This project will investigate factors that control the structural distortions necessary to alter the surface acidity of mesoporous oxides and exfoliated nanosheets to intelligently tailor the reactivity of these materials which have the potential to serve as catalysts, proton conductors, and building blocks for novel nanostructured materials. The goal is to measure the correlation between the metal oxide local structure and the observed surface properties of these materials. To develop this correlation, solid-state Nuclear Magnetic Resonance (NMR) methodologies are employed using the NMR active isotopes of early transition metals, titanium-47, 49 and niobium-93, as the focal point. Information based on the electric field gradient sensed by a quadrupolar nucleus and the chemical shift anisotropy, both created by the arrangement and bonding of atoms surrounding the metal, is used to determine the local symmetry of the metal-centered polyhedra. Double resonance NMR methods correlate the metal atoms with adjacent elements present in adsorbed species to distinguish surface sites and probe the interaction strengths of the surface sites. The project will introduce and train undergraduate and graduate students in the issues and methods associated with materials science research. The P.I is developing materials science curricula, both courses and labs, to increase the exposure of materials chemistry in the undergraduate and graduate programs at Clark University through the establishment of upper-level courses in solid-state chemistry, diffraction, and the incorporation of solid-state chemistry lab modules in introductory chemistry.
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Detailed information about the structure and surface of high surface area materials, such as mesoporous oxides and exfoliated nanosheets, is necessary to improve their performance as catalysts, proton conductors, and building blocks for novel nanostructured materials. The aim of this project is to characterize the correlation between the metal oxide local structures and the observed surface properties of high surface area exfoliated or mesoporous oxides through solid-state NMR methods that probe the niobium and titanium environments in these materials. These results will serve as a guide for optimization of reactive surface structures in high surface area nanomaterials. The project will introduce and train undergraduate and graduate students in the issues and methods associated with materials science research. The P.I. is developing materials science curricula, both courses and labs, to increase the exposure of materials chemistry in the undergraduate and graduate programs at Clark University through the establishment of upper-level courses in solid-state chemistry, diffraction, and the incorporation of solid-state chemistry lab modules in introductory chemistry. The P.I. is working with the Academic Advancement Office of Clark University to mentor ALANA (African American, Latino, Asian and Native American) and first generation students on the research opportunities available and the requirements of careers in chemistry.
As an element selective method, solid-state nuclear magnetic resonance (NMR) has great potential to examine the local structure of specific probe atoms in a material to monitor variations as the composition and morphology of the material is altered. Our efforts centered on using the niobium present in high surface area complex niobium oxides to determine how changes in the composition and structure achieved through acid exchange and exfoliation methods altered the local structure of the materials. Through observation of structurally dependent interaction tensors of the niobium-93 isotope and through correlation experiments spatially linking niobium with other elements in close proximity such as hydrogen, spectroscopic signatures for different niobium structural environments such as surface versus interior sites were determined in layered and exfoliated materials such as Dion-Jacobson layered niobates. These structural signatures were further confirmed and described using density functional theory (DFT) based quantum mechanical calculations. The combined solid-state NMR and DFT approaches in conjunction with the experimentally observed signatures have applications to other complex niobium oxide systems to understand structure-property relationships in these materials. The grant was used to support the research of three graduate students and seven undergraduate students. The undergraduate researchers were trained in a variety of high temperature solid-state synthetic methods and in x-ray powder diffraction characterization techniques. Three of the undergraduates trained were from underrepresented groups in science. Solid-state chemistry experiments based on sol-gel chemistry were introduced to first-year chemistry laboratories to encourage early exposure to materials science. Sessions with incoming undergraduate students from groups underrepresented in science were presented each year to introduce them to the challenges of laboratory science and expose them to materials science.
