Variation of structural disorder in Zr substituted Y2Sn2O7: Its impact on photocatalysis

Abstract

Variation in degree of disorder and its impact on photocatalytic dye degradation has been studied in Y2Sn2-xZrxO7 series. The structural variations of the compositions were thoroughly characterized by X-ray diffraction, Raman spectroscopy, 119Sn MAS NMR, EXAFS and XPS. A phase transition from ordered pyrochlore to disordered fluorite could be observed in the series whilst transiting from Y2Sn2O7 to Y2Zr2O7 without any signature of presence of bi-phasicity. Formation of a random solid solution phase has been confirmed by 119Sn MAS NMR results. All the compositions until x ​= ​1.0 remain as pyrochlore whereas the compositions with x ​≥ ​1.5 preferentially adopt defect-fluorite structure. X-ray photoelectron spectroscopy clearly demonstrates that the coordination environment Zr and O varies with increase in Zr content, however, the coordination environment of Sn does not alter with substitution. The phase transformation from pyrochlore to defect fluorite occurs at relatively higher Zr rich composition than expected from classical radius ratio rule due to higher covalency present in Sn–O bond. With increase in Zr content in the series crystallite size, surface charge, nature BO6 octahedra etc. varies and it has been found that these parameters has strong bearing on catalytic property of the materials. A generic understanding for the photocatalytic degradation of cationic methylene blue dye was achieved as a function of structural disordering in the Y2Sn2-xZrxO7 system.