CN112675922B

CN112675922B - Titanium dioxide photocatalytic film with three-layer structure and preparation method thereof

Info

Publication number: CN112675922B
Application number: CN202011458524.7A
Authority: CN
Inventors: 沈杰; 尹延林; 薛丹妮
Original assignee: Fudan University
Current assignee: Fudan University
Priority date: 2020-12-10
Filing date: 2020-12-10
Publication date: 2022-04-12
Anticipated expiration: 2040-12-10
Also published as: CN112675922A

Abstract

The invention belongs to the technical field of photocatalytic films, and particularly relates to TiO with a three-layer structure₂A photocatalytic film and a preparation method thereof. In the photocatalytic film of the invention, the bottom layer is TiO doped with Mo₂The film, the middle layer is methylamine lead-iodine perovskite film, and the top layer is TiO doped with Mo₂A film; wherein the Mo-doped concentration of the bottom layer and the top layer is the same or different. The invention adopts the vapor deposition technology under the full vacuum environment and utilizes the magnetron sputtering and vacuum evaporation methods to prepare TiO with a three-layer structure₂A photocatalytic film. The invention introduces methylamine lead-iodine perovskite type narrow band gap material into Mo-doped TiO₂The film is used as an intermediate layer and can generate a large number of electron-hole pairs under visible light; and a plurality of built-in electric fields which can be modulated are implanted into the film by utilizing the Fermi energy level difference between the multiple layers of film layers and the layers, so that the mobility of carriers is effectively improved. Thus obtaining a multilayer TiO with high efficiency light absorption and photocatalytic activity₂The film has good practical value.

Description

Titanium dioxide photocatalytic film with three-layer structure and preparation method thereof

Technical Field

The invention belongs to the technical field of photocatalytic films, and particularly relates to TiO with a three-layer structure₂A photocatalytic film and a preparation method thereof.

Background

The photocatalysis can deeply react at room temperature and can directly use sunlight as a light source to drive the reaction and other unique properties, thereby becoming an ideal environmental pollution treatment technology and a clean energy production technology. Among the numerous photocatalysts, TiO₂The optical property is excellent, the light corrosion resistance is strong, the chemical and mechanical properties are stable, the price is low, and no toxicity is caused to human bodies, so that the optical fiber is always favored by people and has wide application prospect. However, due to TiO₂With a wide band gap (anatase E)_g=3.20 eV), it is determined that it can absorb only ultraviolet light or the ultraviolet portion of sunlight, and therefore, the light absorption range is widened and TiO is increased₂The catalytic activity of the photocatalyst is an important task for popularization and application of the photocatalytic technology. Although in relation to TiO₂Modification has been studied a lot, but in TiO₂In the aspect of multilayer films, corresponding research is still few so far, and only a few research reports are just preliminary attempts on the feasibility of multilayer films. Students with study^[1]A metallic molybdenum-doped core-shell structure of TiO was prepared₂The particle is researched and found that after being doped, the Fermi level in the core can be improved, and pure TiO with lower Fermi level is wrapped around the particle₂And the shell layer forms a micro nano particle with the Fermi level gradually increasing from outside to inside, and the result shows that the nano particle has higher catalytic performance. In addition, relevant foreign research shows that^[2]The external electric field can well inhibit the electron-hole recombination, but the electric field generated in the researches basically comes from the external anode bias voltage rather than from the thin film per se, so that the effect is limited in practical application. The research of the face susceptibility and the like shows that^{[3, 4]}A multilayer of doped TiO₂The Fermi level of the film structure is increased along with the increase of the doping amount, so that photogenerated carriers can be diffused at the interface under the drive of the Fermi level difference, positive and negative charges are respectively accumulated at two sides of a crystal boundary to form a built-in electric field, and the homojunction electric field between the two layers of interfaces can accelerateSeparation of photogenerated carriers.

In general, when narrow bandgap semiconductors and TiO₂When combined, the conduction band of the narrow bandgap semiconductor has a specific value to TiO₂And the potential is lower, so that when the photo-induced holes are excited by light irradiation, the photo-induced holes move to a valence band with a more negative energy level, and the photo-induced electrons jump to a conduction band with a higher energy level, and finally, the separation of photo-induced electron-hole pairs is realized. Methylamine lead iodide (CH) as a light collecting material₃NH₃PbI₃) The perovskite material has excellent photoelectric characteristics of high absorption coefficient, high carrier mobility, long diffusion length and the like, so that methylamine lead perovskite and TiO are mixed₂The combination can obviously improve TiO₂Photocatalytic activity. Methylamine lead iodine is however a very unstable material and will decompose in the presence of moisture or at elevated temperatures, making its practical application very difficult. The invention mixes methylamine lead, iodine calcium titanium ore and TiO₂The multilayer films are combined, and Mo is sequentially subjected to vapor deposition under a full vacuum environment: TiO 2₂And CH₃NH₃PbI₃The film layer, the prepared multilayer film has stable chemical property and photocatalytic property compared with pure TiO₂The film is greatly improved, the problem of water vapor erosion to methylamine lead iodine perovskite material is solved, and the film is expected to be widely applied in actual life.

Reference documents:

[1] Liu X G,Ou Z Q,Geng DY, Han Z, J J, Jiang, Liu W, Zhang Z D. Influenceof a graphite shell on the thermal and electromagnetic characteristics of FeNi nanoparticles[J]. Carbon, 2010, 48:891-897.

[2]Domaradzki, J., Kaczmarek, D.,Prociow, E.L., et al. Microstructure and optical propertiesof TiO₂ thin films prepared by low pressure hot target reactive magnelron sputtering[J]. G. Thin Solid Films, 2006, 513(1-2):269-274.

[3]preparation of multilayer molybdenum-doped TiO by magnetron sputtering₂Photoelectric Properties of the film [ D]University of double denier, 2013.

[4] Shenjie, Luo Sheng Tang and Yan Bing, Chinese patent CN 201210350730.5.

Disclosure of Invention

The invention aims to provide a TiO three-layer structure with high-efficiency light absorption efficiency, higher carrier separation capacity and strong practicability₂A photocatalytic film and a preparation method thereof.

The invention provides TiO with a three-layer structure₂The schematic diagram of the photocatalytic film is shown in FIG. 1. Wherein the bottom layer is TiO doped with Mo₂（Mo:TiO₂) The film, the middle layer is methylamine lead iodine perovskite (CH)₃NH₃PbI₃) Film, the top layer is TiO doped with Mo₂（Mo:TiO₂) The film is a molybdenum-doped titanium dioxide-methylamine lead-iodine perovskite-molybdenum-doped titanium dioxide three-layer structure composite film, and is marked as Mo, TiO₂-CH₃NH₃PbI₃- Mo:TiO₂. The Mo-doped concentration of the bottom layer and the top layer can be the same or different.

In the invention, the bottom layer and the top layer are Mo and TiO₂The film may be prepared under the same conditions or under different conditions.

The bottom layer and the top layer are Mo and TiO₂In the film, the doping amount of Mo is 0-3% (preferably 0.1-3%) in terms of Mo/Ti atomic ratio; mo doping amount is zero and is expressed as pure TiO₂Film, bottom and top Mo-TiO₂The doping amount of Mo in the film is not zero at the same time.

The invention provides the TiO with the three-layer structure₂The preparation method of the photocatalytic film adopts a vapor deposition technology under a full vacuum environment and utilizes magnetron sputtering and vacuum evaporation to prepare the photocatalytic film with a three-layer structure. All three film layers are prepared in the same vacuum equipment by adopting a vacuum vapor deposition technology, and are not exposed to any atmosphere or water vapor environment, so that the water vapor is prevented from reacting on CH₃NH₃PbI₃Erosion of the perovskite layer. The preparation method comprises the following specific steps:

(1) depositing a layer of Mo-doped TiO on a cleaned substrate₂A base film;

(2) depositing methylamine lead iodine perovskite (CH) on the bottom layer film₃NH₃PbI₃) An intermediate layer;

(3) on the intermediate layerDeposition of Mo-doped TiO₂A top film.

Mo-doped TiO of bottom layer and top layer₂The preparation of the film adopts a radio frequency magnetron sputtering method and adopts a molybdenum-embedded titanium dioxide ceramic target, wherein the atomic ratio of Mo to Ti is 0-3% (the atomic ratio is 0.1-3%), and the purity is 99.9%. Molybdenum in the molybdenum-embedded titanium dioxide ceramic target is embedded in a sputtering area on the target in a molybdenum sheet form, and the Mo/Ti atomic ratio in the film is controlled by the product of the area ratio of the molybdenum sheet to the titanium dioxide in the sputtering area and the sputtering rate ratio of the molybdenum sheet to the titanium dioxide; the distance between the target and the substrate is 50-75 mm.

Glass or metal is taken as a substrate, Ar ions are used for bombarding a target material during sputtering, and Mo-doped TiO is₂Depositing onto a substrate; wherein the temperature of the substrate is 25-400 ℃; oxygen-argon mixed gas is used during radio frequency magnetron sputtering, the total gas pressure is 0.1 Pa-1.0 Pa, wherein O₂Partial pressure accounts for 0.1-5.0% of the total air pressure ratio, the sputtering time is 30-120 min, and the sputtering power density is 10-80 kW/m²(when the target diameter is 60 mm, the sputtering power is 28 to 226W).

Preparing the methylamine lead-iodine perovskite film of the middle layer by adopting a vacuum transportation method, and doping Mo into TiO at the bottom layer₂Preparing an intermediate layer on the film: thermal evaporation of PbI₂On the bottom layer film; the evaporation boat is tantalum boat, PbI of each evaporation₂The mass of the powder is 0.1-0.5 g, the evaporation current is 60-150A, and the time is 1-5 min, so as to obtain a composite film, which is marked as PbI₂-Mo：TiO₂(ii) a Then the prepared PbI is added₂-Mo：TiO₂Transferring the film into a sealable glass container in a vacuum chamber, wherein 0.1-1.0 g of CH is disposed in the container at a position opposite to the film₃NH₃I, sealing a glass container (the glass container is always in a vacuum state), heating to 100-150 ℃, and preserving heat for 20-120 min to obtain the methylamine lead perovskite film; opening the glass container and taking out the film;

finally, sputtering and depositing a top layer to finish the preparation of the whole three-layer structure film.

In the invention, three layers of Mo and TiO are adopted₂-CH₃NH₃PbI₃-Mo:TiO₂Total thickness of film300nm to 700 nm; wherein the thickness of the bottom layer film is 50 nm-100 nm, the thickness of the intermediate layer methylamine lead iodoperovskite film is 200 nm-500 nm, and the thickness of the top layer film is 50 nm-100 nm.

The invention uses methylamine lead iodide (CH)₃NH₃PbI₃) Introduction of perovskite type narrow band gap material into Mo-doped TiO₂The thin film serves as an intermediate layer, and the semiconductor with the narrow band gap can generate a large number of electron-hole pairs under visible light. On the other hand, a plurality of built-in electric fields which can be modulated are implanted in the film by utilizing the Fermi energy level difference between the multilayer film layer and the interlayer, and the mobility of carriers is effectively improved. Thus, a multilayer TiO having high light absorption and photocatalytic activity is obtained₂The film has good practical value.

Test results show that the three-layer Mo and TiO prepared by the invention₂-CH₃NH₃PbI₃-Mo:TiO₂The film has excellent photocatalytic performance under both ultraviolet light and visible light.

The method has good process stability, and is used for preparing the TiO with high photocatalytic performance₂A novel method for thin films; has industrial production prospect.

Drawings

FIG. 1 shows three layers of Mo and TiO₂-CH₃NH₃PbI₃-Mo:TiO₂The film structure is shown schematically.

FIG. 2 shows the photocatalytic performance of the three-layer structure film prepared in example 1. Wherein, (a) the photoproduction current curve under the ultraviolet-visible light, the test condition: sample area 1X 1cm²The light source is a xenon lamp, the wavelength range is 200-800 nm, and the power density is 30mW/cm²The irradiation distance is 50 cm; (b) photodegradation curve of organic dye methylene blue under ultraviolet-visible light, test conditions: sample area 1X 1cm²The light source is a xenon lamp, the wavelength range is 200-800 nm, and the power density is 30mW/cm²The irradiation distance was 50 cm. The comparative sample was pure TiO of the same thickness₂A film.

Fig. 3 is a graph showing the photocatalytic performance of the three-layer structure film prepared in example 2. Wherein, (a) a photoproduction current curve under ultraviolet-visible light; (b) under ultraviolet-visible lightPhotodegradation curve of organic dye methylene blue. The test conditions were the same as in FIG. 2. The comparative sample was Mo of the same thickness: TiO 2₂A film.

Fig. 4 is a graph showing the photocatalytic performance of the three-layer structure film prepared in example 3. Wherein, (a) a photoproduction current curve under ultraviolet-visible light; (b) photodegradation curve of organic dye methylene blue under UV-visible light. The test conditions were the same as in FIG. 2. The comparative sample was Mo of the same thickness: TiO 2₂A film.

Detailed Description

Example 1:

the bottom layer and the top layer are sputtered by pure titanium dioxide: by using TiO₂The ceramic target has a substrate temperature of 80 deg.C and a total gas pressure of 0.3Pa, wherein O₂The partial pressure accounts for 1.0 percent of the total air pressure, the sputtering time is 60min, the sputtering power is 120W, and the sputtering power density is 42.5kW/m²。

Intermediate perovskite layer CH₃NH₃PbI₃Preparation: firstly PbI₂Depositing TiO on the bottom layer by using a thermal evaporation method₂Above, the sample was placed in a sealable glass container in a vacuum chamber, and CH was placed in a position opposite to the sample₃NH₃And I, sealing the glass container (in this case, the glass container is in a vacuum state). Keeping the temperature for 60min in an environment of 120 ℃. The preparation conditions were as follows: the evaporation boat is a molybdenum boat, and PbI is adopted before each evaporation₂The amount of (A) is 0.3g, the evaporation current is 100A, the time is 2min, CH₃NH₃The amount of I was 0.5 g.

The photocurrent density and photocatalytic degradation performance test results of the sample under ultraviolet-visible light are respectively shown in fig. 2(a) and fig. 2 (b). Three-layer TiO₂-CH₃NH₃PbI₃-TiO₂Photocurrent of the film sample was about 5.7 × 10^-4A/cm²Is pure TiO of the same thickness₂Thin film (photocurrent about 6X 10)^-5A/cm²) 9.5 times of the total weight of the powder. The photocatalytic degradation rate constant of the three-layer sample is-0.016, and the pure TiO with the same thickness₂The film is about-0.011, and the photocatalytic degradation rate is pure TiO₂1.45 times of the film.

Example 2:

the pure titanium dioxide layers of the bottom layer and the top layer are both changed into Mo: TiO 2₂Layer, wherein the Mo/Ti atomic ratio in the Mo-doped titania ceramic target was about 0.5%, and the other set-up conditions were the same as in example 1.

The photocurrent density and photocatalytic degradation performance test results of the sample under ultraviolet-visible light are shown in fig. 3(a) and fig. 3(b), respectively. Three layers of Mo: TiO 2₂-CH₃NH₃PbI₃-Mo：TiO₂Photocurrent of about 8.2 x 10 for the thin film sample^-4A/cm²The thickness is Mo: TiO 2₂Thin film (photocurrent about 8X 10)^-5A/cm²) 10.3 times of that of pure TiO with the same thickness₂The film was 13.7 times brighter. The photocatalytic degradation rate constant of the three-layer sample is-0.022, and the thickness of Mo: TiO 2₂The film was about-0.013, the photocatalytic degradation rate was Mo: TiO 2₂1.7 times of the film is pure TiO ₂2 times of the film.

Example 3:

mo of the bottom layer and the top layer: TiO 2₂The sputtering power in the preparation conditions of the layer was changed to 200W, and the sputtering power density was 70.8kW/m². The other conditions were the same as in example 2.

The photocurrent density and photocatalytic degradation performance test results of the sample under ultraviolet-visible light are shown in fig. 4(a) and fig. 4 (b), respectively. Three layers of Mo: TiO 2₂-CH₃NH₃PbI₃- Mo：TiO₂Photocurrent of about 8.6 x 10 for the thin film sample^-4A/cm²The thickness is Mo: TiO 2₂Thin film (photocurrent about 8X 10)^-5A/cm²) 10.8 times of that of pure TiO with the same thickness₂The film was 14.3 times light. The photocatalytic degradation rate constant of the three-layer sample is-0.026, and the ratio of Mo: TiO 2₂The film was about-0.013, the photocatalytic degradation rate was Mo: TiO 2₂2 times of the film is pure TiO₂2.4 times of the film.

Claims

1. TiO with three-layer structure₂The photocatalytic film is prepared by the following method:

the bottom layer and the top layer are Mo: TiO 2₂Layer (b): by using Mo-doped titanium dioxideThe Mo-doped titanium dioxide ceramic target has Mo/Ti atomic ratio of 0.5%, substrate temperature of 80 deg.c and total oxygen-argon gas pressure of 0.3Pa, wherein O₂The partial pressure accounts for 1.0 percent of the total air pressure, the sputtering time is 60min, the sputtering power is 200W, and the sputtering power density is 70.8kW/m²；

Intermediate perovskite layer CH₃NH₃PbI₃Preparation: firstly PbI₂Mo deposited on the bottom layer by a thermal evaporation method: TiO 2₂On top of the layer, the sample was placed in a sealable glass container in a vacuum chamber, and CH was placed in a position opposite to the sample₃NH₃I, sealing the glass container, wherein the glass container is in a vacuum state; keeping the temperature at 120 ℃ for 60 min; the preparation conditions were as follows: the evaporation boat is a molybdenum boat, and PbI is adopted before each evaporation₂The amount of (A) is 0.3g, the evaporation current is 100A, the time is 2min, CH₃NH₃The amount of I was 0.5 g.