Comparison between the removal of Reactive Black 5 from aqueous solutions by 3-amino-1,2,4 triazole, 5-thiol and melamine grafted chitosan prepared through four different routes

Chitosan was modified through four different modification routes. First, epichlorohydrine cross-linked Chitosan was grafted with 3-Amino-1,2,4 triazole, 5-thiol and melamine to produce RI and RII, respectively. Second, glutaraldehyde cross-linked chitosan was chemically modified using ammonium hydroxide then grafted with 3-Amino-1,2,4 triazole, 5-thiol and melamine to produce RIII and RIV, respectively. The prepared polymers were characterized via FTIR, TGA, elemental analysis, water regain and surface area. RIII and RIV shows higher thermal stability, bigger surface area, and lower water regain, than RI and RII. Removal of Reactive Black 5 (RB5) anions from their aqueous solutions were studied using the modified chitosan adsorbents under various parameters such as pH, agitation time, and temperature. The maximum adsorption capacities are 0.492, 0.330, 0.622 and 0.698 mmol g (1) for RI, RII, RIII, and RIV, respectively, at pH 3 and 25 degrees C. The nature of interaction of RB5 with the adsorbents was identified. Uptake kinetics and adsorption isotherms were modeled using conventional and simple equations: best results were respectively obtained with the pseudo-second order rate equation and the Langmuir equation. The thermodynamic parameters have been calculated: the adsorption is endothermic, spontaneous and contributes to increase the entropy (randomness) of the system. RI and RII gives higher desorption yield than RIII and RIV, this probably due to the presence of the quaternary ammonium moiety in the last two sorbents. (C) 2015 Elsevier Ltd. All rights reserved.