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Quaternary metal oxides, particularly those of pyrochlore-type, form a rapidly emerging class of new functional materials for photocatalytic applications in environmental purification and water splitting because of their intriguing structural and photocatalytic properties. In this work, pyrochlore structured compositions with the general formula K3MTe3O12 (M = Cr, Fe, Ga) were synthesized by a solid-state method and their photocatalytic properties are reported. The synthesized materials were subjected to X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM–EDS), transmission electron microscopy-selected area electron diffraction (TEM-SAED), N2 adsorption–desorption, Fourier transform infrared (FT-IR), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) techniques. All the compositions were crystallized in a cubic system with the Fd3m space group. All the compositions were evaluated for the photocatalytic degradation of methylene blue (MB), a toxic aromatic cationic dye, under visible light irradiation. Among the materials tested, K3CrTe3O12 offers the highest photocatalytic activity with a 96% degradation over 180 min of irradiation. Scavenger experiments were performed to find out the role of reactive oxygen species during the photocatalytic degradation of MB. The ·OH radicals were found to play a major role in the MB degradation. Furthermore, the recyclability and the chemical stability of K3CrTe3O12 were also presented. [ABSTRACT FROM AUTHOR]

Defect pyrochlore‐type oxide, KGe0.5Te1.5O6 (KGTO) and its Ag+, Cu2+ and Sn2+ doped compositions were prepared by solid state and ion‐exchange methods respectively. The XRD results suggest that both parent KGTO and Ag+, Cu2+ and Sn2+ doped KGTO have crystallized in cubic lattice. The morphology of all compositions was obtained from SEM‐EDS and TEM‐SAED measurements. The textural properties were obtained from N2 adsorption‐desorption measurements. The FT‐IR and Raman spectra of all compositions are comparable. Surface elemental composition and electron‐hole recombination rate were deduced from XPS and PL measurements respectively. The photocatalytic performance of these materials was tested in the degradation of methylene blue (MB) and methyl orange (MO) dyes. The doping of Ag+, Cu2+ and Sn2+ into the KGTO lattice improved optical characteristics and photocatalytic activity significantly. Among the compositions investigated, Sn‐KGTO shown highest photocatalytic performance with 82 % for MB and 67 % for MO in 180 min. Trapping experiments were conducted to identify the active species participated in the MB degradation over Sn‐KGTO. The generation and participation of ⋅OH and O2−⋅ radicals were studied by terephthalic acid and potassium bromate experiments respectively. The reusability and chemical stability of Sn‐KGTO against MB degradation were also examined. A possible reaction mechanism was proposed to understand the MB degradation in the presence of Sn‐KGTO. [ABSTRACT FROM AUTHOR]