M. J. Godinho

Gadolinium-doped cerium oxide nanorods: novel active catalysts for ethanol reforming

The gadolinium-doped ceria nanorods (Gd0.2Ce0.8O2−x) were synthesized by hydrothermal treatment. It was shown that the use of microwave heating during hydrothermal treatment decreases the treatment time required to obtain gadolinium-doped ceria nanorods and that oriented attachment is the dominant mechanism responsible for anisotropic growth. It was clear that Gd0.2Ce0.8O2−x nanorods were more catalytically active than commercial CeO2 in the ethanol reforming reaction.

Influência do lantânio nas propriedades estruturais do SrSnO3

The tin compounds with perovskite structure have shown promising properties for use as electronic ceramics such as sensors, catalysts and most recently, photoluminescent materials. In this work the effect of lanthanum on the structural properties of LaxSr1-xSnO3 and the evaluation of this system as photoluminescent material were studied. The LaxSr1-xSnO3 powders were synthesized by the polymeric precursor method and thermal treatments at 600, 800 and 1000 oC for 4 h. The systems were characterized by thermal analysis, X-ray diffraction, specific surface area measurements, UV-Visible spectroscopy, infrared spectroscopy, scanning electron microscopy and photoluminescence measurements. X-ray diffraction analysis shows crystalline phase with cubic perovskite structure, as a function of calcination temperature for the additions of lanthanum (1, 5 and 10 mol%). Despite the addition of lanthanum in SrSnO3, the perovskite structure is stable. The crystallite size decreased with the addition of lanthanum, indicating that this dopant may be acting as a possible particle growth inhibitor and hence decreasing crystallite size. The results of the specific surface area show that the addition of lanthanum favors, in general, the formation of higher surface area solids. Values of the optical gap, according to the theory of Tauc, are between 3.81 and 3.98 eV, showing a gradual increase due to the addition of lanthanum. The powders doped with 1 mol% of lanthanum and treated at 600 oC presented higher photoluminescent emission intensity.

Effects of MnO 2 /In 2 O 3 thin films on photocatalytic degradation 17 alpha-ethynylestradiol and methylene blue in water

In recent years, there has been a growing concern about some substances in the aquatic environment such as methylene blue dye (MB) and 17α-ethynylestradiol (EE2) hormone, mainly from waste textile and pharmaceutical industries, respectively. This waste, which is not effectively treated, generates large amounts of contaminated effluents. Textile industries, which use dyes mainly in their dyeing and finishing processes, generate a lot of effluent contamination by dyes. The 17α-ethynylestradiol hormone which is used in different contraceptive pills and in hormone replacement therapy, is the main substance found in the aquatic environment because of its high resistance to biodegradation. It is known that conventional water treatment processes, which involve the steps of coagulation, flocculation and sedimentation among others, have been reported to be ineffective in the removal of dyes and hormones. The heterogeneous photocatalysis has attracted great interest from many research groups around the world due to its potential application as a pollutant degradation method. For this purpose, the present work evaluated the performance of MnO2/In2O3 thin films in the degradation process of the blue methylene and 17α-ethynylestradiol in aqueous solutions. The degradation processes were monitored by UV–Vis spectroscopy and HPLC chromatography. From these analyzes, the concentration of the solutions was evaluated and it was possible to infer that the MnO2/In2O3 thin films significantly promoted a degradation of 89% of 17α-ethynylestradiol, however, the degradation of the methylene blue was not efficient.

Síntese in situ pelo método hidrotérmico de heteroestruturas de titanato-ferritas e sua atividade fotocatalítica

Heterostructured photocatalysts stand out for their ability to degrade various organic compounds in the treatment of wastewater. In this context, the purpose of this work was to produce titanate-ferrite heterostructured composites by in situ hydrothermal synthesis for application in the photo-Fenton process. The synthesized materials were characterized by X-ray diffraction, infrared spectroscopy, diffuse reflectance spectroscopy, specific surface area (by BET) and transmission electron microscopy. The in situ synthesis of SrTiO3-CoFe2O4 and SrTiO3-NiFe2O4 was developed here in a novel way, successfully resulting in heterostructured systems with no secondary phases and a highly homogeneous distribution of the constituent phases with average nanometric size particles. Moreover, this new method was found to be highly reproducible. The photocatalytic activity of the synthesized composites was analyzed based on the degradation of Rhodamine B dye using visible light. The best photocatalytic activity was exhibited by the SrTiO3-CoFe2O4 system, which degraded 82% of the dye.

Novel Gd(OH)3, GdOOH and Gd2O3 Nanorods: Microwave-Assisted Hydrothermal Synthesis and Optical Properties

We present a study of the controlled synthesis and optical properties of single-crystals Gd(OH)3, GdOOH and Gd2O3 nanorods. In this work, Gd(OH)3 nanorods were synthesized by a simple and fast microwave-assisted hydrothermal method. This process combined with the thermal decomposition oxidation of Gd(OH)3 nanorods as precursors enabled the preparation of single-crystalline GdOOH and Gd2O3 structures with well-defined morphology at low temperatures. The crystal structure dependence on the optical properties was investigated. We observed a green shift effect on the photoluminescence (PL) emission spectra from Gd(OH)3 to Gd2O3 nanorods, which can be attributed to different types of surface defects, as well as intrinsic properties that contribute significantly to the modified PL behavior.

Structure, Morphology, and Optical Properties of (Cal(1-3x)Eu(2x)) WO4 Microcrystals

In this letter, we report the efficient, surfactant-free, microwave-hydrothermal method of synthesizing calcium europium tungstate [(Ca1−3xEu2x)WO4, x = 0, 0.05, 0.01, 0.02, and 0.04] microcrystals. The structure and morphology were investigated using X-ray diffraction (XRD), Fourier-transform Raman (FT-Raman) spectroscopy, and field emission scanning electron microscopy (FE-SEM). XRD patterns and FT-Raman spectra indicated that all (Ca1−3xEu2x)WO4 microcrystals has a scheelite-type tetragonal structure. FE-SEM images revealed that the Eu3+ ions systematically affect the crystal shape and that there are two different types of superstructures: rice- and dumbbell-like microcrystals. The photoluminescence emission of the doped microcrystals changed relative to that of pure CaWO4 owing to the presence of defects and new energy levels associated with the Eu3+ content, which promotes the appearance of intermediate electronic levels in the band gap.

Estudo do crescimento de nanofitas de céria dopada com gadolínio por sistema de aquecimento por micro-ondas

) ou ceria e um material cerâmico que tem sido muito estudado por apresentar ampla utilizacao em celulas a combustivel de oxido solido, sensores eletroquimicos, materiais luminescentes, material para polimento, aditivo cerâmico, bloqueadores de UV, biomateriais [1-4]. Dentre os oxidos metalicos, a ceria se destaca por possuir diversas propriedades fisicas interessantes devido a sua configuracao eletronica, sendo hoje amplamente aplicada como catalisador para gases de exaustao, reforma de etanol na obtencao de hidrogenio, para sintese de compostos orgânicos e tambem como catalisadores em exaustores automotivos [5-8]. A ceria tem a propriedade de absorver e liberar oxigenio sob condicoes reversiveis de oxidacao e reducao, processo este denominado estocagem de oxigenio. A causa deste efeito e uma transformacao continua e reversivel entre o sesquioxido e o dioxido de cerio (Ce