Optical functional materials

Abstract

To provide an optical functional material constituted of a Sn oxide and capable of exhibiting sufficient performance to visible light.SOLUTION: The optical functional material contains Sn and O in an amount of more than 80 atom% in total and has peaks at 2θ=27.5±1.0°, 29.4±1.0°, 32.8±1.5°, and 35.9±1.0°, in X-ray diffraction measurement using CuKα rays. The optical functional material contains Sn and O in an amount of more than 80 atom% in total and has peaks at 2θ=27.5±1.0°, 29.4±1.0°, 32.8±1.5°, and 35.9±1.0° and additionally has peaks at one or more positions among 2θ=46.0±0.7°, 47.2±0.7°, 50.4±0.7°, 51.8±0.7°, 54.2±1.0°, 59.8±1.0°, 62.8±1.0°, and 70.1±1.0°, in X-ray diffraction measurement using CuKα rays.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a photo-functional material composed of Sn oxide.

Background Art

[0002] The above-mentioned Sn oxide is a material that exhibits photocatalytic activity upon ultraviolet irradiation, and is used as a photo-functional material in fields related to the production of useful substances by light energy, environmental purification, solar cells, and optical sensors. Here, since the Sn oxide has a low absorption rate in the visible light region, there was a risk that sufficient optical properties could not be exhibited when used in the visible light region.

[0003] Therefore, in Patent Document 1, as a photo-functional material having excellent optical properties in the visible light region, a divalent inorganic tin salt and an alkoxide of a d-block metal selected from the group consisting of titanium(IV) and zirconium(IV) are hydrothermally treated under alkaline conditions to form a tin / d-block metal composite material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, as disclosed in Patent Document 1, when adding additive elements other than Sn and O to improve the optical properties in the visible light region, there are problems such as the manufacturing process becoming complicated and the manufacturing cost increasing. In particular, when adding harmful elements or expensive rare elements, it is difficult to manage these elements, and the manufacturing cost tends to be even higher. Therefore, there is a need for optically functional materials that exhibit excellent optical properties in the visible light range, even with low content of elements other than Sn and O.

[0006] This invention has been made in view of the circumstances described above, and aims to provide a photo-functional material composed of Sn oxide that exhibits sufficient performance even in the presence of visible light. [Means for solving the problem]

[0007] To solve the above problems, the inventors conducted diligent research and found that controlling the crystal structure of Sn oxide to a specific structure improves the light absorption characteristics in the visible light range. This invention is based on this finding.

[0008] A photo-functional material according to one aspect of the present invention contains more than 80 atomic percent of Sn and O in total. It consists of Sn oxides, X-ray diffraction measurements using CuKα rays showed peaks at 2θ = 27.5±1.0°, 29.4±1.0°, 32.8±1.5°, and 35.9±1.0°. Furthermore, it has peaks at one or more of the following positions: 2θ = 46.0±0.7°, 47.2±0.7°, 50.4±0.7°, 51.8±0.7°, 54.2±1.0°, 59.8±1.0°, 62.8±1.0°, and 70.1±1.0°, and its crystal structure has a unit structure consisting of three mutually orthogonal axes, and in the atomic arrangement projected onto a plane normalized to the shortest c-axis direction, it has a hollow quadrilateral structure with four Sn atoms at its vertices. It is characterized by the following.

[0009] Furthermore, a photo-functional material according to one aspect of the present invention contains more than 80 atomic percent of Sn and O in total. It consists of Sn oxides, X-ray diffraction measurements using CuKα rays showed peaks at 2θ = 27.5±1.0°, 29.4±1.0°, 32.8±1.5°, and 35.9±1.0°, and further peaks at one or more of the following positions: 2θ = 46.0±0.7°, 47.2±0.7°, 50.4±0.7°, 51.8±0.7°, 54.2±1.0°, 59.8±1.0°, 62.8±1.0°, and 70.1±1.0°. Furthermore, the crystal structure has a unit structure consisting of three mutually orthogonal axes, and in the atomic arrangement projected onto a plane normalized to the

[0111] direction formed from these three axes, there is an atomic arrangement in which the orientation connecting the two Sn atoms in a dumbbell structure consisting of two Sn atoms is parallel to the direction in which the shortest c-axis direction is projected onto the plane, and an atomic arrangement in which the orientation connecting the two Sn atoms in a dumbbell structure consisting of two Sn atoms is orthogonal to the direction in which the shortest c-axis direction is projected onto the plane. It is characterized by the following. [Effects of the Invention]

[0012] According to the optical functional material of the present invention, since the X-ray diffraction pattern and crystal structure are defined as described above, even if the composition contains more than 80 atomic percent of Sn and O in total, it exhibits particularly excellent light absorption characteristics in the visible light range. Therefore, according to the present invention, it is possible to provide a photo-functional material composed of Sn oxide that exhibits sufficient performance even with respect to visible light. [Brief explanation of the drawing]

[0013] [Figure 1] This is an example of EDS measurement results for the Sn oxide constituting the photo-functional material of this embodiment. [Figure 2] This graph shows the atomic ratio (Sn / O) of the Sn oxides that constitute the photo-functional material of this embodiment. [Figure 3] This is a schematic diagram of the conventional crystal structure of Sn oxide. [Figure 4] This figure shows the fitting results from Rietveld analysis and the results from X-ray diffraction measurements. [Figure 5] This is a schematic diagram of the crystal structure of the Sn oxide that constitutes the photo-functional material of this embodiment. [Figure 6] This is a HAADF-STEM observation image of the Sn oxide constituting the photofunctional material of this embodiment. [Figure 7] This graph shows the light absorption characteristics of the Sn oxide that constitutes the photo-functional material of this embodiment. [Figure 8] This graph shows the measurement results of the valence electron energy edge of the Sn oxide that constitutes the optical functional material in this embodiment. [Figure 9] This graph shows the results of a manufacturing experiment for the photo-functional material according to this embodiment. [Figure 10] This graph shows the results of a manufacturing experiment for the photo-functional material according to this embodiment. [Figure 11] This graph shows the results of a carbon dioxide (CO2) reduction test when the photo-functional material of this embodiment is used as a photocatalyst. [Modes for carrying out the invention]

[0014] Below, an optical functional material, which is one embodiment of the present invention, will be described with reference to the attached figure. The optical functional material according to one embodiment of the present invention is suitably used, for example, in solar cells, photocatalysts, optical sensors, and the like.

[0015] The optical functional material according to this embodiment is composed of a tin oxide containing a total of more than 80 atomic% of Sn and O. In addition, in this embodiment, it is preferable that the atomic ratio Sn / O of Sn and O is within the range of 70% or more and less than 80%. Note that the total content of Sn and O is preferably 90 atomic% or more, more preferably 95 atomic% or more, and still more preferably 99 atomic% or more. Also, the lower limit of the atomic ratio Sn / O of Sn and O is more preferably 71% or more, and still more preferably 72% or more. On the other hand, the upper limit of the atomic ratio Sn / O of Sn and O is more preferably 79% or less, and still more preferably 78% or less. Note that the optical functional material according to this embodiment may contain one or more selected from H, Li, Be, B, C, N, F, Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sb, lanthanoids, Hf, Ta, W, Re, Os, Ir, Pt, Au, Pb, Bi in a total range of less than 20 atomic% due to unavoidable or intentional factors caused by impurities in raw materials, manufacturing processes, post-processes, handling during sample evaluation, functional evaluation, functional imparting, substrates, containers, and the like.

[0016] Here, an example of the EDS measurement result of the optical functional material according to this embodiment is shown in FIG. 1. The EDS measurement was carried out in the STEM mode with an acceleration voltage of 200 kV using a JED-2300T detector on a JEM-ARM200F manufactured by JEOL Ltd. As shown in FIG. 1, the optical functional material according to this embodiment contains a total of more than 80 atomic% of Sn and O. Also, the atomic ratio Sn / O of Sn and O is within the range of 70% or more and less than 80%. Figure 2 shows the results of measuring the atomic ratio (Sn / O) of Sn to O in the photo-functional material of this embodiment. The average value of the atomic ratio (Sn / O) is 76.2%. In other words, in the optical functional material of this embodiment, if the atomic ratio Sn / O is set to the nearest integer ratio, it can be said that it is composed of Sn3O4. Hereinafter, the Sn oxide constituting the optical functional material of this embodiment may be referred to as Sn3O4.

[0017] The optically functional material of the present invention can be confirmed, for example, by measuring the diffraction peak using an X-ray diffractometer. For example, using Rigaku Corporation's SmartLab as the X-ray diffractometer, CuKα rays can be used as the incident X-ray, and the diffraction intensity peak can be measured using the Out-of-Plane method, i.e., the θ / 2θ method, or the In-Plane method. The incident X-ray can also be concentrated or equilibrium beam. The sample used for X-ray diffraction measurement can be in powder, thin film, or bulk form. Furthermore, as long as the X-ray diffraction peak of the functional material of the present invention can be identified, the method is not limited to the Rigaku Corporation X-ray diffractometer.

[0018] Furthermore, in the Sn oxide (Sn3O4) constituting the photofunctional material of this embodiment, X-ray diffraction measurements using CuKα rays show peaks at 2θ = 27.5±1.0°, 29.4±1.0°, 32.8±1.5°, and 35.9±1.0°. Furthermore, in the Sn oxide (Sn3O4) constituting the photofunctional material of this embodiment, X-ray diffraction measurements using CuKα rays show peaks at 2θ = 27.5±1.0°, 29.4±1.0°, 32.8±1.5°, and 35.9±1.0°, and also at one or more of the following positions: 2θ = 46.0±0.7°, 47.2±0.7°, 50.4±0.7°, 51.8±0.7°, 54.2±1.0°, 59.8±1.0°, 62.8±1.0°, and 70.1±1.0°. Furthermore, in the case of the Sn oxide (Sn3O4) constituting the photofunctional material of this embodiment, it is preferable that the X-ray diffraction measurement using CuKα rays has peaks at 2θ = 27.5±0.5°, 29.4±0.5°, 32.8±0.5°, and 35.9±1.0°. Furthermore, in the case of the Sn oxide (Sn3O4) constituting the photofunctional material of this embodiment, it is even more preferable that it has peaks at 2θ = 27.5±0.2°, 29.4±0.2°, 32.8±0.2°, and 35.9±0.5° in X-ray diffraction measurements using CuKα rays. In other words, the Sn oxide (Sn3O4) constituting the photo-functional material of this embodiment differs from conventional Sn oxide (Sn3O4) in terms of the peak position in X-ray diffraction measurements and its crystal structure.

[0019] The conventional crystal structure of Sn oxide (Sn3O4) is disclosed in Figure 1(a) of J. Wang, et al., Adv. Energy Mater., 6, 201501190 (2016). Figure 3 shows a schematic diagram of the conventional crystal structure of Sn oxide (Sn3O4). In conventional sn oxides (Sn3O4), it has been confirmed that there are plate-like voids (indicated by the arrows in Figure 3) where oxygen atoms are not sandwiched between sn atoms.

[0020] Next, using CuKα-based X-ray diffraction measurements, the crystal structure of Sn oxide (Sn3O4) with peaks at 2θ = 27.5±1.0°, 29.4±1.0°, 32.8±1.5°, and 35.9±1.0° was derived by Rietveld analysis. Furthermore, the crystal structure of Sn oxide (Sn3O4) with peaks at 2θ = 27.5±1.0°, 29.4±1.0°, 32.8±1.5°, and 35.9±1.0°, and with a peak at one or more of the following positions: 2θ = 46.0±0.7°, 47.2±0.7°, 50.4±0.7°, 51.8±0.7°, 54.2±1.0°, 59.8±1.0°, 62.8±1.0°, and 70.1±1.0° was derived by Rietveld analysis. The Rietveld analysis was performed using software (Fullprof.), and the initial structure used for the analysis was the crystal structure of Sn(PbO2)2 in which Pb was replaced with Sn. For this initial structure, atomic coordinates at 300K obtained from the non-patent document JRGavarri, et al., J. Solid State Chem. 36, 81 (1981) were used, and the constraints on parameters such as atomic position, peak shape, peak intensity, and background were removed one by one to refine the structure. Subsequently, the number of parameters whose constraints were gradually removed was increased to further refine the structure, resulting in the fitting results shown above.

[0021] Figure 4 shows a comparison between the fitting results (fitted intensity) from Rietveld analysis and the X-ray diffraction measurement results (raw data). The error bar represents the difference between the raw data and the fitted intensity, but the difference is small. Therefore, the fitting results of the X-ray diffraction measurements to the obtained crystal structure were able to reproduce the X-ray diffraction measurement results of the Sn oxide (Sn3O4) constituting the optical functional material of this embodiment with extremely good accuracy.

[0022] Next, to confirm whether the crystal structure obtained by Rietveld analysis can exist stably, first-principles calculations were performed as follows. First-principles calculations using a plane wave basis and pseudopotential were employed. Quantum Espresso ver.6.7Max was used as the first-principles software, and the norm-conserving pbe-mt_fhi type was selected as the pseudopotential. PBE and dispersion force XDM were used for the exchange-correlation interaction. After confirming convergence, the wave function cutoff energy was set to 80 Ry, the electron density cutoff energy to 320 Ry, and k-point sampling was performed using the Monkhorst-Pack method with a (4,4,4) partition. The resulting partition points were then shifted in reciprocal space by a vector component equal to half the sampling interval. In the aforementioned J. Wang, et al., Adv. Energy Mater., 6, 201501190 (2016), it is pointed out that dispersion forces are important for calculating "a flat void between Sn atoms where no O atoms exist."

[0023] Therefore, we adopted the XDM described in AD Becke and ER Johnson, J. Chem. Phys. 127, 154108 (2007); ibid, 124108 (2007). as the dispersion force, and by determining the XDM parameters that reproduce the crystal structures of α-SnO and rutile-structured SnO2, for which detailed crystal structures have been reported, we confirmed the stability of the crystal structure of Sn3O4, which has an atomic ratio of Sn / O between those two. A parameter set (a1=0.9, a2=1.4) was obtained for the dispersion force XDM used to evaluate the crystal structure by first-principles calculations. From the results in Tables 1 and 2 using these parameters, it was determined that calculation conditions with predictive power for unknown crystal structures within the range of Sn-O mixed valency systems were obtained. Note that the "literature values" in Tables 1 and 2 are the values ​​described in J. Wang, et al., Adv. Energy Mater., 6, 201501190 (2016).

[0024] [Table 1]

[0025] [Table 2]

[0026] Following the above procedure, calculations were performed, and for a Sn oxide (Sn3O4) that has peaks at 2θ = 27.5±1.0°, 29.4±1.0°, 32.8±1.5°, and 35.9±1.0° in X-ray diffraction measurements using CuKα rays, and also has peaks at one or more of the following positions: 2θ = 46.0±0.7°, 47.2±0.7°, 50.4±0.7°, 51.8±0.7°, 54.2±1.0°, 59.8±1.0°, 62.8±1.0°, and 70.1±1.0°, the crystal structure confirmed to be energetically stable in first-principles calculations was found to have a unit structure consisting of three mutually orthogonal axes, as shown in Figure 5. In the atomic arrangement projected onto a plane normalized to the shortest c-axis direction, it was confirmed to have a hollow quadrilateral structure with four Sn atoms at its vertices. In this invention, "orthogonal" is defined as 90°±3°, and "parallel" is defined as 0°±3°. Also, in Figure 5, the larger spheres represent Sn atoms, and the smaller spheres represent O atoms.

[0027] Furthermore, for Sn oxides (Sn3O4) that have peaks at 2θ = 27.5±1.0°, 29.4±1.0°, 32.8±1.5°, and 35.9±1.0° in X-ray diffraction measurements using CuKα rays, and also have peaks at one or more of the following positions: 2θ = 46.0±0.7°, 47.2±0.7°, 50.4±0.7°, 51.8±0.7°, 54.2±1.0°, 59.8±1.0°, 62.8±1.0°, and 70.1±1.0°, the Sn atomic image was evaluated using high-angle scattering annular dark-field scanning transmission microscopy (HAADF-STEM). For HAADF-STEM measurements, a JEM-ARM200F from JEOL was used, and Sn atomic images were measured in STEM mode with an acceleration voltage of 200kV. Powdered samples dispersed on a Cu microgrid were used as the sample for STEM observation.

[0028] As a result, as shown in Figure 6, an arrangement of Sn atoms with high electron density was observed, confirming that the Sn oxide (Sn3O4) constituting the photofunctional material of this embodiment has a unit structure consisting of three mutually orthogonal axes, and that in the atomic arrangement projected onto a plane normalized to the

[0111] direction formed from these three axes, there is an atomic arrangement in which the orientation connecting the Sn atoms in a dumbbell structure consisting of two Sn atoms is parallel to the direction in which the shortest c-axis direction is projected onto the plane, and an atomic arrangement in which the orientation connecting the Sn atoms in a dumbbell structure consisting of two Sn atoms is orthogonal to the direction in which the shortest c-axis direction is projected onto the plane. In the schematic diagram in Figure 6, the larger spheres represent Sn atoms, and the smaller spheres represent O atoms.

[0029] Next, the light absorption characteristics of conventional sn oxide (Sn3O4) and the sn oxide (Sn3O4) constituting the photofunctional material of this embodiment were evaluated using a UV-Vis spectrophotometer. The results are shown in Figure 7. For the UV-Vis spectrophotometer, a V-670 from JASCO Corporation was used, and the wavelength range of 300-800 nm was measured using the diffuse reflectance method with an integrating sphere unit. Barium sulfate powder was used as a standard sample for calibration of the diffuse reflectance during the measurement. As shown in Figure 7, the Sn oxide (Sn3O4) constituting the photo-functional material of this embodiment is confirmed to have superior light absorption characteristics in the visible light range compared to conventional Sn oxide (Sn3O4).

[0030] Furthermore, in order to evaluate the ionization potential, i.e., the valence band energy levels, of (Orthorhombic)Sn3O4, the photofunctional material of this embodiment, the valence energy edge of a powdered sample was measured at room temperature in an atmospheric environment using RIKEN Instruments' Photoemission Yield Spectroscopy (PYS, instrument name: AC-3). The results are shown in Figure 8. As shown in Figure 8, the valence band levels of (Orthorhombic)Sn3O4, the photofunctional material of this embodiment, are shallower than those of conventional (Monoclinic)Sn3O4, and electrons can be excited with lower light energy. In other words, this is consistent with the result that (Orthorhombic)Sn3O4, the photofunctional material of this embodiment, absorbed more visible light than conventional (Monoclinic)Sn3O4 in the optical absorption spectrum. SnO, which has a narrow band gap and low photocatalytic performance, has its valence energy edge on the low energy side, while SnO2, which has a wide band gap and does not respond to visible light, has its valence energy edge on the high energy side, and conventional (Monoclinic)Sn3O4 is in between. In contrast to these, the valence energy edge of (Orthorhombic)Sn3O4, the photofunctional material of this embodiment, is located at almost the same position as SnO, and the results suggest that it has the characteristics of being both visible light responsive and having photocatalytic performance.

[0031] The reason why the Sn oxide (Sn3O4) constituting the photo-functional material of this embodiment exhibits superior light absorption characteristics in the visible light range compared to conventional Sn oxide (Sn3O4) is presumed to be as follows. In conventional sn oxides (Sn3O4), as shown in Figure 3, there are plate-like voids between sn atoms where oxygen atoms are absent. In this way, the electronic state of sn atoms facing these plate-like voids weakens the interaction between sn atoms. On the other hand, the Sn oxide (Sn3O4) constituting the photo-functional material of this embodiment has a hollow quadrilateral structure with four Sn atoms at its vertices, as shown in Figure 5. In this way, the Sn atoms facing the voids of the hollow quadrilateral have stronger interactions with each other. This is thought to enhance the light absorption characteristics in the visible light region compared to conventional Sn oxide (Sn3O4).

[0032] Furthermore, in the Sn oxide (Sn3O4) constituting the photofunctional material of this embodiment, as shown in Figure 6, it has a unit structure consisting of three mutually orthogonal axes, and in the atomic arrangement projected onto a plane normalized to the

[0111] direction formed from these three axes, it is believed that the responsiveness to visible light is improved due to the interaction between Sn atoms, resulting from the atomic arrangement in which the orientation connecting the Sn atoms in a dumbbell structure consisting of two Sn atoms is parallel to the direction in which the shortest c-axis direction is projected onto the plane, and the atomic arrangement in which the orientation connecting the Sn atoms in a dumbbell structure consisting of two Sn atoms is orthogonal to the direction in which the shortest c-axis direction is projected onto the plane.

[0033] Next, we will describe an example of a manufacturing experiment for the photo-functional material according to this embodiment. 0.90 g of stannous chloride dihydrate (SnCl2·2H2O) and 2.94 g of trisodium citrate dihydrate (Na3(C3H5O(COO)3)·2H2O) were dissolved in 10 mL of pure water. To this solution, 10 mL of 0.2 mol / L sodium hydroxide (NaOH) aqueous solution was added and stirred to obtain a raw material solution of the desired concentration. This aqueous solution was added to a 100 mL Teflon® container (a flat-bottomed Teflon® container manufactured by San-ai Kagaku Co., Ltd.) for hydrothermal reaction, and the crystalline phase could be controlled by the fill factor (%) of the aqueous solution filling the container.

[0034] In experiments where the fill factor was varied, the total volume of the solution was appropriately increased or decreased while the solution composition remained constant, and these were used as raw material solutions for synthesis. Specifically, the fill factors of the raw material solutions were set to 20%, 40%, 60%, and 80%, and the container was filled with the raw material solution and the remainder with air. Hydrothermal synthesis was performed at 180°C for 12 hours. Immediately after the hydrothermal reaction, the container was cooled with water, the sample was filtered and dried to synthesize a powdered sample, and XRD measurements were taken.

[0035] As shown in Figure 9, under conditions where the fill factor was 40% or higher, X-ray diffraction measurements using CuKα rays yielded Sn oxide (Sn3O4) with peaks at 2θ = 27.5±1.0°, 29.4±1.0°, 32.8±1.5°, and 35.9±1.0°. In particular, under conditions where the fill factor was 60% or higher, Sn oxide (Sn3O4) was obtained that had peaks at 2θ = 27.5±1.0°, 29.4±1.0°, 32.8±1.5°, and 35.9±1.0°, and further peaks at one or more of the following positions: 2θ = 46.0±0.7°, 47.2±0.7°, 50.4±0.7°, 51.8±0.7°, 54.2±1.0°, 59.8±1.0°, 62.8±1.0°, and 70.1±1.0°.

[0036] Furthermore, under conditions of a fill factor of 20%, hydrothermal synthesis was similarly performed in the headspace of the hydrothermal reaction vessel, which was filled with air as described above, as well as under conditions of air, oxygen, and nitrogen. As a result, as shown in Figure 10, in a nitrogen atmosphere, X-ray diffraction measurements using CuKα radiation revealed that Sn oxide (Sn3O4) had peaks at 2θ = 27.5±1.0°, 29.4±1.0°, 32.8±1.5°, and 35.9±1.0°, and further peaks at one or more of the following positions: 2θ = 46.0±0.7°, 47.2±0.7°, 50.4±0.7°, 51.8±0.7°, 54.2±1.0°, 59.8±1.0°, 62.8±1.0°, and 70.1±1.0°.

[0037] These experimental results suggest that, during hydrothermal synthesis, controlling the amount of oxygen in the space outside the aqueous solution when the container is filled with the aqueous solution alters the crystal structure of the resulting Sn oxide (Sn3O4).

[0038] Next, to confirm the effect of using the photo-functional material of this embodiment as a photocatalyst, a carbon dioxide (CO2) reduction test was conducted under visible light irradiation. The evaluation results are shown in Figure 11. In a closed-system glass reactor (with a quartz window for light irradiation), 40 mL of pure water, 10 mL of triethanolamine (TEAOH), and 0.1 g of the photo-functional material powder of this embodiment were mixed in the reactor using a stirring bar. During mixing, CO2 gas (G1 grade) was bubbled through a glass tube for 30 minutes.

[0039] Subsequently, a xenon lamp (Hayashi Repic, LA-410UV-3, output: 150W) was irradiated through a quartz window via an ultraviolet cutoff filter (430nm cutoff) onto the solution containing the dispersed powder of the photo-functional material according to this embodiment. At predetermined intervals, 1 mL of gas from the headspace of the reactor was collected using a gas-tight syringe (VICI Pressure-Lok syringe), and the CO concentration was analyzed using a gas chromatograph (Shimadzu BID-2010) equipped with a barrier discharge ionization detector. All evaluations were performed at room temperature of approximately 25°C.

[0040] As shown in Figure 11, CO generation was confirmed by irradiation with visible light, confirming that the photo-functional material of this embodiment can be effectively used as a photocatalyst. Carbon monoxide (CO), the reduced product, is a high-value gas that constitutes synthesis gas. Therefore, this embodiment of the photo-functional material, which has excellent photocatalytic activity in the visible light range, is particularly useful because it can generate carbon monoxide (CO) by using carbon dioxide, a greenhouse gas, as a photocatalyst in the visible light range.

[0041] As described above, in this embodiment of the optical functional material, it was confirmed that even though it is a Sn oxide (Sn3O4), it exhibits excellent optical properties in the visible light range due to having a specific crystal structure.

Claims

1. It consists of a sn oxide containing more than 80 atomic percent of Sn and O in total. In X-ray diffraction measurements using CuKα rays, peaks were found at 2θ = 27.5±1.0°, 29.4±1.0°, 32.8±1.5°, and 35.9±1.0°, and further, at one or more of the following positions: 2θ = 46.0±0.7°, 47.2±0.7°, 50.4±0.7°, 51.8±0.7°, 54.2±1.0°, 59.8±1.0°, 62.8±1.0°, and 70.1±1.0°. A photo-functional material characterized by having a crystal structure with a unit structure consisting of three mutually orthogonal axes, and in the atomic arrangement projected onto a plane normalized to the shortest c-axis direction, having a hollow quadrilateral structure with four Sn atoms at its vertices.

2. It consists of a sn oxide containing more than 80 atomic percent of Sn and O in total. In X-ray diffraction measurements using CuKα rays, peaks were found at 2θ = 27.5±1.0°, 29.4±1.0°, 32.8±1.5°, and 35.9±1.0°, and further, at one or more of the following positions: 2θ = 46.0±0.7°, 47.2±0.7°, 50.4±0.7°, 51.8±0.7°, 54.2±1.0°, 59.8±1.0°, 62.8±1.0°, and 70.1±1.0°. A photo-functional material characterized in that its crystal structure has a unit structure consisting of three mutually orthogonal axes, and in the atomic arrangement projected onto a plane normalized to the [111] direction formed from the three axes, it has an atomic arrangement in which the orientation connecting the two Sn atoms in a dumbbell structure consisting of two Sn atoms is parallel to the direction in which the shortest c-axis direction is projected onto the plane, and an atomic arrangement in which the orientation connecting the two Sn atoms in a dumbbell structure consisting of two Sn atoms is orthogonal to the direction in which the shortest c-axis direction is projected onto the plane.

Images