Confinement effects within metal organic nanotubes: Relationships between hydrophobicity and water structure, diffusion, and selectivity

PART 1: NON-TECHNICAL SUMMARY

Water confined in nanosized channels can behave in unexpected ways and controlling this behavior could lead to the development of new materials for water purification applications. The identity of the chemical components that line the interior wall of these nanochannels may be the crucial design principle that can be used to create new materials with controllable water properties. The overall hypothesis for this project is that the identity and placement of the chemical components that make up the channel wall are key to controlling water confined within these spaces. Metal organic nanotubes (MONTs) are used to test this hypothesis because they contain one-dimensional channels, have tunable channel walls, and exhibit stability in water. Within this project, supported by the Solid State and Materials Chemistry program within the Division of Materials Research, MONTs are designed with chemical components that will either attract or repel the water molecules in specific locations along the interior wall. Then the behavior of the confined water within these new materials is explored by identifying how the confined water molecules are organized within the channel, measuring the rate of water movement through the channels, and testing the ability of the MONTs to selectively take up water over other molecules. Gaining this fundamental knowledge of confined water is important for creating advanced materials for water purification and treatment. Additional educational initiatives for this project include training in resiliency and overcoming failure to improve retention of students in science. This includes curriculum development at both the undergraduate and graduate level that will be freely disseminated to others in the field. These efforts will also include assessment and evaluation of best practices to further our understanding of the role of resiliency training in improving STEM retention.

PART 2: TECHNICAL SUMMARY

Predicting and controlling the behavior of nanoconfined water is important for the development of advanced applications, but structurally engineering these desired effects are dependent on the complexity of the pore walls. Metal organic nanotubes (MONTs) are optimal for probing the relationships between structural features and nanoconfinement effects due to their 1-D pore structure, tunable structural features, and relative stability in water. The overall hypothesis for this project is that increasing the hydrophobicity of the pore wall will lead to more structural ordering of the water and faster diffusion of water through the nanotube. Furthermore, combining hydrophilic and hydrophobic regions within the walls will lead to chemical selectivity of the nanopore to water. Within this project, MONTs are used to test the central hypotheses through 1) identifying clusters topologies within nanochannels and relating water structure with hydrophobicity; 2) delineating the relationship between variability hydrophobicity and water diffusion rates; and 3) determining how spatial variability of hydrophobic regions impacts water selectivity. The proposed research is expected to contribute to our fundamental understanding of the behavior of nanoconfined water in complex materials. With this systematic understanding, these ideas are translatable to the behavior and modification of other materials and may have far-reaching effects on our fundamental understanding of nanoconfined water, which is of interest to researchers in the fields of material science, chemistry, geology, engineering, and biology. Education initiatives will include specific training in resiliency and overcoming failure to improve retention of underrepresented groups in science. This includes curriculum development at both the undergraduate and graduate level that will be freely disseminated to the field to reach a broader audience. These efforts will also include assessment and evaluation of best practices to further our understanding of the role of resiliency training in improving STEM retention. This project is supported by the Solid State and Materials Chemistry program in the Division of Materials Research.

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.