Tungsten and gold modified g-C3N4 hydrogen production composite catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of photocatalysts, and discloses a tungsten and gold modified g-C3N4 hydrogen production composite catalyst as well as a preparation method and application thereof. The catalyst provided by the invention is a composite material of tungsten, gold and a polymer semiconductor, and is composed of ultrathin g-C3N4 nanosheets, highly dispersed W monatomic and Au nanoclusters. The invention also discloses a method for preparing the catalyst. The method specifically comprises the following steps: step 1, preparing a yellow g-C3N4 block; step 2, preparing a white g-C3N4 sheet; step 3, mixing CN and Na2WO4 raw materials; step 4, preparing a g-C3N4 sheet loaded with W monatomic atoms; 5, the g-C3N4 thin sheet and HAuCl4 are mixed; and step 6, preparing a g-C3N4 sheet loaded with the Au nanocluster and the W single atom. The invention also discloses a method for applying the catalyst to photocatalytic water decomposition for hydrogen production. The system provided by the invention solves the common problems of low active site density, poor photon-generated carrier separation efficiency, narrow spectral response range and the like of the g-C3N4-based photocatalyst, and realizes high-efficiency photocatalytic water decomposition hydrogen production.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysts, and particularly relates to a hydrogen production composite catalyst modified by tungsten and gold on g-C3N4, and a preparation method and application thereof. Background Art

[0002] The polymer semiconductor material graphitic carbon nitride (g-C3N4) has attracted much attention in the field of photocatalytic water splitting for hydrogen production due to its unique two-dimensional layered structure, adjustable electronic band characteristics, high stability, easy preparation, environmental friendliness and other advantages. However, the intrinsic properties of g-C3N4 still have problems such as insufficient density of active sites, high recombination rate of photo-generated carriers, and narrow spectral response range, resulting in the photocatalytic hydrogen production rate of pure-phase g-C3N4 generally being lower than 10 μmol·h -1 ·g -1 , which is difficult to meet the actual application requirements. At present, most studies are carried out by hetero-structure construction, defect engineering or molecular modification, but how to optimize the carrier migration path and synergistically enhance the active sites is still the core problem to be solved urgently. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the present invention provides a hydrogen production composite catalyst modified by tungsten and gold on g-C3N4, and a preparation method and application thereof. By innovatively designing an ultrathin g-C3N4 composite system co-modified by W single atoms and Au nanoclusters, based on the atom-cluster cross-scale interfacial electron regulation mechanism, the common problems of g-C3N4-based photocatalysts such as low density of active sites, poor separation efficiency of photo-generated carriers and narrow spectral response range are systematically solved, and efficient photocatalytic water splitting for hydrogen production is realized.

[0004] In order to achieve the purpose of efficient photocatalytic water splitting for hydrogen production of the above-mentioned tungsten and gold modified g-C3N4 hydrogen production composite catalyst, the present invention provides the following technical solutions:

[0005] A hydrogen production composite catalyst modified by tungsten and gold on g-C3N4, wherein the catalyst is a composite material of tungsten, gold and a polymer semiconductor.

[0006] Furthermore, the catalyst is composed of ultrathin g-C3N4 nanosheets, highly dispersed W single atoms and Au nanoclusters.

[0007] Preferably, the size of the highly dispersed Au nanoclusters in the catalyst is 3-4 nm.

[0008] Furthermore, the mass percentages of the loaded metals W and Au in the catalyst are respectively:

[0009] 0.2-0.5% wt and 1% wt.

[0010] Preferably, the mass percentages of metal W and Au loaded in the catalyst are 0.2% wt and 1% wt, respectively.

[0011] A preparation method of a hydrogen production composite catalyst for tungsten and gold modified g-C3N4, the preparation method comprising the following steps:

[0012] Step 1: Treat 10 g of melamine in a muffle furnace at 500 °C for 4 h to obtain yellow g-C3N4 bulk;

[0013] Step 2: Take 1 g of g-C3N4 bulk and evenly spread it on a 5×5 cm magnetic boat, and thermally exfoliate it in a muffle furnace at 520 °C for 2 h to obtain white g-C3N4 flakes;

[0014] Step 3: Add 0.1 g of CN and 0.2 - 0.5% wt of Na2WO4 to 40 mL of ultrapure water, stir at room temperature for 2 h, dry in an oven and collect the powder;

[0015] Step 4: Place the powder in Step 3 in a tubular furnace, and treat it at 400 °C for 2 h under a 5% H2 / Ar atmosphere to obtain g-C3N4 flakes loaded with W single atoms;

[0016] Step 5: Add 50 mg of the flakes obtained in Step 4 and 1% wt of HAuCl4 to 50 mL of a triethanolamine aqueous solution with a volume fraction of 10% vol, and mix evenly;

[0017] Step 6: Irradiate the solution in Step 5 with a 300 W xenon lamp for 10 - 30 min for photodeposition, centrifuge to collect the sample, wash the sample three times with ultrapure water and dry it to obtain g-C3N4 flakes loaded with Au nanoclusters and W single atoms.

[0018] Preferably, the concentration of Na2WO4 in Step 3 is 0.2% wt.

[0019] Preferably, the photochemical deposition time in Step 5 is 10 min.

[0020] A method for applying a hydrogen production composite catalyst for tungsten and gold modified g-C3N4 to photocatalytic water splitting for hydrogen production, comprising the following steps:

[0021] Step 1: Add 10 mg of the hydrogen production composite catalyst for tungsten and gold modified g-C3N4 described in Claim 1 to 100 mL of a triethanolamine aqueous solution with a volume fraction of 10% vol, ultrasonically disperse it and transfer it to a quartz reactor;

[0022] Step 2: Connect and fix the quartz reactor to the all-glass automatic on-line trace gas analysis system. Turn on the vacuum pump and the plunger pump to evacuate the reaction system. Inject high-purity argon gas into the quartz reactor and evacuate again, repeating the cycle three times.

[0023] Step 3: Inject 10 mL of high-purity Ar gas into the quartz reactor, turn on the xenon lamp for reaction, and take samples every 30 min to measure the activity.

[0024] Compared with the prior art, the present invention provides a hydrogen production composite catalyst modified with tungsten and gold on g-C3N4, its preparation method and application, having the following beneficial effects:

[0025] The tungsten and gold modified g-C3N4 hydrogen production composite catalyst of the present invention uses melamine as a precursor to prepare ultrathin g-C3N4 nanosheets by thermal polymerization combined with thermal exfoliation method. The wet chemical method is used to covalently anchor W single atoms on g-C3N4 to form atomically dispersed W-N3 sites, and then Au nanoclusters with a size of 3-4 nm are loaded by photochemical deposition method. The Au nanoclusters are the active centers of the hydrogen evolution reaction. Their surface plasmon resonance (LSPR) can enhance the light absorption performance of the system, and the generated hot electrons can effectively reduce the reaction activation energy barrier; while the W sites and the Au nanoclusters form a Z-type carrier migration path, which can optimize the charge transfer and accelerate the reaction kinetics. Under the synergistic action of the bimetals, the hydrogen production activity of the catalyst can reach 3737.74 μmol·h -1 ·g -1 -1, which is 65 times higher than that of the unmodified system, and the catalyst remains stable during six-cycle tests, showing excellent stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 TEM (a), STEM (b) and EDX (c, d, e, f) diagrams of AuW-CN prepared in Example 1;

[0027] Figure 2 XRD diagrams of CN, W-CN, Au-CN and WAu-CN prepared in Example 1;

[0028] Figure 3 UV-visible spectra of CN, W-CN, Au-CN and WAu-CN prepared in Example 1;

[0029] Figure 4 Photocurrent response diagrams of CN, W-CN, Au-CN and WAu-CN prepared in Example 1;

[0030] Figure 5 Hydrogen production cycle stability test diagram of AuW-CN prepared in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0031] CN: Graphite-phase carbon nitride polymer semiconductor material, which is a simple expression of g-C3N4.

[0032] W-CN: A simple expression for a g-C3N4 thin sheet loaded with single W atoms.

[0033] Au-CN: A simple expression for a g-C3N4 thin sheet loaded with Au nanoclusters.

[0034] WAu-CN: A simple expression for a g-C3N4 thin sheet loaded with Au nanoclusters and single W atoms.

[0035] Next, in combination with the accompanying drawings in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0036] Example 1

[0037] A hydrogen production composite catalyst modified with tungsten and gold on g-C3N4 and its preparation method. The catalyst preparation method includes the following steps:

[0038] Step 1: Treat 10 g of melamine in a muffle furnace at 500 °C for 4 h to obtain yellow g-C3N4 bulk.

[0039] Step 2: Take 1 g of g-C3N4 bulk and evenly spread it on a 5×5 cm magnetic boat, and thermally exfoliate it in a muffle furnace at 520 °C for 2 h to obtain white g-C3N4 thin sheets.

[0040] Step 3: Add 0.1 g of CN and 0.2% wt of Na2WO4 to 40 mL of ultrapure water, stir at room temperature for 2 h, dry in an oven and collect the powder.

[0041] Step 4: Place the powder in Step 3 in a tube furnace, and treat it at 400 °C for 2 h under a 5% H2 / Ar atmosphere to obtain a g-C3N4 thin sheet loaded with single W atoms.

[0042] Step 5: Add 50 mg of the W-CN thin sheets obtained in Step 4 and 1% wt of HAuCl4 to 50 mL of a 10% vol triethanolamine aqueous solution, and mix evenly.

[0043] Step 6: Irradiate the solution in Step 5 with a 300 W xenon lamp for 10 min for photodeposition, centrifuge to collect the sample, wash the sample three times with ultrapure water and dry it to obtain a g-C3N4 thin sheet loaded with Au nanoclusters and single W atoms.

[0044] The microscopic morphology of the catalyst prepared in this example was characterized by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). Please refer to the appendix Figure 1 , and 3-4 nm Au nanoclusters are dispersed on the g-C3N4 flakes. Au lattice fringes can be seen in the high-resolution mode. W is uniformly dispersed on the surface of the g-C3N4 nanosheets in the form of single atoms.

[0045] XRD was used to analyze the crystal phase structure of the catalyst sample prepared in this example. Please refer to the appendix Figure 2 , and all the diffraction peaks of the catalyst prepared in this example are consistent with those of g-C3N4. The positions of the diffraction peaks do not shift, and no other phases appear. The characteristic peak of Au cannot be observed in the spectrum because the loading amount is too small to form relevant crystal planes.

[0046] UV-visible spectroscopy was used to analyze the light absorption performance of the catalyst sample prepared in this example. Please refer to the appendix Figure 3 , and it can be found that after introducing single-atom W, the light absorption of the sample in the 450-700 nm range is significantly enhanced; after further introducing Au nanoclusters, the light absorption of WAu-CN in the 500-650 nm range is further enhanced due to the local surface plasmon resonance (LSPR effect) of the Au nanoclusters.

[0047] Photocurrent response tests were used to characterize the carrier migration status of the catalyst sample prepared in this example in the photocatalytic water splitting hydrogen production reaction. Its photocurrent response was studied under the same light intensity. Please refer to the appendix Figure 4 , and WAu-CN has the strongest photocurrent, indicating that it has a higher efficiency of generating photoinduced carriers, and the electron-hole separation and migration efficiency are also the highest.

[0048] The tungsten and gold modified g-C3N4 hydrogen production composite catalyst prepared in this example was applied to photocatalytic water splitting for hydrogen production, including the following steps:

[0049] Step 1: Add 10 mg of the tungsten and gold modified g-C3N4 hydrogen production composite catalyst prepared in this example to 100 mL of a triethanolamine aqueous solution with a volume fraction of 10% vol, ultrasonically disperse it, and transfer it to a quartz reactor.

[0050] Step 2: Connect the quartz reactor to a fully automated on-line micro gas analysis system and fix it. Open the vacuum pump and the piston pump, evacuate the reaction system, inject high-purity argon into the quartz reactor and evacuate it again, and repeat the cycle three times.

[0051] Step 3: Inject 10 mL of high-purity Ar gas into the quartz reactor, turn on the xenon lamp (AM 1.5G) for reaction, and take samples every 30 min to measure the activity. The reaction results are listed in Table 1.

[0052] Under simulated sunlight irradiation, the photocatalytic hydrogen production performance of the catalyst prepared in this example reaches 3737.74 μmol·h -1 ·g -1 , which are 65 times, 10 times, and 2.7 times that of CN, W-CN, and Au-CN, respectively. The stability test of the catalyst is carried out. Please refer to the appendix Figure 5 , and the catalyst remains stable in six cyclic tests, showing excellent stability.

[0053] Example 2

[0054] A hydrogen production composite catalyst modified with tungsten and gold on g-C3N4 and its preparation method. The catalyst preparation method includes the following steps:

[0055] Step 1: The specific process is the same as that of Step 1 in Example 1;

[0056] Step 2: The specific process is the same as that of Step 2 in Example 1;

[0057] Step 3: Add 0.1 g of CN and 0.5% wt of Na2WO4 to 40 mL of ultrapure water, stir at room temperature for 2 h, dry in an oven and collect the powder;

[0058] Step 4: The specific process is the same as that of Step 4 in Example 1;

[0059] Step 5: The specific process is the same as that of Step 5 in Example 1;

[0060] Step 6: The specific process is the same as that of Step 6 in Example 1.

[0061] TEM and EDX tests show that due to the increase in the W loading amount, the number of W single atoms on the g-C3N4 flakes increases, and Au maintains Au nanoclusters with a size of 3 - 4 nm. The ultraviolet-visible diffuse reflection spectrum shows that its light absorption range and intensity are similar to those in Example 1, and the photocurrent response intensity is slightly weaker than that in Example 1.

[0062] The hydrogen production composite catalyst modified with tungsten and gold on g-C3N4 prepared in this example is applied to photocatalytic water splitting for hydrogen production. The specific process is the same as that of the hydrogen production composite catalyst modified with tungsten and gold on g-C3N4 applied to photocatalytic water splitting in Example 1, and the results are listed in Table 1.

[0063] Example 3

[0064] A hydrogen production composite catalyst modified with tungsten and gold on g-C3N4 and its preparation method. The catalyst preparation method includes the following steps:

[0065] Step 1: The specific process is the same as that of Step 1 in Example 1;

[0066] Step 2: The specific process is the same as that of Step 2 in Example 1;

[0067] Step 3: The specific process is the same as that of Step 3 in Example 1;

[0068] Step 4: The specific process is the same as that of Step 4 in Example 1;

[0069] Step 5: The specific process is the same as that of Step 5 in Example 1;

[0070] Step 6: The solution in Step 5 is irradiated under a 300W xenon lamp for 30 min for photodeposition. The sample is collected by centrifugation, washed three times with ultrapure water and dried to obtain a g-C3N4 sheet loaded with Au nanoclusters and W single atoms.

[0071] TEM and EDX tests show that W maintains a single-atom structure. Due to the extended photodeposition time, Au is transformed from nanoclusters into nanoparticles with a size of 10 - 13 nm. Due to the increase in the size of Au nanoparticles, its LSPR peak redshifts to 580 nm, and its light absorption intensity is slightly higher than that in Example 1. However, its photocurrent response intensity is weaker than that in Example 1, and the carrier separation and migration ability decreases.

[0072] The hydrogen production composite catalyst of tungsten and gold modified g-C3N4 prepared in Example 3 is applied to photocatalytic water splitting for hydrogen production. The specific process is the same as that of the hydrogen production composite catalyst of tungsten and gold modified g-C3N4 applied to photocatalytic water splitting for hydrogen production in Example 1. The results are listed in Table 1.

[0073] Table 1 Test results of photocatalytic water splitting hydrogen production performance

[0074]

[0075] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the existence of additional identical elements in the process, method, article or device comprising the element.

[0076] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A tungsten and gold modified g-C3N4 hydrogen production composite catalyst, characterized in that: The catalyst is a composite material of tungsten, gold and polymer semiconductor.

2. The tungsten and gold modified g-C3N4 hydrogen production composite catalyst according to claim 1, characterized in that: The catalyst consists of ultrathin g-C3N4 nanosheets, W single atoms and Au nanoclusters.

3. The tungsten and gold modified g-C3N4 hydrogen production composite catalyst according to claim 2, characterized in that: The size of the Au nanoclusters in the catalyst is 3-4 nm.

4. The tungsten and gold modified g-C3N4 hydrogen production composite catalyst according to claim 2, characterized in that: The weight percentages of the loading amounts of metal W and Au in the catalyst are 0.2-0.5%wt and 1%wt respectively.

5. The tungsten and gold modified g-C3N4 hydrogen production composite catalyst according to claim 2, characterized in that: The weight percentages of the metal W and Au loadings in the catalyst are 0.2%wt and 1%wt respectively.

6. A method for preparing the tungsten and gold modified g-C3N4 hydrogen production composite catalyst according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: Step 1: 10 g of melamine was treated in a muffle furnace at 500 °C for 4 h to obtain yellow g-C3N4 bulk; Step 2: Take 1g of g-C3N4 block and spread it evenly on a 5×5cm magnetic boat, and thermally peel it at 520℃ in a muffle furnace for 2h to obtain white g-C3N4 flakes; Step 3: Add 0.1 g CN and 0.2-0.5% wt Na2WO4 to 40 mL ultrapure water, stir at room temperature for 2 h, dry in an oven and collect the powder; Step 4: Place the powder in step 3 in a tube furnace and treat it at 400 °C for 2 h in a 5% H2 / Ar atmosphere to obtain a g-C3N4 sheet loaded with W single atoms; Step 5: Add 50 mg of the flakes obtained in step 4 and 1% wt HAuCl4 into 50 mL of 10% vol triethanolamine aqueous solution and mix well; Step 6: Irradiate the solution in step 5 under a 300 W xenon lamp for 10-30 min for photodeposition, collect the sample by centrifugation, wash the sample three times with ultrapure water and dry it to obtain g-C3N4 thin sheets loaded with Au nanoclusters and W single atoms.

7. The method for preparing the tungsten and gold modified g-C3N4 hydrogen production composite catalyst according to claim 6, characterized in that: The concentration of Na2WO4 in step 3 is 0.2%wt.

8. The method for preparing the tungsten and gold modified g-C3N4 hydrogen production composite catalyst according to claim 6, characterized in that: The photochemical deposition time in step 5 is 10 minutes.

9. The tungsten and gold modified g-C3N4 hydrogen production composite catalyst according to any one of claims 1 to 5 is applied to a photocatalytic water decomposition hydrogen production process, comprising the following steps: Step 1: adding 10 mg of the tungsten and gold modified g-C3N4 hydrogen production composite catalyst according to claim 1 to 100 mL of a 10% vol triethanolamine aqueous solution, ultrasonically dispersing and transferring to a quartz reactor; Step 2: Connect and fix the quartz reactor to the all-glass automatic online trace gas analysis system, turn on the vacuum pump and plunger pump, evacuate the reaction system, inject high-purity argon gas into the quartz reactor to evacuate again, and repeat three times; Step 3: Inject 10 mL of high-purity Ar gas into the quartz reactor, turn on the xenon lamp for reaction, and take samples every 30 minutes to measure the activity.

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