A novel approach for synthesis of exfoliated biopolymeric-LDH hybrid nanocomposites via in-stiu coprecipitation with gum Arabic: Application towards REEs recovery

Delamination and exfoliation of layered double hydroxides (LDH) is an interesting way for the synthesis of novel nanocomposites. Herein, we report the synthesis of various exfoliated biopolymeric-LDH nanocomposites via in-situ coprecipitation method with gum Arabic (GA). The influence of various divalent ions on the morphological characteristics of GAnXA (n= wt% of GA and X= Mg, Ca, Ba, Sr) was explored Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), and Scanning Electron Microscopy (SEM). X-ray diffraction pattern was used for the determination of phase composition of synthesized nanocomposites. The surface functional groups of GAnXA were investigated by Fourier Transform Spectroscopy (FTIR). Furthermore, the surface charge characteristics was explored by zeta potential analysis. Specific surface area of GAnXA was determined by BET analysis. The overall adsorption of REEs decreased with an increase in ionic size of divalent ions and the noticeable difference in the morphologies of exfoliated GAnXA was observed. In a single component system, the REEs adsorption capacities followed the order: Sc > Y > Nd > Ce > Eu > La, whereas, in multicomponent system, adsorption seems to be competitive and presence of competing ions affect the overall REEs removal. Moreover, HREEs removal superseded over LREEs and the nanocomposites (GA5CA, GA5SA, GA5BA) were highly selective for Sc recovery. The post-adsorption FTIR and SEM results revealed the importance of surface hydroxyl and carboxyl functional groups enacting as the principal REE binding sites. Overall, ability to extract REEs at pH 4 (slightly acidic) presented a facile route for the recovery and separation of REEs from aqueous medium and enhances the possibility of its use in many industrial applications.