Investigation of interactions between cationic surfactants modified Unye bentonite and tartrazine dyestuff by using of XRD, TG/DTA, FTIR techniques and evaluation of adsorption data

In this study, the removal of Tartrazine from aqueous solution using cetylpyridinium (CP) and hexadecylammonium (HDTMA) cationic surfactant materials modified Unye bentonites (CP- and HDTMA-bentonites) was investigated with particular reference to the effects of pH, temperature, clay amount and ionic strength on adsorption process. In addition, thermal stabilities and structural properties of modified dye-clay composites were illuminated by XRD, TG/DTA and FTIR techniques.The d001 basal spacing values of CP- and HDTMA-bentonites were increased to 22.34 Å and 18.42 Å, respectively, while the d001 basal spacing value in the XRD spectrum of Unye bentonite with major Ca-montmorillonite component was 14.47 Å at 6.10 (2?). In addition, those of CP- and HDTMA-bentonite-Tartrazine composites were determined as 22.74 Å and 18.69 Å, respectively. In the TG curve of raw Unye bentonite, the total mass losses by 8.1 and 7.5 % in the temperature ranges 20-160 ºC and 160-800 ºC, respectively, due to thermal evolution of water species coordinated to the interlayer cations and removal of structural OH groups and external clay components, respectively, were determined. However, the total mass losses by 29.9 and 43.1 % in the temperature range 160-800 ºC corresponding to the gradual decomposition of the organic cation for the TG curves of CP- and HDTMA-bentonite composites, respectively, were observed. Similarly, the total mass losses for CP- and HDTMA-bentonite-Tartrazine composites increased 31.9 % and 45.5 %, respectively, because of organic substance decomposition. The C-H stretching and in plane bending peaks of alky groups at 2918 and 2850 cm-1; 1488 and 1470 cm-1, respectively, seen in the of FTIR spectra of CP- and HDTMA-bentonites can be attributed to the presence of cationic surfactant species. The IR bands of dye molecules are clearly not observed for CP- and HDTMAB-bentonite-Tartrazine complexes, which is probably due to overlapping by water and Si-O stretching peaks of bentonite.Adsorption isotherms and kinetic data for adsorption of Tartrazine by CP-bentonite were well described by the Langmuir and pseudo-second order kinetic model, respectively, while those of HDTMA-bentonite fitted well the Freundlich and pseudo-first order kinetic model, respectively.The Gibbs energy (DG), enthalpy (DH) and entropy (DS) changes observed the temperature range 25-55 ºC shows clearly that the adsorption of Tartrazine both on CP- and HDTMAB-bentonites is a thermodynamically feasible process.Furthermore, the decreases in the amounts of Tartrazine adsorbed by modified bentonites (CP- and HDTMA-bentonites) with increasing pH and ionic strength were determined.