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1.
Dalton Trans ; 41(47): 14354-9, 2012 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-23044719

RESUMO

Growth kinetics of CdSe nanocrystals generated inside three selected polymers (polyvinylpyrrolidone--PVP, polyethyleneglycol--PEG and polyvinylalcohol--PVA) are demonstrated to follow a self-catalytic path, with growth rates depending on the nature of the polymer, i.e. on the capability to activate the cadmium species present in the solution of a metal precursor. A two-step process drives the size evolution of nanocrystals and a critical diameter value can be identified at which the growth regime changes. The medium-term stability evaluation of nanocomposites indicates that, after an initial rearrangement, polymers keep stable the embedded CdSe nanocrystals.

2.
Chemphyschem ; 13(9): 2342-8, 2012 Jun 18.
Artigo em Inglês | MEDLINE | ID: mdl-22532392

RESUMO

CuO/ZnO nanocomposites were synthesized on Al(2)O(3) substrates by a hybrid plasma-assisted approach, combining the initial growth of ZnO columnar arrays by plasma-enhanced chemical vapor deposition (PE-CVD) and subsequent radio frequency (RF) sputtering of copper, followed by final annealing in air. Chemical, morphological, and structural analyses revealed the formation of high-purity nanosystems, characterized by a controllable dispersion of CuO particles into ZnO matrices. The high surface-to-volume ratio of the obtained materials, along with intimate CuO/ZnO intermixing, resulted in the efficient detection of various oxidizing and reducing gases (such as O(3), CH(3)CH(2)OH, and H(2)). The obtained data are critically discussed and interrelated with the chemical and physical properties of the nanocomposites.

3.
Nanoscale ; 4(9): 2813-25, 2012 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-22434486

RESUMO

The present paper aims at extracting key physical and chemical concepts for the development of inorganic nanomaterials with controlled size, shape, and topology. In particular, efforts are made to identify general guiding principles for the rational design of 0D, 1D, 2D and 3D architectures, focusing on selected model systems as representative case studies. To this aim, different strategies and approaches are discussed, in an attempt to unify concepts and ideas common to solid-, liquid- and gas-phase synthetic routes. Furthermore, the importance of tailoring the nanomaterial composition, structure and morphology is also highlighted in relation to their eventual technological applications.

4.
Nanotechnology ; 23(2): 025502, 2012 Jan 20.
Artigo em Inglês | MEDLINE | ID: mdl-22166305

RESUMO

Ag/ZnO nanocomposites supported on polycrystalline Al2O3 were synthesized by an unprecedented approach combining plasma enhanced chemical vapor deposition (PE-CVD) of ZnO matrices and the subsequent deposition of Ag nanoparticles (NPs) by radio frequency (RF) sputtering. The system structure, composition and morphology were investigated by glancing incidence x-ray diffraction (GIXRD), secondary ion mass spectrometry (SIMS), field emission scanning electron microscopy (FE-SEM) and energy dispersive x-ray spectroscopy (EDXS). A tailored dispersion and distribution of silver particles could be obtained under mild conditions by the sole variation of the sputtering time. Gas sensing properties toward flammable and toxic gases, both reducing (CH3CH2OH, CH3COCH3) and oxidizing (O3), were investigated in the temperature range 100-400 °C. Beside the high sensitivity, the developed sensors exhibited a response proportional to Ag content, thanks to catalytic and electronic effects promoted by silver NPs. In addition, discrimination between oxidizing and reducing analytes was enabled by a suitable choice of the adopted working temperature.


Assuntos
Gases/análise , Nanoestruturas/química , Prata/química , Óxido de Zinco/química
5.
Dalton Trans ; 41(1): 149-55, 2012 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-22048471

RESUMO

Iron oxide is a key multi-functional material in many different fields of modern technology. The ß-Fe(2)O(3) cubic phase, one of the least studied Fe-O systems, was obtained by Chemical Vapor Deposition (CVD) using for the first time a Fe(II) ß-diketonate diamine complex, Fe(hfa)(2)·TMEDA, as the molecular source (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N',N'-tetramethylethylenediamine). The strong visible light absorption of ß-Fe(2)O(3) deposits highlights their possible functional application in photocatalytic hydrogen production under solar light. A comprehensive investigation on the Fe(ii) complex, performed by a joint experimental-theoretical approach, explains the molecular origin of its excellent thermal behaviour and reveals why this species is a successful precursor for the CVD of iron oxide nanostructures.

6.
J Am Chem Soc ; 133(48): 19362-5, 2011 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-22053896

RESUMO

p-Type Co(3)O(4) nanostructured films are synthesized by a plasma-assisted process and tested in the photocatalytic production of H(2) from water/ethanol solutions under both near-UV and solar irradiation. It is demonstrated that the introduction of fluorine into p-type Co(3)O(4) results in a remarkable performance improvement with respect to the corresponding undoped oxide, highlighting F-doped Co(3)O(4) films as highly promising systems for hydrogen generation. Notably, the obtained yields were among the best ever reported for similar semiconductor-based photocatalytic processes.


Assuntos
Cobalto/química , Etanol/química , Flúor/química , Hidrogênio/química , Nanoestruturas/química , Óxidos/química , Água/química , Catálise , Luz , Processos Fotoquímicos , Semicondutores
7.
J Nanosci Nanotechnol ; 11(9): 8206-13, 2011 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-22097556

RESUMO

Plasma processing represents an attractive and versatile option for the fabrication of low-dimensional nanomaterials, whose chemical and physical properties can be conveniently tailored for the development of advanced technologies. In particular, Plasma Enhanced-Chemical Vapor Deposition (PE-CVD) is an appealing route to multi-functional oxide nanoarchitectures under relatively mild conditions, owing to the unique features and activation mechanisms of non-equilibrium plasmas. In this context, the potential of plasma-assisted fabrication in advanced nanosystem development is discussed. After a brief introduction on the basic categories of plasma approaches, the perspectives of application to CVD processes are commented, reporting on the growth and characterization of Co3O4 nanomaterials as a case study. Besides examining the interrelations between the material properties and the synthesis conditions, special focus is given to their emerging applications as catalysts for photo-assisted hydrogen production and solid state gas sensors.

8.
Chemistry ; 17(39): 10864-70, 2011 Sep 19.
Artigo em Inglês | MEDLINE | ID: mdl-21853489

RESUMO

Cu(x)O (x=1,2) nanomaterials with tailored composition and properties-a hot topic in sustainable technologies-may be fabricated from molecular sources through bottom-up processes that involve unexpected changes in the metal oxidation state and open intriguing challenges on the copper redox chemistry. How copper(II) sources may lead to copper(I) species in spite of the absence of any explicit reducing agent, and even in the presence of oxygen, is one such question-to date unanswered. Herein, we study copper "reduction without reductants" within one molecule and reveal that the actual reducing agent is abstracted atomic hydrogen. By investigating the fragmentation of a copper(II) precursor for copper oxide nanostructures by combined ESI-MS with multiple collisional experiments (ESI/MS(n)) and theoretical calculations, we highlight a copper-promoted C-H bond activation, leading to reduction of the metal center and formation of a Cu(I)-C-NCCN six-membered ring. Such a novel ring system is the structural motif for a new family of cyclic copper(I) adducts, which show a bonding scheme, herein reported for the first time, that may shed unprecedented light on copper chemistry. Beyond the relevance for the preparation of copper oxide nanostructures, the hydrogen-abstraction/proton-delivery/electron-gain mechanism of copper(II) reduction disclosed herein appears to be a general property of copper and might help to understand its redox reactivity.

9.
Langmuir ; 27(10): 6409-17, 2011 May 17.
Artigo em Inglês | MEDLINE | ID: mdl-21517025

RESUMO

We report on the fabrication of Cu(x)O-TiO(2) (x = 1, 2) nanomaterials by an unprecedented vapor-phase approach. The adopted strategy involves the growth of porous Cu(x)O matrices by means of chemical vapor deposition (CVD), followed by the controlled dispersion of TiO(2) nanoparticles. The syntheses are performed on Si(100) substrates at temperatures of 400-550 °C under wet oxygen atmospheres, adopting Cu(hfa)(2)·TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N',N'-tetramethylethylenediamine) and Ti(O-(i)Pr)(2)(dpm)(2) (O-(i)Pr = isopropoxy; dpm = 2,2,6,6-tetramethyl-3,5-heptanedionate) as copper and titanium precursors, respectively. Subsequently, finely dispersed gold nanoparticles are introduced in the as-prepared systems via radio frequency (RF)-sputtering under mild conditions. The synthesis process results in the formation of systems with chemical composition and nano-organization strongly dependent on the nature of the initial Cu(x)O matrix and on the deposited TiO(2) amount. The decoration with low-size gold clusters paves the way to the engineering of hierarchically organized nanomaterials.

10.
Inorg Chem ; 50(2): 489-502, 2011 Jan 17.
Artigo em Inglês | MEDLINE | ID: mdl-21141945

RESUMO

Three different zirconium thio and oxothio clusters, characterized by different coordination modes of dithioacetate and/or monothioacetate ligands, were obtained by the reaction of monothioacetic acid with zirconium n-butoxide, Zr(O(n)Bu)4, in different experimental conditions. In particular, we isolated the three polynuclear Zr3(µ3-SSSCCH3)2(SSCCH3)6·2(n)BuOH (Zr3), Zr4(µ3-O)2(µ-η(1)-SOCCH3)2(SOCCH3)8(O(n)Bu)2 (Zr4), and Zr6(µ3-O)5(µ-SOCCH3)2(µ-OOCCH3)(SOCCH3)11((n)BuOH) (Zr6) derivatives, presenting some peculiar characteristics. Zr6 has an unusual star-shaped structure. Only sulfur-based ligands, viz., chelating dithioacetate monoanions and an unusual ethane-1,1,1-trithiolate group µ3 coordinating the Zr ions, were observed in the case of Zr3. 1D and 2D NMR analyses confirmed the presence of differently coordinated ligands. Raman spectroscopy was further used to characterize the new polynuclear complexes. Time-resolved extended X-ray absorption fine structure measurements, devoted to unraveling the cluster formation mechanisms, evidenced a fast coordination of sulfur ligands and subsequent relatively rapid rearrangements.


Assuntos
Oxigênio/química , Enxofre/química , Zircônio/química , Ácidos Carboxílicos/química , Cristalografia por Raios X , Indicadores e Reagentes , Ligantes , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Conformação Molecular , Estrutura Molecular , Espectroscopia de Infravermelho com Transformada de Fourier , Análise Espectral Raman , Compostos de Sulfidrila/química
11.
J Nanosci Nanotechnol ; 10(12): 8054-61, 2010 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-21121296

RESUMO

Al2O3-supported Co3O4 nanosystems were grown by a Chemical Vapor Deposition route under O2 + H2O atmospheres at 500 degrees C. Subsequently, the preparation of Au/Co3O4 composites was attained by Radio Frequency-Sputtering of gold onto the previous Co3O4 nanodeposits. Important data on the system structure, morphology and chemical composition were obtained by the combined use of complementary techniques, namely Glancing Incidence X-ray Diffraction, Field Emission-Scanning Electron Microscopy, Atomic Force Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray Photoelectron Spectroscopy and Secondary Ion Mass Spectrometry. Finally, the gas sensing properties of the synthesized systems were probed in the detection of ethanol and hydrogen. The obtained results revealed significant responses already at moderate temperatures, which could be further enhanced by Co3O4 functionalization with Au nanoparticles.


Assuntos
Cobalto/química , Ouro/química , Nanopartículas/química , Nanotecnologia/métodos , Óxidos/química , Óxido de Alumínio/química , Etanol/análise , Gases/análise , Gases/química , Hidrogênio/análise , Microscopia Eletrônica de Varredura , Espectroscopia Fotoeletrônica , Difração de Raios X
12.
ACS Nano ; 4(9): 5147-54, 2010 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-20707317

RESUMO

A novel two-step bottom-up approach to construct a 2D long-range ordered, covalently bonded fullerene/porphyrin binary nanostructure is presented: in the first place, reversible supramolecular interactions between C60 and 5,15-bis(4-aminophenyl)-10,20-diphenylporphyrin are exploited to obtain large domains of an ordered binary network, subsequently a reaction between fullerene molecules and the amino-groups residing on porphyrin units, triggered by thermal treatment, is used to freeze the supramolecular nanostructure with covalent bonds. The resulting nanostructure resists high temperature treatments as expected for an extended covalent network, whereas very similar fullerene/porphyrin nanostructures held together only by weak interactions are disrupted upon annealing at the same or at lower temperatures.

14.
J Phys Chem A ; 114(16): 5295-8, 2010 Apr 29.
Artigo em Inglês | MEDLINE | ID: mdl-20373795

RESUMO

Room-temperature results of cathodoluminescence (CL) spectroscopy investigations are presented for nanostructured titanium dioxide (anatase) thin films (500 nm thick) deposited via RF magnetron sputtering on high-purity silica substrates. The collected CL bands of the anatase thin films, as deposited and after different annealing cycles, showed a broad morphology consisting of three Voigtian bands located at 500, 550, and 610 nm that were partially overlapping. The overall CL emission increased with increasing temperature and time of the annealing cycle as a consequence of the increased crystallinity of the thin film. A clear trend was found for the oxygen-vacancy-related band (located at 610 nm), whose relative intensity decreased, as compared with the as-grown sample, after annealing in air; the higher the annealing temperature, the lower the relative intensity. We evaluated the photoactivity of the nanostructured thin film samples by measuring their photocatalytic activity in aqueous solution toward the degradation of phenol. A relationship between the decrease in oxygen vacancy concentration as a consequence of the annealing and the increase in the photoactivity was highlighted.


Assuntos
Medições Luminescentes/métodos , Membranas Artificiais , Nanoestruturas/química , Titânio/química , Catálise , Fotoquímica , Dióxido de Silício/química
15.
Inorg Chem ; 49(9): 4099-108, 2010 May 03.
Artigo em Inglês | MEDLINE | ID: mdl-20356058

RESUMO

A Zn(II) 2-mercaptonicotinate coordination polymer (Zn1), with Zn(II) ions chelated by both sulfur and oxygen in a distorted square pyramidal environment, and a molecular Zn(II) 2-hydroxynicotinate complex (Zn2) were synthesized by the reaction of zinc acetylacetonate with 2-mercaptonicotinic (Zn1) and 2-hydroxynicotinc (Zn2) acid, respectively, under hydrothermal conditions. The crystal structures of Zn1 and Zn2 were determined by single crystal X-ray diffraction measurements. Dispersion-corrected density functional theory (DFT) calculations reproduce very well the experimental structures and show that Zn1 is stable against hydration, whereas Zn2 is stable against dehydration over wide ranges of temperature and pressure, in agreement with thermogravimetric analysis results. The electronic structure of the two compounds is computed with the DFT+U method. The theoretical valence band agrees well with the X-ray photoelectron spectroscopy experiments. Furthermore, the band gap of Zn1 is found to be narrower than that of Zn1 and is characterized by the presence of sulfur lone pairs at the edge of the valence band.


Assuntos
Simulação por Computador , Elétrons , Modelos Químicos , Ácidos Nicotínicos/química , Compostos Organometálicos/síntese química , Compostos de Sulfidrila/química , Zinco/química , Cristalografia por Raios X , Modelos Moleculares , Estrutura Molecular , Compostos Organometálicos/química , Espectroscopia Fotoeletrônica , Teoria Quântica
17.
Chemphyschem ; 10(18): 3249-59, 2009 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-19882618

RESUMO

The present work is devoted to the preparation of Ag/TiO(2) nanosystems by an original synthetic strategy, based on the radio-frequency (RF) sputtering of silver particles on titania-based xerogels prepared by the sol-gel (SG) route. This approach takes advantage of the synergy between the microporous xerogel structure and the infiltration power characterizing RF-sputtering, whose combination enables the obtainment of a tailored dispersion of Ag-containing particles into the titania matrix. In addition, the system's chemico-physical features can be tuned further through proper ex situ thermal treatments in air at 400 and 600 degrees C. The synthesized composites are extensively characterized by the joint use of complementary techniques, that is, X-ray photoelectron and X-ray excited Auger electron spectroscopies (XPS, XE-AES), secondary ion mass spectrometry (SIMS), glancing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), electron diffraction (ED), high-angle annular dark field scanning TEM (HAADF-STEM), energy-filtered TEM (EF-TEM) and optical absorption spectroscopy. Finally, the photocatalytic performances of selected samples in the decomposition of the azo-dye Plasmocorinth B are preliminarily investigated. The obtained results highlight the possibility of tailoring the system characteristics over a broad range, directly influencing their eventual functional properties.

18.
Phys Chem Chem Phys ; 11(28): 5998-6007, 2009 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-19588023

RESUMO

The physico-chemical properties of the beta-diketonate diamine Cu(ii) compound with hfa (1,1,1,5,5,5-hexafluoro-2-4-pentanedionate) and TMEDA (N,N,N',N' tetramethylethylenediamine), Cu(hfa)(2).TMEDA, have been thoroughly investigated via an integrated multi-technique experimental-computational approach. In the newly found orthorhombic polymorph, as revealed by low temperature single-crystal X-ray studies, the complex is present as a monomer with a distorted octahedral geometry at the Cu(ii) centre. The compound sublimates, without premature side decompositions, at 343 K and 10(-3) Torr. The structural, vibrational, electronic and thermal behavior of the neutral Cu(hfa)(2).TMEDA complex has been investigated along with its fragmentation pathways, initiated by the release of an anionic hfa ligand with formation of a positive Cu(hfa).TMEDA(+) ion. Joint experimental and theoretical analyses led to the rationalization of the first fragmentation steps in terms of the Cu(ii)-ligands bonding properties and Jahn-Teller distortion. The present study suggests applications of Cu(hfa)(2).TMEDA as a precursor for copper and copper oxide materials by Chemical Vapor Deposition.


Assuntos
Cobre/química , Etilenodiaminas/química , Compostos Organometálicos/química , Cristalografia por Raios X
19.
Chemistry ; 15(19): 4931-43, 2009.
Artigo em Inglês | MEDLINE | ID: mdl-19308978

RESUMO

N,N-Dialkylcarbamato complexes of copper(II), [Cu(O(2)CNR(2))(2)] (R = All = allyl, C(3)H(5); iPr, CH(CH(3))(2)) were prepared with the aim of functionalizing silica and nanostructured silica-zirconia matrices. The mixed matrices for the grafting reactions were prepared by copolymerizing MAPTMS (methacryloxypropyltrimethoxysilane), the precursor for the silica matrix, with the zirconium tetranuclear derivative [Zr(4)O(2)(OMc)(12)] (OMc = methacrylate), the precursor for the zirconia nanoparticles. Suspension of the silica and silica-zirconia matrices in a solution of the copper dialkylcarbamate led to the functionalization of the respective substrates. The composition, microstructure, morphology, and physicochemical nature of the copper species grafted on the matrices were investigated by FTIR, X-ray photoelectron spectroscopy (XPS), EPR, X-ray absorption spectroscopy (XAS), XRD, TEM, and dinitrogen adsorption. The effect of selected experimental parameters (the nature of the copper precursor and of the matrix, grafting time, thermal treatment) on the grafting reaction was investigated. The Cu/Si ratio is increased by increasing the grafting time and the ZrO(2)-SiO(2) matrix is more reactive to attack by the carbamato complexes than either prepared or commercial SiO(2). After functionalization of the matrix, thermal treatment yielded nanostructured copper(II) oxide clusters, average diameter 12-15 nm, uniformly supported on the silica and on the silica-zirconia matrices.

20.
ChemSusChem ; 2(3): 230-3, 2009.
Artigo em Inglês | MEDLINE | ID: mdl-19235823

RESUMO

Hy wire: Supported Cu(2)O nanosystems and CuO nanowires obtained by chemical vapor deposition were used in the photocatalytic splitting of methanol/water solutions to produce hydrogen. The results obtained with these systems open appealing perspectives for the clean conversion of sunlight into storable chemical energy.


Assuntos
Cobre/química , Hidrogênio/química , Nanoestruturas/química , Processos Fotoquímicos , Catálise , Metanol/química , Volatilização
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