A CdS@ZnO core-sheath nanoarray photocatalyst, its preparation method and application

Abstract

This invention discloses a CdS / ZnO core-sheath nanoarray photocatalyst, its preparation method, and its application. First, a dense CdS nanorod array material is grown on FTO conductive glass via a hydrothermal method. Then, ZnO is deposited on the CdS nanorod array material through atomic layer deposition to obtain a CdS@ZnO core-sheath nanorod array. This preparation method is simple, and the thickness of the deposited ZnO is controllable. The thickness of ZnO on the surface of the CdS nanorod array material can be arbitrarily adjusted according to different needs to obtain an excellent heterojunction structure, improve the carrier transport and separation efficiency, and thus enhance its catalytic performance.

Description

Technical Field

[0001] This invention belongs to the field of photoelectrocatalyst technology, specifically relating to a CdS@ZnO core-sheath nanoarray photoelectrocatalyst, its preparation method, and its application. Background Technology

[0002] The 21st century is an era of rapid global economic development, with economic globalization continuously driving societal progress. According to the 2020 BP Statistical Review of World Energy, the world is moving towards a more sustainable path, with renewable energy maintaining strong growth momentum and reaching a record high (3.2 EJ), with China being the largest contributor to this growth (0.8 EJ). Currently, my country's main power generation methods are thermal power, hydropower, nuclear power, and wind power, with thermal power being the dominant method. Thermal power generation uses fossil fuels (such as coal, oil, and natural gas) to produce electricity. Fossil fuel reserves are limited and non-renewable; excessive extraction will inevitably lead to energy depletion. Simultaneously, thermal power generation inevitably emits flue gas into the atmosphere, causing a series of environmental problems. Therefore, developing green and environmentally friendly new energy sources and reducing the use of fossil fuels is a crucial issue facing my country's development and an essential path towards sustainable development.

[0003] Hydrogen energy is a clean secondary energy source, and its development is of great significance in solving the energy crisis and environmental pollution. Currently, the main methods of hydrogen production are fossil fuel reforming and water electrolysis. While fossil fuel reforming is lower in cost, this technology still uses non-renewable fossil fuels as raw materials and still emits harmful gases during the reforming process. Water electrolysis is a relatively mature technology that produces hydrogen with high purity, but the cost of using electricity to produce hydrogen is too high, consuming far more electricity than the hydrogen produced. Therefore, water electrolysis is not an ideal method for hydrogen production. Solar energy is considered an inexhaustible and clean energy source, and converting solar energy into hydrogen energy is a highly promising and applicable method. Currently, the main methods for converting solar energy into hydrogen energy include photovoltaic water electrolysis, photothermal hydrogen production, photoelectrochemical water splitting, and biophotocatalytic hydrogen production. Photoelectrochemical water splitting technology has great potential and application prospects.

[0004] The performance of hydrogen production through photoelectric water splitting depends on the photoelectrochemical catalyst. CdS, as a photoelectric material, has a suitable band position and strong light absorption capacity, and is therefore widely studied in the field of optoelectronics. However, due to its own photocorrosion and fast carrier recombination rate, its photoelectric conversion efficiency as a single semiconductor material is relatively low. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a CdS / ZnO core-sheath nanoarray photocatalyst and its preparation method. First, a dense CdS nanorod array material is grown on FTO conductive glass via a hydrothermal method. Then, ZnO is deposited on the CdS nanorod array material via atomic layer deposition to obtain a CdS@ZnO core-sheath nanorod array. This preparation method is simple, and the thickness of the deposited ZnO is controllable, allowing for arbitrary adjustment of the ZnO thickness on the surface of the CdS nanorod array material according to different requirements.

[0006] The present invention also provides the application of CdS / ZnO core-sheath nanoarray photocatalyst as a hydrogen production catalyst. The CdS / ZnO core-sheath nanoarray photocatalyst has excellent photoelectric properties and can be used to produce hydrogen by splitting water under sunlight.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a CdS@ZnO core-sheath nanorod array photocatalyst, the method comprising the following steps:

[0009] (1) Dissolve cadmium salt, thiourea and glutathione in ultrapure water, transfer to a reaction vessel, place FTO conductive glass in the vessel with its coating side facing down, and perform a hydrothermal reaction at 180-200℃ for 4.5-6.0h. After the reaction is completed, clean and dry to obtain FTO conductive glass with CdS nanorod array material.

[0010] (2) The FTO conductive glass with CdS nanorod array material is fixed on the silicon wafer and sent into the atomic layer deposition equipment cavity. Diethyl zinc and ultrapure water are used as zinc source and oxygen source, respectively, and ZnO is grown on the surface of CdS nanorod array material by atomic layer deposition.

[0011] In step (1), the molar ratio of cadmium salt, thiourea, and glutathione is 0.2–0.7: 0.4–0.8: 0.05–0.5 mmol; the concentration of cadmium salt in ultrapure water is 0.005–0.025 M.

[0012] The cadmium salt is cadmium nitrate tetrahydrate.

[0013] Step (2) specifically includes the following steps:

[0014] (2-1) The FTO conductive glass with CdS nanorod array material is fixed on the silicon wafer, and after being purged with nitrogen, it is sent into the chamber of the atomic layer deposition equipment, and the temperature in the reaction chamber is maintained at 220-280℃.

[0015] (2-2) Diethylzinc is introduced into the reaction chamber so that the vaporized diethylzinc is adsorbed on the surface of the CdS nanorod array material;

[0016] (2-3) Purge the reaction chamber with nitrogen gas to remove unadsorbed diethylzinc;

[0017] (2-4) Pass ultrapure water into the reaction chamber to allow the vaporized water vapor to react with the diethylzinc adsorbed on the surface monolayer to generate zinc oxide.

[0018] (2-5) Purge the reaction chamber with nitrogen gas to remove excess water vapor;

[0019] (2-6) Repeat steps (2-2) to (2-5) multiple times to adjust the thickness of the zinc oxide layer and obtain CdS@ZnO core-sheath structured nanorod array photocatalysts with different ZnO layer thicknesses.

[0020] In step (2-2), the flow rate of diethylzinc is 0.5-3 mL / min, and the residence time of diethylzinc in the reaction chamber is 10-30 min.

[0021] In steps (2-4), the flow rate of ultrapure water is 0.5-3 mL / min, and the residence time of water vapor in the reaction chamber is 10-30 min.

[0022] In steps (2-6), the thickness of the zinc oxide layer is 0.2–8 nm.

[0023] This invention also provides a CdS@ZnO core-sheath nanorod array photocatalyst prepared by the aforementioned method. In the CdS@ZnO core-sheath nanorod array photocatalyst, the molar ratio of CdS to ZnO is 5-8:1. ZnO is uniformly coated on the outer surface of the CdS nanorods to form a core-sheath heterojunction structure. This structure has the characteristics of being ultrathin, having a tight interface, and being uniform over a large area. ZnO is a hexagonal phase.

[0024] This invention also provides the application of the CdS@ZnO core-sheath nanorod array photoelectrocatalyst as a hydrogen production catalyst.

[0025] The method for preparing the CdS / ZnO core-sheath nanoarray photocatalyst provided by this invention first involves growing a dense CdS nanorod array on FTO conductive glass via a hydrothermal method. The one-dimensional single-crystal nanorod structure provides a faster radial carrier transport path, and the array structure has a larger specific surface area. Incident light between the nanorods can be refracted and scattered multiple times, thereby improving light absorption. Then, ZnO is deposited on the CdS nanorod array material via atomic layer deposition (ALD) to obtain a CdS@ZnO core-sheath nanorod array. Atomic layer deposition (ALD) is a thin film preparation method based on a saturated self-limiting gas-solid interface reaction. This method has the following characteristics: 1) excellent three-dimensional adhesion and large-area uniformity; 2) sub-nanometer controllability of film thickness; and 3) the ability to deposit high-quality thin films with fewer defects and impurities at low temperatures. In this invention, ZnO is deposited on CdS nanorod arrays using atomic layer deposition (ALD), which has the following advantages: 1) It can form a three-dimensional, tightly bonded, and large-area uniform CdS@ZnO heterojunction interface, which can significantly improve the transfer efficiency of photogenerated carriers; 2) It can effectively improve the sensitivity of carrier migration mechanism based on interface control. Most of the electrons and holes generated by photoexcitation in semiconductors are recombinated during bulk diffusion or after migrating to the surface. The thickness of the semiconductor film determines the bulk diffusion distance of carriers, which ultimately determines the number of carriers migrating to the surface. This invention can flexibly control the number of carriers migrating to the surface by controlling the film thickness at the sub-nanometer scale through ALD; 3) It can effectively reduce the recombination of photogenerated carriers. Defects and impurities are often sites for electron-hole recombination. Atomic layer deposition can form high-quality films with fewer defects and impurities, thus effectively reducing the recombination of photogenerated carriers.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. Compared to unarrayed CdS, the dense array structure prepared in this invention has significant advantages in photoelectric performance. Due to the selective growth of single crystals on advantageous crystal planes, the array structure possesses a relatively ordered and continuous crystal structure and fully exposed active surfaces, providing longitudinal charge transport channels within the material. This not only greatly reduces the probability of photogenerated electron-hole recombination but also extends carrier lifetime, thereby improving photoelectric performance. Furthermore, the array structure exhibits light scattering and refraction phenomena, further enhancing light absorption efficiency. The construction of the array structure has a positive impact on improving the photoelectric performance of photoelectrodes.

[0028] 2. The addition of ZnO can reduce the impact of photocorrosion on the stability of CdS. The core-sheath heterojunction formed by the Z-type transport mechanism can promote the separation of photogenerated electrons and holes, greatly improve the carrier transport efficiency, and thus enhance the overall optoelectronic performance.

[0029] 3. Compared with the traditional liquid-phase method for synthesizing ZnO, this invention uses atomic layer deposition technology. Its advantage lies in the fact that the thickness of the ZnO sheath can be precisely controlled within the range of 0.2 to 8 nm by the number of atomic layer deposition cycles, so as to obtain the optimal heterojunction structure, improve the carrier transport and separation efficiency, and thus improve its catalytic performance. Since the CdS core can absorb visible light, an excessively thick ZnO sheath (more than 8 nm) will shield the CdS core from absorbing light.

[0030] 4. The CdS@ZnO core-sheath nanorod array photocatalyst prepared in this invention exhibits excellent photocatalytic performance, with a photocurrent density reaching 2.38 mA·cm⁻¹. -2 It is about 3.2 times that of single CdS, and its photoelectric conversion efficiency reaches 48% at 365nm. Attached Figure Description

[0031] Figure 1 SEM image of the CdS@ZnO core-sheath nanorod array photoelectrocatalyst;

[0032] Figure 2 TEM image of the CdS@ZnO core-sheath nanorod array photocatalyst;

[0033] Figure 3 The image shows a SEM image of CdS attached to FTO conductive glass prepared in Comparative Example 1. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the embodiments.

[0035] The photoelectric performance of the CdS@ZnO core-sheath nanorod array photoelectrocatalysts in each embodiment was tested in a three-electrode reaction cell connected to an electrochemical workstation (CHI 660E). The CdS@ZnO core-sheath nanorod array grown on FTO glass was used as the working electrode, Pt foil as the counter electrode, and Ag / AgCl (3 mol / L KCl) as the reference electrode. An aqueous solution containing 0.25 M Na₂S and 0.35 M Na₂SO₃ was used as the electrolyte. A xenon lamp (300 W) with an AM 1.5G filter was used as the light source, illuminating the working electrode vertically from the side. Argon gas was used as the carrier gas, and the hydrogen released during the reaction was detected by an online gas chromatograph (GC-9720). Photocurrent density and photoelectric conversion efficiency were measured using a CEL-PEAC-200A photoelectrochemical reactor.

[0036] Example 1

[0037] A method for preparing a CdS@ZnO core-sheath nanorod array photocatalyst includes the following steps:

[0038] (1) First, FTO conductive glass with a specification of 1×3cm was ultrasonically cleaned with acetone, ethanol and ultrapure water for 5 minutes and then dried in a drying oven at 50-80℃. Then, 0.5mmol cadmium nitrate tetrahydrate, 0.5mmol thiourea and 0.25mmol glutathione were dissolved in 30mL of ultrapure water to obtain a mixed solution containing cadmium source, sulfur source and glutathione. The dried FTO conductive glass was placed in the lining of a 50mL hydrothermal reactor with the conductive coating side facing down. The prepared mixed solution was then injected into the reactor lining and hydrothermally reacted at 200℃ for 5 hours. After the hydrothermal reaction was completed, it was naturally cooled to room temperature. The FTO conductive glass was taken out, washed several times with ultrapure water and dried at 60℃ to obtain FTO conductive glass with CdS nanorod array material.

[0039] (2) Fix the FTO conductive glass with CdS nanorod array material on the silicon wafer, purge with nitrogen and send it into the atomic layer deposition equipment chamber. Use diethylzinc and ultrapure water as the zinc source and oxygen source for the atomic layer deposition process, respectively. Set the temperature in the reaction chamber to 250℃ so that the diethylzinc and ultrapure water introduced later can be completely vaporized.

[0040] (3) Diethylzinc was introduced into the reaction chamber at a flow rate of 2 mL / min, and the vaporized diethylzinc was kept in the reaction chamber for 20 min to achieve its adsorption on the surface of CdS nanorods.

[0041] (4) Purge the reaction chamber with nitrogen gas to remove unadsorbed diethylzinc;

[0042] (5) Purified water is introduced into the reaction chamber at a flow rate of 2 mL / min, and the water vapor stays in the reaction chamber for 20 min to react with the diethyl zinc adsorbed on the surface to generate zinc oxide.

[0043] (6) Purge the reaction chamber with nitrogen gas to remove excess water vapor.

[0044] (7) Repeat steps (3) to (6) multiple times, and after 200 cycles of deposition, a CdS@ZnO core-sheath structure nanorod array photocatalyst is obtained. In this catalyst, ZnO is uniformly coated on the outer surface of CdS nanorods to form a core-sheath heterojunction structure. The molar ratio of CdS to ZnO is 6.5:1, and the thickness of ZnO is about 5.0 nm.

[0045] This catalyst exhibits excellent photoelectric properties, with a photocurrent density reaching 2.37 mA·cm⁻¹. -2 The photoelectric conversion efficiency at 365 nm reached 47%, and the hydrogen evolution rate reached 26.85 μmol·h⁻¹. -1 ·cm -2 .

[0046] Example 2

[0047] A method for preparing a CdS@ZnO core-sheath nanorod array photocatalyst includes the following steps:

[0048] (1) First, FTO conductive glass with a specification of 1×3cm was ultrasonically cleaned with acetone, ethanol and ultrapure water for 5 minutes and then dried in a drying oven at 60℃. Then, 0.5mmol cadmium nitrate tetrahydrate, 0.6mmol thiourea and 0.3mmol glutathione were dissolved in 35mL of ultrapure water to obtain a mixed solution containing cadmium source, sulfur source and glutathione. The dried FTO conductive glass was placed in the lining of an 80mL hydrothermal reactor with the conductive coating side facing down. The prepared mixed solution was then poured into the reactor lining and hydrothermally reacted at 205℃ for 5 hours. After the hydrothermal reaction was completed, the glass was naturally cooled to room temperature. The FTO conductive glass was then removed, washed several times with ultrapure water and dried at 70℃ to obtain FTO conductive glass with CdS nanorod array material.

[0049] (2) Fix the FTO conductive glass with CdS nanorod array material on the silicon wafer, and send it into the atomic layer deposition equipment chamber after purging with nitrogen; use diethylzinc and ultrapure water as zinc source and oxygen source in the atomic layer deposition process, respectively, and set the temperature in the reaction chamber to 240℃ so that the diethylzinc and ultrapure water introduced later are completely vaporized.

[0050] (3) Diethylzinc was introduced into the reaction chamber at a flow rate of 1 mL / min, and the vaporized diethylzinc was kept in the reaction chamber for 25 min to achieve its adsorption on the surface of CdS nanorods.

[0051] (4) Purge the reaction chamber with nitrogen gas to remove unadsorbed diethylzinc;

[0052] (5) Purified water is introduced into the reaction chamber at a flow rate of 1 mL / min, and the water vapor stays in the reaction chamber for 25 min to react with the diethyl zinc adsorbed on the surface to generate zinc oxide.

[0053] (6) Purge the reaction chamber with nitrogen gas to remove excess water vapor;

[0054] (7) Repeat steps (3) to (6) multiple times, and after 190 cycles of deposition, a CdS@ZnO core-sheath structure nanorod array photocatalyst is obtained. In this catalyst, ZnO is uniformly coated on the outer surface of CdS nanorods to form a core-sheath heterojunction structure. The molar ratio of CdS to ZnO is 6.9:1, and the thickness of ZnO is about 4.8 nm.

[0055] This catalyst exhibits excellent photoelectric properties, with a photocurrent density reaching 2.24 mA·cm⁻¹. -2The photoelectric conversion efficiency at 365 nm reached 41%, and the hydrogen evolution rate reached 23.37 μmol·h⁻¹. -1 ·cm -2 .

[0056] Example 3

[0057] A method for preparing a CdS@ZnO core-sheath nanorod array photocatalyst includes the following steps:

[0058] (1) First, FTO conductive glass with a specification of 1×3cm was ultrasonically cleaned with acetone, ethanol and ultrapure water for 5 minutes and then dried in a drying oven at 60℃. Then, 0.45mmol cadmium nitrate tetrahydrate, 0.7mmol thiourea and 0.35mmol glutathione were dissolved in 32mL of ultrapure water to obtain a mixed solution containing cadmium source, sulfur source and glutathione. The dried FTO conductive glass was placed in the lining of a 60mL hydrothermal reactor with the conductive coating side facing down. The prepared mixed solution was then injected into the reactor lining and hydrothermally reacted at 195℃ for 5 hours. After the hydrothermal reaction was completed, the glass was naturally cooled to room temperature. The FTO conductive glass was then removed, washed several times with ultrapure water and dried at 65℃ to obtain a CdS nanorod array grown on the FTO conductive glass.

[0059] (2) Fix the FTO conductive glass with CdS nanorod array on the silicon wafer, purge with nitrogen and send it into the atomic layer deposition equipment chamber; use diethylzinc and ultrapure water as zinc source and oxygen source in the atomic layer deposition process, respectively, and set the temperature in the reaction chamber to 235℃ so that the diethylzinc and ultrapure water introduced later are completely vaporized.

[0060] (3) Diethylzinc was introduced into the reaction chamber at a flow rate of 2.5 mL / min, and the vaporized diethylzinc was kept in the reaction chamber for 28 min to achieve its adsorption on the surface of CdS nanorods.

[0061] (4) Purge the reaction chamber with nitrogen gas to remove unadsorbed diethylzinc;

[0062] (5) Water vapor is introduced into the reaction chamber at a flow rate of 2.5 mL / min, and the water vapor stays in the reaction chamber for 28 min to achieve the reaction with the diethyl zinc adsorbed on the surface to generate zinc oxide.

[0063] (6) Purge the reaction chamber with nitrogen gas to remove excess water vapor;

[0064] (7) Repeat steps (3) to (6) multiple times, and after 210 cycles of deposition, a CdS@ZnO core-sheath structure nanorod array photocatalyst is obtained. In this catalyst, ZnO is uniformly coated on the outer surface of CdS nanorods to form a core-sheath heterojunction structure. The molar ratio of CdS to ZnO is 6.1:1, and the thickness of ZnO is about 5.3 nm.

[0065] This catalyst exhibits excellent photoelectric properties, with a photocurrent density reaching 2.21 mA·cm⁻¹. -2 The photoelectric conversion efficiency at 365 nm reached 38.5%, and the hydrogen evolution rate reached 20.02 μmol·h⁻¹. -1 ·cm -2 .

[0066] Comparative Example 1

[0067] Screening experiments were conducted on the reaction conditions in step (1). Without the addition of glutathione, CdS nanorod arrays could not be grown on FTO conductive glass.

[0068] First, 1×3cm FTO conductive glass was ultrasonically cleaned with acetone, ethanol, and ultrapure water for 5 minutes each, and then dried in a 60℃ drying oven. Next, 0.45 mmol of cadmium nitrate tetrahydrate and 0.7 mmol of thiourea were dissolved in 32 mL of ultrapure water to obtain a mixed solution containing cadmium and sulfur sources. The dried FTO conductive glass was placed in the lining of a 60 mL hydrothermal reactor with the conductive coating side facing down. The prepared mixed solution was then poured into the reactor lining, and the hydrothermal reaction was carried out at 195℃ for 5 hours. After the hydrothermal reaction was completed, the glass was allowed to cool naturally to room temperature. The FTO conductive glass was then removed, washed several times with ultrapure water, and dried at 65℃. No CdS nanorod arrays were obtained on the FTO conductive glass; instead, spherical CdS particles were attached to the FTO conductive glass.

[0069] The above detailed description of a CdS@ZnO core-sheath nanoarray photocatalyst, its preparation method, and its application, with reference to the embodiments, is illustrative rather than limiting. Several embodiments may be listed within the defined scope. Therefore, variations and modifications that do not depart from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a CdS@ZnO core-sheath nanorod array photocatalyst, characterized in that, The preparation method includes the following steps: (1) Dissolve cadmium salt, thiourea and glutathione in ultrapure water, transfer to a reaction vessel, place FTO conductive glass in the vessel with its coating side facing down, and perform a hydrothermal reaction at 180-200℃ for 4.5-6.0h. After the reaction is completed, clean and dry to obtain FTO conductive glass with CdS nanorod array material. (2) The FTO conductive glass with CdS nanorod array material is fixed on the silicon wafer and sent into the atomic layer deposition equipment cavity. Diethyl zinc and ultrapure water are used as zinc source and oxygen source, respectively, and ZnO is grown on the surface of CdS nanorod array material by atomic layer deposition. In step (1), the molar ratio of cadmium salt, thiourea, and glutathione is 0.2–0.7: 0.4–0.8: 0.05–0.5; the concentration of cadmium salt in ultrapure water is 0.005–0.025 M. In the CdS@ZnO core-sheath nanorod array photocatalyst, the molar ratio of CdS to ZnO is 5–8:1; the thickness of the zinc oxide layer is 0.2–8 nm.

2. The preparation method according to claim 1, characterized in that, The cadmium salt is cadmium nitrate tetrahydrate.

3. The preparation method according to claim 1, characterized in that, Step (2) specifically includes the following steps: (2-1) The FTO conductive glass with CdS nanorod array material is fixed on the silicon wafer, and after being purged with nitrogen, it is sent into the chamber of the atomic layer deposition equipment, and the temperature in the reaction chamber is maintained at 220-280℃. (2-2) Diethylzinc is introduced into the reaction chamber so that the vaporized diethylzinc is adsorbed on the surface of the CdS nanorod array material; (2-3) Purge the reaction chamber with nitrogen gas to remove unadsorbed diethylzinc; (2-4) Pass ultrapure water into the reaction chamber to allow the vaporized water vapor to react with the diethylzinc adsorbed on the surface monolayer to generate zinc oxide. (2-5) Purge the reaction chamber with nitrogen gas to remove excess water vapor; (2-6) Repeat steps (2-2) to (2-5) multiple times to adjust the thickness of the zinc oxide layer and obtain CdS@ZnO core-sheath structured nanorod array photocatalysts with different ZnO layer thicknesses.

4. The preparation method according to claim 3, characterized in that, In step (2-2), the flow rate of diethylzinc is 0.5-3 mL / min, and the residence time of diethylzinc in the reaction chamber is 10-30 min.

5. The preparation method according to claim 3, characterized in that, In steps (2-4), the flow rate of ultrapure water is 0.5-3 mL / min, and the residence time of water vapor in the reaction chamber is 10-30 min.

6. The CdS@ZnO core-sheath nanorod array photocatalyst prepared by the preparation method according to any one of claims 1-5.

7. The CdS@ZnO core-sheath nanorod array photocatalyst according to claim 6, characterized in that, In the CdS@ZnO core-sheath nanorod array photocatalyst, ZnO is uniformly coated on the outer surface of CdS nanorods to form a core-sheath heterojunction structure, and ZnO is a hexagonal phase.

8. The application of the CdS@ZnO core-sheath nanorod array photoelectrocatalyst as described in claim 6 as a hydrogen production catalyst.

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