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

Journal of the Brazilian Chemical Society

USP, São Carlos, Brazil¹  Gushikem, Yoshitaka¹  Dias Filho, Newton L¹  Unicamp, Campinas, Brazil¹  Rodrigues, Edson¹  UNESP, Ilha Solteira, Brazil¹ 

关键词: silica gel;    benzimidazole;    cobalt-benzimidazole surface complex;    cobalt electron spin resonance;    silica gel modified with benzimidazole     Introduction Organic molecules containing nitrogen atoms have been chemically bonded to a silica gel surface in order to adsorb metal ions from aqueous or non aqueous solvents1-5. As in solution phase;    many complex species may be formed at the solid-solution interface by the reaction of the metal ion with the immobilized functional organic molecule6-8. Techniques such as 13C CPMAS NMR9;    10 and electron spin resonance (ESR)8;    11 have been used to determine the structures of these complex species. The second technique has been particularly useful for copper complexes10;    12. Cobalt (II) is adsorbed from acetone solution by the attached benzimidazole yielding a pale blue complex13. The adsorption of the metal ion occurs according to the reaction: m ºSiL + CoX2 ® (ºSiL)mCoX2;    where ºSiL is the attached neutral functional organic group on the silica surface. The stepwise complex formation;    which consists of a change in the average number of the ligand;    m;    coordinating one metal ion is a function of the metal loading in the present case because the surface density of attached ligands is constant. The correlation between the structure of the complexes in the solution phase and that on the solid surface is not straightforward because from a steric point of view the attached ligands have limited mobility while in the solution phase this restriction does not exist. In this work the structure of cobalt perchlorate adsorbed on the surface of silica modified with benzimidazole is reported. The perchlorate counterion was chosen because it has low coordination ability and thus;    the resulting structure of the reaction between Co(ClO4)2 and ºSiL may be exclusively determined by the interaction of the immobilized ligand and the metal ion. On the other hand;    this study is of great interest because the silica gel surface is morphologically very heterogeneous;    the ligands are not uniformly distributed on the surface and to our knowledge;    little information on complex formation in porous materials is available in the literature.   ExperimentalPreparationsSilica gel 60 (Merck) having a particle size between 0.2 and 0.05 mm was activated at 420 K under vacuum (0.13 Pa). This silica (ca. 50 g) was suspended in dry xylene (200 cm3) and 3-chloropropyltrimethoxysilane (15 cm3) was added;    the mixture was stirred for 24 h at 380 K under a nitrogen atmosphere. The resulting modified silica was immersed in pure dimethylformamide (150 cm3) and benzimidazole (17.5 g;    0.15 mol) was added. The mixture was stirred for 24 h at 380 K under a nitrogen atmosphere. The resulting modified silica was filtered off and washed with dimethylformamide and ethanol. The product was heated for 8 h at 353 K under vacuum (0.13 Pa). The amount of benzimidazole attached to the silica surface was No= 0.48 x 10-3 mol g-1. The reactions which describe the preparation can be represented by the equations in Scheme 1;    where for simplification (A) will hereafter be designated as SiL.   Isotherm of AdsorptionThe isotherm adsorption of Co(ClO4)2 from an acetone solution by ºSiL was determined at 298 K. About 0.1 g of ºSiL was immersed in 50 mL solutions of Co(ClO4)2 of variable concentrations. The suspension was shaken for 60 min and then allowed to stand for 20 min;    time necessary for all the solid material to deposit at the bottom of the flask. About 10 mL of the supernatant solution was evaporated;    the residue dissolved in water and the metal was analyzed by conventional EDTA complexometric titration. The quantity of the adsorbed metal was determined by applying the equation:where Na is the initial metal mole number;    Ne the metal mole number in equilibrium with the solid phase and m the mass of the adsorbent.Infrared spectraInfrared spectra of the samples were obtained in the region 2000 to 1000 cm-1;    using the technique of self supported disk described elsewhere3. The equipment used was a Nicolet FT-IR spectrophotometer.Electronic spectraThe electronic spectra of the samples were obtained by immersing the solid with Co(ClO4)2 adsorbed on the surface;    (ºSiL)mCo(ClO4)2;    in spectral grade carbon tetrachloride in a quartz cell having 1mm path length. A Cary 2300 spectrophotometer was used. Good quality spectra were obtained since the refractive index of both;    silica and the liquid;    are nearly the same14.ESR spectraSpectra of the samples were obtained in a quartz tube at 77 K;    at band X (9 Ghz);    40 mW microwave power;    modulation frequency of 100 kHz and a magnetic field with sweeping of 1000 Gauss centered at 2850 or 2900 Gauss. The equipment used was a Bruker ECS 106 electron spin resonance spectrometer.   Results and DiscussionIsotherm of adsorptionFigure 1 shows the isotherm of adsorption of Co(ClO4)2 by the solid phase ºSiL;    from acetone solution. The adsorption capacity;    Ns;    and the equilibrium constant;    b;    were determined by applying the Langmuir equation:;   

DOI  :  10.1590/S0103-50531997000400015

学科分类：化学（综合）

来源: SciELO

【 摘 要 】

Organic molecules containing nitrogen atoms have been chemically bonded to a silica gel surface in order to adsorb metal ions from aqueous or non aqueous solvents1-5. As in solution phase, many complex species may be formed at the solid-solution interface by the reaction of the metal ion with the immobilized functional organic molecule6-8. Techniques such as 13C CPMAS NMR9,10 and electron spin resonance (ESR)8,11 have been used to determine the structures of these complex species. The second technique has been particularly useful for copper complexes10,12. Cobalt (II) is adsorbed from acetone solution by the attached benzimidazole yielding a pale blue complex13. The adsorption of the metal ion occurs according to the reaction: m ºSiL + CoX2 ® (ºSiL)mCoX2, where ºSiL is the attached neutral functional organic group on the silica surface. The stepwise complex formation, which consists of a change in the average number of the ligand, m, coordinating one metal ion is a function of the metal loading in the present

【 授权许可】

Unknown