Sustainable and environmentally friendly methods for nanomaterials synthesis have been emerging recently. The use of extracts of polyphenol-rich plants with high reducing and chelating power is advantageous because the polyphenol can protect the nanomaterial from agglomeration and deactivation. Green nanomaterials have been applied in several areas, including remediation of toxic organic pollutants from contaminated effluents. Herein, we describe the preparation of green iron oxide nanoparticles (IONPs) with extracts of the plant Camellia sinensis as black tea for dye removal application. The as-prepared IONPs were composed of amorphous FeOOH and FeII/III-polyphenol complexes. To obtain crystalline and pure iron-based nanomaterials, the amorphous precursor was annealed at 900 ºC. Samples of black tea from different regions were used to verify the reproducibility of the iron phases formed. The same iron phases were obtained for all black tea samples, α-Fe2O3 (hematite), FePO4, and Fe3PO7, but in different proportions. The materials were applied as heterogeneous-Fenton catalysts for the removal of the dye methyl orange. The amorphous as-prepared IONPs were more active than the respective annealed IONPs due to the proton release from the polyphenol into the reaction medium, setting the pH to around 3, which is the optimum pH for the Fenton system.

This work describes a green approach to the synthesis of iron nanoparticles supported in silica using tea extract of the South American plant yerba mate (Ilex paraguariensis). Catalysts with different iron contents were obtained according to the reaction conditions employed. Characterization by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) revealed the amorphous nature of the nanoparticles, tentatively ascribed to iron(II)/iron(III) oxide composites, as Fourier transform infrared (FTIR) and thermogravimetric analyses confirmed their functionalization by the tea polyphenolic compounds. For the sake of comparison, crystalline zero-valent iron nanoparticles were prepared by the classical method using NaBH4. Both materials were tested in the degradation of methyl orange and led to complete decolourization; the green nanoparticles were very active as heterogeneous Fenton-like catalysts in presence of hydrogen peroxide, while the nanoparticles prepared with NaBH4 were efficient in the reductive degradation of the dye.

Zeolite-encapsulated complexes have been widely applied in hydrocarbon oxidation catalysis. The "ship-in-a-bottle" encapsulation of iron(III) complexes containing piperazine and piperazine-derivative ligands in zeolite-Y is described. The flexible ligand methodology was employed and the efficiency and reproducibility of the procedure was investigated. The catalysts were characterized employing several techniques and the results indicate the presence of coordinated and uncoordinated iron(III) ions inside and outside the zeolitic cage.

Neste artigo são apresentadas a síntese e a caracterização de dois compostos binucleares de ferro, os quais contêm uma ponte μ-oxo. Os compostos [(SO4)(L5)Fe(μ-O)Fe(L5)(SO4 )]•6H2O, 1, e [Cl(L5)Fe(μ-O)Fe(L5)Cl]Cl2• 2H2O, 2, foram obtidos nas reações entre 1-(bis-piridin-2-ilmetil-amino)-3-cloropropan-2-ol (L5) e os sais FeSO4•7H2 O e FeCl3•6H2 O, respectivamente. Os espectros eletrônicos dos complexos apresentam absorções somente na região do ultravioleta, sendo que a análise eletroquímica revelou que, após a formação da espécie FeIII FeII, a unidade binuclear do composto 1 é mais estável do que a do composto 2. Os ligantes monodentados (sulfato e cloreto) exercem influência sobre os parâmetros Mössbauer determinados para 1 e 2, particularmente sobre os desdobramentos de quadrupolo. Os compostos foram empregados como catalisadores em reações de oxidação do cicloexano, usando H2O2 e t-BuOOH como oxidantes em uma razão substrato:oxidante:catalisador de 1000:1000:1. Os resultados indicam que o composto 2 é um catalisador mais eficiente que o composto 1.

We report herein the synthesis and characterization of two dinuclear μ-oxo iron compounds obtained through the reactions of FeSO4•7H2 O and FeCl3•6H2 O with 1-(bis-pyridin-2-ylmethyl-amino)-3-chloropropan-2-ol (L5), which resulted in the compounds [(SO4)(L5)Fe(μ-O)Fe(L5)(SO4 )]•6H2O, 1, and [Cl(L5)Fe(μ-O)Fe(L5)Cl]Cl2• 2H2O, 2. The electronic spectra of both compounds show absorption bands only in the UV range. The electrochemical analysis showed that the dinuclear unit is more stable under reduction in compound 1 than in compound 2, while the Mössbauer spectroscopy revealed that the monodentate ligands (sulfate and chloride) have a significant influence on the Mössbauer parameters determined for 1 and 2, particularly on the quadrupole splitting values. Both compounds were studied as catalysts in reactions of cyclohexane oxidation, using H2O2 and t-BuOOH as oxidants, in a substrate:oxidant:catalyst ratio of 1000:1000:1. Cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide, t-butyl cyclohexyl peroxide and adipic acid were formed during the process. The experiments revealed that compound 2 is, in general, more active than compound 1 in promoting cyclohexane oxidation.

The Michaelis-Menten equation is used in many biochemical and bioinorganic kinetic studies involving homogeneous catalysis. Otherwise, it is known that determination of Michaelis-Menten parameters K M, Vmax, and k cat by the well-known Lineweaver-Burk double reciprocal linear equation does not produce the best values for these parameters. In this paper we present a discussion on different linear equations which can be used to calculate these parameters and we compare their results with the values obtained by the more reliable nonlinear least-square fit.