The orientation and bonding of adsorbed 9,10-phenanthrenequinone (PQ) on onion-like carbon (OLC) were determined by combining spectroscopy and density functional theory (DFT) calculations. Electrochemical measurements demonstrated relatively strong bonding of PQ to the OLC as indicated by persistent and reversible features in the cyclic voltammetry. Spectra of bulk solid and adsorbed PQ were obtained by inelastic neutron scattering (INS) and Raman spectroscopy, and the bands were compared with vibrational energies calculated from DFT. At energy losses (frequencies) above 400 cm-1, no band shifts in INS or Raman spectra were observed between bulk solid and adsorbed PQ. However, adsorption of PQ resulted in shifts in the lowest frequency modes (<400 cm-1), compared to crystalline PQ, which could only be identified by INS. DFT calculations also provided adsorption energies and from these and comparison of computed and experimental spectra it is determined that the molecule adsorbs parallel to the onion-like carbon surface through π-π stacking interaction.
Bibliographical noteFunding Information:
This work was supported as part of the FIRST Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. INS experiments at the Spallation Neutron Source and Raman measurements at Center for Nanophase Materials Sciences were supported by the Scientific User Facility Division, Office of Basic Energy Sciences, US Department of Energy. The authors wish to thank John McDonough and Yury Gogotsi for providing the OLC and for useful discussions.