José G.P. Espínola

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.

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.

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.

Kinetics of the thermal decomposition of bis(dialkyldithiocarbamate) of palladium(II) complexes in isothermal and nonisothermal conditions

Abstract Dialkyldithiocarbamate of palladium(II) complexes, Pd(S2CNR2)2, with R=C2H5, n–C3H7, n–C4H9, i-C4H9 and C5H11 were synthesized from the direct reaction of PdCl2 with corresponding amine and carbon disulphide. The complexes were characterized by the techniques of melting points, infrared absorption spectroscopy and mass spectrometry. The thermal decomposition reaction of complexes have been studied by isothermal and nonisothermal thermogravimetry. Superimposed curves of TG/DTG/DSC show that these reactions occur in the liquid phase. The kinetic isothermal model that best adjusted the experiment data were the R1 model.

Brazilian Palygorskite as Adsorbent for Metal Ions from Aqueous Solution—Kinetic and Equilibrium Studies

Natural palygorskite was used as an adsorbent for the removal of copper, cobalt and nickel from an aqueous solution. All assays were performed under controlled conditions to establish the adsorption capacity of the solid. Initially, the clay was characterized by chemical analysis, XRD, infrared spectroscopy and thermogravimetry. Adsorption experiments for the ions in aqueous solution were carried out by a batch method through which the reaction time, initial concentration of cations, temperature and pH of the aqueous solution were systematically varied. First-order, pseudo-second-order and intraparticle diffusion models were used to describe the kinetic data. The results show that the processes were fitted well by the pseudo-second-order model. Moreover, the equilibrium solid–cation systems followed the Langmuir isotherm model. The results indicate that raw palygorskite could be employed as a low-cost material for the removal of heavy metals from aqueous solution.

Chemisorption of some divalent cations on silica modified through the reaction of pentane-2,4-dione with 3-propylethylenediamine silica gel

Abstract The reaction of 3-propylethylenediamine groups covalently bonded to silica gel with pentane-2,4-dione in benzene resulted in a modified surface having 11.4·10 −4 mol g −1 of ligand sites which adsorb the divalent cations Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ from ethanol solution with maximum adsorptions of 5.0·10 −4 mol g −1 , 2.0·10 −4 mol g −1 , 5.0·10 −4 mol g −1 and 5.9·10 −4 mol g −1 , respectively. The adsorption isotherms are very similar in shape for all the cations and conform to the Langmuir model. The complexes formed on the surface have a molar composition or one cation to two anchored groups of Schiff bases and the geometries of the complexes are similar to those obtained in solution.

Quimissorção de cátions divalentes em sílica gel modificada com ácido tioglicólico: a influência do pH e força iônica

A novel type of heavy metal adsorbent was prepared by the covalent grafting of thioglycolic acid molecules on a silica gel surface previsiouly modified with 3-aminopropyltrimethoxysilane. The amount of thioglycolic acid immobilized was 1.03 mmol per gram of silica. This material displayed a chelating moiety containing nitrogen, sulfur, and oxygen basic centers which are potentially capable of extracting from aqueous solutions cations such as Cu(II), Ni(II), Co(II), influenced by pH and ionic strength. This process of extraction was carried out by the batch method when similar chemisorption isotherms were observed for all cations. A modified Langmuir equation describes the experimental data.

Thermochemical study of adducts of tetramethylthiourea with antimony and bismuth triiodides

Abstract The adducts MI 3 -tmtu (M = Sb, Bi; tmtu = tetramethylthiourea) were prepared, characterized and studied through reaction-solution calorimetry at 298.15 K. The molar standard enthalpy Δ r H m ⊖ of the reaction MI 3 (cr)+tmtu(cr)= MI 3 ·tmtu(cr) gave −19.84 ± 0.46 and −13.01 ± 0.17 kJ mol −1 for Sb and Bi, respectively. From Δ r H m ⊖ values the standard molar enthalpies of formation of the crystalline Sb and Bi adducts were calculated as −158.5 and −201.3 kJ mol −1 , respectively. The mean element-sulphur bond enthalpies were also calculated as 122 and 147 kJ mol −1 for Sb-S and Bi-S bonds, respectively. The acidity order AsI 3 &>; SbI 3 &>; BiI 3 was established.