Nitrogen fixation method and nitrogen fixation device

Abstract

[Problem] To provide a nitrogen fixation method and a nitrogen fixation device which are capable of significantly reducing energy and cost and are easy to put into practical use. [Solution] According to the present invention, water 14, which is brought into contact with air and has dissolved the air, is brought into contact with a photocatalyst (photocatalyst layer 5), and the photocatalyst is irradiated with ultraviolet rays (light source 91), and thus ammonia, nitric acid, or nitrous acid is generated in the water 14 from nitrogen molecules in the air dissolved in the water 14 by a photocatalytic reaction.

Description

Nitrogen fixation method and nitrogen fixation device

[0001] The present invention relates to a nitrogen fixation method and a nitrogen fixation apparatus for producing ammonia and the like from nitrogen in the air.

[0002] The Haber-Bosch process has traditionally been well-known as a method for synthesizing ammonia, which is used as a chemical fertilizer, etc. In the Haber-Bosch process, nitrogen and hydrogen are reacted at 600°C and 200 atmospheres using a doubly promoted iron catalyst made of Fe3O4 to synthesize ammonia. Currently, the Haber-Bosch process is the only practical method for synthesizing ammonia. However, because it requires high temperature and pressure conditions, it requires a great deal of energy and has the drawback of being costly, including for equipment.

[0003] In response to this, various catalysts have been proposed that enable the synthesis of nitrogen and hydrogen under lower temperature conditions, such as a catalyst for ammonia synthesis that uses ruthenium (Ru) (see, for example, Patent Document 1). However, these catalysts have low reactivity and are difficult to put into practical use, and because they are all synthesis methods based on reactions based on the Haber-Bosch process, there are limitations to the energy and cost reductions that can be achieved.

[0004] JP 2006-231229 A (Japan)

[0005] In view of the above circumstances, the present invention aims to provide a method and apparatus for nitrogen fixation that can significantly reduce energy consumption and costs and can be easily put into practical use.

[0006] The present invention encompasses the following: (1) A nitrogen fixation method comprising bringing water containing dissolved air into contact with a photocatalyst and irradiating the photocatalyst with ultraviolet light, thereby generating ammonia, nitric acid, or nitrous acid in the water from nitrogen molecules in the air dissolved in the water through a photocatalytic reaction.

[0007] (2) The nitrogen fixation method according to (1), wherein a photocatalyst layer having a photocatalyst attached thereto is provided on a contact surface of a member that comes into contact with the water containing dissolved air, and the ultraviolet light is irradiated onto the photocatalyst of the photocatalyst layer, whereby ammonia, nitric acid, or nitrous acid is produced in the water from nitrogen molecules in the air that are dissolved in the water by the photocatalytic reaction on the contact surface side of the member.

[0008] (3) A nitrogen fixation device comprising: a water treatment section made of a member that comes into contact with water containing dissolved air, the contact surface of the member being provided with a photocatalytic layer made of a photocatalyst that undergoes a photocatalytic reaction in response to ultraviolet light; and an ultraviolet irradiation section that irradiates ultraviolet light onto the photocatalyst in the photocatalytic layer of the water treatment section, wherein the water is stored or circulated through the water treatment section, and the ultraviolet irradiation section irradiates the photocatalyst layer with ultraviolet light, thereby producing ammonia, nitric acid, or nitrous acid in the water from nitrogen molecules in the air that are dissolved in the water through a photocatalytic reaction.

[0009] (4) The nitrogen fixation apparatus according to (3), wherein at least a part of the contact surface of the water treatment section that comes into contact with the water is made of a glass substrate, the photocatalyst layer carrying a photocatalyst is provided on the contact surface of the glass substrate, and the ultraviolet irradiating section is provided on the surface of the glass substrate opposite the contact surface, and ultraviolet light passes through the glass substrate and irradiates the photocatalyst in the photocatalyst layer.

[0010] The nitrogen fixation method and apparatus according to the present invention, which are completely different from the Haber-Bosch process in which nitrogen and hydrogen are reacted under high temperature and pressure, do not require high temperature and high pressure conditions, and therefore can significantly reduce energy and costs and can be easily put into practical use.

[0011] 1 is a perspective view showing a nitrogen fixation apparatus according to a representative embodiment of the present invention. FIG. 2 is an exploded perspective view of the nitrogen fixation apparatus. FIG. 3 is a longitudinal cross-sectional view of the nitrogen fixation apparatus from the side. FIG. 4 is a longitudinal cross-sectional view of the nitrogen fixation apparatus from the front. FIG. 5 is an explanatory diagram showing a procedure for supporting a photocatalytic layer. FIG. 6 is an explanatory diagram showing another embodiment of the nitrogen fixation apparatus. FIG. 7 is a longitudinal cross-sectional view of the nitrogen fixation apparatus. FIG. 8 is an explanatory diagram showing yet another embodiment of the nitrogen fixation apparatus. FIG. 9 is a longitudinal cross-sectional view of the nitrogen fixation apparatus. FIG. 10 is an explanatory diagram showing yet another embodiment of the nitrogen fixation apparatus. FIG. 11 is a longitudinal cross-sectional view of the nitrogen fixation apparatus. (a) is a graph showing the measurement results of the ammonia ion concentration in Example 1, (b) is a graph showing the measurement results of the nitrate ion concentration in Example 1, and (c) is a graph showing the measurement results of the nitrite ion concentration in Example 1. FIG. 12 is a graph showing the calculation results of the total amount of fixed nitrogen in Example 1. (a) is a graph showing the measurement results of the ammonia ion concentration in Example 2, (b) is a graph showing the measurement results of the nitrate ion concentration in Example 2, and (c) is a graph showing the measurement results of the nitrite ion concentration in Example 2. FIG. 13 is a graph showing the calculation results of the total amount of fixed nitrogen in Example 2. 1A is a graph showing the measurement results of the ammonium ion concentration in Comparative Example 1, FIG. 1B is a graph showing the measurement results of the nitrate ion concentration in Comparative Example 1, and FIG. 1C is a graph showing the measurement results of the nitrite ion concentration in Comparative Example 1. FIG. 1C is a graph showing the calculation results of the total amount of fixed nitrogen in Comparative Example 1.

[0012] Next, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0013] The nitrogen fixation method of the present invention is characterized by bringing water containing dissolved air into contact with a photocatalyst and irradiating the photocatalyst with ultraviolet light, thereby producing ammonia, nitric acid, or nitrous acid in the water from the nitrogen molecules in the air dissolved in the water through a photocatalytic reaction. The water in which ammonia, nitric acid, or nitrous acid has been produced can be used as liquid fertilizer as is, or the ammonia, nitric acid, or nitrous acid can be extracted from the water and used.

[0014] Various methods are possible for dissolving air into water. For example, a water channel with an open top and exposed to air is provided as a water flow component, and air is dissolved in the water by flowing the water through the channel; a container with an open top and exposed to air is provided as a water storage or flow component, and water is stored in the container and stirred or allowed to fall; air is pumped into the water using a tube or the like (aeration); an ultrafine bubble device is used; rainwater that originally contains air is used; and various other methods are possible. The means (structures) for dissolving air into water using the nitrogen fixation devices 1, 1A, and 1B described below are merely examples.

[0015] Various methods are possible for contacting the aerated water with the photocatalyst. For example, a photocatalyst layer with a photocatalyst attached thereto may be provided on the contact surface of a member (such as a container or waterway) that comes into contact with the aerated water, a support with a photocatalyst layer formed thereon may be placed in a water container so as to be immersed in the water, or a panel over which water flows may be used as the member and a photocatalyst layer may be formed on the surface thereof, and various other methods are possible. The structures of the photocatalyst support in the nitrogen fixation devices 1, 1A, 1B, and 1C described below are merely examples.

[0016] The means for irradiating the photocatalyst of the photocatalyst layer in contact with water with ultraviolet light is not limited to irradiation from the backside of the glass plate of the photocatalyst carrier 2, as in the nitrogen fixation devices 1, 1A, and 1B described below. It does not have to be a glass plate, and irradiation may of course be through water from the front side where the photocatalyst layer is present. The ultraviolet light can be emitted from an LED substrate having an ultraviolet LED light source, but is not limited to this. It also includes a configuration in which sunlight is irradiated.

[0017] The mechanism by which ammonia is produced by photocatalytic reaction is that nitrogen atoms N dissolved in water react with OH radicals generated from water by photocatalysis. ２is broken down by breaking down the triple bond, and combines with hydrogen generated from water by the photocatalysis or with hydrogen ions in the water, producing ammonia through the following chemical reaction: N + 4H → NH4 (ammonia). The produced ammonia is then converted into O instead of hydrogen by the active oxygen generated by the photocatalytic reaction from OH radicals and oxygen dissolved in the water. ２ (active oxygen) combines with nitrite NO2, as shown in the following chemical reaction: NH4 + 4OH + O2 → NO2 + 4H2O Nitrite is further oxidized in the same way, changing into NO3.

[0018] Next, an embodiment of a nitrogen fixation apparatus for realizing the nitrogen fixation method described above will be described.

[0019] 1 to 4, the nitrogen fixation apparatus 1 according to the present invention includes containers 7 and 30 for storing or circulating water 14 containing dissolved air as components that come into contact with the water 14, a water treatment section 8 having a photocatalytic layer 5 made of a photocatalyst that undergoes a photocatalytic reaction in response to ultraviolet light on the inner surface (contact surface) of one of the containers 7 that comes into contact with the water, and an ultraviolet irradiation section 9 that irradiates ultraviolet light onto the photocatalyst in the photocatalytic layer 5 of the water treatment section 8. By storing or circulating the water in the water treatment section 8 and irradiating the photocatalytic layer 5 with ultraviolet light by the ultraviolet irradiation section 9, ammonia, nitric acid, or nitrous acid is produced in the water from nitrogen molecules in the air dissolved in the water through a photocatalytic reaction, as described above.

[0020] More specifically, at least a portion of the inner surface of the water treatment section 8 that comes into contact with the water is made of a glass substrate 4, and a photocatalyst layer 5 carrying a photocatalyst is provided on the inner surface side of the glass substrate 4. The ultraviolet irradiation section 9 is provided on the outer surface side of the glass substrate 4 opposite the contact surface, and is configured to irradiate ultraviolet light through the glass substrate 4 to the photocatalyst in the photocatalyst layer 5. The photocatalyst layer 5 has good adhesion to the glass substrate 4, and is preferably made of an aggregate of titanium oxide crystals formed by thermal hydrolysis of titanium (IV) tetrabutoxide on the surface, and titanium oxide particles having an average particle size of 1 μm or less that are carried on the surface together with the aggregate of titanium oxide crystals, using the aggregate of titanium oxide crystals as a binder.

[0021] The aggregates of titanium oxide crystals in titanium (IV) tetrabutoxide adhere to the surface 4a of an unroughened glass substrate 4. Titanium oxide particles have high photocatalytic reactivity, but when used alone, they have low adhesion to the surface 4a of an unroughened glass substrate 4. By combining the two, their mutual affinity allows the titanium oxide crystals in titanium (IV) tetrabutoxide to function as a binder supporting the titanium oxide particles, and the titanium oxide particles also penetrate between the titanium (IV) tetrabutoxide crystals, functioning as a binder to strengthen the bonds between the crystals and preventing peeling off of the crystal units.

[0022] As shown in Figure 5, the photocatalytic layer 5 is formed by first preparing a mixed solution by mixing titanium oxide particles with an average particle size of 1 μm or less with an alcohol-diluted solution of titanium(IV) tetrabutoxide (S101). The concentration of titanium(IV) tetrabutoxide in the mixed solution is 2% to 5%. The particle size of the titanium oxide particles is preferably 7 to 100 nm, with particles of 20 to 70 nm being more preferable. If the particle size is too small, ultraviolet light, decomposition substances, and adsorption substances will not reach the interior of the photocatalytic layer 5, and improved catalytic function will not be expected. The weight ratio of titanium(IV) tetrabutoxide to titanium oxide particles in the mixed solution is 0.5 to 3.

[0023] Next, this mixture is applied to the surface 4a of the glass substrate 4 (S102), and the titanium(IV) tetrabutoxide in the mixture is hydrolyzed by heating to 150°C or higher (S103). By applying the mixture to the surface of the glass substrate that has been preheated to 150°C or higher, the titanium(IV) tetrabutoxide in the mixture can be efficiently hydrolyzed. This hydrolysis converts the titanium(IV) tetrabutoxide into aggregates of titanium oxide crystals, and together with the aggregates, the photocatalyst layer carrying titanium oxide particles is formed (S104).

[0024] As shown in FIG. 2 , a pair of photocatalyst carriers 2 each comprising such a glass substrate 4 and a photocatalyst layer 5 are provided on a front and rear side of a frame 6 for a housing, which is made up of an upper plate 61, side plates 62 and 63, and a bottom plate 64, so as to close the front and rear openings 6 a and 6 b, and each photocatalyst carrier 2 is attached to the openings 6 a and 6 b with the front side on which the photocatalyst layer 5 is formed facing the inside of the frame 6 for a housing.

[0025] Water 14 is circulated and supplied inside the housing frame 6 to which each photocatalyst carrier 2 is attached, and ammonia and the like are produced in the water 14 from the air dissolved in the water 14 due to the photocatalytic reaction of the photocatalytic layer 5 of the front and rear photocatalyst carriers 2 facing the internal space. In other words, the internal space S1 of the housing frame 6 becomes the main treatment space of the water treatment unit 8.

[0026] As shown in Figures 1 to 4, a container 30 for storing water 14 is provided below the water treatment unit 8 consisting of the container 7, and between the two is a pumping passage 33 consisting of a pumping pipe 32 whose upper end is connected to an opening 64a formed in the bottom plate 64 of the housing frame 6 of the container 7 and whose lower end is connected to a pumping pump 31 arranged inside the container 30, and a return passage 35 consisting of a return pipe 34 whose one end is connected to openings 62a, 63a formed at a position above the internal space S1 in the left and right side plates 62, 63 of the frame 6 and whose other end extends into the container 30, for returning the water 14 supplied to the internal space S1 through the pumping passage 33 back to the container 30.

[0027] The water 14 supplied to the lower part of the internal space S1 of the water treatment section 8 (container 7) through the pumping path 33 flows upward through the internal space S1, generating ammonia and the like through a photocatalytic reaction caused by the photocatalyst carrier 2 in the process, and is then returned to the container 30 from an upper position through the return path 35 and supplied again to the internal space S1 of the container 7 through the pumping path 33, thereby repeatedly generating ammonia and the like through a photocatalytic reaction. The opening 61a in the upper plate 61 is an open hole that opens the upper space of the internal space S1 to the atmosphere and is configured to take in and discharge air, thereby maintaining a constant water pressure and allowing the water 14 to circulate smoothly through the pumping path 33 and the return path 35.

[0028] Regarding the supply of air (nitrogen, oxygen) into the water 14, since the containers 7 and 30 are both open to the atmosphere, the atmosphere (room air if indoors) is naturally constantly taken into the water 14 in the containers 7 and 30. In particular, since the water 14 is circulated through the pumping path 33 and the return path 35 as described above, the containers 7 and 30 are in a state where air can easily be taken in from the water surface.

[0029] In this embodiment, a tube 150 is inserted and fixed from the upper housing plate 61 of the container 7 (water treatment unit 8) into the container 7, and an aeration unit 15 is provided that supplies air from an air pump 151 through the tube 150 to the water 14 in the container 7. This allows air to be more actively supplied to the water 14 in the water treatment unit 8. Since the water 14 is circulated as described above, a similar aeration unit may be provided on the container 30 side instead of the aeration unit 15.

[0030] The supply of water 14 through the pumping channel 33 may be continuous or intermittent. The supply speed and timing can be appropriately set by controlling the pumping pump 31. In this example, water is supplied to the internal space S1 from below and returned from above, but this is not limiting. Water may be supplied from above and returned from below, or an appropriate wall may be provided in the internal space S1 to form a longer return flow path, with the pumping channel and return flow path connected at both ends of the path.

[0031] In this embodiment, the water treatment unit 8 (container 7) made up of the housing frame 6 having the photocatalyst carrier 2 is supported above by a gate-shaped support frame 11, and water is circulated between the water treatment unit 8 and the container 30 provided below, but this positional relationship is not limited to this. Also, although water circulates vertically in the internal space S1, it is of course possible to turn the housing frame 6 sideways and have the water flow horizontally.

[0032] The ultraviolet irradiation unit 9 is configured such that LED substrates 90 having ultraviolet LED light sources 91 are arranged in parallel at intervals on the back side (outside the opposite side from the internal space S1) of each photocatalyst carrier 2, and ultraviolet light is transmitted from the back side through the glass substrate 4 of the photocatalyst carrier 2 to irradiate the photocatalyst in the photocatalyst layer 5 on the front side. The LED substrate 90 is attached to the contact surface facing the photocatalyst carrier 2 of a metal support plate 92 that extends vertically and has a bent U-shaped cross section, and is configured so that heat generated by the ultraviolet LED light sources 91 can be dissipated from the support plate 92 to the outside.

[0033] To further promote heat dissipation, a metal cover plate 80, also bent in a U-shape in cross section and extending vertically, is provided outside the ultraviolet irradiation unit 9. A vertically extending gap S2 is formed between the cover plate 80 and the surface opposite the contact surface of the support plate 92, allowing outside air to be introduced / exhausted from upper and lower openings 80a, 80b. A through-hole 80c is formed in the approximate center of the cover plate 80, allowing outside air to be introduced / exhausted from the gap S2, and an electric fan 82 is provided to introduce / exhaust air through the through-hole 80c. This allows the heat generated by the ultraviolet irradiation unit 9 to be efficiently dissipated to the outside.

[0034] 6 and 7 show another embodiment of the nitrogen fixation apparatus according to the present invention. The nitrogen fixation apparatus 1A of this embodiment comprises a photocatalyst carrier 2 having a photocatalyst layer 5 provided on the outer peripheral surface of a peripheral wall 41 of a beaker-shaped glass substrate 4 having a bottom plate, and an ultraviolet irradiation unit 9 provided inside the glass substrate 4 for irradiating ultraviolet rays toward the inner peripheral surface of the peripheral wall 41.

[0035] Then, by immersing this photocatalyst carrier 2 in a container 7A containing water 14 with air dissolved in it, with the upper opening 12 above the water surface, ammonia and the like are generated from the water 14 in the container 30 that contacts the photocatalyst layer 5 on the outer surface. In this way, by immersing the photocatalyst carrier 2 as a member that comes into contact with the water 14 in the container 7A containing the water 14, ammonia and the like can be generated in the water in the container 7A by the photocatalyst layer 5 formed on the surface that comes into contact with the water 14. Here, an aeration unit 15 that actively takes in air is provided, but this is not necessary. Alternatively, water with air dissolved in it may be prepared using a separate device or the like and then supplied to the container 7A.

[0036] 8 and 9 show still another embodiment of the nitrogen fixation apparatus according to the present invention. In the nitrogen fixation apparatus 1B of this embodiment, a slider 13 (water channel) with a U-shaped cross section and a photocatalyst carrier 2 as a bottom plate is provided on a cover plate 301 of a container 30 for water 14, inclined at an appropriate angle as a member that comes into contact with the water 14, and the water 14 is supplied to the top of the slider 13 by a water pump 31 and a water pumping pipe 32, and is returned by dropping the water from the bottom into the container 30.

[0037] As shown in Figure 9, the photocatalyst carrier 2 of this example has a photocatalyst layer 5 formed on the upper surface of a plate-shaped glass substrate 4, and an ultraviolet irradiator 9 is arranged parallel to the back surface of the photocatalyst carrier 2. The photocatalyst layer 5 that forms the bottom surface of the slider 13 produces ammonia and the like in the water 14 as it flows over it. Air naturally dissolves through the open part of the slider 13, and air is actively taken into the container 30 as the water 14 falls from the slider 14.

[0038] 10 and 11 show still another embodiment of the nitrogen fixation apparatus according to the present invention. In this embodiment, a nitrogen fixation apparatus 1C includes a photocatalyst carrier 2 having a photocatalyst layer 5 provided on the inner circumferential surface of a peripheral wall 41 of an open-topped, beaker-like glass container 7C for holding water 14. An ultraviolet irradiation unit 9 for irradiating ultraviolet light toward the peripheral wall 41 is provided on the outer side of the peripheral wall 41 of the container 7C. More specifically, the ultraviolet irradiation unit 9 includes a flat, annular base plate 83 surrounding the bottom of the container 7C and a plurality of support plates 92 standing on the upper surface of the base plate at predetermined intervals in the circumferential direction. A plurality of LED substrates 90 having ultraviolet LED light sources 91 are arranged at vertical intervals on the surface of the support plate 92 facing the container 7C.

[0039] Container 7C (and ultraviolet irradiation unit 9) is placed on a stirrer device 16, and is configured so that by rotating a stirrer bar 161 placed on the bottom of container 7C using the stirrer device 16, the water 14 in container 7C can be stirred and external air can be actively dissolved into the water from the water surface. When ultraviolet light is irradiated from ultraviolet irradiation unit 9 while rotating the stirrer bar 161 in this way, the ultraviolet light passes through peripheral wall 41 and hits photocatalyst layer 5 that is in contact with the water 14 on the inner side, and the photocatalyst layer 5 can generate ammonia and the like in the water in container 7C.

[0040] Although the embodiments of the present invention have been described above, the present invention is not limited to these examples and can, of course, be embodied in various forms without departing from the spirit of the present invention. For example, although the photocatalyst carrier 2 of this embodiment is used as a component of the nitrogen fixation device 1, it is also a preferred embodiment to configure it as a panel such as a glass window panel of a building or a glass panel constituting the wall of a plant cultivation greenhouse, and to install the photocatalyst layer 5 facing outdoors so that ultraviolet rays from the sun cause a photocatalytic reaction to occur, thereby producing ammonia and the like in rainwater flowing over the outer surface of the panel that comes into contact with the photocatalyst layer.

[0041] Next, the results of a test conducted using the nitrogen fixation apparatus 1 described with reference to FIGS. 1 to 4 to confirm the effect of nitrogen fixation depending on whether a photocatalytic reaction is present or absent and whether the system is open or closed will be described.

[0042] The presence or absence of a photocatalytic reaction was determined by irradiating / non-irradiating ultraviolet light. The difference between the open system and the closed system was that the device shown in Figures 1 to 4 was an open system, while the closed system was configured such that the opening 61a was closed and the opening of the container 30 was also closed with a lid, preventing contact with the outside air after the photocatalytic reaction started due to ultraviolet light irradiation. The test for Example 1 was performed in an open system with ultraviolet light irradiation, the test for Example 2 was performed in a closed system with ultraviolet light irradiation, and the test for Comparative Example 1 was performed in an open system without ultraviolet light irradiation.

[0043] As a common feature, the photocatalyst carrier loading process began by diluting 100 ml of titanium(IV) tetrabutoxide monomer with ethanol to a 2% concentration. To this was added 4 g of a slurry containing titanium oxide particles (a slurry containing 3% titanium oxide particles with an X-ray particle size of 7 nm (Ishihara Sangyo Kaisha, Ltd.'s "ST-01") to form a mixed solution. A borosilicate glass plate was then heated to 150-350°C and sprayed with the mixed solution. As a result, the ethanol evaporated on the glass surface, and the titanium(IV) tetrabutoxide hydrolyzed to form titanium oxide crystals. At the same time, the relatively small titanium oxide particles became enmeshed in the titanium oxide crystals and were loaded onto the glass surface.

[0044] The water used was ultrapure water that had been thoroughly mixed with air beforehand. The water temperature was 25°C, the amount of water was 8 liters, and the ultraviolet light used was Nichia Corporation's "NVSU119C" U375 rank.

[0045] The effect of nitrogen fixation was confirmed by measuring the concentrations (ppm) of ammonia, nitrate, and nitrite ions in the container 30 at the same time every day using an ion chromatograph analyzer (ICA-7000, manufactured by DKK-TOA Corporation). The total amount of nitrogen fixed by ammonia, nitrate, and nitrite was calculated from the results of each measurement.

[0046] The measurement results and calculation results are shown in the graphs of Figures 12 to 17. Figure 12(a) shows the measurement results of the ammonia ion concentration in Example 1, Figure 12(b) shows the measurement results of the nitrate ion concentration in Example 1, Figure 12(c) shows the measurement results of the nitrite ion concentration in Example 1, and Figure 13 shows the calculation results of the total nitrogen fixation amount in Example 1 calculated from these results. Figure 14(a) shows the measurement results of the ammonia ion concentration in Example 2, Figure 14(b) shows the measurement results of the nitrate ion concentration in Example 2, Figure 14(c) shows the measurement results of the nitrite ion concentration in Example 2, and Figure 15 shows the calculation results of the total nitrogen fixation amount in Example 2 calculated from these results. Figure 16(a) shows the measurement results of the ammonia ion concentration in Comparative Example 1, Figure 16(b) shows the measurement results of the nitrate ion concentration in Comparative Example 1, Figure 16(c) shows the measurement results of the nitrite ion concentration in Comparative Example 1, and Figure 17 shows the calculation results of the total nitrogen fixation amount in Comparative Example 1 calculated from these results. 12 to 17, nitrogen fixation was not achieved in Comparative Example 1, in which no photocatalytic reaction occurred, whereas in the present invention (Examples 1 and 2), ammonia, nitrate, and nitrite all increased, demonstrating that nitrogen fixation progressed.

[0047] DESCRIPTION OF SYMBOLS 1, 1A, 1B, 1C Nitrogen fixation device 2 Photocatalyst carrier 4 Glass substrate 4a Surface 5 Photocatalyst layer 6 Housing frame 6a, 6b Opening 7, 7A, 7C Container 8 Water treatment section 9 Light irradiation section 11 Support frame 12 Opening 13 Slider 14 Water 15 Aeration section 16 Stirrer device 30 Container 31 Water pump 32 Water pumping pipe 33 Water pumping path 34 Circumferential flow pipe 35 Circumferential flow path 41 Peripheral wall 61 Top plate 61a Open hole 62, 63 Side plates 62a, 63a Opening 64 Bottom plate 64a Opening 80 Cover plate 80a, 80b Opening 80c Through hole 82 Electric fan 90 LED substrate 91 Light source 92 Support plate 93 Base plate 150 Tube 151 Air pump 161 Stirring bar 301 Cover plate S1 Internal space S2 Gap

Claims

1. A nitrogen fixation method comprising contacting water containing dissolved air with a photocatalyst and irradiating the photocatalyst with ultraviolet light, thereby producing ammonia, nitric acid, or nitrous acid in the water from nitrogen molecules in the air that are dissolved in the water through a photocatalytic reaction.

2. The nitrogen fixation method according to claim 1, wherein a photocatalyst layer having a photocatalyst attached thereto is provided on a contact surface of a member that comes into contact with the water containing dissolved air, and the photocatalyst of the photocatalyst layer is irradiated with the ultraviolet light, thereby generating ammonia, nitric acid, or nitrous acid in the water from nitrogen molecules in the air that are dissolved in the water through the photocatalytic reaction on the contact surface side of the member.

3. A nitrogen fixation device comprising: a water treatment unit consisting of a member that comes into contact with water containing dissolved air, the contact surface of the member being provided with a photocatalytic layer made of a photocatalyst that causes a photocatalytic reaction in response to ultraviolet light; and an ultraviolet irradiation unit that irradiates ultraviolet light onto the photocatalyst in the photocatalytic layer of the water treatment unit, wherein the water is stored or circulated through the water treatment unit, and the ultraviolet irradiation unit irradiates the photocatalyst layer with ultraviolet light, thereby producing ammonia, nitric acid, or nitrous acid in the water from nitrogen molecules in the air that are dissolved in the water through a photocatalytic reaction.

4. A nitrogen fixation apparatus according to claim 3, wherein at least a portion of the contact surface of the water treatment section that comes into contact with the water is made of a glass substrate, the photocatalyst layer carrying a photocatalyst is provided on the contact surface of the glass substrate, and the ultraviolet irradiating section is provided on the surface of the glass substrate opposite the contact surface and irradiates ultraviolet light that passes through the glass substrate and onto the photocatalyst in the photocatalyst layer.

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