Tailoring the Composition, Morphology and Assembly of MXene Nanosheets

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MXenes are a recently discovered fascinating class of 2-D transition metal (M) - carbon (X) nanosheets that hold promise to advance the national prosperity and defense in numerous areas associated with advanced energy, electronics, and defense applications. This grant advances the processing of MXene nanostructures with different compositions and morphologies and their assembly into functional nanofilms. The grant will address the major research challenges associated with the production of MXenes and develop the processing techniques to form these into usable films as well as determine the resultant process-property relationships. A variety of MXenes are theoretically possible, but have yet to be experimentally obtained. MXenes exist as 2D sheets and extending their lateral dimension from nano-to-macro size remains challenging. This project will develop processing methodologies for producing MXenes with compositions and functional groups that have previously been impossible. The planned incorporation of these interesting materials into polymer composites would allow their integration into many coating technologies. The control over the material properties through manipulation of composition, shape, structure, and multi-layer architectures will allow an expansion of the range of their physical properties. The researchers and students will engage in multiple outreach efforts to foster education, research, diversity, and representation in materials science at the graduate, undergraduate, and K-12 levels, with the special focus on developing students entrepreneurship skills. The major current limitations in both MXene synthesis and processing and the underlying process-structure-property relationships at both the nano or individual nanosheet level and the macroscopic films and composites level will be investigated. These materials are derived from layered ceramics (i.e., MAX phases) and have a wide range of possible compositions and functional groups. The "MX" name refers to the M (transition metal) and X (typically carbon) in these layered structures; a common example includes Ti3C2Tx, where T stands for various terminal groups. The specific research tasks include the following: (1) The compositional space of existing MXenes will be extended by altering the composition of the parent MAX phase to achieve easy etching of A layers and by applying an electrochemical bias; (2) Capillary forces during spray drying will manipulate MXene morphology and create shelf-stable 3-D MXene particles; and (3) Properties and performance of macroscopic MXene-polymer structures created using layer-by-layer assembly as a function of MXene interlayer spacing and morphology will be determined. At each stage, MXene composition, functional groups, and architecture will be connected to the bulk mechanical and electrical properties.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.