Photocatalytic structure, method for preparing the same, and photocatalyst having the same
By forming a photocatalyst layer with a semiconductor heterojunction on the substrate, the problems of low efficiency and poor stability of direct Z-type photocatalysts are solved, achieving efficient photo-total water splitting and a simple preparation process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- 吕锋仔
- Filing Date
- 2021-04-15
- Publication Date
- 2026-07-21
AI Technical Summary
Existing direct Z-type photocatalysts have an unsuitable structure, resulting in low photocatalytic water splitting efficiency, insufficient stability, complex preparation process, and difficult recovery.
First and second photocatalyst layers are formed on a substrate using physical vapor deposition to form a semiconductor heterojunction or homojunction, ensuring that the surfaces of the two layers are in contact with the reaction solution or gas, enhancing the built-in electric field and optimizing the band structure. Nanofilms are then prepared by methods such as electron beam evaporation deposition.
This improved the light conversion efficiency of the photocatalytic water splitting system, enhanced its stability, simplified the preparation process, and made it easy to recycle, thus achieving efficient utilization of visible light.
Smart Images
Figure CN115212895B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of photocatalysis, specifically relating to a photocatalytic structure, its preparation method, and a photocatalyst having the same. Background Technology
[0002] In recent years, energy shortages and environmental pollution have become global concerns. Semiconductor photocatalysis, capable of using solar energy to decompose water into hydrogen and oxygen, and eliminate various pollutants, is considered the most ideal and cleanest technology, thus attracting widespread attention. Among these, photocatalytic water splitting for hydrogen production is particularly noteworthy because it directly decomposes water into hydrogen and oxygen using solar energy, making it the simplest and most economical method for hydrogen production. Furthermore, its redox capabilities can degrade pollutants, thereby purifying the environment and contributing to a sustainable society, thus garnering significant attention. In 1972, Professors Fujishima and Honda first reported the discovery of photocatalytic water splitting using TiO2 single-crystal electrodes to produce hydrogen, opening the research path for using solar energy to split water. However, the wide band gap of TiO2 means it can only utilize about 4% of ultraviolet light, while visible light constitutes a large proportion of solar energy; therefore, visible light photocatalytic water splitting is a key research focus and hot topic.
[0003] Photocatalytic water splitting in the visible light region can be achieved using either a single semiconductor photocatalyst or a Z-type photocatalyst. A Z-type photocatalyst is formed by linking hydrogen evolution semiconductors and oxygen evolution semiconductors through an intermediate medium. It is widely used because it can more effectively separate electron-hole pairs and possesses stronger redox capabilities. While single photocatalysts can effectively perform photocatalytic water splitting with an absorption edge down to approximately 500 nm, Z-type photocatalysts can utilize a wider range of visible light. Currently, depending on the intermediate medium, Z-type photocatalysts can be formed using reversible redox chemical media, metal media, or even media-free direct Z-type photocatalysts. Direct Z-type photocatalysts have gained significant attention in recent years due to their simpler preparation, lower cost, and superior separation of photogenerated electron-hole pairs. In 2018, an aza-fused microporous polymer (CMP) / C2N direct Z-type heterojunction photocatalyst (nanopowder structure) achieved photocatalytic water splitting under visible light irradiation, achieving a solar energy utilization rate of 0.4%. Although direct Z-type photocatalysts have been proven to achieve photo-total water splitting under visible light irradiation, their photo-total water splitting efficiency is low due to the following problems:
[0004] 1. Current direct Z-type photocatalysts have an unreasonable structure, including an imperfect geometry (such as insufficient effective active surface and difficulty in controlling the contact interface between semiconductors, resulting in a weak built-in electric field) and an imperfect band structure matching (which limits the range of visible light utilization), resulting in low photocatalytic efficiency.
[0005] 2. Existing direct Z-type photocatalysts are not stable enough. They dissolve to varying degrees in water or solution, and most of them suffer from photocorrosion and / or reverse reaction. Their service life is only a few hours to tens of hours, and their stability is not good enough.
[0006] 3. The preparation process is relatively complex and recovery is difficult.
[0007] Therefore, existing direct Z-type photocatalysts and their preparation methods require further investigation. Summary of the Invention
[0008] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one objective of this invention is to propose a photocatalytic structure, its preparation method, and a photocatalyst having the same. This photocatalytic structure, its preparation method, and the photocatalyst having the same possess controllable effective active surface, enhanced built-in electric field, flexible band structure matching, and better stability, thereby improving the photoconversion efficiency of the photocatalytic water splitting catalytic system based on the photocatalytic structure and expanding the selection of photocatalytic materials. This can, to some extent, solve the problem of low efficiency in the photocatalytic water splitting of existing direct Z-type photocatalysts.
[0009] In one aspect of the present invention, a photocatalytic structure is provided. According to an embodiment of the present invention, the photocatalytic structure comprises:
[0010] First photocatalyst layer;
[0011] The second photocatalyst layer, wherein the first photocatalyst layer is disposed on the second photocatalyst layer;
[0012] in,
[0013] The first photocatalyst layer and the second photocatalyst layer form a semiconductor heterojunction / homogeneity; the thickness of the first photocatalyst layer and the thickness of the second photocatalyst layer both exceed the space charge region width of the semiconductor heterojunction / homogeneity they form;
[0014] The outer surface of the first photocatalyst layer includes a first region that can directly contact the reaction solution or gas;
[0015] The outer surface of the second photocatalyst layer includes a second region that can directly contact the reaction solution or gas.
[0016] According to the photocatalytic structure of the present invention, by directly contacting the second photocatalyst layer with the first photocatalyst layer, the surfaces of both the first and second photocatalyst layers can be partially or completely contacted with the reaction solution / gas, making the effective active area of the photocatalytic structure controllable. Simultaneously, because the second and first photocatalyst layers are in complete contact, the built-in electric field is significantly enhanced, which is beneficial for the separation of photogenerated carriers and their rapid migration, thereby improving the photocatalytic efficiency of the structure. Furthermore, the formation of a semiconductor heterojunction / homogeneity between the first and second photocatalyst layers allows for flexible band structure matching and improves stability. Additionally, since the thicknesses of both the first and second photocatalyst layers exceed the space charge region width of the semiconductor heterojunction / homogeneity they form, this also benefits the long-term operation of the photocatalytic structure. Therefore, this photocatalytic structure has a controllable effective active surface, an enhanced built-in electric field, flexible band structure matching, and better stability, thereby improving the photoconversion efficiency of the photocatalytic water splitting catalytic system based on the photocatalytic structure and expanding the range of selectable photocatalytic materials. This can, to some extent, solve the problem of low efficiency in the photocatalytic water splitting of direct Z-type photocatalysts in the existing technology.
[0017] In addition, the photocatalytic structure according to the above embodiments of the present invention may also have the following additional technical features:
[0018] In some embodiments of the present invention, the area of the first region accounts for M of the outer surface area of the first photocatalyst layer, where M is greater than or equal to 5% and less than or equal to 100%, and the area of the second region accounts for N of the outer surface area of the second photocatalyst layer, where N is greater than or equal to 5% and less than or equal to 100%.
[0019] In some embodiments of the present invention, the photocatalytic structure further includes: a substrate layer, wherein the second photocatalyst layer is disposed on the substrate layer.
[0020] In some embodiments of the present invention, the substrate is a microporous substrate.
[0021] In some embodiments of the present invention, the average pore size of the microporous structure substrate is 0.1 μm-20 μm.
[0022] In some embodiments of the present invention, the total open area of all micropores on the microporous structure substrate accounts for 30%-70% of the outer surface area of the substrate.
[0023] In some embodiments of the present invention, the area of the largest single micropore on the microporous structure substrate is 100 times or less the area of the smallest single micropore.
[0024] In some embodiments of the present invention, the band gap of the first photocatalyst layer and the second photocatalyst layer is independently not less than 1.8 eV.
[0025] In some embodiments of the present invention, the conduction band bottom of the first photocatalyst layer is more negative than the reduction potential of H2O / H2, and the valence band top of the second photocatalyst layer is more positive than the oxidation potential of O2 / H2O.
[0026] In some embodiments of the present invention, the work function of the second photocatalyst layer is greater than that of the first photocatalyst layer.
[0027] In some embodiments of the present invention, the absorption edges of the first photocatalyst layer and the second photocatalyst layer are each independently no higher than 688 nm. This maximizes the utilization of the potential of visible light.
[0028] In another aspect of the invention, a method for preparing the above-described photocatalytic structure is provided. According to an embodiment of the invention, the method includes: sequentially forming a second photocatalyst layer and a first photocatalyst layer on a substrate by physical vapor deposition. Thus, a photocatalytic structure with direct contact between the first and second photocatalyst layers, a controllable effective active surface, an enhanced built-in electric field, flexible band structure matching, and better stability can be prepared by physical vapor deposition.
[0029] In addition, the method for preparing photocatalytic structures according to the above embodiments of the present invention may also have the following additional technical features:
[0030] In some embodiments of the present invention, the substrate is a removable solid substrate, and the process includes removing the substrate after the second photocatalyst layer and the first photocatalyst layer are sequentially formed on the substrate by physical vapor deposition. This maximizes the effective active area of the photocatalytic structure.
[0031] In some embodiments of the present invention, the physical vapor deposition includes electron beam evaporation, barrier evaporation, sputtering, or ion plating. This ensures that the photocatalytic structure exhibits excellent photocatalytic efficiency.
[0032] In a third aspect, the present invention provides a photocatalyst. According to embodiments of the present invention, the photocatalyst comprises the photocatalytic structure described above or a photocatalytic structure obtained by the method described above. Thus, the photocatalyst possesses the aforementioned excellent performance, can effectively utilize visible light for photocatalytic water splitting, and therefore exhibits excellent photocatalytic efficiency, thereby partially solving the problem of low efficiency in photocatalytic water splitting using direct Z-type photocatalysts in the prior art.
[0033] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description
[0034] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:
[0035] Figure 1 This is a schematic diagram of a photocatalytic structure according to an embodiment of the present invention;
[0036] Figure 2 This is a schematic diagram of a photocatalytic structure according to another embodiment of the present invention;
[0037] Figure 3 This is a band structure diagram of a photocatalytic structure according to an embodiment of the present invention;
[0038] Figure 4 This is a schematic diagram of the photocatalytic structure of Embodiment 1 of the present invention;
[0039] Figure 5 This is a physical diagram of the photocatalytic structure of Embodiment 1 of the present invention;
[0040] Figure 6 This is a SEM image of the ceramic substrate in Embodiment 1 of the present invention; Detailed Implementation
[0041] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.
[0042] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.
[0043] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.
[0044] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.
[0045] In one aspect of the invention, a photocatalytic structure is proposed. According to an embodiment of the invention, reference is made to... Figure 1 The photocatalytic structure includes a first photocatalyst layer 100 and a second photocatalyst layer 200, with the first photocatalyst layer 100 disposed on the second photocatalyst layer 200. The inventors discovered that by directly contacting the second photocatalyst layer with the first photocatalyst layer, the surfaces of both layers can be partially or completely contacted with the reaction solution / gas, making the effective active area of the photocatalytic structure controllable. Simultaneously, the complete contact between the second and first photocatalyst layers significantly enhances the built-in electric field, facilitating the separation and rapid migration of photogenerated carriers, thereby improving the photocatalytic efficiency of the structure. Furthermore, the constraint that the first and second photocatalyst layers form a semiconductor heterojunction / homogeneity allows for flexible band structure matching and improves stability. Additionally, the fact that the thicknesses of both the first and second photocatalyst layers exceed the space charge region width of the semiconductor heterojunction / homogeneity they form also benefits the long-term operation of the photocatalytic structure. Thus, this photocatalytic structure possesses a controllable and effective active surface, an enhanced built-in electric field, flexible band structure matching, and better stability.
[0046] It should be noted that the shape of the first photocatalyst layer 100 and the second photocatalyst layer 200 is not particularly limited, as long as the first photocatalyst layer 100 and the second photocatalyst layer 200 can be in close contact and their outer surfaces can be in partial or complete contact with the reaction solution / gas. Preferably, both the first photocatalyst layer 100 and the second photocatalyst layer 200 are flat.
[0047] Further, refer to Figure 2 The aforementioned photocatalytic structure further includes a substrate layer 300, on which a second photocatalyst layer 200 is disposed. Preferably, the substrate layer 300 includes, but is not limited to, a substrate layer with a microporous structure. Further, the average pore size of the micropores in the substrate layer 300 is defined as 0.1 μm-20 μm, the total open area of all micropores in the substrate layer 300 is defined as 30%-70% of the outer surface area of the substrate, and the area of the largest single micropore on the substrate layer 300 is defined as 100 times or less the area of the smallest single micropore. Specifically, by providing micropores in the substrate layer and defining the size and distribution of the micropores, it is ensured that the surfaces of the first photocatalyst layer 100 and the second photocatalyst layer 200 are active yet relatively uniform, and it is also possible to ensure that water or solution permeates to the surface of the second photocatalyst layer 200 and helps the gas generated after photolysis to escape. It should be noted that the pore size of "micropore" in this application is defined as the circumference of the micropore divided by π, regardless of whether the micropore is regular or irregular in shape.
[0048] Furthermore, the band gap energies of the first photocatalyst layer 100 and the second photocatalyst layer 200 are each independently not less than 1.8 eV, thereby enabling the photocatalytic structure to effectively utilize the visible light region for photocatalytic water splitting, maximizing the potential of visible light. It is also stipulated that before the formation of the photocatalytic structure, the work function of the second photocatalyst layer 200 is greater than that of the first photocatalyst layer 100, so that after they contact to form the photocatalytic structure, the direction of their built-in electric field points from the first photocatalyst layer 100 to the second photocatalyst layer 200. Furthermore, it is also stipulated that before the formation of the photocatalytic structure, the conduction band bottom of the first photocatalyst layer 100 is more negative than the reduction potential of H2O / H2, and the valence band top of the second photocatalyst layer 200 is more positive than the oxidation potential of O2 / H2O, thus enabling the first photocatalyst layer 100 to reduce water to produce hydrogen and the second photocatalyst layer 200 to oxidize water to produce oxygen. Specifically, refer to... Figure 3When the surface of the first photocatalyst layer 100 is illuminated, photogenerated electrons in the space charge region and the surrounding area drift towards the first photocatalyst layer 100 under the drive of the built-in electric field, while photogenerated holes drift towards the second photocatalyst layer 200, thereby avoiding catalyst consumption. Some of the photogenerated electrons that migrate to the surface of the first photocatalyst layer 100 reduce water to hydrogen, while some of the photogenerated holes that migrate to the surface of the second photocatalyst layer 200 oxidize water to oxygen. In addition, due to the obstruction of the interface potential barrier peak, some photogenerated electrons and holes can cross the barrier peak (such as the tunneling effect), while the remaining photogenerated electrons and holes that migrate to the interface basically recombine here, which is beneficial to the separation and migration of photogenerated charge carriers and can avoid photocorrosion and reverse reaction. Therefore, this photocatalytic structure is feasible for photocatalytic water splitting, and has a controllable effective active surface, enhanced built-in electric field, flexible band structure matching and better stability, thereby improving the photoconversion efficiency of the photocatalytic water splitting catalytic system based on the photocatalytic structure and expanding the selection of photocatalytic materials. In this way, it can solve the problem of low efficiency in the photocatalytic water splitting of direct Z-type photocatalysts in the existing technology to a certain extent.
[0049] The absorption edges of the first photocatalyst layer 100 and the second photocatalyst layer 200 in this application are each independently no higher than 688 nm. That is, the first photocatalyst layer 100 and the second photocatalyst layer 200 can effectively utilize visible light with a wavelength no higher than 688 nm, thereby maximizing the potential of visible light.
[0050] In another aspect of the invention, a method for preparing the above-mentioned photocatalytic structure is proposed. According to an embodiment of the invention, the method includes: sequentially forming a second photocatalyst layer and a first photocatalyst layer on a substrate by physical vapor deposition. The inventors have found that physical vapor deposition can produce a photocatalytic structure with direct contact between the first and second photocatalyst layers, enabling photocatalytic water splitting, and possessing a controllable effective active surface, enhanced built-in electric field, flexible band structure matching, and better stability. Further, the physical vapor deposition used in this application includes, but is not limited to, electron beam evaporation coating, barrier evaporation, sputtering coating, or ion plating, preferably electron beam evaporation coating. It should be noted that the specific operations of sequentially forming the second and first photocatalyst layers on the substrate using electron beam evaporation coating, barrier evaporation, sputtering coating, or ion plating in this application are conventional operations in the art, and those skilled in the art can select appropriate operating conditions according to actual needs, which will not be elaborated here.
[0051] According to an embodiment of the present invention, if the substrate is a removable solid substrate, the process includes removing the substrate after the second photocatalyst layer and the first photocatalyst layer are sequentially formed on the substrate by physical vapor deposition. Specifically, the substrate is a soluble substrate (NaCl crystal material) or an easily removable solid substrate (plastic material). A second photocatalyst layer and the first photocatalyst layer of appropriate thickness are sequentially deposited on the substrate, ensuring close contact between the second and first photocatalyst layers. Then, the soluble substrate is dissolved or the easily removable substrate is removed, forming a substrate as described above. Figure 1 The photocatalytic structure shown; however, if the substrate is a plate-shaped microporous structure substrate (the plate-shaped microporous structure substrate has micropores), a second photocatalyst layer of appropriate thickness is deposited on the plate-shaped microporous structure substrate, and then a first photocatalyst layer of appropriate thickness is deposited on the second photocatalyst layer, forming a structure as shown. Figure 2 The structure shown.
[0052] It should be noted that the features and advantages described above for the photocatalytic structure also apply to the method for preparing the photocatalytic structure, and will not be repeated here.
[0053] In a third aspect, the present invention provides a photocatalyst. According to embodiments of the present invention, the photocatalyst comprises the photocatalytic structure described above or a photocatalytic structure obtained by the method described above. Therefore, this photocatalyst is feasible for photocatalytic water splitting, can effectively utilize the visible light region for photocatalytic water splitting, and thus exhibits excellent photocatalytic efficiency. This can, to some extent, solve the problem of low efficiency in photocatalytic water splitting using existing direct Z-type photocatalysts. It should be noted that the features and advantages described above regarding the photocatalytic structure and its preparation method also apply to this photocatalyst, and will not be repeated here.
[0054] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.
[0055] Example 1
[0056] Photocatalytic structure: The first photocatalyst layer consists of a 180 nm thick CdS film and a 0.5 nm thick Pt cocatalyst; the second photocatalyst layer is a 180 nm thick Ag3PO4 film; and a microporous ceramic plate serves as the substrate. Its structure is as follows: Figure 4 As shown.
[0057] Main raw materials: microporous (φ5μm) ceramic substrate (φ20mm thick 1mm): the total open area of all micropores on the substrate accounts for 46% of the surface area of the substrate, the area of the largest single micropore on the substrate is 5 times that of the smallest single micropore, Ag3PO4 film material (purity 99%), CdS film material (purity 99.999%), Pt film material (purity 99.99%).
[0058] The method for preparing photocatalytic structures is as follows:
[0059] (1) Microporous ceramic substrate treatment: Rinse with distilled water and dry;
[0060] (2) Sequential deposition of Ag3PO4 / CdS on a microporous ceramic substrate: The treated microporous ceramic substrate, Ag3PO4 film, and CdS film are loaded into a vacuum coating machine, and a vacuum of 2.0*10 is drawn. -3 Pa, the coating machine is heated to 100 degrees Celsius and held at that temperature for 20 minutes. The ion source is turned on (argon gas 10 sccm) to etch the substrate for 3 minutes, and then the ion source is turned off. Then Ag3PO4 evaporation begins, with the electron gun beam current set to 15 mA. The film material is pre-melted for 30 seconds, the electron gun baffle is opened, and the deposition rate is about 0.5 nm / s. Crystal control is used to complete the deposition of a 180 nm Ag3PO4 thin film. CdS is then deposited, with the electron gun beam current set to 3 mA. The film material is pre-melted for 10 seconds, the electron gun baffle is opened, and the deposition rate is about 2 nm / s. Crystal control is used to complete the deposition of a 180 nm CdS thin film. After the coating machine cools to 70 degrees Celsius, the coating machine is purged and cooled down, and the coated wafer is removed.
[0061] (3) Coating Pt co-catalyst onto CdS film: Load the Ag3PO4 / CdS coated wafer and Pt film material into a vacuum coating machine, and evacuate to 2.0*10. -3 Pa, the coating machine is heated to 80 degrees Celsius and held at that temperature for 25 minutes. Then, Pt is deposited on the CdS film. The electron gun beam current is set to 360mA. The film material is pre-melted for 10 seconds, the electron gun baffle is opened, and the deposition rate is about 0.1nm / s. Crystal control is used to complete the deposition of 0.5nm of Pt. After the coating machine cools down to 70 degrees Celsius, the coating machine is gasified and cooled down. The coated wafer is then taken out.
[0062] (4) Next, within half an hour, place the coated wafer in an oven and bake at 250 degrees Celsius for 24 hours. Then, after naturally and slowly cooling to 70-80 degrees Celsius (approximately 16 hours), remove it. The resulting photocatalytic structure is as follows: Figure 5 As shown.
[0063] Sample characterization
[0064] (1) Micropore detection of microporous ceramic substrates:
[0065] Micropores in a ceramic substrate were observed using a scanning electron microscope (SEM). Figure 6The ceramic substrate is shown to have numerous irregularly shaped micropores with a size of about 5 μm. These micropores ensure that the CdS and Ag3PO4 film surfaces are active yet relatively uniform, and that water or solution can easily penetrate the Ag3PO4 film surface and help the gas generated after photolysis to escape.
[0066] (2) Band structure
[0067] The visible light absorption spectra of CdS and Ag3PO4 films were obtained by spectrophotometry. The results showed that the visible light absorption edge of the Ag3PO4 film reached as high as 570 nm, while the CdS film exhibited strong absorption in the 420–550 nm range. Since CdS is a direct-transition semiconductor, its absorption is influenced by (Ahv)... 2 Plotting hv yields a band gap energy of 2.37 eV for the CdS thin film; since Ag3PO4 is an indirect transition semiconductor, (Ahv) 0.5 Plotting hv yielded a band gap energy of 2.15 eV for the Ag3PO4 thin film. The band positions of semiconductors can be determined using the empirical formulas ECB = X - Ee - 0.5Eg and EVB = ECB + Eg, where X is the electronegativity of the semiconductor, Eg is the geometric mean of the electronegativity of the various atoms constituting the semiconductor, Ee is the band gap energy of the semiconductor, and Ee is the energy of the highest occupied energy level of an electron at the standard hydrogen electrode (NHE). Calculations showed that the ECB of the prepared CdS thin film was -0.51 eV and the EVB was 1.86 eV, while the ECB of the Ag3PO4 thin film was 0.38 eV and the EVB was 2.53 eV. The work functions of the CdS and Ag3PO4 films were determined by photoelectron spectroscopy. The results showed that the work function of the Ag3PO4 film was approximately 0.8 eV higher than that of the CdS film. Therefore, it is estimated that after a heterojunction is formed between the CdS and Ag3PO4 layers, the conduction band bottom of CdS is still more negative than the reduction potential of H2O / H2, while the valence band top of Ag3PO4 is more positive than the oxidation potential of O2 / H2O. These detection and calculation results can be confirmed by the photochemical water splitting test results of the samples.
[0068] (3) Test process and results of photocatalytic water splitting in the visible light region:
[0069] A) Experimental Setup: To evaluate the performance of this system in future practical applications, the test conditions simulated real-world usage conditions, namely, one standard atmosphere, room temperature (20±1℃), and simulated solar visible light irradiance (a 300-watt xenon lamp was used, which emitted 400nm-780nm visible light after filtering; the distance between the reactor and the light source was adjusted to increase the light intensity on the sample to 0.04 W / cm², equivalent to the visible light irradiance of one sun). 2 Therefore, the test results can reflect its performance in actual use;
[0070] B) Experimental Results:
[0071] Visible light intensity irradiating the sample: 0.04 W / cm² 2 The effective area of the sample is 1.5 cm². 2 (This is because when the sample is fixed, the clamps are intentionally used to block the edge area of the sample, so that only the central area (with fewer defects) is illuminated.) Therefore, the total visible light energy received by the sample per hour is: 0.04 * 1.5 * 3600 = 216 J. The hourly production is 1.8 μmol of H2 and 0.8 μmol of O2. The Gibbs free energy change (ΔG) for water decomposition into H2 and O2 is 237 kJ. Therefore, the energy required to decompose water to obtain 1.8 μmol of hydrogen is: 1.8 * 10^6 kJ. -3 *237 = 0.43 J, meaning the sample can effectively utilize 0.43 J of visible light energy per hour. Visible light utilization rate: 0.43 / 216*100% ≈ 0.2%. This is the only Ag3PO4-CdS photocatalytic system capable of photocatalytic water splitting to date, apart from previous inventions by the same applicant.
[0072] (4) Sample performance stability test:
[0073] Some samples of this Ag3PO4-CdS-Pt photocatalytic structure have been used for over 100 hours, and the film remains intact without any corrosion.
[0074] This photocatalytic structure avoids reverse reactions due to the built-in electric field in a specific direction. In addition, under the action of the built-in electric field, some photogenerated electrons and holes can cross the potential barrier peak (such as the tunneling effect), while the remaining photogenerated electrons and holes that migrate to the interface recombine here, which can avoid photocorrosion of itself, and therefore there is no photocorrosion phenomenon. Moreover, compared with nanopowders, the nanofilm prepared by the present invention using appropriate processes is almost insoluble in water, so its performance is very stable.
[0075] (5) The preparation process of this invention is mature, and the samples are easy to recover:
[0076] The Ag3PO4-CdS-Pt photocatalytic structure prepared in this application is deposited on a microporous ceramic substrate using electron beam evaporation coating. This is a mature process with good repeatability, which can be mass-produced industrially and is easy to recycle, making it suitable for practical applications.
[0077] Example 2
[0078] The preparation method is the same as in Example 1, except that the microporous (φ7μm) ceramic substrate (φ20mm thick 1mm) has the following characteristics: the total opening area of all micropores on the substrate accounts for 62% of the outer surface area of the substrate, and the area of the largest single micropore on the substrate is 100 times that of the smallest single micropore.
[0079] Example 3
[0080] The preparation method is the same as in Example 1, except that the microporous (φ0.1μm) ceramic substrate (φ20mm thick 1mm) has the following characteristics: the total opening area of all micropores on the substrate accounts for 30% of the outer surface area of the substrate, and the area of the largest single micropore on the substrate is 100 times that of the smallest single micropore.
[0081] Example 4
[0082] The preparation method is the same as in Example 1, except that the microporous (φ20μm) ceramic substrate (φ20mm thick 1mm) has the following characteristics: the total opening area of all micropores on the substrate accounts for 70% of the outer surface area of the substrate, and the area of the largest single micropore on the substrate is 100 times that of the smallest single micropore.
[0083] Example 5
[0084] The preparation method is the same as in Example 1, except that ink is printed on the outer surface of the CdS film and micropores (φ100μm) are evenly distributed. The total opening area of all micropores accounts for 50% of the outer surface area of the CdS film.
[0085] Example 6
[0086] The preparation method is the same as in Example 1, except that ink is printed on the outer surface of the CdS film and micropores (φ100μm) are evenly distributed. The total opening area of all micropores accounts for 5% of the outer surface area of the CdS film.
[0087] The visible light utilization rates of the photocatalytic structures obtained in Examples 2-6 were calculated using the method described in Example 1, and the results are shown in Table 1.
[0088] Table 1
[0089] Example 2 0.04％ Example 3 0.02％ Example 4 0.01％ Example 5 0.12％ Example 6 0.01％
[0090] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention, which should also fall within the scope of protection of this application.
[0091] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.
Claims
1. A photocatalyst, characterized in that, include: First photocatalyst layer: CdS thin film; The second photocatalyst layer is an Ag3PO4 thin film, and the first photocatalyst layer is disposed on the second photocatalyst layer; in, The first photocatalyst layer and the second photocatalyst layer form a semiconductor heterojunction; the thickness of the first photocatalyst layer and the thickness of the second photocatalyst layer both exceed the space charge region width of the semiconductor heterojunction they form; The outer surface of the first photocatalyst layer includes a first region that can directly contact the reaction solution or gas; The outer surface of the second photocatalyst layer includes a second region that can directly contact the reaction solution or gas; The conduction band bottom of the first photocatalyst layer is more negative than the reduction potential of H2O / H2, and the valence band top of the second photocatalyst layer is more positive than the oxidation potential of O2 / H2O. The work function of the second photocatalyst layer is greater than that of the first photocatalyst layer.
2. The photocatalyst according to claim 1, characterized in that, The area of the first region accounts for M% of the outer surface area of the first photocatalyst layer, where M is greater than or equal to 5% and less than or equal to 100%, and the area of the second region accounts for N% of the outer surface area of the second photocatalyst layer, where N is greater than or equal to 5% and less than or equal to 100%.
3. The photocatalyst according to claim 1, characterized in that, Further includes: The substrate layer, on which the second photocatalyst layer is disposed.
4. The photocatalyst according to claim 3, characterized in that, The substrate is a microporous substrate.
5. The photocatalyst according to claim 4, characterized in that, The average pore size of the microporous structure substrate is 0.1 μm - 20 μm.
6. The photocatalyst according to claim 4, characterized in that, The total open area of all micropores on the microporous substrate accounts for 30%-70% of the outer surface area of the substrate.
7. The photocatalyst according to claim 4, characterized in that, The area of the largest single micropore on the microporous structure substrate is 100 times or less than the area of the smallest single micropore.
8. A method for preparing the photocatalyst according to any one of claims 1-7, characterized in that, include: The second photocatalyst layer and the first photocatalyst layer are sequentially formed on the substrate by physical vapor deposition.
9. The method according to claim 8, characterized in that, The substrate is a removable solid substrate. After the second photocatalyst layer and the first photocatalyst layer are sequentially formed on the substrate by physical vapor deposition, the process includes: removing the substrate.
10. The method according to claim 8, characterized in that, The physical vapor deposition includes electron beam evaporation coating, barrier evaporation, sputtering coating, or ion plating.