A palladium monatomic loaded cobalt-doped bismuth oxychloride photocatalyst, a preparation method and application thereof

Abstract

The present application is a kind of palladium monatomic supported cobalt-doped bismuth oxychloride photocatalyst and its preparation method and application. The photocatalyst includes cobalt-doped bismuth oxychloride and palladium monatomic; wherein the palladium monatomic is supported on the cobalt-doped bismuth oxychloride; the mass fraction of cobalt doping accounts for 1-3.5% of the total mass of the catalyst, and the mass fraction of palladium monatomic accounts for 0.5-1% of the total mass of the catalyst. In the preparation method, the same kind of anion salt is selected as raw material, and cobalt element is doped into bismuth oxychloride by one-step hydrothermal method to prepare cobalt-doped bismuth oxychloride. By controlling the ratio of soluble palladium source and cobalt-doped bismuth oxychloride, the dispersion state of the loaded palladium species is ensured, and finally the palladium monatomic supported cobalt-doped bismuth oxychloride photocatalyst is obtained. The palladium monatomic supported cobalt-doped bismuth oxychloride photocatalyst prepared by the present application has excellent photocatalytic methane chlorination reaction performance.

Description

Technical Field

[0001] The present invention belongs to the field of nanomaterials and catalysis technology, and in particular relates to a palladium single atom-loaded cobalt-doped bismuth oxychloride photocatalyst, a preparation method and an application thereof. Background Art

[0002] Methyl chloride is an important basic chemical raw material, primarily used in the production of high-value products such as organosilicon materials and agricultural chemicals. Traditionally, methane is converted to methyl chloride using corrosive chlorine gas at temperatures exceeding 200°C. This process is energy-intensive, polluting, and easily leads to deep chlorination of the product. In recent years, the solar-powered photocatalytic methane chlorination reaction, using sodium chloride as a chlorine source, has gained increasing attention. Its mild reaction conditions and environmentally friendly energy source make it a promising technology for producing methyl chloride.

[0003] Bismuth oxychloride (BiOCl) has been widely used in various solar-driven photocatalytic reactions due to its stable chemical properties and safe, non-toxic semiconductor properties. However, due to the low carrier separation efficiency and insufficient catalytic active sites of BiOCl alone, researchers have attempted to modify BiOCl by introducing other components. For example, patent CN119500194A discloses a sulfur-doped BiOCl photocatalyst. Sulfur doping improves the overall photogenerated electron-hole separation efficiency of the catalyst, resulting in superior performance in the photocatalytic degradation of enrofloxacin. However, due to the 1:2 molar ratio of metal elements (Bi) to non-metallic elements (O and Cl) in the BiOCl crystal structure, further doping with non-metallic elements, when the non-metallic elements predominate, can easily lead to structural distortion and collapse of the catalyst. Doping with metal elements is more conducive to the stability of the BiOCl structure and its photocatalytic application. Patent CN113145139B discloses a cuprous oxide-loaded bismuth oxychloride catalyst. The cuprous oxide loading increases the number of active sites, effectively improving the catalyst's ammonia synthesis performance. However, the cuprous oxide is present as particles with an average diameter of tens of nanometers. The atoms within the particles cannot directly participate in the reaction, so the atomic utilization of the active sites still needs to be improved. Ideally, metal nanoclusters or single metal atoms with a loading atomic utilization approaching 100% would be ideal. To achieve metal doping and improve the atomic utilization of the loaded metal, it is necessary to rationally select the type and dosage of the doping metal precursor salt while avoiding excessive agglomeration of the loaded metal species. However, no BiOCl material has yet been produced that combines metal doping with single-atom metal loading. Summary of the Invention

[0004] The purpose of the present invention is to provide a palladium single-atom-loaded cobalt-doped bismuth oxychloride photocatalyst and its preparation method and application in response to the limitations of current technology. The catalyst is a bismuth oxychloride that is both cobalt metal doped and palladium single-atom loaded; the bismuth oxychloride material is doped with cobalt metal elements to improve the separation and utilization efficiency of the overall photogenerated carriers; then, by loading palladium single atoms, efficient active sites are introduced to promote the progress of the photocatalytic reaction; in the preparation method, similar anion salts are selected as raw materials, and cobalt elements are incorporated into bismuth oxychloride by a one-step hydrothermal method to prepare cobalt-doped bismuth oxychloride, and then by controlling the ratio of soluble palladium source to cobalt-doped bismuth oxychloride, the dispersed state of the loaded palladium species is ensured, and finally a palladium single-atom-loaded cobalt-doped bismuth oxychloride photocatalyst is obtained. The palladium single-atom-loaded cobalt-doped bismuth oxychloride photocatalyst prepared by the present invention has excellent photocatalytic methane chlorination reaction performance.

[0005] The technical solution of the present invention is:

[0006] A palladium single atom-supported cobalt-doped bismuth oxychloride photocatalyst comprises cobalt-doped bismuth oxychloride and palladium single atoms; wherein the palladium single atom is supported on the cobalt-doped bismuth oxychloride;

[0007] The mass fraction of the cobalt doping in the whole catalyst is 1-3.5%, and the mass fraction of the palladium single atom in the whole catalyst is 0.5-1%.

[0008] The preparation method of the cobalt-doped bismuth oxychloride photocatalyst supported by a single palladium atom comprises the following steps:

[0009] 1) Add bismuth nitrate pentahydrate, potassium chloride, and cobalt nitrate hexahydrate to ethylene glycol, stir at room temperature for 0.5-1 hour, then transfer to a reactor, hydrothermally react at 120-170°C for 12-24 hours, and separate to obtain cobalt-doped bismuth oxychloride powder;

[0010] Wherein, 3-5 mmol of bismuth nitrate pentahydrate was added to every 70 mL of ethylene glycol;

[0011] The molar ratio of the bismuth nitrate pentahydrate, potassium chloride and cobalt nitrate hexahydrate is 1:1:0.1-0.2;

[0012] 2) dispersing the cobalt-doped bismuth oxychloride in deionized water and stirring at room temperature for 0.5 to 1 hour to obtain a cobalt-doped bismuth oxychloride solution;

[0013] Wherein, 400-600 mg of cobalt-doped bismuth oxychloride was added to every 10 mL of deionized water;

[0014] 3) mixing the cobalt-doped bismuth oxychloride solution and the soluble palladium source solution, stirring at room temperature for 0.5 to 1 hour, and separating after the stirring to obtain a palladium source-loaded cobalt-doped bismuth oxychloride powder;

[0015] The mass ratio of cobalt-doped bismuth oxychloride powder to soluble palladium source is 20:1-3;

[0016] The soluble palladium source is potassium tetrachloropalladate; the concentration of the soluble palladium source solution is 2-3 g / L.

[0017] 4) placing the palladium source-supported cobalt-doped bismuth oxychloride powder into a tube furnace and calcining it at 150-250° C. for 1-3 hours under an inert atmosphere to obtain a palladium single atom-supported cobalt-doped bismuth oxychloride photocatalyst;

[0018] The inert atmosphere is nitrogen or argon.

[0019] The application of the palladium single atom-supported cobalt-doped bismuth oxychloride photocatalyst is used as a photocatalyst in the photocatalytic methane chlorination reaction;

[0020] Specifically, the process comprises the following steps: placing a cobalt-doped bismuth oxychloride photocatalyst supported by a single palladium atom in a reactor, dripping a sodium chloride solution, then purging with methane, and irradiating with a xenon lamp light source for 1 to 3 hours to obtain methyl chloride;

[0021] The mass ratio of catalyst powder to sodium chloride is 10:1~4;

[0022] The concentration of the sodium chloride solution is 3-4 mol / L;

[0023] The methane flow rate of the methane purge is 20-40 mL / min, and the methane purge time is 10-20 minutes;

[0024] The irradiation distance between the xenon lamp light source and the reactor is 10-30 cm, and the intensity of the xenon lamp light source is 100-250 mW / cm 2 .

[0025] The essential features of the present invention are:

[0026] To metal-dope bismuth oxychloride, the present invention uses cobalt nitrate hexahydrate, a salt with the same anion as bismuth nitrate pentahydrate, as the raw material. By precisely controlling the molar ratio of bismuth nitrate pentahydrate, cobalt nitrate hexahydrate, and potassium chloride, a cobalt-doped bismuth oxychloride is synthesized via a one-step hydrothermal method, achieving controllable cobalt metal doping of the bismuth oxychloride. Furthermore, by adjusting the mass ratio of a soluble palladium source to cobalt-doped bismuth oxychloride powder to ensure the dispersion of the loaded palladium species, a single-atom palladium-loaded cobalt-doped bismuth oxychloride photocatalyst is obtained.

[0027] In order to prepare the cobalt-doped bismuth oxychloride photocatalyst supported by palladium single atoms, a soluble palladium source potassium tetrachloropalladate (K2PdCl4) was added to a solution containing cobalt-doped bismuth oxychloride powder, stirred at room temperature, and separated after stirring to obtain the cobalt-doped bismuth oxychloride powder supported by the palladium source. 2+ The ions diffuse to the surface of the cobalt-doped bismuth oxychloride support and chemically adsorb to the chlorine sites on its surface to form bonds; the role of stirring is to promote mass transfer and contact, to ensure that the palladium source precursor and the cobalt-doped bismuth oxychloride are fully mixed, so that Pd 2+ The ions diffuse rapidly and are initially fixed. On this basis, the cobalt-doped bismuth oxychloride powder supported by the palladium source is calcined under an inert atmosphere. The role of this step is to further stabilize the metal-support interaction through heat treatment and form stable palladium-chloride coordinated single atoms.

[0028] The palladium single atom in the present invention is mainly palladium-chlorine coordination ( Figure 5 ), because BiOCl material is composed of Cl - layer and [Bi2O2] 2+ The layers are arranged alternately, in which the oxygen element has been coordinated with the bismuth element, and Cl - layer with [Bi2O2] 2+ The layers are mainly bonded by ionic bonds, so the additionally introduced palladium metal sites tend to coordinate with another non-metallic chlorine element.

[0029] The reproducibility of the palladium single atom preparation process in the present invention is good, because the chlorine sites on the surface of the cobalt-doped bismuth oxychloride support that can be used to anchor palladium are limited and relatively fixed. On the basis of ensuring the stable preparation of the support, by controlling the mass ratio of the soluble palladium source and the support powder, the palladium loading and the content of the chlorine sites for anchoring palladium can be controlled to be in a relatively balanced ratio. When the amount of the soluble palladium source added is further increased, the chlorine sites on the support surface for anchoring palladium may be insufficient, resulting in excess Pd 2+ The ions further agglomerate to form palladium clusters or particles.

[0030] The introduction of palladium single atoms in the present invention has a more significant effect on improving catalytic performance. Palladium single atoms are loaded on the surface of the carrier by the method of impregnation-calcination. Since the catalytic reaction occurs directly on the surface, palladium single atoms can directly participate in the reaction with an atomic utilization rate of nearly 100%, promoting the adsorption, activation and conversion of the reactants; for clusters, particles and other systems, although the metal loading has increased, the metal atoms inside them cannot directly contact the reactants, resulting in the atomic utilization rate of their active sites generally not reaching 100%. Therefore, despite the low loading, the atomic utilization rate of the active sites of palladium single atoms in the catalytic reaction is high, which effectively guarantees its effect on improving catalytic performance.

[0031] The BiOCl material alone consists of Cl - layer and [Bi2O2] 2+ Layers are arranged alternately, and its Cl - layer with [Bi2O2] 2+ The layers are mainly bonded by ionic bonds, and the interaction is weak, which limits the migration and utilization efficiency of photogenerated carriers between layers. After doping with cobalt metal elements, cobalt elements react with Cl - Chlorine and [Bi2O2] in the layer 2+ The oxygen in the layer coordinates to form an additional transfer channel between the two layers, which can effectively promote the separation, transfer, and utilization of photogenerated electrons and holes. On this basis, the palladium single atom with a nearly 100% atomic utilization rate can increase the efficient active sites and significantly improve the catalytic conversion ability of the reactants, all of which are beneficial to the photocatalytic methane chlorination reaction.

[0032] The beneficial effects of the present invention are:

[0033] The palladium single-atom-supported cobalt-doped bismuth oxychloride photocatalyst provided by the present invention exhibits excellent catalytic performance in the photocatalytic methane chlorination reaction, with a high yield of chloromethane and good stability. The doped cobalt metal element can serve as an additional photogenerated carrier transport channel in the bismuth oxychloride, promoting the separation, transfer and utilization of photogenerated electrons and holes ( Figure 1 ). In addition, the palladium single atom with nearly 100% atomic utilization can increase the efficient catalytic active sites. In the photocatalytic methane chlorination reaction, the cobalt-doped bismuth oxychloride photocatalyst supported by palladium single atoms showed a chloromethane yield of 8.1μmol / h, which is thirteen times that of bismuth oxychloride alone ( Figure 6 ), and its catalytic performance showed no obvious attenuation within 5 cycles ( Figure 7 ), showing good stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0035] Figure 1 The photocurrent test spectra of the catalysts of Example 1 and Example 2 are shown;

[0036] Figure 2 1 is the SEM image of the catalyst of Example 1, Example 2 and Example 3;

[0037] Figure 3The XRD spectra of the catalysts of Example 1, Example 2 and Example 3 are shown;

[0038] Figure 4 Cu-K edge EXAFS spectrum of the catalyst of Example 3

[0039] Figure 5 This is the Pd-K edge EXAFS spectrum of the catalyst of Example 3;

[0040] Figure 6 This is a performance diagram of methyl chloride product in the photocatalytic methane chlorination reaction of the catalysts of Example 1, Example 2, and Example 3;

[0041] Figure 7 This is a performance diagram of a chloromethane product cycle test of the photocatalytic methane chlorination reaction of the catalyst of Example 3; DETAILED DESCRIPTION

[0042] The present invention provides a palladium single-atom-supported cobalt-doped bismuth oxychloride photocatalyst, a preparation method thereof, and an application thereof, comprising cobalt-doped bismuth oxychloride and a palladium single atom supported on the cobalt-doped bismuth oxychloride;

[0043] In the present invention, the molar ratio of the bismuth nitrate pentahydrate, potassium chloride and cobalt nitrate hexahydrate powder is preferably 1:1:0.1-0.2, more preferably 1:1:0.1-0.12, such as 1:1:0.1, 1:1:0.11, 1:1:0.12, and preferably a range value with any of the above values ​​as the upper or lower limit.

[0044] In the present invention, the concentration of the soluble palladium source solution is preferably 2-3 g / L, more preferably 2-2.5 g / L, such as 2.0 g / L, 2.1 g / L, 2.2 g / L, 2.3 g / L, 2.4 g / L, 2.5 g / L, preferably a range value with any of the above values ​​as the upper or lower limit.

[0045] The present invention also provides an application of the palladium single atom-loaded cobalt-doped bismuth oxychloride photocatalyst described above in a photocatalytic methane chlorination reaction. The palladium single atom-loaded cobalt-doped bismuth oxychloride photocatalyst provided by the present invention can exhibit excellent catalytic performance in the photocatalytic methane chlorination reaction, with a high chloromethane yield and good stability.

[0046] In the above-mentioned photocatalytic methane chlorination reaction using the palladium single atom-loaded cobalt-doped bismuth oxychloride photocatalyst of the present invention, the chloromethane yield reached 8.1 μmol / h at room temperature, and the cycle stability could be maintained for 5 cycles, with a reaction time of 2 hours per cycle.

[0047] To further illustrate the present invention, a palladium single atom-supported cobalt-doped bismuth oxychloride photocatalyst provided by the present invention, its preparation method and application are described in detail below in conjunction with examples, but it should not be understood as limiting the scope of protection of the present invention.

[0048] Example 1:

[0049] (1) 4 mmol of bismuth nitrate pentahydrate and 4 mmol of potassium chloride powder were added to 70 mL of ethylene glycol and stirred at room temperature for 0.5 hours. After stirring, the mixture was transferred to a reactor for hydrothermal reaction at a temperature of 160°C for 12 hours. After the reaction, the mixture was separated to obtain bismuth oxychloride (BiOCl).

[0050] Example 2:

[0051] (1) 4 mmol of bismuth nitrate pentahydrate, 4 mmol of potassium chloride and 0.4 mmol of cobalt nitrate hexahydrate powder were added to 70 mL of ethylene glycol and stirred at room temperature for 0.5 hours. After stirring, the mixture was transferred to a reactor for hydrothermal reaction at a temperature of 160°C for 12 hours. After the reaction, the mixture was separated to obtain cobalt-doped bismuth oxychloride (Co-BiOCl).

[0052] Example 3:

[0053] (1) 4 mmol of bismuth nitrate pentahydrate, 4 mmol of potassium chloride and 0.4 mmol of cobalt nitrate hexahydrate powder were added to 70 mL of ethylene glycol and stirred at room temperature for 0.5 hours. After stirring, the mixture was transferred to a reactor for hydrothermal reaction at a temperature of 160°C for 12 hours. After the reaction, the mixture was separated to obtain cobalt-doped bismuth oxychloride powder.

[0054] (2) Disperse 500 mg of the powder obtained in step (1) into 10 mL of deionized water and stir at room temperature for 0.5 h;

[0055] (3) mixing the solution obtained in step (2) with 10 mL of a 2.5 g / L potassium tetrachloropalladate solution, stirring at room temperature for 0.5 hours, and separating after stirring to obtain a palladium source-loaded cobalt-doped bismuth oxychloride powder;

[0056] (4) The powder obtained in step (3) was placed in a tube furnace and calcined at 200° C. for 2 hours under an argon atmosphere to obtain cobalt-doped bismuth oxychloride supported by palladium single atoms (Pd1 / Co-BiOCl); the mass fraction of cobalt doping in the entire catalyst was 2.08%, and the mass fraction of palladium single atoms in the entire catalyst was 0.72%, as determined by plasma mass spectrometry.

[0057] The present invention performs photocurrent spectrum analysis on the catalysts obtained in Example 1 and Example 2, and the results are as follows: Figure 1 As shown, from Figure 1 It can be seen that the overall photocurrent value of the catalyst increased by 1.3 times after cobalt doping, indicating that cobalt doping is beneficial to the separation, transfer and utilization of photogenerated carriers in the system.

[0058] The present invention carried out SEM image analysis on the catalysts obtained in Example 1, Example 2 and Example 3, and the results were as follows: Figure 2 As shown, from Figure 2 It can be seen that Examples 1, 2 and 3 all have nanosphere structures with an average particle size of about 1 μm, and the doping of cobalt and the loading of single palladium atoms have no significant effect on the overall morphology of the catalyst.

[0059] The present invention carried out XRD spectrum analysis on the catalysts obtained in Example 1, Example 2 and Example 3, and the results were as follows: Figure 3 As shown, from Figure 3 It can be seen that Example 1, Example 2 and Example 3 all correspond to the physical phase of bismuth oxychloride, and the doping of cobalt and the loading of palladium single atoms have no obvious effect on the overall physical phase of the catalyst.

[0060] The present invention performs Co-K edge EXAFS spectrum analysis on the catalyst obtained in Example 3, and the results are as follows: Figure 4 As shown, from Figure 4 It can be seen that the cobalt element in Example 3 is mainly coordinated with cobalt-oxygen and cobalt-chlorine, which proves that the doped cobalt forms bonds with the oxygen and chlorine elements in bismuth oxychloride.

[0061] The present invention performs Pd-K edge EXAFS spectrum analysis on the catalyst obtained in Example 3, and the results are as follows: Figure 5 As shown, from Figure 5 It can be seen that there is no obvious palladium-palladium or palladium-oxygen-palladium coordination in the Pd1 / Co-BiOCl catalyst, which proves that the occurrence form of palladium species is atomically dispersed, that is, it exists in the form of single palladium atoms.

[0062] The present invention subjected the catalysts obtained in Example 1, Example 2, and Example 3 to a photocatalytic methane chlorination reaction, respectively. The specific steps were as follows: 500 mg of the catalyst was placed in a vacuum thick-walled pressure-resistant reaction vessel, and 500 μL of a 3.4 mol / L sodium chloride solution was dripped into it. Subsequently, methane was purged at a flow rate of 30 mL / min for 15 minutes. After the purge, a xenon lamp light source was turned on. The catalyst was reacted under the irradiation of the xenon lamp light source for 2 hours. The irradiation distance between the xenon lamp light source and the reactor was 10 cm, and the intensity of the xenon lamp light source was 200 mW / cm 2After the reaction, the chloromethane product in the reaction vessel was injected into a gas chromatograph for detection using a syringe. The chloromethane product performance diagram of the photocatalytic methane chlorination reaction of the catalysts of Example 1, Example 2 and Example 3 was obtained, as shown in FIG. Figure 6 As shown, from Figure 6 It can be seen that the yield of chloromethane when BiOCl catalyst is used to catalyze methane chlorination is 0.6 μmol / h; the yield of chloromethane when Co-BiOCl catalyst is used to catalyze methane chlorination is 4.2 μmol / h; the yield of chloromethane when Pd1 / Co-BiOCl catalyst is used to catalyze methane chlorination is 8.1 μmol / h.

[0063] The present invention also analyzes the cyclic stability of the photocatalytic methane chlorination reaction of the catalyst obtained in Example 3. The specific steps are as follows: 500 mg of the catalyst is placed in a vacuum thick-walled pressure-resistant reaction vessel, and 500 μL of a sodium chloride solution with a concentration of 3.4 mol / L is dripped into it. Then, methane is purged at a flow rate of 30 mL / min for 15 minutes. After the purge is completed, a xenon lamp light source is turned on, and the catalyst is reacted under the irradiation of the xenon lamp light source. The irradiation distance between the xenon lamp light source and the reactor is 10 cm, and the intensity of the xenon lamp light source is 200 mW / cm 2 , every 2 hours as a reaction cycle. After each reaction cycle, the product was collected by centrifugation using a centrifuge at a speed of 6000 rpm, washed three times with deionized water, and then dried in a vacuum drying oven. After thorough drying, the catalyst was weighed using a precision electronic balance and the loss was supplemented to keep its total mass at 500 mg, and then 500 mg of catalyst was put into the next reaction cycle. After each reaction cycle, the chloromethane product in the reaction vessel was injected into the gas chromatograph for detection using a syringe. The results are as follows Figure 7 As shown, from Figure 7 It can be seen that the yield of chloromethane catalyzed by Pd1 / Co-BiOCl catalyst for methane chlorination has no obvious attenuation within 5 reaction cycles, and has good cycle stability.

[0064] Example 4:

[0065] The other steps are the same as those in Example 3, except that the molar amount of cobalt nitrate hexahydrate powder in step (1) is replaced by 0.5 mmol from 0.4 mmol;

[0066] The resulting material is cobalt-doped bismuth oxychloride supported by palladium single atoms, with the cobalt doping accounting for 2.53% of the catalyst mass and the palladium single atoms accounting for 0.70% of the catalyst mass. The photocatalytic methane chlorination performance to produce chloromethane was 7.2 μmol / h.

[0067] Example 5:

[0068] The other steps are the same as those in Example 3, except that the concentration of the potassium tetrachloropalladate solution in step (3) is replaced from 2.5 g / L to 3.0 g / L;

[0069] The resulting material is cobalt-doped bismuth oxychloride supported by palladium single atoms, with the mass fraction of cobalt doping accounting for 2.01% of the overall catalyst and the mass fraction of palladium single atoms accounting for 0.85% of the overall catalyst. The performance of photocatalytic methane chlorination to produce chloromethane is 5.9 μmol / h.

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An application of a palladium single atom-supported cobalt-doped bismuth oxychloride photocatalyst, characterized by: Used as a photocatalyst in the photocatalytic chlorination of methane to produce chloromethane; The palladium single atom-supported cobalt-doped bismuth oxychloride photocatalyst comprises cobalt-doped bismuth oxychloride and palladium single atoms, wherein the palladium single atoms are supported on the cobalt-doped bismuth oxychloride; The mass fraction of the cobalt doping in the catalyst is 1-3.5%, and the mass fraction of the palladium atom in the catalyst is 0.5-1%. The preparation method of the cobalt-doped bismuth oxychloride photocatalyst supported by a single palladium atom comprises the following steps: 1) Add bismuth nitrate pentahydrate, potassium chloride, and cobalt nitrate hexahydrate to ethylene glycol, stir at room temperature for 0.5-1 hour, then transfer to a reactor, hydrothermally react at 120-170°C for 12-24 hours, and separate to obtain cobalt-doped bismuth oxychloride powder; Wherein, 3-5 mmol of bismuth nitrate pentahydrate was added to every 70 mL of ethylene glycol; The molar ratio of bismuth nitrate pentahydrate, potassium chloride and cobalt nitrate hexahydrate is 1:1:0.1-0.2; 2) dispersing the cobalt-doped bismuth oxychloride powder in deionized water and stirring at room temperature for 0.5 to 1 hour to obtain a cobalt-doped bismuth oxychloride solution; Wherein, 400-600 mg of cobalt-doped bismuth oxychloride powder was added to every 10 mL of deionized water; 3) mixing the cobalt-doped bismuth oxychloride solution and the soluble palladium source solution, stirring at room temperature for 0.5 to 1 hour, and separating after the stirring to obtain a palladium source-loaded cobalt-doped bismuth oxychloride powder; The mass ratio of cobalt-doped bismuth oxychloride powder to soluble palladium source is 20:1-3; The concentration of the soluble palladium source solution is 2~3g / L; 4) placing the palladium source-supported cobalt-doped bismuth oxychloride powder into a tube furnace and calcining it at 150-250° C. for 1-3 hours under an inert atmosphere to obtain a palladium single atom-supported cobalt-doped bismuth oxychloride photocatalyst; In step 3), the soluble palladium source is potassium tetrachloropalladate; In step 4), the inert atmosphere is nitrogen or argon atmosphere.

2. The use of the cobalt-doped bismuth oxychloride photocatalyst supported by a single palladium atom as claimed in claim 1, characterized in that: The method comprises the following steps: placing a cobalt-doped bismuth oxychloride photocatalyst supported by a single palladium atom in a reactor, dripping a sodium chloride solution into the reactor, then purging the reactor with methane, and irradiating the reactor with a xenon lamp for 1 to 3 hours to obtain chloromethane; The mass ratio of catalyst powder to sodium chloride is 10:1~4; The concentration of the sodium chloride solution is 3-4 mol / L; The methane flow rate of the methane purge is 20-40 mL / min, and the methane purge time is 10-20 minutes.

3. The use of the cobalt-doped bismuth oxychloride photocatalyst supported by a palladium single atom as claimed in claim 2, characterized in that: The irradiation distance between the xenon lamp light source and the reactor is 10-30 cm, and the intensity of the xenon lamp light source is 100-250 mW / cm 2 .

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