Tragacanth gum based hydrogel nanocomposites for the adsorption of methylene blue: Comparison of linear and non-linear forms of different adsorption isotherm and kinetics models

In the current work, novel eco-friendly hydrogel nanocomposite biosorbents (ef-HNCs) made up from tragacanth gum and modified CaCO3 nanoparticles (CC NPs) were applied for the adsorption of methylene blue dye (MBD). A simple, fast, and safe method regarding green chemistry was used to prepare the ef-HNC, with the aid of ultrasound waves. The ef-HNCs were successfully characterized using several spectroscopic, microscopic, and analytical methods. The results of the adsorption showed that the surface modification of CC NPs has a great impact on the adsorption and increased it and showed this process is more compatible with linear pseudo-first-order kinetic and linear Langmuir isotherm models. Also, thermodynamic parameters showed that the adsorption is spontaneous, although with an increase in temperature the adsorption decreased. Also, the value of the enthalpy and Gibb's free energy showed physiochemical adsorption. The maximum adsorption capacity calculated from linear Langmuir models as 468.62 mg/g, which is an appropriate value for the natural polymer. Furthermore, phenomenological methods displayed that the film diffusion is the predominant mechanism of this adsorption process. (C) 2019 Elsevier B.V. All rights reserved.