Adsorption of phenols on reduced-charge montmorillonites modified by bispyridinium dibromides: Mechanism, kinetics and thermodynamics studies

A series of reduced-charge montmorillonites (RCMs) were modified by hexamethylene bispyridinium dibromides (HMBP), then used to remove phenols from aqueous solution. The effects of concentration of HMBP (C), clay layer charge, contact time (t), temperature (T) and pH were investigated using a batch technique. The results implied that the clay layer charge had significant influence on phenol adsorption and the optimum conditions were as follows: C of 1.0CEC, 120 min, 25 degrees C and pH of 6.0. The adsorption mechanism of phenol on the HMBP-Mt was studied by comparing the adsorption characters of substituted phenols, the results indicated that the uptake of phenols onto HMBP-Mt decreased in the order: phenol > p-chlorophenol > p-methylphenol > p-nitrophenol. This indicated that the pi-pi polar interaction existing between the pyridine ring and benzene ring in phenols played a dominated role in the adsorption of phenols. The adsorption kinetics demonstrated that the adsorption of phenol onto HMBP-Mt followed the pseudo-second-order model. The adsorption isotherms at the temperatures of 25, 40 and 55 degrees C were determined and modeled using four different models. The best-fitted adsorption isotherm models were found to be in the order: Langmiur approximate to Redlich-Peterson > Temkin > Freundlich. The thermodynamic study of adsorption process showed that the adsorption of phenol with HMBP-Mt was carried out spontaneously, and the process was randomly increasing and exothermic in nature. (C) 2015 Elsevier B.V. All rights reserved.