Adsorption of Eriochrome Black T (EBT) Onto Activated Carbons Obtained from Cola Anomala Nut Shells by Chemical Activation with Phosphoric Acid (H3PO4)

The objective of this work is to prepare an active carbon with the best adsorption properties from the shells of Cola nuts (anomala) for the reduction of Eriochrome Black T in aqueous medium. The materials (shells nut of Cola anomala) obtained were characterized by Thermogravimetric Analysis (TGA), pHPCN and Fourier Transform Infrared (FT-IR). The study of adsorption involves discussing the effects of contact time and initial solute concentration using a batch adsorption technique. The effect of temperature made it possible to carry out a thermodynamic study to define the nature of the adsorption phenomena. In addition, different kinetic models (first and second order and Intra-particle) and adsorption isotherms (Langmuir and Freundlich) were used for the evaluation of the adsorption capacity. The TGA analysis illustrates the presence of: hemicellulose, cellulose and lignin thus confirming the lignocellulosic structure of the activated carbon obtained. The CA1/2 and CA1/3 samples prove to be the best absorbers. The measurement of their zero charge point pH gives respectively pHPCN = 6.8 and pHPCN = 6.9, showing the almost neutral character of the surface of these active carbons. The kinetic model of the pseudo-second order better describes the adsorption of EBT on AC with R^2 0.99950. The thermodynamic study gave the negative values of the free energy justifying the spontaneous nature of the process and which thus shows that the adsorption is of physical type. The process is endothermic with respect to the positive values of free enthalpy obtained. Positive values of entropy justify the good affinity of the EBT on the AC due to the swelling of the pores.