Removal of Methylene Blue from aqueous solution by activated carbon of Vigna mungo L and Paspalum scrobiculatum: Equilibrium, kinetics and thermodynamic studies

The adsorption capacity of the activated carbons of the agricultural waste materials of Vigna mungo L (Black gram husk - ACBGH) and Paspalum scrobiculatum (Varagu millet Husk - ACVMH) have been explored for the removal of Methylene Blue (MB) from water and was proved to be an efficient adsorbent. The morphology and chemical structure of the adsorbents have been investigated by using Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Brunauer Emmett Teller (BET). Adsorption studies are conducted on a batch process, to study the effects of contact time, initial concentration, temperature and pH. Equilibrium data has been analysed using Langmuir, Freundlich and Dubinin-Radushkevich isotherm models and the monolayer adsorption capacity of the adsorbents are calculated. Kinetic data has been studied using pseudo-first and pseudo-second order kinetic models. The data fits well 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 is found to be the best for the adsorption of MB by the adsorbents with good correlation. Thermodynamic studies show that the adsorption is spontaneous, endothermic and entropy controlled. The desorption studies suggest that chemisorptions may be the major mode of adsorption.