Sodium
tantalate (NaTaO<sub>3</sub>) photocatalysts doped with
Sr<sup>2+</sup> produce core–shell-structured NaTaO<sub>3</sub>–SrSr<sub>1/3</sub>Ta<sub>2/3</sub>O<sub>3</sub> solid solutions
able to split water efficiently, when prepared via the solid-state
method. In this study, the photocatalysts were chemically etched to
examine the different roles of the core and shell with respect to
the recombination of electrons and holes. Under excitation by Hg–Xe
lamp irradiation, the steady-state population of electrons in the
core–shell-structured photocatalyst with a bulk Sr concentration
of 5 mol % increased by 130 times relative to that of the undoped
photocatalyst. During etching for the first 10 min, the shell detached
from the top of the core, and the electron population in the uncovered
core further increased by 40%. This population enhancement indicates
that electrons are excited in the core and recombined in the shell.
Etching up to 480 min resulted in the reduction of the electron population.
To interpret the population reduction in this stage of etching, a
Sr concentration gradient that controls the electron population in
the core is proposed
