58th Annual Report on Research 2013 Under Sponsorship of the ACS Petroleum Research Fund

Contiguous to the first year research, we have achieved significant progress in the second funding support year. Our research leads to three published articles on prestigious scientific journals and two manuscripts submitted. Derived from the current on-going research, we have developed a long-term research team internationally and submitted a three years’ research proposal to the National Science Foundation.

1.       Documented on Journal of Catalysis, we performed a study combining both experimental and computational effort. In this published work, we demonstrated the superior catalytic activity of Au/SBA-15 modified by pyrrolidone. Different from the conventional pyrrolidone free Au/SBA-15, this novel catalyst exhibits superior catalytic properties in the oxidation of cyclohexene and styrene at mild conditions. Following to this direction, we replaced the SBA-15 with MAO, which is layered Mg-Al mixed oxide structure. The Au nanoparticles were characterized by the transmission electron microscopy techniques. More importantly, these Au nanoparticles supported by MAO exhibit excellent catalytic activity and selectivity in the aerobic homocoupling of phenylboronic acid. Combining the experimental and computational results, we proposed the mechanism for aerobic homocoupling of phenylboronic reaction facilitated by the Au/MAO.

2.      Expanding the research to other applications, we have been studying the interaction between biomolecules and gold nanoparticles. In particular, inspired by the recent progress in gold chemistry, researchers have devoted extensive effort to design sophisticated gold nano-devices for broad applications, including DNA sensors, biological markers and bio-catalysis. In our previous report, we reported the study of the interaction between cysteine and gold nanoparticle, which is published by the journal of Physical Chemistry C. Herein, we further our studies to larger biomolecules, which are synthetic tri-peptides CysAlaAla and AlaAlaCys. Using the Density Functional Theory approach, we found that both peptides prefer the lying orientation on the face site. The CysAlaAla peptide exhibits stronger adsorption energy than that of the AlaAlaCys peptide. By analyzing the electronic properties, we proposed the reason for the stronger adsorption of CysAlaAla on Au₅₅. In CAA peptide, the strong coupling of p-states of S and d-states of Au atoms leads to both bonding-like and anti-bonding-like hybrid states. While in the case of AAC adsorption on Au₅₅, the hybrid between the p-states of the S atom with the d-states of Au atoms is weaker compared with that of CAA adsorption on Au₅₅. These computational results can be applicable to gaining a better understanding of how peptide interacts with the gold nanoparticles. More importantly, the computational results provide guidance for our on-going experimental studies, which can eventually determine the structure of the CysAlaAla and AlaAlaCys peptides on gold nanoparticles. This work has been submitted to Journal of Physical Chemistry C.

3.       By achieving more knowledge of gold nanoparticles, we are curious to know if the activity can be tuned by adjusting the morphology of the support materials. Herein, a question has brought up to our study what happens if Au and TiO₂ anatase nanostructures intimately contact. Since it is really hard to harvest anatase in large crystal manner, experiments in general focus on characterization of anatase TiO₂ at nano-size scale and demonstrate strong morphology and size dependencies. To address this curiosity, we specifically design a nanoparticle/nanoparticle model to mimic the complex features of Au/TiO₂ nanosystem. The gold component is represented by Au₁₃ and Au₂₀, both of which have been well studied theoretically and experimentally. As for the anatase nanoparticles, we have previously undertaken a series of studies by means of a DFT method. In basis of the previous results, we believe our approach should be suitable to deal with the two components involved in this model and aim to provide an insight of the interaction of Au/TiO₂ in this unique contact. Analyzing the electronic properties, we are able to understand these interactions from the principle. The DFT calculations prove it is promising to tone the activity by adjusting the morphology of the support materials, TiO₂ in this case. To reach a more applicable scale, we are carrying out experiments to measure the activity.

In summary, all these studies have been either published as three articles or submitted as two manuscripts. Beside the three years’ research proposal submitted to NSF, the senior scientist (Wang) has also expanded this research direction to a bimetallic nanocatalyst proposal submitted to Alexander Von Humboldt Fellowship. Combining all these achievements, we are able to claim that gold nanocatalysis research has become one of the major research directions in Lewis’ research group.

Educational Impact

Three undergraduate students (Jessica A. Carr, Andrew Rice and Nancy Isner) have been working on in this research direction and they are playing a major role in delivering research results. Since joining Dr. Lewis’ research group, Jessica Carr has been mentored by the senior scientist (Wang) in performing the computational investigation of the interface between ligands and gold nanoparticles. A recent investigation of monolayers and bilayers on Au nanoparticles was submitted for publication to J. Phys. Chem. C and she is first author on this manuscript. In May 2012, she was awarded a Goldwater Scholarship as a result of her remarkable academic record and research contributions related to this research. In her Goldwater Scholarship application, she noted that the research experience gained in Lewis’ research group changed her perspective about chemistry research. As a result of her participation in this research, Jessica has been admitted to MIT graduate school for her Ph. D study in Chemistry Major in May 2013. Current, she is studying as a graduate student in Chemistry department in MIT.

Another student, Andrew Rice, has been working on understanding the fundamental properties of gold nanoparticles with different oxide supports. This current research project is also his capstone research thesis as well. After research months experience in the Lewis’ research group, Andrew Rice has been  admitted as graduate student in Physics Department in West Virginia University.