Green and plant-based adsorbent from tragacanth gum and carboxyl-functionalized carbon nanotube hydrogel bionanocomposite for the super removal of methylene blue dye.

This study aims to prepare a hydrogel bionanocomposite (HBNC) as an efficient adsorbent and introduce it as a suitable replacement for petroleum-based adsorbents. Thus, tragacanth gum (TG), and carboxyl-functionalized carbon nanotube (CFCNT) were used as raw materials. HBNCs were prepared with the aid of ultrasonication, and different methods were employed to characterize them. The surface structures of the HBNCs were altered after the addition CFCNT into TG and exposure to ultrasound, as well. Transmission electron microscopy images showed CFCNTs were well dispersed in TG. Then, the adsorption of methylene blue (MB) was performed using these HBNCs. The removal efficiency was over 80% at optimized conditions. Nonlinear and linear forms of Langmuir, Freundlich, Dubinin-Radushkevich, Sips, and Redlich-Peterson (R-P) were applied to find the proper arrangement of MB onto the adsorbent. Using statistical equations, it was revealed that the process obeyed the linear R-P model, indicating a mixture of mono- and multilayer adsorption (but mostly monolayer). Also, pseudo-second-order was the appropriate kinetic model and suggested chemical adsorption. According to the thermodynamic calculations, this process was exothermic and spontaneous, and the type of interactions between HBNC and MB was physicochemical. Also, the diffusion study indicated that film diffusion is the primary mechanism.