Abstract
Cellulose-based membrane materials allow for separations in both aqueous solutions and organic solvents. The addition of nanocomposites into cellulose structure is facilitated through steric interaction and strong hydrogen bonding with the hydroxy groups present within cellulose. An ionic liquid, 1-ethyl-3-methylimidazolium acetate, was used as a solvent for microcrystalline cellulose to incorporate graphene oxide quantum dots into cellulose membranes. In this work, other composite materials such as, iron oxide nanoparticles, polyacrylic acid, and lignin sulfonate have all been uniformly incorporated into cellulose membranes utilizing ionic liquid cosolvents. Integration of iron into cellulose membranes resulted in high selectivity (>99%) of neutral red and methylene blue model dyes separation over salts with a high permeability of 17 LMH/bar. With non-aqueous (alcohol) solvent, iron–cellulose composite membranes become less selective and more permeable, suggesting the interaction of iron ions cellulose OH groups plays a major role in pore structure. Polyacrylic acid was integrated into cellulose membranes to add pH responsive behavior and capacity for metal ion capture. Calcium capture of 55 mg Ca2+/g membrane was observed for PAA-cellulose membranes. Lignin sulfonate was also incorporated into cellulose membranes to add strong negative charge and a steric barrier to enhance antifouling behavior. Lignin sulfonate was also functionalized on the commercial DOW NF270 nanofiltration membranes via esterification of hydroxy groups with carboxyl group present on the membrane surface. Antifouling behavior was observed for both lignin-cellulose composite and commercial membranes functionalized with lignin. Up to 90% recovery of water flux after repeated cycles of fouling was observed for both types of lignin functionalized membranes while flux recovery of up to 60% was observed for unmodified membranes.
Highlights
Cellulose is the most abundant biopolymer on the earth
Permeability of all composite membrane was shown to be improved over unmodified cellulose membranes
This study has shown 1-ethyl-3-methyl imidazolium acetate ionic liquid can be utilized as a cosolvent to integrate iron, polyacrylic acid (PAA), or lignin sulfonate with cellulose membrane
Summary
Cellulose is the most abundant biopolymer on the earth. The structural significance of cellulose toward life on Earth is profound, as it makes up most of the cell wall in plants, providing structural support. Membranes utilizing ionic liquid as a solvent have been shown to perform in the ultrafiltration or nanofiltration regimes This same ionic liquid approach was used to spin cellulose hollow fibers [12]. Cellulose is a interesting polymer for the integration of composite materials through hydrogen bonding via the hydroxy groups, which aid steric entanglement in nanocomposite retention. Incorporation of graphene quantum dots into cellulose via ionic liquid was demonstrated to add negative charge and improve the selectivity of model dyes [16]. The objective in this work was to further expand on our previous research studying cellulose graphene oxide quantum dots (GQD) membranes into other composite materials to further improve membrane performance and demonstrate flexibility of this technique for membrane development. Lignin sulfonate was functionalized onto the surface of commercial NF membrane (NF270) to demonstrate antifouling behavior of the functionalized membrane surface through the creation of strong acid sulfonate groups on the surface
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