Towards rational design of nanoalloys: predicting stability and mixing behavior of metals at the nanoscale

Significance 

Of late, technology involving metal nanoparticles is blossoming with new potential applications emerging every day. This can be attributed to the fact that the properties of metal nanoparticles differ from both the atomic and bulk size extremes; including, optical, magnetic, electrical and adsorption. Recent technological advances have already helped establish that besides composition, chemical ordering at the atomic level is critical when it comes to determining important nanoalloy properties in magnetic and catalytic applications. First principle methods such as the density functional theory have the ability to capture accurate nanoalloy energetics, unfortunately, their applicability is limited to very small nanoparticle sizes as a result of the exorbitant computational cost involved. Therefore, despite the fact that remarkable applications for metal nanoparticles have already been established, a good comprehension of their stability in relation to morphology and chemical ordering has remained hazy.

Recently, University of Pittsburgh researchers (Zihao Yan, Michael Taylor and Ashley Mascareno) led by professor Giannis Mpourmpakis introduced a novel bond centric (BC) model that could accurately and rapidly determine the energetics of alloy metal nanoparticles with arbitrary morphology, composition, and chemical ordering. They anticipated that their model would capture cohesive energy trends over a range of monometallic and bimetallic nanoparticles and mixing behavior of nanoalloys, in great agreement with density functional theory calculations. Their work is currently published in the research journal, Nano Letters.

The research method employed commenced with the evaluation of the performance of the facile square-root bond cutting (SRB) model on calculating cohesive energies of monometallic and bimetallic metal nanoparticles using density functional theory calculations. Next, based on the performance of the SRB model, they introduced scaling factors that corrected the bimetallics energetics by utilizing highly accurate bimetallic bond strength data from literature. Lastly, the researchers demonstrated the successful application of their model where they effectively screened the thermodynamic stability of alloy metal nanoparticles and compared the results obtained with density functional theory calculations and experiments. “We were very excited to successfully apply our model to an FePt alloy nanoparticle that consisted of 23,196 atoms and show that the experimentally synthesized nanostructure was captured as one of the lowest in energy configurations”, said professor Mpourmpakis.

The authors observed that their novel bond centric model was hypothetically suited to capture 298, which represented a modest 85%, of all the bimetallic transition metal alloys. In addition, they noted that beyond the broad applicability of the bond centric model on nanoalloys, its strong physical basis allowed for important comparisons and extraction of physical learnings.

In a nutshell, Giannis Mpourmpakis and his research team introduced a bond centric model capable of accurately capturing the energetics of metal nanoparticles as well as their mixing behavior. The main observation made was that the novel bond centric model was extremely fast in evaluating arbitrary alloy metal nanoparticles of practically any morphology (size and shape) and metal composition and very accurate capturing similar trends with Density Functional Theory calculations. Altogether, this work has established a facile yet very powerful tool for nanoalloy design that can potentially help elucidate the energetics of alloy metal nano particle genomes.

Towards rational design of nanoalloys: predicting stability and mixing behavior of metals at the nanoscale, Advances in Engineering

About the author

Dr. Giannis Mpourmpakis is the Bicentennial Alumni Faculty Fellow, Assistant Professor of Chemical and Petroleum Engineering at the University of Pittsburgh. His research focuses on the theoretical investigation of the physicochemical properties of nanomaterials, with applications in the nanotechnology and energy arenas. Prior to joining the University of Pittsburgh in 2013, he was a Senior Researcher at the Catalysis Center for Energy Innovation (CCEI), at the University of Delaware (2011-2013). He graduated from the Chemistry Department, at the University of Crete, Greece (2001), where he also earned his MSc (2003) and PhD degrees (2006). In 2006, he joined the Chemical Engineering Department at the University of Delaware as a postdoctoral researcher. He has published more than 70 research articles in high impact journals (Nature, Nature Communications, Science Advances, Nano Letters, JACS, etc.). As a young investigator, he has received various awards, among which are the CAREER award from the National Science Foundation, the Doctoral New Investigator Award from the American Chemical Society, Petroleum Research Funds, the “Marie-Curie” postdoctoral fellowship by the European Commission, and the “60th Nobel Laureate Meeting” where he was selected as one of the top 500 young researchers worldwide in 2010. For his contributions to research, he was named Emerging Investigator by the ACS Journal of Chemical and Engineering Data in 2018, “one of 25 researchers who will be defining our field over the coming decades”. For his contributions to education, Prof. Mpourmpakis was awarded the 2016 James Pommersheim Award for Excellence in Teaching in Chemical Engineering by the University of Pittsburgh. He is serving as the President-elect of the Pittsburgh-Cleveland Catalysis Society and he has organized computational catalysis sessions in several national meetings (ACS, AIChE, NAM, etc.).

About the author

Michael G. Taylor is a Graduate Researcher and a National Science Foundation Graduate Research Fellow in the department of Chemical and Petroleum Engineering at the University of Pittsburgh working towards his PhD. He earned his B.S. in Chemical Engineering from the University of Nebraska-Lincoln. His research interests include nanomaterials growth, stabilization, and catalysis – especially at the atomically-precise scale. His work in Prof. Mpourmpakis group has been highlighted in several high-impact journals including Nature, Science Advances, and Nature Communications.

About the author

Zihao Yan received his B.S. degree in Chemical Engineering at University of California, Berkeley in 2014. From 2015 to 2016, he worked as a junior specialist at University of California, San Francisco (UCSF) under the supervision of Prof. Adam Abate and Prof. Shawn Douglas. In 2018, he received his M.S. degree in Chemical Engineering under the supervision of Prof. Giannis Mpourmpakis at University of Pittsburgh. His M.S. thesis was computational modeling of alloy nanoparticle stability. He is now a Ph.D. student in Chemical Engineering at Virginia Polytechnic Institute and State University (Virginia Tech). His research interests are nanomaterials and catalysis.

About the author

Ashley Mascareno received her B.S. degree in Physics and Astrophysics at Arizona State University in 2017. In the summer of 2017 she participated as an undergraduate student at the REU program (Research Experience for Undergraduates) at the University of Pittsburgh, performing research on simulating the stability of bimetallic nanoparticles in the lab of Prof. Giannis Mpourmpakis.

Reference

Zihao Yan, Michael G. Taylor, Ashley Mascareno, Giannis Mpourmpakis. Size-, Shape-, and Composition-Dependent Model for Metal Nanoparticle Stability Prediction. Nano Letters. 2018, volume 18, page 2696−2704.

Go To Nano Letters

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