CaTaO ₂N-CaZrO ₃ solid solution: Band-structure engineering and visible-light-driven photocatalytic hydrogen production

A series of CaTa _xZr _(1-x)O _(3-x)N _x solid solutions were successfully synthesized through nitriding precursors prepared by the polymerized complex method. The physicochemical properties of these multicomponent semiconductors were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), N ₂ adsorption-desorption isotherms, UV-visible optical absorption spectra (UV-Vis) and density functional theory (DFT) calculations. The diffraction peaks in XRD patterns gradually shifted to higher angles as x increased, indicating that CaTa _xZr _(1-x)O _(3-x)N _x solid solutions had been formed. The absorption edges in UV-Vis spectra red-shifted monotonically as x increased, demonstrating that the band gap of the prepared photocatalysts could be precisely controlled with the adjustment of compositions. The solid solutions rendered photocatalytic H ₂ evolution from a formic acid aqueous solution under visible-light irradiation. The narrow band gap, sufficient crystallization, enough pore volume and large specific surface area resulted in the best photocatalytic activity of CaTa _0.8Zr _0.2O _2.2N _0.8. Highlights: CaTa _xZr _(1-x)O _(3-x)N _x solid solutions were synthesized by PC method. Absorption edges red-shifted monotonically as x increased. CaTa _0.8Zr _0.2O _2.2N _0.8 showed best H ₂ evolution. Band gap and specific surface area were both key factors.