Features of crystalline and electronic structures of Sm2MTaO7 (M=Y, In, Fe) and their hydrogen production via photocatalysis

This paper reports on the crystal structure determination of a new phase of Sm2YTaO7 synthesized by a solid-state reaction. Rietveld refinement using X-ray powder diffraction (XRD) data and electron diffraction using transmission electron microscopy (TEM) revealed that Sm2YTaO7 crystallized into an orthorhombic system with space group C2221, and according to the crystalline arrangement, it can be considered as a weberite-type phase. A detailed analysis of the crystal chemistry of the family with formula Sm2MTaO7 (M=Y, In, Fe, Ga) was performed, which indicated that all of these complex oxides are composed of corner-sharing octahedral layers of TaO6 units within a three-, two- or one-dimensional array. In addition, for comparison, the crystal structure, space group and lattice parameters of approximately 100 previously synthesized oxides in the A23%2bB3%2bB5%2bO7 family were collected and analyzed, and a structural map based on the radius ratio rA/rB is reported. According to the photocatalytic results, all oxides in the Sm2MTaO7 (M=Y, In, Fe, Ga) family showed hydrogen production from pure water without any cocatalyst. The highest (62 μmol/g h) and lowest (24 μmol/g h) hydrogen production rates were observed for Sm2YTaO7 and Sm2FeTaO7, respectively, which reveals that the photoactivity is strongly dependent on the negative potential of the conduction band. © 2016 Elsevier Ltd and Techna Group S.r.l.

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