Bioinspired materials composed of atomically-thin nanosheets and their assemblies

• Online Access: http://hdl.handle.net/2047/D20321696

This doctoral thesis details a novel cavitation method of creating nanopores in 2D materials nanosheets (NSs), resulting in a mixture of one-to-two-layer thick porous NSs and nanodisks (NDs). The power of this straightforward, easy scale-up, and low-cost method is that the size of nanopores as well as finite length of NSs can be controlled by simply adjusting the processing times. Next, I decorate such NSNDs using custom-designed cationic and anionic polypeptide adsorbent molecules. The peptides serve two key functions: first, they help with dispersing the NSNDs in water, and second, they modulate the surface charge of the NSNDs by virtue of their charged amino acid residues. Finally, I prepare NSND laminate membranes (LMs) by vacuum filtration of suspensions. These membranes have a multimodal porous network structure with tunable surface charge, pore size, and interlayer spacing. In forward osmosis experiments NSND membranes reject more than 99% of NaCl and other salts at high salinities. Reverse osmosis experiments also showed efficient filtration of small-molecule organic dyes and salts, with ~100-fold higher permeance values than commercial seawater reverse osmosis membranes and a comparable rejection. The membranes also withstand extreme chlorine exposure and demonstrate stable operation for over a month, demonstrating their potential for use in commercial water purification applications. Likewise, chapter 2 of this dissertation introduces solution-process synthesis of graphene quantum dots (GQDs) with tunable size, surface chemistry, and fluorescence properties. In the size regime 15-35 nm, these quantum dots maintain strong visible light fluorescence (mean quantum yield of 0.64) and achieve 6,500 Göppert-Mayer (GM) units two-photon absorption (TPA) cross section, far exceeding values of organic dyes, while being comparable to semiconductor QDs. Next, through non-covalent tailoring with cationic peptides I obtain water-stable quantum dots, and demonstrate the utility of these cationic GQDs in stalling polymerase-based DNA replication by binding to template and/or primer DNA. Finally, chapter 3 of this dissertation explores cell permeability of GQDs into living epithelial cell, the quantum dots do not enter the cell nucleus, by virtue of their mesoscopic size.