Core-shell bimetallic promoter modified triphase interface structure m@pt / cnn photocatalyst, preparation method and application thereof

Abstract

The application discloses a kind of core-shell bimetallic promoter modified triphase interface structure M@Pt / CNN photocatalyst and its preparation method and application, belong to photocatalysis technical field.The application provides a kind of preparation method of M@Pt / CNN photocatalyst, comprising: dispersing CNN in water, obtain CNN dispersion liquid;Metal salt is added to water, then add dispersing agent, obtain precursor metal salt solution;Precursor metal salt solution is added to CNN dispersion liquid, and drop into reducing agent solution, then drop into H2PtCl6·6H2O aqueous solution, collect precipitate, wash and dry, obtain immediately.The application is prepared by continuous chemical reduction method M@Pt core-shell structure and M@Pt / CNN half core-shell structure photocatalyst, it has the advantages such as large specific surface area, active site is more, hydrogen evolution activity is high, stability, and improve the use efficiency of platinum, using water as solvent, preparation at room temperature, reduce cost.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology, specifically relating to a core-shell bimetallic cocatalyst-modified three-phase interface structure M@Pt / CNN photocatalyst, its preparation method, and its application. Background Technology

[0002] With increasing environmental pollution and the depletion of traditional fossil fuel reserves, there is a need to explore new renewable energy resources to drive sustainable social development. Therefore, photocatalytic hydrogen production is considered one of the promising technologies for providing renewable energy (i.e., hydrogen as an energy carrier) in an environmentally friendly manner. Compared with traditional inorganic photocatalysts, organic photocatalysts based on conjugated frameworks, such as carbon nitride (g-C3N4), have received widespread attention in recent years due to their inherent advantages such as low production cost, non-toxicity, and functional potential for molecular design. g-C3N4 not only possesses visible light response, high chemical stability, and the potential for appropriate C 2p and N 2p orbitals to cross water splitting, but it also has more N atom coordination (in macropore volume), which, by improving metal-supported substrate interactions and preventing metal aggregation, has been widely used as a photocatalyst for water splitting to produce hydrogen. However, pure g-C3N4 itself is not an ideal photocatalyst, exhibiting poor photocatalytic activity, mainly due to the rapid recombination of photogenerated charges. Several strategies, such as doping modification, composite or molecular design, and band structure engineering, have been applied to the modification of g-C3N4.

[0003] Compared to other strategies, co-catalyst modification provides a direct and effective way to improve the photocatalytic activity of photocatalysts. Noble metal (e.g., Ag, Pt, Pd, and Au) and transition metal (e.g., Fe, Co, and Ni) nanoparticles can improve the visible light energy utilization of g-C3N4, attributed to the surface plasmon resonance effect of noble metal nanoparticles and the coherent interface effect of transition metal particles. The heterojunction photocatalyst formed by these metal particles and g-C3N4 exhibits significant advantages in photogenerated electron transfer and separation, photochemical stability, and extended visible light response. Compared to supported monometals, the synergistic effect of bimetallic nanoparticles is more beneficial for extending the visible light response of g-C3N4 semiconductor catalysts and accelerating the separation of photogenerated electron-hole pairs, thereby improving the photocatalytic activity of heterojunction catalysts. Due to the synergistic effect between different active sites, bimetallic nanoparticles (composed of two different metal elements) typically exhibit superior electronic, optical, and photocatalytic properties. These properties are often not achievable in the corresponding monometallic nanoparticles. Therefore, bimetallic nanoparticles offer the potential for more efficient co-catalysts.

[0004] Metal-metal interactions primarily exist in three forms: alloy structures, core-shell structures, and heterostructures. Core-shell catalysts exhibit higher activity than alloy-shell catalysts; their catalytic performance depends on the shell thickness, and the performance of Au-core Pd-shell catalysts even differs from that of pure Pd. Compared to bimetallic alloy catalysts, bimetallic core-shell catalysts have advantages such as larger specific surface area and more active sites. Therefore, constructing core-shell structures is considered an effective way to improve the activity and durability of rare metal catalysts. Generally, platinum atoms are placed on the catalyst surface, and the electronic structure of the surface is altered by adding multiphase elements to the core. A uniformly dispersed layer of platinum atoms on the surface improves the utilization efficiency of platinum, significantly reduces the platinum loading, and thus lowers the cost of the catalyst. Based on these effects, core-shell structured noble metal catalysts have attracted widespread attention. Much work has focused on changing the composition of the core and shell, adjusting the thickness of the platinum shell, and controlling the size and shape of the core-shell catalyst. With changes in geometric parameters, the electronic structure of the core-shell catalyst also changes. In bimetallic core-shell catalysts, the shell material is usually Pt, and the core material is another metal. The simple elemental composition makes it easy to adjust the morphology and electronic structure. Synthesizing M@Pt (where M is a first-row transition metal) bimetallic nanoparticles is an effective method to reduce Pt loading and improve catalytic activity. Uniform catalyst distribution, small size, and ultrathin shell are key characteristics of high-performance core-shell catalysts. Optimizing the chemical composition, morphology, and interfacial properties of noble metal bimetallic catalysts can significantly improve their catalytic performance. It is generally believed that core-shell structures exhibit three types of interactions: ligand effect, surface strain effect, and chain-like effect. Typically, these three effects mutually modulate the d-band structure, the adsorption energy of intermediates, and chemical stability.

[0005] In recent years, the continuous reduction method has been widely used to synthesize various core-shell bimetallic nanomaterials. The continuous reduction method involves first reducing a metal salt to form a "seed" M1 (the core), and then using a process similar to "seed growth," depositing atoms of another metal, M2, onto the surface of the formed M1 seed crystal, thus forming an M1@M2 core-shell structure. Because it involves two consecutive reduction processes, it is called the "continuous reduction method," also known as the "seed growth process," and is a typical strategy of nucleation followed by shell formation. In noble metal core-shell catalysts, the shell material is Pt. Different core materials bind to Pt as different ligands, directly affecting the catalyst's activity and stability.

[0006] Reference 1 (ACS Catal. 2022, 12, 6958-6967.) designed a two-component synergistic photocatalyst (Co) using a photoreduction method. SAs / PtCo@CNN), this catalyst contains dispersed single-atom Co (Co SAsBimetallic PtNi-modified graphitic carbon nitride (g-C3N4) nanotubes were prepared by calcining a mixture of urea and thiourea in the presence of Pluronic F127 and then chemically reducing and depositing bimetallic PtNi nanoparticles (NPs). Reference 2 (international journal of hydrogen energy 43(2018)22215-22225.) prepared bimetallic PtNi-modified graphitic carbon nitride (g-C3N4) nanotubes by chemical reduction deposition of bimetallic PtNi nanoparticles (NPs) on two-dimensional g-C3N4 nanosheets. Reference 3 (international journal of hydrogen energy 48(2023)28277-28288.) established a simple chemical reduction strategy to synthesize bimetallic PtNi nanoparticles PtNi nanoparticles on two-dimensional g-C3N4 nanosheets. 0.6 Ni 0.4 / CN. Reference 4 (ACS Sustainable Chem. Eng. 2019, 7, 15137-15145.) describes a hydrothermal method for processing PtNi. x A novel S-PtNi was prepared by sulfidation with g-C3N4. x / g-C3N4 photocatalyst. Reference 5 (ChemCatChem 2017,9,3779–3785.) synthesized g-C3N4 and PtNi x The composite material, compared to pure g-C3N4, exhibits higher photocatalytic activity, and 2.5% PtNi x The H2 precipitation rate of / g-C3N4 was the highest, reaching 8456 μmol / h / g.

[0007] However, the catalysts obtained in the above literature are not core-shell structures, have a small specific surface area, few active sites, and unstable structures, resulting in poor photocatalytic performance. In particular, they require the use of a large amount of precious metals, which have low utilization rates and high costs.

[0008] Patent application 201911089630.X discloses a CNSs-Ni@Pt / PM-g-C3N4 electrocatalyst and its preparation method. The method first prepares porous rod-shaped graphitic carbon nitride by high-temperature sintering of melamine oxidized with nitric acid. Then, a Ni@Pt core-shell bimetallic nanocatalyst is formed by stepwise reduction of NiCl2·6H2O and H2PtCl6·6H2O precursors using a liquid-phase reduction method. This nanocatalyst is dispersed and attached to the surface of the porous rod-shaped graphitic carbon nitride, while the size of the catalyst nanoparticles is controlled by adjusting the pH. Finally, carbon nanospheres are introduced to obtain the CNSs-Ni@Pt / PM-g-C3N4 electrocatalyst. The scaffold formed by this invention not only has a porous framework structure that ensures mass transfer but also acts as a conductive agent to compensate for the poor conductivity of g-C3N4. The resulting electrocatalyst exhibits excellent electrochemical stability and catalytic performance for the oxygen reduction reaction, making it suitable for high-temperature fuel cell applications. However, in this method, the solvent used for stepwise reduction is ethylene glycol, the reducing agent is sodium citrate, and the temperatures for the two reduction steps are 90-150℃ and 80-100℃, respectively. The reaction conditions are relatively harsh and the safety is relatively low. In addition, it also requires the use of a lot of precious metals. Summary of the Invention

[0009] To address the problems of existing technologies, this invention establishes a simple continuous chemical reduction strategy to synthesize a core-shell structured binary bimetallic cocatalyst (M@Pt, M = Co / Ni / Cu / Mn) on two-dimensional g-C3N4 nanosheets (CNNs). A Schottky junction is formed between the M@Pt bimetallic nanoparticles and the CNN, which can serve as a novel composite photocatalyst (M@Pt / CNN). The CNN exhibits visible light response, improving sunlight utilization. The addition of M@Pt nanoparticles enhances light absorption and provides new H+. + The reduction of sites increases the number of active sites. The synergistic effect between M@Pt nanoparticles and two-dimensional CNNs can modulate the electronic structure, shrink the energy band, accelerate charge transfer efficiency, and reduce photoinduced electron (e-) and hole pairs (h-). +The recombination of the core-shell structure helps improve the hydrogen evolution activity. Three interfaces (CNN with Pt, CNN with Pt, and M with Pt) are formed through the main catalyst (CNN) → co-catalyst I (M) → co-catalyst II (Pt). Simultaneously, the surfaces of CNN and Pt are exposed, serving as active reaction sites. This semi-core-shell structure protects the core co-catalyst Ni from photocorrosion. First, Ni nanoparticles are assembled on g-C3N4 nanosheets to form a Schottky junction, leading to electron accumulation on the Pt surface. The charged Pt nanoparticle surface serves as an active site, promoting the reduction and selective deposition of the Pt shell on the M surface. The interfacial charge polarization between M and Pt further promotes the electron migration pathway CNN→M→Pt, thereby extending the lifetime of photogenerated electrons. Furthermore, the high electron density, unsaturated platinum atoms, and lattice strain generated by the ultrathin platinum shell coating make it an active adsorption site for reactant molecules. Therefore, compared to pure g-C3N4 nanosheets, the photocatalytic hydrogen production rate of M@Pt / CNN is significantly improved. In particular, Ni@Pt / CNN exhibits the best hydrogen evolution rate of 11158 μmol / g / h.

[0010] This invention provides a method for preparing a three-phase interface structure M@Pt / CNN photocatalyst modified with a core-shell bimetallic co-catalyst, comprising the following steps:

[0011] A. Disperse CNN in water, sonicate to obtain CNN dispersion, and continuously stir the CNN dispersion at room temperature.

[0012] B. Add the metal salt to water, then add the dispersant PVP or gelatin, and stir until completely dissolved to obtain the precursor metal salt solution; in step B, the metal salt is selected from cobalt salt, nickel salt, copper salt or manganese salt.

[0013] C. Add the precursor metal salt solution obtained in step B to the CNN dispersion that was continuously stirred in step A, continue stirring, and then add the reducing agent solution dropwise while stirring to obtain a mixture.

[0014] D. Add the aqueous solution of H2PtCl6·6H2O dropwise to the mixture obtained in step C, continue stirring, then collect the precipitate, wash and dry it to obtain the M@Pt / CNN photocatalyst.

[0015] In the above preparation method, in step A, the CNN is prepared by the following method: nitrogen and carbon raw materials are heated at 2-5℃·min -1 The temperature was increased to 500–550℃ and held for 2–4 hours. After cooling to room temperature, g-C3N4 bulk material was obtained. The g-C3N4 bulk material was then ground into powder and heated at 2–5℃·min. -1The heating rate is increased to 500-550℃, held for 3-5 hours, and then naturally cooled to room temperature to obtain CNN; the nitrogen-carbon raw material is selected from at least one of melamine, urea, thiourea or dicyandiamide.

[0016] In the above preparation method, in step A, the mass ratio of CNN to water is 1:50 to 200.

[0017] In the above preparation method, in step A, the ultrasonic treatment time is 3 to 6 hours.

[0018] In the above preparation method, in step B, the metal salt is selected from CoCl2·6H2O, Co(NO3)2·6H2O, Co(CH3COO)2·4H2O, Co(acac)2, NiCl2·6H2O, Ni(NO3)2·6H2O, Ni(CH3COO)2·4H2O, Ni(acac)2, CuCl2·2H2O, Cu(NO3)2·3H2O, Cu(CH3COO)2·H2O, Cu(acac)2, MnCl2·4H2O, Mn(NO3)2·4H2O, Mn(CH3COO)2·4H2O, or Mn(acac)2.

[0019] In the above preparation method, in step B, the mass ratio of the metal salt to water is 7.1–12:10000–40000.

[0020] In the above preparation method, in step B, the amount of PVP or gelatin added is controlled to be 0.2 mmol / L to 1.0 mmol / L in the precursor metal salt solution.

[0021] In the above preparation method, in step B, the stirring time until complete dissolution is 20-40 minutes.

[0022] In the above preparation method, in step C, the mass ratio of the metal salt in the precursor metal salt solution to the CNN in the CNN dispersion is 7.1 to 12:200.

[0023] In the above preparation method, in step C, the reducing agent solution is prepared by mixing borohydride, caustic alkali, and water in a mass ratio of 85-150:50-80:10000-20000 until homogeneous; the borohydride is selected from at least one of NaBH4 and KBH4; the caustic alkali is selected from at least one of NaOH or KOH.

[0024] In the above preparation method, in step C, the volume ratio of the CNN dispersion to the reducing agent solution is 1:0.25-2.

[0025] In the above preparation method, in step C, the stirring time is 30-60 minutes.

[0026] In the above preparation method, in step C, the stirring time is 10 to 40 minutes.

[0027] In the above preparation method, in step D, the concentration of the H2PtCl6·6H2O aqueous solution is 0.001–0.003 g / mL.

[0028] In the above preparation method, in step D, the volume ratio of the H2PtCl6·6H2O aqueous solution used in step D to the precursor metal salt solution used in step C is 7.15–21.4:10–40, and the molar ratio of Pt in H2PtCl6·6H2O to M in the metal salt is controlled to be 0.99–1.01:0.99–1.01.

[0029] In the above preparation method, in step D, the stirring time is 4 to 7 hours.

[0030] In the above preparation method, in step D, the drying temperature is 60-80℃.

[0031] The present invention also provides a three-phase interface structure M@Pt / CNN photocatalyst modified with a core-shell bimetallic co-catalyst, which is prepared by the above method.

[0032] This invention also provides the application of the above-mentioned core-shell bimetallic co-catalyst modified three-phase interface structure M@Pt / CNN photocatalyst in the field of photocatalysis.

[0033] Based on the excellent performance of the photocatalyst of the present invention, it is preferably applied to photocatalytic water splitting to produce hydrogen, photocatalytic degradation of organic pollutants, or photocatalytic reduction of carbon dioxide.

[0034] In this invention, the purity of the water used is generally not lower than that of deionized water.

[0035] The beneficial effects of this invention are:

[0036] This invention presents the first-ever preparation of a novel semi-core-shell composite photocatalyst (M@Pt / CNN (M = Co / Ni / Cu / Mn)) using a continuous chemical reduction method. It utilizes g-C3N4 nanosheets as a carrier, on which bimetallic nanoparticles of transition metal M are first nucleated, followed by a shell of noble metal Pt are prepared. The unique morphological structures are: M@Pt is a core-shell structure; M@Pt / CNN is a semi-core-shell structure. The core-shell structure of this invention, composed of a shell and a core, enhances light scattering in the hollow space, provides a large surface area on both the inner and outer surfaces to generate sufficient active sites, and the shorter shell thickness shortens the charge diffusion distance, thereby significantly improving charge utilization efficiency.

[0037] The core-shell structure M@Pt of this invention has the following advantages: (1) its composition, morphology and electronic structure are adjustable; (2) it controls the reaction kinetics of the multiphase photocatalytic system: the shell structure provides a stable and efficient environment for the molecular adsorption and diffusion of reactants, making the catalyst structure more stable; (3) the core-shell structure can promote light collection, because light can be scattered and reflected multiple times in the cavity between the core and the shell; (4) it has a larger specific surface area and more active sites; (5) the uniformly dispersed platinum atom layer on the surface improves the platinum utilization efficiency and greatly reduces the platinum load, thereby reducing the cost of the catalyst; (6) reducing the amount of raw materials can protect the core and make the core more stable.

[0038] The promoting effects of the core-shell structure M@Pt on g-C3N4 nanosheets of the present invention are as follows: (1) reducing the overpotential of the photocatalytic reaction; (2) three interfaces: promoting interfacial charge transfer; (3) providing reduction active sites and carrying out photocatalytic reactions; (4) enhancing the light absorption of the photocatalyst; (5) enhancing the adsorption of reactant molecules; and (6) inhibiting photocorrosion and enhancing the stability of the photocatalyst.

[0039] The catalyst of this invention has a three-interface structure (between CNN and Pt, between CNN and Pt, and between M and Pt). The lattice strain and composition of the three interfaces affect the catalytic behavior: synergistic stress interaction puts some surface sites in an optimal compressible state, resulting in excellent HER performance; the interfacial charge polarization between M and Pt further promotes the electron migration path of CNN→M→Pt, thereby extending the lifetime of photogenerated electrons; M@Pt improves the atomic utilization of Pt and reduces the Pt loading, thereby reducing costs.

[0040] The method of this invention uses water as a solvent and is carried out entirely at room temperature and in air. The reaction conditions are mild, the operation is simple, and it is extremely suitable for industrial production. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the structure of the M@Pt / CNN photocatalyst of the present invention.

[0042] Figure 2 The XRD patterns of PtM@CNNs in Comparative Examples 2–5 are shown.

[0043] Figure 3 The images show the XRD patterns of CNN in Comparative Example 1, PtNi@CNN in Comparative Example 3, and Ni@Pt / CNN in Example 2.

[0044] Figure 4 The UV-vis diffuse reflectance maps are for CNN in Comparative Example 1, PtNi@CNN in Comparative Example 3, and Ni@Pt / CNN in Example 2.

[0045] Figure 5 The (αhν) values ​​are compared to those of CNN in Comparative Example 1, PtNi@CNN in Comparative Example 3, and Ni@Pt / CNN in Example 2. 1 / 2 The relationship between the band gap energy (hν) and the band gap energy.

[0046] Figure 6 This is a schematic diagram of the photocatalytic mechanism of Ni@Pt / CNN at Eg = 2.46 eV in Example 2.

[0047] Figure 7 The image shown is the SEM image of the CNN in Comparative Example 1.

[0048] Figure 8 This is the SEM image of Ni@Pt / CNN in Example 2.

[0049] Figure 9 The graphs show the photocatalytic water splitting hydrogen production rates of comparative examples 1–5.

[0050] Figure 10 The graphs show the hydrogen production rates from photocatalytic water splitting in Examples 1-4. Detailed Implementation

[0051] Specifically, a method for preparing a core-shell bimetallic co-catalyst-modified three-phase interface structure M@Pt / CNN photocatalyst includes the following steps:

[0052] This invention provides a method for preparing a three-phase interface structure M@Pt / CNN photocatalyst modified with a core-shell bimetallic co-catalyst, comprising the following steps:

[0053] A. Disperse CNN in water, sonicate to obtain CNN dispersion, and continuously stir the CNN dispersion at room temperature.

[0054] B. Add the metal salt to water, then add the dispersant PVP (polyvinylpyrrolidone) or gelatin, and stir until completely dissolved to obtain a precursor metal salt solution; in step B, the metal salt is selected from cobalt salt, nickel salt, copper salt or manganese salt.

[0055] C. Add the precursor metal salt solution obtained in step B to the CNN dispersion that was continuously stirred in step A, continue stirring, and then add the reducing agent solution dropwise while stirring to obtain a mixture.

[0056] D. Add the aqueous solution of H2PtCl6·6H2O dropwise to the mixture obtained in step C, continue stirring, then collect the precipitate, wash and dry it to obtain the M@Pt / CNN photocatalyst.

[0057] In step A of the method of the present invention, the CNN can be prepared using methods commonly found in the art, specifically by the following method: reacting nitrogen and carbon raw materials at 2–5 °C·min -1 The temperature was increased to 500–550 °C and held for 2–4 hours. After cooling to room temperature, g-C3N4 bulk (which is yellow and lumpy) was obtained. The g-C3N4 bulk was then ground into powder and heated at 2–5 °C / min. -1 The heating rate is increased to 500-550℃, held for 3-5 hours, and then naturally cooled to room temperature to obtain CNN; the nitrogen and carbon raw materials are selected from at least one of melamine, urea, thiourea or dicyandiamide. The advantages of this two-dimensional g-C3N4 nanosheet are: (1) short charge / mass transfer path; (2) large specific surface area and abundant reaction sites; (3) easy to functionalize.

[0058] In step A of this invention, the mass ratio of the CNN to water is 1:50 to 200. In step A, the ultrasonic treatment time is controlled to be 3 to 6 hours to ensure that the CNN is fully dispersed.

[0059] In step B of this invention, the metal salt can be a chloride salt, nitrate salt, acetate salt, or acetylacetone salt. Furthermore, hydrated salts are cheaper than anhydrous salts, saving costs. Hydrated salts also have advantages such as high thermal conductivity, high density, and high heat storage density per unit volume. The crystallization hydration reaction (physical adsorption) of salts absorbs and stores heat energy during the hydration process. When energy needs to be released, by controlling the solubility and stability of the salt, the salt crystals dissolve in water, generating an exothermic reaction, thus releasing the stored heat energy and achieving energy conversion. Therefore, the metal salt is preferably selected from CoCl2·6H2O, Co(NO3)2·6H2O, Co(CH3COO)2·4H2O, Co(acac)2, NiCl2·6H2O, etc. The following ingredients are used: H2O, Ni(NO3)2·6H2O, Ni(CH3COO)2·4H2O, Ni(acac)2, CuCl2·2H2O, Cu(NO3)2·3H2O, Cu(CH3COO)2·H2O, Cu(acac)2, MnCl2·4H2O, Mn(NO3)2·4H2O, Mn(CH3COO)2·4H2O, or Mn(acac)2; the mass ratio of metal salt to water is controlled at 7.1–12:10000–40000; the amount of PVP or gelatin added is controlled to maintain its concentration in the precursor metal salt solution at 0.2 mmol / L–1.0 mmol / L. In step B, after adding PVP or gelatin, stirring is continued for 20–40 min to obtain a completely dissolved and clear solution.

[0060] PVP plays a crucial role in the synthesis of core-shell nanoparticles by stabilizing particles, modifying their surfaces, controlling their size and shape, and improving solubility. PVP is a highly efficient dispersant in water and contains a large number of lone pairs of electrons (N and O), allowing it to readily bind with metal ions. As a dispersant, PVP not only significantly improves the uniformity of core-shell particle dispersion in solution but also acts as a structure-directing agent. In solution, PVP may selectively adsorb onto the surface of metal M crystal grains, where its lone pairs of electrons have a greater chance of contacting and reacting with Pt ions. Subsequently, PVP also adsorbs onto the surface of the generated Pt crystal grains, thereby inhibiting their vertical growth rate and ultimately forming an M@Pt core-shell structure. The concentration of PVP as a dispersant has a significant impact on the integrity of the core-shell structure and the uniformity of the particles. Without PVP, it is difficult to form core-shell particles; at low concentrations, the uniformity between particles is poor, and they tend to grow into long rod-like shapes; high concentrations of PVP passivate all seed faces, forming a polyhedral-like structure. Therefore, a PVP concentration of 0.2 mmol / L to 1.0 mmol / L (0.2 to 1.1 mg) is recommended. The same applies to gelatin.

[0061] In step C of this invention, the mass ratio of the metal salt in the precursor metal salt solution to the CNN in the CNN dispersion is 7.1 to 12:200.

[0062] In step C of this invention, the reducing agent solution is prepared by mixing borohydride, caustic alkali, and water at a mass ratio of 85-150:50-80:10000-20000 until homogeneous; the borohydride is selected from at least one of NaBH4 and KBH4; the caustic alkali is selected from at least one of NaOH or KOH; and the volume ratio of the CNN dispersion to the reducing agent solution is controlled to be 1:0.25-2.

[0063] In step C of this invention, the stirring time is 30-60 minutes; the stirring duration is 10-40 minutes.

[0064] In step D of this invention, the concentration of the H2PtCl6·6H2O aqueous solution is 0.001–0.003 g / mL; the volume ratio of the H2PtCl6·6H2O aqueous solution used in step D to the precursor metal salt solution used in step C is 7.15–21.4:10–40; and the molar ratio of Pt in H2PtCl6·6H2O to M (where M refers to the metal in the metal salt) is controlled to be 0.99–1.01:0.99–1.01.

[0065] In step D of this invention, the stirring time is 4 to 7 hours; in step D, the washing is generally carried out by washing with deionized water and ethanol 4 to 6 times to remove impurities, and the drying is generally carried out at 60 to 80°C overnight.

[0066] The present invention also provides a three-phase interface structure M@Pt / CNN photocatalyst modified with a core-shell bimetallic co-catalyst, which is prepared by the above method.

[0067] This invention also provides the application of the above-mentioned core-shell bimetallic co-catalyst modified three-phase interface structure M@Pt / CNN photocatalyst in the field of photocatalysis.

[0068] Based on the excellent performance of the photocatalyst of the present invention, it is preferably applied to photocatalytic water splitting to produce hydrogen, photocatalytic degradation of organic pollutants, or photocatalytic reduction of carbon dioxide.

[0069] The present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited to the embodiments described herein.

[0070] Example 1

[0071] (Co@Pt / CNN): Weigh 200 mg of CNN and disperse it in 30 ml of deionized water, then sonicate for 3 h. After sonication, continuously stir the dispersed CNN at room temperature using a magnetic stirrer. Add 0.0106 g of cobalt(II) acetylacetonate to 10 ml of deionized water, then add 0.0002 g of dispersant PVP, and continue stirring for 30 minutes to obtain a precursor cobalt salt solution. Add the precursor cobalt salt solution to the CNN dispersion and continue stirring for 30 min to form a mixture. Weigh 85 mg of NaBH4 and 50 mg of NaOH and add them to 10 ml of deionized water to form a reducing agent solution. While stirring, add the reducing agent solution dropwise to the mixture and continue stirring for 15 min. Then, measure 7.15 mL of H2PtCl6·6H2O solution (0.003 g / mL) and add it dropwise to the above mixture. After stirring for another 4 hours, the precipitate was collected, washed 6 times with deionized water and ethanol, and dried overnight at 60°C to obtain Co@Pt / CNN composite catalyst powder with a core-shell structure.

[0072] Example 2

[0073] (Ni@Pt / CNN): Weigh 200 mg of CNN and disperse it in 30 ml of deionized water, then sonicate for 4 h. After sonication, continuously stir the dispersed CNN at room temperature using a magnetic stirrer. Add 0.0099 g of NiCl2·6H2O to 10 ml of deionized water, then add 0.001 g of dispersant PVP, and continue stirring for 30 minutes to obtain a precursor nickel salt solution. Add the precursor nickel salt solution to the CNN dispersion and continue stirring for 30 minutes to form a mixture. Weigh 85 mg of NaBH4 and 50 mg of NaOH and add them to 10 ml of deionized water to form a reducing agent solution. While stirring, add the reducing agent solution dropwise to the mixture and continue stirring for 15 minutes. Then, measure 7.15 mL of H2PtCl6·6H2O solution (0.003 g / mL) and add it dropwise to the above mixture. After stirring for another 5 hours, the precipitate was collected, washed 6 times with deionized water and ethanol, and dried overnight at 60°C to obtain Ni@Pt / CNN composite catalyst powder with a core-shell structure.

[0074] Example 3

[0075] (Cu@Pt / CNN): Weigh 200 mg of CNN and disperse it in 30 ml of deionized water, then sonicate for 5 h. After sonication, continuously stir the dispersed CNN at room temperature using a magnetic stirrer. Add 0.0083 g of Cu(CH3COO)2·H2O to 10 ml of deionized water, then add 0.0005 g of dispersant PVP, and continue stirring for 30 minutes to obtain a precursor copper salt solution. Add the precursor copper salt solution to the CNN dispersion and continue stirring for 30 minutes to form a mixture. Weigh 85 mg of NaBH4 and 50 mg of NaOH and add them to 10 ml of deionized water to form a reducing agent solution. While stirring, add the reducing agent solution dropwise to the mixture and continue stirring for 15 minutes. Then, measure 7.15 mL of H2PtCl6·6H2O solution (0.003 g / mL) and add it dropwise to the above mixture. After stirring for another 6 hours, the precipitate was collected, washed 6 times with deionized water and ethanol, and dried overnight at 60°C to obtain Cu@Pt / CNN composite catalyst powder with a core-shell structure.

[0076] Example 4

[0077] (Mn@Pt / CNN): Weigh 200 mg of CNN and disperse it in 30 ml of deionized water, then sonicate for 6 h. After sonication, continuously stir the dispersed CNN at room temperature using a magnetic stirrer. Add 0.0104 g of Mn(NO3)2·4H2O to 10 ml of deionized water, then add gelatin, and continue stirring for 30 minutes to obtain a precursor manganese salt solution with a gelatin concentration of 0.5 mmol / L. Add the precursor manganese salt solution to the CNN dispersion and continue stirring for 30 min to form a mixture. Weigh 85 mg of NaBH4 and 50 mg of NaOH and add them to 10 ml of deionized water to form a reducing agent solution. While stirring, add the reducing agent solution dropwise to the mixture and continue stirring for 15 min. Then, measure 7.15 mL of H2PtCl6·6H2O solution (0.003 g / mL) and add it dropwise to the above mixture. After stirring for another 7 hours, the precipitate was collected, washed 6 times with deionized water and ethanol, and dried overnight at 60°C to obtain Mn@Pt / CNN composite catalyst powder with a core-shell structure.

[0078] Comparative Example 1

[0079] (CNN): 10g of melamine was placed in a covered crucible, which was then placed in a muffle furnace. The temperature was set to 550℃, and the mixture was heated for 4 hours at a rate of 2.3℃·min. -1 After the muffle furnace has completely cooled to room temperature, open the furnace and grind the resulting yellow agglomerate into powder to obtain g-C3N4 bulk. Place the g-C3N4 bulk powder back into the muffle furnace, set the temperature to 500℃, and heat for 5 hours at a heating rate of 5℃·min. -1 After naturally cooling to room temperature, g-C3N4 nanosheet powder (CNN) was obtained.

[0080] Comparative Example 2

[0081] (PtCo@CNN): First, 0.2 g of CNN was dispersed in 20 mL of water and stored under sonication for 6 h to form a CNN support solution. Simultaneously, 0.0120 g of Co(NO3)2·6H2O and 7.15 mL of H2PtCl6·6H2O solution (0.003 g / mL) were added to 10 mL of ethylene glycol (EG) and stirred at 50 °C for 2 h. Then, an EG solution containing Pt and Co was added to the CNN support solution. 3 mL of triethanolamine was added to the mixture, and the solution was irradiated under UV-Vis (λ>300 nm, 300 WXe) under vacuum for 2 h. The photoreduced mixture was washed three times by centrifugation with water and ethanol, respectively. Finally, it was dried overnight at 80 °C to obtain the PtCo@CNN catalyst.

[0082] Comparative Example 3

[0083] (PtNi@CNN): First, 0.2 g of CNN was dispersed in 20 mL of water and stored under sonication for 6 h to form a CNN support solution. Simultaneously, 0.0120 g of Ni(NO3)2·6H2O and 7.15 mL of H2PtCl6·6H2O solution (0.003 g / mL) were added to 10 mL of ethylene glycol (EG) and stirred at 50 °C for 2 h. Then, an EG solution containing Pt and Ni was added to the CNN support solution. 3 mL of triethanolamine was added to the mixture, and the solution was irradiated under UV-Vis (λ>300 nm, 300 WXe) under vacuum for 2 h. The photoreduced mixture was washed three times by centrifugation with water and ethanol, respectively. Finally, it was dried overnight at 80 °C to obtain the PtNi@CNN catalyst.

[0084] Comparative Example 4

[0085] (PtCu@CNN): First, 0.2 g of CNN was dispersed in 20 mL of water and stored under sonication for 6 h to form a CNN support solution. Simultaneously, 0.0100 g of Cu(NO3)2·3H2O and 7.15 mL of H2PtCl6·6H2O solution (0.003 g / mL) were added to 10 mL of ethylene glycol (EG) and stirred at 50 °C for 2 h. Then, an EG solution containing Pt and Cu was added to the CNN support solution. 3 mL of triethanolamine was added to the mixture, and the solution was irradiated under UV-Vis (λ>300 nm, 300 WXe) under vacuum for 2 h. The photoreduced mixture was washed three times by centrifugation with water and ethanol, respectively. Finally, it was dried overnight at 80 °C to obtain the PtCu@CNN catalyst.

[0086] Comparative Example 5

[0087] (PtMn@CNN): First, 0.2 g of CNN was dispersed in 20 mL of water and stored under sonication for 6 h to form a CNN support solution. Simultaneously, 0.0104 g of Mn(NO3)2·4H2O and 7.15 mL of H2PtCl6·6H2O solution (0.003 g / mL) were added to 10 mL of ethylene glycol (EG) and stirred at 50 °C for 2 h. Then, an EG solution containing Pt and Mn was added to the CNN support solution. 3 mL of triethanolamine was added to the mixture, and the solution was irradiated under UV-Vis (λ>300 nm, 300 WXe) under vacuum for 2 h. The photoreduced mixture was washed three times by centrifugation with water and ethanol, respectively. Finally, it was dried overnight at 80 °C to obtain the PtMn@CNN catalyst.

[0088] Note: Comparative Examples 2-5 all used photoreduction to synthesize MPt alloy particle cocatalysts on CNN. This cocatalyst, MPt alloy particles, is a homogeneous bimetallic catalyst without a core-shell structure.

[0089] Comparative Example 6

[0090] 200 mg of CNN was weighed and dispersed in 30 mL of deionized water, and sonicated for 4 h. After sonication, the dispersed CNN was continuously stirred at room temperature using a magnetic stirrer. 0.0099 g of NiCl2·6H2O was added to 10 mL of deionized water, and stirring was continued for 30 min to obtain a precursor nickel salt solution. The precursor nickel salt solution was added to the CNN dispersion, and stirring was continued for 30 min to form a mixture. 85 mg of NaBH4 and 50 mg of NaOH were weighed and added to 10 mL of deionized water to form a reducing agent solution. Under stirring, the reducing agent solution was added dropwise to the mixture, and stirring was continued for 15 min. 7.15 mL of H2PtCl6·6H2O solution (0.003 g / mL) was then added dropwise to the above mixture. After stirring for 5 hours, the precipitate was collected, washed 6 times with deionized water and ethanol, and dried overnight at 60 °C to obtain a composite catalyst powder without a core-shell structure.

[0091] Comparative Example 7

[0092] Weigh 200 mg of CNN and disperse it in 30 ml of deionized water, then sonicate for 4 h. After sonication, continuously stir the dispersed CNN at room temperature using a magnetic stirrer. Add 0.0099 g of NiCl2·6H2O and 0.00005 g of dispersant PVP to 10 ml of deionized water, and continue stirring for 30 minutes to obtain a precursor nickel salt solution. Add the precursor nickel salt solution to the CNN dispersion and continue stirring for 30 minutes to form a mixture. Weigh 85 mg of NaBH4 and 50 mg of NaOH and add them to 10 ml of deionized water to form a reducing agent solution. While stirring, add the reducing agent solution dropwise to the mixture and continue stirring for 15 minutes. Then, measure 7.15 mL of H2PtCl6·6H2O solution (0.003 g / mL) and add it dropwise to the above mixture. After stirring for another 5 hours, the precipitate was collected, washed 6 times with deionized water and ethanol, and dried overnight at 60°C to obtain a composite catalyst powder that does not have a core-shell structure.

[0093] Comparative Example 8

[0094] Weigh 200 mg of CNN and disperse it in 30 ml of deionized water, then sonicate for 4 h. After sonication, continuously stir the dispersed CNN at room temperature using a magnetic stirrer. Add 0.0099 g of NiCl2·6H2O and 0.01 g of dispersant PVP to 10 ml of deionized water, and continue stirring for 30 minutes to obtain a precursor nickel salt solution. Add the precursor nickel salt solution to the CNN dispersion and continue stirring for 30 minutes to form a mixture. Weigh 85 mg of NaBH4 and 50 mg of NaOH and add them to 10 ml of deionized water to form a reducing agent solution. While stirring, add the reducing agent solution dropwise to the mixture and continue stirring for 15 minutes. Then, measure 7.15 mL of H2PtCl6·6H2O solution (0.003 g / mL) and add it dropwise to the above mixture. After stirring for another 5 hours, the precipitate was collected, washed 6 times with deionized water and ethanol, and dried overnight at 60°C to obtain a composite catalyst powder that does not have a core-shell structure.

[0095] Comparative Example 9

[0096] Weigh 200 mg of CNN and disperse it in 30 ml of deionized water, then sonicate for 4 hours. After sonication, continuously stir the dispersed CNN at room temperature using a magnetic stirrer. Add 0.0099 g of NiCl2·6H2O to 10 ml of deionized water, then add 0.002 g of carboxymethyl cellulose dispersant, and continue stirring for 30 minutes to obtain a precursor nickel salt solution. Add the precursor nickel salt solution to the CNN dispersion and continue stirring for 30 minutes to form a mixture. Weigh 85 mg of NaBH4 and 50 mg of NaOH and add them to 10 ml of deionized water to form a reducing agent solution. While stirring, add the reducing agent solution dropwise to the mixture and continue stirring for 15 minutes. Then, measure 7.15 mL of H2PtCl6·6H2O solution (0.003 g / mL) and add it dropwise to the above mixture. After stirring for another 5 hours, the precipitate was collected, washed 6 times with deionized water and ethanol, and dried overnight at 60°C to obtain a composite catalyst powder that does not have a core-shell structure.

[0097] Hydrogen production test method: Weigh 50 mg of catalyst powder and disperse it in 100 mL of solvent (100 mL solvent composition: 90 mL deionized water + 10 mL triethanolamine), and ultrasonically stir for 10 min to form a catalyst-water reaction solution. Place this reaction solution in a photocatalytic reactor and conduct hydrogen production tests in the photocatalytic reaction system under vacuum conditions. The light source is visible light with a wavelength > 420 nm, and the test duration is 3 h.

[0098] Table 1. Results of Photocatalytic Water Splitting for Hydrogen Production

[0099] catalyst <![CDATA[Average H2 production rate (μmol / g / h)]]> Example 1 Co@Pt / CNN 6855 Example 2 Ni@Pt / CNN 11158 Example 3 Cu@Pt / CNN 4890 Example 4 Mn@Pt / CNN 7102 Comparative Example 1 CNN 0 Comparative Example 2 PtCo@CNN 3026 Comparative Example 3 PtNi@CNN 5302 Comparative Example 4 PtCu@CNN 1390 Comparative Example 5 PtMn@CNN 3174 Comparative Example 6 PtNi@CNN 5580 Comparative Example 7 PtNi@CNN 5962 Comparative Example 8 PtNi@CNN 5740 Comparative Example 9 PtNi@CNN 6850

[0100] Table 1 shows the hydrogen production rate values ​​for the comparative examples and embodiments; (1) After loading PtM (M = Co / Ni / Cu / Mn) alloy nanoparticles onto the surface of g-C3N4 nanosheets, the hydrogen production rate was improved. Among them, the hydrogen production rate of Comparative Example 3 (PtNi@CNN) was the most significantly improved, with a rate of 5302 μmol / g / h, indicating that the promoting effect of PtNi alloy nanoparticles was more obvious. (2) When M@Pt core-shell nanoparticles were loaded onto the surface of g-C3N4 nanosheets, the corresponding hydrogen production rates were increased. Among them, the hydrogen production rate of Example 2 (Ni@Pt / CNN) was the highest, at 11158 μmol / g / h. The same result can be obtained in Figure 7 , Figure 8 get.

[0101] Comparison of photocatalytic hydrogen production rates between this invention and existing technologies:

[0102] Table 2 Comparison of photocatalytic hydrogen production rates

[0103]

[0104] As can be seen, the composite catalyst (Ni@Pt / CNN) of carbon nitride nanosheets supported on nickel-platinum core-shell co-catalyst nanoparticles obtained in this invention has a significantly improved hydrogen production rate compared with existing similar technologies.

[0105] Figure 1 This is a schematic diagram of the M@Pt / CNN (M = Co / Ni / Cu / Mn) structure.

[0106] Figure 2 The XRD patterns are for Comparative Examples 1–5. It can be seen that after loading PtM alloy particles, the basic composition and structure of g-C3N4 in Comparative Examples 2–5 remained unchanged, and trace alloy peaks appeared.

[0107] Figure 3 The images show the XRD patterns of Comparative Example 1, Comparative Example 3, and Example 2. In Example 2, loading Ni@Pt core-shell nanoparticles did not affect the main components of the CNN.

[0108] Figure 4 The images show the UV-Vis diffuse reflectance spectra of Comparative Examples 1, 3, and 2. It can be seen that the absorption edge of Example 2 exhibits a redshift, and the light absorption intensity of Comparative Examples 3 and 2 is higher than that of Comparative Example 1. This indicates that both PtNi alloy nanoparticles and Ni@Pt core-shell nanoparticles improve the light absorption intensity of the CNN and enhance visible light utilization. The effect of Ni@Pt core-shell nanoparticles is more pronounced.

[0109] Figure 5 (αhν) is used for Comparative Examples 1, 3, and 2. 1 / 2The relationship between band gap energy (hν) and the band gap energy is shown in the graph. It can be seen that the band gap in Example 2 is narrower, which is more conducive to light absorption and photocatalytic reduction reaction.

[0110] Figure 6 This is a schematic diagram of the photocatalytic mechanism of Example 2 (Ni@Pt / CNN).

[0111] Figure 7 The image shown is a SEM image of Comparative Example 1. Two-dimensional g-C3N4 nanosheets (CNN) were successfully formed by thermal exfoliation and ultrasonic dispersion.

[0112] Figure 8 The image shown is a SEM image from Example 2. A Ni@Pt binary metal co-catalyst with a core-shell structure was successfully synthesized on a CNN via a continuous chemical reduction method, demonstrating the successful synthesis of the Ni@Pt / CNN composite catalyst. Simultaneously, Ni@Pt is clearly deposited on the CNN, with a distinct interfacial contact between Ni@Pt and the CNN. Furthermore, the core-shell structure of the Ni core and Pt shell also forms an interface with the CNN, indicating that Ni@Pt / CNN is a semi-core-shell structure.

[0113] Figure 9 The graph shows the hydrogen production rates of Comparative Examples 1–5.

[0114] Figure 10 The graphs show the hydrogen production rates for Examples 1-4. A higher hydrogen production rate indicates a better hydrogen production effect.

Claims

1. A method for preparing a three-phase interface structure M@Pt / CNN photocatalyst modified with a core-shell bimetallic co-catalyst, characterized in that: Includes the following steps: A. Disperse CNN in water, sonicate to obtain CNN dispersion, and continuously stir the CNN dispersion at room temperature. B. Add the metal salt to water, then add the dispersant PVP or gelatin, and stir until completely dissolved to obtain the precursor metal salt solution; in step B, the metal salt is selected from cobalt salt, nickel salt, copper salt or manganese salt. C. Add the precursor metal salt solution obtained in step B to the CNN dispersion that was continuously stirred in step A, continue stirring, and then add the reducing agent solution dropwise while stirring to obtain a mixture. D. Add the aqueous solution of H2PtCl6·6H2O dropwise to the mixture obtained in step C, continue stirring, then collect the precipitate, wash and dry it to obtain the M@Pt / CNN photocatalyst; In step A, the CNN is prepared by the following method: nitrogen and carbon raw materials are heated at 2~5℃·min -1 The temperature was increased to 500-550℃ and held for 2-4 hours. After cooling to room temperature, g-C3N4 bulk material was obtained. The g-C3N4 bulk material was then ground into powder and heated at 2-5℃·min. -1 The heating rate is increased to 500~550℃, held at that temperature for 3~5 hours, and then naturally cooled to room temperature to obtain CNN; the nitrogen-carbon raw material is selected from at least one of melamine, urea, thiourea or dicyandiamide; In step C, the reducing agent solution is prepared by mixing borohydride, caustic alkali, and water in a mass ratio of 85~150:50~80:10000~20000 until homogeneous; the borohydride is selected from at least one of NaBH4 or KBH4; the caustic alkali is selected from at least one of NaOH or KOH.

2. The preparation method according to claim 1, characterized in that: In step A, the mass ratio of the CNN to water is 1:50~200.

3. The preparation method according to claim 1, characterized in that: In step B, at least one of the following must be satisfied: The metal salt is selected from CoCl2·6H2O, Co(NO3)2·6H2O, Co(CH3COO)2·4H2O, Co(acac)2, NiCl2·6H2O, Ni(NO3)2·6H2O, Ni(CH3COO)2·4H2O, Ni(acac)2, CuCl2·2H2O, Cu(NO3)2·3H2O, Cu(CH3COO)2·H2O, Cu(acac)2, MnCl2·4H2O, Mn(NO3)2·4H2O, Mn(CH3COO)2·4H2O, or Mn(acac)2; The mass ratio of the metal salt to water is 7.1~12:10000~40000; The amount of PVP or gelatin added is controlled to be 0.2 mmol / L to 1.0 mmol / L in the precursor metal salt solution.

4. The preparation method according to claim 1, characterized in that: In step C, the mass ratio of the metal salt in the precursor metal salt solution to the CNN in the CNN dispersion is 7.1~12:

200.

5. The preparation method according to claim 1, characterized in that: In step C, the volume ratio of the CNN dispersion to the reducing agent solution is 1:0.25~2.

6. The preparation method according to claim 1, characterized in that: In step D, at least one of the following must be satisfied: The concentration of the H2PtCl6·6H2O aqueous solution is 0.001~0.003 g / mL; The volume ratio of the H2PtCl6·6H2O aqueous solution used in step D to the precursor metal salt solution used in step C is 7.15~21.4:10~40, and the molar ratio of Pt in H2PtCl6·6H2O to M in the metal salt is controlled to be 0.99~1.01:0.99~1.

01.

7. The preparation method according to claim 1, characterized in that: At least one of the following must be met: In step A, the ultrasonic treatment time is 3-6 hours; In step B, the stirring time until completely dissolved is 20-40 minutes; In step C, continue stirring for 30-60 minutes; In step C, the stirring time is 10~40 min; In step D, the stirring time continues for 4 to 7 hours; In step D, the drying temperature is 60~80°C.

8. The three-phase interface structure M@Pt / CNN photocatalyst modified with a core-shell bimetallic co-catalyst as described in any one of claims 1 to 7.

9. The application of the core-shell bimetallic co-catalyst modified three-phase interface structure M@Pt / CNN photocatalyst of claim 8 in photocatalytic water splitting for hydrogen production, photocatalytic degradation of organic pollutants, or photocatalytic reduction of carbon dioxide.

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