the solution is adjusted by adding an ammonia solution.

[0010] The citric acid solution is an aqueous solution of citric acid with a concentration of 0.1~1 mmol / mL; the concentration of the precipitate in the citric acid solution is 0.05~0.5 mmol / mL.

[0011] In some embodiments of the present invention, the concentration of the citric acid solution is 0.33 mmol / mL.

[0012] The metal ion is copper ion.

[0013] Specifically, the amount of copper ions doped is 0.05 to 1% relative to the molar amount of niobium ions.

[0014] Preferably, the copper ion doping amount is 0.2%.

[0015] Specifically, the copper ions are introduced into the citric acid solution through any one of easily soluble metal salts, including copper nitrate, copper chloride, and copper acetate.

[0016] The hydrothermal reaction is carried out at a temperature of 180-250 °C for a duration of 5-48 h.

[0017] In some embodiments of the present invention, the hydrothermal reaction is carried out at a temperature of 200 °C for a time of 20 h.

[0018] The drying process is carried out at a temperature of 50~80℃.

[0019] In some embodiments of the present invention, the drying process is carried out at a temperature of 60 °C.

[0020] The calcination is carried out at a temperature of 400-800 ℃ for a time of 1-24 h.

[0021] In some embodiments of the present invention, the calcination is carried out at a temperature of 500 °C for 3 h.

[0022] Furthermore, the metal-doped niobium oxide nanocrystals prepared by the above method are also within the scope of protection of this invention.

[0023] Furthermore, the application of the metal-doped niobium oxide nanocrystals prepared by the above method in the photocatalytic reduction of CO2 to produce methane is also within the scope of protection of this invention.

[0024] Specifically, in some embodiments of the present invention, niobium oxide nanocrystals with copper ion doping amounts of 0.05%, 0.2%, 0.4%, and 1% were successfully prepared using the above-described preparation method. Characterization of their material composition and microstructure confirmed the successful construction of a niobium oxide single-atom catalyst. Testing the photocatalytic reduction of CO2 to methanogeny activity of niobium oxide nanocrystals with different copper ion doping amounts revealed that the activity of doped nanocrystals was significantly enhanced compared to undoped nanocrystals. The nanocrystals with 0.2% Cu doping exhibited the highest activity, approximately 2.8 times that of the undoped nanocrystals, demonstrating the promising application prospects of the metal-doped niobium oxide nanocrystals provided by the present invention in the photocatalytic reduction of CO2 to methanogeny.

[0025] The mechanism of this invention lies in using inexpensive raw materials niobium oxide and hydrofluoric acid, and carbonizing citric acid through a hydrothermal reaction. This allows niobium and doped metal elements in the precursor solution to be uniformly encapsulated in the citric acid carbides. After calcination in a muffle furnace, uniformly doped niobium oxide nanocrystals are formed. Taking copper ions as an example, the photocatalytic performance of copper-doped niobium oxide is more than twice that of undoped niobium oxide, and even without metal doping, its performance is much better than commercially available niobium oxide. This is due to several factors: firstly, copper doping modulates the performance of charge carriers; secondly, copper atoms distributed on the surface form single-atom catalytic active sites; thirdly, its smaller crystal size facilitates charge carrier separation; and fourthly, the mesoporous structure provides a large specific surface area, which is beneficial for the adsorption of reactants and the flow of reactants and products. Beneficial effects

[0026] The niobium precursor used in this invention is inexpensive commercial niobium oxide, which is much cheaper than niobium pentachloride, niobium ethoxide, and niobium oxalate, and is easy to store. Other raw materials are also very inexpensive. Furthermore, the niobium oxide crystals synthesized in this invention are small in size (around 20 nanometers), which is beneficial for the separation of photogenerated carriers. Mesoporous channels are formed between the crystal particles, providing a large specific surface area, which is beneficial for the flow of reactants and products, and the adsorption of reactants. The doped metal ions can modulate the band structure of niobium oxide, and multiple metal ions can be easily doped simultaneously in a wide range of amounts, only needing to be added during solution preparation, except for insoluble precursors. The doped metal ions appearing on the surface and the niobium oxide matrix constitute a single-atom catalyst, providing more active sites. The product prepared by this invention has excellent performance, and its application fields can be expanded to electrocatalysis, photoelectrocatalysis, fuel cells, supercapacitors, and other fields that require related nanomaterials. Attached Figure Description

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0028] Figure 1 The XRD patterns of niobium oxide nanocrystals with different copper ion doping levels prepared in the embodiments of the present invention are shown.

[0029] Figure 2 The absorption spectra of niobium oxide nanocrystals with different copper ion doping levels prepared in the embodiments of the present invention are shown below; wherein, Figure 2 In this context, 'a' represents the absorption spectrum in the wavelength range of 200–600 nm. Figure 2 In this context, b represents the amplified absorption spectrum in the wavelength range of 400–600 nm. Figure 2 In this context, COM stands for Commercial Niobium Oxide.

[0030] Figure 3 The images shown are TEM images of undoped and copper-doped niobium oxide nanocrystals prepared in this embodiment of the invention; wherein, Figure 3 In the image, 'a' represents a TEM image of undoped niobium oxide nanocrystals at a scale bar of 100 nm. Figure 3 In the image, b is a TEM image of niobium oxide nanocrystals without copper ion doping at a scale bar of 20 nm. Figure 3 In the image, c represents a TEM image of undoped niobium oxide nanocrystals at a scale bar of 10 nm. Figure 3 In the image, d represents a TEM image of niobium oxide nanocrystals with a copper ion doping concentration of 0.2% at a scale bar of 100 nm. Figure 3 In the image, 'e' represents a TEM image of niobium oxide nanocrystals with a copper ion doping concentration of 0.2% at a scale bar of 20 nm. Figure 3 f in the figure represents a TEM image of niobium oxide nanocrystals with a copper ion doping concentration of 0.2% at a scale bar of 5 nm.

[0031] Figure 4 The figures show the nitrogen isothermal adsorption-desorption curves and BJH pore size distribution diagrams of undoped and copper-doped niobium oxide nanocrystals prepared in this embodiment of the invention. Figure 4 In the figure, 'a' represents the nitrogen isotherm adsorption-desorption curve. Figure 4 In the figure, b represents the aperture distribution curve.

[0032] Figure 5 The figures show the photocatalytic reduction of CO2 to methane activity of niobium oxide nanocrystals with different copper ion doping levels prepared in the embodiments of the present invention. Figure 5 In this context, COM stands for Commercial Niobium Oxide. Detailed Implementation

[0033] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available. Example 1:

[0034] This embodiment provides a method for preparing copper-doped niobium oxide nanocrystals, comprising the following steps:

[0035] S1. Take 2 mmol of commercial niobium oxide (Nb2O5) and dissolve it in 4 mL of hydrofluoric acid solution under stirring in an oil bath at 80 °C to form a clear and transparent solution.

[0036] S2. Adjust the pH of the solution prepared in S1 to about 8.5 with ammonia water to neutralize the excess hydrofluoric acid and generate a white precipitate containing niobium products. Then wash the precipitate with filtered water to remove ammonium ions and fluoride ions.

[0037] S3. Add the precipitate washed in S2 to 30 ml of an aqueous solution containing 10 mmol of citric acid and stir until a clear and transparent solution is formed.

[0038] S4. Add copper nitrate solution to the solution prepared in S3. To avoid significantly affecting the total volume of the solution, the total amount of copper ion solution added should be controlled within 1 ml to prepare a high concentration of copper ion solution. Then, extract the required copper ions using a pipette. Specifically, control the copper ion doping amount to 0.05%, 0.2%, 0.4%, and 1% relative to the molar amount of niobium ions, respectively. After stirring evenly, obtain the corresponding mixed solution.

[0039] S5. The mixed solution in S4 was placed into a hydrothermal reactor with a polytetrafluoroethylene liner for hydrothermal reaction. The temperature was controlled at 200 °C and the reaction was carried out for 20 h. After the reaction was completed, the precipitate was obtained by filtration, washed with deionized water and dried at 60 °C.

[0040] S6. After the precipitate dried in S5 is lightly ground, it is placed in a muffle furnace and calcined at 500 °C for 3 hours. After cooling, niobium oxide nanocrystals with copper ion doping amounts of 0.05%, 0.2%, 0.4% and 1% are obtained. Example 2:

[0041] Undoped niobium oxide nanocrystals were prepared using the method described in Example 1 as a control group. The undoped niobium oxide nanocrystals and the niobium oxide nanocrystals with copper ion doping levels of 0.05%, 0.2%, 0.4%, and 1% prepared in Example 1 were characterized by X-ray diffraction. Figure 1 XRD patterns of niobium oxide nanocrystals with different copper ion doping concentrations, derived from... Figure 1It can be seen that the two main diffraction peaks can be identified as the (001) and (002) peaks of card #30-0873. Copper doping did not significantly change the position of the peaks, which is attributed to the relatively small amount of doping. At the same time, from the magnified XRD pattern, it can be seen that the angle of the (001) peak decreases slightly with the increase of copper ion doping amount, which indicates that the spacing of the (001) crystal plane increases. This is consistent with the fact that the radius of copper ion is larger than that of niobium ion, thus proving that copper ion doping was successful.

[0042] Niobium oxide nanocrystals without copper ion doping and those doped with copper ions at concentrations of 0.05%, 0.2%, 0.4%, and 1% were characterized using ultraviolet absorption spectroscopy. Figure 2 The absorption spectra of niobium oxide nanocrystals with different copper ion doping concentrations are shown, among which... Figure 2 In this context, 'a' represents the absorption spectrum in the wavelength range of 200–600 nm. Figure 2 In this context, 'b' represents the amplified absorption spectrum in the wavelength range of 400–600 nm, derived from… Figure 2 As can be seen from 'a', copper doping did not change the band gap of the material. Compared to commercial niobium oxide, the nanomaterial exhibits a blue shift in the band edge and a larger band gap. Figure 2 As can be seen from b in the image, by comparing the magnified region, a weak absorption band is found in the long wavelength region near the absorption edge, and the absorption intensity increases with the increase of doping amount. This may be attributed to the additional absorption caused by doping, which may indicate that an additional energy level has been formed in the band gap, thus proving that copper ions have been successfully doped.

[0043] The niobium oxide nanocrystals without copper ion doping and those with 0.2% copper ion doping were characterized by transmission electron microscopy. Figure 3 TEM images show undoped and copper-doped niobium oxide nanocrystals with a doping level of 0.2%. Figure 3 In the image, 'a' represents a TEM image of undoped niobium oxide nanocrystals at a scale bar of 100 nm. Figure 3 In the image, b is a TEM image of niobium oxide nanocrystals without copper ion doping at a scale bar of 20 nm. Figure 3 In the image, c represents a TEM image of undoped niobium oxide nanocrystals at a scale bar of 10 nm. Figure 3 In the image, d represents a TEM image of niobium oxide nanocrystals with a copper ion doping concentration of 0.2% at a scale bar of 100 nm. Figure 3 In the image, 'e' represents a TEM image of niobium oxide nanocrystals with a copper ion doping concentration of 0.2% at a scale bar of 20 nm. Figure 3 f in the image represents a TEM image of niobium oxide nanocrystals with a copper ion doping concentration of 0.2% at a scale bar of 5 nm. Figure 3 a and Figure 3As can be seen from 'd' in the figure, the synthesized niobium oxide has a porous structure, while Figure 3 b and Figure 3 The 'e' in the figure directly shows the pores between niobium oxide nanocrystals, indicating that the size of the nanocrystals is around 20 nm, and that there are pores between the grains. Figure 3 c and Figure 3 f in the image is its high-resolution image, and the clear lattice fringes indicate that the niobium oxide nanocrystals have good crystallinity.

[0044] The undoped niobium oxide nanocrystals and niobium oxide nanocrystals with 0.2% copper ion doping were characterized using a specific surface area and porosity analyzer. Figure 4 Nitrogen gas isothermal adsorption-desorption curves and BJH pore size distributions for undoped and copper-doped niobium oxide nanocrystals with a doping concentration of 0.2%. Figure 4 In the figure, 'a' represents the nitrogen isotherm adsorption-desorption curve, derived from... Figure 4 As can be seen from 'a', the BET specific surface areas of undoped and doped niobium oxide are 49.4 m². 2 / g and 53.8 m 2 / g indicates that they all have a large specific surface area and the effect of doping is minimal. Figure 4 In this context, 'b' represents the pore size distribution curve, derived from... Figure 4 As can be seen from b, the pores between the grains are mesopores.

[0045] Further research was conducted on the photocatalytic reduction of CO2 to methane activity of niobium oxide nanocrystals without copper ion doping and niobium oxide nanocrystals doped with copper ions at concentrations of 0.05%, 0.2%, 0.4%, and 1%. The specific steps were as follows: 15 mg of niobium oxide nanocrystals with different doping concentrations were placed as catalysts in a 200 mL sealed container with a quartz window. The container was filled with high-purity carbon dioxide at one atmosphere and contained 0.2 g of liquid water. The catalyst was irradiated through the quartz window by a 300 W xenon lamp to simulate sunlight and carry out the photoreaction. The products were detected by chromatography. Figure 5 The image shows the photocatalytic reduction of CO2 to methane activity of niobium oxide nanocrystals with different copper ion doping concentrations. Figure 5It can be seen that the activity of commercially available niobium oxide is negligible compared to the niobium oxide prepared in this invention. The activity of copper-doped nanocrystals is enhanced compared to undoped nanocrystals, with the 0.2% Cu-doped nanocrystals exhibiting the highest activity, approximately 2.8 times that of the undoped nanocrystals. This indicates that copper doping effectively improves photocatalytic activity, and the mechanism can be attributed to the regulation of carrier performance by copper doping and the formation of copper single-atom catalysts. When the doping amount is relatively small, copper ions may beneficially regulate the band structure, and the surface copper ions may form single-atom catalysts with the niobium oxide substrate, thereby enhancing photocatalytic activity. As the copper ion doping amount increases, the number of active copper ion sites on the surface increases, further improving the activity. However, the doped copper ions also act as recombination centers for electrons and holes; a large doping amount will reduce photocatalytic activity. Therefore, the photocatalytic activity first increases and then decreases with increasing copper ion doping amount.

[0046] This invention provides a concept and method for preparing and applying metal-doped niobium oxide nanocrystals. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing metal-doped niobium oxide nanocrystals, characterized in that, The process includes the following steps: dissolving niobium oxide in hydrofluoric acid, adjusting the pH of the solution to 7-9 to obtain a precipitate; adding the washed precipitate to a citric acid solution, followed by adding a metal ion solution for a hydrothermal reaction; washing, drying, and grinding the reaction product; and calcining and cooling to obtain the metal-doped niobium oxide nanocrystals. The concentration of niobium oxide in hydrofluoric acid is 0.25~1.25 mmol / mL; The citric acid solution is an aqueous solution of citric acid with a concentration of 0.1~1 mmol / mL; the concentration of the precipitate in the citric acid solution is 0.05~0.5 mmol / mL. The metal ion is a copper ion; the doping amount of the copper ion is 0.05~1% relative to the molar amount of the niobium ion. The hydrothermal reaction is carried out at a temperature of 180~250 ℃ for a time of 5~48 h. The calcination is carried out at a temperature of 400~800 ℃ for a time of 1~24 h.

2. The preparation method according to claim 1, characterized in that, The copper ions are introduced into the citric acid solution via any one of copper nitrate, copper chloride, and copper acetate.

3. Metal-doped niobium oxide nanocrystals prepared by the preparation method described in claim 1 or 2.

4. The application of the metal-doped niobium oxide nanocrystals according to claim 3 in the photocatalytic reduction of CO2 to produce methane.

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