[Lecture] Polyoxometalate complexes of metal-oxide cores


Title: Polyoxometalate complexes of metal-oxide cores
Speaker: Prof. Ira A. Weinstock, Ben-Gurion University of the Negev
Venue: Room 324, Building No.2, National Science Park, North Area, Wushan Campus
Time: January 10, Friday, 10:00

Prof. Ira A. Weinstock is currently the Irene Evans Professor of Inorganic Chemistry in Ben-Gurion University of the Negev. He obtained his Ph.D. in 1990 from the Massachusetts Institute of Technology (MIT), where he worked on alkyne metathesis with Richard R. Schrock. After one year at the Sandia National Laboratory, Albuquerque, New Mexico, he served as Team Leader at the U.S. Department of Agriculture, Madison, Wisconsin, where he initiated the use of polyoxometalates as green catalysts for aerobic oxidations of biomass in water. In 2006, he joined the Ben-Gurion University of the Negev, where his research concerns the use of polyoxometalates in molecular and supramolecular chemistry and nanoscience and more recently as redox-active ligands for metal-oxide nanocrystals.

Building on our use of polyoxometalate (POM) cluster-anions as ligands for gold-nanoparticles, POMs are now covalently attached to reactive metal-oxide nanocrystals (NCs), giving soluble assemblies uniquely positioned between molecular macroanions and solid-state metal oxides. For example, redox-active POMs coordinated to anatase titanium-oxide nanocrystals control H2 formation by rationally tuning rates of visible-light driven electron injection into the TiO2 cores, while soluble POM complexes of a-Fe2O3 serve as oxidatively and hydrolytically stable catalysts for visible-light driven water oxidation. Notably, the aqueous solubility and remarkable stability of these POM-complexed 275 iron-atom hematite cores make it possible to investigate visible-light driven water oxidation at this frontier area using the versatile toolbox of solution-state methods typically reserved for molecular catalysis. These methods reveal a unique mechanism, understood as a general consequence of fundamental differences between reactions of solid-state metal oxides and freely diffusing fragments of the same material.More recently, we prepared anionic POM complexes of 2-nm e-MnO2 cores that, via interactions with alkali-metal cations, M, serve as building blocks for the hierarchical assembly of cubic nanostructures whose sizes increase with M in the order: Li+ < Na+ < K+ < Rb+ < Cs+, and which include water-soluble 200-nm cubes comprised of over 600,000 POM-complexed MnO2 cores. This hierarchical assembly induces a shift of UV-vis absorbance into the visible, resulting in enhanced visible-light semiconductor properties, and leading to the first example of visible-light water oxidation by MnO2 in the absence of added photosensitizers. The alkali-metal cation induced assembly is reversible via dialysis against pure water, giving individual POM-complexed cores.

Announced by the School of Molecular Science and Engineering