JP7391298B2 - Method for producing nitrogen element-doped titanium oxide - Google Patents

Description

The present invention relates to a method for producing a photocatalyst material, and particularly to a method for doping titanium oxide (TiO ₂ ) with nitrogen.

When TiO ₂ is irradiated with light having a wavelength shorter than 387 nm, it reacts with water to generate active oxygen species. Reactive oxygen species have strong oxidizing power and have a decomposing effect on chemicals and bacteria. TiO ₂ is used as a photocatalytic material because it has the property of exhibiting a decomposition effect upon irradiation with such light.

Since TiO ₂ has a wide bandgap and responds only to so-called ultraviolet light with a wavelength shorter than 387 nm, it cannot exhibit its maximum performance in an environment where the amount of ultraviolet light irradiation is small. In order to solve this problem, it is known that response characteristics to visible light can be obtained by doping TiO ₂ with nitrogen (N) element (see, for example, Non-Patent Document 1).

"Mechanism for Visible Light Responses in Anodic Photocurrents at N-Doped TiO2 Film Electrodes" Journal of Physical Chemistry B 108, 30, 10617-10620 (2004)

However, methods for doping TiO ₂ with N element include plasma reaction, N ion sputtering and heat treatment (annealing) to reconstruct the crystal structure, firing in a gas atmosphere at an extremely high temperature, and special catalysts. Methods based on the reactions used have been proposed. However, neither method could efficiently dope TiO ₂ with N element at low cost.

An object of the present invention is to solve the above problems and provide an efficient method for producing N element-doped TiO ₂ .

In order to solve the above problems, the method for manufacturing N element-doped TiO ₂ according to the present invention includes the steps of arranging target TiO ₂ at a predetermined position in a vacuum chamber, evacuating the vacuum chamber, and using a nozzle. and a step of irradiating a target with a supersonic molecular beam of NO molecules from the nozzle while maintaining the nozzle at a predetermined temperature. The predetermined temperature is preferably in the range of 1180K to 1420K.

FIG. 2 is a schematic diagram illustrating the configuration of a doping device. It is a flowchart which shows the procedure of a doping process. The results of XPS measurements near the 1s orbit of the N element are shown for the TiO ₂ thin film before and after being irradiated with a supersonic molecular beam of NO molecules. The results of XPS measurements near the 2p _3/2 orbit of Ti are shown for the TiO ₂ thin film before and after being irradiated with a supersonic molecular beam of NO molecules. The results of XPS measurements near the valence band are shown for the TiO ₂ thin film before and after being irradiated with a supersonic molecular beam of NO molecules.

Embodiments of the present invention will be described below based on the drawings. In the following description, the same members are given the same reference numerals, and the description of the members that have been described once will be omitted as appropriate.

[Configuration of doping device]
FIG. 1 is a schematic diagram illustrating the configuration of a doping apparatus 1 used in the method for producing N element-doped TiO ₂ according to the present embodiment.

The doping apparatus 1 includes a vacuum chamber 2, a vacuum pump 3, a target holder 4, a beam source 5, a nozzle 6, and a nozzle heater 7.

The vacuum chamber 2 has a structure in which the inside can be sealed so that the internal pressure can be different from the external pressure. Although not shown in FIG. 1, the vacuum chamber 2 includes a gate valve for taking in and taking out the target T, a transport mechanism for transporting the target T, a leak valve for introducing the atmosphere into the vacuum chamber 2, and the like. Be prepared.

The vacuum pump 3 is a pump for reducing the pressure inside the vacuum chamber 2 from the outside, and reduces the pressure inside the vacuum chamber 2 to a high vacuum (for example, 5×10 ⁻⁸ Pa or less). Any vacuum pump 3 may be used as long as it can reduce the pressure inside the vacuum chamber 2 to a desired degree of vacuum, and for example, a rotary pump, a diffusion pump, a turbomolecular pump, etc. may be used alone or in combination. The target holding unit 4 holds a TiO ₂ material serving as a target T in the vacuum chamber 2 at a position where the supersonic molecular beam B is irradiated. Note that the TiO ₂ material serving as the target T may be in any form such as a substrate, a thin film, or a powder.

The beam source 5 contains molecules (in this example, nitric oxide (NO) molecules) to irradiate the target T, and supplies them to the nozzle 6 . The nozzle 6 communicates the interior space of the vacuum chamber 2 with the doping device 1 through a pore, and ejects the molecules contained in the beam source 5 as a supersonic molecular beam B into the vacuum chamber 2 under reduced pressure. The nozzle heater 7 is a heat source for heating the nozzle 6 to a desired temperature.

[Procedure/Method]
Next, a procedure for doping nitrogen (N) into a TiO ₂ substrate serving as a target T using the doping apparatus configured as described above will be described.

FIG. 2 is a flowchart showing the procedure of doping processing in this embodiment.
In the doping process, first, the target T is introduced into the vacuum chamber 2, and the target T is held at a predetermined position by the target holding section 4 (step S100). As the TiO ₂ used as the target T, it is preferable to use anatase-type TiO ₂ . Subsequently, the vacuum chamber 2 is sealed and evacuated by the vacuum pump 3 to reduce the pressure inside the vacuum chamber 2 to a desired pressure (for example, 5×10 ⁻⁸ Pa or less) (step S110).

Subsequently, the nozzle 6 is heated to a desired temperature (eg, preferably 1100 K (826.85° C.) or higher, more preferably in the range of 1180 K to 1420 K) by the nozzle heater 7 (step S120). Then, while maintaining the nozzle 6 at a desired temperature, the NO molecules contained in the beam source 5 are ejected into the vacuum chamber 2 from the pores of the nozzle 6 (step S130). At this time, the NO molecules are heated by the nozzle 6 and irradiated onto the target T as a supersonic molecular beam B. The translational energy of NO molecules in the supersonic molecular beam is preferably 1 eV or more, and more preferably in the range of 1.90 to 2.10 eV, for example.

After irradiating the target T with the supersonic molecular beam B of NO molecules for a desired time (for example, 100 minutes), the irradiation of the supersonic molecular beam B and the heating of the nozzle are finished (step S140). Subsequently, the vacuum pump 3 is stopped, and the air is gradually introduced into the vacuum chamber 2 using the leak valve, so that the internal pressure of the vacuum chamber 2 matches the external pressure (atmospheric pressure) (step S150). Then, the target T is taken out from the vacuum chamber 2 (step S160), and the process ends.

〔Example〕
First, a single crystal substrate (face orientation: (100)) of strontium titanate (SrTiO ₃ ) was prepared, and a thin film of TiO ₂ was formed on the single crystal substrate by pulsed laser deposition. Specifically, the SrTiO ₃ substrate is introduced into a vacuum chamber, and while the inside of the vacuum chamber is evacuated, the oxygen partial pressure is set to 1.0×10 ⁻⁴ Pa. Then, the SrTiO ₃ substrate was heated to 800° C., and the deposition material target (TiO ₂ ) placed at a position facing the SrTiO ₃ substrate was irradiated with a pulsed laser at a laser power density of 0.8 J/cm ² for 4 hours. As a result, a TiO ₂ thin film of about 100 nm was formed on the surface of the SrTiO ₃ substrate.

The TiO ₂ thin film thus prepared was doped with N element according to the following procedure. First, an SrTiO ₃ substrate on which a TiO ₂ thin film serving as a target T was formed was placed at a predetermined position in the vacuum chamber 2 (a position to be irradiated with the molecular beam from the nozzle 6). Subsequently, the vacuum chamber 2 was evacuated to 5×10 ⁻⁸ Pa or less, and the nozzle 6 was heated to 1400 K using the nozzle heater 7. Then, the TiO ₂ thin film serving as the target T was irradiated with a supersonic molecular beam of NO molecules from the nozzle 6 while maintaining the temperature of the nozzle 6 at 1400K. The translational energy of NO molecules in the irradiated supersonic molecular beam was 2.06 eV, the sample temperature during irradiation was room temperature, and the irradiation time was 2 hours.

3 to 5 show the results of measuring the TiO ₂ thin film by X-ray photoelectron spectroscopy (XPS) before and after irradiation with a supersonic molecular beam of NO molecules as described above.

FIG. 3 shows measurement results near the binding energy corresponding to the 1s orbit of the N element. A peak that was not seen before irradiation with the supersonic molecular beam of NO molecules became visible after irradiation. This shows that the N element contained in the irradiated NO molecules combined with the element in the TiO ₂ thin film, resulting in successful doping.

FIG. 4 shows measurement results near the binding energy corresponding to the 2p _3/2 orbital of Ti. The peak of the orbit is observed unchanged before and after irradiation with the supersonic molecular beam of NO molecules. In the area surrounded by the broken line in FIG. 4, the peak indicating the presence of oxygen vacancies decreases after irradiation. This is considered to be because the oxygen defects that existed before irradiation were compensated by the O element contained in the irradiated NO molecules.

FIG. 5 shows measurement results near the binding energy corresponding to the valence band of TiO ₂ . From FIG. 5, it can be seen that the valence band spectrum is shifted to the conduction band side by about 0.2 eV after irradiation compared to before irradiation with the supersonic molecular beam of NO molecules. From this, it is considered that the band gap was reduced by irradiating with the supersonic molecular beam of NO molecules. If the band gap is reduced, it becomes possible to obtain responsiveness to visible light, which has lower energy than ultraviolet light.

According to the doping process in this embodiment described above, TiO ₂ can be doped with N element efficiently at low cost. In particular, since the object to be heated during the doping process is only the nozzle 6 (and the molecules passing through the nozzle 6), rather than the entire doping device 1 or the target T, the energy required for heating can be suppressed, and the heating and cooling The time required can be shortened and processing efficiency can be increased. In addition, oxygen defects contained in the crystal lattice of TiO ₂ can be compensated for, and carriers excited by light irradiation can be suppressed from decreasing photocatalytic activity due to recombination in the defects. can.

Note that although the present embodiment has been described above, the present invention is not limited to these examples. For example, in the above embodiment, the TiO ₂ target is in the form of a substrate, but the TiO ₂ may be in the form of particles, powder, or the like.

Additionally, those skilled in the art may appropriately add, delete, or change the design of each of the above-described embodiments, or may suitably combine the features of each embodiment, and still have the gist of the present invention. They are included within the scope of the present invention.

1 Doping device 2 Vacuum chamber 3 Vacuum pump 4 Target holder 5 Beam source 6 Nozzle 7 Nozzle heater T Target B Supersonic molecular beam

Claims (2)

Placing a target TiO ₂ in the form of a thin film, particles, or powder in a predetermined position within a vacuum chamber;
evacuating the vacuum chamber;
heating the nozzle to a predetermined temperature;
A method for producing N element-doped _TiO2 , comprising the step of irradiating the target with a supersonic molecular beam of NO molecules from the nozzle while maintaining the nozzle at the predetermined temperature. The manufacturing method according to claim 1, wherein the predetermined temperature is in a range of 1180K to 1420K.

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