Graphene Oxide Quantum Dot Enhanced Nanofiltration Membranes for Water Purification

Graphene Oxide Quantum Dot Enhanced Nanofiltration Membranes for Water Purification

Nanofiltration membranes are used in many separation processes including food processing, drug synthesis, and water desalination. These membranes selectively exclude particles through size exclusion through the pores and electrostatic repulsion via the charged surface of the membrane. This research seeks to enhance the transport and antifouling properties of these membranes by modifying them with graphene. Graphene is a single hexagonal lattice of sp2 hybridized carbon atoms which has many desirable mechanical, optical, and electrical properties. Graphene quantum dots (GQDs), are small (less than 30nm) sectors of graphene which have carboxylic groups all around their periphery. GQDs can be attached to the surface of a nanofiltration membrane through EDC/NHS coupling, The aim of this research is to utilize the abundance of these electron dense carboxylic groups to add a negative charge to the surface of a Nanofiltration membrane. Our experiments developed a method for aminating the surface of a nanofiltration membrane and then attaching GQDs to this surface. Decrease in zeta potential and increased contact angle (gain of approx 15°) indicated that GQDs were attached to the surface of the membrane. This method was unsuccessful, however, in completely coating the surface, and future work will go toward a method that results in higher loading of GQDs to the surface of the membrane.

The next study seeks to create a selective membrane using the layers between graphene particles. This is done by depositing a layer of Graphene Oxide (GO) or GQDs onto a microfiltration membrane (PS35) then reducing the GO to inhibit dispersion into water. This membrane will be used as a support to a nanofiltration membrane under the active layer. The water flux, salt rejection, and mechanical strength of this type of membrane was tested and compared to Nanofiltration membranes.