JP5792927B2 - Method for synthesizing titanium oxide electrode - Google Patents

Description

    The present invention relates to a method for synthesizing a titanium oxide electrode, and more particularly to a method for synthesizing a titanium oxide electrode whose surface is covered with titanium oxide.

Conventionally, oxygen acid ions such as selenate ion, tellurite ion, selenite ion and tellurite ion are reduced to zero-valent elements such as molecular selenium or metallic tellurium by electrolysis using a titanium oxide cathode. It is known that it can precipitate (refer patent document 1). In this electrolysis, the larger the electrode area, the more advantageous.
Japanese Patent No. 2979087

    There are many methods for synthesizing a titanium oxide cathode, but methods for synthesizing a large-area electrode at a low cost are limited. Among them, a method of forming an oxide semiconductor layer on the surface by electrolytic oxidation of a metal titanium electrode in an appropriate electrolytic solution has been known for a long time, and does not require vacuum equipment or heating equipment, and is inexpensive and has a large area. This is an excellent method for obtaining the electrode. However, the conditions for synthesizing an electrode having sufficient activity and durability against electrolytic reduction of oxyacid ions have not been established.

    The titanium oxide layer of the titanium oxide cathode synthesized by electrolytic oxidation of titanium metal has a thickness that is difficult to confirm by X-ray diffraction unless it is electrolytically oxidized by applying a high voltage of 50 to 100 V or higher. It was. For this reason, the obtained cathode has sufficient activity for electrolytic reduction of selenate ions and the like, but there is a problem that the titanium oxide layer on the surface disappears and the activity is lost after several to ten times of use. It was. Although it is possible to increase the thickness of the titanium oxide layer by performing high voltage electrolysis, the electrolysis current increases in proportion to the area of the electrode. A power supply that can be applied is required. In addition, since a high concentration or acidic solution is used as the electrolytic solution, the cost of preparing and discarding the electrolytic solution increases when a large electrode is formed. From either aspect, it was difficult to increase the size in terms of cost.

The present invention has been made in view of such problems of the prior art, and the object of the present invention is to provide a titanium oxide electrode for electrolytic reduction having sufficient activity and high durability for electrolysis of oxygenate ions, Another object of the present invention is to provide a method capable of inexpensively synthesizing a large titanium oxide cathode having a single-sided area of 1 m ² or more.

    As a result of diligent research to solve the above-mentioned problems, the present inventors have used a metal titanium plate formed by rolling or metal titanium obtained by secondary processing of the metal titanium plate, and electrolyzed it in a neutral electrolytic solution. It has been found that the above problem can be solved by oxidizing and forming a titanium oxide layer on the surface thereof, and the present invention has been completed.

    The method for synthesizing a titanium oxide electrode for electroreduction of oxyacid ions of the present invention is a method in which a metal titanium that has been hot-rolled and then cold-rolled is subjected to a voltage of more than 10 V and 30 V or less in a neutral electrolyte having a pH of 5-9 Is applied and electrolytically oxidized to form a titanium oxide layer on the surface.

    Moreover, the suitable form of the said synthesis | combining method of this invention makes the said metal titanium a counter electrode, applies the voltage of more than 10V and 30V or less between electrodes, and is characterized by performing electrolytic oxidation for 1 hour or more.

According to the present invention, rolled titanium metal is subjected to electrolytic oxidation in a neutral electrolyte, and a titanium oxide layer is formed on the surface thereof. Therefore, the activity is high enough for electrolysis of oxygenate ions. A titanium oxide electrode for electrolytic reduction having durability and a large titanium oxide electrode having a single-sided area of 1 m ² or more can be provided at a low cost.

It is explanatory drawing of an electrolytic vessel. It is an X-ray diffraction pattern of a titanium oxide layer. 4 is an X-ray diffraction pattern of electrodes obtained in Example 4 and Comparative Examples 1 and 2. FIG.

    Hereinafter, an example of a method for synthesizing a titanium oxide electrode for electrolytic reduction of oxyacid ions according to the present invention will be described.

    Such a titanium oxide electrode is obtained by hot rolling metal titanium to a thickness of about 3 mm, then cold rolling the metal titanium to a thickness of 1 to 2 mm, and forming a titanium oxide layer on the surface. Here, the hot rolling of titanium metal can typically be performed at 800 to 900 ° C., which shows deformation resistance, and heating is preferably performed in an excess oxygen atmosphere in order to prevent hydrogen absorption. The conditions for the cold rolling process may be the same as those for a general metal cold rolling process. Alternatively, a metal titanium plate rolled only by hot rolling to a suitable thickness as an electrode may be used.

    The titanium oxide layer is formed by electrolyzing titanium metal in a neutral electrolytic solution. The electrolytic oxidation at this time may be performed by applying a voltage exceeding 10 V, preferably 25 V or more, more preferably 30 V between the counter electrode. Furthermore, the electrolytic oxidation is performed for 1 hour or longer, preferably 2 hours. In addition, even if application of a voltage higher than this and electrolysis for a long time are performed, the activity and durability of the electrode are not improved. As the electrolytic solution, for example, a neutral salt aqueous solution having a concentration of about 0.01 to 1 mol / l can be used. As the neutral salt, sodium sulfate, potassium sulfate, sodium chloride, potassium chloride and the like can be used. Moreover, "neutral" here means that it is in the range of pH 5-9.

    By such a synthesis method, an electrode having sufficient activity and high durability can be obtained. In addition, since it can be synthesized at low cost and the electrolyte used is harmless, it can be discharged directly into sewage after the completion of electrolytic oxidation, so that the cost of waste liquid treatment is not required and the environmental load is small.

Next, an electrolytic cell for electrolytic reduction of oxygen acid ions will be described.
Such an electrolytic cell is composed of a cell, an anode which is spaced from each other and sequentially disposed in the cell, and a titanium oxide cathode for electroreduction of oxygenate ions in which a titanium oxide layer is formed on the surface of rolled metal titanium. And a power source for applying a voltage between the anode and the cathode, and an electrolyte containing oxygenate ions filled between the anode and the cathode.

  The cathode may have a mesh shape, an expanded shape, a spiral structure, or a structure provided with a plurality of pores. Examples of the number of combinations of the cathode and anode include 2/1 sheet, 10/11 sheet, but are not limited thereto.

  In addition to the electrolytic cell and the electrodes, a DC rectifier, an ammeter, a control device for energization, a pump and a storage tank for conveying the liquid to be treated, and other safety devices are provided. The current may be energized and controlled by direct current, a pulse waveform, or the like.

    Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto.

Example 1
(Method of synthesizing titanium oxide electrode)
In FIG. 1, 1 is a tank, 2 is an anode, 3 is a cathode, and 4 is a DC power source.

    A rolled metal titanium plate having a width of 360 mm, a height of 460 mm, and a thickness of 2.0 mm is used as the anode 2, and a paste containing platinum is applied onto the same shape of titanium metal, followed by firing, and the surface is densely formed. A platinum-coated and fired electrode with a platinum layer formed thereon is used as the cathode 3, both electrodes 2 and 3 are assembled in the tank 1, a frame (not shown) is sandwiched between the electrodes 2 and 3, and tightened from both sides. A space between 2 and 3 was formed. This space was filled with a solution having a concentration of 0.1 mol / l in which neutral sodium sulfate sulfate was dissolved in tap water as an electrolytic solution. The pH was adjusted to be in the range of 6-8.

    A direct current power source 4 was connected between the anode 2 and the cathode 3, and the current limit was set to 10A and the voltage limit was set to 15V, and electrolysis was performed for 2 hours. Initially, the current flowed to the upper limit of the power capacity, and the voltage did not reach the set voltage. The voltage increased due to the formation of the titanium oxide layer, and reached a set voltage of 15 V in 1 hour. In this state, electrolysis was continued for 1 hour, and then electrolysis was stopped, the electrode was drawn out, washed with water and dried to obtain a titanium oxide electrode.

    FIG. 2 shows a diffraction diagram of the titanium oxide layer formed on the obtained electrode when X-ray diffraction is performed. The horizontal axis indicates the angle, and the vertical axis indicates the intensity.

    The obtained electrode had a clear titanium oxide peak around 25 degrees by X-ray diffraction using Cu-kα rays.

(Examples 2 to 5)
A titanium oxide electrode was obtained by repeating the same operation as in Example 1 except that the interelectrode voltage was changed to 20 V, 25 V, 30 V, and 50 V, respectively.

    As shown in FIG. 2, in the electrode obtained by applying a voltage exceeding 10 V, a clear titanium oxide peak is generated around 25 degrees by X-ray diffraction using Cu-kα rays, and the peak is an increase in voltage. It was getting bigger with.

(Comparative Example 1)
Similar to Example 1 except that a metal titanium plate processed by cold rolling to 0.2 mm was used, adjusted to be in the range of pH 0 to 0.2 in dilute nitric acid, and the interelectrode voltage was 10 V. An electrode was obtained by the procedure described above.

    As shown in FIG. 2, in the obtained electrode, only a titanium oxide film was formed so that the peak could not be confirmed by X-ray diffraction.

(Comparative Example 2)
An electrode having the same shape as that of the metal titanium plate used in Example 1 was formed by cold rolling to 0.2 mm. No titanium oxide layer was formed on the metal titanium plate by electrolytic oxidation. However, since it was stored in the air, an extremely thin titanium oxide layer was formed by air oxidation, which is considered to have some activity in reducing selenate ions. FIG. 3 shows the results of X-ray diffraction of the electrodes obtained in Example 4 and Comparative Examples 1 and 2.

As shown in FIG. 1, as an electrolytic cell, a cell 1 is composed of vinyl chloride having mechanical strength and corrosion resistance, and an anode 2 of a platinum electrode and a cathode 3 of a titanium oxide electrode are provided in the cell 1 at intervals of 10 mm. Sequentially arranged opposite each other. A direct current power source 4 was connected between the anode 2 of the platinum electrode and the cathode 3 of the titanium oxide electrode, and a selenate ion aqueous solution (selenium concentration of 100 mg / dm ³ ) was filled so that both electrodes were immersed. Further, an air diffuser 6 having openings at appropriate intervals is provided at the bottom of the tank 1 so that nitrogen gas 5 can be introduced.

When electrolysis was performed for 30 minutes at a current density of 0.25 mA / cm ² using this electrolytic cell, the current efficiency (the ratio of the current used for the reduction of selenate ions out of the total current) was 50 to 60%. It was. Even when the electrolysis under the above conditions was repeated 5 times or 10 times, the current efficiency, that is, the activity did not change, and sufficient durability was exhibited.

Using the electrode obtained in Comparative Examples 1 and 2 instead of the titanium oxide electrode, electrolytic reduction of the aqueous selenate ion solution was performed.
As a result, the current efficiency decreased with repetition due to the disappearance of the titanium oxide layer.

    As described above, when the titanium oxide electrode included in the scope of the present invention is used, it is found that the electrolytic reduction performance is remarkably suppressed due to the consumption / disappearance of the titanium oxide layer.

DESCRIPTION OF SYMBOLS 1 Electrolytic cell 2 Anode 3 Cathode 4 DC power supply 5 Nitrogen gas 6 Aeration pipe

Claims (2)

A titanium oxide layer is formed on the surface by electrolytically oxidizing metal titanium that has been hot-rolled and then cold-rolled in a neutral electrolytic solution having a pH of 5 to 9 by applying a voltage exceeding 10 V and not exceeding 30 V. And a method for synthesizing a titanium oxide electrode.   The method according to claim 1, wherein the metal titanium is used as a counter electrode, and a voltage of more than 10V and 30V or less is applied between the electrodes, and the electrolytic oxidation is performed for 1 hour or more.

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