  Microdispersed photocatalysts based on titanium dioxide (TiO2) in the form of
hollow core-shell microspheres (microcapsules) with mesoporous structure are
widely demanded in modern critical technologies related to the catalysis of
various chemicals, solving environmental problems, and obtaining cheap fuel. To
date, a number of experimental works are known, showing that geometrical
parameters of microcapsules (size, shell thickness), as well as microstructural
composition (nanosized metal additives, additional inner dielectric core -- the
"yolk") noticeably affect their photocatalytic activity. At the same time, a
valuable physical description of the optical properties of porous microcapsules
has not been presented in the literature so far. Using the finite element
method, we perform a full-wave simulation of the optical field inside a hollow
microsphere whose shell is assembled from multiple TiO2 nanoparticles to form
an irregular nanoporous structure. We give a physical explanation of the
published experimental data on the optical activity of titanium-dioxide
microcapsules and show that the existing theoretical models do not always give
a correct interpretation of the observed empirical behaviors.
