Titanium oxide-based photocatalysts which contain a metal halide in
titanium oxide and which are prepared from titanium oxide and/or its
precursor, which may optionally be heat treated, by contact with a
reactive gas containing a metal halide of the formula MX.sub.n or
MOX.sub.n (wherein M=a metal, X=a halogen, and n=an integer) with heating
stably develop a high photocatalytic activity with visible light
irradiation. The photocatalysts may subsequently be stabilized by contact
with water or by heat treatment, and/or promoted by contact with a
heteropoly acid and/or an isopoly acid so as to include a metal complex
in the titanium oxide. Photocatalysts prepared in this manner exhibit
novel ESR features. The present invention also provides methods for
preparing these photocatalysts, a photocatalyst dispersion and a
photocatalytic coating fluid containing such a photocatalyst, and
photocatalytic functional products and methods for their manufacture
using the photocatalyst.