A method of producing composite particles of titanium dioxide and a compound inactive as a photocatalyst, comprising the steps of preparing a water based slurry of pH 3 to 5 comprising titanium dioxide, preparing a water based solution comprising a compound inactive as a photocatalyst, and reacting the slurry and the water based solution together at a pH within a range from 4 to 10 is provided, together with highly active photocatalyst particles produced using such a method, and potential uses of such photocatalyst particles.