Here we report the photocatalytic activity of CeO 2 nanoparticles. This is carried out with methyl orange as the reference pollutant. Annealing of ceria under vacuum generates oxygen deficient CeO 2 nanoparticles with defects such as oxygen vacancies and formation of Ce 3+ . This is evident from the characterization results of X-ray diffraction, Raman spectroscopy, N 2 adsorption-desorption and X-ray photoelectron spectroscopy. The band gap is red shifted due to the creation of intermediate energy states of Ce 3+ and oxygen vacancies in the band gap. The reduced photoluminescence (PL) intensity of defective ceria indicates that the electron-hole separation is substantially enhanced by the surface trap centers. Air annealed ceria not only has relatively low surface area but also has fewer surface defects. Thus, it is expected to display less photocatalytic activity. Vacuum annealed CeO 2 indeed displays better photocatalytic activity in the degradation of methyl orange under UV and visible light as compared to the air annealed samples.

CeO 2 nanoparticles are annealed in vacuum at 200 C and in air at 200 C, 600 C and 1000 C, respectively. Vacuum-annealed CeO 2 contains high concentration of oxygen vacancies and exhibits very high lattice strain, whereas the corresponding values decrease on air annealing. Oxygen-deficient CeO 2 has redshift in band gap with high Urbach energy. The magnitude of this energy decreases as CeO 2 is annealed in air at 600 C. At 1000 C, thermal disorder increases the Urbach energy. Photoluminescence property of the samples depends on the presence of radiative and non-radiative oxygen vacancy centres. Vacuum-annealed ceria have large numbers of non-radiative oxygen vacancies that act as emission quencher. CeO 2 annealed at 600 C contains requisite amount of oxygen vacancies to show better luminescence property.

The paper investigates, both theoretically and experimentally, the structural and optical changes in SnO2 system brought about by introduction of Cu in a SnO2 system. On the experimental front, a cost effective sol-gel technique is used to prepare hexagonal shaped Cu doped SnO2 nanoparticles. The prepared pristine SnO2 nanoparticle is found to be of random shape by transmission electron microscope (TEM) studies. A structural and morphological study is carried out using X-ray diffraction and TEM techniques. The different phonon interaction in the system is observed by Raman spectroscopy while electron paramagnetic resonance and UV-Visible spectroscopy confirms the presence of Cu in 2+ state. First principle calculations have been performed using “density functional theory”-based MedeA Vienna Ab Initio Simulation package on a SnO2 system where Cu is introduced. The introduction of Cu in the SnO2 system brings distortion which is corroborated by the variation in the corresponding bond lengths. The Density of State calculation of Sn16O32 and CuSn15O32 is also performed. Finally, a correlation is established between the experiment and the theory.

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Experimental and theoretical studies confirm that ferromagnetism in SnO2 appears owing to Sn4+ vacancies.