Bio-fabrication of porous magnetic Chitosan/Fe3O4 nanocomposite using Azolla pinnata for removal of chromium – Parametric effects, surface characterization and kinetics

In this research, a novel porous nanocomposite, namely Chitosan-iron-oxide @ Azolla pinnata nanocomposite, has been synthesized by co-precipitation and hydrothermal method. The effect of process parameter on adsorption process was investigated. Batch removal of chromium (Cr) was optimized with respect to solution pH, batch stirring time, sorbent dose, initial chromium concentration and temperature. The maximum removal efficiency was found to be 98.58%. The Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM) analysis of the nano composite confirmed the presence of characteristic functional groups and porous structure of synthesized nanocomposite. The adsorption data fitted well with Langmuir adsorption isotherm (R2 = 0.996) confirming mono layer sorption and the maximum uptake was found to be 294.12 mg/g. The adsorption was found to follow pseudo second order model (R2 = 0.997). Thermodynamic studies revealed that adsorption is endothermic and spontaneous. Reusability studies have confirmed that removal efficiency attained was 85% after completion of five adsorption-desorption cycles. Electrostatic attraction, ion exchange, coordination bonding and reduction are the major mechanisms responsible for removal of chromium. Surface modification of Azolla pinnata with chitosan and iron oxide improved the ability of Azolla in the adsorption of chromium from aqueous media. The combined effects of facile synthesis, improved adsorption features and easier magnetic separation promotes Chitosan-iron-oxide @ Azolla pinnata nanocomposite as a novel adsorbent.