Papers by Keyword: NaY

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Authors: C. Teixeira, P. Parpot, Isabel Neves, António Maurício C. Fonseca
Abstract: CoPAN complex has been entrapped in the supercages of Y zeolite and the redox properties of this zeolite-encapsulated complex were investigated by cyclic voltammetry with a new method for the preparation of carbon toray-zeolite-modified electrode. Formation of the CoPAN complex was ascertained by surface analysis (SEM, XRD), chemical analysis (CA), spectroscopy methods (FTIR and UV/vis) and cyclic voltammetry in aqueous medium with zeolite-modified electrodes. The cyclic voltammetry studies obtained with a zeolite-modified electrode shows evidence for electroactivity restricted to boundary associated CoPAN complex.
Authors: Maria Teresa Tavares, Cristina Quintelas, Hugo Figueiredo, Isabel Neves
Abstract: This study aims the definition of a new material that may act as a robust and yet cost effective biosorbent for treatment of wastewater with low concentration of heavy metals. A comparative study was made between two biosorption systems composed of an Arthrobacter viscosus biofilm supported on Cuban natural zeolites and on prepared NaY and NaX, in terms of their ability to retain ionic chromium. The bacterium is able to reduce Cr(VI) to Cr(III) and, only then, this smaller and positive ion may be entrapped in the zeolite cages by ion exchange. The first support was tested in a continuous flow semi-packed bed column. The highest removal ratio, 42%, was achieved for initial chromium concentration of 10 mg/L, but the best up-take, 5.5 mg/gzeolite, was obtained for initial concentration of 70 mg/L. Biosorbents prepared with the same biofilm supported in NaY and NaX zeolites were also considered in batch studies, with a typical kinetics of biosorption processes, reaching 20% of initial chromium removal within an initial range of Cr(VI) concentration between 50 and 250 mg/L. These last structures were characterized by spectroscopic methods (FTIR and ICP-AES), surface analysis (DRX) and thermal analysis (TGA). All these techniques indicated that the biosorption process does not modify the morphology and structure of the FAU-zeolites.
Authors: Natércia Nunes, Filomena Costa, António Maurício C. Fonseca, Isabel Neves, M.Alice Carvalho, Cristina Ribeiro
Abstract: The encapsulation of Cu(II) purine derivative complex was carried out by ion exchange of the complex from aqueous solutions into zeolite NaY. The entrapped complex was characterized by spectroscopic methods (FTIR and ICP-AES) and surface analysis (XRD). The various techniques of characterization used show that the Cu(II) complex was effectively encapsulated in the zeolite and this process does not modify the morphology and structure of the NaY zeolite. These materials have potential applications in heterogeneous catalysis in mild reaction conditions.
Authors: Filomena Costa, António Maurício C. Fonseca, Isabel Neves, Ana P. Carvalho, João Pires
Abstract: A hydride tungsten complex, [WH2(η2-OOCCH3)(Ph2PCH2CH2PPh2)2][BPh4], was entrapped in the interlayer of a pillared layered clay (PILC) and in NaY zeolite. The adsorption of the complex in the liquid phase was the immobilization process used. The free complex and the new materials were characterized by several techniques: structural analysis by DRX, nitrogen adsorption isotherms and spectroscopic methods (ICP-AES, FTIR and UV/Vis). Analysis of the data indicates that the tungsten(IV) complex is immobilized in the host microporous structures, and exhibit structural properties that are different from those of the free complex. These differences could arise either from distortions caused by steric effects imposed by the structures or from interactions with the host matrix.
Authors: B. Silva, Hugo Figueiredo, Cristina Quintelas, I.C. Neves, T. Tavares
Abstract: The removal of metallic ions from binary aqueous solutions of Fe(III)/Cr(III) and Fe(III)/Cr(VI) by an Arthrobacter viscosus biofilm supported on NaY zeolite was investigated. Experiments were repeated with suspended biomass for comparison purposes. Batch assays were performed using different concentrations (10, 25 and 40 mg/L), for both metals in solution. Results indicated that Arthrobacter viscosus is able to retain the metallic ions, although not totally. The removal efficiencies were improved when the biofilm was supported on the zeolite, for all the initial concentrations of Cr(III), for the intermediate and higher concentration of Cr(VI) and for all range of initial concentrations of Fe(III), in the presence of Cr(III). The bacteria reduce Cr(VI) to Cr(III) and, only then, this cation may be entrapped in the framework zeolite by ion exchange. Suspended bacteria had higher affinity for Fe(III), than for Cr(VI) or Cr(III), while the conjugated system was selective to Fe(III) when in the presence of Cr(VI). For solutions of Fe(III)/Cr(III), very high removals were achieved by the supported system, ranging from 94 to 100 % for Cr(III) and from 98 to 100 % for Fe(III). The conjugated system also reached the highest removal ratio of Cr(VI), 36 %, for the initial concentration of 40 mg/L. The materials in study were characterized by techniques such as FTIR, SEM and chemical analyses.
Authors: Wen Jie Zhang, Xin Sun
Abstract: Composite of TiO2 and NaY zeolite was prepared by solid-state dispersion method and the simple mixture of TiO2 and NaY was also compared on methyl orange photocatalytic degradation. Methyl orange degradation rate increased constantly with the increase of TiO2 concentration from 50 mg/l to 200 mg/l and declined gradually afterwards. When the ratio of TiO2 and NaY zeolite was 1:10, the photocatalytic activity of the mixed catalyst was close to that of pure TiO2. The photocatalytic activity of TiO2-NaY composite in different ratio prepared by solid-state dispersion was lower than that of pure TiO2. The photocatalytic activity of the composite catalyst in the ratio of 1:20 was close to that of pure TiO2. Composite catalyst can deposit much quicker than pure TiO2 after treatment.
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