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Cu-based cermets suitable for electrodes in Symmetric and Reversible Solid Oxide Fuel Cells (SR-SOFCs) based on the Cerium Gadolinum Oxide (CGO) electrolyte were developed and successfully tested in the intermediate temperature range (600–800 °C). The Cu/CGO cermets were prepared by means of a self-combustion based citrate procedure and the effects of synthesis conditions were studied. Characterization of the Cu/CGO nanocomposites by XPS, XRD, SEM, TPR suggested that this procedure allows obtaining highly dispersed CuO on the cerium gadolinium oxide. Conversion higher than 80% was observed above 600 °C in methane total oxidation. Synthesis parameters affected both properties and catalytic performance. The behaviour under redox conditions was studied by operando high-energy XRD under oscillating H2/O2 feed. Reducing conditions converted CuO into Cu(0) passing through an intermediate Cu2O phase while increasing the conductivity and the reactivity. This structural modification was completely reversible. The high stability, reversibility, catalytic activity and electrochemical performance make these electrodes promising for SR-SOFCs.

Luminescent upconversion nanocrystals (UCNCs) have become one of the most promising nanomaterials for biosensing, imaging, and theranostics. However, their ultimate translation into robust luminescent probes for daily use in biological and medical laboratories requires comprehension and control of the many possible deactivation pathways that cause upconversion luminescence (UCL) quenching. Here, we demonstrate that thorough modeling of UCL rise and decay kinetics using a freely accessible software can identify the UCL quenching mechanisms in small (40 nm) UCNCs with spatial and temporal resolution. Applied to the most relevant β-NaYF

ZnS nanoparticles (NPs) were synthesized using a simple, green, and reproducible hydrothermal method. Transmission electron micrographs show polyhedral NPs having an average diameter of 21 nm; whereas the X-ray diffraction analysis is consistent with the exclusive presence of cubic ZnS; however no oxide could be detected. A comprehensive characterization of the NPs' surface was accomplished through X-ray photoelectron spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), Raman, and thermogravimetric analysis-differential scanning calorimetry, showing a fairly pure ZnS composition and a remarkable amount of adsorbed water molecules. The interaction capabilities of the surface were probed in situ by DRIFT using small molecules (CO, CO2, methanol, pyridine) as molecular probes. The same interactions were also theoretically studied with density functional calculations using a slab model based on the sphalerite ZnS (110) surface. By comparing theoretical and experimental vibrational shifts, insights on the nature of the interaction between molecular probes and surfaces were obtained. Water was found to alter both the structure as well as the reactivity of the surface, mediating the interaction of methanol with the surface, and allowing the conversion of CO2 into surface carbonates. Pyridine was instead evidenced to be able to replace water molecules because of its high adsorption energy (1 eV) which is in tune with the known pyridine-detection capabilities of ZnS. No-SH moieties or Lewis acid behavior of the exposed S atoms were observed.

The precise detection of flammable and explosive gases and vapors remains an important issue because of the increasing demand for renewable energy sources and safety requirements in industrial processes. Metal oxides (TiO2, SnO2, ZnO, etc.) are very attractive materials for the manufacturing of chemical gas sensors. However, their gas selectivity issues and further improvement in the sensing response remain a significant challenge. The incorporation of metal oxides with two-dimensional (2D) graphene oxide (GO) is considered to be a promising approach to obtaining hybrid structures with improved gas-sensing performance. Herein, we report the development of GO and niobium-doped titanium dioxide nanotube (NT) hybrid structures with a tunable selectivity and sensing response against hydrogen gas, achieved by properly controlling the degree of reduction and concentration of GO. The effects of these parameters are systematically studied in terms of the response amplitude and selectivity. It was found that, compared to undoped titanium dioxide nanotubes, the hybrid material with an optimal concentration of reduced-GO and the introduction of niobium shows an increase in hydrogen response of about an order of magnitude and a simultaneous reduction of the response to possible interfering compounds such as carbon monoxide and acetone, thus providing enhanced selectivity. This research may provide an efficient way to enhance the chemical sensing performance of metal oxide nanomaterials.

An approach for the preparation of noble metal nanoparticles supported on nanostructured metal oxides is described herein. The approach is based on the sequential generation of the noble metal nanoparticles and of a metal oxide phase inside a cross-linked polymer colloid (microgel). By tuning the properties of the employed microgel, the nature and amount of both the noble metal nanoparticles and the metal oxide phase can be independently varied. The resulting composite colloids are colloidally stable and, upon isolation by precipitation and subsequent calcination, produce noble metal nanoparticles dispersed on a crystalline, nanostructured oxide phase. Preliminary catalytic tests provide information on the accessibility of the noble metal nanoparticles and, particularly in the case of gold, result in promising catalytic performances in the aerobic oxidation of alcohols.

Halloysite nanotubes (HNTs) can be conveniently used as scaffolds to load catalytic units, to enable efficient heterogeneous catalytic processes. In this contribution, we report a facile strategy to prepare a composite system based on Au nanoparticles (NPs) supported on piranha-etched HNTs. The resulting nano-system was characterized by FTIR, XPS and nitrogen physisorption to highlight its surface properties and porosity. Compared to the non-treated reference HNTs, the increase of hydroxyl groups on the etched HNTs walls allowed to graft a double amount of 3-aminopropyl silane (5.7 wt% vs. 2.8 wt%) and, consequently, to load 15.5 wt% more gold NPs. On the other hand, the interaction of the amino groups with Au NPs stabilizes positively charged NPs, thus leading to excellent catalytic activity and stability. The resulting nano-hybrid can catalyse the reduction of 4-nitrophenol to 4-aminophenol with a kinetic rate constant 53% higher than the reference reaction. In addition, it can be reused for 8 times without significant loss of activity. The supported system also demonstrates its potential in the oxidation of a sugar-derived molecule, i.e., furfural, which is converted into furoic acid with turnover frequency (TOF) 25% higher than the reference.

Catalysts capable of improving the performance of oxygen evolution reaction (OER) and oxygen reduction reactions (ORR) are essential for the advancement of renewable energy technologies. Herein, Ag-decorated vertically aligned MoS2 nanoflakes are developed via magnetron co-sputtering and investigated as electrocatalyst towards OER and ORR. Due to the presence of silver, the catalyst shows more than 1.5 times an increase in the roughness-normalized rate of OER, featuring a very low Tafel slope (58.6 mv dec(-1)), thus suggesting that the catalyst surface favors the thermodynamics of hydroxyl radical (OH center dot) adsorption with the deprotonation steps being the rate-determining steps. The improved performance is attributed to the strong interactions between OOH intermediates and the Ag surface which reduces the activation energy. Rotating ring disk electrode (RRDE) analysis shows that the net disk currents on the Ag-MoS2 sample are two times higher at 0.65 V compared to MoS2, demonstrating the co-catalysis effect of silver doping. Based on the rate constant values, Ag-MoS2 proceeds through a mixed 4 electron and a 2 + 2 serial route reduction mechanism, in which the ionized hydrogen peroxide is formed as a mobile intermediate. The presence of silver decreases the electron transfer number and increases the peroxide yield due to the interplay of a 2 + 2 electron reduction pathway. A 2.5-6 times faster conversion rate of peroxide to OH- observed due to the presence of silver, indicating its effective cocatalyst nature. This strategy can help in designing a highly active bifunctional catalyst that has great potential as a viable alternative to precious-metal-based catalysts. Funding Agencies|Knut & Alice Wallenberg foundation, Sweden; Swedish foundation consolidator fellowship, Sweden; European UnionEuropean Commission [654002, 785219]; Lulea University of Technology laboratory fund program, Sweden; Kempe Foundation, Sweden; VINNOVA under the VINNMER Marie cure incoming Grant, Sweden [2015-01513]; Swedish Research Council, SwedenSwedish Research Council [VR 2019-05577]; MIUR-PON TARANTO, Italy [ARS01_00637]

The biological application of photoactivatable ruthenium anticancer prodrugs is limited by the need to use poorly penetrating high-energy visible light for their activation. Upconverting nanoparticles (UCNPs), which produce high-energy light under near-infrared (NIR) excitation, can solve this issue, provided that they form stable, water (H2O)-dispersible nanoconjugates with the prodrug and that there is efficient energy transfer from the UCNP to the ruthenium complex. Herein, we report on the synthesis and photochemistry of the ruthenium(II) polypyridyl complex [Ru(bpy)2(3H)](PF6)2 ([1](PF6)2), where bpy = 2,2-bipyridine and 3H is a photocleavable bis(thioether) ligand modified with two phosphonate moieties. This ligand was coordinated to the ruthenium center through its thioether groups and could be dissociated under blue-light irradiation. Complex [1](PF6)2 was bound to the surface of NaYF4:Yb3+,Tm3+@NaYF4:Nd3+@NaYF4 core–shell–shell (CSS-)UCNPs through its bis(phosphonate) group, thereby creating a H2O-dispersible, thermally stable nanoconjugate (CSS-UCNP@[1]). Conjugation to the nanoparticle surface was found to be most efficient in neutral to slightly basic conditions, resulting in up to 2.4 × 103 RuII ions per UCNP. The incorporation of a neodymium-doped shell layer allowed for the generation of blue light using low-energy, deep-penetrating light (796 nm). This wavelength prevents the undesired heating seen with conventional UCNPs activated at 980 nm. Irradiation of CSS-UCNP@[1] with NIR light led to activation of the ruthenium complex [1](PF6)2. Although only one of the two thioether groups was dissociated under irradiation at 50 W·cm–2, we provide the first demonstration of the photoactivation of a ruthenium thioether complex using 796 nm irradiation of a H2O-dispersible nanoconjugate., In this work, a water-dispersible nanoconjugate was prepared that is composed of blue-light-emitting core−shell−shell upconverting nanoparticles (CSS-UCNP) surface-functionalized with a blue-light-sensitive ruthenium polypyridyl complex. The photoactivation of this system was studied under 450, 796, and 980 nm light irradiation. Photosubstitution of the bis(thioether)−bis(phosphonate) ligand connecting the ruthenium complex to the UCNP surface was possible using high-power 796 nm near-infrared light irradiation, which led to partial ruthenium release from the nanoparticle surface.

Graphene oxide (GO) and reduced graphene oxide (RGO) have unique properties that can revolutionize the performances of functional devices. Graphene-based materials can be coupled with metal oxide nanomaterials for gas-sensing applications. In this work, we report the synthesis and gas-sensing properties of a composite material based on RGO-loaded TiO2 nanotubes. To properly tune the reduction of GO to RGO, we adopted a gas-phase process that can be applied in situ on each gas sensor device, allowing one to track the process effects through sensor conductance. We systematically investigated the gas-response dependence from the RGO loading and its reduction, showing the occurrence of an optimal RGO concentration arising from the interplay of these two parameters. Hence, these two factors should be considered in parallel to functionalize the metal oxide materials with GO for the fabrication of chemical sensor devices.

Metal oxide semiconductors are interesting for next-generation flexible and transparent electronics because of their performance and reliability. Tin dioxide (SnO2) is a very promising material that has already found applications in sensing, photovoltaics, optoelectronics, and batteries. In this work, we report on electrolyte-gated, solution-processed polycrystalline SnO2 transistors on both rigid and flexible substrates. For the transistor channel, we used both unpatterned and patterned SnO2 films. Since decreasing the SnO2 area in contact with the electrolyte increases the charge-carrier density, patterned transistors operate in the depletion mode, whereas unpatterned ones operate in the enhancement mode. We also fabricated flexible SnO2 transistors that operate in the enhancement mode that can withstand moderate mechanical bending.

La 0.6 Sr 0.4 Ga 0.3 Fe 0.7 O 3 is a MIEC perovskite with great chemical and thermal stability, considered a promising material for oxygen separation dense membranes and as an electrode in SOFCs. An easy, economic and scalable wet chemistry synthesis of La 0.6 Sr 0.4 Ga 0.3 Fe 0.7 O 3 (LSGF) was studied step by step, investigating and optimizing the most important aspects and parameters of the procedure (chemicals, pH, calcination temperature…). The obtained powders were carefully characterized with XRD, XPS, SEM/EDX and TPR. Once optimized the synthesis procedure, the stability in reducing condition and the reversibility of changes were tested submitting the samples to reduction/oxidation cycles at temperatures between 800/1000 °C. The influence of the synthesis parameters on stability/reversibility was investigated. The material is completely stable up to 800 °C even in aggressive reducing atmospheres. Reduction occurring at higher temperatures is reversible: a simple treatment in oxygen is enough to entirely re-absorb the side phases formed during the reduction and obtain the starting material.

The capability of upconverting nanoparticles (UCNPs) to convert near infrared (NIR) into visible light has become an important feature for biosensing, imaging, therapy, and their combination. While significant achievements have been accomplished during the last decade developing nanohybrids based on UCNPs as energy donors in Förster resonance energy transfer (FRET) systems, it is still challenging to understand and control FRET from UCNPs to dyes and to adapt the NIR excitation wavelength. Here, we describe the synthesis, characterization, and steady-state and time-resolved FRET analysis of UCNP-DNA nanohybrids, in which dye labelled single stranded (ss)DNA was attached to Yb-Er-co-doped core UCNPs (c-UCNPs) and c-UCNPs with a thin Nd-doped shell and a second thin undoped shell (css-UCNPs). Despite differences in sizes, compositions, donor-acceptor distances, brightness, and excitation wavelength (980 nm for Yb

The capability of upconverting nanoparticles (UCNPs) to convert near infrared (NIR) into visible light has become an important feature for biosensing, imaging, therapy, and their combination. While significant achievements have been accomplished during the last decade developing nanohybrids based on UCNPs as energy donors in Förster resonance energy transfer (FRET) systems, it is still challenging to understand and control FRET from UCNPs to dyes and to adapt the NIR excitation wavelength. Here, we describe the synthesis, characterization, and steady-state and time-resolved FRET analysis of UCNP–DNA nanohybrids, in which dye labelled single stranded (ss)DNA was attached to Yb–Er-co-doped core UCNPs (c-UCNPs) and c-UCNPs with a thin Nd-doped shell and a second thin undoped shell (css-UCNPs). Despite differences in sizes, compositions, donor–acceptor distances, brightness, and excitation wavelength (980 nm for Yb3+and 808 nm for Nd3+), all UCNP–DNA nanohybrids showed very similar concentration dependent FRET-quenching of UCNP luminescence with efficiencies between 0 and ∼20%. We analyzed luminescence intensities, decay times, and rise times and could show the entanglement of excitation and emission kinetics by simply changing the excitation wavelength from 980 nm to 808 nm for the same css-UCNPs. Time-gated FRET-sensitized dye luminescence showed dye-ssDNA concentration dependence over four orders of magnitude (1 nM to 10 μM), which suggested a possible application to nucleic acid biosensing for both 808 and 980 nm excitation.

Development of high-entropy alloy (HEA) films is a promising and cost-effective way to incorporate these materials of superior properties in harsh environments. In this work, a refractory high-entropy alloy (RHEA) film of equimolar CuMoTaWV was deposited on silicon and 304 stainless-steel substrates using DC-magnetron sputtering. A sputtering target was developed by partial sintering of an equimolar powder mixture of Cu, Mo, Ta, W, and V using spark plasma sintering. The target was used to sputter a nanocrystalline RHEA film with a thickness of ∼900 nm and an average grain size of 18 nm. X-ray diffraction of the film revealed a body-centered cubic solid solution with preferred orientation in the (110) directional plane. The nanocrystalline nature of the RHEA film resulted in a hardness of 19 ± 2.3 GPa and an elastic modulus of 259 ± 19.2 GPa. A high compressive strength of 10 ± 0.8 GPa was obtained in nanopillar compression due to solid solution hardening and grain boundary strengthening. The adhesion between the RHEA film and 304 stainless-steel substrates was increased on annealing. For the wear test against the E52100 alloy steel (Grade 25, 700-880 HV) at 1 N load, the RHEA film showed an average coefficient of friction (COF) and wear rate of 0.25 (RT) and 1.5 (300 °C), and 6.4 × 10-6 mm3/N m (RT) and 2.5 × 10-5 mm3/N m (300 °C), respectively. The COF was found to be 2 times lower at RT and wear rate 102 times lower at RT and 300 °C than those of 304 stainless steel. This study may lead to the processing of high-entropy alloy films for large-scale industrial applications.

Dimethylamine is an important indicator to check the degradation and control the quality of seafood. In this work, we present a novel, simple, fast and inexpensive method to detect dimethylamine in the range of 5–50 ppm that might be potentially useful to control the seafood quality in the future. The developed gas sensor is based on niobium-doped titanium dioxide nanotubes. The tubular structures were successfully synthesized using anodic oxidation method. The sensing properties of the obtained materials were studied towards dimethylamine gas for the first time. Dimethylamine behaves like an electron donor and induces an increase in conductivity of the n-type titanium dioxide. The presence of niobium in the titanium dioxide structure plays a crucial role to improve the functional properties of the material. Niobium acts as a donor promoting the process of gas adsorption on the structure. The response of Nb doped-material towards 10 ppm of dimethylamine is higher more than an order of magnitude compared to the pristine titanium dioxide nanotubes, leading to an essential improvement in their gas sensing performance. The obtained results enable the development of a dimethylamine gas sensor device based on titanium dioxide for the real-time monitoring and freshness detection of seafood products.

The biological application of ruthenium anticancer prodrugs for photodynamic therapy (PDT) and photoactivated chemotherapy (PACT) is restricted by the need to use poorly penetrating high-energy photons for their activation, i.e., typically blue or green light. Upconverting nanoparticles (UCNPs), which produce high-energy light under near-infrared (NIR) excitation, may solve this issue, provided that the coupling between the UCNP surface and the Ru prodrug is optimized to produce stable nanoconjugates with efficient energy transfer from the UCNP to the ruthenium complex. Herein, we report on the synthesis and photochemistry of the two structurally related ruthenium(II) polypyridyl complexes [Ru(bpy)2(5)](PF6)2 ([1](PF6)2) and [Ru(bpy)2(6)](PF6)2 ([2](PF6)2), where bpy = 2,2-bipyridine, 5 is 5,6-bis(dodecyloxy)-2,9-dimethyl-1,10-phenanthroline, and 6 is 5,6-bis(dodecyloxy)-1,10-phenanthroline. [1](PF6)2 is photolabile as a result of the steric strain induced by ligand 5, but the irradiation of [1](PF6)2 in solution leads to the nonselective and slow photosubstitution of one of its three ligands, making it a poor PACT compound. On the other hand, [2](PF6)2 is an efficient and photostable PDT photosensitizer. The water-dispersible, negatively charged nanoconjugate UCNP@lipid/[2] was prepared by the encapsulation of 44 nm diameter NaYF4:Yb3+,Tm3+ UCNPs in a mixture of 1,2-dioleoyl-sn-glycero-3-phosphate and 1,2-dioleoyl-sn-glycero-3-phosphocholine phospholipids, cholesterol, and the amphiphilic complex [2](PF6)2. A nonradiative energy transfer efficiency of 12% between the Tm3+ ions in the UCNP and the Ru2+ acceptor [2]2+ was found using time-resolved emission spectroscopy. Under irradiation with NIR light (969 nm), UCNP@lipid/[2] was found to produce reactive oxygen species (ROS), as judged by the oxidation of the nonspecific ROS probe 2′,7′-dichlorodihydrofluorescein (DCFH2–). Determination of the type of ROS produced was precluded by the negative surface charge of the nanoconjugate, which resulted in the electrostatic repulsion of the more specific but also negatively charged 1O2 probe tetrasodium 9,10-anthracenediyl-bis(methylene)dimalonate (Na4(ADMBMA)).

Hydrogen evolution reaction through electrolysis holds great potential as a clean, renewable, and sustainable energy source. Platinum-based catalysts are the most efficient to catalyze and convert water into molecular hydrogen; however, their large-scale application is prevented by scarcity and cost of Pt. In this work, we propose a new ternary composite of Ag

MoO2 nanocrystals were prepared by solvothermal treatment of a Mo chloromethoxide at 250 °C in oleic acid. The monoclinic MoO2 phase, with a mean crystallite size of 29 nm, formed through reduction of molybdenum bronzes. The as-prepared MoO2 nanocrystals were free from organics, allowing their use in photodegradation tests of organic pollutants (methylene blue, rhodamine B, paracetamol), without any preliminary purification treatment of the nanocrystals. It was found that MoO2 was an efficient adsorbent of methylene blue (43 mg g−1 for 1.5 × 10−4 M concentration) in the dark and an efficient photodegradation catalyst under visible light (all methylene blue removed from the solution after 240 min). From the analysis of the combined photodegradation tests of rhodamine B and paracetamol, it was clarified that direct sensitization was responsible for photodegradation. This finding was related to the work function value of metallic MoO2, placed at more negative values if compared with other metallic materials.

International audience; In the field of solid state electrochemistry, lanthanum cobaltites are very good electronic conductors used as SOFC cathode materials. In this work, Sr and Cu-doped LaCoO3 perovskites (LaCo0.5Cu0.5O3−δ, La0.5Sr0.5Co0.5Cu0.5O3−δ) have been prepared by means of the citrate route procedure and investigated. XRD confirms the formation of the desired phase and no secondary phases are detected. XPS and EDX results suggest that doping affects cations' surface segregation: lanthanum and copper are surface segregated in the LaCo0.5Cu0.5O3−δ whereas this is not observed in the La0.5Sr0.5Co0.5Cu0.5O3−δ. TPD experiments revealed that doping greatly increases the desoprtion of α and β oxygen species. The oxygen permeability was also determined in order to evaluate mixed ionic and electronic conductivity in addition to the surface activity in oxygen reduction reaction: in particular copper doping was observed to enhance permeability even at rather low temperature (500 °C). Finally, electrochemical impedance spectroscopy measurements carried out on a symmetrical half-cell with Ce0.9Gd0.1O2 as electrolyte to characterize the effect of doping on electrochemical properties, revealed that the Cu and Sr doping enhances the performance as SOFC cathode.

Copper-doped PbS polycrystalline thin films were deposited by chemical bath deposition by adding small amount of Cu (y solution = [Cu 2+ ]/[Pb 2+ ]) between 0.5 and 2 at%. The composition, structure, morphology, optical and electrical properties of the films were investigated by means of X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS), UV–visible–near infrared (UV–Vis–NIR) spectrophotometry and Hall effect measurements. The XRD studies showed that the undoped films have PbS face centered cubic structure with (111) preferential orientation, while preferential orientation changes to (200) plane with increasing Cu doping concentration. The AFM and SEM measurements indicated that the film surfaces consisted of nanosized grains with pyramidal shape. Optical band gap was blue shifted from 0.72 eV to 1.69 eV with the increase in Cu doping concentration. The film obtained with the [Cu 2+ ]/[Pb 2+ ] ratio equal to 1.5 at% Cu showed the minimum resistivity of 0.16 Ω cm at room temperature and optimum value of optical band gap close to 1.5 eV. 1.5 at% Cu-doped PbS thin films exhibit the best optical and electrical properties, suitable for solar cells applications.

Hydrogen production as alternative energy source is still a challenge due to the lack of efficient and inexpensive catalysts, alternative to platinum. Thus, stable, earth abundant, and inexpensive catalysts are of prime need for hydrogen production via hydrogen evolution reaction (HER). Herein, we present an efficient and stable electrocatalyst composed of earth abundant TiO2 nanorods decorated with molybdenum disulfide thin nanosheets, a few nanometers thick. We grew rutile TiO2 nanorods via the hydrothermal method on conducting glass substrate, and then we nucleated the molybdenum disulfide nanosheets as the top layer. This composite possesses excellent hydrogen evolution activity in both acidic and alkaline media at considerably low overpotentials (350 mV and 700 mV in acidic and alkaline media, respectively) and small Tafel slopes (48 and 60 mV/dec in acidic and alkaline conditions, respectively), which are better than several transition metal dichalcogenides, such as pure molybdenum disulfide and cobalt diselenide. A good stability in acidic and alkaline media is reported here for the new MoS2/TiO2 electrocatalyst. These results demonstrate the potential of composite electrocatalysts for HER based on earth abundant, cost-effective, and environmentally friendly materials, which can also be of interest for a broader range of scalable applications in renewable energies, such as lithium sulfur batteries, solar cells, and fuel cells.

Hydrogen evolution reaction through electrolysis holds great potential as a clean, renewable, and sustainable energy source. Platinum-based catalysts are the most efficient to catalyze and convert water into molecular hydrogen; however, their large-scale application is prevented by scarcity and cost of Pt. In this work, we propose a new ternary composite of Ag2S, MoS2, and reduced graphene oxide (RGO) flakes via a one-pot synthesis. The RGO support assists the growth of two-dimensional MoS2 nanosheets partially covered by silver sulfides as revealed by high-resolution transmission electron microscopy. Compared with the bare MoS2 and MoS2/RGO, the Ag2S/MoS2 anchored on the RGO surface (the ternary system Ag2S/MoS2/RGO) demonstrated a high catalytic activity toward hydrogen evolution reaction (HER). Its superior electrochemical activity toward HER is evidenced by the positively shifted (-190 mV vs reversible hydrogen electrode (RHE)) overpotential at a current density of -10 mA/cm(2) and a small Tafel slope (56 mV/dec) compared with a bare and binary system. The Ag2S/MoS2/RGO ternary catalyst at an overpotential of -200 mV demonstrated a turnover frequency equal to 0.38 s(-1). Electrochemical impedance spectroscopy was applied to understand the charge-transfer resistance; the ternary sample shows a very small charge transfer resistance (98 Omega) at -155 mV vs RHE. Such a large improvement can be attributed to the synergistic effect resulting from the enhanced active site density of both sulfides and to the improved electrical conductivity at the interfaces between MoS2 and Ag2S. This ternary catalyst opens up further optimization strategies to design a stable and cheap catalyst for hydrogen evolution reaction, which holds great promise for the development of a clean energy landscape.

In this contribution we evaluated the effect of synthesis procedure (complexing molecule, calcination temperature) and doping on the properties and catalytic performance of SrTiO3. Focusing on preparation we compared two complexants: citric acid and glycine calcinating the catalysts at 700 and 850 °C. Moreover, we doped the perovskite substituting Sr with K and Ti with Mn. The obtained catalysts have been characterized by X-Ray diffraction, X-Ray photoelectron spectroscopy, BET, scanning electron microscopy, energy dispersive X-Ray analysis, temperature programmed reduction. To evaluate the effect of upon mentioned aspects on the catalytic activity, the following reactions have been considered: CO oxidation, CO assisted NO reduction, soot oxidation. The obtained results underline the deep effect of dopants, with particular reference to Mn, on the catalytic performance.

We have obtained and studied the sensing properties of porous titania-based nanostructures. The materials have been prepared using cost-effective techniques. The morphological and structural analyses of the prepared materials have been performed. The sensing properties of the samples have been studied towards carbon monoxide. The obtained results demonstrate that the prepared structures are promising for the potential applications in the area of chemical sensors for the environmental monitoring.

The PCBs are known recalcitrant and toxic pollutants and significant values of contamination could be found in water. PCBs can be hydrodechlorinated using Pd-based catalysts and hydrogen, but the research to identify more efficient heterogeneous catalysts, able to work in an aqueous phase, less sensible to deactivation and easily removable at the end of the treatment, remains a considerable interesting goal. A strain of Klebsiella oxytoca, DSM 29614, known to produce a specific exopolysaccaride (EPS), was grown in different media with sodium citrate or with sodium citrate plus ferric citrate, as sole energy and carbon sources under anaerobic conditions. The cultures were amended with 50 mg of palladium as Pd(NO3)2 to generate Pd-EPS (Pd content 13%) or FePd-EPS (Pd content 8.4%; Fe 7.4%) species which were secreted from the cells, isolated by treatment with a cold ethanol solution (70%) and dried under vacuum as powders. The catalytic ability of these mono- and bi-metallic species was tested in the hydrodechlorination reaction of the Aroclor 1260 PCBs mixture under aqueous biphasic conditions. Here we demonstrate that the degree of PCBs hydrodechlorination is dependent by the nature of catalyst and of base used to neutralize HCl produced, the bimetallic species being more active and an organic base resulting more effective. Working with a substrate/catalyst 8/1 molar ratio, at 3 MPa H2 and 60°C in 20 h a significant removal of highly chl orinated PCBs was obtained under the best conditions. The result seems promising for remediation of groundwater contaminated with PCBs.

The energetics of the catalytic oxidation of CO on a complex metal oxide are investigated for the first time via density functional theory calculations. The catalyst, Co-doped SrTiO3, is modelled using periodically repeated slabs based on the SrTiO3(100) surface. The comparison of the energy profiles obtained for the pure host and the Co-doped material reveals the actual pathway followed by the reaction, and shows that Co doping enhances the catalytic properties of SrTiO3 by reducing the energy cost for the formation of oxygen vacancies.

Made available in DSpace on 2022-04-28T19:01:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-09-17 Electrolyte-gated (EG) transistors, based on electrolyte gating media, are powerful device structures to modulate the charge carrier density of materials by orders of magnitude, at relatively low operating voltages (sub-2 V). Tungsten trioxide (WO3) is a metal oxide semiconductor well investigated for applications in electrochromism, sensing, photocatalysis, and photoelectrochemistry. In this work, we report on EG transistors making use of mesoporous nanostructured WO3 thin films easily permeated by the electrolyte as the transistor channel and bis(trifluoromethylsulfonyl)imide ([TFSI])-based ionic liquids as the gating media. The WO3 EG transistors operate at ca. 1 V. Using a combination of cyclic voltammetry, X-ray diffraction, and transistor performance characterizations, complemented by spectroscopic (Raman and infrared) investigations, we correlate the metal oxidation state and the charge transport properties of the metal oxide, shedding light on the doping process in electrically biased WO3 nanostructured thin films exposed to electrolytes. Département de Génie Physique Polytechnique Montréal, C.P. 6079, Succ. Centre Ville Departamento de Físico-Química Universidade Estadual Paulista, Rua Professor Degni, 55 CNR-IENI Dipartimento di Scienze Chimiche Università di Padova, Via F. Marzolo 1 Département de Chimie Université de Montréal, C.P. 6128, Succ. Centre Ville Dipartimento di Chimica giacomo Ciamician Università di Bologna, Via Selmi, 2 Departamento de Físico-Química Universidade Estadual Paulista, Rua Professor Degni, 55

High surface-to-volume ratio Co3O4/TiO2 heterojunctions were fabricated by combining different methods. Atomic layer deposition (ALD) and a photochemical method were used to coat polystyrene (PS) 3D-Direct Opal (3D-DO) structures on conductive ITO substrates. Firstly, 3D-DO of PS were crystallized on ITO substrates to form the high surface-to-volume ratio template via a self-assembly method. A low-temperature ALD TiO2 film was infiltrated onto the PS opal structure. Then, the PS template was removed by a thermal treatment in air at 450 °C for 5 h. Hollow anatase phase nanospheres were obtained, crystallized in a face centered cubic (FCC) lattice with the (111) plane oriented parallel to the substrate surface. Finally, the hollow TiO2 nanospheres were coated with Co3O4 via a photochemical method. This ordered 3D nanostructure with designed morphology may find applications as surface-enhanced materials for photovoltaic devices. TiO2 hollow nanospheres obtained via low-pressure ALD (a) and Co3O4/TiO2 heterostructure (scanned region: 1.5 μm) (b).

The NO reduction in a CO–NO atmosphere at the Co- and Cu-doped SrTiO3(100) surfaces is investigated by density functional theory calculations. The energy profiles for several mechanisms are computed and compared. On this basis, a rationale for the available experimental data is proposed. Oxygen vacancies formed as intermediate species in the CO oxidation process play a key role in the NO reduction. Their concentration is also relevant because, if low, formation of N2O prevails on that of N2, leading to an incomplete reduction. The formation of oxygen vacancies is favored by Co and Cu impurities, the latter being most effective. Overall, doping promotes the catalytic reduction of NO on SrTiO3.

In this contribution several LaCoO3 based nanocomposites have been prepared and tested for application as Three-Way Catalytic Converters (TWC): the aim is in developing Platinum Group Metal (PGM)-free catalysts. To reach this objective we designed and realized nanocomposites in which active CuO nanoparticles are deposited on active LaCoO3. This perovskite is active in oxidation while copper is active in reduction: catalytic bi-functionality is thus built-in via a tailor-made and controlled nanocomposition. The deposition was carried out by means of an innovative Ammonium-Driving-Deposition precipitation (ADP) procedure allowing to obtain nanocomposites in which CuO is highly dispersed on LaCoO3. This increases the reducibility of the nano composites, as revealed by the TPR measurements. The deposition of copper does not alter significantly the surface composition which remains rich in lanthanum oxide/hydroxide, the main effect consisting in a slight increment of surface hydroxylation. Moreover, the copper amount on the LaCoO3 surface does not increase linearly with the nominal composition. Both model reactions (CO oxidation and CO assisted NO reduction) and tests with a synthetic automotive exhaust mixture, including 10 % steam, were carried out. Activity before and after high-temperature aging in steam was also evaluated. We compared the obtained results with the ones of CuO/nickelates of a previous work, to highlight the functionalities gained. In simple CO + NO and CO + O-2 mixtures, the deposition of copper oxide on LaCoO3 greatly increases the activity of the nanocomposites in NO reduction (100 % conversion at 350 degrees C) without significantly affecting the reactivity in CO oxidation. Results with the synthetic automotive exhaust mixture show that Cu loading on ADP prepared catalysts can significantly improve the NO reduction activity of LaCoO3. Still, NO reduction remains more relevant in O-2-poor mixtures (about 100 % conversion around 400 degrees C in the 10 wt.% Cu loaded), even slightly below the stoichiometric. Some deactivation on hydrocarbon oxidations occurs at low temperatures due to thermal aging, apparently due to coking and surface Cu depletion. Compared to CuO deposited by ADP on LaNiO3 of our earlier studies, cobaltites gain in oxidation activity, but NO reduction remains easier on nickelates. However, the promising performance and the absence of noble critical metals are promising features to develop PGM-free catalysts for the automotive industry.

We demonstrate a fast and large area-scalable methodology for the fabrication of efficient dye sensitized solar cells (DSSCs) by simple addition of graphene micro-platelets to TiO2 nanoparticulate paste (graphene concentration in the range of 0 to 1.5 wt%). Two dimensional (2D) Raman spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirm the presence of graphene after 500°C annealing for 30 minutes. Graphene addition increases the photocurrent density from 12.4 mA cm-2 in bare TiO2 to 17.1 mA cm-2 in an optimized photoanode (0.01 wt% graphene, much lower than those reported in previous studies), boosting the photoconversion efficiency (PCE) from 6.3 up to 8.8%. The investigation of the 2D graphene distribution showed that an optimized concentration is far below the percolation threshold, indicating that the increased PCE does not rely on the formation of an interconnected network, as inferred by prior investigations, but rather, on increased charge injection from TiO2 to the front electrode. These results give insights into the role of graphene in improving the functional properties of DSSCs and identifying a straightforward methodology for the synthesis of new photoanodes.

In this work, an easy, quick and reproducible wet-synthesis coprecipitation route starting from oxalate precursors was optimised to synthesise cobalt, nickel, zinc and magnesium spinel ferrites CoFe2O4, NiFe2O4, ZnFe2O4 and MgFe 2O4, as well as the manganese perovskite ferrite MnFeO3. Crystalline purity and crystallite sizes ranging from 30 to 190 nm were investigated by means of powder X-ray diffraction, and uniform morphology of the particles was shown through transmission electron microscopy. The chosen synthetic route afforded an excellent stoichiometric control over the products, as confirmed by combined X-ray photoelectron spectroscopy and inductively coupled plasma atomic emission spectroscopy analyses. The site geometry, degree of inversion in the spinels and chemical environments in the ferrites were explored by Mössbauer spectroscopy. The thermal evolution of the compounds during calcination and the decomposition pattern of the oxalates were studied through differential scanning calorimetry coupled with thermogravimetric analysis as well as in situ temperature-programmed X-ray diffraction. Magnetic properties of these oxides, as well as the transition of the perovskite from paramagnetic to ferrimagnetic behaviour at low temperatures, were investigated by superconducting quantum interferometer magnetometry. Cobalt, nickel, zinc and magnesium spinel ferrites CoFe2O 4, NiFe2O4, ZnFe2O4 and MgFe2O4, as well as the manganese perovskite MnFeO 3, with high purities, crystallinity and yields have been synthesised through the coprecipitation of oxalates. The obtained oxides have been thoroughly characterised from a structural, compositional, morphological and functional point of view.

We study the electronic structure of Co, Ni, and Cu impurities and of their vacancy-associated complexes in SrTiO 3 crystals by means of density functional theory (DFT) and DFT + U calculations. Simple substitutionals prefer low-spin states, as expected from ligand field theory. On the other hand, the formation energy of vacancies (which tend to stay close to the impurity) is rather low for all the doped systems, and decreases with Z. This reflects the low stability of the +IV oxidation state for the impurities. Contrary to simple impurities, high-spin states are predicted to be stable when impurities are associated to vacancies.

The mononuclear tricationic bis(di-N-heterocyclic carbene) gold(III) complex 13+ of formula [Au(MeImCH2ImMe)2]3+ (Im = imidazol-2-ylidene) was successfully synthesized by transmetalation of the di(N-heterocyclic carbene) ligand from the corresponding silver(I) complex to KAuBr4. The counteranion of the gold(III) cationic complex depends on the synthetic procedure. The crude product, isolated by the transmetalation reaction, consists of infinite (Ag4Br7 3-)n ribbons. By adding a stoichiometric amount of AgPF6, the complete precipitation of AgBr is achieved, and the counteranions are PF6 -. If substoichiometric amounts of silver salts are added, then the (Ag4Br7 3-)n ribbon breaks, and silverbromides anionic aggregates of lower nuclearity are obtained, for example, Ag2Br6 4-. The X-ray crystal structures of 1-Ag4Br7, 1-PF6, and 1-Br,(Ag2Br6)0.5 were determined. The complexes with any type of bromide present interactions between the Au center and two bromides of the counteranions so that the geometry around gold is pseudo-octahedral. The gold-bromide interaction has been investigated via DFT calculations and is mainly electrostatic.

Several perovskites of the type La 1-x A x Co 0.5 Cu 0.5 O 3 (A = K, Sr, Ba; x = 0, 0.25, 0.5) and a Sr-doped understoichiometric one, have been prepared by citrate method aiming at application as noble metals free catalysts for automotive application. The catalysts have been characterized by BET, X-ray diffraction (XRD), Temperature Programmed Reduction (TPR), X-Ray Photoelectron Spectroscopy (XPS), and Scanning Electron Microscopy (SEM) and the effect of A-doping has been investigated. The catalytic activity was studied in model reactions (CO oxidation, CO assisted NO reduction), and in a complex three way catalysts (TWC) mixture approaching automotive exhaust composition at both stoichiometric and O 2 -limiting conditions and the obtained results are discussed in relation with characterization results. A-doping induces the formation of highly dispersed cubic CuO particles, as observed in the understoichiometric samples. Doping also influences the surface segregation. La segregation is observed in the undoped LaCo 0.5 Cu 0.5 O 3 sample whereas K is surface segregated in La 0.75 K 0.25 Co 0.5 Cu 0.5 O 3 ; Co segregates in the Ba-doped perovskite and Sr in the understoichiometric La 0.35 Sr 0.35 Co 0.5 Cu 0.5 O 3 . The reducibility (TPR) is altered by A-doping. The reactivity results suggest that in simple CO + O 2 and CO + NO mixtures the activation temperature is increased by any doping, but at 400 °C the conversion in the CO assisted NO reduction is not significantly different with respect to the one obtained in the undoped catalyst. Activity with a more complex mixture, simulating actual engine exhaust, reveals the interesting activity of the Sr-doped catalysts, that outperform LaCo 0.5 Cu 0.5 O 3 at both stoichiometric and O 2 -lean conditions. NO reduction can be achieved at lean O 2 conditions, where it is quantitative from 400 °C. The possibility to reach similar or better activity by replacing the use of La, which is a Rare Earth Element, by using Sr is particularly interesting. Stability at high temperatures and at fast fluctuations of O 2 in inlet stream for 50% Sr-doped catalyst confirms these results.

Several nanocomposites of the type CuO/LaNiO3 (Cu@LaNiO3) have been developed for application as noble metal free catalysts in TWC. The nanocomposites have been obtained by depositing copper oxide on lanthanum nickelate. The supporting perovskite has been prepared by means of the citrate route; copper, in contrast, was deposited by means of an innovative procedure: ammonia driven deposition precipitation method (ADP) optimized for deposition on perovskites. The nanocomposites have been developed based on the catalytic activity of LaNiO3 in oxidation and reforming reactions and of copper in reduction reactions. Nanocomposition is thus used to deposit a highly dispersed active specie (CuO) on an active support (LaNiO3) with the aim of building catalytic functionality. The obtained nanocomposites have been characterized by means of XRD, XPS, SEM, TPR, BET, EDX, and ICP and the obtained results are correlated to the amount of copper deposited and to the reactivity. The reactivity was studied first in two model reactions, CO oxidation and CO assisted NO reduction, in order to investigate the role played by the different species. Moreover, the reactivity under real conditions, i.e. with a complex mixture reflecting the actual automotive exhaust composition, was considered to evaluate the real applicability. Finally, high-temperature deactivation was investigated. XPS reveals that the deposition of copper oxide affects the surface composition of the nanocomposites; the XRD, SEM, and TPR results confirm that CuO is deposited on the LaNiO3 surface and no diffusion below surface is observed. CuO species are deposited both as highly dispersed phase and as bigger particles; the relative amount of these phases depends on the total amount of copper deposited. The reactivity in the CO oxidation reaction is not significantly affected by the copper deposition. In contrast the reactivity in NO reduction is strongly enhanced by the presence of highly dispersed copper species. Activity tests with mixture reflecting actual automotive exhaust, reveal an enhancement in CO oxidation, but no NO decomposition at stoichiometric conditions. Complete NO reduction is achieved at rich conditions; also, hydrocarbons reforming reactions typically occurring at substoichiometric O2, with CO and H2 production, are less supported, preserving the activity in NO reduction. Finally, the high-temperature aging test confirmed an interesting stability of catalytic activity.

The energetics of the catalytic oxidation of CO on a complex metal oxide are investigated for the first time via density functional theory calculations. The catalyst, Co-doped SrTiO

Lead sulphide (PbS) thin films represent a direct band gap IV–VI p-type semiconductor material (Eg= 0.41 eV) and have a good potential application in solar cells, infrared detector devices, sensors ...

The role played by the counter electrode (CE) in quantum dot sensitized solar cells (QDSSCs) is crucial: it is indeed responsible for catalyzing the regeneration of the redox electrolyte after its action to take back the oxidized light harvesters to the ground state, thus keeping the device active and stable. The activity of CE is moreover directly related to the fill factor and short circuit current through the resistance of the interface electrode-electrolyte that affects the series resistance of the cell. Despite that, too few efforts have been devoted to a comprehensive analysis of this important device component. In this work we combine an extensive electrochemical characterization of the most common materials exploited as CEs in QDSSCs (namely, Pt, Au, Cu2S obtained by brass treatment, and Cu2S deposited on conducting glass via spray) with a detailed characterization of their surface composition and morphology, aimed at systematically defining the relationship between their nature and electrocatalytic activity.

Two Zinc-Magnesium Oxide powders were prepared by means of a sol-gel method based on the mixing of nitrates of Mg and Zn, followed by complexation with citric acid. The samples are characterized by a nominal (i.e. calculated from the weighted amount of precursors) Zn/Mg atomic ratio of 0.01 (specimen 1, Accession #1232), and 0.5 (specimen 2, Accession #1233). The surface properties and the influence of the Zn/Mg atomic ratio are investigated by means of XPS (using a standard Al Kα). Besides the wide scan spectra, detailed spectra for the Mg 1s, Zn 2p3/2 and O 1s regions and related data are presented and discussed. XP analysis confirms the presence of Mg (II) and Zn (II). The XPS Zn/Mg atomic ratio is always lower than the nominal one; this is particularly evident in specimen 1 (Accession #1232) thus suggesting a certain surface segregation of magnesium. The O/(Mg + Zn) atomic ratio is higher than the nominal one and decreases with increasing the Zn/Mg atomic ratio (from 1.5 for [Zn/Mg]nom = 0.01 to 1.3 f...

La0.6Sr0.4Co0.2Fe0.8O3-delta perovskite powder was prepared by a single-step process based on a microwave-assisted citrate gel route. The structure, morphology, as well as surface properties and th ...