Preparation method of iron-based tungstate based on chemical vapor deposition

Abstract

The invention belongs to the technical field of chemical vapor deposition, and particularly discloses a preparation method of iron-based tungstate based on chemical vapor deposition, which comprises the following steps: S1, precursor pretreatment: mixing FeCl2 and WO3 in proportion; s2, substrate pretreatment: cleaning a mica sheet, blow-drying the mica sheet with nitrogen, and then fixing the mica sheet in a chemical vapor deposition reaction chamber; s3, reaction chamber atmosphere replacement: argon is introduced for purging; s4, heating and reacting: adjusting the argon flow and the hydrogen flow, heating to 550-700 DEG C, and reacting for 5-20 minutes at a constant temperature; and S5, cooling and collecting: keeping the argon atmosphere, cooling to room temperature, and obtaining the FeWO4 nanosheet on the mica substrate. According to the preparation method of the iron-based tungstate based on the chemical vapor deposition, introduction of impurities in the synthesis process is avoided, and synthesis of high-crystallinity FeWO4 and accurate design of the FeWO4 nanosheet morphology are achieved.

Description

Technical Field

[0001] This invention relates to the field of chemical vapor deposition technology, and in particular to a method for preparing iron-based tungstates based on chemical vapor deposition. Background Technology

[0002] Tungstate-based composite oxides have emerged as potential candidate materials for highly efficient photocatalytic applications. Tungstates, with the general formula MWO4 (M representing a divalent cation), are widely used in luminescence, microwave ceramics, and catalysis due to their self-activated fluorescence effect, microwave performance, and optical properties. Because of the diversity of divalent cations, the crystal structure of MWO4 depends on the size of the cation radius. For small-radius M... 2+ Cations (such as Fe, Co, Sn, Ni) typically exhibit a monoclinic scheelite structure in MWO4; however, for large-radius M... 2+ Cations (such as Ca, Ba, Pb, and Sr) have a tetragonal scheelite structure. Currently, large-radius cationic MWO4, such as CaWO4, BaWO4, PbWO4, and SrWO4, have been synthesized using various methods. However, the band gap of these MWO4 photocatalysts is much larger than that of TiO2, making them unsuitable for practical photocatalytic applications. In contrast, small-radius cationic MWO4 has a significantly smaller band gap than TiO2, making it a potential choice for efficient solar energy utilization.

[0003] Ferrous tungstate (FeWO4), as a multifunctional material with a distorted tungstate structure, has attracted widespread attention and in-depth research. Particularly in terms of magnetic properties, single-crystal tungstate AWO4 (A=Zn, Fe, Mn) nanorods / nanowires with a scheelite structure have been successfully fabricated. Correlation analysis shows that FeWO4 microsheets exhibit excellent photocatalytic activity. FeWO4 contains a hybridization of O2p and Fe 3d orbitals, and this hybridization is widely distributed in the valence band. The conduction band floor of FeWO4 originates from empty Fe 4s orbital-like states, while the contribution of W 5d orbital-like states to the conduction band is located in a higher energy range. However, its room-temperature multiferroic nature remains controversial, and its magnetic properties are significantly affected by the Fe content. Therefore, preparing high-quality FeWO4 crystals and analyzing their magnetic properties is crucial.

[0004] In existing technologies, hydrothermal synthesis is commonly used to synthesize FeWO4 materials, which has significant limitations in terms of scale. While morphology engineering can enhance catalytic activity by controlling crystal structure, particle size, and specific surface area, current synthesis methods are difficult to scale up (especially for nanoscale materials). Furthermore, current methods struggle to guarantee crystal quality. In addition, past research has largely focused on MWO4 materials composed of single-valence metal ions (such as Cd, Zn, and Sn), while research on multi-valence metal-based MWO4 materials such as cobalt (Co), iron (Fe), and nickel (Ni) remains insufficient in terms of surface engineering and theoretical calculations. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing iron-based tungstates based on chemical vapor deposition, avoiding the introduction of impurities during the synthesis process, achieving the synthesis of highly crystalline FeWO4 and the precise design of FeWO4 nanosheet morphology.

[0006] To achieve the above objectives, the present invention provides a method for preparing iron-based tungstates based on chemical vapor deposition, comprising the following steps: S1. Precursor pretreatment: Mix FeCl2 and WO3 in proportion; S2. Substrate pretreatment: The mica sheet is cleaned, dried with nitrogen, and then fixed in the chemical vapor deposition reaction chamber. S3. Atmosphere replacement in the reaction chamber: Argon gas is introduced for purging; S4. Heating and reaction: Adjust the argon and hydrogen flow rates, heat to 550~700℃, and react at a constant temperature for 5~20 minutes. S5. Cooling and Collection: Keep the argon atmosphere at room temperature to obtain FeWO4 nanosheets on the mica substrate.

[0007] Preferably, in S1, the mass ratio of FeCl2 to WO3 is 5:8. Preferably, S3 specifically comprises: After closing the reaction chamber, purge with 50-200 sccm of argon gas for 30 minutes.

[0008] Preferably, in S4, the argon flow rate is 20 sccm, the hydrogen flow rate is 0~2 sccm, and the heating rate is 3~8℃ / min.

[0009] Preferably, S4 is as follows: Adjust the argon flow rate to 20 sccm and the hydrogen flow rate to 0 sccm, heat to 600℃ at a rate of 5℃ / min, and react at a constant temperature for 5~20 min.

[0010] Preferably, S4 is as follows: Adjust the argon flow rate to 20 sccm and the hydrogen flow rate to 2 sccm, heat to 700℃ at a rate of 5℃ / min, and react at a constant temperature for 5~20 min.

[0011] Preferably, S4 is as follows: Adjust the argon flow rate to 20 sccm and the hydrogen flow rate to 0.2 sccm, heat to 620℃ at a rate of 5℃ / min, and react at a constant temperature for 5~20 min.

[0012] Therefore, the present invention employs the above-mentioned method for preparing iron-based tungstates based on chemical vapor deposition, which has the following beneficial effects: The product of this invention exhibits excellent purity: Ferrous chloride and tungsten trioxide are used as precursors, mica as the growth substrate, and chemical vapor deposition is employed. The FeWO4 grows after nucleation on the substrate, avoiding the introduction of impurities during synthesis. The product shows only the standard characteristic peaks of FeWO4 and a weak mica substrate signal, with no WO3 (714 cm⁻¹). -1 Characteristic peaks), Fe2O3 (225 cm⁻¹) -1 Impurity phases (characteristic peaks, etc.) are used to synthesize FeWO4 with high crystallinity.

[0013] This invention features high precision in morphology control: different shapes emerge under the influence of hydrogen gas flow rate and temperature. By controlling the growth temperature and the flow rates of precursor argon and hydrogen, precise morphology design of FeWO4 nanosheets is achieved. As the temperature continuously increases from 600℃ to 700℃, the size of the nanosheets continuously increases, enabling a precise transformation from dispersed small flakes (600℃, 0 sccm H2) to long rod-shaped aggregates (700℃, 2 sccm H2), with a grain size variation coefficient ≤15%. The high-density flake-like product with a small amount of slender rod-like products prepared under conditions of 620℃ and 0.2 sccm H2 provides a structural basis for its applications in catalysis, sensing, and other fields.

[0014] This invention is green and environmentally friendly: the reaction process only generates HCl gas (which can be neutralized and treated by the chamber tail gas absorption device), with no heavy metal ion emissions. Argon is used as a protective gas, avoiding the use of toxic gases and reducing the risk of environmental pollution.

[0015] The CVD process of this invention has the foundation for large-scale scale-up, breaking through the technical bottleneck of traditional hydrothermal methods that make it difficult to mass-produce nanoscale FeWO4. It provides a new path for the large-scale preparation of multivalent metal-based MWO4 materials. FeWO4 nanosheets with different morphologies can specifically meet the needs of multiple fields, providing high-performance material support for strategic emerging industries such as new energy and environmental protection, and has significant social application value.

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of an apparatus for an embodiment of a method for preparing iron-based tungstates based on chemical vapor deposition according to the present invention; Figure 2 These are morphology images of FeWO4 nanosheets at different growth temperatures in an embodiment of a method for preparing iron-based tungstates based on chemical vapor deposition according to the present invention, wherein (a) is the morphology image of Example 1, (b) is the morphology image of Example 2, (c) is the morphology image of Example 3, and (d) is the morphology image of Example 4. Figure 3 These are morphology images of FeWO4 nanosheets under different hydrogen flow rates in an embodiment of the preparation method of iron-based tungstate based on chemical vapor deposition of the present invention, wherein (a) is the morphology image of Example 5, (b) is the morphology image of Example 6, (c) is the morphology image of Example 7, and (d) is the morphology image of Example 8. Figure 4 This is a Raman spectrum of an embodiment of the preparation method of iron-based tungstate based on chemical vapor deposition according to the present invention; Figure 5 This is an energy dispersive X-ray spectroscopy (EDS) spectrum of an embodiment of the preparation method of iron-based tungstate based on chemical vapor deposition of the present invention, wherein (a) is the full EDS spectrum, (b) is the W (tungsten) element ratio spectrum, (c) is the O (oxygen) element ratio spectrum, and (d) is the Fe (iron) element ratio spectrum. Figure 6 This is a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of an embodiment of the preparation method of iron-based tungstate based on chemical vapor deposition of the present invention, wherein (a) is a low-magnification image and (b) is a magnified image of a portion of (a). Figure 7 This is an example of the atomic-level EDS mapping test results of an embodiment of the preparation method of iron-based tungstate based on chemical vapor deposition of the present invention, wherein (a) is the EDS mapping diagram of O element, (b) is the EDS mapping diagram of W element, (c) is the EDS mapping diagram of Fe element, and (d) is the superimposed diagram of Fe / W / O elements. Detailed Implementation

[0018] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0020] In the following embodiments, chemical vapor deposition (CVD) was used to synthesize iron-based tungstates. The structure of the CVD apparatus is as follows: Figure 1 As shown. In the following embodiments, ferrous chloride and tungsten trioxide were used as precursors, and mica was used as the growth substrate. The chemical reactions that occurred during the experiment were as follows: FeCl3(g)+WO3(g)+3H2(g)→FeWO4(s)+3HCl(g) Example 1: An iron-based tungstate based on chemical vapor deposition, with T=600℃ and H2=1sccm, is prepared as follows: S1. Precursor pretreatment: Take 0.5g of analytical grade FeCl2 and 0.8g of analytical grade WO3 and place them in a quartz boat.

[0021] S2. Substrate pretreatment: Take a 2cm×2cm mica sheet and fix it on the substrate support of the chemical vapor deposition (CVD) reaction chamber.

[0022] S3. Atmosphere replacement in the reaction chamber: After closing the reaction chamber, purge with 50 sccm of argon gas for 30 minutes to remove oxygen and impurity gases from the reaction chamber.

[0023] S4. Heating and reaction: Adjust the argon flow rate to 20 sccm and heat to 600℃ at a rate of 5℃ / min; keep the hydrogen flow rate at 1 sccm and react at a constant temperature for 20 min.

[0024] S5. Cooling and Collection: Stop heating and keep the argon atmosphere at room temperature to obtain dispersed small-scale FeWO4 nanosheets on the mica substrate.

[0025] Example 2: An iron-based tungstate based on chemical vapor deposition, with T=620℃ and H2=1sccm, is prepared as follows: S1. Precursor pretreatment: Take 0.5g of analytical grade FeCl2 and 0.8g of analytical grade WO3 and place them in a quartz boat.

[0026] S2. Substrate pretreatment: Take a 2cm×2cm mica sheet and fix it on the substrate support of the CVD reaction chamber.

[0027] S3. Atmosphere replacement in the reaction chamber: After closing the reaction chamber, purge with 200 sccm of argon gas for 30 minutes to remove oxygen and impurity gases from the reaction chamber.

[0028] S4. Heating and reaction: Adjust the argon flow rate to 20 sccm, heat to 620℃ at a rate of 5℃ / min, introduce hydrogen at a flow rate of 1 sccm, and react at a constant temperature for 15 min.

[0029] S5. Cooling and Collection: Stop heating and keep the argon atmosphere at room temperature to obtain high-density sheet-like + a small amount of slender rod-like FeWO4 nanosheets on the mica substrate.

[0030] Example 3: An iron-based tungstate based on chemical vapor deposition, with T=650℃ and H2=1sccm, is prepared as follows: S1. Precursor pretreatment: Take 0.5g of analytical grade FeCl2 and 0.8g of analytical grade WO3 and place them in a quartz boat.

[0031] S2. Substrate pretreatment: Take a 2cm×2cm mica sheet and fix it on the substrate support of the CVD reaction chamber.

[0032] S3. Atmosphere replacement in the reaction chamber: After closing the reaction chamber, purge with 200 sccm of argon gas for 30 minutes to remove oxygen and impurity gases from the reaction chamber.

[0033] S4. Heating and reaction: Adjust the argon flow rate to 20 sccm, heat to 650℃ at a rate of 5℃ / min, introduce hydrogen at a flow rate of 1 sccm, and react at a constant temperature for 10 min.

[0034] S5. Cooling and Collection: Stop heating and keep the argon atmosphere at room temperature to obtain high-density sheet-like + a small amount of slender rod-like FeWO4 nanosheets on the mica substrate.

[0035] Example 4: An iron-based tungstate based on chemical vapor deposition, with T=700℃ and H2=1sccm, is prepared as follows: S1. Precursor pretreatment: Take 0.5g of analytical grade FeCl2 and 0.8g of analytical grade WO3 and place them in a quartz boat.

[0036] S2. Substrate pretreatment: Take a 2cm×2cm mica sheet and fix it on the substrate support of the CVD reaction chamber.

[0037] S3. Atmosphere replacement in the reaction chamber: After closing the reaction chamber, purge with 200 sccm of argon gas for 30 minutes to remove oxygen and impurity gases from the reaction chamber.

[0038] S4. Heating and reaction: Adjust the argon flow rate to 20 sccm, heat to 700℃ at a rate of 5℃ / min, introduce hydrogen at a flow rate of 1 sccm, and react at a constant temperature for 10 min.

[0039] S5. Cooling and Collection: Stop heating and keep the argon atmosphere at room temperature to obtain long rod-shaped, aggregated FeWO4 nanosheets on the mica substrate.

[0040] Example 5: An iron-based tungstate based on chemical vapor deposition is prepared using the same method as in Example 1, except that T=600℃ and H2=0sccm.

[0041] Example 6: An iron-based tungstate based on chemical vapor deposition is prepared using the same method as in Example 1, except that T=600℃ and H2=0.2sccm.

[0042] Example 7: An iron-based tungstate based on chemical vapor deposition is prepared using the same method as in Example 3, except that T=600℃ and H2=1sccm.

[0043] Example 8: An iron-based tungstate based on chemical vapor deposition is prepared using the same method as in Example 1, except that T=600℃ and H2=2sccm.

[0044] Experimental testing: The FeWO4 nanosheets prepared in Examples 1 to 8 were analyzed by microscopic morphology analysis, and the results are as follows: Figures 2-3 As shown.

[0045] Depend on Figure 2 The evolution of the microstructure of the target material under different preparation temperatures (labeled as T) is as follows: When the temperature T=600℃, the number of crystals in the system is small, and they are dispersed small flake / short strip grains with good size uniformity and a clean background substrate; when the temperature is increased to T=620℃, the crystal density increases significantly, the proportion of flake grains increases, and a small number of slender rod-shaped crystals appear, with a slight tendency for local agglomeration; when the temperature is increased to T=650℃, the crystals are mainly short rod-shaped, the grain size increases slightly, and some crystal surfaces show differences in optical contrast (such as blue areas), and the proportion of impurity particles in the system increases slightly; when the temperature is further increased to T=700℃, the crystal morphology is mainly long rod-shaped and irregular strip-shaped, the grain agglomeration phenomenon is significantly enhanced, and a small number of irregular crystals (such as those with protruding structures) appear, with the overall distribution density reaching the peak under this series of conditions.

[0046] Depend on Figure 3It can be seen that the microstructure of the crystal material prepared under different hydrogen flow rates changes as follows: When the hydrogen flow rate H2 = 0 sccm, the material exhibits a large number of dispersed plate-like / short rod-shaped crystals with relatively uniform grain size distribution and no obvious impurities in the background substrate; as the hydrogen flow rate increases to H2 = 0.2 sccm, the crystal aggregation slightly increases, a small number of slender rod-shaped grains appear locally, and the crystal color (optical contrast) shows differences; when H2 = 1 sccm, the crystal morphology is mainly short rod-shaped, the overall grain size is slightly reduced, and trace particulate impurities appear in the system; when the hydrogen flow rate is further increased to H2 = 2 sccm, the crystal morphology is mainly long rod-shaped, the grain distribution density is significantly increased, and the aggregation phenomenon between crystals is more obvious.

[0047] Raman spectroscopy analysis was performed on the FeWO4 material prepared in Example 2 (test conditions: 532 nm laser excitation, power 1 mW, scanning range 100~800 cm⁻¹). -1 ), the result is as follows Figure 4 As shown.

[0048] Depend on Figure 4 The characteristic peak assignment and phase verification are as follows: 132 cm⁻¹ -1 92cm -1 The peak corresponds to Fe in the FeWO4 crystal. 2 + -O 2- The bending vibration mode of the bond; 210cm -1 176cm -1 Peak is WO4 2- Characteristic peak of torsional vibration of functional group; 328 cm⁻¹ -1 302cm -1 Peak corresponds to WO4 2- Bending vibration mode; 401cm -1 The peak is an in-plane bending vibration peak of the FeWO4 lattice; 509 cm⁻¹ -1 533cm -1 Peak corresponds to WO4 2- The superposition mode of stretching vibrations and lattice distortion vibrations; 683cm -1 775cm -1 (Peak is WO4) 2- The antisymmetric stretching vibration characteristic peak (a hallmark of the FeWO4 phase) is shown in the figure. The weak peak marked in light blue (Mica) corresponds to the background signal of the mica substrate. There are no other impurity phase characteristic peaks, indicating that the product is high-purity FeWO4. The above characteristic peaks perfectly match the vibrational modes of the standard FeWO4 Raman spectrum, verifying the phase purity of the product.

[0049] The FeWO4 material prepared in Example 2 was characterized, and the energy-dispersive X-ray spectroscopy (EDS) spectrum is shown below. Figure 5 As shown, the image is from a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM). Figure 6 As shown, the atomic-level EDSmapping test results are as follows: Figure 7 As shown.

[0050] Depend on Figure 5 It can be seen that characteristic peaks of Fe (iron), W (tungsten), and O (oxygen) are present, with no other impurity peaks. The atomic ratio of Fe, W, and O is close to 1:1:4, indicating that the precursor reacted completely in the CVD process, with no residual impurities and meeting the purity standards. Figure 6 It can be seen that the material has a sheet-like structure, and the sheets are thick (usually a few nanometers), large in size, highly crystalline, and have ordered atomic arrangement. From... Figure 7 This indicates that Fe, W, and O are continuous and overlapping throughout the entire nanosheet, without segregation, with uniform elements and stable performance.

[0051] Therefore, the present invention adopts the above-mentioned method for preparing iron-based tungstates based on chemical vapor deposition, avoiding the introduction of impurities during the synthesis process, and realizing the synthesis of highly crystalline FeWO4 and the precise design of FeWO4 nanosheet morphology.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing iron-based tungstates based on chemical vapor deposition, characterized in that, Includes the following steps: S1. Precursor pretreatment: Mix FeCl2 and WO3 in proportion; S2. Substrate pretreatment: The mica sheet is cleaned, dried with nitrogen, and then fixed in the chemical vapor deposition reaction chamber. S3. Atmosphere replacement in the reaction chamber: Argon gas is introduced for purging; S4. Heating and reaction: Adjust the argon and hydrogen flow rates, heat to 550~700℃, and react at a constant temperature for 5~20 minutes. S5. Cooling and Collection: Keep the argon atmosphere at room temperature to obtain FeWO4 nanosheets on the mica substrate.

2. The method for preparing iron-based tungstates based on chemical vapor deposition according to claim 1, characterized in that, In S1, the mass ratio of FeCl2 to WO3 is 5:

8.

3. The method for preparing iron-based tungstates based on chemical vapor deposition according to claim 1, characterized in that, S3 specifically refers to: After closing the reaction chamber, purge with 50-200 sccm of argon gas for 30 minutes.

4. The method for preparing iron-based tungstates based on chemical vapor deposition according to claim 1, characterized in that, In S4, the argon flow rate is specifically 20 sccm, the hydrogen flow rate is specifically 0~2 sccm, and the heating rate is specifically 3~8℃ / min.

5. The method for preparing iron-based tungstates based on chemical vapor deposition according to claim 1, characterized in that, S4 specifically refers to: Adjust the argon flow rate to 20 sccm and the hydrogen flow rate to 0 sccm, heat to 600℃ at a rate of 5℃ / min, and react at a constant temperature for 5~20 min.

6. The method for preparing iron-based tungstates based on chemical vapor deposition according to claim 1, characterized in that, S4 specifically refers to: Adjust the argon flow rate to 20 sccm and the hydrogen flow rate to 2 sccm, heat to 700℃ at a rate of 5℃ / min, and react at a constant temperature for 5~20 min.

7. The method for preparing iron-based tungstates based on chemical vapor deposition according to claim 1, characterized in that, S4 specifically refers to: Adjust the argon flow rate to 20 sccm and the hydrogen flow rate to 0.2 sccm, heat to 620℃ at a rate of 5℃ / min, and react at a constant temperature for 5~20 min.

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