Large-scale synthesis of TiO₂microspheres with hierarchical nanostructure for highly efficient photodriven reduction of CO₂to CH₄

In this study, a simple and reproducible synthesis strategy was employed to fabricate TiO₂microspheres with hierarchical nanostructure. The microspheres are macroscopic in the bulk particle size (several hundreds to more than 1000 μm), but they are actually composed of P25 nanoparticles as the building units. Although it is simple in the assembly of P25 nanoparticles, the structure of the as-prepared TiO₂microspheres becomes unique because a hierarchical porosity composed of macropores, larger mesopores (ca. 12.4 nm), and smaller mesopores (ca. 2.3 nm) has been developed. The interconnected macropores and larger mesopores can be utilized as fast paths for mass transport. In addition, this hierarchical nanostructure may also contribute to some extent to the enhanced photocatalytic activity due to increased multilight reflection/scattering. Compared with the state-of-the-art photocatalyst, commercial Degussa P25 TiO₂, the as-prepared TiO₂microsphere catalyst has demonstrated significant enhancement in photodriven conversion of CO₂into the end product CH₄. Further enhancement in photodriven conversion of CO₂into CH₄can be easily achieved by the incorporation of metals such as Pt. The preliminary experiments with Pt loading reveal that there is still much potential for considerable improvement in TiO₂microsphere based photocatalysts. Most interestingly and significantly, the synthesis strategy is simple and large quantity of TiO₂microspheres (i.e., several hundred grams) can be easily prepared at one time in the lab, which makes large-scale industrial synthesis of TiO₂microspheres feasible and less expensive.