Fabrication of single to few layered graphene oxide membranes with tunable nanopores for separation of biomolecules

Abstract

The advent of 2 dimensional (2 D) materials opened new avenues in realizing an ideal membrane which has ultrathin thickness while not limiting the selectivity. Graphene oxide (GO) due to its water solubility and functionality has attracted a lot of attention for membrane application. However, the synthesis of an infallible and high performing membrane is still limited by thickness of GO membranes which leads to a loss of capacity of the membrane. In addition to this, tunable pores on GO is desired for its real-world application in various separation methodologies. Another challenge is developing single to few layered GO is the grain boundary defects which provide uncontrolled pathway for transport of molecules thereby limiting the selectivity. Alternative separation techniques are desired in the downstream of biotechnology industry due to the massive cost that they incur. Membrane technologies can offer a relatively non expensive alternative but the major problem with achieving the above targets is present use membrane with large pore size variation (log normal pore distribution of present polymeric membranes) will not give us adequate control over the process which is of prime importance as a regulatory standard as well as to produce desired product in biotechnology industry. Moreover, there is very limited literature on GO based membranes being used for protein separation. Identifying the gap in literature gave us an impetus to work towards finding solutions for the aforementioned problems leading to amalgamation of 2 D material (GO) based membranes, and separations in biotechnology industry to outline my thesis. In this work, a new methodology (sequential deposition) is developed in order to fabricate single layered GO membrane with the vision of providing requisite selectivity without losing its inherent property of being one atom thick. With the objective of controlling and developing tunable transport pathways, oxygen plasma is employed for different intervals of time resulting in tunable pores on the surface of GO. We have also demonstrated rejection mechanism of different model proteins (BSA, Lysozyme & IgG) and mixed protein separation efficiency for similar sized molecules (Myoglobin and Lysozyme) with separation factor of ~6 & purity of 92% through the as synthesized GO membrane. These findings enhance the understanding of the synthesis of single layer GO membrane on polymeric support along with opening new avenues for fabrication of tunable GO membrane and its applications in biotechnology industry.