Slurry type photocatalytic reactor is efficient reactor in a reuse that it provides the highest radiation area per unit volume of a reactor. However, when nanosize powder such as Degussap P-26, is used seperation of the used powder is difficult. In this work, porous catalyst of micrometer size was prepared and the photoactivities of the as-prepared catalyst were compared with that of Degussa P25.
For general use of photocatalysis the development of photocatalyst to have reactivity under natural light is important. $TiO_2$ has too large bandgap energy to utilize visible portion of the solar irradiation. Only 5 % of solar energy can activate $TiO_2$ photocatalyst. For this reason reduction of bandgap energy of $TiO_2$ is important work.
In this study transient metal, Co was doped to reduce the bandgap energy of $TiO_2$. Micron-sized photocatalyst was prepared by spray pyrolysis. The spray pyrolysis is well known to reduce the phase seperation in multi-component materials. Co doping increased the photoactivity under visible light.
To reduce the rutile formation at hight preparation temperature, $SiO_2$ was added to porous $TiO_2$. $SiO_2$/$TiO_2$ mixed oxide had higher photoactivity than the pure anatase $TiO_2$. Co-doped $SiO_2$/$TiO_2$ porous photocatalyst was also prepared by spray pyrolysis. That photocatalyst had higher photoactivity than the undoped catalyst.