José C. Moreira

Determination of Metal Ions in Natural Waters by Flame-AAS after Preconcentration on a 5-Amino-1,3,4-Thiadiazole-2-Thiol Modified Silica Gel.

ABSTRACT 5-amino-1,3,4-thiadiazole-2-thiol groups attached on a silica gel surface have been used for adsorption of Cd(II), Co(II), Cu(II), Fe(III), Ni(II), Pb(II) and Zn(II) from aqueous solutions. The adsorption capacities for each metal ion were (in mmol.g−1): Cd(II)= 0.35, Co(II)= 0.10, Cu(II)= 0.15, Fe(III)= 0.20, Hg(II)= 0.46, Ni(II)= 0.16, Pb(II)= 0.13 and Zn(II)= 0.15. The modified silica gel was applied in the preconcentration and quantification of trace level metal ions present in water samples (river, and bog water).

Development of a chemically modified electrode based on carbon paste and functionalized silica gel for preconcentration and voltammetric determination of mercury(II)

Abstract A mercury-sensitive chemically modified electrode (CME) based on modified silica gel-containing carbon paste was developed. The functional group attached to the silica gel surface was 3-(2-thiobenzimidazolyl)propyl, which is albe to complex mercury ions. This electrode was applied to the determination of mercury(II) ions in aqueous solution. The mercury was chemically preconcentrated on the CME prior to voltammetric determination by anodic stripping in the differential-pulse mode. A calibration graph covering the concentration range from 0.08 to 2 mg 1 −1 was constructed. The precision for six determination of 0.122 and 0.312 mg 1 −1 Hg(II) was 3.2 and 2.9% (relative standard deviation), respectively. The detection limit for a 5-min preconcentration period was 0.013 mg 1 −1 . A study for foreign ions was also made.

Determination of Metal Ions in Fuel Ethanol after Preconcentration on 5-Amino-1,3,4-Thiadiazole-2-Thiol Modified Silica Gel

This work describes the synthesis and characterization of 5-amino-1,3,4-thiadiazole-2-thiol modified silica gel (SiATT), and the results of a study of the adsorption and preconcentration (in batch, and in flow using a column technique) of Cd(II), Co(II), Cu(II), Fe(III), Ni(II), Pb(II) and Zn(II) in ethanol medium. The adsorption capacities for each metal ion were (in mmol g-1): Cd(II) = 0.11, Co(II) = 0.10, Cu(II) = 0.20, Fe(III) = 0.20, Ni(II) = 0.16, Pb(II) = 0.08 and Zn(II) = 0.12. The results obtained in the flow experiments, showed a recovery of ca. 100% of the metal ions adsorbed in a column packed with 2 g of SiATT, using 5 mL of 2.0 mol L-1 HCl solution as eluent. The sorption-desorption of the metal ions made possible the development of a preconcentration method and quantification by Flame AAS of metal ions at trace level in fuel ethanol.

Preparation and characterization of Ti (IV) oxide grafted onto silica on a silica gel surface

Abstract Silica gel with a surface area of 500 m2g-−1 and an average pore diameter of 60 A was chemically modified with Ti(IV) oxide using the grafting method. The amount of metal oxide attached to the surface was 1.8·10−3 mol g−1. The X-ray photoelectron spectra showed that the metal ion species on the surface are Ti(IV) in TiO2 and MTiO3 (MCa2+, Sr2+, Ba2+ and Pb2+), i.e. they have the binding energy of Ti 2p 3 2 =458.7 eV. The dehydration of the solid at higher temperature increased the OII/Ti (OII=oxygen bound to titanium atom) ratio, presumably due to a reticulation of the hydrous Ti(IV) oxide on the silica surface at higher temperatures. Migration of Ti(IV) into the silica gel matrix was observed but the specific surface area was not significantly changed.

Adsorption of Cu(II), Zn(II), Cd(II), Hg(II) and Pb(II) from aqueous solutions on a 2-mercaptobenzimidazole-modified silica gel

The chemically modified silica, obtained by reacting 2-mercaptobenz-imidazole with 3-chloropropyl silica gel, was used to adsorb Cu(II), Zn(II), Cd(II) and Pb(II) from aqueous solutions at various pH. Between pH 3–5, the order of selectivity was Hg(II) > Cd(II) ≫ Cu(II) ∼ Zn(II) ∼ Pb(II). Under batch conditions retentions of 100% were achieved for all metals except for Pb(II) where 93% was attained. Under column conditions recoveries of 100% were obtained for all metals.

Adsorption of metal ions from ethanol on an iminosalicyl-modified silica gel

Iminosalicyl groups attached to a silica gel surface have been used for the adsorption of metal ions from ethanol. This organofunctionalised silica adsorbs iron, nickel, cobalt, copper, zinc and cadmium from ethanol by both batch and column techniques. The average distribution coefficient determined for each metal ion was as follows (ml g–1): FeIII, 4.5 × 102; CoII, 1.4 × 102; NiII, 1.1 × 102; CuII, 3.6 × 102; ZnII, 3.0 × 102; and CdII, 2.2 × 102.

Adsorption of chromium(VI) by titanium(IV) oxide coated on a silica gel surface

Titanium(IV) oxide, coated on the surface of silica gel (surface area, 308 m2 g–1; amount of TiIV per gram of modified silica gel, 1.8 × 10–3 mol), was used to adsorb CrO42– ions from acidic solutions. The exchange capacity increased at lower pH values and was affected to some extent by the acid used. The material was used to preconcentrate CrVI from 0.5 ppm solutions of chromate very efficiently and virtually 100% recovery was achieved in every instance.

Small angle X-ray scattering study of structural changes in silica gel modified with organofunctional groups

Abstract Silica gel surfaces, organofunctionalized with 2-mercaptobenzimidazole, iminosalicylaldehyde and imidazole groups were examined using the small angle X-ray scattering technique (SAXS). From the scattering intensity data it was concluded that particles have a uniform size after the coupling reaction. The chemical treatment of the silica gel leads to an attachment of the organofunctional groups on the solid-pore interface of the silica with an increase of the mean size of the solid phase and some coalescence of the pores.

ELECTRON-PARAMAGNETIC RESONANCE STUDY OF CUCL2 ADSORBED ON SILICA-GEL SURFACE MODIFIED WITH 3(1-IMIDAZOLYL)PROPYL GROUPS

Abstract The electron paramagnetic resonance spectrum of CuCl 2 adsorbed on a silica-gel surface modified with 3(1-imidazolyl)propyl groups showed that the surface complex has an octahedral symmetry with tetragonal distortion. The measured magnetic parameters were g | = 2.298, g ⊥ = 2.086, A | = 162 G and superhyper fine splitting A N = 15 G. The calculated energy difference between E x 2 − y 2 and E xz , E yz was 14600 cm −1 and the observed ligand field maximum was ∼ 14300 cm −1 .

Structure of copper complexes adsorbed on a silica gel surface chemically modified with benzimidazole

Silica gel having a particle size between 0.2 and 0.05 mm and a specific surface area, SBET= 473 m2 g–1, was chemically modified with benzimidazole. Adsorption isotherms of CuX2(X = Cl, Br or ClO4) from ethanol and acetone solutions were studied at 298 K. The metal is bonded to the surface through the free nitrogen atom of the attached benzimidazole. The average number of ligands co-ordinated to the central metal ion was shown to depend on the solid surface loading by the solute. At low loading the electronic and ESR spectral parameters indicated that the copper ion is in a distorted-tetragonal symmetry field.