Metal monatomic photocatalyst as well as preparation method and application thereof

Abstract

The invention provides a metal monatomic photocatalyst and a preparation method and application thereof, and the preparation method comprises the following steps: mixing a nitrogen-containing precursor and an ammonia water solution of a metal precursor, evaporating and roasting to obtain metal-loaded polymer carbon nitride powder; and mixing the powder with a lithium salt and a potassium salt, and roasting in vacuum to obtain the metal monatomic catalyst with optical activity. The metal monatomic catalyst prepared by the preparation method disclosed by the invention is used for photocatalytic carbon-nitrogen coupling reaction, trifluoromethylation reaction, cyanation reaction and cyano trifluoromethylation reaction, and good yield can be obtained. The catalyst is simple to prepare and wide in application range, and can better meet the requirements of the actual production process.

Description

Technical Field

[0001] The present invention belongs to the field of photocatalyst preparation, and specifically relates to a metal single-atom photocatalyst and a preparation method and application thereof, which are used for photocatalytic reactions. Background Art

[0002] Over the past few decades, energy shortages and environmental remediation have become serious challenges for human long-term development. Semiconductor-based photocatalysis is an advanced green technology that uses inexhaustible sunlight as its power and suitable semiconductors as catalysts to generate photogenerated electrons and holes, thereby carrying out photoredox reactions. Semiconductor catalysts include inorganic semiconductors and organic semiconductors. Among them, inorganic semiconductors, such as TiO2, SnO2, ZnO, etc., are a widely used photocatalyst with advantages such as high free carrier concentration, high carrier mobility, and high physicochemical stability. However, such catalysts are usually limited by narrow and fixed absorption spectra. In addition, their structural modification usually involves complex manufacturing processes or harsh conditions.

[0003] Compared to inorganic semiconductors, organic semiconductors offer structural diversity and synthetic functionality, allowing for the modulation of optoelectronic properties through structural and functional engineering. Conjugated polymers such as g-C3N4, polypyrrole (PPy), polyaniline (PANI), polyimide (PI), poly(3-hexylthiophene) (P3HT), and polyhydroxybutyrate (PHB) have been widely used for photocatalytic purposes due to their ability to modulate optoelectronic properties at the molecular level. Graphitic carbon nitride (g-C3N4) is a class of polymer materials primarily composed of carbon and nitrogen and is the most stable allotrope of carbon nitride in the ambient atmosphere. It possesses a rich variety of surface properties and is attractive for many applications due to its structural and electronic properties.

[0004] Furthermore, single-atom catalysts (SACs) have demonstrated significant advantages in catalysis due to their fully exposed active sites, 100% atomic utilization, and unique electronic structure. Carbon-supported SACs, owing to their high surface area, tunable electron transfer properties, and excellent chemical stability, have become a research hotspot and have demonstrated exceptional performance in heterogeneous catalytic systems. Structurally, SACs, through the precise assembly of metal atoms and support-coordinating atoms, form a localized coordination environment similar to that of organometallic complexes. This characteristic makes them an ideal bridge between homogeneous and heterogeneous catalysis, providing a unique platform for atomic-scale analysis of the structure-activity relationship between active site configuration and catalytic performance. SACs, due to their high reactivity and recyclability, have demonstrated significant economic value and have been successfully applied to a number of organic synthesis reactions, but their scope of application remains relatively limited. Existing research has primarily focused on thermal catalytic systems, while the development of SACs for photo-driven organic synthesis (such as visible-light-induced CC or CN couplings, trifluoromethylation, and cyanation reactions) remains significantly underdeveloped. Summary of the Invention

[0005] The present invention provides a metal single-atom photocatalyst and a preparation method thereof. The carbon nitride-supported metal single-atom catalyst achieves uniform distribution of the metal on the carbon nitride carrier at the atomic level. The prepared metal single-atom catalyst has good catalytic activity and stability.

[0006] The present invention also provides an application of a metal single-atom photocatalyst for photocatalytic reactions, especially for carbon-nitrogen coupling reactions, trifluoromethylation reactions, cyanation reactions, and cyanotrifluoromethylation reactions.

[0007] The specific technical solutions of the present invention are as follows:

[0008] A method for preparing a metal single-atom photocatalyst comprises the following steps:

[0009] 1) mixing an aqueous solution of a nitrogen-containing precursor and an aqueous ammonia solution of a metal precursor to obtain a mixed liquid, and evaporating the mixed liquid to obtain a powder 1;

[0010] 2) calcining the powder 1 to obtain metal-loaded polymer carbon nitride;

[0011] 3) mixing and grinding the metal-loaded polymer carbon nitride with potassium salt and lithium salt to obtain powder 2;

[0012] 4) The powder 2 is calcined in an inert gas, washed, and dried to obtain a metal single-atom photocatalyst.

[0013] Step 1) in, the ratio of metal precursor to ammoniacal liquor in the ammoniacal liquor containing metal precursor is 1g / L-200g / L;Described metal precursor is transition metal precursor, including iron precursor, copper precursor, nickel precursor, cobalt precursor, manganese precursor or zinc precursor;Described iron precursor is selected from FeBr2, described nickel precursor selects NiCl2, described cobalt precursor is selected from CoCl2, described manganese precursor selects MnCl2, described zinc precursor selects Zn(OAc)2, described copper precursor is selected from cuprous bromide, cuprous chloride, cupric chloride, cupric bromide, copper sulfate or cuprous iodide, preferably cuprous iodide. The present invention utilizes ammoniacal liquor to dissolve the metal precursor with poor solubility, on the one hand improves the solubility of metal precursor and facilitates it to be uniformly mixed with other nitrogen-containing precursors, on the other hand improves the nitrogen content of metal precursor, is conducive to the synthesis of single-atom dispersed catalyst, obtains high metal loading, dispersible metal single-atom catalyst.

[0014] In step 1), the concentration of the aqueous ammonia is 25%-29%;

[0015] In step 1), the mass ratio of the nitrogen-containing precursor to the metal-containing precursor is 20-200:1;

[0016] In step 1), the nitrogen-containing precursor is urea or a mixture of urea and oxalamide; when the nitrogen precursor is a mixture of urea and oxalamide, the mass ratio of urea to oxalamide is 1:1000-1000:1.

[0017] In step 1), in the aqueous solution of the nitrogen-containing precursor, the amount ratio of the nitrogen-containing precursor to water is 0.1-5.0 / g / mL;

[0018] In step 1), the mixing refers to ultrasonic mixing;

[0019] In step 1), there is no special requirement for the evaporation time, and the liquid in the mixed liquid can be evaporated to dryness.

[0020] In step 2), the calcination is carried out in a muffle furnace under the following conditions: air atmosphere, 1-5°C·min -1 The temperature is raised to 500-560°C at a heating rate of 100-200°C and calcined at 500-560°C for 1-3h.

[0021] In step 3), the mass ratio of the supported polymer carbon nitride to the potassium salt and the lithium salt is 1:100:100-100:10:10; the potassium salt is selected from potassium chloride, and the lithium salt is selected from lithium chloride.

[0022] In step 4), the calcination is carried out in a tube furnace under the following conditions: high purity argon gas at a temperature of 1-5°C·min -1 The temperature is raised to 510-560°C at a heating rate of 100-200°C and calcined at 510-560°C for 1-3h.

[0023] The present invention provides a metal single atom photocatalyst, which is prepared by the above method. The metal single atom is loaded on a carbon nitrogen (CN) carrier. The carbon nitrogen carrier is a flaky structure with a size of 10-900nm, and the metal single atom size is 0.1-0.4nm.

[0024] The present invention provides an application of a metal single-atom photocatalyst for photocatalytic reactions, especially for carbon-nitrogen coupling reactions, trifluoromethylation reactions, cyanation reactions and cyanotrifluoromethylation reactions.

[0025] The photocatalytic reaction is carried out under light with a wavelength of 400-520 nm, preferably under light with a wavelength of 450 nm.

[0026] The photocatalytic reaction is carried out at a reaction temperature of 20-80°C, preferably 40-50°C.

[0027] In the photocatalytic reaction, the reaction solvent is any one or more of acetonitrile, water, acetone, dimethyl sulfoxide, 1,4-dioxane, N,N-dimethylformamide, N,N-dimethylacetamide and toluene.

[0028] When used for photocatalytic carbon-nitrogen coupling reaction, preferably, the reaction substrate is alkyl halide / boric acid or aryl halide / boric acid, wherein the general formula of aryl halide / boric acid is Wherein X is iodine, bromine, chlorine, R is hydrogen, phenyl, methyl, trifluoromethyl, methoxy, hydroxyl, bromine, chlorine, fluorine, cyano, methyl formate, ethyl formate, etc., and the substituents of the alkyl group include C1-C 10 Alkyl, C3-C 10 Cycloalkyl, 3-10 membered heterocyclic group.

[0029] When used for photocatalytic trifluoromethylation reaction, cyanation reaction and cyano trifluoromethylation reaction, preferably, the reaction substrate is an alkyl terminal olefin or an aryl terminal olefin, wherein the aryl terminal olefin has the general formula Where n is the number of carbon atoms in the chain, n is a natural number greater than or equal to 1 and less than 5, R is phenyl, methyl, trifluoromethyl, methoxy, hydroxyl, bromine, chlorine, fluorine, cyano, methyl formate, ethyl formate, and the substituents of the alkyl terminal olefin include C1-C 10 Alkyl, C3-C 10 Cycloalkyl, 3-10 membered heterocyclic group.

[0030] The beneficial effects of the present invention are as follows:

[0031] The present invention uses ammonia water to dissolve metal precursors to obtain ammonia-coordinated metal precursors with better solubility, which is beneficial to enhancing the dispersion of the metal in the support material and preventing the agglomeration of metal atoms during the catalyst synthesis process; the technical solution of the present invention can obtain high metal loading, dispersed metal single-atom catalysts, and can use metal precursors with poor solubility, thereby expanding the universality of catalyst synthesis; and the strategy of dissolving metal precursors with ammonia water adopted in the present invention to prepare single-atom catalysts can be extended to other transition metal precursors other than copper, such as FeBr2, NiCl2, CoCl2, MnCl2, Zn(OAc)2, and thus prepare single-atom catalysts loaded with other metals.

[0032] The metal single-atom catalyst with photocatalytic activity prepared by the present invention has a high metal dispersion. During the reaction process, each atom can participate in the reaction as an active site, which significantly improves the utilization efficiency of the metal. At the same time, the high metal loading can have better catalytic activity in the reaction.

[0033] Unlike traditional catalysts that can mostly complete only one type of reaction, the metal single-atom catalyst with photocatalytic activity prepared by the present invention can simultaneously complete carbon-nitrogen coupling reaction, trifluoromethylation reaction, cyanation reaction and trifluoromethylcyanation reaction; there are currently no reports on the use of single-atom photocatalysts to achieve trifluoromethylation reaction, cyanation reaction and trifluoromethylcyanation reaction of olefins.

[0034] Unlike nanocatalysts that are deactivated by the recombination of electron-hole pairs generated by light during the entire reaction process, and expensive ligands are introduced to avoid deactivation, the metal single-atom catalyst with photocatalytic activity prepared by the present invention has good stability and recyclability;

[0035] The carbon nitride material used in the present invention is widely used to drive photocatalytic reactions due to its high surface area, structural electronic properties, and optical band gap properties. However, its absorption efficiency of visible light in the solar spectrum is low, resulting in its photocatalytic activity being at a low level. The metal single-atom catalyst with photocatalytic activity prepared by the present invention loads the metal on a carbon nitride carrier, greatly expanding its light response range and promoting the better application of photogenerated charge separation in the field of photocatalysis.

[0036] In addition, the metal single-atom catalyst with photocatalytic activity prepared by the present invention does not require a high-temperature and high-pressure working environment for photocatalytic reactions, and can avoid the use of high-energy ultraviolet light used by other photocatalytic systems. The catalyst mainly uses light sources in the visible light band, such as blue light, which is beneficial for improving the functional group compatibility of the substrate and reducing the probability of high-energy ultraviolet light activating non-reactive groups, thereby improving the reaction selectivity.

[0037] The synthesis method of the metal single-atom catalyst with photocatalytic activity prepared by the present invention is simple, has low dependence on equipment during preparation, can be widely promoted in actual production, and can better meet the needs of the production process.

[0038] Compared with the existing technology, the present invention studies metal single-atom photocatalysts for organic synthesis reactions with wide applications. It improves the photoactivation mechanism of complex organic molecular systems and the efficiency of photogenerated carrier separation of catalysts, and can expand its application scenarios in the fields of drug synthesis, fine chemical preparation, etc., thereby promoting single-atom catalytic technology towards industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is the XRD pattern of the copper single atom catalyst in Example 1;

[0040] Figure 2 This is a spherical aberration corrected scanning transmission electron microscopy (AC-STEM) image of the copper single-atom catalyst in Example 1;

[0041] Figure 3 This is the X-ray absorption fine structure (EXAFs) spectrum of the copper single-atom catalyst in Example 1, where Cu2O is +1-valent copper, CuO is +2-valent copper, and Cu foil is 0-valent copper, all of which are purchased; Cu-CN is a sample prepared by the present invention;

[0042] Figure 4 is the CN coupling reaction equation of aryl iodide and imidazole in Example 3;

[0043] Figure 5 This is the H NMR spectrum of 1-phenylimidazole;

[0044] Figure 6 This is the NMR carbon spectrum of 1-phenylimidazole;

[0045] Figure 7 is the CN coupling reaction equation of arylboronic acid and benzimidazole in Example 4;

[0046] Figure 8 It is the hydrogen spectrum of 1-phenyl-1H-benzimidazole;

[0047] Figure 9 It is the carbon spectrum of 1-phenyl-1H-benzimidazole;

[0048] Figure 10 is the reaction equation for the trifluoromethylation of styrene with Togni I in Example 5;

[0049] Figure 11 This is the hydrogen spectrum of the trifluoromethylation product of styrene and Togni I;

[0050] Figure 12This is the carbon spectrum of the trifluoromethylation product of styrene and Togni I;

[0051] Figure 13 is the cyanation reaction equation of 4-phenyl-1-butene with in Example 6;

[0052] Figure 14 It is the hydrogen spectrum of 2-phenylacrylonitrile;

[0053] Figure 15 It is the carbon spectrum of 2-phenylacrylonitrile;

[0054] Figure 16 is the reaction equation for the cyano-trifluoromethylation of 4-phenyl-1-butene with in Example 7;

[0055] Figure 17 The hydrogen spectrum of the cyano-trifluoromethylation product of 4-phenyl-1-butene;

[0056] Figure 18 The carbon spectrum of the cyano-trifluoromethylation product of 4-phenyl-1-butene;

[0057] Figure 19 This is a diagram showing the trifluoromethylation cyclicity test described in Example 8;

[0058] Figure 20 is the carbon-nitrogen coupling reaction equation of 4-bromotrifluorotoluene and tetrahydropyrrole in Example 9;

[0059] Figure 21 is the hydrogen spectrum of 1-(4-(trifluoromethyl)phenyl)pyrrolidine;

[0060] Figure 22 This is the carbon spectrum of 1-(4-(trifluoromethyl)phenyl)pyrrolidine. DETAILED DESCRIPTION

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0062] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0063] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the field or according to the product instructions.

[0064] Example 1

[0065] A method for preparing a copper single-atom photocatalyst comprises the following steps:

[0066] 1) First, 0.23 g of cuprous iodide was dispersed in 5 mL of a 28 wt% ammonia solution by stirring and ultrasonication. Then, urea and oxalamide were mixed in a mass ratio of 20:1 to obtain 21 g of a nitrogen-containing precursor. The mixture was added to 20 mL of an aqueous solution, stirred and ultrasonicated to obtain a nitrogen-containing precursor aqueous solution. Subsequently, the ammonia solution of cuprous iodide was added dropwise to the nitrogen-containing precursor aqueous solution, stirred and ultrasonicated, and then evaporated to obtain powder 1.

[0067] 2) The obtained powder 1 was then placed in a muffle furnace in an air atmosphere at 3°C·min -1 The heating rate was increased to 500°C and calcined for 2h to prepare copper-loaded polymer carbon nitride.

[0068] 3) 1.2 g of copper-loaded polymeric carbon nitride was mixed with 6.6 g of potassium chloride and 5.4 g of lithium chloride, and the mixture was thoroughly ground to obtain powder 2;

[0069] 4) The obtained powder 2 was placed in a porcelain boat and placed in the middle of a quartz tube; the quartz tube was placed in a tube furnace and heated at 4.6°C·min under a flow of 99.9999% high-purity argon. -1 The heating rate was increased to 550°C and calcined for 2 hours. The obtained solid was washed with water and dried in a vacuum drying oven at 80°C for 8 hours to obtain a copper single-atom catalyst with photocatalytic activity supported on a polymer carbon nitride substrate. The copper content was determined to be 6.37 wt% by ICP.

[0070] No Cu-related nanoparticles were detected or observed in the prepared copper single-atom catalyst (see Figure 1 XRD spectrum), while Cu atoms are uniformly dispersed in the support (see Figure 2 AC-STEM diagram and Figure 3 EXAFs diagram). Figure 3 This reflects the comparison between the sample of the present invention and copper compounds of different valence states, thereby indicating that there are no Cu nanoparticles in Cu-CN, and Cu mainly exists in the form of Cu single atoms.

[0071] Example 2

[0072] A method for preparing a copper single-atom photocatalyst, specifically comprising:

[0073] 1) First, 0.12 g of cuprous iodide was dispersed in 5 mL of a 28 wt% ammonia solution by stirring and ultrasonication. Then, urea and oxalamide were mixed at a ratio of 20:1 to obtain 21 g of a nitrogen-containing precursor. The mixture was added to 20 mL of an aqueous solution with stirring and ultrasonication. Subsequently, the ammonia solution of cuprous iodide was added dropwise to the nitrogen-containing precursor aqueous solution with stirring and ultrasonication, and then evaporated to obtain powder 1.

[0074] 2) The obtained powder 1 was then placed in a muffle furnace and heated at 4°C·min -1 The heating rate was increased to 500°C and calcined for 2h to prepare copper-loaded polymer carbon nitride.

[0075] 3) 1.2 g of copper-loaded polymeric carbon nitride was mixed with 6.6 g of potassium chloride and 5.4 g of lithium chloride, and the mixture was thoroughly ground to obtain powder 2;

[0076] 4) The obtained powder 2 was placed in a porcelain boat and placed in the middle of a quartz tube; the quartz tube was placed in a tube furnace and heated at 4.6°C·min under a flow of 99.9999% high-purity argon. -1 The heating rate was increased to 550° C. and calcined for 2 h. The obtained solid was washed with water and dried in a vacuum drying oven at 80° C. for 8 h to obtain a copper single atom catalyst with photocatalytic activity supported on a polymer carbon nitride substrate, with a copper content of 3.05 wt%.

[0077] Example 3

[0078] An application of a copper single-atom photocatalyst for a photocatalytic reaction, specifically: using the copper single-atom catalyst prepared in Example 1 as a catalyst to catalyze the CN coupling reaction of an aryl iodide and imidazole, specifically as follows:

[0079] Take a 10mL Schlenk flask and add a suitable magnetic stirrer. Then add t-BuOK (2.0equiv.), imidazole (3.0equiv.), and 40mg of the catalyst prepared in Example 1 to the Schlenk flask in sequence. After evacuating the double-row tube, add iodobenzene (0.25mmol) and ultra-dry acetonitrile (0.6mL) under argon protection. The reaction was carried out under 450nm blue light for 48h, and the temperature was about 45°C. After the reaction was completed, it was separated and purified by column chromatography. The eluent used for column chromatography was a mixed solvent of petroleum ether and ethyl acetate. The volume ratio of petroleum ether and ethyl acetate in the eluent was 1:1 to obtain the purified target product (reaction equation as shown in FIG. Figure 4 ), the yield was 95%, and the product was characterized 1 H. 13 C NMR spectrum Figure 5 、 Figure 6 The specific values ​​are as follows:

[0080] 1 H NMR (400MHz, CDCl3) δ = 7.83 (br s, 1H), 7.47-7.43 (m, 2H), 7.36-7.33 (m, 3H), 7.26 (br s, 1H), 7.18 (br s, 1H).

[0081] 13C NMR (100MHz, CDCl3) δ = 137.14, 135.38, 130.24, 129.72, 127.30, 121.23, 118.05.

[0082] Example 4

[0083] An application of a copper single-atom photocatalyst for a photocatalytic reaction, specifically: using the copper single-atom catalyst prepared in Example 1 as a catalyst to catalyze the CN coupling reaction of an arylboronic acid and a benzimidazole, specifically as follows:

[0084] Take a 10mL Schlenk flask and add a suitable magnetic stirrer. Then add t-BuOK (2.0equiv.), benzimidazole (3.0equiv.), and 40mg of the catalyst prepared in Example 1 to the Schlenk flask in sequence. After evacuating the double-row tube, add phenylboric acid (0.25mmol) and ultra-dry acetonitrile (0.6mL) under argon protection. The reaction was carried out under 450nm blue light for 48h at a temperature of about 45°C. After the reaction was completed, it was separated and purified by column chromatography. The eluent used for column chromatography was a mixed solvent of petroleum ether and ethyl acetate. The volume ratio of petroleum ether and ethyl acetate in the eluent was 2:1 to obtain the purified target product (reaction equation as shown in FIG. Figure 7 ), the yield was 89%, and the product was characterized 1 H. 13 C NMR spectrum Figure 8 、 Figure 9 The specific values ​​are as follows:

[0085] 1 H NMR (400MHz, CDCl3) δ = 8.42 (s, 1H), 7.97 (d, J = 7.0Hz, 1H), 7.69-7.47 (m, 6H), 7.45-7.35 (m, 2H).

[0086] 13 C NMR (100MHz, CDCl3) δ = 143.77, 141.66, 136.28, 133.66, 130.10, 128.13, 124.07, 123.81, 122.93, 120.55, 110.55.

[0087] Example 5

[0088] An application of a copper single-atom photocatalyst for a photocatalytic reaction, specifically: using the copper single-atom catalyst prepared in Example 1 as a catalyst to catalyze the trifluoromethylation reaction of 4-vinyl-1,1'-biphenyl and Togni I, specifically as follows:

[0089] Take a 10mL Schlenk flask and add a suitable magnetic stirrer. Then, add 4-vinyl-1,1'-biphenyl (0.1mmol), Togni I (2equiv), DBU (2equiv), and 40mg of the catalyst prepared in Example 1 to the Schlenk flask in sequence. After evacuating the double-row tube, add 1mL of 1,4-dioxane under argon protection. The reaction is carried out under 450nm blue light for 24h. After the reaction is completed, the purified target product is separated and purified by column chromatography (reaction equation as shown below) Figure 10 ), the yield was 98%, and the product was characterized 1 H. 13 C NMR spectrum Figure 11 、 Figure 12 The specific values ​​are as follows:

[0090] 1 H NMR (400MHz, CDCl3) δ=7.65-7.60(m,4H),7.54(d,J=8.3Hz,2H),7.47(dd,J=8.3,6.8H z,2H),7.42-7.36(m,1H),7.20(dd,J=16.2,2.3Hz,1H),6.25(dq,J=16.2,6.5Hz,1H).

[0091] 13 C NMR(101MHz, CDCl3)δ=142.84,140.12,137.26,137.20,132.36,128.95,128.82,128.05,1 27.88,127.60,127.35,127.26,127.08,126.99,126.67,115.88,115.55,115.21,113.93.

[0092] Example 6

[0093] An application of a copper single-atom photocatalyst for a photocatalytic reaction is described, specifically: using the copper single-atom catalyst prepared in Example 1 as a catalyst to catalyze the cyanation reaction of 4-vinyl-1,1'-biphenyl with , as follows:

[0094] Take a 10mL Schlenk flask and add a suitable magnetic stirrer. Then add 4-vinyl-1,1'-biphenyl (0.2mmol), Selectfluoro reagent (0.3mmol), trimethylsilyl cyanide (50μL), and 60mg of the catalyst prepared in Example 1 to the Schlenk flask in sequence. After the double-row tube is evacuated, 1mL of a mixed solvent of acetone and water (2:1) is added under argon protection. The reaction is carried out under 450nm blue light for 12h at a temperature of 25°C. After the reaction is completed, it is separated and purified by column chromatography to obtain the purified target product (reaction equation as shown in FIG. Figure 13 ), the yield was 80%, the product was characterized 1 H. 13 C NMR spectrum Figure 14 、 Figure 15 The specific values ​​are as follows:

[0095] 1 H NMR (400MHz, Chloroform-d) δ = 7.67 (d, J = 4.2Hz, 3H), 7.63-7.60 (m, 2H), 7.52-7.43 (m, 3H), 7.40 (d, J = 7.2Hz, 1H), 6.38 (s, 1H), 6.13 (s, 1H).

[0096] 13 C NMR (101MHz, Chloroform-d) δ = 135.72, 134.49, 133.70, 131.22, 128.64, 128.22, 126.18, 125.88, 125.76, 123.81 (d, J = 13.4Hz), 117.23.

[0097] Example 7

[0098] An application of a copper single-atom photocatalyst for a photocatalytic reaction, specifically: using the copper single-atom catalyst prepared in Example 1 as a catalyst to catalyze the cyano-trifluoromethylation reaction of 4-vinyl-1,1'-biphenyl, as follows:

[0099] Take a 10mL Schlenk flask and add a suitable magnetic stirrer. Then add 4-vinyl-1,1'-biphenyl (0.2mmol), Togni I reagent (0.3mmol), trimethylsilyl cyanide (75μL), and 60mg of the catalyst prepared in Example 1 to the Schlenk flask in sequence. After the double-row tube is evacuated, 1mL of dimethyl sulfoxide is added as a solvent under argon protection, and the reaction is carried out under 450nm blue light at a temperature of 50°C for 12h. After the reaction is completed, the purified target product is obtained by separation and purification by column chromatography (reaction equation as shown in FIG. Figure 16), the yield was 80%, the product was characterized by 1H, 13 C NMR spectrum Figure 17 、 Figure 18 The specific values ​​are as follows:

[0100] 1 H NMR(400MHz,Chloroform-d)δ=7.66-7.63(m,2H),7.60-7.56(m,2H),7.49-7.43(m,4H),7.42-7.37(m ,1H), 4.15(dd,J=9.6,5.1Hz,1H), 2.88(dt,J=15.1,9.6Hz,1H), 2.64(ddd,J=15.0,10.0,5.1Hz,1H).

[0101] 13 C NMR(101MHz,Chloroform-d)δ=134.28,130.15,129.81,129.37,129.00,127.81,1 26.67, 125.85 (d, J = 43.7Hz), 121.35, 118.96, 39.81-38.21 (m), 28.36 (q, J = 3.3).

[0102] Example 8

[0103] The copper single atom catalyst prepared in Example 1 was used as a catalyst to catalyze the trifluoromethylation reaction of 4-vinyl-1,1'-biphenyl with Togni I. The specific test is as follows:

[0104] 4-vinyl-1,1'-biphenyl (0.1 mmol), Togni I (2 equiv), DBU (2 equiv), and 40 mg of the catalyst prepared in Example 1 were added to a 10 mL Schlenk tube in sequence. The reaction tube was then quickly evacuated and 1 mL of 1,4-dioxane was added under argon protection. The reaction was carried out under 450 nm blue light for 12 h. After the reaction was completed, the mixture was cooled to room temperature, and the product and the catalyst were separated by centrifugation and then separated by silica gel column chromatography to obtain the yield. The recovered catalyst was then dried and the above operation was repeated. The data obtained from the five cycles were plotted as shown in FIG. Figure 19 As shown in the figure, after 5 cycles, the catalytic effect is still high.

[0105] Example 9

[0106] A method for preparing a nickel single-atom photocatalyst, specifically comprising:

[0107] 1) First, 816 mg of nickel chloride was dispersed in 5 mL of 28 wt% ammonia solution by stirring and ultrasonication. Then, urea and oxalamide were mixed at a ratio of 20:1 to obtain 21 g of a nitrogen-containing precursor. The mixture was added to 20 mL of aqueous solution with stirring and ultrasonication. Subsequently, the ammonia solution of nickel chloride was added dropwise to the nitrogen-containing precursor aqueous solution with stirring and ultrasonication, and then evaporated to obtain powder 1.

[0108] 2) The obtained powder 1 was then placed in a muffle furnace and heated at 4°C·min -1 The heating rate was increased to 500°C and calcined for 2h to prepare nickel-loaded polymer carbon nitride.

[0109] 3) 1.2 g of nickel-loaded polymeric carbon nitride was mixed with 6.6 g of potassium chloride and 5.4 g of lithium chloride, and the mixture was thoroughly ground to obtain powder 2;

[0110] 4) The obtained powder 2 was placed in a porcelain boat and placed in the middle of a quartz tube; the quartz tube was placed in a tube furnace and heated at 4.6°C·min under a flow of 99.9999% high-purity argon. -1 The heating rate was increased to 550° C. and calcined for 2 h. The obtained solid was washed with water and dried in a vacuum drying oven at 80° C. for 8 h to obtain a nickel single atom catalyst with photocatalytic activity supported on a polymer carbon nitride substrate, with a nickel content of 2.76 wt%.

[0111] Example 10

[0112] An application of a nickel single-atom photocatalyst for a photocatalytic reaction, specifically: using the nickel single-atom catalyst prepared in Example 9 as a catalyst to catalyze the CN coupling reaction of an aryl bromide and tetrahydropyrrole, specifically as follows:

[0113] Take a 10mL Schlenk flask and add a suitable magnetic stirrer. Then add DABCO (1.5equiv.) and 30mg of the catalyst prepared in Example 9 to the Schlenk flask in sequence. After evacuating the double-row tube, add 4-bromotrifluorotoluene (0.25mmol), tetrahydropyrrole (3.0equiv.), and 1.0mL of ultra-dry N,N-dimethylacetamide (DMAc) under argon protection. The reaction was carried out under 460nm blue light for 24h at a temperature of about 45°C. After the reaction was completed, it was separated and purified by column chromatography. The eluent used for column chromatography was a mixed solvent of petroleum ether and ethyl acetate. The volume ratio of petroleum ether and ethyl acetate in the eluent was 10:1 to obtain the purified target product (reaction equation as shown in FIG. Figure 20 ), the yield was 93%, and the product was characterized 1 H. 13 C NMR spectrum Figure 21 、 Figure 22 The specific values ​​are as follows:

[0114] 1 H NMR (400MHz, CDCl3) δ = 7.44 (d, J = 8.5Hz, 2H), 6.54 (d, J = 8.5Hz, 2H), 3.32 (s, 4H), 2.02 (s, 4H).

[0115] 13 C NMR (100MHz, CDCl3) δ=149.88, 126.51 (q, J=3.7Hz), 124.15, 116.75 (d, J=32.6Hz), 110.95, 47.64, 25.60.

[0116] In the actual production operation of the present invention, the factors affecting the yield of metal single-atom catalysts with photocatalytic activity include: the factors affecting the catalytic effect of metal single-atom catalysts with photocatalytic activity include: the wavelength and intensity of the light source. In this experimental scheme, the preferred photocatalytic device is a 10-24W 450nm band light source. Replacing it with other wavelengths may affect the catalytic efficiency and yield; the temperature of the reaction device. In this experimental scheme, the preferred photocatalytic device temperature is about 40-50°C. Replacing it with other photocatalytic devices may affect the catalytic reaction effect.

[0117] The above embodiments are described to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a metal single atom photocatalyst, characterized in that: The preparation method comprises the following steps: 1) mixing a nitrogen-containing precursor and an ammonia solution containing a metal precursor in an aqueous solution to obtain a mixed liquid, and evaporating the mixed liquid to obtain a powder 1; 2) calcining the powder 1 to obtain metal-loaded polymer carbon nitride; 3) mixing and grinding the metal-loaded polymer carbon nitride with potassium salt and lithium salt to obtain powder 2; 4) The powder 2 is calcined in an inert gas, washed, and dried to obtain a metal single-atom photocatalyst.

2. The preparation method according to claim 1, characterized in that In step 1), the ratio of the metal precursor to the ammonia water solution of the metal precursor is 1 g / L-200 g / L.

3. The preparation method according to claim 1 or 2, characterized in that The metal precursor is a transition metal precursor.

4. The preparation method according to claim 1 or 2, characterized in that In step 1), the mass ratio of the nitrogen-containing precursor to the metal-containing precursor is 20-200:

1.

5. The preparation method according to claim 1, characterized in that In step 1), the nitrogen-containing precursor is urea or a mixture of urea and oxamide.

6. The preparation method according to claim 1, characterized in that In step 2), the calcination is carried out at a temperature of 1-5°C / min. -1 The temperature is raised to 500-560°C at a heating rate of 100-200°C and calcined at 500-560°C for 1-3h.

7. The preparation method according to claim 1, characterized in that In step 4), the calcination is carried out under high-purity argon conditions at 1-5 ° C. min -1 The temperature is raised to 510-560°C at a heating rate of 100-200°C and calcined at 510-560°C for 1-3h.

8. A metal single atom photocatalyst, characterized in that The metal single atom photocatalyst is prepared by the preparation method according to any one of claims 1 to 7. The metal single atom is loaded on a carbon-nitrogen carrier after calcining polymer carbon nitride. The size of the metal single atom is 0.1-0.4 nm.

9. An application of a metal single atom photocatalyst, characterized in that: Used for photocatalytic reactions, including carbon-nitrogen coupling reaction, trifluoromethylation reaction, cyanation reaction and cyanotrifluoromethylation reaction.

10. The use according to claim 9, characterized in that The photocatalytic reaction is carried out under light with a wavelength of 400-520 nm.

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