A photocatalyst and its preparation method and application

Abstract

The present invention relates to the field of photocatalyst technology, and in particular to a photocatalyst, its preparation method, and its application. The present invention provides a photocatalyst comprising alternating hexagonal cadmium sulfide and cubic cadmium sulfide. The photocatalyst of the present invention comprises cadmium sulfide having a tandem heterojunction structure, which effectively enhances the effective separation and migration of charges in the cadmium sulfide catalyst, thereby significantly improving its photocatalytic activity. Compared with single-crystalline cadmium sulfide and cadmium sulfide without a tandem heterojunction structure, the photocatalyst of the present invention exhibits significantly improved photocatalytic activity.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysts, and in particular to a photocatalyst and a preparation method and application thereof. Background Art

[0002] With the growing global energy crisis and environmental concerns, photocatalytic water splitting to produce hydrogen has attracted widespread attention as a clean, efficient, and renewable alternative to fossil fuels. Among various hydrogen production technologies, photocatalytic hydrogen production powered by renewable energy sources such as solar energy is one of the most promising approaches to achieving a hydrogen economy. Currently, a wide range of semiconductor photocatalysts, such as sulfides, nitrides, and metal / metal oxide materials, have been studied.

[0003] Cadmium sulfide (CdS) stands out among high-performance solar photocatalytic materials due to its excellent visible light response and suitable band gap. However, during the photocatalytic reaction, rapid recombination of photoinduced electron-hole pairs and severe photocorrosion still limit the hydrogen evolution efficiency of CdS photocatalysts. Currently, the construction of heterostructures has been proven to be one solution to suppress photocorrosion in metal-sulfide photocatalysts. This can also limit and enhance the separation efficiency of photogenerated electron-hole pairs. Furthermore, heterojunctions form between different crystalline forms of the same semiconductor, and the spatial electric field formed at the heterojunction interface promotes electron-hole separation. However, from a practical perspective, the electron-hole separation efficiency of a single heterojunction structure is far from sufficient. If heterojunctions can be arranged in series, the electron-hole separation efficiency will be far from sufficient. If heterojunctions can be arranged in series, the electron and hole transfer between multiple phases can be achieved, thereby significantly enhancing the separation of photogenerated electron-hole pairs and significantly improving the photocatalytic activity of the semiconductor. CdS has two distinct crystalline phases: hexagonal cadmium sulfide (h-CdS) and cubic cadmium sulfide (c-CdS). The differences in atomic arrangement give them distinct electronic structures, resulting in unique energy band properties. Literature research and experiments have shown that the formation of a heterojunction between h-CdS and c-CdS improves the separation efficiency of photogenerated electrons and holes. However, this simple heterojunction structure is insufficient. Therefore, exploring how to finely tune the heterojunction structure to further improve the efficiency of photogenerated charge separation is a major challenge. Summary of the Invention

[0004] The object of the present invention is to provide a photocatalyst and a preparation method and application thereof, wherein the photocatalyst has higher photogenerated charge separation efficiency and thus has higher photocatalytic performance.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The invention provides a photocatalyst comprising alternately arranged hexagonal cadmium sulfide and cubic cadmium sulfide.

[0007] Preferably, the mass ratio of hexagonal cadmium sulfide to cubic cadmium sulfide is (1-10):(1-49).

[0008] The present invention also provides a method for preparing the photocatalyst described in the above technical solution, comprising the following steps:

[0009] mixing a sulfur source, a cadmium metal salt and water to obtain a mixed solution;

[0010] The mixed solution is subjected to hydrothermal treatment to obtain the photocatalyst.

[0011] Preferably, the mixing comprises mixing a sulfur source and water and then adding the cadmium metal salt.

[0012] Preferably, the sulfur source includes one or more of thioacetamide, thiourea and sodium sulfide.

[0013] Preferably, the cadmium metal salt includes one or more of cadmium nitrate, cadmium acetate and cadmium chloride.

[0014] Preferably, the molar ratio of sulfur in the sulfur source to cadmium in the cadmium metal salt is (0.7-3):1.

[0015] Preferably, the concentration of the sulfur source in the mixed solution is 0.01 to 0.06 mol / L.

[0016] Preferably, the temperature of the hydrothermal treatment is 160-180° C., and the time is 100-168 hours.

[0017] The present invention also provides the use of the photocatalyst described in the above technical solution or the photocatalyst prepared by the preparation method described in the above technical solution in the field of photocatalytic water decomposition.

[0018] The present invention provides a photocatalyst comprising alternating hexagonal cadmium sulfide and cubic cadmium sulfide. The differences in atomic arrangement impart distinct electronic structures, thereby exhibiting unique energy band characteristics. The photocatalyst of the present invention comprises cadmium sulfide with a tandem heterojunction structure, which can achieve a gradient distribution of energy band bending, optimize the kinetic behavior of photogenerated carriers during transport, and effectively enhance the cadmium sulfide catalyst's ability to facilitate effective charge separation and migration, thereby significantly improving its photocatalytic activity. Compared to single-crystalline cadmium sulfide and cadmium sulfide without a tandem heterojunction structure, the photocatalyst of the present invention exhibits significantly enhanced photocatalytic activity.

[0019] The present invention also provides a method for preparing the photocatalyst described in the above technical solution, comprising the following steps: mixing a sulfur source, a cadmium metal salt, and water to obtain a mixed solution; and subjecting the mixed solution to a hydrothermal treatment to obtain the photocatalyst. The preparation method is simple, easy to operate, and low-cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 XRD patterns of the photocatalysts described in Example 1, Example 3 and Comparative Example 1;

[0021] Figure 2 HRTEM image of the photocatalyst described in Example 1;

[0022] Figure 3 Activity diagram of CdS-1, CdS-2, and CdS-3 photocatalytic decomposition of water to produce hydrogen;

[0023] Figure 4 Activity diagram of CdS-4, CdS-5, and CdS-6 photocatalytic decomposition of water to produce hydrogen. DETAILED DESCRIPTION

[0024] The invention provides a photocatalyst comprising alternately arranged hexagonal cadmium sulfide and cubic cadmium sulfide.

[0025] In the present invention, the mass ratio of hexagonal cadmium sulfide to cubic cadmium sulfide is preferably (1-10):(1-49), more preferably (1-4):(1-4), and most preferably 13:7.

[0026] The present invention also provides a method for preparing the photocatalyst described in the above technical solution, comprising the following steps:

[0027] mixing a sulfur source, a cadmium metal salt and water to obtain a mixed solution;

[0028] The mixed solution is subjected to hydrothermal treatment to obtain the photocatalyst.

[0029] In the present invention, unless otherwise specified, all preparation raw materials are commercially available products well known to those skilled in the art.

[0030] The sulfur source, the cadmium metal salt and water are mixed to obtain a mixed solution.

[0031] In the present invention, the sulfur source preferably includes one or more of thioacetamide, thiourea and sodium sulfide; when the sulfur source is two or more of the above specific options, the present invention has no special limitation on the ratio of the specific substances, and they can be mixed in any ratio.

[0032] The cadmium metal salt described in the present invention preferably includes one or more of cadmium nitrate, cadmium acetate and cadmium chloride; when the cadmium metal salt is two or more of the above-mentioned specific selections, the present invention has no special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio.

[0033] In the present invention, the water is preferably deionized water.

[0034] In the present invention, the molar ratio of sulfur in the sulfur source to cadmium in the cadmium metal salt is preferably (0.7-3):1, more preferably (1-2.8):1, and most preferably (1.6-2.6):1.

[0035] In the present invention, the concentration of the sulfur source in the mixed solution is preferably 0.01 to 0.06 mol / L, more preferably 0.02 to 0.04 mol / L, and most preferably 0.02 to 0.03 mol / L.

[0036] In the present invention, the mixing preferably includes mixing a sulfur source and water and then adding the cadmium metal salt.

[0037] In the present invention, the mixing of the sulfur source and water is preferably carried out under stirring conditions. The present invention does not have any special limitation on the stirring process, and the stirring process can be carried out using a process well known to those skilled in the art.

[0038] After adding the cadmium metal salt, the present invention further preferably includes continued stirring; the time for the continued stirring is preferably 10 to 200 minutes, more preferably 50 to 150 minutes, and most preferably 80 to 120 minutes; the present invention does not have any special restrictions on the speed of the continued stirring, and the speed familiar to those skilled in the art is used and the obtained mixed solution is ensured to be uniform within the above time.

[0039] After obtaining the mixed solution, the present invention performs hydrothermal treatment on the mixed solution to obtain the photocatalyst.

[0040] In the present invention, the temperature of the hydrothermal treatment is preferably 160-180°C, more preferably 165-175°C, most preferably 168-172°C; the time is preferably 100-168h, more preferably 120-150h, most preferably 130-140h.

[0041] After the hydrothermal treatment is completed, the present invention preferably further includes drying. The present invention does not have any special limitation on the drying process, and the drying process can be carried out using a process well known to those skilled in the art.

[0042] The present invention also provides the use of the photocatalyst described in the above technical solution or the photocatalyst prepared by the preparation method described in the above technical solution in the field of photocatalytic water decomposition.

[0043] After the photocatalyst described in the above technical solution is mixed with water, photocatalytic decomposition is carried out.

[0044] In the present invention, the usage ratio of the photocatalyst to water is preferably (0.01 g to 0.05 g):100 mL, more preferably (0.02 g to 0.04 g):100 mL, and most preferably 0.03 g:100 mL.

[0045] In the present invention, the mixing is preferably carried out under stirring conditions. The present invention does not have any special limitation on the stirring process, and the stirring process can be carried out using a process well known to those skilled in the art.

[0046] In the present invention, vacuuming is preferably performed for 25 minutes before the photocatalytic decomposition to remove dissolved oxygen in the water.

[0047] In the present invention, the photocatalytic decomposition is preferably carried out under the irradiation of a 300W xenon lamp (λ>420nm) light source with a filter.

[0048] The photocatalyst provided by the present invention, its preparation method and application are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0049] Example 1

[0050] 0.36 g of thioacetamide was added to a beaker, and 112 mL of deionized water was added thereto, stirred until dissolved, and then added to 1.4808 g of cadmium nitrate tetrahydrate (the molar ratio of Cd to S was 1), and stirred for 30 min to obtain a mixed solution;

[0051] The mixed solution was subjected to a hydrothermal treatment (the temperature of the hydrothermal treatment was 170° C. and the time was 144 h), and then washed, dried and ground in sequence to obtain the photocatalyst (including alternatingly arranged hexagonal cadmium sulfide and cubic cadmium sulfide, the mass ratio of the hexagonal cadmium sulfide to the cubic cadmium sulfide being 13:7, and denoted as CdS-1).

[0052] Example 2

[0053] Referring to Example 1, except that the mass of thioacetamide is 0.1442 g, the molar ratio of Cd to S is 2.5, and a photocatalyst (comprising alternating hexagonal cadmium sulfide and cubic cadmium sulfide, the mass ratio of the hexagonal cadmium sulfide to the cubic cadmium sulfide being 7:3, recorded as CdS-4) is obtained.

[0054] Example 3

[0055] Refer to Example 1, except that the hydrothermal treatment time is 3 hours, and a photocatalyst is obtained (including hexagonal cadmium sulfide and cubic cadmium sulfide with a heterojunction structure, the mass ratio of the hexagonal cadmium sulfide to the cubic cadmium sulfide is 1:49, recorded as CdS-2).

[0056] Example 4

[0057] Referring to Example 1, except that the mass of thioacetamide is 0.7212 g, the molar ratio of Cd to S is 0.5, a photocatalyst is obtained (including alternating hexagonal cadmium sulfide and cubic cadmium sulfide, the mass ratio of hexagonal cadmium sulfide to cubic cadmium sulfide is 1:9, recorded as CdS-5).

[0058] Example 5

[0059] Referring to Example 1, except that the mass of thioacetamide is 1.0819 g, the molar ratio of Cd to S is 0.3, and a photocatalyst (comprising alternating hexagonal cadmium sulfide and cubic cadmium sulfide, the mass ratio of the hexagonal cadmium sulfide to the cubic cadmium sulfide being 1:15, recorded as CdS-6) is obtained.

[0060] Comparative Example 1

[0061] Refer to Example 1, except that the hydrothermal treatment time is 1 hour, and a photocatalyst (including a single crystal phase of cadmium sulfide, the single crystal phase of cadmium sulfide is cubic phase cadmium sulfide, denoted as CdS-3) is obtained.

[0062] Test Case

[0063] The photocatalysts described in Example 1, Example 3 and Comparative Example 1 were subjected to XRD testing. The test results are as follows: Figure 1 As shown by Figure 1 It can be seen that for Examples 1 and 3, diffraction peaks belonging to c-CdS were observed at 2θ = 26.449°, 30.634°, 43.872°, 51.96°, and 54.456°, and diffraction peaks belonging to h-CdS were observed at 2θ = 24.812°, 26.526°, 28.192°, 36.638°, 43.692°, 47.869°, and 51.845°, indicating that CdS-1 and CdS-2 are composed of c-CdS and h-CdS. For Comparative Example 1, diffraction peaks belonging to c-CdS were observed at 2θ = 26.449°, 30.634°, 43.872°, 51.96°, and 54.456°, indicating that CdS-1 is completely composed of c-CdS.

[0064] The photocatalyst described in Example 1 was subjected to HRTEM test, and the test results are as follows: Figure 2 As shown by Figure 2Clear lattice fringes are evident in the CdS prepared by the present invention, indicating a well-defined crystal structure. Furthermore, alternating arrangements of h-CdS and c-CdS can be identified, demonstrating the formation of a tandem heterojunction structure, significantly improving the electron transport properties and effective spatial isolation of photogenerated carriers.

[0065] Application Examples

[0066] 0.03g of the photocatalyst described in Examples 1 to 5 and Comparative Example 1 and 100mL of deionized water were placed in a reactor, mixed under stirring to form a suspension system, the reactor was connected to a photocatalytic test system, vacuumed for 25 minutes to remove the dissolved oxygen in the water, and irradiated with a xenon lamp. The photocatalytic water decomposition reaction was carried out under the irradiation of a 300W xenon lamp (λ>420nm) with a filter. The timing was started after the light was turned on, and samples were taken for 1 hour every 0.5 hours, and the sampling was continued until the second hour after the timing was started. The activity test results were displayed by a gas chromatograph connected to the photocatalytic test system;

[0067] Figure 3 The activity diagram of CdS-1, CdS-2, and CdS-3 photocatalytic decomposition of water to produce hydrogen. Figure 3 It can be seen that the cadmium sulfide photocatalyst with a tandem heterojunction structure provided by the present invention can effectively photocatalytically decompose water to produce hydrogen. After 2 hours of illumination, the photocatalytic decomposition of water to produce hydrogen by CdS-1 is more effective than that of CdS-2 and CdS-3 samples. This shows that the cadmium sulfide with a tandem heterojunction structure formed in the cadmium sulfide photocatalyst provided by the present invention is conducive to improving the catalytic activity of the photocatalyst;

[0068] Figure 4 The activity diagram of CdS-4, CdS-5 and CdS-6 photocatalytic decomposition of water to produce hydrogen is shown in Figure 2. Figure 4 It can be seen that after 2 hours of illumination, the photocatalytic decomposition of water by CdS-4 to produce hydrogen was significantly more effective than that of CdS-5 and CdS-6 samples. This indicates that the reduction of the S source induces a transition in the nucleation mode from a kinetically controlled to a thermodynamically dominated process. This mechanism changes the subsequent arrangement of CdS atoms throughout the hydrothermal process, thereby regulating the phase transition from hexagonal to cubic phase and the gradient distribution of phase junctions, which is more conducive to the separation and transfer of photogenerated charges and significantly improves the photocatalytic performance.

[0069] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A photocatalyst, characterized in that Includes alternating hexagonal cadmium sulfide and cubic cadmium sulfide; The photocatalyst has a series heterogeneous junction structure and an energy band bending gradient distribution; The molar ratio of S to Cd in the photocatalyst is (1-2.8):1; The method for preparing the photocatalyst comprises the following steps: mixing a sulfur source, a cadmium metal salt and water to obtain a mixed solution; subjecting the mixed solution to hydrothermal treatment to obtain the photocatalyst; The temperature of the hydrothermal treatment is 160-180° C., and the time is 100-168 hours.

2. The photocatalyst according to claim 1, wherein The mass ratio of the hexagonal cadmium sulfide to the cubic cadmium sulfide is (1-10):(1-49).

3. The method for preparing a photocatalyst according to claim 1 or 2, characterized in that: The following steps are involved: mixing a sulfur source, a cadmium metal salt and water to obtain a mixed solution; subjecting the mixed solution to hydrothermal treatment to obtain the photocatalyst; The temperature of the hydrothermal treatment is 160-180°C and the time is 100-168h; The molar ratio of sulfur in the sulfur source to cadmium in the cadmium metal salt is (1-2.8):

1.

4. The preparation method according to claim 3, wherein The mixing comprises mixing a sulfur source and water, and then adding the cadmium metal salt.

5. The preparation method according to claim 3 or 4, characterized in that The sulfur source includes one or more of thioacetamide, thiourea and sodium sulfide.

6. The preparation method according to claim 3 or 4, characterized in that The cadmium metal salt includes one or more of cadmium nitrate, cadmium acetate and cadmium chloride.

7. The preparation method according to claim 3, wherein The concentration of the sulfur source in the mixed solution is 0.01-0.06 mol / L.

8. Use of the photocatalyst according to claim 1 or 2 or the photocatalyst prepared by the preparation method according to any one of claims 3 to 7 in the field of photocatalytic water decomposition.

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