Mn3O4 thin films were fabricated on SrTiO3(111) and Y3Al5O12(100) substrates by chemical vapor deposition (CVD) under O2 atmospheres, starting from a fluorinated Mn(II) diketonate-diamine adduct. The ...obtained systems were investigated by a multi-technique characterization in order to elucidate the interplay between preparation conditions and their chemico-physical properties. The results highlighted the formation of phase-pure and homogeneous α-Mn3O4 (haussmannite) films, characterized by a smooth morphology, an appreciable Vis light absorption and structural features directly dependent on the used substrate. The target systems were uniformly doped with fluorine, due to the used Mn compound acting as a single-source precursor for both Mn and F. In addition, magnetic force microscopy measurements revealed the formation of spin domains and long-range magnetic order in the target materials, paving the way to their future implementation as magnetic media toward device integration for data storage.
F-doped phase-pure α-Mn3O4 films were grown by a convenient chemical vapor deposition route on single-crystal substrates and characterized by magnetic force microscopy for the first time. Display omitted
•First report on the chemical vapor deposition of Mn3O4 films on Y3Al5O12(100) and SrTiO3(111).•Fluorine-doped α-Mn3O4 (haussmannite) systems with tailored structure and morphology.•Compositional, optical and magnetic force microscopy investigation of the target materials.
Nanocomposite Fe2O3Co3O4 photoanodes for photoelectrochemical H2O splitting were prepared by a plasma‐assisted route. Specifically, Fe2O3 nanostructures were grown by plasma enhanced‐chemical vapor ...deposition, followed by cobalt sputtering for different process durations. The systems were annealed in air after, or both prior and after, sputtering of Co, to analyze the treatment influence on functional performances. The interplay between processing conditions and chemico‐physical features was investigated by a multi‐technique characterization. Photocurrent density measurements in sunlight‐assisted H2O splitting revealed a performance improvement upon Co3O4 loading. A cathodic shift of the onset potential was also observed, highlighting Co3O4 activity as catalyst for the oxygen evolution reaction.
Fe2O3Co3O4 nanomaterials are fabricated on FTO substrates by means of a two‐step strategy, consisting in the plasma enhanced‐CVD of Fe2O3 followed by cobalt sputtering. A thorough characterization of the obtained systems as a function of thermal treatment conditions and cobalt loading is presented, followed by functional testing in photoelectrochemical water splitting activated by solar light.
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•β-Fe2O3/CuO and β-Fe2O3/WO3 nanoheterostructures are developed via a two-step vapor-phase route.•The fabricated materials are tested as De-NOx photocatalysts.•The target ...heterostructures show an enhanced NO photochemical removal with negligible release of toxic intermediates.•The performances higher than those of single oxides are attributed to O defectivity and enhanced charge carrier separation.••O2− radicals are the main species contributing to NOx oxidation.
The increasing release and accumulation of harmful nitrogen oxides (NOx with x = 1,2) in industrial and urban environments renders the efficient removal of these atmospheric pollutants an urgent and obligatory issue. In this regard, the advantages yielded by photocatalytic oxidation processes have triggered the search for eco-friendly catalysts featuring an improved efficiency. In this work, we propose the use of heterostructures based on β-Fe2O3, a scarcely investigated iron(III) oxide polymorph, as viable De-NOx photocatalysts with appealing functional performances. The present materials were fabricated in supported form by chemical vapor deposition (CVD) of Fe2O3. A proof-of-principle investigation on the modulation of material performances by heterostructure formation is explored through Fe2O3 functionalization with CuO or WO3 by radio frequency (RF)-sputtering. The obtained results reveal a controllable dispersion of CuO or WO3 in close contact with β-Fe2O3, a crucial issue to profitably exploit their mutual interplay for De-NOx applications. A preliminary analysis in this regard evidenced very encouraging conversion efficiency and selectivity towards nitrate formation, outstanding among non-titania oxide-based De-NOx photocatalysts. The improved photoactivity with respect to bare Fe2O3, CuO and WO3 was related to a higher oxygen defectivity and an enhanced separation of photogenerated charge carriers, enabled by the matched band edges in the target heterostructures.
A single-step plasma enhanced-chemical vapor deposition (PE-CVD) route for the synthesis of F-doped iron(III) oxide nanomaterials is presented. Growth experiments, performed from a fluorinated Fe(II) ...β-diketonate precursor on Indium Tin Oxide (ITO) between 200 and 400 °C, yielded columnar β-Fe2O3 arrays with a preferential (100) growth direction. The fluorine content in the deposits could be adjusted by the sole variation of the deposition temperature controlling, in turn, the optical absorption and energy bandgap. Photocurrent measurements and Mott–Schottky analyses, carried out in Na2SO4 solution under one sun illumination, evidenced a conductivity switch from n- to p-type upon increasing fluorine amount in the obtained nanomaterials. The sample photocurrent density, donor content and flatband potential support the hypothesis that a progressive substitution of oxygen by fluorine in the iron(III) oxide lattice can alter electronic structure and extend charge carrier lifetimes, making anion-doped β-Fe2O3 an efficient water oxidation catalyst.
•Novel PE-CVD approach to β-Fe2O3 nanomaterials on ITO substrates.•Fabrication of columnar arrays with an homogeneous in-depth fluorine doping.•First example of β-Fe2O3 application in photoelectrochemical water splitting.•Modulation of optical and photoelectrochemical properties as a function of fluorine content.
Harnessing solar energy for the production of clean hydrogen by photoelectrochemical water splitting represents a very attractive, but challenging approach for sustainable energy generation. In this ...regard, the fabrication of Fe2O3–TiO2 photoanodes is reported, showing attractive performances ≈2.0 mA cm−2 at 1.23 V vs. the reversible hydrogen electrode in 1 M NaOH under simulated one‐sun illumination. This goal, corresponding to a tenfold photoactivity enhancement with respect to bare Fe2O3, is achieved by atomic layer deposition of TiO2 over hematite (α‐Fe2O3) nanostructures fabricated by plasma enhanced‐chemical vapor deposition and final annealing at 650 °C. The adopted approach enables an intimate Fe2O3–TiO2 coupling, resulting in an electronic interplay at the Fe2O3/TiO2 interface. The reasons for the photocurrent enhancement determined by TiO2 overlayers with increasing thickness are unraveled by a detailed chemico‐physical investigation, as well as by the study of photogenerated charge carrier dynamics. Transient absorption spectroscopy shows that the increased photoelectrochemical response of heterostructured photoanodes compared to bare hematite is due to an enhanced separation of photogenerated charge carriers and more favorable hole dynamics for water oxidation. The stable responses obtained even in simulated seawater provides a feasible route in view of the eventual large‐scale generation of renewable energy.
The performances of ≈2.0 mA cm−2 photocurrent at 1.23 V vs. RHE under simulated solar irradiation, along with the system activity even in seawater, pave the way to the sustainable generation of renewable energy starting from abundant natural resources.
Among oxide semiconductors, p-type Mn3O4 systems have been exploited in chemo-resistive sensors for various analytes, but their use in the detection of H2, an important, though flammable, energy ...vector, has been scarcely investigated. Herein, we report for the first time on the plasma assisted-chemical vapor deposition (PA-CVD) of Mn3O4 nanomaterials, and on their on-top functionalization with Ag and SnO2 by radio frequency (RF)-sputtering, followed by air annealing. The obtained Mn3O4-Ag and Mn3O4-SnO2 nanocomposites were characterized by the occurrence of phase-pure tetragonal α-Mn3O4 (hausmannite) and a controlled Ag and SnO2 dispersion. The system functional properties were tested towards H2 sensing, yielding detection limits of 18 and 11 ppm for Mn3O4-Ag and Mn3O4-SnO2 specimens, three orders of magnitude lower than the H2 explosion threshold. These performances were accompanied by responses up to 25% to 500 ppm H2 at 200 °C, superior to bare Mn3O4, and good selectivity against CH4 and CO2 as potential interferents. A rationale for the observed behavior, based upon the concurrence of built-in Schottky (Mn3O4/Ag) and p-n junctions (Mn3O4/SnO2), and of a direct chemical interplay between the system components, is proposed to discuss the observed activity enhancement, which paves the way to the development of gas monitoring equipments for safety end-uses.
Nanocomposite materials based on metal nanoparticles (NPs,
guest) in/on oxide matrices (
host) have attracted increasing attention thanks to their intriguing chemico-physical properties that can be ...tailored as a function of NP size, shape and mutual interactions. The possibility to obtain a controlled dispersion of metal particles in/on suitable oxides (
inside- and
outside-
cluster systems, respectively) paves the way to a broad spectrum of technological applications, ranging from heterogeneous catalysis, to gas sensing and non-linear optics. The control of functional performances relies on tailoring the system properties by design through a suitable choice of the synthesis and processing routes.
In this context, the present review provides a synoptic overview on our recent research activity concerning nanocomposites containing 11th group metal clusters (Cu, Ag and Au), dispersed in/on oxide matrices (SiO
2, TiO
2, Al
2O
3). We begin by briefly outlining the interest and size-dependent properties of such systems. Subsequently, the attention is switched to a survey on the preparation strategies previously adopted in the literature, focusing in particular on the use of
soft methods, such as sol–gel (SG), RF-sputtering and their innovative combination. The most relevant results on M′/M
x
O
y
nanocomposites (where M′
=
Cu, Ag, Au and M
=
Si, Ti, Al) obtained by these routes are then comparatively discussed, highlighting analogies and differences between them. Finally, the most attractive research perspectives in the field are briefly presented.
CuO/ZnO nanocomposites were synthesized on Al2O3 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 O3, CH3CH2OH, and H2). The obtained data are critically discussed and interrelated with the chemical and physical properties of the nanocomposites.
Trapped in the array: High‐purity p‐type CuO/n‐type ZnO nanocomposites were prepared by Cu sputtering on columnar ZnO arrays obtained by plasma‐enhanced chemical vapor deposition, followed by annealing in air. Preliminary gas‐sensing tests revealed very attractive responses, along with the possibility of discriminating between oxidizing and reducing species.
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