Lab profile: Yugang Sun, Temple University

Using solar energy to drive important chemical reactions is a sustainable way to conserve fossil fuels and the environment. However, the energy coupling between photons and electrons in the chemical bonds of reactant molecules is challenging because their unmatched quantum states lead to low efficiency.

Yugang Sun of Temple University hopes to tackle this challenge using quantum-sized metal nanoparticles, which have a high-density of free electrons. Free electrons in metal quantum-size metal nanoparticles could relay the energy flow from photons to the chemical bonds of molecules adsorbed on the surface to catalyze reactions. Sun has also developed high-energy synchrotron X-ray techniques to provide a real-time insight into the formation/transformation kinetics of nanoparticles. Together the approaches support the rational design, synthesis, and utilization of nanomaterials with precisely tailored properties and functions for catalysis.

Before joining Temple University in 2016, Sun was a scientist at Argonne National Laboratory for 10 years. He has a PhD in chemistry from the University of Science and Technology of China and was a postdoctoral fellow at the University of Washington and the University of Illinois at Urbana-Champaign. He was listed among the top 100 chemists and materials scientists with the highest impact score according to Thomson Reuters. As well as his academic duties at Temple, Sun is also Associate Editor of Applied Materials Today. Materials Today talked to Yugang Sun about his work in nanomaterials…

How long has your group been running?

The group at Temple University has been running since 2016 – for four years until now.

How many staff make up your group?

Currently, there are about ten members in our group, including both graduate and undergraduate students.

What are the major themes of research in your group?

Our primary research themes include catalytic photochemistry on quantum-sized metal nanoparticles, operando study of formation/transformation kinetics of nanoparticles, and scalable synthesis of nanomaterials.

We are using quantum-sized metal nanoparticles, which possess high-density of free electrons, to mediate the energy flow from photons to the chemical bonds of molecules adsorbed on nanoparticle surfaces. The ensemble of high-population free electrons in one quantum-sized metal nanoparticle enables the nanoparticle to strongly absorb light, resulting in the generation of so-called ‘hot electrons’. The small size (i.e. 2-5 nm) of these nanoparticles strengthens the inverse Coulomb blockade effect on the nanoparticle surfaces to favor the transfer of hot electrons to the adsorbate reactant molecules, promoting the energy flow from photons to the reactant molecules to drive the desirable chemical reactions with high photo-to-chemical energy conversion efficiency. Moreover, the coupling of photoenergy (i.e. one type of non-thermal energy) to chemical reactions may alter the thermodynamics of the reactions, improving product selectivity.

Hot-electron-mediated photochemistry on quantum-sized metal nanoparticles holds promise for many important reactions, as demonstrated by my group over the past five years, including CO₂ reduction, partial oxidation, selective hydrogenation of nitroarenes, and coupling reactions. As an example, the case of selective coupling of nitrobenzene into azoxybenzene on quantum-sized ruthenium nanoparticles under photo-illumination is shown. 

My group has developed a series of in situ high-energy synchrotron X-ray techniques over the past decade for probing the formation/transformation kinetics of nanoparticles under operando conditions, including synthesis and catalysis.  The real-time measurements are capable of providing unprecedented knowledge to benefit the rational design, synthesis, and utilization of nanomaterials with precisely tailored properties and functions. 

How and why did you come to work in these areas?

Although ‘kinetic control’ is a well-accepted approach to synthesizing colloidal nanoparticles with high quality, quantitative descriptions of evolving kinetics of colloidal nanoparticles are barely reported in the literature. The absence of quantitative kinetics information motivated my group to develop in situ synchrotron X-ray techniques over the past decade to tackle this challenge.

‘Quantum entanglement’ represents another research frontier. As a chemist, I am interested in the possibility of entanglement between photons and electrons of chemical bonds, which can enable photochemistry with efficient photo-to-chemical energy conversion. Such curiosity has sparked my group into exploring catalytic photochemistry on quantum-sized metal nanoparticles over the last five years.

What has been your highest impact/most influential work to date?

I expect that understanding the correlation between surface chemistry and photoresponse of quantum-sized metal nanoparticles will be the most influential work of my group.

What facilities and equipment does your group have?

In our lab, we have facilities for colloidal nanoparticle synthesis including microwave reactors and microfluidic reactors, photospectrometers with integrating spheres, DRFIT spectrometer with in situ photocatalytic reactor, multiple sets of photocatalysis reactors for both gas- and liquid-phase reactions, setup for electrochemical catalysis, Schlenk lines, ovens, furnaces, and a glove box. My group also has full access to the materials characterization facilities of Temple Materials Institute, the chemical analysis facilities of the Department of Chemistry, and the synchrotron X-ray facilities of the Advanced Photon Source at Argonne National Laboratory.

Do you have a favorite piece of kit or equipment?

The light sources of different designs are my favorite toys because they can shine a light on new ideas to explore.

What is the key to running a successful group?

Intelligent and hard-working students, who are motivated to explore the unknown world with critical thinking, are the crucial elements making up a successful lab.

How do you plan to develop the group in the future?

In the future, the promise of catalytic photochemistry on quantum-sized metal nanoparticles will be extensively excised to explore its potential in a broad range of important chemical reactions. We will focus on the reactions that require high product selectivity, including regioselectivity and stereoselectivity.

Key publications

1. S. Peng et al. Reversing the size-dependence of surface plasmon resonances. Proceedings of the National Academy of Sciences of the USA, 107 (2010) 14530-14534. https://doi.org/10.1073/pnas.1007524107
2. N. Zhang et al. Near-field dielectric scattering promotes optical absorption by platinum nanoparticles. Nature Photonics, 10 (2016) 473-482. https://doi.org/10.1038/nphoton.2016.76
3. Z. Li et al. Reversible modulation of surface plasmons in gold nanoparticles enabled by surface redox chemistry. Angewandte Chemie International Edition, 54 (2015) 8948-8951. https://doi.org/10.1002/anie.201502012
4. Q. Wei et al. Quantum-sized metal catalysts for hot-electron-driven chemical transformation. Advanced Materials, 30 (2018) 1802082. https://doi.org/10.1002/adma.201802082
5. Y. Sun et al. Photocatalytic hot-carrier chemistry. MRS Bulletin, 45 (2020) 20-25. https://doi.org/10.1557/mrs.2019.290
6. X. Dai et al. Enabling selective aerobic oxidation of alcohols to aldehydes by hot electrons in quantum-sized Rh nanocubes. Materials Today Energy, 10 (2018) 15-22. https://doi.org/10.1016/j.mtener.2018.08.003
7. Y. Sun et al. Quantitative 3D evolution of colloidal nanoparticle oxidation in solution. Science, 356 (2017) 303-307. https://doi.org/10.1126/science.aaf6792
8. Q. Liu et al. Quantifying the nucleation and growth kinetics of microwave nanochemistry enabled by in-situ high-energy X-ray scattering. Nano Letters, 16 (2016) 715-720. https://doi.org/10.1021/acs.nanolett.5b04541
9. S. Wu et al. In situ synchrotron X-ray characterization shining light on the nucleation and growth kinetics. Angewandte Chemie International Edition, 58 (2019) 8987-8995. https://doi.org/10.1002/anie.201900690
10. Y. Sun. Watching nanoparticle kinetics in liquid. Materials Today, 15 (2012) 140-147. https://doi.org/10.1016/S1369-7021(12)70067-6