Luiza N.H. Arakaki

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.

Ethylenimine in the synthetic routes of a new silylating agent: chelating ability of nitrogen and sulfur donor atoms after anchoring onto the surface of silica gel

Abstract Using a heterogeneous route, the precursor silylating agent 3-mercaptopropyltrimethoxysilane (mts) was first grafted onto silica gel and then condensed to one molecule of ethylenimine (etn). In the homogeneous route, mts reacted with etn to yield 3-trimethoxypropylthioethylamine (mptt), which was covalently anchored onto silica gel. In both cases, the new silylating agent displayed a chelating moiety containing nitrogen and sulfur basic centres. The amount of nitrogen immobilized was 1.73 and 1.74 mmol g −1 silica for the heterogeneous and homogeneous methods, respectively. In both routes of synthesis ν (N–H) stretching bands appeared at 3361 and 3284 cm −1 with the absence of a ν (S–H) stretching band. 13 C NMR of the new silylating agent, (CH 3 O) 3 SiCH 2 CH 2 CH 2 SCH 2 CH 2 CH 2 NH 2 , showed chemical shifts for methoxy groups at 50.0 ppm and signals at 8.4, 23.0, 34.4, 36.1 and 41.2 ppm for the sequence of carbons from the silicon atom to the NH 2 group at the end of the organic chain. The 1 H NMR spectrum presented a singlet peak which was attributed to methoxy groups at 3.52 ppm; a triplet at 2.76, quintet at 1.64 ppm, multiplet at 2.49 and triplet at 0.65 ppm were assigned to hydrogen atoms bonded to carbons in the same sequence as above. A broad amidic proton peak appeared at 1.08 ppm. 13 C NMR–CPMAS (cross-polarization magic-angle spinning) of the immobilized surface gave a series of peaks similar to those of the free silylating agent. Thermal and elemental analyses confirmed the covalent attachment of the organic species onto the silica gel surface. The chelating moiety formed by basic centre atoms of the pendant groups on the silica surface have a pronounced ability to extract divalent copper from aqueous solution.

Adsorption and separation of cations on silica gel chemically modified by homogeneous and heterogeneous routes with the ethylenimine anchored on thiol modified silica gel

Ethyleneimine (etn) has been covalently bonded onto silica gel via homogeneous (SiSN1) and heterogeneous (SiSN2) routes. Both synthesised silica gel surfaces have been applied to adsorb divalent cations from aqueous solution at room temperature. The series of isotherms of adsorption were adjusted to a modified Langmuir equation, after collecting the data from the solid/MCl2 solution (M = Co, Ni, Cu, Pb and Hg) interfaces. The maximum adsorption were 1.08, 1.20, 1.70, 1.34 and 4.02 mmol g−1 for SiSN1 and 0.72, 1.74, 1.91, 2.19 and 2.89 mmol g−1 for SiSN2, for a the sequence of divalent cations: Co, Ni, Cu, Pb and Hg, respectively. Columns loaded with immobilised silica show resolutions (R) for separating metal ion couples: RCo–Ni = 0.22, RCo–Pb = 0.76, RCo–Cu = 1.12, : RCo–Hg = 2.06, RNi–Pb = 0.50, RNi–Cu = 1.17, RNi–Hg = 2.38, RPb–Cu = 0.33, RPb–Hg = 1.83 and RCu–Hg = 1.60 for the SiSN1 surface. The sequence: RCo–Ni = 1.10, RCo–Pb = 1.44, RCo–Cu = 1.63, : RCo–Hg = 2.26, RNi–Pb = 0.08, RNi–Cu = 0.33, RNi–Hg = 1.40, RPb–Cu = 0.38, RPb–Hg = 1.82 and RCu–Hg = 1.55 was determined for SiSN2.

Immobilization of ethylenesulfide on silica surface through sol–gel process and some thermodynamic data of divalent cation interactions

The silylant precursor agent 3-aminopropyltrimethoxysilane (APTS) reacted with ethylenesulfide to yield 2-{2-{3-(trimethoxysilyl)propylamino}ethylthio}-ethanethiol, which was anchored on silica gel by using the sol–gel process. The new synthetic silylant agent displayed a chelating moiety containing one nitrogen and two sulfur basic centers, which are potentially favored for adsorbing divalent cations from aqueous solution. Thus, the similar chemisorption isotherms for all cations were obtained by batchwise method and the data were adjusted to a modified Langmuir equation to give the sequence of the maximum retention capacity as Cu>Co>Ni. The same adsorption was followed by calorimetric titration and the enthalpic values of −7.40±0.01, −1.50±0.10 and −0.98±0.02 kJ mol−1 for copper, nickel and cobalt respectively, were obtained. From the calculated Gibbs free energy −25.8±0.1, −35.1±0.1 and −30.8±0.1 kJ mol−1, the variation in entropy were also obtained as 62±1, 42±1 and 100±1 J K−1 mol−1 for the same above sequence. All thermodynamic values are in agreement with the spontaneity of the proposed cation-basic center interactions for these chelating processes.

O relevante papel do agente sililante na modificação de superfícies de polímeros

The applicability of the silylant agents of the general formula Y3Si-R-X, depends on the reactivity of Y group (halide or alcoxide) attached to silicon and the organic function X (halide, amine, thiol, cyanide, etc) in the extreme position of the chain. Both groups are linked together by an organic chain R, containing usually three methylene groups. A series of these agents can be covalently bonded to an inorganic matrix, since the available OH groups are distributed on the surface, making silica gel the most common support. However, other inorganic oxides, zeolites, lamellar inorganic phosphates and chrysotile can also have these agents anchored. Some illustration are presented for immobilized surface in the use as extractors of cations from dilute aqueous or non-aqueous solutions, catalysts agents, ionic exchanged materials, support for enzyme immobilization, chromatographic applications, use in some industrial features and in many other areas. The evolution of this exciting research field to produce new materials, for many tecnological applications, is strongly dependent on the development of a sensible systematic process for the synthesis of a series of new specific silylant agents.

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.

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.

Synthesis, characterization and thermal behavior of cobalt(II) 5-chloro-piridylamides complexes

Abstract Purple cobalt(II) complexes containing 5-chloro-2-aminepyridylacetamide (CPA), 5-chloro-2-aminepyridylpropionamide (CPP) and 5-chloro-2-aminepyridylbutyramide (CPB) ligands were prepared from ethanolic solutions. The general stoichiometry CoL 2 Cl 2 (L=ligand) was determined from elemental analysis data. Infrared results show monodentate CPA and CPP ligands through the aromatic nitrogen atom, CPB is bidentate through the aromatic nitrogen atom and carboxyl group. Thermogravimetric curves under nitrogen showed in the final stage all complexes presented a mixture of cobalt(II) chloride and metallic cobalt as residue. The complexes containing CPA and CPP ligands decomposed in various stages with integral loss of ligand or partial loss of the chloride. Only two steps of decomposition are seen for CPB compound.