CaMoO4 nanoparticles, a preparation method and application thereof

Abstract

The application provides a CaMoO4 nanoparticle and a preparation method and application thereof, and belongs to the technical field of inorganic nanometer material preparation, and the method comprises the following steps: mixing calcium nitrate, ammonium heptamolybdate and oxalic acid, adding anhydrous ethanol, grinding and mixing, and then grinding into powder after low-temperature treatment at 50-60 DEG C to obtain a precursor mixture; the precursor mixture is pretreated at medium temperature for 10-15 min at 160-180 DEG C, and then taken out and ground to obtain a medium-temperature treatment powder; the medium-temperature treatment powder is calcined at high temperature for 1-3 h at 400-600 DEG C, and the heating rate is 3-7 DEG C / min to obtain the CaMoO4 nanoparticle. The oxalic acid is introduced and cooperated with a three-stage temperature process, the stoichiometric ratio of Ca:Mo is effectively maintained, the generation of by-products such as MoO3 is effectively inhibited, and pure-phase scheelite structure CaMoO4 is obtained. The obtained product has small particle size, large specific surface area and good environmental purification application prospect.

Description

Technical Field

[0001] This invention belongs to the field of inorganic nanomaterial preparation technology, specifically relating to a CaMoO4 nanoparticle, its preparation method, and its application. Background Technology

[0002] CaMoO4 is an inorganic functional material with a scheelite structure. Due to its excellent photoluminescence properties and catalytic activity, it has broad application prospects in phosphors, photocatalysts, and other fields. The material's performance is strongly dependent on its size and morphology. When the size is reduced to the nanoscale, significant quantum size effects and surface effects are observed. Therefore, the preparation of small-sized, high-purity CaMoO4 nanoparticles is of great significance.

[0003] Currently, the main methods for synthesizing CaMoO4 nanomaterials include hydrothermal synthesis, coprecipitation, sol-gel synthesis, and traditional high-temperature solid-phase synthesis. While hydrothermal and coprecipitation methods can yield nanoscale products, they are complex, costly, and require cumbersome post-processing, and are prone to introducing impurities. Traditional high-temperature solid-phase synthesis suffers from high reaction temperatures, high energy consumption, large product particles, and a tendency to agglomerate, making it difficult to obtain uniform nanoparticles.

[0004] Existing literature reports on the synthesis of similar molybdates (such as CdMoO4) using a molar ratio of metal salt:ammonium heptamolybdate:oxalic acid of 1:1:4. This ratio actually corresponds to a Ca:Mo molar ratio of 1:7, resulting in an excess of Mo and the appearance of the MoO3 impurity phase in the product.

[0005] In related syntheses, oxalic acid is often considered as a simple acidic medium or auxiliary complexing agent, but its role in regulating the final phase purity and morphology of the product is often simplified. In particular, its role as an "in-situ molecular precursor" and "nanoscale structure directing agent" is rarely systematically explained.

[0006] For heat treatment process design, conventional solid-state methods either employ direct high-temperature one-step processing or simply perform segmented drying-calcination. While these methods can sometimes yield the target product, the phase purity, particle size uniformity, and dispersibility of the product are often uncontrollable and have poor reproducibility. Therefore, there is an urgent need to develop a solid-state method with a clear principle, precise control, and the ability to stably prepare high-purity, uniform nanocrystals. Summary of the Invention

[0007] In view of this, the present invention provides CaMoO4 nanoparticles, their preparation method and application, to solve the technical problems in the prior art such as the generation of impurity phases due to improper raw material metering, large particle size and severe agglomeration of products, and uncontrollable purity and particle size uniformity.

[0008] To achieve the above-mentioned objective, this invention provides a method for preparing CaMoO4 nanoparticles, comprising the following steps: S1. Mix calcium nitrate, ammonium heptamolybdate and oxalic acid, add anhydrous ethanol, grind and mix, then treat at a low temperature of 50-60℃ and grind into powder to obtain a precursor mixture. The molar ratio of calcium nitrate, ammonium heptamolybdate and oxalic acid is 7:1:14-56. S2. The precursor mixture is pretreated at 160-180°C for 10-15 min, then taken out and ground to obtain the pretreated powder. S3. The medium-temperature treated powder is calcined at 400-600℃ for 1-3 h with a heating rate of 3-7℃ / min to obtain CaMoO4 nanoparticles.

[0009] Preferably, the molar ratio of calcium nitrate, ammonium heptamolybdate, and oxalic acid in S1 is 7:1:42.

[0010] Preferably, the low-temperature treatment time in S1 is 5-15 min.

[0011] Preferably, the temperature of the medium-temperature pretreatment in S2 is 170°C and the time is 10 min.

[0012] Preferably, the high-temperature calcination temperature in S3 is 500℃, the holding time is 2 h, and the heating rate is 5℃ / min.

[0013] The CaMoO4 nanoparticles prepared by the method of the present invention have a pure phase scheelite structure and an average particle size of 55-75 nm.

[0014] An application of the CaMoO4 nanoparticles of the present invention in the photocatalytic degradation of organic pollutants.

[0015] In the solid-phase synthesis pathway of this invention, oxalic acid dihydrate (H2C2O4·2H2O) is not merely a proton source providing an acidic environment; its role includes: (1) Chelation and in-situ calcium source sustained release: Oxalate ions (C2O4) 2- It is a strong bidentate chelating ligand that can bind to calcium ions (Ca) in solution. 2+ During the intermediate-temperature pretreatment stage (160-180°C), a highly stable calcium oxalate (CaC₂O₄·H₂O) complex is efficiently formed. This complex is uniformly dispersed in the precursor system in a solid state, and during subsequent heating, it releases Ca... 2+ The release of calcium is delayed until ammonium molybdate has partially decomposed and formed active molybdenum oxide species, thus achieving time- and space-controlled release of the calcium source. This slow-release mechanism avoids the premature release of calcium. 2+ It undergoes a local enrichment reaction with undecomposed ammonium molybdate in the low-temperature range (<200 °C).

[0016] (2) Thermal decomposition pore formation and in-situ spatial confinement: During the paste grinding stage, the oxalate complex network formed coexists with the reaction system. As the subsequent heat treatment (medium and high temperature) proceeds, oxalic acid decomposes in stages and generates gases (CO, CO2, etc.) that escape. The "gaps" left by these decomposition processes or the thermodynamic discontinuities formed around the reaction crystal nuclei constitute "physical barriers" that inhibit the free diffusion and migration of crystal particles at high temperatures, thus achieving in-situ spatial confinement.

[0017] The present invention relates to a three-stage temperature synergistic effect.

[0018] Step 1 (50-60℃ Low-Temperature Treatment): Initial Molecular Homogenization and Formation of "Solid-Phase Reaction Precursor Powder". The addition of ethanol serves a dual purpose: firstly, as a dispersion medium, it helps the solid raw materials form a homogeneous slurry during grinding, promoting uniform mixing of components at the microscale; secondly, the low surface tension of ethanol helps form a loose precursor powder during subsequent low-temperature drying, avoiding hard agglomeration caused by capillary forces. During heating at 50-60℃, ethanol gradually evaporates, and the fully dispersed salts and in-situ generated oxalate complexes undergo initial self-assembly and arrangement. After solvent removal, a uniform and dry "precursor mixture" is formed at the microscale, providing a homogeneous chemical environment for subsequent reactions—the physical basis for the homogeneity of all subsequent chemical transformations. Ethanol completely evaporates at this temperature, introducing no impurities and having no interference with subsequent reactions. This step is crucial to ensuring a uniform distribution of the macroscopic Ca:Mo ratio of 1:1. If this step is skipped, even if the raw material ratio is correct, the product will still contain the impurity phase MoO3, and the pure phase CaMoO4 cannot be obtained.

[0019] Step Two (Medium-Temperature Pretreatment at 160-180℃): Chemical Stabilization of the "Precursor" and "Consolidation and Locking" of the Ca:Mo = 1:1 Ratio. Based on the microscopically homogeneous precursor constructed in Step One, this stage is the key chemical window for achieving a pure phase. With the complete formation of calcium oxalate (CaC₂O₄·H₂O) precipitation, Ca… 2+ It binds with oxalate to form a stable solid precursor; simultaneously, Mo in the adjacent ammonium heptamolybdate... 6+Partial reduction occurs in the weakly reducing atmosphere created by oxalic acid (manifested as the powder color changing from white to blue, which serves as a visual indicator of the completion of the intermediate-temperature pretreatment), and acidic gases are released along with the partial decomposition of nitrates. The thermodynamic and kinetic pathway of the entire reaction system's transformation to the CaMoO4 crystal form is initially established. This process is equivalent to "programming" the correct elemental ratios and reaction intermediate states into the solid precursor, preparing the chemical foundation for the next step of precise nucleation. This step is crucial to ensuring the purity of the product. If the Ca:Mo atomic ratio deviates from 1:1 or this intermediate-temperature pretreatment step is skipped, a significant MoO3 impurity phase will appear in the product, making it impossible to obtain pure CaMoO4.

[0020] The third step (high-temperature calcination at 400-600℃): controlled crystallization growth based on limited "molecular modules". On the uniformly distributed and chemically stabilized Ca and Mo source "reaction units" (formed by an oxalate network) constructed in the first two steps, a final high-temperature heat treatment is used to promote the crystallization of Ca... 2+ With MoO4 2- Ion diffusion occurs within confined nanoscale regions, forming calcium molybdenum oxide tetrahedra and growing into CaMoO4 crystals with a scheelite structure. The relatively low heating rate (3-7 °C / min) provides sufficient time for uniform thermodynamic recombination, limiting sudden, heterogeneous nucleation. Combined with the previously formed network-like calcium oxalate spatial structure, this effectively suppresses severe grain boundary migration and merging, as well as large-scale agglomeration, during grain growth. The role of this temperature range is to guide crystal maturation and stabilization, rather than simply achieving a "high-temperature reaction," which differs from traditional solid-state high-temperature calcination.

[0021] Compared with the prior art, the present invention has the following beneficial effects: This invention introduces oxalic acid as a multifunctional additive, constructing a synergistic mechanism of "chelation-slow release-pore formation-confinement" in a solid-phase synthesis system. Oxalate ions form a highly stable calcium oxalate complex with calcium ions, preventing localized enrichment of calcium ions with undecomposed ammonium molybdate at low temperatures, thus inhibiting abnormal grain growth and hard agglomeration from the source. Simultaneously, oxalic acid decomposes in stages and releases gas during subsequent heat treatment, forming a thermodynamically discontinuous interface around the reaction nuclei, constituting a physical barrier that inhibits the free diffusion and migration of crystal particles.

[0022] This invention utilizes oxalic acid-Ca 2+The synergistic effect of the chelation system and the three-stage temperature process ensures the effective maintenance of the Ca:Mo stoichiometric ratio of 1:1 throughout the entire reaction. The microscopic homogenization treatment in the low-temperature stage eliminates macroscopic imbalances caused by solid-phase mixing deviations; the chemical stabilization in the medium-temperature stage "locks" the correct elemental ratios within the solid precursor; and the high-temperature stage completes crystallization growth within a confined space. These mechanisms collectively ensure that the product is a pure-phase scheelite structure CaMoO4, effectively suppressing the formation of thermodynamic byproducts such as MoO3, resulting in a product with high phase purity and good crystallinity.

[0023] The CaMoO4 nanoparticles obtained by this invention have the structural characteristics of small particle size, large specific surface area and abundant surface active sites. Under simulated sunlight irradiation, they exhibit highly efficient photocatalytic degradation activity for organic dyes (such as crystal violet), with a removal rate of over 90%, and have good prospects for environmental purification applications. Attached Figure Description

[0024] Figure 1 The X-ray diffraction pattern of the CaMoO4 nanoparticles prepared in Example 3; Figure 2 The images show the XRD patterns of the CaMoO4 nanoparticles prepared in Examples 1-4 and Comparative Example 1. Figure 3 Here is a SEM image of the CaMoO4 nanoparticles prepared in Example 1; Figure 4 Here is a SEM image of the CaMoO4 nanoparticles prepared in Example 2; Figure 5 Here is a SEM image of the CaMoO4 nanoparticles prepared in Example 3; Figure 6 Here is a SEM image of the CaMoO4 nanoparticles prepared in Example 4; Figure 7 SEM image of the CaMoO4 nanoparticles prepared in Comparative Example 1. Figure 8 The image shows the XRD pattern of the CaMoO4 nanoparticles prepared in Comparative Example 2. Figure 9 The image shows the XRD pattern of the CaMoO4 nanoparticles prepared in Comparative Example 3. Figure 10 The image shows the XRD pattern of the CaMoO4 nanoparticles prepared in Comparative Example 4. Figure 11 The image shows the XRD pattern of the CaMoO4 nanoparticles prepared in Comparative Example 5. Figure 12 The image shows the XRD pattern of the CaMoO4 nanoparticles prepared in Comparative Example 6. Figure 13The image shows the XRD pattern of the CaMoO4 nanoparticles prepared in Comparative Example 7. Figure 14 SEM image of the CaMoO4 nanoparticles prepared in Comparative Example 8; Figure 15 The graphs show the photocatalytic degradation of crystal violet dye by the CaMoO4 nanoparticles prepared in Examples 3, 7, and 8. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] The calcium nitrate used in the following examples and comparative examples is calcium nitrate tetrahydrate (Ca(NO3)2·4H2O), analytical grade; the ammonium heptamolybdate is ammonium heptamolybdate tetrahydrate ((NH4)6Mo7O). 24 ·4H2O), analytical grade; oxalic acid is oxalic acid dihydrate (H2C2O4·2H2O), analytical grade; anhydrous ethanol, analytical grade.

[0027] Example 1 A method for preparing CaMoO4 nanoparticles includes the following steps: S1. Weigh the raw materials according to the molar ratio of calcium nitrate: ammonium heptamolybdate: oxalic acid = 7:1:14. Weigh 0.23615 g (1 mmol) of calcium nitrate tetrahydrate, 0.17655 g (0.142 mmol) of ammonium heptamolybdate tetrahydrate and 0.2521 g (2 mmol) of oxalic acid dihydrate. Place the calcium nitrate, ammonium heptamolybdate and oxalic acid in an agate mortar and grind and mix for 10 min. Add 2 mL of anhydrous ethanol and continue grinding for 10 min to form a uniform slurry. Pour the slurry into a crucible and treat it at 50℃ for 10 min. Then grind it into powder to obtain the precursor mixture. S2. The precursor mixture is pretreated at 160°C for 15 min, then taken out and ground to obtain the pretreated powder. S3. The medium-temperature treated powder is placed in a muffle furnace and calcined at 400°C for 3 h at a heating rate of 3°C / min. After cooling, CaMoO4 nanoparticles are obtained.

[0028] Example 2 A method for preparing CaMoO4 nanoparticles includes the following steps: S1. Weigh the raw materials according to the molar ratio of calcium nitrate: ammonium heptamolybdate: oxalic acid = 7:1:28. Weigh 0.23615 g (1 mmol) of calcium nitrate tetrahydrate, 0.17655 g (0.142 mmol) of ammonium heptamolybdate tetrahydrate and 0.5043 g (4 mmol) of oxalic acid dihydrate. Place the calcium nitrate, ammonium heptamolybdate and oxalic acid in an agate mortar and grind and mix for 10 min. Add 2 mL of anhydrous ethanol and continue grinding for 10 min to form a uniform slurry. Pour the slurry into a crucible and treat it at a low temperature of 60℃ for 5 min. Then grind it into powder to obtain the precursor mixture. S2. The precursor mixture is pretreated at 180°C for 10 min, then taken out and ground to obtain the pretreated powder. S3. The medium-temperature treated powder is placed in a muffle furnace and calcined at 600°C for 1 hour with a heating rate of 7°C / min. After cooling, CaMoO4 nanoparticles are obtained.

[0029] Example 3 A method for preparing CaMoO4 nanoparticles includes the following steps: S1. Weigh the raw materials according to the molar ratio of calcium nitrate: ammonium heptamolybdate: oxalic acid = 7:1:42. Weigh 0.23615 g (1 mmol) of calcium nitrate tetrahydrate, 0.17655 g (0.142 mmol) of ammonium heptamolybdate tetrahydrate and 0.7564 g (6 mmol) of oxalic acid dihydrate. Place the calcium nitrate, ammonium heptamolybdate and oxalic acid in an agate mortar and grind and mix for 10 min. Add 2 mL of anhydrous ethanol and continue grinding for 10 min to form a uniform slurry. Pour the slurry into a crucible and treat it at 50℃ for 10 min. Then grind it into powder to obtain the precursor mixture. S2. The precursor mixture is pretreated at 170°C for 10 min, then taken out and ground to obtain the pretreated powder. S3. The medium-temperature treated powder is placed in a muffle furnace and calcined at 500°C for 2 hours at a heating rate of 5°C / min. After cooling, CaMoO4 nanoparticles are obtained, and their X-ray diffraction pattern is shown below. Figure 1 It appears as pure phase CaMoO4.

[0030] Example 4 A method for preparing CaMoO4 nanoparticles includes the following steps: S1. Weigh the raw materials according to the molar ratio of calcium nitrate: ammonium heptamolybdate: oxalic acid = 7:1:56. Weigh 0.23615 g (1 mmol) of calcium nitrate tetrahydrate, 0.17655 g (0.142 mmol) of ammonium heptamolybdate tetrahydrate and 1.0086 g (8 mmol) of oxalic acid dihydrate. Place the calcium nitrate, ammonium heptamolybdate and oxalic acid in an agate mortar and grind and mix for 10 min. Add 2 mL of anhydrous ethanol and continue grinding for 10 min to form a uniform slurry. Pour the slurry into a crucible and treat it at 55℃ for 15 min. Then grind it into powder to obtain the precursor mixture. S2. The precursor mixture is pretreated at 170°C for 12 min, then taken out and ground to obtain the pretreated powder. S3. The medium-temperature treated powder is placed in a muffle furnace and calcined at 500°C for 2 h at a heating rate of 5°C / min. After cooling, CaMoO4 nanoparticles are obtained.

[0031] Comparative Example 1 This comparative example is similar to Example 1, except that the amount of oxalic acid dihydrate in this comparative example is 0 g (0 mmol).

[0032] Figure 2 The X-ray diffraction (XRD) patterns of the CaMoO4 nanoparticles prepared in Examples 1-4 and Comparative Example 1 are shown below. Figures 3 to 7 The images show scanning electron microscope (SEM) images of the CaMoO4 nanoparticles prepared in Examples 1, 2, 3, 4, and Comparative Example 1 of this invention. The product obtained in Example 1 is pure-phase CaMoO4, with an average particle size of approximately 65 nm as observed by SEM. The product obtained in Example 2 is pure-phase CaMoO4, with an average particle size of approximately 65 nm as observed by SEM. The product obtained in Example 3 is pure-phase CaMoO4, with an average particle size of approximately 55 nm as observed by SEM. The product obtained in Example 4 is pure-phase CaMoO4, with an average particle size of approximately 75 nm as observed by SEM. The product obtained in Comparative Example 1 is also pure-phase CaMoO4, but SEM observation shows severe particle aggregation and a larger particle size, approximately 120 nm.

[0033] Without oxalic acid (Comparative Example 1), Ca 2+ From the outset, it is uniformly distributed in the system as a soluble salt. Although it can eventually complete the reaction to form pure-phase CaMoO4 through solid-phase diffusion, the lack of a calcium source for slow release constrains the Ca... 2+At low temperatures, the reaction with Mo species occurs over a large area, resulting in low nucleation density, unrestricted grain growth, and severe agglomeration of the final product with a large particle size (~120 nm). In contrast, in Examples 1-4, the calcium source slow-release effect induced by oxalic acid synergistically works with the subsequent thermal decomposition pore-forming effect, thereby effectively controlling the product particle size to the range of 55-75 nm.

[0034] Comparative Example 2 Weigh the raw materials according to the molar ratio of calcium nitrate:ammonium heptamolybdate:oxalic acid = 1:1:4. Weigh 0.23615 g (1 mmol) of calcium nitrate tetrahydrate, 1.236 g (1 mmol) of ammonium heptamolybdate tetrahydrate, and 0.75642 g (6 mmol) of oxalic acid dihydrate. Place the above raw materials in an agate mortar and grind and mix for 10 min. Add 2 mL of anhydrous ethanol and continue grinding for 10 min to form a uniform slurry. Pour the slurry into a crucible and heat in a 60°C oven for 10 min, then transfer it to a 170°C hot plate and heat for another 10 min. Transfer the resulting powder into a muffle furnace and heat to 500°C at a rate of 5°C / min, hold for 2 h, and allow to cool naturally. Figure 8 The XRD pattern of the obtained product shows obvious characteristic diffraction peaks of MoO3 in addition to the characteristic peaks of CaMoO4, indicating that the product is a mixture of CaMoO4 and MoO3, and is not a pure phase. This is because the Ca:Mo atomic ratio is 1:7 at this ratio, with Mo in severe excess.

[0035] Comparative Example 3 This comparative example is similar to Example 3, except that in S1 of this comparative example, the slurry is poured into a crucible and ground into powder after being treated at room temperature (i.e., without low-temperature treatment at 50-60°C) to obtain a precursor mixture. Figure 9 The XRD pattern of the obtained product shows that, in addition to the characteristic peaks of CaMoO4, there are obvious characteristic diffraction peaks of MoO3, indicating that skipping the low-temperature treatment step will result in the formation of the MoO3 impurity phase in the product, and pure phase CaMoO4 cannot be obtained.

[0036] Comparative Example 4 This comparative example is similar to Example 3, except that step S2 (i.e., no medium-temperature pretreatment at 160-180°C) is performed in this comparative example, and the precursor mixture obtained in S1 is directly calcined at high temperature. Figure 10 The XRD pattern of the obtained product shows that the product contains two phases, CaMoO4 and MoO3. This indicates that skipping the intermediate temperature pretreatment step will cause the reaction path to be deviated, resulting in the formation of the thermodynamic byproduct MoO3 at the high temperature stage, and the inability to obtain pure phase CaMoO4.

[0037] Comparative Example 5 This comparative example is similar to Example 3, except that steps S1 and S2 are not included in this comparative example. The raw materials are directly mixed and ground, and then calcined at 500°C for 2 hours after being heated to 500°C at a rate of 5°C / min. Figure 11 The XRD pattern of the product shows that it contains two phases, CaMoO4 and MoO3, indicating that pure CaMoO4 cannot be obtained by traditional high-temperature solid-state reaction without low-temperature drying and medium-temperature pretreatment.

[0038] Comparative Example 6 This comparative example is the same as Example 3, except that oxalic acid is replaced with an equimolar amount of citric acid. Figure 12 The XRD pattern of the obtained product shows that although citric acid is a solid organic acid and also has the ability to complex calcium ions, the product contains a MoO3 impurity phase after it replaces oxalic acid, and the pure phase CaMoO4 cannot be obtained. The strong complexing and reducing properties of citric acid interfere with the formation of the pure phase of CaMoO4.

[0039] Comparative Example 7 This comparative example is the same as Example 3, except that oxalic acid is replaced with an equimolar amount of tartaric acid. Figure 13 The XRD pattern of the product is shown. Tartaric acid is also a solid dihydroxycarboxylic acid, but the XRD of the product shows that the product contains a MoO3 impurity phase.

[0040] In this invention, oxalic acid does not simply act as an acidic medium or complexing agent, but rather exerts its effects through a unique synergistic combination of "chelation-release-spatial confinement-reaction guidance," a combination not found in other organic acids (including citric acid, tartaric acid, etc.). The introduction of oxalic acid significantly refines the product particle size from approximately 120 nm to 55-75 nm.

[0041] Comparative Example 8 This comparative example is similar to Example 3, except that in Example S3, the medium-temperature treated powder was placed in a muffle furnace and calcined at 700°C for 2 hours at a heating rate of 5°C / min. After cooling, CaMoO4 nanoparticles were obtained. Figure 14 The SEM image shows that the particles are relatively large, with a diameter reaching the micrometer level.

[0042] Photocatalytic degradation of crystal violet test Take 10 mL of a 10 mg / L crystal violet solution and add 20 mg of CaMoO4 nanoparticles obtained in Example 3, Comparative Example 7, or Comparative Example 8. Stir in the dark for 30 min to reach adsorption-desorption equilibrium. Then, under 500 W xenon lamp irradiation, take 5 mL samples every 10 min, centrifuge, collect the supernatant, and measure the absorbance at 590 nm using a UV-Vis spectrophotometer to calculate the degradation rate. The test results are as follows: Figure 15In Example 3, the CaMoO4 nanoparticles prepared achieved a 91.5% removal rate of crystal violet within 40 min, while the degradation rate of the Comparative Example 7 sample containing the MoO3 impurity phase was only 77.62%, indicating that the presence of impurities significantly inhibited the catalytic effect. The sample obtained in Comparative Example 8 had a particle size in the micrometer range, a significantly reduced specific surface area, and a greatly reduced number of available active sites, with a degradation rate of only 9.7%. The CaMoO4 nanoparticles obtained in this invention exhibit excellent photocatalytic activity.

[0043] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing CaMoO4 nanoparticles, characterized in that, Includes the following steps: S1. Mix calcium nitrate, ammonium heptamolybdate and oxalic acid, add anhydrous ethanol, grind and mix, then treat at a low temperature of 50-60℃ and grind into powder to obtain a precursor mixture. The molar ratio of calcium nitrate, ammonium heptamolybdate and oxalic acid is 7:1:14-56. S2. The precursor mixture is pretreated at 160-180°C for 10-15 min, then taken out and ground to obtain the pretreated powder. S3. The medium-temperature treated powder is calcined at 400-600℃ for 1-3 h with a heating rate of 3-7℃ / min to obtain CaMoO4 nanoparticles.

2. The method according to claim 1, characterized in that, The molar ratio of calcium nitrate, ammonium heptamolybdate, and oxalic acid in S1 is 7:1:

42.

3. The method according to claim 1, characterized in that, The low-temperature treatment time described in S1 is 5-15 min.

4. The method according to claim 1, characterized in that, The temperature for the medium-temperature pretreatment described in S2 is 170°C, and the time is 10 min.

5. The method according to claim 1, characterized in that, The high-temperature calcination described in S3 is at a temperature of 500℃, a holding time of 2 h, and a heating rate of 5℃ / min.

6. A CaMoO4 nanoparticle prepared by the method according to any one of claims 1-5, characterized in that, The CaMoO4 nanoparticles have a pure phase scheelite structure and an average particle size of 55-75 nm.

7. The application of the CaMoO4 nanoparticles as described in claim 6 in the photocatalytic degradation of organic pollutants.

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