Robson Fernandes de Farias

O uso de sílica gel organofuncionalizada como agente sequestrante para metais

An overview about the homogeneous and heterogeneous methods of synthesizing silylating agents and applications of the organofunctionalized silica-gel samples was explored. The pendant molecules attached covalently to the inorganic surface displayed important properties to act as sequestrating agents for metals in aqueous and non-aqueous solutions. The large variety of basic centres anchored on organic molecules improve the capacity in adsorbing cations. The increase in adsorption is dependent on the number of basic atoms disposed on the pendant molecules on the surface. The combination of acidic and basicity properties favours the selectivity, such is exemplified by the thiol modified silicas towards mercury (II) cations.

Adsorption of crude oil on anhydrous and hydrophobized vermiculite.

This publication reports the adsorption of crude oil on vermiculite samples, expanded and hydrophobized with carnauba (Copernicia Cerifera) wax. The adsorption studies were performed by using columns filled with the vermiculite matrices and by dispersion of the vermiculite samples in an oil-water (50 ppm of oil) emulsion. The hydrate vermiculite exhibits a very low adsorption capacity against crude oil. On the other hand, anhydrous (expanded) and hydrophobized matrices show a high adsorption capacity. The 10% hydrophobized matrix show a 50% increased adsorption capacity, in comparison with the expanded one. For adsorption performed in the water-oil emulsion, saturation of the solid hydrophobized matrix is achieved after 60 min. The hydrophobized samples exhibit adsorption factors in the 0.7-1.0 range.

The intercalation of n-alkyldiamines into crystalline layered titanate

Abstract The synthesis, characterization, and intercalation of n-alkyldiamines H 2 N(CH 2 ) n NH 2 (n = 2, 3, 4, 6, 7, and 8) into layered hydrous tetratitanic acid H 2 Ti 4 O 9 ·nH 2 O are reported. From the elemental analysis, the following formula were proposed for the intercalated compounds: (C 2 H 8 N 2 ) 0.3 H 2 Ti 4 O 9 ·0.40H 2 O, (C 3 H 10 N 2 ) 0.6 H 2 Ti 4 O 9 ·0.89H 2 O, (C 4 H 12 N 2 ) 0.3 H 2 Ti 4 O 9 ·0.40H 2 O, (C 6 H 16 N 2 ) 0.6 H 2 Ti 4 O 9 ·0.92H 2 O, (C 7 H 18 N 2 ) 0.5 H 2 Ti 4 O 9 ·0.50H 2 O and (C 8 H 20 N 2 ) 0.6 H 2 Ti 4 O 9 ·0.60H 2 O. X-ray diffraction patterns for these matrices showed that the 920 pm interlayer space of the original matrix has the d-spacing values increased to 1118, 1318, 1549, 1662, 1720, and 1766 pm, respectively, for the C 2 –C 8 sequence of intercalated n-alkyldiamine. The infrared data are in agreement with the protonated nitrogen atoms of the diamines located in the cavity space. The hydrous matrix showed two mass loss steps in the thermogravimetric curve, corresponding to the release of physisorbed and lattice water molecules. A third mass loss was observed for the intercalated matrices due to the release of organic moiety. From these values, the intercalated matrices represented by the number of carbons in the organic chains can be ordered in the following sequence of thermal stability: C 4 > C 2 > C 3 ≅ C 6 > C 7 ≅ C 8 . The lowest amount of intercalated n-alkyldiamines gave the largest thermal stability of the hybrid.

Synthesis of new compounds involving layered titanates and niobates with copper(II)

Abstract A series of titanates and niobates, K 2 Ti 4 O 9 , Na 2 Ti 3 O 7 , KNb 3 O 8 , K 4 Nb 6 O 17 , and their respective acid forms were prepared and characterized by X-ray diffraction, thermogravimetry and scanning electron microscopy. The ion exchange capacity of the alkaline and acid forms towards Cu(II) was studied and it is concluded that, as general behavior, the alkaline titanates and niobates have a higher ion exchange capacity towards copper cations than their respective acid forms. Furthermore, the sodium matrix Na 2 Ti 3 O 7 exhibits the highest ion exchange capacity of 3.00 mmol g −1 . Based on the thermogravimetric results, the Cu(II) cation is coordinated to two water molecules when adsorbed on the titanate and niobate matrices.

Synthesis, characterization and catalytic properties of sol–gel derived mixed oxides

Abstract Alumina and 1:1 mixed oxides of Al2O3–ZrO2, Al2O3–TiO2, SiO2–TiO2 and ZrO2–TiO2 were synthesized via a sol–gel process by the so-called neutral amine route, followed by calcination at 600 °C. The mixed oxides were characterized before calcination by X-ray diffraction, revealing ordered hexagonal (Al2O3, Al2O3–ZrO2, ZrO2–TiO2) and lamellar (SiO2–TiO2, Al2O3–TiO2) structures. After calcination, all samples exhibited amorphous structures. Surface areas and pore characteristics of all materials were determined by nitrogen adsorption isotherms. The calcined oxides are active catalysts in the epoxidation of cyclooctene with tert-butyl hydroperoxide as oxidant. Epoxide yields from 14 to 45% were found for reaction times of 24 h. The titanium oxide containing catalysts are the most active and selective ones. On the other hand, the poisoning of acidic centers yields a decreasing activity while increasing selectivity.

Thermoanalytical investigations about the metal–amino acid interactions

Abstract The adducts CdCl2·xGly (x=1, 2; Gly=glycine) were synthesized and characterized by IR spectroscopy, thermogravimetry (TG) and differential scanning calorimetry (DSC). The bisadduct was prepared in a water medium and the monoadducts were isolated with water or water–ethanol mixtures as solvents. IR, TG and DSC data obtained showed that metal–amino acid interactions can be strongly influenced by the total amount of amino acid present. By using TG data, the kinetic parameters, activation energy (Ea), frequency factor (A) and order of reaction (n), were calculated. Ea values can provide very important information about the influences of the stoichiometry and polarity of the medium on cation–amino acid interactions at pH values of about 7.0. CdCl2·2Gly lost both ligands in a single step with an Ea value of 113 kJ mol−1. CdCl2·Gly prepared from water or a water–ethanol mixture lost the single ligand in two steps, whose activation energy values are 193; 134 and 88; 156 kJ mol−1, respectively.

Thermochemical features of lamellar silica, copper, nickel and cobalt-doped forms synthesized from neutral amine route

Abstract Lamellar silica prepared from sol–gel process through neutral amine route, was doped with cobalt, nickel or copper. X-ray diffraction pattern, thermogravimetry, and differential scanning calorimetry and reaction–solution calorimetry characterized these synthesized hybrids. The wetting enthalpy, Δ wet H m θ , for lamellar matrix doped with 10.0 and 15.0 mmol of CuCl 2 gave 41.81±0.02 and 40.54±0.02 J g −1 , respectively. The enthalpy of cation adsorption was carried out by using 100.0 cm 3 of 8.0×10 −3 or 0.127 mol dm −3 solutions of Co 2+ , Ni 2+ or Cu 2+ . The measurements were also performed using 50.0/50.0 cm 3 mixture of Co 2+ and Cu 2+ solutions. The results gave 20.73±0.07;−69.22±0.03; 10.91±0.06 and−34.44±0.06 J g −1 for nickel, copper, cobalt and copper–cobalt solutions, for a concentration of 8.0×10 −3 mol dm −3 . The same sequence of cations gave the enthalpic values −97.12±0.06, −106.90±0.01, 42.56±0.06, 34.97±0.12 J g −1 for 0.127 mol dm −3 solution. The results showed that the lamellar silica matrix can be used as a sequestrating agent for these cations with a capacity of adsorption established as Ni 2+ >Cu 2+ >Co 2+ . The wetting enthalpic values as well as the thermal stability of these matrices are associated to the crystallinity of the samples.

Towards the thermochemical data of adducts involving glycine and cadmium chloride

Abstract The prepared adducts CdCl2·xgly (x=1, 2 and gly=glycine) were characterized by infrared spectroscopy, thermogravimetry and differential scanning calorimetry. The infrared spectra showed that cadmium is coordinated through the carbonyl oxygen and the nitrogen atoms in the monoadduct and only carbonyl groups are involved in the bisadduct. The monoadduct melted before thermal degradation, suggesting the existence of a weaker intermolecular force as confirmed by standard molar enthalpy of dissolution values of 16.47±0.01 and 28.94±0.01 kJ mol−1 for 1:1 and 1:2 adducts, respectively. The standard molar enthalpy of reaction in the condensed phase: CdCl2(c)+xgly(c)=CdCl2·xgly(c); ΔrHmθ, gave −9.52±0.05 and −8.10±0.10 kJ mol−1 and the interaction in aqueous medium: CdCl2(aq)+xgly(aq)=CdCl2·xgly(aq); ΔaqHmθ, gave −0.13±0.07 and 0.00±0.14 kJ mol−1 for CdCl2·gly and CdCl2·2gly, respectively. From ΔrHmθ values the standard molar enthalpies of formation of the adducts were calculated as −912.48±6.60 and −1444.40±13.60 kJ mol−1. The enthalpies of decomposition 130.5±10.8 and 209.3±8.4, lattice −190.7±0.1 and 271.9±21.6 and reaction in the gaseous phase 599.8±16.8 and −329.3±5.0 kJ mol−1 for CdCl2·gly and CdCl2·2gly adducts were also calculated. From data of the reaction in the gaseous phase the mean enthalpy of the cadmium–oxygen bond was calculated as 82.3±5.0 kJ mol−1 for the bisadduct, which was restricted for a monoadduct due to the presence of distinct isomers.

Alcóxidos como precursores na síntese de novos materiais através do processo sol-gel

An overview about the role of alkoxides in the most recent uses of the sol-gel process in the synthesis of new materials is presented. Special attention is focused on the uses of silicon, aluminum, zirconium and titanium alkoxides. This review shows that the alkoxides enable the synthesis of new matrices with controlled surface area, acidity and porosity, as well as some unusual properties. The property associated with the solubility of metal alkoxides opens enormous possibilities of combining them for the synthesis films of powders with a very large range of metal compositions.

Spectroscopic study of Eu(fod)3 complex adsorbed on an amorphous silicon inorganic–organic hybrid

Abstract By using tetraethylorthosilicate (TEOS) and N-[3(trimethoxysilyl) propyl]-ethylenediamine as precursors, an inorganic–organic hybrid is synthesized, which is employed as a substrate to adsorption and hence spectroscopic study of the Eu(fod)3 complex. Eu(fod)3 and the silicon hybrid were mixed in stoichiometric amounts to produce samples with 1%, 5% and 10% (m/m) of adsorbed complex, with the matrices being pressed at 380 mPa for 0.5, 30 and 60 min. It is verified that the intensity of the 5 D 0 → 7 F 2 emission band decreases as the percentage of complex is increased, which is interpreted as consequence of the modification of the coordination sphere of the complex.