A double-shell photo-limited catalyst, its preparation method and application

Abstract

The application provides a double-core-shell light-limited catalyst and a preparation method and application thereof. The light-limited catalyst with the specific structure is prepared by using the principle of refraction and reflection of light transmission in a non-uniform refractive index medium, adopting a double-core-shell structure to utilize light sources multiple times to realize a light-limited function, and thereby enhancing the light absorption effect of the catalyst. The preparation method is as follows: (1) an inner core: adding yttrium chloride hexahydrate, ytterbium chloride hexahydrate, thulium chloride hexahydrate, ethylenediaminetetraacetic acid and sodium fluoride into deionized water to obtain a NaYF4:Yb / Tm inner core by a hydrothermal method, (2) a core-shell structure: dispersing the inner core in the step (1) in an anhydrous ethanol solution, adding ammonia water and tetraethyl orthosilicate, and obtaining a core-shell structure of the inner core wrapped by silicon dioxide after hydrolysis, and (3) a double-core-shell structure: dispersing the core-shell structure in the step (2) in deionized water, adding trisodium citrate, cadmium nitrate tetrahydrate, ammonia water and thiourea, and preparing the double-core-shell light-limited catalyst by water bath heating.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photocatalytic water splitting, in particular to a preparation method of a double-shell light confinement catalyst and application thereof in the field of photocatalytic water splitting. BACKGROUND

[0002] Photocatalysis is a technology that uses light energy to drive chemical reactions, which is widely used in environmental protection, energy conversion and chemical synthesis. Photocatalytic reaction involves three processes of light absorption, carrier separation and transport, and surface interface redox reaction. Among them, the spectral response range and light absorption capacity of the photocatalyst determine the generation concentration of the carrier, thereby affecting the separation and migration of the carrier and the redox reaction of the catalyst surface interface. Therefore, expanding the light absorption range and enhancing the light absorption capacity of the photocatalyst is an important way to fully utilize solar energy resources and improve the efficiency of the catalyst.

[0003] Generally in photocatalysts, the energy band structure of the semiconductor determines its light absorption characteristics and redox potential. Therefore, regulating the energy band structure is a common means of designing and constructing efficient catalysts, such as metal and non-metal element doping, heterostructure construction and noble metal deposition. Since element doping is easy to introduce recombination centers when adjusting the energy band structure, it is not conducive to the separation of electron-hole pairs in the catalytic reaction process. The interface between the heterojunction structure is prone to dislocation and defects in the construction process, thereby inhibiting the effective transport of carriers. The low abundance of noble metals in the earth's crust leads to high cost in industrial large-scale application. Therefore, the preparation of double-shell structure can effectively accelerate the transport and separation of carriers in the catalyst reaction process, enhance the light absorption efficiency and reduce the production cost. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of a double-shell light confinement catalyst for realizing multiple use of light by light confinement. The method realizes large-scale and low-cost preparation of double-shell structure through simple and continuous hydrothermal, hydrolysis and water bath. The present application provides a preparation method of up-conversion inner core, which realizes conversion of infrared light to visible light, expands the spectral response range of the catalyst and achieves the purpose of fully utilizing solar energy resources. Another purpose of the present application is to provide a double-shell light confinement catalyst. Another purpose of the present application is to provide an application of the double-shell light confinement catalyst.

[0005] Technical scheme: The preparation method of the double-shell light confinement catalyst of the present application comprises the following steps:

[0006] Step S1: preparing NaYF4:Yb / Tm inner core;

[0007] Step S2: after dispersing NaYF4:Yb / Tm core into anhydrous ethanol solution, adding ammonia water and tetraethyl orthosilicate, and obtaining the core-shell structure of silica-coated core after hydrolysis;

[0008] Step S3: dispersing the above core-shell structure into deionized water, adding trisodium citrate, cadmium nitrate tetrahydrate, ammonia water and thiourea, and then heating in water bath, and obtaining the double core-shell light confinement catalyst after vacuum drying.

[0009] Preferably, in step S1, the method for preparing NaYF4:Yb / Tm core is as follows: adding yttrium source, thulium source, ytterbium source, ethylenediaminetetraacetic acid and sodium fluoride into deionized water respectively, stirring uniformly, and then preparing NaYF4:Yb / Tm core by hydrothermal method.

[0010] More preferably, in step S1, the yttrium source is yttrium chloride hexahydrate, the thulium source is thulium chloride hexahydrate, and the ytterbium source is ytterbium chloride hexahydrate.

[0011] More preferably, in step S1, the hydrothermal temperature is 150-180℃, and the reaction time is 10-24h.

[0012] Preferably, in step S2, the hydrolysis time is 1-10h.

[0013] Preferably, in step S3, the concentration of cadmium nitrate tetrahydrate is 0.5-2.0mol / L, the water bath temperature is 60-80℃, and the reaction time is 1-3h.

[0014] Preferably, in step S3, the vacuum drying conditions are as follows: the vacuum degree is 10 -3 -10 -6 MPa, the drying temperature is 60-100℃, and the drying time is 10-36h.

[0015] On the other hand, the present application provides a double core-shell light confinement catalyst prepared by the above method, wherein the double core-shell light confinement catalyst has NaYF4:Yb / Tm as the core, a silica outer core coated on the surface of the core, and a cadmium sulfide shell layer coated on the surface of the outer core.

[0016] On the other hand, the present application provides the application of the above double core-shell light confinement catalyst in photocatalytic hydrogen evolution reaction.

[0017] The specific application method is as follows: under light irradiation, dispersing the double core-shell light confinement catalyst in deionized water solution, then adding chloroplatinic acid and a sacrificial reagent (the sacrificial reagent is composed of sodium sulfide and sodium sulfite), collecting hydrogen after the hydrogen evolution reaction is completed.

[0018] Advantages: compared with the prior art, the present application has the following obvious advantages:

[0019] 1.The present application makes full use of the difference in refractive index between materials to realize multiple reflection of light, prolong the propagation path of light in the cadmium sulfide shell, and further realize the light confinement effect to improve the light absorption capacity of the catalyst. On this basis, the regulation of the thickness of the cadmium sulfide shell can further realize the effective absorption and reuse of the light source.

[0020] 2.In the present application, the NaYF4:Yb / Tm inner core converts infrared light into visible light that can be absorbed by the catalyst, expanding the spectral response range. This dual-core structure provides a general strategy for maximizing the use of solar energy for hydrogen evolution reaction, and has wide application prospects in the fields of photocatalytic reaction, solar cell and photo-thermal conversion. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 Flow chart of the preparation method of the present application;

[0022] Figure 2 Schematic diagram of the principle of light confinement in the dual-core-shell light confinement catalyst;

[0023] Figure 3 Physical demonstration diagram of the light confinement phenomenon;

[0024] Figure 4 TEM image of the light confinement catalyst prepared in Example 2. DETAILED DESCRIPTION

[0025] The present application will be further described below in conjunction with examples and comparative examples, which can enable the skilled person in the art to more fully understand the present application, but in no way limit the present application.

[0026] As shown in Figure 1 , the present application provides a preparation method of a dual-core-shell light confinement catalyst, comprising the following steps:

[0027] (1) Inner core: NaYF4:Yb / Tm inner core is obtained by hydrothermal method after adding yttrium chloride hexahydrate, ytterbium chloride hexahydrate, thulium chloride hexahydrate, ethylenediaminetetraacetic acid and sodium fluoride into deionized water; wherein the hydrothermal temperature is 150-180℃, and the reaction time is 10-24h;

[0028] (2) Core-shell structure: the inner core in (1) is dispersed in anhydrous ethanol solution, then ammonia water and tetraethyl orthosilicate are added, and a core-shell structure of the inner core wrapped by silicon dioxide is obtained after hydrolysis; wherein the hydrolysis time is 1-10h;

[0029] (3) Double core-shell structure: the core-shell structure in (2) is dispersed in deionized water, and then trisodium citrate, cadmium nitrate tetrahydrate, ammonia water and thiourea are added, and then a double core-shell light confinement catalyst is prepared by water bath heating; wherein the concentration of cadmium nitrate tetrahydrate is (0.5-2.0 mol / L), the water bath temperature is 60-80℃, the reaction time is 1-3h, the vacuum degree is 10 -3 ~10 -6 MPa, and the drying temperature is 60-100℃, and the drying time is 10-36h.

[0030] As shown in Figures 2-3 , the light catalyst with this specific structure utilizes the principle of refraction and reflection of light transmission in a non-uniform refractive index medium, adopts a double core-shell structure to utilize the light source multiple times to realize light confinement function, thereby enhancing the light absorption effect of the catalyst. The double core-shell structure takes the upconversion material (NaYF4:Yb / Tm) as the inner core, takes silicon dioxide as the outer core, and takes cadmium sulfide as the shell layer. On the one hand, light is multiply reflected between the cadmium sulfide and the silicon dioxide interface, prolonging the propagation path of light in the cadmium sulfide shell layer, which can maximize the light confinement in the cadmium sulfide shell layer, effectively improving the multiple absorption and reuse of light by cadmium sulfide. On the other hand, by controlling the thickness of the cadmium sulfide shell layer, the light absorption efficiency can be adjusted, so the structure of the double core-shell catalyst can be optimized to ensure that the catalyst has excellent photocatalytic hydrogen production performance.

[0031] As shown in Figure 4 , the double core-shell catalyst is a uniform nanosphere composed of a double core-shell structure of cadmium sulfide, silicon dioxide and an upconversion inner core.

[0032] Example 1:

[0033] The double core-shell light confinement catalyst is prepared according to the following steps:

[0034] Step 1, preparation of NaYF4:Yb / Tm inner core: 1.0L yttrium chloride hexahydrate (0.20mol / L), 1.0L thulium chloride hexahydrate (0.01mol / L), 1.0L ytterbium chloride hexahydrate (0.08mol / L), 0.20kg ethylenediaminetetraacetic acid and 0.15kg sodium fluoride are generated by hydrothermal method at 180℃ for 12h to generate the inner core.

[0035] Step 2, preparation of core-shell structure: the inner core is dispersed in 50L anhydrous ethanol, 1.0L ammonia water and 1.0L tetraethyl orthosilicate are added, and the mixture is hydrolyzed for 3h to generate a core-shell structure of the inner core wrapped by silicon dioxide.

[0036] Step 3, preparation of double core-shell structure: the core-shell structure was dispersed into 100 L deionized water, 1.0 L of cadmium nitrate tetrahydrate (0.5 mol / L), 0.3 kg of trisodium citrate, 1.0 L of ammonia water and 0.1 kg of thiourea were added into a water bath at 80 ℃ for 12 h to generate the double core-shell photo-limited catalyst. The average shell thickness of the double core-shell photo-limited catalyst was 23 nm.

[0037] The double core-shell photo-limited catalyst provided by the embodiment of the present application is applied to photocatalytic hydrogen production.

[0038] Photocatalytic performance test: the photocatalytic activity of the catalyst was investigated in a 10 ℃ sealed quartz reactor. The light source was a 300 W xenon lamp with a filter (λ>400 nm). The distance between the light source and the reactor was about 5 cm. 10 mg of the catalyst was dispersed in 20 mL of deionized water solution, 0.8 mL of chloroplatinic acid (0.1 mol / L) and 10 mL of sacrificial reagent (sodium sulfide 0.35 mol / L, sodium sulfite 0.25 mol / L) were added. After mixing uniformly, it was transferred to the quartz reactor and sealed, and then the air was removed by Ar purging system. A gas chromatograph (Agilent 7890A GC) was used to analyze the generated gas. In this embodiment, the hydrogen evolution rate under (λ>400 nm, 100 mW / cm 2 ) light intensity was 62.13 mmol / g / h.

[0039] Example 2:

[0040] The double core-shell photo-limited catalyst of this embodiment was prepared by the same method as that of Example 1, except that in step (3), cadmium nitrate tetrahydrate (1.0 L, 1.0 mol / L) was used. The average shell thickness of the double core-shell photo-limited catalyst obtained in this embodiment was 30 nm.

[0041] The photocatalytic performance of the double core-shell photo-limited catalyst of this embodiment was tested by the method described in Example 1.

[0042] In this embodiment, the hydrogen evolution rate under (λ>400 nm, 100 mW / cm 2 ) light intensity was 74.67 mmol / g / h.

[0043] Example 3

[0044] The double core-shell photo-limited catalyst of this embodiment was prepared by the same method as that of Example 1, except that in step (3), cadmium nitrate tetrahydrate (1.0 L, 2.0 mol / L) was used. The average shell thickness of the double core-shell photo-limited catalyst prepared in this embodiment was 39 nm.

[0045] The photocatalytic performance of the double core-shell photo-limited catalyst of this embodiment was tested by the method described in Example 1.

[0046] The hydrogen evolution rate under the light intensity of (λ>400nm, 100mW / cm 2 ) was 51.45mmol / g / h.

[0047] Example 4

[0048] The double-shell photoredox catalyst of the present example was prepared by the same method as that of Example 1, except that cadmium nitrate tetrahydrate (1.0L, 3.0mol / L) was used in step (3). The average shell thickness of the double-shell photoredox catalyst prepared in the present example was 48nm.

[0049] The double-shell photoredox catalyst of the present example was subjected to photocatalytic performance test by the method described in Example 1.

[0050] The hydrogen evolution rate under the light intensity of (λ>400nm, 100mW / cm 2 ) was 40.07mmol / g / h.

[0051] Example 5

[0052] The double-shell photoredox catalyst of the present example was prepared by the same method as that of Example 1, except that cadmium nitrate tetrahydrate (1.0L, 4.0mol / L) was used in step (3). The average shell thickness of the double-shell photoredox catalyst prepared in the present example was 60nm.

[0053] The double-shell photoredox catalyst of the present example was subjected to photocatalytic performance test by the method described in Example 1.

[0054] The hydrogen evolution rate under the light intensity of (λ>400nm, 100mW / cm 2 ) was 33.41mmol / g / h.

[0055] Comparative Example 1

[0056] The present comparative example provides a cadmium sulfide single-core structure catalyst.

[0057] The cadmium sulfide single-core structure of Comparative Example 1 is different from that of Example 1 in that no silica and up-conversion inner core needs to be added before the generation of cadmium sulfide. Specifically, the preparation method of the cadmium sulfide single-core structure catalyst is as follows: 1.0L cadmium nitrate tetrahydrate (0.5mol / L), 0.3kg trisodium citrate, 1.0L ammonia water and 0.1kg thiourea are added to 100L deionized water, and the mixture is heated in a water bath at 80℃ for 12h to generate the cadmium sulfide single-core structure catalyst.

[0058] The catalyst of the present comparative example was subjected to photocatalytic performance test by the method described in Example 1.

[0059] The hydrogen evolution rate of the core-shell catalyst measured in the present comparative example under light intensity (λ > 400 nm, 100 mW / cm 2 ) was 6.51 mmol / g / h.

[0060] Comparative Example 2:

[0061] The present comparative example provides a core-shell structure catalyst of cadmium sulfide coated silica.

[0062] The core-shell structure of cadmium sulfide coated silica in Comparative Example 2 is different from that of Example 1 in that it is not necessary to add an upconversion inner core before generating silica. Specifically, the preparation method of the core-shell structure catalyst of cadmium sulfide coated silica is as follows:

[0063] 1.0 L of ammonia water and 1.0 L of tetraethyl orthosilicate were added to 50 L of anhydrous ethanol and hydrolyzed for 3 h to generate a silica inner core.

[0064] The silica inner core was dispersed into 100 L of deionized water, 1.0 L of cadmium nitrate tetrahydrate (0.5 mol / L), 0.3 kg of trisodium citrate, 1.0 L of ammonia water, and 0.1 kg of thiourea were added to generate a core-shell structure catalyst of cadmium sulfide coated silica in a water bath at 80°C for 12 h.

[0065] The catalyst of the present comparative example was tested for photocatalytic performance using the method described in Example 1.

[0066] The hydrogen evolution rate of the core-shell catalyst measured in the present comparative example under light intensity (λ > 400 nm, 100 mW / cm 2 ) was 36.78 mmol / g / h.

[0067] Comparative Example 3:

[0068] The present comparative example provides a core-shell structure catalyst of cadmium sulfide coated carbon spheres.

[0069] The core-shell structure of cadmium sulfide coated carbon spheres in Comparative Example 3 is different from that of Example 1 in that it is necessary to add carbon spheres before synthesizing cadmium sulfide. Specifically, the preparation method of the core-shell structure catalyst of cadmium sulfide coated carbon spheres is as follows:

[0070] The carbon spheres were dispersed into 100 L of deionized water, 1.0 L of cadmium nitrate tetrahydrate (0.5 mol / L), 0.3 kg of trisodium citrate, 1.0 L of ammonia water, and 0.1 kg of thiourea were added to generate a core-shell structure catalyst of cadmium sulfide coated carbon spheres in a water bath at 80°C for 12 h.

[0071] The catalyst of the present comparative example was tested for photocatalytic performance using the method described in Example 1.

[0072] The hydrogen evolution rate of the core-shell catalyst measured in this comparative example was 8.13 mmol / g / h under (λ > 400 nm, 100 mW / cm 2 ) light intensity.

Claims

1. A method for preparing a binuclear-shell photoconfined catalyst, characterized in that, The method includes the following steps: Step S1: Preparation of NaYF4:Yb / Tm core; The method for preparing NaYF4:Yb / Tm core is as follows: Yttrium source, thulium source, ytterbium source, ethylenediaminetetraacetic acid and sodium fluoride are added to deionized water and stirred evenly, and then NaYF4:Yb / Tm core is prepared by hydrothermal method; Step S2: After dispersing the NaYF4:Yb / Tm core into an anhydrous ethanol solution, ammonia and tetraethyl orthosilicate are added. After hydrolysis, a core-shell structure with silica encapsulating the core is obtained. Step S3: Disperse the above core-shell structure in deionized water, add trisodium citrate, cadmium nitrate tetrahydrate, ammonia and thiourea, heat in a water bath, and dry under vacuum to obtain a dual-core-shell photoconfined catalyst.

2. The method for preparing the dual-core-shell photoconfined catalyst according to claim 1, characterized in that, In step S1, the yttrium source is yttrium trichloride hexahydrate, the thulium source is thulium trichloride hexahydrate, and the ytterbium source is ytterbium trichloride hexahydrate.

3. The method for preparing the binuclear-shell photoconfined catalyst according to claim 1, characterized in that, In step S1, the hydrothermal temperature is 150~180 ℃, and the reaction time is 10~24 h.

4. The method for preparing the dual-core-shell photoconfined catalyst according to claim 1, characterized in that, In step S2, the hydrolysis time is 1~10 h.

5. The method for preparing the dual-core-shell photoconfined catalyst according to claim 1, characterized in that, In step S3, the concentration of cadmium nitrate tetrahydrate is 0.5~2.0 mol / L, the water bath temperature is 60~80 ℃, and the reaction time is 1~3 h.

6. The method for preparing the dual-core-shell photoconfined catalyst according to claim 1, characterized in that, In step S3, the vacuum drying conditions are: a vacuum degree of 10. -3 ~10 -6 The drying pressure is MPa, the drying temperature is 60~100 ℃, and the drying time is 10~36 h.

7. A dual-core-shell photoconfined catalyst prepared according to any one of claims 1-6, characterized in that, The aforementioned dual-core shell photocontainment catalyst has a NaYF4:Yb / Tm core, a silica outer core coated on the surface of the core, and a cadmium sulfide shell coated on the surface of the outer core.

8. The application of the binuclear-shell photoconfined catalyst of claim 7 in the photocatalytic hydrogen evolution reaction.

Images