Removal of methylene blue from aqueous solution by activated carbon of Vigna mungo L and Paspalum scrobiculatum - Equilibrium, kinetics and thermodynamic studies

S. Valliammai, Y. Subbareddy,

Abstract

The adsorption capacity of the activated carbons of Vigna mungo L (Black gram husk - ACBGH) and Paspalum scrobiculatum (Varagu millet Husk - ACVMH) were studied for the removal of Methylene blue (MB) from aqueous solutions. The surface area of the ACBGH and ACVMH was found to be 480.10 m2/g and 397.33 m2/g respectively. The adsorbents were also characterized by using Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM). Adsorption studies were performed to study the effects of contact time, initial concentration, temperature and pH. The data best fitted with the Langmuir model, with a maximum adsorption capacity of 198.40 mg g-1 and 166.30 mg g-1 for ACBGH and ACVMH respectively. The pseudo-second-order kinetics was the best for the adsorption of MB by the adsorbents. Thermodynamic studies showed that the adsorption was spontaneous, endothermic and entropy controlled. The results suggest that ACBGH and ACVMH can be used as a potential low-cost adsorbent for the MB dye removal from aqueous solution.