Functionalization of Graphite Oxide with Magnetic Chitosan for the Preparation of a Nanocomposite Dye Adsorbent

In the current study, the functionalization of graphite oxide (GO) with magnetic chitosan (Chm) was investigated to prepare a nanocomposite material (GO-Chm) for the adsorption of a reactive dye (Reactive Black 5). The synthesis mechanism was investigated by various techniques (SEM/EDAX, FTIR spectroscopy, XRD, XPS, DTA, DTG, VSM). Characterization results indicated that a significant fraction of the amines of the chitosan (i) were inserted between the GO layers and (ii) reacted with carboxyl and epoxy groups of GO, leading to its reduction and hence the destruction of the layered structure. The concentrations of iron were found to be similar to 25% for Chm and similar to 12% for GO Chm. A VSM plot presents the value of 9 emu/g for the saturation magnetization of GO Chm. The adsorption behavior of the prepared composite was elucidated with a series of experiments. The tests of the effects of pH revealed that the adsorption mechanism dominated (between dye molecules and the GO Chm matrix) and showed that acidic conditions were the optimum for the adsorption process (pH 3). Kinetic experiments presented the relatively "fast" adsorption phenomenon using pseudo-first-order, pseudo-second-order, and modified pseudo-second-order equations. The equilibrium data were fitted to the Langmuir, Freundlich, and Langmuir Freundlich (L-F) models, calculating the maximum adsorption capacities at 25, 45, and 65 degrees C (391, 401, and 425 mg/g, respectively). Thermodynamic analysis was also performed to calculate the changes in free energy (Delta G(0)), enthalpy (Delta H-0), and entropy (Delta S-0).