Band-gap change and photocatalytic activity of silica/titania composites associated with incorporation of CuO and NiO - M. A. Nazarkovsky; V. M. Gunko; G. Wójcik; B. Czech; A. Sobieszek; J. Skubiszewska-Zieba; W. Janusz; E. Skwarek (Chemistry, physics and technology of surface, 2014)