Our research is in the fields of laser spectroscopy and mass spectrometry, chemical catalysis, and materials chemistry. We are interested in spectroscopy of chemically reactive intermediates, solvent- and ligand-free metal catalysis, and laser synthesis and processing of nanomaterials.
1. Laser spectroscopy and mass spectrometry of transient species
We develop and use a variety of spectroscopic and imaging techniques to characterize transient metal-containing intermediates formed in molecular activation and functionalization reactions. These techniques include photoionization time-of-flight mass spectrometry, pulsed field ionization-zero electron kinetic energy (ZEKE) (J. Phys. Chem. Lett. 2, 25(2011)), mass analyzed threshold ionization (MATI) (J. Chem. Phys. 152, 144304(2020)), infrared-ultraviolet (IR-UV) resonant photoionization (J. Chem. Phys. 129, 124309 (2008)), and photoelectron velocity-map imaging (VMI) (J Phys. Chem. A 121, 8440 (2017)). In parallel to the laboratory measurements, we perform computational modeling to compare with the experimental spectra. The field is widely open, and we are well positioned as a major player. The new knowledge created from this project includes accurate ionization energies, metal-ligand and ligand-based vibrational frequencies, electron configurations, and molecular structures of the chemical intermediates. Our goals are to come up with general rules or concepts that can be used to predict the formation, structures, and properties of such species present in catalytic processes.
2. Chemical catalysis
We design chemical reactions that minimize the use and generation of hazardous substances, proceed with appreciable rates under a mild condition, and don’t require a tedious process for product isolation. We do chemical catalysis with metal catalysts in solutions, heterogeneous phases, or solvent-free gaseous environment. Metal catalysts are made by laser ablation in situ or as precatalysts. Gas-phase reactions are monitored with time-of-flight mass spectrometry, and reaction intermediates and products are characterized with laser spectroscopy and computations. Solution-phase or heterogenous reactions are tracked with techniques used in modern synthetic chemistry (GC/LC-MS, TLC, NMR, optical spectroscopy, etc.). Solid metal catalysts before and after reactions are characterized with state-of-the-art methods used in materials chemistry (TEM, SEM, XPS, XRD, XAS, etc). Currently, we work on C-C bond coupling (ACS Appl. Nano. Mater. March 3, 2022, https://doi.org/10.1021/acsanm.2c00389; J. Phys. Chem. C 2022, https://doi.org/10.1021/acs.jpcc.3c00268 J. Am. Chem. Soc. 138, 2468 (2016); J. Phys. Chem. A 121, 1233 (2017), J. Chem. Phys. 146, 184304 (2017).) and C-X (X-H, C, and N)/N-H activation (J. Organomet. Chem. 880, 187 (2019); J. Chem. Phys. 149, 034303 & 234301(2018), 153, 064304 (2020), 155, 034302 (2021).). We aim at the fundamental understanding of reaction mechanisms and the development of green, efficient, and selective processes for designing organic compounds with valuable industrial applications.
3. Laser synthesis and processing of nanomaterials
Laser synthesis and processing in liquid is a clean and fast method for producing ligand-free nanomaterials with high-purity surfaces. The laser-generated particles are thus ideal for studying surface adsorbates under ambient environment and for surface functionalization in a stepwise manner. The ability to control the surface functionality step by step makes it possible to tailor nanoparticles for a wide range of applications in optics, energy, catalysis, or biomedicine. We currently work on rare-earth doped (J. Chem. Phys., 153, 064701(2020)) and carbon-based materials (ACS Appl. Nano. Mater. 2, 6948 (2019); Mater. Today Energy 13, 50 (2019), Nano Express, 1, 020018 (2020).). Raw materials for making carbon nanoparticles are cheap and abundant. Rare-earth doped particles show large anti-stokes shifts, sharp emission lines, long luminescence lifetimes, and superior photostability. We investigate effects of particle sizes and structures, surface functional groups, and identities of metal ions on the optical properties of nanomaterials.
Our research activities provide broad training for students and prepare them effectively for promising careers. Our research group consists of students of both genders with diverse cultural backgrounds and has ongoing national and international collaborations. The students in our group have gone on successful positions in technical or educational workforce. Our research activities have been supported by the National Science Foundation, the Department of Energy, Petroleum Research Fund of the American Chemical Society, and Kentucky Science and Engineering Foundation.