SERS chemical enhancement by copper ‐ nanostructures: Theoretical study of Thiram pesticide adsorbed on Cu20 cluster

Abstract

AbstractSurface‐enhanced Raman spectroscopy (SERS), a surface‐sensitive technique, allows the practicability of detecting chemical compounds in ultra‐low concentration. In this work, a chemical enhancement mechanism of SER process of Thiram pesticide adsorbed on copper nanomaterial surface was proposed based on density functional theory (DFT) approaches. Structural and electronic properties of Thiram and Thiram‐Cu20 complexes were optimized using PBE method with LanL2DZ basis set for copper atoms and cc‐pVDZ basis set for the non‐metal atoms. In the most stable adsorption configuration, Thiram interacted with Cu20 cluster via two S(sp2) atoms. The main peaks on normal Raman spectrum of Thiram were characterized at 371, 576, 1414 and 1456 cm‐1 responsible for the stretching vibrations of C–S, C=S, S–C–S and C–N groups, respectively. Otherwise, the main peaks of Thiram‐Cu20 SERS spectrum were found at 534, 874, 982, 1398 and 1526 cm‐1 corresponding to the stretching vibrations of S–S, C‐S, S–C–S, C–N and CH3–N bonds, respectively. The SERS chemical enhancement of Thiram by Cu20 cluster was about 2 and 6 times stronger than those obtained from Ag20 and Au20 cluster, respectively. The chemical enhancement mechanism was also explained by analyzing HOMO and LUMO energies gap and density of states.