Nanoparticle Ligand Chemistry and Control of Surface Ensemble Geometry
We are interested in inorganic nanoparticle ligands, specifically metal halides, metal oxides, and metal chalcogenides that can be utilized for catalytic applications. These ligands are capable of supporting colloidally stable particles in high dielectric solvents, and we have developed several colloidal ligand-exchange methods to generate core-shell structures with tunable electronic and geometric properties based on the interaction between the nanoparticle core and surface ligand.
We have utilized metal halide ligands to generate Au@Pd and Au@Pt nanoparticles for electrocatalytic oxygen reduction and formic acid oxidation (JACS 2018, ACS Appl. Mater. Interfaces 2019) as well as bifunctional Pt nanoparticles coated with a thin layer of metal oxides for CO oxidation (Polyhedron 2019). We are also using anionic metal chalcogenides complexes as ligands, which serve as precursors to oligomeric structures that resemble the active sites in amorphous MoS2 on a molecular level. This project has been carried out in collaboration with Prof. Jeff Greeley’s group in chemical engineering, who has worked with us to computationally model how MoS4 interacts with our nanoparticle surfaces (ACS Catal. 2020). While a variety of ligands and cores are utilized in the above projects, we ask the same key question in every case: how can we use the interaction between the nanoparticle core and the surface ligand to enhance the catalytic properties of the material?
Control of the active site geometry at the active surface of a nanoparticle is also critical toward controlling chemo- and stereoselectivity of heterogeneous reactions. We have developed several Pd and Pt alloy systems with well-defined surface ensemble geometries targeted toward selective and stable alkane dehydrogenation (ACS Catal. 2020) as well as diastereoselective hydroxyl-directed hydrogenation of organic substrates.
Doping of Colloidal 2D Materials
Another major effort in our group focuses on solution-phase doping of two-dimensional metal hydroxide and metal chalcogenide materials. We developed a chemical method to activate sulfide binding sites on the basal plane of colloidal WS2 nanosheets in order to functionalize the surface with Ni ions for oxygen evolution electrocatalysis (ACS Nano 2020). We are now expanding this methodology to other transition metal and post-transition metal dopants and additional electrocatalytic reactions. In a similar vein, we have utilized strong chemical reductants to electron-dope metal hydroxide nanosheets in order to tune their electronic and conductivity properties. We have focused on understanding how the layered structure of the metal hydroxide material enables stable electron storage (Nano Lett. 2020, Inorg. Chem. 2021) and plan to expand these methods towards transparent conducting oxides and electrochromic materials.
