Adsorption Isotherms and Thermodynamics of Thymol Blue Removal from Aqueous Solution Using Native Pear (Dacryodes edulis) Seed Biomass

Abstract

The release of dyes into watercourses not only upsets their beautiful nature but also hinders the transmission of sunlight into streams,  reducing photosynthesis and resulting in the loss of aquatic life and reduction of water quality. Therefore, there is need to remove such  colored substances. One of such dyes is thymol blue. This study was conducted with a view to removing thymol blue (TB) dye from an aqueous solution using a low-cost agricultural biomass, the African native pear (Dacryodes edulis), as the adsorbent. Batch experiments  showed that the process was affected by pH, temperature, contact time, and initial thymol blue concentration. Optimum dye adsorption  was achieved at pH 12. The data was analyzed using Langmuir and Freundlich isotherm models. The latter isotherm better described this  process than the former. The thermodynamic quantities like free energy change (∆G°), enthalpy change (∆H°), and entropy change (∆S°)  were also evaluated. It was inferred from the results that the adsorption process was spontaneous, feasible, endothermic in nature, and  occured by a physisorption mechanism. These findings indicate that the native peer seed is an efficient biosorbent for thymol blue   removal from an aqueous environment.