Highly active photocatalyst particles, method of production therefor, and use thereof

A coating agent which produces a film with photocatalytic properties, comprising a slurry (a) comprising photocatalyst particles, and at least a binder,

• wherein the photocatalyst particles are composite photocatalyst particles of titanium dioxide and a compound inactive as a photocatalyst, wherein
• when 3.5 g of said photocatalyst particles spread uniformly across a flat surface of diameter 9 cm, placed within 5 L of dry air containing 20 ppm by volume of acetaldehyde, is irradiated with a day white fluorescent lamp producing an ultraviolet light intensity of 6 μW/cm2 at a wavelength of 365 nm, a ratio of decomposition of said acetaldehyde after one hour of irradiation is at least 20%,
• wherein said ratio of decomposition is at least 80%,
• wherein a BET specific surface area of said photocatalyst particles of titanium dioxide and a compound inactive as a photocatalyst is within a range from 10 to 300 m2/g,
• wherein said compound inactive as a photocatalyst is present in a quantity within a range from 0.01 to 50 mass % based on a mass of said titanium dioxide, and
• wherein said photocatalyst particles of titanium dioxide and a compound inactive as a photocatalyst are produced by a method, comprising the steps of:
• preparing a water based slurry (b) of pH 3 to 5 comprising titanium dioxide,
• preparing a water based solution comprising a compound inactive as a photocatalyst, and
• reacting said slurry (b) and said water based solution together at a pH of 4 to 10.