CuO nanoparticles (NPs), Cu 2 O/CuO and CuO/TiO 2 nanocomposites (NCs) have been synthesized by using modified co-precipitation method with three different schemes of synthesis.Crystal structure and morphology of the samples have been investigated by the synchrotron Xray diffraction and transmission electron microscopy, respectively. The detailed local electronic structure of NPs and NCs has been determined by the X-ray absorption near edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS) spectroscopy. O K-edge, Cu K-and Cu L-edge XANES spectra revealed the dominating +2 valence state of Cu in case of CuO NPs and CuO/TiO 2 NCs, although Cu +1 was dominated in the Cu 2 O/CuO NCs. A comparison of local atomic structure around the Cu sites revealed the shorter Cu -O bond distances in the as-synthesized samples with respect to the bulk CuO or Cu 2 O. The Ti K-edge EXAFS fittings for CuO/TiO 2 NCs revealed that the local anatase TiO 2 phase has been formed, with Ti -O bond distance of 1.98 Å. We further demonstrated that the CuO NPs, Cu 2 O/CuO and CuO/TiO 2 NCs can serve as effective photocatalyst towards the degradation of two novel water 2 pollutants, (i) methyl orange (MO) and (ii) potassium dichromate (PD), under the visible lightirradiation. It was found that the Cu 2 O/CuO NCs exhibit higher photocatalytic activity towards the degradation of MO and PD than the CuO NPs or CuO/TiO 2 NCs. The mechanism of the photodegradation of MO and PD is also discussed in terms of possible chemical reactions, along with the electronic structure and surface properties of the samples.

Single phase nanoparticles (NPs) of CeO2, Ce0.5Zr0.5O2, Ce0.5Hf0.5O2 and Ce0.5Hf0.25Zr0.25O2 were successfully synthesized by co-precipitation method at constant pH and temperature. The X-ray diffraction results revealed that the additive atoms did not segregate to form secondary phases but led to grain size variation in the NPs. The 10 Dq values in the near edge X-ray absorption fine structure (NEXAFS) spectra at the O K-edge did not vary in the same way as the average grain size was changed for the doped CeO2 NPs. The deconvolution of Ce M5-edge and detailed analysis of O K pre-edge peak have shown the higher Ce(+3)/(Ce(+3) + Ce(+4)) ratio in the Zr- and Hf-doped samples. The local atomic structure around the Ce, Zr and Hf atoms was investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy at Ce K-edge, Zr K-edge and Hf L3-edge, respectively, and the EXAFS data were fitted with the theoretical calculations. The 4f occupancy, Ce(+3)/(Ce(+3) + Ce(+4)) ratio of Ce ions, coordination number of Ce and Ce-Ce/Ce-O bond distances were sensitive to the additive atoms but not explicitly changed according to the grain size variation in the NPs.

Chemically synthesized pyro-vanadates exhibit sub-pentavalent V ions and white-light emission via charge transfer transitions of VO4 tetrahedra.

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