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The structural, electronic and photocatalytic properties of five vacancy-containing 2D BiI3 monolayers are investigated by the first-principle calculations. The electronic structures show that the five structures are stable and have comparable binding energies to that of the pristine BiI3 monolayer, and the defects can tune the band gaps. Optical spectra indicate that the five structures retain high absorption capacity for visible light. The spin-orbit coupling (SOC) effect is found to play an important role in the band edge of defective structures, and the VBi and VBi-I3 defective BiI3 monolayers can make absolute band edges straddle water redox potentials more easily.

The first-principles calculations are performed to investigate the adsorption of O2 molecules on an Sn(111) 2 × 2 surface. The chemisorbed adsorption precursor states for O2 are identified to be along the parallel and vertical channels, and the surface reconstructions of Sn(111) induced by oxygen adsorption are studied. Based on this, the adsorption behaviours of O2 on X(111) (X=Si, Ge, Sn, Pb) surfaces are analysed, and the most stable adsorption channels of O2 on X(111) (X=Si, Ge, Sn, Pb) are identified. The surface reconstructions and electron distributions along the most stable adsorption channels are discussed and compared. The results show that the O2 adsorption ability declines gradually and the amount of charge transferred decreases with the enhancement of metallicity.