CN109225182B - Ultrathin silicon nanosheet photocatalyst and preparation method and application thereof - Google Patents
Ultrathin silicon nanosheet photocatalyst and preparation method and application thereof Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
- B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
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- B01J35/23—
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- B01J35/39—
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
- C01B3/04—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of inorganic compounds, e.g. ammonia
- C01B3/042—Decomposition of water
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
- C01B2203/02—Processes for making hydrogen or synthesis gas
- C01B2203/0266—Processes for making hydrogen or synthesis gas containing a decomposition step
- C01B2203/0277—Processes for making hydrogen or synthesis gas containing a decomposition step containing a catalytic decomposition step
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
Abstract
The invention discloses an ultrathin silicon nanosheet photocatalyst and a preparation method and application thereof, wherein crystalline silicon powder is used as a precursor, the precursor is dispersed into a solvent after being soaked and pretreated in ultralow-temperature liquid gas, an ultrathin silicon nanosheet suspension is obtained through ultrasonic-assisted liquid phase stripping, and the ultrathin silicon nanosheet photocatalyst with the thickness of 0.3-2.1 nm and the size of 0.1-6.5 microns is obtained after the suspension is centrifuged and freeze-dried. When the silicon nanosheet obtained by the invention is used for photocatalytic hydrogen production by visible light, the hydrogen production efficiency can reach 5.102 mmol.h‑1·g‑1And the efficiency of the photocatalytic hydrogen production is about 93 times higher than that of the photocatalytic hydrogen production of the original crystal silicon powder. The preparation method of the silicon nanosheet disclosed by the invention is simple to operate and low in cost, can realize large-scale preparation, and the obtained silicon nanosheet has excellent visible light photocatalytic hydrogen production performance, so that a new thought is provided for constructing a stable and efficient material for producing hydrogen by water photolysis.
Description
Technical Field
The invention belongs to the field of nano semiconductor photocatalysis, and particularly relates to a preparation method of an ultrathin silicon nanosheet photocatalyst.
Background
Since the 21 st century, the energy crisis and environmental pollution problems faced by human beings have become more serious, and the search for efficient and clean renewable energy is the necessary way for the sustainable development of human society. Among a plurality of new energy sources, the hydrogen gas which has the advantages of cleanness, high efficiency, storage and transportation and the like is the most ideal green energy source for replacing traditional energy sources such as coal and the like. Thus, photocatalytic hydrogen productionAs a promising hydrogen production method, the method is highly valued by countries in the world. Under the intense search of researchers, TiO has been discovered2CdS, ZnO and other photocatalyst materials with excellent performance. But TiO 22Wide band gap semiconductors such as ZnO have limited absorption in the visible light region due to the large band width; although a narrow-bandgap semiconductor such as CdS has high performance of hydrogen production by visible light catalysis, the stability of the semiconductor is poor, and CdS has toxicity and is easy to pollute the environment.
The silicon nanosheet as an important semiconductor nano material has the advantages of narrow band gap, high carrier mobility, large specific surface area and the like, and is a photocatalyst with great potential. Silicon has strong light absorption and light response performance in a visible light region due to the advantage of narrow band gap; the higher carrier mobility is beneficial to the separation and migration of photo-generated electrons and holes, so that the photo-generated electrons are more easily migrated to the surface of the material to participate in the photocatalytic reaction; the large specific surface area provides sufficient active sites for photocatalytic reaction, and the silicon nanosheets are more easily combined with other materials to construct the composite photocatalyst. In addition, the silicon also has the advantages of abundant reserves, environmental friendliness and the like, and the prepared silicon nanosheet is expected to realize industrial application as a photocatalyst.
At present, methods for preparing silicon nanosheets include a chemical vapor deposition method, a graphene oxide template method, a magnesiothermic reduction method and a silicide stripping method, but the methods still have many defects, such as: the chemical vapor deposition method has high cost and low yield, and is not suitable for large-scale production; the graphene oxide template method, the magnesiothermic reduction method and the like are complex in process flow, and impurities and structural defects which are difficult to completely remove are introduced, so that the performance of the silicon nanosheets is influenced; silicide stripping process requires preparation of CaSi2And the precursor is stripped into sheets and then reduced into silicon nanosheets, the flow is complex, the yield is low, and the obtained silicon nanosheets are easily oxidized.
Disclosure of Invention
In order to avoid the defects of the prior art, the invention provides an ultrathin silicon nanosheet photocatalyst and a preparation method and application thereof, and aims to quickly realize batch preparation of the ultrathin silicon nanosheet photocatalyst and enable the obtained silicon nanosheet to have excellent visible light photocatalytic hydrogen production performance.
In order to achieve the above purpose, the invention provides the following technical scheme:
the invention firstly discloses a preparation method of an ultrathin silicon nanosheet photocatalyst, which is characterized by comprising the following steps: taking crystal silicon powder as a precursor, dipping and pretreating the crystal silicon powder in ultralow-temperature liquid gas, dispersing the crystal silicon powder into a solvent, and then carrying out ultrasonic-assisted liquid phase stripping to obtain an ultrathin silicon nanosheet suspension; and centrifuging and freeze-drying the ultrathin silicon nanosheet suspension to obtain the ultrathin silicon nanosheet photocatalyst. The method specifically comprises the following steps:
(1) soaking the crystal silicon powder in ultralow-temperature liquid gas for 2-48 h;
(2) taking out the soaked crystal silicon powder, dispersing the crystal silicon powder into a solvent after the liquid gas is completely volatilized, carrying out ultrasonic treatment for 2-10 h under the power of 100-180W, centrifuging the sample at low speed for 30min after ultrasonic treatment, and taking supernatant to obtain an ultrathin silicon nanosheet suspension;
(3) and (3) centrifuging the ultrathin silicon nanosheet suspension at a high speed, taking the precipitate, cleaning with deionized water, and freeze-drying for 48h to obtain the ultrathin silicon nanosheet photocatalyst.
Preferably, the particle size of the crystal silicon powder is 75-500 μm.
Preferably, the liquid gas is one of ultralow temperature liquid gases such as liquid nitrogen, liquid oxygen and liquid argon.
Preferably, the solvent is a mixed solvent formed by mixing one of NMP, ethanol and isopropanol with water according to a volume ratio of 1: 0.1-5.
Preferably, the mass-to-volume ratio of the crystalline silicon powder in the step (1) to the solvent in the step (2) is 0.1-5 g: 50-1000 mL.
Preferably, the rotating speed of the low-speed centrifugation in the step (2) is 500-3000 rpm, the rotating speed of the high-speed centrifugation in the step (3) is 8000-12000 rpm,
the invention also discloses the ultrathin silicon nanosheet photocatalyst prepared by the preparation method, wherein the ultrathin silicon nanosheet photocatalyst is 0.3-2.1 nm in thickness and 0.1-6.5 microns in diameter.
The ultrathin silicon nanosheet photocatalyst obtained by the invention can be used for visible light photocatalytic hydrogen production, and the hydrogen production efficiency can reach 5.102 mmol.h-1·g-1And the efficiency of the photocatalytic hydrogen production is about 93 times higher than that of the raw material crystal silicon powder.
The invention adopts a liquid phase stripping method to prepare the silicon nanosheet. Silicon powder is immersed in ultralow-temperature liquid gas, silicon particles are easily broken by using the embrittlement effect of the material at ultralow temperature, and then large-particle crystalline silicon powder is peeled into ultrathin silicon nanosheets by combining a liquid phase peeling process. Because the raw material is high-purity crystalline silicon powder, the obtained silicon nanosheet is high in purity and free of impurities, and still keeps good crystallinity. The adopted liquid phase stripping method has simple process flow, short time consumption and low equipment cost, can be produced in large batch and is expected to realize industrialized preparation of the silicon nanosheet; the silicon nanosheet powder obtained by freeze drying can be used for visible light photocatalytic hydrogen production, has high photocatalytic activity and great application potential.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the invention, the high-purity crystalline silicon powder is directly used for stripping to obtain the silicon nanosheet, the obtained silicon nanosheet is free of impurities and few in defects, the thickness is 0.3-2.1 nm, the size is 0.1-6.5 microns, and the performance and application research of the silicon nanosheet is expected to be promoted.
2. The liquid gas low-temperature pretreatment and ultrasonic liquid phase stripping method adopted by the invention has the advantages of simple process flow, short time consumption, low equipment cost, low process cost and higher production efficiency, and is expected to be used for industrial preparation.
3. The silicon nanosheet photocatalyst prepared by the invention has excellent photocatalytic performance, the hydrogen production rate is 93 times of that of the raw material crystal silicon powder, and the industrial application is expected to be realized.
Drawings
FIG. 1 is an SEM image of a commercial crystalline silicon powder used.
FIGS. 2(a), (b), and (c) are the XRD, Raman, and XPS characterization charts of the ultrathin silicon nanosheet photocatalyst and the raw powder obtained in example 1, respectively.
Fig. 3(a) is a physical diagram of the ultrathin silicon nanosheet suspension obtained in example 1, and fig. 3(b) is an SEM image of the silicon nanosheet light obtained in example 1.
Fig. 4 is an AFM image (fig. 4(a)) of the ultrathin silicon nanosheets obtained in example 1 and a sample thickness curve (fig. 4(b)) corresponding to a white line on the image.
Fig. 5 is a TEM image (fig. 5(a)) and an electron diffraction pattern (fig. 5(b)) of the ultrathin silicon nanosheets obtained in example 1.
Fig. 6 is a graph of hydrogen production performance by visible light photocatalysis of 10mg silicon nanosheet powder and crystalline silicon raw powder, wherein the left graph is a 5-hour hydrogen production curve of a sample, and the right graph is average hydrogen production per hour.
Detailed Description
In order to facilitate understanding of the present invention for those skilled in the art, the present invention will be further described with reference to the accompanying drawings and examples.
The commercial crystalline silicon powders used in the following examples had particle sizes of 75 μm to 500 μm and purities of 99.99%. FIG. 1 is an SEM image of a commercial crystalline silicon powder (raw powder) used in the following examples.
Example 1
In this example, an ultrathin silicon nanosheet photocatalyst was prepared as follows:
(1) weighing 1g of commercial crystal silicon powder, and soaking in liquid nitrogen for 12 hours;
(2) taking out the soaked crystal silicon powder, dispersing the crystal silicon powder into 200mL of mixed solvent formed by isopropanol and water according to the volume ratio of 1:1 after liquid nitrogen is completely volatilized, carrying out ultrasonic treatment for 8h under the power of 120W, centrifuging the sample at 1000rpm for 30min after ultrasonic treatment, and taking supernatant to obtain ultrathin silicon nanosheet suspension;
(3) and (3) centrifuging the ultrathin silicon nanosheet suspension at 10000rpm for 30min, taking the precipitate, washing with deionized water, and freeze-drying for 48h to obtain the ultrathin silicon nanosheet photocatalyst.
Fig. 2(a), (b), and (c) are XRD, Raman, and XPS characterization diagrams of the ultrathin silicon nanosheet photocatalyst and the raw powder obtained in this example in sequence, and it can be seen from the diagrams that the silicon nanosheet on the XRD diagram only retains the peak of 28.4 ° (corresponding to the (111) crystal plane), the other peaks disappear, the Raman peak of the silicon nanosheet is red-shifted, and the silicon nanosheet in the XPS diagram has no significant change compared with the raw powder, which indicates that the silicon only changes in particle size during the peeling process, and the silicon nanosheet is peeled from a large particle to a smaller nanosheet without a change in composition.
Fig. 3(a) is a real object diagram of the ultrathin silicon nanosheet suspension obtained in the embodiment, and fig. 3(b) is an SEM diagram of the silicon nanosheets obtained in the embodiment, and it can be seen from the diagram that the obtained silicon nanosheet suspension is a brown liquid, and the obtained nanosheets are well dispersed and have no obvious agglomeration phenomenon.
FIG. 4 shows an AFM (AFM) chart of the ultrathin silicon nanosheets obtained in the present example (FIG. 4(a)) and a sample thickness curve (FIG. 4(b)) corresponding to the white line on the chart, wherein the silicon nanosheets have a thickness of 0.3-1.2 nm and a diameter of 0.2-4.5 μm.
Fig. 5 shows a TEM image (fig. 5(a)) and an electron diffraction pattern (fig. 5(b)) of the ultrathin silicon nanosheet obtained in this example, and it can be seen that the obtained silicon nanosheet has a small thickness and still maintains good crystallinity.
The performance of the ultra-thin silicon nano-chip photocatalyst obtained in the present example for the visible light photocatalytic hydrogen production was tested in the following manner, and crystalline silicon raw powder was used as a comparison: 10mg of the silicon nanosheet powder (or crystalline silicon raw powder) obtained in example 1 is added to 90mL of deionized water, 10mL of triethanolamine is added, and the mixture is stirred for 30min to be uniformly mixed. The amount of hydrogen gas generated was measured in a gas chromatograph under irradiation with a 300W xenon lamp (>420 nm).
Fig. 6 is a graph of performance of visible light photocatalytic hydrogen production of 10mg silicon nanosheet powder and crystalline silicon raw powder, wherein fig. 6(a) is a 5-hour hydrogen production curve of a sample, and fig. 6(b) is an average hydrogen production per hour. As can be seen from the figure, the hydrogen production efficiency of the silicon nano-sheet is obviously higher than that of the crystalline silicon raw powder, and the average hydrogen production rate can reach 5.102 mmol.h-1·g-1And the efficiency of the photocatalytic hydrogen production is about 93 times higher than that of the photocatalytic hydrogen production of the original crystal silicon powder.
Example 2
(1) Weighing 400mg of commercial crystal silicon powder, and soaking in liquid nitrogen for 24 hours;
(2) taking out the soaked crystal silicon powder, dispersing the crystal silicon powder into 100mL of mixed solvent formed by isopropanol and water according to the volume ratio of 1:1 after liquid nitrogen is completely volatilized, carrying out ultrasonic treatment for 4h under the power of 100W, centrifuging the sample at 2000rpm for 30min after ultrasonic treatment, and taking supernatant to obtain ultrathin silicon nanosheet suspension;
(3) and (3) centrifuging the ultrathin silicon nanosheet suspension at 10000rpm for 30min, taking the precipitate, washing with deionized water, and freeze-drying for 48h to obtain the ultrathin silicon nanosheet photocatalyst.
The ultra-thin silicon nanosheet obtained in the embodiment is characterized by having a thickness of 0.9-1.8 nm and a diameter of 1.5-6.5 microns; the performance test of visible light photocatalytic hydrogen production is carried out according to the same method as the embodiment 1, and the result shows that the average hydrogen production rate of the sample is 3.537 mmol.h-1·g-1。
Example 3
(1) Weighing 600mg of commercial crystal silicon powder, and soaking in liquid oxygen for 48 hours;
(2) taking out the soaked crystal silicon powder, dispersing the crystal silicon powder into 200mL of mixed solvent formed by isopropanol and water according to the volume ratio of 1:1 after liquid oxygen is completely volatilized, carrying out ultrasonic treatment for 6h under the power of 120W, centrifuging a sample at 3000rpm for 30min after ultrasonic treatment, and taking supernatant to obtain ultrathin silicon nanosheet suspension;
(3) and (3) centrifuging the ultrathin silicon nanosheet suspension at 10000rpm for 30min, taking the precipitate, washing with deionized water, and freeze-drying for 48h to obtain the ultrathin silicon nanosheet photocatalyst.
The ultra-thin silicon nanosheet obtained in the embodiment is characterized by having a thickness of 0.6-1.5 nm and a size of 0.3-5.0 μm; the performance test of visible light photocatalytic hydrogen production is carried out according to the same method as the embodiment 1, and the result shows that the average hydrogen production rate of the sample is 3.970 mmol.h-1·g-1。
Example 4
(1) Weighing 800mg of commercial crystal silicon powder, and soaking in liquid oxygen carbon dioxide for 12 hours;
(2) taking out the soaked crystal silicon powder, dispersing the crystal silicon powder into 100mL of mixed solvent formed by isopropanol and water according to the volume ratio of 1:3 after liquid oxygen is completely volatilized, carrying out ultrasonic treatment for 10h under the power of 160W, centrifuging the sample at 3000rpm for 30min after ultrasonic treatment, and taking supernatant to obtain ultrathin silicon nanosheet suspension;
(3) and (3) centrifuging the ultrathin silicon nanosheet suspension at 10000rpm for 30min, taking the precipitate, washing with deionized water, and freeze-drying for 48h to obtain the ultrathin silicon nanosheet photocatalyst.
The ultra-thin silicon nanosheet obtained in the embodiment is characterized by having a thickness of 0.6-1.8 nm and a size of 0.2-3.5 microns; the performance test of visible light photocatalytic hydrogen production is carried out according to the same method as the embodiment 1, and the result shows that the average hydrogen production rate of the sample is 4.580 mmol.h-1·g-1。
Example 5
(1) Weighing 200mg of commercial crystal silicon powder, and soaking in liquid argon for 2 hours;
(2) taking out the soaked crystal silicon powder, dispersing the crystal silicon powder into a mixed solvent of 50mL isopropanol and water according to the volume ratio of 3:1 after liquid argon is completely volatilized, carrying out ultrasonic treatment for 4h under the power of 120W, centrifuging the sample at 1000rpm for 30min after ultrasonic treatment, and taking supernatant to obtain an ultrathin silicon nanosheet suspension;
(3) and (3) centrifuging the ultrathin silicon nanosheet suspension at 10000rpm for 30min, taking the precipitate, washing with deionized water, and freeze-drying for 48h to obtain the ultrathin silicon nanosheet photocatalyst.
The ultra-thin silicon nanosheet obtained in the embodiment is characterized by having a thickness of 1.2-2.1 nm and a size of 0.9-3.0 μm; the performance test of visible light photocatalytic hydrogen production is carried out according to the same method as the embodiment 1, and the result shows that the average hydrogen production rate of the sample is 2.863 mmol.h-1·g-1。
The above examples are typical examples of the present invention, and are not intended to limit the present invention, for example, the amount of silicon powder and solvent used, the liquid nitrogen freezing and embrittlement treatment time, the ultrasonic peeling time and power, and the centrifugal rotation speed and time can be further adjusted. Therefore, it is within the scope of the present invention that one skilled in the art could make adjustments and modifications to the process parameters described without departing from the spirit of the invention or exceeding the scope defined by the claims.
Claims (6)
1. A preparation method of an ultrathin silicon nanosheet photocatalyst is characterized by comprising the following steps: taking crystal silicon powder as a precursor, dipping and pretreating the crystal silicon powder in ultralow-temperature liquid gas, dispersing the crystal silicon powder into a solvent, and then carrying out ultrasonic-assisted liquid phase stripping to obtain an ultrathin silicon nanosheet suspension; centrifuging and freeze-drying the ultrathin silicon nanosheet suspension to obtain an ultrathin silicon nanosheet photocatalyst; the method specifically comprises the following steps:
(1) soaking the crystal silicon powder in ultralow-temperature liquid gas for 2-48 h, wherein the ultralow-temperature liquid gas is liquid nitrogen, liquid oxygen or liquid argon;
(2) taking out the soaked crystal silicon powder, dispersing the crystal silicon powder into a solvent after the liquid gas is completely volatilized, carrying out ultrasonic treatment for 2-10 h under the power of 100-180W, centrifuging the sample at low speed for 30min after ultrasonic treatment, and taking supernatant to obtain an ultrathin silicon nanosheet suspension; the solvent is a mixed solvent formed by mixing one of NMP, ethanol and isopropanol with water according to the volume ratio of 1: 0.1-5;
(3) and (3) centrifuging the ultrathin silicon nanosheet suspension at a high speed, taking the precipitate, cleaning the precipitate with deionized water, and freeze-drying for 48 hours to obtain the ultrathin silicon nanosheet photocatalyst, wherein the ultrathin silicon nanosheets have the thickness of 0.3-2.1 nm and the diameter of 0.1-6.5 microns.
2. The method for preparing an ultra-thin silicon nanosheet photocatalyst as recited in claim 1, wherein: the particle size of the crystal silicon powder is 75-500 mu m.
3. The method for preparing an ultra-thin silicon nanosheet photocatalyst as recited in claim 1, wherein: the mass volume ratio of the crystal silicon powder in the step (1) to the solvent in the step (2) is 0.1-5 g: 50-1000 mL.
4. The method for preparing an ultra-thin silicon nanosheet photocatalyst as recited in claim 1, wherein: the rotating speed of the low-speed centrifugation in the step (2) is 500-3000 rpm, and the rotating speed of the high-speed centrifugation in the step (3) is 8000-12000 rpm.
5. An ultra-thin silicon nanosheet photocatalyst obtained by the preparation method of any one of claims 1 to 4.
6. Use of the ultra-thin silicon nanosheet photocatalyst of claim 5, wherein: the method is used for visible light photocatalysis hydrogen production.
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