Preparation, optical, and photocatalytic studies of defect pyrochlores: KCr < inf > 0.33 < /inf > W < inf > 1.67 < /inf > O < inf > 6 < /inf > and A < inf > x < /inf > Cr < inf > 0.33 < /inf > W < inf > 1.67 < /inf > O < inf > 6 < /inf > ·nH < inf > 2 < /inf > O

Abstract

Nano sized defect pyrochlores of compositions KCr0.33W 1.67O6 and AxCr0.33W 1.67O6·nH2O (A = Sn, Ag, Bi, Sm, Eu, and Gd) have been synthesized by sol-gel and ion exchange methods, respectively. These oxides were characterized by thermogravimetric analysis, powder X-ray diffraction, energy dispersive spectra, transmission electron microscopy, UV-Vis diffuse reflectance spectra, Raman spectra, and Fourier transform infrared spectra. Spontaneous exchange of K+ with A ion is accompanied by insertion of water also into the lattice. KCr0.33W 1.67O6 and AxCr0.33W 1.67O6·nH2O crystallize in cubic lattice and isomorphous with KSbWO6. The optical properties of Cr 3+ were investigated. Substitution of K+ by A ion leads to a shift of absorption onset to longer wavelengths marginally. The Raman spectra of all the samples are characteristic of defect pyrochlore system. The photocatalytic degradation of methylene blue aqueous solution was investigated using these oxides. The results obtained were fitted with the Langmuir-Hinshelwood model to study the degradation kinetics. Both Sn 2+ and Bi3+-doped KCr0.33W1.67O 6 exhibit higher photoactivity in the degradation of methylene blue. The structure/composition of the photocatalyst remains the same even after fourth cycle of photodegradation. © 2013 Springer Science+Business Media.