Polyacid functionalized cellulose nanofiber membranes for removal of heavy metals from impaired waters

This contribution describes the development and performance of high-productivity nanofiber membranes for removal of heavy metal ions from impaired waters. Cellulose acetate nanofiber membranes were prepared by electrospinning, strengthened by thermal-mechanical annealing and then converted to cellulose nanofiber mats. Subsequent surface modification transformed the membranes into ion-exchange membranes. Poly(acrylic acid) (PAA) was grafted to the surfaces of individual nanofibers that had been modified with poly(glycidyl methacrylate). Permeabilities and cadmium ion-exchange capacities were measured for membranes prepared using different molecular weights of PAA that were grafted from different solvents. Membrane permeabilities were found to depend strongly on PAA molecular weight as a result of chain swelling in water; whereas, Cd ion-exchange capacities were independent of PAA molecular weight. Solvents used for PAA grafting were found to be a primary factor for achieving high Cd binding capacities, which increased with increasing solvent quality. Uptake isotherms at constant pH were well described by the Langmuir model, with maximum capacities that exceeded 160 mg/g, comparable to traditional ion-exchange media. Competitive sorption measurements using representative concentrations of sodium and calcium ions were used to illustrate the selectivity of the membranes for Cd ions and demonstrate their potential for commercial application.