If you call a substance a composite, then it is a macro material. It has no size effect. Size effect - the dependence of the properties of a substance (photocatalytic activity) on its size. Photocatalytic activity is inherent in nanomaterials. Doping is done to improve photocatalytic activity. Therefore, doped nano TiO2 has better photocatalytic activity.
Article CHARACTERIZATION AND PHOTOCATALYTIC PROPERTIES OF TITANIUM D...