Methylene Blue removal using polyamide-vermiculite nanocomposites: Kinetics, equilibrium and thermodynamic study

Abstract

A novel low-cost adsorbent was produced from clay mineral of vermiculite using chemical modification. The vermiculite was modified with polyamide through in-situ interfacial polymerization. Adsorption performance of the modified adsorbent was investigated for methylene blue removal from aqueous solution. The influence of various operational parameters of the adsorption process was studied through kinetics, thermodynamics, and equilibrium. Noticeable enhancement in methylene blue removal was achieved for modified vermiculite compared to that of un-modified samples. The obtained equilibrium results were fitted to Langmuir, Freundlich, Temkin, Dubinin – Radushkevich, and Sips, where Langmuir model was best followed. Maximum removal uptake was found to be 76.42 mg/g, whereas maximum removal efficiency of 99% was achieved. Pseudo-second order kinetic model was best followed for the experimental kinetics. The modified vermiculite was characterized by scanning electron microscope coupled with energy dispersive spectrometer (SEM/EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Brunauer–Emmett–Teller (BET). The characterization outcome revealed that polymer chain was successfully attached to the vermiculite surface. The thermodynamic investigations showed that negative values of the free energy ΔG were reported, and the negativity was found to increase with increasing the temperature, which implies that the adsorption is spontaneous, energetic and favorable. Moreover, a positive value of enthalpy ΔH (10.98 KJ/mole) was reported, which indicated that the nature of adsorption is endothermic.