Emergence of defect fluorite structure in nano‐sized thoria through doping with some divalent transition‐metal ions

Abstract

With the objective of incorporating some divalent transition‐metal ions in thoria and to comprehend its effect on the crystal structure, electronic as well as catalytic properties, Ni2+, Cu2+ and Cd2+ substituted thoria samples were synthesized by the epoxide gel method. Of the two concentrations investigated, 10 mol% of Ni2+, Cu2+, and Cd2+ could be substituted retaining the fluorite structure and phase separation into individual oxides was noticed for 15 mol%. The average crystallite size of thoria and 10 mol% substituted samples was 14 nm. Le‐Bail structural refinements of Powder X‐ray diffraction (PXRD) patterns indicated marginal increase in unit cell constant for the Cd2+ substituted sample and a decrease for Ni2+ and Cu2+ substituted samples. In addition to broadening of the band at around 460 cm−1 (F2g vibration of the fluorite), less intense band near 560‐590 cm−1 emerged for all the transition‐metal ion‐containing samples in the Raman spectra implying the formation of oxygen defects. The absorption edge in the UV‐visible spectra moved toward higher wavelength for Cd2+, Ni2+ and Cu2+ containing samples as compared to pure thoria. In addition, d‐d transition was observable for Ni2+ and Cu2+ containing samples. By virtue of these changes in the electronic structure of transition‐metal ion‐containing samples, they were examined as catalysts for the degradation of aqueous Rhodamine‐6G (Rh‐6G) dye solutions under visible radiation.