Method for synthesizing monatomic supported catalyst through laser ice-phase assisted migration

Abstract

The invention provides a method for synthesizing a monatomic supported catalyst through laser ice-phase assisted migration, and belongs to the technical field of monatomic catalyst synthesis. The preparation method comprises the following steps: performing liquid nitrogen freezing on a chloroplatinic acid aqueous solution, performing laser reduction on chloroplatinic acid ice cubes in liquid nitrogen, mixing the obtained reduced ice cubes with a g-C3N4 dispersion liquid to melt water in the reduced ice cubes, and drying the obtained g-C3N4 loaded platinum monatomic dispersion liquid to obtain the monatomic supported catalyst. Carrier-free metal single atoms are directly synthesized through laser reduction under the ice phase condition, the single atoms are migrated to the g-C3N4 carrier through a melting (namely low-temperature migration) method under the freezing condition, the limitation of laser reduction on the carrier can be eliminated, the g-C3N4 carrier can be directly used, the single atoms are obtained on the g-C3N4 carrier, and the preparation method is simple and easy to implement. And the prepared monatomic supported catalyst shows excellent photocatalytic hydrogen production activity and stability.

Description

Technical Field

[0001] The present invention relates to the technical field of the synthesis of single-atom supported catalysts, and particularly relates to a method for synthesizing single-atom supported catalysts by laser ice-phase assisted migration. Background Art

[0002] Single-atom catalysts are a new type of catalysts in which metals are supported on carriers in the form of single atoms. Compared with traditional catalysts, single-atom catalysts can significantly improve the selectivity and activity of catalytic reactions because each metal atom exists in the form of a monomer during the catalytic process and can participate in the reaction to the greatest extent. In recent years, single-atom catalysts have shown broad application prospects in the fields of energy conversion, environmental governance, and organic synthesis. Common methods for synthesizing single-atom catalysts include chemical vapor deposition, photoreduction, pyrolysis, etc. Although these methods have their own characteristics, they often require complex equipment and strict reaction conditions, and there are problems such as poor catalyst dispersion and easy agglomeration, which limit their practical applications.

[0003] The application of laser technology in material synthesis has gradually attracted attention. Pulsed lasers have advantages such as high energy density, short action time, and strong controllability, and can achieve efficient processing of nanomaterials. For example, laser technology is used to synthesize graphene-supported platinum materials. While synthesizing laser-induced graphene, graphene-supported platinum single atoms are synthesized by laser reduction method, improving the dispersion of single atoms. However, in this method, the reduction of single atoms must occur simultaneously with the generation of graphene, and single atoms cannot be synthesized on other types of carriers. Therefore, there is a need to develop a laser synthesis method for single-atom catalysts that is independent of carriers. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for synthesizing single-atom supported catalysts by laser ice-phase assisted migration. The present invention directly synthesizes carrier-free metal single atoms by laser reduction under ice-phase conditions, and migrates the single atoms to the g-C 3 N 4 carrier by melting under freezing conditions (i.e., low-temperature migration), getting rid of the limitation of laser reduction on the carrier, and directly using the g-C 3 N 4 carrier to obtain single atoms on the g-C 3 N 4 carrier.

[0005] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a method for synthesizing single-atom supported catalysts by laser ice-phase assisted migration, comprising the following steps:

[0007] The aqueous solution of chloroplatinic acid is frozen with liquid nitrogen to obtain chloroplatinic acid ice cubes;

[0008] In liquid nitrogen, the chloroplatinic acid ice cubes are laser-reduced to obtain reduced ice cubes;

[0009] The reduced ice cubes are mixed with the g-C 3 N 4 dispersion to melt the water in the reduced ice cubes, obtaining a g-C 3 N 4 supported platinum single-atom dispersion;

[0010] The g-C 3 N 4 supported platinum single-atom dispersion is dried to obtain the single-atom supported catalyst.

[0011] Preferably, the concentration of the aqueous solution of chloroplatinic acid is 0.05 - 2 mg / mL.

[0012] Preferably, when frozen with liquid nitrogen, the volume ratio of the aqueous solution of chloroplatinic acid to liquid nitrogen is 1:15.

[0013] Preferably, the parameters of the laser reduction include: the planar scanning speed of the laser beam is 100 - 900 mm / s, and the vertical scanning speed is 0.1 - 1 mm / min.

[0014] Preferably, the power of the laser reduction is 1 - 5 W, the pulse frequency is 30 - 100 kHz, and the pulse width is 8 - 50 ns.

[0015] Preferably, the wavelength of the laser reduction is 355 nm.

[0016] Preferably, the concentration of the g-C 3 N 4 dispersion is not more than 5 mg / mL.

[0017] Preferably, the mass ratio of chloroplatinic acid in the aqueous solution of chloroplatinic acid to g-C 3 N 4 in the g-C 3 N 4 dispersion is not more than 5%, and the mass of the chloroplatinic acid is not 0.

[0018] Preferably, the temperature of the freezing condition is 0 - 10 °C.

[0019] Preferably, the melting is carried out under stirring, and the rotation speed of the stirring is not less than 600 rpm; after the melting is completed, continuous stirring is also included, and the time of the continuous stirring does not exceed 1 min.

[0020] The present invention provides a method for synthesizing a single-atom supported catalyst assisted by laser ice-phase migration, comprising the following steps: subjecting an aqueous solution of chloroplatinic acid to liquid nitrogen freezing to obtain chloroplatinic acid ice cubes; performing laser reduction on the chloroplatinic acid ice cubes in liquid nitrogen to obtain reduced ice cubes; mixing the reduced ice cubes with a g-C 3 N 4 dispersion to melt the water in the reduced ice cubes, obtaining a g-C 3 N 4 supported platinum single-atom dispersion; drying the g-C 3 N 4 supported platinum single-atom dispersion to obtain the single-atom supported catalyst.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] The present invention directly synthesizes carrier-free metal Pt single atoms by laser reduction under ice-phase conditions, and migrates the Pt single atoms to the g-C 3 N 4 carrier by a method of melting under freezing conditions (i.e., low-temperature migration), which can get rid of the limitation of laser reduction on the carrier, and can directly use the g-C 3 N 4 carrier to obtain Pt single atoms on the g-C 3 N 4 carrier, and the prepared single-atom supported catalyst exhibits excellent photocatalytic hydrogen production activity and stability. At the same time, the method of the present invention is simple, easy to promote, and has important industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart for preparing the single-atom supported catalyst in the embodiment of the present invention;

[0024] Figure 2 is an XRD pattern of the single-atom supported catalysts prepared in Examples 1-3 of the present invention;

[0025] Figure 3 is an element distribution map of the single-atom supported catalyst prepared in Example 2 of the present invention;

[0026] Figure 4 is a HAADF-STEM image of the single-atom supported catalyst prepared in Example 2 of the present invention;

[0027] Figure 5 is an XANES spectrum of the single-atom supported catalyst prepared in Example 2 of the present invention;

[0028] Figure 6 is a photocatalytic hydrogen production rate graph of the single-atom supported catalysts prepared in Examples 1-3 of the present invention;

[0029] Figure 7 It is the photocatalytic hydrogen production stability diagram of the single-atom supported catalyst prepared in Example 2 of the present invention;

[0030] Figure 8 It is the photocatalytic hydrogen production rate diagram of the single-atom supported catalysts prepared in Example 4 and Example 1 of the present invention;

[0031] Figure 9 It is the photocatalytic hydrogen production rate diagram of the single-atom supported catalysts prepared in Example 5 and Example 1 of the present invention. Detailed implementation manners

[0032] The present invention provides a method for synthesizing a single-atom supported catalyst by laser ice-phase assisted migration, comprising the following steps:

[0033] Freeze the chloroplatinic acid aqueous solution with liquid nitrogen to obtain chloroplatinic acid ice cubes;

[0034] In liquid nitrogen, laser reduce the chloroplatinic acid ice cubes to obtain reduced ice cubes;

[0035] Mix the reduced ice cubes with the g-C 3 N 4 dispersion to melt the water in the reduced ice cubes, and obtain a g-C 3 N 4 supported platinum single-atom dispersion;

[0036] Dry the g-C 3 N 4 supported platinum single-atom dispersion to obtain the single-atom supported catalyst.

[0037] The present invention freezes the chloroplatinic acid aqueous solution with liquid nitrogen to obtain chloroplatinic acid ice cubes.

[0038] In the present invention, the concentration of the chloroplatinic acid aqueous solution is preferably 0.05-2 mg / mL, specifically it can be 0.05, 0.1, 0.5, 1, 1.5 or 2 mg / mL. If the concentration of the chloroplatinic acid aqueous solution is too high, the concentration of platinum ions generated in water is too high, and it is easy to cause the aggregation of single atoms during the laser reduction process, generating particles. The catalytic effect of particles is much worse than that of single atoms. If the concentration of the chloroplatinic acid aqueous solution is too low, the catalytic effect of the obtained single-atom supported catalyst is poor.

[0039] In the present invention, when freezing with liquid nitrogen, the volume ratio of the chloroplatinic acid aqueous solution to liquid nitrogen is preferably 1:15.

[0040] In a specific embodiment of the present invention, pour the chloroplatinic acid aqueous solution into a stainless steel cup, and then quickly freeze it with liquid nitrogen to obtain the chloroplatinic acid ice cubes.

[0041] After obtaining the chloroplatinic acid ice cubes, in the present invention, the chloroplatinic acid ice cubes are laser-reduced in liquid nitrogen to obtain reduced ice cubes, and the reduced ice cubes contain ice-confined platinum single atoms.

[0042] In the present invention, the function of the liquid nitrogen is to prevent the chloroplatinic acid ice cubes from melting.

[0043] In the present invention, the planar scanning speed of the laser beam for the laser reduction is preferably 100 - 900 mm / s, specifically it can be 100, 300, 500, 700, or 900 mm / s, and the vertical scanning speed is preferably 0.1 - 1 mm / min, specifically it can be 0.1, 0.3, 0.5, 0.7, or 1 mm / min; during the laser reduction process, platinum ions are laser-reduced to form platinum single atoms; the laser spot for the laser reduction has a certain size, and the planar scanning speed will determine the time that each unit area within the planar range is irradiated by the laser. If the time is too short, the synthesis rate of Pt single atoms is low, and if it is too long, Pt single atoms will agglomerate due to the laser thermal effect. Controlling the vertical scanning speed is because the laser has a recoating effect, and too fast or too slow vertical scanning speed will affect both the synthesis rate of Pt single atoms and the dispersion degree of Pt single atoms.

[0044] In the present invention, the power of the laser reduction is preferably 1 - 5 W, specifically it can be 1, 2, 3, 4, or 5 W, the pulse frequency is preferably 30 - 100 kHz, specifically it can be 30, 40, 50, 60, 70, 80, 90, or 100 kHz, and the pulse width is preferably 8 - 50 ns, specifically it can be 8, 10, 20, 30, 40, or 50 ns. Controlling the power, pulse frequency, and pulse width of the laser reduction within the above ranges serves to control the size of the single-pulse energy, that is, the number of instantaneous photons generated during the laser reduction process, control the generation rate of Pt single atoms, and at the same time be able to control the cooling process after laser heating to avoid the agglomeration of Pt single atoms.

[0045] In the present invention, the wavelength of the laser reduction is preferably 355 nm.

[0046] In a specific embodiment of the present invention, the chloroplatinic acid ice cubes are placed under a nanosecond laser with a wavelength of 355 nm, the laser beam is focused on the upper surface of the chloroplatinic acid ice cubes, and three-dimensional scanning of the chloroplatinic acid ice cubes is started.

[0047] After obtaining the reduced ice cubes, the present invention mixes the reduced ice cubes with a g-C 3 N 4 dispersion to melt the water in the reduced ice cubes, obtaining a g-C 3 N 4 platinum single atom-loaded dispersion.

[0048] In the present invention, the concentration of the g-C 3 N 4 dispersion is preferably not more than 5 mg / mL, and specifically can be 1, 2, 3, 4 or 5 mg / mL. If the concentration of the g-C 3 N 4 dispersion is too high, it will lead to poor uniformity of the adsorption of Pt single atoms by g-C 3 N 4 .

[0049] In the present invention, Pt single atoms are first prepared in chloroplatinic acid ice cubes. However, Pt single atoms cannot exist stably by themselves. Once the ice cubes melt, the Pt single atoms will aggregate together to form particles. Therefore, a carrier is required to have a strong adsorption effect on Pt single atoms. The g-C 3 N 4 in the dispersion contains intrinsic six-fold cavities and has a strong adsorption property for Pt single atoms, and can adsorb Pt single atoms into the cavities of g-C 3 N 4 before they aggregate. 3 N 4 .

[0050] In the present invention, the mass ratio of chloroplatinic acid in the chloroplatinic acid aqueous solution to g-C 3 N 4 in the dispersion is preferably not more than 5%, and the mass of chloroplatinic acid is not 0. Specifically, it can be 1%, 2%, 3%, 4% or 5%. Controlling the mass ratio of chloroplatinic acid to g-C 3 N 4 can limit the loading amount of Pt single atoms in the final product and avoid the aggregation of Pt atoms caused by too high a loading amount. 3 N 4

[0051] In the present invention, there is no special limitation on the source of the g-C 3 N 4 dispersion, and a method well-known to those skilled in the art can be used. Specifically, for example: dispersing g-C 3 N 4 nanosheets into deionized water and performing ultrasonic treatment to obtain the g-C 3 N 4 dispersion.

[0052] In the present invention, the power of the ultrasonic treatment is preferably 50 - 2000 W, and specifically can be 50, 100, 500, 1000, 1500 or 2000 W, and the time is preferably 2 h.

[0053] ​In the present invention, the temperature of the freezing condition is preferably 0 to 10 °C, specifically it can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 °C. The temperature of the freezing condition can control the melting rate of the ice cubes after reduction, avoiding the too-fast melting of the ice cubes after reduction, g-C 3 N 4 is unable to adsorb Pt single atoms simultaneously, resulting in the problem of Pt single atom aggregation.

[0054] In the present invention, the melting is carried out under stirring. The rotation speed of the stirring is preferably not less than 600 rpm. The faster the stirring speed, the better the dispersion of the Pt single atoms adsorbed on g-C 3 N 4 However, too fast speed will cause the solution to splash. After the melting is completed, it preferably further includes continuous stirring. The time of the continuous stirring is preferably not more than 1 min, and the rotation speed of the continuous stirring is preferably not less than 600 rpm. During the melting process of the ice cubes after reduction, the release of Pt single atoms and g-C 3 N 4 adsorbing Pt single atoms are carried out simultaneously. The continuous stirring is to ensure that the finally released Pt single atoms are also fully adsorbed as much as possible. If the time of the continuous stirring is too long, it may be due to the collision between g-C 3 N 4 to produce Pt single atom aggregation.

[0055] In a specific embodiment of the present invention, it is preferred to put the ice cubes after reduction into g-C 3 N 4 dispersion liquid, and stir under the freezing condition to make the Pt single atoms fully anchored on g-C 3 N 4 support.

[0056] After obtaining the g-C 3 N 4 platinum single atom loaded dispersion liquid, in the present invention, the g-C 3 N 4 platinum single atom loaded dispersion liquid is dried to obtain the single atom loaded catalyst.

[0057] In the present invention, before drying, it preferably further includes carrying out solid-liquid separation and washing on the g-C 3 N 4 platinum single atom loaded dispersion liquid in sequence.

[0058] In the present invention, the solid-liquid separation is preferably centrifugation. The rotation speed of the centrifugation is preferably 3000 to 10000 rpm, the time is preferably 5 to 10 min, and the number of centrifugation times is preferably 2 to 3 times.

[0059] In the present invention, the detergent for washing is preferably water. There are no special limitations on the specific parameters of the washing in the present invention, and the methods well-known to those skilled in the art can be adopted.

[0060] In the present invention, the drying is preferably freeze-drying, and the freeze-drying is preferably carried out in a freeze dryer. There are no special limitations on the specific parameters of the freeze-drying in the present invention, and the methods well-known to those skilled in the art can be adopted.

[0061] In the present invention, the single-atom supported catalyst is a pale yellow g-C 3 N 4 powder supporting Pt single atoms.

[0062] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts belong to the scope of protection of the present invention.

[0063] Figure 1 It is a flow chart for preparing the single-atom supported catalyst in the embodiment of the present invention. The aqueous solution of chloroplatinic acid is quickly frozen with liquid nitrogen to obtain ice cubes of chloroplatinic acid. In liquid nitrogen, the ice cubes of chloroplatinic acid are scanned by a laser to obtain ice-confined Pt single atoms; g-C 3 N 4 nanosheets are ultrasonically dispersed to obtain a g-C 3 N 4 dispersion; the ice-confined Pt single atoms are adsorbed onto g-C 3 N 4 to obtain a g-C 3 N 4 supported Pt single atom dispersion, and the g-C 3 N 4 supported Pt single atom dispersion is freeze-dried to obtain the single-atom supported catalyst, which is also a g-C 3 N 4 supported Pt single atom supported catalyst.

[0064] Example 1

[0065] A method for synthesizing a single-atom supported catalyst assisted by laser ice phase migration includes the following steps:

[0066] (1) Pour 10 mL of an aqueous solution of chloroplatinic acid with a concentration of 0.1 mg / mL into a stainless steel cup with an inner diameter of 3 cm, and quickly freeze it into ice cubes with 150 mL of liquid nitrogen. Transfer the ice cubes of chloroplatinic acid and liquid nitrogen together to a nanosecond laser with a wavelength of 355 nm, a power of 4 W, a pulse width of 20 ns, and a frequency of 50 kHz.

[0067] (2) Focus the laser beam on the upper surface of the chloroplatinic acid ice block, with a spot diameter of 50 μm, and conduct a three-dimensional scan of the entire ice block once from top to bottom. The planar scan speed is 700 mm / s, and the vertical scan speed is 0.3 mm / min to obtain platinum single atoms confined in the ice block.

[0068] (3) Disperse 50 mg of g-C 3 N 4 nanosheet powder into 10 mL of deionized water and use 400 W ultrasonic treatment for 2 h to prepare a stable dispersion. Put the scanned ice block into the prepared g-C 3 N 4 dispersion, stir (600 rpm) at 2 °C for 4 h to enable the low-temperature adsorption and sufficient anchoring of Pt single atoms on the g-C 3 N 4 support. Centrifuge (3000 rpm) and wash the obtained g-C 3 N 4 supported platinum single atom dispersion 3 times, and put it into a freeze dryer for freeze drying to finally obtain a single-atom supported catalyst, denoted as Pt / g-C 3 N 4 -0.3 VS, where 0.3 VS refers to the vertical scan rate of 0.3 mm / min during the laser reduction process.

[0069] Example 2

[0070] A method for synthesizing a single-atom supported catalyst by laser ice-phase assisted migration, comprising the following steps:

[0071] (1) Pour 10 mL of an aqueous chloroplatinic acid solution with a concentration of 0.1 mg / mL into a stainless steel cup with an inner diameter of 3 cm, and quickly freeze it into an ice block with 150 mL of liquid nitrogen. Transfer the chloroplatinic acid ice block together with the liquid nitrogen to a nanosecond laser with a wavelength of 355 nm, a power of 4 W, a pulse width of 20 ns, and a frequency of 50 kHz.

[0072] (2) Focus the laser beam on the upper surface of the chloroplatinic acid ice block, with a spot diameter of 50 μm, and conduct a three-dimensional scan of the entire ice block once from top to bottom. The planar scan speed is 700 mm / s, and the vertical scan speed is 0.5 mm / min to obtain platinum single atoms confined in the ice block.

[0073] (3) Disperse 50 mg of g-C 3 N 4 nanosheet powder into 10 mL of deionized water and use 400 W ultrasonic treatment for 2 h to prepare a stable dispersion. Put the scanned ice block into the prepared g-C 3 N 4In the dispersion, stir at 2 °C (600 rpm) for 4 h to fully anchor Pt single atoms on g-C 3 N 4 support. Centrifuge (3000 rpm) and wash the obtained g-C 3 N 4 platinum single atom loaded dispersion three times, and then put it into a freeze dryer for freeze drying. Finally, a single atom loaded catalyst is obtained, denoted as Pt / g-C 3 N 4 -0.5 VS, where 0.5 VS means the vertical scanning rate is 0.5 mm / min during the laser reduction process..

[0074] Example 3

[0075] A method for synthesizing a single atom loaded catalyst assisted by laser ice phase migration, comprising the following steps:

[0076] (1) Pour 10 mL of an aqueous solution of chloroplatinic acid with a concentration of 0.1 mg / mL into a stainless steel cup with an inner diameter of 3 cm, and quickly freeze it into an ice block with 150 mL of liquid nitrogen. Transfer the chloroplatinic acid ice block and liquid nitrogen together to a nanosecond laser with a wavelength of 355 nm, a power of 4 W, a pulse width of 20 ns, and a frequency of 50 kHz.

[0077] (2) Focus the laser beam on the upper surface of the chloroplatinic acid ice block, with a spot diameter of 50 μm, and perform a three-dimensional scan of the entire ice block once from top to bottom. The planar scanning speed is 700 mm / s, and the vertical scanning speed is 0.7 mm / min to obtain ice-confined platinum single atoms.

[0078] (3) Disperse 50 mg of g-C 3 N 4 nanosheet powder into 10 mL of deionized water, and use ultrasonic treatment at 400 W for 2 h to prepare a stable dispersion. Put the scanned ice block into the prepared g-C 3 N 4 dispersion, stir at 2 °C (600 rpm) for 4 h to fully anchor Pt single atoms on g-C 3 N 4 support. Centrifuge (3000 rpm) and wash the obtained g-C 3 N 4 platinum single atom loaded dispersion three times, and then put it into a freeze dryer for freeze drying. Finally, a single atom loaded catalyst is obtained, denoted as Pt / g-C 3 N 4 -0.7 VS single atom powder, where 0.7 VS means the vertical scanning rate is 0.7 mm / min during the laser reduction process.

[0079] Example 4

[0080] Method for synthesizing single-atom supported catalyst by laser ice-phase assisted migration, comprising the following steps:

[0081] (1) Pour 10 mL of an aqueous solution of chloroplatinic acid with a concentration of 0.1 mg / mL into a stainless steel cup with an inner diameter of 3 cm, and quickly freeze it into an ice cube with 150 mL of liquid nitrogen. Transfer the chloroplatinic acid ice cube and liquid nitrogen together to a nanosecond laser with a wavelength of 355 nm, a power of 4 W, a pulse width of 20 ns, and a frequency of 30 kHz.

[0082] (2) Focus the laser beam on the upper surface of the chloroplatinic acid ice cube, with a spot diameter of 50 μm, and perform a three-dimensional scan of the entire ice cube once from top to bottom. The planar scan speeds are 100, 300, 500, or 900 mm / s respectively, and the vertical scan speed is 0.3 mm / min to obtain ice-confined platinum single atoms.

[0083] (3) Disperse 50 mg of g-C 3 N 4 nanosheet powder into 10 mL of deionized water, and ultrasonically treat it for 2 h with 400 W to prepare a stable dispersion. Put the scanned ice cube into the prepared g-C 3 N 4 dispersion, stir at 2 °C (600 rpm) for 4 h to enable low-temperature adsorption and sufficient anchoring of Pt single atoms on the g-C 3 N 4 support. Centrifuge (3000 rpm) and wash the obtained g-C 3 N 4 supported platinum single atom dispersion 3 times, and put it into a freeze dryer for freeze drying to finally obtain a single-atom supported catalyst.

[0084] Example 5

[0085] Method for synthesizing single-atom supported catalyst by laser ice-phase assisted migration, comprising the following steps:

[0086] (1) Pour 10 mL of an aqueous solution of chloroplatinic acid with a concentration of 0.1 mg / mL into a stainless steel cup with an inner diameter of 3 cm, and quickly freeze it into an ice cube with 150 mL of liquid nitrogen. Transfer the chloroplatinic acid ice cube and liquid nitrogen together to a nanosecond laser with a wavelength of 355 nm, a power of 4 W, a pulse width of 20 ns, and frequencies of 20, 30, 40, 60, and 70 kHz respectively.

[0087] (2) Focus the laser beam on the upper surface of the chloroplatinic acid ice cube, with a spot diameter of 50 μm, and perform a three-dimensional scan of the entire ice cube once from top to bottom. The planar scan speed is 700 mm / s, and the vertical scan speed is 0.7 mm / min to obtain ice-confined platinum single atoms.

[0088] (3) Disperse 50 mg of g-C 3 N 4 nanosheet powder into 10 mL of deionized water, and use 400 W ultrasonic treatment for 2 h to prepare a stable dispersion. Put the scanned ice cubes into the prepared g-C 3 N 4 dispersion, stir at 2 °C (600 rpm) for 4 h, so that Pt single atoms are adsorbed at low temperature and fully anchored on g-C 3 N 4 support. Centrifuge (3000 rpm) and wash the obtained g-C 3 N 4 supported platinum single atom dispersion 3 times, and put it into a freeze dryer for freeze drying to finally obtain a single atom supported catalyst.

[0089] Example 6

[0090] Use GB / T 26915-2011 "Calculation of Energy Conversion Efficiency and Quantum Yield of Solar Photocatalytic Water Splitting Hydrogen Production System" to test the photocatalytic performance of the prepared single atom supported catalyst, including the following steps: Put 50 mg of the single atom supported catalyst prepared in each example, 80 mL of deionized water and 20 mL of triethanolamine into a photocatalytic reactor. The reactor is connected to the closed gas circulation system of the photocatalytic evaluation system, and the vacuum pump is turned on to evacuate the closed system for 20 min to ensure that the pipeline is in a vacuum state. Use a 300 W xenon lamp as the experimental light source for simulating sunlight, and the reactor temperature is maintained at 2 °C by the cooling water circulation system. Using N 2 as the carrier gas, sample every 30 min and analyze the gas composition by gas chromatography.

[0091] Figure 2 is the XRD pattern of the single atom supported catalyst prepared in Examples 1-3 of the present invention, Figure 3 is the element distribution map of the single atom supported catalyst prepared in Example 2 of the present invention, Figure 4 is the HAADF-STEM image of the single atom supported catalyst prepared in Example 2 of the present invention. It can be seen from Figures 2 to 4 that Pt atoms are distributed in the form of isolated single atoms on g-C 3 N 4 , without aggregating into clusters, proving that the g-C 3 N 4 supported Pt single atom supported catalyst has been successfully prepared.

[0092] Figure 5 is the XANES pattern of the single atom supported catalyst prepared in Example 2 of the present invention. It can be seen that the highest point positions of the Pt single atoms of the single atom supported catalyst prepared in Example 2 are at the R space and k space respectively as and is quite different from the Pt sheet, indicating that no Pt-Pt bond is formed in the material, that is, no agglomeration of platinum atoms occurs. And the position of the highest point is close to that of PtO 2 close, indicating that the Pt atoms in the single-atom supported catalyst prepared in Example 2 are in an electron-losing state, and the possible coordination environment is Pt-N coordination.

[0093] Figure 6 is the photocatalytic hydrogen production rate diagram of the single-atom supported catalysts prepared in Examples 1-3 of the present invention, Figure 7 is the photocatalytic hydrogen production stability diagram of the single-atom supported catalyst prepared in Example 2 of the present invention. It can be seen that the single-atom supported catalyst prepared by the present invention has excellent photocatalytic hydrogen production activity and stability.

[0094] Figure 8 is the photocatalytic hydrogen production rate diagram of the single-atom supported catalysts prepared in Example 4 and Example 1 of the present invention, Figure 9 is the photocatalytic hydrogen production rate diagram of the single-atom supported catalysts prepared in Example 5 and Example 1 of the present invention. It can be seen that the optimal synthesis conditions for preparing the single-atom supported catalyst of the present invention are: the horizontal scanning rate is 700 mm / s, the vertical scanning rate is 0.7 mm / min, and the laser pulse frequency is 50 kHz.

[0095] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for synthesizing single-atom supported catalysts by laser ice phase assisted migration, characterized in that: The following steps are involved: Freezing the chloroplatinic acid aqueous solution with liquid nitrogen to obtain chloroplatinic acid ice cubes; In liquid nitrogen, the chloroplatinic acid ice cube is subjected to laser reduction to obtain a reduced ice cube; Mixing the reduced ice cubes with a g-C3N4 dispersion to melt water in the reduced ice cubes, thereby obtaining a g-C3N4-loaded platinum single atom dispersion; The g-C3N4-loaded platinum single atom dispersion is dried to obtain the single atom supported catalyst.

2. The method according to claim 1, characterized in that: The concentration of the chloroplatinic acid aqueous solution is 0.05-2 mg / mL.

3. The method according to claim 1 or 2, characterized in that: When the liquid nitrogen is frozen, the volume ratio of the chloroplatinic acid aqueous solution to the liquid nitrogen is 1:

15.

4. The method according to claim 1, characterized in that: The conditions for the laser reduction include: the plane scanning speed of the laser beam is 100 to 900 mm / s, and the vertical scanning speed is 0.1 to 1 mm / min.

5. The method according to claim 1 or 4, characterized in that: The power of the laser reduction is 1-5W, the pulse frequency is 30-100kHz, and the pulse width is 8-50ns.

6. The method according to claim 1 or 4, characterized in that: The wavelength of the laser reduction is 355 nm.

7. The method according to claim 1, characterized in that The concentration of the g-C3N4 dispersion is no more than 5 mg / mL.

8. The method according to claim 1 or 7, characterized in that: The mass ratio of chloroplatinic acid in the chloroplatinic acid aqueous solution to g-C3N4 in the g-C3N4 dispersion is not greater than 5%, and the mass of the chloroplatinic acid is not 0.

9. The method according to claim 1, characterized in that: The temperature of the freezing condition is 0-10°C.

10. The method according to claim 1, characterized in that The melting is carried out under stirring, and the stirring speed is not less than 600 rpm; after the melting is completed, the stirring is continued, and the stirring time does not exceed 1 minute.

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