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•Pt-based carbonyl clusters are suitable precursor for small Pt NPs.•Cluster derived materials are effective in base-free HMF oxidation.•Sn addition enhances catalyst activity and ...stability.
In the present work, Pt and Pt/Sn nanoparticles (NPs), synthesized from carbonyl cluster precursors were deposited on TiO2 and the resulting materials were tested as catalysts in selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). The work was mainly focused on the study of the formation of bimetallic or mixed oxide-metal nanoparticles on TiO2 starting with Pt/Sn carbonyl clusters and on the structure-activity relationship in the reaction of HMF oxidation in base-free conditions. The developed synthesis procedure allowed to obtain very small mono and bimetallic particles characterized by a narrow particle size distribution. Promising results in base-free FDCA production have been achieved using the prepared samples. In particular, the introduction of Sn in an equimolar amount with Pt improved the catalyst activity as well as its time stability upon operation, demonstrating that the modification of Pt electronic configuration by Sn is a key factor for the mastering of functional performances.
Sunlight‐driven hydrogen production via photoreforming of aqueous solutions containing renewable compounds is an attractive option for sustainable energy generation with reduced carbon footprint. ...Nevertheless, the absence of photocatalysts combining high efficiency and stability upon solar light activation has up to date strongly hindered the development of this technology. Herein, two scarcely investigated iron(III) oxide polymorphs, β‐ and ε‐Fe2O3, possessing a remarkable activity in sunlight‐activated H2 generation from aqueous solutions of renewable oxygenates (i.e., ethanol, glycerol, glucose) are reported. For β‐Fe2O3 and ε‐Fe2O3, H2 production rates up to 225 and 125 mmol h−1 m−2 are obtained, with significantly superior performances with respect to the commonly investigated α‐Fe2O3.
Sunlight‐activated photoreforming of renewable oxygenates promoted by Fe2O3 nanosystems is a very attractive process for hydrogen production. In this context, scarcely investigated β‐ and ε‐Fe2O3 polymorphs, fabricated by chemical vapor deposition, show very promising performances for photocatalytic solar hydrogen generation. The present approach holds a remarkable potential even for the synthesis of added‐value by‐products, paving the way to manifold technological applications.
Transition metal complexes with β-diketonate and diamine ligands are valuable precursors for chemical vapor deposition (CVD) of metal oxide nanomaterials, but the metal-ligand bond dissociation ...mechanism on the growth surface is not yet clarified in detail. We address this question by density functional theory (DFT) and ab initio molecular dynamics (AIMD) in combination with the Blue Moon (BM) statistical sampling approach. AIMD simulations of the Zn β-diketonate-diamine complex Zn(hfa)
TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA =
,
,
,
-tetramethylethylenediamine), an amenable precursor for the CVD of ZnO nanosystems, show that rolling diffusion of this precursor at 500 K on a hydroxylated silica slab leads to an octahedral-to-square pyramidal rearrangement of its molecular geometry. The free energy profile of the octahedral-to-square pyramidal conversion indicates that the process barrier (5.8 kcal/mol) is of the order of magnitude of the thermal energy at the operating temperature. The formation of hydrogen bonds with surface hydroxyl groups plays a key role in aiding the dissociation of a Zn-O bond. In the square-pyramidal complex, the Zn center has a free coordination position, which might promote the interaction with incoming reagents on the deposition surface. These results provide a valuable atomistic insight on the molecule-to-material conversion process which, in perspective, might help to tailor by design the first nucleation stages of the target ZnO-based nanostructures.
Hy wire: Supported Cu2O 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.
Hy wire: Supported Cu2O 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.
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.
ZnO−TiO2 nanocomposites were synthesized by an innovative chemical vapor deposition (CVD) strategy, based on the initial growth of ZnO nanoplatelets (host) and the subsequent dispersion of TiO2 ...nanoparticles (guest). Ti(O i Pr)2(dpm)2 and Zn(hfa)2·TMEDA (O i Pr: iso-propoxy; dpm: 2,2,6,6-tetramethyl-3,5-heptanedionate; hfa: 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; and TMEDA: N,N,N‘,N‘-tetramethylethylenediamine) were adopted as Ti and Zn molecular sources, respectively. The syntheses were performed in nitrogen plus wet oxygen atmospheres at relatively low temperatures (350−400 °C) on Si(100) and Al2O3 substrates, avoiding ex-situ thermal treatment to preserve the chemical identity of the host and guest phases. The process resulted in the formation of ZnO−TiO2 nanocomposite deposits with an average thickness of 140 nm, whose characteristics were directly affected by the host matrix porosity and the guest amount and dispersion, tailored by varying the TiO2 deposition time. In this framework, particular attention was devoted to the investigation of the composite chemico-physical properties as a function of the adopted processing parameters. Furthermore, the gas sensing performances of the nanocomposites in the detection of volatile organic compounds (CH3COCH3, CH3CH2OH, and CO) resulted in being directly dependent on their composition and morphology, revealing better performances than the pristine ZnO systems. These results disclose intriguing perspectives for the development of sensing devices for environmental purposes and food control monitoring.
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.
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