Adsorption isotherm, kinetic modeling and thermodynamics of crystal violet dye on coconut husk-based activated carbon

Abstract

The present study shows that the H₂SO₄-modified coconut husk derived activated carbon powder (CHACP) can be used as a potential adsorbent for the removal of crystal violet (CV, basic dye) from aqueous solutions. Experiments were carried out as a function of contact time, concentration, pH, mass dosage, and temperature, the equilibrium was attained in 60 min. The amount of dye uptake (mg/g) was found to increase with increase in dye concentration, pH, temperature, and contact time. The kinetics of CV on to the adsorbent can be described well by pseudo-second order  >  Elovich  >  pseudo-first order > intra-particle diffusion equation. The applicability of the isotherm’s model for the present data follows the order: Freundlich  >  Temkin  >  Langmuir. Based on the calculated thermodynamic parameters such as enthalpy (ΔH°), entropy (ΔS°), activation energy (E_a), sticking probability (S^*), and Gibbs free energy changes (ΔG°), it is noticeable that the sorption of CV dye onto CHACP was a spontaneous and endothermic process. The morphological and chemical characteristics of the adsorbent were established by scanning electron microscopy and Fourier transform infrared spectroscopy.

Keywords:

• Adsorption
• Coconut husk
• Activated carbon
• Crystal violet
• Activation energy