Preparation method of three-dimensional iodine-doped Nb2O5 catalyst assembled by ultrathin nanosheets

Abstract

The application provides a preparation method of a three-dimensional iodine-doped Nb2O5 catalyst assembled by ultrathin nanosheets, which uses NbCl5 as a precursor, generates niobate layers through a hydrothermal method, disperses the washed niobate layers into an aqueous solution of HIO3, then performs freeze-drying on the mixture, and finally performs calcination, so that the iodine exists in the form of elemental iodine in the interstitial space of the Nb2O5 crystal lattice, and finally forms a three-dimensional cross-linked structure iodine-doped Nb2O5 catalyst assembled by ultrathin nanosheets, which is composed of nanosheets and has an ultrathin structure, has a larger specific surface area and more exposed active sites than pure Nb2O5, and can participate in a catalytic reaction more quickly; under visible light, the catalyst has excellent and stable photocatalytic degradation performance and has a wider spectral working range than pure Nb2O5.

Description

Technical Field

[0001] This invention relates to the field of Nb2O5 catalyst technology, and more specifically to a method for preparing a three-dimensional iodine-doped Nb2O5 catalyst assembled from ultrathin nanosheets. Background Technology

[0002] In wastewater treatment, insufficient removal of nonsteroidal anti-inflammatory drugs (NSAIDs) such as diclofenac leads to their accumulation in aquatic ecosystems, sewage sludge, and soil, causing environmental and health problems. Photocatalysis has emerged as an attractive technology for degrading organic pollutants, heavily reliant on catalyst development. Utilizing photocatalysts to convert inexhaustible solar energy into directly usable energy for the complete mineralization and degradation of various organic and inorganic pollutants shows immense promise in environmental protection.

[0003] Among numerous photocatalysts, semiconductor photocatalysts have attracted widespread attention due to their advantages such as low cost, strong oxidation activity, and high photosensitivity. Among various semiconductor photocatalysts, niobium pentoxide (Nb₂O₅), as an n-type photocatalyst, exhibits many unique physicochemical properties, including low toxicity, excellent chemical and thermal stability, good eco-friendliness, strong oxidation capacity, and relatively high photocatalytic activity, making it a suitable photocatalyst for photodegradation. Despite its many advantages, its catalytic performance is hindered by problems such as insufficient visible light response, limited active reaction sites, and the rapid recombination rate of photogenerated charges. Notably, the relatively wide band gap of Nb₂O₅ limits its responsiveness to visible light, making it responsive only under ultraviolet light, but ultraviolet light only accounts for a small portion (3%-5%) of sunlight. Therefore, it is necessary to address these limiting factors and develop innovative Nb₂O₅ photocatalysts with superior visible light photocatalytic activity to improve their effectiveness in environmental remediation applications.

[0004] In recent years, researchers both domestically and internationally have explored various strategies to modify Nb₂O₅, including morphology control, elemental doping, and the construction of semiconductor composites. These efforts aim to modulate its band gap, broaden its photoresponse range, reduce carrier recombination, and significantly improve its photocatalytic performance. Among these strategies, elemental doping is a widely used semiconductor modification method, encompassing both metal and non-metal doping. While metal doping has traditionally been more prevalent, its application is limited by cost and environmental concerns. Non-metal doping, on the other hand, can effectively broaden the response range of Nb₂O₅ in the ultraviolet region and enhance its photocatalytic activity. Furthermore, the technology of using non-metal-doped Nb₂O₅ photocatalysts to degrade organic pollutants has green and environmentally friendly advantages, which is of great significance for further research in niobium-based catalysts and the field of photocatalysis.

[0005] Currently, nonmetallic doping mainly involves nitrogen, carbon, and fluorine doping. During doping, nitrogen, carbon, and fluorine dopants enter the matrix lattice and replace O or Nb atoms in Nb₂O₅. However, the applicant's research found that iodine doping also shows potential in improving the visible light absorption of Nb₂O₅. However, there is a lack of research literature on iodine-doped Nb₂O₅; therefore, it is necessary to design and synthesize iodine-doped Nb₂O₅ catalysts and explore their doping mechanisms.

[0006] It is worth noting that although iodine doping has shown potential in enhancing the visible light absorption of Nb₂O₅, it is insufficient in effectively increasing its specific surface area and surface reaction sites. Therefore, there is an urgent need to develop an innovative regulatory strategy to enable iodine-doped Nb₂O₅ to possess enhanced visible light response, as well as high specific surface area and abundant reactive sites. Ultrathin two-dimensional catalysts have attracted considerable attention due to their advantages such as expanded surface area, abundant low-coordination surface atoms, inherent quantum confinement effects, and high surface reactivity. However, a common challenge faced by ultrathin two-dimensional nanosheets is the tendency for structural stacking during catalysis, leading to a reduction in the number of active reaction sites. Assembling ultrathin two-dimensional nanosheets into structurally stable three-dimensional cross-linked aggregates can effectively alleviate the stacking problem while retaining the unique advantages of ultrathin two-dimensional nanosheets. Therefore, a method for preparing three-dimensional cross-linked structures assembled from ultrathin iodine-doped Nb₂O₅ nanosheets by modifying Nb₂O₅ with iodine doping and combining it with morphology control can effectively solve the above problems. Summary of the Invention

[0007] This invention designs and develops a method for preparing a three-dimensional iodine-doped Nb₂O₅ catalyst assembled from ultrathin nanosheets. The method uses NbCl₅ as a precursor, generates a niobate layer via a hydrothermal method, disperses the washed niobate layer in an aqueous solution of HIO₃, freeze-dries the mixture, and finally calcines it. The doped iodine exists as elemental iodine in the interstitial spaces of the Nb₂O₅ lattice, ultimately forming a three-dimensional cross-linked iodine-doped Nb₂O₅ catalyst assembled from ultrathin nanosheets. This catalyst, composed of nanosheets, has an ultrathin structure, a larger specific surface area and more exposed active sites than pure Nb₂O₅, and can participate in catalytic reactions more rapidly. Under visible light, this catalyst exhibits excellent and stable photocatalytic degradation performance and a wider spectral operating range than pure Nb₂O₅.

[0008] The technical solution adopted to achieve the above-mentioned objectives of this invention is as follows:

[0009] A method for preparing a three-dimensional iodine-doped Nb₂O₅ catalyst assembled from ultrathin nanosheets includes the following steps:

[0010] (1) Dissolve NbCl5 in ethanol until transparent, then add a certain amount of water and ammonia under stirring, continue stirring, and then centrifuge to obtain the precipitate;

[0011] (2) Disperse the precipitate obtained in step (1) in water and PVP, and hydrothermally react the solution at 120-200℃ for a period of time.

[0012] (3) After the hydrothermal reaction is completed, the mixture is cooled, centrifuged to obtain a precipitate, the precipitate is washed with water several times, a certain amount of iodic acid is added, and then freeze-dried.

[0013] (4) Grind the dried powder obtained in step (3) evenly and anneal it in air for 1-4 hours to obtain an ultrathin iodine-doped Nb2O5 catalyst.

[0014] Furthermore, in step (1), the amount of ammonia added is (10-20) mL: 1 g compared to the amount of NbCl5 added.

[0015] Furthermore, in step (2), the mass ratio of PVP added to NbCl5 is (1-3):1;

[0016] Furthermore, the hydrothermal reaction in step (2) lasts for 12-24 hours.

[0017] Furthermore, in step (3), the mass ratio of iodic acid added to NbCl5 is (0.1-0.5):1.

[0018] Furthermore, the annealing temperature in step (4) is 450-550℃.

[0019] Compared with the prior art, the beneficial effects of the preparation method of the three-dimensional iodine-doped Nb2O5 catalyst assembled by ultrathin nanosheets in this invention are as follows: 1. In this invention, NbCl5 is used as a precursor, and a niobate layer is generated by hydrothermal method. The washed niobate layer is dispersed in an aqueous solution of HIO3, and the mixture is then freeze-dried and finally calcined. During the calcination process, iodic acid decomposes into elemental iodine, which exists in the interstitial space of Nb2O5 in the form of elemental iodine, and finally forms a three-dimensional cross-linked structure iodine-doped Nb2O5 catalyst assembled by ultrathin nanosheets. The raw materials are readily available and the cost is low. The preparation method is simple and easy to mass-produce.

[0020] 2. The catalyst in this invention exhibits excellent and stable photocatalytic degradation performance under visible light, and has a wider spectral operating range than pure Nb2O5, making it widely applicable to the visible light photocatalytic degradation of organic pollutants (such as diclofenac).

[0021] 3. In this invention, the catalyst is composed of ultrathin nanosheets with a large specific surface area, which provides more reactive sites for the photocatalytic reaction, thus exhibiting excellent photocatalytic activity. However, excessive iodine doping will reduce the specific surface area of ​​the catalyst, decrease its catalytic activity, and affect the catalytic degradation of organic pollutants (such as diclofenac). Attached Figure Description

[0022] Figure 1 The images show the surface morphology of the three-dimensional iodine-doped Nb2O5 catalysts assembled from ultrathin nanosheets prepared in Examples 1-3; where 1a and 1b are SEM and AFM images of INO-1, respectively; 1c and 1d are SEM images of INO-2 at different magnifications; and 1e and 1f are SEM images of INO-3 at different magnifications.

[0023] Figure 2 XRD patterns of the three-dimensional iodine-doped Nb2O5 catalysts assembled from ultrathin nanosheets prepared in Examples 1-3 and the pure Nb2O5 catalysts prepared in the comparative examples;

[0024] Figure 3 XPS images of catalyst INO-1 prepared in Example 1 and catalyst Nb2O5 prepared in the comparative example;

[0025] Figure 4 This is an enlarged XPS image of the catalyst INO-1 prepared in Example 1;

[0026] Figure 5 The UV-Vis diffuse reflectance spectra of the three-dimensional iodine-doped Nb2O5 catalysts assembled from ultrathin nanosheets prepared in Examples 1-3 and the pure Nb2O5 catalysts prepared in the comparative examples.

[0027] Figure 6 The figures show the removal effects of the three-dimensional iodine-doped Nb2O5 catalyst assembled from ultrathin nanosheets prepared in Examples 1-3 and the pure Nb2O5 catalyst prepared in the comparative example on the organic pollutant dichlorophenolic acid. Detailed Implementation

[0028] The following examples further illustrate the above-described content of the present invention, but it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention.

[0029] Example 1

[0030] First, 400 mg of NbCl5 was dissolved in 10 mL of ethanol until transparent. Then, 80 mL of water and 4 mL of ammonia were added under stirring, and stirring was continued for 1 h. The precipitate was then obtained by centrifugation. The precipitate was dispersed in 80 mL of water and 0.4 g of PVP, and the solution was subjected to hydrothermal reaction at 160 °C for 12 h. After cooling, the precipitate was obtained by centrifugation, washed several times with water, and 65 mg of iodic acid was added. The precipitate was then freeze-dried. The dried powder was then ground evenly and annealed at 450 °C for 1 h under air conditions to obtain a three-dimensional iodine-doped Nb2O5 catalyst assembled from ultrathin nanosheets (named INO-1).

[0031] Example 2

[0032] First, 400 mg of NbCl5 was dissolved in 10 mL of ethanol until transparent. Then, 80 mL of water and 8 mL of ammonia were added under stirring, and stirring was continued for 2 h. The precipitate was then obtained by centrifugation. The precipitate was dispersed in 80 mL of water and 0.8 g of PVP, and the solution was hydrothermally heated at 180 °C for 24 h. After cooling, the precipitate was obtained by centrifugation, washed several times with water, and 130 mg of iodic acid was added. The precipitate was then freeze-dried. The dried powder was then ground evenly and annealed at 500 °C for 2 h under air conditions to obtain a three-dimensional iodine-doped Nb2O5 catalyst assembled from ultrathin nanosheets (named INO-2).

[0033] Example 3

[0034] First, 400 mg of NbCl5 was dissolved in 20 mL of ethanol until transparent. Then, 50 mL of water and 8 mL of ammonia were added under stirring, and stirring was continued for 3 h. The precipitate was then obtained by centrifugation. The precipitate was dispersed in 50 mL of water and 0.6 g of PVP, and the solution was subjected to hydrothermal reaction at 180 °C for 18 h. After cooling, the precipitate was obtained by centrifugation, washed several times with water, and 195 mg of iodic acid was added. The precipitate was then freeze-dried. The dried powder was then ground evenly and annealed at 550 °C for 3 h under air conditions to obtain a three-dimensional iodine-doped Nb2O5 catalyst assembled from ultrathin nanosheets (named INO-3).

[0035] Comparative Example

[0036] In the comparative example, a pure Nb2O5 catalyst was prepared. The preparation method of this catalyst was basically the same as that of Example 2, except that iodic acid was not added during the preparation process.

[0037] The catalysts prepared in Examples 1-3 and the comparative examples were characterized in terms of structure and performance. The results are as follows:

[0038] The microstructure of the prepared samples was characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Figure 1It can be seen that the prepared catalysts INO-1, INO-2, and INO-3 all exhibit a three-dimensional cross-linked structure assembled from ultrathin nanosheets, and the catalyst thickness is only about 2 nm. Figure 1 b).

[0039] X-ray diffraction (XRD) characterization results are as follows Figure 2 As shown, the results indicate that the prepared three-dimensional iodine-doped Nb2O5 catalyst exhibits an orthorhombic crystal phase and good crystallinity. No iodine-related diffraction peaks were found, indicating that iodine doping did not alter the crystal structure of Nb2O5.

[0040] Further X-ray photoelectron spectroscopy (XPS) was performed on the surface of the catalyst INO-1 prepared in Example 1, and the results are as follows: Figure 3 As shown, the catalyst is composed of I, Nb, and O elements, confirming the successful doping of iodine. Furthermore, in the high-resolution I3d spectrum of INO-1, only characteristic peaks of the II bond were found, such as... Figure 4 As shown, this indicates that iodine exists in the interstitial spaces of Nb₂O₅ as elemental iodine and does not replace Nb atoms.

[0041] The light absorption capacity of the catalyst was characterized using UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), and the results are as follows: Figure 5 As shown in the figure, the analysis indicates that, under the influence of iodine doping, the visible light absorption capacity of INO-1, INO-2, and INO-3 is significantly higher than that of Nb2O5, exhibiting a wider spectral operating range. Furthermore, with increasing iodine doping concentration, the visible light absorption capacity of the catalyst gradually improves. The visible light absorption capacity of INO-2 is significantly higher than that of INO-1, while the visible light absorption capacity of INO-3 is further improved compared to INO-2, although the rate of improvement slows down considerably.

[0042] The specific surface area of ​​the catalyst was analyzed using a specific surface area analyzer, and the results are shown in the table below:

[0043]

[0044] The results showed that the specific surface areas of INO-1, INO-2, and INO-3 were all greater than that of Nb₂O₅, indicating that the prepared iodine-doped Nb₂O₅ catalysts possessed abundant reactive sites, which contributed to the improvement of their catalytic activity. However, with the increase of iodine doping concentration, the specific surface area of ​​the iodine-doped Nb₂O₅ catalysts showed a decreasing trend, with INO-1 having a specific surface area of ​​98.51 m². 2 g -1 The specific surface area of ​​INO-2 is 97.43 m². 2 g -1 The specific surface area of ​​INO-3 is 74.72 m². 2 g-1 This indicates that excessive iodine doping reduces the specific surface area of ​​the catalyst and decreases its catalytic activity.

[0045] Application examples

[0046] Take 30 mL of a 10 mg / L diclofenac solution, then add the three-dimensional iodine-doped Nb₂O₅ catalyst prepared in Examples 1-3 and the Nb₂O₅ catalyst prepared in the comparative example. Stir in the dark for 30 min, then turn on the light source and start timing. Samples are taken at specific time points for filtration and analysis. After reacting under visible light for 90 min, the removal rates of diclofenac in the solution by INO₁, INO₂, INO₃, and Nb₂O₅ are as follows: Figure 6 As shown in the figure. The results indicate that the ultrathin three-dimensional structure and iodine doping can significantly enhance the visible light photocatalytic activity of Nb₂O₅, and this catalytic activity increases with increasing iodine doping amount within a certain range. However, when the iodine doping amount is too high, it will cause a decrease in the specific surface area of ​​the catalyst, thereby reducing the visible light photocatalytic activity of the catalyst.

[0047] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are only illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from the scope of the principles of the present invention, and all such changes and modifications fall within the protection scope of the present invention.

Claims

1. A method for preparing a three-dimensional iodine-doped Nb₂O₅ catalyst assembled from ultrathin nanosheets, characterized in that... Includes the following steps: (1) Dissolve NbCl5 in ethanol until transparent, then add a certain amount of water and ammonia under stirring, continue stirring, and then centrifuge to obtain the precipitate; (2) Disperse the precipitate obtained in step (1) in water and PVP, and hydrothermally react the solution at 120-200℃ for a period of time. (3) After the hydrothermal reaction is completed, the mixture is cooled, centrifuged to obtain a precipitate, the precipitate is washed with water several times, a certain amount of iodic acid is added, and then freeze-dried. (4) Grind the dried powder obtained in step (3) evenly and anneal it in air for 1-4 hours to obtain an ultrathin iodine-doped Nb2O5 catalyst.

2. The method for preparing the three-dimensional iodine-doped Nb₂O₅ catalyst assembled from ultrathin nanosheets according to claim 1, characterized in that: In step (1), the amount of ammonia added is (10-20) mL: 1 g compared to the amount of NbCl5 added.

3. The method for preparing the three-dimensional iodine-doped Nb₂O₅ catalyst assembled from ultrathin nanosheets according to claim 1, characterized in that: In step (2), the mass ratio of PVP to NbCl5 is (1-3):

1.

4. The method for preparing the three-dimensional iodine-doped Nb₂O₅ catalyst assembled from ultrathin nanosheets according to claim 1, characterized in that: The hydrothermal reaction in step (2) lasts for 12-24 hours.

5. The method for preparing the three-dimensional iodine-doped Nb₂O₅ catalyst assembled from ultrathin nanosheets according to claim 1, characterized in that: In step (3), the mass ratio of iodic acid added to NbCl5 is (0.1-0.5):

1.

6. The method for preparing the three-dimensional iodine-doped Nb₂O₅ catalyst assembled from ultrathin nanosheets according to claim 1, characterized in that: The annealing temperature in step (4) is 450-550℃.

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