In summer 2019, I researched in the synthesis of noble-metal nanocrystals for energy applications through the Research Experience for Undergraduates (REU) Program at Georgia Tech. With Dr. Younan Xia as my advisor, I successfully synthesized high-quality platinum (Pt) nanobars with tunable aspect ratios in collaboration with a graduate student. Using FTIR spectroscopy, I confirmed that carbon monoxide was produced from the decomposition of the solvent at high temperature. This molecule then effectively functioned as a capping agent for Pt {100} facets and facilitated the formation of Pt nanobars. My analyses of transmission electron microscopy (TEM) images enabled me to propose a mechanism to account for the symmetry breaking involved in the formation of Pt nanobars. By the end of the 10-week program, I gathered data for both oral and poster presentations detailing my findings at the research symposia at Georgia Tech and Agnes Scott College, and the 2019 Gulf Coast Undergraduate Research Symposium at Rice University. I am currently in the process of writing the manuscript for publication. Continuing to work in the Xia group during my senior year, I will evaluate the catalytic properties of Pt nanobars for the methanol oxidation reaction. Throughout my research experience in noble-metal nanocrystals, I developed an interest in materials chemistry, with a concentration in nanomaterials synthesis, through which I can address a multitude of environmental challenges. 

Carbon Monoxide-Mediated Synthesis of Pt Nanobars and A Mechanistic Understanding of Their Symmetry Breaking

Nguyen, Quynh N¹, Chen, Ruhui², Xia, Younan^{2, 3} 

1. Department of Chemistry, Agnes Scott College, Decatur, Georgia
2. School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia
3. The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia

Abstract

Despite the notable progress in controlling the shapes of noble-metal nanocrystals, it remains a grand challenge to synthesize nanocrystals with less symmetric structures relative to their cubic lattice. Among the noble-metal nanocrystals taking various shapes with reduced symmetry, Pt nanobars have attracted much interest because of their asymmetric growth during the synthesis and the anisotropic structure as compared to Pt nanocubes. There are only a few reports on the synthesis of Pt nanobars with limitation in controlling aspect ratio and lack of a well-resolved mechanistic understanding of their anisotropic growth. Here we report a facile route to high quality Pt nanobars, in which N,N-dimethylformamide (DMF) was used as a reducing agent in the presence of poly (vinyl pyrrolidone) (PVP) as a stabilizer and a mild reducing agent. The aspect ratio of the Pt nanobars could be tuned by simply varying the amount of Pt precursor. Arising from the decomposition of DMF, CO served as a capping agent on Pt {100} facets, which facilitated the formation of Pt nanobars. The anisotropic growth of Pt nanobars was induced by particle coalescence during the early stage of a synthesis, followed by localized oxidative etching and further preferential growth by atomic addition.

Acknowledgement– This work was supported by a grant from the National Science Foundation REU No. CHE-1560335. TEM imaging was performed at the Georgia Tech’s Institute for Electronics and Nanotechnology, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation No. ECCS-1542174.

Project 2:

Anomalous redox behavior of bis(serinato)copper(II) complex and comparison to closely related bis(homoserinato)copper(II) complex: An update

Nguyen, Quynh N.,¹ Venable, T. Leon ¹

1. Department of Chemistry, Agnes Scott College, Decatur, Georgia 30030, United States

Abstract

Despite being a vital nutrient and having important roles in biological processes, unbound copper ions are toxic when acting as a redox catalyst in the formation of free radicals, which in turn may lead to the oxidation of biologically active molecules. As part of our extended studies on the synthesis and behavior of Cu(aminoacidato)₂ complexes, we have continued to investigate the anomalous redox behavior of the cis-bis(L-serinato)Cu complex, which is readily prepared from the reaction of [Cu(CH₃COO)₂•H₂O]₂  and the appropriate amino acid. This bis(L-serinato)Cu complex is distinctively different from all other known Cu(aminoacidato)₂ complexes in that it undergoes a spontaneous redox reaction upon exposure to atmospheric oxygen to yield reduced Cu(I) in the form of Cu₂O. The identity of the oxidized species in the reaction has been elusive. This unusual redox reaction was determined to be a multi-step process. Under slightly acidic conditions in the presence of atmospheric O₂, a significant shift in λ_max of the bis(L-serinato)Cu solution (from 625 nm to 704 nm) occurred with no evidence of Cu₂O formation. In turn, this solution rapidly reacts with O₂bubbled into the solution to yield the previously described red Cu₂O. From a comparison with bis(L-homoserinato)Cu, the primary OH functional group on L-serine was not shown to be the key to the anomalous behavior of bis(L-serinato)Cu; the attempted oxidation of the closely related trans-bis(L-homoserinato)Cu did not occur under the same conditions. We will also report on attempts to compare the bis(cysteinato)Cu complex, which has a primary thiol group, to the bis(L-serinato)Cu with a primary alcohol group.

Nguyen, Q. N; Venable, T. L.; “Anomalous redox behavior of bis(serinato)copper(II) complex andcomparison to closely related bis(homoserinato)copper(II) complex: An update.” Southeastern Regional Meeting of the American Chemical Society (SERMACS), Savannah, GA, October 2019 (Poster presentation)

Nguyen, Q. N.; Chen, R.; Xia, Y.; “Carbon monoxide-mediated synthesis of Pt nanobars and amechanistic understanding of their symmetry breaking.” Research Experience for Undergraduate (REU) Symposium at Georgia Institute of Technology, Atlanta, GA, July 2019 (Poster and oral presentation)

Nguyen, Q. N.; Caven, C.; Romero, S. C.; Venable, T. L.; “Anomalous redox behavior of bis(serinato)copper(II)complex and comparison to closely related bis(homoserinato)copper(II) complex.” Spring Annual Research Conference (SpARC), Agnes Scott College, Decatur, GA, April 2019 (Poster presentation)

Inorganic Chemistry

Nanotechnology

Nanomaterials

Materials Science

Electrochemistry