Gamma-Fe2O3 nanospindles for environmental remediation: a study on the adsorption and desorption characteristics of acridine orange and direct red dyes.

In this paper, the adsorption and desorption characteristics of two harmful dyes, i.e., acridine orange (AO; cationic dye) and direct red 81 (DR; anionic dye) from aqueous solutions onto gamma-Fe2O3 nanospindles have been investigated. The nanospindles were synthesized by facile chemical precipitation method and characterized in detail in terms of their morphological, compositional and optical properties. Batch mode experiments were conducted to examine the adsorption process by investigating several factors such as effect of pH, amount of adsorbent dose, and effect of dye concentrations. The experimental results indicated that the maximum adsorption capacity occurred at pH = 6.0 for AO and at pH = 4.0 for DR, respectively with 0.03 gm of adsorbent. Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models have been used to evaluate the ongoing adsorption. Kinetic parameters for the adsorption have also been applied. Moreover, the gamma-Fe2O3 nanospindles and the adsorbed dyes were desorbed with good performance and could be reused to absorb the dyes again.