Equilibrium and Thermodynamic Studies for Adsorption of Crystal Violet onto Spent Tea Leaves (STL)
Sunil Kumar Bajpai1* and Arti Jain2
1 Polymer Research Laboratory, Dept. of Chemistry, Govt. Model Science College (Auton.) Jabalpur (M.P.) 482001 India
2 Dept. of Chemistry, Shri Ram Institute of Science & Technology, Jabalpur (M.P.) 482001 India
*Correspondence E-mail: [email protected]
Key Words: Adsorption, Crystal violet, Isotherm, Gibbs free energy
Received November 22nd, 2011; Accepted July 23rd, 2012; Published November 11th, 2012; Available online November 15th, 2012
Summary
In this work, equilibrium sorption of crystal violet (CV) has been carried out onto spent tea leaves at different temperature in batch experiments. The specific surface area (BET) of spent tea leaves is 1.141 m2/g. The adsorption is found to be favored at higher temperature. The order to fitness of various isotherm models, when applied on equilibrium uptake data, was found to be Langmuir = Temkin > Freundlich. The values of Langmuir constants, Qo(mg g-1)and b(lmol-1)ere found to be 114.94 and 80457.6;185.18 and 52795.2;285.71 and 41983.2 at 25º, 37º and 50ºC respectively. The value of sorption mean free energy from the Dubinin-Radushkevich isotherm was found to be in the range of 9.45 to 11.11 kJ mol-1, indicating ion-exchange mechanism. Thermodynamic quantities, i.e. ∆Gºads, ∆Hºads and ∆Sºads have also been evaluated using Langmuir isotherm model. The negative ∆Gºads values indicated spontaneous nature of the adsorption process.