Adsorption of 5.5’-Disulfonicindigotin (5.5’-DI) onto Green Coconut Fiber (Cocos nucifera L.): Kinetic and Isotherms

Green coconut fiber (Cocos nucifera L.) has been largely used in solid-phase extraction. The effect of the initial dye concentration (1.91, 3.02 and 4.02) × 10−5 mol∙L−1 and solid phase contact (SPE) time were evaluated at different temperatures (283, 298 and 313) K at pH 2. Kinetic experimental data were applied to three simplified kinetic models: pseudo-first order, pseudo-second order, and intraparticle diffusion. The adsorption of 5.5’-DI onto the solid phase showed excellent fit to the pseudo-second order model. At 283, 298 and 313 K the maximum sorption, qmax,exp, for the lowest initial concentration (Co = 1.91 × 10−5 mol∙L−1) of 5.5’-DI were (5.01, 5.24 and 6.14) × 10−4 g∙g−1; for Co = 3.02 × 10−5 mol∙L−1 (0.93, 1.01 and 1.03) × 10−3 g∙g−1 and for Co = 4.02 × 10−5 mol∙L−1 (1.32, 1.40 and 1.49) × 10−3 g∙g−1, respectively. The adsorption of 5.5’-disulfonicindigotin (5.5’-DI) onto green coconut fiber has been investigated and the experimental equilibrium data were fitted to the Langmuir, Freundlich and Dubinin-Radushkevich models at different temperatures (283, 298 and 313) K. The evaluation of the mean sorption energy characterized the adsorption as physical and the adsorbent surface energetically homogeneous (n < 1). Thermodynamic studies show adsorption process to be endothermic ΔHo (+11.6 kJ∙mol−1) and spontaneous ΔGo (−9.7 kJ∙mol−1 at 283 K, −10.8 kJ∙mol−1 at 298 K and −11.9 kJ∙mol−1 at 313 K).