Adsorption of polychlorinated biphenyls on gold colloid by surface-enhanced Raman spectroscopy and density functional theory

Both the adsorption orientation and the charge transfer mechanism of two polychlorinated biphenyls (PCBs, 4, 4′-dichlorobiphenyl (PCB15) & 2, 4, 4′-trichlorobiphenyl (PCB28)) on the gold nanoparticles surface were studied based on theory and surface-enhanced Raman spectroscopy (SERS) in this paper. To explore the spectral differences, the PCBs-(Au) 3 model was established by comparing the calculation with the actual spectra. The results showed that destruction of structural symmetry led to benzene vibration peak split in Raman spectra. The adsorption orientation was found that the molecules are adsorbed on the gold cluster at a specific angle (76.640° for PCB15, 77.774° for PCB28) through the π-type orbit. It usually appears as a gold cluster at the top bridging position of the inter-ring bond. The energy gap between PCBs and gold cluster is small that electrons could transfer from molecules to metal substrate smoothly. The charge distribution state has been used successfully to explain the structural change and the peak shift trend. This paper lays a theoretical foundation for an in-depth study of the SERS chemical mechanism, SERS spectra prediction, and PCBs homologues identification.