A nanocrystalline graphite-like amorphous carbon, (graphite from the University of Idaho thermolyzed asphalt reaction, GUITAR) shares morphological features with classical graphites, including basal and edge planes (BP, EP). However, unlike...

Abstract. This study reports the equilibrium adsorption mechanism and thermodynamics for the removal of Malachite Green (MG) from acidic solution using Used Black Tea Leaves (UBTL) as a low cost adsorbent. The effect of initial dye concentration, processing temperature and the presence of electrolytes on the adsorption from acidic solutions were investigated in batch process. Adsorption process was attained to the equilibrium at about 24 hours. Adsorption isotherms of MG on UBTL for different temperatures were constructed at pH 2.0 and the equilibrium adsorption data were analyzed using different model equations such as Langmuir, Freundlich, Temkin, DubininRadushkevich (D-R), Harkin-Jura, Halsey, Elovich-Larionov and Flory-Huggens isotherms. The experimental results were reasonably correlated by Langmuir, Flory-Huggins and D-R models than other isotherm models. The maximum adsorption capacity (q m ), intensity of adsorption (b) and separation factor (R b ) were calculated from Langmuir plot and activation energy of adsorption (E ad ) was determined from D-R isotherm. At pH 2.0, the equilibrium adsorption capacity of UBTL to MG is 110 mg•g -1 at 30°C, which was increased with increasing temperature suggested endothermic nature of adsorption. Thermodynamics parameters: ΔG ads , ΔH ads and ΔS ads were calculated from Langmuir constant (b). The positive values of enthalpy and free energy, and negative value of entropy suggested that the adsorption is less spontaneous and surface migration or fragmentation of MG molecules on UBTL surface might be occur. Again, the low value of activation energy of adsorption (E ad = 0.3 kJ•mol -1 <8 kJ•mol -1 ) suggested that the adsorption is controlled by physical in nature. A possible mechanism involvement of protonation is proposed from the effect of electrolytes during the adsorption of MG on UBTL at pH 2.0.

This study reports the equilibrium adsorption mechanism and thermodynamics for the removal of Malachite Green (MG) from acidic solution using Used Black Tea Leaves (UBTL) as a low cost adsorbent. The effect of initial dye concentration, processing temperature and the presence of electrolytes on the adsorption from acidic solutions were investigated in batch process. Adsorption process was attained to the equilibrium at about 24 hours. Adsorption isotherms of MG on UBTL for different temperatures were constructed at pH 2.0 and the equilibrium adsorption data were analyzed using different model equations such as Langmuir, Freundlich, Temkin, Dubinin-Radushkevich (D-R), Harkin-Jura, Halsey, Elovich-Larionov and Flory-Huggens isotherms. The experimental results were reasonably correlated by Langmuir, Flory-Huggins and D-R models than other isotherm models. The maximum adsorption capacity (qm), intensity of adsorption (b) and separation factor (Rb) were calculated from Langmuir plot and activation energy of adsorption (Ead) was determined from D-R isotherm. At pH 2.0, the equilibrium adsorption capacity of UBTL to MG is 110 mg∙g-1 at 30°C, which was increased with increasing temperature suggested endothermic nature of adsorption. Thermodynamics parameters: ΔGads, ΔHads and ΔSads were calculated from Langmuir constant (b). The positive values of enthalpy and free energy, and negative value of entropy suggested that the adsorption is less spontaneous and surface migration or fragmentation of MG molecules on UBTL surface might be occur. Again, the low value of activation energy of adsorption (Ead = 0.3 kJ∙mol-1 <8 kJ∙mol-1) suggested that the adsorption is controlled by physical in nature. A possible mechanism involvement of protonation is proposed from the effect of electrolytes during the adsorption of MG on UBTL at pH 2.0.