A method for preparing cobalt phosphide nanomaterials by visible light reduction of cobalt salt in aqueous solution

Abstract

The present application relates to the field of new materials and photocatalysis, and specifically provides a preparation method for synthesizing cobalt phosphide nanomaterials by visible light reduction of cobalt salt in aqueous solution, which uses LED lamps simulating the visible light section of sunlight as light source at normal temperature and pressure, and reduces metal cobalt salt to generate cobalt phosphide materials in an aqueous solution containing organic dye molecule fluorescein as photosensitizer, sodium hypophosphite as phosphorus source, and triethylamine as electron sacrificial agent, thus overcoming the shortcomings of high pollution and high energy consumption in the traditional preparation process of phosphide materials, and having the advantages of low consumption and environmental protection; and by adding water-soluble CTAB (bromohexadecyl trimethylamine) as a template agent, the morphology of the generated cobalt phosphide can be controlled to be nanosheet clusters. The cobalt phosphide nanoclusters prepared by the present application can be used as catalysts for the process of electrocatalytic reduction of nitrite to synthesize ammonia at normal temperature and pressure, and have significant catalytic effect and excellent cyclic catalytic stability.

Description

A method for preparing cobalt phosphide nanomaterials by visible light reduction of cobalt salts in aqueous solution. Technical Field

[0001] This invention relates to the fields of new materials and photocatalysis, and specifically discloses a method for preparing cobalt phosphide nanomaterials by visible light reduction of cobalt salts in aqueous solution. Background Technology

[0002] Solar energy, as the safest, most stable, and sustainably available clean energy source, delivers approximately 120 TW of energy to the Earth's surface annually. Looking at the spectral composition of solar energy, over 50% of solar radiation energy is in the visible light region, with the maximum energy wavelength around 475 nm. By exciting certain substances with visible light, causing electrons to transition within the material, a series of electron transfer reactions can produce the desired materials. Therefore, fully and efficiently utilizing visible light catalysis from solar energy is a clean, efficient, and practically significant method for material preparation.

[0003] Transition metal phosphides (TMPs: CoP, Ni2P, FeP, etc.) have been extensively studied as hot catalysts in photocatalytic and electrocatalytic reduction and splitting of water. In metal phosphides, the metal and phosphorus exist in a covalent bond, and phosphorus-rich or nickel-rich metal phosphides can be synthesized by controlling the ratio of metal to phosphorus, thus achieving different catalytic properties. Currently, the synthesis of metal phosphides mainly uses temperature-programmed heating methods (>300℃), organic precursor thermal decomposition methods (>300℃), and solvothermal methods (>150℃). These methods mostly suffer from problems such as harsh reaction conditions and high energy consumption, high toxicity of phosphorus precursors (white phosphorus) or intermediates (PH3), expensive precursors (such as organonitrile compounds and organophosphorus reagents), and pollution from residual phosphorus precursors. Furthermore, most reports mainly focus on the preparation of metal phosphides (Ni2P, CoP) with individual fixed element compositions, and there is still a lack of effective synthetic strategies to continuously control the synthesis of TMPs (M... x P y )Material.

[0004] Photo-assisted synthesis offers a promising approach to solving this problem: 1) It can provide uniformly distributed light throughout the reaction solution under ambient temperature and pressure. 2) It can optimize the maximization of light absorption by reactant species by adjusting factors such as light intensity and wavelength. 3) By varying the concentration and ratio of different substances in the reaction system, using template agents, controlling the pH of the reaction system, and optimizing the light exposure time and intensity, the nucleation and growth process of nanoparticles can be controlled to obtain nanomaterials with ideal elemental composition and special structural morphologies.

[0005] Ammonia (NH3) is a carbon-free energy carrier with advantages such as high energy density and ease of transmission, making it crucial for social development. Nitrates and nitrites are abundant in water bodies, and their accumulation pollutes the environment and harms human health. Electrocatalytic reduction of nitrates and nitrites to synthesize ammonia offers advantages such as high Faraday efficiency and high ammonia yield, potentially alleviating industrial demand for ammonia production via the traditional Haber-Bosch pathway. This has significant dual implications from the perspectives of addressing environmental issues and reducing energy consumption. Developing efficient, stable, and selective electrocatalysts based on inexpensive metals for the reduction of nitrates to NH3 is of paramount importance. The transition metal cobalt phosphide, with its reversible adsorption of active hydrogen and charge-separated selective adsorption of species, can serve as an ideal catalyst for the electrocatalytic production of ammonia from nitrates.

[0006] Therefore, it is very important to develop a low-temperature, economical, energy-saving, simple, safe, and controllable composition and structure-based visible light reduction synthesis strategy for preparing transition metal cobalt phosphide. Summary of the Invention

[0007] This invention addresses the numerous shortcomings of existing technologies by providing a method for synthesizing cobalt phosphide nanomaterials through visible light reduction of cobalt salts in aqueous solution. This method utilizes an LED lamp simulating the visible light range of sunlight as a light source under ambient temperature and pressure. In an aqueous solution containing the organic dye fluorescein as a photosensitizer, sodium hypophosphite as a phosphorus source, and triethylamine as an electron sacrificial agent, metallic cobalt salts are reduced to generate cobalt phosphide. This method overcomes the drawbacks of traditional phosphide material preparation processes, such as high pollution and high energy consumption, and offers advantages such as low consumption and environmental friendliness. Furthermore, by adding water-soluble CTAB (hexadecyltrimethylammonium bromide) as a template agent, the morphology of the generated cobalt phosphide can be controlled to form nanosheet clusters. Using the cobalt phosphide nanoclusters of this invention as a catalyst, it can be used in the electrocatalytic reduction of nitrite to ammonia synthesis under ambient temperature and pressure conditions, exhibiting significant catalytic effects and excellent cyclic catalytic stability.

[0008] The specific technical solution of the present invention is as follows:

[0009] The inventors first provided a method for preparing cobalt phosphide nanomaterials by visible light reduction of cobalt salts in aqueous solution, comprising the following steps:

[0010] First, a mixed cobalt chloride hexahydrate (CoCl2·6H2O) and sodium hypophosphite (NaHPO2·H2O) precursor was added to a mixed solvent at a molar ratio of 3:100 under normal temperature and pressure. Then, the organic dye fluorescein (Fl, C) was added. 20 H 12 O5) is used as a photosensitizer, and the molar mass ratio of phosphate salt to fluorescein is 1:20 moles per gram;

[0011] The mass-to-volume ratio of fluorescein to the mixed solvent is 1:3 mg / mL. The volume percentage of triethylamine (TEA) in the mixed solvent is 5%, and the volume percentage of deionized water is 95%.

[0012] The above substances were mixed evenly according to the proportion, and high-purity nitrogen was introduced to remove oxygen for 30 minutes. The deoxygenated mixed solution was placed under a visible white LED light source for illumination and stirred for 48 hours to prepare nanosheet CoP material. The material obtained at this time is in solution state. The visible white LED light source has λ≥420nm and 30×3W.

[0013] The roles of each substance in the above reaction process are as follows:

[0014] Organic dye molecule fluorescein C 20 H 12 Using O5 as a photosensitizer, cobalt chloride and sodium hypophosphite phosphate as catalyst precursors, and triethylamine as an electron sacrificial agent, stable cobalt phosphide nanomaterials, namely CoP, are directly generated in situ in pure aqueous solution by visible white LED illumination.

[0015] The reaction mechanism in the above reaction process is as follows:

[0016] Under illumination, fluorescein (Fl) will reach an excited state and generate a singlet state of fluorescein (Fl). 1 In the case of Fl*), the singlet state of luciferin is first quenched by the abundant triethylamine, generating the unstable Fl*. -， It will transfer excited-state electrons to the metal precursor, prompting the metal ions to be reduced and generate metal nanoparticles. In the process of forming metal nanoparticles, sodium hypophosphite uses its reducing properties to combine P with the metal, forming cobalt phosphide nanomaterials.

[0017] The cobalt phosphide material with a special morphology obtained above is in solution state. It needs to stand for 30 minutes, pour off the supernatant, add a small amount of deoxygenated anhydrous ethanol, sonicate for 10 minutes to clean, centrifuge for 10 minutes, repeat 3 times, finally wash with deoxyacetone, centrifuge, place in vacuum drying at 60℃ for 1 hour, grind, and collect the cobalt phosphide nanomaterial. At this time, the cobalt phosphide prepared is in the form of a block formed by the stacking of flakes.

[0018] To obtain cobalt phosphide materials with special morphologies, the inventors added CTAB (hexadecyltrimethylammonium bromide) template agent to the original system to regulate the morphology of cobalt phosphide. The specific steps are as follows:

[0019] A mixed cobalt-phosphorus precursor, consisting of cobalt chloride hexahydrate (CoCl2·6H2O) and sodium hypophosphite (NaHPO2·H2O), was added to a mixed solvent at a molar ratio of 3:100 under ambient temperature and pressure. This was followed by the addition of the organic dye fluorescein (Fl, C). 20 H 12O5) is used as a photosensitizer, and the molar mass ratio of phosphate salt to fluorescein is 1:20 moles per gram;

[0020] Simultaneously, 0.2 g of template agent CTAB (hexadecyltrimethylamine bromide) was added per millimole of phosphate salt; the mass-to-volume ratio of the template agent to the mixed solvent was 3:1 mg / mL, and the volume percentage of triethylamine (TEA) in the mixed solvent was 5%, and the volume percentage of deionized water was 95%.

[0021] The above substances were mixed evenly according to the proportion, and high-purity nitrogen was introduced to remove oxygen for 30 minutes; the deoxygenated mixed solution was placed under a visible white LED light source for illumination and stirred for 48 hours to prepare nano-flower-like CoP material; the visible white LED light source had λ≥420nm and 30×3W.

[0022] Furthermore, the role of the template agent in the reaction process is as follows:

[0023] When CTAB is used as a template agent, stable petal-shaped cobalt phosphide nanomaterials with special morphology can be directly generated in situ in pure aqueous solution by visible white LED illumination, which is known as CoP / CTAB.

[0024] The reaction mechanism in the above reaction process is as follows:

[0025] Under illumination, fluorescein (Fl) will reach an excited state and generate a singlet state of fluorescein (Fl). 1 In the case of Fl*), the singlet state of luciferin is first quenched by the abundant TEA, generating an unstable Fl*. -， It will transfer excited-state electrons to the metal precursor. As a cationic surfactant, CTAB has strong adsorption properties, which promotes the reduction of metal ions to generate metal nanoparticles and make them combine rapidly to form nanoflower-like structures. In the process of forming metal nanoparticles, sodium hypophosphite uses its reducing properties to combine P with the metal to form cobalt phosphide petal-like nanomaterials.

[0026] Adding CTAB as a template agent to a homogeneous solution system before illumination allows for the regulation of the nucleation and growth process of nanoparticles during illumination. Photoreduction generates a cobalt phosphide material with a special nanopetal-like structure. CTAB as a template agent forms a cobalt phosphide material with a special nanoflower-like morphology, giving the material a larger specific surface area and abundant exposed active sites, thereby further increasing the catalytic efficiency and stability of the material.

[0027] The cobalt phosphide material with the special morphology obtained above is in solution state. It needs to stand for 30 minutes, pour off the supernatant, add a small amount of deoxygenated anhydrous ethanol, sonicate for 10 minutes to clean, centrifuge for 10 minutes, repeat 3 times, and finally wash with deoxyacetone, centrifuge, place in vacuum drying at 60℃ for 1 hour, grind, and collect to obtain nano-flower-like CoP / CTAB material. At this time, the cobalt phosphide prepared is nano-flower-like with a particle size of about 500nm, and the formed nano-flower-like cobalt phosphide is formed by the agglomeration of plate-like cobalt phosphide, which makes its catalytic activity more excellent in subsequent application.

[0028] After obtaining the above-mentioned cobalt phosphide nanomaterials, the inventors further disclosed the following specific applications:

[0029] It is mainly used as a catalyst for the electrocatalytic synthesis of ammonia from nitrite. The specific application process is as follows: the mass feeding range of cobalt phosphide and sodium nitrite is 4000-8000 grams per gram of material. The following example uses 4 mg of catalyst:

[0030] Take 4 mg each of the nanosheet CoP sample and the nanosphere CoP / CTAB sample prepared above, dissolve them in a mixed solution of 0.375 mL water and 0.125 mL anhydrous ethanol, add 50 μL of 5% perfluorosulfonate naphthol membrane solution, sonicate at room temperature for 1 h to ensure full dispersion, take 5 μL of the solution and add it to a glassy carbon electrode, dry it under an infrared lamp, and then perform electrochemical tests.

[0031] Special attention should be paid to the other components added above, whose main function is to attach the CoP material to the electrode so that electrocatalytic testing can be performed.

[0032] The assembly of the electrocatalytic nitrite-to-ammonia synthesis electrode and the preparation of the electrolyte are as follows:

[0033] 50 mL of 1 mol / L NaOH solution was placed in an H-type electrolytic cell, and 2 mmol of NaNO2 was added to the electrolyte. Under the conditions of a voltage range of -0.5 V vs. RHE to 0.2 V vs. RHE and a scan rate of 0.005 V / s, the linear voltammetry (LSV) test of CoP for nitrite was performed. It was found that the starting voltage for the catalytic reduction of nitrite by cobalt phosphide was around -0.15 V.

[0034] Take 50 mL of 1 mol / L NaOH solution into an electrolytic cell, add 5 mmol of NaNO2 to the electrolyte, and test the 1 h electrolysis (BE) of CoP under the conditions of -0.2 V vs. RHE, -0.3 V vs. RHE, -0.4 V vs. RHE, -0.5 V vs. RHE and -0.6 V vs. RHE.

[0035] After the reaction was complete, 0.5 mL of electrolyte was transferred to a 25 mL colorimetric tube and diluted to 25 mL with 1 mol / L NaOH. Potassium sodium tartrate solution and potassium mercuric iodide solution were then added dropwise (Nessler's reagent spectrophotometric method). After standing for 15 min, the absorbance at 420 nm was measured using a UV-Vis absorption spectrometer. A standard curve was prepared using standard ammonia solution according to the national standard Nessler's reagent spectrophotometric method. Based on the sample test results, the ammonia yield of the nanosheet CoP electrocatalytic system was found to be 27.7 μg·h⁻¹. -1 The Faraday efficiency was 73.6%, and the ammonia yield of the nanoflower-like CoP / CTAB electrocatalytic system was 31.4 μg·h⁻¹. -1 The Faraday efficiency was 88.4%, confirming that the CoP material synthesized by this method has the ability to synthesize ammonia. At the same time, the addition of a template agent increased the ammonia yield by 14.8%.

[0036] Compared with the prior art, the superior effects of the present invention are as follows:

[0037] This invention provides a method for synthesizing cobalt phosphide nanomaterials by visible light reduction of cobalt salts in aqueous solution. The method uses an LED lamp simulating the visible light range of sunlight as a light source under ambient temperature and pressure. The morphology of the generated cobalt phosphide is controlled to form nanosheet clusters by adding water-soluble CTAB (hexadecyltrimethylammonium bromide) as a template agent. This method overcomes the drawbacks of traditional phosphide material preparation processes, such as high pollution and high energy consumption, and has the advantages of low consumption and environmental friendliness. Using the cobalt phosphide nanomaterials obtained by this invention, combined with the preparation method of this invention, it is possible to use them in the electrocatalytic reduction of nitrite to ammonia synthesis process under ambient temperature and pressure. Attached Figure Description

[0038] Figure 1 is a SEM image of the CoP prepared in Example 1 of this invention.

[0039] Figure 2 is a TEM image of the CoP prepared in Example 1 of this invention.

[0040] Figure 3 is a TEM elemental mapping distribution diagram of CoP prepared in Example 1 of the present invention.

[0041] Figure 4 is an XPS image of the CoP prepared in Example 1 of this invention.

[0042] Figure 5 is a SEM image of the CoP / CTAB prepared in Example 2 of this invention.

[0043] Figure 6 is a TEM image of the CoP / CTAB prepared in Example 2 of this invention.

[0044] Figure 7 shows the TEM elemental mapping distribution of CoP / CTAB prepared in Example 2 of this invention.

[0045] Figure 8 is an XPS image of CoP / CTAB prepared in Example 2 of the present invention.

[0046] Figure 9 shows the reduction of NO2 by Co-P and Co-P / CTAB under different voltages in Examples 1 and 2 of the present invention. - The Faraday efficiency and ammonia yield curves. Detailed implementation method:

[0047] To enable those skilled in the art to better understand the technical solutions of this application, the technical solutions of this application will be described in detail below with reference to specific embodiments. Unless otherwise specified, experimental conditions not detailed in the embodiments are generally based on conventional conditions or conditions recommended by the reagent company; reagents, consumables, etc., used in the following embodiments can be obtained commercially unless otherwise specified.

[0048] Example 1: Preparation of CoP sheet-like nanomaterials

[0049] Place 0.015 mmol of CoCl2·6H2O, 0.5 mmol of NaHPO2·H2O, and 10 mg of the organic dye fluorescein into a 60 mL test tube. Measure 1.5 mL of triethylamine and 28.5 mL of deionized water to form a 30 mL aqueous solution and pour it into the test tube. Shake well, add a magnetic stir bar, seal with a rubber stopper, and purge with high-purity nitrogen for 20 minutes to remove oxygen. Place the test tube under an LED light source (visible white LED light source, λ≥420 nm, 30×3W); turn on the magnetic stirrer.

[0050] After reacting for 48 hours, cobalt phosphide material in solution was obtained. After standing for 30 minutes, the supernatant was discarded, a small amount of deoxygenated anhydrous ethanol was added, and the mixture was ultrasonically cleaned for 10 minutes, centrifuged for 10 minutes, and repeated 3 times. Finally, the mixture was washed with deoxyacetone, centrifuged, and vacuum dried at 60°C for 1 hour. After grinding, the sheet-like cobalt phosphide nanomaterials were collected.

[0051] As shown in Figure 1, SEM characterization shows that the generated material is stacked together in sheet-like form to form a blocky material; as shown in Figure 2, TEM testing shows that sheet-like material corresponding to the SEM image is stacked together; as shown in Figure 3, TEM elemental mapping distribution testing shows that Co and P are uniformly distributed in all materials within the selected material region, confirming the successful loading of P and the formation of cobalt phosphide; as shown in Figure 4, XPS testing confirms that the material surface is composed of phosphorus and cobalt.

[0052] Example 2: Preparation of CoP / CTAB nanomaterials

[0053] Place 0.015 mmol of CoCl2·6H2O, 0.5 mmol of NaHPO2·H2O, 10 mg of the organic dye fluorescein, and 0.1 g of CTAB into a 60 mL test tube. Measure 1.5 mL of triethylamine and 28.5 mL of deionized water to form a 30 mL aqueous solution and pour it into the test tube. Shake well, add a magnetic stir bar, seal with a rubber stopper, and purge with high-purity nitrogen for 20 minutes to remove oxygen. Place the test tube under an LED light source (visible white LED light source, λ≥420 nm, 30×3W); turn on the magnetic stirrer.

[0054] After reacting for 48 hours, cobalt phosphide in solution was obtained. After standing for 30 minutes, the supernatant was discarded, a small amount of deoxygenated anhydrous ethanol was added, and the mixture was ultrasonically cleaned for 10 minutes, centrifuged for 10 minutes, and repeated 3 times. Finally, it was washed with deoxyacetone, centrifuged, and vacuum dried at 60°C for 1 hour. After grinding, petal-shaped cobalt phosphide nanomaterials, namely CoP / CTAB, were obtained.

[0055] As shown in Figure 5, SEM characterization revealed that the generated material formed a petal-like nanoflower structure from nanosheets, exhibiting a larger specific surface area. As shown in Figure 6, TEM analysis showed that the formed material consisted of very thin nanosheets, consistent with the SEM results. As shown in Figure 7, TEM elemental mapping analysis indicated that Co and P were uniformly distributed throughout the selected material region, further confirming the successful loading of P and increasing the loading amount to 12.12%, resulting in a cobalt phosphide with a unique morphology. As shown in Figure 8, XPS analysis confirmed that the material surface was composed of a combination of phosphorus and cobalt.

[0056] Application Example 1: CoP Electrocatalytic Synthesis of Ammonia from Nitrite

[0057] 4 mg of the flake-shaped CoP sample prepared in Example 1 was dissolved in a mixed solution of 0.375 mL of water and 0.125 mL of anhydrous ethanol. 50 μL of 5% perfluorosulfonate naphthol membrane solution was added dropwise. The solution was sonicated at room temperature for 1 h to ensure thorough dispersion. 5 μL of the solution was then added dropwise to a glassy carbon electrode and dried under an infrared lamp. Electrochemical tests were then performed.

[0058] Special note that the other components added above are mainly used to prevent the CoP material from falling off the electrode, making testing easier.

[0059] The assembly of the electrocatalytic nitrite-to-ammonia synthesis electrode and the preparation of the electrolyte are as follows:

[0060] 50 mL of 1 mol / L NaOH solution was placed in an H-type electrolytic cell, and 2 mmol of NaNO2 was added to the electrolyte. Under the conditions of a voltage range of -0.5 V vs. RHE to 0.2 V vs. RHE and a scan rate of 0.005 V / s, the linear voltammetry (LSV) test of CoP for nitrite was performed. It was found that the starting voltage for the catalytic reduction of nitrite by cobalt phosphide was around -0.15 V.

[0061] 50 mL of 1 mol / L NaOH solution was added to an electrolytic cell, and 5 mmol of NaNO₂ was added to the electrolyte. The electrolysis (BE) of CoP was tested for 1 h under the conditions of -0.2 V vs. RHE, -0.3 V vs. RHE, -0.4 V vs. RHE, -0.5 V vs. RHE, and -0.6 V vs. RHE. After the reaction was complete, 0.5 mL of electrolyte was transferred to a 25 mL colorimetric tube, diluted to 25 mL with 1 mol / L NaOH, and potassium sodium tartrate solution and potassium mercuric iodide solution were added dropwise (Nessler's reagent spectrophotometric method). After standing for 15 min, the absorbance at 420 nm was measured using a UV-Vis absorption spectrometer. A standard curve was prepared using a standard ammonia solution according to the national standard Nessler's reagent spectrophotometric method. The ammonia yield and Faradaic efficiency of the electrocatalytic system were obtained based on the sample test results.

[0062] As shown in Figure 9, the maximum Faradaic efficiency of the CoP nanomaterial electrocatalytic system reached 73.6% at -0.5 V. The ammonia yield reached 27.7 μg·h⁻¹ at -0.6 V. -1 This demonstrates that the prepared CoP nanomaterials possess excellent catalytic performance for the electrocatalytic synthesis of ammonia from nitrite. Application Example 2: CoP / CTAB electrocatalytic synthesis of ammonia from nitrite.

[0063] 4 mg of the petal-shaped CoP / CTAB sample prepared in Example 2 was dissolved in a mixed solution of 0.375 mL of water and 0.125 mL of anhydrous ethanol. 50 μL of 5% perfluorosulfonate naphthol membrane solution was added dropwise. The solution was sonicated at room temperature for 1 h to ensure thorough dispersion. 5 μL of the solution was then added dropwise to a glassy carbon electrode and dried under an infrared lamp. Electrochemical tests were then performed.

[0064] Special note that the other components added above are mainly used to prevent the CoP material from falling off the electrode, making testing easier.

[0065] The assembly of the electrocatalytic electrode for ammonia synthesis from nitrite and the preparation of the electrolyte were as described in Application Example 1. The results are also shown in Figure 9. The maximum Faradaic efficiency of the CoP / CTAB nanomaterial electrocatalytic system reached 88.4% at -0.5V, a 20.1% improvement compared to the Faradaic efficiency of directly generated CoP nanomaterials. The ammonia yield reached 31.4 μg·h⁻¹ at -0.6V. -1 The ammonia yield increased by 14.8% compared to directly generated CoP nanomaterials, indicating that the prepared CoP / CTAB nanoflower-like material has a larger specific surface area and better electrocatalytic performance in the synthesis of ammonia from nitrite compared to directly generated CoP nanomaterials.

[0066] In summary, the cobalt phosphide nanomaterials obtained by the above method can be used as catalysts in the electrocatalytic reduction of nitrate to ammonia synthesis under normal temperature and pressure conditions, exhibiting significant catalytic effects and excellent cyclic catalytic stability.

[0067] The above embodiments are one specific implementation of the present invention. Ordinary changes and substitutions made by those skilled in the art within the scope of this technical solution should be included within the protection scope of the present invention.

Claims

1. A method for preparing cobalt phosphide nanomaterials by visible light reduction of cobalt salts in aqueous solution, characterized in that, The process includes the following steps: First, at room temperature and pressure, a mixed cobalt chloride hexahydrate and sodium hypophosphite precursor are added to a mixed solvent at a molar ratio of 3:

100. Then, an organic dye, fluorescein, is added as a photosensitizer, wherein 1 mole of sodium hypophosphite is added for every 20 grams of fluorescein. The mass-to-volume ratio of fluorescein to the mixed solvent is 1:3 mg / mL. The volume percentage of triethylamine in the mixed solvent is 5%, and the volume percentage of deionized water is 95%. The above substances are mixed evenly according to the proportions, and high-purity nitrogen is introduced to remove oxygen for 30 minutes. The deoxygenated mixed solution is placed under a visible white LED light source for illumination and stirred for 48 h to prepare nanosheet-like CoP materials. The visible white LED light source has a wavelength of λ≥420 nm and a wavelength of 30×3 W.

2. The method for preparing cobalt phosphide nanomaterials according to claim 1, characterized in that, The prepared cobalt phosphide material was allowed to stand for 30 minutes, the supernatant was discarded, a small amount of deoxygenated anhydrous ethanol was added, and the mixture was ultrasonically cleaned for 10 minutes, centrifuged for 10 minutes, and repeated 3 times. Finally, it was washed with deoxyacetone, centrifuged, and placed in a vacuum dryer at 60°C for 1 hour. After grinding, the cobalt phosphide nanomaterials were collected.

3. The method for preparing cobalt phosphide nanomaterials according to claim 1, characterized in that, During preparation, 0.2 g of template agent CTAB is added to the reaction system per millimole of phosphate salt, and petal-shaped cobalt phosphide nanomaterials CoP / CTAB can be obtained.

4. The application of the cobalt phosphide nanomaterials obtained according to claim 1 or 3 as a catalyst in the electrocatalytic synthesis of ammonia from nitrite.

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