Adsorption Characteristics of Pyronin B on Bentonite Particles

Clay minerals and their composites are hot topic research area because of the intriguing feature of clay minerals [1]. The intriguing features of clay minerals are the large surface area, swelling behavior, ion-exchange capacity, low-cost, and catalytic behavior [2]. The lamellar structures of clay minerals play a key role in clay based-composites used in many applications [3]. They have both external surface (water/clay interfaces) and an internal surface (inter lamellar interface), which are attractive regions for other materials [4]. Pyronin B that is xanthenes derivatives which are water-soluble, very sensitive to the local microenvironment and cationic dye, has lamellar structure [4,5].The present study focused on the adsorption properties of pyronin B (PyB) in bentonite aqueous dispersions. The adsorption process comprises the rate of adsorption, distribution of adsorbed cations over the surfaces of clay particles, especially at low coverage, and the distribution of adsorbed molecules over different particles [6].The interaction of the dye with bentonite particles in the aqueous dispersion was spectroscopically followed depending on certain parameters such as interaction time and the initial dye concentration. With the change of concentration of PyB from 1.0x10−5 to 1.0x10−4M, the amount of adsorbed PyB increased from 0.37 mg (62% removal) to 4.77 mg (67% removal). The percentage of the removal did not change noticeably with regard to the initial adsorbate concentration. The equilibrium time for PyB was found to be 33 min for 1.0x10−5M, 29 min for 5.0x10−5M and 32 min for1.0x10−4M. It was also found out that the adsorption was rapid in the initial stages and gradually decreased with the progress of adsorption. All experiments were done at 25ºC and pH 7.0.The surface phase can be considered as a monolayer or multilayer. For this aim, Langmuir and Freundlich isotherms were applied to the experimental data and linear regression correlation values were calculated for both models. The adsorption isotherm was good-fitted by the Freundlich model with a linear regression correlation value of 0.999, therefore adsorbent surface phase is a multilayer.The adsorption data were examined by using two kinetic models as the pseudo-first-order and pseudo-second-order kinetic models. It is found that the correlation coefficient of the second order kinetics was high for PyB adsorption on the bentonite. Additionally, the equilibrium rate constant of the second order kinetics was higher than that of the first order kinetics. Therefore, the adsorption process of PyB obeyed the second-order kinetic model. In this case, it can be said that the adsorption of PyB on to the bentonite particles occurs via an activated process

کلیدواژه ها:

Adsorption ، Bentonite ، Clay minerals ، Pyronin B