Carbon nanosphere templates for the preparation of inverse opal titania photonic crystals by atomic layer deposition

•Carbon nanospheres are novel templates for inverse opal photonic crystals.•Visible absorption of TiO2 can be increased using the slow photon effect.•TiO2 visible absorption is tuned by different template size for inverse opals.•A new method has been elaborated for measuring photocatalysis over films.•Photocatalysis can be followed on the surface with UV–Vis and Raman spectroscopy.