Tailoring Structural, Electronic, Optical, and Photocatalytic Properties of Y2Ti2O7 through a Passivated Codoping Approach

The large band gap of the Y2Ti2O7 photocatalyst has limited its application only in the ultraviolet region. To enhance its photocatalytic activity for overall water splitting in the visible-light region, we have utilized a passivated codoping approach to construct eleven (X + M)-doped Y2Ti2O7 systems (X = C, N, M = Ti, V, Zr, Nb, Mo, Hf, Ta, W), where a Ti/Y site is replaced with a metal dopant. The calculated negative formation energies indicate that all of the (X + M)-doped systems are easy to synthesize, especially under the O-rich condition. The implantation of dopants can change the crystal structure to different extents. The less the deformation of the crystal, the easier the formation of the (X + M)-doped Y2Ti2O7. The passivated codoping can effectively narrow the band gap without generating isolated defect states in the forbidden gap. (X + M)-doped Y2Ti2O7 retains the direct band gap characteristics and possesses the separation rate of photogenerated carriers similar to or even higher than that of the pure crystal. Compared to (N + M)-doped systems, (C + M)-doped systems exhibit more remarkable influence on narrowing the band gap and extending the absorption edge mainly because the C dopant has deeper acceptor energy levels and a stronger interaction with the metal dopant than the N dopant. The capabilities of photooxidation and photoreduction of water have been enhanced by adopting the codoping strategy. By considering the binding energy, band gap, optical absorption, and the relative position of band edges, we propose that (C + Mo)-, (C + W)-, (N + V)-, (C + V)-, (C + Nb)- and (C + Ta)-doped Y2Ti2O7 are potential visible-light-responsive photocatalysts for overall water splitting.