Tailored Molecular Transport In Low-Dimensional Hybrid Materials From 1D Nanocrystals And 2D Nanosheets

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Many important applications in fine chemistry, pharmaceutical research, and other sophisticated purification processes rely on separation processes that effectively separate molecules from solutions and suspension. Current amorphous polymer- or paper-based membranes have random morphologies, poorly controlled porosities, and lack mechanical strength. Balancing the membrane’s permeance and selectivity performance using these materials is also challenging. These combined factors limit the utility of amorphous polymer- and paper-based membranes for fast and effective molecular separations in high-pressure applications. The random morphology of porous polymeric materials with varied pore sizes, shapes, and surface chemistries makes it difficult to rationally design molecular transport properties. Therefore, this project will examine the molecular transport phenomena and materials properties of membranes with long-range ordered low-dimensional structural elements to advance fundamental knowledge and develop new membranes using fibrous and two-dimensional materials. Additionally, this research project will provide graduate and undergraduate students from diverse backgrounds with interdisciplinary research training opportunities, helping prepare them for careers in industry. Undergraduate students at Georgia Tech will also benefit from the investigator’s soft nanomaterials curriculum development efforts.The ultimate research goal of this project is to understand the principles of directional, spatial, and scale-dependent molecular transport in highly organized one- and two-dimensional (1D and 2D) nanostructures with ordered nanochannels and nanosheets as well as fast and enantiotropic selectivity. Such media can potentially be used in membrane-based separations of ions, organic molecules, and even chiral species within the intermediate region at the transition from the nanofiltration and ultrafiltration regimes. The research will explore factors such as the materials’ organized porosity, pore shapes and orientation (channel-like or slit-like), narrow size distribution, and potential chiral-biased interactions to tailor molecular transport and membrane separation performance. The first research objective is synthesizing nanocrystals and nanosheets and modifying the materials’ surfaces to tailor their organization, surface chemistries, and inter-structural interactions, achieving ordered morphologies with controlled pore organization. The second objective is fabricating robust ultrathin membranes with organized helicoidal and stacked structures. The membranes will be fabricated using chemically modified needle-like (1D) cellulose nanocrystals and 2D titanium carbide nanosheets with chiral nematic organization and tailored porosity shape and orientation, pitch length, and local chirality. The performance will be assessed using a set of common dyes in solution. The third objective is to characterize the organized low-dimensional materials' internal nanoscale organization, porosity, orientation, and mechanical performance. This information can be applied to control local and global molecular-nanoscale transport through shortened tortuosity, directional channels, and chiral bias and, thus, for studying the transport of select metal ions, dyes, and chiral molecules. The project will yield a deep fundamental understanding of the complex transport phenomena in organized multiphase membranes with long-range organized nanocrystal and nanosheet assemblies; such knowledge is essential to the design of mechanically robust molecular separation membranes with high permeance, selectivity, and rejection rate.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.