Electrostatically self-assembled composite metal catalysts, methods of making and use thereof

Abstract

The application provides an electrostatic self-assembly composite metal catalyst and a preparation method and application thereof. The composite metal catalyst comprises a carrier and composite metal nanoparticles loaded on the surface and / or inside of the carrier; the carrier comprises protonated carbon nitride; the composite metal nanoparticles comprise an alloy with an ordered phase structure, the alloy comprising a first metal element and a second metal element, the first metal element comprising a copper element, and the second metal element comprising a noble metal element; the surface of the composite metal nanoparticles is negatively charged, and the surface of the carrier is positively charged, so that the composite metal nanoparticles and the carrier can form a composite heterostructure. The composite metal catalyst of the application realizes uniform dispersion and high dense adhesion of the composite metal particles on the nanosheet carrier. The carrier heterojunction interface of the catalyst effectively promotes the transfer of photo-generated electrons from the carrier to the composite metal nanoparticles, prolongs the carrier lifetime, is beneficial to improve the photocatalytic activity, and exhibits significant product selectivity.

Description

Technical Field

[0001] This invention relates to an electrostatically self-assembled composite metal catalyst, its preparation method and applications, belonging to the field of photocatalytic material preparation and environmental energy conversion technology. Background Technology

[0002] Photocatalytic conversion of carbon dioxide (CO2) into high-value-added multi-carbon (C) 2+ Products such as liquid fuel ethanol are key pathways to achieving sustainable energy development and a closed carbon cycle. Among numerous heterogeneous catalytic materials, copper (Cu) has proven to be the most promising for catalyzing the realization of C2C2. 2+ The metal element required for the CC coupling step in product formation. However, the practical application of copper-based photocatalysts is currently limited by their extremely low target product selectivity and slow CC coupling kinetics, leading to the limited application of C-type catalysts such as ethanol. 2+ The yield and selectivity of the product are far from meeting practical requirements.

[0003] Gold (Au) has high electronegativity. Introducing it into the Cu lattice to form a bimetallic alloy can effectively regulate the adsorption of carbon-based intermediates by Cu through electron redistribution, thereby optimizing surface reaction kinetics and altering the reaction pathway. To date, most synthetic strategies for supported alloy catalysts rely on methods such as impregnation reduction or chemical deposition, which suffer from problems such as uneven particle size, weak interfacial bonding, and difficulty in precisely controlling the alloy composition, thus limiting the catalytic activity and stability.

[0004] Reference 1 discloses a method for preparing CuAu alloy-supported carbon nitride materials for photocatalytic reduction of carbon dioxide. First, copper nitrate is reduced and loaded onto CN using a sodium borohydride reduction method. The resulting dispersion is reacted with CN and then treated to obtain a CuCN sample. After calcination, the noble metal Au is loaded onto its surface using a metal substitution method to obtain a series of CuAuCN samples. This method uses an impregnation-reduction loading method to form CuAu alloys, which suffers from problems such as uneven particle size, weak interfacial bonding, and difficulty in precisely controlling the alloy composition.

[0005] Reference 2 discloses a copper alloy-modified titanium dioxide / carbon nitride heterojunction photocatalyst and its preparation method. The catalyst is expressed as MxCu / TC, where MxCu represents copper-based alloy nanoparticles, M represents noble metals Au, Pt, and Pd, x represents the molar ratio of noble metal M to Cu, which is 0.25–4, the mass percentage of copper-based alloy nanoparticles is 0.1–10.0 wt%, and TC is a carbon dioxide / carbon nitride heterojunction with a honeycomb-like nanosheet array morphology. This method uses chemical deposition to form copper-based alloy nanoparticles, but it also suffers from problems such as uneven particle size, weak interfacial bonding, and difficulty in precisely controlling the alloy composition.

[0006] Therefore, there is an urgent need to develop a synthesis strategy that can precisely control the electronic properties of Cu and achieve stable bonding between the alloy and the support, in order to realize the conversion of CO2 into C. 2+ Efficient and targeted conversion of products.

[0007] References:

[0008] Reference 1: CN121314653A

[0009] Reference 2: CN109876843A Summary of the Invention

[0010] The problem the invention aims to solve

[0011] In view of the technical problems existing in the prior art, the present invention first provides an electrostatically self-assembled composite metal catalyst to solve the problems of uneven particle size, weak interfacial bonding, and difficulty in precisely controlling the alloy composition in the prior art, so as to realize the conversion of CO2 to C 2+ Efficient and targeted conversion of products.

[0012] The present invention also provides a method for preparing a composite metal catalyst. This method can precisely control the electronic properties of Cu and achieve a stable synthesis strategy that combines the alloy with the support. The preparation method is simple and easy to implement, the raw materials are readily available, and it is suitable for mass production.

[0013] Solution for solving the problem

[0014] [1] A composite metal catalyst, comprising a support and composite metal nanoparticles loaded on and / or inside the support; wherein,

[0015] The carrier includes protonated carbon nitride;

[0016] The composite metal nanoparticles comprise an alloy with an ordered phase structure, the alloy comprising a first metallic element and a second metallic element, the first metallic element comprising copper and the second metallic element comprising a noble metal element; and...

[0017] The surface of the composite metal nanoparticles is negatively charged, and the surface of the carrier is positively charged, enabling the composite metal nanoparticles and the carrier to form a composite heterostructure.

[0018] [2] According to the composite metal catalyst described in [1] above, the atomic ratio of the first metal element and the second metal element is 3:1 to 1:3;

[0019] Preferably, the second metallic element includes one or more of gold, silver, platinum, rhodium, and palladium.

[0020] [3] The composite metal catalyst according to [1] or [2] above, wherein the average particle size of the composite metal nanoparticles is 4.0~5.5 nm;

[0021] Based on the mass of the carrier being 100%, the loading of the composite metal nanoparticles is 0.1~5%.

[0022] [4] The composite metal catalyst according to any one of [1]-[3] above, wherein the composite metal nanoparticles and the support are combined by electrostatic self-assembly to form a composite heterostructure.

[0023] [5] A method for preparing a composite metal catalyst according to any one of [1]-[4] above, comprising the step of loading composite metal nanoparticles onto the surface and / or interior of a support by electrostatic self-assembly.

[0024] Preferably, the preparation method includes the following steps:

[0025] Support preparation steps: Obtain graphitic carbon nitride and protonate the graphitic carbon nitride to obtain the support;

[0026] Preparation steps of composite metal nanoparticles: After the copper precursor and noble metal precursor are reduced by a reducing agent in the liquid phase, composite metal nanoparticles with negative charge are obtained.

[0027] Electrostatic self-assembly step: The support and composite metal nanoparticles are mixed and electrostatically self-assembled to obtain the catalyst precursor;

[0028] Annealing treatment step: The catalyst precursor is annealed under a reducing atmosphere to obtain a composite metal catalyst.

[0029] [6] According to the preparation method described in [5] above, the protonation treatment includes placing graphitic carbon nitride in an acidic solution for protonation treatment; preferably, the concentration of the acidic solution is 5~15 mol / L; more preferably, the acidic solution includes sulfuric acid solution or hydrochloric acid solution; even more preferably, the protonation treatment time is 2~10h.

[0030] [7] According to the preparation method described in [5] or [6] above, wherein the liquid-phase reduction reaction is carried out in an alcohol solvent in the presence of a surfactant;

[0031] Preferably, the liquid-phase reduction reaction is obtained through a stepwise heating process.

[0032] [8] According to the preparation method described in [7] above, the step heating treatment includes heating the reduction product to 170~180℃ and holding it for 0.5~1.5h; then adding the surfactant and further heating to 280~300℃ and holding it for 15~30 min.

[0033] [9] The preparation method according to any one of [5]-[8] above, wherein the reducing atmosphere comprises a mixture of hydrogen and an inert gas, preferably, the content of hydrogen in the mixture is 1-5%;

[0034] The annealing process includes heating the catalyst precursor to 280~320℃ and holding it at that temperature for 0.5~2 h; preferably, the heating rate of the annealing process is 2~8℃ / min.

[0035]

[10] A method for using a composite metal catalyst according to any one of [1]-[4] above in the photocatalytic reduction of carbon dioxide to prepare a multi-carbon compound; preferably, the multi-carbon compound includes ethanol.

[0036] The effects of the invention

[0037] The composite metal catalyst of this invention achieves uniform dispersion and high-density adhesion of composite metal particles on a nanosheet support. The heterojunction interface of the catalyst effectively promotes the transfer of photogenerated electrons from the support to the composite metal nanoparticles, prolongs the carrier lifetime, improves photocatalytic activity, and exhibits significant product selectivity.

[0038] The method for preparing the composite metal catalyst of the present invention can precisely control the electronic properties of Cu and achieve a stable combination of alloy and support. The preparation method is simple and easy to implement, the raw materials are readily available, and it is suitable for mass production. Attached Figure Description

[0039] Figure 1 The transmission electron microscopy (TEM) results of the Au1Cu1 / PCN composite metal catalyst of Example 1 and the PCN sample of Comparative Example 1 are shown.

[0040] Figure 2 The zeta potentials of CN, Au1Cu1 composite metal particles Au1Cu1 / PCN composite metal catalyst in Example 1 of the present invention and PCN in Comparative Example 1 are shown.

[0041] Figure 3 The EDS elemental mapping diagram and elemental content analysis results of the Au1Cu1 / PCN composite metal catalyst in Example 1 of the present invention are shown.

[0042] Figure 4The X-ray diffraction (XRD) spectra of the composite metal catalysts of Examples 1-3 and the samples of Comparative Examples 1-3 are shown.

[0043] Figure 5 The fluorescence (PL) spectra of the Au1Cu1 / PCN composite metal catalyst in Example 1 of the present invention and the PCN sample of Comparative Example 1 are shown in comparison.

[0044] Figure 6 The graphs show the photocatalytic CO2 reduction reaction performance of the composite metal catalysts prepared in Examples 1-5 and the samples of Comparative Examples 1-3 of the present invention.

[0045] Figure 7 The images show photographs of the PCN sample of Comparative Example 1, the Au1Cu1 / CN composite metal catalyst of Comparative Example 4, and the Au1Cu1 and Au1Cu1 / PCN composite metal catalysts in Example 1, as well as a comparison diagram of the photocatalytic CO2 reduction reaction performance of the Au1Cu1 / CN composite metal catalysts of Comparative Example 4 and Example 1. Detailed Implementation

[0046] Various exemplary embodiments, features, and aspects of the present invention will be described in detail below. The term "exemplary" as used herein means "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as superior to or better than other embodiments.

[0047] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced without certain specific details. In other instances, methods, means, apparatus, and steps well known to those skilled in the art have not been described in detail in order to highlight the spirit of the present invention.

[0048] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0049] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0050] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

[0051] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0052] <First Aspect>

[0053] A first aspect of the present invention provides a composite metal catalyst comprising a support and composite metal nanoparticles supported on the surface and / or interior of the support; wherein,

[0054] The carrier includes protonated carbon nitride;

[0055] The composite metal nanoparticles comprise an alloy with an ordered phase structure, the alloy comprising a first metallic element and a second metallic element, the first metallic element comprising copper and the second metallic element comprising a noble metal element; and...

[0056] The surface of the composite metal nanoparticles is negatively charged, and the surface of the carrier is positively charged, enabling the composite metal nanoparticles and the carrier to form a composite heterostructure.

[0057] The composite metal catalyst of this invention achieves uniform dispersion and high-density adhesion of composite metal particles on a nanosheet support. The heterojunction interface of the catalyst effectively promotes the transfer of photogenerated electrons from the support to the composite metal nanoparticles, prolongs the carrier lifetime, improves photocatalytic activity, and exhibits significant product selectivity.

[0058] In some specific embodiments, the atomic ratio of the first metal element to the second metal element is 3:1 to 1:3, preferably 2.5:1 to 1:2.5, for example: 2:1, 1.5:1, 1:1, 1:1.5, 1:2, etc. The inventors of this invention have discovered that when the atomic ratio of the first metal element to the second metal element is 3:1 to 1:3, the photocatalytic activity of the composite metal catalyst is even more superior.

[0059] Preferably, the second metallic element includes one or more of gold, silver, platinum, rhodium, and palladium; more preferably, the second metallic element includes gold.

[0060] In some specific implementations, the average particle size of the composite metal nanoparticles is 4.0~5.5 nm; the composite metal nanoparticles can be uniformly distributed on the surface of the carrier.

[0061] With the carrier's mass as 100%, the loading of the composite metal nanoparticles is 0.1% to 5%, for example: 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, etc. When the loading of the composite metal nanoparticles is 0.1% to 5%, the composite metal nanoparticles can effectively exert their function.

[0062] Furthermore, since the surface of the composite metal nanoparticles carries a negative charge and the surface of the support carries a positive charge, the composite metal nanoparticles and the support can form a composite heterostructure through electrostatic self-assembly. The inventors of this invention have discovered that, compared to methods such as impregnation reduction or chemical deposition, forming a composite heterostructure through electrostatic self-assembly results in more uniform particle size and stronger interfacial bonding of the composite metal nanoparticles. Moreover, the alloy composition allows for precise control of the content of the first and second metal elements, which is more conducive to the exertion of catalytic activity and stability.

[0063] <Second aspect>

[0064] A second aspect of the present invention provides a method for preparing a composite metal catalyst according to the first aspect of the present invention, comprising the step of loading composite metal nanoparticles onto the surface and / or interior of a support by electrostatic self-assembly.

[0065] The preparation method of this invention is a synthesis strategy that enables precise control of the electronic properties of Cu and stable bonding between the alloy and the support, thereby achieving the conversion of CO2 into C. 2+ Efficient and targeted conversion of products.

[0066] Preferably, the preparation method includes the following steps:

[0067] Support preparation steps: Obtain graphitic carbon nitride and protonate the graphitic carbon nitride to obtain the support;

[0068] Preparation steps of composite metal nanoparticles: After the copper precursor and noble metal precursor are reduced by a reducing agent in the liquid phase, composite metal nanoparticles with negative charge are obtained.

[0069] Electrostatic self-assembly step: The support and composite metal nanoparticles are mixed and electrostatically self-assembled to obtain the catalyst precursor;

[0070] Annealing treatment step: The catalyst precursor is annealed under a reducing atmosphere to obtain a composite metal catalyst.

[0071] Carrier preparation steps

[0072] In this invention, graphitic carbon nitride can be obtained by high-temperature calcination. Specifically, aromatic amine compounds are calcined in air at high temperatures in stages to obtain graphitic carbon nitride nanosheets.

[0073] The present invention does not impose any particular limitation on aromatic amine compounds, and any aromatic amine compound commonly used in the art can be used. Specifically, the aromatic amine compound can be one or a combination of two or more of urea, cyanamide, dicyandiamide, melamine, etc.

[0074] Furthermore, the present invention does not specifically limit the temperature for staged calcination, but it can be 500~600℃.

[0075] The staged calcination process can specifically include the following steps: heating the aromatic amine compound to 500-600℃ at a heating rate of 1-5℃ / min and holding for 2-6 hours, followed by natural cooling; then heating to 500-600℃ at a heating rate of 3-8℃ / min and holding for 0.5-2 hours, followed by natural cooling; finally heating to 500-600℃ at a heating rate of 1-5℃ / min and holding for 0.5-2 hours, followed by natural cooling, thereby obtaining graphitic carbon nitride. The cooling range can be room temperature. In this invention, room temperature is generally 15-25℃.

[0076] Furthermore, the graphitic carbon nitride is protonated to obtain the support.

[0077] Specifically, the protonation treatment includes placing graphitic carbon nitride in an acidic solution for protonation treatment; preferably, the concentration of the acidic solution is 5~15 mol / L; more preferably, the acidic solution includes sulfuric acid solution or hydrochloric acid solution; even more preferably, the protonation treatment time is 2~10 h.

[0078] For protonation treatment, stirring or ultrasound can be used. When stirring, the stirring speed can be 200~600 rpm.

[0079] Following protonation, the process includes a solid-liquid separation and drying step of the protonation product to obtain the carrier. The present invention does not specifically limit the method of solid-liquid separation; it can be centrifugation or filtration, etc.

[0080] Specifically, when using centrifugation, water can be used for repeated centrifugation until the pH of the product is neutral (e.g., 6.5~7.5). Furthermore, the centrifugation speed can be 6000~10000 rpm, and each centrifugation process can last 1~5 minutes.

[0081] The present invention does not impose any particular limitation on the drying process, but vacuum drying can be used. Specifically, the vacuum drying temperature is 60~100℃, and the drying time is 8~16 hours.

[0082] Preparation steps of composite metal nanoparticles

[0083] By using a reducing agent to reduce copper precursors and noble metal precursors in the liquid phase, negatively charged composite metal nanoparticles are obtained.

[0084] The reducing agent is not particularly limited in this invention and can be any reducing agent commonly used in the art. Specifically, the reducing agent can be one or a combination of two or more of sodium borohydride, potassium borohydride, lithium borohydride, etc.

[0085] The present invention does not specifically limit the copper precursor, which can be a commonly used copper precursor in the art, such as copper salts. Specifically, it can be an organic or inorganic salt of copper. Specifically, the copper precursor can be one or a combination of two or more of copper sulfate, copper carbonate, copper nitrate, copper chloride, copper oxalate, and copper acetate.

[0086] The present invention does not impose any particular limitation on the noble metal precursor, which can be any noble metal precursor commonly used in the art. Specifically, it can be an acid or salt of a noble metal. Taking gold as an example, the gold precursor can be one or a combination of two or more of the following: HAuCl4·3H2O, NaAuCl4, KAuCl4, AuCl3, Au(PPh3)Cl, etc.

[0087] In some specific embodiments, the liquid-phase reduction reaction is carried out in an alcohol solvent in the presence of a surfactant.

[0088] Specifically, the surfactant is preferably a nonionic surfactant. The present invention does not impose particular limitations on the nonionic surfactant, and it can be any nonionic surfactant commonly used in the art. Specifically, the nonionic surfactant can be one or a combination of two or more of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyether (F-127), oleylamine, etc.

[0089] Furthermore, the present invention does not impose a particular limitation on the molecular weight of the surfactant, which can be 40,000 to 60,000 Da.

[0090] The present invention does not particularly limit the use of alcohol solvents, and any alcohol solvent commonly used in the art can be used. Specifically, the alcohol solvent can be tetraethylene glycol (TEG), triethylene glycol (TriEG), etc.

[0091] Specifically, the liquid-phase reduction reaction is carried out under an inert atmosphere. In this invention, the inert atmosphere refers to an atmosphere that does not cause the reactants to undergo other reactions, such as nitrogen or argon.

[0092] Furthermore, the liquid-phase reduction reaction can be carried out using a stepped heating treatment. In some specific embodiments, the stepped heating treatment includes raising the temperature to 170~180℃ and holding it for 0.5~1.5h; then adding the surfactant, and further raising the temperature to 280~300℃ and holding it for 15~30 min.

[0093] Finally, after the stepwise heat treatment is completed, the product can be precipitated using an antisolvent to obtain composite metal nanoparticles. The antisolvent is not particularly limited in this invention and can be anything such as ethanol.

[0094] Furthermore, composite metal nanoparticles are obtained again through solid-liquid separation. The present invention does not specifically limit the method of solid-liquid separation; it can be centrifugation or filtration, etc. Specifically, when centrifugation is used, the centrifugation speed can be 8000~12000 rpm, and the centrifugation time for each process can be 1~5 minutes.

[0095] Electrostatic self-assembly steps

[0096] The catalyst precursor was obtained by electrostatic self-assembly of the support and composite metal nanoparticles.

[0097] In this invention, since the surface of the composite metal nanoparticles is negatively charged and the surface of the carrier is positively charged, the composite metal nanoparticles and the carrier can be electrostatically self-assembled to form a composite heterostructure through the action of opposite charges.

[0098] The inventors of this invention have discovered that, compared with methods such as impregnation reduction or chemical deposition, forming composite heterostructures through electrostatic self-assembly can result in more uniform particle size and stronger interfacial bonding of composite metal nanoparticles. Furthermore, the alloy composition can be precisely controlled to regulate the content of the first and second metal elements, which is more conducive to the exertion of catalytic activity and stability.

[0099] Furthermore, the electrostatic self-assembly takes place in water. The carrier is dispersed in water and then mixed with composite metal nanoparticles to perform electrostatic self-assembly.

[0100] Specifically, electrostatic self-assembly can be performed using stirring or ultrasound. When stirring, the stirring speed can be 200-600 rpm, and the stirring time can be 6-18 hours, meaning the electrostatic self-assembly time can be 6-18 hours.

[0101] Annealing process

[0102] The catalyst precursor was annealed under a reducing atmosphere to obtain a composite metal catalyst. This invention reveals that annealing can enhance interfacial bonding and remove residual organic matter.

[0103] In some specific embodiments, the reducing atmosphere comprises a mixture of hydrogen and an inert gas, preferably, the hydrogen content in the mixture is 1-5%.

[0104] Furthermore, the annealing treatment includes heating the catalyst precursor to 280~320℃ and holding it at that temperature for 0.5~2 h; preferably, the heating rate of the annealing treatment is 2~8℃ / min.

[0105] <Third aspect>

[0106] A third aspect of the present invention provides a method for using the composite metal catalyst according to the first aspect of the present invention in the photocatalytic reduction of carbon dioxide to prepare a multi-carbon compound; preferably, the multi-carbon compound includes ethanol.

[0107] Specifically, the photocatalytic reduction of carbon dioxide includes the following steps: under normal temperature and pressure conditions, the composite metal catalyst is fully dispersed in pure deionized water, and carbon dioxide gas is introduced under full-spectrum irradiation to carry out the reduction reaction.

[0108] Example

[0109] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0110] Example 1

[0111] Step 1: Calcine 15 g of urea in air in stages: First, heat to 550°C at a rate of 2°C / min and hold for 4 h, then allow to cool naturally to room temperature; then heat to 550°C again at a rate of 5°C / min and hold for 1 h, then allow to cool naturally to room temperature; finally, heat to 550°C at a rate of 2°C / min and hold for 1 h, then allow to cool naturally to room temperature to obtain the CN sample.

[0112] Step 2: 250 mg of CN sample was dispersed in 40 mL of 10 mol / L hydrochloric acid solution and stirred at 400 rpm for 6 h at room temperature for protonation treatment. After repeated centrifugation with water (8000 rpm for 3 min) and vacuum drying at 80℃ for 12 h, a positively charged PCN sample was obtained.

[0113] Step 3: 6.8 mg Cu(CH3COO)2, 13.3 mg HAuCl4·3H2O, and 100 mg PVP (molecular weight 55000 Da) were dissolved in 50 mL TEG. Under a N2 atmosphere, 25 mL of a prepared 0.010 mol / L NaBH4 solution was rapidly injected to initiate a liquid-phase reduction reaction. The mixture was then heated to 175 °C and held for 1 h. Afterward, an additional 100 mg of PVP was added, followed by heat treatment at 290 °C for 20 min. After cooling to room temperature, 100 mL of anhydrous ethanol was added as an antisolvent to precipitate the product. The negatively charged Au1Cu1 composite metal nanoparticles were then collected by centrifugation at 10000 rpm for 3 min.

[0114] Step 4: 100 mg of the PCN carrier obtained in Step 2 was ultrasonically dispersed in 20 mL of deionized water, and 3 mg of the Au1Cu1 composite metal nanoparticles obtained in Step 3 were added. After stirring for 12 h (400 rpm), the precursor powder was obtained by electrostatic self-assembly using the effect of opposite surface charges.

[0115] Step 5: Anneal the precursor powder obtained in Step 4 under a 5% H2 / Ar reducing mixed atmosphere, heating it to 300℃ at a rate of 5℃ / min and holding it for 1 h. This process is beneficial for strengthening the interfacial bonding and removing residual organic matter, thus obtaining the composite metal catalyst, denoted as Au1Cu1 / PCN.

[0116] Example 2

[0117] The only difference between Example 2 and Example 1 is that the mass of Cu(CH3COO)2 and HAuCl4·3H2O added in step 3 is 3.4 mg and 20 mg respectively (the molar ratio of Au to Cu is 3:1). The amount of other raw materials and the preparation method are exactly the same, thus obtaining a composite metal catalyst, denoted as Au3Cu1 / PCN.

[0118] Example 3

[0119] The only difference between Example 3 and Example 1 is that the mass of Cu(CH3COO)2 and HAuCl4·3H2O added in step 3 is 10 mg and 6.6 mg respectively (the molar ratio of Au to Cu is 1:3). The amount of other raw materials and the preparation method are exactly the same, thus obtaining a composite metal catalyst, denoted as Au1Cu3 / PCN.

[0120] Example 4

[0121] The only difference between Example 4 and Example 1 is that the mass of Au1Cu1 composite metal added in step four is 1 mg, while the amount of other raw materials and the preparation method are exactly the same, thus obtaining a composite metal catalyst, denoted as 1 wt% Au1Cu1 / PCN.

[0122] Example 5

[0123] The only difference between Example 4 and Example 1 is that the mass of Au1Cu1 composite metal added in step four is 5 mg, while the amount of other raw materials and the preparation method are exactly the same, thus obtaining a composite metal catalyst, denoted as 5 wt% Au1Cu1 / PCN.

[0124] Comparative Example 1

[0125] Step 1: Calcine 15 g of urea in air in stages: First, heat to 550°C at a rate of 2°C / min and hold for 4 h; then heat to 550°C again at a rate of 5°C / min and hold for 1 h; finally, heat to 550°C at a rate of 2°C / min and hold for 1 h; then obtain the CN sample.

[0126] Step 2: 250 mg of CN sample was dispersed in 40 mL of 10 mol / L hydrochloric acid solution and stirred at 400 rpm for 6 h at room temperature for protonation treatment. After repeated centrifugation with water (8000 rpm for 3 min) and vacuum drying at 80℃ for 12 h, a positively charged PCN sample was obtained.

[0127] Comparative Example 2

[0128] The only difference between Comparative Example 2 and Example 1 is that the mass of Cu(CH3COO)2 added in step 3 is 0 mg, while the amount of other raw materials and the preparation method are exactly the same, thus obtaining a composite metal catalyst, denoted as Au / PCN.

[0129] Comparative Example 3

[0130] The only difference between Comparative Example 3 and Example 1 is that the mass of HAuCl4·3H2O added in step 3 is 0 mg, while the amount of other raw materials and the preparation method are exactly the same, thus obtaining a composite metal catalyst, denoted as Cu / PCN.

[0131] Comparative Example 4

[0132] Step 1: Calcine 15 g of urea in air in stages: First, heat to 550°C at a rate of 2°C / min and hold for 4 h, then allow to cool naturally to room temperature; then heat to 550°C again at a rate of 5°C / min and hold for 1 h, then allow to cool naturally to room temperature; finally, heat to 550°C at a rate of 2°C / min and hold for 1 h, then allow to cool naturally to room temperature to obtain the CN sample.

[0133] Step 2: 6.8 mg Cu(CH3COO)2, 13.3 mg HAuCl4·3H2O, and 100 mg PVP (molecular weight 55000 Da) were dissolved in 50 mL TEG. Under a N2 atmosphere, 25 mL of a prepared 0.010 mol / L NaBH4 solution was rapidly injected to initiate a liquid-phase reduction reaction. The mixture was then heated to 175 °C and held for 1 h. Afterward, an additional 100 mg of PVP was added, followed by heat treatment at 290 °C for 20 min. After cooling to room temperature, 100 mL of anhydrous ethanol was added as an antisolvent to precipitate the product. The Au1Cu1 composite metal nanoparticles were then collected by centrifugation at 10000 rpm for 3 min.

[0134] Step 3: Disperse 100 mg of CN carrier obtained in Step 1 in 20 mL of deionized water by ultrasonication, add 3 mg of Au1Cu1 composite metal nanoparticles obtained in Step 3, and stir for 12 h (400 rpm) to obtain precursor powder.

[0135] Step 4: The precursor powder obtained in Step 4 is annealed in a 5% H2 / Ar reducing mixed atmosphere, heated to 300℃ at a rate of 5℃ / min and held for 1 h. This process is beneficial to strengthen the interfacial bonding and remove residual organic matter, thus obtaining the composite metal catalyst, denoted as Au1Cu1 / CN.

[0136] Performance testing

[0137] 1. Morphology testing of composite metal catalysts

[0138] The Au1Cu1 / PCN composite metal catalyst of Example 1 and the PCN sample of Comparative Example 1 were analyzed by transmission electron microscopy (TEM) to obtain transmission electron microscopy (TEM) images.

[0139] Particle size distribution was obtained by measuring TEM images, and aberration-corrected scanning transmission electron microscopy (STEM) images were obtained by aberration-corrected STEM testing. Furthermore, atomic column intensity analysis spectra were obtained using DigitalMicrograph software. The results are as follows: Figure 1 As shown.

[0140] Figure 1 The morphology and structure characterization results are shown for the Au1Cu1 / PCN composite metal catalyst of Example 1 and the PCN sample of Comparative Example 1. Figure 1 Image a is a transmission electron microscope (TEM) image of the pure PCN sample in Comparative Example 1 without the addition of gold-copper composite metal particles. Figure 1 b is a transmission electron microscope (TEM) image of the Au1Cu1 / PCN sample. (From...) Figure 1 It can be seen that the gold-copper composite metal nanoparticles are uniformly dispersed on the PCN carrier surface, while no obvious loaded species are observed on the pure PCN surface.

[0141] Figure 1 c is a particle size distribution diagram of gold-copper composite metal nanoparticles on the surface of Au1Cu1 / PCN sample. The results show that the particle size distribution is in the range of 4.0~5.5 nm.

[0142] Figure 1 d is an aberration-corrected scanning transmission electron microscope image of the Au1Cu1 / PCN sample, used to observe the atomic-level structure of the gold-copper composite metal particles.

[0143] Figure 1 e is Figure 1 The atomic column intensity analysis spectrum of the corresponding region in d. Figure 1 f represents the ordered structure model of the L10 phase Au1Cu1 composite metal. (Comparison) Figure 1 e and Figure 1 As can be seen from f, the prepared gold-copper composite metal nanoparticles have an ordered L10 phase structure.

[0144] 2. Characterization of Zeta potential

[0145] The zeta potential of the sample surface was measured using a laser particle size analyzer, and the results are as follows: Figure 2 As shown.

[0146] Figure 2 The zeta potentials are those of CN, Au1Cu1 composite metal particles, Au1Cu1 / PCN composite metal catalyst in Example 1 of this invention, and PCN in Comparative Example 1. Figure 2As can be seen, protonated PCN exhibits a positive Zeta potential (+2.92 mV), while the Au1Cu1 composite metal nanoparticles have a negative surface charge (-5.54 mV). The opposite charges facilitate uniform self-assembly through electrostatic attraction. In contrast, the unprotonated pristine CN exhibits a negative Zeta potential (-20.33 mV), exhibiting electrostatic repulsion with the similarly negatively charged Au1Cu1 composite metal, making it difficult to form a stable and uniform composite structure. These results indicate that the positively charged surface of PCN is key to promoting the effective loading of Au1Cu1 composite metal, providing a direct basis for the subsequent construction of electrostatically self-assembled composite metal catalysts.

[0147] 3. Element mapping analysis

[0148] The surface morphology of the samples was observed using transmission electron microscopy, and elemental mapping analysis was performed using energy dispersive spectroscopy (EDS). The results are as follows: Figure 3 As shown

[0149] Figure 3 Image 'a' is a transmission electron microscope (TEM) image of the Au1Cu1 / PCN composite metal catalyst prepared in Example 1 of this invention. Figure 3 As can be seen from a, Au and Cu elements exhibit a uniform, co-regional distribution on the PCN support surface, without any obvious elemental segregation or aggregation. Figure 3 Figure b shows the EDS elemental content analysis results of the Au1Cu1 / PCN composite metal catalyst prepared in Example 1 of this invention. The figure shows that the atomic percentages of Cu and Au are 0.38 and 0.36 at%, respectively, with a ratio close to 1:1, which is basically consistent with the theoretically designed stoichiometric ratio of the Au1Cu1 composite metal. This result further confirms that the Au1Cu1 composite metal nanoparticles are well dispersed on the PCN surface, and the alloy structure is maintained. The atomic composition meets expectations, and the nanoparticles are successfully loaded onto the PCN support surface through electrostatic self-assembly.

[0150] 4. Powder X-ray diffraction test

[0151] The composite metal catalysts of Examples 1-3 and the samples of Comparative Examples 1-3 were analyzed by powder X-ray diffraction using CuK. α Analysis of radiation experimental conditions, the 2θ (°) of the diffraction peak and the intensity of the diffraction peak are as follows: Figure 4 As shown.

[0152] Figure 4The X-ray diffraction (XRD) spectra of the composite metal catalysts of Examples 1-3 and the samples of Comparative Examples 1-3 are shown. The figures show characteristic diffraction peaks of PCN (approximately 12.7° and 27.7°) and the characteristic peak of the ordered tetragonal phase (L10) of the Au1Cu1 composite metal of Example 1 (approximately 39.5°). The alloy diffraction peaks are located between the standard diffraction peaks of pure Au and pure Cu, and no independent diffraction peaks of elemental Au or elemental Cu were observed in the composite metal catalysts of Examples 1-3, confirming the formation of the gold-copper composite metal and its successful composite on PCN.

[0153] 5. Fluorescence (PL) spectroscopy analysis

[0154] The fluorescence intensity of the sample was measured using a steady-state fluorescence spectrometer, and the results are as follows: Figure 5 As shown.

[0155] Figure 5 The image shows a comparison of the fluorescence (PL) spectra of the Au1Cu1 / PCN composite metal catalyst prepared in this embodiment of the invention and the PCN sample of Comparative Example 1. The results show that the PL emission intensity of the Au1Cu1 / PCN sample is significantly lower than that of the PCN sample, indicating that the introduction of the Au1Cu1 composite metal effectively suppresses the recombination of photogenerated electron-hole pairs, promotes the separation and migration of interfacial charges, and is beneficial to improving the efficiency of photocatalytic reaction.

[0156] 6. Evaluation of photocatalytic carbon dioxide reduction performance

[0157] The photocatalytic carbon dioxide reduction performance was evaluated at room temperature. A 300 W xenon lamp was used as the light source in this invention. Gas products were detected by gas chromatography, and liquid products were detected by high-performance liquid chromatography.

[0158] 10 mg of the photocatalysts from Examples 1-5 and Comparative Examples 1-3 were weighed and dispersed in 50 mL of deionized water, then sonicated for 15 min to ensure thorough dispersion. Subsequently, high-purity CO2 was introduced into the reactor at a flow rate of 50 mL / min for 30 min to displace the air in the system; after closing the outlet, CO2 was continued until the pressure reached 0.1 MPa. A 300 W xenon lamp (without filter) was used as the light source, and photocatalytic activity testing began after the light source was turned on. During the reaction, 4 μL of gas samples were extracted every 1 h, and the composition of the gaseous products was analyzed by gas chromatography. After the reaction, 1 mL of the reaction solution was filtered through a 0.22 μm filter membrane, and the liquid products were analyzed by high-performance liquid chromatography. For specific results, see [link to results]. Figure 6 and Figure 7 .

[0159] Figure 6The figures show the photocatalytic CO2 reduction performance of the composite metal catalysts prepared in Examples 1-5 and the samples in Comparative Examples 1-3 of this invention. Figure 6 As can be seen from a, the ethanol formation rate and electron selectivity of the Au1Cu1 / PCN sample are appropriately superior to those of Au3Cu1 / PCN and Au1Cu. 13 / PCN samples. Among them, Au1Cu1 / PCN showed the highest ethanol yield (44.52 μmol g). -1 ·h -1 The composite metal catalysts of Examples 1-3 of this invention exhibited the best electron selectivity (99.18%), while the activities of Au3Cu1 / PCN and Au1Cu3 / PCN were reduced. However, the composite metal catalysts of Examples 1-3 of this invention all showed superior performance compared to the samples of Comparative Examples 1-3.

[0160] Depend on Figure 6 As can be seen from the comparison of the photocatalytic CO2 reduction reaction of the composite metal catalysts in Examples 1 and 4-5, the ethanol production rate gradually increases as the loading increases from 1 wt% to 3 wt%; when the loading is further increased to 5 wt%, the activity decreases slightly.

[0161] Figure 7 Photographs of the PCN sample from Comparative Example 1, the Au1Cu1 / CN composite metal catalyst from Comparative Example 4, and the Au1Cu1 and Au1Cu1 / PCN composite metal catalysts from Example 1, along with a comparison graph of the photocatalytic CO2 reduction performance of the Au1Cu1 / CN composite metal catalyst from Comparative Example 4 and the Au1Cu1 / PCN composite metal catalyst from Example 1. Figure 7 As can be seen from a, Au1Cu1 is mainly dark black, Au1Cu1 / PCN is dark gray, while Au1Cu1 / CN is light gray in optical color, indicating that CN that has not been protonated is not conducive to the adhesion of Au1Cu1 composite metal particles.

[0162] Depend on Figure 7 As can be seen from the comparison of the photocatalytic CO2 reduction reaction of the composite metal catalysts in Comparative Example 4 and Example 1, the ethanol production rate decreases due to the decrease in Au1Cu1 loading caused by the lack of protonation of CN.

[0163] It should be noted that although the technical solution of the present invention has been described with specific examples, those skilled in the art will understand that the present invention should not be limited thereto.

[0164] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A composite metal catalyst, characterized in that, Includes a carrier and composite metal nanoparticles loaded on and / or inside the carrier; wherein, The carrier includes protonated carbon nitride; The composite metal nanoparticles comprise an alloy with an ordered phase structure, the alloy comprising a first metallic element and a second metallic element, the first metallic element comprising copper and the second metallic element comprising a noble metal element; and... The surface of the composite metal nanoparticles is negatively charged, and the surface of the carrier is positively charged, enabling the composite metal nanoparticles and the carrier to form a composite heterostructure.

2. The composite metal catalyst according to claim 1, characterized in that, The atomic ratio of the first metallic element to the second metallic element is 3:1 to 1:3; Preferably, the second metallic element includes one or more of gold, silver, platinum, rhodium, and palladium.

3. The composite metal catalyst according to claim 1 or 2, characterized in that, The average particle size of the composite metal nanoparticles is 4.0~5.5 nm; Based on the mass of the carrier being 100%, the loading of the composite metal nanoparticles is 0.1~5%.

4. The composite metal catalyst according to any one of claims 1-3, characterized in that, The composite metal nanoparticles and the carrier are combined through electrostatic self-assembly to form a composite heterostructure.

5. A method for preparing a composite metal catalyst according to any one of claims 1-4, characterized in that, This includes the step of loading composite metal nanoparticles onto the surface and / or interior of a carrier via electrostatic self-assembly. Preferably, the preparation method includes the following steps: Support preparation steps: Obtain graphitic carbon nitride and protonate the graphitic carbon nitride to obtain the support; Preparation steps of composite metal nanoparticles: After the copper precursor and noble metal precursor are reduced by a reducing agent in the liquid phase, composite metal nanoparticles with negative charge are obtained. Electrostatic self-assembly step: The support and composite metal nanoparticles are mixed and electrostatically self-assembled to obtain the catalyst precursor; Annealing treatment step: The catalyst precursor is annealed under a reducing atmosphere to obtain a composite metal catalyst.

6. The preparation method according to claim 5, characterized in that, The protonation treatment includes placing graphitic carbon nitride in an acidic solution for protonation treatment; preferably, the concentration of the acidic solution is 5~15 mol / L; more preferably, the acidic solution includes sulfuric acid solution or hydrochloric acid solution; even more preferably, the protonation treatment time is 2~10 h.

7. The preparation method according to claim 5 or 6, characterized in that, The liquid-phase reduction reaction is carried out in an alcohol solvent in the presence of a surfactant; Preferably, the liquid-phase reduction reaction is obtained through a stepwise heating process.

8. The preparation method according to claim 7, characterized in that, The stepped heating treatment includes heating the reduction product to 170~180℃ and holding it at that temperature for 0.5~1.5h; then adding the surfactant and further heating to 280~300℃ and holding it at that temperature for 15~30min.

9. The preparation method according to any one of claims 5-8, characterized in that, The reducing atmosphere comprises a mixture of hydrogen and an inert gas, preferably, the hydrogen content in the mixture is 1-5%; The annealing process includes heating the catalyst precursor to 280~320℃ and holding it at that temperature for 0.5~2 h; preferably, the heating rate of the annealing process is 2~8℃ / min.

10. A method for using a composite metal catalyst according to any one of claims 1-4 in the photocatalytic reduction of carbon dioxide to prepare a multi-carbon compound; preferably, the multi-carbon compound includes ethanol.

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