A method and device for photocatalytic degradation of ammonia gas

Abstract

The application provides a method and device for photocatalytic degradation of ammonia, and relates to the technical field of odor treatment.The method for photocatalytic degradation of ammonia provided by the application comprises the following steps: preparing a Cu / TiO2 catalyst film on the surface of a substrate; and introducing a gas to be treated into the surface of the Cu / TiO2 catalyst film, and performing a photocatalytic reaction under light to degrade ammonia in the gas to be treated.The application can efficiently and at low cost achieve the purpose of removing ammonia by using photocatalytic technology based on the Cu / TiO2 catalyst film.Compared with the prior art, the application has a wide application range, a rapid reaction, low energy consumption, low cost, easy operation and convenience in application, and has great application potential in odor treatment in sewage treatment plants and kitchen waste treatment plants.

Description

Technical Field

[0001] This invention relates to the field of odor treatment technology, specifically to a method and apparatus for photocatalytic degradation of ammonia. Background Technology

[0002] Odors are typically generated during wastewater treatment and conventional food waste disposal. Therefore, odor problems have become an unavoidable issue in wastewater and food waste treatment. The composition of odors is complex and greatly influenced by the substrate; studies show that ammonia is one of the main odor-causing substances. Currently, deodorization technologies can be broadly categorized into physical, chemical, biological, and combined methods. Physical methods mainly include adsorption; chemical methods mainly include chemical absorption and oxidation; and biological methods mainly include soil treatment, biofilters, biotrickling filtration, and biowashing.

[0003] In recent years, photocatalytic oxidation technology has been widely used to degrade various pollutants in the environment due to its advantages of high efficiency, relatively low cost, and no secondary pollution. It is considered one of the most practical methods because photocatalysis can better control the generation of free radicals and utilize solar radiation as energy input. Among photocatalyst materials, TiO2 has the advantages of low cost, non-toxicity, and strong chemical stability. Therefore, TiO2 is considered a suitable catalyst for the photocatalytic removal of ammonia. However, TiO2 photocatalysis suffers from low efficiency and difficulty in recycling. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for photocatalytic degradation of ammonia. This invention utilizes a Cu / TiO2 catalyst film to remove ammonia, which can improve catalytic efficiency, and the Cu / TiO2 catalyst film is easier to recover.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for photocatalytic degradation of ammonia, comprising the following steps:

[0007] A Cu / TiO2 catalyst film was prepared on the substrate surface;

[0008] The gas to be treated is introduced into the surface of the Cu / TiO2 catalyst film, and under light irradiation, a photocatalytic reaction is carried out to degrade the ammonia in the gas to be treated.

[0009] Preferably, the method for preparing the Cu / TiO2 catalyst film includes: preparing Cu / TiO2 powder by photoreduction deposition; mixing the Cu / TiO2 powder and a dispersant to obtain a mixed slurry; and coating the mixed slurry onto a substrate surface to obtain a Cu / TiO2 catalyst film.

[0010] Preferably, the method for preparing the Cu / TiO2 powder includes: mixing copper salt, water, sacrificial agent and titanium dioxide powder, and carrying out a reduction reaction under light irradiation to obtain Cu / TiO2 powder.

[0011] Preferably, the mass ratio of copper to titanium dioxide in the Cu / TiO2 powder is 0.25 to 5:100.

[0012] Preferably, the substrate comprises a titanium sheet, a copper sheet, glass, or ITO conductive glass.

[0013] Preferably, the photocatalytic reaction is carried out in a closed reactor.

[0014] Preferably, the concentration of ammonia in the gas to be treated is 10–50 mg / m³. 3 .

[0015] Preferably, the residence time of the gas to be treated on the surface of the Cu / TiO2 catalyst film is 12 to 36 s.

[0016] The present invention provides an apparatus for photocatalytic degradation of ammonia, comprising a reactor; the reactor is provided with a Cu / TiO2 catalyst film inside.

[0017] Preferably, the reactor is a closed reactor.

[0018] This invention provides a method for photocatalytic degradation of ammonia, comprising the following steps: preparing a Cu / TiO2 catalyst film on a substrate surface; introducing a gas to be treated onto the surface of the Cu / TiO2 catalyst film; and, under illumination, carrying out a photocatalytic reaction to degrade ammonia in the gas. This invention utilizes photocatalytic technology based on the Cu / TiO2 catalyst film to degrade ammonia. Cu, as a transition metal, can coordinate with ammonia and synergistically work with TiO2, achieving efficient and low-cost ammonia removal. Compared with existing technologies, this invention has a wide applicability, rapid reaction, low energy consumption, low cost, ease of operation, and convenient application, showing great potential for odor treatment in wastewater treatment plants and food waste treatment plants. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the device for photocatalytic degradation of ammonia in an embodiment of the present invention; Figure 1 In the diagram, 1 is a gas cylinder, 2 is a flow meter, 3 is the first valve, 4 is the air inlet, 5 is a Cu / TiO2 catalyst film, 6 is a light source, 7 is the air outlet, 8 is the second valve, and 9 is the absorption tank.

[0020] Figure 2 A schematic diagram of the fabrication process of Cu / TiO2 catalyst thin films;

[0021] Figure 3 This is a schematic diagram of the photocatalytic ammonia removal reaction device in the embodiment;

[0022] Figure 4 This is a schematic diagram illustrating the effect of different copper to titanium dioxide mass ratios on ammonia degradation in Examples 1-5;

[0023] Figure 5 This is a schematic diagram illustrating the effect of different gas residence times on ammonia degradation in Examples 6-10;

[0024] Figure 6 This is a schematic diagram illustrating the effect of different copper and different gas residence times on the degradation effect of ammonia in Examples 11-15. Detailed Implementation

[0025] This invention provides a method for photocatalytic degradation of ammonia, comprising the following steps:

[0026] A Cu / TiO2 catalyst film was prepared on the substrate surface;

[0027] The gas to be treated is introduced into the surface of the Cu / TiO2 catalyst film, and under light irradiation, a photocatalytic reaction is carried out to degrade the ammonia in the gas to be treated.

[0028] This invention prepares a Cu / TiO2 catalyst film on a substrate surface. In this invention, the substrate preferably comprises a titanium sheet, a copper sheet, glass, or ITO conductive glass. In this invention, the thickness of the Cu / TiO2 catalyst film is preferably 0.01–0.3 mm, more preferably 0.06–0.1 mm. In this invention, the mass ratio of copper to titanium dioxide in the Cu / TiO2 catalyst film is preferably 0.25–5:100.

[0029] In this invention, the preferred method for preparing the Cu / TiO2 catalyst film includes: preparing Cu / TiO2 powder by photoreduction deposition; mixing the Cu / TiO2 powder and a dispersant to obtain a mixed slurry; and coating the mixed slurry onto a substrate surface to obtain a Cu / TiO2 catalyst film.

[0030] In this invention, the preferred method for preparing the Cu / TiO2 powder includes: mixing copper salt, water, a sacrificial agent, and titanium dioxide powder, and carrying out a reduction reaction under light irradiation to obtain Cu / TiO2 powder. In this invention, the mixing of the copper salt, water, sacrificial agent, and titanium dioxide powder is preferably carried out by: dissolving the copper salt in water, sequentially adding the sacrificial agent and titanium dioxide powder, and stirring in the dark. In this invention, the copper salt contains or decomposes in aqueous solution to produce copper ions (Cu). 2+ ) and / or cuprous ions (Cu +The copper salt is preferably copper sulfate pentahydrate. In this invention, the water is preferably deionized water. In this invention, the sacrificial agent is preferably anhydrous ethanol. In this invention, the titanium dioxide powder is preferably titanium dioxide P25. In this invention, the mass ratio of the copper salt to water is preferably 1:25-510, more preferably 1:63-255; the volume ratio of the sacrificial agent to water is preferably 1:1-20, more preferably 1:10. In this invention, the stirring time in the dark is preferably 10 min. Stirring in the dark in this invention prevents the copper salt and titanium dioxide powder from absorbing impurities under visible light. In this invention, a high-pressure mercury lamp is preferably used to provide illumination; the dominant wavelength of the high-pressure mercury lamp is preferably 254 nm. In this invention, the high-pressure mercury lamp is preferably inserted into the solution to provide illumination. In this invention, the reduction reaction time is preferably 1 h; the reduction reaction temperature is preferably 20-30°C. This invention utilizes photoreduction deposition to reduce and deposit Cu (divalent copper and zero-valent copper) onto the surface of titanium dioxide powder. After the reduction reaction, the present invention preferably filters, washes and dries the resulting system in sequence to obtain Cu / TiO2 powder.

[0031] In this invention, the preferred mass ratio of copper to titanium dioxide in the Cu / TiO2 powder is 0.25 to 5:100.

[0032] After obtaining Cu / TiO2 powder, the present invention preferably mixes the Cu / TiO2 powder with a dispersant to obtain a mixed slurry. In the present invention, the dispersant is preferably anhydrous ethanol. In the present invention, the mixing is preferably ultrasonic mixing; the ultrasonic mixing power is preferably 50-100W, more preferably 60-80W; the ultrasonic mixing time is preferably 60 min. In the present invention, the concentration of Cu / TiO2 powder in the mixed slurry is preferably 50-200 mg / mL, more preferably 100-150 mg / mL.

[0033] After obtaining the mixed slurry, the present invention preferably coats the mixed slurry onto the surface of a substrate to obtain a Cu / TiO2 catalyst film. Before coating, the substrate is preferably cleaned and dried sequentially. In the present invention, the cleaning preferably includes a first water wash, an ethanol wash, and a second water wash performed sequentially. In the present invention, the first water wash and ethanol wash are preferably performed three times; the second water wash is preferably performed under ultrasonic conditions; and the second water wash time is preferably 20 minutes. In the present invention, the first water wash and the second water wash are preferably deionized water washes; and the ethanol wash is preferably anhydrous ethanol wash.

[0034] In this invention, the coating is preferably drop-coating. Preferably, after coating, the resulting material is dried to obtain a Cu / TiO2 catalyst film. In this invention, the coating amount of the mixed slurry is preferably 50–300 mL / m³. 2 In this invention, the drying temperature is preferably 60°C; the drying time is preferably 24 hours.

[0035] After obtaining the Cu / TiO2 catalyst film, the present invention introduces the gas to be treated onto the surface of the Cu / TiO2 catalyst film, and performs a photocatalytic reaction under light irradiation to degrade ammonia in the gas to be treated. In the present invention, the concentration of ammonia in the gas to be treated is preferably 10-50 mg / m³. 3 More preferably 40 mg / m 3 In this invention, the light source providing the illumination conditions is preferably a mercury lamp, a xenon lamp, or a tungsten lamp.

[0036] In this invention, the photocatalytic reaction is preferably carried out in a closed reactor. In this invention, the residence time of the gas to be treated on the surface of the Cu / TiO2 catalyst film is preferably 12–36 s, more preferably 14 s. In the photocatalytic reaction process of this invention, the reaction that occurs is as follows: This invention also provides a device for photocatalytic degradation of ammonia, comprising a reactor; the reactor is internally disposed of with a Cu / TiO2 catalyst film. In one embodiment of this invention, the reactor is a closed reactor. In another embodiment of this invention, the reactor is made of plexiglass. In another embodiment of this invention, the reactor includes an inlet for introducing the gas to be treated. In another embodiment of this invention, the reactor includes an outlet for discharging the gas produced by the photocatalytic reaction. In another embodiment of this invention, the inlet and outlet are respectively located on opposite sides of the reactor.

[0037] As an embodiment of the present invention, the photocatalytic degradation device for ammonia further includes a light source. In this invention, the light source is a light source capable of exciting the separation of photogenerated electrons and holes in the Cu / TiO2 catalyst film, specifically preferably a mercury lamp, xenon lamp, or tungsten lamp, and more preferably an ultraviolet lamp with a dominant wavelength of 254 nm. The present invention does not have special requirements regarding the position of the light source, as long as it can irradiate the surface of the Cu / TiO2 catalyst film. In a specific embodiment of the present invention, when the Cu / TiO2 catalyst film is disposed at the bottom of the reactor, the light source is disposed at the top of the reactor.

[0038] As an embodiment of the present invention, the photocatalytic degradation device for ammonia further includes an absorption cell for absorbing unreacted ammonia. In the present invention, the absorption cell is filled with an absorbent liquid; the composition of the absorbent liquid is preferably a 0.005 mol / L dilute sulfuric acid aqueous solution.

[0039] In a specific embodiment of the present invention, the photocatalytic degradation device for ammonia is as follows: Figure 1 As shown, the reactor comprises a gas cylinder 1, a reactor, and an absorption tank 9 connected in sequence. The reactor is a closed reactor. A Cu / TiO2 catalyst film 5 is installed at the bottom of the reactor. A light source 6 is installed at the top of the reactor. The gas cylinder 1 and the reactor's inlet 4 are connected by an inlet pipe. A flow meter 2 and a first valve 3 are installed on the inlet pipe. The reactor's outlet 7 and the absorption tank 9 are connected by an outlet pipe. A second valve 8 is installed on the outlet pipe. The absorption tank 9 is filled with an absorbent liquid.

[0040] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0041] Examples 1-5

[0042] The experimental procedure is as follows Figure 2 As shown in Figure S1, Cu / TiO2 powder was prepared using photoreduction deposition: 0.0098 g, 0.0196 g, 0.0393 g, 0.0786 g, and 0.196 g of copper sulfate pentahydrate were dissolved in 5 mL of deionized water, and then 10% of the total solution volume of anhydrous ethanol was added as a sacrificial agent and stirred until homogeneous. According to the mass ratio of copper to titanium dioxide, titanium dioxide powder was added to the above mixed solution and stirred in the dark for 10 min. A 254 nm main wavelength submersible mercury lamp was inserted into the solution and irradiated for 1 h. After filtration, washing, and drying, Cu / TiO2 powder was obtained.

[0043] S2, Preparation of Cu / TiO2 catalyst film by drop coating: Glass was used as a substrate and cleaned three times each with deionized water and anhydrous ethanol. The substrate was then immersed in deionized water and ultrasonically cleaned for 20 min, followed by drying. The Cu / TiO2 powder was mixed with anhydrous ethanol as a dispersant and ultrasonically dispersed (80 W power) for 60 min to form a mixed drop coating slurry with a Cu / TiO2 powder concentration of 100 mg / mL. The dried substrate was placed horizontally, and the mixed drop coating slurry was slowly dripped onto the substrate surface using a dropper until the slurry uniformly covered the substrate surface. The substrate was then dried at 60°C for 24 h to obtain a Cu / TiO2 catalyst film with a thickness of 0.06 mm. In Examples 1-5, the mass ratios of Cu and TiO2 in the Cu / TiO2 catalyst films were 0.25%, 0.5%, 1%, 2%, and 5%, respectively.

[0044] S3, Photocatalytic removal of ammonia: Utilizing... Figure 3 The apparatus shown introduces ammonia gas into a closed reactor via an inlet pipe, with an ammonia concentration of 40 mg / m³. 3 The exhaust gas is discharged into the absorption tank through the outlet pipe. The Cu / TiO2 catalyst film is fixed at the bottom of the sealed reactor, and a 254nm ultraviolet lamp is installed at the top of the sealed reactor. The absorption tank is filled with a 0.005mol / L dilute sulfuric acid aqueous solution. Valves are opened to control the inlet and outlet flow rates, allowing ammonia to flow on the surface of the Cu / TiO2 catalyst film, with a residence time controlled at 14s. The built-in light source in the reactor is turned on to irradiate the film surface for photocatalytic reaction. Samples of the absorbent are taken at fixed time intervals to test the ammonia nitrogen concentration, thereby calculating the ammonia removal rate. The results are as follows: Figure 4 As shown.

[0045] Depend on Figure 4 It can be seen that at a residence time of 14 seconds, 40 mg / m³ 3 Ammonia removal rates ranged from 60% to 80% under five different catalyst conditions. The ammonia removal rate increased with increasing Cu percentage, but excessive Cu content actually decreased the ammonia removal rate.

[0046] Examples 6-10

[0047] S1. Cu / TiO2 powder was prepared by photoreduction deposition: 0.0393 g of copper sulfate pentahydrate was dissolved in 5 mL of deionized water, and then 10% of the total solution volume of anhydrous ethanol was added as a sacrificial agent and stirred until homogeneous. Titanium dioxide powder was added to the above mixed solution according to the mass ratio of copper to titanium dioxide, and stirred in the dark for 10 min. A 254 nm main wavelength submersible mercury lamp was inserted into the solution and irradiated for 1 h. After filtration, washing and drying, Cu / TiO2 powder was obtained.

[0048] S2. Preparation of Cu / TiO2 catalyst film by drop coating: Glass was used as a substrate and cleaned three times each with deionized water and anhydrous ethanol. The substrate was then immersed in deionized water and ultrasonically cleaned for 20 min, followed by drying. The Cu / TiO2 powder was mixed with anhydrous ethanol as a dispersant and ultrasonically dispersed (80 W) for 60 min to form a mixed drop coating slurry with a Cu / TiO2 powder concentration of 100 mg / mL. The dried substrate was placed horizontally, and the mixed drop coating slurry was slowly dripped onto the substrate surface using a dropper until the slurry uniformly covered the substrate surface. The substrate was then dried at 60°C for 24 h to obtain a Cu / TiO2 catalyst film with a thickness of 0.06 mm. The mass ratio of Cu to TiO2 in the Cu / TiO2 catalyst film was 1%.

[0049] S3, Photocatalytic removal of ammonia: Utilizing... Figure 3 The apparatus shown introduces ammonia gas into a closed reactor via an inlet pipe, with an ammonia concentration of 40 mg / m³. 3 The exhaust gas is discharged into the absorption tank through the outlet pipe. The Cu / TiO2 catalyst film is fixed at the bottom of the sealed reactor, and a 254nm ultraviolet lamp is installed at the top of the sealed reactor. The absorption tank is filled with a 0.005mol / L dilute sulfuric acid aqueous solution. Valves are opened to control the inlet and outlet flow rates, allowing ammonia to flow on the surface of the Cu / TiO2 catalyst film. The residence times are controlled at 12s, 14s, 18s, 24s, and 36s. The built-in light source in the reactor is turned on to irradiate the film surface for photocatalytic reaction. Samples of the absorbent are taken at fixed time intervals to test the ammonia nitrogen concentration, thereby calculating the ammonia removal rate. The results are as follows: Figure 5 As shown.

[0050] Depend on Figure 5 It can be seen that a 1% Cu / TiO2 catalyst film is effective against 40 mg / m³ catalysts. 3 The ammonia removal rate is between 60% and 100%. Within a time frame of 12 to 36 seconds, as the time increases, the ammonia will fully react with the free radicals generated by photocatalysis, thereby increasing the ammonia removal rate.

[0051] Examples 11-15

[0052] S1. Cu / TiO2 powder was prepared by photoreduction deposition: 0.0098 g, 0.0196 g, 0.0393 g, 0.0786 g, and 0.196 g of copper sulfate pentahydrate were dissolved in 5 mL of deionized water, and then 10% of the total solution volume of anhydrous ethanol was added as a sacrificial agent and stirred until homogeneous. Titanium dioxide powder was added to the above mixed solution according to the mass ratio of copper to titanium dioxide, and stirred in the dark for 10 min. A 254 nm main wavelength submersible mercury lamp was inserted into the solution and irradiated for 1 h. After filtration, washing, and drying, Cu / TiO2 powder was obtained.

[0053] S2, Preparation of Cu / TiO2 catalyst film by drop coating: Glass was used as the substrate and cleaned three times each with deionized water and anhydrous ethanol. The substrate was then immersed in deionized water and ultrasonically cleaned for 20 min, followed by drying. The Cu / TiO2 powder was mixed with anhydrous ethanol as a dispersant and ultrasonically dispersed (80 W power) for 60 min to form a mixed drop coating slurry with a Cu / TiO2 powder concentration of 100 mg / mL. The dried substrate was placed horizontally, and the mixed drop coating slurry was slowly dripped onto the substrate surface using a dropper until the slurry uniformly covered the substrate surface. The substrate was then dried at 60°C for 24 h to obtain a Cu / TiO2 catalyst film with a thickness of 0.06 mm. In Examples 11-15, the mass ratios of Cu and TiO2 in the Cu / TiO2 catalyst films were 0.25%, 0.5%, 1%, 2%, and 5%, respectively.

[0054] S3, Photocatalytic removal of ammonia: Utilizing... Figure 3 The apparatus shown introduces ammonia gas into a closed reactor via an inlet pipe, with an ammonia concentration of 40 mg / m³. 3 The exhaust gas is discharged into the absorption tank through the outlet pipe; the Cu / TiO2 catalyst film is fixed at the bottom of the sealed reactor, and a 254nm ultraviolet lamp is installed at the top of the sealed reactor; the absorption tank is filled with a 0.005mol / L dilute sulfuric acid aqueous solution; the valves are opened to control the inlet and outlet flow rates, allowing ammonia to flow on the surface of the Cu / TiO2 catalyst film, and the residence time in each embodiment is controlled to be 12s, 14s, 18s, 24s, and 36s, respectively; the light source built into the reactor is turned on to irradiate the film surface for photocatalytic reaction, and samples of the absorbent liquid are taken at fixed time intervals to test the ammonia nitrogen concentration, thereby calculating the ammonia removal rate, and the results are as follows. Figure 6 As shown.

[0055] Depend on Figure 6 It can be seen that the five catalysts have an effect on 40 mg / m³ within 12–36 s. 3 The ammonia removal rate was generally between 50% and 100%, with 5wt% Cu / TiO2 (the mass ratio of Cu to TiO2 in the Cu / TiO2 catalyst film being 5%) showing the lowest ammonia removal rate compared to other catalysts. Specifically, when the residence time was <15s, 2wt% Cu / TiO2 (the mass ratio of Cu to TiO2 in the Cu / TiO2 catalyst film being 2%) achieved the highest ammonia removal rate of 75%; when the residence time was >15s, 0.5wt% Cu / TiO2 (the mass ratio of Cu to TiO2 in the Cu / TiO2 catalyst film being 0.5%) showed the highest ammonia removal rate, reaching 97% at 36s.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for photocatalytic degradation of ammonia, characterized in that, Includes the following steps: A Cu / TiO2 catalyst film was prepared on the substrate surface; The gas to be treated is introduced into the surface of the Cu / TiO2 catalyst film, and under light irradiation, a photocatalytic reaction is carried out to degrade the ammonia in the gas to be treated. The method for preparing the Cu / TiO2 catalyst film includes: Cu / TiO2 powder was prepared by photoreduction deposition; the Cu / TiO2 powder and a dispersant were mixed to obtain a mixed slurry; the mixed slurry was coated on the surface of a substrate to obtain a Cu / TiO2 catalyst film. The thickness of the Cu / TiO2 catalyst film is 0.01~0.3 mm; The preparation method of the Cu / TiO2 powder includes: mixing copper salt, water, sacrificial agent and titanium dioxide powder, and carrying out a reduction reaction under light irradiation to obtain Cu / TiO2 powder; The copper element in the Cu / TiO2 powder is divalent copper and zero-valent copper.

2. The method according to claim 1, characterized in that, The mass ratio of copper to titanium dioxide in the Cu / TiO2 powder is 0.25~5:

100.

3. The method according to claim 1, characterized in that, The substrate includes titanium sheets, copper sheets, glass, or ITO conductive glass.

4. The method according to claim 1, characterized in that, The concentration of ammonia in the gas to be treated is 10~50 mg / m³. 3 .

5. The method according to claim 1 or 4, characterized in that, The residence time of the gas to be treated on the surface of the Cu / TiO2 catalyst film is 12~36s.

6. A device for photocatalytic degradation of ammonia, characterized in that, The apparatus includes a reactor; a Cu / TiO2 catalyst film is disposed inside the reactor; the reactor is a closed reactor; the photocatalytic degradation of ammonia further includes a light source, wherein when the Cu / TiO2 catalyst film is disposed at the bottom of the reactor, the light source is disposed at the top of the reactor; the photocatalytic degradation of ammonia further includes an absorption tank filled with an absorbent liquid; the absorbent liquid is composed of a 0.005 mol / L dilute sulfuric acid aqueous solution, and the Cu / TiO2 catalyst film is the Cu / TiO2 catalyst film prepared by the method described in any one of claims 1 to 5.

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