ABSTRACT
The efficiency of acid modified locust bean pod (ALBP) as low cost adsorbent to remove
Rhodamine-B (Rh-B) dye from aqueous solution was studied. The morphology, functional groups and
elemental analysis of the adsorbent were investigated by SEM, FTIR, pH (pzc), and Boehm titration analytical
techniques. Operational parameters such as contact time, initial dye concentration and solution temperature
were investigated. The amount of Rh-B dye adsorbed was found to increase as these operational parameters
increased. Kinetic data for Rh-B dye adsorption onto ALBP were best represented by the pseudo secondorder kinetic model. The Weber-Morris diffusion model result showed that intraparticle diffusion is not the
rate limiting step. Four different isotherms namely Langmuir, Freundlich, Temkin, and DubininRadushkevich models were used to test the adsorption data. It fitted the Langmuir isotherm model most with
maximum monolayer adsorption capacity of 1111.1 mgg-1
. Increase in temperature resulted in a
corresponding increase in Rh-B dye adsorbed, suggesting that the adsorption process was endothermic. ΔG0
values were negative (-31.892 to -26.355 K J mol-1
), indicating that the process of Rh-B dye adsorption onto
ALBP was spontaneous. The positive value of ΔS0
(0.281 KJ mol-1 K
-1
) suggests that the process of dye
adsorption was endothermic. ALBP adsorbent was found to be both effective and viable for the removal of
Rh-B dye from aqueous solution.
Keywords: Rhodamine-B dye (Rh-B); Locust bean pod; Isotherm; Kinetics; Thermodynamics.
Field of Research: Physical Chemistry – Adsorption Technology
