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 second￾order 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 Dubinin￾Radushkevich 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