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.

No abstract

Ce1-xEuxO2 (0 ≤x≤ 0.3) nanoparticles (NPs) were synthesized by the chemical precipitation method. The microstructures and morphology were characterized by synchrotron X-ray diffraction and high resolution transmission electron microscopy. X-ray absorption near edge structure (XANES) spectra at the Eu M5,4-edge and atomic-multiplet calculations revealed that Eu(3+) was predominantly present in the CeO2 lattice and Eu(2+) was negligibly present within the entire doping range. The detailed analysis of the Ce M5,4-edge and the O K-edge has shown strong dependence of the Ce(3+)/Ce(4+) ratio and oxygen vacancy with Eu content. Extended X-ray absorption fine structure (EXAFS) spectra at the Ce K-edge, along with theoretical fitting, have shown systematic variation in the coordination number, bond length and Debye-Waller factor with Eu doping. A blue shift in the absorption edge was observed which implies a net increase in the charge transfer gap between the O 2p and Ce 4f bands due to the increased number of Ce(3+) ions in the Eu doped samples. The excitation and emission spectra of pure CeO2 NPs did not show any photoluminescence (PL) characteristic; however, Ce1-xEuxO2 (x = 0.1-0.3) NPs showed significant improvements in the 4f-4f, (5)D0-(7)F2 and (5)D0-(7)F1 transitions induced luminescence properties. Eu doping has two major effects on the electronic structure and optical properties of CeO2 NPs: the first, at an Eu content of 10 mol%, is the formation of Ce(4+)-O-Eu(3+) networks, i.e., Eu(3+) ions substitute the Ce(4+) ions and introduce oxygen vacancies and Ce(3+) ions in the host lattice, which favors the (5)D0-(7)F2 induced PL properties. The other, at an Eu doping over 10 mol%, is the formation of both Ce(4+)-O-Eu(3+) and Ce(3+)-O-Eu(3+), i.e., Eu(3+) ions not only take substitutional sites of Ce(4+) ions but also replace a fraction of Ce(3+) ions in the CeO2 lattice which favors (5)D0-(7)F1 induced PL properties. As an application of CeO2 NPs towards the degradation of water pollutants, we demonstrated that the Ce1-xEuxO2 (0 ≤x≤ 0.3) NPs can serve as effective photocatalyst materials towards the degradation of the methyl-orange aqueous pollutant dye under UV light irradiation.

Correlations among the B-O6 octahedra distortions, existing polymorphous phases, band structures and electronic conductivities of ABO perovskites are matters for debate and require a deep understanding of their local atomic/electronic structures and diverse assets. In this study, to illustrate the distortion in V-O6 octahedra and its implication on the band structure and electronic properties, spectroscopic investigations on the RF-sputtering grown insulating SrVO thin films were employed using X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). V K-edge and V L-edge XANES, along with atomic multiplet calculations, have confirmed the 4+ oxidation state of V ions in the pristine and annealed SrVO thin films. Lower t/e peak intensity ratio and smaller energy separation between t and e peaks in the O K-edge XANES spectra, compared to the VO reference sample, have confirmed a larger V-O6 distortion in the orthorhombic SrVO thin films. Moreover, from the EXAFS data analysis, the local orthorhombic structure has been identified in the pristine and annealed SrVO thin films, compelling significant distortion in the V-O6 octahedra. Dimerization in the vanadium chains and V-V twisting, caused by V-O6 octahedra distortion, manifests a miscellaneous ligand field interaction between O 2p and V 3d orbitals and facilitates (i) a larger separation between the bonding and antibonding d orbitals and (ii) an upward shift of the π* band in the band structure, leading to larger band gaps in the insulating SrVO thin films. Our spectroscopy results may open up new avenues for the mechanism of insulating/conducting character in other complicated perovskite materials using XANES-EXAFS.

In this work, we report the room temperature ferromagnetism in Sn1‐xFexO2 and Sn1‐xNixO2 (x = 0.00, 0.03 and 0.05) nano‐crystalline powders. All the samples were prepared using co‐precipitation method. X‐Ray Diffraction (XRD), transmission electron microscopy (TEM), energy dispersive x‐ray analysis (EDAX), UV‐ visible absorption spectroscopy and room temperature magnetization measurements were performed to study the crystal structure, morphology, elemental analysis, optical band gap and magnetic properties of Fe and Ni doped SnO2. TEM results depict the formation of spherically shaped and small sized nanoparticles of the diameter of ~ 3 nm. The band gap energy of the Fe and Ni doped samples found to decrease with increasing their concentrations. The higher saturation magnetization was observed in low concentration Fe and Ni doped tin oxide

No abstract