The encapsulation of a pyridazine Cr(III) complex was prepared from a robust biosorption system consisting of a bacterial biofilm supported on NaY or NaX zeolites. The maximum removal efficiency was 20% for Cr in both systems based in NaY or NaX. The bacterial biofilm, Arthrobacter viscosus, supported on the zeolite reduce Cr(VI) to Cr(III). The Cr(III) is retained in the zeolite by ion exchange. These occluded complexes were characterized by chemical analysis, spectroscopic methods (FTIR and UV/Vis) and surface analysis (DRX).
The various techniques of characterization used show that the Cr(III) complex was effectively encapsulated in the zeolite and this process does not modified the morphology and structure of the NaY/NaX zeolites. These materials have potential applications in heterogeneous catalysis in mild conditions.; Departamento de Ciências da Terra of Universidade do Minho; Fundação para a Ciência e a Tecnologia (FCT)
The immobilization of transition metal complexes with redox catalytic activity in solid supports has attracted much interest due to their potential use as hete rogeneous catalysts in mild conditions.
One of the most common strategies for the preparation of zeolites with metal transition complexes is the flexible ligand method. The incorporation of the cation requires the exchange with the charge-balancing cation from zeolite framework. Two different procedures for ion exchange are: the traditional ion exchange from aqueous solutions containing the metal and metal biosorption by microorganisms supported
on the zeolite. In previous work, we reported the development of a biosorption system for Cr(IV) removal from industrial wastewater, by using bacterial biofilm supported on zeolites. The system has shown ability to remove chromium from aqueous solutions with concentrations ranging 10 – 250 mg/L. The biological activity of the employed bacteria, Arthrobacter viscosus, induces reduction of the Cr (VI) to Cr (III) species.
The aim of this work is to evaluate the traditional ion exchange and the biosorption paths for the immobilization of chromium complexes in NaY zeolite. The bio-monomer under investigation, the 3-methoxy-6-chloropyridazine...
Immobilization of Fe(III) complexes of pyridazine derivatives was achieved in NaY zeolite, loaded with iron through the action of a robust biosorption mediator consisting of a bacterial biofilm, Arthrobacter viscosus, supported on the zeolite. The objective of this study is the preparation and characterization of new catalytic materials to be used in oxidation reactions under mild conditions. The biosorption of Fe(III) ions was performed starting from aqueous solutions with low concentrations of iron and the highest values of biosorption efficiency for Fe(III) were reached at the beginning of the contact period with the sorbents. The Fe(III) biosorption process was compared with the one of Cr(III) under the same experimental conditions, as this latter case has been well characterized. The sample used in the immobilization of Fe(III) complexes of pyridazine derivatives was prepared from an aqueous solution of 100.0 mgFe/L, without the competing effect of other metals. Fe(III) is retained in the zeolite by ion exchange and coordination with two different pyridazine derivative ligands, 3-ethoxy-6-chloropyridazine (A) and 3-piperidino-6-chloropyridazine (B). The resulting materials were fully characterized by different spectroscopic methods (EPR...
Fonte: Universidade do MinhoPublicador: Universidade do Minho
Tipo: Tese de Doutorado
Publicado em 03/04/2012ENG
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Tese de doutoramento em Engenharia Química e Biológica; Heavy metal contamination of aquifers by industrial effluents is a known environmental
concern for which a recent effort for the development of treatment/remediation
technologies has been conducted. Nevertheless, technologies that allow
recuperation/reutilization of the metals are still of limited application.
This work presents the development of a clean technology allowing treatment and recovery
of heavy metals in industrial effluents. The proposed recovered metals will be used as
catalysts in liquid-phase oxidation reactions. The proposed system consists in bridging the
biosorption capacity of the Arthrobacter viscosus bacterium with the intrinsic ion-exchange
capacity of synthetic zeolites. This system was tested in the treatment of Cr(VI) solutions,
in batch conditions (either in single step or sequencing reactor operation).
The system showed capacity for the treatment of Cr(VI) solutions. Although zeolites have
natural limitation to exchanging Cr(VI) species, as they are anionic in solution, the
bacterium is able to reduce Cr(VI) to Cr(III) and the last is cationic in solution and
therefore has access to the zeolites.
Several operational parameters were evaluated in order to increase the performance of this
system in the treatment of Cr(VI) solutions up to 100 mgCr/g. The pH in each reactor was
allowed to vary freely in early studies. It was observed that the chemical composition of the
zeolitic support had influence on the efficiency of the bioreduction of Cr(VI) to Cr(III). H+-
containing zeolites allowed higher reduction than the Na+-containing counterparts. Despite