Nitrogen Containing Organosilicon Bonded an Al2O3-Cellulose Acetate Hybrid Material: Preparation, Characterization and Use for Adsorption of Fe(III), Cu(II) and Zn(II) from Ethanol Solutions

Journal of the Brazilian Chemical Society

Gushikem, Yoshitaka¹  Universidade Estadual de Campinas, Campinas, Brazil¹  Lazarin, Angélica M.¹ 

关键词: cellulose acetate fiber;    organofunctional groups;    adsorption isotherms;    flow experiments ;   

DOI  :  10.1590/S0103-50532002000100014

学科分类：化学（综合）

来源: SciELO

【 摘 要 】

Cellulose acetate is a polymer that can be easily molded into different forms such as membranes, fibers, and spheres. To conjugate the mechanical properties of the cellulose acetate with the intrinsic properties of an inorganic compound, hybrid organic/inorganic materials have been prepared.1-10 Composites with many metal oxides, such as TiO2,1,11 ZrO2,12 Fe2O3,13 Nb2O514 and Sb2O3,15 have been prepared and the resulting materials have been demonstrated to be useful in ion-exchange processes,3 for enzyme immobilization,16 to prepare semi-permeable membranes,17 in reverse osmosis experiments,9 in catalytic reactions8 and to support electroactive chemical species for use as electrochemical sensors.14 These hybrid materials are normally made by mixing the polymer solution and the metal alkoxide solution, followed by a phase inversion process.10, 18 Al2O3 dispersed on the cellulose fiber surface can efficiently immobilize organofunctional molecules, (RO)3Si(CH2)3L, since the Al-OH groups can easily react with the precursor alkoxysilane by forming the very stable Al-O-Si bond.19 However, the amount of metal oxide, as a thin film, that can be loaded onto the cellulose fiber is limited by its surface area. When a larger amount of the metal oxide is required for incorporation in a matrix, the use of cellulose acetate is desirable. The reason is that cellulose acetate, in comparison to pure cellulose, is easily dissolved in organic solvents and the metal oxide can be entrapped in the matrix in the phase inversion process step of the preparation.20 This work reports the preparation of a cellulose acetate/Al2O3, Cella/Al2O3, hybrid material and its further reaction with (RO)3Si(CH2)3L to obtain Cella/Al2O3/Si(CH2 )3L (L= -NH2, -NH(CH2)2NH2, -NH(CH2)2NH(CH2) 2NH2 and imidazole group). The materials obtained were characterized by scanning electron microscopy, nuclear magnetic resonance (CPMAS 13C and MAS 27Al NMR) and thermal analyses. Retention capacities of the attached basic organic groups for Fe(III), Cu(II) and Zn(II) from ethanol solutions were determined.  Experimental Preparation of cellulose acetate/Al2O3 (Cella/Al2O3)A viscous syrup containing 10 g of cellulose acetate dissolved in a mixture of glacial acetic acid (53 mL) and acetone (37 mL) was prepared. About 15 g of aluminum isopropoxide (Aldrich), dissolved in a small amount of trifluoroacetic acid, was added to the syrup (100 g) and the mixture was stirred to homogenize the phase. The resulting syrup was slowly poured into a flask containing about 1000 mL of doubly distilled water, under rapid stirring. The fibers were collected by filtration, washed with water and dried under vacuum at room temperature.Attachment of organofunctional groups on Cella/Al2O3 About 5 g of Cella/Al2O3 was immersed in 100 mL of dry toluene, 10 mL of (RO)3Si(CH2)3L (Aldrich) (L= -NH2, -NH(CH2)2NH2, -[NH(CH2)2 ]2NH2 was added and the mixture was stirred for 8h under an argon atmosphere. The mixture was filtered, washed with ethanol and water and then dried under vacuum (10-3 Torr) at room temperature. To prepare the material with the imidazole attached group, the procedure was as follows: 9.2 mL of (MeO)3Si(CH2)3Cl (50 mmol; Aldrich) was dissolved in 50 mL of dry toluene and 3.4 g (53 mmol) of imidazole was added and the mixture was refluxed for 3 h under argon. The solvent was removed by distillation under vacuum and the resulting oil, containing essentially 3(N-imidazolyl) propyltrimethoxysilane was redissolved in 100 mL of toluene. About 5 g of Cella/Al2O3 was added and the mixture, was stirred for 12 h at room temperature. The mixture was filtered, washed with pure ethanol, water, and dried under vacuum at room temperature.Characterization of the hybrid materialsThe amount of aluminum in Cella/Al2O3 was determined by calcinating 0.3 g of the sample at 1173 K, for 2 h, and the residue was weighed as Al2O3. The amount of nitrogen in Cella/Al2O3/Si(CH2 )3L was determined, for each sample, by the Kjeldhal method. The SEM images were obtained for samples dispersed on a double faced conducting tape adhered on an aluminum support. The samples were coated with graphite by the low voltage sputtering deposition technique using a Plasma Science Model LVC 76 apparatus. The measurements were made with a JSM T-300 microscope connected to a secondary electron detector and X-ray energy dispersive spectrometer (EDS) from Northern. The solid state 13C and 27Al NMR spectra were obtained on a Bruker AC 300P spectrometer at room temperature. 13C CPMAS NMR spectra were obtained using pulse sequences with 1 ms contact time, an interval between pulses of 2s and an acquisition time of 156 ms. The chemical shift was calibrated against standard TMS. 27Al MAS NMR spectra were obtained using pulse sequences with an interval between pulses of 1s and acquisition time of 49 ms. The chemical shift was calibrated by using an external solution of 1.0 mol L-1 Al(NO3)3 dissolved in 0.1 mol L-1 HNO3. The thermogravimetric analyses of the cellulose acetate and the composites were carried out on a Dupont TGA 2050 apparatus. About 5 mg of the samples were heated with a scan rate of 5 K min-1 under an argon atmosphere. The adsorption isotherms for FeCl3, CuCl2 and ZnCl2 from ethanol solutions were determined by using the batch technique. About 0.1 g of the modified cellulose acetate was shaken for 3h, with variable concentration of the metal halides, at a constant temperature of 298.0 ± 0.2 K. The concentration of the metal ion in the solution phase, in equilibrium with the solid phase, was determined by complexometric titration using a 0.01 mol L-1 EDTA standard solution. The amount of the adsorbed metal was determined by applying the equation: Nf= (Na-Ns)/m, where m is the mass of the adsorvent, and Na and Ns are the initial and the equilibrium condition mole numbers of the metal in the solution phase, respectively.Metal retention experimentsA column with 10 mm length and 5 mm internal diameter was filled with about 1 g of the material and connected on line with a peristaltic pump. Individual ethanol solutions containing of FeCl3= 5.7, CuCl2= 6.5 and ZnCl2= 6.5 mg L-1 were passed through the column with a flow rate of 0.65 mL min-1. The column was washed with pure ethanol and the metals eluted with a mixture of (ethanol):(0.1 mol L-1 aqueous HCl solution) in a 4:1 (v/v) proportion. The eluted metals were analyzed on a Perkin Elmer Model 5100 atomic absorption spectrometer. For each metal, triplicate determinations were carried out.  Results and Discussion Characteristics of the materialThe amount of Al2O3 in Cella/Al2O3 was 3.7 wt%, corresponding to 1.4 mmol g-1 of aluminum. The amount of incorporated oxide in the matrix is very high, in comparison with that obtained by using pure cellulose fiber for the reaction to give Cel/Al2O3, where 2.0 wt % (0.6 mmol g-1 of aluminum ion) was observed. The high yield obtained is due to the preparation procedure of Cella/Al2O3, where the Al2O3 particles are immobilized-entrapped in the matrix, while in the

【 授权许可】

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