Uniform Bi12TiO20 microtetrahedrons exposed by {111} facets were synthesized by a controlled hydrothermal method. Well resolved density functional theory (DFT) calculations showed that {111} facet was the most active facet with the highest surface energy among the low index facets of Bi12TiO20. Series of facet coupled microtetrahedronal Bi12TiO20/g-C3N4 composites were prepared via a simple two-step method. The interface structure of composite was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), and fourier transform infrared (FT-IR) spectroscopy analyses, showing that the interface of Bi12TiO20/g-C3N4 composite was connected by the {111} facets of Bi12TiO20 and the {002} facets of g-C3N4. Owing to this typical structure, the Bi12TiO20/oig-C3N4 composite with mass ratio 0.5:0.02 of Bi12TiO20 to g-C3N4 presented higher photo catalytic activity for degradation of gaseous formaldehyde under visible light irradiation (lambda >= 400 nm) as compared to the pure g-C3N4 and the as-obtained Bi12TiO20. Furthermore, the band structure calculations were employed to investigate the photocatalytic mechanism of Bi12TiO20/g-C3N4 composite. (C) 2016 Elsevier B.V. All rights reserved.