Adsorption Studies of Methylene Blue using Activated Carbon Derived from Sweet Detar Seed Shell

Abstract

Adsorption capacity of sweet detar seed shell activated carbon (SDAC) was evaluated using batch adsorption technique. The SDAC was  characterized by pH at point of zero charge (pHPZC), Fourier transform infrared spectroscopy (FTIR) and Scanning Electron Microscopy  (SEM). In batch optimization studies, the maximum adsorption capacity obtained at the optimum levels of different parameters were;  9.78 mg/g at 60 minutes, 8.61 mg/g at 0.1g adsorbent dose, 97.61 mg/g at 75µm particle size, 500 mg/g at 247.45 mg/g initial dye concentration, 10.99 mg/g at pH12 and 9.85 mg/g at temperature of 303 K. The adsorption data were found to closely fit to Freundlich  isotherm model. The adsorption mechanism was found to be best described by the pseudo-second order kinetic model. Thermodynamic  investigations indicates that the adsorption was spontaneous, exothermic, and decreased in the system randomness at adsorbent –  adsorbate interfaces due to the negative values of enthalpy change (ΔH = -75.72 kJ/mol), entropy change (ΔS = -0.22 kJ/K) and Gibbs free energy change of adsorption; ΔG = -8.58 kJ/mol, 7.47 kJ/mol, 6.36 kJ/mol, 5.25 kJ/mol and 4.15 kJ/mol at 303, 308, 313, 318 and 323 K  respectively. Desorption studies for adsorbent regeneration revealed that hydrochloric acid offered the highest recovery and reusability  test revealed the good adsorbent performance after five successive adsorption cycles. Therefore, this study confirmed that activated  sweet detar seed shell adsorbent could be used as an alternative low cost adsorbent for the removal of toxic dyes such as methylene blue  dye.