Shaping the Synthesis and Assembly of Metal Nanostructures

Inorganic crystals with nanoscale dimensions are emerging as important building blocks for multifunctional device fabrication. The properties of metal nanocrystals depend on physical parameters that include crystallite size, shape, composition, and architecture and tremendous achievements have been made regarding the colloidal synthesis of structurally well-defined nanocrystals. Even with these advances, fundamental questions about nanocrystal formation remain and many materials have yet to be synthesized as high-quality nanoscale samples. Our research aims to demonstrate new synthetic strategies to nanomaterials and study both their emergent properties and the processes that account for their formation.

Although the synthesis of structurally-defined monometallic nanocrystals is well demonstrated, there are far fewer examples of bimetallic nanostructures being achieved with defined properties. This discrepancy arises from the challenges in nucleating a defined bimetallic phase via co-reduction methods, and the Skrabalak Laboratory is addressing this challenge by demonstrating new synthetic strategies to bimetallic nanostructures that include seed-mediated co-reduction and ligand-controlled co-reduction. These strategies have facilitated the synthesis of symmetrically branched, dendritic, shape-controlled alloyed, concave core@shell, and core@shell nanostructures in model systems. New synthetic strategies are currently being explored and the synthetic versatility of these methods is being tested. As new bimetallic nanostructures are achieved, we also study their fundamental properties as they are applied to catalysis and chemical sensing.

Interaction of light with matter is one of the oldest and most fascinating topics in science, and new light-matter interactions are being explored that could lead to technologies for solving global problems from sustainable energy to population aging and disease. Toward the goal of designing new metallo-dielectric materials that combine the optical properties of dielectrics and of nanoscale metal particles, we are studying how shape and composition influence the optical properties of bimetallic nanocrystals via correlated single particle spectroscopy-electron microscopy analysis in collaboration with the Dragnea Laboratory (IU). These nanostructures will self-assemble into metallo-dielectric superstructures via control of building block morphology and site selective surface chemistry and to enable characterization of the collective, system-level optical properties that emerge from specific nanocrystal arrangements.

Complex interplay between growth kinetics and thermodynamics account for the shape and architecture adopted by nanocrystals prepared via colloidal methods. Unfortunately, decoupling these parameters is challenging experimentally, and as a result, nanomaterial synthesis is often a qualitative practice. To address this critique and provide a quantitative framework for morphology development in nanomaterial synthesis, the Skrabalak Laboratory is using synchrotron X-ray scattering techniques to measure nanocrystal growth kinetics and aggregation processes in real-time, in solution-phase.

Spraying the Way to Shape- and Architecturally-Controlled Nanomaterials

As the utility of nanomaterials is further demonstrated, it will be necessary to develop scalable routes to such materials and address the critical need for nanomanufacturing methods. Aerosol methods are an industrial favorite for the continuous production and processing of compositionally complex inorganic solids. However, only recently have aerosol methods been applied to the synthesis of shape and architecturally-controlled nanomaterials. Our research aims to achieve structurally well-defined nanomaterials by integrating new chemical methods into ultrasonic spray pyrolysis, an aerosol synthetic technique that uses ultrasound for nebulization. Our synthetic results are correlated with the decomposition behavior of the selected precursors to provide insight into structure formation and guide the rational design of new nanostructures. These methods are currently being applied to the synthesis of shape-controlled nanocrystals for photocatalytic applications and nanoporous microspheres for utility in affinity chromatography.

New Materials for Photocatalysis

Solar energy conversion represents the most viable means of sustainably producing 13 TW (consistent with global human demand). Photocatalytic water-splitting represents one way of using solar energy to convert a low value substance (water) into a useable fuel (hydrogen), with minimized environmental and political consequences. Spray pyrolysis provides access to the compositionally-complex materials that typify most modern photocatalysts. We are currently using this synthetic technique to enhance the photocatalytic performance of valence band modified metal oxides and to study the shape-dependent photocatalytic properties of metal oxides. Advances in photocatalytic materials for solar water splitting can be directly applied to environmental remediation projects.

Nanoporous Microspheres for Advanced Separations

Research efforts have long been directed toward the development of new, high-resolution and ultra-sensitive bioanalytical separation techniques. Via aerosol-assisted self-assembly, we have achieved macroporous microspheres that maintain a high surface area which is ideal for chromatographic separations of complex biological mixtures. In collaboration with the Novotny Laboratory (Indiana University), we are currently evaluating our platform for lectin affinity enrichment of glycoproteins, as altered glycosylation is linked to cancer, inflammatory, and degenerative diseases.

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