SYNTHESIS AND ANALYTICAL APPLICATION OF NOVEL POLYMERIC CALIXARENES

Abstract

The present study demonstrates the synthesis and characterization of calixarene based polymeric resins (13-19) through the immobilization of different calixarene derivatives (1-4, 7-9) onto the backbones of modified silica and polymeric materials (11 and 12). In addition, the analytical and environmental application of these synthesized resins have been investigated in order to check their efficiency in the removal of selected azo dyes from the aqueous media and unwanted species including coloring species, metal ions, FFA and reduction of peroxide values from the edible oil. All the synthesized resins were characterized by spectroscopic techniques, i.e. elemental analysis, FT-IR spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and energy dispersive spectroscopy (EDS). Synthetic work was carried out according to the methods as described in the experimental section (chapter 3). Thus, at first, different calix[n]arenes (1-6) were synthesized and their sulphonated derivatives (7, 8, 9) were obtained after the treatment of 25,26,27,28- tetra-hydroxycalix[4]arene (4), 37,38,39,40,41,42-hexa-hydroxycalix[6]arene (5) and 49,50,51,52,53,54,55,56-octa-hydroxycalix[8]arene (6) with conc. Sulphuric acid. Besides this, following the nitration and reduction of Amberlite XAD-4 (i) the modified Amberlite XAD-4 (11) was successfully prepared in a quantitative yield. Consequently, pure silica (ii) was treated with SiCl4 to have modified silica (12) in order to immobilize calix[n]arenes onto these polymeric resins (11 and 12) and get the desired calixarene based polymeric resins (13-19). In the 1st phase of present study; the synthesized resins 13-16 as described in schemes (1- 4) were used for the removal of selected azo dyes, i.e. Reactive Black-5 (RB-5), Reactive Red-45 (RR-45), Congo Red (CR) and Direct Black-38 (DB-38) from the aqueous media including the real samples from industrial effluents. The batch wise adsorption study of resins 13-16 was carried out to optimize various experimental parameters such as effect of adsorbent dosage, pH, electrolyte, contact time, temperature and dye concentration. The kinetic studies revealed that the adsorption process followed the pseudo-second- order kinetic model. The positive and negative values of ∆H and ∆G demonstrated that the nature of adsorption process was endothermic and spontaneous. The adsorption i behavior was analyzed by Langmuir and Freundlich isotherms, the linearity of plot as well as the values of correlation coefficients (R2) for the selected azo dyes showed a good agreement with the Langmuir and Freundlich adsorption isotherm. During the adsorption process, various kinds of interactions such as electrostatic repulsion, deprotonation of the hydroxyl groups of synthesized resins 13-16, dissociation of azo dyes into anions/cations and structural variations were monitored and found that they are highly pH dependent. In the 2nd phase of study; the synthesized resins 17-19 as described in schemes (5-7) were used for edible oil bleaching. The extraction efficiency of synthesized resins 17-19 scrutinized in solid-liquid extraction studies show that the metal ions, i.e. Pb, Cd, Ni, Cu, Co and Fe could be significantly extracted. Thus, it has been noticed that the synthesized resins 17-19 are potentially more effective bleaching materials as compared to the conventional bleaching clay and pure silica (ii). Moreover, the color content, conc. of FFA as well as peroxide value has also been reduced by the application of these resins 17-19 on the crude oils.