CN115805091B - A method for preparing copper-silver double single atom pair photocatalyst - Google Patents

Abstract

The invention belongs to the technical field of preparation methods of photocatalysts, and discloses a preparation method of a copper-silver diatomic photocatalyst, which comprises the following steps of S1, adding C ₃N₄ photocatalyst powder loaded with copper diatomic atoms into absolute ethyl alcohol, and uniformly dispersing; s2, adding 100-500 mu L of silver nitrate solution into the dispersion system obtained in the step S1, performing ultrasonic reaction for 1-5 hours, fully dispersing solid powder by utilizing the mechanical effect of ultrasonic waves, and enhancing the reaction between C ₃N₄ base powder and silver nitrate by the cavitation effect of the ultrasonic waves in the liquid; s3, continuously stirring the dispersion system obtained in the step S2 for 2-10 hours, then centrifugally separating out precipitate at a high speed, and drying to obtain the copper-silver double single-atom photocatalyst; the method is used for preparing the copper-silver double-single-atom photocatalyst, has the advantages of simple operation steps, short time consumption, low raw material cost and the like, and the prepared photocatalyst has good electron selectivity and high catalytic activity, and has wide application prospects in the fields of industrial production, environmental engineering and the like.

Description

A method for preparing copper-silver double single atom pair photocatalyst

Technical Field

The invention relates to the technical field of photocatalyst preparation methods, and in particular to a method for preparing a copper-silver double single atom pair photocatalyst.

Background technique

Single-atom catalysts refer to metal catalysts that are uniformly dispersed and deposited on the surface of a carrier in the form of single atoms. The catalytic active sites are exposed to the maximum extent, which improves the utilization efficiency of the catalyst and reduces the cost of the catalyst. When the particle dispersion reaches the single-atom size, many new properties will arise, such as a sharp increase in surface free energy, quantum size effect, unsaturated coordination environment and metal-carrier interaction. These properties are significantly different from those of nano or sub-nano particles, giving single-atom catalysts superior activity and selectivity, which can further improve catalytic performance and reduce manufacturing costs. Therefore, single-atom catalysts have great application potential in industrial catalysis.

As a new type of photocatalytic substrate material, C ₃ N ₄ has become a research hotspot in the field of photocatalysis in recent years due to its simple material preparation, rich types of single atoms that can be loaded, and excellent catalytic performance. However, the current active sites of single metal atoms are difficult to catalyze a series of reactions such as the reduction of CO ₂ and the decomposition of H ₂ O, resulting in low production of high value-added products such as CH ₄ , which limits the further improvement and application of C ₃ N ₄ materials.

Summary of the invention

The present invention is intended to provide a method for preparing a copper-silver double single atom pair photocatalyst, which utilizes the electrostatic adsorption between an electropositive C ₃ N ₄ photocatalyst anhydrous ethanol dispersion system and an electronegative silver nitrate solution to form a copper-silver double single atom pair, thereby achieving a step-by-step catalytic effect on different metal atoms. The method for preparing a copper-silver double single atom photocatalyst is simple in operation, low in raw material cost, short in time consumption, high in production efficiency, and the prepared photocatalyst has good electronic selectivity, high catalytic activity, and broad application prospects.

In order to achieve the above object, the present invention provides the following technical solutions:

A method for preparing a copper-silver double single atom pair photocatalyst comprises the following steps:

S1. Add C ₃ N ₄ photocatalyst powder loaded with copper single atoms into anhydrous ethanol and disperse evenly;

S2, adding 100-500 μL of silver nitrate solution to the dispersion obtained in step S1 and subjecting to ultrasonic reaction for 1-5 hours, using the mechanical effect of ultrasound to fully disperse the solid powder, while the cavitation effect of ultrasound in the liquid enhances the reaction between the C ₃ N ₄ base powder and the silver nitrate;

S3, stirring the dispersion obtained in step S2 for 2 to 10 hours, and then separating the precipitate by high-speed centrifugation, and obtaining the copper-silver double single atom pair photocatalyst after drying.

Furthermore, in S1, the obtained C ₃ N ₄ anhydrous ethanol dispersion is electropositive, and in S2, the silver nitrate solution is electronegative. The electropositive C ₃ N ₄ anhydrous ethanol dispersion and the electronegative silver nitrate solution load silver single atoms onto the C ₃ N ₄ substrate material through electrostatic adsorption.

Furthermore, in S2, the concentration of the silver nitrate solution added is 2 mg/mL, which can effectively load the silver atoms while avoiding agglomeration and achieve the best catalytic effect.

Furthermore, during the continuous stirring of S3, the copper single atom and the silver single atom form a double single atom pair on the C ₃ N ₄ substrate material through a copper-silver metal bond to prepare a copper-silver double single atom pair photocatalyst.

The principle and beneficial effects of the technical solution are:

The loading amount of copper and silver metal atoms is a key factor affecting the catalytic activity of the catalyst. If the amount of copper and silver elements added during the preparation process is too little, the copper and silver atoms cannot be effectively loaded on the C ₃ N ₄ substrate material; and if the amount added is too much, it is easy to cause the metal single atoms to agglomerate and form nanoclusters, and the catalytic effect of the copper-silver double single atom pair cannot be achieved. The present invention utilizes the electrostatic adsorption between the electropositive C ₃ N ₄ photocatalyst anhydrous ethanol dispersion system and the electronegative silver nitrate solution to form a copper-silver double single atom pair, which can ensure that the metal single atoms are effectively loaded on the C ₃ N ₄ substrate material and effectively avoid the agglomeration of metal atoms. The method breaks through the limitation of the low CH ₄ output of the traditional C ₃ N ₄ substrate photocatalyst, and the preparation process is simple to operate, low in raw material cost, short in time, and high in production efficiency. The prepared photocatalyst has good electronic selectivity and high catalytic activity, and has broad application prospects in industrial production, environmental engineering and other fields.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the synthesis of a copper-silver double single atom pair photocatalyst using a copper single atom C ₃ N ₄ photocatalyst loaded with copper in the present invention;

FIG2 is a Zeta potential diagram of anhydrous ethanol dispersion system of C ₃ N ₄ catalyst powder loaded with copper single atoms and a silver nitrate aqueous solution of the present invention;

FIG3 is a spherical aberration corrected electron micrograph of a copper-silver double single atom pair photocatalyst prepared by a method for preparing a copper-silver double single atom pair photocatalyst of the present invention;

FIG4 is an X-ray diffraction spectrum of a copper-silver double single atom pair photocatalyst prepared by a method for preparing a copper-silver double single atom pair photocatalyst of the present invention;

FIG5 is an extended X-ray absorption fine structure spectrum of a copper-silver double single atom pair photocatalyst at copper K-edge prepared by a method for preparing a copper-silver double single atom pair photocatalyst of the present invention;

FIG6 is an extended X-ray absorption fine structure spectrum of a copper-silver double single atom pair photocatalyst prepared by a method for preparing a copper-silver double single atom pair photocatalyst of the present invention at the silver K-edge;

FIG. 7 is a performance test result of catalytic reduction of CO ₂ by a copper-silver double single atom pair photocatalyst prepared by a method for preparing a copper-silver double single atom pair photocatalyst of the present invention.

Detailed ways

The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments:

As shown in FIG1 , a method for preparing a copper-silver double single atom pair photocatalyst comprises the following steps:

S1. Adding C ₃ N ₄ photocatalyst powder loaded with copper single atoms into anhydrous ethanol and dispersing the powder evenly, the obtained C ₃ N ₄ anhydrous ethanol dispersion is electrically positive; wherein the method for preparing C ₃ N ₄ photocatalyst powder loaded with copper single atoms comprises the following steps:

A1. Weigh 30g thiourea and add it into 120mL pure water. Heat at 60℃ and stir with magnetic stirring for 10min until the solution becomes clear.

A2, weigh 0.4 g of cupric chloride dihydrate and add it to the transparent solution obtained in step A1, and continue heating and stirring for 10 minutes;

A3, the solution obtained in step A2 was allowed to stand and cool to room temperature, the supernatant was discarded, and the precipitate was placed in a drying oven for drying;

A4, placing the dried precursor in step A3 into a covered alumina porcelain boat, calcining it in a tubular furnace under Ar conditions for 1 to 5 hours, and then cooling it naturally to room temperature;

A5, ball-milling the product obtained by calcination in step A4 to obtain C ₃ N ₄ photocatalyst powder loaded with copper single atoms;

S2, adding 100-500 μL of silver nitrate solution to the dispersion obtained in step S1 and subjecting it to ultrasonic reaction for 1-5 hours, utilizing the mechanical effect of ultrasound to fully disperse the solid powder, and at the same time enhancing the reaction between the C ₃ N ₄ base powder and the silver nitrate by the cavitation effect of ultrasound in the liquid; wherein the silver nitrate solution added is: weighing 0.1 g of silver nitrate solid and dissolving it in 50 mL of pure water to prepare a silver nitrate solution with a concentration of 2 mg/mL, the silver nitrate solution is electronegative, and the electropositive C ₃ N ₄ anhydrous ethanol dispersion in S1 and the electronegative silver nitrate solution load silver single atoms onto the C ₃ N ₄ base material through electrostatic adsorption;

S3. Stirring the dispersion obtained in step S2 for 2 to 10 hours, and then separating the precipitate by high-speed centrifugation. After drying, a copper-silver double single atom pair photocatalyst is obtained. During the continuous stirring process, the copper single atom and the silver single atom form double single atom pairs on the C ₃ N ₄ substrate material through copper-silver metal bonds to prepare the copper-silver double single atom pair photocatalyst.

In order to verify that the present embodiment can produce the target catalyst product, the produced product was subjected to various characterizations. The following is a description of the characterization results.

Characterization Experiment 1:

As shown in Figure 2, the Zeta potential of the anhydrous ethanol dispersion of C ₃ N ₄ catalyst powder loaded with single copper atoms and the silver nitrate aqueous solution were tested. The test results showed that the anhydrous ethanol dispersion of C ₃ N ₄ catalyst powder loaded with single copper atoms was positively charged, and the silver nitrate aqueous solution was negatively charged. Due to the electrostatic effect, the silver atoms can be effectively loaded onto the C ₃ N ₄ substrate.

Characterization Experiment 2:

This application uses the American FEI Titan Themis model spherical aberration corrected electron microscope to perform transmission imaging of the catalyst sample powder, and the test voltage is 300kV. As shown in Figure 3, the distance between the copper atoms and the silver atoms in the four tested areas is This indicates that copper and silver are loaded on the C ₃ N ₄ substrate in the form of double single atom pairs.

Characterization Experiment 3:

The present application uses a PANalytical BVX'Pert X-ray diffractometer (Cu Kα, λ=0.154nm, working voltage and working current are 40kV and 40mA respectively) to perform XRD characterization test on the catalyst sample powder. As shown in Figure 4, the XRD results show that the catalyst sample powder has two peaks at about 13° and 27°, which are typical diffraction peaks of C ₃ N ₄ materials, wherein the 13° peak corresponds to the stacking (100) between C ₃ N ₄ units between planes, and the 27° peak corresponds to the stacking (002) between C ₃ N ₄ crystal planes; in addition, no other obvious characteristic peaks are observed. This proves that this embodiment is non-doped, and the loaded single atom pairs do not affect the synthesis of C ₃ N ₄ materials.

Characterization Experiment 4:

The present application tests the extended X-ray absorption fine structure of the catalyst sample powder at the copper and silver K-edges, respectively. As shown in Figures 5 and 6, the fitting results show that no copper-copper and silver-silver metal bonds appear in the C ₃ N ₄ sample loaded with copper single atoms and the C ₃ N ₄ sample loaded with copper-silver double single atom pairs, indicating that the copper atom is loaded on the C ₃ N ₄ substrate in the form of a single atom; in addition, there are three coordinations between copper and nitrogen in the C ₃ N ₄ sample loaded with copper single atoms, while there are only two coordinations between copper and nitrogen in the C ₃ N ₄ sample loaded with copper-silver double single atom pairs. The addition of silver single atoms results in an unsaturated coordination environment of copper atoms, thereby proving that copper and silver are loaded on the C ₃ N ₄ substrate in the form of double single atom pairs. The extended X-ray absorption fine structure fitting parameters of the samples at the copper K-edge and silver K-edge are shown in Tables 1 and 2:

Table 1 Extended X-ray absorption fine structure fitting parameters of samples at copper K-edge

Where CN is the coordination number, R is the distance between the absorber and the backscattering atom, σ ² is the Debye-Waller factor that explains thermal and structural disorder, ΔE ₀ is the internal potential correction, and the R factor indicates the degree of fit. Based on the X-ray absorption fine structure fitting spectrum of copper obtained by fixing CN as a known crystal value in the experiment, S ₀ ² was fixed at 0.892. The fitting range is: and/> and A reasonable range of X-ray absorption fine structure fitting parameters is 0.700<S ₀ ² <1.000;CN>0;/> |ΔE ₀ |<10eV; R factor<0.02.

Table 2 Extended X-ray absorption fine structure fitting parameters of samples at silver K-edge

Where CN is the coordination number, R is the distance between the absorber and the backscattering atom, σ ² is the Debye-Waller factor that explains thermal and structural disorder, ΔE ₀ is the internal potential correction, and the R factor indicates the degree of fit. Based on the X-ray absorption fine structure fitting spectrum of silver obtained by fixing CN as a known crystal value in the experiment, S ₀ ² was fixed at 0.8. A reasonable range of X-ray absorption fine structure fitting parameters is 0.700<S ₀ ² <1.000;CN>0; |ΔE ₀ |<10eV; R factor<0.02.

Characterization Experiment 5:

As shown in Figure 7, this experiment also carried out a performance test experiment of photocatalytic reduction of CO _2. The experimental method is as follows:

First, weigh 5 mg of catalyst powder into a glass culture dish, add appropriate amount of pure water, ultrasonically homogenize, and then dry to make the catalyst powder evenly distributed at the bottom of the culture dish;

Then, the culture dish filled with the catalyst was placed in a transparent quartz reactor with a volume of 150 mL, and 200 μL of ultrapure water was added to the reactor and then sealed;

Then connect the vacuum pump to the reactor to exhaust the air in the reactor, and then introduce 99.99% pure _CO2 into the reactor until the pressure in the reactor is balanced with the atmospheric pressure;

Then turn on the 300W xenon lamp (PLS-SXE300/300UV), set the current to 15A, and then place the light source above the reactor and irradiate the culture dish for 2 hours. During this period, coolant is continuously introduced outside the reactor to control the reactor temperature at about 15°C.

After the illumination was completed, 2 mL of gas sample was extracted from the reactor and injected into a gas chromatograph (Shimadzu GC-2014C, Japan) to detect the concentration of _CO2 reduction products.

The test results show that the _CH4 output performance in this experiment reached 13.14 μmol·g ^-1 ·h ^-1 , the CO output performance reached 5.33 μmol·g ^-1 ·h ^-1 , and the electron selectivity exceeded 90%. In addition, the catalyst sample was tested for five cycles according to the above steps, and the results showed that its photocatalytic performance did not decrease, and no _CH4 and CO were detected in the control group experiment conducted at the same time, indicating that the CH4 and CO detected in the experiment were the products of the catalytic carbon dioxide reaction, rather than the decomposition of the catalyst itself. This proves that the copper-silver double single atom pair photocatalyst prepared in this embodiment has stable chemical properties.

The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the technical solution of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims (1)

1. A method for preparing a copper-silver double single atom pair photocatalyst, characterized in that it comprises the following steps: S1. Adding C ₃ N ₄ photocatalyst powder loaded with copper single atoms into anhydrous ethanol and dispersing the powder evenly, the obtained C ₃ N ₄ anhydrous ethanol dispersion is electrically positive; wherein the method for preparing C ₃ N ₄ photocatalyst powder loaded with copper single atoms comprises the following steps: A1. Weigh 30g thiourea and add it into 120mL pure water. Heat at 60℃ and stir with magnetic stirring for 10min until the solution becomes clear. A2, weigh 0.4 g of cupric chloride dihydrate and add it to the transparent solution obtained in step A1, and continue heating and stirring for 10 minutes; A3, the solution obtained in step A2 was allowed to stand and cool to room temperature, the supernatant was discarded, and the precipitate was placed in a drying oven for drying; A4, placing the dried precursor in step A3 into a covered alumina porcelain boat, calcining it in a tubular furnace under Ar conditions for 1 to 5 hours, and then cooling it naturally to room temperature; A5, ball-milling the product obtained by calcination in step A4 to obtain C ₃ N ₄ photocatalyst powder loaded with copper single atoms; S2, adding 100-500 μL of silver nitrate solution to the dispersion obtained in step S1 and subjecting it to ultrasonic reaction for 1-5 hours, utilizing the mechanical effect of ultrasound to fully disperse the solid powder, and at the same time enhancing the reaction between the C ₃ N ₄ base powder and the silver nitrate by the cavitation effect of ultrasound in the liquid; wherein the silver nitrate solution added is: weighing 0.1 g of silver nitrate solid and dissolving it in 50 mL of pure water to prepare a silver nitrate solution with a concentration of 2 mg/mL, the silver nitrate solution is electronegative, and the electropositive C ₃ N ₄ anhydrous ethanol dispersion in S1 and the electronegative silver nitrate solution load silver single atoms onto the C ₃ N ₄ base material through electrostatic adsorption; S3. Stirring the dispersion obtained in step S2 for 2 to 10 hours, and then separating the precipitate by high-speed centrifugation. After drying, a copper-silver double single atom pair photocatalyst is obtained. During the continuous stirring process, the copper single atom and the silver single atom form double single atom pairs on the C ₃ N ₄ substrate material through copper-silver metal bonds to prepare the copper-silver double single atom pair photocatalyst.