Polysulfone membranes with CNTs/Chitosan biopolymer nanocomposite as selective layer for remarkable heavy metal ions rejection capacity

Chitosan (CHIT) biopolymer has a remarkable adsorption capacity for heavy metal ions. The incorporation of multiwall carbon nanotubes (CNTs) into the CHIT matrix should enhance the water permeability and separation performance of the CHIT. The use of carboxylic acid functionalised multiwall carbon nanotubes (CNTS-COOH) as an additive is aimed at adding the COOH functional group to the CHIT matrix without blocking its adsorption sites. Therefore, two nanocomposites CNTs-COOH/CHIT and CNTs/CHIT are used as a selective layer on top of polysulfone (PS) to form CNTs-COOH/CHIT/PS and CNTs/CHIT/PS membranes. To the best of our knowledge, the efficiency of the CNTs-COOH/CHIT nanocomposite as a selective layer on polysulfone sheet to enhance the membrane's rejection for metal ions is reported for the first time. Both fabricated membranes are investigated in terms of morphology, wettability, surface charge, porosity and water permeability. CNTs-COOH/CHIT/PS membrane recorded water flux rate 64.4 L m−2 h−1 at transmembrane pressure 22 bar, where CNTs/CHIT/PS membrane recorded 57.15 L m−2 h−1 at transmembrane pressure 22 bar. Heavy metal ions rejection capabilities of both membranes are evaluated at various pHs and transmembrane pressures. Both CNTs-COOH/CHIT/PS and CNTs/CHIT/PS membranes effectively reject Cu+2, Ni+2, Pb+2, Cd+2, and Co+2 ions from aqueous solutions. At pH 3, CNTs-COOH/CHIT/PS and CNTs/CHIT/PS membranes presented significant rejection ranged 71–92.2% for examined metal ions. Where at pH range (6–8), Co+2 rejection reached up to 92.2% and 89.6% by CNTs /CHIT/PS and CNTs-COOH/CHIT/PS membranes, respectively. Overall, the CNTs-COOH/CHIT/PS membrane shows metal ions rejection superior to that of the CNTs/CHIT/PS membrane.