CN114160175A - Semiconductor photocatalytic structure, preparation method thereof and photocatalyst with semiconductor photocatalytic structure - Google Patents
Semiconductor photocatalytic structure, preparation method thereof and photocatalyst with semiconductor photocatalytic structure Download PDFInfo
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- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
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- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
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Abstract
The invention discloses a semiconductor photocatalytic structure, a preparation method thereof and a photocatalyst with the semiconductor photocatalytic structure, wherein the semiconductor photocatalytic structure comprises a semiconductor transition layer, a first semiconductor layer and a second semiconductor layer, the first semiconductor layer is directly contacted with the semiconductor layer in the semiconductor transition layer, the second semiconductor layer is directly contacted with the semiconductor layer in the semiconductor transition layer, and the first semiconductor layer is not contacted with the second semiconductor layer; the band gap energy of the first semiconductor layer and the second semiconductor layer is not less than 1.8ev, the thickness of the first semiconductor layer and the thickness of the semiconductor layer in direct contact with the first semiconductor layer exceed the width of the space charge region, the direction of the built-in electric field of the first semiconductor layer points to the semiconductor layer in direct contact with the first semiconductor layer, and the first semiconductor layer is conductiveBelt bottom ratio H2O/H2The reduction potential is more negative, the thickness of the second semiconductor layer and the thickness of the semiconductor layer in direct contact with the second semiconductor layer exceed the width of the space charge region, the direction of the built-in electric field points to the second semiconductor layer from the semiconductor layer in direct contact with the second semiconductor layer, and the valence band top ratio O of the second semiconductor layer2/H2O oxidation potential correction.
Description
Technical Field
The invention belongs to the field of photocatalysis, and particularly relates to a semiconductor photocatalysis structure, a preparation method thereof and a photocatalyst with the semiconductor photocatalysis structure.
Background
In recent years, energy shortage and environmental pollution have been the focus of world attention. Semiconductor photocatalytic technology is capable of decomposing water into hydrogen and oxygen by using solar energy and eliminating various pollutants, is the most ideal and clean technology, and is thus receiving wide attention. Among them, photocatalytic hydrogen production by total hydrolysis is particularly important, because it can utilize solar energy to directly decompose water into hydrogen and oxygen, it is the simplest and most economical hydrogen production method, and at the same time, it can utilize its redox ability to degrade pollutants so as to purify environment, and is helpful for realizing sustainable society, so that it is receiving much attention. In 1972, two professors Fujishima and Honda reported the discovery of TiO for the first time2The single crystal electrode photocatalytically decomposes water to generate hydrogen, and opens up a research way for decomposing water by using solar energy. However, TiO2The wide band gap makes it possible to utilize only ultraviolet light in 4% of sunlight, while visible light has great weight in solar energy, so that full hydrolysis in visible light region is the focus of research.
The visible light full-hydrolysis water can adopt a single semiconductor photocatalyst and also can adopt a Z-type photocatalyst. The so-called Z-type photocatalyst is formed by coupling a hydrogen-evolving semiconductor and an oxygen-evolving semiconductor through an intermediate medium, and is widely used because it can more effectively separate electron-hole pairs and has a stronger redox ability, and is more active only up to about 500nm at most than the full water-splitting absorption edge of a single photocatalyst, but can utilize a wider range of visible light. At present, Z-type photocatalysts linked by reversible redox chemical mediators, Z-type photocatalysts linked by metal mediators and even direct Z-type photocatalysts without mediators can be formed according to different intermediate mediators. In 2010, one Pt-loaded ZrO2Pt-loaded WO with TaON as hydrogen-evolving semiconductor3As oxygen-evolving semiconductors, and IO3 -/I-"Z-type" light as redox mediatorThe catalyst realizes the full water decomposition under the irradiation of visible light, and the quantum efficiency of the catalyst at 420nm is 6.3 percent; in 2016, La, Rh-coded SrTiO was used by Domen et al3Hydrogen-producing, Mo-doped BiVO4Oxygen generation, the Au layer as an electron transfer mediator, the quantum efficiency of this system at 419nm wavelength is 33% (solar energy utilization rate about 1.1%), which is the highest repeatable solar energy utilization value achieved so far using the full hydrolysis photocatalyst; 2018, aza-fused microporous Polymer (CMP)/C2The N direct Z-type heterojunction photocatalyst realizes full-hydrolytic decomposition under the irradiation of visible light, and the solar energy utilization rate reaches 0.4%. The above several Z-type photocatalysts have been proved to be capable of achieving full-hydrolytic decomposition under irradiation of visible light, however, the full-hydrolytic decomposition efficiency is low because of the following problems:
1. the existing semiconductor Z-type photocatalyst has an unreasonable structure, and comprises an imperfect geometric structure (such as an imperfect effective active surface, weak built-in electric field intensity caused by difficult regulation of a contact interface between semiconductors and the like) and an imperfect energy band structure matching (causing the limitation of the utilization range of visible light) so that the photocatalytic efficiency is low.
2. The existing semiconductor Z-type photocatalyst has insufficient stability, is dissolved in water or solution to different degrees, mostly has photo-corrosion and (or) reverse reaction, has a service life of only a few hours to dozens of hours, and has poor stability.
3. The preparation process is complex and the recovery is difficult.
Therefore, the existing semiconductor Z-type photocatalyst and the preparation method thereof need to be further researched.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, one object of the present invention is to provide a semiconductor photocatalytic structure, a preparation method thereof and a photocatalyst having the same, wherein the semiconductor photocatalytic structure has feasibility of complete water splitting, and has a maximized effective active surface, a controllable built-in electric field, flexible energy band structure matching and better stability, so that the light conversion efficiency of a complete water splitting catalytic system based on the semiconductor photocatalytic structure is improved, a selectable photocatalytic material is expanded, and the problem of low complete water splitting efficiency of a Z-type photocatalyst in the prior art can be solved to a certain extent.
In one aspect of the invention, a semiconductor photocatalytic structure is provided. According to an embodiment of the invention, the semiconductor photocatalytic structure comprises:
a semiconductor transition layer comprising at least one semiconductor layer;
the first semiconductor layer is in direct contact with the semiconductor layer in the semiconductor transition layer;
a second semiconductor layer in direct contact with the semiconductor layer in the semiconductor transition layer, and the first semiconductor layer is not in contact with the second semiconductor layer;
wherein the content of the first and second substances,
the band gap energies of the first semiconductor layer and the second semiconductor layer are respectively and independently not lower than 1.8 ev;
the thickness of the first semiconductor layer and the thickness of the semiconductor layer in direct contact with the first semiconductor layer exceed the space charge region width of a heterojunction/homojunction formed by the first semiconductor layer and the first semiconductor layer, the direction of an internal electric field of the first semiconductor layer points to the semiconductor layer in direct contact with the first semiconductor layer, and the conduction band-to-bottom ratio of the first semiconductor layer is H2O/H2More negative reduction potential;
the thickness of the second semiconductor layer and the thickness of the semiconductor layer in direct contact with the second semiconductor layer exceed the space charge region width of the semiconductor heterojunction/homojunction formed by the second semiconductor layer and the second semiconductor layer, the direction of the built-in electric field is directed to the second semiconductor layer from the semiconductor layer in direct contact with the second semiconductor layer, and the valence band top ratio O of the second semiconductor layer2/H2The oxidation potential of O is more positive.
According to the semiconductor photocatalytic structure of the embodiment of the present invention, the first semiconductor layer and the second semiconductor layer are arranged at different positions of the semiconductor transition layer, that is, the first semiconductor layer and the second semiconductor layer are in contact through the semiconductor transition layer, and the surfaces of the first semiconductor layer and the second semiconductor layer are both provided with the semiconductor transition layerCan be fully contacted with water or solution, so that the effective active area of the semiconductor photocatalytic structure is maximized. Meanwhile, the second semiconductor layer and the first semiconductor layer are in complete contact with the semiconductor layer in the semiconductor transition layer, so that a built-in electric field is obviously enhanced, separation of photon-generated carriers is facilitated, the carriers are enabled to migrate rapidly, and the photocatalytic efficiency of the semiconductor photocatalytic structure is improved. The band gap energy of the first semiconductor layer and the band gap energy of the second semiconductor layer are respectively and independently not lower than 1.8ev, namely the first semiconductor layer and the second semiconductor layer both have visible light absorption capacity, so that the photocatalytic structure can effectively utilize a visible light region to carry out full water splitting, and the potential of visible light is utilized to the maximum extent; the thickness of the first semiconductor layer and the thickness of the semiconductor layer in direct contact with the first semiconductor layer are both limited to exceed the space charge region width of the semiconductor heterojunction/homojunction formed by the first semiconductor layer and the semiconductor layer, the direction of the built-in electric field of the first semiconductor layer points to the semiconductor layer in direct contact with the first semiconductor layer, and the conduction band-to-bottom ratio H of the first semiconductor layer2O/H2The reduction potential of the first semiconductor layer is more negative, namely the first semiconductor layer has the capability of reducing water to produce hydrogen; simultaneously defining the thickness of the second semiconductor layer and the thickness of the semiconductor layer directly contacted with the second semiconductor layer to exceed the space charge region width of the semiconductor heterojunction/homojunction formed by the second semiconductor layer and the second semiconductor layer, wherein the direction of the built-in electric field is directed to the second semiconductor layer from the semiconductor layer directly contacted with the second semiconductor layer, and the valence band top ratio O of the second semiconductor layer2/H2The oxidation potential of O is corrected, i.e., the second semiconductor layer has the ability to oxidize water to produce oxygen. Therefore, the semiconductor photocatalytic structure has the feasibility of complete water splitting, has a maximized effective active surface, a controllable built-in electric field, flexible energy band structure matching and better stability, improves the light conversion efficiency of a complete water splitting catalytic system based on the semiconductor photocatalytic structure, expands selectable photocatalytic materials, and further can solve the problem of lower complete water splitting efficiency of a Z-type photocatalyst in the prior art to a certain extent.
In addition, the semiconductor photocatalytic structure according to the above-described embodiment of the present invention may also have the following additional technical features:
in some embodiments of the present invention, the first semiconductor layer and the second semiconductor layer are disposed on the same side or both sides of the semiconductor transition layer.
In some embodiments of the invention, the semiconductor transition layer comprises: a conductive layer; a third semiconductor layer disposed on the conductive layer, the first semiconductor layer disposed on the third semiconductor layer; a fourth semiconductor layer disposed on the conductive layer and not in contact with the third semiconductor layer, the second semiconductor layer disposed on the fourth semiconductor layer.
In some embodiments of the present invention, a work function of the first semiconductor layer is smaller than a work function of the third semiconductor layer, and a work function of the second semiconductor layer is larger than a work function of the fourth semiconductor layer.
In a further aspect of the invention, the invention provides a method of preparing the above semiconductor photocatalytic structure. According to an embodiment of the invention, the method comprises: and forming a first semiconductor layer and a second semiconductor layer at different positions of the semiconductor transition layer respectively by physical vapor deposition. Therefore, the semiconductor photocatalytic structure with the maximized effective active surface, controllable built-in electric field, flexible energy band structure matching and better stability can be prepared by contacting the first semiconductor layer and the second semiconductor layer through the semiconductor transition layer in a physical vapor deposition mode and has the feasibility of full water decomposition.
In addition, the method for preparing a semiconductor photocatalytic structure according to the above embodiment of the present invention may also have the following additional technical features:
in some embodiments of the invention, the physical vapor deposition comprises electron beam evaporation coating, vapor barrier coating, sputter coating, or ion coating.
In some embodiments of the present invention, the method of preparing a semiconductor photocatalytic structure further comprises annealing the semiconductor transition layer formed by the physical vapor deposition to form the first semiconductor layer and the second semiconductor layer.
In some embodiments of the present invention, the physical vapor deposition employs an e-beam evaporation coating, and after the first semiconductor layer and the second semiconductor layer are formed on the semiconductor transition layer through the e-beam evaporation coating, the method further includes: taking the semiconductor transition layer on which the first semiconductor layer and the second semiconductor layer are formed out of the film coating machine, and then putting the semiconductor transition layer into an oven for baking; naturally cooling after baking or cooling according to a set cooling rate. Therefore, the crystallinity of the film can be improved, the defects of the film can be reduced, and the semiconductor photocatalytic structure is ensured to have excellent photocatalytic efficiency.
In a third aspect of the present invention, a photocatalyst is presented. According to an embodiment of the present invention, the photocatalyst includes the above semiconductor photocatalytic structure or the semiconductor photocatalytic structure obtained by the above method. Therefore, the photocatalyst has the feasibility of full-hydrolytic light, can effectively utilize visible light to perform full-hydrolytic light, has excellent photocatalytic efficiency, and can further solve the problem of low efficiency of the Z-type photocatalyst in the prior art in full-hydrolytic light to a certain extent.
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.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic structural view of a semiconductor photocatalytic structure according to one embodiment of the present invention;
FIG. 2 is a schematic structural view of a semiconductor photocatalytic structure according to yet another embodiment of the present invention;
FIG. 3 is a band structure diagram of a semiconductor photocatalytic structure according to one embodiment of the present invention;
FIG. 4 is a schematic structural view of a semiconductor photocatalytic structure according to yet another embodiment of the present invention;
FIG. 5 is a schematic structural view of a semiconductor photocatalytic structure according to yet another embodiment of the present invention;
FIG. 6 is a band structure diagram of a semiconductor photocatalytic structure according to yet another embodiment of the present invention;
FIG. 7 is a graph showing the change in the gas composition in the system measured by a gas chromatograph before and after the irradiation of the semiconductor photocatalytic structure of the example placed in the reactor;
FIG. 8 is a graph showing the change in the gas composition in the system measured by a gas chromatograph before and after the irradiation of light with the semiconductor photocatalytic structure of the example which is not placed in the reactor.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and are not to be considered limiting of the invention.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.
In one aspect of the invention, a semiconductor photocatalytic structure is provided. According to an embodiment of the present invention, referring to fig. 1, the semiconductor photocatalytic structure comprises a semiconductor transition layer 100, a first semiconductor layer 200 and a second semiconductor layer 300, wherein the semiconductor transition layer comprises at least one semiconductor layer (not shown), and the semiconductor layers in the first semiconductor layer 200 and the semiconductor transition layer 100 are in direct contact, the semiconductor layers in the second semiconductor layer 300 and the semiconductor transition layer 100 are in direct contact, and the first semiconductor layer 200 is not in contact with the second semiconductor layer 300; wherein the band gap energy of the first semiconductor layer 200 and the second semiconductor layer 300 is not less than 1.8ev, the thickness of the first semiconductor layer 200 and the thickness of the semiconductor layer in direct contact therewith exceed the space charge region width of the semiconductor heterojunction/homojunction formed by them, the direction of the built-in electric field is directed from the first semiconductor layer 200 to the semiconductor layer in direct contact therewith, and the conduction band-to-bottom ratio H of the first semiconductor layer 2002O/H2The thickness of the second semiconductor layer 300 and the thickness of the semiconductor layer in direct contact therewith both exceed the space charge region width of the semiconductor heterojunction/homojunction formed by them, the direction of the built-in electric field is directed from the semiconductor layer in direct contact therewith to the second semiconductor layer 300, and the valence band top ratio O of the second semiconductor layer 300 is more negative2/H2The oxidation potential of O is more positive. The inventors have found that by applying a first semiconductor layerThe second semiconductor layer is arranged at different positions of the semiconductor transition layer, namely the first semiconductor layer and the second semiconductor layer are in contact through the semiconductor transition layer, the surfaces of the first semiconductor layer and the second semiconductor layer can be fully contacted with water or solution, so that the effective active area of the semiconductor photocatalytic structure is maximized, and meanwhile, as the second semiconductor layer and the first semiconductor layer are in complete contact with the semiconductor layer in the semiconductor transition layer, the built-in electric field is obviously enhanced, the separation of photon-generated carriers is facilitated, and the carriers can be rapidly transferred, so that the photocatalytic efficiency of the semiconductor photocatalytic structure is improved. For example, referring to fig. 1, the first semiconductor layer 200 and the second semiconductor layer 300 are disposed on the same side of the semiconductor transition layer 100; or referring to fig. 2, the first semiconductor layer 200 and the second semiconductor layer 300 are respectively disposed at both sides of the semiconductor transition layer 100. The band gap energy of the first semiconductor layer and the band gap energy of the second semiconductor layer are respectively and independently not lower than 1.8ev, namely the first semiconductor layer and the second semiconductor layer both have visible light absorption capacity, so that the photocatalytic structure can effectively utilize a visible light region to carry out full water splitting, and the potential of visible light is utilized to the maximum extent; the thickness of the first semiconductor layer and the thickness of the semiconductor layer in direct contact with the first semiconductor layer are both limited to exceed the space charge region width of the semiconductor heterojunction/homojunction formed by the first semiconductor layer and the semiconductor layer, the direction of the built-in electric field of the first semiconductor layer points to the semiconductor layer in direct contact with the first semiconductor layer, and the conduction band-to-bottom ratio H of the first semiconductor layer2O/H2The reduction potential of the first semiconductor layer is more negative, namely the first semiconductor layer has the capability of reducing water to produce hydrogen; simultaneously defining the thickness of the second semiconductor layer and the thickness of the semiconductor layer directly contacted with the second semiconductor layer to exceed the space charge region width of the semiconductor heterojunction/homojunction formed by the second semiconductor layer and the second semiconductor layer, wherein the direction of the built-in electric field is directed to the second semiconductor layer from the semiconductor layer directly contacted with the second semiconductor layer, and the valence band top ratio O of the second semiconductor layer2/H2The oxidation potential of O is corrected, i.e., the second semiconductor layer has the ability to oxidize water to produce oxygen.
Specifically, referring to fig. 3, when the surface of the first semiconductor layer 200 is illuminated, the photo-generated electrons in the space charge region and the nearby region drift toward the first semiconductor layer 200 under the driving of the built-in electric field, and the photo-generated holes drift toward the semiconductor transition layer 100, and part of the photo-generated electrons moving to the surface of the first semiconductor layer 200 reduce water to hydrogen, and similarly, when the surface of the second semiconductor layer 300 is illuminated, the photo-generated holes in the space charge region and the nearby region drift toward the second semiconductor layer 300 under the driving of the built-in electric field, and the photo-generated electrons drift toward the semiconductor transition layer 100, part of the photo-generated holes moving to the second semiconductor layer 300 oxidize water to oxygen, and the photo-generated holes and the photo-generated electrons moving to the semiconductor transition layer 100 are recombined there, and in addition, due to the blocking of the interface barrier peak, part of the photo-generated electrons and holes can cross the barrier peak (such as tunneling effect and the like), and the rest of the photon-generated electrons and holes transferred to the interface are basically compounded, so that the separation and the transfer of photon-generated carriers are facilitated, and the photo-corrosion and the reverse reaction can be avoided. Therefore, the semiconductor photocatalytic structure has the feasibility of complete water splitting, has a maximized effective active surface, a controllable built-in electric field, flexible energy band structure matching and better stability, improves the light conversion efficiency of a complete water splitting catalytic system based on the semiconductor photocatalytic structure, expands selectable photocatalytic materials, and further can solve the problem of lower complete water splitting efficiency of a Z-type photocatalyst in the prior art to a certain extent.
It should be noted that the shapes of the semiconductor transition layer 100, the first semiconductor layer 200, and the second semiconductor layer 300 are not particularly limited as long as the indirect contact of the first semiconductor layer 200 and the second semiconductor layer 300 through the semiconductor transition layer 100 and the maximized contact with the effective active surface of water or a solution can be achieved, and it is preferable that the semiconductor transition layer 100, the first semiconductor layer 200, and the second semiconductor layer 300 are all flat plates.
Further, referring to fig. 4 and 5 (fig. 4 shows that the first semiconductor layer 200 and the second semiconductor layer 300 are disposed on the same side of the semiconductor transition layer 100, and fig. 5 shows that the first semiconductor layer 200 and the second semiconductor layer 300 are disposed on both sides of the semiconductor transition layer 100), the semiconductor transition layer 100 includes a conductive layer 11, a third semiconductor layer 12 and a fourth semiconductor layer 13, the third semiconductor layer 12 is disposed on the conductive layer 11, the first semiconductor layer 200 is disposed on the third semiconductor layer 12, the fourth semiconductor layer 13 is disposed on the conductive layer 11, and the third semiconductor layer 12 and the fourth semiconductor layer 13 are not in contact, the second semiconductor layer 300 is disposed on the fourth semiconductor layer 13, and the work function of the first semiconductor layer 200 is smaller than that of the third semiconductor layer 12, and the work function of the second semiconductor layer 300 is larger than that of the fourth semiconductor layer 13, so that the directions of the built-in electric fields thereof are respectively directed from the first semiconductor layer 200 to the third semiconductor layer 12 after they form a semiconductor heterojunction/homojunction The semiconductor layer 12 and from the fourth semiconductor layer 13 towards the second semiconductor layer 300. Specifically, referring to fig. 6, when the surface of the first semiconductor layer 200 is illuminated, the photo-generated electrons in the space charge region and the neighboring region drift toward the first semiconductor layer 200 under the driving of the built-in electric field, and the photo-generated holes drift toward the third semiconductor layer 12; part of the photo-generated electrons that have migrated to the surface of the first semiconductor layer 200 reduce water to hydrogen, and at the same time, part of the photo-generated holes that have migrated to the surface of the third semiconductor layer 12 move toward the conductive layer 11 (the material of the conductive layer 11 ensures that the interface formed between the third semiconductor layer 12 and the conductive layer 11 is favorable for the migration of the photo-generated holes). Similarly, when the surface of the second semiconductor layer 300 is illuminated, the photo-generated electrons in the space charge region and the nearby region drift toward the fourth semiconductor layer 13 under the driving of the built-in electric field, and the photo-generated holes drift toward the second semiconductor layer 300; while part of the photogenerated holes migrated to the surface of the second semiconductor layer 300 oxidize water into oxygen, part of the photogenerated electrons migrated to the surface of the fourth semiconductor layer 13 migrate to the conductive layer 11 (similarly, the material of the conductive layer 11 ensures that the interface formed between the fourth semiconductor layer 13 and the conductive layer 11 facilitates the migration of the photogenerated electrons), and recombine with the photogenerated holes. Preferably, the conductive layer 11 includes a conductive substance therein. It should be noted that, a person skilled in the art may select a specific type of the conductive substance according to actual needs, as long as the above effects can be achieved, and details are not described herein.
In a further aspect of the invention, the invention provides a method of preparing the above semiconductor photocatalytic structure. According to an embodiment of the invention, the method comprises: and forming a second semiconductor layer and a first semiconductor layer at different positions of the semiconductor transition layer by physical vapor deposition. The inventor finds that the semiconductor photocatalytic structure which has the advantages of maximized effective active surface, controllable built-in electric field, flexible energy band structure matching and better stability can be prepared by the physical vapor deposition mode, wherein the first semiconductor layer and the second semiconductor layer are in contact with each other through the semiconductor transition layer, and the semiconductor photocatalytic structure has the feasibility of full water decomposition. Further, the method for preparing the semiconductor photocatalytic structure further comprises annealing the semiconductor transition layer formed by the physical vapor deposition, wherein the first semiconductor layer and the second semiconductor layer are formed by the physical vapor deposition. Therefore, the amorphous region can be partially crystallized, fine crystal grains can grow up, and impurity atoms at certain gap positions can enter the substitution positions, so that the crystallinity of the film can be improved, the defects of the film can be reduced, and the semiconductor photocatalytic structure is ensured to have excellent photocatalytic efficiency. Further, physical vapor deposition as used herein includes, but is not limited to, electron beam evaporation coating, vapor barrier coating, sputter coating, or ion coating, preferably electron beam evaporation coating. Further, according to an embodiment of the present invention, after the forming the first semiconductor layer and the second semiconductor layer on the semiconductor transition layer by the electron beam evaporation plating, the physical vapor deposition further includes: taking the semiconductor transition layer for forming the first semiconductor layer and the second semiconductor layer out of the film coating machine, and then baking the semiconductor transition layer in an oven within half an hour; naturally cooling after baking or cooling according to a set cooling rate. Therefore, the crystallinity of the film can be improved, the defects of the film can be reduced, and the semiconductor photocatalytic structure is ensured to have excellent photocatalytic efficiency. It should be noted that, in the present application, the specific operations of forming the second semiconductor layer and the first semiconductor layer on the semiconductor transition layer by using the electron beam evaporation coating, evaporation resistance, sputtering coating or ion coating are conventional in the art, and those skilled in the art can select appropriate operation conditions according to actual needs, and details are not described here.
It should be noted that the features and advantages described above for the semiconductor photocatalytic structure apply equally to the method of preparing the semiconductor photocatalytic structure and are not described in detail here.
In a third aspect of the present invention, a photocatalyst is presented. According to an embodiment of the present invention, the photocatalyst includes the above semiconductor photocatalytic structure or the semiconductor photocatalytic structure obtained by the above method. Therefore, the photocatalyst has the feasibility of full-hydrolytic light, can effectively utilize a visible light region to perform full-hydrolytic light, has excellent photocatalytic efficiency, and can further solve the problem of low efficiency of the Z-type photocatalyst in the prior art in full-hydrolytic light to a certain extent. It should be noted that the features and advantages described above for the semiconductor photocatalytic structure and the preparation method thereof are also applicable to the photocatalyst, and are not described herein again.
The invention will now be described with reference to specific examples, which are intended to be illustrative only and not to be limiting in any way.
Example 1
Semiconductor photocatalytic structure: the first semiconductor layer is CdS film with thickness of 120nm, Pt with thickness of 0.5nm is used as cocatalyst, and the second semiconductor layer is Ag with thickness of 150nm3PO4Film, the third semiconductor layer is 150nm of Ag3PO4The film, the fourth semiconductor layer is a 120nm thick CdS film, the conductive layer is a silver-based alloy with phi of 20mm, and the first semiconductor layer and the second semiconductor layer are positioned on the same side of the conductive layer, and the structure of the film is shown in FIG. 4;
the main raw materials are as follows: silver-based alloy (phi 20mm), Ag3PO4Membrane material (purity 99%), CdS membrane material (purity 99.999%), Pt membrane material (purity 99.99%);
the method of preparing the semiconductor photocatalytic structure is as follows:
(1) silver-based alloy treatment: washing with distilled water and oven drying;
(2) covering the arc part of the silver-based alloy larger than the semicircle, and leaving the arc part (with the arc height of 9.5mm) smaller than the semicircle for film coating;
(3) plating Ag on the silver-based alloy in sequence3PO4[ CdS ]: treated silver-based alloy, Ag3PO4Filling the film material and the CdS film material into a vacuum coating machine, and vacuumizing to 2.0 x 10-3Pa, heating the coating machine to 100 ℃, keeping the temperature for 20 minutes, starting an ion source (filling argon gas for 10sccm) to etch the substrate for 3 minutes, and closing the ion source; then, the evaporation of Ag is started3PO4Setting the beam current of an electron gun to be 15mA, pre-melting the film material for 30 seconds, opening a baffle of the electron gun, ensuring that the deposition rate is about 0.5nm/s, and completing 150nm Ag by crystal control3PO4Depositing a thin film; then plating CdS, setting 3mA of beam current of an electron gun, pre-melting the film material for 10 seconds, opening a baffle of the electron gun, and controlling the crystal control to finish the deposition of a 120nm CdS film; after the coating machine is cooled to 70 ℃, the coating machine is inflated and cooled, and the coated wafer is taken out;
(4) plating a catalyst promoter Pt on the CdS film layer: already plated with Ag3PO4Putting the CdS wafer and Pt film material into a vacuum coating machine, and vacuumizing to 2.0 x 10-3Pa, heating the coating machine to 80 ℃ and keeping the temperature for 25 minutes, then starting to evaporate Pt on the CdS film layer, setting the beam current of an electron gun to be 360mA, pre-melting the film material for 10 seconds, opening a baffle of the electron gun, and controlling the deposition rate to be about 0.1nm/s in a crystal control mode to finish the deposition of Pt of 0.5 nm; after the coating machine is cooled to 70 ℃, the coating machine is inflated and cooled, and the coated wafer is taken out;
(5) covering the arc part of the silver-based alloy larger than the semicircle (including the Ag plated part3PO4The arched part where/CdS/Pt is located) and leaving an arched part (the arch height is 9.5mm) which is smaller than a semicircle for coating, so that the coated layer is not contacted with the to-be-coated layer;
(6) CdS/Ag plating on silver-base alloy in sequence3PO4: treated silver-based alloy, Ag3PO4Filling the film material and the CdS film material into a vacuum coating machine, and vacuumizing to 2.0 x 10-3Pa, heating the coating machine to 100 ℃, keeping the temperature for 20 minutes, starting an ion source (filling argon gas for 10sccm) to etch the substrate for 3 minutes, and closing the ion source; then, evaporating CdS, setting the beam current of an electron gun to be 3mA, pre-melting the film material for 10 seconds, opening a baffle of the electron gun, and controlling the crystal control to finish the deposition of a 120nm CdS film, wherein the deposition rate is about 2 nm/s; followed by Ag plating3PO4Electron ofSetting the gun beam current to be 15mA, pre-melting the film material for 30 seconds, opening a baffle of an electron gun, ensuring the deposition rate to be about 0.5nm/s, and completing 150nm Ag by crystal control3PO4Depositing a thin film; after the coating machine is cooled to 70 ℃, the coating machine is inflated and cooled, and the coated wafer is taken out;
(7) then, within half an hour, the plated wafer is placed in an oven, baked at 250 ℃ for 24 hours, and then naturally and slowly cooled to 70-80 ℃ (about 16 hours), and then taken out, so that the obtained semiconductor photocatalytic structure is shown in fig. 4.
Sample characterization
(1) Energy band structure
CdS thin film and Ag3PO4The visible light absorption spectrum of the film is detected by a spectrophotometer, and the result shows that Ag3PO4The visible light absorption edge of the film is as high as 570nm, and the CdS film has strong absorption at 420-550 nm. Since CdS is a direct transition semiconductor, the CdS is composed of (Ahv)2Plotting the hv to obtain the CdS film band gap energy of 2.37 eV; due to Ag3PO4Is an indirect transition semiconductor consisting of (Ahv)0.5Mapping to hv to obtain Ag3PO4The film band gap energy was 2.15 eV. The band position of a semiconductor can be determined by calculation using empirical formulas ECB-X-Ee-0.5 Eg and EVB-ECB + Eg, where X is the electronegativity of the semiconductor and the geometric average of the electronegativities of the various atoms constituting the semiconductor, Eg is the band gap energy of the semiconductor, and Ee is the energy at which the electron occupies the highest energy level at a standard hydrogen electrode (NHE); the prepared CdS film has ECB of-0.51 eV, EVB of 1.86eV and Ag3PO4The film ECB was 0.38eV, and the EVB was 2.53 eV. CdS thin film and Ag3PO4The work function of the film is determined by the detection of a photoelectron spectrometer, and the detection result shows Ag3PO4The work function of the film was about 0.8eV greater than that of CdS film, and thus CdS layer and Ag were estimated3PO4After the heterojunction is formed between the layers, the conduction band bottom of the CdS is still higher than H2O/H2Is more negative than that of Ag3PO4Valence band crest ratio of O2/H2The oxidation potential of O is more positive. The detection and calculation result can be obtained by the test result of the photo-total hydrolysis of the sampleAnd confirmed.
(2) The test process and the result of the full water splitting of the visible light region of the semiconductor photocatalytic structure are as follows:
A) experimental apparatus: in order to evaluate the performance of the system in future practical application, the test conditions simulate the practical use conditions, namely a standard atmospheric pressure, room temperature (20 +/-1 ℃) and simulated solar visible light irradiation (a 300-watt xenon lamp is adopted in the experiment, visible light of 400nm-780nm is emitted after filtering, the distance from a reactor to a light source is adjusted, and the light intensity irradiated on a sample is adjusted to 1 sun of visible light irradiation of 0.04w/cm2). Therefore, the test result can reflect the performance of the test in practical use;
B) the experimental results are as follows:
a. variation of gas composition in pre-and post-illumination experimental system
FIG. 7 is a graph showing the measurement results of the change in the gas composition in the system obtained by the gas chromatograph measurement before and after the sample is placed in the reactor and the sample is irradiated with light, and H is not detected before the irradiation2After 4 hours of illumination H2The peaks are very distinct; oxygen, after light irradiation, O before light irradiation2The peak was clearly elevated. FIG. 8 is a graph showing the results of measuring the change in gas composition before and after the irradiation of a sample in a reactor, and H was not detected before and after the irradiation of the sample2And O is2The peak value of (a) does not change significantly before and after the light irradiation.
b. Calculating the utilization rate of the visible light:
intensity of visible light irradiated to the sample: 0.04w/cm2The effective area of the sample: 1.5cm2(because the sample is held with the clamps intentionally blocking the edge regions of the sample so that only the central region (less defects) is illuminated) then the total amount of visible light received by the sample per hour is: 0.04 × 1.5 × 3600 ═ 216J. Hourly H production2: 5.5. mu. mol, water split to H2And O2Gibbs free energy change (Δ G): 237KJ, the energy required to decompose water to give 5.5 μmol hydrogen is: 5.5*10-3237 ═ 1.3J, i.e., 1.3J of visible light energy that the sample can effectively utilize per hour. Visible light utilization rate: 1.3/216 ≈ 100% ≈ 0.6%.
(3) And (3) testing the performance stability of the sample:
the Ag is3The semiconductor photocatalytic structure part sample of PO4-CdS-Pt is used for more than 100 hours, and the film layer is intact without corrosion.
The semiconductor photocatalysis structure can avoid reverse reaction due to the existence of a built-in electric field in a specific direction; in addition, part of the photo-generated electrons and holes can cross over a potential barrier peak (such as a tunneling effect) under the action of the built-in electric field, and the rest of the photo-generated electrons and holes which are transferred to the interface are basically compounded at the position, so that the photo-corrosion of the self-generated electrons and holes can be avoided, and the phenomenon of photo-corrosion does not exist; compared with the nano powder, the nano film prepared by adopting the proper process is almost insoluble in water, so the performance is very stable.
(4) The preparation process is mature, and the sample is easy to recover:
ag prepared by the application3PO4the-CdS-Pt semiconductor photocatalytic structure adopts electron beam evaporation coating to coat Ag on the silver-based alloy3PO4the/CdS/Pt film layer is a mature process, has good repeatability, can be industrially produced in large quantity, is easy to recover and is fit for practical use.
Example 2
The preparation method is the same as that of embodiment 1, except that the first semiconductor layer and the second semiconductor layer are positioned on two sides of the semiconductor transition layer, and the obtained semiconductor photocatalytic structure is shown in fig. 5.
Example 3
The preparation method is the same as that of example 1, except that 150nm thick Ag is sequentially plated on a micropore (phi 5 mu m) ceramic substrate (phi 20mm thick 1mm)3PO4NiS with the thickness of 100nm (the coating method refers to CdS coating), CdS with the thickness of 120nm and Pt with the thickness of 0.5 nm; the first semiconductor layer is 120nm CdS film, 0.5nm Pt is used as cocatalyst, and the second semiconductor layer is 150nm Ag3PO4The film and the semiconductor transition layer are NiS films with the thickness of 100 nm.
The results of calculating the visible light utilization of the semiconductor photocatalytic structures obtained in examples 2 to 3 by the method of reference example 1 are shown in table 1.
TABLE 1
| Utilization rate of visible light | |
| Example 2 | 0.4％ |
| Example 3 | 0.1％ |
Although the embodiments of the present invention have been shown and described, it is understood that the above embodiments are illustrative and not to be construed as limiting the present invention, and those skilled in the art can make changes, modifications, substitutions and alterations to the above embodiments within the scope of the present invention and shall fall within the protection scope of the present application.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Claims (9)
1. A semiconductor photocatalytic structure, comprising:
a semiconductor transition layer comprising at least one semiconductor layer;
the first semiconductor layer is in direct contact with the semiconductor layer in the semiconductor transition layer;
a second semiconductor layer in direct contact with the semiconductor layer in the semiconductor transition layer, and the first semiconductor layer is not in contact with the second semiconductor layer;
wherein the content of the first and second substances,
the band gap energies of the first semiconductor layer and the second semiconductor layer are respectively and independently not lower than 1.8 ev;
the thickness of the first semiconductor layer and the thickness of the semiconductor layer in direct contact with the first semiconductor layer exceed the space charge region width of the semiconductor heterojunction/homojunction formed by the first semiconductor layer and the semiconductor layer in direct contact with the first semiconductor layer, the direction of the built-in electric field of the first semiconductor layer is directed to the semiconductor layer in direct contact with the first semiconductor layer, and the conduction band-to-bottom ratio of the first semiconductor layer is H2O/H2More negative reduction potential;
the thickness of the second semiconductor layer and the thickness of the semiconductor layer in direct contact with the second semiconductor layer exceed the space charge region width of the semiconductor heterojunction/homojunction formed by the second semiconductor layer and the second semiconductor layer, the direction of the built-in electric field is directed to the second semiconductor layer from the semiconductor layer in direct contact with the second semiconductor layer, and the valence band top ratio O of the second semiconductor layer2/H2The oxidation potential of O is more positive.
2. A semiconductor photocatalytic structure according to claim 1, characterized in that the first semiconductor layer and the second semiconductor layer are provided on the same side or on both sides of the semiconductor transition layer.
3. A semiconductor photocatalytic structure as set forth in claim 2 wherein the semiconductor transition layer comprises:
a conductive layer;
a third semiconductor layer disposed on the conductive layer, the first semiconductor layer disposed on the third semiconductor layer;
a fourth semiconductor layer disposed on the conductive layer and not in contact with the third semiconductor layer, the second semiconductor layer disposed on the fourth semiconductor layer.
4. A semiconductor photocatalytic structure as set forth in claim 3 wherein the work function of the first semiconductor layer is less than the work function of the third semiconductor layer and the work function of the second semiconductor layer is greater than the work function of the fourth semiconductor layer.
5. A method of making a semiconductor photocatalytic structure as recited in any of claims 1-4, comprising: and forming a first semiconductor layer and a second semiconductor layer at different positions of the semiconductor transition layer respectively by physical vapor deposition.
6. The method of claim 5, wherein the physical vapor deposition comprises electron beam evaporation coating, vapor block coating, sputter coating, or ion coating.
7. The method of claim 5 or 6, further comprising: and annealing the semiconductor transition layer which forms the first semiconductor layer and the second semiconductor layer through the physical vapor deposition.
8. The method of claim 6, wherein the physical vapor deposition is performed by using an electron beam evaporation coating, and further comprises, after forming the first semiconductor layer and the second semiconductor layer on the semiconductor transition layer by using the electron beam evaporation coating:
taking the semiconductor transition layer on which the first semiconductor layer and the second semiconductor layer are formed out of the film coating machine, and then putting the semiconductor transition layer into an oven for baking;
naturally cooling after baking or cooling according to a set cooling rate.
9. A photocatalyst characterised in that it comprises a semiconductor photocatalytic structure according to any one of claims 1 to 4 or obtained by a process according to claims 5 to 8.
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