Preparation of organic polymer-silica nanocomposites and study of their adsorption characteristics

Abstract

Polymerization of aniline, o-toluidine and 2-chloroaniline from an aqueous solution containing sodium silicate yielded stable poly(aniline)/silica, . poly( o-toluidine )/silica and poly(2-chloroaniline )/silica composites. Synthesis was carried out at different pH, viz. 3.1, 7.0 and 11.3 and at different temperatures, viz. oDe, 270e and 500e and stable poly(aniline)/silica, poly(otoluidine )/silica and poly(2-chloroaniline )/silica nanocomposites was found to be formed in the reaction mixture under the experimental conditions employed. These composites have been characterized in their solid states by a wide range of experimental techniques including optical mIcroscopy, infra-red spectroscopy and sedimentometry for particle sizing. Adsorption studies with . these composites employed inverse gas chromatography and BET surface area measurement. Elemental analysis for the silica content of the composites was performed by well known hydrofluorization method and silica content up to 11% in the matrix was obtained. Density of the bulk polymer and the polymer/silica samples were measured by micromeritics multivolume auto pycnometer and clearly different density values were obtained for the samples. The particle size distribution of the composites observed with sedigraph shows that the particle diameter varies from 40-1 /lm. However particle size below IJlffi could not be detected due to the limitation of the micromeritics instrument. A wide distribution of white images in the micrographs of polymer/silica samples was .o.bserved and this may be attributed to the presence of silica particles in th.e composite matrix. '- .. Infra-red spectroscopic studies yielded qualitative information on the polymer/silica composites. In the spectra, the characteristic bands of aniline, 0- toluidine and 2-chloroaniline were observed which confirmed the presence of these monomer rings in the respective polymer. The infra-red spectra observed for the studied samples exhibited absorption bands attributable to both the polymer and the silica components. Characterization of poly( aniline) and polymer/silica nanocomposites by inverse gas chromatographic technique was performed. For this purpose, composite materials were used as fine column materia!. These composite materials when packed in the IGC column were found to be capable of separating a mixture of alkanes (CS-C9) indicating that these -composites can be used as column materials. IGC measurements also indicated higher surface energy values of the composite materials than that of the bulk polymer. BET technique was employed to measure surface area of the bulk poly(aniline) and the polymer/silica composites. In order to evaluate the surface area of the matrix the adsorption isotherms were fitted to the BET equation. Surface area was evaluated for all the studied samples from the linear plots of the adsorption data according to the BET equation. Experimentally observed surface area of the bulk polymer was much smaller than that of the corresponding polymer/ silica matrices. Change in the synthesis conditions e.g., pH and temperature, yielded products with different surface areas although all the samples contain almost the same amount of silica. This finding indicates that the synthesized materials may differ in porosity and particle size to exhibit different surface area of the studied samples which were prepared under different synthesis conditions. H.owever, BET m- easurements with poly(o-t.oluidine)/silica and poly(2-chloroaniline )/silica indicated relatively smaller surface area than the 2 other composites investigated and may be due to the presence of bulky -CH3 and -Cl groups in the polymer backbone. These bulky moieties may hinder the accumulation of appreciable amount of nanoparticles into the sample framework and consequently results in a relatively lower surface area.