Biopolymer composite from cellulose nanocrystals of almond (Prunus dulcis) shell as effective adsorbents for Cu2+ ions from aqueous solutions

This study deals with the preparation of biopolymer composite from cellulose nanocrystals (CPCNCs) of almond (Prunus dulcis) shell. These composites were obtained through a simple process based on the dissolution of cellulose nanocrystals (CNCs) in green ionic liquid (IL) 1-butyl-3-methylimidazolium chloride (BmimCl). Structural, textural and morphological analyses of CPCNCs were performed using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques, while thermal stability was evaluated by means of thermogravimetric analysis (TGA) measurements. The performance of CPCNCs as adsorbent for Cu2+ ion removal from aqueous solutions was further investigated in batch mode, the maximum experimental adsorption capacity being 131.16 mg g(-1). The equilibrium data was successfully fitted to the DubininRadushkevich model. The kinetic studies showed that the adsorption of Cu2+ ions was well described by the Elovich kinetic model, suggesting that the adsorption was mainly attributed to the chemical process onto heterogeneous surface. Various thermodynamic parameters, such as Delta G degrees, Delta H degrees and Delta S degrees, derived from adsorption data over the temperature range 30-60 degrees C, accounted for an endothermic and spontaneous process. A possible adsorption mechanism implying electrostatic reactions and surface complexation was proposed based on XPS, FTIR, TEM and pH dependence. The CPCNC adsorbent could be regenerated using diluted HCl (0.1 M) solution, showing excellent recyclability: 81% removal of Cu2+ ions after four adsorption-desorption cycles. Therefore, the synthesized biopolymer composite could be considered as promising adsorbent for Cu2+ ion removal from polluted waters.