National Institute Of Materials Physics - Romania

Mesoporous CeO2:Mn3O4 materials (3:7 and 7:3 molar ratio) were prepared by co-precipitation and deposited as porous thick films over alumina (Al2O3) planar substrate provided with Pt meander. The aim was oriented towards detecting low levels methane (CH4) at moderate operating temperatures. Herein we demonstrated that the sensitivity of catalytic micro-converters (CMCs) towards a given peak of CH4 concentration corresponds to specific gas-surface interaction phenomena. More precisely, a transition from thermal conductivity to combustion rate is likely to occur when CMCs are operated under real atmospheric conditions (normal pressure, presence of relative humidity, and constant operating temperature). The response to CH4 was analyzed over different gas flows and different gas concentrations under the same operating regime. The materials were fully characterized by adsorption-desorption isotherms, H-2-Temperature Programmed Reduction (H-2-TPR), X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), and Raman spectroscopies. Thus, the applicative aspect of using CeO2:Mn3O4 as moderate temperature CMC for CH4 detection is brought to the fore.

In this study, the synergistic behavior of Ni species and bimodal mesoporous undoped SnO2 is investigated in oxygen evolution reactions (OERs) under alkaline conditions without any other modification of the compositional phases or using noble metals. An efficient and environmentally friendly hydrothermal method to prepare bimodal mesoporous undoped SnO2 with a very high surface area (>130 m(2) g(-1)) and a general deposition-precipitation method for the synthesis of well-dispersed Ni species on undoped SnO2 are reported. The powders were characterized by adsorption-desorption isotherms, TG-DTA, XRD, SEM, TEM, Raman, TPRH2, and XPS. The best NiSn composite generates, under certain experimental conditions, a very high TOF value of 1.14 s(-1) and a mass activity higher than 370 A g(-1), which are remarkable results considering the low amount of Ni deposited on the electrode (3.78 ng). Moreover, in 1 M NaOH electrolyte, this material produces more than 24 mA cm(-2) at an overpotential value of approximately +0.33 V, with only 5 wt % Ni species. This performance stems from the dual role of undoped SnO2, on the one hand, as a support for active and well-dispersed Ni species and on the other hand as an active player through the oxygen vacancies generated upon Ni deposition.

In this work, the effect of aliovalent substitution of Pb2+ by Eu3+ on structural, morphological and optical properties of CH3NH3PbI3 (MAPbI(3)) was studied, aiming to improve the properties of perovskite films used in solar cells application. The surface morphology, the microstructure and the optical properties of the obtained films containing different Europium (Eu) concentrations were characterized by atomic force microscopy, x-ray photoelectron spectroscopy, x-ray diffraction, UV-vis spectroscopy and photoluminescence spectroscopy.

Graphene oxide has been synthesized, additionally derivatized with chloroacetic acid for increase the number of available carboxylic groups and further functionalized with crown-ether moieties. The thus obtained material was characterized by IR, thermal analysis, SEM, Raman, and XPS. Tests on adsorption of several metal cations showed that cooper and iron are more retained than potassium.

Correlating dopant distribution to its optical response represents a complex challenge for nanomaterials science. Differentiating the "true" clustering nature from dopant pairs formed in statistical distribution complicates even more the elucidation of doping-functionality relationship. The present study associates lanthanide dopant distribution, including all significant events (enrichment, depletion and surface segregation), to its optical response in upconversion (UPC) at the ensemble and single-nanoparticle level. A small deviation from the Er nominal concentration of a few percent is able to induce clear differences in Er UPC emission color, intensity, excited-state dynamics and ultimately, UPC mechanisms, across tetragonal to monoclinic phase transformation in rationally designed Er doped ZrO2 nanoparticles. Rare evidence of a heterogeneous dopant distribution leading to the coexistence of two polymorphs in a single nanoparticle is revealed by Z- and phase contrast transmission electron microscopy (TEM). Despite their spatial proximity, Er in the two polymorphs are spectroscopically isolated, i.e. they do not communicate by energy transfer. Segregated Er, which is well imaged in TEM, is absent in UPC, while the minor phase content overlooked by X-ray diffraction and TEM is revealed by UPC. The outstanding sensitivity of combined TEM and UPC emission to subtle deviations from uniform doping in the diluted concentration regime renders such an approach relevant for various functional oxides supporting lanthanide dopants as emitters.

This study presents the synthesis and characterization of lanthanum-modified alumina supported cerium-manganese mixed oxides, which were prepared by three different methods (coprecipitation, impregnation and citrate-based sol-gel method) followed by calcination at 500 degrees C. The physicochemical properties of the synthesized materials were investigated by various characterization techniques, namely: nitrogen adsorption-desorption isotherms, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and H-2-temperature programmed reduction (TPR). This experimental study demonstrated that the role of the catalytic surface is much more important than the bulk one. Indeed, the incipient impregnation of CeO2-MnOx catalyst, supported on an optimized amount of 4 wt.% La2O3-Al2O3, provided the best results of the catalytic combustion of methane on our catalytic micro-convertors. This is mainly due to: (i) the highest pore size dimensions according to the Brunauer-Emmett-Teller (BET) investigations, (ii) the highest amount of Mn4+ or/and Ce4+ on the surface as revealed by XPS, (iii) the presence of a mixed phase (Ce2MnO6) as shown by X-ray diffraction; and (iv) a higher reducibility of Mn4+ or/and Ce4+ species as displayed by H-2-TPR and therefore more reactive oxygen species.

We propose a simple strategy to obtain a luminescence intensity ratio nanothermometer operating in the near infrared range (1000-1700 nm) by use of binary mixtures of lanthanide doped Y2O3 selected as 1% Ho - Y2O3 + 1%Er - Y2O3 and 1%Ho - Y2O3 + 1%Nd - Y2O3. All nanoparticles were synthetized by citrate complexation method and thermally annealed at 800 degrees C. The temperature evolution of the emission properties was monitored in the range of 297-472 K and analyzed in terms of emission shape, intensity, dynamics, excitation wavelength, acquisition mode and weight ratio of the binary mixture. A maximum relative sensitivity of 1%K-1 at 297 K was recorded for the 3/1 weight ratio Ho - Y2O3 + Er - Y2O3 binary mixture upon excitation at 536.8 nm. For the more appropriate excitation wavelength for bioimaging applications at 649.7 nm, a relative sensitivity of 0.55-0.6% K-1 was recorded in the relevant physiological temperature range (300-320 K) for the 3/1 weight ratio Ho - Y2O3 + Er - Y2O3 binary mixture. To the best of our knowledge, our study also represents a first report on the near -infrared luminescence (around 1200 nm) lifetime thermometry for a Ho doped nanoparticle. Comparison with the literature demonstrates that our system represents a promising near-infrared thermometer, with a non-sophisticated and reproducible configuration that is open to multiple optimization routes. (C) 2019 Elsevier B.V. All rights reserved.

We investigate how far the hysteresis-free behavior of perovskite solar cells can be reproduced using particular pre-conditioning and measurement conditions. As there are currently more and more reports of perovskite solar cells without J-V hysteresis it is crucial to distinguish between genuine performance improvements and measurement artifacts. We focus on two of the parameters that influence the dynamic J-V scans, namely the bias scan rate and the bias poling voltage, and point out measurement conditions for achieving a hysteresis-free behavior. In this context we discuss the suitability of defining a hysteresis index (HI) for the characterization of dynamic J-V scans. Using HI, aging effects are also investigated, establishing a potential connection between the sample degradation and the variation of the maximal hysteresis on one hand, and the relaxation time scale of the slow process on the other hand. Pre-poling induced recombination effects are identified. In addition, our analysis based on sample pre-biasing reveals potential indications regarding two types of slow processes, with two different relaxation time scales, which provides further insight regarding ionic migration.

The influence of the B type cation from the ABO(3) perovskite formulation La0.75Sr0.25XO3 (LSX, where X is Fe, Mn or Cr) on the C and H2S tolerance and its catalytic activity for the methane/water reaction has been studied. The samples were prepared by a simple and cost-efficient citrate method. The exhaustive characterization of the bulk and surface properties of the catalysts has been accomplished by means of complementary methods: nitrogen adsorption-desorption isotherm measurements, XRD, TPR and XPS. Their catalytic properties in CH4/H2O reactions (CH4/H2O molar ratios of 10 and 1) were studied in the presence and absence of H2S in order to evaluate their potential use as anode materials in solid oxide fuel cells operated on natural gas. Before addition and upon suppression of H2S, the activity varied in the following order: LSF > LSM >> LSC. This correlates with the oxygen mobility determined by TPR. A strong promoting effect of H2S on the catalytic activity is observed for LSC, which makes this sample the most active of the series, while H2S has a weak influence on the other perovskites. The oxygen vacancies and the presence of S2- were identified as being responsible for the enhanced catalytic activity upon H2S addition.

1-D coordination polymers, (1)(infinity)[Zn(fl)(2)]center dot 2EtOH and (1)(infinity)[Zn(fl)(2)]center dot 2MeOH, and a dinuclear complex, [{Zn(fl)(2)}(2)(dienpip)]center dot 4H(2)O center dot 4EtOH (dienpip= N,N '-bis(2-aminoethyl)piperazine), were obtained using Zn(II) ions and fluorescein anions (fl). Thermal analysis shows stability of the polymers after solvent removal up to more than 400 degrees C. Crystallization solvent molecules were removed under reduced pressure with the preservation of the polymeric structure, (1)(infinity)[Zn(fl)(2)]. Desolvated crystals were exposed to I-2 vapors and the crystal structure determination by X-ray diffraction confirmed the presence of I-2 molecules in the channels generated in crystals by the metal-organic framework. The iodine content, evaluated by X-ray diffraction, corresponds to the overall formula (1)(infinity)[Zn(fl)(2)]center dot 0.3I(2). The optical properties of the coordination polymers and the dinuclear complex have been investigated. [GRAPHICS] .