A MoO3@Pt@Fe2O3 ternary nanocomposite and its preparation method and application

Abstract

The present invention belongs to the field of photocatalysis technology, and specifically relates to a MoO3@Pt@Fe2O3 ternary nanocomposite material, a preparation method thereof, and an application. The MoO3@Pt@Fe2O3 ternary nanocomposite material is successfully synthesized by a step-by-step method. The structure of this material takes MoO3 nanorods as the core, Pt nanoparticles are supported on the surface of the MoO3 nanorods, and the Pt nanoparticles are coated with an Fe2O3 nanocoating layer, forming a very regular "sandwich" structure. This ternary catalyst has good photocatalytic activity and stability, and the Pt located between MoO3 and Fe2O3 can effectively inhibit the growth and leaching of Pt grains.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysis, and particularly relates to a MoO3@Pt@Fe2O3 ternary nanocomposite material, a preparation method thereof, and an application thereof. Background Art

[0002] In the field of photocatalysis, semiconductor photocatalysis technology has been used to treat organic dyes in wastewater due to its advantages such as greenness and high efficiency. Among existing semiconductor photocatalysts, MoO3 has attracted much attention. In addition, the band gap of Fe2O3 is about 2.2 eV, which can absorb most visible light (absorption edge ~ 600 nm), has obvious advantages over other traditional photocatalytic materials (such as TiO2, ZnO, etc.), and this material has good chemical stability, low cost, and non-toxicity in water, making it an ideal material for photocatalytic water treatment and water splitting.

[0003] In addition, noble metal materials have excellent catalytic performance and can improve photocatalytic activity, but the loss and grain growth of noble metals are the main reasons affecting their low activity. Summary of the Invention

[0004] The present invention provides a MoO3@Pt@Fe2O3 ternary nanocomposite material, which has good photocatalytic activity and stability, and can simultaneously inhibit the grain growth and loss of noble metals.

[0005] The technical solution of the present invention is as follows:

[0006] The present invention provides a MoO3@Pt@Fe2O3 ternary nanocomposite material, with MoO3 nanorods as the core, Pt nanoparticles supported on the surface, and an outermost layer of Fe2O3 nanocoating.

[0007] The size of the Pt nanoparticles in the present invention is 3 - 10 nm, the thickness of the Fe2O3 nanocoating is 5 - 10 nm, and the diameter of the MoO3 nanorods is 100 - 150 nm.

[0008] The lattice fringe d = 0.38 nm of the MoO3 nanorods in the present invention is the (100) crystal plane of MoO3, and the lattice fringe d = 0.29 nm of the Fe2O3 nanocoating is the (110) crystal plane of Fe2O3.

[0009] The MoO3@Pt@Fe2O3 ternary nanocomposite material of the present invention is prepared through the following steps:

[0010] Pt nanoparticles were supported on MoO3 nanorods to obtain Pt@MoO3. Then, under the condition of an oil bath, an Fe(OH)3 colloidal solution was dropped into the Pt@MoO3 dispersion. After aging and calcination, a MoO3@Pt@Fe2O3 ternary nanocomposite was obtained.

[0011] In the oil bath described in the present invention, the temperature is 60 - 80 °C; for the aging, the time is 1 - 3 h; the calcination is carried out at 300 - 400 °C for 3 - 5 h.

[0012] In the present invention, the loading amount of the Pt nanoparticles is 0.25% - 0.75% of the addition amount of MoO3, and the molar ratio of Fe(OH)3 to MoO3 nanorods is 0.2 - 0.4:1.

[0013] The Fe(OH)3 colloidal solution described in the present invention is obtained by adding ammonium ferric sulfate to hot water and then filtering.

[0014] The Pt@MoO3 in the present invention is specifically obtained by impregnating MoO3 nanorods with the same volume in a solution of H2PtCl6·6H2O for 2 - 5 h.

[0015] The present invention also provides the application of the MoO3@Pt@Fe2O3 ternary nanocomposite in the degradation of organic pollutants.

[0016] The application described in the present invention is the application of the MoO3@Pt@Fe2O3 ternary nanocomposite in improving the degradation rate of methylene blue in the visible light region.

[0017] Beneficial effects

[0018] Compared with the conventional technology, Pt nanoparticles were successfully supported in the MoO3@Fe2O3 biphasic interlayer by a stepwise method, and the growth and leaching of Pt grains could be effectively inhibited;

[0019] For the MoO3@Pt@Fe2O3 ternary nanocomposite, the Pt nanoparticles located at the interlayer position improved the performance of MoO3@Fe2O3, and showed good photocatalytic activity and stability in the degradation of methylene blue in the visible light region. Description of the drawings

[0020] Figure 1 XRD patterns of MoO3@Fe2O3 and MoO3@0.5%Pt@Fe2O3 samples

[0021] Figure 2Morphology structure diagram of the MoO3@0.5%Pt@Fe2O3 ternary nanocomposite prepared in Example 2, where (a) and (b) are TEM photos of MoO3@0.5%Pt@Fe2O3, and (c) and (d) are HRTEM photos of MoO3@0.5%Pt@Fe2O3.

[0022] Figure 3 TEM photo of the 0.5%Pt@MoO3@Fe2O3 ternary nanocomposite prepared in Comparative Example 2

[0023] Figure 4 Photocatalytic degradation curves of methylene blue by MoO3@Fe2O3, MoO3@Pt@Fe2O3 with different Pt loadings, and 0.5%Pt@MoO3@Fe2O3

[0024] Figure 5 Stability of photocatalytic degradation of methylene blue by MoO3@0.5%Pt@Fe2O3

[0025] Figure 6 UV-visible absorption spectra of MoO3, MoO3@Fe2O3, and MoO3@0.5%Pt@Fe2O3 samples Detailed implementation manners

[0026] The following examples are intended to illustrate the present invention rather than further limit the present invention.

[0027] The present invention provides a MoO3@Pt@Fe2O3 ternary nanocomposite with a MoO3 nanorod as the core, Pt nanoparticles supported on the surface, and an Fe2O3 nanocoating on the outermost layer.

[0028] Preferably, the size of the Pt nanoparticles is 3 - 10 nm, the thickness of the Fe2O3 nanocoating is 5 - 10 nm, and the diameter of the MoO3 nanorods is 100 - 150 nm.

[0029] Preferably, the lattice fringe d = 0.38 nm of the MoO3 nanorods is the (100) crystal plane of MoO3, and the lattice fringe d = 0.29 nm of the Fe2O3 nanocoating is the (110) crystal plane of Fe2O3.

[0030] The MoO3@Pt@Fe2O3 ternary nanocomposite of the present invention is prepared through the following steps:

[0031] Pt nanoparticles are supported on MoO3 nanorods to obtain Pt@MoO3. Then, under the condition of an oil bath, an Fe(OH)3 colloidal solution is dropped into the Pt@MoO3 dispersion. After aging and calcination, a MoO3@Pt@Fe2O3 ternary nanocomposite is obtained.

[0032] Preferably, the Pt@MoO3 is specifically obtained by isovolumetric impregnation of MoO3 nanorods in a solution of H2PtCl6·6H2O for 2 - 5 h.

[0033] Preferably, the loading amount of the Pt nanoparticles is 0.25% - 0.75% of the addition amount of MoO3, preferably 0.25% - 0.5%, and most preferably 0.5%. The molar ratio of Fe(OH)3 to MoO3 nanorods is 0.2 - 0.4:1.

[0034] Preferably, the Fe(OH)3 colloidal solution is obtained by adding ammonium ferric sulfate to 80 mL of hot water at 70 °C and filtering. Preferably, the concentration of the Fe(OH)3 colloidal solution is 0.025 mol / L.

[0035] Preferably, the temperature of the oil bath is 60 - 80 °C; the aging time is 1 - 3 h; the calcination is carried out at 300 - 400 °C for 3 - 5 h.

[0036] The present invention also provides the application of the MoO3@Pt@Fe2O3 ternary nanocomposite in the degradation of organic pollutants.

[0037] Preferably, the application is the application of the MoO3@Pt@Fe2O3 ternary nanocomposite in improving the photocatalytic performance of methylene blue in the visible light region.

[0038] Preferably, the application is the application of the MoO3@Pt@Fe2O3 ternary nanocomposite in improving the degradation rate of methylene blue in the visible light region.

[0039] Example 1

[0040] The present invention provides a MoO3@Pt@Fe2O3 ternary nanocomposite, which is prepared by the following steps:

[0041] (1) Preparation of MoO3 nanorods: 4.5 g of ammonium molybdate is placed in a muffle furnace and calcined at 400 °C for 5 h in an air atmosphere to obtain MoO3. Take 1.44 g of the calcined MoO3 in a beaker, add an H2O2 solution, stir at room temperature for 4 h, then add an HNO3 solution, continue to stir for 20 min, and carry out a solvothermal reaction at 150 °C for 48 h to obtain MoO3 nanorods, where the molar ratio of H2O2 to HNO3 is 1:1;

[0042] (2) Preparation of Pt@MoO3: MoO3 nanorods were impregnated in an equal volume of H2PtCl6·6H2O solution for 5 h, with the loading amount of Pt nanoparticles being 0.5% of the added amount of MoO3. The obtained Pt@MoO3 was denoted as 0.5% Pt@MoO3;

[0043] (3) Preparation of MoO3@0.5% Pt@Fe2O3 ternary nanocomposite: Under the condition of an 80 °C oil bath, an Fe(OH)3 colloidal solution was dropped into the 0.5% Pt@MoO3 dispersion. After aging for 2 h, it was calcined at 350 °C for 4 h to obtain the MoO3@0.5% Pt@Fe2O3 ternary nanocomposite, where the molar ratio of Fe(OH)3 to MoO3 nanorods was 0.3:1.

[0044] Example 2

[0045] (1) Preparation of MoO3 nanorods: 4.5 g of ammonium molybdate was placed in a muffle furnace and calcined at 500 °C for 5 h in an air atmosphere to obtain MoO3. 1.44 g of the calcined MoO3 was taken in a beaker, and H2O2 solution was added. After stirring at room temperature for 6 h, HNO3 solution was added, and stirring was continued for 30 min. Then, a solvothermal reaction was carried out at 170 °C for 45 h to obtain MoO3 nanorods, where the molar ratio of H2O2 to HNO3 was 1:1.5;

[0046] (2) Preparation of Pt@MoO3: MoO3 nanorods were impregnated in an equal volume of H2PtCl6·6H2O solution for 4 h, with the loading amount of Pt nanoparticles being 0.5% of the added amount of MoO3. The obtained Pt@MoO3 was denoted as 0.5% Pt@MoO3;

[0047] (3) Preparation of MoO3@0.5% Pt@Fe2O3 ternary nanocomposite: Under the condition of a 70 °C oil bath, an Fe(OH)3 colloidal solution was dropped into the 0.5% Pt@MoO3 dispersion. After aging for 1 h, it was calcined at 400 °C for 3 h to obtain the MoO3@0.5% Pt@Fe2O3 ternary nanocomposite, where the molar ratio of Fe(OH)3 to MoO3 nanorods was 0.2:1.

[0048] Example 3

[0049] (1) Preparation of MoO3 nanorods: 4.5 g of ammonium molybdate was placed in a muffle furnace and calcined at 550 °C for 5 h in an air atmosphere to obtain MoO3. 1.44 g of the calcined MoO3 was taken in a beaker, and H2O2 solution was added. After stirring at room temperature for 7 h, HNO3 solution was added, and stirring was continued for 60 min. Then, a solvothermal reaction was carried out at 160 °C for 24 h to obtain MoO3 nanorods, where the molar ratio of H2O2 to HNO3 was 1:2;

[0050] (2) Preparation of Pt@MoO3: MoO3 nanorods were impregnated in an equal volume of H2PtCl6·6H2O solution for 2 h, where the loading amount of Pt nanoparticles was 0.5% of the added amount of MoO3. The obtained Pt@MoO3 was denoted as 0.5% Pt@MoO3;

[0051] (3) Preparation of MoO3@0.5% Pt@Fe2O3 ternary nanocomposite: Under the condition of an oil bath at 60 °C, an Fe(OH)3 colloidal solution was dropped into the 0.5% Pt@MoO3 dispersion. After aging for 3 h, it was calcined at 300 °C for 5 h to obtain the MoO3@0.5% Pt@Fe2O3 ternary nanocomposite, where the molar ratio of Fe(OH)3 to MoO3 nanorods was 0.4:1.

[0052] Example 4

[0053] (1) Preparation of MoO3 nanorods: 4.5 g of ammonium molybdate was placed in a muffle furnace and calcined at 500 °C for 5 h in an air atmosphere to obtain MoO3. 1.44 g of the calcined MoO3 was taken in a beaker, and an H2O2 solution was added. It was stirred at room temperature for 6 h, then an HNO3 solution was added, and stirring was continued for 30 min. Then, a solvothermal reaction was carried out at 170 °C for 45 h to obtain MoO3 nanorods, where the molar ratio of H2O2 to HNO3 was 1:1.5;

[0054] (2) Preparation of Pt@MoO3: MoO3 nanorods were impregnated in an equal volume of H2PtCl6·6H2O solution for 4 h, where the loading amount of Pt nanoparticles was 0.25% of the added amount of MoO3. The obtained Pt@MoO3 was denoted as 0.25% Pt@MoO3;

[0055] (3) Preparation of MoO3@0.25% Pt@Fe2O3 ternary nanocomposite: Under the condition of an oil bath at 70 °C, an Fe(OH)3 colloidal solution was dropped into the 0.25% Pt@MoO3 dispersion. After aging for 1 h, it was calcined at 400 °C for 3 h to obtain the MoO3@0.25% Pt@Fe2O3 ternary nanocomposite, where the molar ratio of Fe(OH)3 to MoO3 nanorods was 0.2:1.

[0056] Example 5

[0057] (1) Preparation of MoO3 nanorods: 4.5 g of ammonium molybdate was placed in a muffle furnace and calcined at 500 °C for 5 h in an air atmosphere to obtain MoO3; 1.44 g of the calcined MoO3 was taken in a beaker, H2O2 solution was added, and stirred at room temperature for 6 h. Then, HNO3 solution was added and stirred for another 30 min. After that, a solvothermal reaction was carried out at 170 °C for 45 h to obtain MoO3 nanorods, where the molar ratio of H2O2 to HNO3 was 1:1.5;

[0058] (2) Preparation of Pt@MoO3: The MoO3 nanorods were impregnated in an equal volume of H2PtCl6·6H2O solution for 4 h, where the loading amount of Pt nanoparticles was 0.75% of the addition amount of MoO3. The obtained Pt@MoO3 was denoted as 0.75% Pt@MoO3;

[0059] (3) Preparation of MoO3@0.75% Pt@Fe2O3 ternary nanocomposite: Under the condition of an oil bath at 70 °C, the Fe(OH)3 colloidal solution was dropped into the 0.75% Pt@MoO3 dispersion. After aging for 1 h, it was calcined at 400 °C for 3 h to obtain the MoO3@0.75% Pt@Fe2O3 ternary nanocomposite, where the molar ratio of Fe(OH)3 to MoO3 nanorods was 0.2:1.

[0060] Comparative Example 1

[0061] Compared with Example 2, Comparative Example 1 provides a MoO3@Fe2O3 binary nanocomposite without Pt loading. In the preparation method, step (2) is absent. Instead, the Fe(OH)3 colloidal solution is dropped into the MoO3 dispersion for aging, and the remaining operations are the same as those in Example 2, and the same reaction conditions as in Example 2 are adopted.

[0062] Comparative Example 2

[0063] Compared with Example 2, Comparative Example 2 provides a ternary nanocomposite with Pt loaded on the outer surface of MoO3@Fe2O3. Specifically:

[0064] (1) Preparation of MoO3 nanorods: 4.5 g of ammonium molybdate was placed in a muffle furnace and calcined at 500 °C for 5 h in an air atmosphere to obtain MoO3; 1.44 g of the calcined MoO3 was taken in a beaker, H2O2 solution was added, and stirred at room temperature for 6 h. Then, HNO3 solution was added and stirred for another 30 min. After that, a solvothermal reaction was carried out at 170 °C for 45 h to obtain MoO3 nanorods, where the molar ratio of H2O2 to HNO3 was 1:1.5;

[0065] (2) Preparation of MoO3@Fe2O3 binary nanocomposite: Under the condition of 70 °C oil bath, the Fe(OH)3 colloidal solution was dropped into the MoO3 dispersion. After aging for 1 h, it was calcined at 400 °C for 3 h to obtain the MoO3@Fe2O3 binary nanocomposite, where the molar ratio of Fe(OH)3 to MoO3 nanorods was 0.2:1;

[0066] (3) Preparation of 0.5%Pt@MoO3@Fe2O3: The MoO3@Fe2O3 binary nanocomposite was impregnated in an equal volume of H2PtCl6·6H2O solution for 4 h, where the loading amount of Pt nanoparticles was 0.5% of the addition amount of MoO3, and 0.5%Pt@MoO3@Fe2O3 was obtained.

[0067] Characterization of phase composition

[0068] The phases of the samples in Example 2 and Comparative Example 1 were characterized using a PANalytical X-ray powder diffractometer, with a scanning range of 15 - 70° and a scanning speed of 10° / min. As Figure 1 shown.

[0069] The diffraction peaks of the MoO3@Fe2O3 binary nanocomposite were consistent with the standard pattern of pure-phase MoO3 (standard card number JCPDS No: 05 - 0508), indicating that the main phase in the MoO3@Fe2O3 binary nanocomposite was orthorhombic MoO3. The Fe2O3 phase was not detected, probably because the content of Fe2O3 was small and the diffraction intensity was weaker compared to the MoO3 phase. The diffraction peaks of the MoO3@0.5%Pt@Fe2O3 ternary nanocomposite were the same as those of the MoO3@Fe2O3 binary nanocomposite, both being the diffraction peaks of orthorhombic MoO3, indicating that depositing Pt on the surface of MoO3 by the impregnation method and then depositing and loading Fe2O3 did not change the crystal structure of MoO3, and both Pt and Fe2O3 only modified the surface of MoO3. There were no obvious Pt diffraction peaks in the XRD pattern, mainly because the Pt loading amount was small and evenly dispersed.

[0070] Morphology characterization

[0071] The morphologies of the samples in Example 2 and Comparative Example 2 were characterized using a JEM-2100PLUS electron microscope, with a working voltage of 40 kV. As Figure 2 、 Figure 3 shown.

[0072] Figure 2Figures (a) and (b) are TEM images of MoO₃@0.5%Pt@Fe₂O₃. It can be seen that the synthesized MoO₃@0.5%Pt@Fe₂O₃ sample has a uniform nanorod morphology. The diameter of the nanorods is 100 - 150 nm. There is a coating layer on the surface of the rod-shaped sample, and the thickness of the surface coating layer is 5 - 10 nm. There are many nanoparticles sandwiched between the surface coating layer and the nanorods, and the size of the nanoparticles is 3 - 10 nm. Figures (c) and (d) are HRTEM images of MoO₃@0.5%Pt@Fe₂O₃. In (c), the lattice fringe d = 0.38 nm is attributed to the (100) crystal plane of MoO₃, and in (d), the lattice fringe d = 0.29 nm is attributed to the (110) crystal plane of Fe₂O₃. This result proves that the core of the composite material is MoO₃ nanorods, the surface coating layer is Fe₂O₃, and the interspersed nanoparticles are Pt nanoparticles.

[0073] Figure 3 Figures (a)-(d) are TEM images of 0.5%Pt@MoO₃@Fe₂O₃. The synthesized 0.5%Pt@MoO₃@Fe₂O₃ sample has a uniform nanorod morphology. The diameter of the nanorods is 100 - 150 nm. There is a coating layer on the surface of the rod-shaped sample, and the thickness of the surface coating layer is 5 - 10 nm. Many Pt nanoparticles are supported on the outer surface of the surface coating layer, and the size of the Pt nanoparticles is 3 - 10 nm.

[0074] Application

[0075] Photocatalytic performance test

[0076] The photocatalytic performance evaluation was carried out under simulated visible light (λ > 400 nm) conditions, and the reactor was a quartz flask. Test conditions: 40 mg of the sample was added to 80 mL of methylene blue solution with a concentration of 5 ppm. After dark treatment for 30 min under stirring to achieve the adsorption-desorption equilibrium between the sample and the methylene blue solution. The xenon lamp source was turned on, and the ultraviolet light with a wavelength less than 400 nm was removed through a filter. Under magnetic stirring, the solution was irradiated for 2 h. Every 20 min, 5 mL of the solution was taken, centrifuged at high speed for 5 min to remove the sample, and the supernatant was taken. The absorbance of the supernatant was measured using a UV-visible spectrophotometer to obtain the change curve of C / C₀ with time (min).

[0077] The test samples were the samples prepared in Example 2 and Comparative Example 1. In addition, the cyclic reaction performance of the sample in Example 2 was also evaluated under the same test conditions.

[0078] Figure 4The conversion rate (C / C0) of methylene blue photocatalytic degradation by MoO3@Fe2O3, MoO3@Pt@Fe2O3 with different Pt loading ratios, and 0.5% Pt@MoO3@Fe2O3 versus time (min) is shown in the change curve. From the degradation curve, it can be seen that the degradation rate of methylene blue by MoO3@0.5% Pt@Fe2O3 is close to 100% at 80 min, far higher than that of MoO3@Fe2O3 (the degradation rate is 70.1% at 120 min). Therefore, introducing an appropriate amount of Pt can greatly improve the photocatalytic performance of MoO3@0.5% Pt@Fe2O3 for methylene blue in the visible light region. Additionally, compared with MoO3@0.25% Pt@Fe2O3 and MoO3@0.75% Pt@Fe2O3, MoO3@0.5% Pt@Fe2O3 has better photocatalytic performance. Thus, the optimal Pt loading ratio is 0.5%. Compared with 0.5% Pt@MoO3@Fe2O3, MoO3@0.5% Pt@Fe2O3 has better photocatalytic performance. Therefore, the location of Pt nanoparticles between MoO3 and Fe2O3 is more conducive to the degradation of methylene blue.

[0079] The degradation rates of methylene blue by MoO3@Fe2O3, 0.5% Pt@MoO3@Fe2O3, and MoO3@Pt@Fe2O3 with different Pt loading ratios in the visible light region are shown in the following table:

[0080]

[0081] It can be seen from the above table that compared with MoO3@Fe2O3 without Pt loading (the degradation rate is 70.1% at 120 min), the degradation rates of methylene blue by MoO3@0.25% Pt@Fe2O3 (the degradation rate is 73.7% at 120 min) and MoO3@0.5% Pt@Fe2O3 (the degradation rate is 98.4% at 120 min) are improved, indicating that introducing Pt can greatly improve the photocatalytic performance of MoO3@Pt@Fe2O3 for methylene blue in the visible light region. The degradation rate of methylene blue by MoO3@0.75% Pt@Fe2O3 (the degradation rate is 68.6% at 120 min) is close to that of MoO3@Fe2O3, indicating that the Pt loading amount cannot be too much. Introducing an appropriate amount of Pt can greatly improve the photocatalytic performance of MoO3@Pt@Fe2O3 for methylene blue in the visible light region. Compared with 0.5% Pt@MoO3@Fe2O3 (the degradation rate is 62.4% at 120 min), MoO3@0.5% Pt@Fe2O3 has better photocatalytic performance. Therefore, the location of Pt nanoparticles between MoO3 and Fe2O3 is more conducive to the degradation of methylene blue.

[0082] Figure 5The stability of MoO3@0.5%Pt@Fe2O3 for photocatalytic degradation of methylene blue. In three cyclic experiments, the degradation rates of methylene blue by the MoO3@0.5%Pt@Fe2O3 ternary nanocomposite were 98.4%, 97.2%, and 95.3% respectively, without an obvious decrease. This result indicates that the prepared MoO3@0.5%Pt@Fe2O3 ternary nanocomposite has good photocatalytic activity and stability.

[0083] UV-Vis diffuse reflectance absorption spectroscopy

[0084] The UV-Vis diffuse reflectance absorption spectra of the samples in Example 2 and Comparative Example 1 were measured using a UV-Vis diffuse reflectometer from Shimadzu, Japan. The scanning range was 200 - 800 nm, with standard BaSO4 as the reference.

[0085] Figure 6 The UV-Vis diffuse reflectance absorption spectra of the pure-phase MoO3, MoO3@Fe2O3, and MoO3@0.5%Pt@Fe2O3 samples. As Figure 6 (a) shows, the absorption spectrum of pure-phase MoO3 is mainly in the ultraviolet region, while the absorption of the MoO3@Fe2O3 and MoO3@0.5%Pt@Fe2O3 composites in the visible region is significantly enhanced, and the absorption of the MoO3@0.5%Pt@Fe2O3 ternary nanocomposite in the visible region is slightly lower than that of the MoO3@Fe2O3 binary nanocomposite.

[0086] According to the relationship between the band gap of a semiconductor and the band-edge absorption: αhυ = (hυ - E g ) n , where α, h, E g and υ are the absorption coefficient, Planck's constant, photon frequency, and band-gap energy of the sample respectively. The n value of MoO3 is 1 / 2. Plotting (αhυ) 2 against hυ gives the band-gap diagrams of different samples, as shown in Figure 6 (b). After calculation, the band-gap widths of MoO3, MoO3@Fe2O3, and MoO3@0.5%Pt@Fe2O3 are 3.10, 2.47, and 2.78 eV respectively. Combining with the performance curve of methylene blue degradation, the activity of MoO3@0.5%Pt@Fe2O3 in degrading methylene blue in the visible region is significantly better than that of MoO3@Fe2O3, while the absorption of MoO3@0.5%Pt@Fe2O3 in the visible region is lower than that of MoO3@Fe2O3, indicating that Pt plays a very crucial role in the MoO3@0.5%Pt@Fe2O3 ternary nanocomposite.

Claims

1. A MoO3@Pt@Fe2O3 ternary nanocomposite, characterized in that, With MoO3 nanorods as the core, Pt nanoparticles are supported on the surface of the MoO3 nanorods, and the Pt nanoparticles are coated with an Fe2O3 nanocoating.

2. The MoO3@Pt@Fe2O3 ternary nanocomposite according to claim 1, characterized in that, The size of the Pt nanoparticles is 3 - 10 nm, the thickness of the Fe2O3 nanocoating is 5 - 10 nm, and the diameter of the MoO3 nanorods is 100 - 150 nm.

3. The MoO3@Pt@Fe2O3 ternary nanocomposite according to claim 2, characterized in that, The lattice fringe d = 0.38 nm of the MoO3 nanorods is the (100) crystal plane of MoO3, and the lattice fringe d = 0.29 nm of the Fe2O3 nanocoating is the (110) crystal plane of Fe2O3.

4. The MoO3@Pt@Fe2O3 ternary nanocomposite according to claim 1, characterized in that it is Prepared by the following steps: Pt nanoparticles are supported on the MoO3 nanorods to obtain Pt@MoO3. Then, under the condition of an oil bath, an Fe(OH)3 colloidal solution is dropped into the Pt@MoO3 dispersion, and after aging and calcination, a MoO3@Pt@Fe2O3 ternary nanocomposite is obtained.

5. The MoO3@Pt@Fe2O3 ternary nanocomposite according to claim 4, characterized in that, For the oil bath, the temperature is 60 - 80 °C; for the aging, the time is 1 - 3 h; the calcination is carried out at 300 - 400 °C for 3 - 5 h.

6. The MoO3@Pt@Fe2O3 ternary nanocomposite according to claim 4, characterized in that, The loading amount of the Pt nanoparticles is 0.25% - 0.75% of the addition amount of MoO3, and the molar ratio of Fe(OH)3 to MoO3 nanorods is 0.2 - 0.4:

1.

7. The MoO3@Pt@Fe2O3 ternary nanocomposite according to claim 4, characterized in that, The Fe(OH)3 colloidal solution is obtained by adding ammonium ferric sulfate to hot water and filtering.

8. The MoO3@Pt@Fe2O3 ternary nanocomposite according to claim 4, characterized in that, The Pt@MoO3 is specifically obtained by impregnating the MoO3 nanorods in an equal volume of a solution of H2PtCl6·6H2O for 2 - 5 h.

9. Application of the MoO3@Pt@Fe2O3 ternary nanocomposite according to claim 1 in degrading organic pollutants.

10. The application according to claim 9, characterized in that, Application of the MoO3@Pt@Fe2O3 ternary nanocomposite in improving the degradation rate of methylene blue in the visible light region.

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