Cellulose-graphene quantum dot composite membranes using ionic liquid.

Selective separation of small molecules by membranes is inhibited by the performance gap between nanofiltration and ultrafiltration membranes. In this work, a membrane that can efficiently remove small molecules (> 300 Da) was created by incorporating graphene oxide quantum dots (GQDs) into a cellulose membrane using an ionic liquid (1-ethyl-3-methylimidazolium acetate). Incorporation of GQD into cellulose membranes using an ionic liquid brings several advantages over traditional mixed matrix membranes: 1) GQDs are abundant in peripheral hydroxyl and carboxyl groups, thus GQDs have strong binding with cellulose through hydrogen bonding and forms a stable composite membrane. 2) Negative surface charge of GQDs helps prevent aggregation. 3) The size (5 nm) of GQD is smaller than most nanoparticles used in membranes, allowing for interesting pore forming properties. GQD-cellulose membranes were prepared by non-solvent induced phase separation in water. It was determined that about 45% of GQDs are incorporated from solution to membrane. GQDs were determined to be located on the membrane surface, giving the membrane negative surface charge and improved hydrophilicity. GQDs showed no leaching after convective flow through the membrane. Impact of GQD on membrane permeability and rejection was studied through convective flow experiments, and through longer term permeability studies.