Controlled synthesis and visible light photocatalytic activity of Bi12GeO20 uniform microcrystals.

We successfully synthesized uniform Bi12GeO20 microspheres and microtetrahedrons enclosed by four {111} facets using a controlled hydrothermal method for the first time. The photocatalytic activity of these regular-shaped products was further investigated by the degradation of RhB and gaseous formaldehyde under visible light irradiation (λ>420 nm). The Bi12GeO20 microtetrahedrons (s) exhibited enhanced photocatalytic activity and stability which is closely related to the high capacity of exposed {111} facets for uptake of O2. The formation mechanism studies indicate that the Bi12GeO20 seeds were directed to grow into truncated microcubes, truncated microtetrahedrons, and then microtetrahedrons when the NaOH concentration was 5 M. The same batch of seeds only evolved into microspheres when the NaOH concentration was switched to 3 M. The difference in Bi12GeO20 morphology could be attributed to the rates of both crystal nucleation and crystal growth.