Date of Award
Doctor of Philosophy
Bamin Khomami, Ramakrishnan Kalyanaraman, Robert Counce
Tailoring the heteronanostructures of nanoscale materials to tune their structure-property relations for desirable interfacial energetics is imperative for their catalytic, optoelectronic and electrochemical applications. Current PhD thesis develops a facile, yet “green” synthesis route that uses laser ablation synthesis in solution in tandem with galvanic replacement reaction (tandem LASiS-GRR) as a one-pot, one-step technique for manufacturing diverse and complex heteronanostructures of metal oxides, hydroxides, nanocomposites (NCs), and nanoalloys (NAs). The scientific concept here is that the non-equilibrium thermodynamics and kinetics of high-energy LASiS-GRR can be tuned by laser parameters and solvent chemistry to form complex NCs/NAs of tailored sizes/shapes, metastable structures and compositions.
The results indicate that the presence or absence of solution-phase oxygen (O2) during LASiS on bulk Cobalt (Co) produces cobalt monoxide (CoO) or, single crystal beta-cobalt hydroxide (β-cobalt hydroxide), nanoparticles (NPs) respectively as the metastable states. These intermediates finally transform into cobaltosic oxide (Co3O4) NPs, along with the formation of Co3O4 nanorods with enhanced localized surface plasmon resonance (LSPR) at high pH. In contrast, LASiS-GRR on Co in Potassium tetrachloride palatinate (K2PtCl4) salt solution produces NCs of PtCo NAs embedded in cobalt oxide (CoOx) matrices (i.e., PtCo/CoOx). These NCs exhibit outstanding bifunctional electrocatalytic activities for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) along with better stability, which are attributed to the shrunken lattice constants of alloyed PtCo that promote oxygen adsorption, and synergic “spillover” effects from high surface area CoOx matrices that promote symbiotic adsorption/desorption of intermediate species. Subsequent acid wash of the aforementioned PtCo/CoOx NCs results in spherical PtCo NAs with tunable sizes, compositions and degrees of alloying. These NAs exhibit uniformly alloyed core encapsulated in few nanometers of Pt-rich shell. Such core-shell NA structures along with high degrees of alloying promote their outstanding electrocatalytic ORR activities in acid electrolytes. Finally, preliminary results for LASiS-GRR on bulk zinc/titanium (Zn/Ti) in silver nitrate (AgNO3) salt solution indicate the formation of plasmonic Ag NPs embedded in zinc oxide (ZnO) or titania (TiO2) matrices, with the majority of Ag NPs covered by spherical TiO2 that are anti-corrosive in acid.
Hu, Sheng, "Tandem Laser Ablation Synthesis in Solution-Galvanic Replacement Reaction (LASiS-GRR): A facile route for the synthesis of complex intermetallic nanomaterials with engineered functionalities. " PhD diss., University of Tennessee, 2016.