Severino F. de Oliveira

Influence of the N-[methylpyridyl]acetamide ligands on the photoluminescent properties of Eu(III)-perchlorate complexes

Abstract This work reports the synthesis, characterization and spectroscopic studies of Eu(III)-perchlorate complexes with amide ligands derived from N -[ x -methylpyridyl]acetamide where x =3, 4 and 6. The Eu(ClO 4 ) 3 3( x -mpa) complexes were characterized by elemental analyses, molar conductance, TG analyses and vibrational spectroscopy. Raman and infrared data show that the perchlorate ion, (ClO 4 − ), is bonded to Eu(III) as a monodentate ligand and that in these three complexes water molecules are not coordinated to the rare earth ion. The profiles of the emission spectra of the complexes with 3- and 4-mpa ligands are very similar but they differ from the complex containing 6-mpa ligand. This spectroscopic behavior can be rationalized in terms of the Ω λ ( λ =2 and 4) and R 02 experimental intensity parameters. The values of Ω 2 (∼6.5×10 −20 cm 2 ) in these complexes are smaller than in Eu(III)-TTA compounds ( Ω 2 ∼35.0×10 −20 cm 2 ), indicating that in the former case the rare earth ion is in a chemical environment less polarizable. Lifetime and emission quantum efficiency measurements for the emitting level 5 D 0 were carried out and the results are discussed.

Silica gel containing sulfur, nitrogen and oxygen as adsorbent centers on surface for removing copper from aqueous/ethanolic solutions

Silica gel was modified firstly with aminepropyltrimethoxisilane obtaining the matrix named as SILNH(2). The SILNH(2) silica reacted subsequently with thioglycolic acid Sil-Ntga. The elemental analysis showed the presence of 0.98mmolg(-1) of organic moieties immobilized on silica. Infrared and (13)C NMR spectroscopic data in conjunction with thermogravimetric measurements are in agreement with the suggested functionalization. The ion adsorption properties of the silica Sil-Ntga were studied using copper ions in aqueous/ethanolic solutions in concentrations ranging from 4.0x10(-3) to 5.0x10(-2)moldm(-3) at different temperatures. The new modified silica showed a good sorption ability for copper at lower temperatures and its reuse capacity was demonstrated.

Chemisorption of CuII and CoII chlorides and β-diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Abstract Silica gel chemically modified with the silylating agent 3-aminopropyltrimethoxysilane (SAPS) adsorbs CuII and CoII in the form of chlorides, acetylacetonates and dipivaloylmethanoates from ethanolic solution. The profiles of the chemisorption isotherms present good correlation with the proposed Langmuir model. The amount of adsorbed species in these chemisorption processes showed that only a fraction of the number of active sites was effectively used by β-diketonates, in comparison with the total available number disposed on the matrix. Based on the equilibrium constant the selectivity of the SAPS matrix with β-diketonates, follows the order CoII>CuII. The chelate of dipivaloylmethanoate with CoII is more pronounced adsorbed on the surface than the correspondent complex of CuII. This fact reveals the possibility of separating both complexes by using this functionalized silica gel surface. However, for chlorides, this modified surface has preference for both cations.

On the thermochemistry of intercalation of n-alkylamines into α-titanium hydrogenphosphate

Lamellarα-titanium hydrogenphosphate (α-TiP) suspended in water or 1,2-dichloroethane (dce) intercalates ≈7.70 meq g1 ofn-alkylamines (C1-C4), as determined by potentiometry and thermogravimetry. The thermal decomposition of the intercalates takes place in three stages: dehydration, removal of amines, and condensation of the hydrogenphosphate to pyrophosphate. The increase in theα-TiP interlayer distance (7.56×102 pm) during the intercalation was followed by x-ray powder diffraction. The standard enthalpy (δrHmo) involved in the overall reaction O3PO-H + RNH2→ O3P-O−+H3NR, which was determined by reaction-dissolution calorimetry, correlates linearly with the number of carbons in the alkyl chain and with the interlamellar distance. An intercalation mechanism is proposed, starting from the amine protonation by POH groups and its insertion between the sheets. An increase in enthalpy of −2.67 and +2.56 kJ mol−1 or −1.24 and +1.20 kJ mol−1/102 pm for each CH2 group of then-alkyl chain in dce and water, respectively, for this series of amines is proposed.

New thiol adsorbent grafted on silica gel: synthesis, characterization and employment for heavy metal adsorptions.

Silica gel surface has been modified in two reaction steps: (i) the silylating agent 3-mercaptopropyltrimetoxysilane was firstly immobilized to give a surface Sil-SH and (ii) this precursor incorporated an ethylene sulfide molecule to obtain the surface denoted Sil-SSH. This material was characterized by elemental analysis, IR spectroscopy, thermogravimetry, solid state 13C and 29Si NMR, and surface area measurement. These materials were employed as adsorbents for divalent heavy cations from aqueous solutions at room temperature and the isotherms were adjusted to a modified Langmuir equation. The maxima number of moles adsorbed were 1.0, 1.5, 1.6, 2.2, 2.4 and 3.3 mmol g(-1) for Co, Cu, Ni, Cd, Pb, and Hg, respectively.

Kinetic study of the decomposition of hydrogen peroxide catalysed by Co(II) acetylacetonate supported on a silica-propylpiperazine matrix

Abstract The catalytic decomposition of hydrogen peroxide by Co(II) acetylacetonate supported on a propylpiperazine-silica matrix (Co(II)(acac)-PPS) was studied in aqueous media. The results showed that the reaction was first order in H2O2. It was found that the reaction eate was pH dependent with a maximum at around pH = 8. Activation parameters were determined in the temperature range 30–45°C. The low value obtained for the activation energy is in accordance with the proposed free-radical mechanism.

Adducts of cadmium diethyldithiocarbamate with bidentate nitrogen ligands

Abstract Reactions of Cd(S2CNEt2)2 with 1,10-phenanthroline or 2,2′-bipyridine produce crystalline 1:1 adducts. Thermogravimetric studies show that the 2,2′-bipyridine adduct initiates decomposition by loss of the neutral ligand whereas the 1,10-phenanthroline adduct undergoes a more complex decomposition. The crystal structure of the adducts show their monomeric nature with hexacoordination of the metal in a distorted octahedral geometry.

Isotherm data of Fe3+, Cr3+ and Co2+ adsorved on surface of silica-propylpiperazinedithiocarbamato

Abstract The silylant agent chloropropyltrimetoxysilane immobilized on silica gel reacts with piperazine, followed by another reaction with carbon disulfide in the presence of sodium hydroxide, to produce a new matrix sodium propylpiperazinedithiocarbamato silica. The basic centres of the resulting surface complexes are the Cr3+, Fe3+ and Co2+ cations from aqueous solution. The adsorbed isotherms for cations were adjusted to fit Giles models. The isotherm for Cr3+ could be classified as L2, while those for Fe3+ and Co2+ fitted the subgroup 2 of C class. The isotherm data show that the capacity of the final carbamate surface to chemisorb Fe3+ and Co2+ is only one third that observed for Cr3+.

Immobilized dithiocarbamate groups on silica: Chemisorption of some cations from ethanolic solution

Abstract Immobilized dithiocarbamate was prepared by reacting a 3-propylethylenediamine group, covalently bonded to silica gel, with carbon disulfide in toluene. This modified surface has 6.7 × 10−4 mol g−1 of ligand sites available to extract cobalt, nickel, copper and zinc from ethanol solution. The adsorption isotherms are very similar in shape for all cations and conform to the Langmuir model. However, the degree of adsorption indicated a metal: a ligand ratio of 1:3 for cobalt, 1:2 for nickel and 1:1 for copper and zinc complexes. These cations are sulfur-bonded to the anchored ligand. The isotherm of the cobalt chemisorption data agrees with oxidation of cobalt to the trivalent state. The geometries of these complexes are similar to those obtained in solution. The results suggest a very similar behavior of the dithiocarbamate chemically bonded on silica gel with that of these ligands in the unbonded state.

Some ion exchange properties of amorphous titanium (IV) phosphate

An amorphous titanium (IV) phosphate exchanger has been synthesised and characterized through elemental analysis, infrared, and thermogravimetric techniques. Divalent cations Mn, Co, Ni, Cu, Zn, Cd, Hg and Pb in bidistilled water have been exchanged with the proton of the exchanger matrix using a batch method. From these results the thermodynamic selectivity constants and distribution coefficients were calculated, whose values indicate a high selectivity for Pb and Hg. Both cations were successfully separated from a mixture containing all cations studied through column separation experiments.