Sorption and preconcentration of metal ions in ethanol solution with a silica gel surface chemically modified with benzimidazole

The adsorption isotherms of MCl(2) (M = Mn, Ni, Cu, Zn and Cd) and FeCl3 by silica gel chemically modified with benzimidazole molecules (= SI(CH2)(3)-NC7H5N) were studied in ethanol solution at 298 K. A column made of modified silica was used to adsorb and preconcentrate the above metal ions from ethanol solution. Elution was done with 0.1 M hydrochloric acid in an ethanol/water mixture having a mole fraction of water of 0.8. The material was applied in the preconcentration of metal ions from commercial ethanol normally used as engine fuel.

Sorption and preconcentration of metal ions on silica gel modified with 2,5-dimercapto-1,3,4-thiadiazole

Silica gel, chemically modified with 2,5-dimercapto-1,3,4-thiadiazole [=Si(CH2)(3)-NC2HNS3], abbreviated as SiB, was used to adsorb metal ions from ethanol by both batch and column techniques. Elution of Cu(II) was done with a solvent mixture of acetone and hydrochloric acid (9:1 v/v). Zn(II), Cd(II), Ni(II), Pb(II), Co(II) and Fe(III) were eluted with 0.5 mol l(-1) HC1 in ethanol solution. The modified silica was applied in the preconcentration of metal ions from commercial ethanol, normally used as engine fuel. The method is suitable for quantifying these metals at low mu g l(-1) levels.

Small angle X-ray scattering and IR spectroscopy study of metal carbonyl complexes immobilized on a silica gel surface chemically modified with piperazine

The carbonyl complexes [WCl(CO)(3)(bipy) (HgCl)] (1), [Fe(CO)(4)(HgCl)(2)] (2) and W(CO)(6)] (3) were immobilized on a silica gel surface organofunctionalized with piperazine groups. The products obtained were studied by IR spectroscopy and small angle X-ray scattering (SAXS) techniques. The IR data show that the immobilization of heterobimetallic compounds 1 and 2, on the functionalized surface, occurred through the mercury atom, while for 3 the displacement of one CO group by the nitrogen of a piperazine molecule was observed. The data obtained from SAXS indicate that particles have a uniform size and reveal suitable modifications on the functionalized surface after immobilization of metal carbonyl complexes. The average intermolecular distance (l(ij)) for piperazine ligands on support is 8.7 Angstrom, for the metal carbonyl complex 1 it is 18.8 Angstrom, for complex 2 it is 16.2 Angstrom and for complex 3 it is 15.3 Angstrom. Copyright (C) 1996 Elsevier B.V. Ltd

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

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. © 1989.

Adsorption of various ions from acetone and ethanol on silica gel modified with 2-, 3-, and 4-aminobenzoate

Chemically bonded phases were obtained by reaction of 2-, 3-, and 4-aminobenzoate with 3-chloropropyl-silica gel. These phases were employed for metal cation adsorption in a batch method and applied to the separation of transition metal cations by chromatographic analysis.

Structure of cobalt (II) perchlorate adsorbed on silica gel surface chemically modified with benzimidazole molecule

Covalently attached benzimidazole molecules on silica gel surface, ≡SiL (where L = N-propyl-benzimidazole), adsorbs Co(ClO4)2 from non-aqueous solvent by forming a surface complex according to the reaction: m ≡SiL + Co(ClO4)2 → (≡SiL)mCo(ClO4)2. The equilibrium constant and the adsorption capacity, determined by applying the Langmuir equation were b = 3.0 × 103 L mol-1 and Ns= 0.098 × 10-3 mol g-1, respectively. The metal is bonded through the nitrogen atom and the perchlorate ion is not coordinated. The ESR study indicated that the complex has essentially an octahedral geometry with tetragonal distortion, with the electrons of the four nitrogen atoms interacting with the cobalt central metal ion in the equatorial plane. Only one complex species was detected on the surface.

Preparation of a silica gel modified with 2-amino-1,3,4-thiadiazole for adsorption of metal ions and electroanalytical application

Silica gel with a specific area of 382 m2 g-1 and an average pore diameter of 60 Å was chemically modified with 2-amino-1,3,4-thiadiazole, for the purpose of selective adsorption of heavy metals ions and possible use as a chemically modified carbon paste electrode (CMCPE). The following properties of this functionalized silica gel are discussed: selective adsorption of heavy metal ions measured by batch and chromatographic column techniques, and utilization as preconcentration agent in a chemically modified carbon paste electrode (CMCPE) for determination of mercury(II). The chemical selectivity of this functional group and the selectivity of voltammetry were combined for preconcentration and determination. ©2006 Sociedade Brasileira de Química.

Determination of copper in different ethanolic matrices using a chloropropyl silica gel modified with a nanostructured cubic octa(3-aminopropyl)octasilsesquioxane

The chloropropyl silica gel was modified with octa(3-aminopropyl) octasilsesquioxane and characterized by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), spectroscopies, and surface and area porosity. The specific sorption capacity of metallic ions (Cu2+ and Ni2+) increases in the following solvent order: water < ethanol 42% < ethanol < ketone. The high values of the constant (K) in the order of 103 L mol-1 suggested the high adsorbent capacity of the modified silica (SGAPC) for Cu2+ and Ni2+. SGAPC was applied to a separation column and shows recoveries of around 100% of copper in samples of sugar cane spirit, vodka, ginger brandy, and ethanol fuel. © 2013 Devaney Ribeiro Do Carmo et al.

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, S BET = 473 m 2 g -1, was chemically modified with benzimidazole. Adsorption isotherms of CuX 2 (X = Cl, Br or ClO 4) 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.

Biogenic modified silica as a sorbent of cadmium ions: Preparation and characterization

This work describes the preparation and characterization of biogenic modified silica from rice hull ash and its use as a sorbent of cadmium ions. Thus, an agro-industrial residue has been used to produce a new adsorbent product which is able to remove toxic elements. Mesoporous biogenic silica was obtained by alkaline extraction of sodium silicate by hydrolysis with the sol-gel process, and it was modified with salen using 1,2-dichloroethane as a spacer. The surface area of the silica was measured by nitrogen adsorption/desorption analysis. Surface modification was measured by Fourier transform infrared spectroscopy. The degree of functionalization was obtained by elemental analysis. This work showed that biogenic modified silica can be produced in aqueous media from rice hull ash using a simple method, providing an alternative method for adsorbent preparation. Thermogravimetric analysis showed that the salen-modified silica is stable up to 209 C. The modified silica displays appropriate structural characteristics for an adsorbent. The cylindrical pores, open at both ends, allow free diffusion of cadmium ions to the adsorption sites on the silica surface. The surface modification increases cadmium adsorption on the silica surface 100-fold. The salen-modified silica showed specific adsorption for Cd2+ of 44.52 mg/g SiO2 at cadmium concentration of 100 mg/l.

Hydrothermal Stability of Modified Silica Membranes for Gas Separation

A new class of hybrid molecular sieve silica (MSS) membranes is developed and tested against standard and organic templated membranes. The hybrid membrane is synthesized by the standard sol-gel process, integrating a template (methyltriethoxysilane - MTES) and a C6 surfactant (triethylhexylammonium bromide) into the silica film matrix. After hydro treatment under a relative humidity of 96% for 50h, the hybrid membrane shows no changes in its gas separation capabilities or energy of mobility. The structural characteristics and integrity of the hybrid membrane are retained due to a high concentration of organophilic functional groups and alkoxides observed using 29 Si NMR. In contrast, the structural integrity of the membranes prepared with non-templated films deteriorated during the hydro treatment due to a large percentage of silanol groups (Si-OH) which react with water. The hybrid membranes underwent a decrease in the H2/CO2 selectivity of only 1% whereas for the non-templated membrane a 21% decrease was observed. The transport mechanism of the hybrid membranes is activated as permeation increased with temperature. The activation energy for the permeation of H2 is positive while negative for CO2. The H2 permeation obtained was 3x 10 -8 mol.m -2 .s -1 .Pa -1 and permselectivities for H2/CO2 and H2/N2 varied between 1-7 and 31-34, respectively.

Hexagonal mesoporous silica modified with 2-mercaptothiazoline for removing mercury from water solution

A method for the attachment of 2-mercaptothiazoline (MTZ) to modified silica gel has been developed. In the first step, a new silylant agent was synthesized, named SiMTZ, by the reaction between MTZ molecule and chloropropyltrimethoxysilane (SiCl). SiMTZ and tetraethylortosilicate were co-condensed in the presence of n-dodecylamine, a neutral surfactant template, to produce a modified ordered hexagonal mesoporous silica named HMTZ. The modified material contained 0.89 +/- 0.03 mmol of 2-mercaptothiazoline per gram of silica. FT-IR, FT-Raman, Si-29- and C-13-NMR spectra were in agreement with the proposed structure of the modified mesoporous silica in the solid state. HMTZ material has been used for divalent mercury adsorption from aqueous solution at 298 I K. The series of adsorption isotherms were adjusted to a modified Langmuir equation. The maximum number of moles of mercury adsorbed gave 2.34 +/- 0.09 mmol/g of material. The same interaction was followed by calorimetric titration on an isoperibol calorimeter. The HMTZ presented a high capacity for the removal of the contaminant mercury from water. The Delta H and Delta G values for the interaction were determined to be -56.34 +/- 1.07 and -2.14 +/- 0.11 kJ mol(-1). This interaction process was accompanied by a decrease of entropy value (- 182 J mol(-1) K-1). Thus, the interaction between mercury and HMTZ resulted in a spontaneous thermodynamic system with a high favorable exothermic enthalpic effect. (c) 2007 Elsevier B.V. All rights reserved.

Copper Hexacyanoferrate Formation on the Modified Silica Surface with DAB-Am-16 Dendrimer

The third generation (G-3) polypropylenimine hexadecaamine dendrimer (DAB-Am-16) was grafted onto the silica gel surface. The modified silica interacts easily with Cu(2+) and then with potassium ferrocyanide to form copper hexacyanoferrate. The modified silica was characterized by the following techniques: Nuclear Magnetic Resonance (NMR), FTIR spectroscopy, Energy Dispersive X-ray (EDX) and Cyclic Voltammetry. The modified silica containing copper hexacyanoferrate (CuHCFSD) was tested for a voltammetric determination of nitrite using a modified graphite paste electrode.