CN114308075A

CN114308075A - Efficient and stable visible light photocatalyst and preparation method thereof

Info

Publication number: CN114308075A
Application number: CN202111440951.7A
Authority: CN
Inventors: 阎佳滢; 杨忠美; 李轩; 许静仪; 李解; 潘长江; 张秋阳; 叶玮
Original assignee: Huaiyin Institute of Technology
Current assignee: Huaiyin Institute of Technology
Priority date: 2021-11-30
Filing date: 2021-11-30
Publication date: 2022-04-12
Anticipated expiration: 2041-11-30
Also published as: CN114308075B

Abstract

The invention discloses a high-efficiency stable visible light photocatalyst which mainly comprises CdS, carbon and transition metals Fe, Co and Ni. The invention also discloses a preparation method thereof, which comprises the steps of firstly ultrasonically dispersing the CdS nanocrystal and glucose in ultrapure water, and carrying out hydrothermal reaction for several hours to obtain the carbon-coated CdS nanocrystal; then one or more of transition metal elements Fe, Co and Ni are in-situ deposited on the surface of the carbon coating layer by adopting a photo-deposition method, and then products are ultrasonically cleaned and centrifugally separated; and finally sintering under the protection of inert atmosphere to obtain the final product. The composite photocatalyst material prepared by the method has excellent photocatalytic performance in a visible light spectrum range and stable physical and chemical properties. The deposition of the transition metal element can optimize the photocatalytic hydrogen evolution effect of the prepared catalyst and promote the graphitization of surface carbon, thereby further improving the transmission efficiency of photon-generated carriers.

Description

Efficient and stable visible light photocatalyst and preparation method thereof

Technical Field

The invention belongs to the field of photocatalysis, and particularly relates to a high-efficiency stable visible light photocatalyst and a preparation method thereof.

Background

The photocatalytic water splitting hydrogen production technology is one of the ideal ways for producing green hydrogen, is also one of the most challenging scientific and technical skills, and has great practical significance for solving the future environmental energy crisis. CdS is an excellent visible light photocatalyst. However, the defects of high recombination efficiency and easy photoetching of the photogenerated electron hole pair of the intrinsic CdS greatly limit the application of the intrinsic CdS. Related studies have shown that carbon materials can improve the photocatalytic performance of CdS and can enhance the optical stability of CdS. However, amorphous carbon does not have the same ability to transport carriers as graphitic carbon due to its lack of conjugated structure. Therefore, the use of graphitic carbon to improve the photocatalytic activity of CdS is a desirable option.

Based on the prior relevant literature reports and patents, most of the methods adopt a chemical adsorption mode or a physical blending mode to prepare the composite material of the graphitic carbon and the CdS. In the materials prepared by the methods, the contact between graphite and CdS is not firm, so that the improvement of the photocatalytic performance is not obvious, and the problem can be solved by adopting an in-situ preparation method. However, the graphitization temperature of carbon is close to 3000 ℃ and the decomposition temperature of CdS is only around 650 ℃, so that in-situ generation of a coating of graphitic carbon on the CdS surface is almost impossible. Therefore, the invention adopts the transition metal element to reduce the graphitization temperature of the carbon from the perspective of reducing the graphitization temperature of the carbon, thereby preparing the transition metal-graphitic carbon-CdS composite nanomaterial.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide a high-efficiency and stable visible light photocatalyst and a preparation method thereof.

The technical scheme is as follows: the composite photocatalyst with visible light photocatalytic activity comprises CdS, carbon and one or more of transition metal elements Fe, Co and Ni; the mass ratio of the CdS nanocrystals to glucose is kept between 5 and 0.1; the carbonized layer is coated on the surface of the CdS nanocrystal and has the thickness of 1-20 nm; the mass percentage of the deposited transition element in the CdS is kept between 0.1 and 10 percent.

The preparation method of the composite photocatalyst with visible light photocatalytic activity comprises the following steps:

(1) ultrasonically dispersing the CdS nanocrystal and glucose in ultrapure water, and then carrying out hydrothermal reaction to obtain the carbon-uniformly-coated CdS nanocrystal;

(2) uniformly dispersing one or more of transition metal elements Fe, Co and Ni on the surface of the carbon coating layer by adopting a photo-deposition method, separating a product after ultrasonic cleaning, and drying in vacuum;

(3) and (3) placing the dried sample in the previous step into a tube furnace, and sintering for 1-10h at 300-800 ℃ under the protection of inert gas to obtain a final product.

Further, in the step (1), the hydrothermal reaction temperature is 140-.

Further, in the step (2), the specific steps of the photo-deposition are as follows:

(11) ultrasonically dispersing the carbon-coated CdS nanocrystalline prepared in the step (1) in a mixed solution of water and methanol, and then adding a salt solution of Fe, Co and Ni into the solution;

(12) turning on a light source under the condition of continuously stirring, and continuously illuminating for 3-24 hours;

(13) repeatedly cleaning the solid precipitate with ultrapure water for several times under the ultrasonic condition until the solution does not contain salt;

(14) the washed product was placed in a vacuum drying oven and dried under vacuum.

Further, in the step (11), in the mixed salt solution, the molar ratio between the metal elements is 1: 1.

further, in the step (12), the wavelength of the light source is greater than 400nm, and the power of the light source is between 50 and 500W.

Further, in the step (14), the temperature of the vacuum drying is 70-80 ℃, and the drying time is 24-30 h.

Further, in the step (3), the specific steps of the high-temperature sintering are as follows:

(31) and (3) putting the dried product in the step (14) into a corundum crucible, putting the corundum crucible into a tube furnace, continuously introducing inert gas, and sintering for 1-10h at the temperature range of 300-800 ℃.

According to the invention, a hydrothermal method is adopted, and a layer of carbon is uniformly coated on the surface of the CdS nanocrystal to act as a protection shield, so that the CdS is prevented from being directly irradiated by a light source, the photoetching behavior of the CdS is inhibited, and the separation of photo-generated electron-hole pairs is accelerated; then the hydrogen evolution performance of the carbon is improved by depositing transition metal elements, and the transition from the carbon layer to graphitization is induced. Tests show that the composite photocatalyst has excellent visible light catalytic performance, and the quantum efficiency at the wavelength of 420nm exceeds 20%. The test of photochemical stability also shows that the stability of the composite photocatalyst is greatly improved, and the photocatalytic performance of the composite photocatalyst is not obviously reduced after repeated tests for 50 hours.

Has the advantages that: compared with the prior art, the invention has the following remarkable advantages:

1. the process flow is simple, complex equipment is not needed, and the cost of raw materials is low;

2. the coating thickness of the carbonized layer can be controlled by adjusting the mass ratio of the CdS nanocrystals to the glucose;

3. the invention innovatively utilizes one or more of transition metal elements Fe, Co and Ni to improve the structure of the carbon layer and provide more photocatalytic hydrogen evolution active sites;

4. the outer carbon coating can improve the photochemical stability of the CdS nanocrystal of the core.

5. The photocatalytic performance can be optimized by adjusting the mass percentage of the transition element in the CdS.

6. The synergistic catalytic action among all metal elements can be improved by adding one or more of transition metal elements Fe, Co and Ni;

7. the composite photocatalyst material prepared by the method has stable physical and chemical properties and good catalytic activity under the condition of visible light.

Drawings

FIG. 1 is a TEM image of a nanocomposite prepared according to the protocol of example 1 as a photocatalyst;

FIG. 2 is a TEM contrast of a photocatalyst prepared according to the embodiment of example 1 and the embodiment of example 2;

FIG. 3 is a graph comparing the Raman spectra of photocatalysts prepared according to the embodiment of example 1 and the embodiment of example 5.

Detailed Description

The technical scheme of the invention is further explained by combining the attached drawings.

Example 1

Firstly, 1.0g of CdS nanocrystalline and 1.0g of glucose are ultrasonically dispersed in 80ml of ultrapure water, and after being ultrasonically treated for 30min, the CdS nanocrystalline and the glucose are placed in a hydrothermal reaction kettle with a polytetrafluoroethylene lining and react for 6h at 160 ℃ in a forced air drying oven. And respectively ultrasonically cleaning the product obtained by the hydrothermal reaction for 3 times by using ethanol and ultrapure water, and performing vacuum drying for 12 hours at 70 ℃. Then, 0.5g of the dried sample was weighed and ultrasonically dispersed in a mixed solution of methanol and water for 30min, followed by addition of a solution containing 0.13g of FeCl₃Stirring the solution for 10min, applying illumination (100W LED light with light source wavelength within the range of 400-800 nm), keeping the illumination for 6 hours, gradually deepening the solution after the light deposition is finished, separating and filtering the product until no chloride ions are detected in the filtrate, and vacuum-drying the separated product for 12 hours at 70 ℃; finally, the dried sample in the previous step is placedPutting the mixture into a tube furnace, vacuumizing the tube furnace, introducing high-purity Ar gas, and sintering the tube furnace for 3h at 500 ℃. And after sintering, obtaining the Fe-C-CdS composite photocatalyst. As shown in fig. 1, the core-shell structure is very obvious, and a layer of graphite is uniformly coated on the surface of CdS.

Example 2

Firstly, 1.0g of CdS nanocrystalline and 2.0g of glucose are ultrasonically dispersed in 80ml of ultrapure water, and after being ultrasonically treated for 30min, the CdS nanocrystalline and the glucose are placed in a hydrothermal reaction kettle with a polytetrafluoroethylene lining and react for 6h at 160 ℃ in a forced air drying oven. And respectively ultrasonically cleaning the product obtained by the hydrothermal reaction for 3 times by using ethanol and ultrapure water, and performing vacuum drying for 12 hours at 70 ℃. Then, 0.5g of the dried sample was weighed and ultrasonically dispersed in a mixed solution of methanol and water for 30min, followed by addition of a solution containing 0.13g of FeCl₃Stirring the solution for 10min, applying illumination (100W LED light with light source wavelength within the range of 400-800 nm), keeping the illumination for 6 hours, gradually deepening the solution after the light deposition is finished, separating and filtering the product until no chloride ions are detected in the filtrate, and vacuum-drying the separated product for 12 hours at 70 ℃; and finally, placing the dried sample in the previous step into a tube furnace, vacuumizing, introducing high-purity Ar gas, and sintering at 500 ℃ for 3h. And after sintering, obtaining the Fe-C-CdS composite photocatalyst.

Following the procedure of example 1, example 2 differs in that the mass ratio of CdS to glucose is 1: 2, and in the preparation process of example 1, the mass ratio of CdS to glucose was 1: 1. as shown in fig. 2, the core-shell structure is characterized clearly, and the thickness of the graphite layer coated on the surface of CdS has a distinct difference.

Example 3

Firstly, 1.0g of CdS nanocrystalline and 1.0g of glucose are ultrasonically dispersed in 80ml of ultrapure water, and after being ultrasonically treated for 30min, the CdS nanocrystalline and the glucose are placed in a hydrothermal reaction kettle with a polytetrafluoroethylene lining and react for 6h at 160 ℃ in a forced air drying oven. And respectively ultrasonically cleaning the product obtained by the hydrothermal reaction for 3 times by using ethanol and ultrapure water, and performing vacuum drying for 12 hours at 70 ℃. Then, 0.5g of the dried sample was weighed and ultrasonically dispersed in a mixed solution of methanol and water for 30min, followed by addition of a solution containing 0.13g of FeCl₃And 0.1g of NiCl₂Stirring the mixed solution for 10min, applying illumination (100W LED light with the light source wavelength within the range of 400-800 nm), keeping the illumination for 6 hours, gradually deepening the solution after the light deposition is finished, separating and filtering the product until no chloride ions are detected in the filtrate, and vacuum-drying the separated product at 70 ℃ for 12 hours; and finally, placing the dried sample in the previous step into a tube furnace, vacuumizing, introducing high-purity Ar gas, and sintering at 500 ℃ for 3h. And after sintering, obtaining the Fe-Ni-C-CdS composite photocatalyst.

According to the method of example 1, example 3 is different in that two transition metal elements of Fe and Ni are simultaneously deposited, whereas only Fe is deposited during the preparation of example 1.

Example 4

Firstly, 1.0g of CdS nanocrystalline and 1.0g of glucose are ultrasonically dispersed in 80ml of ultrapure water, and after being ultrasonically treated for 30min, the CdS nanocrystalline and the glucose are placed in a hydrothermal reaction kettle with a polytetrafluoroethylene lining and react for 6h at 160 ℃ in a forced air drying oven. And respectively ultrasonically cleaning the product obtained by the hydrothermal reaction for 3 times by using ethanol and ultrapure water, and performing vacuum drying for 12 hours at 70 ℃. Then, 0.5g of the dried sample was weighed and ultrasonically dispersed in a mixed solution of methanol and water for 30min, followed by addition of a solution containing 0.13g of FeCl₃、0.11gCoCl₂And 0.1g of NiCl₂Stirring the mixed solution for 10min, applying illumination (100W LED light with the light source wavelength within the range of 400-800 nm), keeping the illumination for 6 hours, gradually deepening the solution after the light deposition is finished, separating and filtering the product until no chloride ions are detected in the filtrate, and vacuum-drying the separated product at 70 ℃ for 12 hours; and finally, placing the dried sample in the previous step into a tube furnace, vacuumizing, introducing high-purity Ar gas, and sintering at 500 ℃ for 3h. And after sintering, obtaining the Fe-C-CdS composite photocatalyst.

According to the method of example 1, three transition metal elements of Fe, Co and Ni were simultaneously deposited in example 4, while only Fe was deposited in the preparation process of example 1.

Example 5

First, 1.0g CdS nanocrystal and 1.0g glucose were sonicatedDispersing in 80ml of ultrapure water, carrying out ultrasonic treatment for 30min, placing in a hydrothermal reaction kettle with a polytetrafluoroethylene lining, and reacting for 6h at 160 ℃ in an air-blast drying oven. And respectively ultrasonically cleaning the product obtained by the hydrothermal reaction for 3 times by using ethanol and ultrapure water, and performing vacuum drying for 12 hours at 70 ℃. Then, 0.5g of the dried sample was weighed and ultrasonically dispersed in a mixed solution of methanol and water for 30min, followed by addition of a solution containing 0.13g of FeCl₃Stirring the solution for 10min, applying illumination (100W LED light with light source wavelength within the range of 400-800 nm), keeping the illumination for 6 hours, gradually deepening the solution after the light deposition is finished, separating and filtering the product until no chloride ions are detected in the filtrate, and vacuum-drying the separated product for 12 hours at 70 ℃; and finally, placing the dried sample in the previous step into a tube furnace, vacuumizing, introducing high-purity Ar gas, and sintering at 600 ℃ for 3h. And after sintering, obtaining the Fe-C-CdS composite photocatalyst.

According to the method of example 1, example 5 is different in that the sintering temperature of the last step is 600 ℃, whereas in the preparation of example 1, the sintering temperature of the last step is 500 ℃. As shown in fig. 3, the graphitization degree of the material surface coating layer is obviously improved after different heat treatments.

Claims

1. The efficient and stable visible light photocatalyst is characterized in that the components comprise CdS, carbon and one or more of transition metal elements Fe, Co and Ni; the carbon is obtained by hydrothermal carbonization of an organic matter and uniformly coated on the surface of the CdS, and the thickness of the carbon is 1-20 nm; the transition metal elements Fe, Co and Ni are in-situ deposited on the surface of the carbonized layer by a light deposition method, and the loading amount of the transition metal elements Fe, Co and Ni is 1-5% by mass.

2. A method for preparing a composite photocatalyst having a full spectrum absorption characteristic as claimed in claim 1, comprising the steps of:

3. The method for preparing the highly efficient and stable visible light photocatalyst according to claim 2, wherein in the step (1), the mass ratio of the CdS nanocrystal to the glucose is maintained between 5 and 0.1, and the carbon coating layer is formed by carbonizing organic carbide at high temperature and high pressure.

4. The method according to claim 3, wherein the organic carbide comprises glucose.

5. The preparation method of the high-efficiency stable visible light photocatalyst according to claim 2, wherein in the step (1), the ultrasonic dispersion time is 10-60 min; the hydrothermal reaction time is 6-12 h; the temperature of the hydrothermal reaction is 140-200 ℃.

6. The method for preparing the highly efficient and stable visible light photocatalyst according to claim 2, wherein in the step (2), the mass percent of the deposited transition element in CdS is maintained between 0.1% and 10%; selecting one or more of Fe, Co and Ni for deposition or codeposition; the time of the light deposition is between 3 and 24 hours.

7. The method as claimed in claim 2, wherein in the step (3), the sintering temperature is 300-800 ℃ and the sintering time is 1-10 h.