Anatase-Rutile phase transition of Ca@TiO2 nanostructures for the removal of environmental pollutants under visible photon illumination

•Sonochemical synthesis of Ca@TiO2 nanostructures from anatase to rutile phase transition.•To outline the structural and optoelectronic characteristics of Ca@TiO2 nanostructures by employing different physicochemical techniques.•To facilitate feasible approaches for degrading Congo Red dye over the catalyst surface.•To evaluate the photocatalytic degradation proficiency and plausible schematic dye degradation mechanism.