Methylene blue adsorption onto crosslinked sago starch

Abstract

Crosslinked sago starch was prepared by crosslinking native sago starch with sodium trimetaphosphate (CSS-STMP) and epichlorohydrin (CSS-EPCH) as renewable adsorbents. CSS-STMP and CCS-EPCH were used to remove methylene blue (MB) from aqueous solution based on its characterization tests. The adsorption capacity of CSS-STMP and CSS-EPCH were evaluated as a function of pH, adsorbent dosage, initial MB concentration, contact time and temperature. It was favorable for adsorption under condition of pH 7 and at 50 ppm for both adsorbent. The adsorption capacity trend was reduced with increasing adsorbent dosage where 0.05 g dose of adsorbent was chosen. Equilibrium adsorption capacity (qe) of MB adsorption onto CSS-STMP and CSS-EPCH were 2.224 mg g-1 and 1.303 mg g-1, respectively. CSS-STMP adsorbent was employed for further experiment due to its better performance than CSS-EPCH. The equilibrium isotherms were conducted using Langmuir, Freundlich and Tempkin models. It has been demonstrated that a better agreement was Langmuir isotherm with a correlation coefficient (R2) of 0.990, complete monolayer adsorption capacity (qm) of 3.731 mg g-1, chi-square test (2) of 0.029% and corresponding contact time of 4 hours. The pseudo-first-order, pseudosecond- order and intra-particle diffusion were used to fit adsorption data in the kinetic studies. The results show that the adsorption kinetic was more accurately described by the pseudo-second-order model with the mechanism via film diffusion where R2 is 0.999 and variance is 0.152%. The adsorption of MB on CSS-STMP was exothermic and non-spontaneous in nature at temperature of 303K. Regeneration study also indicated that CSS-STMP adsorbent have the potential to be reused at the same adsorption performance for numbers of cycle. The obtained results suggest that CSS-STMP could be a promising candidate as an adsorbent for MB removal.