Fundamental Understanding of Ultrathin, Highly Stable Self-Assembled Liquid Crystalline Graphene Oxide Membranes Leading to Precise Molecular Sieving through Non-equilibrium Molecular Dynamics

Abstract

Self-assembled graphene oxide lyotropic liquid crystal (GO LLC) structures are mostly formed in aqueous medium; however, most GO derivatives are water insoluble, so processing GO LLCs in water poses a practical limitation. The use of polar aprotic solvent (like dimethyl sulfoxide) for the formation of GO LLC structures would be interesting, because it would allow incorporating additives, like photoinitiators or cross-linkers, or blending with polymers that are insoluble in water, which hence would expand its scope. The well-balanced electrostatic interaction between DMSO and GO can promote and stabilize the GO nanosheets’ alignment even at lower concentrations. With this in mind, herein we report mechanically robust, chlorine-tolerant, self-assembled nanostructured GO membranes for precise molecular sieving. Small-angle X-ray scattering and polarized optical microscopy confirmed the alignment of the modified GO nanosheets in polar aprotic solvent, and the LLC structure was effectively preserved even after cross-linking under UV light. We found that the modified GO membranes exhibited considerably improved salt rejection for monovalent ions (99%) and water flux (120 LMH) as compared to the shear-aligned GO membrane, which is well supported by forward osmosis simulation studies. Additionally, our simulation studies indicated that water molecules traveled a longer path while permeating through the GO membrane compared to the GO LLC membrane. Consequently, salt ions permeate slowly across the GO LLC membrane, yielding higher salt rejection than the GO membrane. This begins to suggest strong electrostatic repulsion with the salt ions, causing higher salt rejection in the GO LLC membrane. We foresee that the ordered cross-linked GO sheets contributed to excellent mechanical stability under a high-pressure, cross-flow, chlorine environment. Overall, these membranes are easily scalable, exhibit good mechanical stability, and represent a breakthrough for the potential use of polymerized GO LLC membranes in practical water remediation applications.

Graphene oxide offers precise molecular sieving, structural integrity, microplastic removal, and closed-loop circularity in water-remediating membranes through a covalent adaptable network

“…25 The deconvolution of the 1s O spectra revealed peaks at 530.63, 532.13, and 533.63 eV, providing additional evidence for the presence of CO, C–O, and C–O–C bonds on the membrane surface. 4 Finally, the m-IPN membrane exhibited a prominent presence of 1s F, which originated from the PVDF component. This observation further confirmed the presence of –C–F bonds in the membrane structure.…”

“…1–3 To remediate this crisis, steps should be taken as a priority to come up with sustainable solutions of water purification, even from non-conventional sources. Membrane separations, although they fit all the criteria mentioned above , 4 suffer heavily from fouling and scaling issues which greatly impair basic membrane performance. 5 In general, PVDF is the most widely used polymer for the fabrication of membranes owing to its chemical inertness, significantly high mechanical strength, robustness, thermal integrity and stability, as well as aging resistance.…”

Tuning the surface charge and pore size of IPNs arrests covalent organic nanostructures through in situ exchangeable bonds for the removal of persistent contaminants

“…1 Improper and inadequate sanitation has exposed nearly 2.4 billion people to the aftermath of waterborne diseases. 2–4 According to official statistical records, nearly two million children die every year from diarrheal diseases alone. With the ever-increasing global population and expanding anthropogenic activities, the universal demand for freshwater has increased manifold, thus exacerbating the scarcity of this fundamental resource.…”

“…From this perspective, the importance of adopting measures for sustainable water treatment has reached a climax. 4,5…”