Chiara Maccato

Efficient water oxidation at carbon nanotube–polyoxometalate electrocatalytic interfaces

Water is the renewable, bulk chemical that nature uses to enable carbohydrate production from carbon dioxide. The dream goal of energy research is to transpose this incredibly efficient process and make an artificial device whereby the catalytic splitting of water is finalized to give a continuous production of oxygen and hydrogen. Success in this task would guarantee the generation of hydrogen as a carbon-free fuel to satisfy our energy demands at no environmental cost. Here we show that very efficient and stable nanostructured, oxygen-evolving anodes are obtained by the assembly of an oxygen-evolving polyoxometalate cluster (a totally inorganic ruthenium catalyst) with a conducting bed of multiwalled carbon nanotubes. Our bioinspired electrode addresses the one major challenge of artificial photosynthesis, namely efficient water oxidation, which brings us closer to being able to power the planet with carbon-free fuels.

The Potential of Supported Cu2O and CuO Nanosystems in Photocatalytic H2 Production

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.

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?gel route, the latter are synthesized by an innovative hybrid RF-sputtering/sol?gel approach, followed by ex situ annealing in air up to 600??C. 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 systems 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.

F-Doped Co3O4 Photocatalysts for Sustainable H2 Generation from Water/Ethanol

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.

Co3O4/ZnO nanocomposites: from plasma synthesis to gas sensing applications.

Herein, we describe the design, fabrication and gas sensing tests of p-Co(3)O(4)/n-ZnO nanocomposites. Specifically, arrays of (001) oriented ZnO nanoparticles were grown on alumina substrates by plasma enhanced-chemical vapor deposition (PECVD) and used as templates for the subsequent PECVD of Co(3)O(4) nanograins. Structural, morphological and compositional analyses evidenced the successful formation of pure and high-area nanocomposites with a tailored overdispersion of Co(3)O(4) particles on ZnO and an intimate contact between the two oxides. Preliminary functional tests for the detection of flammable/toxic analytes (CH(3)COCH(3), CH(3)CH(2)OH, NO(2)) indicated promising sensing responses and the possibility of discriminating between reducing and oxidizing species as a function of the operating temperature.

Knitting the Catalytic Pattern of Artificial Photosynthesis to a Hybrid Graphene Nanotexture

The artificial leaf project calls for new materials enabling multielectron catalysis with minimal overpotential, high turnover frequency, and long-term stability. Is graphene a better material than carbon nanotubes to enhance water oxidation catalysis for energy applications? Here we show that functionalized graphene with a tailored distribution of polycationic, quaternized, ammonium pendants provides an sp(2) carbon nanoplatform to anchor a totally inorganic tetraruthenate catalyst, mimicking the oxygen evolving center of natural PSII. The resulting hybrid material displays oxygen evolution at overpotential as low as 300 mV at neutral pH with negligible loss of performance after 4 h testing. This multilayer electroactive asset enhances the turnover frequency by 1 order of magnitude with respect to the isolated catalyst, and provides a definite up-grade of the carbon nanotube material, with a similar surface functionalization. Our innovation is based on a noninvasive, synthetic protocol for graphene functionalization that goes beyond the ill-defined oxidation-reduction methods, allowing a definite control of the surface properties.

Vertically oriented CuO/ZnO nanorod arrays: from plasma-assisted synthesis to photocatalytic H2 Production

1D CuO/ZnO nanocomposites were grown on Si(100) substrates by means of an original two-step synthetic strategy. ZnO nanorod (NR) arrays were initially deposited by plasma enhanced-chemical vapor deposition (PE-CVD) from an Ar–O2 atmosphere. Subsequently, tailored amounts of CuO were dispersed over zinc oxide matrices by radio frequency (RF)-sputtering of Cu from Ar plasmas, followed by thermal treatment in air. A thorough characterization of the obtained systems was carried out by X-ray photoelectron and X-ray excited-Auger electron spectroscopies (XPS and XE-AES), glancing incidence X-ray diffraction (GIXRD), field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDXS), atomic force microscopy (AFM), transmission electron microscopy (TEM), electron diffraction (ED) and energy filtered-TEM (EF-TEM). Pure and highly oriented CuO/ZnO NR arrays, free from ternary Zn–Cu–O phases and characterized by a copper(II) oxide content controllable as a function of the adopted RF-power, were successfully obtained. Interestingly, the structural relationships between the two oxides at the CuO/ZnO interface were found to depend on the overall CuO loading. The obtained nanocomposites displayed promising photocatalytic performances in H2 production by reforming of ethanol–water solutions under simulated solar illumination, paving the way to the sustainable conversion of solar light into chemical energy.

Columnar CeO2 nanostructures for sensor application

CeO2 columnar nanostructures with tailored properties were synthesized by chemical vapour deposition on Si(100) and Al2O3 substrates between 350 and 450 °C and characterized in their structure, composition and morphology by means of a multi-technique approach. Their higher sensitivity in the detection of gaseous ethanol and nitrogen dioxide with respect to continuous CeO2 thin films opens interesting perspectives for the development of nanosized sensor devices.

Controlled vapor-phase synthesis of cobalt oxide nanomaterials with tuned composition and spatial organization

Cobalt oxide nanostructures are deposited by Chemical Vapor Deposition (CVD) on Si(100) substrates at temperatures between 300 and 550 °C, using for the first time a novel Co(II) adduct as molecular precursor [Co(hfa)2·TMEDA; hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate, TMEDA = N,N,N′,N′-tetramethylethylenediamine]. The preparation is conducted either under dry (O2) or wet (O2 + H2O) oxygen atmospheres, at total pressures of 3.0 or 10.0 mbar. The obtained results evidence that, upon dry O2 at 10.0 mbar, the initial nucleation of CoO occurs, followed by its progressive oxidation to Co3O4 during the subsequent growth stages. In a different way, cobalt monoxide can be selectively obtained at 3.0 mbar. In all cases, water vapor acts as an oxidant towards cobalt, favoring the formation of Co3O4 phases with a more pronounced {111} and {110}-type faceting. Structural, compositional and morphological characterization evidences the possibility of obtaining high purity CoO/Co3O4 systems with tailored morphological features, from films to columnar nanostructures, thus highlighting the potential and versatility of the proposed synthetic strategy.

Bismuth oxychloride nanoflakes: Interplay between composition-structure and optical properties

Strongly (001) oriented BiOCl nanoflakes have been prepared at room temperature by the controlled hydrolysis of bismuth chloride in the presence of acetylacetone. The nanoflakes thermally treated in air up to 600 °C have been studied by X-Ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Composition, structure and morphology of the nanoflakes have been correlated to their electronic absorption and luminescence properties. Irrespective of the thermal treatments, the samples are characterized by transmittance higher than 98% in the near-infrared region. In the mildly annealed specimen (≤ 200 °C), the absorption bands in the ultraviolet can be effectively exploited for the selective excitation of the blue (394 nm) and green (520 nm) photoluminescence, the latter being visible only for λ(exc) > 310 nm. Conversely, at higher temperature only the blue emission is observed which, on the basis of the observed trend, can be assigned to emitting centres located in the oxide sheet of the Bi-O-Cl stacks.