Adsorption of Congo red dye from aqueous solution using raw cowpea (Vigna Unguiculata) husk

Abstract

An agricultural residue, cowpea (Vigna unguiculata) husk (CPH), was used for the removal of Congo red dye from aqueous solution using a batch adsorption method. The adsorbent was characterized using FTIR and SEM techniques. The optimization of adsorption variables including pH, contact time, adsorbent dosage and initial dye concentration at 25 °C were also carried out. The results indicated the dependence of the adsorption system on the studied variables and equilibrium was attained in 60 min. The adsorption kinetics was fitted to four models (pseudo first order, pseudo second order, Elovich and intra-particle diffusion) to validate the kinetics, which resulted in pseudo second order as the best model for the description of Congo red dye uptake. Equilibrium isotherm modeling was also carried out using the Langmuir, Freundlich, and Temkin models. The Langmuir isotherm relatively giving the best fitting to the experimental results. The maximum loading capacity (qm) of the adsorbent for Congo red obtained from the Langmuir isotherm model is 161.29 mg/g. This result indicates that the CPH residue could serve as a good adsorbent for the removal of Congo red dye from aqueous system.

Keywords

• adsorption
• congo red
• isotherm
• kinetics
• vigna unguiculata