Epitaxial-like growth of Co 3O 4/ZnO quasi-1D nanocomposites

The development of quasi-1D Co3O4/ZnO nanocomposites by a two-step plasma enhanced-chemical vapor deposition (PE-CVD) process is presented. Arrays of < 001 > oriented ZnO nanorods were first grown on Si(100) and subsequently used as templates for the PE-CVD of Co3O4, whose amount was tailored as a function of deposition time. The obtained composites were thoroughly characterized by means of a multitechnique approach, involving field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDXS), micro-Raman and Fourier-transform infrared (FT-IR) spectroscopies, X-ray photoelectron and X-ray excited Auger electron spectroscopies (XPS, XE-AES), glancing incidence X-ray diffraction (GIXRD), and reflection high energy electron diffraction (RHEED). The use of moderate deposition temperatures (<= 300 degrees C), together with the unique activation provided by nonequilibrium plasmas, prevented state reactions between the two oxides and promoted Co3O4 growth on the tips of vertically aligned ZnO nanostructures. In particular, the resulting quasi-1D Co3O4/ZnO composites were characterized by an interface epitaxial-like relationship, an important issue for the development of semiconductor-based functional nanosystems. Photoinduced hydrophilic (PH) and photocatalytic (PC) performances of the present nanocomposites were preliminarily investigated, showing attractive results toward the possible fabrication of advanced smart materials

Photocatalytic and antibacterial activity of TiO2 and Au/TiO2 nanosystems

This work focuses on the photocatalytic performances and antibacterial activity of TiO2 and Au/TiO2 nanosystems. While the former are obtained by a sol\u2013gel route, the latter are synthesized by an innovative hybrid RF-sputtering/sol\u2013gel approach, followed by ex situ annealing in air up to 600 \u25e6C. Important information on nanoparticle size, shape and distribution is obtained by the combined use of glancing incidence x-ray diffraction (GIXRD) and field emission-scanning electron microscopy (FE-SEM). Subsequently, the photocatalytic performances of the obtained nanosystems in the decomposition of the azo-dye Plasmocorinth B and their antibacterial activity in the elimination of Bacillus subtilis are illustrated and discussed in comparison with films obtained from standard Degussa P25 powders. The obtained results show a significant dependence of the functional performances on the system\u2019s compositional, structural and morphological properties. In particular, the dispersion of gold nanoparticles on the TiO2 matrix has a beneficial influence on the azo-dye photodegradation, whereas the antimicrobial activity of Au/TiO2 films is retarded with respect to pure TiO2

Zr and Hf oxoclusters as building blocks for the preparation of nanostructured hybrid materials and binary oxides MO2\u2013SiO2 (M = Hf, Zr)

Silica materials embedding ZrO2 or HfO2 were prepared by copolymerisation of organically modified oxozirconium or oxohafnium clusters M4O2(OMc)12 (M = Zr, Hf and OMc = methacrylate) with (methacryloxymethyl)triethoxysilane or (methacryloxypropyl)trimethoxysilane. Free radical copolymerisation of the oxoclusters bearing 12 methacrylate groups with the methacrylate-functionalized siloxanes allows stable anchoring of the clusters to the silica network formed by the hydrolysis and condensation of the alkoxy groups. This route represents a valuable strategy to yield a very homogeneous dispersion of the MO2 precursors inside the silica matrix. The composition and the microstructural features of the starting hybrid gels were studied by solid state 13C and 29Si NMR spectroscopy and FT IR transmission spectroscopy. Their evolution upon mild heating (up to 180 \ub0C) was followed by FT-IR Attenuated Total Reflectance spectroscopy (ATR), while their thermal behaviour was studied by thermogravimetric analysis (TGA). The covalent incorporation of the clusters into the silica hybrid matrix was studied at several temperatures. Through X-Ray Diffraction (XRD) and Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) it is demonstrated that temperatures above 800 \ub0C yield binary oxides MO2\u2013SiO2 (M = Zr, Hf). Delayed crystallisation of HfO2 and tetragonal ZrO2 from 450 \ub0C to at least 800 \ub0C was detected, which is ascribed to the presence of a homogeneous dispersion of the guest oxide in the silica matrix

XAS and GIXRD Study of Co Sites in CoAl2O4 Layers Grown by MOCVD

The chemical environment of Co sites in CoAl2O4 layers grown by metal-organic chemical vapor deposition has been investigated by X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD). It is shown that the air- or [O2 + H2O]-annealing at 500 °C of the layers deposited at low temperature induce a partial crystallization with the formation of (Co1-2ηAl2)(Co2Al2η)(Co 2ηAl2(1-η)))O4 spinel (η = 0.2-0.27). Nevertheless, slightly more than half of Co remains in an amorphous phase, and XAS data are consistent with the formation of a medium-range ordered Co3O4 phase, especially upon air-annealing. Layers grown at higher temperatures (600-650 °C) exhibit a similar but more complex structure, since the presence of an additional medium-range ordered phase (likely, CoAl2O4) is also revealed. The air-annealing at high temperature (800 °C) generates blue, almost completely crystalline, CoAl2O4 layers. Optical properties of deposited layers are discussed by referring to the outcomes of structural results. In particular, the optical absorption spectrum results negligibly affected by the presence of the amorphous phase, while absorptions present in the 300-500 nm range, responsible for the green layer color and evident in samples annealed in an oxidizing atmosphere or grown at high temperature, are likely caused by the octahedrally coordinated Co ions of the partially inverted spinel (Co;- 2ηAl2η)(Co2(1-η)Al 2(1-η))O4 -))O4 phase. Despite the XRD analysis that ultimately demonstrates the presence of octahedrally coordinated Co ions, whose oxidation state in the spinel phase is in majority Co(II), the occurrence of Co(III) species with an octahedral environment cannot be ruled out