Francisco S. Dias

Adsorption of polycyclic aromatic hydrocarbons from aqueous solutions by modified periodic mesoporous organosilica

A novel procedure was developed for the synthesis of a periodic mesoporous organosilica (PMO), which was used to remove polycyclic aromatic hydrocarbons (PAHs) from aqueous solutions. Adsorption equilibrium isotherms and adsorption kinetics experiments were carried out in solutions of PAHs (2-60 mg L(-1)), using the PMO as adsorbent. Adsorption models were used to predict the mechanisms involved. The adsorption kinetics data best fitted the pseudo-first-order kinetic model for naphthalene, and to the pseudo-second-order model for fluorene, fluoranthene, pyrene, and acenaphtene. The intraparticle model was also tested and pointed to the occurrence of such processes in all cases. The isotherm models which best represented the data obtained were the Freundlich model for fluoranthene, pyrene, and fluorene, the Temkin model for naphthalene, and the Redlich-Peterson model for acenaphtene. PAHs showed similar behavior regarding kinetics after 24 h of contact between adsorbent and PAHs. FTIR, XRD, BET, and SEM techniques were used for the characterization of the adsorbent material.

Adsorption of BTX (benzene, toluene, o-xylene, and p-xylene) from aqueous solutions by modified periodic mesoporous organosilica

The capacity of a periodic mesoporous organosilica (PMO) to adsorb the aromatic compounds benzene, toluene, o-, and p-xylenes (BTX), which are usually present in produced waters, was investigated under both column and batch processes. The PMO was synthesized by condensation of 1,4 bis(triethoxisilyl)benzene (BTEB) under acidic conditions by using structure-directing agent (SDA) Pluronic P123 in the presence of KCl. Thermogravimetric analysis showed that the presence of the surfactant decreases the thermal stability of the PMO. The small-angle X-ray diffraction pattern, as well as the nitrogen adsorption/desorption isotherm measurements, revealed that the synthesized material has a crystalline structure, with hexagonally-ordered cylindrical mesopores. The adsorption kinetics study indicated an adsorption equilibrium time of 50 min and also showed that the data best fitted the pseudo-first order kinetic model. The intraparticle diffusion model was also tested and pointed to the occurrence of such process in all cases. Both Langmuir and Temkin models best represented the adsorption isotherms of toluene; Langmuir and Redlich-Peterson models best represented the data obtained for the other compounds. Adsorption capacity decreases in the order benzene>o-xylene>p-xylene>toluene. Satisfactory results were observed in the application of the synthesized PMO for the removal of BTX from aqueous solution.

Um sistema simples para preparação de microesferas de quitosana

This article describes the construction and optimization of an inexpensive apparatus for the production of uniform and porous chitosan microspheres. It also describes the control of the main operational parameters and strategies for the production of uniform chitosan microspheres.

New trisubstituted cyclopentadienyl ligands: synthesis, characterisation and catalytic properties of mono and dinuclear cobalt, rhodium, iron and ruthenium complexes

Abstract The synthesis of a set of dialkyl 4-alkoxycarbonylcyclopenta-1,3-diene-1,2-diacetates (1a–e) is described. Their coordinating abilities as anions have been investigated in relation to the formation of new sandwich, half-sandwich and dinuclear complexes and their structural features. We report here the preparation and characterisation of some complexes such as a mononuclear half-sandwich cobalt(1,5-COD) complex which has shown to be a very efficient catalyst for the cyclocotrimerisation reaction of alkynes and nitriles to pyridines. Half-sandwich rhodiumdicarbonyl complexes containing trisubstituted cyclopentadienyl ligands with ester chains of different length have been employed successfully as catalysts for hydroformylation of styrene. Finally ligands 1a–e have been used for the synthesis of ferrocenes and dinuclear carbonyl complexes of iron and ruthenium. The structures of the complexes 1,5-cycloctadiene[1-methoxycarbonyl-3,4-di(methoxycarbonylmethylene)cyclopentadienyl]cobalt [Co(MDMCp)COD] (9), dicarbonyl[1-methoxycarbonyl-3,4-di(methoxycarbonylmethylene)cyclopentadienyl]rhodium [Rh(MDMCp)(CO)2] (2a) and of a new ferrocene complex [Fe(MDMCp)2] (15a) have been determined by X-ray diffraction methods.

A NEW CYCLOPENTADIENE AND ITS USE AS A LIGAND FOR CATALYTICALLY ACTIVE RHODIUM COMPLEXES

Abstract Dimethyl 4-methoxycarbonylcyclopenta-1,3-diene-1,2-diacetate has been prepared from benzyl methyl malonate by reaction with 2-propynyl bromide, followed by palladium-catalyzed ring-forming oxidative carbonylation and by elimination of the benzyloxycarbonyl group and double bonds isomerization. The anion of the diacetate readily reacts with transition metal complexes, to give the corresponding cyclopentadienyl derivatives. We describe here some complexes, obtained from [{RhCl(L)2}2] [L = CO, C2H4 or 1,5-cyclooctadiene (COD)], which are efficient catalysts for the alkyne-nitrile co-cyclization to pyridines and for the hydroformylation of styrene and 1-hexene.

Pluriannual watershed discharges of hg into a tropical semi-arid estuary of the Jaguaribe river, NE Brazil

Mercury fluxes were measured during the dry and rainy seasons (2005 to 2009) at the Jaguaribe River estuary, which discharges into the Equatorial Atlantic Ocean in NE Brazil. During rainy periods, the water masses exhibited a short residence time within the estuary (0.8 days). During dry periods, seawater choked the fluvial discharge, resulting in longer residence times (3.1 days). Dissolved (< 0.7 µm) and particulate Hg concentrations and fluxes were greater from the river to the estuary than from the estuary to the sea, producing accumulated particulate Hg in the estuary. Particulate Hg export (1.8 to 12.6 mg s-1) to the ocean occurred during extremely rainy periods, while dissolved Hg export was practically nonexistent during rainy periods and increased up to 0.45 mg s-1 during dry periods. Because continental runoff in semi-arid regions is affected by land use and global climate changes, the increasing accumulation of particulate Hg in the estuaries and increasing export of dissolved Hg to the ocean are expected.

A thermochemical study of adducts of 2-pyrrolidone with zinc(III), cadmium(II) and mercury(II) halides

Abstract The standard molar enthalpies of acid-base reactions in the condensed state ( Δ r H ⦵ ) of the adducts MX 2 · n BuL (where M is Zn, Cd, Hg; X is Cl, Br, I; n = 1, 2, 3; BuL is 2-pyrrolidone) were determined from enthalpies of dissolution ( Δ i H ⦵ ) of metal halide ligands and adducts, at 298.15 K, obtained by calorimetric methods in solution. Using the values of Δ r H ⦵ and auxiliary data from the literature the standard enthalpies of formation ( Δ f H ⦵ ), decomposition ( Δ d H ⦵ ) and lattice enthalpy ( Δ latt H ⦵ ) of these adducts were determined. The enthalpy of vaporization of BuL, Δ vap H ⦵ ( BuL ) , was found to be 41.71 ± 0.56 kJ mol −1 and, from this value, the enthalpies of reaction in the gaseous state ( Δ g H ⦵ ) were estimated. The values of Δ g H ⦵ were used in calculations of the mean dissociation enthalpy of the metal-oxygen bond, D (MO), of the obtained adducts, and are correlated with energetic parameters of the metal halides.

Thermochemical data for adducts of ε-caprolactam with zinc(II) family metal halides

From solution calorimetry and appropriate thermodynamic cycles, the standard molar enthalpies of acid-base reactions in the condensed state (ΔrH°) for MX2·nCL (M is Zn, Cd, Hg; X is Cl, Br, I; n = 1, 2, 3 or 4; CL is e-caprolactam) adducts have been determined. From ΔrH° values and literature data, the following thermochemical quantities have been calculated: standard enthalpy of formation (ΔfH°), standard enthalpy of decomposition (ΔdH°), standard lattice enthalpy (ΔlattH°), standard enthalpy of acid-base reaction in the gaseous phase (ΔgH°) and the mean dissociation enthalpy of the metal-oxygen bond, D(MO). The thermochemical data are compared with those previously published for analogous BuL compounds (BuL is γ-butyrolactam or 2-pyrrolidone), with the purpose of evaluating the effect of ring strain on the donor oxygen strengths of both lactams. The thermochemical quantities are discussed in terms of acidity and basicity of the species and ΔgH° values correlated with ionic or covalent character of the metal halides.

The Arctic Paradox: Impacts of Climate Changes on Rivers from the Arctic and the Semiarid Increase Mercury Export to the Ocean

The semi-arid coast of Brazil is being strongly affected by regional land use and global climate changes, resulting in decreasing continental runoff to the ocean and increasing the water residence time in estuaries and expanding mangrove areas; these in turn may induce an increase of particulate Hg accumulation within the estuaries and increase the export of dissolved Hg to the ocean. This is, paradoxically, what is presently happening in Arctic rivers due to increasing, not decreasing, continental runoff associated with global climate changes.

Energetics of formation of adducts of N-methyl-2-pyrrolidone with zinc(II) family metal halides — A thermochemical study

Abstract Thermochemical data for adducts of N -methyl-2-pyrrolidone (NMP) with zinc(II), cadmium(II) and mercury (II) halides have been obtained from solution calorimetry. The technique provided the values for the dissolution enthalpies ( Δ i H 0 ) of MX 2 (M = Zn, Cd, Hg; X = Cl, Br, I) metal halides, the NMP lactam and MX 2 · n NMP adducts, which were used to determine the standard molar enthalpies of acid-base reaction in the condensed state ( Δ r H 0 ) for the adducts, by using appropriate thermodynamic cycles. From Δ r H 0 values and literature data, the following thermochemical parameters have been calculated: standard enthalpy of formation ( Δ f H 0 ), standard enthalpy of decomposition ( Δ d H 0 ), standard lattice enthalpy ( Δ latt H 0 ), standard enthalpy of acid-base reaction in the gaseous phase ( Δ g H 0 ) and the mean dissociation enthalpy of the metal-oxygen bond, D (MO) have been established. In order to evaluate the methyl group influence on the donor oxygen strength of the NMP lactam, the obtained thermochemical data are compared with those previously published for analogous 2-pyrrolydone (BuL) compounds. The influence of the ionic and covalent character of the metal halides has been taken into account in the metal-oxygen interaction processes.