Two-dimensional composite catalyst as well as preparation method and application thereof

Abstract

The invention provides a two-dimensional composite catalyst as well as a preparation method and application thereof, and relates to the technical field of photocatalysis. The preparation method comprises the following steps: mixing a first organic metal complex (organic palladium complex), a second organic metal complex (organic molybdenum, organic tungsten or organic iridium complex), a ligand, a reducing agent and a first solvent, and carrying out ligand exchange and metal-metal coupling reduction reaction; and mixing the obtained PdX-ene (X is Mo, W or Ir) powder with a graphite phase carbon nitride nanosheet and a second solvent, and carrying out a self-assembly reaction to obtain the two-dimensional composite catalyst. The two-dimensional composite catalyst has a unique two-dimensional structure, a relatively large mass transfer specific surface area, relatively high photo-induced electron and hole space separation efficiency and photo-induced carrier transmission efficiency, so that the two-dimensional composite catalyst has excellent performance of photocatalytic decomposition of water to produce hydrogen. The two-dimensional composite catalyst is used for hydrogen production through water photolysis, the hydrogen production performance is obviously improved compared with that of a precious metal Pt-loaded g-C3N4 photocatalyst, and the cost is low.

Description

Technical Field

[0001] The present invention relates to the field of photocatalysis technology, and in particular to a two-dimensional composite catalyst and a preparation method and application thereof. Background Art

[0002] Hydrogen energy, with its high calorific value, pollution-free nature, and zero greenhouse gas emissions, is gaining increasing popularity. Currently, achieving efficient and clean hydrogen production remains a bottleneck in its development. Harnessing sunlight, a clean and abundant energy source, to split water to produce hydrogen and oxygen is a cutting-edge technology in clean hydrogen production. The core challenge lies in developing high-performance photocatalysts.

[0003] Currently, the two-dimensional non-metallic material graphitic carbon nitride (g-C3N4) is widely used in the photocatalytic decomposition of water to produce hydrogen as a new, low-cost, visible light-responsive photocatalyst. It has the advantages of simple preparation method and good chemical stability. However, the photogenerated electrons and holes generated by g-C3N4 under light are very easy to recombine, and the photogenerated carrier transport efficiency is low. These problems seriously limit its application in the field of photocatalysis. By loading the precious metal Pt on the surface of g-C3N4 as a co-catalyst, the efficiency of photocatalytic decomposition of water to produce hydrogen can be improved. However, the high price and resource shortage of Pt seriously restrict the application of this photocatalyst in actual production and life. Summary of the Invention

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

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions: The present invention provides a method for preparing a two-dimensional composite catalyst, comprising the following steps: mixing a first organometallic complex, a second organometallic complex, a ligand, a reducing agent, and a first solvent, and performing a ligand exchange and metal-metal coupling reduction reaction to obtain PdX-ene powder; wherein 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; The PdX-ene powder is mixed with graphite-phase carbon nitride nanosheets and a second solvent to undergo a self-assembly reaction to obtain the two-dimensional composite catalyst.

[0006] Preferably, the organic palladium complex includes palladium acetylacetonate, the organic molybdenum complex includes molybdenum hexacarbonyl, the organic tungsten complex includes tungsten hexacarbonyl, and the organic iridium complex includes tetrairidium dodecacarbonyl.

[0007] Preferably, the mass ratio of the first organometallic complex to the second organometallic complex is 1:1 to 4:1.

[0008] 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.

[0009] Preferably, when the second organometallic complex is an organic iridium complex, the ligand is ammonium bromide, the reducing agent is tungsten hexacarbonyl, and the first solvent is oleylamine.

[0010] 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° C., and the time is 8-12 hours.

[0011] Preferably, when the second organometallic complex is an organic iridium complex, the temperature of the ligand exchange and metal-metal coupling reduction reaction is 120-160° C., and the time is 6-8 hours.

[0012] Preferably, the mass ratio of the graphite phase carbon nitride nanosheets to the PdX-ene powder is 50:1~5:1; the second solvent is a hexadecyltrimethylammonium bromide aqueous solution; the self-assembly reaction includes sequentially performing ultrasound and stirring, the ultrasound time is 60~120min, the stirring speed is 300~500rpm, and the time is 12~14h.

[0013] The present invention provides a two-dimensional composite catalyst prepared by the preparation method described in the above technical solution. The two-dimensional composite catalyst is a two-dimensional / two-dimensional composite formed by ultrathin PdX-ene two-dimensional nanosheets loaded onto the surface of graphite phase carbon nitride nanosheets, and X in PdX-ene is Mo, W or Ir.

[0014] The present invention provides the use of the two-dimensional composite catalyst described in the above technical solution in photocatalytic water decomposition to produce hydrogen.

[0015] The present invention provides a method for preparing a two-dimensional composite catalyst. Compared with the prior art, the present invention has the following beneficial effects: The present invention first prepares a two-dimensional bimetallic material, PdX-ene (X is Mo, W, or Ir), which is then combined with graphitic carbon nitride nanosheets (g-C3N4) as a co-catalyst to produce a two-dimensional / two-dimensional PdX-ene / g-C3N4 composite catalyst, the two-dimensional composite catalyst. This composite catalyst effectively reduces the recombination of photogenerated electrons and holes, improving the transport efficiency of photogenerated carriers. Furthermore, the PdX-ene nanosheets have excellent surface compatibility with the two-dimensional g-C3N4 material, forming excellent contact with the g-C3N4 surface, facilitating the rapid transfer of photogenerated electrons to the PdX-ene surface. Furthermore, the preparation method provided by the present invention is simple, low-cost, and amenable to large-scale production.

[0016] The present invention provides a two-dimensional composite catalyst prepared by the preparation method described in the above technical solution. The two-dimensional composite catalyst provided by the present invention has a unique two-dimensional structure, a large specific surface area for mass transfer, high spatial separation efficiency of photogenerated electrons and holes, and high photogenerated carrier transport efficiency, thereby having good photocatalytic water decomposition and hydrogen production performance.

[0017] The present invention provides the use of the two-dimensional composite catalyst described in the above technical solution in the photocatalytic decomposition of water to produce hydrogen. The two-dimensional composite catalyst of the present invention has high efficiency and good photocatalytic cycle stability when used in the photocatalytic water decomposition reaction to produce hydrogen. Its hydrogen production performance is significantly improved compared to that of precious metal Pt-loaded g-C3N4 photocatalysts, and its cost is relatively low. Therefore, the two-dimensional composite catalyst of the present invention is an ideal and more efficient catalyst to replace precious metal Pt-loaded g-C3N4 photocatalysts in the field of photocatalysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 TEM image of the PdMo-ene powder prepared in Example 1; Figure 2 TEM image of the 2D / 2D PdMo-ene / g-C3N4 composite photocatalyst prepared in Example 1; Figure 3 TEM image of the 2D / 2D PdIr-ene / g-C3N4 composite photocatalyst prepared in Example 2; Figure 4 The two-dimensional / two-dimensional PdX-ene / g-C3N4 (X is Mo, W or Ir) composite photocatalyst and g-C3N4 nanophotocatalyst prepared in Example 1, the Pt prepared by the photodeposition method in Comparative Example 1 NC / g-C3N4 (Pt loading 2wt%) and PdMo prepared in Comparative Example 2 NC Comparison of hydrogen production rates of / g-C3N4 (PdMo loading is 2wt%). DETAILED DESCRIPTION

[0019] The present invention provides a method for preparing a two-dimensional composite catalyst, comprising the following steps: mixing a first organometallic complex, a second organometallic complex, a ligand, a reducing agent, and a first solvent, and performing a ligand exchange and metal-metal coupling reduction reaction to obtain PdX-ene powder; wherein 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; The PdX-ene powder is mixed with graphite-phase carbon nitride nanosheets and a second solvent to undergo a self-assembly reaction to obtain the two-dimensional composite catalyst.

[0020] In the present invention, unless otherwise specified, all raw materials involved are commercially available products well known in the art.

[0021] The present invention mixes a first organometallic complex, a second organometallic complex, a ligand, a reducing agent and a first solvent, performs ligand exchange and metal-metal coupling reduction reaction, and obtains PdX-ene powder.

[0022] In the present invention, the first organometallic complex is an organopalladium complex, and the second organometallic complex is an organomolybdenum complex, an organotungsten complex or an organoiridium 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 organoiridium complex preferably includes tetrairidium dodecacarbonyl (Ir4(CO)6). 12 ).

[0023] In the present invention, the mass ratio of the first organometallic complex to the second organometallic complex is preferably 1:1 to 4:1, and may 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 facilitates the production of uniformly sized, ultrathin metalloalkene nanosheets, i.e., PdX-ene.

[0024] First, the case of preparing PdX-ene powder when the second organometallic complex is an organomolybdenum complex or an organotungsten complex is described.

[0025] In the present invention, when the second organometallic complex is an organic molybdenum complex or an organic tungsten complex, the ligand is preferably hexadecyltrimethylammonium bromide. The present invention has no special requirements for the amount of the ligand, as long as the ligands in the first organometallic complex and the second organometallic complex can be fully exchanged; the first solvent is preferably water, and the water is preferably deionized water; the reducing agent is preferably ascorbic acid. The present invention has no special requirements for the amount of the reducing agent, as long as the metal elements in the first organometallic complex and the second organometallic complex can be fully reduced.

[0026] In the present invention, the method for mixing the first organometallic complex, the second organometallic complex, the ligand, the reducing agent and the first solvent is preferably: Dissolving the ligand in a first solvent to obtain a ligand solution; the concentration of the ligand solution is preferably 0.1-0.5 mol / L; The first organometallic complex and the second organometallic complex are added to the ligand solution, stirred until dissolved, and then a reducing agent is added thereto, and ultrasonic dispersion is performed; the ultrasonic dispersion time can be 60 minutes.

[0027] In the present invention, when the second organometallic complex is an organomolybdenum complex or an organotungsten complex, the ligand exchange and metal-metal coupling reduction reaction is preferably performed at a temperature of 60-80°C, preferably 60, 70, or 80°C, and for a time of 8-12 hours, preferably 8, 9, 10, 11, or 12 hours. The ligand exchange and metal-metal coupling reduction reactions are preferably performed under stirring. During the ligand exchange and metal-metal coupling reduction reactions, the first organometallic complex (organopalladium complex), the second organometallic complex (organomolybdenum complex or organotungsten complex), and the ligand (hexadecyltrimethylammonium bromide) react to form a palladium-tungsten (or palladium-molybdenum)-organic intermediate. This intermediate is then reduced with a reducing agent to produce 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.

[0028] After the ligand exchange and metal-metal coupled reduction reaction, the resulting reaction solution is preferably centrifuged and washed and dried sequentially to obtain PdX-ene powder, wherein X is Mo or W. In the present invention, the washing agent used in the centrifugal washing is preferably deionized water, and the number of centrifugal washings can be three; the centrifugal washing is performed to remove organic byproducts generated during the ligand exchange and metal-metal coupled reduction reaction.

[0029] Next, the preparation of PdX-ene powder when the second organometallic complex is an organoiridium complex will be described.

[0030] In the present 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. The present invention does not require a specific amount of the ligand, as long as it can fully exchange the ligands in the first and second organometallic complexes. The present invention also requires a specific amount of the reducing agent, as long as it can fully reduce the metal elements in the first and second organometallic complexes. In the present invention, the first solvent is preferably oleylamine, and the preferred ratio of oleylamine to the first metal complex is 50 mL:100 mg.

[0031] In the present invention, when the second organometallic complex is an organic iridium complex, the method for mixing the first organometallic complex, the second organometallic complex, the ligand, the reducing agent and the first solvent is preferably: adding the first organometallic complex and the second organometallic complex to the first solvent, stirring until dissolved, and then adding the reducing agent and the ligand thereto, and ultrasonically dispersing; the ultrasonic dispersion time can be 60 minutes.

[0032] In the present invention, when the second metal source is an organic iridium complex, the ligand exchange and metal-metal coupling reduction reaction is preferably carried out at a temperature of 120-160°C, preferably 120, 130, 140, 150, or 160°C, and for a time of 6-8 hours, preferably 6, 7, or 8 hours. The ligand exchange and metal-metal coupling reduction reactions are preferably carried out under stirring. During the ligand exchange and metal-metal coupling reduction reactions, the first organometallic complex (organopalladium complex), the second organometallic complex (organoiridium complex), and the ligand (ammonium bromide) react to form a palladium-iridium-organic intermediate. This organic intermediate is then reduced with a reducing agent (tungsten hexacarbonyl) to produce palladium-iridium two-dimensional nanosheets (i.e., PdX-ene, where X is Ir) and an organic byproduct.

[0033] After the ligand exchange and metal-metal coupling reduction reaction, the resulting reaction solution is preferably centrifuged and washed and dried in sequence to obtain PdX-ene powder, wherein X is Ir; the washing reagent used in the centrifugal washing is preferably deionized water, and the number of centrifugal washings can be 3; the organic byproducts generated during the ligand exchange and metal-metal coupling reduction reaction are washed away by the centrifugal washing.

[0034] After obtaining the PdX-ene powder, the present invention mixes the PdX-ene powder with graphite phase carbon nitride nanosheets (g-C3N4 nanosheets) and a second solvent to perform a self-assembly reaction to obtain the two-dimensional composite catalyst.

[0035] In an embodiment of the present invention, the g-C3N4 nanosheets are preferably prepared by the following method: The carbon source and the nitrogen source are mixed and calcined once to obtain bulk C3N4; Grinding and sieving the C3N4 block in sequence to obtain C3N4 powder; The C3N4 powder is subjected to secondary calcination to obtain the g-C3N4 nanosheets.

[0036] In the present invention, the carbon and nitrogen sources are preferably dicyandiamide; the primary calcination temperature is preferably 550-600°C, the heating rate from room temperature to the primary calcination temperature is preferably 2-5°C / min, and the primary calcination time is preferably 2-5 hours. During the primary calcination, dicyandiamide undergoes thermal polymerization at high temperature to form bulk carbon nitride. After the primary calcination, the mixture is naturally cooled to room temperature.

[0037] In the present invention, the size of the sieve used for the screening is preferably 200 mesh; by-products such as C6N8 generated due to the existence of the temperature gradient are removed by the screening, and the obtained sieve residue is the C3N4 powder.

[0038] In the present invention, the secondary calcination temperature is preferably 450-520°C, the heating rate from room temperature to the secondary calcination temperature is preferably 2-5°C / min, and the secondary calcination time is preferably 5-7 hours. Through the secondary calcination, high-temperature exfoliation is performed to obtain g-C3N4 nanosheets.

[0039] In the present invention, the mass ratio of the graphitic carbon nitride nanosheets to PdX-ene powder is preferably 50:1 to 5:1, and can be 50:1, 40:1, 30:1, 33.3:1, 20:1, 10:1, or 5:1. As the graphitic carbon nitride content gradually decreases, the metalloene nanosheet (i.e., PdX-ene) loading gradually increases. As the metalloene content continues to increase, the catalyst's active sites gradually decrease, and excessive metalloene loading on the carbon nitride surface affects the catalyst's absorption of photons, resulting in a gradual decrease in performance.

[0040] In the present 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, wherein hexadecyltrimethylammonium bromide is conducive to the dispersion of graphite phase carbon nitride nanosheets and PdX-ene powder; the present invention has no special requirements for the amount of the second solvent, as long as it can fully disperse the graphite phase carbon nitride nanosheets and PdX-ene powder.

[0041] In the present invention, g-C3N4 nanosheets and PdX-ene powder are preferably added to the second solvent.

[0042] In the present invention, the self-assembly reaction preferably includes sequential sonication and stirring. The sonication time is preferably 60 to 120 minutes, the stirring speed is preferably 300 to 500 rpm, and can be 350, 400, or 450 rpm. The stirring time is preferably 12 to 14 hours, and can be 12, 13, or 14 hours. The self-assembly reaction is preferably carried out at room temperature (i.e., without the need for additional heating or cooling). In the present invention, the self-assembly reaction specifically constructs a PdX-ene / g-C3N4 composite photocatalyst through metal-g-C3N4 electronic interactions combined with intermolecular forces, and PdX-ene is loaded onto the surface of graphite-phase carbon nitride nanosheets as a co-catalyst.

[0043] After the self-assembly reaction is completed, the obtained reaction solution is preferably centrifugally washed and dried in sequence to obtain the two-dimensional composite catalyst; the washing reagent used in the centrifugal washing is preferably deionized water, and the number of centrifugal washings is preferably 3 times; the drying can be vacuum drying.

[0044] The preparation method provided by the present invention has simple process and equipment, short preparation cycle, easy control of process parameters, low cost, and is easy for large-scale production.

[0045] The present invention provides a two-dimensional composite catalyst prepared by the preparation method described in the above technical solution. The two-dimensional composite catalyst is a two-dimensional / two-dimensional composite formed by ultrathin PdX-ene two-dimensional nanosheets supported on the surface of graphite-phase carbon nitride nanosheets. In the present invention, the size of the ultrathin PdX-ene two-dimensional nanosheets is preferably 30-100 nm. In an embodiment of the present 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 the present invention has a unique two-dimensional structure, a large specific surface area for mass transfer, high spatial separation efficiency of photogenerated electrons and holes, and high transport efficiency of photogenerated carriers, resulting in excellent photocatalytic performance for water decomposition to produce hydrogen, and low cost.

[0046] The two-dimensional composite catalyst provided by the present invention is a two-dimensional / two-dimensional (i.e., 2D / 2D) complex constructed from PdX-ene nanosheets and graphite-phase carbon nitride nanosheets. The PdX-ene nanosheets are a two-dimensional bimetallic material, exhibiting both bimetallic electronic synergy and a unique two-dimensional structure. In the present invention, they serve as excellent co-catalysts, well-matched with the two-dimensional g-C3N4 structure and capable of tightly binding to it. PdX in the form of metal nanoparticles (X is 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, their co-catalytic performance is not significantly superior to that of Pt nanoparticles, and these alloy particles are not highly compatible with the two-dimensional nanophotocatalyst 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 and g-C3N4. Compared with PdX nanoparticles, the compatibility with the g-C3N4 photocatalyst is improved, the number of active sites is increased, and the connection between the sheets forms a built-in electric field, which promotes the transmission of electrons, greatly improving the spatial separation of photogenerated electrons and holes and the transmission efficiency of photogenerated carriers, thereby improving the photocatalyst's performance in producing hydrogen from water, making the hydrogen production performance higher than that of g-C3N4 photocatalysts loaded with precious metal Pt.

[0047] The present invention provides the application of the two-dimensional composite catalyst described in the above technical solution in the photocatalytic decomposition of water to produce hydrogen. The present invention has no special requirements for the method of application, and the application method familiar to those skilled in the art can be used. The two-dimensional composite catalyst provided by the present invention is low in cost and has high efficiency and stability in the visible light decomposition of water to produce hydrogen. The results of the examples show that the two-dimensional composite catalyst provided by the present invention is used for the photocatalytic decomposition of water to produce hydrogen, and the yield can reach 52029μmol·g -1 ·h -1 .

[0048] In order to further illustrate the present invention, the two-dimensional composite catalyst provided by the present invention, its preparation method and application are described in detail below with reference to examples, but they should not be construed as limiting the scope of protection of the present invention.

[0049] In various embodiments, the preparation method of g-C3N4 nanosheets is as follows: Dicyandiamide was placed in a crucible and heated to 550°C at a heating rate of 5°C / min for 2 hours to obtain bulk C3N4. After naturally cooling to room temperature, the bulk C3N4 was ground and sieved with a 200-mesh sieve. The C3N4 powder that passed the sieve was placed in a corundum crucible and heated to 500°C at a heating rate of 2°C / min for secondary calcination. The calcination time was 5 h to obtain g-C3N4 nanosheets.

[0050] Example 1 Preparation of two-dimensional composite catalysts: (1) 100 mg of Pd(acac)2 and 40 mg of Mo(CO)6 were added to 40 mL of 0.1 mol / L hexadecyltrimethylammonium bromide aqueous solution and stirred until dissolved. Then, 24 mg of ascorbic acid was added and ultrasonicated for 60 min. The mixture was heated at 80 °C and stirred for 12 h. The mixture was washed with deionized water three times, centrifuged, and vacuum dried for 12 h to obtain PdMo-ene powder. (2) 100 mg of g-C3N4 nanosheets and 2 mg of PdMo-ene powder were added to 100 mL of 0.1 mol / L hexadecyltrimethylammonium bromide aqueous solution, placed in a 150 mL flask and ultrasonicated for 60 min, then stirred at 350 rpm for 12 h, washed with deionized water three times, centrifuged, and vacuum dried for 12 h to obtain a two-dimensional / two-dimensional PdMo-ene (2 wt%) / g-C3N4 composite photocatalyst (also expressed as PdMo-ene / g-C3N4 (2 wt%)), namely the two-dimensional composite catalyst.

[0051] Figure 1 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 ultra-thin, large specific surface area 2D nanosheet structure, and has excellent light transmittance and carrier transport ability.

[0052] Figure 2 This is the 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 ultra-thin two-dimensional nanosheet structure onto the surface of g-C3N4 nanosheets, and the size (sheet diameter) of the two-dimensional PdMo-ene is about 30 nm.

[0053] Example 2 Preparation of two-dimensional composite catalysts: (1) 100 mg Pd(acac)2 and 25 mg Ir4(CO) 12Add to 50 mL of oleylamine and stir until dissolved. Then add 300 mg of W(CO)6 and 250 mg of NH4Br, sonicate for 60 min, heat and stir at 150 ° C for 8 h, wash with deionized water three times, centrifuge, and vacuum dry for 12 h to obtain PdIr-ene powder; (2) 100 mg of g-C3N4 nanosheets and 2 mg of PdIr-ene powder were added to 100 mL of 0.1 mol / L hexadecyltrimethylammonium bromide aqueous solution, placed in a 150 mL flask and ultrasonicated for 60 min, then stirred at 350 rpm for 12 h, washed with deionized water three times, 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.

[0054] Figure 3 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.

[0055] Example 3 Preparation of two-dimensional composite catalysts: (1) 100 mg of Pd(acac)2 and 40 mg of W(CO)6 were added to 40 mL of 0.1 mol / L hexadecyltrimethylammonium bromide aqueous solution and stirred until dissolved. Then, 24 mg of ascorbic acid was added and ultrasonicated for 60 min. After stirring at 80 °C for 12 h, the mixture was washed with deionized water three times, centrifuged, and vacuum dried for 12 h to obtain PdW-ene powder. (2) 100 mg of g-C3N4 nanosheets and 2 mg of PdW-ene powder were added to 100 mL of 0.1 mol / L hexadecyltrimethylammonium bromide aqueous solution, placed in a 150 mL flask and ultrasonicated for 60 min, stirred at 350 rpm for 12 h, washed with pure water three 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.

[0056] Example 4 Preparation of two-dimensional composite catalysts: (1) 100 mg of Pd(acac)2 and 40 mg of Mo(CO)6 were added to 40 mL of 0.1 mol / L hexadecyltrimethylammonium bromide aqueous solution and stirred until dissolved. Then, 24 mg of ascorbic acid was added and ultrasonicated 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. (2) 100 mg of g-C3N4 nanosheets and 3 mg of PdMo-ene nanopowder were added to 100 mL of 0.1 mol / L hexadecyltrimethylammonium bromide aqueous solution, placed in a 150 mL flask and ultrasonicated for 60 min, stirred at 350 rpm for 12 h, washed with deionized water three times, centrifuged, and vacuum dried for 12 h to obtain a two-dimensional / two-dimensional PdMo-ene (3 wt%) / g-C3N4 composite photocatalyst (also expressed as PdMo-ene / g-C3N4 (3 wt%)), namely the two-dimensional composite catalyst.

[0057] Comparative Example 1 Pt NC Preparation of g-C3N4 (where NC stands for “nanoparticle loading”) was performed as follows: 50 mg of g-C3N4 was dispersed in 50 mL of 10% (volume percentage) triethanolamine solution, and ultrasonically dispersed for 5 minutes. Then, 2.6 mL of 1 mg / mL H2PtCl6·6H2O solution was added and ultrasonically dispersed for 5 minutes to obtain a dispersion. After argon was passed through the equipment for 20 minutes to remove the air, a 300 W xenon lamp was used as a light source to illuminate the dispersion for 2 hours. After that, the Pt nanoparticle-loaded g-C3N4 composite catalyst was obtained by washing with water and centrifuging. NC / g-C3N4 (Pt loading 2wt%).

[0058] Comparative Example 2 PdMo NC Preparation of g-C3N4, the steps are as follows: 50 mg of g-C3N4 was dispersed in 100 mL of deionized water and ultrasonically dispersed for 20 min. 2.3 mL of 1 mg / mL sodium chloropalladate solution and 5 mL of 0.1 mg / mL ammonium tetrahydrate heptamolybdate solution were added dropwise. After stirring for 1 h, 20 mL of 0.1 mg / mL sodium borohydride solution was added. The mixture was stirred for 1 h and then washed with deionized water for 4 to 6 times to obtain PdMo nanoparticle-loaded g-C3N4 composite photocatalyst, namely the PdMo nanoparticles. NC / g-C3N4 (PdMo loading is 2wt%).

[0059] 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 mixed with pure g-C3N4 nanosheets and Pt NC / g-C3N4 and PdMo NCThe photocatalytic hydrogen production performance of g-C3N4 nanoparticles was tested. The conditions for photocatalytic hydrogen production were as follows: 5 mg of the catalyst was placed in an aqueous solution containing 10% (volume percentage) triethanolamine (as a sacrificial agent to consume holes to improve hydrogen purity and promote hydrogen production reaction). A 300W xenon lamp was used as a simulated sunlight light source. Under continuous irradiation of the light source, samples were taken every 30 minutes and the hydrogen production was detected by gas chromatography, and the rate was calculated. The results are shown in the figure below. Figure 4 shown.

[0060] Figure 4 show: The 2D / 2D PdMo-ene / g-C3N4 (2 wt%) composite photocatalyst obtained in Example 1 has good photocatalytic hydrogen production performance, with an output of up to 52029 μmol·g -1 ·h -1 , and its performance is significantly better than that of g-C3N4 nanosheets and Pt NC / Photocatalytic hydrogen production performance of g-C3N4 catalyst (the 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 ), indicating that the photocatalytic performance of 2D / 2D PdMo-ene nanosheets is significantly superior to that of precious metal Pt nanoparticles. Furthermore, under simulated sunlight, the apparent quantum efficiency (AQY) of the PdMo-ene / g-C3N4 (2wt%) catalyst reached 8.52%, further demonstrating that the PdMo-ene cocatalyst can promote the stable hydrogen evolution reaction. Performance of the 2D / 2D PdIr-ene / g-C3N4 composite photocatalyst prepared in Example 2 (hydrogen production of 49722 μmol·g -1 ·h -1 ) Compared with Example 1, there is no significant decrease, indicating that the PdX-ene ultrathin nanosheet structure has excellent coupling with the g-C3N4 nanosheet, which is beneficial to the transfer of photogenerated electrons and provides ideas for the design of PdX-ene type co-catalysts; 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 (3 wt%) composite photocatalyst prepared in Example 4 was 40035 μmol·g -1 ·h -1 , which were significantly better than Pt NC / g-C3N4 catalyst and PdMo NC / g-C3N4 catalyst (hydrogen production of 26831μmol·g -1 ·h -1 ); The catalyst with a loading of 3 wt % prepared in Example 4 has a lower hydrogen production performance compared to the catalyst with a loading of 2 wt % prepared in Example 1, indicating that the catalyst performance is higher at a lower loading, which is beneficial to reducing the amount of metal used and reducing the catalyst cost in actual production.

[0061] In addition, after three photocatalytic hydrogen production cycle tests, the performance of the PdX-ene / g-C3N4 composite catalysts prepared in Examples 1 to 4 of the present invention did not change significantly, indicating that the PdX-ene / g-C3N4 photocatalyst has efficient and stable photocatalytic water decomposition and hydrogen production performance.

[0062] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation thereto. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications shall 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: The following steps are involved: mixing a first organometallic complex, a second organometallic complex, a ligand, a reducing agent, and a first solvent, and performing a ligand exchange and metal-metal coupling reduction reaction to obtain PdX-ene powder; wherein 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; The PdX-ene powder is mixed with graphite-phase carbon nitride nanosheets and a second solvent to undergo a self-assembly reaction to obtain the two-dimensional composite catalyst.

2. The preparation method according to claim 1, characterized in that The organic palladium complex includes palladium acetylacetonate, the organic molybdenum complex includes molybdenum hexacarbonyl, the organic tungsten complex includes tungsten hexacarbonyl, and the organic iridium complex includes tetrairidium dodecacarbonyl.

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 or 2, characterized in that 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.

5. The preparation method according to claim 1 or 2, characterized in that When the second organometallic complex is an organic iridium complex, the ligand is ammonium bromide, the reducing agent is tungsten hexacarbonyl, and the first solvent is oleylamine.

6. The preparation method according to claim 4, 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° C., and the time is 8-12 hours.

7. The preparation method according to claim 5, characterized in that When the second organometallic complex is an organic iridium complex, the temperature of the ligand exchange and metal-metal coupling reduction reaction is 120-160° C., and the time is 6-8 hours.

8. The preparation method according to claim 1, characterized in that The mass ratio of the graphite phase carbon nitride nanosheets to the PdX-ene powder is 50:1~5:1; the second solvent is a hexadecyltrimethylammonium bromide aqueous solution; the self-assembly reaction includes sequentially performing ultrasound and stirring, the ultrasound time is 60~120 minutes, the stirring speed is 300~500rpm, and the time is 12~14 hours.

9. The two-dimensional composite catalyst prepared by the preparation method according to any one of claims 1 to 8, wherein the two-dimensional composite catalyst is a two-dimensional / two-dimensional composite formed by ultrathin PdX-ene two-dimensional nanosheets loaded onto the surface of graphite phase carbon nitride nanosheets, wherein X in PdX-ene is Mo, W or Ir.

10. Use of the two-dimensional composite catalyst according to claim 9 in photocatalytic water decomposition to produce hydrogen.

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