Sr2MgTeO6 (SMT) and Ba2MgTeO6 (BMT) ceramics with the double perovskite structure have been synthesized by solid-state route and by thermal decomposition of nitrate solution precursor. Both compounds possess interesting and unexpected emission properties in the visible and NIR regions, never reported before for this type of materials. These properties have been measured in different experimental conditions in order to characterize their nature. The literature information on tellurium containing luminescent materials is not rich and the data are somewhat contradictory: nevertheless, they agree in assigning the emission properties to Te4+ in octahedral coordination, whereas the Te6+ ion is considered not luminescent. The presence of Te4+ ions has then been verified by XPS measurements. On the basis of the experimental evidences, the visible luminescence has been assigned to a transition between the electronic levels of the Te4+ ion. The origin of the NIR emission appears more difficult to assess: among the explored hypotheses, the most convincing one, at the present level of the information, involves the possible interactions between the Te4+ and Te6+ ions with consequent formation of an optically active charge transfer state, as already observed for other ns2-type ions (Bi3+, Sb3+).

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 synthesized pure, mixed and multicomponent structures by coupling different cost-effective techniques.Prepared TiO2-based hierarchically assembled nanostructures have been thoroughly characterized by scanning electron microscope, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy.The sensing properties of materials have been studied towards explosive and toxic gaseous compounds.Investigations have shown the material crystalline structure, the variation of mixture concentration in the material and the modification of carbon-based layers have crucial effect on the response and the selectivity of materials.The obtained results demonstrate that the prepared multicomponent structures can be applied in the area of chemical sensors for the environmental monitoring and medical diagnoses.

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.

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 degrees 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 degrees 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 H-2/O-2 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. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The reactivity of Bi0.5Sr0.5MnO3, Bi0.5Sr0.5Mn0.7Cu0.3O3, Bi0.5Sr0.5Mn0.7Ni0.3O3, La0.5Sr0.5Mn0.7Cu0.3O3 and La0.5Sr0.5Mn0.7Ni0.3O3 in ethanol steam reforming was studied. Different steam to carbon ratios have been tested (therefore referred as S/C = 1.5, and S/C = 6). The effect of an ad hoc reduction pre-treatment was also investigated. Ethanol conversion is highest in La0.5Sr0.5Mn0.7Ni0.3O3 and significant selectivity toward hydrogen and CO2 is observed. The reduction pre-treatment is more effective on nickel containing catalysts, enhancing both ethanol conversion and H2 and CO2 selectivity.

Several perovskites of the type La(1-x)A(x)Co(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 02-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 LaCo0,5Cu0.5O3 sample whereas K is surface segregated in La0.75K0.25Co0.5O3; Co segregates in the Ba-doped perovskite and Sr in the understoichiometric La0.35Sr0.35Co0.5O3. 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 degrees 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 LaCo0.5Cu0.5O3 at both stoichiometric and O-2-lean conditions. NO reduction can be achieved at lean O-2 conditions, where it is quantitative from 400 degrees 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.

La0.6Sr0.4Ga0.3Fe0.7O3 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 La0.6Sr0.4Ga0.3Fe0.7O3 (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.

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 O-2, with CO and H-2 production, are less supported, preserving the activity in NO reduction. Finally, the high-temperature aging test confirmed an interesting stability of catalytic activity. (C) 2017 Elsevier B.V. All rights reserved.

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-delta, La0.5Sr0.5Co0.5Cu0.5O3-delta) 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-delta whereas this is not observed in the La0.5Sr0.5Co0.5Cu0.5O3-delta. TPD experiments revealed that doping greatly increases the desoprtion of alpha and beta 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 degrees 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. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Doping of LaCoO3 with copper to add reduction functionality in addition to the known oxidation properties has been investigated, aiming at three-way catalysis (TWC) applications. Nanoscale perovskites with nominal composition LaCo1-xCuxO3, (x=0, 0.1, 0.3, and 0.5) have been synthesized by means of the citrate method. A stable perovskitic phase with rhombohedral geometry up to an unprecedented x = 0.5 has been obtained and characterized by BET, X-ray diffraction (XRD), Temperature Programmed Reduction (TPR), X-ray Photoelectron Spectroscopy (XPS), and Scanning Electron Microscopy (SEM). The crystallite size decreases with increasing the copper amount and also the morphology differs; moreover the surface reactivity with respect to atmospheric moisture and carbon dioxide is more evident in the sample with x = 0.5. Reactivity has been measured in simple NO + CO and CO + O-2 model reactions, as well as with complex mixtures approaching automotive exhaust composition, at both stoichiometric and O-2 limiting conditions. The catalysts have been characterized after reaction as well. The perovskite with the highest Cu amount, LaCo0.5Cu0.5O3, exhibits an interesting compromise of oxidation and NO reduction functionality at interesting, low temperatures with very short contact time (GHSV = 1,000,000 h(-1)). Still, activity for NO reduction in real mixtures requires substoichiometric O-2. (C) 2015 Elsevier B.V. All rights reserved.

Luminescent anionic β-diketonate complexes of formula [P8,8,8,1][Ln(dbm)4], (Ln = Eu3+and Sm3+, [P8,8,8,1] = trioctylmethylphosphonium and dbm = 1,3-diphenylpropane-1,3-dione) were synthesized, characterized and their photoluminescence properties studied.

Layered multi-oxide concept was applied for fabrication of photoanodes for dye-sensitized solar cells based on ZnO and SnO2, capitalizing on the beneficial properties of each oxide. The effect of different combinations of ZnO@SnO2 layers was investigated, aimed at exploiting the high carrier mobility provided by the ZnO and the higher stability under UV irradiation pledged by SnO2. Bi-oxide photoanodes performed much better in terms of photoconversion efficiency (PCE) (4.96%) compared to bare SnO2 (1.20%) and ZnO (1.03%). Synergistic cooperation is effective for both open circuit voltage and photocurrent density: enhanced values were indeed recorded for the layered photoanode as compared with bare oxides (Voc enhanced from 0.39 V in case of bare SnO2 to 0.60 V and Jsc improved from 2.58 mA/cm2 pertaining to single ZnO to 14.8 mA/cm2). Improved functional performances of the layered network were ascribable to the optimization of both high chemical capacitance (provided by the SnO2) and low recombination resistance (guaranteed by ZnO) and inhibition of back electron transfer from the SnO2 conduction band to the oxidized species of the electrolyte. Compared with previously reported results, this study testifies how a simple electrode design is powerful in enhancing the functional performances of the final device.

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.

SrTi0.7Co0.3O3, SrTi0.7Cu0.3O3, SrTi0.7Co0.15Cu0.15O3 were prepared by the “citrate route” and characterized (XRD, XPS, SEM, TPR). Their reactivity with respect to CO oxidation and NO reduction was investigated and compared with that of CuO/SrTi0.7Co0.3O3 nanocomposite. High conversions were obtained in CO oxidation (90 % at 350 °C for SrTi0.7Co0.3O3). Only CuO/SrTi0.7Co0.3O3 was observed to be active in NO reduction (100 % at 350 °C).

N-type metal oxide solar cells sensitized by infrared absorbing PbS quantum dots (QDs) represent a promising alternative to traditional photovoltaic devices. However, colloidal PbS QDs capped with pure organic ligand shells suffer from surface oxidation that affects the long term stability of the cells. Application of a passivating CdS shell guarantees the increased long term stability of PbS QDs, but can negatively affect photoinduced charge transfer from the QD to the oxide and the resulting photoconversion efficiency (PCE). For this reason, the characterization of electron injection rates in these systems is very important, yet has never been reported. Here we investigate the photoelectron transfer rate from PbS@CdS core@shell QDs to wide bandgap semiconducting mesoporous films using photoluminescence (PL) lifetime spectroscopy. The different electron affinity of the oxides (SiO2, TiO2 and SnO2), the core size and the shell thickness allow us to fine tune the electron injection rate by determining the width and height of the energy barrier for tunneling from the core to the oxide. Theoretical modeling using the semi-classical approximation provides an estimate for the escape time of an electron from the QD 1S state, in good agreement with experiments. The results demonstrate the possibility of obtaining fast charge injection in near infrared (NIR) QDs stabilized by an external shell (injection rates in the range of 110-250 ns for TiO2 films and in the range of 100-170 ns for SnO2 films for PbS cores with diameters in the 3-4.2 nm range and shell thickness around 0.3 nm), with the aim of providing viable solutions to the stability issues typical of NIR QDs capped with pure organic ligand shells.

Nowadays the employment of renewable and sustainable energy sources, and solar light as main option, becomes an urgent need. Photocatalytic processes received great attention in wastewater treatment due to their cheapness, environmental compatibility and optimal performances. Despite the general low selectivity of the photocatalysts, an accurate optimisation of the operational parameters needs to be carried out in order to maximise the process yield. Because of this reason, the present contribution aims to deepen either the knowledge in boron and/or nitrogen doped TiO2-based systems and their employment in methyl red removal from aqueous solutions. The samples were obtained by coprecipitation and characterised by XRD, SEM, BET specific surface area, UV-vis and XPS techniques. The catalytic activity was for the first time carefully evaluated with respect to methyl red photodegradation in different conditions as a function of working pH, counter-ions and pre-adsorption time. An ad-hoc study was performed on the importance of the pre-adsorption of the dye, suggesting that an extended adsorption is useless for the catalyst photoactivity, while a partial coverage is preferable. The photocatalytic tests demonstrate the positive influence of boron doping in photo-activated reactions and the great importance of the operational parameters with respect to the simple methyl red bleaching rather than the overall pollutant mineralisation. It is proved, indeed, that different working pH, acidifying means and substrate pre-adsorption time can enhance or limit the catalyst performances with respect to the complete pollutant degradation rather than its partial breakage. (C) 2014 Elsevier B.V. All rights reserved.

The reactivity of La0.7Sr0.3CuO3−δ with methanol and ethanol was investigated in oxidation and steam reforming. The conversion is higher in the oxidation reactions (about 100 %) than in steam reforming (78 % for methanol, 23 % for ethanol). Significant amounts of hydrogen form during methanol steam reforming. Acetaldehyde is observed with ethanol.

The synthesis of strontium ferrite SrFeO(3-δ) has been explored through wet-chemistry methods in order to optimize a quick, easy and reproducible method to obtain the perovskite in pure crystalline form with a high yield. Among the three investigated synthetic paths, (i) coprecipitation of hydroxides, (ii) coprecipitation of oxalates and (iii) polyol-assisted coprecipitation, only the second one was effective in obtaining the desired perovskite modification as a single phase. The products were analyzed by means of powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), to determine the crystalline structure and the chemical composition of the sample surface, respectively, and to optimise the synthetic process. Pure samples were further characterised by means of inductively coupled plasma (ICP-AES) analysis, nitrogen adsorption, elemental analysis, temperature programmed reduction (TPR) and Mössbauer spectroscopy.

LaCo0.7Cu0.3O3 perovskite powder was prepared by means of the citrate method and treated at different temperatures from 873 to 1323K. The samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption (TPD, O2-TPD), and scanning electron microscopy (SEM); the BET specific surface area was also determined. The reactivity of the perovskite with methanol and ethanol was investigated under steam reforming and oxidative steam reforming conditions and correlated to its chemical and structural properties. Different oxygen/alcohol molar ratios were used to study the influence of oxygen on catalytic activity and products distribution. LaCo0.7Cu0.3O3 begins to be active in alcohol steam reforming at about 523K. The catalyst calcined at 873K shows the higher conversion in methanol steam reforming. Ethanol steam reforming conversion, in contrast, is rather low and not significantly affected by the catalyst calcination temperature. The conversions increase when oxygen is present reaching 93% for methanol and 78% for ethanol. Beside the steam reforming and oxidative steam reforming, other secondary reaction paths occur: methanol decomposition and ethanol dehydrogenation.