1,721,187 research outputs found
Nanoarchitectonics of metal oxide materials for sustainable technologies and environmental applications
Full text linkSustainable development compliant with environment and human health protection motivates researchers to explore green solutions towards improved economic and social wellbeing. These objectives, still very far from being achieved especially in developing countries, must necessarily be pursued through the tailored fabrication of low-cost, eco-friendly, efficient and stable multi-functional materials. In particular, nanostructures based on first-row transition metal oxides are amenable candidates for clean energy production, air purification and self-cleaning/anti-fogging purposes, especially if obtained through fabrication strategies allowing a careful modulation of their characteristics. In this highlight, after a brief introduction of the above issues, we provide selected representative examples of green oxide-based nanoarchitectures for the targeted end-uses. Attention is focused on the interplay between the material chemico-physical properties and the resulting functional performances, with the aim of providing some hints to control material behavior by design. In addition, we provide a critical outlook not only on the unique opportunities, but also on the main open challenges related to the use of the above multi-functional materials, in an attempt to stimulate further advancements in these emerging research areas
CVD of nanophasic (Zn,Cd)S thin films: From multi-layers to solid solutions
No full textNanostructured ZnxCd1-xS (0<x<1) thin films were synthesized by CVD on SiO2 substrates using M(O-iPrXan)2 (M=Zn,Cd; O-iPrXan=S2COCH(CH3)2) as precursor compounds. The adopted preparative strategy consisted in the sequential deposition of single-phase MS coatings (M=Zn,Cd) at 300°C in N2 flow, followed by ex-situ annealing in an inert atmosphere at different temperatures in the range 400-700°C. The obtained specimens were thoroughly characterized before and after thermal treatments, with particular attention to their structure, composition, morphology and optical properties. Annealing in N2 at 600°C for 3 h resulted in the formation of a homogeneous ZnxCd1-xS solid solution. Lower temperatures did not allow to obtain an uniform sample composition, while more severe annealing conditions induced CdS sublimation. Moreover, a compositional control of the ZnxCd1-xS ternary phase could be achieved by varying the ZnS overlayer deposition time.
Irrespective of the annealing conditions, all the obtained films resulted contaminant-free and nanophasic (≈25 nm), and possessed an hexagonal crystal structure whose lattice parameters decreased linearly with increasing zinc molar fraction. A parallel evolution of optical absorption spectra was also observed. In the present paper, the interrelations between film properties and processing conditions are investigated, focusing in particular on the (Zn,Cd)S evolution to ZnxCd1-xS solid solutions
MnO2nanomaterials functionalized with Ag and SnO2: An XPS study
No full textThe present study is devoted to the characterization of MnO2-Ag and MnO2-SnO2 nanocomposites of technological interest as gas sensors for food quality control and security applications. In particular, MnO2 nanomaterials were deposited on polycrystalline alumina substrates by plasma enhanced-chemical vapor deposition and functionalized with either Ag or SnO2 nanoparticles by means of radio frequency-sputtering. The target materials were investigated by a multitechnique approach, evidencing the successful formation of nanocomposites with tailored morphology, featuring an intimate contact of their components. Herein, the attention is dedicated to the characterization of system surface composition by x-ray photoelectron spectroscopy. Besides wide scan spectra, data obtained by the analysis of the C 1s, O 1s, Mn 2p, Mn 3s, Ag 3d, Sn 3d, and silver Auger signal spectral features are presented and critically discussed. The results highlight the occurrence of phase-pure MnO2 and SnO2 free from other Mn and Sn oxidation states and of appreciable silver surface oxidation in the target nanomaterials
Sol-gel and CVD Co3O4 thin films characterized by XPS
No full textThe present investigation is focused on x-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XE-AES) analysis of the main core levels (O 1s, Co 2p, and Co LVV) of nanocrystalline Co3O4 coatings. The samples were obtained by CVD and sol-gel routes. Co(dpm)2 (Hdpm = 2,2-6,6-tetramethyl-3,5-heptanedione) was chosen as CVD precursor thanks to its appreciable volatility, the absence of direct Co–C bonds and the presence of thermally labile Co–O moieties. The preparation of the sol-gel films was accomplished starting from methanolic solutions of Co(OCOCH3)2⋅4H2O due to the clean conversion of cobalt acetate into cobalt oxides. The obtained Co3O4 films were bluish-brown, homogenous, crack-free, and adhered well to the substrates. The microstructural analyses revealed the formation of single-phase nanostructured layers with average crystallite dimensions ranging between 15 and 26 nm
Fe2O3-WO3 and Fe2O3-CuO nanoheterostructures by XPS
Full text linkThe detrimental effects of gaseous nitrogen oxides (NOx, with x = 1 and 2) on both human health and the environment have triggered efforts aimed at the development of solar-activated photocatalysts for their efficient removal. In this regard, Fe2O3-WO3 and Fe2O3-CuO nanoheterostructures were prepared by a two-step vapor phase route. In particular, chemical vapor deposition (CVD) of β-Fe2O3, a scarcely investigated iron(III) oxide polymorph, was followed by radio frequency-sputtering of WO3 or CuO under mild conditions. The adopted strategy enabled the obtainment of nanoheterostructures with a peculiar pyramidal morphology and a uniform dispersion of CuO or WO3 onto the pristine iron(III) oxide. In this work, the chemical composition of the target systems was investigated by means of x-ray photoelectron and x-ray excited-Auger electron spectroscopies. In addition to the identification of elemental chemical states, the reported results confirmed the formation of pure and O-deficient systems, in which the direct interplay between the single components opens the door to air purification using the developed systems as photocatalysts
Plasma-Assisted Growth of β-MnO2Nanosystems as Gas Sensors for Safety and Food Industry Applications
No full textImpact of -OH surface defects on the electronic and structural properties of nickel oxide thin films
No full textNickel oxide-based thin films and nanomaterials are a current focus of intense research efforts due to the broad range of end uses in a variety of applications. While the chemico-physical properties of bulk NiO crystals, characterized by a wide band gap (4.0-4.3 eV), antiferromagnetic ordering and p-type character, have been extensively studied, for NiO films/nanomaterials the microscopic-level relationships between the surface defect structure and electronic properties are far from being completely elucidated. In the present work, we show that, by using density functional theory with the Hubbard correction (DFT+U), -OH surface defects, almost ubiquitous on oxide surfaces, can directly influence the electronic structure of NiO(100) model slabs. Depending on the exact defect chemical structure and surface defect density, the energy gap of the -OH bearing NiO(100) system can be engineered, and its behaviour can be modulated from p-type to n-type. The insights provided herein may be of importance for the modulation of NiO nanosystem properties as a function of specific applications, an important issue for their eventual real-world utilization
Electrochemical and surface characterisation of poly(3,4-ethylenedioxythiophene) dodecylbenzenesulfonate layers
No full textPoly(3,4-ethylenedioxythiophene) (PEDOT) films were electrochemically synthesised with sodium dodecylbenzenesulfonate (DBS) and chloride acting as dopant anions within the polymer matrix. Upon redox switching of the PEDOT/DBS film between conducting and non-conducting states, the DBS anion remained within the polymer and cation insertion and expulsion occurred, as confirmed by Electrochemical Quartz Crystal Microbalance (EQCM) measurements. Electrolytes composed of alkali metal cations of varying masses (Li+, Na+, K+) were employed to investigate the cation insertion/expulsion processes, thereby resulting in varying mass changes being observed upon film redox switching. The charging and discharging of bulky anion doped polymer films presented higher capacitance upon charging and lower capacitance when discharging, which is expected during doping and de-doping as confirmed by AC impedance. In this work, the main results obtained by chemical-physical characterisation are presented and critically discussed, with regard to the possible use of a viable conducting polymer as a drug delivery vehicle
Magnetic properties of ε iron(III) oxide nanorod arrays functionalized with gold and copper(II) oxide
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