Monodisperse tungsten oxide nanowires loaded with metal, and preparation method and application thereof

Abstract

The application discloses a kind of monodisperse metal loaded tungsten oxide nanowires and its preparation method and application, tungsten oxide nanowire is mixed uniformly by impregnation method and soluble metal salt, then it is placed in H2 / Ar atmosphere and is burned to obtain monodisperse metal / tungsten oxide;The metal is at least one of Fe, Cu, Co.This catalyst has abundant oxygen vacancy, as electron trap center, is favorable to nitrogen adsorption and activation, significantly improves the activity of photocatalytic nitrogen fixation;Single dispersion metal as new nitrogen adsorption site and active site is loaded simultaneously, is favorable to NRR reaction, significantly improves the performance of photocatalytic nitrogen fixation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalytic materials, and particularly relates to a monodisperse metal-loaded tungsten oxide nanowire, a preparation method thereof and application thereof in photocatalytic nitrogen fixation. BACKGROUND

[0002] Ammonia is not only an important agricultural fertilizer and chemical raw material, but also a potential hydrogen energy carrier. At present, the Haber-Bosch method used in industry usually needs to be carried out under high temperature and high pressure conditions to realize the conversion of nitrogen into ammonia, which consumes a large amount of energy (1%-2% of the total energy in the world) and emits a large amount of greenhouse gases. Therefore, developing a green and clean method for synthesizing ammonia has been a research hotspot in the academic field. Since the bond energy of N≡N is as high as 940.95 kJ / mol, the dissociation of N≡N is considered to be the rate-determining step for synthesizing ammonia. Therefore, the key to realizing the activation of N≡N lies in that the catalyst has both N2 adsorption sites and active sites for efficiently activating N≡N. SUMMARY

[0003] In order to solve the problems existing in the prior art, the purpose of the present application is to provide a monodisperse metal-loaded tungsten oxide nanowire, a preparation method thereof and application thereof in photocatalytic nitrogen fixation. The catalyst has rich oxygen vacancies as electron trap centers, which is beneficial to the adsorption and activation of nitrogen, and obviously improves the activity of photocatalytic nitrogen fixation. Meanwhile, the monodisperse metal loaded as new nitrogen adsorption sites and active sites is beneficial to the NRR reaction, and obviously improves the photocatalytic nitrogen fixation performance.

[0004] In order to achieve the above technical purpose, the technical scheme adopted by the present application is as follows:

[0005] A preparation method of a monodisperse metal-loaded tungsten oxide nanowire, tungsten oxide nanowires are mixed uniformly with soluble metal salt by impregnation method, and then placed in H2 / Ar atmosphere for calcination to obtain monodisperse metal / tungsten oxide; the metal is at least one of Fe, Cu and Co.

[0006] The W in the present application 18 O 49 The nanowire can be prepared by using existing conventional methods, for example, using WCl6 as a reactant and anhydrous ethanol as a solvent to synthesize W 18 O 49 nanowires by solvothermal method.

[0007] As a preferred, the soluble metal salt is a nitrate, sulfate or chloride of the metal.

[0008] As a preferred, the mass ratio of the metal in the soluble metal salt to the tungsten oxide is 0.01-0.08:1; further preferably 0.02-0.04:1.

[0009] As a preference, the metal is Fe.

[0010] As a preference, the H2 volume ratio in the H2 / Ar atmosphere is 5%.

[0011] As a preference, the burning temperature is 300℃ and the time is 60 min.

[0012] The application also provides the monodisperse metal-loaded tungsten oxide nanowires prepared by the preparation method.

[0013] The application also provides the application of the monodisperse metal-loaded tungsten oxide nanowires, which is used for photocatalytic nitrogen fixation.

[0014] Compared with the prior art, the application has the following advantages:

[0015] The application realizes the loading of single-atom metal (i.e. the generation of unsaturated valence state M n+ O 18 (M is at least one of Fe, Cu and Co) and the generation of surface oxygen vacancies in the catalyst) and the generation of surface oxygen vacancies by the impregnation method and the reduction atmosphere (H2 / Ar) treatment, to obtain the M-SACs / W 49 O 18 (M is at least one of Fe, Cu and Co) composite catalyst. The oxygen vacancies in the composite catalyst can act as electron trap centers, which are beneficial to the adsorption and activation of nitrogen. The loading of monodisperse metal has an atomic utilization rate close to 100%, and is highly dispersed, the active centers are uniform, and the active sites are highly exposed. On one hand, the monodisperse metal can act as nitrogen adsorption sites and new active sites, and on the other hand, the monodisperse metal can adjust the energy band structure of the catalyst, promote the separation of photo-generated carriers, and promote the nitrogen reduction reaction. For example, under full-spectrum light irradiation, the ammonia production rate of Fe4-SACs / W 49 O 18 can reach 188.6 μmol / g / h, which is obviously superior to pure W 49 O . BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 SEM images of the samples W 18 O 49 (a) and Fe4-SACs / W 18 O 49 (b) prepared in Example 1;

[0017] Figure 2 EDX mappings of the sample Fe4-SACs / W 18 O4 prepared in Example 1;

[0018] Figure 3 SEM images of the sample W18 O 49 and Fe4-SACs / W 18 O 49 XRD patterns;

[0019] Figure 4 Sample W prepared in Example 1 18 O 49 and Fe4-SACs / W 18 O 49 ESR spectrum;

[0020] Figure 5 Sample W prepared in Example 1 18 O 49 and Fe4-SACs / W 18 O 49 The photocatalytic nitrogen fixation performance diagram. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0022] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the reagents and materials used in the following examples are commercially available unless otherwise specified.

[0023] Photocatalytic nitrogen fixation:

[0024] 10 mg of catalyst powder was weighed and added to a reaction tube, followed by 20 ml of ultrapure water. Nitrogen gas was then purged for 30 min under stirring at a flow rate of 80 ml / min. The xenon lamp was then turned on, and nitrogen gas was continuously purged for 1 h under full-spectrum light irradiation. After the reaction was completed, the catalyst was centrifuged and filtered through a 0.22 μm filter. The generated ammonium ions in the supernatant were detected using an ion-selective electrode and a colorimetric method.

[0025] Example 1

[0026] (1) Mix 200g of tungsten chloride and 60ml of anhydrous ethanol, stir for 20 minutes, then place in a crystallization vessel and treat at 180℃ for 12h. After cooling to room temperature, wash several times with anhydrous ethanol and dry under vacuum at 60℃ to obtain W. 18 O 49 .

[0027] (2) Add 100mg W 18 O 49The iron / tungsten oxide was dispersed in 20 ml of anhydrous ethanol. Then, 13.11 mg of FeCl3 was weighed and added to the mixture (the mass ratio of iron to tungsten oxide in ferric chloride was 0.04). The mixture was stirred for 2 hours, then centrifuged and washed several times with deionized water. The sample was then vacuum-dried at 60 °C. The dried sample was then placed in a tube furnace and calcined at 300 °C for 60 minutes under a H2 / Ar (5 / 95%) atmosphere. After cooling, the sample was washed several times with deionized water and vacuum-dried at 60 °C to obtain a monodisperse iron / tungsten oxide material. The resulting sample was designated Fe4-SACs / W 18 O 49 .

[0028] like Figure 1 As shown, W 18 O 49 After being loaded with monodisperse Fe, its morphology did not change significantly; it remained a nanosphere composed of nanowires with uniform size.

[0029] like Figure 2 As shown, monodisperse iron / tungsten oxide materials contain W, O, and Fe elements, with Fe being the most abundant element in W. 18 O 49 The surface is uniformly dispersed.

[0030] like Figure 3 As shown, W 18 O 49 and Fe4-SACs / W 18 O 49 The XRD patterns and diffraction peaks on the standard cards correspond one-to-one.

[0031] like Figure 4 As shown, W 18 O 49 The EPR signal is almost non-existent, while Fe4-SACs / W 18 O 49 The material exhibits a strong EPR signal, indicating that Fe4-SACs / W 18 O 49 The material contains abundant oxygen vacancies.

[0032] like Figure 5 As shown, this illustrates Fe4-SACs / W 18 O 49 The catalyst exhibits excellent photocatalytic nitrogen fixation performance, significantly superior to pure W. 18 O 49 .

[0033] Example 2

[0034] Same as Example 1, except that the mass ratio of iron to tungsten oxide in ferric chloride is 0.01, and the resulting sample is denoted as Fe1-SACs / W. 18 O49 .

[0035] Example 3

[0036] The same as Example 1, except that the mass ratio of iron in the ferric chloride to tungsten oxide is 0.02, and the prepared sample is denoted as Fe2-SACs / W 18 O 49 .

[0037] Example 4

[0038] The same as Example 1, except that the mass ratio of iron in the ferric chloride to tungsten oxide is 0.08, and the prepared sample is denoted as Fe8-SACs / W 18 O 49 .

[0039] The samples prepared in Examples 1-4 are used for photocatalytic nitrogen fixation reaction, and the results are shown in Table 1:

[0040] Table 1 Results of the samples prepared in Examples 1-4 for photocatalytic nitrogen fixation reaction

[0041]

[0042] As can be seen from Table 1, the mass ratio of iron in the ferric chloride to tungsten oxide is 0.04 is optimal. FeCl3 is uniformly dispersed on the surface of WO3 by the impregnation method, and then the material is treated at 300°C for 60 min in a H2 / Ar (5 / 95%) atmosphere. The reduction atmosphere treatment simultaneously achieves: first, the material generates abundant oxygen vacancies, and second, it generates unsaturated valence state Fe, which realizes the coordination of Fe-O bonds in the catalyst. The production of ammonium ions is shown in Table 1, and as can be seen from the figure, pure WO3 has a generation rate of only 0.8 μmol / g / h per hour under full-spectrum light, while Fe4-SACs / W has an ammonia production rate of 188.6 μmol / g / h, which is a huge improvement over the original WO3. 18 O 49 n+ Table 1 Figure 5 18 O 49 18 O 49 18 O 49

[0043] Example 5

[0044] (1) 200 g of tungsten chloride and 60 ml of anhydrous ethanol are mixed, stirred for 20 minutes, and then placed in a crystallization kettle, treated at 180°C for 12 h. After cooling to room temperature, washed with anhydrous ethanol several times, and then vacuum dried at 60°C, WO3 is obtained. 18 O 49 . ​​​​​

[0045] (2) 100 mg of pure WO3was dispersed in 20 ml of absolute ethanol, then 12.01 mg of copper chloride was weighed and added to the mixture (mass ratio of copper to tungsten oxide in the copper chloride was 0.04), stirred for 2 h, then the mixture was centrifuged, washed with deionized water several times, and dried at 60°C under vacuum. The dried sample was then placed in a tube furnace and calcined at 300°C for 60 min under a H2 / Ar (5 / 95%) atmosphere, after cooling, washed with deionized water several times, and dried at 60°C under vacuum to obtain a monodisperse copper / tungsten oxide material. The sample prepared is denoted as Cu4-SACs / W 18 O 49 dispersed in 20 ml of absolute ethanol, then 12.01 mg of copper chloride was weighed and added to the mixture (mass ratio of copper to tungsten oxide in the copper chloride was 0.04), stirred for 2 h, then the mixture was centrifuged, washed with deionized water several times, and dried at 60°C under vacuum. The dried sample was then placed in a tube furnace and calcined at 300°C for 60 min under a H2 / Ar (5 / 95%) atmosphere, after cooling, washed with deionized water several times, and dried at 60°C under vacuum to obtain a monodisperse copper / tungsten oxide material. The sample prepared is denoted as Cu4-SACs / W 18 O 49 .

[0046] Example 6

[0047] The same as Example 1, except that the mass ratio of copper to tungsten oxide in the copper chloride was 0.01, and the sample prepared is denoted as Cu1-SACs / W 18 O 49 .

[0048] Example 7

[0049] The same as Example 1, except that the mass ratio of copper to tungsten oxide in the copper chloride was 0.02, and the sample prepared is denoted as Cu2-SACs / W 18 O 49 .

[0050] Example 8

[0051] The same as Example 1, except that the mass ratio of copper to tungsten oxide in the copper chloride was 0.08, and the sample prepared is denoted as Cu8-SACs / W 18 O 49 .

[0052] Table 2 Results of the samples prepared in Examples 5-8 for photocatalytic nitrogen fixation reaction

[0053]

[0054] Example 9

[0055] (3) 200 g of tungsten chloride and 60 ml of absolute ethanol were mixed, stirred for 20 min, then placed in a crystallization kettle, and treated at 180°C for 12 h. After cooling to room temperature, washed with absolute ethanol several times, and dried at 60°C under vacuum to obtain W 18 O 49 .

[0056] (4) 100 mg of pure WO3was dispersed in 20 ml of absolute ethanol, then 12.01 mg of copper chloride was weighed and added to the mixture (mass ratio of copper to tungsten oxide in the copper chloride was 0.04), stirred for 2 h, then the mixture was centrifuged, washed with deionized water several times, and dried at 60°C under vacuum. The dried sample was then placed in a tube furnace and calcined at 300°C for 60 min under a H2 / Ar (5 / 95%) atmosphere, after cooling, washed with deionized water several times, and dried at 60°C under vacuum to obtain a monodisperse copper / tungsten oxide material. The sample prepared is denoted as Cu4-SACs / W 18 O 49The dispersion was dispersed in 20 ml of absolute ethanol, then 24.69 mg of cobalt nitrate hexahydrate was weighed into the mixture (the mass ratio of cobalt in the cobalt nitrate hexahydrate to tungsten oxide was 0.04), stirred for 2 h, then the mixture was centrifuged, washed with deionized water multiple times, and vacuum dried at 60°C. Then the dried sample was placed in a tube furnace and calcined at 300°C for 60 min in a (5%) H2 / Ar atmosphere, after cooling, washed with deionized water multiple times, and vacuum dried at 60°C to obtain a monodisperse cobalt / tungsten oxide material. The prepared sample is denoted as Co4-SACs / W 18 O 49 .

[0057] Example 10

[0058] The same as Example 1, except that the mass ratio of cobalt in the cobalt nitrate hexahydrate to tungsten oxide was 0.01, and the prepared sample is denoted as Co1-SACs / W 18 O 49 .

[0059] Example 11

[0060] The same as Example 1, except that the mass ratio of cobalt in the cobalt nitrate hexahydrate to tungsten oxide was 0.02, and the prepared sample is denoted as Co2-SACs / W 18 O 49 .

[0061] Example 12

[0062] The same as Example 1, except that the mass ratio of cobalt in the cobalt nitrate hexahydrate to tungsten oxide was 0.08, and the prepared sample is denoted as Co8-SACs / W 18 O 49 .

[0063] Table 3 Results of the samples prepared in Examples 9-12 for photocatalytic nitrogen fixation reaction

[0064]

[0065]

[0066] As can be seen from Table 2 and Table 3, monodisperse copper / tungsten oxide catalysts and monodisperse cobalt / tungsten oxide catalysts were synthesized by the same impregnation method and reduction atmosphere treatment. Among them, the Cu2-SACs / W 18 O 49 catalyst can reach 119.1 μmol / g / h under full spectrum light without any sacrificial agent, and the pure Co-SACs / W 18 O 49 catalyst can reach 130.2 μmol / g / h under full spectrum light without any sacrificial agent.

[0067] Comparative Example 1

[0068] 200 g of tungsten chloride and a certain mass of FeCl3 were added to 60 ml of anhydrous ethanol (the mass ratio of iron in ferric chloride to tungsten oxide was 0.02, 0.04, respectively), stirred for 20 minutes, and then placed in a crystallization kettle for treatment at 180°C for 12 h. After cooling to room temperature, the product was washed with anhydrous ethanol several times and then dried at 60°C under vacuum to obtain Fe-doped WO 18 O 49 , which was denoted as Fe2-W 18 O 49 and Fe4-W 18 O 49 .

[0069] Comparative Example 1

[0070] 200 g of tungsten chloride and a certain mass of FeCl3 were added to 60 ml of anhydrous ethanol (the mass ratio of iron in ferric chloride to tungsten oxide was 0.02, 0.04, respectively), stirred for 20 minutes, and then placed in a crystallization kettle for treatment at 180°C for 12 h. After cooling to room temperature, the product was washed with anhydrous ethanol several times and then dried at 60°C under vacuum to obtain Fe-doped WO 18 O 49 , which was denoted as Fe2-W 18 O 49 and Fe4-W 18 O 49 .

[0071] Table 4 Results of the samples prepared in Comparative Examples 1-2 for photocatalytic nitrogen fixation reaction

[0072]

[0073] As can be seen from Table 4, metal-doped tungsten oxide catalysts were synthesized by one-step solvothermal method. Among them, the Fe4-W 18 O 49 catalyst had an ammonia production rate of only 24.7 μmol / g / h under full-spectrum light without any sacrificial agent; and the Co4-W 18 O 49 catalyst had an ammonia production rate of only 14.2 μmol / g / h under full-spectrum light without any sacrificial agent.

Claims

1. Use of monodisperse metal-loaded tungsten oxide nanowires, characterized in that: Use it for photocatalytic nitrogen fixation; The specific preparation process of the monodisperse metal-loaded tungsten oxide nanowires is as follows: The tungsten oxide nanowires are mixed uniformly with a soluble Fe salt by an impregnation method, and then are placed in an H2 / Ar atmosphere to obtain monodisperse metal / tungsten oxide by calcination; The mass ratio of Fe in the soluble Fe salt to tungsten oxide is 0.04:

1.

2. Use according to claim 1, characterized in that: The soluble Fe salt is a nitrate, sulfate or chloride of Fe.

3. Use according to claim 1, characterized in that: In the H2 / Ar atmosphere, the volume ratio of H2 is 5%.

4. Use according to claim 1, characterized in that: The calcination temperature is 300 DEG C, and the time is 60 min.

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