JPH0527459B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application] The present invention relates to rare earth element compounds having photocatalytic activity.

When photodecomposing an aqueous solution of alkali metal sulfide or sulfite using visible light using a catalyst based on a complex oxide of a rare earth element, there are mainly four properties required of the photocatalyst. (1) is the property of absorbing visible light, (2) is the property of removing electrons from electron-donating substances such as sulfide ions and sulfite ions, that is, a photooxidation function, and (3) is the property of absorbing visible light. This is the property of transferring electrons received from a donating substance to an electron-accepting substance, that is, photoreducibility. Part (4)
is a property that prevents the recombination reaction, which is a reaction in which the oxidized substance and the reduced substance generated in the processes (2) and (3) above combine and return to the substance before being oxidized or reduced. . Photocatalytic activity is exhibited only when these four functions function in a well-balanced manner.

These properties are included in the properties of rare earth element oxides and rare earth element sulfides as semiconductors. The photocatalytic function of many semiconductor substances has been studied so far, and it is known that the ability of these substances to take two states, an oxidized state and a reduced state, is essentially related to the photocatalytic function. The photocatalytic material produced in the present invention also has a reaction activity capable of reversibly changing between an oxidized state and a reduced state.

[Means for solving problems]

The present inventors discovered that in photoactive catalysts made of oxides and sulfides of rare earth elements, the light absorption of oxides is generally biased toward the ultraviolet region, whereas the light absorption of sulfides is biased toward the visible region. However, sulfides have the disadvantage of being unstable in aqueous solutions, and composite materials that incorporate both the light absorption ability of sulfides and the chemical stability of oxides can be obtained. , and that it can be used as a photocatalytic material that is stable in the visible light region, and as a result of intensive research,
The present inventors have discovered a rare earth element compound that is characterized by producing SO ₂ ^- in catalyst particles, and have completed the present invention.

That is, according to the present invention, on the surface of rare earth element composite oxide particles containing nickel oxide,
The present invention provides a rare earth element compound having high catalytic activity and characterized by the formation of SO ₂ ^- with a high degree of dispersion.

The rare earth element compound of the present invention is produced by firing a mixture of an alkaline earth metal and a rare earth element compound to form a composite oxide of both, and then adding nickel oxide and re-firing to incorporate nickel into the particles. Create a scattering of things. Sulfurization can be carried out by heating this powder to a temperature of about 800° C. to 1000° C. in a sulfiding gas atmosphere containing carbon disulfide, methyl sulfide, etc. as a sulfurizing agent. By heating the partially sulfide thus produced to a temperature of about 600° C. in oxygen or an atmosphere containing oxygen, it can be converted into an oxide or an oxide containing a small amount of sulfur. In the present invention, rare earth elements refer to 15 elements ranging from yttrium and lanthanum with atomic number 57 to lutetium with atomic number 71.

In the present invention, a weak sulfiding agent such as carbon disulfide or methyl sulfide is used during the sulfiding treatment. The pressure is also preferably set to about 1/10,000 to 2/10,000 atmospheres of the sulfurizing agent partial pressure, and during oxidation treatment, the oxygen partial pressure is reduced in order to separate and oxidize areas with high sulfide concentration. Make the pressure around 1 atm. By performing three cycles of the sulfurization treatment and the oxidation treatment alternately, a photocatalytic material having both photooxidation and photoreduction functions can be obtained.

〔Effect of the invention〕

The rare earth compound of the present invention has an SO ₂ ^- intermediate electron band in the middle of the band cap to expand and improve the light absorption characteristics from the ultraviolet region to the visible region, and the addition of nickel improves the reducing ability. Combined with the photo-oxidation ability inherent to semiconductor catalysts, it exhibits high catalytic ability. According to the present invention, in addition to aqueous solutions of sulfides and sulfites, liquids with strong electron donating properties (for example, methanol, ethylamine, etc.), or solid substances with strong electron donating properties (for example, glucose,
When visible light is irradiated with the rare earth compound of the present invention in contact with an aqueous solution of glutamic acid, etc., reducing substances (hydrogen, etc.) and oxidizing substances (sulfur, sulfate ions, or the above reaction substrates are oxidized. resulting aldehydes, nitroso compounds, etc.).

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples.

Example 1 A mixed pulverized mixture of SrDy ₂ O ₄ powder and NiO powder at a weight ratio of 19:1 was heated in CS ₂ at 1000°C for 30 minutes, and further heated in O ₂ at 600°C for 30 minutes. This series of operations was repeated three times to obtain activated SrDy ₂ O ₄ .

Next, add 0.3g of SrDy ₂ O ₄ obtained from this to 10ml of 0.24M
Put it in a concentrated Na ₂ S solution, and light wavelength range 480 nm-
7508 nm light was irradiated with a 300μ einstein beam.
As a result, 1.62ml of hydrogen with an energy conversion efficiency of 45%
was able to occur.

Example 2 A mixture of SrSm ₂ O ₄ powder and NiO powder at a weight ratio of 19:1 and pulverization was heated in CS ₂ at 1000°C for 30 minutes, and then heated in O ₂ at 600°C for 30 minutes. .

Repeat this series of operations three times to activate
_{SrSm2O4 was} obtained.

Next, 0.3 g of SrSm ₂ O ₄ obtained in this way was added to 10 ml of
Placed in 0.24M concentration Na ₂ S solution, light wavelength range 480nm
Light of ~750 nm was irradiated with 300μ insitutan.
As a result, 1.60ml of hydrogen with an energy conversion efficiency of 44%
was able to occur.

Example 3 A mixture of SrY ₂ O ₄ powder and NiO powder at a weight ratio of 19:1 and pulverization was heated in CS ₂ at 1000°C for 30 minutes, and then heated in O ₂ at 600°C for 30 minutes. . This series of operations was repeated three times to activate SrY ₂ O ₄
The compound was obtained.

Next, 0.3 g of SrY ₂ O ₄ obtained from this was placed in 10 ml of 2-propanol, and a light wavelength range of 480 nm to 750 nm was added.
It was irradiated with 300μ einstein light. As a result, we were able to generate 0.35ml of hydrogen with an energy conversion efficiency of 10%.

Claims (1)

[Claims] 1 SO _{2 -} produced by alternately repeating sulfurization treatment and oxidation treatment of a composite oxide of rare earth elements and alkaline earth metal elements mixed with a small amount (around 5% by weight) of nickel oxide and ^calcined. A rare earth element compound characterized in that it exhibits a photocatalytic action when exposed to visible light.