Molecular Modeling of Nanostructures, Polymer Electrolytes, and Ionic Liquids for Energy, Environmental, and Catalysis Applications

This thesis centers around the structural, electronic, and physicochemical properties of some nanostructures, polymer electrolytes, and ionic liquids for energy, environmental, and catalysis applications. A variety of theoretical tools are employed to enable predictive
study, design, and development of the systems. Theoretical concepts are developed for rational explanation of reaction mechanism, surface activity, ionic conductivity, formation,
and fragmentation of the materials with respect to structure-activity and structure selectivity correlations. The outline of this thesis is as follows: First, the structural stability of isoreticular metal organic frameworks (IRMOFs) confining ionic liquids (ILs) inside their nano-porous cavities is studied. It is shown the IRMOFs are structurally unstable and deforms dramatically from its crystal structure in the
presence of ILs. Simulation results also show that metallic parts of IRMOF-1 mainly interact with anions. These results raise an important question if IL/IRMOF composites are
good candidates for gas storage or separation. Second, interactions of the lithium bis(trifluoromethane sulfonyl)imide (LiTf2N) salt with polyethers are investigated to shed light on the origin of difference in ionic conductivity of the two electrolytes: (1) polyethyleneoxide (PEO) and (2)
perfluoropolyether (PFPE). Results indicate that substitution of hydrogens by fluorines leads to less interaction of cation Li+ with the polymers, which provide an atomistic
understanding of experimental ionic conductivity results.
Third, Au25(SR)18 nanoclusters with atomic precision is served as a model system to scrutinize structure-reactivity correlation of thiolate protected gold nanoclusters. In particular, the promotional catalytic effect by imidazolium-based ILs, transition metal ions, and aromatic thiolate ligands are studied. Results show the ILs and the ions can
significantly enhance activation of the nanoclusters at relatively low temperatures via partial removal of “Au-SR” units from Au25 cluster. Further, guidelines are offered for
tailoring nanoclusters’ properties by ligand engineering for specific applications. Fourth, controllable incorporation of a single dopant metal to specific sites of gold nanoparticle is studied. A centrally hollow, Au24 nanoparticle is used to investigate single atom shuttling in/out of the nanoparticle. Using Ag and Cu as the tracers, the pathways of
single atom shuttling are mapped out. The results not only demonstrate single-atom level doping via hollow nanoparticles, but also reveal the intriguing atom shuttling behavior. Finally, mechanistic insights into promotional effects of ionic liquids on transesterification of cellulose is provides. Results explains IL anions play the most crucial
role to facilitate the reaction. This study provides molecular insights for experimentalists to optimize reaction conditions of protocols of cellulose modifications using ILs. I believe a key element to research is collaborating with chemists in other fields, as complex problems require input from many chemists with different specialties. I have had the
opportunity to collaborate closely with experimental groups at Carnegie Mellon University (Prof. Rongchao Jin), Anhui University (Prof. Zhu), Dalian Institute of Chemical Physics (Prof. Gao Li), and Kanazawa University (Prof. Kenji Takahashi) to develop the third-to-fifth projects mentioned above. Our collaborative works require clearly communicating the intrinsic principles behind the complex results. This involve regular exchanges of different viewpoints
to establish guidelines for the development of materials with desired performance. This thesis emphasizes on the computational contribution to the projects.