Novel chitosan/poly(vinyl) alcohol thin adsorptive membranes modified with amino functionalized multi-walled carbon nanotubes for Cu(II) removal from water: Preparation, characterization, adsorption kinetics and thermodynamics

In the current study, amino functionalized multi-walled carbon nanotubes (MWCNT-NH ₂) were synthesized from raw MWCNTs and utilized to prepare novel chitosan/PVA thin adsorptive membranes for copper ion removal from water. Various weights of the CNTs were embedded in the membranes to obtain the optimum MWCNTs content. Finger-like nanochannels appeared in the compact structure of the CS/PVA membrane by addition of 0.5 wt.% of the MWCNTs; however, fibril-shape and dense structures were generated at higher percent weights i.e. 1 and 2 wt.%, respectively. Adsorption capacity of the membrane containing 2 wt.% MWCNTs (20.1 mg/g at 40 °C) was almost twice as large as that of the plain membrane (11.1 mg/g); however, capacity enlargement was not significant (<3 mg/g), when MWCNTs content raised from 1 to 2 wt.%. This indicates that the optimum CNT loading is 1 wt.%. Freundlich isotherm could, thus, superiorly describe the adsorption equilibria. Thermodynamic studies revealed spontaneous (ΔG° < 0) and endothermic (ΔH° > 0) adsorption together with entropy generation (ΔS° > 0) at the solid/liquid interface. Additionally, kinetic studies showed that membranes with higher MWCNTs content could support faster adsorption rate. No significant adsorption capacity loss (∼3%) was observed for the membrane containing MWCNT-NH ₂ in comparison to the capacity loss of the plain membrane (∼10%) after four successive adsorption/regeneration cycles. The results suggested that the novel CS/PVA/MWCNT-NH ₂ composite membranes can be effectively applied for the adsorptive removal of copper ions from aqueous solutions.