  Porous materials are used in a variety of industrial applications owing to
their large surface areas, large pore volumes, hierarchical porosities, and low
densities. The motion of particles inside the pores of porous materials has
attracted considerable attention. We investigated nano-particle motion in a
porous material using the single-particle tracking method. Particle motion such
as absorption and desorption at the wall was observed. The displacement
probability distribution deviated from the Gaussian distribution at the tail,
indicating non-Gaussian motion of the particles. Moreover, an analysis of the
relative angle between three consecutive particle positions revealed that the
probability of the particle moving backward was approximately twice that of the
particle moving forward. These results indicate that particle motion inside
porous materials is highly complex and that a single-particle study is
essensital for fabricating a structure that is suitable for applications.
