Ozone generating method

1. An ozone generating method for generating ozone using an ozone generator which has first and second electrodes facing each other and a dielectric formed on said first electrode and has a discharge space between said dielectric and said second electrode,

said ozone generator further having a metal compound layer provided on at least one surface of said second electrode and said dielectric,

said metal compound layer satisfying the following conditions (1) to (4):

(1) said metal compound layer is not a material promoting ozone decomposition,

(2) said metal compound layer is not a conductor,

(3) the band gap of said metal compound layer is in a range of 2.0 to 4.0 eV, and

(4) the hole potential of a valence band portion formed in an excited state of said metal compound layer is larger than a binding potential 1.25 eV of an oxygen molecule,

said ozone generating method comprising the steps of:

(a) supplying a raw material gas mainly including oxygen gas to said discharge space;

(b) giving external energy, generating dielectric barrier discharge in said discharge space, and bringing said metal compound layer into a photocatalytic state by a discharge light which is emitted by the dielectric barrier discharge to generate oxygen atoms from the raw material gas supplied in said step (a);

(c) generating ozone by a collision chemistry reaction between the oxygen atoms generated in said step (b) and the oxygen gas contained in said raw material gas; and

(d) executing said steps (a) to (c) under an environment in which an ozone decomposition suppression requirement for suppressing a decomposition amount of ozone is imposed on said ozone generator, wherein

a metal compound constituting said metal compound layer is a powder having a particle diameter of 0.1 to 50 μm,

a main metal element contained in said metal compound layer includes at least one of chromium (Cr), vanadium (V), tungsten (W), molybdenum (Mo), niobium (Nb), tantalum (Ta) and bismuth (Bi), and

said metal compound layer includes a metal oxide layer.

2. The ozone generating method according to claim 1 , wherein said metal compound layer has a body-centered cubic structure as a crystal structure of the metal compound layer.

3. The ozone generating method according to claim 1 , wherein said metal compound layer is fixed to said at least one surface of said second electrode and said dielectric by coating, blowing, baking, or surface bonding.

4. The ozone generating method according to claim 1 , wherein as said ozone decomposition suppression requirement imposed on said ozone generator in said step (d), the following requirements (d1) to (d3) are satisfied:

(d1) high purity oxygen gas having an oxygen gas purity of 99.99% is used as said raw material gas,

(d2) a gas flow rate at the time of supplying said raw material gas is not less than 3 L/min, and

(d3) a discharge power density in said dielectric barrier discharge is set within a range of 1 to 5 W/cm 2 , and a specific power amount W/Q value is set within a range of 300 to 500 Wmin/L.

5. The ozone generating method according to claim 1 , wherein as the ozone decomposition suppression requirement imposed on said ozone generator in said step (d), the following requirement (d4) is satisfied:

(d4) a temperature of said first and second electrodes in said ozone generator is set to not more than 20° C.

6. The ozone generating method according to claim 1 , wherein as the ozone decomposition suppression requirement imposed on said ozone generator in said step (d), the following requirements (d5) and (d6) are satisfied:

(d5) a gap length in a discharge space of said ozone generator is set within a range of 0.02 to 0.12 mm, and

(d6) a gas pressure in said discharge space is set within a range of 0.2 to 0.4 MPa as an absolute pressure.