A two-dimensional composite catalyst, a preparation method and application thereof

Abstract

The application provides a two-dimensional composite catalyst and a preparation method and application thereof, and relates to the technical field of photocatalysis. The first organic metal complex (organic palladium complex), the second organic metal complex (organic molybdenum, organic tungsten or organic iridium complex), a ligand, a reducing agent and a first solvent are mixed to carry out ligand exchange and metal-metal coupling reduction reaction; the obtained PdX-ene (X is Mo, W or Ir) powder is mixed with graphite phase carbon nitride nanosheet and a second solvent to carry out self-assembly reaction, and a two-dimensional composite catalyst is obtained. The two-dimensional composite catalyst has a unique two-dimensional structure, a large mass transfer specific surface area, high light-generated electron and hole spatial separation efficiency and light-generated carrier transport efficiency, and thus has excellent photocatalytic water decomposition hydrogen production performance. The two-dimensional composite catalyst is used for photocatalytic water decomposition hydrogen production, and the hydrogen production performance is obviously improved compared with the noble metal Pt loaded g-C3N4 photocatalyst, and the cost is low.

Description

Technical Field

[0001] This invention relates to the field of photocatalysis technology, and in particular to a two-dimensional composite catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen energy, due to its high calorific value, lack of pollution, and zero greenhouse gas emissions, has been increasingly widely used. Currently, achieving efficient and clean hydrogen production remains one of the bottlenecks in its development. Utilizing sunlight, a clean and abundant energy source, to decompose water and produce hydrogen and oxygen represents an advanced technology in clean hydrogen production. The core challenge of this technology is the preparation of high-performance photocatalysts.

[0003] Currently, two-dimensional non-metallic material graphitic carbon nitride (g-C3N4) is widely used as a novel, low-cost photocatalyst with visible light response in photocatalytic water splitting to produce hydrogen, offering advantages such as simple preparation methods and good chemical stability. However, the easy recombination of photogenerated electrons and holes and the low transport efficiency of photogenerated carriers generated under light irradiation severely limit its application in the field of photocatalysis. By loading the noble metal Pt onto the surface of g-C3N4 as a co-catalyst, the efficiency of photocatalytic water splitting to produce hydrogen can be improved. However, Pt is expensive and scarce, severely restricting the application of this photocatalyst in practical production and daily life. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a two-dimensional composite catalyst, its preparation method, and its application. The two-dimensional composite catalyst prepared by this invention exhibits excellent photocatalytic water splitting for hydrogen production and is low in cost.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a two-dimensional composite catalyst, comprising the following steps:

[0007] A first organometallic complex, a second organometallic complex, a ligand, a reducing agent, and a first solvent are mixed and subjected to ligand exchange and metal-metal coupling reduction reactions to obtain PdX-ene powder; the first organometallic complex is an organopalladium complex, the second organometallic complex is an organomolybdenum complex, an organotungsten complex, or an organiridium complex, and X in PdX-ene is Mo, W, or Ir;

[0008] The PdX-ene powder was mixed with graphitic carbon nitride nanosheets and a second solvent to undergo a self-assembly reaction, thereby obtaining the two-dimensional composite catalyst.

[0009] Preferably, the organopalladium complex comprises palladium acetylacetonate, the organomolybdenum complex comprises molybdenum hexacarbonyl, the organotungsten complex comprises tungsten hexacarbonyl, and the organiridium complex comprises tetrairidium dodecylcarbonyl.

[0010] Preferably, the mass ratio of the first organometallic complex to the second organometallic complex is 1:1 to 4:1.

[0011] Preferably, when the second organometallic complex is an organomolybdenum complex or an organotungsten complex, the ligand is hexadecyltrimethylammonium bromide, the reducing agent is ascorbic acid, and the first solvent is water.

[0012] Preferably, when the second organometallic complex is an organoiridium complex, the ligand is ammonium bromide, the reducing agent is tungsten hexacarbonyl, and the first solvent is oleylamine.

[0013] Preferably, when the second organometallic complex is an organomolybdenum complex or an organotungsten complex, the temperature of the ligand exchange and metal-metal coupling reduction reaction is 60~80℃ and the time is 8~12h.

[0014] Preferably, when the second organometallic complex is an organoiridium complex, the temperature of the ligand exchange and metal-metal coupling reduction reaction is 120~160℃, and the time is 6~8h.

[0015] Preferably, the mass ratio of the graphitic carbon nitride nanosheets to PdX-ene powder is 50:1 to 5:1; the second solvent is an aqueous solution of hexadecyltrimethylammonium bromide; the self-assembly reaction includes sequential ultrasonication and stirring, wherein the ultrasonication time is 60 to 120 min, the stirring speed is 300 to 500 rpm, and the stirring time is 12 to 14 h.

[0016] This invention provides a two-dimensional composite catalyst prepared by the preparation method described above. The two-dimensional composite catalyst is a two-dimensional / two-dimensional composite formed by loading ultrathin PdX-ene two-dimensional nanosheets onto the surface of graphitic carbon nitride nanosheets, wherein X in PdX-ene is Mo, W or Ir.

[0017] This invention provides the application of the two-dimensional composite catalyst described above in photocatalytic water splitting for hydrogen production.

[0018] This invention provides a method for preparing a two-dimensional composite catalyst. Compared with the prior art, this invention has the following advantages:

[0019] This invention first prepares a two-dimensional bimetallic material, PdX-ene (where X is Mo, W, or Ir), and then combines it as a co-catalyst with graphitic carbon nitride nanosheets (g-C3N4) to obtain a two-dimensional / two-dimensional PdX-ene / g-C3N4 composite catalyst, i.e., the two-dimensional composite catalyst. On the one hand, this composite catalyst can effectively reduce the recombination of photogenerated electrons and holes, and improve the photogenerated carrier transport efficiency; on the other hand, the PdX-ene nanosheets have good surface matching with the two-dimensional g-C3N4 material, forming excellent contact with the g-C3N4 surface, which is conducive to the rapid transfer of photogenerated electrons to the PdX-ene surface. Furthermore, the preparation method provided by this invention is simple, low-cost, and easy to mass-produce.

[0020] This invention provides a two-dimensional composite catalyst prepared by the method described above. The two-dimensional composite catalyst provided by this invention possesses a unique two-dimensional structure, a large mass transfer specific surface area, high photogenerated electron-hole spatial separation efficiency, and high photogenerated carrier transport efficiency, thus exhibiting good photocatalytic water splitting for hydrogen production performance.

[0021] This invention provides the application of the two-dimensional composite catalyst described above in photocatalytic water splitting for hydrogen production. Using the two-dimensional composite catalyst of this invention in the photocatalytic water splitting hydrogen production reaction exhibits high efficiency and good photocatalytic cycle stability. The hydrogen production performance is significantly improved compared to the noble metal Pt-supported g-C3N4 photocatalyst, and the cost is relatively low. Therefore, the two-dimensional composite catalyst of this invention is an ideal and more efficient catalyst to replace the noble metal Pt-supported g-C3N4 photocatalyst in the field of photocatalysis. Attached Figure Description

[0022] Figure 1 TEM image of PdMo-ene powder prepared in Example 1;

[0023] Figure 2 TEM image of the two-dimensional / two-dimensional PdMo-ene / g-C3N4 composite photocatalyst prepared in Example 1;

[0024] Figure 3 TEM image of the two-dimensional / two-dimensional PdIr-ene / g-C3N4 composite photocatalyst prepared in Example 2;

[0025] Figure 4 The two-dimensional / two-dimensional PdX-ene / g-C3N4 (X is Mo, W or Ir) composite photocatalyst prepared for the examples and the g-C3N4 nanophotocatalyst, and the Pt prepared by photodeposition method in Comparative Example 1 NC / g-C3N4 (Pt loading 2wt%) and PdMo prepared in Comparative Example 2 NCComparison of hydrogen production rates for g-C3N4 (PdMo loading of 2wt%). Detailed Implementation

[0026] This invention provides a method for preparing a two-dimensional composite catalyst, comprising the following steps:

[0027] A first organometallic complex, a second organometallic complex, a ligand, a reducing agent, and a first solvent are mixed and subjected to ligand exchange and metal-metal coupling reduction reactions to obtain PdX-ene powder; the first organometallic complex is an organopalladium complex, the second organometallic complex is an organomolybdenum complex, an organotungsten complex, or an organiridium complex, and X in PdX-ene is Mo, W, or Ir;

[0028] The PdX-ene powder was mixed with graphitic carbon nitride nanosheets and a second solvent to undergo a self-assembly reaction, thereby obtaining the two-dimensional composite catalyst.

[0029] Unless otherwise specified, all raw materials involved in this invention are commercially available products well known in the art.

[0030] The present invention mixes a first organometallic complex, a second organometallic complex, a ligand, a reducing agent and a first solvent, and performs ligand exchange and metal-metal coupling reduction reactions to obtain PdX-ene powder.

[0031] In this invention, the first organometallic complex is an organopalladium complex, and the second organometallic complex is an organomolybdenum complex, an organotungsten complex, or an organiridium complex; the organopalladium complex preferably includes palladium acetylacetonate (Pd(acac)2), the organomolybdenum complex preferably includes molybdenum hexacarbonyl (Mo(CO)6), the organotungsten complex preferably includes tungsten hexacarbonyl (W(CO)6), and the organiridium complex preferably includes tetrairidium dodecacarbonyl (Ir4(CO)). 12 ).

[0032] In this invention, the mass ratio of the first organometallic complex to the second organometallic complex is preferably 1:1 to 4:1, and can be 1.7:1, 2.5:1, 2.8:1, 3:1, or 4:1. Controlling the mass ratio of the first organometallic complex to the second organometallic complex within the above range is beneficial for obtaining uniformly sized, ultrathin metalene nanosheets, i.e., PdX-ene.

[0033] First, the preparation of PdX-ene powder when the second organometallic complex is an organomolybdenum complex or an organotungsten complex will be explained.

[0034] In this invention, when the second organometallic complex is an organomolybdenum complex or an organotungsten complex, the ligand is preferably hexadecyltrimethylammonium bromide. This invention does not have a particular requirement for the amount of the ligand added, as long as it can fully exchange the ligands in the first and second organometallic complexes. The first solvent is preferably water, and the water is preferably deionized water. The reducing agent is preferably ascorbic acid. This invention does not have a particular requirement for the amount of the reducing agent used, as long as it can fully reduce the metal elements in the first and second organometallic complexes.

[0035] In this invention, the preferred method for mixing the first organometallic complex, the second organometallic complex, the ligand, the reducing agent, and the first solvent is as follows:

[0036] The ligand is dissolved in a first solvent to obtain a ligand solution; the concentration of the ligand solution is preferably 0.1~0.5 mol / L.

[0037] The first organometallic complex and the second organometallic complex are added to the ligand solution and stirred until dissolved. Then, a reducing agent is added and the mixture is ultrasonically dispersed. The ultrasonic dispersion time can be 60 minutes.

[0038] In this invention, when the second organometallic complex is an organomolybdenum complex or an organotungsten complex, the temperature of the ligand exchange and metal-metal coupling reduction reaction is preferably 60-80°C, which can be 60, 70, or 80°C, and the time is preferably 8-12 hours, which can be 8, 9, 10, 11, or 12 hours. The ligand exchange and metal-metal coupling reduction reaction is preferably carried out under stirring conditions. During the ligand exchange and metal-metal coupling reduction reaction, the first organometallic complex (organopalladium complex), the second organometallic complex (organomolybdenum complex or organotungsten complex), and the ligand (hexadecyltrimethylammonium bromide) react to generate a palladium-tungsten (or palladium-molybdenum)-organic intermediate. The intermediate is reduced by a reducing agent to obtain palladium-molybdenum (tungsten) two-dimensional nanosheets (i.e., PdX-ene, where X is Mo or W, i.e., bimetallic ene nanosheets formed by metal Pd and X) and organic byproducts.

[0039] Following the ligand exchange and metal-metal coupling reduction reaction, the resulting reaction solution is preferably subjected to centrifugation, washing, and drying sequentially to obtain PdX-ene powder, where X is Mo or W. In this invention, the washing reagent used for centrifugation is preferably deionized water, and the centrifugation can be performed three times; the centrifugation washes away the organic byproducts generated during the ligand exchange and metal-metal coupling reduction reaction.

[0040] The following describes the preparation of PdX-ene powder when the second organometallic complex is an organoiridium complex.

[0041] In this invention, when the second organometallic complex is an organoiridium complex, the ligand is preferably ammonium bromide (NH4Br), and the reducing agent is preferably tungsten hexacarbonyl (W(CO)6). The ligand promotes the conversion of the iridium source into an active intermediate, and the reducing agent reduces the active intermediate to form palladium-iridium two-dimensional nanosheets. This invention does not have specific requirements on the amount of ligand added, as long as it is sufficient to fully exchange the ligands in the first and second organometallic complexes; this invention also does not have specific requirements on the amount of reducing agent used, as long as it is sufficient to fully reduce the metal elements in the first and second organometallic complexes. In this invention, the first solvent is preferably oleylamine, and the preferred ratio of oleylamine to the first metal complex is 50 mL: 100 mg.

[0042] In this invention, when the second organometallic complex is an organoiridium complex, the preferred method for mixing the first organometallic complex, the second organometallic complex, the ligand, the reducing agent, and the first solvent is as follows: the first organometallic complex and the second organometallic complex are added to the first solvent and stirred until dissolved, then the reducing agent and the ligand are added thereto, and the mixture is ultrasonically dispersed; the ultrasonic dispersion time can be 60 min.

[0043] In this invention, when the second metal source is an organoiridium complex, the temperature of the ligand exchange and metal-metal coupling reduction reaction is preferably 120~160℃, which can be 120, 130, 140, 150 or 160℃, and the time is preferably 6~8h, which can be 6, 7 or 8h; the ligand exchange and metal-metal coupling reduction reaction is preferably carried out under stirring conditions. During the ligand exchange and metal-metal coupling reduction reaction, the first organometallic complex (organopalladium complex), the second organometallic complex (organopalladium complex), and the ligand (ammonium bromide) react to generate a palladium-iridium-organic intermediate. The organic intermediate is reduced by a reducing agent (tungsten hexacarbonyl) to obtain palladium-iridium two-dimensional nanosheets (i.e., PdX-ene, where X is Ir) and organic byproducts.

[0044] After the ligand exchange and metal-metal coupling reduction reaction, the resulting reaction solution is preferably centrifuged, washed and dried sequentially to obtain PdX-ene powder, where X is Ir; the washing reagent used for centrifugation and washing is preferably deionized water, and the number of centrifugation and washing can be 3 times; the organic byproducts generated during the ligand exchange and metal-metal coupling reduction reaction are washed away by the centrifugation and washing.

[0045] After obtaining PdX-ene powder, the present invention mixes the PdX-ene powder with graphitic carbon nitride nanosheets (g-C3N4 nanosheets) and a second solvent to carry out a self-assembly reaction to obtain the two-dimensional composite catalyst.

[0046] In this embodiment of the invention, the g-C3N4 nanosheets are preferably prepared by the following method:

[0047] The carbon source and nitrogen source are mixed and calcined once to obtain bulk C3N4;

[0048] The C3N4 block was successively ground and sieved to obtain C3N4 powder;

[0049] The C3N4 powder was calcined a second time to obtain the g-C3N4 nanosheets.

[0050] In this invention, the carbon source and nitrogen source are preferably dicyandiamide; the temperature of the first calcination is preferably 550-600°C, and the heating rate from room temperature to the first calcination temperature is preferably 2-5°C / min; the calcination time is preferably 2-5 hours. During the first calcination, dicyandiamide undergoes a thermal polymerization reaction at high temperature to generate bulk carbon nitride. After the first calcination, it is naturally cooled to room temperature.

[0051] In this invention, the preferred screen size for the sieving process is 200 mesh; the sieving process removes byproducts such as C6N8 generated due to the temperature gradient, and the resulting undersize is the C3N4 powder.

[0052] In this invention, the preferred temperature for the secondary calcination is 450~520℃, and the preferred heating rate from room temperature to the secondary calcination temperature is 2~5℃ / min; the preferred calcination time is 5~7h. Through the secondary calcination, g-C3N4 nanosheets are obtained by high-temperature exfoliation.

[0053] In this invention, the preferred mass ratio of the graphitic carbon nitride nanosheets to PdX-ene powder is 50:1 to 5:1, which can be 50:1, 40:1, 30:1, 33.3:1, 20:1, 10:1, or 5:1. As the content of graphitic carbon nitride gradually decreases, the loading of metal ene nanosheets (i.e., PdX-ene) gradually increases. When the content of metal ene continues to increase, the active sites of the catalyst gradually decrease, and excessive metal ene is loaded on the surface of carbon nitride, affecting the absorption of photons by the catalyst and causing its performance to gradually decrease.

[0054] In this invention, the second solvent is preferably an aqueous solution of hexadecyltrimethylammonium bromide, and the concentration of the aqueous solution of hexadecyltrimethylammonium bromide is preferably 0.1~0.5 mol / L. The hexadecyltrimethylammonium bromide is beneficial to the dispersion of graphitic carbon nitride nanosheets and PdX-ene powder. This invention does not have any special requirements on the amount of the second solvent, as long as it can fully disperse the graphitic carbon nitride nanosheets and PdX-ene powder.

[0055] In this invention, g-C3N4 nanosheets and PdX-ene powder are preferably added to the second solvent.

[0056] In this invention, the self-assembly reaction preferably includes sequential ultrasonication and stirring. The ultrasonication time is preferably 60-120 min, the stirring speed is preferably 300-500 rpm (350, 400, or 450 rpm), and the stirring time is preferably 12-14 h (12, 13, or 14 h). The self-assembly reaction is preferably carried out at room temperature (i.e., without additional heating or cooling). Specifically, in this invention, the self-assembly reaction constructs a PdX-ene / g-C3N4 composite photocatalyst through metal-g-C3N4 electronic interactions combined with intermolecular forces, with PdX-ene acting as a co-catalyst loaded onto the surface of graphitic carbon nitride nanosheets.

[0057] After the self-assembly reaction is completed, the resulting reaction solution is preferably subjected to centrifugation, washing and drying in sequence to obtain the two-dimensional composite catalyst; the washing reagent used for centrifugation is preferably deionized water, and the number of centrifugation washings is preferably 3 times; the drying can be vacuum drying.

[0058] The preparation method and equipment provided by this invention are simple, have a short preparation cycle, are easy to control in terms of process parameters, are low in cost, and are easy to mass-produce.

[0059] This invention provides a two-dimensional composite catalyst prepared by the method described above. The two-dimensional composite catalyst is a two-dimensional / two-dimensional composite formed by loading ultrathin PdX-ene two-dimensional nanosheets onto the surface of graphitic carbon nitride nanosheets. In this invention, the size of the ultrathin PdX-ene two-dimensional nanosheets is preferably 30-100 nm. In the embodiments of this invention, the two-dimensional composite catalyst is represented as a two-dimensional / two-dimensional PdX-ene / g-C3N4 composite photocatalyst (X is Mo, W, or Ir). The two-dimensional composite catalyst provided by this invention has a unique two-dimensional structure, a large mass transfer specific surface area, high photogenerated electron and hole space separation efficiency, and high photogenerated carrier transport efficiency, thus exhibiting good photocatalytic water splitting for hydrogen production performance, and is low in cost.

[0060] The two-dimensional composite catalyst provided by this invention is a two-dimensional / two-dimensional (i.e., 2D / 2D) composite constructed from PdX-ene nanosheets and graphitic carbon nitride nanosheets. PdX-ene nanosheets are two-dimensional bimetallic materials, possessing both bimetallic electronic synergy and a unique two-dimensional structure. In this invention, they serve as excellent co-catalysts, exhibiting good structural compatibility with two-dimensional g-C3N4 and enabling tight bonding with it. PdX in the form of metal nanoparticles (X being Mo, W, or Ir) possesses empty d orbitals and bimetallic electronic synergy, which can also promote carrier transfer efficiency and spatial separation of photogenerated electrons and holes to a certain extent, thereby improving photocatalytic efficiency. However, its co-catalytic performance does not have a significant advantage over Pt nanoparticles, and these alloy particles cannot be highly matched with the two-dimensional nanocatalyst g-C3N4. The present invention provides a two-dimensional / two-dimensional composite photocatalyst constructed by combining PdX (X = Mo, W, Ir)-ene two-dimensional nanosheets with g-C3N4. Compared with PdX nanoparticles, it improves the matching degree with g-C3N4 photocatalyst, increases the number of active sites, and the connection between the sheets forms a built-in electric field, which promotes electron transport and significantly improves the spatial separation of photogenerated electrons and holes and the transport efficiency of photogenerated charge carriers. This improves the photocatalyst's performance in water splitting and hydrogen production, making its hydrogen production performance higher than that of g-C3N4 photocatalysts supported by noble metal Pt.

[0061] This invention provides the application of the two-dimensional composite catalyst described above in photocatalytic water splitting for hydrogen production. The method of application is not particularly demanding; any method well-known to those skilled in the art can be used. The two-dimensional composite catalyst provided by this invention is low in cost and exhibits high efficiency and stability in visible light water splitting for hydrogen production. Example results show that using the two-dimensional composite catalyst provided by this invention for photocatalytic water splitting for hydrogen production can achieve a yield of 52029 μmol·g. -1 ·h -1 .

[0062] To further illustrate the present invention, the two-dimensional composite catalyst, its preparation method, and its application are described in detail below with reference to examples, but these should not be construed as limiting the scope of protection of the present invention.

[0063] In each implementation, the preparation method of g-C3N4 nanosheets is as follows:

[0064] Dicyandiamide was placed in a crucible and heated to 550°C at a heating rate of 5°C / min for a calcination time of 2 hours to obtain bulk C3N4.

[0065] After naturally cooling to room temperature, the bulk C3N4 was ground and sieved through a 200-mesh sieve. The C3N4 powder that passed through the sieve was placed in a corundum crucible and calcined at 500°C at a heating rate of 2°C / min for 5 hours to obtain g-C3N4 nanosheets.

[0066] Example 1

[0067] Preparation of two-dimensional composite catalysts:

[0068] (1) 100 mg Pd(acac)2 and 40 mg Mo(CO)6 were added to 40 mL of 0.1 mol / L hexadecyltrimethylammonium bromide aqueous solution and stirred until dissolved. Then 24 mg ascorbic acid was added, and the mixture was sonicated for 60 min. The mixture was heated and stirred at 80 °C for 12 h, washed three times with deionized water, centrifuged, and vacuum dried for 12 h to obtain PdMo-ene powder.

[0069] (2) 100 mg g-C3N4 nanosheets and 2 mg PdMo-ene powder were added to 100 mL of 0.1 mol / L hexadecyltrimethylammonium bromide aqueous solution, placed in a 150 mL flask, sonicated for 60 min, and stirred at 350 rpm for 12 h. The mixture was washed three times with deionized water, centrifuged, and vacuum dried for 12 h to obtain a two-dimensional / two-dimensional PdMo-ene(2wt%) / g-C3N4 composite photocatalyst (which can also be expressed as PdMo-ene / g-C3N4(2wt%)), i.e., the two-dimensional composite catalyst.

[0070] Figure 1 This is a TEM image of the PdMo-ene powder prepared in Example 1. Figure 1 It can be seen that the prepared PdMo-ene has the characteristics of an ultrathin 2D nanosheet structure with a large specific surface area, and has excellent light transmittance and carrier transport capability.

[0071] Figure 2 The image shows a TEM image of the two-dimensional / two-dimensional PdMo-ene / g-C3N4 composite photocatalyst prepared in Example 1. It can be seen that in the two-dimensional / two-dimensional PdMo-ene / g-C3N4 composite photocatalyst obtained in Example 1, PdMo is a composite material formed by loading an ultrathin two-dimensional nanosheet structure onto the surface of g-C3N4 nanosheets. The size (sheet diameter) of the two-dimensional PdMo-ene is about 30 nm.

[0072] Example 2

[0073] Preparation of two-dimensional composite catalysts:

[0074] (1) Mix 100mg Pd(acac)2 and 25mg Ir4(CO) 12Add to 50 mL of oleylamine, stir until dissolved, then add 300 mg W(CO)6 and 250 mg NH4Br, sonicate for 60 min, heat and stir at 150 °C for 8 h, wash 3 times with deionized water, centrifuge, and vacuum dry for 12 h to obtain PdIr-ene powder;

[0075] (2) 100 mg g-C3N4 nanosheets and 2 mg PdIr-ene powder were added to 100 mL of 0.1 mol / L hexadecyltrimethylammonium bromide aqueous solution, placed in a 150 mL flask, sonicated for 60 min, and stirred at 350 rpm for 12 h. The mixture was washed three times with deionized water, centrifuged, and vacuum dried for 12 h to obtain a two-dimensional / two-dimensional PdIr-ene / g-C3N4 composite photocatalyst, namely the two-dimensional composite catalyst.

[0076] Figure 3 This is a TEM image of the two-dimensional PdIr-ene / g-C3N4 composite photocatalyst prepared in Example 2. Figure 3 It can be seen that PdIr-ene is an ultrathin two-dimensional nanosheet structure.

[0077] Example 3

[0078] Preparation of two-dimensional composite catalysts:

[0079] (1) 100 mg Pd(acac)2 and 40 mg W(CO)6 were added to 40 mL of 0.1 mol / L hexadecyltrimethylammonium bromide aqueous solution and stirred until dissolved. Then 24 mg ascorbic acid was added, and the mixture was sonicated for 60 min. After stirring at 80 °C for 12 h, the mixture was washed three times with deionized water, centrifuged, and vacuum dried for 12 h to obtain PdW-ene powder.

[0080] (2) 100 mg g-C3N4 nanosheets and 2 mg PdW-ene powder were added to 100 mL of 0.1 mol / L hexadecyltrimethylammonium bromide aqueous solution, placed in a 150 mL flask, sonicated for 60 min, stirred at 350 rpm for 12 h, washed with pure water 3 times, centrifuged, and vacuum dried for 12 h to obtain a two-dimensional / two-dimensional PdW-ene / g-C3N4 composite photocatalyst, namely the two-dimensional composite catalyst.

[0081] Example 4

[0082] Preparation of two-dimensional composite catalysts:

[0083] (1) 100 mg Pd(acac)2 and 40 mg Mo(CO)6 were added to 40 mL of 0.1 mol / L hexadecyltrimethylammonium bromide aqueous solution and stirred until dissolved. Then 24 mg ascorbic acid was added, and the mixture was sonicated for 60 min. After stirring at 80 °C for 12 h, the mixture was washed three times with deionized water, centrifuged, and vacuum dried for 12 h to obtain PdMo-ene powder.

[0084] (2) 100 mg g-C3N4 nanosheets and 3 mg PdMo-ene nanopowder were added to 100 mL of 0.1 mol / L hexadecyltrimethylammonium bromide aqueous solution, placed in a 150 mL flask, sonicated for 60 min, stirred at 350 rpm for 12 h, washed 3 times with deionized water, centrifuged, and vacuum dried for 12 h to obtain a two-dimensional / two-dimensional PdMo-ene(3wt%) / g-C3N4 composite photocatalyst (which can also be expressed as PdMo-ene / g-C3N4(3wt%)), i.e. the two-dimensional composite catalyst.

[0085] Comparative Example 1

[0086] Pt NC The preparation of / g-C3N4 (where NC represents "nanoparticle loading") is as follows:

[0087] 50 mg g-C3N4 was dispersed in 50 mL of 10% (v / v) triethanolamine solution and ultrasonically dispersed for 5 min. Then, 2.6 mL of 1 mg / mL H2PtCl6·6H2O solution was added, and ultrasonic dispersion was continued for another 5 min to obtain a dispersion. After purging the equipment with argon gas for 20 min, the dispersion was irradiated with a 300 W xenon lamp for 2 h. After washing with water and centrifugation, the Pt nanoparticle-supported g-C3N4 composite catalyst was obtained, i.e., the Pt nanoparticle-supported g-C3N4 composite catalyst. NC / g-C3N4 (Pt loading 2wt%).

[0088] Comparative Example 2

[0089] PdMo NC The preparation of / g-C3N4 is as follows:

[0090] 50 mg g-C3N4 was dispersed in 100 mL of deionized water and ultrasonically dispersed for 20 min. Then, 2.3 mL of 1 mg / mL sodium chloropalladium solution and 5 mL of 0.1 mg / mL ammonium heptamolybdate tetrahydrate solution were added dropwise. After stirring for 1 h, 20 mL of 0.1 mg / mL sodium borohydride solution was added, and stirring continued for 1 h. The mixture was then washed 4–6 times with deionized water to obtain the PdMo nanoparticle-supported g-C3N4 composite photocatalyst, i.e., the PdMo nanoparticle-supported g-C3N4 composite photocatalyst. NC / g-C3N4 (PdMo loading is 2wt%).

[0091] The two-dimensional / two-dimensional PdMo-ene / g-C3N4, PdW-ene / g-C3N4 and PdIr-ene / g-C3N4 composite photocatalysts prepared in the examples were combined with pure g-C3N4 nanosheets and Pt prepared in the comparative example. NC / g-C3N4 and PdMo NC The photocatalytic hydrogen production performance of / g-C3N4 nanoparticles was tested. The photocatalytic hydrogen production conditions were as follows: 5 mg of catalyst was placed in an aqueous solution containing 10% (volume percentage) triethanolamine (as a sacrificial agent to consume holes, thereby improving hydrogen purity and promoting the hydrogen production reaction). A 300W xenon lamp was used as a simulated sunlight source. Samples were taken every 30 minutes under continuous irradiation, and the hydrogen production was detected by gas chromatography. The rate was calculated. The results are as follows: Figure 4 As shown.

[0092] Figure 4 show:

[0093] The two-dimensional / two-dimensional PdMo-ene / g-C3N4 (2wt%) composite photocatalyst obtained in Example 1 exhibits good photocatalytic hydrogen production performance, with a yield of up to 52029 μmol·g. -1 ·h -1 Its performance is significantly better than g-C3N4 nanosheets and Pt. NC Photocatalytic hydrogen production performance of g-C3N4 catalyst (hydrogen production of g-C3N4 nanosheets is 152 μmol·g). -1 ·h -1 Pt NC The hydrogen production of / g-C3N4 nanoparticles is 7952 μmol·g. -1 ·h -1 This indicates that the photocatalytic performance of two-dimensional / two-dimensional PdMo-ene nanosheets is significantly better than that of noble metal Pt nanoparticles. Furthermore, under simulated sunlight irradiation, the apparent quantum efficiency (AQY) of the PdMo-ene / g-C3N4 (2wt%) catalyst reaches 8.52%, further demonstrating that the PdMo-ene co-catalyst can promote the stable conduct of the hydrogen production reaction.

[0094] The performance of the two-dimensional / two-dimensional PdIr-ene / g-C3N4 composite photocatalyst prepared in Example 2 (hydrogen yield of 49722 μmol·g) -1 ·h -1 Compared to Example 1, there was no significant decrease, indicating that the PdX-ene ultrathin nanosheet structure and g-C3N4 nanosheet have excellent coupling properties, which is beneficial to the transfer of photogenerated electrons and provides ideas for the design of PdX-ene type cocatalysts.

[0095] The hydrogen production of the two-dimensional / two-dimensional PdW-ene / g-C3N4 composite photocatalyst prepared in Example 3 was 29036 μmol·g. -1 ·h -1 The hydrogen production of the two-dimensional / two-dimensional PdMo-ene / g-C3N4 (3wt%) composite photocatalyst prepared in Example 4 was 40035 μmol·g. -1 ·h -1 Both are significantly better than Pt NC / g-C3N4 catalyst and PdMo NC / g-C3N4 catalyst (hydrogen yield 26831 μmol·g) -1 ·h -1 );

[0096] The catalyst prepared in Example 4 with a 3 wt% loading showed a decrease in hydrogen production performance compared to the catalyst prepared in Example 1 with a 2 wt% loading. This indicates that the catalyst performance is actually higher at a lower loading, which is beneficial for reducing the amount of metal used and lowering the cost of the catalyst in actual production.

[0097] Furthermore, after three photocatalytic hydrogen production cycle tests, the performance of the PdX-ene / g-C3N4 composite catalysts prepared in Examples 1-4 of this invention did not change significantly, indicating that the PdX-ene / g-C3N4 photocatalyst has efficient and stable photocatalytic water splitting for hydrogen production.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a two-dimensional composite catalyst, characterized in that, Includes the following steps: A first organometallic complex, a second organometallic complex, a ligand, a reducing agent, and a first solvent are mixed and subjected to ligand exchange and metal-metal coupling reduction reactions to obtain PdX-ene powder. The first organometallic complex is an organopalladium complex, and the second organometallic complex is an organomolybdenum complex, an organotungsten complex, or an organoiridium complex. In PdX-ene, X is Mo, W, or Ir. When the second organometallic complex is an organomolybdenum complex or an organotungsten complex, the ligand is hexadecyltrimethylammonium bromide, the reducing agent is ascorbic acid, and the first solvent is water. When the second organometallic complex is an organoiridium complex, the ligand is ammonium bromide, the reducing agent is hexacarbonyltungsten, and the first solvent is oleylamine. The PdX-ene powder is mixed with graphitic carbon nitride nanosheets and a second solvent to carry out a self-assembly reaction to obtain the two-dimensional composite catalyst; the second solvent is an aqueous solution of hexadecyltrimethylammonium bromide; the self-assembly reaction includes sequential ultrasonication and stirring.

2. The preparation method according to claim 1, characterized in that, The organopalladium complex includes palladium acetylacetonate, the organomolybdenum complex includes molybdenum hexacarbonyl, the organotungsten complex includes tungsten hexacarbonyl, and the organiridium complex includes tetrairidium dodecylcarbonyl.

3. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of the first organometallic complex to the second organometallic complex is 1:1 to 4:

1.

4. The preparation method according to claim 1, characterized in that, When the second organometallic complex is an organomolybdenum complex or an organotungsten complex, the temperature of the ligand exchange and metal-metal coupling reduction reaction is 60~80℃ and the time is 8~12h.

5. The preparation method according to claim 1, characterized in that, When the second organometallic complex is an organoiridium complex, the temperature of the ligand exchange and metal-metal coupling reduction reaction is 120~160℃, and the time is 6~8h.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the graphitic carbon nitride nanosheets to the PdX-ene powder is 50:1 to 5:1; the ultrasonication time is 60 to 120 minutes; the stirring speed is 300 to 500 rpm; and the stirring time is 12 to 14 hours.

7. The two-dimensional composite catalyst prepared by the preparation method according to any one of claims 1 to 6, wherein the two-dimensional composite catalyst is a two-dimensional / two-dimensional composite formed by loading ultrathin PdX-ene two-dimensional nanosheets onto the surface of graphitic carbon nitride nanosheets, and X in PdX-ene is Mo, W or Ir.

8. The application of the two-dimensional composite catalyst according to claim 7 in photocatalytic water splitting for hydrogen production.

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