INFLUENCE OF ACID AND BASE SURFACE MODIFICATION ON Cr (VI) IONS ADSORPTION ONTO ACTIVATED CARBONS PREPARED FROM BARK OF THESPESIA POPULNEA-ISOTHERM AND THERMODYNAMICS STUDY

Abstract

Thespesia populnea barks were utilized to prepare activated carbon by using orthogonal array experimental design method with the parameters such as microwave radiation power, radiation time and concentration of H3PO4. Optimized conditions were found to be; radiation power 850W, radiation time 15 min, 50% of H3PO4 and impregnation time 24 hours. Carbon prepared was designated as TPBC (Thespesia populnea Bark Carbon). Ten g TPBC was impregnated with 20% concentrations of hydrochloric acid and sodium hydroxide solution separately and heated in a microwave oven (radiation power 850W, radiation time 10 min) to improve the structural characteristics of the adsorbents for enhanced Cr(VI) ions removal. These two carbons were designated as A20TPBC (20% HCl acid surface modified Thespesia populnea Bark Carbon) and B20TPBC (20% NaOH base surface modified Thespesia Populnea Bark Carbon). Influence of the parameters such as initial metal ion concentration and temperature on adsorption was studied. Equilibrium data were fitted with Langmuir, Freundlich, Tempkin and D-R isotherms. The order of best describing isotherms was given based on R2 value. Various thermodynamic parameters such as ΔH°, ΔS°, and ΔG° have been evaluated using Vant Hoff plots. Analysis of these values inferred that this adsorption was endothermic, spontaneous and proceeded with increased randomness.