Nanoscale Mn3O4 Thin Film Photoelectrodes Fabricated by a Vapor-Phase Route

\u3b1-Mn3O4 (hausmannite) nanostructured films were fabricated by chemical vapor deposition (CVD) on indium tin oxide (ITO)-coated glass substrates from a \u3b2-diketonate 12diamine Mn(II) precursor. Materials were grown in a N2 + O2 atmosphere in the presence of water vapor, investigating the influence of growth temperature and total pressure on the system structural, compositional, morphological, and optical properties through a multitechnique characterization approach. The obtained \u3b1-Mn3O4 nanodeposits were ultimately tested as catalysts in the photoelectrochemical (PEC) splitting of water under simulated solar illumination, with particular focus on the interplay relationships between the adopted preparative conditions and the resulting functional performances. The amphoteric semiconducting behavior along with the PEC properties markedly dependent on the deposit nanoscale organization opens interesting avenues to an eventual implementation of the target materials in view of sustainable applications

Controlled Surface Modification of ZnO Nanostructures with Amorphous TiO2 for Photoelectrochemical Water Splitting

The utilization of solar radiation to trigger photoelectrochemical (PEC) water splitting has gained interest for sustainable energy production. In this study, attention is focused on the development of ZnO\u2013TiO2 nanocomposite photoanodes. The target systems are obtained by growing porous arrays of highly crystalline, elongated ZnO nanostructures on indium tin oxide (ITO) by chemical vapor deposition. Subsequently, the obtained nanodeposits are functionalized with TiO2 via radio frequency-sputtering for different process durations, and subjected to final annealing in air. Characterization results demonstrate the successful formation of high purity composite systems in which the surface of ZnO nanostructures is decorated by ultra-small amounts of amorphous titania, whose content can be conveniently tailored as a function of deposition time. Photocurrent density measurements in sunlighttriggered water splitting highlight a remarkable performance enhancement with respect to single-phase zinc and titanium oxides, with up to a threefold photocurrent increase compared to bare ZnO. These results, mainly traced back to the formation of ZnO/TiO2 heterojunctions yielding an improved photocarrier separation, show that the target nanocomposites are attractive photoanodes for efficient PEC water splitting

Particle size effects on the reducibility of titanium dioxide and its relation to the water–gas shift activity of Pt/TiO2 catalysts

Summarization: The effect of primary particle size of titanium dioxide on the reducibility of Pt/TiO2 catalysts by carbon monoxide and hydrogen was investigated using temperature-programmed reduction (TPR) techniques and in situ Raman and Fourier transform infrared spectroscopy (FTIR). Experiments were conducted over Pt catalysts supported on four commercial titanium dioxide carriers of variable structural characteristics, the water–gas shift (WGS) activity of which increases significantly with decreasing primary crystallite size of the support. TPR profiles obtained for the preoxidized catalysts using H2 as a reductant are characterized by a low-temperature consumption peak, attributed to the reduction of PtOx species, and a high-temperature peak, attributed to the reduction of TiO2. The intensity of the latter peak, which is a measure of the reducibility of the support, increases drastically with increasing specific surface area of the catalyst or, conversely, with decreasing primary particle size of TiO2. In situ Raman experiments conducted under hydrogen flow verified that formation of substoichiometric TiOx species begins at lower temperatures and is more facile over Pt/TiO2 catalysts with smaller titania particle sizes. The TPR profiles obtained using CO as a reductant gave qualitatively similar results, exhibiting two CO2 peaks corresponding to reduction of PtOx at low temperatures and of TiO2 at high temperatures. An additional CO2 peak located at intermediate temperatures, which was always accompanied by evolution of gas-phase H2, is attributed to the WGS reaction. FTIR experiments indicate that the reaction occurs via interaction between CO and hydroxyl groups of the support, with intermediate formation of formates. The effect of the titanium dioxide particle size on the reducibility of Pt/TiO2 catalysts and its relation to their WGS activity is discussed with respect to the “regenerative” and “associative” reaction mechanisms.Παρουσιάστηκε στο: Journal of Catalysi

Self-Organized TiO₂ Nanotube Arrays: Synthesis by Anodization in an Ionic Liquid and Assessment of Photocatalytic Properties

Self-organized TiO2 nanotube (NT) arrays were produced by anodization in ethylene glycol (EG) electrolytes containing 1-n-butyl-3-methyl-imidazolium tetrafluoroborate (BMI.BF4) ionic liquid and water. The morphology of the as-formed NTs was considerably affected by changing the anodization time, voltage, and water and ionic liquid electrolyte concentrations. In general, a nanoporous layer was formed on the top surface of the TiO2 NTs, except for anodization at 100 V with 1 vol % of BMI.BF4, where the NT’s mouth was revealed. The length and bottom diameter of the NTs as well as the pore diameter of the top layer showed a linear relationship with increased anodization voltage. These TiO2 NTs were tested as photocatalysts for methyl orange photodegradation and hydrogen evolution from water/methanol solutions by UV light irradiation. The results show that the TiO2 NTs obtained by anodization in EG/H2O/BMI.BF4 electrolytes are active and efficient for both applications