This contribution describes the development, performance evaluation and modeling of polyelectrolyte-modified nanofiber membranes for heavy metal recovery from impaired water. High-capacity membranes were prepared by grafting poly(acrylic acid) (PAA) and poly(itaconic acid) (PIA) to cellulose nanofiber mats. The success of polymer grafting was confirmed by attenuated total reflectance Fourier-transform infrared spectroscopy. Membrane permeabilities for a series of polymer grafted nanofiber membranes were measured by direct-flow filtration. Single-component ion-exchange isotherms were measured at constant pH for cadmium, nickel, and calcium ions. The higher metal-polymer complex stability of Cd-PIA over Cd-PAA was found to be an impact factor for achieving high Cd binding capacities. Single-component ionexchange isotherms were well described by the Langmuir model, with maximum capacities of PIA-modified membranes that exceeded 220 mg Cd/g, comparable to traditional resin-based ionexchange media. Moreover, membranes were selective for Cd over Ni and Ca because of different hydration energies and ionization potentials. Competitive ion-exchange measurements were made using environmentally relevant concentrations of these ions to determine the selectivity of the membranes for cadmium ion. Experimental isotherms for Cd-Ca and Cd-Ni were compared to model predictions from the competitive Langmuir model with Langmuir
An evaluation of the performance of polyelectrolyte-modified nanofiber membranes was undertaken to determine their efficacy in the rapid uptake and recovery of heavy metals from impaired waters. The membranes were prepared by grafting poly(acrylic acid) (PAA) and poly(itaconic acid) (PIA) to cellulose nanofiber mats. Performance measurements quantified the dynamic ion-exchange capacity for cadmium (Cd), productivity, and recovery of Cd(II) from the membranes by regeneration. The dynamic binding capacities of Cd(II) on both types of nanofiber membrane were independent of the linear flow velocity, with a residence time of as low as 2 s. Analysis of breakthrough curves indicated that the mass flow rate increased rapidly at constant applied pressure after membranes approached equilibrium load capacity for Cd(II), apparently due to a collapse of the polymer chains on the membrane surface, leading to an increased porosity. This mechanism is supported by hydrodynamic radius (Rh) measurements for PAA and PIA obtained from dynamic light scattering, which show that Rh values decrease upon Cd(II) binding. Volumetric productivity was high for the nanofiber membranes, and reached 0.55 mg Cd/g/min. The use of ethylenediaminetetraacetic acid as regeneration reagent was effective in fully recovering Cd(II) from the membranes. Ion-exchange capacities were constant over five cycles of binding-regeneration.
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